US2398687A - Method of treating cresylic pitch to obtain tar-acids therefrom - Google Patents

Description

April c. F. wlNANs Patented Apr. 16, 1946" METHOD OF TREATIN G CRESYLIC PITCH TO OBTAIN TAR-ACIDS THEREFROM .Charles F. Winans, Borough of Beaver, Beaver o County, Pa., assigner, by mesne assignments, to Koppers Company, Inc., a corporation of `Delaware Application December 18, 1942, Serial No. 469,446

. 3 Claims; )(Cl. 260--627) This invention relates to the treatment of a pitchy carbonaceous material, formed in tar acid recovery processes, to obtain valuable products from such material.V

The particular material treated by the process of the present invention is known as cresylic pitc It is formed as a pitchy residue inthe distillation of tar acids obtained from coal tar or n other tar acid bearing oils. These oils containing tar acids are initially treated in a well-known manner with caustic 'alkali to form tar acid salts which are separated from the unreacted, undissolved oil. The `separated tar acid salts are sprungby means ofcarbon dioxide or the equivalent, to form free tar acids. The recovered free tar acids are subjected to fractional distillation to obtain such tar acids as phenol, cresols, and xylenols. i .i

The cresylic pitch obtained as a residue in the distillation of the recovered tar acids is a very viscous, black, tarry material of characteristic odor, and is highly complex in its chemical composition. It is difficult to handle, and, in general, it is considered a distress product, little speciiic use having heretofore been found for it, and accumulations thereof being somewhat of a plant nuisance.

A cresylic pitch sample was found by analysis Ito contain approximately 10.15% water,^9.23% ash (8.15% sodium carbonate, 0.93% iron oxide,

and 0.15% other inorganic oxides such as those of aluminum and silicon) and 80.72% organic matter. Mere distillation of cresylic pitch by itself under vacuum yieldsonly small amounts of distillate and mainly a residue ofcoke. In fact it is impossible to distill the pitch without excessive coking and consequent decomposition.

An object of the present invention isto provide processes for converting cresylic Pitch into more readily distillable fractions yielding various valuable compounds, including particularly tar acids, and also varioususeful hydrocarbons. A further object is to provide a method of treating cresylic pitch under conditions favorable for the generation of tar acids from such pitch. Another object is to provide a process `for cyclically treating cresylic pitch whereby relatively high yields of commercially useful products are obtained.

The invention comprises, broadly, hydrogenating cresylic pitch with or. without catalyst preferably at raised temperatures and preferably at superatmospheric pressures. Before hydrogenation, the cresylic pitch may, if desired, be treated with a mineral acid, by which treatment some tar acids are rendered available. The acid treatment in itself may be employed as a means of providing appreciable yields of tar acids. `The Y acid treatment followed byhydrogenation, however, is a more highly elfective method of beneciating the cresylic pitch. l

' If the cresylic pitch as received from atar acid plant is to be subjected to a preliminary acid treatment before hydrogenation, it is mixed with an excess of dilute mineral acid such as sulphuric or hydrochloric acids, thereby completely destroying the alkalinity ofthe cresylic pitch. The

resulting mixture is washed with hot onwarm water to remove the excess acid, or to render the pitch neutral, and also to .remove soluble inorganic salts. The wet material is heated under reduced pressure to remove Water, whereaiter the material is heated in a still to about 1505A C. at about 1.5 mm. to removetar acids. A yield of agout 20% to 30% tar `acids is thereby obtaina e.

The pretreated cresylic pitch, from which `inorganic material and acid-converted products are removed, is in excellent condition for hydrogenation. Either this pretreated pitch or the raw .cresylic pitch is subjected to the hydrogenation treatment described hereinbelow.

When the pitch is subjected to the action of hydrogen or of a hydrogenating `gas undersutable conditions, a liquefaction of the pitch occurs, thereby furnishing a mobile liquid from which a major portion is distillable up to about 275 C. at atmospheric pressure. The' distillate contains up to, or about tar acids comprising phenol (CsHsOH) cresols, xylenols, and some higher phenolic bodies. The non-phenolic portion of the distillate comprises benzene, toluene, xylene,

'cyclohexana cyclohexanol, solvent naphtha,

naphthalene, and other neutral oil constituents. Fractions of the distillate boilingin a range of 200 to 250 C. also contain small proportions of tar bases such as quinoline, quinaldine,isoquin oline and others which may be separated from the said distillate. The residue left after distilling desired fractions fromfthe beneciated pitch may be further hydrogenated to furnish additional amounts of valuable products.

The temperature and pressures and time ofY treatment of cresylic pitch during hydrogenation may vary and are preferably kept within certain desirable ranges. The. temperatures which have been useful are from about 300 to about 500 C. and preferably in the range of about 350 to 450 C. At 350 C. a relatively long reaction time is required to produce a desired degree of liquefaction while at 450 C. the time is considerably shor- Vamounts of tar acids.

tened. Temperatures over 450 C. may be employed, but such temperatures are less desirable for tar acid production than those of 450 C. and lower.

