US2983665A

US2983665A - Utilization of low-temperature tars

Info

Publication number: US2983665A
Application number: US704575A
Authority: US
Inventors: Dell Manuel Benjamin; Philip T Stroup
Original assignee: Aluminum Company of America
Current assignee: Howmet Aerospace Inc
Priority date: 1957-12-23
Filing date: 1957-12-23
Publication date: 1961-05-09
Anticipated expiration: 1978-05-09

Description

May 9, 1961 M. B. DELL ETAL UTILIZATION OF LOW-TEMPERATURE TARS Filed Deo. 25, 1957 lNyENTcEs Nanas] Benjamin el] g.,

BY Philip 7.' Sirou ATTORNEY" United States Patent i 2,983,665 UTILIZATION QF LOW-TEMPERATURE TARS Manuel Benjamin Dell, New Kensington, and Philip T. `Stroup, Lower Burrel Township, Westmoreland County, Pa., assignors 'to Aluminum Company of America, Pittsburgh, Pa., a corporation of Pennsylvania Filed nec. z3, 1957, ser. No. 704,575 7 claims. (c1. 20s- 39) Thisinvention relates to the utilization of tars produced in the low-temperature carbonization of bituminous materials.` More particularly, it is directed to a method wherein'loW-temperature tars, or fractions thereof, are thermally decomposed to high-quality coke suitable as an electrode aggregate and to liquid products which are thermolytically treated to obtain an aromatic pitch suitable as an electrode binder.

Peat, brown coal, lignite, sub-bituminous and bituminous coals are bituminous materials which have been proposed as feedstocks for low-temperature carbonization processes to secure chars or cokes for use as fuel,

and tars from which valuable products might be obtained. The present invention is directed to the utilization of such low-temperature tars and to the thermal treatment of fractions thereof to produce aromatic pitch and other valuablematerials. i t

The term low-temperature carbonization, as used herein, `refers to a process for the carbonization of bituminous materials at temperatures lower than about 1300 F.` Representative of such a process is that described by V. F. Parry in U.S. Patent 2,773,018 and in Drying and Carbonizing Fine Coal in Entrained and Fluidized State, Bureau of Mines Report of Investigations 4954, U.S. .Department of Interior, dated April 1953.

The term low-temperature tar, as used herein, refers to tars produced by low-temperature carbonization of peat, brown coal, lignite, sub-bituminous or bituminous coals. Such tars are generally oily, tarry organic masses ranging from viscous liquids to soft semi-solid materials at room temperature and may contain small quantities of char, ash or other inert material, dissolved gases and water.

A typical analysis of low-temperature tar obtained by carbonization of Texas lignite at 946 F. utilizing the Parry Process, supra, is shown in Table 1 below:

Patented May 9, 1961 Analysis of distillate, vol. percent:

Tar bases 4.3

Tar acids 23.9

Neutral oil aa., 71.8

Saturates 14 Olens 40 Aromatics 46 1 Method disclosed in article by G. U. Dinneen et al., Shale Oil Naphthas: Analysis of Small Samples by Silica Gel Aditzim Method, Analytical Chemistry, Vol. 19, p. 992

Low-temperature carbonization is generally favored for the production of large quantities of tar as compared to high-temperature processes, thus permitting recovery of considerably greater amounts of tar oils. However, considerable diierences eXist in thenature of the tars. High-temperature tars are completely aromatic and about percent consists of 3 to 7 ring aromatic compounds with molecular weights up to 400, the remainder consisting of higher molecular Weight carbonaceous compounds; in addition, the percentage of phenolic constituents is low, about 5 to 12 percent, but substantially all of these are low-boiling tar acids. Low-temperature tar is only partially aromatic, i.e. about 10-45 percent. It contains relatively large quantities of phenolic constituents, ranging from 20 to 45 percent of the tar; however, these are about evenly distributed in the valuable low-boiling phenolic range and in the higher boiling fraction.

The by-product recovery treatment of such tars may involve a distillation process to recover low-boiling oils from which tar acids are recovered. These phenolic constituents are usually a readily marketable commodity andconstitute a definite enhancement to the value of the products obtainable from the process. Tar bases may also be extracted from the distillate, although they are of less commercial signicance. Heretofore, the neutral oils remaining after such extraction have been considered generally only as fuel oils because of the high content of sulfur and other heteroatorns. The pitch residue, which constitutes about 25 to 80 percent of the original tar, has generally been considered of poor economic value and used as a fuel or briquetting binder. Much experimental work has been devoted to the development of more valuable uses for this pitch, including the preparation of binders for carbon products.

