US2310500A

US2310500A - Fractional distillation of tar

Info

Publication number: US2310500A
Application number: US354676A
Authority: US
Inventors: Zavertnik Joseph
Original assignee: Allied Chemical and Dye Corp
Current assignee: Allied Corp
Priority date: 1940-08-29
Filing date: 1940-08-29
Publication date: 1943-02-09
Anticipated expiration: 1960-02-09

Description

Feb. 9, 1943. 1 ZAVERTNlK 2,310,500

FRACTIONAL DISTILLATION OF TAR INVENTOR ATTORNEY Feb. 9, 1943. J. ZAVERTNlK 2,310,500

FRACTIONAL DISTILLATION OF TAR Filed Aug. 29, 1940 2 Sheets-Sheet 2 TTORNEY distillate fractions.

atented Feb. 9, i943 FRAUIIONAL DISTILLATION OF TAR Joseph Zavertnik, Englewood, N. J., assignor, by mesne assignments, to Allied Chemical & Dye Corporation, a, corporation of New York Application August 29, i940, serial No. 354,676

7 claims. (c1. 1st-76) This invention relates to an improved method for the distillation of tar to produce valuable tar By tar is meant coal tar, including coke oven tar, gas h'ousetar, and coal tars obtained from the low temperature carbonization or gasification of coal, and water gas tar.

In accordance with thejoint invention of myself and A. A. MacCubbin disclosed and claimed in United States Patent No. 1,759,816, granted May 20, 1930, tar is distilled by heating the tar while flowing in a restricted stream of narrow cross-section and preventing vaporization of the tar, discharging the heated tar into an expansion zone where sudden volatilization of a large portion of the normal oil content of the tar takes place, cooling the vapors to condense distillate oils, withdrawing the pitch residue and subjecting this residue to a high vacuum while it is still at a temperature suiiciently high to eiect distillation of additional oils therefrom and obtain a high melting point pitch. Many millions of gallons of tar have been distilled in accordance with the invention of this patent to produce valuable oils and pitch. Invariably the oils produced, with particular reference to those fractions containing naphthalene and tar acids, i. e. phenolic bodies such as phenol, cresol, xylenol, have an undesirable low content of naphthalene and tar acids, as the case may be, and in order to produce cuts having relatively high naphthalene and tar acid contents respectively, it has been found necessary to redistill the condensates. Furthermore, distillates produced in accordance with the process of this patent, including distillates containing low boiling oils, contain relatively high coke residues, i. e. upon distillation to dryness have high coke contents; for example, the heavy creosote oil produced at times has had a coke residue content as high as 4.5 per cent, the light creosote oil as high as 3.0 per cent, the fraction rich in naphthalene as high as 1.0 per cent, and oil rich' in tar acids as high as 1.0 per cent. Such high coke residue content indicates decomposition of the hydrocarbon oils, with consequent loss of valuable product. Moreover, for many purposes oils having such high coke residues are objectionable and in order to produce satisfactory oils'they must be subjected to fur-ther distillation, with consequent further loss of product due to decomposition and the obvious disadvantages of expense and labor involved in conducting such distillation.

By heavy creosote oil as used herein is meant a coal tar fraction about 90 per cent of which boils above 300 C. By light creosote oil as used herein is meant a fraction less than 15 per cent of which boils off at 250 C. and about 85 per c ent of which boils below 350 C.

It is an object of this invention to provide a process for distilling tar to produce directly a light creosote oil cut, a second out rich' in naphthalene, a third cut rich in tar acids, and a fourth cut rich in light oils, such as benzol, toluol and solvent naphtha, the naphthalene and tar acid content of the respective cuts being such that naphth'alene and tar acids can be recovered directly therefrom without subjecting the cuts to a further distillation.

It is a further object of this invention to provide a process for distiliing tar to produce a high yield of'valuable oils such as heavy creosote oil, light creosote oil, oil rich in naphthalene, and oil rich in tar acids, which' oils have only a relatively low coke residue such as to meet existing specifications therefor, or no coke residue at all. Other objects and advantages of this invention will appear from the following detailed description thereof.

In accordance with this invention, tar is continuously flowed and heated in a restricted stream of narrow cross section at a rate such that substantial decomposition of the tar does not occur, substantial vaporization of the tar being prevented during this heating. Th'e heated tar is introduced into an expansion zone where vaporization of a large -part of the normal oil content of the tar takes place. If the tar is to be distilled to produce directly a light creosote oil fraction and fractions rich in naphthalene, tar acids and light oils, the distillation is carried out so as to heat the tar to `a temperature within the range of 470'F. to 640 F., preferably to a temperature within th'e Frange of 550 to 570 F., tar at this temperature being introduced into the ash box or expansion zone and vapors from this zone at a temperature of from 450 to 630 F. passed through a series of condensing zones. In each succeeding zone of the series the vapors are cooled to successively lower temperatures for condensation of successively lower boiling fractions such as light creosote oil, naphthalene and tar acid fractions. The vapors pass through each' condensing Zone along a series of successively higher paths so that flow of vapors takes place up through each zone, the cooling medium owing in^series downwardly through these zones countercurrent to and in indirect heat exchange relation with th'e vapors. The condensate formed in each condensing zone ows downwardly through the zone countercurrent to the vapors, cascading from path to path so that vaporization of the lower boiling constiturespective condensingzones.