The pressure of hydrogen or hydrogenating gases duringv hydrogenation may be 500 lbs.per square inch or higher. The extent of liqueface tion is increased at higher pressures, other variables remaining constant. 300 lbs. per square inch may be used, Vor higher pressures up to 3000 lbs. per square inch or upV to the limit obtainable in the apparatus'in which the conversion is effected.

With increase of reaction timein batch processes there is an appreciable increase in yield. From about one half hour to about 3 hours are desirable for effecting a lioluefaction` of over 50% or of about 50% to 55% of the pitch.

The hydrogenation of the cresylic pitch, as indicated above, may be conducted either in the presence of or in the'absence of a catalyst. In certain instances the Walls of the'hydrogenation chamber have some catalytick eifect. The small proportion vof iron oxide generally present inthe pitch may also be catalyti'callyV active. Improved resultsare obtained when the hydrogenation is conducted in the presence of an added catalytic substance. Various types of' catalytic substances are applicable such as certain metallic elements including iron,. nickel', et'c., and particularly moiybdenum sulphide, stannous sulphide, other metallic sulphides, such as those of iron,-cobalt, nickel,A zinc, silver, mercury, lead, copper and tungsten. These `sulphid'es maybe used alone or with additions of halids such as iodine, or halogen compounds such as iodoform, ethylene chloride, bromof'orm, and the. like. Molybdenum oxides, tungsten oxides,.and others with or without the addition of elemental sulphur or of a compound containing sulphur may also beused. Any of the Vwe11 known sulfactive catalysts and particularly those ofthe typewhich resist poisoning by sulphur are highly effective in the present hydrogenation process.`

In the accompanying drawings, flow diagrams are presented which illustrate severalexamples of methods for beneficiating `cresylic pitch. As illustrated inFigure 1 cresylic pitch is hydrogenated in a closed vessel, such as an autoclave at elevated temperatures and. pressures and for a period as indicated above. After the desired liquefaction hasV taken place the hydrogenated cresylic pitch is subjected to distillation to removertar acids and other compounds. The residue which remains after removal ,of the tar acids and other compounds generated during hydrogenationare further hydrogenated under conditions indicated above to yield additional 'Ihe tar acids are separated from the hydrogenated residue by distillation and residues from the` distillation of this secondary hydrogenation product can be further treated if desired.

Owing to the lfact that vthe residues from the distillation of the" secondary hydrogenation products can be further hydrogenated, a continuous process is feasible. Such ka'prccess is illustrated in Figure 2. Cresylic pitch is hydrogenated in an autoclave which may be represented by a rectangle I. The hydrogenated cresylic pitch is distilled in a still represented by a rectangle 2 to remove tar acids, hydrocarbons, etc. The residue from the distillation is mixed with fresh cresylic pitch and the mixture is introduced into Pressures as low as` the autoclave l to be hydrogenated. A cyclic process is thus carried on and the complete utilization of the cresylic pitch is made possible.

In Figure 3, a flow diagram is shown to illus- 5 trate the pretreatment of cresylic pitch before hydrogenation. By such pretreatment a certain amountof tar acids is formed which are separated from the pretreated cresylic pitch. The remaining portion of the pretreated pitch is then hydrogenated to form further amounts of tar acids and other compounds.

During hydrogenation, vent gases from the autoclave may be passed through dilute sulphuric aciclv for the purpose of removing ammonia that may be present. The gases may also be condensed or they may be washed with oil to remove lighter hydrocarbons that form. Such lighter hydrocarbons' have a boiling range of 4 to about 20 C.

The following examples are given by way of illustration and are not to be considered asl limitations. f

Example 1v1-A charge oi' cresylic pitch in the absence of a catalyst is placedin` an autoclave under an initial. pressure of about 900 lbs. per

square inch and` heatedA toabout 450 C. in the presence ofA ahydro'genat'ing gas. The temperature is held at this point for about. one hour.

The apparatus is thereafter cooled'. to room temperature, the pressure falling to about 4'00 lbs.

per square inch. The liquid product formed is removedfrom the autoclave anddistilled.. The distillate comprises about 3.2% water, 8.55% of materialsl boiling to 180 (712,441470A distillate boiling from about 180 C. at" atmospheric pressure to about 150- C. at 2 mm. pressur`e and a residue of about 35.9% pitch. The above 44.4% fraction contains about 84% tar acid. Thisfraction is treated to remove tar acids therefrom.