Binder pitches for carbon products, especially anodes for use in the electrolytic production of aluminum, must meet certain minimum standards. Generally, such anodes must have low resistivity and low reactivity, and it has been found that these. properties are obtained when the binder is one of high aromaticity and. relatively low quinoline-insolubles content. Pitches obtained by distillation of low-temperature tars fail to meet these criteria, especially with respect to aromaticity.

Aromaticity of Ibinder pitch as measured by the infrared indexl is considered to be a substantially reliable guide to the suitability of a binder. Analysis of various data on binders when related to the properties of the electrode have indicated that the aromaticity of the binder pitch is one of themost significant factors in producing electrodes having low resistivities and low reactivities. Indicative of this is Table 2 in which properties of various pitches and the carbon anodes produced thereby are listed.

lThe infrared index of the various pitches indicated herein was determined by a method in which 0.250 gram of pitch is dissolved in 10 m1. of carbon disulfide and allowed to stand for two hours. The infrared spectrum of the supernatant liquid is determined using a cell width of 0.50 mm. in a (Perkin-Elmer Model 112) Spectrometer. After correcting for absorption of the solvent, the infrared index is taken as the ratio of the transmittance at the 3.4 microns aliphatic absorption range divided by the transmittance at the 33 microns aromatic absorption range.

TABLE 2 Properties of anodes prepared with various binders Pitch Properties Anode Properties Binder Baked I Regis! summa A *Y B.P.,1 C-I. O-II,I Ooking4 Infrared Apparent tivitya Reac- C. Percent Percent Value Index Density ohm.-in. tivity1 Percent Coke-Oven.;L;- .;-Q;.- 109 16.5 33.0 .1 1. 38. 1.46 0.0028 2.4 f Coke-Oven 109 7. 6 32.0 1. 37 1. 43 0.0029 4. 7

nknown Foreign 104 11.5 24.8 35.2 1.08 1.41 0.0030 5.7 Petroleium Oil-Gas.-. 116 13. 3 37.2 42.8 1.01 1. 41 0.0028 7.0 Straight Dlstillation of Bituminous Lowf Temperature Tar- 87 0. 2 4.6 11. 1 0.47 1. 39 0. 0031 80.0 Straight Distillation of Lignite Low-Temperature Tar.. 111 17.7 28.4 29.3 0.29 1. 37 0.0042 f -100.0

l Softening point determined by cube-inair (Barrett method). 2 Quinoline-insolubles content.

3 riccione-insolubles less C-I (quinollne-insolubles).

4 ASTM D271-48 (paragraph 14e).

l The anode is weighed dry, then soaked for 24 in water and weighed; then it is removed, dried with a towel and weighed while wet.

hours in water containing few drops of a detergent solution. I It is suspended The dierenoe between the weight in Water 1 and wet weight is determined and then this figure is divided into the dry weight to give the baked apparent density. i

A current of known amperage is passed through a cylindrical anode, and a set of probes is used to determine the voltage drop along the longitudinal axis. Resistivity is then calculated by the formula:

Forum p=resistlvity in ohmeinches E=everage voltage drop across probes A=crosssectional area of sample (square inches) I=cuxrent passed through samples (amperes) D=d.ista.nce between probes (inches) 7 Sulfate reactivity is the loss in weight of a carbon specimen, 1 inch in diameter by B inch, when immersed in sulfate at 940 C. It is considered an excellent measure ofthe reactivity of an anode in a bath for the the Hall process.

It has now been found that low-temperature tars, or fractions thereof may be converted substantially non-aromatic material to an aromatic tar yfrom which a binder pitch suitable for carbon electrodes may be obtained by distillation. This conversion is effected by thermally cracking the tar or tar fraction at a temperature of 700 C. to 900 C. and at atmospheric or low superatmospheric pressure. The yaromaticity of the binder pitch is indicated lby the infrared index, as hereinbefore described. Table Three illustrates the conversion eiected and the quality of the binder pitch obtained by such thermal conversion of la lignite tar fraction.

