US2955079A

US2955079A - Solvent extraction of low-temperature tar and products therefrom

Info

Publication number: US2955079A
Application number: US624456A
Authority: US
Inventors: Dennis D Foley
Original assignee: Texas Power and Light Co; Aluminum Company of America
Current assignee: Texas Power and Light Co; Howmet Aerospace Inc
Priority date: 1956-11-26
Filing date: 1956-11-26
Publication date: 1960-10-04
Anticipated expiration: 1977-10-04

Description

Oct. 4, 1960 D FOLEY 2,955,079

D. SOLVENT EXTRACTION OF LOW-TEMPERATURE TAR AND PRODUCTS THEIREFROM Filed NOV. 26, 1956 AQUEOUS ALCOHOL 3 :EX' L N" SOLUTION LIQUID ,qa

ALKANE WATER H AND LOW-TEMPERATURE TAR n ALCOHOL "1 db |4\ ALCOHOL 2 L ALKANE f EXTRACT EXTRACT l6 com fi bsrs j 7 [-22 2o POLAR NONSOLUBLE NONPOLAR MATERIAL RESIDUE OIL AQUEOUS ALCOHOL SOLUTION DISTIL- msm- 24 COUNTER- LATION LATION 38 CURRENT COLUMN COLUMN EXTRACTION COLUMN POLAR MATERIAL INVENTOR. 28 DENNIS D. FOLEY BY LIQUID j ALKANE 3 M" W ATTORN EYS SOLVENT EXTRACTION OF LOW-TEMPERATURE TAR AND PRODUCTS THEREFROM Dennis D. Foley, Columbus, Ohio, assignor, by mesne assignments, to Texas Power & Light Company, Dallas, Tex., a corporation of Texas, and Aluminum Company of America, Pittsburgh, Pa., a corporation of Pennsylvania Filed Nov. 26, 1956, Ser. No. 624,456

15 Claims. (Cl. 208-22) This invention relates to a new and useful pitch and a process for separating the pitch from a tar obtained from a low-temperature carbonization of coal. Also included within the scope of the invention are new and useful products, such as a polar material from a low-temperature tar.

Pitches are used commercially, for example, as binders, coatings, impregnants, preservatives, etc. The utilization of a pitch for impregnation of fiber pipe and the use of a pitch as an electrode binder are typical commercial applications. A satisfactory pitch for a particular application requires particular properties. For example, in fiber pipe impregnation, one requirement is that the pitch have an extremely low leachability under alkaline conditions; and in an electrode binder usage, one requirement is that the pitch have an extremely low ash. Requirements for various usages are well known.

The new pitch of the invention has suitable properties for fulfilling numerous known uses and differs significantly from known pitch materials. The pitch of this invention has a distinctively aliphatic nature and a substantial resistance to alkaline leaching. Pitches from tars obtained from high-temperature carbonization of coal are characteristically aromatic in nature, and known pitches from low-temperature tars, while aliphatic in nature, do not have the desirable properties of the pitch of the in-. vention.

Polar materials, such as tar acids, are useful, for example, for preparation of resins, for disinfectants, etc. The polar material of the invention has properties that make the material useful in many applications of presently 'known polar materials. The polar material of the invention has a content of at least 80 percent soluble in aqueous caustic and has a content of at least 50 weight percent nonvolatile at 300 C. In comparison, known commercial polar materials, such as tar acids, from tars obtained from carbonization of coal have a content of less than 5.0 percent nonvolatile at 300 C.

The pitch, polar material, and other products of the invention are prepared from tars obtained from the lowtemperature carbonization of coals. In general, the process of the invention for preparing these products from the tars comprises treatment of the tars with a combination of liquid solvents to obtain solvent extracts, separation of the extracted solubles from the solvent extracts to obtain from one extract the polar material of the invention, and from the other extract a nonpolar constituent which may be further processed to yield a nonpolar oil and the pitch of the invention.

A tar suitable for treatment by the process of the in-- United States Patent 2,955,079 Ice Batented Oct. 4, 1960 coal is sometimes called a primary tar. The residual coke, char, and liberated gas of a low-temperature carbonization are separate products from the primary tar and are not considered suitable starting materials for this invention.

The exact cqmre ifiq of a tar. dep d p n the nature of the particular coal from which it is obtained and the process conditions for obtaining the tar.

Coals have been classified and ranked in many various manners. A particularly useful classification is that of the American Society of Testing Materials wherein coals, in decreasing rank, are classified: anthracite; low volatile, medium-volatile, and high-volatile bituminous; subbituminous; and lignitic coals. Commercial hightemperature carbonization processes are directed primarily toward low or medium volatile bituminous coals, and low-temperature carbonization processes are directed primarily towards high-volatile bituminous coals, subbituminous, and lignitic coals. For any particular set 'of either low-temperature or high-temperature carbonization conditions, as various coals are successively carbonized under these same conditions, there will be a variance in the composition of the tars obtained. For example, under fixed conditions of carbonization, a change to a lower ranking coal will provide a tar having an increased polar or tar acid content, as shown by increased oxygen content of the tar. For a particular coal or coal-like material, a change in the conditions of carbonization, such as from high-temperature to low-temperature carbonization conditions, will provide a tar having an increased polar or tar acid content as shown by an increased oxygen content of the tar. Tars produced from coals by carboniza tion at temperatures of about 1400 F. or higher are known to the trade as high-temperature tars and generally are characterized by higher specific gravity, higher aromatic hydrocarbon content, and lower tar acid content when compared to low-temperature tars produced from the same coals by carbonization at temperatures some what lower than about 1400 F. Representative of lowtemperature carbonization methods is that described by V. F. Parry et al. in Drying and Carbonizing Fine Coatl in Entrained and Fluidized State, Bureau of Mine Reports of Investigations 4954, US. Department of Interior (April 1953).

It is to be understood that by the term low-tempera-- ture tar in the specification and claims there is meant primary tar obtained from the carbonization of coal or coal-like materials at temperatures less than about 1150 F. Low-temperature tars from carbonization of coal are comprised substantially of an oily, tarry, organic mass which ranges from a viscous liquid to a soft semisolid material at room temperature. Minor amounts of char, inert material, water, and dissolved gaseous lay-products may be present. Low-temperature tars, especially those obtained from lignitic coal, contain an appreciable amount of reactive organic materials.

