US2044764A - Distillation of tar - Google Patents

Description

June 23, 1936. W. M BYWATER msTIpLATIoN 0F TAR Filed July 8, 1931 7 Sheets-Sheet 1 INVENR Vo-J' )4. raf/b1 vBY 162.. ATTORNEYS June 23, 1936... y W, M. BYWATER 2,044,764

` DISTILLATION oF TAR Filed July 8, 1931 '7 Sheets-Sheet 2 ATTORNEYS .lumel 23, 1936. W. M. BYWATER @044,764

DISTILLATION OF TAR Filed VJuly e, 1931 'r sheets-sheet s INVENTQR 72@ 'xnwomaws June 23, 1936 w. M. BYWATER 1 2,044,764 A DISTILLATION OF TAR I Filed July 8, 1951 l '7 Sheets-Sheet 4 'INVESTOR BY /-...Lwamir ATTORN EYS R E T. A W Y B M. W.

DI STILLATION OF TAR Filed July 8, 1951 '7 Sheets-Sheet 5 June 23, 1936 w. M. BYWATER f DISTILLATION oF TAR 7 ySheets-Sheen 6 Filed July 8, 1951 INVENTOR: B( ./Sr;

ATTORNEYS June 23A, 1936.. 'W M BYWATERv 2,044,764

DISTILLATION OF TAR Filed July a, 1931 7 sheets-sheet 7 @maar INVENTOR l i.; @M 1mg-,M

ATTORNEYS Patented June 23, 1936 UNITED STATES PATENT OFFICE;

DISTILLATION F TAR Application July 8, 1931, Serial No. 549,429`

19 Claims.

This invention relates to the distillation of tar, etc., to produce pitch and distillate oil kand the simultaneous recovery of tar acids as carbolate, and includes both the method of distillation and apparatus therefor.

To recover tar acids from tar it is customary to distill the tar and to extract the resulting liquid distillate with an alkaline reagent. The distillate is preferably collected in fractions and one or more of the tar-acid-containing fractions is then extracted to recover tar acids. This method requires large tar-acid-oil storage facilities and extensive liquid extraction tanks, etc.

According to the present invention, tar acids are recovered by alkaline extraction in the vapor phase, i. e., by bringing a solution of caustic soda or other alkaline reagent into intimate contact With vapors of tar acids in admixture with vapors of non-acid oils. The tar acids are extracted by the caustic and recovered as carbolate Without necessarily condensing any large proportion of non-acid constituents. In the apparatus employed, the tar-acid extraction is carried out simultaneously with and as a part of the distillation.

In extracting tar acids in the vapor phase from admixture with vapors of neutral oils, i. e. nonacid constituents, if the vapors are not too hot the condensation of substantial amounts of neutral cils can be avoided by using a hot, strong,

alkaline solution for the extraction, the heat effect of evaporation of the alkaline solution being insufficient to effect substantial cooling and condensation of vapors of non-acidicconstituents. In distilling tar, if the tar is heated to a sufciently high temperature to vaporize the greater part of the tar acids, the vapors are at such a high temperature that it is impracticable to maintain a solution of caustic in contact with them Without considerable evaporation. At temperatures of about 190 to 210 C., however, hot commercial caustic solutions containing about 47 to 50% of caustic can be employed toextract tar distillation vapors; although there will be some evaporation from such concentrated solutions `at this temperature, the amount will not cause undue and disadvantageous-cooling of the vapors.

If the tar is heated to such a temperature that only the lower boiling constituents are distilled, then the vapors may be treated `directly with caustic, but if the vapors are at too high a temperature, their temperature must rstbe reduced by fractionally cooling them and condensing the higher boiling constituents before bringing the residual vapors in contact with caustic.

