US3079326A - Double solvent refining of tar - Google Patents

Description

Feb. 26, 1963 M. B. NEUWORTH 3,079,326

DOUBLE SOLVENT REFINING OF TAR Filed March so, 1960 2 Sheets-Sheet 1 PRIMARY AQUEOUS METf/A/VOL z IQU/D -L IQU/D X7Q4C770A/ VESSEL r NAPl/THA 50L VENT AQUEOUS METl/A/VOL EXTRACT PITCH PHASE IN VEN TOR.

M4477 5 Nil/WORTH Feb. 26, 1963 M. B. NEUWORTH DOUBLE SOLVENT REFINING OF TAR 2 Sheets-Sheet 2 Filed March $0, 1960 3,079,326 BOUBLE SOLVENT REFENENG F TAR Martin 3. Neuworth, Pittsburgh, Pa, assignor to Consolidation Coal Company, Pittsburgh, Pa., 2 corporation of Pennsylvania Filed Mar. 39, B66, Ser. No. 18,695 6 Claims. (Cl. 2ti845) This invention relates to a process wherein a double solvent treatment is used for fractionating the liquid products obtained by the low-temperature pyrolysis of naturally occurring carbonaceous solids. It is particularly concerned with the fractionation of primary low-temperature tar using aqueous methanol and a parafiinic naphtha fraction as solvents under selected conditions.

When naturally occurring carbonaceous solid fuels, such as bituminous coal and lignite, are subjected to low-temperature carbonization, i.e., at a temperature below 1400 F., the product tar is evolved as a vapor. Subsequent condensation of the vapor produces a highly viscous liquid tar product that is variously designated as primary, whole, unprocessed, unrefined, raw or crude tar. The term primary tar is ordinarily applied to tar obtained at low temperatures where a maximum yield of tar is obtained with a minimum of tar decomposition or alteration. These conditions represent an ideal state, and consequently no tar can be said to be entirely primary. As used herein, the terms primary, whole, and raw are considered essentially synonymous to indicate that substantially all of the low-temperature tar obtained as a liquid product by condensation of the tar vapors is initially subjected to a solvent treatment process as described herein, and is not fractionally distilled prior to this solvent treatment. This tar product contains virtually all of the condensable ingredients of the carbonization vapors along with entrained finely divided particles of coal and partially carbonized coal. The recovery of valuable constituents contained in the tar is of considerable commercial importance. The process of this invention enables the recovery of these valuable constituents from low-temperature tar, Whether derived from low rank noncoking coals, e.g., lignite, brown coal and sub-bituminous coals, or from high-volatile highly caking coals, e.g., Pittsburgh seam bituminous coal.

Wherethe tar is obtained by a low-temperature carbonization process under fluidized conditions, additional problems of recovery are presented. First, the finely divided particles of coal and partially devolatilized coal contained in the fluidized low-temperature tar are unusually small in size and are present in greater quantity because of the attrition and entrainment caused by the turbulent conditions prevailing within a fluidized lowtemperature carbonization processing vessel. Such tars may contain 25 percent or more by weight of finely divided particles of coal and partially carbonized coal. Second, the tars obtained from fluidized low-temperature carbonization processes tend to be of a more primary character, i.e., the tar constituents tend to be closely related in structure to the constituents of the coal that is carbonized because there is little opportunity for cracking'the constituents prior to recovery. Hence these tars tend to be more viscous than other types of low-temperature tars.

Various techniques and plans have been proposed for processing primary tar for recovery of the valuable liquid constituents therein. All of these plans suffer from certain drawbacks. In some, operability is achieved at the expense of significant tar yield. In others, fractional distillation of the tar, reducing its primary character, results in the cracking of the more valuable constituents to yield less valuable constituents that may be obtained more 3,079,326 tPatented Feb. 26, 1%53 economically from other sources. In still other methods, relatively expensive solvents are required in large volumes in treating the tar in order to avoid gumming and plugging of equipment and associated operability problems. In yet others of these plans, attempts have been made to first remove finely divided particles present by use of conventional mechanical separation techniques such as filtration, centrifugation and settling. Such techniques without further modification have been generally found lacking with respect to operability and commercial feasibility, particularly where a high percentage of solids is present in the tar. In general, the foregoing plans either introduce additional processing steps that are frequently costly and hence of laboratory interest only, or significantly alter the basic caracteristics of the tar, whereby a lesser amount of valuable liquid products is recovered.