Typical of the low-temperature tars which are suitable for the invention are, for example, lignite tars. Distillation of low-temperature lignite tars characteristically yields residues of from 30 to 60 percent and distillates of from 40 to percent. These distillates, when dry,

be present in the low-temperature tars.

'A suitable primary tar, representative of lignite tars,

was obtained by the Parry low-temperature carbonize tion of a lignitic coal Characteristic properties of this tar are set forth in Table'I. Y

hind in the distillation residues.

Table I Ash, weight percent 0.35 Specific gravity, pycnometer, 25/25 0.9867

- 1 By azeotropic distillation with toluene.

- Based on dehydrated sample. For test procedure see the American Society for Testing Materials, Standards on Bituminous Construetional Materials." Low-temperature tars as obtained from low-ranking coals, such as high-volatile bituminous coals, subbituminous coals, and brown or lignitic coals, contain appreciable amounts of high-molecular-weight tar acids and other reactive organic materials. The term reactive organic materials is intended to mean organic materials that undergo reactions, such as polymerization, condensation, decomposition, etc., 'upon exposure to heat or chemical processing conventionally applied to tar and distillates. Known pitches from low-temperature tars obtained from low-ranking coals have not been so generally useful as pitches from high-temperature tars. In view of the present invention, it appears that the inferiority of such pitches may be due to the presence therein of significant amounts of polar materials and reactive organic materials or their, reaction products, which'prior art processes failed to remove.

Tars obtained from both high-temperature or lowtemperature carbonization of coals generally are subjected to distillation to obtain useful products. Since low-temperature carbonization processes yield tars of relatively high tar acid contents, emphasis has been predominantly toward the isolation of the tar acids of suitable commercial purity from tar acid oil fractions (distillates' of these tars), rather than other potentially valuableconstituents of the tar, such as a pitch. In tar distillations relatively nonvolatile tar acids and reactive constituents fail to distill and as such are reacted or left be- As such, these constituents contaminate the residue, making it virtually impossible to obtain a pitch from the residue which is satisfactory for certain commercial applications, for example, those applications where substantial leaching re sistance to aqueous alkaline solutions is needed. In fact, no method is known by which these contaminants may be removed from such distillation residues, and the present-commercial practice still continues to subject the tar directly to a distillation, irrespective of whether or not the tar is a'high-tem-perature or low-temperature' tar. In the case of tars obtained from present'commercial high-temperature ca'rbonization of coals appar ently problems of this nature are not encountered for commercial pitches are prepared from distillation residues. I rating tar acids is taught by US. Patent 2,666,796, Gorin et al. Gorin et al. is exemplary of the present practice and specifically teaches solvent extraction of a tar acid oil fraction (a distillate of a tar), rather than solvent extraction of primary tar itself. In the case of lowtemperaturejtars, the process of Gorin et al. inherently yields a contaminated distillation. residue from which it is virtually impossible to obtain a satisfactory pitch by known methods. Other prior art methods have other disadvantages. For example; caustic treatment for obtaining tar acids involves reaction of the tar-acid-con taining materials with the caustic toobtain water-solu- A representative commercial process for sepable tar acid salts which are separated and then treated with mineral acids to spring the tar acids. Inherent disadvantages of caustic treatment are that reagents are consumed; contaminants may be found with the tar 5 acids; mixing of the causticand a tar is difficult; even if suitable mixing is obtained, discernible phase separation may not be obtained; and reactive organic materials and high-molecular-weight tar acids undergo reactions and are not recoverable as such.

Of the many prior art teachings of, tar treatments, none teach solvent extraction for the purposes of obtaining'thenew and novel pitch and polar material of the'invention. Y

Accordingly, low-temperature tar constituents having desirable properties, such'as the pitch and polar materials of the invention, and a process which permits a' large recovery of constituents having useful applications, are extremely valuable and useful. I

It is an object of the present invention to provide a new and useful pitch from a low-temperature tar.

An additional object is to provide a new and useful polar material having more than 50 weight percent nonvolatile at 300 C., from a low-temperature tar.

A further object is to provide a process for obtaining a new and useful pitch from a low-temperature tar comprising extracting the tar with a combination of im miscible solvents and separating the pitch from material extracted by one solvent.

A further object is to provide a process for obtaining a new and useful polar material from a low-temperature tar comprising extracting the tar with a combination of immiscible solvents and separating the polar material from one solvent extract.

Further objects and advantages of the present invention will be apparent in view of the following detailed disclosure.

Generally the process comprises treating lowstemperature tars with a combination of liquid solvents, one a polar solvent, i.e. a solvent which has good solvent powers for polar materials and poor solvent powers for nonpolar materials, and the other a nonpolar solvent, i.e. a solvent which has good solvent powers for nonpolar materials and poor solvent powers for polar materials. The treatment of the tar with these solvents yields separable solvent extracts, one containing most of the pre dominantly polar materials, and another containing most of the predominantly nonpolar materials. The pitch of the invention is separated from the material soluble in the nonpolar extract. The polar material of the invention is the material soluble in the polar solvent. The process may be readily practiced by batch or continuous operation. The process may be carried forth with certain treatment steps with each solvent separately, but preferably is carried forth with treatment steps of the tall 'by both solvents simultaneously. Preferably, the process is practiced as a simultaneous continuous countercurrent extraction of the tar in a suitable apparatus.

For a better understanding of the invention, its objectsand advantages, reference should be had to the accompanying drawings of which:

Fig. 1 is a diagrammatic flowsheet of the process for obtaining the products of the invention; and V Fig. 2 is a diagrammatic illustration of an apparatus adapted to the practice of the preferred embodiment of the process of the invention. 7

Referring to Fig. 1, a polar solvent, such as an aqueous alcohol solution 10, and a nonpolar solvent, such as a liquid alkane 11, are brought into contact with a lowtemperature tar 12 and intimately mixed therewith by means, such as a stirrer 13 After mixing, the mixture of the tar 12 and solvents 10 and 11 is permitted to separate into discernible phases. An aqueous alcohol extract 14, one of the discernible phases, is withdrawn and processedinto fractions, one a water-alcohol fraction 15 and another a'polar material 16. Y A liquid alkane extract 17,

one of the discernible phases, is withdrawn and processed into a liquid alkane fraction 18 and the nonpolar con-. stituent fraction 19. The nonpolar constituent fraction 19 is then separated into parts, such as one a nonpolar oil 20 and the other a pitch 21. The water-alcohol fraction 15, after adjustment to a suitable alcohol concentration, may be reused in the process for further extraction. The liquid'alkane fraction 18, after purification, if necessary, may be reused in the process for further extraction. Any residue portion 22 of the low-temperature tar 12, not soluble in either the aqueous alcohol solution or the liquid alkane 11, is withdrawn. Depending upon the particular low-temperature tar, there may or may not be a nonsoluble residue portion 22. Generally, the nonsoluble residue portion comprises ash, char, and condensed organic material and amounts to only a few percent or is nil in most low-temperature tars.

