GB2497330A - Layered double hydroxide for treating solutions containing phthalate - Google Patents

Abstract

A process for treating an aqueous solution having a pH of 4 or greater, the solution comprises at least one phthalate ion or salt of formula (I), wherein m is 0, 1, 2, 3 or 4 and R is a C1 to C8 hydrocarbyl or OR2, R2 is H or C1 to C8 hydrocarbyl and when more than one R group is present the R groups may be the same or different. The process involves contacting the aqueous solution with a first material comprising a layered double hydroxide of formula [Mz+1-xAlx(OH)2]q+(Xn-)q/n.yH2O for a predetermined time, wherein M is a metal cation, z is 1 or 2, x is 0.1 to 1, y is 0 to 5, X is an anion, n is 1, 2 or 3 and q is determined by x and z. The aqueous solution to be treated may further comprise at least one aliphatic carboxylic acid, for example adipic acid, succinic acid, butyric acid, propionic acid, acetic acid or formic acid. Preferably, the anion (X) of the layered double hydroxide is a halide or nitrate. The alkaline solution may be an alkaline waste effluent from an anthraquinone process for the production of hydrogen peroxide.

Description

TREATMENT OF SOLUTIONS

The present invention relates to processes for treatment of aqueous oIutibns containhig' phthalate spetles, preferably subsfltuted phttislate s species, and the mutejials resulting frd' áuch treatment.

Layered dout4e hydro$des (LDHs) are a elSa of ç,rnpbth' Us which comprise two metaLeatiocis and have a Iayered'structure:4 A review of'LDHs, Is' provided in:Stftjctw* and BondThg; Vol 119,2006 Layemd Double t4*oxklss S. X Duan and b& Evans., The tydtOtalcites, perhaps'the most weJl4nowri to examples of Lot-is, have been studied for mafly'years. LOWs can intercalate anions between, the layers of the siructure WO 99124139 discloses use of LDHs to separate anions Including aromatic and aliplj*tie dnions.

Substituted phthalate anions are not biodegradable products and irnpurttk' in a number of Indusidal processes. Qonsequently is liquid waste. cnt*ktg phthalatS IbM requires treatment before ft. can be dispoed of whlh. can be both e$pefl&veafld en&'. Wiefflc lent.

Phthalate Ions may be present. in the effluent of a number.01 Mdostrial processes including' chlorination of phtbalic anhydlide, synthesi Of amino levulinic acid, qulnophthalone dye synthesis and esterification of philiaflo add oranhydride JP I t5365 A relates to trSent of a wSste Qquor discharged during chlorination of' ptithailc anhydride,, us4-6583317 relates to a method, of preparing an acid additibA, Stat delta amino levulinic acid.

USA.4396768 discloses syntheilt of qulnophthaione dyestttfft US*4086835 disclosE" a process for treating effluent obtained hi production of anester piastloizeic One of the prcesses with can lead te Substituted phthalater, ion by-products is the flir*qulnone process for production of' hydrogen p*A"de in 3O which an anthraquiflone is sequentially hydrogenated and oxidised. There are well known rcycIIng methods for the over-hydrogenated compounds produced in the hydrogenation step; however, there Is a need for treatment I: methods for the waste products from the oxidation stage of the reaction.

During this stage. the anthráhydroquinone may be over-oxidised, whih es It to break down into substituted phihalic acid derivatives and a large rimber of other organie anions Indutg allphatlt species &g. adipate).

s There isa need to find asysteni thaflanremovephthaiateloflso( s$s froni obtflon preferaIy selectively in, Order to ité the Slütion.

btodegiadábje. ideafly the phthalate' Ions sPtd be recpverab(e and the.

protess should work rapidly In aUpline conditions and at close to room, tèfflperature'.

S It is an aim of the present invention to address these needs.

The present invention accordingly provides i a first aspect, a ptøcess for treating an aqueous solution, the process compñsing, provldin9 an aqueous solution 1t be treated, the solution having a pH of to or greatór and comprising' at tèast'one pttthalate peóSs & fonnula: Is wherein m is 0, 1, 2, 3, or 4 (preferably 1, 2, 3 or 4) and R is aCt tO C8 hydrocarbyl or QR R is H or Cj to Ce hydrocarbyl, and, Wherein when more than' one R group is present the R groups may be t,' same or different p:id1ng a'first mateilal comprising a layered double hydro9de of formula,.