TABLE 3 anodes prepared with various molten sodium production of aluminum by the high-boiling tar acids in low-temperature tars to more valuable low-boiling tar acids.

AFurther objects and advantages of the present inveni tion will `be evident from the attached drawingand following detailed description. i Y wel 'Y i lt has .been found that low-temperature tarsmay .be substantially completely utilized by a. method in which the tar, or -a fraction thereof, is thermally decomposed into a high-quality coke, vgas and condensible oils. Y The condensible oils, ofr a fraction thereof, are then thermally cracked at a temperature between 700 C.v and 900 C. and at a pressure between atmospheric rand low superatmospheric, the products being gas, liquid products 1inl Lignite thermolytic pitch was obtained by thermally cracking lignite low-temperature tar residue by a cyclic regenerative process at an average temperature of 779 C. and at 1.10

atmospheres pressure.

It is an object of this invention to provide a method for the substantially complete utilization of low-temperature tars.

Another object is to provide a method for the treatment of low-*temperature tars whereby an .aromatic pitch suitable as an electrode binder is obtained..

It is also an Object to provide a method wherein lowtemperature tars are utilized to produce high-quality coke suitable as an aggregate for carbon electrodes and other valuable products.

A further object is to provide a method for cracking cluding av thermolytic tar, and carbonor coke. The thermolytic tar is then distilled to au aromatic `pitch having the desired physical properties and an aromatic oil.

Preferably, the whole or `crude low-temperature tar is initially distilled to recover phenolic oil `prior `to the thermal decomposition; it is also desirable to fractionate the condensible oils from the thermal decomposition so as to recover a second phenolic'oil, theV balance ot the condensible oil-s,V or middle oil, `being used as .the feedstock for the thermal cracking. These phenolic oils are desirably processed to recover'taracids.and"trbases,

agences leaving a `neutral oil which also may be thermally cracked, either separately or in adm-ixture with the middle oil. The aromatic oil from the pitch distillation is also desirably fractionated into phenolic and middle oils, land the tar acids and tar bases may be removed also from this phenolic oil. Similarly, the various oils may be caustic-Washed only to remove the-tar acids alone.

More particularly, the thermal decomposition is effected at a temperature between 375 C. `and 475 C. 'and a pressure between atmospheric and 100 pounds per square inch.

A cyclic regenerative process has been found essential to the practicable thermal cracking of low-temperature tats because off `the `tendency of this material to form large quantities of `carbon iat cracking conditions. This carbon deposition will choke a continuous reactor, prevent maintenance of uniform `cracking conditions and contaminate the product stream, especially the tar from which the Iaromatic pitch -is derived.

The terms flow-temperature tar feedstock or tar feedstock, as used herein, refer to crude or whole llo/wtemperature ters, or to fractions thereof, such as the residues upon topping, or distillates.

. The term phenolic oil, as `used herein, refers to a tar distillate relatively rich in valuable phenolic constituents, such as phenol, cresols, Xylenols, and ethyl phenols. It is preferred to use about 235 C. as the end point for this distillate although variations may be made dependent upon the compounds desired in this fraction.

The term middle oil, as used herein, refers to a tar distillate boiling above the phenolic oil range.

The term tar distillate, as used herein, refers to any distillate from low-temperature tars or from tars formed in the thermal treatment of low-temperature tar, and may encompass phenolic oil, or middle oil, or both. i The apparatus for effecting the thermal decomposition may be of any type capable of affording the conditions of temperature and pressure herein described. A delayed coker is preferably employed, although other types, such as a pot still, may be satisfactorily utilized.

. Generally, the temperature ofthe thermal decomposition is between 375 C. and 475 C. and preferably between 380 C. and 420 C. The pressures employed may vary between atmospheric and 100 pounds per square inch. The pressure selected will depend largely upon the character of the feedstock," but about 402to 60 pounds per square inch is, preferable.

A portion of the condensible oils Ysuch as the 'middle oil fraction may bewrecycled and mixed with the tar feedstock prior to the preheater. By so doing, especially inthe case of topped tar, the feedstock is more easily transportedV and premature` coking is substantially eliminated. Generally, `this recycle ratio may be `between 0.3 and 3.0 times `thefe,edstockan'd preferably between 0.5 and 1.5.