Example 2.-A charge of cresylic pitch is mixed' with about 1% by weight ofmolybdenum sulphide as catalyst. The mixture in an autoclave is submittedto an initial pressureof 900 lbs.'per' square in'ch and heatedv to 450 C. in the presence of a hydrogenating gas. The temperature is held at' this point for about one hour. The apparatus is cooled to room temperature and the pressure is gradually reduced.. The hydrogenation product isdistilled. The distillate comprises about 3.21% water, 8.5% of material boiling to 180 C., about 55.3% distillate boiling from 180 at atmospheric pressure to 150 at 2 mm. pressure, and a residue of about' 29.7% pitch. The 55.3% fraction is treated to obtain tar acids. This fraction contains about 82% tar acids.

Example 3.-Cresyli'c pitch is placed in an autoclave and submitted toan initial partial hydrogenating pressure of ab'out- 1400 lbs. per square inch and av temperature upto about'450" C. The

autoclave Vis cooled and the liquefied product is treatedV to' obtain free tar acids. Onv distillation there are obtained aboutl 3.6% water, 8% material up to. 180 C., 5.218% distillate' fronrl80 at atmospheric pressure to 150 at 2 min. pressure containing about 82% tar acids, and a residue of about 28.4% pitch.

Example 4.-Cresylic pitch mixed with about 1% molybdenum sulphide is hydrogenated for about one-half hour at` 450 C., the.` initial hydrogenating pressureqbeing. 4about 1950 lbs. per square inch. The beneciated pitch comprises about. 3.7% water, 9%. material boiling up to aboutv180A C.,49.6%. distillate from' 180? at. atmospheric pressure to 150 ati 2 mm; pressure taining the greater proportion of tar acids on discontaining about 79% tar acids, and a `residue of 31.3%. i

Example 5.-Cresylic pitch is hydrogenated .for about one hour at 400 C. in the presence of 1% molybdenum sulphide underfpressure, the initial partial hydrogenating pressure being about 1950 lbs. per square inch. `The hydrogenated product contains about `2.8% water, 4.5% material boiling to 180 C., 37% distillate from 180 at atmospheric pressure to 150 at 2 mm. pressure containing 85% tar acids, and 43.7% pitch residue. 1 Y

Example 6.--A charge of cresylic pitch is h f- `drogenated at 350-C`. for 51/2 hours in the presence of 1% molybdenum, sulphide, the initial pressure being about 1700 lbs. per sduare inch. The reaction product contains 2% water, 5.1% material boiling up to 180 C., 24% distillate from 180 at atmospheric pressure to 150 at 2 mm. pressure containing about 79% `tar acids, and 67.1% pitch residue.

Example 7.-Cresylic pitch in the presence of about 5% nickel catalyst is hydrogenated at about 275 C. for about 2 hours, the initial pressure being 1200 lbs. per square inch. The hydrogenated material is distilled to obtain a tar acid fraction. The yield of tar acids is about 32.1%.

Example 8.--Ptch residues obtained from a number o hydrogenated cresylic pitch batches after distillation of tar acids, are combined and hydrogenated'for 51/2 hours at 450 C. in the presence of 1% molybdenum sulphide, the initial pressure being 1700 lbs. per square inch. The product comprises 3.8% water, 12.8% material boiling up to 180 C., 45.4% distillate from 180 at atmospheric pressure to 150 C. at 2 mm. pressure containing 41% tar acids, and 28.8% pitch residue. This residue is rehydrogenated under similar conditions. prises 25% Water, 4.95% materials boiling up to 180 C., 37% distillate from 180 at atmospheric pressure to 150 C. at 2 mm. pressure containing 20% tar acids, and 48.8% pitch residue. The latter residue may be further hydrogenated.

In the last example the pitch residue instead of being separately hydrogenated is alternatively mixed with fresh cresylic pitch and the resultant mixture is hydrogenated. Each residue obtained thereafter is remixed with fresh batches of cresylic pitch to be hydrogenated.

Example 9.-Raw cresylic pitch is thoroughly mixed with an excess of about dilute mineral acid (sulphuric acid or hydrochloric acid). The excess is beyond the amount necessary to neutralize alkalinity of the cresylic pitch. The resulting mixture is washed with warm water to remove soluble inorganic salts and excess acid. The washed pitch is subjected to vacuum distillation to remove water. It is subjected to further distillation to obtain a tar acid fraction which yields about 26% tar acids.A The pitch residue remaining in the still is subjected to hydrogenation in the presence of a catalyst at about 450 C. under a partial hydrogenating pressure of over 300 lbs. per square inch for one hour either continuously or intermittently. The' hydrogenated product is distilled to recover volatile products including hydrocarbons, tar acids and a residue. The distillate is .treated to separate tar acids from neutral oil. About 50% of the hydrogenated product boils up to about 275 C. at atmospheric pressure. The distillate thus obtained contains about 80% tar acids.