H

whereinMlsarnetalcation,ztsl or2,xisO.1 te1yis0'to5,Xisanàfli0n.

n is I to 3 and q is determined by x and z, and contacting the aquOous solution with thernater1ai for a predetermined time.

Surprisingly, the treatment process of the invention results in at. least partial removal.f the phthalate species from the aqueous. solution. ThUs, the protess is advantageous as a method of waste water treatment fr Industrial waste that containsphthalate lent It is particularly: advantageous for alkaline $ aqueous soluti na Where the Works well.

The pH of the aqueous sc!uUon will usually be alkaline, of pH 7 or greater and is preferably pH fior greater4 The layered double hydrozde, mey be gepeçaliy any kind of LDH. M may be a slngtá metal cation or a mixture of different metal cation,. for io example Mg, Zn, Fe for a MgFeZn(Al LOH. Preferred M are Mg. Zn, Fe, Ca or a mixture of twg' r more of these, Preferably,z:IszandMis'CaorMgorzls'iandMiSLL Thusthe preferred OHs are Mg/Al, Ca/Al or Li/Pd, The preferred I: kns are halIde prefetably Cl, or nhtrat Nitrateis most prefe., begaMse it appears to result is lAthe removal of t"bit phthalate species from:theaqueots solution,,. Usuaflyx is 0.3 to OS.

The R substituerit (or R sustitUerits It more. than 1) may be at any position on the benzene ring 0 he phthalate,in Species. Generally, substituted pMhatate ions relatively common In waste streams have substituents at the 4-posItion. Consequently, the phthalate species will usually be of formula: 2%:," o In' 2$ R wIll commonly be H or Ott2 (R2 most commonly being H) or a C1 to C8 aikyl, preferable C, to Cs alkyl. :3'

Treatment will usually be performed at a temperature of 80°C or lower for 0.1 to 28 hours, preferably 60°C or lower for up to 24 hours.

The process of the invention will often be performed on an aqueous solution wherein the aqueous solution to be treated further comprises at least s one aliphatic earb.oxylic acid, for example acidic acid, s.uccinic acid, butyric acid, propionic acid, acetic acid, formic acid, or a salt thereof. It is, in fact, often beneficial if alphatic carboxyllo acids are not removed because they may serve as food for bacteria in water treatment stations. The selectivity of the present invention is consequently even more advantageous.

An aqueous solution most advantageously treated in the process of the invention is alkaline waste effluent from an anthraqui.none process for the production of hydrogen peroxide (which usually additionaHy comprises e.g..

adipate as a by..product), The great advantage of the process is that the process results in a reduction in the concentration of the phthalate species and is (at least parfially) selective for reduction of the concentration of the phthalate species over reduction in the concentration of other (especially aliphatic) species and, in. particular, any adipate present in the aqueous sclution.

The process preferably involves a step of purging the aqueous solution of carbonate before treatment with the first material. This may be achieved by purging with nitrogen.

In one embodiment of the invention, the process further comprises at least one further step of contacting the aqueous solution with a second matérial, the second material comprising the same or a different layered double hydroxide to the first material. This can advantageously improve the overall reduction in concentration of phthalate species in the aqueous solution an can, for exarnple1be used to remOve other anions (ag. carbonate) anions.

which can interfere with the removal or reduction of phthalate species by LDH.

Generally, the LDH removes at [east some of the phthalate species by intercalation wherein the layered double hydroxide intercalates the phthalate species. Advantageously, the intercalated guest phthalate species may be recovered by treatment of the iniercalated LDH with a solution of another anion.

In a second aspect the present invention provides a layered double hydro9de of formula: Al (OH)(X)qm.yH2O wherein M is a metal cation, z is I or 2, xis 0.1 to 1, y IsO to 5, X is an anion, n is I to 3 and q is determined by x and z, having intercalated therein a to phihalate species of formula: Rm h wherein m isO, 1, 2, 3 or 4 (preferably 1, 2, 3 or 4) and wherein R is a is C1 to C.8 hydrocarbyI and wherein when more than one R group is present the R groups may be the same or different.