Fractional distillation has been principally used heretofore to eifect an initial fractionation of the primary tar. By topping of the tar, the more volatile tar acid oils may be recovered therefrom as an overhead distil late. However, depending on the nature of the tar and the thermal treatment, many of the tar constituents may polymerize, decompose or be carbonized. As a consequence, valuable liquid constituents present are lost by conversion to simpler hydrocarbons of 'less value or to core.

Because of the highly complex chemical composition of primary low-temperature tar, the initial treatment of the whole tar by selective solvent techniques to effect separation of the valuable constituents of the tar has been considered too difficult to be of commercial importance. Direct solvent treatment of the whole tar must overcome problems of high t-ar viscosity, poor miscibility of the tar with most solvents, and prolonged period of contact required between the tar and solvent for complete extraction and separation of components, together with high solvent to tar ratios. Ordinarily, any finely divided solids present must first be removed to prevent plugging of the equipment. Emulsification and agglomeration occurring in the tar-solvent system further interfere with operability. Also, the lack of selec+ tivity of various solvent systems used introduces the further problem of after-recovery of sought-for constituents from both the extract and the reject phases of the solvent system. In addition, solvent techniques suitable for high-temperature tar are not ordinarily applicable to lowtemperature tar because of the considerably different physical and chemical properties of the two types of tar. At present, then, no satisfactory technique of commercial utility is known for the initial solvent treatment of primary low-temperature tar. Where .the low-temperature tar is produced under fluidized conditions, the problem of separation becomes even more difiicult.

Accordingly, it is an object of the present invention to provide a process for the fractionation of primary tar free from the disadvantages heretofore known.

It is a further object to fractionate tar by an initial solvent treatment into useful acidic and neutral tarfractions. v

It is yet another object to provide a method for the continuous countercurrent extraction of primary tar obtained by the low-temperature carbonization of bituminous coal under fiuidizedconditions.

In accordance with the broad aspects of this invention,- one volume of a primary low-temperature tar is treated under liquid-liquid contacting conditions at a temperature between 50 and 150 C. in a liquid-liquid extraction system operated at autogenous pressure and including one or more extraction zones, with a double solvent extraction system consisting of (1) 0.5 to 5 volumes of aqueous methanol containing 40 to weight percent methanol and the balance water and (2) 0.5 to 5. volumes of a parafiinic naphtha fraction having a boi'ing range between 60 and 130 C. and a density less than 0.80, whereby the tar is fractionated into three phases. The volume ratio of the two solvents is further ma ntained between 0.5 and 2.

In the more specific and commercially preferred aspects of this invention, a primary low-temperature tar obtained by the carbonization of naturally occurring carbonaceous solids at a temperature below 1400 F., and preferably between 8C0 and 1400 F., is fed into the central portion of a continuous countercurrent double solvent center-feed vertical extraction column. The tar is simultaneously contacted by an aqueous methanol solution, which is fed into the top of the column, and by a low boiling essentially parafiinic naphtha fraction, which is fed into the bottom of the column. The aqueous methanol passes downwardly through the column dissolving substantially all of the low-boiling tar acids, a substantial portion of the high-boiling tar acids, and a small portion of neutral oils. The naphtha fraction, being lighter than the aqueous methanol, passes upwardly through the column and contains almost all of the neutral oils. In this process, three phases are formed: 21 methanol extract, which is essentially acidic; a naphtha extract, which is essentially neutral; and a pitch phase, which is a conglomerate mixture. This latter phase is not miscible with either the aqueous methanol extract or the naphtha extract. Since the pitch phase is heavier than both of the solvent streams, it drops through the extraction tower and may be decanted from the aqueous methanol extract.

The process of this invention is generally suitable for the treatment of tars obtained by the pyrolytic decomposition of carbonaceous solids at temperatures below 1400 F. Such carbonaceous solids include all ranks of coal, such as bituminous, sub-bituminous, brown coal, lignite and the like. This process may also be used for the treatment of those tars obtained by the low-temperature carbonization of bituminous coals, e.g., highvolatile caking bituminous coals, under fluidized conditions. The resulting tars contain varying amounts of finely divided solids and are ordinarily particularly ditficult to treat without substantial loss of valuable crnstituents. Where an excessive amount of finely d'vided solids is present, these are preferably removed by agglomerating them by a prior solvent treatment of the tar, followed by filtration, e.g., as shown in US. 2,774,- 716.

