IE880051L - Separation of citric acid from fermentation broth - Google Patents

Description

'A ^01 o I ^ ^ I rw Use field of art to which this invention pertains is the solid feed adsoiptive separation of citric acid from fermentation broths containing citric acid, carbohydrates, amino adds, proteins and salts. More specifically, the invention relates to a process for separating citric acid from fermentation broths containing same which process employs a non-zeolite polymeric adsorbent, which selectively adsorb citric acid, and is selected from the group consisting of a neutral, crosslinked polystyrene polymer, a nonionic hydrophobic polyacrylic ester polymer, a weakly basic anionic exchange resin possessing tertiary amine or pyridine functional groups, and a strongly basic anionic exchange resin possessing quaternary amine functional groups and mixtures thereof .

Citric acid is used as a food addiilant, and in pharmaceutical, industrial and detergent formulations. Hie increased popularity of liquid detergents formulated with citric add has been primarily responsible for growth of worldwide production of dtric add to about 320 million Kg per year which is expected to continue in the future.

Citric add is produced by a submerged culture fermentation process which employs molasses as feed and the microorganism, Aspergillus Niger. The fermentation product will contain carbohydrates, amino adds, proteins and salts as well as dtric add, which must be separated from the fermentation broth.

There are two technologies currently employed for the separation of dtric add. Ik Srst involves calcium salt precipitation of dtric add. Tbensahiag caldum dtrate is acidified with sulfuric add. la the secood process, citric add is extracted from the fennentation broth with a mixture of trilausyi^mai&e, n-oda&ol a&d a Cj0 or Cj n isoparafSia. Otric add is reextracted from the solvent phase Mto water with the addition of heat. Both techniques, however, are complex, expensive astd they generate a substantia] amount of waste far disposal. *3_ The patent literature has suggested a possible third method for separating dtric add iron?, the fermentation broth, which involves membrane filtration to remove raw materials or high molecular weight impurities and then adsorption of contaminants onto a nonionic resin based on polystyrene or 5 polyacrylic resins and collection of the dtric add in the rejected phase or raffinate and crystallization of the dtric add after concentrating the solution, or by predpitating the dtric add as the caldum salts then addifying with H2SO4, separating the CaSO^ and contacting cation- and anion-exchangers. This method, disdosed in European Published Application No. 151,470, August 14,1985, is also a lo rather complex and lengthy method for separating the dtric add. In contrast, the present method makes it possible to separate the dtric add in a single adsorption step and to recover the dtric add from the adsorbent to obtain the purified dtric add using an easily separated desorhent.

This invention relates to a process for adsorbing dtric add &ora a 15 fermentation broth onto a polymeric adsorbent selected from the group consisting of a neutral, crosdinked polystyrene polymer, a sonionic hydrophobic polyaoylc ester polymer, a weakly basic anionic exchange resin possessing tertiary amine or pyridine functional groups, and a strongly basic anionic exchange resin possessing quaternary amine functional groups and mixtures thereof and thereafter recovering 20 tibe dtric add by desoiption thereof with a suitable desorbent under desorption conditions. One aspect of the invention is In the discovery that highly selective separation of dtric add from salts and carbohydrates is only achieved by adjusting and maintaining the pH of the feed soMtim lower than die first ionization constant (pK&j) of dtric add (3.15). The degree to which the pH most fee lowered to 25 maintain adequate selectivity appears to be interdependent on the eon.ceiatrata©ia of dtric add in the feed smxtcre; tine pH is inversely dependent om the concxsatration. As concentrations are decreased below 13% to very low concentrations, the pH may be near the pKaj of dtric add of 3.13; at 139k the pH may range from 0l9 to 1.7; however, at 40% dtric add feed concentration, the pH must be lowered to at least 30 about 12 or lower. At higher concentrations, the pH must m even lower; for csasnple, at 50% dtric add, the pH most be at or below 1.0. It is thus preferred to maintain {fa© pH of tbe feed mixture m the range of 0 J to 23 with a range of 0.5 to 22 giving best results. Another aspect of the invention Is the discovery that the temperature of adsorption can be reduced for the polymeric adsorbent used herein % the addition of acetone, oar other low molecular weight ketone, to tiie desorbent; tbe Mgfeer temperatures associated wife adsorbent breakdown can tfous he avoided.

Tee invention also relates to a process for separating dtric add from a feed mixture comprising a fermentation broth containing same, wMds process employs a polymeric adsorbent selected from tbe group consisting of a nested, crosslinked polystyrene polymer, a nonionic hydropliobic polyacrylic ester p©lymer9 a weakly basic anionic exchange resla possessing ternary amine or pyridine functional groups, and a strongly basic anionic exchange resla possessing quaternary amine functional groups and mixtures thereof which comprises the steps of: (a) maintaining set fluid flow thoragh a column of said adsorbent in a single direction, which column oontains at least three zones having separate operational functions occurring therein and being serially interconnected with the terminal zones of said column connected to provide a continuous cosmeetkm of said zoses; (b) maintaining an adsorption zone in said column, said zone defined by tbe adsorbent located between a feed input streais at as upstream boeBdasy of said zone and a ra£Gnate emtput stream! at & downstream boundary of said zone; (c) maintaining a purification sswse immediately upstream from said adsorption zone, said purification zone defined by tie adsorbent located between an extract output stream at an upstream boundary of said purification zone and said feed input stream at a downstream boundary of said purificati<m zone; (d) maintaining a desoipdoo zone immediately upstream froia said pEiiScatlo® zone, said desoiptioE zone defined % the adsorbent located between a deserbest input stream at as spsteeam boundary of said zone and said extras! output stream at a downstream kiepdaiy of said mnc; (e) passing said feed mixture ioto said adsMptk»i zone at tdscxptkn conditions to effect the selective acbMpdaa of said citric add by said adsorbcat In said adsorption zone and withdrawing a raffimate output stream mmpmmg the nonadsorbed components of said fermentation broth ftora said adssrptk® zone; *j» (f) passing a desorbent material into said desorption zone at desoiption conditions to effect tbe displacement of said citric acid from the adsorbent la said desoiption zmc; (g) withdrawing an extract output stream eomprissBg said citric add sad desorbent material Stcmj said desoiption zone; (h) passing at least a portion of said extract output stream to a separation means and therein separating at separation conditions at least a portion, of said desorbent material; and, (i) pssfedlcally advancing tJbroEgjb said column of adsoftsesit in a downstream direction with respect to fluid Bow m said adsorption zone tbe feed input stream, raffmate output stream,, desorbent input stream, and extract output ' stream to effect the shifting of zones through said adsorbent and tbe production of extract output and raffimate output streams to produce a raffinate jeodaet hsmag a reduced concentration of desorbent material Further, a buffer zone may be maintained immediately upstream firom said desoiption zone, said buffer zone defined as is adsorbent located between tbe desorfceM input stream as a downstream boundary of said Ibtiffer zone and the raffinate output stream as an upstream boundary of said biu&r zone.

Ote aspects of the invention encompass details of feed stees, ads©rbenitss desorbents and operating conditions which are laerelaafter disclosed.

Figure 1 is a plot of concentration of various dtric acid species versus iepHtif citric acid dissociation wMdh shows tbe shifting of the equaBbriusa point of the dtric acid dissociation by varying tbe ©aecsntrstloia of citric acid, citrate sates and the hydrogen km.

Figure 2 is a static plot to detenonae tbe effect ofpH on amount of dtric add mat can fee adsorbed by the adsosrbent.

Hgares 3A, 3B and 3C are tbe plets oftbe pulse teste la Bcarssle I using XAD-4 to separate citric add from a feed containing 13% dtric addatpHfcof 24, L7 and 0.9, respectimelsr.

Fsgsres 4A, 4B, 4Q 4D and 4E are plots of the pels® tests of EwsapSe H at pBPs of 2.4, 17, 0l9, 2.8 .and 14, respectively, nan on different adwwbent samples. 6 Figures 5A and SB are plots of the pulse tests of Example M at pH's of 2.8 and 14, respectively, and temperatures of 93° C Figures 6A, 6B and 5C are plots of the pulse tests of Example IV at pH's of L94, U3 and 0 J, respectively.

Figures 7A, 7B and 7C are plots of the pulse tests of Example V at pH's of L82,0.5 and 03, respectively.

Figures 8A and 8B are plots of the pulse tests of Example VI at pH's of 1.5 and 1.0, respectively.

Figure 9isaplot of tbe pulse test In Example VU showing the adsorption achieved at lower temperatures (93°C versus 45°C) through tbe incorporation of 10% acetone m the desorbent water.

Figure 10 is the plot of the pulse test in Example VDI using a weakly basic anionic exchange resin having a tertiaiy amine functionality in a aoss-Iinked acrylic resin matrix to separate citric add from a feed containing 40% citric acid at a pH of 1.6, desorbed with water.

Figures SUA, !1B and HC are plots of the pulse tests of Example DC, at pH's of 7.0,3.5 and 2.4, respectively.

Figures 32,13A and 13B are the plots of the pulse test of Example X at a pH of 1.6 man on several different adsorbent samples of weakly basic anionic exchange resin possessing pyridine functionality in a cross-linked polystyrene resin matrix. The dtric add is desorbed with 0.05N sulfuric add or water.

Figure 14 is a plot of the pulse test of Example XM at a pH of 16.

Figure 35 is the plot of the pulse test of Example XIV at a pH of 22 ran on a different adsorbent sample of a less strongly basic anionic exchange resin possessing quaternary ammonium firactionality in a cross-linked potystyreme resin matrix, desorbed with dilute sulfuric add. ■ At the outset tbe definitions of various terms ased throughout the specification will be useful in making dear the operation, objects and advantages of the instant process.

A feed mixture* is a mixture containing one or more extract components and one or mare rafBnate components to be separated by tbe present process. The term "feed stream" indicates a stream of a feed mixture which passes I© the adsorbent used in the process.