I have found that by fractionally cooling the vapors from distilling tar so as to obtain taracid-containing distillate and then subjecting thedistillate while still hot to inert gas distillation, tar acids can readily be recovered by vapor phase extraction of the gasesand vapors resulting from this inert gas distillation and the tar acid recovery may be carried on in conjunction with the tar distillation. My process is designed more particularly for the extraction of distillate obtained by the condensation of vapors which leave the still at a temperature above about 200 C. 15

According to this invention the vapors from the tar still are subjected to fractional condensation inV any suitable Wayto obtain a high boiling tar-acid-Containing fraction and the tar acids are then vaporized from this fraction in 20 a eurent of inert gases, preferably by utilization of the self-contained heat of the oil and without any further addition of heat. Y This inert gas distillation is -advantageously a. cyclic process, in which the inert gases pass in succession thru the oil, then through a caustic extractor (when the tarracids are recovered `by direct contactwith an alkaline reagent), andare then recycled thru the oil fraction. All or Vonly a part of the gases may be recycled. The cycle `may include a condenser before or after thecaustic extractor or some `cooling may be eiiected within the caustic extractor. Any cooling which, may occur in the cycle is preferably regulated so. that,:at most, only a part of the oil vapors are condensed and the recycled gases, when they are again brought into contact with the distillate oil, contain vaporsof neutral or non-acid constituents. These neutraloilV vapors present or inhibit the vaporizationof neutral oils from theoil fraction, but, owing to 40.

the removal of thetar acids `from the recycled gases by caustic extraction in the vapor phase, tar'acids present Vin the distillate oil fraction are readily vaporized. 1n` this Way the tar acids are selectively distilled and the oil fraction after treatment Ycontains a lower content of tar acids thanbeforetreatment; it may be a substantially neutral oil, i. e., an oil substantiallyfree from tar acids.

When the processis applied to a batch still operation, the tar is heated, and thevapors coming olf up to a temperature of about 200 C may be treated in any of several'ways. They may-be treated, directly with strong caustic for extractioniof the tar acids and subsequently condensed.

as neutral oil, or they may be condensed as acid oil and this acid oil may be run to a tar-acid still for removal of the tar acids by inert gas distillation. In any case, oil fractions coming off at vapor temperatures in excess of 200 C. are condensed and run 'to the tar-acid still in which the tar acids are removed by inert gas distillation in a manner entirely similar to that previously described. This treatment continues until such time as the tar-acid content of the vapors becomes too low, or their commercial value becomes too small, to warrant further treatment.

When tar is continuously distilled in a simple still, then the vapors coming off include the total oil vapors corresponding to the pitch being made. The vapors are fractionally condensed and a hot oil fraction containing tar acids is selected and sent to the tar-acid still for inert gas distillation, the operation of which is substantially the same as that previously described. In a pipe still distillation the tar is heated and then flashed in a vapor box. The vapors are fractionally cooled to produce a tar-acid oil fraction which is treated for the recovery of tar acids. If low melting point pitch is produced, fractional condensation may not be necessary; the entire distillate may be treated to recover its tar-acid content. In addition to the extraction of tar acids from the distillate, tar acids may also be recovered by treating any vapors leaving the fractional condenser that remain uncondensed, at a temperature of 200 C., or lower, by treating these vapors directly with caustic solution.

When tar is continuously distilled in a series of simple stills, which may, for example, be arranged on the cascade principle, then vapors from any of the first stills, which may be at a temperature lower than about 200 C., may be treated directly by caustic for recovery of acids, but vapors coming from stills at higher temperatures than this are first condensed, either totally or fractionally, and the hot condensate, containing tar acids, is treated by inert gas for redistillation of the tar acids followed by subsequent recovery by extraction with caustic.

The apparatus of this invention includes a tar still and condensing means. Any suitable type of condenser may be employed. The condenser may be a fractional condenser or total condenser. The condensation may occur in connection with a fractionating column. Ordinary reiiuxing means may be used to advantage in separating distillate fractions. If tar acids are to be recovered directly from the vapors from the still after condensation of one or more distillate fractions by contact with an alkaline reagent, this extraction may take place in one section of a fractionating column equipped for this purpose, or extraction may take place in any other suitable type of gas and liquid contact apparatus.

The receptacle in which the oil fraction is distilled by the inert gases may advantageously be a packed tower or a grid tower, although'any suitable type of gas and liquid contact apparatus may be employed.