Certain critical conditions must be observed in order to obtain operability in this process. Thus to achieve effective continuous countercurrent extraction of the primary low-temperature tar, it is considered critical that the aqueous methanol solution contain from about 40 to 80 weight percent methanol and the balance water. In concentrations below 40 percent, emulsification more readily occurs and phase separation consequently becomes almost unobtainable. When the methanol concentration of the solvent exceeds 80 percent by weight, selectivity begins to fall off markedly, with excessive amounts of neutral oils being dissolved along with the tar acids which are in solution. In general, for optimum phase separation and selectivity, a methanol concentration of the aqueous methanol solvent between 55 and 70 percent by weight is preferred. The process of this invention is further critically conditioned by the characteristics of the naphtha solvent. It must be essentially parafiinic in character. Such solvents may be obtained from the distillation of parafiinic petroleum stocks. Its boiling range should be 60 to 130 C., and preferably 60 to 100 C. in order to simplify the subsequent separation of the naphtha fraction from the naphtha extract by distillation. And finally, the densi'y naphtha extract in the extraction column to effect a ready separation of these two phases. The hexane cut of parafiinic naphtha combines all of these critical properties and accordingly is preferred as the naphtha solvent in this invention. WhiIe the process of this invention may be practiced with either the naphtha fraction or the aqueous methanol as the continuous phase in the tarcontacting portion of the extraction column, it is preferred to use the naphtha fraction as the continuous phase, particularly because the pitch phase also contains naphtha solvent associated therewith. Also, by using the naphtha fraction as the continuous phase, separation between the aqueous methanol extract and the pitch phase is facilitated.

In operating this system, temperatures below 40 C. are unsuitable. Where the temperature in the column falls below 40 C., the tar becomes gummy, cannot be readily extracted and plugs the column. An extraction temperature of about 50 C. is therefore conside ed minimal. To prevent boiling of the solvents and consequent interference with extraction, a pressurized system is required, the pressure maintained being the pressure that is internally generated. Temperatures above 150 C. are not contemplated because of the undesirably high associated pressures. For the operative temperature range of 50 to 150 C., which is considered critical, the corresponding internally generated pressures will range from about 1 to 20 atmospheres. It is generally preferred to preheat the tar, methanol, and naphtha fraction to the extraction temperature used. A preferred temperature range is between 75 and 125 C.; at these temperatures the tar shows a suitable fluidity, the pressure is convenient to maintain, and satisfactory sepa-'- ration between the three phases is obtained.

The achieving of adequate contact between the solvents and the tar is of considerable importance for obtaining satisfactory phase separation and extraction efiiciency in a continuous countercurrent extraction process. Various systems are known for achieving continuous counter current liquid-liquid extraction. For example, a horizontal multistage contactor may be used with highly viscous liquids such as tars. Of the many types of ver tical columns that have been used in liquid extraction processes, such as packed columns, spray columns, bafiie columns, and perforated plate columns, not all are suit able for use with highly viscous tars. In general, columns containing packing are to be avoided because of impedance to proper flow of the tar and interference with the maintenance of suitable phase separation. Because of the ordinarily highly viscous nature of primary low-temperature tar, in addition to operating the extraction column at a temperature between 50 and 150 C., the use of a rotating disk contactor column is considered particularly suitable for obtaining the required continuous countercurrent extraction efliciency while maintaining the desired phase separation. Various rotating shaft extraction columns are known and may be used. However,

. because of the physical characteristics of low-temperature of the naphtha fraction should be lessthan 0.80 and tar, it is preferred that the settling or calming sections of such columns be free from packing and thus be in unobstructed communication with the mixing sections. In operating a rotating disk contactor column, a rotor speed providing a peripheral disk velocity of between 0.5 and 5 feet per second is generally preferred. Where the rotor speed falls below the preferred range, there is poor contact between the tar and the solvents with relatively low extraction efficiency. At higher speeds, emulsification occurs with consequent poor phase separation. An extraction efficiency obtained with from 10 to 20 sections is suitable. Elimination of packing in the calming sections will not deleteriously affect plate efiiciency. At the same time this eliminates interference with the ready transportof solids by the countercurrently flowing liquids. Ease of transport is particularly important where there-is 'erated within the vessel.

U a substantial amount of-finely divided-carbonaceous solids present in the tar.