-`The ash content of the coke produced by theprocess` will be dependent upon that of the feedstock. Particularly for the production of anodes for electrolytic reduction cells, itis desirable that the coke contain as little ash as possibleand generally less `than about 01.8 percent. Thus `when employing low-temperature tars which usually contain considerable quantities of ash, it has been found desirable to reduce the solids contained in the feed tar. prior to the thermal decomposition. For this purpose,` several` methods .may be Memployed such as, for example, those disclosed in U.S. Patents 2,631,982 to Doneganand 2,774,716 to Kulik. i

The. term cyclic regenerative process, as used herein, refers.. to a semi-continuous process -for thermolytic cracking of `tar feedstocks wherein a cycle Aof operation fiorithe cracking `apparatus includes a period in which the carbon deposits within the apparatus are removed by combustion. Such a cycle generally includes a heating-.period in whichthe apparatus is heated to cracking 6 temperatures, a cracking or make period in which thermolysis of feed takes place, anda blast period" in which the carbon deposits are burned, the last of which may be in conjunction with the heating period. The heat developed by combustion of the carbon deposits is transferred substantially to heat-storing surfaces which `subsequently impart heat to the feed and to the carrier gas if such is used. Subsequent to the cracking period, heat retained by these heat-storing surfaces is transferred to the oxidizing gas Which is introduced to burn the carbon deposits. This type of process is extensively used to produce fuel gas from petroleum oils and the apparatus employed may conveniently be of the type known as the oil-gas set.

The term oil-gas set, as used herein, refers to any cyclic, regenerative thermal cracking apparatus, and may be of the type illustrated and described in U.S. Patent 2,721,123 to E. S. Pettyjohn et al. and U.S. Patent 2,580,766 to E. L. Hall. The essential features-of this apparatus are that it be cyclic, regenerative, capable of providing temperatures of about 700 C. to 1100" C., and afford suitable collecting means for the tar and other products.

Generally, an apparatus for cyclic regenerative cracking comprises one or more generating vessels or zones in communication with two or more regenerator (superheater) vessels or zones, the several vessels or zones being provided With heat-storing surfaces, preferably of a highly heat-conductive material such as carborundum or silicon carbide.

In the operation of the apparatus, there is a blast period in which the generator vessel or zone is heated to cracking temperatures by combustion of carbon previously deposited on the heat-storing surfaces and/or fuel oil or gas. The combustion products are usually discharged through one of the regenerator vessels or zones in order to heat the surfaces therein. In the make or cracking period, a diluent or carrier gas is usually provided and is introduced into the apparatus (generally through the heated regenerator) wherein it is heated by contact with the heat-storing surfaces. The feed# stock is sprayed into thegenerator, usually` with the aid of an atomizing diluent or carrier gas, wherein it admixes with the heated carrier gas and wherein it is initially cracked. These initial products are conducted through the second regenerator wherein further cracking may take place prior to disch-arge. In some apparatus cracking iS completed in the generators and the cracking products discharged vvithout passing through the regenerators. Suitable means are` provided to collect both the process gas and the condensible products such as tar and light oil, either separately or together. i

Referring nov'v` to the attached drawing, diagrammatically illustrated isl a process embodying the present invention. A low-temperature tar 2 is preferably topped in still 4 to recover a phenolic oil 6, leaving a residue 8, which is` then thermally decomposed in retort 10 to yield green coke 12, process gas vv14 and condensible oils `or condensate 16.

In column 18 Vthe condensate 16 is fractionated into phenolic oil 20 and middle oil 22, a part of which is desirably recycled and admixed` with the residue 8 prior to thermal decomposition. The middle oil 22 is then thermolyticallycracked in `retort 24, preferably in the presence of a `carrier gas 26, and the products withdrawn are process gas 28, which is right in oleiins, and liquid products including a thermolytic tar 30 (a. light oil fraction may be collected separately if so desired). After separation of water, the thermolytic tar 30 is distilled or topped in still 32 to a highly aromatic pitch 34 suitable as a carbon electrode binder, and an aromatic oil 36 which may be fractionated in the column `338 to middle-oil 40 and phenolic oil 42 from which considerable quantities of 4valuable low-boiling tar acids, tar bases and other chemicals may be extracted.