The caustic extraction tower may be a packed or grid tower. It is advantageously constructed in such a way as to provide for two or more passages of the gases and vapors thru it and with means for respraying partially saturated causticcarbolate solution into the gases. Fresh caustic is advantageously added to one of the towers and blended with carbolate therein and sprayed into the gases before being drawn off into the second tower in which it is again sprayed into the gases before being drawn off as the make" of carbolate. It is advantageous to thus recycle carbolate thru the extraction apparatus in admixture with the caustic in order to provide for a large surface of liquid-gas contact. 5

When the tar is distilled by a continuous process the temperature at which the vapors leave the still will vary with the kind of tar treated, and the melting point of the pitch desired, etc. If the vapors leave the still at a sufliciently high tem- 10 perature, one or more oil fractions which are not treated for tar acids may be condensed from the gases before a tar-acid oil is obtained. In general, it will be desirable to condense only part of the tar-acid-containing oils and then remove 15 the tar acids from this condensate by distilling in a current of inert gases, and it will generally be preferable to cool the vapors to a temperature not lower than about 200 C. to obtain a fraction for treatment according to this process.

Although the vapors may be cooled to an even lower temperature to obtain tar-acid distillate to be treated according to this invention, yet by cooling only to about 200 C., high boiling distillate will be recovered at a temperature usually 25 somewhat above 200 C., and with sufiicient heat content to permit the distillation of tar acids in an atmosphere of inert gas largely or entirely by its self-contained heat. The non-condensed vapors from the partial condenser can be extract- 30 ed directly in the vapor phase at this temperature to recover tar acids. If the oils are not suiiiciently hot to effect the distillation by their selfcontained heat, they may be heated or the inert gases' may be heated before they enter the appa- 35 ratus for the distillation of tar acids.

By proper regulation of the temperatures at which the vapors from the still enter each section of the fractional condenser, and by proper regulation of the removal of tar acids from one or more selected distillate fractions by inert gas distillation, tar acids of a particular boiling range may be selectively recovered. For example, ordinary coke-oven tar may be heated and flashed and the resulting vapors may be cooled to a tem- 45 perature around 280 C. before they enter the condenser in which that distillate fraction is condensed from which tar acids are to be recovered.

In this condenser they may be cooled to about 200 C. Generally the condensate obtained is at 50 a sufficiently high temperature (intermediate between the gas inlet and outlet temperatures), say 250 C., to allow distillation of the tar acids by recirculation of an inert gas without the addition of heat. 55

By regulating the rate at which the gases are recirculated thru the oil and the temperature in the treating chamber, the amount of tar acids vaporized is controlled.

The tar acids which remain in vapor form in 60 the uncondensed vapors from the condenser may be extracted directly in the vapor phase by contact with caustic solution, After the extraction of the tar acids in vapor form, the resulting vapors may be cooled to condense one or more 65 fractions of neutral oil.

Inert gasA is used herein to refer generally to a gaseous medium, which is chemically inert to tar acids and caustic or other alkaline reagent employed, and which is suitable for use as a "0 carrier for the tar-acid vapors. It is used to include condensable vapors such as steam and the vapors of neutral oils, as well as gases such as nitrogen, etc. Steam or other inert gas may be added to the inert gas system in carrying out this 75 operation orthe inert gases. may be composed entirely of uncondensed vapors resulting from the.

distillation. A vent to the system is provided to Atake care of additions or accumulations of steam orother inert gas or excess gases and vapors that may be produced during the cycle, asby decomposition of oil and vaporization of Va portion of the lower boiling oils being treated, and this vent is advantageously thru a condenser for condens.

ingand collecting any oil vapors contained in the vented gases.

In the inert gas distillation cycle in which the tar acids are distilled from the hot, higher boiling distillate, Vthe vapor phase extraction of the tar acids may be effected without any substantial cooling in the system so that the inert gases are recycled at a substantially constant temperature.

However, if desired, oils may be condensed from the cycle either in the caustic extractor thru vaporization of Water from the caustic solution or. by the use of special cooling means in the caustic extractor, etc., or oils may be condensed from the recycled gases and vapors before they enter the caustic extractor, or after they have left the caustic extractor. Oil condensed after the extraction of tar acids is neutral oil or oil of 10W tar-acid content, depending upon the degree of completeness of the tar acid extraction in the caustic tower. Oil condensed before the extraction of tar acids is a tar-acid-containing oil.

One oil fraction may be subjected to successive inert gas distillations to remove differenttar acids. The hot condensate may first be treated for the removal of phenol which is the lowest boiling tar acid and after a substantial recovery of phenol the oil may be drawn off into another treating chamber for the recovery of higher boiling tar acids by inert gas distillation. It may be necessary to heat the oil somewhat before the removal of the vhigher boiling tar acids or the gases employed may be heated before entering the second treating chamber.