denserunit preferred for the practice of the innarrow boiling.light creosote oil fraction and fractions richin naphthalene andtaracids in the g l In the'flrst of the condensing zones, 4vapors at a temperature of from 450 to 630 F., preferably vention; and l Figure 3 is a diagrammatic showing of an arl rangement of apparatus for the practice of the at a temperature ofA from 530 to"560F. are

cooled to the temperature ofV 390 to 430 F. producing-a light creosote oil fraction; AIn the second of these zones the vapors at a temperature of 390 to 430 F. are cooled to a temperature of 330 to 350 F. to produce a fraction rich in naphthalene. This fraction may contain as much as 80 per cent of the total naphthalene content in the vapors and may be constituted of about from 40 to 55 per cent of naphthalene. The vapors at a temperature of 330 to 350 F. are cooled in a third zone to 250 to 270 F. to produce a fraction rich in tar acids. This fraction may contain up to 60 per cent of the total desirable tar acid content of the vapors and may be constitutedl of about from 15 to 25 per cent of tar acids. The residual vapors are then cooled in a water-cooled condenser to producer a fraction rich in light oils such as benzol, toluol or solvent naphtha.

If the tar is to be distilled to produce a heavy creosote oil fraction as well as a light creosote oil fraction and fractions rich in naphthalene and tar acids, the tar is introduced into the expansion zone at a temperature above 570 F. and preferably at a temperature of from 780 to 800 F. The vapors leaving 'theexpansion zone at a temperature above 570 F. and`preferably from 760 to 790 F. are cooled as quickly as possible to a temperature of from 530 to 560 F. at which the heavy creosote oil constituents are condensed and the heavy creosote oil condensate is removed from contact with the heated vapors substantially as rapidly as formed. I have found that the time factor, i. e. the time during which each particle of the creosote oil is subjected to temperatures above 570 F. should not exceed two minutes and preferably should be less than ten seconds. Operation in accordance with these conditions minimizes the tendency of heavy creosote oil vapors to polymerize and decompose and gives a high yield of heavy creosote oil having a low coke residue." After condensation of the heavy creosote oil fraction, the vapors may be passed through additional condensing zones for the production of narrow boiling fractions of light creosote oil, naphthalene and tar acids as hereinabove described.

I have also found that the coke residue and free carbon content of the heavy creosote oil and of the other fractions may be further reduced by condensing a portion of the vapors leaving the expansin zone and returning the condensate to the expansion zone. This condensate removes tar fog from the vapors and returns it to the expansion zone, thereby reducing the amount of carbonaceous material in the vapors with consequent reduction of the coke residue and free carbon content of the distillate oils.

The invention will be further described in connection with the accompanying drawings, in which,

Figure l is a diagrammatic showing of the arrangement of the apparatus for the practice of the invention involving distillation of tar for the direct production of a light creosote fraction and fractions rich in naphthalene and tar acids, respectively, i. e. without forming a heavy creosote oil fraction;

Figure 2 is a side elevation of the type of coninvention including the formation of a heavy 1 creosote oil fraction.

In Figure 1 are shown storage tank I for the tar to be distilled, a continuous pipe coil still 2 vand flash box or expansion zone 3, a condenser unit 4 for removal of tar fog" from the vapors, and a fractional condenser comprising three banks 5, 6 and 1, respectively, of condenser units 8 for condensation of the desired fractions. Tar to Ibe distilled containing up to 6 per cent, preferably2 to 3 per cent, moisture is pumped from tank I through pipe 8 by pump I0 to the heat exchangers I I where it is heated by indirect heat exchange with the condensate from condenser banks 1, B and 5 and thence to the units 8 of condenser banks 1, 6 and 5 and condenser unit 4. The tar flows through the units 8 and 4 in indirect heat-exchange relation with vapors to be condensed in the respective units in reverse order to the order in which the units 4 and 8 are traversed by the vapors to be'condensed. In the condensing units 8 and 4 the tar serves as a cooling medium and receives a preliminary heating to a. temperature of about 430 to 500 F. Bypasses or valves 8a control the flow of tar through banks 5, 6 and 1 to regulate the rate of cooling in the banks. The tar from unit 4 then flows through supply pipe I2 and is mixed with tar pumped directly from tank I through pipe 9a by pump Illa. The proportion of tar pumped by pump Illa depends upon the degree of fractionation desired, the larger the proportion of tar pumped, the sharper (narrower) the fractionation obtained. The tar mixture then passes through the pipe coil still 2 rapidly and under pressure, and ls heated in the pipe coil still 2 preferably to a temperature of from between 550 and 570 F. without substantial vaporization or substantial decomposition. The rate of flow of the tar in cubic feet per minute per square inch of internal transverse area of pipe exposed to heat is preferably equal to 0.5 to 1.5 and is preferably about 10 to 14 per cent of the cubical capacity in cubic feet of the pipe coil still. From the still 2 the heated tar passes through pipe I3 to the ash box 3, which is at a pressure lower than that of the still 2 and preferably at atmospheric pressure or approximately so. In the flash box 3 a substantial portion of the oil content of the tar vaporizes, leaving pitch; the pitch is withdrawn from the flash box 3 desirably to a vacuum box (not shown in Figure 1), where additional oils are distilled off, leaving behind a high melting point pitch.