An "extract component" is a 'Compound or type of compound that is more selectively adsorbed by the adsoibent while a "raffinate component" is a 5 compound or type of compound that Is less selectively adsorbed. In this process, citric acid is an extract component and salts and carbohydrates are raffinate components. Hie term "desorbent material" shall mean generally a material capable of desoibing an extract component Hie term "desorbent stream" or "desorbent input stream" indicates the stream through which desorbent materiel 10 passes to the adSsorbest, The term "raffinate stream" or "raffinate output stream" means a stream through which a raffinate component is removed from the adsorbent The composition of the raffinate stream can vary from essentially 100% desorbent material to essentially 100% raffinate components. The term, "extract stream" or "extract output stream" shall mean a stream through which an extract 15 material which has been desorbed by a desorbent material Is removed from the adsorbent Use composition of the extract stream, likewise, can vary mm essentially 100% desorbent material to essentially 100% extract components. At least a portion of the extract stream and preferably at least a portion of the raffinate stream from the separation process are passed to separation means, typically 20 firactionators, where at least a portion of desorbent material Is separated to produce an extract product and a raffinate product'The terms "extract product" end "raffinate product" mean products produced by the process containing, respectively, m extract component and a raffinate component ia higher concentrations than those found in the extract stream and the raffinate stream. Although it is possible 25 by the process of this ioventsoQ to produce a high purity, citric acid product at high recoveries, it will be appreciated that an extract component Is never completely adsorbed by the adsorbent likewise, a raffinate component Is completely nonadsoxbed by tbe adsoxbesft. Therefore, varying amounts of a raffinate component can appear in the extract stream and, likewise, varying amounts of an 30 extract component can appear in the raffinate stream. The extract and raffinate streams then are further dnstiegisislied! frost each other and firem the feed sjte» by tbe ratio of tbe concentrations of an extract component and a raffinate component appearing in the particular stream. Mote specifically, the ratio of the concentration of dtric add to that of the less selectively adsorbed components will be lowest la the \ 8 rafSnate stream, next highest in the feed mixture, and the highest in the extract stream. likewise, the ratio of the concentration of the less selectively adsorbed components to that of the more selectively adsorbed dtric add will be highest in the raffinate stream, next highest in the feed mixture, and the lowest in the extract streant The term "selective pore volume" of the adsorbent is defined as the volume of the adsorbent which selectively adsorbs an extract component from tbe feed mixture. The term "nonselective void volume" of the adsorbent is the volume of the adsorbent which does not selectively retain an extract component from the feed mixture. This volume indudes the cavities of the adsorbent which contain no adsorptive sites and the interstitial void spaces between adsorbent particles. The selective pore volume and the nonselective void volume are generally expressed in volumetric quantities and are of importance in determining the proper flow rates of fluid required to be passed into an operational zone for effident operations to take place for a given quantity m adsorbent. When adsorbent "passes'3 Into an operational zone (hereinafter defined and described) employed in one embodiment of this process its nonselective void volume'together with Its selective pore vttae carries fluid into that zone. The nonselective void volume is utilized in mt&rmmmg tbe amount of fluid which should pass into she same zone in a countercarreat direction to tbe adsorbent to displace the fluid present in the nonselective void volume. If the fluid flow rate passing into a zone is smaller than the nonselective void volume rate of adsorbent material passing into that zone, there is a net entrainment of liquid into the zone by the adsorbent Since this net entrainment is a fluid present in nonselective void volume of the adsorbent, it in most instances comprises less selectively retained feed components. Use selective pore volume of an adsorbent can in certain instances adsorb portions of raffinate material from the fluid surrounding the adsorbent since in certain instances there is oooopetitiGB between extract sosgterlal and raffinate material for adsoiptive sites witWB the selective pore volume. If e large quantity of raffinate material with respect to extract material sunouads the adsorbent, raffinate material can be competitive enough to be adsorbed by the adsorbent Tbe feed material contemplated in this invention is the fermentation predict obtained Sresas the sufemeiged culture fermentation of molasses % the microorganism, Aspergillus Niger. The fermentation product will save a composition exemplified by the following: ' Citric add 12.9% + 3% Salts 6,000 ppm Carbohydrates (sugars) 1% Others (proteins and amino adds) 535 The salts will be K, Na, Ca, Mg and Fe. The carbohydrates are sugars including glucose, xylose, mannose, oligosaccharides of DP2 and DP3 plus as many as 12 or more unidentified saccharides. The composition of the feedstock may vary from that given above and still be used in the invention. However, juices such as citrus fruit juices, are not acceptable or contemplated because other materials contained therein will be adsorbed at the same time rather than dtric add alone. Johnson, i, Sd. Food Agric.. Vol 33 (3) pp 287-93.

It has now been discovered that the separation of dtric add can be enhanced significantly by adjusting the pH of the feed to a level below the first ionization constant of dtric add. The first ionization constant (pKaj) of dtric add is 3.13. Handbook of Chemistry & Physics. 53rd Edition, 1972-3, CRC Press, and therefore, the pH of the dtric add feed should be below 3.13. When the pH for a 13% concentrated solution of dtric add is 2.4 or greater, for example, as in Figure 3A (Example I), dtric add "breaks through" (Is desorbed) with the salts and carbohydrates at the beginning of the cyde, indicating that all the dtric add is sot adsorbed. In contrast, less "break through" of dtric add is observed when the pH is L7 and ao ""break through" when the pH Is 0.9 at tbe 13% level, for example as in Figures 3B and 3C, respective^.

Is aqueous solution, txmouized dtric add exists in equilibrium with the several tftrateanions and bydrcigesa loos. This is shown ia the fclkwing equations, where the add dissociation constants* pKaj, pKaj aad pK&j of dtric add at 25®€ are 3 J3„ 4.74 sad 5.40, respectively: Equation 1 pltej « 3.13 7 V*"1 ~ pfe9 ■ 4.74 He egmirDriMm point of dtric add dissodation can be shifted fey vai^iing the concentrations of dtiie add, the dtrate anion or the sydrcgeE ion. ITbls Is demonstrated m Figure I, for the concentration of the several dtric add spedes Is solution versus pH at 9Q°C Use result sbio^s a higher percent of nonionized dtric add (H3CA) at a higher irydrogen ion concentration (kmrnr pH). Decreasing the pH (raising the HT km concentration) will introduce more nonionized citric add while reducing the dtrate anionic spedes (HgC&'l, HGC*4 and OC^Jm the solution.

Based on the dtric add equilibrium and the resin properties mentioned above, nonionized dtric add wil fee separated from Giber ionic spedes (indixding dtrate anions) in the fermentation tooths using the rcsm adsorbents described However, for a higher citric acid recovery, a fenar pH soWoei is required. The static adsorptitoiai isotherm of a particular resin falling within the invention, Amberiite XAD-4, for dtric add was carried out at room temperature about 25®C; asa&sctiQOofjbdpE Figure 2 shows the results of the study. The results show adsozption of the nonionic dtric add as the pH is lowered. Without the intention of feeing limited % this explanation, It appears that the soniosuc dtric add spedes is the solution is psefeseotiaHy adsorbed oa the adsorbents of the present invention either tSaroiiigSa as add-base Interaction mechanism or a hydrogen bonding mechanism or a medNam'sm based on a strong affinity fear relatively isydr®pMoMc species or a ©o^Mmatlos! of these iBedsaiassss, processes vaiy depending upon sods feetoes as the type of operation ©showed, la the mmg bed system, ia which tbe selectively adsorbed feed component Is removed from the adsorbeat by a posge stream, desorbent selection is sot as critical and desorbent materials gaseous fcjydrocaxboos sodi as agtoe, etee^ etc, or other $pes of gases such as aittqgesi or hydrogen ussy fee used as okrvsted Desorbent materials used in various prior ait adsoiptivie separation n temperatures or reduced pressures or both to effectively purge the adsorbed feed component from the adsorbent. However, in adsorptive separation processes which are generally operated continuously at substantially constant pressures and temperatures to ensure liquid phase, the desorbent material must be jjudiciousty selected to satisfy many criteria. First, the desorbent material should displace an extract component from the adsorbent with reasonable mass flow rates without itself being so strongly adsorbed as to unduly prevent an extract component from displacing the desorbent material in a following adsorption cycle. Expressed in terms of the selectivity (hereinafter discussed in more detail), it is preferred that the adsorbent be more selective for all of the extract components with respect to a raffinate component than it is for the desorbent material with respect to a raffinate component. Secondly, desorbent materials must be compatible with the particular adsorbent and the particular feed mixture. More specifically, they must not reduce or destroy the critical selectivity of the adsorbent for an extract component with respect to a raffinate component Desorbent materials should additionally be substances which are easily separable from the feed mixture that is passed into the process. Both the raffinate stream and the extract stream are removed from the adsorbent in admixture with desorbent material and without a method of separating at feast a portion of the desoibent material the purity of the extract product and tbe raffinate product would not be veiy high, nor would the desorbent material be available for reuse in the process. It is therefore contemplated that any desorbent material used in this process will preferably lave a substantially different average telling point than that of the feed mixture to allow separation of at least a portion of tbe desorbent material from feed components in the extract end raffinate streams by simple fractional distillation thereby permitting reuse of desorbent material in the process. Use term "substantially different" as used herein shall mesa that the difference between tbe average boiling points between the desorbent material and the feed mixture shall be as least about 5°C Ik boiling range of the desorbent material may be higher or lower than that of the feed mixture. Finally, desorbent materials should also be materials which are readily available asd therefore reasonable in cost la the preferred Isothermal, isobaric, liquid phase opcT&tim of the process of the present invention, it has been found that water is a partiailariy effective desorbent material. Also^ it has been determined that acetone and other low molecular weight ketones, soda as metisyleitiy! ketone and diethyl ketone to be 12 effective ia admixture with water In small amounts, up to 15 wt%. The key to their usefulness lies ia their solubility an'water. Their advantage* however, lies ia their ability to reduce the temperature at which the desoiption can take place. With some adsorbates and water as desorbent, the temperature imist be raised to aid the 5 desorption step. Increased temperatures can cause premature deactivation of the adsorbent A solution to that problem in this particular separation is to add acetone in the amount of 1 to 15 wt.% of the desorbent, preferably, I to 10 wl% with the most preferred range of 5 to-10 wt%. Hae low molecular weight ketone may also affect the adsorbent stability ia possibly two ways, fey removing solubflizing components 10 which cause deactivation or by effecting regeneration, Le., by removing tbe deactivating agent or reversing its effect For example, a reduction of tbe desorption temperature of this separation by approximately 50°C has been achieved by adding 10 wt% acetone to the desoibent A reduction of from about 5°C to about 70°C can be achieved by the addition of 1 to 15 wi.% acetone to the water 15 desoibent Dilute inorganic acids have also been found to give good results when used as desorbents. Aqueous solutions of sulfuric acid, nitric acid, hydrochloric acid, phosphoric add and mixtures thereof can be used in amounts corresponding to Q,0I to LON (normal), with best results obtained with dilute sulfuric add at 0.11 to LQN.