Referring to Fig. 2, a low-temperature tar from a storage tank 23 is fed continuously through a pipeline 24 into a continuous countercurrent, double-solvent extraction column 25. An aqueous alcohol solution is fed continuously from a storage tank 26 through a pipeline 27 into the extraction column 25 near the top of column 25. A liquid alkane is fed continuously from a storage tank 28 through a pipeline 29 into the extraction column 25 near the base of the column 25. Tar is fed into the extraction column 25 at a point between the feed points of the aqueous alcohol solution and the liquid alkane.

Aqueous alcohol extract is withdrawn continuously from the extraction column 25 near the bottom of column 25 through a pipeline 3t) and fed into a distillation column 31 for separation of alcohol and water and solubles therein. The solubles, polar materials, separated from the aqueous alcohol extract, leave the distillation column 31 through a pipeline 32 and pass into a tank 33. Alcohol and water leave the distillation column 31 through a pipeline 34.

Liquid alkane extract is withdrawn continuously from the extraction column 25 at or near the top of column 25 through a pipeline 35 and fed into a distillation column 36 for separation of the liquid alkane and the solubles therein. The solubles, nonpolar constituents, separated from the liquid alkane extract, leave the distillation column 36 in fractions; one, a nonpolar oil leaves through a pipeline 37 and passes into a tank 38, and another, a pitch, is withdrawn through a pipeline 39 and passes into a tank 40. Liquid alkane leaves the distillation column 36 through a pipeline 41.

Any residue portion of the tar not dissolved and not soluble in the aqueous alcohol or liquid alkane is withdrawn, as required, from the extraction column 25 at the bottom of column 25 through a pipeline 42 into a storage tank 43. In some low-temperature tars, there may be no insoluble residue portion and pipeline 4-2 and storage tank 43 may be omitted.

The alcohol and water leaving the distillation column 31 through pipeline 34, maybe adjusted to a suitablealcohol-water ratio and be reused in the process. The liquid alkane leaving the distillation column 36 through pipeline 41, may be purified, if necessary, and be reused in the process.

For etfective phase separation of the extracts in the continuous process just described wherein aqueous methanol and hexane are the solvents, the process must be carried forth at temperatures not less than about 100 F., with a temperature of IZOEpreferred. At temperatures lower than about 100"---F.- for'continuous operation, emulsions of the'tar and solvenfsjform which are difficult to break, and the viscosity of the tar is increased making handling of the tar diflicult is not impossible. At temperatures higher than about 140 F. depending upon the particular solvents, phase separation of the solvent extracts may not be possible because of an insufficient difference in density between the two solvent extracts, and because bubbling or vaporization of a solvent may be 6: detrimental to successful operation of the process. At the preferred process temperature of about -1 thereiis a clear and distinct phase separation that permits. separation of the solvent extracts.

To illustrate the effect of temperatures on the process, a'mixture of one part of a low-temperature lignite tar, eight parts of a 7 0 percent aqueous methanol solution, and eight parts of a hexane cut of paraflinic hydrocarbons, having a boiling range of to F.was heated to progressively higher temperatures within a range of 66 F. to about 120 F. The mixture at various increments of temperature within this range, was thoroughly mixed, permitted to stand several minutes, and examined visually for phase separation. As the temperature was increased from 66 F. to 129 R, there was a noticeable darkening of both solvent extracts, thus indicating extraction of larger proportions of the tar by each solvent. At a temperature of less than about 100 F., while there was a phase separation of the extracts, there was a dispersion of small tarry particles throughout the aqueous methanol extract. At temperatures slightly above 100' F., there were only a few small tarry clumps in the aqueous methanol extract with a noticeable phase separation of both solvent extracts. At 120 F., there was a noticeable phase separation of a hexane extract, an aqueous methanol extract, and an insoluble residue with no apparent small tarry particles or clumps in the aqueous methanol extract. At temperatures somewhat above 120 F., bubbling was visible in the hexane phase, indicating boiling or vaporization of a part of the hexane phase.

For every part of the low-temperature tar, there should be employed from about 3 to 12 parts by weight of a polar solvent and from about 3 to 12 parts by weight of a nonpolar solvent for the process of the invention. Preferably there are used 4 to 5 parts by weight of an aqueous alcohol solution and 4 tov 5 parts by weight of an aliphatic hydrocarbon, although some variation is permissible depending'on the nature of the tar, the par ticular alcohol, and the particular aliphatic hydrocarbon. For obtaining optimum separation of the pitch and polar constituents of the invention, the ratio of each sol vent to the tar may be varied somewhat. With less than about 3 parts of either solvent, the process may be inoperable due to insufiicient difference of the specific gravities of the solvent extracts. With more than about 12 parts of either solvent, process operation will be possible, but not economically feasible. Where a ratio of one solvent to the other solvent varies greatly from a 1 to 1- ratio, the pitch and polar materials of the invention are not obtained in maximum yield, in optimum concentrations, or with the most useful properties.

In the following table II are tabulated typical results of a number of runs of the process of the invention, illustrating batch and continuous operation and effectof such process variables as temperature, feed ratio, and methanol concentration. Typical runs listed under columns l to 3 inclusive were carried forth by batch operation, while typical runs listed under columns 4 to 14 inclusive, were carried forth by continuous operation according to the preferred embodiment of the process of the invention. The primary tar for these process runs was obtained from the low-temperature carbonization of a lignitic coal and was a tar having the properties as tabulated in Table I. The runs, carried forth in a batch manner, utilized a closed-container extraction apparatus having a stirring means therein. In the batch runs, approximately one-half of the duration of the run was conducted with thorough mixing of the tar and solvents. During the other half of the run the mixture was permitted to settle and separate into discernible phases. The runs, carried forth in a continuous manner, utilized a compound countercurrent extraction column with a continuous feeding of tar and solvents along with a continuous withdrawal of solvent extracts for the dura tion of the run. The extraction column was a rotating 7 disc type extractor about' seven feet high by four inches, inside diameter, and had an extraction section consisting of 19 .units and a scrub'section consisting of 26 units.