Other advantageous features are as discussed in relation to the first aspect and as specified in the c[aitns.

The invention is illustrated by the Figures in which: Figure 1 illustrates the XRD pattern of the CaAI-N03 LDH before and after intercalation with tbutyl phthaiate, Figure 2 illustrates the XRD pattern of MgAktbutyl phthalate, Figure 3 illustrates the XRD pattern of LiAkOl LDH and after intercalation with methyl phthatate and tbutyl phthalate., Figure 4 is a schematic illustration of the Tntercalation of akyl phihalates to form a huayer, showing the change in interlayer spacing upon intercalation for each of the LIJHs, Figure 5 is a graph of the concentration of the various components of c waste water after three treatment cydes with LIAI-N03 at. 60°C, FigureS' Isa graPh of the concenttation of the vatious components of waste water after fgqr treatnienicydes With CaALN03 at room tempefature, Figure 7 is a raph of the total aromatic copcent,tØ'fl in waste waiSt after three treMment cycles with C'aAt-N03. MgAl-NO an LiAI-NOi at,roQfli tern peratute and Figure 8 IS a graph Of the total concentration of aromatic anions In: waste water after three freatmotS with LIPJ-NOjCi at 20 d 60'C.

to The Invention is further illuitratid by the following Examples.

Examples

Pøaratn of LDH materials and ChaffiOtetisatlgP Methbd is Elemental analysIs was carøed qut, using a quantitative combustion technique.

PoWder X-ray dlffraothrt (XRO) data were collected on a PAN Analytical)CPert Pro diffractcnieter In reflection mode at 40 ky and 40 i.' using Cu 1(0 radiation (a' = 1.54067 A, U = 4.64433 A, weighted average = o 1.54178 A). Samples were mounted on stainless steel sample holders.

oprecipItation and intercalation reactions werc carried out in rund-bottomed flasks or finger ampoules ppmpdate, to the scale of the reaction, cqittning a sultabi solvent and a x''netlc follower with, a pivot ring; the contents of the flask were stirred for the reqUisite time at a suitable temperature. The mixture was allowed to cool and flM5d using a sintered glass Mt. if the filtrate was required, it was collected in a Buchner flask and removed before Washing jhe,:soM residue with delonised -and abetoneA The powder was left to.&y in ak before pt,aracterliatton byXRD. 6'

ynthesisof1jAl2.QHj.sICFnH2O [UA12(OH)e]ClnH2O was synihesised using the method of Eogg, A M.; CHare, 0. Cheni. Mater; 1999, ii, 1771-1775 where a four-fold molar excess of LiCI was added to a suspension of gibbsite in water, and the s resulting mixture was stirred at Dot for 24 hours. The LDH formed as a white powder, which was then filtered and dried..

Synthesis of fLiAi7QH)TNO3'hH2O [L1AI2(OH)6]NOa'nH2O was synthesised by ion exchange.

[UAI2(OH)5}CNnH2O was added to a 9 M solution of NaNO3 in deionised water and stirred at 80°C for 12 hours. The solid product was filtered and dried.

*$yjiesis of [Mg2AI(OH)e]NOrnH2O was synthesised by coprecipitation. A mixec is metal nitrate solution was prepared by *dissoMng 21.4 g of Mg(NO)26.H2O and 10.5 g of AF.(N03)39H20 in 100 ml of water. This was added dropwise to a solution of 6 g of NaOH and 9.5 g of NaNO Th of water over a period of about 30 minutes. The mixture, which was thoroughly purged with nitrogen gas at all stages, was stirred vigorously for 24 hours at 80°C. The product formed as a white powder which was collected.

[Ca2AI(OH)s]ChnH2O was produced by the same method, En which CaCI2 and AICIa were added dropwisato a solution of NaGH and NaCI.

Synthesis of CagOH6LNO2nH.Q [Ca2AI(QH)5INO3'nH2.Q was synthesised by a saR-oxde method.. 2.48 g of CaO was added to 100 hi of water and stirred until fully suspended. Then.

to this suspension, 472. g of AKNOs) was added and stirred until dissolved.