The prior art has also recognized that certain characteristics of adsorbents are highly desirable, if sot absolutely necessary, to the successful operation of a selective adsorption process. Such characteristics are equally important to this process. Among such characteristics are: (1) adsoiptive capacity for some volume of an extract component per volume of adscubent; (2) the 25 selective adsorption of an extract component with respect to a raffinate component and the desorbent material; and (3) suffidently fast rates of adsorption and dbKptm of an extract component to and &om tbe adsorbent Cfepadfy of the adsorbent for adsorbing a specific volume of an extract component is, of course, a necessity; without such capadty the adsorbent is useless for adsoiptive separation. 30 Ffertbennore, t!be higher tbe adsorbent's capadty for an extract component fee better is the adsorbent Increased eapadty of a psxticalar adsorbeM makes It possible to reduce tbe amount of adsorbent needed to separate an extract component of known concentration contained in a particular charge rate of feed Btee. A reduction in the amount of adsorbent required for a specific adsosptive 13 separation reduces the cost of the separation process. It is important that tae good Initial capacity of tbe adsorbent 'be maintained during actsal isse in tbe separation process over seise economically desirable life. The second neoessaiy adssrbesi dhar&crteiistle is the ability of the adsorbent to separaie components of Ac feed; or, in ©tiher words, that tbe adsorbent possess ads©yptwe selectivity, (B), for one component as compared to another component Relative selectivity can be pressed sot im% for om i&ed wmpo&mi as compared to amotSier but can also be expressed between any feed mixture component and the desorbent material. Use selectivity, {B)„ as used throughout this spedfi^tlon Is defrnec! as tbe sail© of tie two components of the adsorbed phase over the ratio of the same two components in the unadsoxbed phase at equilibrium eenditions. Relative selectivity is shows as Equation .2 below: Equation 2 .

Selectivity - (E) = Evol. Dercent C/vol. percant fVol. percent C/vol. percent 0jy where C and D are two cossapmmms of the feed represented in veksae percent and the subscripts A and U represent the adsorbed and unadsorbed phases respectively. Tbe equilibrium conditions were detennined when the feed passing over a bed of adsorbent did sot change oonipositioai' after contacting the bed of a&offbenL Ik other words, there was m set transfer of material occurring between the tsaadsoibed and adsorbed phases. Where selectivity of two components approaches 1J tfeere is no prefereiaiial adsorption of ease component % the adsoibeat with respect to the other; they are both adsorbed! (or sooadsorbed) to about the same » degree with respect to each other. As the (B) becomes less than or greater than LO there is a prefereMial adsorption % the adsccbeat fee one component with respect to the other. When comparing the selectivity by the adsorbent of ooe component C over eonpoeat D, a (B) larger than LO indicates preferential adsorption of coccponent C within the adsssibessL A <B) less than LO would indicate that component D is prefereetiglly adsorbed leaving an tmadsosbed phase ridher in component C and an adsoibed phase ridbsr is composes^ D. Ideally desota materials should have a sdectivxtjr eqasd to dboot 1 or sHghtly less than I wifla respeel to 211 extract components so that aE of the extract components can be desorbed as a dass with reasonable flow rates of desorbent material and so that extract components can displace desorbent material in a subsequent adsorption step. Whale separation of an extract component from a raffinate component is theoretically possible when the selectivity of the adsorbent for the extract component with respect to tbe raffinate component is greater than 1, it is preferred that such selectivity approach a value of Z like relative volatility, the higher the selectivity, tfes easier the separation is to perform. Higher seSectivMes permit a smaller amount of adsorbent to hs esecl Tika third important characteristic is the rate of exchange of the extract component of tbe feed mixture material or, in other wards, tbe relative rate of desoiption of tbe extract component. This characteristic relates directly to tbe amount of desorbent material that must be employed in the process to recover tbe extract component from the adsorbent; faster rates of exchange reduce the amount of desorbent material needed to remove the extract component and therefore permit a reduction in tbe operating otxst of the process. With faster rates of exchange, less desorbent material has to be punaped through the iprmcss aad separated from the extract stream for reuse in the process.

Resolution Is a measure of tbe degree of separation of a two-component system, and can assist is quantifying tbe effectiveness of a particular combination of adsorbent, desorbent, conditions, etc. for a particular separation. Resolution for purposes of this application is defined as tbe distance between tbe two peak centers divided by tbe average width of tbe peaks as 1/2 the peak height as determined fey tbe pulse tests described hereinafter. The equation for calculating resolution is tbsss: Equation 3 H nc J»2 ~ i-i ■1/2 where Lj and Lj are tbe distance,, in em* respectively, from a reference point, zero to the centers of tbe peaks and Wj and W2 are tbe widths of tbe peaks as 1/2 lb® height of tbe peats.

A dynamic testing apparatss is employed to test various adsorbents with a particular feed mixture and desoroent Eaaterfal to measure tbe adsoribeat characteristics of adsoiptive capacity, selectivity and exchange rate. The apparatus consists of an adsorbent chamber comprising a helical column of approximately 70 cc volume having inlet and outlet portions at opposite ends of the chamber. The chamber is contained within a temperature control means and, in addition, pressure 5 control equipment is used to operate the chamber at a constant predetennined pressure. Quantitative and qualitative analytical equipment such as refractometers, polarimeters and chromatographs can be attached to the outlet line of the chamber and used to detect quantitative^ or detenmne qualitatively one or snore components in the effluent stream leaving the adsorbent chamber. A pebe test, 20 performed using this apparatus and the following general procedure, is used to determine selectivities and other data for various adsorbent systems. The adsorbent is filled to equilibrium with a particular desorbent material by passing the desorbent material through the adsorbent chamber. At a convenient time, a pulse of feed containing known concentrations of a tracer and of a particular extract component 15 or of a raffinate component or both, all diluted in desoxbent, is injected for a duration of several minutes. Desorbent flow is resumed, and the tracer asd tbe extract component or the raffinate component (or both) are aimed as in a iiqnid> solid chromatographic operation. Hie effluent can be analyzed oostream or, alternatively, effluent samples can be collected periodically and later analyzed 20 separately by analytical equipment and traces of the envelopes of correspocdmg component peaks developed.

From information derived from the test adsorbent, performance can fee ia terms of void volume,, retention volume for as extract ©r a rsJaiagse component, selectivity for one component with respect to the other, and the rate of 25 desorption of an extract component by the deswbeai Tbe retention vote of as extract or a raffinate component may be diaracterized by the distance between lbs center of the peak envelope of an extract or a raffinate component asd the peak envelope of the tracer composes! or some other known reference point It is expressed is terms of the vsfeae is tabic centimeters of desorbent pomped deriag 30 this time interval represented by fee distance between tbe peak envelopes.

Selectivity, (B), for as extract component with respect to a raffinate component may be dbiaracterized by the ratio of the distance between the center of tbe extract component peak earoslope asd the tracer peak envelope (or otber reference pok) to tbe corresponding distance between fee center of fee raffinate oompoaeag peak A 0 envelope and the tracer peak envelope. Tbe rate of exchange of an extract component 'with the desorbent can generally be characterized by the width of the peak envelopes at half intensity. Tbe narrower tbe peak width, the faster the desorption rate. The desoiption rate can also be characterised by the distance between the center of the tracer peak envelope and the disappearance of an extract component which has just been desorbed. This distance is again the volume of desorbent pumped during this time interval.

To further evaluate promising adsorbent systems and to translate this type of data into a practical separation process requires actual testing of the best system in a continuous countercurrent liquid-solid contacting device. The general operating principles of such a device have been previously described and are found in Broughton U.S. Patent 2,985,589. A specific laboratory size apparatus utilizing these principles is described in deRosset et at., U.S. 3,706,812. The equipment comprises multiple adsorbent beds with a number of access lines attached to distributors within the beds and terminating at a rotary distributing vahe. At a given valve position, feed and desorbent are being introduced through two of the Maes and the raffinate and extract streams are being withdrawn through two more. AH remaining access lines are inactive and when the position of the distributing valve is advanced by one index, all active positions will be advanced by one bed This simulates a condition in which the adsorbent physically moves ia a direction countercurrent to the liquid flow. Additional details on the above-mentioned nonionic adsorbent testing apparatus and adsorbent evaluation techniques may be found in the paper "Separation of Cg Aromatics by Adsorption" by A. J. deRosset, R. W. Neuzil, D. J. Korous, and D. H. Rosback presented at the American Chemical Society, Los Angeles, California, March 28 through April 2,1971.

One class of adsorbents to be used la the process of this invention will comprise nonionogenic, hydrophobic, water-insoluble, crosslinked styreae-po^visytybenzese copolymers and copolymers thereof with momoethylesaicalty unsaturated compounds or polyethylenically unsaturated moaomers other than poly(vi!nyl)henzenes, iadiadixig the acrylic esters, such as those described In Gustafson U.S. Patent Nos. 3,531,463 and 3,663,,467, although not limited thereto., As stated in U..S ,, Patent No. 3f531f 4S3t, the polymers may be made by techniques disclosed in U.S. Serial No. 749,526, fifed July m,BS8immPa^stNos.4MM; 4,224,415; 4J56&40; 4297,22®; 4382,124 and 17 4,501 ,,826 to Meitzner et al.