In each of the above examples a fraction contillation of the hydrogenated pitch, is treated in the. conventional manner for obtaining free tar acids and neutral oil. vFor example, the tar acid fraction is mixed withl sodium hydroxide to form sodium phenolates which separate out of the neuti'aloil in the form-of a layer. vThe phenolateA layer is then subjected to a springing treatment with carbon dioxide.` The phenols are set free and may be' fractionated? to obtain individual phenolic compounds. From a i hydrogenated cresylic pitch yielding tar acids to the extent of about 50% of the total yield of liquefied product, there is obtained the following:

. Per cent Phenol 1.2 Cresols 23.1 Xylenols .g c 33.1 `Tar acids boiling from 220 to 240 C 27.5 Tar acids boiling above240"` C 15.1

The resulting product com- Alternatively, ineach of the above examples, tar acid oil produced and'containing Vthe tar acids and neutral oilis a valuable product as such. Among other uses the tar acid oil serves, for instance, as a material in the manufacture of certain insecticide oils. Y

By means of the process of the present invention, cresylic pitch which has heretofore been commercially valueless, is converted into products that are of considerably greater value than the pitch. The tar acids are combined with those of the tar acid plant, thereby increasing single ring tar acid production. Neutral oil and hydrocarbons obtained in the hydrogenation process are important commodities otherwise lost and now finding increased diversified application.

While certain periods of time, temperatures, and pressures are prescribed in the above examples, these factors may be so adjusted to each other that a substantial proportion of constituents in the pitch is converted intotar acid fractions distillable without decomposition.

It is apparent from the above description that various changes may be made in the procedures without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the procedures hereinbefore cited by way of illustration being merely the preferred embodiments thereof.

What is claimed is:

1. In a process of producing free tar-acids from cresylic pitch residue that is non-distillable Without excessive decomposition and coking, and that is formed by distillation of a distilland substantially completely consisting of chemically separated free tar-acids, which tar-acids are obtainable by reacting tar-acids in tar-acid-bearing oil with caustic alkali to form tar-acid salts, removing so-formed tar-acid salts from unreacted oil, and freeing the tar-acids from said salts in a springing operation; subjecting the said cresylic pitch residue to a pressure of over 300 pounds per square inch at a temperature in substantially the range of 300 C. to 500 C. in contact with hydrogen to eiect liquefaction of material in the said cresylic pitch residue and thereby to obtain taracid material from which free tar-acids are distillable without decomposition, and separating free tar-acids comprising phenol, cresols and xylenols from the resulting mass.

2. In a process of producing free tar-acids from cresylic pitch residue that is non-distillable without excessive decomposition and coking, and that is formed by distillation of a distilland substanlagsaegaem tiallyfv completely'gconsistings offY chemicallyL separated;- free tari-acids;` which tar-acids are; obtainable by: reactingtan-acidsam tar-acdi-bearing; oil

with caustic alkaliitiol form tan-acidsalts; remowing so-formedv tar-acid salts from unreaeted; oil, and freeing: the' tari-acids from4 said. salts? in.A a springing operation; subjectingthesaid cresy-lic pitch residue` to4 av pressure of; from substantially 20 atmospheres; tou 200 atmospheres: at: a; tempera@- turev in substantially: the rangetof'f`300f 0;. to 500 C; in the presence: off a catalyst'. andl in-v contact with hydrogen tot effect: liquefacti'on. of: material in thev said cresylic pitch residue and thereby to obtain tar-acid material: from which: freev taracidsI are distillable without decomposition, and distilling free tar-acids comprising phenol,.cresols and xylenols from the resulting massL 3'. In a process of` producing. freeitar-acids from cresylicpitch residue that isfnondisti1lable without' excessive decompcsitionzandY coking,xand that 20 is formed by distillation of a distilland substantially completely consisting of chemically sepa.- rated free. tar-acids, which tar-acids. are obtainable by reacting tar-acids in' tar-acid-bearing oil with caustic alkali to form tar-acid salts', removing so-formed tar-acid saltsifrom unreacted oil, and'freeing thei tar-acids from said salts in a springing operation; contacting the said cresylic pitchi residuev and dilute,l mineral acid to acidify theY mass, Washing the acidied mass to remove free` mineral acid therefrom', distilling the sotreated cresylic pitch residue to obtain a fraction containing free tar-acids, subjecting the resulting undistilled residual portion o f the acid-treated cresylic pitch residue to a pressure of over 300 pounds. per square inch at a temperature in substantially the range of 300 C. to 500 C. in contact With hydrogen to effect liquefaction of the said undistilled residual portion of the` said acidtreated cresylic pitch residue and thereby to obtain' tar-acid material from which free tar-acids are distillable; Without decomposition, and distilling free tar-acids comprising phenol, cresols and xylenols from the resulting said tar-acid material.

CHARLES F. WINANS.

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