Inasmuch as both the methanol extract and the immiscible pitch phase descend to the bottom of the tower, this bottom portion is so constructed as to permit ready settling of the pitch phase and decantation of the supernatant extract therefrom. In general, from 0.5 to vol umes of aqueous methanol and from 0.5 to 5 volumes of naphtha solvent per volume of tar will be required for efiicient countercurrent extraction While still maintaining the desired phase separation. Further, the volume ratio of the aqueous methanol to naphtha solvent should be maintained between 0.5 and 2. By further suitable regulation of the relative feed rates of the aqueous methanol and of the naphtha fraction, either solvent may be maintained as the continuous phase. It is preferred that the naphtha solvent be the continuous phase.

For a more complete understanding of this invention, its objects, features and advantages, reference should be had to the accompanying drawings in which:

' KG. 1 is a generalized schematic illustration of the process of fractionating primary tar by an initial double solvent treatment using aqueous methanol and a naphtha fraction as solvents.

FIG. 2 is a pr ferred commercial embodiment, shown schematically, for fractionating primary tar by an initial double solvent treatment in a continuous countercurrent center-feed vertical extraction column using aqueous methanol and a naphtha fraction as solvents.

Referring to FIG. 1, a low-temperature primary tar contained in a storage vessel 1 is fed through a suitable conduit to a stirred liquid-liquid extraction vessel 2.

Aqueous methanol contained in a storage vessel 3 is fed through a suitable conduit to vessel 2. Naphtha solvent contained in a storage vessel 4 is fed through a suitable conduit to vessel 2. The primary tar is obtained by the pyrolytic decomposition of carbonaceous solids at temperatures below l400 F., and is not fractionally distilled prior to solvent treatment. The aqueous methanol solution contains from about 40 to 80 weight percent methanol and the balance water. The naphtha solvent is essentially parafiinic in character, having a boiling range between 60 and 130 C. and a density less than 0.80. The liquid-liquid extraction vessel 2 may consist of a single unit or of several units combined for multistage operation. The system shown in HS. 1 may be op- .erated on a batch basis, for example, when the extraction and settling steps are performed in a single zone, or it may be operated as a continuous countercurrent system. A preferred commercial embodiment of a continuous countercurrent system will be subsequently discussed.

Preferably the primary tar, aqueous methanol and naphtha solvent are preheated to the reaction temperature before being fed to vessel 2. The extraction temperature is maintained between 50 and 150 C. as critical operative limits.

Vessel 2 is operated at the appropriate autogenous pressure, i.e., at the combined pressure gen- This will in all instances result in the maintenance of liquid-liquid extraction conditions.

From 0.5 to 5 volumes of aqueous methanol and from 0.5 to 5 volumes of naphtha solvent are used per volume of tar. The ratio of the aqueous methanol to the naphtha solvent is maintained between 0.5 and 2. Where the system shown in FIG. 1 is operated in a continuous countercurrent manner, the feed rates to vessel 2 are 1 gram tar per ml. of petroleum ether. asphaltenes, most of which will appear in the aqueous density,-may be removed through a conduit 8. This extract is essentially an acidic tar fraction. The pitch phase, which is not miscible with either of the other two phases, is the most dense phase and may be removed through a conduit 9. The pitch phase, which is a conglomerate mixture, may be suitably processed to form electrode carbon.

In FIG. 2 is shown a preferred commercial embodiment for processing low-temperature tar in accordance with this invention. Referring to FIG. 2, a suitably preheated tar obtained by a low-temperature carbonization (LTC) process is pumped from a storage tank 10 continuously through a conduit 11 into a countercurrent double solvent center teed vertical extraction column 12. Subject to the limitations previously mentioned, the extraction column may be of any convenient design capable of providing a sutficient number of theoretical extraction stages to produce effective extraction of the tar. The tar will be introduced at any suitable point intermediate the bottom and top of the column, generally at a point above the geometric center of the extraction column.

Aqueous methanol solution is fed continuously from a methanol storage tank 13 through a conduit 14 into the top of extraction column 12. A naphtha fraction is fed continuously from a naphtha storage tank 15 through a conduit 16 into the bottom of extraction column 12.

The feed point of the naphtha fraction to the extraction column will be above the point at which the aqueous methanol extract and pitch phase are removed from the bottom of column 12.