Adsorbents such as just described are manufactured by tbe Rohm .sad Haas Company, and sold under the trade name "Amberlite." Toe types of Amberlite polymers known to be effective for use by this invention are referred to in Rohm 5 and Haas Company literature as Amberlite adsorbents XAD-1, XAD-2, XAD-4, XAD-7 and XAD-8, and described in the literature as "hard, insoluble spheres of high surface, porous polymer." The various types of Amberlite polymeric adsorbents differ somewhat in physical properties such as porosity volume percent, skeletal density and nominal mesh sizes, but more so in surface area, average pore lo diameter and dipole moment The preferred adsorbents will have a surface area of 10-2000 square meters per gram and preferably from 100-1000 m*/S» These properties are listed in the following table: 18 TABLE 1 Properties of Amberlite Polymeric Adsorbents XAD-1 XAD-7 XAD-8 Poly- XAD-2 »UM Acrylic Acrylic ^ Cherolca 1 Wature styrene Polystyrene Polystyrene Ester Ester_ Porosity Vol one % 37 42 51 SS 52 Try© Wet Density graiss/ec 1.02 1.02 1.02 1.05 1.09 lo Surface Area NVgran 100 300 7S0 450 160 Average Pore Diameter Angstroms t **3 OS? g f Si Skeletal Etensity grams/cc 1.07 1.07 1.08 1.24 1.23 Nominal FtesSi Size 20-50 20-EO 20-50 20-50 25-50 IDipole Moment of Functional Groups 0,3 0.3 0.3 1.8 1.8 Applications for AmberMte polymeric adsorbents suggested in the Rohm and Haas Company literature include decolorizing pulp mill bleaching effluent, decolorising dye wastes and removing pesticides from waste effluent There is, of course, no hint In the literature of my surprising discovery of the effectiveness of Amberlite polymeric adsorbents in the separation of citric acid from Aspeigillus-Niger fermentation broths.

A second class of adsorbents to be used in the process of this invention will comprise weakly basic anion exchange resins possessixsg tertiaiy amine or pyridine functionality in a cross-linked polymeric matrix, e.g.s acrylic or styrene. They are especially suitable when produced in bead form, fasve a high degree of uniform polymeric porosity, exhibit chemical and physical stability and good resistance to attrition (not common to macroreticular resins).

Adsorbents such as Just described are manufactured by the Rohm and Haas Company, and sold under the trade name "AmberMte." The types of AmberMte polymers known to be effective for use by this invention are referred to in Rohm and Haas Company literature as AmberMte adsorbents XB-275 (IRA-35), IRA-68, and described in the literature as "insoluble in all common solvents and having open structure for effective adsorption and desorption of large molecules without loss of capacity, due to organic fooling." Also,, suitable are AG3-X4A and AG4-X4 manufactured by Bio Rad and comparable resins sold by Dow Chemical Co., such as Dowsx 66, and Dow experimental resins made in accordance with US. Patents 4,031,038 asad 4 J98#5X Use various types of polymeric adsorbents of these classes available, will differ somewhat in physical properties such as porosity volume percent, skeletal density and nominal mesh sizes, and perhaps ssose so in surfiaoe area, average pore diameter and dipole momeM. Use preferred adsorbents wall a surface area of 10-2000 square meters per gram and preferably from 100-1000 m*/fr Specific properties of the materials listed above can be found sn company literature and technical brochures, such as tbose in tbe following Table 2 which are incorporated hoeia by reference. Others of the general class are also svaitebie.

AG3-4A (Bio Rad) AG4-X4 jDO^ Expenmental Resins Mmm Ty Polystyrene Acrylic Polystyrene Kegierence to <^ommiw jLiterature Chromatography Electrophoresis Ixnmumochemistiy Molecular Biology - hplc - Fries list M April 1987 (Bio-Rad) Chromatography Electrophoresis hamunochermstrv Molecular Biology - HPLC 'Price List M April 1987 (Bio-Rad) U.S. Patent Nos. 4.031,038 and 4,098,867 Dowsx 66 ira~35 (xe-275) mA-m Polystyrene AciyMe Acsyiie Material Safety Data Sheet Printed 2/17/6? (Dow Chemical USA) Amberlite Ion Exchange Resms (XE-275) Rohm & Haas Co. 1975 Amberlite Ion Exchange Resins - Amberlite IRA-68 Rohm & Haas Co. April 1977 Applications for Amberlite polymeric adsorbents suggested in the Rohm and Haas Company literature include decolorizing pulp mill bleaching effluent, decolorizing dye wastes and removing pesticides from waste effluent Here is, of course, oo hint ia the literature of my surprising discovery of she effectiveness of AinfeerMte polymeric adsorbents in tbe separation of citric add from AspcigQlus-Niger femncMBMon broths.

A third dass of adsorbents to be used in the process of this inventKm will comprise strongly basic anion exchange resins possessing quaternaiy ammonium m a cross-linked polymeric matrix, e.g.a dwiisylbemsEe cross-linked aaylic or styrene resias. They are especially suitable when produced in bead form and haw a high degree of uniform polymeric porosity asd exhibit chemical asd physical stability. Im the instant case, the resins can be gelular (or "gdkype") or 'taaeroreticulai'' as she tens is used in same recent literature, namely Basin and 21 Hetheriqgton, A Progress Report on the Removal of Colloids From Water by Macroretirnfer Ton Exchange Resins, paper presented at the International Water Conference, Pittsburg, PA, October 1969, reprinted by Rohm & Haas Co. in recent adsorption technology, "the tenn microreticular refers to the gel structure per se, size of the pores which are of atomic dimensions and depend upon the swelling properties of the gel" while "macroreticular pores and trae porosity refer to structures in which the pores are larger than atomic distances and are sot part of the gel structure. Their size and shape are not greatly influenced by changes is tbe environmental conditions such as those that result an osmotic pressure variations" while the dimensions of gel structure are "markedly dependent upon tfiie environmental conditions." In "classical adsorption" "the terms microporous asd macroporous normally refer to those poresless than 20 A and greater than 200 A, respectively. Pores of diameters between 20 A and 200 A are referred to as transitional pores." Hie authors selected the tern "macroreticular", instead, to apply to tbe new ion exchange resins used in this invention, which "have both a microreticular as well as a macroreticular pore structure. The former refers to the distances between the chains and crosslinks of the swollen gel structure aad tbe latter to the pores that are sot part of the actual diemical strcctere. Tbe macroreticular portion of structure may actually consist of nricfo-, aad transitional-pores depending upon tbe pore size distribution." (QBCsles are from page I of tbe Kunin et aL article). Tbe macroreticular structured adsorbents also haws good resistance to attrition (mot common to cosivestioaal maartOT'esaslgjf resins). Ia this application, therefore, all reference to %iacr©FetIcaI!isrs indicates adsorbent of tbe types described above having the dual porosity defined by Kseoia asd Hethesing. "Gel" asd "gel-type" are used in their cosvestiosal sense.

Looking at both tbe quaternary ammonium &sctioi»^ai»naisiqg ion exchange resins of tbe invention, tbe quaternary amine has a positive charge asd can form SB ionic bond with the sulfate ion. Hbe sulfate form of quaternary ammonium 22 anion exchange resin lias a weakly basic property, which in turn, can adsorb citric add through an arid-base interaction.

P - K* CR)S or P - N+ ~ (R)2 CC2Ha0H) 0" 0~ " I •- .. « „* :o * s « o: id — IT - C.A." I" H+-C.A.' where P * resinous nofety R * lower altyl, C-^ C.A. ■ citrate lo Adsorbents sudu as just described are manufactured by fee Rohm and 5 Haas Company, and sold under the trade name "Amberlite." The types of Amberlite polymers known to be effective far me by this invention are referred to in Rohm and Haas Company literature as Amberlite IRA 400 and 900 series adsorbents described in tbe literature as Insoluble in all common solvents, open structure for effective adsorption and desorption cm large molecules without loss of 10 capacity, due to organic fouling." Also suitable are AG!, AG2 issnd AGMP-1 resins manufactured by Bio Rad and comparable resins sold by Dow Chemical Co* soda as Dowex 1,2,11, MSA-1 and MSA-2, etc Abo useful ia tMs invention are the so-called intermediate base ion exchange wMda are mixtures of strong and weak base exchange resins. Among these are the following commercially available resins: Bio-15 Rex 5 (Bio-Rad 1); Amberlite IRA-47 and Duolite A-340 (boils Rohm & Haas).

For example, they may be useful where a basic ion exchange resim is seeded which is not as basic as tbe stmmg base resins, or one wjaidh is naosre basic than tbe weaMy basic resins.

Use various types of polymeric adsorbents of these dasses avaiScMe 20 wH differ somewhat ia pbgpsicael properties suds as porosity vttee percent, skdbtal density and nominal mesh sizes, and perhaps more so ia surface area, average pore diameter and dipole nxmeBL Tbe preferred adsorbents will have a surface area of 10*2000 square meters per gram and preferably feona 100-1000 at'/g, Specific properties of the materials listed' above can b® found m m>mpsmy literature and 2 5 tedisaleal ferockares, such as those siemtioned in tbe &Mqg Table 3 . \ 23 TABLE I PROPERTIES OF ADSORBENTS Adsorbent IRA 458 CRohsn 5 Haas) IRA 958 IRA 900 IRA 904 IRA 910 IRA 400» 402 IRA 410 AG I {Bio m z Bio Rex S CBIo Rad) Matrix Resin Type Acrylic gel-type Acrylic macroporous Polystyrene macroporous Polystyrene aiacroporous Polystyrene macroporous Polystyrene macroponis Polystyrene gel-type Polystyrene gel-type Polystjreiae gel-type Polystyrene raacroporous Mixture of strong base bwA weak base resins (e.g. ftS»2 a nid A£-3 ©r AS-4 Reference to Company literature Amberlite Ion Exchange Resins 1186 & Technical Bulletin IE-207-74 34 Technical Bulletin and Material Safety Data Sheet are available Technical Bulletin is available and Itanberlite Jon Exchange Resins* IE-100-66.