8 may comprise onlya' part of the portion nonvolatile at 300 '0. Depending on the exact cutoff point of the separation, such as a distillation, it is possible to vary Table 11 Run No 1 2 3 4 5 6 7 8 9 1O 11 12 13 14 TM sample:

Weight (grams) 1, 500 950 905 Feed (gallons/hour) 2 2 1 2 1 1 1 1 1 1 1 Duration of run (hours) 1. 5 1. 5 1. 5 1. 5 1. 5 2. 3 2 2 2 2 1. 5 2 32 Process temperature F.) 120 120 70 120 120 120 120 120 120 120 120 120 120 120 Feed ratio (by weight):

ar 1 1 1 1 l 1 l 1 1 l 1 1 1 1 70% methanol--- 4 8 8 4. 4 2 9.1 B 4. 3 5. 5 9. 6 I 4. 9 a 10.1 b 5.6 4. 3 4. He e 4 8 8 4.6 2 8.5 4.4 9.8 4.7 10.3 8.6 4.8 6.8 4.3 Products (weight percent of tar): M h 18. 7 24. 9 19. 3 22. 7 25. 4 28. 7 19. 7 28. 6 24. 9 28. 17. 7 20. l 22. 9 67. 5 69. 9 59. 8 74. 7 72. 6 67. 9 76. 8 67. 9 70. 2 66. 8 75. 8 74. 0 71. 9 9.3 4.5 9.8 2.6 2.0 3.4 .3.5. 3.6 4.9 4.7 6.5 5.9 5.2 bl 4.5 0.7 11.1 solubles (weight percent) 84. G 83. 2 87. 4 93. 1 93. 9 92. 6 95. 5 90. 9 95 9 91. 6 95. 1 95. 8 93. 7

I 75% methanol, balance water. b 60% methanol, balance water.

' B A commercially available saturated paraflin hydrocarbon solvent, essentially normal hexane, having a boiling range of 140 to 160 F. This solvent is sold under the name "Skellysolve B" d No apparent phase separation.

" The determinations of caustic solubility of methanol solubles, as reported in Table II, were made on anhydrous, methanol-free samples of the polar materials. To obtain the anhydrous, methanol-free samples, the aqueous methanol extracts were distilled to remove the methanol. Benzene was then added to the residue of methanolsolubles and water; a water layer, which separated, was removed. The mixture of benzene-methanol soluhles was then distilled to remove the benzene and any remaining traces of water to obtain an anhydrous, methanol-free sample of the methanol solubles. A given weight of an anhydrous methanol-free sample was reacted with a warm aqueous percent by weight sodium hydroxide solution, cooled to room temperature, and extracted with ethyl ether. The ether layer was separated and the ether removed by heating on a steam bath under reduced pressure. The residue from the ether extract, after ether removal, was the portion of the anhydrous sample not soluble in caustic, and, by difference, thcrewas caluclatcd the portion soluble in caustic reported as caustic solubility in methanol solubles in Table II.

A small amount of nonpolar oils may be removed, if desired, from the hexane solubles, and the resulting distillate and residue are useful products having suitable properties forcertain commercial applications. For example, a distillation of the hexane soluhles may be carried forth to yield low-boiling nonpolar oils and a residue containing the higher-boiling nonpolar oils and the pitch of the invention. The low-boiling nonpolar oils are useful commercially for solvents and this residue, containing the higher-boiling nonpolar oils and the pitch, is useful commercially as a protective coating, for example'as a tar paint coating for roofs, papers, etc.

'The pitch of the invention is separated from the nonpolar extract obtained by the process of the invention from a low-temperature tar. Preferably this is accomplished as follows, although other means known to the art may be used. The nonpolar extract is distilled to' remove the nonpolar solvent and leave the solubles.

' The solubles, nonpolar constituents, are then distilled to' yield a distillate of a nonpolar oil and a residue which is the pitch of the invention. While the solubles may be fractionally distilled to any desired degree or separated by other'known. means to any desired degree, the pitch of the invention is only that'portion of the hexane solubles nonvolatilefat about 300 'C. or higher, and

by Skelly Oil 00., Kansas City, Missouri.

the amount of pitch obtained and certain properties of the pitches of the invention, such as their softening point. For example, various pitches were prepared by distillation of various nonpolar constituents; from the nonpolar constituent of run 4 of Table II one pitch comprising 471 percent of the nonpolar constituent had a softening point of less than 40 C., and another pitch comprising 27.5 percent of the nonpolar constituent had a softening point of 74 C.; from the nonpolar constitu ent of run 2 of Table II, one pitch comprising 38.0 percent of the nonpolar constituent had a softening point of 40' 0, another pitch comprising 23.0 percent of the nonpolar constituent had a softening point of 64 C., and still another pitch comprising 17.0 percent of the nonpolar constituent had a softening point of 112 C. All softening points were determined by the ASTM Ring and Ball Method (D-3 6-26).

Table III that follows tabulates some typical physical and chemical properties of two pitches of the invention. Samples A and B are pitches from the hexane solubles of run 4 of Table II. Generally the pitches of the invention have a content of at least 20 percent or more insoluble in benzene and in carbon tetrachloride. In Table 111 all percentages are expressed in terms of weight percent.

Table III Pitchr.

- signifies not determined.

Pitches from low-temperature tars obtained from bituminous and lower'ranking coals are more aliphatic in nature than pitches from high-temperature tars, but

heretofore unfortunately had a relatively high oxygen content. It'has been discovcredthat a pitch may be produced from low-temperature tars, which although aliphatic in nature surprisingly contains a relatively low oxygen content. Pitches from commercial high-temperature tars are more aromatic in nature than pitches from low-temperature tars. I

Aliphaticity of pitches may be compared by infrared spectra. The procedure for obtaining a measurement of aliphaticity from infrared spectra and measurements therefrom follow.