The oil vapors leave the flash box 3 at a temperature of from 530 to 560 F. and may next be passed through condenser unit 4 for tar fog" removal. Where the tar was initially heated in the coil still 2 to a temperature of 550 to 570 F., the temperature of the vapors will preferably be reduced in unit 4 to between 510 and 550 F., and a portion of the oil vapors, which may be from l to 3 per cent based on tar distilled, preferably about 1.5 per cent, is condensed. This condensate washes out tar fog" entrained in the vapors from the flash box 3 and flows back to flash box 3 by gravity, carrying the washed out tar with it. The lower boiling portion of this condensate is revaporized by the heat of the pitch in the flash box 3 and passes again to the condensers.

The vapors from the condenser unit 4 or from the flash box 3, in case the unit 4 is not employed,

are fractionally condensed to produce a light creosote oil fraction, a naphthalene fraction, and a tar acid fraction, respectively, in banks 5. 5. and 1 of the fractional condenser, eachoi which banks comprises a series oi' condenser units v8. As shown in Figure 1, bank comprises eight units, bank 8 five units, and bank 7 five unita/' The vapors enter the lowest unit 8 of ba/nk 5 at a temperature of about 510 to 560 F. depending upon whether or not condenser unit 4 is used, pass through the bank 5 to the highestaunit of the bank 5 and flow through pipe I3' to the low- 'est unit 8 of the next bank 6 of the fractional condenser. Similarly, the vapors pass through the bank 6 to the highest unit 8 thereof, thence through pipe I4 to the lowest unit 8 of the third bank 1 and from the'highest unit 8 of the bank 1 through pipe I5 to a water-cooled condenser I6. The condensate formed in the units 8 of each of banks 5, 5 and 1 ilows through the units 8 counter to and in contact with the vapors passing through the units 8, passes to successively lower units, andisremoved from the lowest unit 8 of each bank. The vapors passed from the bank 1 are condensed in the water-cooled condenser I6 to yield a light oil fraction, including benz'ol and toluol.

The vapors are iiowed through the condensing Zones or banks 5, 6 and 1 and cooled in the Zones or banks at a rate such that the vapor at an initial temperature of about 510 to 560 F. passes through the first zone 5 and is cooled therein to about 390 to 430 F., passes through the second zone 6 and is cooled to about 330 to 250 F., and passes through the third zone 1 and is cooled to about 250 to 270 F. If sharper fractionation is desired a portion or al1 of the condensate from the lowest unit 8 of banks 6 and 1 may be pumped or, by suitable arrangement of the banks, caused to ow by gravity into the highest unit 8 of banks 5 and 6, respectively. The condensates from the respective zones are a light creosote oil having a boiling range of about 215 to 370 C. less than per cent of which boils at 250 C., a naphthalene-rich fraction having a boiling range of from 210 to 290 C. at least 80 per cent of which boils at 250 C. and containing about 40 to 55 per cent naphthalene, which may be as much as 80 per cent of the total naphthalene content of the vapors, and a tar acid fraction having a boiling range of about 170 to 260 C. at least 80 per cent of which boils at 220 C. containing about 15 to 25 per cent tar acids and which may be as much as 60 per cent total desirable tar acid content of the vapors.

In the practice of my inventionI have foun it desirable to employ a single condenser unit of the type shown in Figure 2 as the tar fog removal condenser 4, and a number of similar units arranged in series with the vapor outlet of one unit connected to the vapor inlet of the succeeding unit as the condenser units 8 of the condenser banks 5, 6 and 1. The condenser unit of Figure 2 and the arrangement of condenser units in condenser banks are described and claimed in my copending applications Serial Nos. 354,677 and 354,678, led August 24, 1940. Briefly, the condenser unit of Figure 2 comprises a horizontally disposed substantially cylindrical shell I1 having a vapor inlet I8 and Vapor outlet I9 located near opposite ends of the shell I1 to provide a path for the vapors through the shell past two hairpin tubes within the shell I1 which constitute the cooling surface of the condensing unit. These tubes 20 extend within the shell I1 in series and leaves through the connection 23..