Technical Bulletin, 1979 and IE-208/74, Jan. 1974 Technical Bulletin, 1579 and IE-I01-56, Hay 1912 Amberlite Ion Exchange Resirss,,, Oct., Sept. 1976j, April 1972 IE-69-52', October 1976 .Amberlite Son Exchange Resins IE-72-53* August 1970 Chromatography Electrophoresis Immunochemistry Molecular Biology HPLC, Price List H April 1987 Chromatography Electrophoresis Immunochemi stry Molecu!ar Biology HPLC, Prise List 8 Upril 198? Chromatography Electrophoresi s Immunochemistry Molecular Biology HPLC, Price List H April 198? Chromatography Electrophores1s Immunochemistry Molecular Biology HPLC, Price List M April 2987 Use adsorbent :may be employed m the fonn of a dense compact fked feed which is alternatively contacted "with tbe feed mixture and desorbent materials.

In the simplest embodiment of the invention the adsorbent Is employed ia the fonn ef a single static bed ia which case the process is only semicontinuous. In another embodiment a set of two or more static beds may be employed in fixed bed contacting with appropriate valving so that the feed mixture is passed through one or more adsorbent beds while the desorbent materials can be passed through one or more of the other beds in the set The flow of feed mixture and desorbent materials may be either up or down through the desorbent Any of the conventional apparatus employed in static bed fhisd-5olid contacting may be used.

Countercurrent moving bed or simulated moving bed oountercurrent flow systems, however, have a much greater separation efficiency than fixed adsorbent bed systems and are therefore preferred. In the moving bed or simulated moving bed processes the adsorption and desoiption operations are continuously taking place which allows both continuous production of an extract and a raffinate stream and the continual use of feed and desorbent streams. One preferred embodiment of this process utilizes what is known in the art as the simulated moving bed oountercurrent flow system. The operating principles and sequence of such a flow system are described in U.S. Patent 2,985,589.

In such a system it is the progressive movement of multiple ligui access points down an adsorbent chamber that simulates tbe upward movement of adsorbent contained in the chamber. Only four of the access lines are active at any one time; the feed input stream, desorbent inlet stream, raffinate outlet stream, and extract outlet stream access lines. Coincident with this simulated upward movement of the. solid adsorbent is the movement of tbe liquid occupying the void volume of tie packed bed ofadsoibent So that countercurrent contact is maintained, a liquid flow down tbe adsorbent chamber may be provided by a pump. As an active liquid access point moves through a cycle, tbst is, from the top of the chamber to tbe bottom, tbe chamber tiroalation pump moves through different zones which require different flow rates. A programmed flow controller may be provided to set and regulate these flow rates.

T« active liquid access points effectively divided tbe adsosbest chamber into separate zones, each of which has a different function, fa tMs embodiment of my process it is generally necessary that three separate operational zones be present in order for the process to take place although in some instances an optional fourth gone may be nised.

Hie adsorption zone, zone 1, is defined as the adsorbent located between the feed inlet stream and the raffinate outlet stream. Ia this zone, the 5 feedstock contacts the adsorbent, extract component is adsorbed, and a raffinate stream is withdrawn. Since the general flow through zone 1 is from the feed stream which passes into the zone to the raffinate stream which passes out ef the zone, the flow in this zone is considered to be a downstream direction when proceeding from tbe feed Met to the raffinate outlet streams. io Immediately upstream with respect to fluid flow in zone 1 is the purification zone, zone 2. The purification zone is defined as the adsorbent between the extract outlet stream and the feed inlet stream. Hie basic operations taking place in zone 2 are the displacement from the nonselective void volume of the adsoibent of any raffinate material carried into zone 2 by shifting of adsorbent into 15 tMs zone and the desoiption of any raffinate material adsorbed within tbe selective pore volume of the adsorbent or adsorbed on the surfaces of the adsorbent particles. Purification is achieved by passing a portion of extract stream material leaving zone 3 into zone 2 at zone 2's upstream boundary, the extract outlet stream, to effect the displacement of raffinate material The flow of material in zone 2isina 20 downstream direction from the extract outlet stream to the feed inlet stream.

Immediately upstream of zone 2 with respect to the fluid flowing m zone 2 is the desoiption zone or zone 3. Hie desorption zone is defined as the adsoibent between the desoibent inlet and the extract outlet stream. The fraction of the desoiption zone is to allow a desorbent material which passes into tMs zone 2 5 to displace the extract component which was adsorbed upon the adsorbent during a previous contact with feed in zone lma prior cycle of operation. The flow of fluid in zone 3 is essentially in tbe same direction as that of zones 1 and 2.

In some instances an optional buffer zone, zone 4, may be utilized. TMs zone, defined as the adsoibent between the raffinate outlet stream and tbe 30 desorbent inlet stream, If used, is located immediately upstream with respect to tbe feid flow to zone 3. Zone 4 would be utilised to conserve the amount of desorbent utilized in tbe desorption step since a portion of tbe raffinate stream wMdh is removed from zone 1 can be passed into saoxte 4 to displace desorbent material present in that zone out of that zone into the desorption zone. Zone 4 will contain \ 26 enough adsoibent so that raffinate material present in the raffinate stream passing out of zone 1 asd into zone 4 can be prevented from passing into sine 3 thereby contaminating extract stream removed firom zone 3. In the instances which the fourth operational zone is not utilized the raffinate stream passed from zone 1 to 5 zone 4 must be carefully monitored in order that the flow directly firom zone 1 to zone 3 can be stopped when there is an appreciable quantity of raffinate material present in the raffinate stream passing firom zone 1 into zone 3 so that tbe extract outlet stream is not contaminated.

A cyclic advancement of the input and output streams through tbe 10 fixed bed of adsoibent can be accomplished by utilizing a manifold system in which the valves in the manifold are operated in a sequential manner to effect the shifting of the input and output streams thereby allowing a flow of fluid with respect to solid adsoibent in a countercurrent manner. Another mode of operation which can effect the countercurrent flow of solid adsorbent with respect to fluid involves the use of a 15 rotating disc valve in which the input and output streams are connected to the valve and the lines through which feed input, extract output, desorbent input and raffinate output streams pass are advanced in the same direction through tbe adsorbent bed. Both tbe manifold arrangement and disc valve are known in the art Specifically rotary disc valves which can be utilized in this operation can be M in US. 20 Patents 3,040,777 and 3,422,848. Both of the aforementioned patents disclose a rotaxy type connection valve in which the suitable advancement of the various input and output streams from fixed sources can be adneved without difficulty.

In many instances, one operational zone will contain a much larger quantity of adsoibent than some other operational zone. For instance, in some 2 5 operations the buffer zone can contain a msBor amount of adsoibent as compared to the adsorbent required for tbe adsorption and purification zones. It can also be seen that in instances ica wMcs desorbent is used which cam easily desoxb extract materia! from the adsofbeat that a relatively smal amount ef adsnbent wiffi fee needed in a desoiption zone as compared to tbe adsorbent needed in the buffer 30 2an© er adsoiptioa smie ©r purification sose or all erf them* Since it is not required feat the adsorbent be located ia a siagle column, the use ef multiple chambers or a series of columns is within the scope off tbe invention.

It is not necessasy that all of tbe input or output streams fee simultaneously used, and in feet, in many instances one of tbe streams can be skat 27 off while others effect .an input or output of material. Hie apparatus which can be utilized to effect the process of this invention can also contain a series of iD.divtd.ual feeds connected by connecting conduits upon which are placed input or output taps to which the various input or output streams can be attached and alternately and 5 periodically shifted to effect continuous operation. In some instances, tihe connecting conduits can be connected to transfer taps which during the normal operations do aot function as a conduit through which material passes into or out of fJhe process.

It is contemplated that at least a portion of the extract output stream 10 will pass into a separation means wherein at least a portion of the desorbent material can be separated to produce an extract product containing a reduced concentration of desorbent material. Preferably, but not necessaiy to tbe operation of the process, at least a portion of the raffinate output stream will also be passed to a separation means wherein at least a portion of tbe desorbent material can be 15 separated to produce a desorbent stream which can be reused in tbe process and a raffinate product containing a reduced concentration of desoibent material. Tbe separation means will typically be a fractionation column, the design and operation of which is well-known to tbe separation art Reference can be made to D. B. Broughton U.S. Patent 2,985,589, and 20 to a paper entitled "Continuous Adsoiptive Processing~A New Separation Technique" by D. B. Broughton presented at the 34th Annual Meeting of the Society of Chemical. Engineers at Tokyo £, Japan on April 2t, 1969, for further explanation of the simulated moving bed countercurrent process flow scheme. 2 5 Although both liquid and vapor phase operations can be used in many adsoiptive separation processes, liquid-phase operation is preferred far this process because of the lower temperature requirements and because of the Mgher yields of extract product than can be obtained with Hquld-phase operation <wer those obtained with vapor-phase operation. Adsorption conditions will indtidb a 30 temperature of Sroxn. 2QPC to ' 2O0°C with ' 6S°C to . 100°C being mure preferred and a pressure range o>£ frosa ■ atmospheric to 500 psig (3450 kPa gauge) being more preferred to ensure liquid phase. Desoiption conditions will include the same range of temperatures and pressures as used for adsoipte conditions. 28 The sixe of the units which can utilize the process of this invention can vary anywhere fr©m those of pilot plant scale (see for example our assignee's U.S. Patent 3,706,812,. to those of conunercial scale and can range in flow rates firom as little as a few cc an boor up to many thousands 5 of gallons per hour.

The ffoHowing examples arc presented to illustrate the selectivity relationship that makes she process of my invention possible. Tbe example is not intended to unduly restrict the scope and spirit of claims attached hereto.

EXAMPLE I in this example, three pulse tests were run with a neutral styrene divinylbenzene polymeric adsorbent (XAD-4 made by Rohm & Haas Company) to determine the ability of the adsorbent to separate citric acid, at different pH's, from its fermentation mixture of carbohydrates (DPI DP2, D3P3, Including glucose, xyHose. arabinose and ra£5nose) and ions of salts, isicfedmg Na**", K"1", Mg~ +, 15 Ca+ *rJFe'r"r "% CT, SO^, FO^s and NCkf, amino adds and proteins. The first test was mm at a pH of 2.4 and 45°G. Two further tests were run at a pH ef 1.7 asd 0.9. Citric add was desorbed with water. Use fermentation feed mixture had the following composition: Feed Composition Amount Citric Add 12.9% Salts (K+, Na+f Ca+ +, Mg* + Fe+*+) i.60% (6000 ppm) Carbohydrates (Sugars) 1% Others <S04", CT, P042, NOf, 5% pldBs aad mono ados) .