In infrared spectral studies, a variation in the absorp tion intensities in the region 3.2 to 3.5 microns, characteristic of CH stretching in aliphatic (3.38 to 3.48 microns) and aromatic (3.27 microns) hydrocarbons, may be used to provide an index of the aromaticity or aliphaticity of a sample. Such an index, based on optical densities, is free of the ambiguities inherent in other methods of aromatics determination, such as sulfonation, chromatograms, etc., and is certainly more sensitive, quantitative, and reliable than specific gravity and refractive index comparisons. This spectral method of comparison is independent of the mode of occurrence of aliphatic groups; that is whether the aliphatic groups are present as free molecular species or as substituted groups attached to an aromatic nucleus.

The ratio CH aliphatic CH aromatic is the ratio of the optical densities of the bands at 3.42 microns (aliphatic) and 3.27 microns (aromatic), which ratio is hereinafter called the aliphaticity ratio. The optical density of an infrared absorption band (or log I /I, where I is the radiation transmitted by the sample at that wave length and I is the radiation incident upon the sample) is directly proportional to the concentration of the absorbing group.

An absolute number for per cent aromatic may be obtained if the value k, or absorption coefficient, is inserted into the equation log I /I=klc where l is the sample thickness and c is the concentration of the absorbing group, usually expressed in moles per liter. The value k is obtained from measuring the optical density of a pure aromatic compound Where "1 and c are known. Of course, since k varies from one aromatic compound to another, the absolute aromatic concentration in mixtures of unknown qualitative composition, such as pitches, cannot be measured in this way for total percent aromatic.

In order to obtain sufiicient resolution of the CH aliphatic and CH aromatic bands for quantitative measurements, it is necessary to use a lithium fluoride prism. The instrument used for these measurements was a Beckman Infrared Spectrometer, Model IR-Z, sold by Beckman Instruments, Inc., Fullerton, California.

Spectra were obtained on the solid pitch by allowing a portion to melt slowly between two rock salt plates.

One plate was removed While the sample Was still molten leaving a layer of sample on a single rock salt plate.

The typical observed CH aliphatic CH aromatic ratios, as determined for several pitches, are tabulated below in Table IV. Sample A is pitch of the invention obtained from the nonpolar constituent of run 4 of Table II. Pitch B is a commercially available coal-tar pitch from a tar of high-temperature carbonization of'coal and may be considered representative of present commercial pitches used for fiber pipe impregnation. Pitch C is 'a commercially available coal-tar pitch from a tar obtained from high-temperature carbonization of coal and may be considered representative of present commercial pitches used for electrode binders.

From the ratios of Table IV it is immediately apparent that the pitch of this invention is strikingly more aliphatic in nature than representative pitches from hightemperature coal-tars. The optical density of the pitch of the invention, as illustrated in Table IV, at 3.42 microns (aliphatic) is 12 or more times the optical density at 3.27 microns (aromatic). As illustrated in Table IV, the aliphaticity ratio of the pitch of the invention is many times the aliphaticity ratio of the representative pitches from high-temperature coal-tars. High-temperature pitches are predominantly aromatic in nature rather than aliphatic. On the other hand the pitches of the invention always have an aliphaticity ratio greater than one. Ordinarily the aliphaticity ratio of the pitches of the invention is not less than three. Therefore the pitch of the invention is more aliphatic in nature than pitch obtained from high-temperature tar. As far as is known, heretofore, pitches with aliphaticity ratios such as the pitches of the invention have never been produced with the superior properties, such as resistance to alkaline leaching, of the pitches of the invention.

Alkaline leachability of pitches is one property which is determinative of commercial suitability for such uses as fiber pipe impregnants, or exterior coatings, for example. These predominantly aliphatic pitches of the invention from low-temperature tars exhibit excellent resistance to alkaline leaching.

A standard test of leaching resistance may be made by the method described in Commercial Standard CS 116-54, Bituminous Fiber Drain and Sewer Pipe, US. Department of Commerce, but the results obtained do not afford quantitative measurements. Where pitches have comparatively good resistance to alkaline leaching, it is difiicult to obtain accurate measurements of the small amount of leaching that may occur. For ex-. ample, the water susceptibility of various pitches varies and if weight change of a pitch is measured as an indication of resistance to alkaline leaching, there may be obtained erratic and irreproducible test results.

It was determined that accurate comparative measurements of resistance to leaching for various pitches could be made by measurement of the light transmittance of .the leach liquor if sample size and other test conditions were held uniform. Tests were run according to a modified procedure of CS 116-54. The test procedure Was scaled down for convenient laboratory handling and the light transmittance measurements made on0.1 N Na CO leach liquors with a colorimeter at a wave length of 500 millimicrons. A Bausch & Lomb Spectronic 20" Colorimeter, sold by Bausch & Lomb Corporation, Rochester, New York, was employed to make the light transmittance measurements. Measurements of the leach liquors were made immediately after sample removal and are reported as percent transmittance, which is inversely proportional to optical density. Measurements by the aforesaid procedure of various samples are tabulated below in Table V. Sample A was a pitch from a distillation residue of a low-temperature lignite tar and is illustrative of the poor leaching resistance of pitches obtained by such conventional methods. Sample B is a commercially available high-temperature coke-oven coal-tar pitch used for fiber pipe impregnation. Sample C is a pitch of the invention from the hexane solubles of run 4 of Table, II.

tabulated below in Table VI.

Percent Light; Transmittance of Leach Liquor at 500 Millimicrons Number Days Leeched in 0.1 N NazOOs Sample a It is generally understood by those skilled in the art that the presence of certain oxygen-containing compounds, such as'tar acids, affect the alkaline le'acha-bility of pitches. The pitches obtained from low-temperature tars in accordance with this invention, in addition to high resistance to alkaline leaching, also have low oxygen content. Significantly, the oxygen content of the pitches of the invention is lower than the oxygen content of pitches from the distillation residue or low-temperature tars.

While the oxygen content of some materials may be obtained by direct chemical anaylsis, it has not been possible to determine theoxygen content of pitches of the invention by direct chemical anaylsis in that inconsistent values were obtained for successive analyses of replicates of the same pitch. However, the oxygencontents of the pitches of. the invention may be calculated by diflierence after direct chemical analysis for other elemental chemical constituents of the pitch. Typical oxygen contents, by diiference, of several materials are Samples A and B, are pitches of the invention obtained from the hexane solubles of process run No. 4 reported in Table II. Sample C is a pitch with a softening point of 68C. (Ring and Ball) obtained by a conventional distillation method from the same low-temperature tar from which Samples A and B were prepared. The low-temperature tar, from which all Samples A, B and C were prepared, upon direct oxygen analysis had an oxygen content of 8.1 percent (average of two determinations).