,The phenolic, oil 6 isv desirably subjected to a conventional treatment 44 to recover the tar bases 46, which treatment may be of the type utilizing dilute acid, and to a second treatment 48 to remove the tar acids 50, such as by the conventional methods of washing with caustic 'solution or solvents, leaving a neutral oil 52. The phenolic oil contains considerable quantities of low-boiling tar acids and tar bases which have been formed by the higher-boiling constituents during the thermal decomposition in retoht 10, and is desirably processed in treatment plants such as 44 and 48.

The thermolytic phenolic oil 42 from the column 38 is also desrably processed to recover the low-boiling phenolic compounds and nitrogen-bases; the

plants

44 and 48 may be conveniently employed although it is preferable that this material be processed separately to maintain the identity of the neutral oil resulting from treatment of this highlyaromatic oil.

The process gas 28 which consists largely of methane, ethane, ethylene and hydrogen may be treated to extract the olens and recycled as the carrier gas 26 for the thermolytic cracking, or it may be used as -a heating gas.

' 'Ihe green coke 12 is desirably calcined in retort 54 at -a temperature above 1000 C. to obtain a high-quality aggregate 56 suitable for carbon electrodes.

The average eectve temperature in the thermal cracking apparatus is generally maintained between about 700 C. and 900 C., 'and preferably about 760 C. to 820 C. Higher temperatures are found to favor the formation of deposited carbon over the formation of liquid products, and to increase the C-I (quinoline-insoluble) content of the tar, whereas lower temperatures do not generally provide suicient cracking to form aromatic tars. The conditions of temperature may be varied, of course, if the residence time is varied; i.e., higher temperatures may be compensated by lower residence times, and vice versa. When the pressure within the apparatus is varied within the usual nange, namely, from atmospheric to about pounds per square inch, the throughput rate may be adjusted to maintain constant residence time. Higher pressures, up to about 50 p.s.i., may be employed; however, there is little increase in tar yield because of increased carbon Vformation due to increased tendency to the occurrence of stagnant conditions. The residence times normally employed )at atmospheric or low super-atmospheric pressure are from 1 to 10 seconds, and preferably about 2 to 5 seconds; shorter times are not sucient to produce the degree of cracking desired unless higher temperatures are also employed, whereas longer residence times produce excessive cracking unless reduced temperatures are employed. For an average cracking temperature of 760 C. to 820 C. at atmospheric or low superatmospheric pressure, a residence time of 2li/z to 4 seconds has been found most eiective.

The operating cycle (or half-cycle if -a symmetrical unit is employed) may be between 1 `and 20 minutes and is usually about 3 to 6 minutes. The length of the cycle is, of course, determined 'by the physical capabilities of the unit and the degree of variation in conditions which may be tolerated. However, for a unit of the type described in the Pettyjohn patent, supra, a cycle (half-cycle) on the order of about 4 minutes is preferred.

In the operation of a cyclic regenerative unit, a carrier gas has been found desirable to assist in the transportation of the cracking products as Well as to function as a heat-carrier. However, the cracking products themselves may be -used as the motivating agent, although much less effective. Various carrier gases may be employed, such as steam, inert gas, hydrogen-rich gas, or the like; an amount of steam up to about 2 pounds per gallon of feedstock is usually employed in such units.

In accordance with this invention, lignite low-temperature tar, substantially as described in Table 1, Was distilled to recover phenolic oil. Data `on this distillation sented in Table 4 below: i

TABLE 4 Initial distillation of crude lignite tar l i Lignite low-temperature tar residue from phenolic oil distillation, substantially as dcribed in rTable 4,v was thermally decomposed in a delayed coker to obtain process gas, green coke and condensate as shown in Tables Five and Six below.