The mixture) wNch was thoroughly purged with nitrogen at all stages, stirred vigorously for 12 hours at cot. The solid product was collected. The product formed as a white powder..

Intercalation Reactions Alkyl Phthalate lnteitalatbn These reactions were.accompUshed by addition Of a 1.2 molar excess s of the guest to a vigorously stirred suspension of the host in water at around 80t. The mixture was allowed to age for 24 hours at. this temperature, then removed and the solid product recovered. In the case of a typical &kyl phthalate intercStion by ion exchange, 1.33xi0 moles of sodium tbuty!-phthalate (Na2C1.2H2O4) were dissolved in 10 ml of water, and to this added to 1..11x103 moles of LDH. Such a reaction would norrnaUy produce 1..03x104 L09x10 moles of the alkyl phthalate LDH.

CompetItive Intercalation Reactions Competitive Entercalations between alkyl phthaiates and adipate were i5 carried out with the addition of disodiurn adipate in a 1.2 molar excess to the reaction mixture, The [OH host, alkyl phthalate and adipate were then stirred at 80"C fo.r 24. hours before filtering.

Intrial Effluent Treatment These reactions were accomplished by purging the effluent with nitrogen gas to remove carbonate followed by the addition of LDH host. These reactions were carried out at a variety of temperatures and were stirred vigorously for 24 hours before the solid product was removed by filtration and the liquid filtrate was collected for ailalysis. In the case of a typical reaction, 10 ml of effluent was purged wrth N2 and 0 3 g of [LAl2(OH)1NO3 nH2O was added and the suspension was stirred at for 24 hours at specified temperatures ranging from 20ThYC. Such a reaction would typically produce 0.19-0.22 g of scud product.

Dc-intercalation Reactions Deinterca1ations were performed by adding 0.2 g of the relevant LDH to 10 ml of a 0 09 M solution of Na2CO3 in H20 or to a 0 1 lvi solution of NaNO3 in H20. This was sUrred for 120 minutes before fiFtedng, The solid was washed and dried.

ijtmeptofAueopsso!uUons s Model studies were performed to study the selectivity of anion ifltercalatio.n in LDHs. An excess of a 1:1 mixture of disothum alkyl phthalate and disodium adipate was added to a syspension of S selected LDHs. The CaAL-N03, MgAlCl and L1AF-N03 compounds are shown to be 100% selective for the alkyl phthalate under the conditions examined, and the MgAI-N03 in hybrid shows 93% s&ectivity for the methyl phthak te/adipate system and 100% preference for the butyl phthalate/adipate mixture.

These LDHs were then used to treat a sample of actual aqueous effluent from a hydrogen peroxide process. The efficiency of selective intercalation of aU alkyl phthalate derivatives from. this solution was is determined. All three [OH systems show sefectMty for the phthaiate dedvatives, with the LIAI-CI compound exhibiting a 2:1 preference, whilst removing over 95% of the toxic, anions within three intercalation cycles.

Initial pro. of of concept involved demonstrating the intercalation of alkyl phthalates into three selected LOHs by ion exchange. 4alkyl phthalates (methyl phthalate and tbutyl p:hthalate were choosen as examplars of phthalates found in this type of waste stream), Both 4-alkyl phthalates were successfully intercalated into three different LDHs by treatment of the host LbH with a solution of disodium alkyl phthatate at.80t for 24 hours. The products were analysed by powder X-ray diffraction (XRD)., IR spectroscopy, themiogravirnetric analysis (TGA). elemental analysis (EA) and solid state MAS NMR. Selected analytical data are detailed below.

Structure AnalysI The X.RD data was indexed on the basis of a hexagonal unit cell with lattice constants a, h, and c, where a = b and a.90000 y 120.00°. The latUce parameters for the precursor LDHs, the LDH-methyl phthalates and the LDHtbutyl phthaiates are given in Table 1.

The a and b lattice parameters remain larg&y unchanged since these depend on the arrangement of the metal cations within the layers, which changes very little with ion exchange. The c parameter is indicative of the expansion of the layers upon intercalation of the larger guest anion; the CaAI $ and LIAl LDH.s contain two layers within the unit cell, whereas the MgAI has three layers in the unit cell.