Since the density of the aqueous methanol solution exceeds the density of the naphtha fraction, the aqueous methanol solution descends through the column and dissolves tar acids, both low-boiling and high-boiling, while the lighter naphtha fraction passes countercurrently upward through the column and dissolves neutral oils contained in the tar. At the same time the pitch phase, which includes high molecular weight components of the tar such as some acidic asphaltenes, and almost all of the neutral asphaltenes, and may include finely divided particles of partially carbonized and carbonized carbonaceous solids, drops through extraction column 12 to the bottom thereof.

Asphaltenes are defined as that fraction of solids-free tar insoluble at room temperature (20-25 C.) in petroleum ether (boiling range 35-60" C.) at a dilution of Acidic methanol extract, are soluble in dilute alkali and have a distillation temperature range at about 375 C., "completing their distillation at above 550 C. The neutral asphaltenes, which are insoluble in dilute alkali, do not distill below 550 C., and are therefore considered essentially non-distillable.

Aqueous methanol extract contained as a supernatant layer 17 is withdrawn continuously from extraction column 12 through a conduit 18 and fed into a distillation column 19 for the separation of the methanol solvent from the water and tar acids, both of which leave distillation column 19 as a bottoms product through a conduit 20 and pass into a phase separation tank 21. Since the solubility of tar acids in water decreases with reduction in temperature, a cooler 22 may be placed in conduit 20 to cool the water and tar acids passing through conduit 20 and thereby decrease the proportion of residual tar acids in the aqueous layer in phase separation tank 21. Purified tar acids, being virtually immiscible in water, separate from the aqueous layer in phase separation tank 21 and are withdrawn either continuously or intermittently as a bottoms product through a conduit 23. The tar acids obtained may be separated by fractional distillation at a temperature between 200 and 300 C. to low-boilin and high-boiling tar acid fractions. Generally, those tar acids boiling below 230 C. are the most valuable components commercially. The supernatant aqueous phase from tank 21 is withdrawn through a conduit 24 and sent to the aqueous methanol storage tank 13 for recirculation.

Anhydrous methanol passes overhead from distillation column 19 through a conduit 25 to a reflux condenser 26. Condensed anhydrous methanol leaves reflux condenser 26 and passes through a conduit 27 to aqueous methanol storage tank 13 for recirculation. A portion of the condensed methanol may be returned through a conduit 28 to the top of distillation column 19 as reflux.

It should be noted that in the preparation of the aqueous methanol solution contained in storage tank 13, caution should be exercised where the solution is prepared and its composition regulated by specific gravity measurement. The recirculated methanol is saturated with naphtha solvent and this fact must of course be considered in determining the specific gravity required to produce a solution containing 40 to 80 weight percent methanol. Fresh make-up methanol may be added to aqueous methanol storage tank 13 through a conduit 29 to make the necessary 40 to 80 weight percent methanol solution.

The naphtha extract phase containing dissolved neutral oils, particularly the high boiling neutral oils, leaves the top of extraction column 12 through a conduit 30 and passes to a distillation column 31 where the naphtha solvent is separated from the neutral oils. This naphtha fraction passes overhead from distillation column 31 through a conduit 32 and a reflux condenser 33. A portion of the condensed naphtha may be returned through a conduit 34 as reflux for distillation column 31. The remainder of the naphtha fraction is returned through conduit 32 to naphtha storage tank 15 for recirculat-ion. The neutral oil 35 which leaves distillation column 31 as a bottoms product through a conduit 36 is of utility as a carbon black feedstock. Particularly preferred as a carbon black feedstock is that portion of neutral oil 35 which includes substantially all of the constituents thereof boiling above an initial boiling temperature between 300 and 425 C. To obtain this desired carbon black feedstock fraction, neutral oil 35 is fed through a conduit 37 to a distillation column 38 and fractionally distilled therein. The low-boiling constituents are removed as an overhead product through a conduit 39, leaving the desired carbon black feedstock as a bottoms residue. This may be removed through a conduit 40. A cooler 41 may be inserted in exit conduit to 0001 this carbon black feedstock product. Depending upon the composition of the specific fraction of tar present in the naphtha extract, which may be varied by varying the methanol concentration of the aqueous methanol solvent, the neutral oil bottoms products 35 may also be of utility as a hydrogenation feedstock for gasoline. A cooler 42 may be inserted in exit conduit 36 to cool the neutral oil product.