Water SI 5% ReteBilcm volumes asd ressktioa were obtained uising tlie pulse test apparatus asd procedure previous^ described. Spedfica%, the adsorbent was tested is a 70 cc straight column using Use ffoB©wsbg sequence ef operations fear the pdse test Desorbent material was cootimKwsJy run upwardly tbnw^i the cotea \ 9Q containing the adsoibent at a nominal liquid hourly space velocity (LHSV) of about 1.0. A void volume was detennined by observing tbe volume of desorbent required t© fill the packed diy column. At a convenient time toe flow of desoibent material was stopped, and a 10 ©c sample of feed mixture was injected into the oolumn via a sample loop and the flow of desorbent material was resumed. Samples of the effluent were automatically collected in an automatic sample collector and later analyzed for salts and citric add by chromatographic analysis. Some later samples were also analyzed for carbohydrates, but since they were eluted at approximately the same rate as the caibohydrates, they were not analyzed in these examples nor were other minor ingredients, amino acids and proteins. From the analysis of these samples, peak envelope concentrations were developed for the feed mixture components. Hie retention volume for the dtric add was calculated by measuring the distance firom the midpoint of the net retention volume of the salt envelope as the reference point to the midpoint of the citric add envelope. The resolution, R, is calculated firom Equation 3, given earlier. Tbe separation factor, B, was calculated as previously indicated.

Tbe results for these pulse tests are shown in the following Table 4.

Test A - pH - 2-4 Component Salts Citric acid Met retention Volume 44.4 Test B - pH - 1.7 Component Salts CltHe acid Net retention Volume 0 42.2 y 5S %• Peak Width st P..5 Height 14.4 Resolution (0.5 Height) 1 *50 Ms l« Reference Peak Width at 0»5 Heiaht - - ** t — 11-6 45.1 Resolution {0.5 Height) 1.49 Reference lest C ~ dH - Q.

Component Salts Citric acid Ket retention Wolssie 40.9 Peak Width at 0.5 Height 13.3 45.1 Resolution (0.5 Height) 1.4 Reference He results are also shown m Figure 3A is wtada It is clear that wbie citric add Is more strongly adsorbed than tbe other coBapojaemts,, these Is a substantial loss of dmc acid which is irasdsosbed asd tcmmed the salts m& carbohydrates (mi sbmm). Qtric add Is satisfactodly separated is the process la Figure 3B where the results are jpdged good and ia Figure 3C where tlie resalts are judged oedOoEt "The process clearly wH have cosj®©rda3 feasibility as a pH of 3L7 asd fewer. At a pH of 2.4 (Figure 3A), however, it is noted ssbst^tlal aanoat of the dtric acid wSI be weowstd in the form of the citrate, H^A*\ is the rafiSstate with the salts and carbohydrates. From this,, It Is evident ilsat tise ioaized, 3i soluble species should be reduced, as explained previously, by maintaining a lower pH in the feed, thereby driving the equilibrium ia Equation 1 to the left.

EXAMPLE II lais example presents tbe results of using a neutral arosslinked styrene divinylbeozene (XAD-4) and a neutral arosslinked polyacrylic ester copolymer (XAD-8) with the same separation feed mixture as Example I at different pHs to demonstrate the poor separation when tbe pH is 2.4 or higher, or above the first ionization constant, pK&j « 3.13, of citric add. TOae same procedure and apparatus previously described in Example I were used in the separation, except the temperature was 60°C and 5 ml of feed mixture was used.

Figures 4A, 4E amd 4C are, respectively, graphical presentations of the results of the pulse tests using XAD-4 at pHs, respectively, of 2.4,1.7 xad 0l9.

Figure 4A shows that dtric add "breaks through" with the salts (and caibohydratcs). TMs problem can be partially alleviated by lowering the pH to 1.7 as In Figure 4B. Ai* excellent separation csya be achieved by lowering the pH fertiher to 0.9 as in Figure 4C This separation, with adjustment of the pH, again, dearfy has OQsami&rdsI ntMky.

Figures 4D and 4E are, respective^, graphical representations of the results of pulse tests, ran under the same conditions as above, using XAD-8 at pHs of 2J asd 1.4 and temperatures of 65°C Figure 4D, which was made at a pH of 2.8, shows no separation, but rather the salts, carbohydrates and dtric add elutisg together initially. After atoomt 67 ml, after most of tie cark&ydrates and salts and some of the dtric add haw been recovered, some relatively pore dtric add can be obtained, but meoovety is low. Figure 4JEL, which was made at a pH of IA, shows a selectivity between dtric add and carbohydrates and salts whidi results In a satisfactory separation and recovery of the citric acid.

This example presents the results of using a neutral csosslinked styrene djvinyroenzese copolymer (XAD-4) with the same separation feed mixture as Exansple I at two different pHs to demonstrate fee poor sqperatfea when the pH 32 is 2.4 or higher. The same procedure and apparatus previously described in Example I were used, except the temperature was 93°€ m Figures 5A and 5B and the ataount of feed mixture W.ES 10 ml.

Figures 5A and SB are, respectively, graphical presentations of the 5 results of pulse tests using XAD-4 at pHs. respectively, of 2.8 and 1.4. Figure 5A shows that dtric add "breaks through" with tee salts and carbohydrates. TMs problem can be alleviated by lowering the pH to 1.4 as in Figure SB. This separation, with adjustment of the pH, again,, clearly has commercial utility. msmmm The procedure and apparatus previously described in Example I was used mi the samples of this example. The temperature was 60°C and 5 ml. of feed mixture was used. The feed composition was similar to that previously used except that dtric add has been concentrated to 40% in the feed mixture. The effect of concentration on the pH will be seen. M Figure 6A, even with the temperature at 15 60°c; the pH of 1.9 is too high to separate the dtric add at 40% concentration. By adjusting the pH downward as in Figures 6B and 6Q the dtric add is preferentially adsorbed and excellent separation is achieved at a pH of U3 and at a pH of 05. In each of these samples, carbohydrates were not analyzed, but it can be assumed that tike carbohydrates dosely followed the salts in the separation.

EXAMPLE ¥ The procedure and apparatus previously described in Example I was used ©n the three samples of this example. The temperature was 93°C and the amount of feed mixture was 5 mL The feed composition was similar to that previously used except that citric add has been concentrated to 40% in the feed 2 5 mixture to demonstrate fhe further effect of eoneeetratiosi on the pH. fo Figure 7A, even with the temperature at tbe pH of 1.8 is too high to separate the dtric add at 40% concentration. By adjusting the pH downward as in Figures 7B asd the dtric add is preferentially adsorbed and excellent separation is achieved.

Again, carbohydrates were not analyzed, but it can be assumed that the 30 caibohydrates closely followed tbe salts in tbe seporatkm. 33 BXAMWJi VI The pulse test of Example I was repeated on two 50% dtric acid samples using XAD-4 adsorbent The desorbent in both eases was water. Use composition of the feed used was tbe same as used in Example I except that dtric add has been concentrated to 50%. Tbe temperature was 93°C In the first sample, tbe pH was 15. As shown m Figure 8A, dtric add was not separated. After reducing the pH to 1.0 in the second sample, dtric add was readily separated as seen in Figure 8B. Again, carbohydrates were not analyzed, but assumed to dosely follow the salts. The separation in Figure SB was Judged good.

EXAMPLE VP Tbe separation example represented by Figures 7B end 7C required high temperatures, e»g<,9 93°C to achieve the separation of 40% dtric add due to the difficulty in desoibing dtric add from tbe XAD-4 adsoibent In this example, high temperatures, which adversely affect the adsorbent Mfe and the cost to operate, are eliminated and the separation is readily achieved at 45°C through the use of a desorbent mixture of 10% (by wt) acetone and 90% water. Referring to Figure 9, a feed comprising 40% (wt) dtric add, 4% carbohydrates and 2% salts of the following elements: Kx, Na*, Mg* "% Fe* 'r *rt Ca* * plus protdss asd amino adds, was introduced into the pulse test apparatus as set forth previous^ asd tlie test ran as Ibefore except that the temperature was 45®C la tMs test, the pH was maintained at 05, but the desorbent contained acetone as mentioned above. The net retention volume lor dtric add was 10.7 sal, and the R«Ma was 0l61 and, therefore, the separation was easily made.

EXAMPLE vm h finis example, jfoor poise tests were nsa with a wealkly basic anion exchange resin having a tertsaiy amine function hydrogen bonded to a ssalfefce mm* ia a cross-linked gel-type acrylic resin matrix (AG4-X4 made by Bio Rad Laboratories, Kidaoood, California) having a tertiary amine function hydrogen hooded to a 34 sulfate ion, in a cross-linked acrylic resin matrix to determine the ability of the adsorbent to separate citric acid firom its fermentation mixture of caiboihydbrates (DPI, DP2, DP3, induding glucose, xylose, arabinose and raffinose) and ions of salts, indudingNa+,K+,Mg+ +, Ca+ +JFe+ + +, CT, S04ss, VOf and NOf, amino adds and proteins at a pH of 1.6. Hie first test was run at a temperature of 75°G Tbe remaining tests were run at 60®C. Citric add was desorbed with water in False Test No. 1 (Figure 10) and sulfuric add in two concentrations: 0.05 (Pulse Test No. 2) and 0.25N (Pulse Test No. 3). Pulse Test No. 4 was like Poise Test No, 2 except that it was made after the adsorbent was used with 24 bed volumes of feed. Hie fermentation feed mixture had tbe following composition: Feed Composition Per Cent Citric Add 4©% Salts (K4,»Na*, Ca4" *, Mg+ + Fe+ + +) 15% Carbohydrates (Sugars) 4% Others (SQ4^\ CT, P©4% NO3-, 5% proteins and amino adds) Water 495% Retention volumes and separation factor (5) were obtained using the pulse test apparatus and procedure previously described m Example I except that a 5cc sample was used. The net retention volume (NRV) for tbe dtric add was calculated by measuring tbe distance from tbe midpoint of tbe salt envelope as tie reference point to tbe midpoint of tbe dtric add envelope. Tbe separation factor, 8, is calculated from tbe ratio of the retention volumes of tbe components to be separated to tbe retention voJume for tbe first salt componet (Le. Salts!).