The lateral opening 24 is for the insertion of a thermocouple. Each of the condenser banks 5, 6 and 1 comprises a series of such condensing units arranged usually one above another, for example,

as disclosed in Figures 9 and 10 of my copending application Serial No. 354,678, and the vapor outlet I9 of each unit of a bank is connected to the inlet I8 of the next higher unit to conduct vapor from the lowest unit through the horizontal paths defined by consecutively higher units to the uppermost unit of the bank. Only the lowest unit of each bank is provided with a liquid outlet for removal of condensate from the bank, and the condensate formed in each higher unit of the bank ows along the bottom of the unit until it reaches the vapor inlet through which it cascades into the vapor outlet 'of the next lower unit of the bank. Thusthe condensate cws through the bank in a series of consecutively lower horizontal paths countercurrent to the flow of vapors through the banks,

and is discharged from the lowest unit 8 in each bank, so that the condensate and the vapors are in contact for a relatively long time and over a relatively large area. By this arrangement the condensate is warmed by contact with the hot vapors and shells of the condensing units which are at a higher temperature, and ample opportunity is provided for a revaporization of the lower boiling portions of the condensate so that the fraction withdrawn from the lowest unit of the bank has a relatively narrow boiling range.

The apparatus shown in Figure 3 is suitable for the production of a heavy creosote oil fraction as well as light creosote oil, naphthalene, tar acid and light solvent fractions, and comprises storage tanks 3| and 32 for the tar to be distilled, a vapor box 33 for topping crude tar, a reflux condenser 34 for the vapor box 33, a continuous pipe coil still' 35, ilash box 36, a vacuum box 31, a vacuum distillate condenser 38 connected to vacuum box 31, a condenser unit 38' connected to the iiash box-for removal of tar fog from the vapors, a condenser assembly 39 4for condensation of heavy creosote oil and a series of banks of

condenser units

4I, 42 and 43 for condensation of light creosote oil, naphthalene and tar acid fractions, respectively. An evacuating system or vacuum pump 39' is provided for maintaining a vacuum in vacuum box 31. Crude tar usually at a temperature of F. to F. and containing up to about 6 per cent moisture is pumped from tank 3| by pump 44 through` pipe 45 to heat exchangers 48 where the tar is heated by indirect heat exchange with heavy creosote oil condensate from the condenser assembly 39. The tar then passes through the vacuum distillate condenser 38 and reflux condenser 34 in indirect heat exchange with the vapors in the respective condensers, whereby it is further heated, and is discharged through pipe to 570 F. into the 52 of the condenser banks 43. 42 and 4| the condenser units 53 of condenser assembly 39, and the condenser 38', in indirect heat exchange relation with the vapors in the respective condensers, and is discharged through pipe 41 at a temperature of 530 to 570 F. into the vapor box 33. Tar from condenser unit 34, if desired, may be discharged into a separate vapor box similar to box 33 at a temperature preferably of 450 to 530 F. to produce saturants and soft road binders. In the vapor box 33 all of the moisture and a portion of the lighter oils present in the crude tar are vaporized from the crude tar introduced through the pipe 41, and the vapors are passed through the reflux condenser 34. The vapors leaving the reflux condenser 34 may be passed to a water-cooled condenser 54, or may be injected into the vapor line 55 leading from the condenser assembly 39 to the condenser bank 4|.

The dehydrated, topped tar at a temperature of 500 to 550 F. is then passed from the vapor box 33 to the tank 32 which is insulated to minimize heat losses. Crude tar from tank 3| containing up to 6 per cent of moisture or dehydrated tar from tank 32 or a mixture of both, preferably containing 2 to 3 per cent of moisture is pumped by the

pumps

50 and 50a throug.. pipe 56 to the pipe coil still 35 where it is heated rapidly under pressure without substantial vaporization or decomposition to a temperature above 570 F. and preferablv to about 780 to 800 F. and the heated tar is passed to the flash box 36, which is at atmospheric pressure or substantially so. In the ash box 36 a substantial portion of the normal oil content of the tar vaporizes. leaving a pitch at a temperature of between 760 and 790 F., and the pitch is withdrawn from the flash box 36 to the vacuum box 31 wherein additional oils are distilled oil' under a vacuum of about 29.7 to 29.9 inches of mercury. leaving behind a high melting point pitch. The vapors from the vacuum box 31 are condensed in the vacuum distillate condenser 38 and water-cooled condenser 51.

The oil vapors from the flash box 36 are passed rapidly through condenser unit 38' where the vapors are cooled from a temperature of between '160 and 790 F. to a temperature of between 730 to 760 F.. and a portion of the oil vapors, which maybe from 1 to 3 per cent. preferably about 1.5 ner cent based on tar distilled. is condensed. 'I'his condensate washes out "tar fog" entrained in the vapors from the flash box 3S and flows back to the Hash box 36 bv gravity. carrying the washed out tar with it. The lower boiling portion of this condensate is revaporized by heat of the pitch in the flash box '36 and passes again to the condenser-s.