The lower or subjacent pitch'phase layer 43 is removed from the bottom of extraction column 12 at the lowest point in the column through a conduit 44. Where the pitch phase layer contains a relatively high amount of finely divided solids, these are preferably removed therefrom by a filtration process, or by a combined agglomeration and filtration process, as shown for example in US. 2,774,716. The pitch phase is then fed through conduit 44 to a distillation column 45 where it is freed of traces of solvent. Ordinarily only small amounts of naphtha solvent will be included with the pitch, and these may be readily removed as an overhead from distillation column 45 through a conduit 46 and a reflux condenser 47. If desired, a portion of the condensed naphtha fraction may 'be returned through a conduit 48 as reflux for distillation column 45. The remainder of the naphtha fraction is returned to naphtha storage tank 15 through conduit 46 for recirculation. The pitch may be recovered from column 45 through a conduit 49.

The following example is illustrative of this invention but is not intended as a limitation thereof. A filtered whole tar prepared by a low-temperature carbonization (Disco process) of a bituminous coal was solvent refined in a single-stage extraction and recovery zone using aqueous methanol and hexane as a solvent pair to give a threephase system. In the single-stage fractional extraction system used, 245 grams (223 ml.) of low-temperature tar was added to a 2-liter pressure vessel. To this was then added 446 ml. of aqueous methanol (50 percent methanol by weight) and then 446 ml. of n-hexane. Thus the aqueous methanol and hexane to tar volume ratios used were 2.0:1, with an aqueous methanol to hexane ratio of 1:1. The pressure vessel was sealed, the stirrer was started, and the temperature was brought to C. from room temperature in about 1 /2 hours. When the temperature had leveled off, the stirrer was stopped and the phases formed were allowed to separate for about one hour. The three phases obtained consisted of an aqueous methanol extract phase, a hexane-soluble fraction, and pitch. These three phases were then removed and analyzed. The product distribution was as shown in Table I.

TABLE I Double Solvent Extraction of Low-Temperature Tar The following ultimate analyses of the hexane and pitch phases were obtained:

Hexane Pitch Phase Phase Hydro en 7. 80 6. 12 as 3-22 rmmn Oxygen- 5. 86 8. 61 Sulfur 1. O2 1. 59 A sh 0. 02 O. 09

In a double-solvent run made using aqueous methanol containing 30 weight percent methanol, very low tar acid yields were obtained.

According to the provision of the patent statutes, I have explained the principle, preferred construction, and mode of operation of my invention and have illustrated and described what I now consider to represent its best embodiment. However, I desire to have it understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.

I claim:

1. A process for the fractionation of primary low-temperature tar by double solvent extraction of said tar obtained from the low-temperature carbonization of bituminous coal, which comprises the steps of feeding to a liquid-liquid extraction zone one volume of said primary low-temperature tar, from 0.5 to 5 volumes of a first solvent consisting of an aqueous methanol solution containing about 40 to 80 weight percent methanol and the balance water, and from 0.5 to 5 volumes of a second solvent consisting of a paraflinic naphtha fraction boiling within the range of 60 to C. and having a density of less than 0.8, the volume ratio of the first and second solvents being maintained between 0.5 and 2, maintaining said tar, aqueous methanol and naphtha fraction under liquid-liquid contacting conditions at a temperature between 50 and 150 C. whereby three phases are formed, recovering an aqueous methanol extract containing tar acids as a first phase, recovering a naphtha extract as a second phase, and recovering an insoluble pitch residue as a third phase.

2. A process for preparing a carbon black feedstock from primary low-temperature tar by double solvent extraction of said tar obtained from the low-temperature carbonization of bituminous coal, which comprises the steps of feeding to a liquid-liquid extraction zone one volume of said primary low-temperature tar, from 0.5 to volumes of a first solvent consisting of an aqueous methanol solution containing about 40 to 80 weight percent methanol and the balance water, and from 0.5 to 5 volumes of a second solvent consisting of a paraffinic naphtha fraction boiling Within the range of 60 to 130 C. and having a density of less than 0.8, the volume ratio of the first and second solvents being maintained between 0.5 and 2, maintaining said tar, aqueous meth anol and naphtha fraction under contacting conditions at a temperature between 50 and 150 C. whereby three phases are formed, recovering an aqueous methanol extract containing tar acids as a first phase, recovering a naphtha extract as a second phase, recovering an insoluble pitch residue as a third phase, and further recovering from said naphtha extract as a carbon black feedstock substantially all of the constituents thereof boiling above an initial boiling temperature between 300 and 425 C.