The oxygen content of a pitch makes no distinction as to the particular oxygen-containing materials in the pitch in that the oxygen may be present as hydroxyl compounds (e.g. tar acids), carbonylic compounds (e.g. ketones), heterocyclic oxygen compounds, etc, and not all of these compounds may be detrimental to obtaining pitch properties suitable for commercial applications. The oxygen content may range as high as about 4 percent by weight for the pitches of the invention, and the pitches still will have properties superior to properties of pitches from the same low-temperature tar that are. obtained by conventional means. Similar to the manner in which index of a'romaticity? or aliphaticity of a sample may be determined, it is possible by infrared spectral examinations to determine the index of the hydroxyl content of a sample. The hydroxyl (OH) band was measured at 3.0 microns and the aliphatic C H band measured at 3.42 microns as an indication of film thickness. The ratio CH aliphatic is the ratio of the optical density of the bands at microns (hydroxyl) and 3.42 microns (aliphatic), which 12 ratiois hereinafter called the hydroxyl ratio. These measurements were obtained using a Perkin-Elmer Model 21'Sp'ectrophotometer with a sodium chloride prism; The Perkin-Elmer Model 21 Spectrophotometer is manufactured and sold by the Perkin-Elmer Corporation, Norwallt, Connecticut. Typical:

O- H aliphatic ratios are tabluated below in Table VII. Sample A is a substantially water-free pitch obtained from the nonpolar constituent of run No. 4 of Table II. Sample B is a substantially Water-free pitch-like residue of a distillation wherein a 68 percent distillate was removed front the primary low-temperature lignite tar.

Table VII Sample OH C-H aliphatic A l 0. 00 B' 0. 23

From the ratios of Table VII it'is immediately apparent that the pitch of the invention has a strikingly low hydroxyl ratio. Apparently the hydroxyl ratio may be as high as about 0.12 'for the pitches of the invention, and the pitches still will have properties superior to properties of pitches from the same low-temperature tar that areob: tained by conventional means.

An important requirement for many applications is that the pitch have an extremely low ash content. The typical data tabulated in the following Table VI-II illustrate the superiority of pitches of the invention in this respect. Sample A is a pitch of the invention obtained from the hexane solubles of run 4 of Table II. Sample B is a pitch prepared from low-temperature tar by a conventional distillation method. Sample C is the low-temcontent of the pitches of the invention when compared to the tar used for the preparation of the pitch and to a pitch obtained from the same tar by a conventional distillation method.

It is believed that the pitches of the invention, having desirable properties for many known applications, exhibit these properties because most of the ash and most of the predominantly polar and reactive materials have been removed. The above data substantiates the fact that the process of this invention yields a new and different pitch. The separation of the reactive materials, which appear to be primarily polar materials, from low-temperature tars and the embodiment of these materials in a separate polar material comprising predominantly tar acids pro vides a new and useful material. The polar material of the invention is separated from the polar solvent extract obtained by the process of the invention from a-lowtemperature tar. Preferably the polar material is sep a rated from an alcohol extract by distilling off the alcohol and the water, but other means known to the art may be used. To illustrate the composition of the polar material of the invention, there are presented in Table IX, below, typical results ofgASTM D 20S2 distill-ations of two samples. Sample A is the alcohol solubles (polar 'm'ateriw ably a liquid alkane.

' 13 al) of run No. 4 of Table II and Sample B the alcohol solubles (polarmaterial) of run No. 12 of Table II.

Table IX Samnln A B ASTM D 20-52 Distillation (weight percent):

To 170 C 5.0 7.2 17023-5 C 16. 4 9. 6 235-270" C 11.8 14.3 270-300 C 10. 3 11. 9 300-Decomposition temperature, C... 23. 24. 7 Residue at decomposition temperature, C 29. 7 27. 3 Residue at 300 C 53. 2 52.0 L 3. 3 5.0 Decomposition temperature, C 335 335 The polar materials of the invention, as illustrated by the ASTM D 2052 distillation results of Table IX, contain polar materials having boiling points over the entire range of boiling points of the corresponding low-temperature tar from which they were obtained. By known art processes, it is not possible to recover the equivalent of the'polar materials of the invention, for the prior art does not teach the separation of polar materials of this type and especially polar materials having a content of at least 50 percent by weight nonvolatile at 300 C. from low-temperature tars.

While the invention has been specifically illustrated with an aqueous methanol-hexane solvent combination, it is to be understood that various suitable combinations of solvents can be used. The polar solvent, i.e. a solvent which has good solvent powers for the polar constituents and poor solvent powers for the nonpolar constituents of the tar, preferably is an aqueous alcohol solution. Suitable alcohols are the hydroxy derivatives of paraflinic hydrocarbons and, as such, are distinguished from aromatic alcohols. Preferably, the alcohols have at least one primary hydroxyl group and are the simple members of the series, such as methyl alcohol, ethyl alcohol, propyl alcohol, etc., with methyl alcohol preferred. The aqueous alcohol solution may range in alcohol content from about 60 percent by weight to about 75 percent by weight, depending upon the particular alcohol and upon the particular water content of the tar. In the case of an aqueous methanol solution, the preferred percentage of methanol is 70 percent by weight. In general, as the alcohol content of the aqueous alcohol solution is decreased from 70 percent by weight, there is a corresponding, although not proportional, decrease in the total recovery of the constituents soluble in the alcohol solution, and a corresponding, although not proportional, increase in the concentration of the tar acid constitutents therein. In general, as the alcohol content of the aqueous alcohol solution is increased from about 70 percent by weight, there is a corresponding increase in the total recovery of the constituents soluble in the alcohol solution and a corresponding decrease in the concentration of the tar acid constituents therein, the tar acid concentration being determined by solubility of the alcohol-soluble material inaqueous caustic solution. Mixtures of several suitable aqueous alcohol solutions having alcohol contents within the aforesaid limitations may be used The nonpolar solvent, i.e. a solvent which has good solvent powers for nonpolar constituents and poor solvent powers for polar constituents of the tar, should be predominantly a liquid aliphatic hydrocarbon, prefer- The preferred liquid alkanes are hexanes and pentanes with commercial materials, such as hexane and pentane cuts of paraifinic hydrocarbons being suitable liquid alkanes. The liquid aliphatic hydrocarbon may contain from about 4 to 8 carbons and preferably contains 5 to 7 carbon atoms. Mixtures of liquid aliphatic hydrocarbons, within the aforesaid limitations, may be used. Small amounts of certain solvents, other than liquid aliphatic hydrocarbons, may be present in the nonpolar solvent; for example liquid aromatic hydrocarbons containing up to about 8 carbon atoms may constitute up to about 25 percent of the nonpolar solvent.