TABLE 5 Thermal decomposition Conditions:

Temp., C. 425 Pressure, p.s.i.g 50 Product Yields:

Coke, green, wt. percent of -feed 26.1 Gas, cu. ft. per lb. of feed 1.18 Condensate, wt. percent of feed 62.8 Phenolic oil (to 235 C.), vol. percent of condensate 32.0 Middle'oil (over 235 C.), vol. percent of condensate 68.0

TABLE 6 Product anaylss Gas, mol percent:

H2 y 4.9 CH, V 46.3 02H6 15.4 03H8 7.7 C2H4 2.5 CSHG 3.8 CO 5.6 CO2 5.7 Condensate composition, vol. percent:

Tar bases 2.6 Tar acids 18.7 Neutral oil 78.7

-`Hydrocarbon types, vol. percent- Saturates 2.5 Aromatics 40 Olens 35 Distillation ASTM D86: Y

Initial, C. 51 Il0 ml. 167 l20 ml. 207 30 ml. 231 40 m1. 251 50ml. 260 60 m1. 284 7i() m1. 331 85.8 ml. 337 Decomposition, C. 337 Residue, percent 10.8

- The condensate was fractionated into phenolic oil and middle oil. The middle oil was then thermally cracked Properties of pitch: 7 to yield thermolytic tar, light .oil and a process. gas; the Softening point, C. 107 carbon or coke formed by the cracking was substantially Specic gravity, 60/ 60 F. 1.263 deposited the apparatus and, subsequently re- Ash, percent by wt. '0.310 moved by combustion. Data on this thermolysis are pre- 5 C-I (quinoline-insolubles), ercent by wt. 9.9 sentedin Table 7.4 Infrared index f 1.01 TABLE 7 Sulfur, percent by wt. 0.97 i Y Analysis of aromatic oil: f 7 y Ihermvlyfic cracking suifenation index (ASTM D872) 0.9 Operating wnditins; 7 10 V Tar acids, vol. percent 14.1 Carrier gas, type Steam Tar bases. vol. percent 5.5 Carrier gas, s.`c.f./gal. 2.2.8 NCutr-l 011 V01- Pernt 80A Total pressure, atm. 1-.0 Cracking temp., average, f'C- 7,56 As is evident `from the infrared index, the low-tempera 1Reidene time, Sec, 3 4 15 ture tarhas been converted to an aromatic pitch of relaprodmt yields: 7 tively low C-I (quinoline-insolubles) content. Ther- Tot-a1 ggg, S c,f /ga1 46,7 molytic pitches having these properties are suitable bind- 'I'hrmolyc can percent .by WL of feed @3 7 ers for carbon electrodes and produce anbdes of low-re Light oil, percent by WL of feed 1 8 sistivities, as shown in Table 3. Further, the binder of product gs1c0mp0siti0n, m01 percent: 20 the present invention may be used alone or in combina- 2 15,1 tion with other pitches such as, for example, coke-oven `CH4 39 9 pitch as shown in Table 3.

CZH@ 5.1 The green coke from the thermal decomposition was C21-14 20j calcinated at a temperature of about 1200 C. for` 2.0 (33H75 7 2 25 hours. The properties of the calcined material and of `C() 8 9 anodes prepared therewith were determined, comparison Others 3,1 determinations being made for commercially available Heating Value, BLR/ggf, 1145 petroleum coke. As evidenced by the data in Table 9, Thermolytic tar properties: 7 7 the `coke made in accordance with the present. invention Spedc gravity, '6m/60 11`'" 111() 30 produces electrodes of greatly improved resistivity; the C I (quinolinednsombles), wt, percent 5,0 baked apparent density is superior and the sulfate re#` Y activity is in the acceptable range and substantially equiv- 7 The therni-olytic tar described in Table `7 was topped alent tothat of petroleum coke.

TABLE 9 Coke Anode 1 Coke Volatile Baked Matter, Ash, Wt. Resistivity,2 Apparent Reslstivlty, Sulfate Wt. percentohms-in. Density ohms-1n. Reactivitya percent Petroleum o. i4 o. 45 0. 0549 1. 50 .0026 5e Ligni'te-- o. 00 4.14 0. 0484 i. 52 .0022 69 l Anodes made with 110 C. softening point coke-ovei1 pitch. 3 Great Lakes Carbon Co. Procedure No. C-12A. 3 Sulfate reactivity determined at 960 O.

in a pitch still to obtain an aromatic binder pitch having a softening point of about 110 C. and a highly aromatic oil distillate which contained low-boiling phenolic constituents. The properties of the pitch and the aromatic oil are shown in Table 8.