Table 1: Lattice parameters determined for the precursor LDHs and their methyl phthalate analogues.

Material alA cIA CaAI-Cl 5.72 15.52 CaAknethy jhthaiate r572t2772 CaAi3butyl phthalate 5,72 3316.

NOã.05* 2562 MgAlJhutyl phihalate 3.03 50.79 UAI-Cl 4.65 15.27 LiAlmethyl phthalate 4.85 33.02 LiAlbutyl phthalate 4.81 33.48 The CaAI.methyl phthalate exhibits a distinct shift of reflections to higher vaftie.s as the interlayer spacing increases by 6.10 A. The XRD pattern of GaAlbutyl phtha.late * of Figure 1 demonstrates an increase in interlayer spaang relatve to the methyl phthalato analogue upon ntercalation The (004) reflection overlaps with the (002) reflection of the starting material, hence, the absence of all of the startlIng material cannot be established, A similar shift of reflections indicating an increase of 7.27 A in intedayer spacing can be seen for the MgAI-methyl phthalate, although a small amount of starting material is present, with the (003) and (006) reflections of the starting material overlapping the (006) and (0012) reflections of the product

IC

respectiv&y, leading to increased intensities on these reflections. This is also seen in the XRD of the MgAlbutyl phthalate; the (003) reflection can be identified at 1&93 A showing an increase in interlayer spacing of 8.39 A compared to the starting material (Figure 2), The reflections are broad and of s low intensity as is typical for MgAI-LDHs.

The XRD patterns for LiAkCI and LiAI-rnethyl phthalate are shown in Figure 3. The sharp pattern indicates a highly crystafline product characteristic f the L1AI derivatives. The increase in. interlayer spacing upon intercalation is 9.49 A. The UAl-butyl phthalate is also crystalline, with no evidence of 0 reflections due to starting material or LiAI-C03, The reflections ahsetved in the XR[) patterns for the MgAl system are due to the systematic absences in accordance with the selection rule (-h + k + I 3n). This is consistent with the: reflections exhibited in the XRD spectra..

The LiAl-LDHs show a more complex series of Bragg reflections due to their s differing structure. They crystalUse in a hexagonal structure, as the gibbsite polyrnorph of Ai(OH)3 was used in the synthesis (use of the baeyerite or nordstrandite polymorphs resuits in rhombohedral l..DHs).

The methyl phthalate ion has a maximum length of 6.81 A. The interlayer spacings are consistent with the formation of a bilayer in which the hydrophobic methyl-groups lie in the centre of the interlayer space, while the negatively charged carhoxylate groups interact with the positively charged LDH layers. The patterns for all three tbutyl phthalate LDHs indicate a greater increase in interlaye.r spacing compared to the methyl phthalate LDHs, which is to be expected as the guest anion is larger. The nature of the intercalation IS shown schematically in Figure 4.

Infrared (IR) spectroscopy was quahtatively used to identify the p.resnce of alkyl phthatate in the LDHs and, in the case of CaAl-NOs and M9AI-N03. whether or not the characteristic N03 absorption is present after ion exchange.

Broad absorptions at around 3400 cm4 were present and are interpreted as being caused by the \QFs absorptions of the co-intercalated water and are generally seen in LOtHs. The absorpticns observed due to the presence of the methyl phthalate anion are at 1373 (methyl umbrella deformation), 1408 (vs COO), 1500 and 1545 cm1 (S/as COO).

The characteristic butyl phihalate absorptions were identified at 1373 (methyl umbrella mOde), 1404 (v6 000), 1500 and 1541 cm4 (S/as COO) s CaAltbutyl phthatate showed absoiptions at 1374 1410, 1502, 1545 and 3669 cm4, identii.ing the tbutyl phthalate and the off absorptions. The absence of the degenerate nitrate absorption at 1350 cm1 indicates complete.

reaction.

MgAmethyi phthalate exhibited the phthalate absorptions at 1391, io 1505 and 1543 cm4, but the absorption at 1375 crn1 was broadened by overlap with that of the nitrate which gives an absorption at 1350 cnh\ aJso observed in the MgAI-N03 starting materiaL The MgAl-butyl phthalate spectrum also showed broadening of the peak at 1373 cm1 as wefl as peaks at 1402, 1543 and 3369 cm1 This. broadening implies that some unexchanged nitrate i tell after reaction.