3. A process for the fractionation of primary lowtemperature tar by double solvent extraction of said tar obtained from the low-temperature carbonization of bituminous coal, which comprises the steps of feeding to a liquid-liquid extraction Zone one volume of said primary low-temperature tar, from 0.5 to 5 volumes of a first solvent consisting of an aqueous methanol solution containing about 40 to 80 weight percent methanol and the balance water, and from 0.5 to 5 volumes of a second solvent consisting of a paraffinic naphtha fraction boiling Within the range of 60 to 130 C. and having a density of less than 0.8, the volume ratio of the first and second solvents being maintained between 0.5 and 2, maintaining said tar, aqueous methanol and naphtha fraction under liquid-liquid contacting conditions at a temperature be tween and 125 C. whereby three phases are formed, recovering an aqueous methanol extract containing tar acids as a first phase, recovering a naphtha extract as a second phase, and recovering an insoluble pitch residue as a third phase.

4. The process according to claim 3 wherein said second solvent is a hexane cut of the paratfinic naphtha fraction.

5. A process for preparing a carbon black feedstock from primary low-temperature tar by double solvent extraction of said tar obtained from the low-temperature carbonization of bituminous coal, which comprises the steps of feeding to a liquid-liquid extraction zone one volume of said primary low-temperature tar, from 0.5 to 5 volumes of a first solvent consisting of an aqueous methanol solution containing about 40 to Weight percent methanol and the balance water, and from 0.5 to 5 volumes of a second solvent consisting of a parafiinic naphtha fraction boiling Within the range of 60 to 130 C. and having a density of less than 0.8, the volume ratio of the first and second solvents being maintained between O.5 and 2, maintaining said tar, aqueous methanol and naphtha fraction under contacting conditions at a temperature between 75 and C. whereby three phases are formed, recovering an aqueous methanol extract con taining tar acids as a first phase, recovering a naphtha extract as a second phase, recovering an isoluble pitch residue as a third phase, and further recovering from said naphtha extract as a carbon black feedstock substantially all of the constituents thereof boiling above an initial boiling temperature between 300 and 425 C.

6. The process according to claim 5 wherein said second solvent is a hexane cut of the paraffinic naphtha fraction.

References Cited in the file of this patent UNITED STATES PATENTS Foley Oct. 4, 1960 OTHER REFERENCES Low-Temperature Carbonization of Bituminous Coal, McCulloch & Simpkins, H. F. and G. Witherby, London, 1923, pp. 25, 26.

Coal, Coke and Coal Chemicals, Wilson and Wells, McGraW-Hill, N.Y., 1950, page 421.

Claims (1)

1. A PROCESS FOR THE FRACTIONATION OF PRIMARY LOW-TEMPERATURE TAR BY DOUBLE SOLVENT EXTRACTION OF SAID TAR OBTAINED FROM THE LOW-TEMPREATURE CARBONIZATION OF BITUMINOUS COAL, WHICH COMPRISES THE STEPS OF FEEDING TO A LIQUID-LIQUID EXTRACTION ZONE ONE VOLUME OF SAID PRIMARY LOW-TEMPERATURE TAR, FROM 0.5 TO 5 VOLUMES OF A FIRST SOLVENT CONSISTING OF AN AQUEOUS METHANOL SOLUTION CONTAINING ABOUT 40 TO 80 WEIGHT PRECENT METHANOL AND THE BALANCE WATER, AND FROM 0.5 TO 5 VOLUMES OF A SECOND SOLVENT CONSISTING OF A PARAFFINIC NAPHTHA FRACTION BOILING WITHIN THE RANGE OF 60 TO 130*C. AND HAVING A DENSITY OF LESS THAN 0.8, THE VOLUME RATIO OF THE FIRST AND SECOND SOLVENTS BEING MAINTAINED BETWEEN 0.5 AND 2, MAINTAINING SAID TAR, AQUEOUS METHANOL AND NAPHTHA FRACTION UNDER LIQUID-LIQUID CONTACTING CONDITIONS AT A TEMPERATURE BETWEEN 50 AND 150*C. WHEREBY THREE PHASES ARE FORMED, RECOVERING AN AQUEOUS METHANOL EXTRACT CONATINING TAR ACIDS AS A FIRST PHASE, RECOVERING A NAPTHA EXTRACT AS A SECOND PHASE, AND RECOVERING AN INSOLUBLE PITCH RESIDUE AS A THIRD PHASE.

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