TABLE 8 Distllatz'on of thermolylic lar Distillation, wt. percent:

The use of a hydrogen-rich carrier gas has been found desirable in the production of an aromatic pitch. The process gas, which consists largely 0f methane (25 to 35 percent) and hydrogen (15 to 20 percent), may be stripped of the olens and used to decrease materially the C-I (quinoline-insolubles) or carbon content of the thermolytic tar and resultant binder pitch. Illustrative of this eifect are the analyses shown in Table 10, wherein the results from using hydrogen and methane are compared to those from using steam.

TABLE 10 Properties of binder pitch Carrier Gas Steam Methane Hydrogen Softening point, C 105 115 110 Specific gravity, 60/60 F 1.294 1.296 1.289 C-I (quinoline-insolubles), wt., percent- 23. 3 17. 9 12.1 Infrared index 1.00 1. 13 1. 09 Sulfur, wt. percent 0. 71 0. 78

98eme lseparately from other streams to preserve its identity and to facilitate recovery of these constituents.

` Having thus described the invention, we claim:

,l 1. In the production of high-quality coke andaromatic pitch from low-temperature tars, the method comprising thermally` decomposing a low-temperature tar feedstock ata temperature'between 375 and 475 C. and a pressure between vatmospheric and '100 pounds per square inch to obtain coke, gas and condensible oils; thermally cracking atleast part of said condensible oils at a temperature between 700 and 900v C., at a pressure between atmospheric and .low superatmospheric and at a residence time of 1 to .10seconds to yield gaseous and liquid products including a thermolytic tar; and distlling said thermolytic tar to' an aromatic pitch and an aromatic oil.

2. 'I'he method in accordance with claim 1 wherein the low-temperature tar feedstock is whole low-temperature tal'.

3. 'I'he method in accordance with claim 1 wherein the low-temperature tar feedstock is the residue from distilling whole low-temperature tar to recover phenolic oil. 4. In the production of coke and aromatic pitch from low-temperature tars, the method comprising distilling low-temperature tar to recover phenolic oil; thermally decomposing the residue from said phenolic oil distillation vatta temperature between 375 C. and 475 C. and a pressure between atmospheric and 100 pounds per square inch, Ithereby yielding coke, gas and condensible oils containing phenolic constituents; thermally cracking at least part of said condensible oils by a cyclic regenerative process at a temperature between 700 C. and 900 C., at a pressure between atmospheric and low superatmospheric andat a residence time of 1 to 10 seconds to obtain gaseous and liquid products including a thermolytic 'tary distilling said,` thermolytic tar to an aromatic pitch; recovering from said second-mentioned distillation anl aromatic oil containing phenolicv constituentsrand extracting phenolic constituents from said phenolic oil, from at least part of said condensible oils and from at least part of said aromatic oil. I

5. The method in accordance with claim 4 wherein condensible oils are recycled and admixed with said residue in an vamount between 0.3 Sand `3.0 'to 1.0`prio tothe saidl thermal decomposition step. f

6. The method in accordance with claim 4 wherein said condensible oils are thermally cracked in the presence of a hydrogen-rich carrier gas. -1

7. The method in accordance with claimo wherein at least part of said gaseous products fromithe s'aid"ther` molytic cracking are Arecycled to providesaid hydrogenrich carrier gas.

OTHER REFERENCES l Egloi et al.: .Cracking of Low Temperature CoalTar by the' Dubbs Process, published by Universal Oil '-Products Co. (1926), pp. 1 to 1l.

Dunstan: Internal Conference on Btuminous Coal, November 1928, pp. 210 to 231, volume 1.

Claims

1. IN THE PRODUCTION OF HIGH-QUALITY COKE AND AROMATIC PITCH FROM LOW-TEMPERATURE TARS, THE METHOD COMPRISING THERMALLY DECOMPOSING A LOW-TEMPERATURE TAR FEEDSTOCK AT A TEMPERATURE BETWEEN 375 AND 475*C. AND A PRESSURE BETWEEN ATMOSPHERIC AND 100 POUNDS PER SQUARE INCH TO OBTAIN COKE, GAS AND CONDENSIBLE OILS, THERMALLY CRACKING AT LEAST PART OF SAID CONDENSIBLE OILS AT A TEMPERATURE BETWEEN 700* AND 900*C., AT A PRESSURE BETWEEN ATMOS-