Tbe results sew these poise tests are shown in tbe MlowingTaMe No.

. TABLE NO. 5 Pulse Test Resin/Desorbent 1 AG4-X4/Water 2 AG4-X4/0.05N H2S04 3 AG4-X4/0.25N H9SO4 4 A64-X4/0.05N H9SO4 . Feed Component MRV B Salts 1 1.6 34.25 Citric Acid 54.8 Reference Unknowns A 0 Tracer Unknowns B .6 8.30 Salts 2 54.6 1.00 Salts 3.2 11.87 Citric Acid 38.0 Reference Unknown A 0 Tracer Unknown B 2.7 14.07 Unknowns A 0 Tracer Citric Acid .9 Reference Salts 2.3 11.70 Unknowns B 7.6 3.54 Unknowns A 0 Tracer Citric Acid 38.0 Reference Salts 2.4 .8 Unknowns B 7.2 .28 Use results of Pulse Teste 2*4 are similar to Figure 10. From Table 5, it Is dear that while citric acid is satisfactorily separated in the process, in highly purified form, with water, desoiption with water is slower than with dilute sulfuric add as evidenced by larger net retention volume. After aging the adsorbent with 24 bed volumes of feed, the adsorbent shows oo signs of deactivation, as observed in Figure 13, which is substantially identical to Figure 11 (conducted under identical conditions with fresh adsorbent).

EXAMPLE IX Tbe first pulse test of Example VIS was repeated using the same procedure and apparatus except that the temperature was 65°G Tbe desoibent was water. This example presents tbe results of using a maaroporous weakly basic anionic exchange resin possessing a cross-linked polystyrene matrix (Dowex 66) witb the same separation feed mixture as Example VM (40% dtric add) an the first two poise tests at a pH of 7.0 and 35 (Figures HA and HB> respectively) to demonstrate the failure to accomplish the desired separation when tbe pH is above tbe first ionization constant, pKaj « 3.13, of dtric add, and more specifically m these two samples, where tbe concentration of dtric add is 40%, when the pH is above 1.7. In tbe third part erf tbe example (represented by Figure HC), the feed was diluted to 13% dtric add and the pH reduced to 2.4. While toe is evident Improvement, it is apparent that tbe pH and/or concentration will have to be reduced farther to prevent "breakout" of the dtric add. For example, at 13% concentration, it is estimated that tbe pH must be lowered to about 1.6 to 2J2 Figures HA and MB are, respectively, graphical presentation ef the results of the pulse test using Dowex 66 at pHs, respectively, of 7.0 and 3 J. Figures !A and BE show that dtric add "breaks through* with the salts (and esrfeolwdrEies) as tbe higher pHs. His problem can be partially alleviated by redudsg the ooncentratioa to 13% and lowering tbe pH to 2.4 as in Figure HQ where it is shown that only a smaH amount of citric add is not adsorbed and "breaks through* in the raffinate while most is adsorbed onto the adsoibent resin (but not desorbed in this Figure). This separation, with adjustment of the concentration and pH to optimum levels, dearly will have eoxiunerdtel utility. 3? gXAMPLB X Three additional pulse tests insider the same conditions as Example ¥111, except as noted, were made ©a dtfic acid samples of tlie same food composition, but with two different adsorbents. The desoibent m the Sm two samples was 0.05 N H2SO4 (Figures 12 and 13A) wmk water was used in tbe third sample (Figure BB). The composition of the feed ased was the same as used m Example VUL The temperature was &PC and tbe pH was 1.6- Ibe adsoibent #1 in the first test was a macroporous pyridiae fianclion^ntaimbng divinylfoeazene cross-linked resin of the ibllowHEjg took flDtulti '■s I s P - CH« - I - GK9 £. £ Xo) K4S§4" where F Is tlie polystyrene moiety fonaing the resin. The second adsorbest (#2), Ksed in tbe second and third samples* is a tertiary amine, also with a pyridine functional group, having tlie following tek -© p - ch - I - chl I * 1 m2 emu 1 ©ig where P Is as, defined above. Beds rcsiss are cxoss4siiked with divinylbenzene. In some cases, while water is an effective desoibeat, with excellent separation if is not strong enough to recover the adsorbed citric add qeickiy enoogh to make tbe process eosnmesdafy attractive. See Figeare 13E, in which Ae 20 sc©ditfess are the same as above, using adsorbent #2, where water is the desorbent. Iks tMs case dtric add does not elate wstS about 95 ml of desorbent haw passed fliroEgbi tic adsote Efflnte ssl&ric add is, Mbc, the preferred desoebent, as 38 win be apparent firom Hie results shown in Figures J2 and BA, Also, firom Figures 12, !3A and BB. It wiil Ibe seen that an excellent separation of citric acid is obtained.

Tii® procedure, conditions and apparatus previously described in Example VIE were nsed to separate four samples of citric add Srom the same feed with two different resins of the same dass of adsoibent as Example YJOEL, (except that in tbe first and Mi samples, the column temperature was 50®C and tbe desorbent was 0.Q5N H^SO*; m the second and third samples the pH was 22 and Hie desorbent was dihite sulfuric add at 0.15 N concentration). Both resins, XRA-68 and IRA-35, obtained firom Rohm and Haas, have an amine function sad the following structural fonanla: R" P - CH2 NiH+SO^ R" where Pis the poly acrylic matrix, asd R'aadR* « €3%.

Amberlite IRA-68 (Sample Nos. i 2 and 3) Is a gel-type resin. IRA-35 (Sample No. 4) is a raacroreticular-type resin. Sample No. 3 was identical to Sample No. 2, except that the adsorbent had prewmssly been used to separate 69 bed oohmaos of the feed Sample Nos. I and 2 are both excellent adsorbents £br separating citric add from Its fermentation broth within the pH range ef W to 22. Sample No. 3, after aging the adsorbent with 69 feed volumes of feed, demonstrates tin© stability of the resin (little or no deactivation has taken place) in this separation. Net retention vctoae (NRV) and selectivity (0) are shown in tbe felowiBg TaMe 6. 39 TABLE 6 Sanrple No.

Resin Component urn 1 Amber 11 ita Salts .5 8.24 IRA-68 Citric Acid 45.3 Reference 'Unknown A 0 Tracer Unknown B 9.3 4.87 2 Amber!ite Sal ts 2.3 12.6) IRA-68 Citric Acid 29.0 Reference Unknown A 0 Tracer Unknown 8 6.5 ' 4.46 3 Amber!i te Salts '2.85 .32 1RA-58 Citric Acid 29.4 Reference Unknown A 0 Tracer Unknown B 7.0 4.2 4 Awberli te Salts 1.3 27.38 IRA-35 Citric Acid 36.9 Reference Unknown A 0 Tracer Unknown 3 .9 6.25 In £ farther comparison of die dauned adlsoroesss of ficgs^es I throegh VDt with Examples VBDf tihroKgh XI, several samples of the earacs: were analyzed for readily carbonizable impurities (RCS) (Food & Chemical Codex (FCC) Monograph #3) asd potassium level. ECS is determined in the foBcrwiag maimer: a I jpa sanople ef tine extract (acsoal concentration of dtric add Is determined) is carbonized at 90°C with 10 ml erf 95% H2SO4. Tine carboaibsd substance is spectrophatometrically measured at 500 urn ssiig a 2-csa ©si with a OS inch diameter tube aad tihe amosmt of RCS is calculated for 50% dtric add solution. Toe number arrived at can be compared with that obtained by esing tMs procedure on the cobalt standard solution of tlie FCC test mentioned above. Potassium is determined % atomic adsorption spectroscopy. For comparison, tbe same analytical determinations were made cm a sample of the same feed and RCS calculated far 50% citric add with XAD-4, AG4-X4, and adsosbe&ts No. I and No. 2 of Example SI. Tlie results are shown in TuaMe 7. 48 P 7 RCS XAIM AG4-X4 #2 (Ex. X) #1 (Ex. X) h2O .05NJH2S04 .Q5KH2S04 .05N.H2SQ4 Calculated iffor 50% CA.) ppmK CA. Net JteuVol. 6.86, 8.98 59, 137 13.0 1.77,1.42 24,81 34.8 3.17,333 . 24,54 .8 2.17 62 31.0 An improvement in both reduction of levels of RCS and K for the weakly basic resins compared to the neutral resins is indicated by tMs data In ell samples, RCS was reduced by at least 50% asd In two samples, K was reduced by over 50%. It is Eoted from the Bet retention volume that boiia dasses of adsorbents ha^e good resolution, but the strong base adsorbents suffer somewhat firom increased cycle times. The cycle times can be reduced by using higher concentrations of sal&sic acid, e.g., Hp to about Ci2R in the preferred range of 0.1 to Q2N.