The vapors from the tar fog removal condenser 39', or from the ash box 36. in case the unit 38' is not employed, are then owed rapidly through the units 53 of condenser assembly 39 in a direction counter to the direction of ow of the cooling medium therethrough. The condenser assembly 39 comprises a series of condensing units 53, usually arranged side by side in a horizontal row for flow of vapor through each unit of the assembly consecutively. The units 53 are different from the condenser units described in connection with Figures 1 and 2 in that a condensate outlet 58 is provided at the bottom of each unit so that the condensate ows along a relatively short horizontal path, preferably counter to the flow of vapor in each unit in the assembly, and is continuously discharged from each unit substantially immediately as formed. with relatively long condenser units 53, it may be desirable to have two or more condensate outlets 58 in each unit to keep the time of contact between hot vapors and condensate at a minimum. The vapors are flowed at such rate through these condensers that each vapor particle will pass from the flash box 39 through the tar fog removal condenser 38' and the condenser assembly 39 in less than two minutes, and preferably less than ten seconds. The cooling capacity of the condenser units 53 oi the condenser assembly 39 is regulated by the by-pass or valve 40 which controls the rate of flow of the crude tar cooling medium so that the vapors from the flash box are cooled to a temperature below 570 F., preferably 530 to 560 F., and the heavy creosote oil is condensed and removed from the vapors passing through the units. I have found that the heavy creosote oil condensed in the condenser assembly 39 under the conditions of operation outlined above contains less than 1% per cent coke residue, usually less than 1 per cent, as compared with as much as 4.5 per cent obtained by methods heretofore in use. 'I'he condensate from the condenser assembly 39 is passed through the pipes 59 to the heat exchangers 46 to heat the incoming crude tar, and thence to the oil receivers.

From the last unit of the condenser assembly 39 the vapors flow through the vapor line 55 to the condenser banks 4|, 42 and 43, which constitute a fractional condenser and to the Watercooled condenser 60. The banks 4|, 42 and 43 are substantially the same as the banks 5, 6 and 1 described above in connection with Figure 1 and are tted with by-passes or valves 62 to control the rate of iiow of the crude tar cooling medium and thereby regulate the cooling capacity of the banks. The condensate outlets 6| from the lowest units of the banks are connected to pass the condensates through the aforementioned heat exchangers 5| to condensate receivers.

The vapors are owed through the condensing zones or banks 4|, 42 and 43 and cooled in the zones or banks at a rate such that the vapor at an initial temperature of about 530 to 560 F. passes through the rst zone 4I and is cooled therein to about 390 to 430 F., passes through the second zone 42 and is cooled to about 330 to 350 F., and passes through the third zone 43 and is cooled to about 250 to 270 F. 'I'he oondensates from the respective zones are a light creosote oil having a boiling range of about 215 to 370 C. less than 15 per cent of which boils at 250 C., a naphthalene-rich fraction having a boiling range of from 210 to 290 C. at least 80 per cent of which boils at 250 C., and containing about 40 to 55 per cent naphthalene, which may be as much as per cent of the total naphthalene content of the vapors, and a tar acid fraction having a boiling range of about to 260 C. at least 80 per cent of which boils at 220 C., containing about 15 to 25 per cent tar acids and which may be as much as 60 per cent of the total desirable tar acid content of the vapors.

The residual vapors from the condenser 43 are condensed in the water-cooled condenser 60 to obtain light condensates comprising benzol, toluol and solvent n-aphtha.

The following examples are given as illustrative of the practice of my invention; the invention is not to be construed as limited to the details recited therein otherwise than as dened in the claims.

Example I Using the arrangement of apparatus shown in Figure 1, coal tar (moisture content 3.5 per cent) is pumped from the tank I by pump I8 through the heat exchangers I I, the condenser umts 8 of the condenser bank l, i and 5, and the tar fog removal condenser 4, to the pipe still 2. A supplementary stream of tar is pumped directly from the tank by pump Illa through pipe 9a into pipe I2 prior to entering the pipe still 2, to form a tar mixture comprising equal parts of preheated and unheated tar. The tar mixture flows through the coils of the still 2 at a rate so that the volume of tar entering the still 2 per minute is equal to 12 per cent of the cubical capacity of the still. In the still 2 the tar is heated to a temperature of 563 F. The heated tar is then discharged from the still 2 through pipe I3 to the fi-ash box 3, where the oil content of the tar is flashed into vapor, leaving behind a pitch having a melting point of 144 F., (Cube-in-water method) which is withdrawn and subjected to vacuum treatment for removal of further distillate.

.The vapors, together with entrained tar fog. are passed into the condenser unit 4 wherein the temperature is yreduced to 548 F. and 2.0'l per cent of the vapors, based on tar distilled, is condensed to remove tar fog, and returned to the flash box carrying the removed tar with it. The vapors from the condenser 4 are then passed at a temperature of 548 F. to the lowest unit of the bank 5 an-d flowed through successively higher units of the bank. In passing through the bank 5 the vapors are cooled from an initial temperature of 548 F. to an exit temperature of 422 F. and then passed to the next bank 6 of the fractional condenser.