Besides the v absorptions at 3437 cm1, the spectrum of the L1AI-methyl phthaiate showed three absorptions due to the methyl phthalate at 1371, 1501 and 1.48 crn1. The peak expected at 1408 cm1 was disguised by broadening of the acH umbrella mode. The LjAltbutyl phthalate showed broad absorptionsat 1373, 1543 and 3373cm1.

Elemental analysis of each of the alKyl phthalate LDHs was performed.

Since alkyl phthalate is dianionic, complete occupation of guest sites leads to an ideal chemical formula of [LDH](CqHO4)o.B'flH2O nd [LDH1(C2Hl2O4)acflH2.O for the methyl and tbutyl phthalate respecthely, (the value of n can be determined by TGA). Since the successive deprotonations of the methyl phthalic acid occur at pH 4.1 arid 101., the unexpectedly high percentage of carbon in the LiALmethyl phthalate and CaAlbutyl phthalate.

can be understood as the intercalation of the alkyl phthalate monoanion, XRD provides evidence of the presence of un.exchanged chloride in the CaAI-methyl phth?Iate and unexehanged nitrate in the MgAmethyl phthalate (which can also be identified in the IR spectrum). i.

Table 2: Elemental composition results for LDH-methyl phthalates (O*bs, compared to those predicted by chemical formulae (Pred.) as a percentage of total mass.

Prod. Obs.

Formula %H %C %H %N [a2AKOH)cRCHeOC643HaO 1068 4.22 o,00 0'.39 4.24 EMgAF(Q} XGQI1bO4s(NO4)o2 3HO 1371 460 089 12 09 451 087 [LIAk(0H)l(C9H?04)'2H20 28.59 2. 24 3.20 j0.OO Table 3: Elemental composition results for LDHb.tyl phthalates (Obs.) compared to those predicted by chemical formulae (Pied.) as % of total mass..

Prod. Ohs.

Formula. %C %H %N MC %H %N Ca2Al(OH)6jC12Hi3O4H2O 32.44 4.72 0,00 32.54 3.51 0.1 t9,25 5.20 0.42 10.73 4.72 0.65 [LAI(OH)G](Cl2Rl2O4)oA2Cl.o,l3H2O 19.21 5.45 0.00 19.23 4,52 0.00 o Treatment of Endustrial Waste Water A sample of waste water from the anthraquinone process for synthesis of F1202 was contacted 3 times wIth different batches of Loll. Each reaction was stirred for 24. hours at 20 40, 60 and 80°C in order to compare the activities of the LOWs used and to determine the influences on the selectivity i of absorption. The treated waste water was analysed y UVNis spectroscc.py, HPLC and ionic chromatography UVNis spectroscopy was used to qualitatively determine the absorption of anions from the waste effluent.

The UVNIs absorption spectrum of the waste water showed a very strong, broad absorbance between 200 and 300 nm, and a weaker absorption at ca. 430 nrn. For all but the lowest concentrations1 the Arn value of the first peak was above the measurable intensity of the spectrometer, leading to a

II

fine structure seen at high intensfties, which was of no physical significance and is mer&y an artefact of the spectrometer.

Since the absorption of blue light occurs between 450 arid 40 nrn, the solution appears orange. This absorption is due to the bydroxy phthalate anions in the waste effluent, and the intensity of this peak can be i.sed to judge the effective uptake of anions. The MgAkNO3 arid LiAI-N03 systems at 60°C show the complete absence of this absorbance for wastewater, whilst the CaAI-analogues, both at room temperature and at 80°C, stilt show a significant absorption, which, upon comparison to the waste water calibration in curves, was found to correspond to approximately 50% of the concentration Of the waste effluent.

1-IPLU was used to elucidate the exact concentrations of the various aromatic anions pre$nt in the treated waste water.

Table 4: Concentrations of the various aromatic components of Waste water after three reaction cycles with CaAI-N03, MgAI--N03 and LiAI-NO at 80°C.