In another embodiment, citric add adsorbed on the adsorbent may be converted in situ to a dtrate before being desorbed, for example, by reaction with an alkaline earth metal or alkali metal hydroxide or ammonium hydroxide and then immediately doted lasimg a metal fydrosride, amnxmhim hydroxide car water as the desorbent Deactivation ef tine adsorbent fey the unknown impurities may take place sb time, but the adsorbent may fee regenerated by fleshing with a stronger desoibent, e.g* a higher concentration of sulfuric acid teas the desorbemt, an alkali metal bydiosride car NH4OEL or an organic solvent, e.g^ acetone or alcohol .AMFIJB All la this example, two pulse tests were run with a gel-type strongly basic ankm exchange resm (IRA 458 aoade by Rohm & Haas Co.) having thc stmctal tesla like (I) oo pegejl above, substituted with three methyl groups, to determine the ability ef the adsorbent to separate citric add from its fermeatatioM mixture ef carbohydrates (DPI, DP2, DP3, including glucose, xylose, arabinose and raf&nose) and ions of salts, including Na"1", K*1*, Mg+ *r, CaT T CT, 804®, PO4S and NOj", amino adds and proteins at a pH of 22. P is aoylic arosslinked with divinylbenzene. Pulse test Sample No. 1 was ran at a temperature of 50®C Pulse test Sample No. 2 was run at 60°C, but after tbe bed had been aged with 33 bed volumes of feed. Further rams 'to 62 bed volumes have been made with no signs of deactivation of the adsoibent Citric add was desorbed with 0.xn solution of sulfuric acid in both samples. The fermentation feed mixture had the following composition: 'er urn1 Qtric Add 40 Salts (K+, Na+, Oa* +, Mg+ + Fe* + +) 15 Carbohydrates (Sugars) 4 ©tjfaers (SO*®, O", PO| NO3", 5 proteins and amino ados) Water 495 Retention volumes and separation factor were obtained using tSae pulse test apparatus and procedure previously described in Example L The results for these pulse tests are shown in die following Table No. g. 42 imgms Feed Sample No.

Resin Component HRV 3 . 1 !RA~458 Salts 1.0 38.9 ' Citric Acid 38.9 Reference Unknowns A 0 __ Tracer Unknowns 3 S.S .89 2 IRA-458 Sal ts 0.9 43.3 Citrflc Acid 39.0 Reference Unknown A 0 Tracer Unknown B 7.1 .49 Is Is dear that citric acid is satisfactorily separated Is the process, asd after aging the adsoibent with 33 bed volumes of feed, the adsorbent shows no saigas of deactivation, which is substantially identical to the results under dtosefy Identical 15 conditions with fresh adsorbsM.

EXAMPLE Xm The pake test of EiaiBple XII was repeated on additional dtric add samples using the same feed, but a different, saacroporous, strongly basic anionic exchange adsorbents, BRA-958, possessing quaternary ammonium functions and an 20 acrylic resin matrix cross-linked with dmnylbenzene matrix, Tiae desorbent was QMS N H2SO4. Tbe composition of the feed used was tbe same as used in Example XBL Use temperature was 60°C asd the pH was 14. The adsorbent in tMs test was a resin obtained from Rohm & Haas having the stracsure (1) shown on page. 21, where R is methyL As shorni in Figure 14, citric add starts diaiSBg after 45 ml of desoshest have passed feo# tbe adsorbent and is vesy effective^ separated to the fermentation mixture in Mgli potior with awriSent recovery. 43 F.XAMP1 .F. XIV Tie pulse test of Example XH was repeated an an additional dtric add sample using the same feed, but a different, strongly basic anionic exchange resin adsorbent, AG2-X8 (obtained from Bio Rad Company) having a structure like 5 formula (2) above, (page£f) where R is methyl, with a cross-linked polystyrene gel- type resin matrix having quaternary ammonium functional groups thereon. The desoibent was 0.X5N H2SO4. The composition of the feed used was the same as used in. Example XI. The temperature was 50°C and the pH 'was 22.

As shown in Figure 15, dtric acid starts eluting at about 43 ml of 10 desoibent have passed through the adsoibent and is veiy effectively separated from the fermentation mixture in high purity with excellent recoveiy.

In a further comparison of adsorbents of Examples I through VH with Examples XII through XIV, several samples of the extract were analysed for readily carbonizable impurities (RCS) (Pood & Chemical Codex (FCC) Monograph #3) 15 and potassium level as described above. The results for each of the adsorbents, XAD-4, BRA 458, IRA 959 and AG 2-X4 with the indicated desorbent are shown ia the following Table 9.

TABIB9 EXTRACT QUALITY fRCS/POTASSIUM) BY PULSE TEST CANet Retention Volume 13.0 37.9 32 43 An iapswsaeat in both reduction of levels of RCS and K for the strongly basic resins compared to the neutral resins is Indicated by this data. Ia all samples* RCS rcs XAD-4 MA 458 IRA 958 AG2-X4 Desorpent h2O OLIN H25Q4 aQ5HH2SQ4 ol15NH2so4 (Calculated at 50% CA) (Units) ppjnK (Calculated at 50% CA.) 6.86 59 8.98. 137 SO 2.73 82 53 131 44 was reduced by between 40*85% and K was reduced between 0-20%. It its noted from Examples XII, XM and XIV (Fig. 14), that both classes of adsorbents haw good separation, but the present adsorbents suffer somewhat firom increased cyde times. The cyde times can be reduced by tasing higher concentrations of sulfuric ad4 e.g., up to about OJSN in tbe preferred range of 0.1 to 0.2N.

In another embodiment, dtric add, adsorbed on the adsoibent may be conversed in sfea to a dtrate before being desoibed, for example, by reaction with an alkaline earth metal hydroxide, alkali metal hydroxide or ammonium hydroxide and then immediately eluted using a metal hydroxide, ammonium hydroxide or water, as tbe desorbent Deactivation off tbe adsorbent by tbe nnksown impurities may sake place in time, but tbe adsoibent may be regenerated by flushing witis a stronger desorbent, e.g., a high concentration of sulfuric add than tbe desorbent, an alkali metal hydroxide or NH4OH, or an oiganic solvent, e.g.s acetone or alcoboL 45

Claims (14)

claims:

1. a process for separating citric acid from a fermentation broth feed mixture containing citric acid characterized in that said mixture is contacted with a 5 polymeric adsorbent selected from a neutral, crosslinked polystyrene polymer, a nonionic hydrophobic polyacrylic ester polymer, a weakly basic anionic exchange resin possessing tertiary amine or pyridine functional groups, and a strongly basic anionic exchange resin possessing 10 quaternary amine functional groups, and mixture thereof at adsorption conditions whereby selectively to adsorb said citric acid, and thereafter said citric acid is recovered from said adsorbent with a desorbent at desorption conditions. 15

2. A process according to claim 1 characterized in that said adsorption and desorption conditions include a temperature of from 20 to 200°C and a pressure of from atmospheric to 500 psig (3450 kPa gauge).

3. A process according to claim 1 or 2 characterized 20 in that said desorption is effected in the liquid phase with water or an aqueous inorganic acid or a ketone or mixtures thereof.

4. A process according to any one of claims 1 to 3 characterized in that said absorbent comprises a 25 tertiary amine functional group supported on a matrix comprising a crosslinked acrylic resin.

5. A process according to any one of claims 1 to 3 characterized in that said adsorbent comprises a pyridine functional group supported on a matrix 30 comprising a crosslinked polystyrene resin. A <Jc U

6. a process according to any one of claims 1 to 3 characterized in that said adsorbent comprises a quaternary amine functional group supported on a matrix comprising a crosslinked acrylic resin. 5

7. A process according to any one of claims 1 to 3 characterized in that said adsorbent comprises a quaternary ammonium salt of pyridine supported on a matrix comprising a crosslinked polystyrene resin.

8. A process according to any one of claims 1 to 3, 10 6 and 7 characterised in that the quaternary ammonium group is in the sulphate form.

9. A process according to any one of claims 1 to 3 wherein said adsorbent is in the sulphate form.

10. A process according to any one of claims 1 to 9 15 characterized in that it comprises the steps of: (a) maintaining net fluid flow in a single direction, through a column of said adsorbent containing at least three zones having separate operational functions occurring therein and being serially interconnected, 20 with the terminal zones of said column connected to provide a continuous connection of said zones; (b) maintaining in said column an adsorption zone, defined by the adsorbent located between a feed input stream at an upstream boundary of said zone and a 25 raffinate output stream at a downstream boundary of said zone; (c) maintaining immediately upstream from said adsorption zone, a purification zone defined by the adsorbent located between an extract output stream at an 30 upstream boundary of said purification zone and said feed input stream at a downstream boundary of said purification zone; 47 (d) maintaining immediately upstream from said purification zone, a desorption zone defined by the adsorbent located between a desorbent input stream at an upstream boundary of said zone and said extract output 5 stream at a downstream boundary of said zone; (e) passing said feed mixture into said adsorption zone at adsorption conditions to effect the selective adsorption of said citric acid by said adsorbent in said adsorption zone and withdrawing a raffinate output 10 stream comprising the nonadsorbent components of said fermentation broth from said adsorption zone; (f) passing the desorbent material into said desorption zone at desorption conditions to effect the displacement of said citric acid from the adsorbent in said 15 desorption zone; (g) withdrawing an extract output stream comprising said citric acid and desorbent material from said desorption zone; (h) passing at least a portion of said extract output 20 stream to a separation means and therein separating at separation conditions at least a portion of said desorbent material; and (i) periodically advancing through said column of adsorbent in a downstream direction with respect to fluid flow in said adsorption 25 zone, the feed input stream, raffinate output stream, desorbent input stream, and extract output stream to effect the shifting of zones through said adsorbent and the production of extract output and raffinate output streams. 30

11. A process according to claim 10 characterized in that a buffer zone is maintained immediately upstream from said desorption zone, said buffer zone defined as the adsorbent located between the desorbent input stream at a downstream boundary of said buffer zone and the raffinate output stream at an upstream boundary of said buffer zone.

12. An adsorption process for separating citric acid from a fermentation broth feed mixture containing citri acid characterized in that said mixture is contacted at a pH lower than the first ionization constant PKa-j of citric acid, with a weakly basic anionic exchange resin possessing tertiary amine or pyridine functional groups at adsorption conditions whereby selectively to adsorb said citric acid, converting the citric acid into a sal by reaction with an alkaline earth metal hydroxide, alkali metal hydroxide or ammonium hydroxide, and eluting the salt with a metal hydroxide, ammonium hydroxide or water as eluant.

13. A process according to claim 1 for separating citric acid from a fermentation broth feed mixture, substantially as hereinbefore described and exemplified

14. Citric acid whenever obtained by a process claimed in a preceding claim. F. R. KELLY & CO-, AGENTS FOR THE APPLICANTS.