The condensate flows from the highest unit to the lowest unit of the bank 5, and the product withdrawn has a boiling range of from 218 to 364 C. 13 per cent of which boils at 250 C. The product meets light creosote oil specifications setting a boiling range of from 215 to 370 C. less than 15 per cent of which boils at 250 C. The vapors from the highest unit of the bank 5 are passed to the lowest "unit of the bank 6 and up through the units of the bank to the highest unit thereof and are cooled during passage to a temperature of 340 F. The condensate ows from the highest unit to the lowest unit of the bank 6 in about four minutes, andthe product withdrawn has a boiling range of from 212 to 278 C. and consists of 52 per cent naphthalene. The vapors from the highest unit of the bank 6 are passed to the lowest unit of the bank I and up through successively higher units of the bank to the outlet of the bank and are discharged at a temperature of 260 F. The condensate ows from the highest unit to the lowest unit of the bank 'I and the product withdrawn from the bank 'I consists of 17 per cent tar acids comprising 24 per cent of phenol fraction, 10 per cent of ortho cresol fraction and 30 per cent of meta paracresol fraction. The vapors from the highest unit of bank 1 are passed to the water-cooled condenser I6 and condensed therein to form a light oil fraction comprising about 10 per cent benzol, toluol and xylol fraction and about 30 per cent solvent naphtha.

. Example II Using the arrangement of apparatus shown in Figure 3, crude tar (moisture content 3.5 per cent) is pumped to the vapor box 33 by pump 44 through the heat exchangers 46, vacuum distillate condenser 38, and redux condenser 34, and by pump 48 through heat exchangers 5I,

condenser banks

43, 42 and 4I, condenser assembly 39 and condenser 38. I'he tar enters the vapor box 33 at a temperature of 563 F.k andv is partially vaporized, with removal of all of the water; 4the residual dehydrated, topped tar is passed at a temperature of 548 F. to the tank 32.

A mixture of crude tar (moisture content 3.5

per cent) from tank 3| and dehydrated tar from4 tank 32 in the ratio of 57 to 43 parts, respectively, at a temperature of 360 F. is pumped by

pumps

58 and 50a through supply pipe 56 and pipe still 35 at a rate per minute equal to 12 per cent of the cubical capacity of the pipe coil of the still. In passing through the still, the tar is heated to a temperature of 799 F. without substantial evolution of vapors. The heated tar is then discharged from the still 35 to the ash box 36, where the oil content of the tar is ashed into vapor, leaving behind a-pitch having a melting point of 245 F. (Cube-in-air method), which l is withdrawn and passed tothe vacuum -box 31 which is at a vacuum of 29.86 inches. The vapors from vacuum box 31 are passed through tar cooled condenser 38 and water cooled condenser 5l for condensation of a resinous vacuum distill-ate and heavy'creosote oil, respectively.

The vapors from the ash box 36, together with entrained tar fog, are passed through the condenser unit 38 wherein the temperature is reduced to 749 F., and 1.5 per cent of the vapors, based on tar distilled, is condensed to remove tar fog" and returned to the flash box 36 carrying the removed tar with it. The vapors from the outlet of the condenser 38 are then passed through the condenser assembly 39 wherein the temperature is reduced to 560, F. for condensation of the heavy creosote oil fraction. The time factor for the passage of a particle of vapor through the condenser unit 38 and condenser assembly 39 is about 4.5 seconds. The heavy creosote oil obtained from the units 53 of the condenser assembly contains only 1.0 per cent coke residue.

The vapors from the condenser rassembly 39 are then passed at a temperature of 560 F. in conjunction with vapors from condenser 34 to the lowest unit of the bank 4I and flowed through successively higher units to the highest unit of the bank. In passing through the bank 4I the vapors are cooled from an initial temperature of 548 F. to an exit temperature of 422 F. Each particle of condensate formed in the highest unit i'lows from the highest unit to the lowest unit of the bank 4I and the light creosote oil product Withdrawn has a boiling range of from 218 to 364 C. 13 per cent of which boils at 250 C. The vapors from the highest unit of the bank 4I are passed to the lowest unit of the bank 42, iiow up through the units of the bank to the highest unit thereof and are cooled during passage to a temperature of 340 F. The condensate formed ows from the highest unit to the lowest unit of the bank 42 and the product withdrawn has a boiling range of from 212 to 278 C. and consists of 52 per cent naphthalene. 'I'he vapors from the highest unit of the bank 42 are passed to the lowest unit ofthe bank 43 and up through successively higher units of the bank to the highest unit of the bank and are discharged at a temperature of 260 F. The condensate formed ows from the highest unit to the lowest unit of the bank and the product withdrawn from the bank 43 consists of 17 per cent tar acids comprising 24 per cent of phenol fraction, 10 per cent ortho cresol fraction, and 30 per cent meta para-cresol fraction. The vapors from the highest unit of bank 43 are passed to the water-cooled condenser 60 and condensed to form a light oil fraction comprising about 10 per cent benzol, toluol and xylol fraction, and about 30 per cent solvent naphtha fraction.