Target anion Untreated CaM-MgAI-N03 LiM-NOs

NO

aiateimgF 70 28 36 4-tert amyl phthalate JrngLfl 696 158 346 158 4-sec amyt phthalate /rngL 529 103 277 1.9 other alkyl hthatateslmgLf 214 82 130 97 - 4hydroxyphthalate /mgL 268 -64 91 23 The concentratic ns of the various phthalate derivatives in the treated waste water after three reaction cycles with LDHNO3. at 80°C are give.n in Table 4. The L1AI LDI is more absorbent: for the 4-sec--amyl phthalate, MgAI-NO3 absorbs *4T6% of the available anions, CaAl44O absorbs 80,5% and LiAI--N03 absorbs 99.6% of the anions from the waste water.

Table 5: Concentrations of the various aromatic components of waste watef after three reaction cycles with LiAl-NO and LiAI-CI at 80°C.

Target anion Untreated LiAt-N03 iLiAl-CI ae/mgtC70 2 25 4-ted amyl phtha!ate fliigL'T 696 8.8 36 - 4-sec amyiphthalate/mgL1 529 1.9 20 other alkyl phthakte!mgL -214 9.7 -55 4-hydroxy phthalatefrngL'1.268 2 346 The LIAI-NOa also removed more anions from solution than L1AI-CI, as S shown in Table.5, although LiAI-CI is stifi significantly more effective than the other LDH materials, absorbing 06.2% of the sec:amyl phthalate ions from solution The concentrations of the phthalate derivatives after each reaction cycle with LiAl-NO at 60°C are plotted in Figure 5 The graph shows that the to majority of the organic ions are removed in the second cycle, after the carbonate is removed in the first cycle. Figure 6 jtgws the changing concentrations of the phthalate derivatives after each reaction cyce with aAl-NO3 at room temperature. It is clear that a smaller proportion of the aromatic anions are absorbed in this systerr, in comparison to the LiAI-N03 systems.

The change in the total concentration of aromatic anions in the waste eI:fluent with each reaction cycle for the three LDH-NO3 systems at room temperature is shown in Figure 7. From this data, M9AI-NOa and LiAI-N03 can be identified as being much more absorbent towards the alkyl phthalate ions than CaN-NO3, Figure 8 shows the dependence of anion aborptFon on temperature for LIAI-N03 and LIAI-Ci at 20°C and 60°C. Regardless of the initial guest anion, greater alkyl phtha[ate absorption is exhibited at higher temperatures. Raising the temperature of reaction from 20 to 60°C increases the degree of absorbance of the aromatic anions, with the LiAl-NO3 host showing an

S

increase in removal of &kyl phthatates from 95.4 to 97.0% with the rise in temperature.

tonic chromatography has been used to determine the concentrations of the allphaflc constituents of the treated waste effluent. The sample of s industrial waste water used contained 1092 mgL1 of aliphatic anions. Of aU the anions present, onty adipate, acetate and formate are present in concentrations of over 100 mgL1, so the other anions were disregarded.

Tabte 6: Concentrations of the various aUphatic components of waste waterC io after three reaction cycles with CaAI-N03, MgAI.-N03 and LiAI-CL Treatment untreated CaAt-MgAI-N03 LIAI-CI method NO3 Adipate /mgL 540 105 262 180 do 141 170 Formate ThigL 140 109 123 140 For aH LDH systems, uptake of aliphatic anions was exhibited.; for example LiAI-CI remcves 66,7% o. the adipate from solution, CaAl4'JO is removes 63.9%, and 51.5% of the adipate anions are removed from waste water by the MgAkNO3 host,

Conclusion

LDHs cn he effective for the selective remova of aromatic anions from industrial waste. Not all LOll are equally effective, we find that the LiAI-NOs/CI system exhibits th.e best absprp.tion of alkyt phthá!ates from solution.

Table 7: Breakdown of the organic components of waste water into 94 aromatic and % atiphatic before treatment, and after three reaction cycles with each LOll.