Essential to the operation, of the process is a selection of the solvents with reference to each other. It is a prerequisite in the selection of the solvents that for simultaneous use the solvent extracts be immiscible and have sufiicient difference in their specific gravities to permit gravity separation into distinguishable phases.

In the practice of the process, specific .gravities of less than about 0.75 for the liquid alkane and of greater than about 0.85 for the aqueous alcohol solution are preferred.

In solvent seleotiomthe lower-boiling alcohols and aliphatic hydrocarbons are preferred so that separations of the solvents from their extracts may be carried forth, for example, by distillation at relatively low temperatures, without undue eifect on reactive materials. Necessarily, the process temperature and presstue need be considered in solvent selection so that both the aqueous alcohol solution and the liquid aliphatic will be liquids at the process temperature and operating pressure.

Using the preferred selection of solvents as described heretofore, the process is preferably carried forth at ,atmosphericpressureL However, certain combinations of solvents may require somewhat different pressures for operation of the process. Somewhat higher or lower pressures than atmospheric pressure may be used, pro-. vided the solvent extracts are liquids and are separable at these pressures. I

While a preferred pitch, polar material, and method have been shown and described, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from the invention in its broadest aspects and the appended claims are intended to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

l. A process for obtaining a pitch, characterized by having substantial leaching resistance to aqueous alkaline solutions andby being more aliphatic in nature than pitch obtained from high-temperature tar, from a tar obtained from a low-temperature carbonization of coal comprising: extracting said tar at a temperature of 100 to 140 F. with an aqueous alcohol solution containing 60 to 75 weight percent of an alcohol selected from the group consisting of methyl, ethyl, and propyl alcohols, and with a liquid aliphatic hydrocarbon of from 4 to 8 carbon atoms; recovering a liquid aliphatic hydrocarbon extract comprising the liquid aliphatic hydrocarbon, neutral oils, and said pitch from said extracting; and separating said pitch from said liquid aliphatic hydrocarbon extract; said aqueous alcohol solution and liquid aliphatic hydrocarbon being immiscible and having a dilference in specific gravities with 3 to 12 parts by weight of each being employed for every part by weight of said tar.

2. A process as in claim 1 including: recovering an aqueous alcohol extract comprising the aqueous alcohol solution and polar materials from said extracting; and separating from the aqueous alcohol extract a polar material having at least 50 weight percent nonvolatile at 300 C. and at least weight percent soluble in an aqueous 20 percent by weight sodium hydroxide solution.

3. A process for obtaining a pitch, characterized by having an oxygen content of less than 4 weight percent, by being more aliphatic in nature than pitch obtained from a high-temperature tar, and by having a hyd-roxyl ratio of less than 0.12, from a tar obtained from a lowtemperature carbonizaition of a lignite coal, comprising: extracting said tar at a temperature of at least F. with an aqueous methanol solution, containing from 60 to 75 weight percent methanol and the balance water, and a liquid alkane containing from 4 to 8 carbon atoms, said solution and said a-lk'ane being immiscible and having a 15 alkane, neutnal oils, and said pitch; and se'para'tihg said pitch from said liquid alkane extract.

4. A process as in claim 3 including: recovering an aqueous methanol extract from theextraction'of said tar, said aqueous methanol extract comprising the aqueous methanol solution and polar materials; and separating a polar material from said aqueous methanol extract; said polar material having more than 50 weight percent nonvolatile at 300 C. and at least 80 weight percent soluble in an aqueous 20 percent by weight sodium hydroxide solution.

5. In a process for obtaining a pitch, having substantial leaching resistance to aqueous alkaline solutions and having an aliphaticity ratio of at least 3, from a; tar obtained from the low-temperature carbonization of lignite coal, the combination comprising: feeding said tar to a vertical extraction zone at a point located between the ends thereof; feeding an aqueous alcohol solution containing 60 to 715 percent of an alcohol selected from the group consisting of methyl, ethyl, and propy'l alcohols, to the top of said extraction zone; feeding a liquid aliphatic hydrocarbon of from 4 to 8 carbon atomssiinultaneously with said feeding of said alcohol solution to and near the bottom of said extraction zone, said aqueous alcohol solution and liquid aliphatic hydrocarbon being immiscible and having a difference in specific gravities with 3 to 12 parts by weight of each being employed for every part by weight of said tar; passing said aqueous alcohol solution and said liquid aliphatic hydrocarbon through said vertical extraction zone in countercurrent relation, said vertical extraction zone being at a temperature of 100 to 140 F.; recovering a liquid aliphatic hydrocarbon extract from the top of said vertical extraction zone; and distilling said liquid aliphatic hydrocarbon extract to obtain distillates of said liquid aliphatic hydrocarbon and a nonpolar oil and a residue of the pitch.

6. In a process for obtaining a pitch, having substantial leaching resistance to aqueous alkaline solutions and having an aliphaticity ratio of at least 3, from a tin obtained from the low-temperature carbonization of lignite coal, the combination comprising: feeding said tar to a vertical extraction zone at a point located between the ends thereof; feeding an aqueous methanol solution containing 60 to 75 weight percent methanol and the balance water to the top of said extraction zone; feeding hexane simultaneously with said feeding of said methanol solution to and near the bottom of said extraction zone; passing said aqueous methanol solution and said hexane through said vertical extraction zone in countercurrent relation; recovering a hexane extract from the top of said vertical extraction zone; and distilling said hexane extract to obtain distillates of said hexane and nonpolar oil and a residue containing said pitch.

7. In a process as in claim 6 including: preheating said tar, said aqueous methanol solution, and said hexane be fore feeding the same to said extraction zone to a temperature of at least 100F. and no more than 140 F.; maintaining said extraction zone at said temperature; recovering an aqueous methanol extract from and near the bottom of said extraction zone; and separating from said aqueous methanol extract a polar material, said polar material having at least weight percent nonvolatile at 300 C. and having at least 80 weight percent soluble in :an aqueous caustic solution.