Thus it will be seen the invention provides a simple and eillcient process for distilling tar to produce narrow boiling fractions of light creosote oil, naphthalene and tar acids. The naphthalene and tar acid fractions are suciently rich in these materials so that the naphthalene and tar acids can be recovered directly therefrom without subjecting them to a further distillation. In accordance with the invention, a heavy creosote oil fraction of high quality may also be obtained. 'Ihe distillate oils, owing to the removal of tar fog from the vapors and condensation of the fractions under conditions such that polymerization anddecomposition do not occur to a substantial extent, are of exceptionally low coke residue and free carbon content.

Cast iron is the preferred metal from which the condenser is fabricated for use in the condensation of coal tar. For distillation of other materials other suitable metals resistant to corrosion may be used. It will be understood the condenser system is suitably insulated to prevent excessive cooling to obtain the desired degree of condensation and loss of heat to the atmosphere.

Since certain changes may be made in the above without departing from the scope of the invention, it is intended that the above shall be interpreted as illustrative and not in a limiting sense.

I claim:

1. A process of distilling tar which comprises flowing tar in a restricted stream of narrow crosssection, heating the stream of tar Without substantial vaporization of the tar to a temperature above 570 F., introducing heated tar from the stream into an expansion zone to volatilize a substantial portion of the normal oil content of the tar, rapidly cooling the vapors to a temperature of about 530 to 560 F. to condense heavy creosote oil so that the time during which each particle of the heavy creosote oil vapors is subjected to temperatures above about 570 F. does not exceed two minutes, continuously withdrawing heavy creosote oil condensate from contact with the residual vapors substantially immediately upon formation, flowing the residual vapors after separation of heavy creosote oil through a series of condensing zones, controlling the temperatures in each of said condensing zones so that the vapors leaving the first zone are cooled to a temperature of 390 to 430 F., the vapors leaving the second zone are cooled to a temperature of 330 to 350 F., and the vapors leaving the third zone to a temperature of 250 to 270 F., and removing the condensate from each of said zones.

2. A process of distilling tar which comprises flowing tar in a restricted stream of narrow cross-section, heating the stream of tar without substantial vaporization of the tar to a temperature above 570 F., introducing heated tar from the stream into an expansion zone to volatilize a substantial portion of the normal oil content of the tar, rapidly cooling the vapors to a temperature of about 530 to 560 F. to condense heavy creosote oil so that the time during which each particle of the heavy creosote oil vapors is subjected to temperatures above about 570 F. does not exceed two minutes, continuously withdrawing heavy creosote oil condensate from contact with the vapors substantially immediately upon formation, owing the vapors after separation of heavy creosote oil through a series of condensing zones. passing the vapor in each zone along a series of horizontal and consecutively higher paths, owing the condensate formed countercurrent to and in contact with the vapors along consecutively lower paths in each zone, controlling the rate of flow of the vapors and the temperatures in each of said condensing zones so that the vapors are cooled in the iirst zone to a temperature of 390 to 430 F., in the second zone to a temperature of 330 to 350 F., and in the third zone to a temperature of 250 to 270 F., and removing the condensate from the lowest path in each zone.

3. A process of distilling tar which comprises flowing tar in a restricted stream of narrow cross-section, heating the stream of' tar without substantial vaporization of the tar to a temperature of 780 to 800 F., introducing heated tar from the stream into an expansion zone to volatilize suddenly a substantial portion of the normal oil content of the tar to form vapors at a temperature of between 700 and 790 F., rapidly cooling the vapors to a temperature of 530 to 560 F. to condense heavy creosote oil vapors, so that the time during which each particle of .the heavy creosote oil vapors is subjected to temperatures above about 510 F. does not exceed two minutes, continuously withdrawing heavy creosote oil condensate Iroin contact with the vapors substantially immediately upon formation, flowing the vapors through a series of condensing zones, passing the vapors in each zone along a series of horizontal and consecutively higher paths, iiowing the condensate formed countercurrent to and in contact with the vapors along consecutively lower paths in each zone, removing the condensate from the lowest path in each zone, and controlling the temperature in each oi' said condensing zones so that the vapors 4leaving the rst zone are cooled to a temperature of 390 to 430 F., the vapors leaving the second zone are cooled to a temperature of 330 to 350 F., and the vapors leaving the .third zone are cooled to a temperature of 250 to 270 F., to condense in the respective zones a light creosote oil fraction, a fraction comprising at least 40 per cent of naphthalene, and a fraction comprising at least l5 per cent of tar acids.