Treatment method untreated CaA M9AI-N03 LiA-C3 NO3 % aromatic by mass 61.9 45.7 57,7 2.6 % aliphatic by mass 38.1 54.3 42,3 76.4 The highest sele.ctiv[ty is exhibited by LiAl-C L.DH, which removes 89.8% of the aromatic anions from the waste effluent, whilst removing cn.ly 46.1% of the aliphatic constituents a selectivity of 2:1), MgAI-N03 uptakes s 50.5% of the aroniatics and 40.9% of the.aliphatics (a.seiectMty of 1.2:1) and CaA44O3 removes 75.5% of the aromatic anions and 52.8% of the aliphatic components (a selectivity of 1,3:1).

Recycling of the substituted. phthalate intercalated LDHs can be achieved by a number of different methods such as ion exchange or diiute lo acid treatment We believe these systems show enormous potential n the possibflity of selective rcmoval of (alkyl or unsubstituted) phthalates salt from the industrial waste stream.

Claims (1)

1. <claim-text>CLAIMS1. A process for treating an aqueous solution, the process comprising, a. providing an aqueous solution to be treated, the solution having s a pH of 4.0 or greater and comprising at least one phthalate ion or salt comprising a species of formula: wherein m is 0, 1, 2, 3, or 4 and R is a C, to C3 hydrocarbyl or OR2, R2 is H or C1 to C5 hydrocarbyl, and wherein when more than one R group is present, the R groups may be the same or different; b. providing a first material comprising a layered double hydroxide Is of formula: * EMzticAL (oH)z(x)qin.yH2o * * wherein M is a metal cation, z is 1 or 2, x is 0.1 to 1, y is 0 to 5, *"* 20 Xis an anion, n is 1, 2 or 3 and q is determined by x and z, and **t*.* * * c. contacting the aqueous solution with the material for a predetermined time.</claim-text> <claim-text>2. A process as claimed in claim 1, wherein the solution has a pH of 7.0 or greater. Is</claim-text> <claim-text>3. A process as claimed in either claim 1 or claim 2, wherein M is a single metal cation or a mixture of 2 or more different metal cations.</claim-text> <claim-text>4. A process as claimed in any one of the preceding claims, wherein z is 2 and M isC or Mg orzis'i and Mis Li.</claim-text> <claim-text>5. A process as claimed in any one of the preceding Saims, wherein X is hafide, preferably Cl, or nitrate.o 6. A process as claimed in any one of the preceding claims, wherein x Fs 0.3 to 01.7. A process as claimed in any one of the preceding claims, wherein the phthalate on or salt comprises a species of formula 8. A process as claimed in any one of the precedtng claims, wherein R is H or OR2 cr a C1 to C aikyl.9. A process as claimed in any one of the preceding claims, wherein the aqueous solution to be treated is alkaline waste effluent, from an anthraquinone process for the production of hydrogen peroxide.10. A process as claimed in any one of the preceding claims, wherein the aqueous solution to be treated further comprises at least one aliphatic carboxylic acid, for example adipic acid, succirüc acid, butyric acid, propionic acid, acetic acid, formic acid, or a salt thereoL 11. A process as claimed in any one of the preceding claims, wherein the process resuks in a reduction in the concentration of the phthalate ion or sfl and is at least partially selective for reduction of the concentration of the phthalate ion or salt compared to reduction in the concentration, of aliphatic species present in the aqueous solution.in 12. A process as claimed in any one of the preceding claims, further comprising at east one further step of contacting the aqueous solution with a second material, the second material compdsing the same or a different layered double hydroxide. to the first materiaL is 13. A process as clahued in any one of the preceding claims, wherein the layered double hydroxide intercalates the phthalate species..14. A layered double hydroxide.of formula: AL (OH)2r(X)qJn.yH2O wherein M is a metal cation, z is I or 2, x is 0.1 to 1, y is C) to 5, X is an anion, n is 1 2 or 3 and q is determined by x and z, having intercalated therein a phthalate species of formula: ii s/tt I wherein m is 0, It 2, 3 or 4 and wherein R is a C1 to C8 hydrocarbyL or OR2, R2 is H or C1 to C hydrocarhyl, and wherein, when more than one Rgrottp is present, the R groups may he the same or different.s 15. A layered double hydroxide as claimed in claim 14, wherein between 0.1 and 1 mol of phthaate species is intereSted per mel of Al in the layered double hydroxide.</claim-text>