8. In a process as in claim 6 including: separating from said extraction zone at the bottom of said zone a residue. 7

9. A process for obtaining a pitch, characterized by substantial leaching resistance to aqueous alkaline solutions and by being more aliphatic in nature than pitch obtained from high-temperature tar, from a tar obtained from a low-temperature carbonization of coal comprising: extracting said tar with an aqueous alcohol solution containing to 75 weight percentof anal'cohol selected from the group consisting of methyl, ethyl, and propyl Y6 alcohols, with a liquid mixture of a li'qhid aliphati d hydrocarbon of from 4 to 8 carbon atoms and a minor amount up to about 25 weight percent of a liquid aromatic hydrocarbon 'of up to 8 carbon atoms; recovering an ex tract from said extracting, saidextractcomprising said mixture, neutral oils, and said pitch; and separating said pitch from said extract; said aqueous alcohol solution and said liquid mixture being'irnmisciblejand having a dilference in specific 'gravities with 3 to 12 parts by Weight of each being employed for every part by weight of said tar.

10. A polar productconsisting' essentially of a portion of a low-temperature tar dissolved and extracted by an aqueous alcohol solution containing 60 to weight percent of an alcohol selected from the group consisting of methyl, ethyl, and propyl alcohols; said tar being from low-temperature carbonization of a coal selected from the group consisting of bituminous, subbituminous, brown and lignite coals, said product characterized by having more than 50 weight percent nonvolatile at 300C. and more thanweight percent soluble in an aqueous 20 percent by weight sodium hydroxide solution.

11. A polar material consisting essentially of a po'r tion of a low-temperature tar dissolved and extracted by an aqueous alcohol solution containing 60 to 75 weight percentof an alcohol selected from the group consisting of methyl, ethyl, and propyl alcohols, said tar obtained, from the low-temperature carbonization of a lignite coal, said polar material having more than 80 weight percent soluble in an aqueous 20 percent by weight sodium hydroxide solution and at least 50 weight percent nonvolatile at 300 C.

12. A pitch consistingessentially of that portion of a tar which was dissolved and extracted by a liquid aliphatic hydrocarbon of from 4 to 8 carbon atoms, and which was nonvolatile at about 300 C., said tar being from low temperature carbonization of a coal selected from the group consisting of bituminous, subbituminous, brown, and lignite coals, the pitch having the following charac teristics: substantial leaching resistance to an aqueous dilute sodium carbonate solution; an oxygen content less than 4 percent by weight; a hydroxyl ratio of at least 0.12 as determined by infrared absorption analysis; and sufliciently aliphatic in nature that the pitch has an. aliphaticity ratio of at least one as determined by infrared absorption analysis.

13. The pitch of claim 12 in which the tar was from lignite coal and in which the pitch is additionally characterized as having an aliphaticity ratio of at least three.

14. The pitch of claim 13 havingthe additional characteristics of an ash content of less than 0.1. percent by weight and a carbon-plus-hydrogen content of at least 94 percent by weight.

15. A pitch consisting essentially of that portion of a tar which was dissolved and extracted by a nonpolar, liquid aliphatic hydrocarbon of from 4 to 8 carbon atoms and which was nonvolatile at about 300 C., said tar being from low-temperature carbonization of lignite coal, the pitch having the following characteristics: substantial leaching resistance to'an aqueous dilute sodium carbonate solution; an oxygen content of less than 4 percent by weight; acarbon-plus-hydrogen content of at least 94 percent by weight; an ash content of lessthan 0.1 percent by w i ht: a o tenin": o nt (Ring and Ball) of from about 40 C. to'about 112 C.; at least- 20 percent by weight of the pitch insoluble in benzene; at least 20 percent by weight'of the-pitch insoluble in carbon tetrachloride; pnmary characteristic absorption bands in the infrared spec: trum at 3.42, 3.27, and 3.00 micron wave lengths with an optical density at the 3.42 micron wave length at least'three timesthe optical densityat the 3.27 micron wave length and at least eight times the optical density at the 3.00 micron wave length;

' (References on following page) References Cited in the file of this patent UNITED STATES PATENTS Wittek June 26, 1928 Weindel Sept. 3, 1929 5 Parkhurst May 29, 1934 Neuworth Mar. 31, 1953 Gorin et a1 Jan. 19, 1954 Jones et al Oct. 9, 1956 18 FOREIGN PATENTS Great Britain July 4, 1930 Great Britain June 9, 1932 Great Britain Dec. 30, 1953 OTHER REFERENCES Abraham: Asphalts and Allied Substances, 5th edition, volume 1, 1945, Van Nostrand Company, New York (pages 381-412).

Claims

1. A PROCESS FOR OBTAINING A PITCH, CHARACTERIZED BY HAVING SUBSTANTIAL LEACHING RESISTANCE TO AQUEOUS ALKALINE SOLUTIONS AND BY BEING MORE ALIPHATIC IN NATURE THAN PITCH OBTAINED FROM HIGH-TEMPERATURE TAR, FROM A TAR OBTAINED FROM A LOW-TEMPERATURE CARBONIZATION OF COAL COMPRISING: EXTRACTING SAID TAR AT A TEMPERATURE OF 100* TO 140*F. WITH AN AQUEOUS ALCOHOL SOLUTION CONTAINING 60 TO 75 WEIGHT PERCENT OF AN ALCOHOL SELECTED FROM THE GROUP CONSISTING OF METHYL, ETHYL, AND PROPYL ALCOHOLS, AND WITH A LIQUID ALIPHATIC HYDROCARBON OF FROM 4 TO 8 CARBON ATOMS, RECOVERING A LIQUID ALIPHATIC HYDROCARBON EXTRACT COMPRISING THE LIQUID ALIPHATIC HYDROCARBON, NEUTRAL OILS, AND SAID PITCH FROM SAID EXTRACTING, AND SEPARATING SAID PITCH FROM SAID LIQUID ALIPHATIC HYDROCARBON EXTRACT, SAID AQUEOUS ALCOHOL SOLUTION AND LIQUID ALIPHATIC HYDROCARBON BEING IMMISCIBLE AND HAVING A DIFFERENCE IN SPECIFIC GRAVITIES WITH 3 TO 12 PARTS BY WEIGHT OF EACH BEING EMPLOYED FOR EVERY PART BY WEIGHT OF SAID TAR.