4. A process of distilling tar which comprises flowing tar in a restricted stream of narrow cross-section, heating the stream of tar without substantial vaporization of the tar to a temperature of about 780 to about 800 F., introducing heated tar from the stream into an expansion. zone to volatilize suddenly a substantial portion of the normal oil content of the tar to form Vapors at a temperature of between 760 and 790 F., rapidly cooling the vapors to a temperature of about 530 to 560 F. to condense heavy creosote oil vapors, so that the time during which each particle of the creosote oil vapors is subjected to `temperatures above about 570 F. does not exceed two minutes, continuously withdrawing heavy creosote oil condensate from contact with the vapors substantially immediately upon formation, flowing the vapors through a series of condensing zones, passing the vapors in each zone along a series of horizontal and consecutively higher paths, controlling the rate of iiow of the vapors and the temperature in each of said condensing zones so that the vapors are cooled in the rst zone 4to a temperature of about 390 to 480 F., in the second zone to a temperature of 330 to 350 F., and in the third zone to a temperature of 250 to 270 F., iiowing the condensate formed countercurrent to and in contact with the vapors along consecutively lower paths in each zone, and removing the condensate `:from the lowest path in each zone, to obtain from the respective zones a light creosote oil fraction, a fraction comprising at least 40 per cent of naphthalene, and a fraction-comprising at least per cent of tar acids.

5. A process of distilling tar which comprises iiowing tar in a restricted stream of narrow cross-section, heating the stream of tar without substantial vaporization of ,the tar to a temperature above 570 F., introducing heated tar from the stream into an expansion zone to volatilize a substantial portion of the oil content of ythe tar, flowing the vapors from said expansion zone to a cooling zone, removing tar fog from the vapors by condensing a portion of the vapors during ow through the cooling zone, and passing the condensate to the expansion zone in contact with vapors leaving said zone, passing vapors through a second cooling zone, rapidly cooling the vapors in the second cooling zone to a temperature of about 530 to 560 F. to condense heavy creosote oil so that the time during which each particle of the heavy creosote oil vapors is subjected to temperatures above about 570 F. does not exceed two minutes, continuously withdrawing heavy creosote oil condensate from contact with the vapors substantially immediately upon formation, iiowing the vapors after separation of heavy creosote oil through a series of condensing zones, passing the vapor in each zone along a series of horizontal and consecutively higher paths, iiowing .the condensate formed countercurrent to and in contact with the vapors along consecutively lower paths in each zone so that the vapors leaving the rst zone of said series are cooled to a temperature of 390 to 430 F., in the second zone to a temperature of 330 to 350 F., and in the third zone to a temperature of 250 to 270 F., and removing the condensate from the lowest path in each zone.

6. A process for distilling tar which comprises owing tar in a restricted stream of narrow cross-section, heating the stream of tar without Asubstantial vaporization of the tar to a temperature above 570 F., introducing heated tar from the stream to an expansion zone to volatilize a substantial portion of the normal oil content of the tar, rapidly cooling the vapors to a. tempera- .ture of about 530 to 560 F. to condense heavy creosote oil so that the time during which each particle of the heavy creosote oil vapors is subjected to a temperature above 570 F. does not exceed two minutes, continuously withdrawing heavy creosote oil condensate from contact with the residual vapors substantially immediately upon formation, flowing the residual vapors after separation of heavy creosote oil through a series of three condensing zones. and controlling the temperature in each of said condensing zones so as to condense in the respective zones a light creosote oil fraction, a fraction comprising at least 40% naphthalene, and a fraction comprising at least 15% tar acids.

7. A process of distilling tar which comprises flowing tar in a, restricted stream of narrow cross-section, heating the stream of tar without substantial vaporization of the tar, introducing heated tar from the stream into an expansion zone to volatilize suddenly a substantial portion of the normal oil content of .the tar, owing the vapors thus produced at a temperature within the range of 450 to 630 F. through a cooling zone to condense a-portion of the vapors and passing the condensate thus formed to said expansion zone in contact with the vapors leaving said zone thereby returning to the said expansion zone the condensate formed in said cooling zone and tar fog" removed from said vapors by the condensation of said vapors taking place in said cooling zone and the Washing of the vapors with said condensate taking place as the said vapors and the said condensate liow respectively in contact with each other from and to the said expansion zone, revaporizing the lower boiling portion of the condensate thus returned to the expansion zone and causing .the vapors thus formed to Iiow with the first mentioned vapors through the said cooling zone, owing the vapors from the cooling zone through a, series of condensing zones, passing the vapors in each of said condensing zones along a series of horizontal and consecutively higher paths, and flowing the condensate formed by condensation of a portion of said vapors countercurrent to and in contact with the vapors along consecutively lower paths in each of said condensing zones so that the vapors leaving the first zone are cooled to a .temperature of 390 to 430 F., in the second zone to a temperature of 330 to 350 F., and in the third zone to a temperature of 250 to 270 F., and removing the condensate from the lowest path in each of said zones.

JOSEPH ZAVERTNIK.