The invention will be further described in connection with the accompanying drawings, but it isintended and is to be understood that it is not limited thereto.

In the drawings: Y

Fig. 1 shows the tar acid still and extractor in combination with a pipe still and fractionating column;

Fig. 2 is similar to Fig. 1 but shows a condenser following the extractor in the tar acid recovery cycle;

Fig. 3 shows a pipe still in combination with a series of fractional condensers equipped for carrying out this invention.

Fig. 4 is similar to Fig. 3 but shows a con; denser preceding the extractor in the tar acid recovery cycle;

Figs. 5 and 6 show diagrammatically a pipe still connected with fractional condensers, means for caustic extraction of the partially cooled vapors and means for the recovery of tar acids from the condensate from one of the condensers.

Fig. 7 shows a simple still equipped for carrying out the process of this invention as a batch process;

Fig. 8 shows a simple still equipped for carrying out the process of this invention as a continuous process; and

Fig. 9 shows a cascade of simple stills equipped for carrying out this invention.

In the various figures the same numeral is used to designate like parts with the addition of a distinguishing letter.

In .'distilling'tar in a pipe still it is heated in the coil 4or heating tubes to a temperature above its initial boiling point and flashed in the vapor box.,l The vapor box is ordinarily maintained at pressures slightly above atmospheric although pressures higher or lower than this may be employed, if desirable. Referring to Fig. 1, the tar is heated on passing. thruthe pipe coil heater I and is then flashed into the vapor box 2. The vapors pass to. the condensing system and the undistilledresidue, which is pitch, is drawn ofi thru the line 3 into the receiver 4. This pitch maybe of high or low melting point, as desired. The vapors pass from thevapor box thru the insulated 4main 5 tothe fractionating column, which is composed of the sections 6, l, B and 9. Each of these sections comprises a set of cooling coils I0 in the top with rectifying means below, which may be bubble-cap plates or suitable grids or other packing.

The highest boiling oil fractions which condense in the sections 6 and 1, will generally contain little or no tar acids of commercial value, although this will depend upon the kind of pitch being produced. These fractions are therefore generally not treated for tar acids. The fraction condensed in section 8 contains valuable tar acids and is drawn off into the treating chamber, or tar-acid still, II. The oil vapors subsequently condensed in section 9 and in the worm condenser 9 will also contain valuable tar acids. These may be recovered by extraction of the condensed oils or by extraction of the vapors before condensation, as described below. Furthermore, depending upon the conditions of operation, especially upon the melting point of the pitch produced, oil containing valuable acids may be produced in section 1 and this oil may then be run into the tar-acid still II, together with oil from section 8 and treated simultaneously with it, or it may be separately treated. The neutral oil or oil of relatively 10W tar-acid content which results from this selective distillation of tar acids from the tar-acid-containing distillate in the still II, is drawn off into the tank I8.

Fresh caustic is added to the caustic extractor I5 thru the feed pipe I9. Carbolate formed in the extractor together with fresh caustic is drawn off thru the line 20, passed by the pump 2l to the heat interchanger 22 and sprayed into the gases by means of the nozzles 23. Similarly, the partly saturated caustic-containing carbolate is Withdrawn thru the line 20', to the pump 2| and forced thru the heat interchanger 22 to the sprays 23. The temperature of the causticcarbolate solution is controlled by the heat interchangers 22 and 22 so that there is little cr no condensation of neutral oils in the caustic extractor. The carbolate formed is drawn oif thru the line 24 and collected in the tank 25.

As one example of carrying out the process in the apparatus of Fig. 1, the treatment of cokeoven tar with a tar-acid content of 3% will be considered. The tar enters the heater I at a temperature in the neighborhood of C. It is heated in the pipe coil or tubular heater to a temperature of 400 C. and is ashed in the vapor box 2. The vapors leave the Vapor box thru the mainI 5 at a temperature of about 380 C. and contain oils boiling up to and above a temperature of 400 C. The pitch drawn off from the Vapor box has a melting point in the neighborhood of 210 F. and is suitable for use as fuel pitch. The fraction collected from section 8 may boilfrom 198 C. to 270 C. and is drawn off into the tar-acid still II where it is treated for tar acids. This oil represents, for example, 15 to 20% of the total distillate and contains, for example, 20 to 40% of the tar acids present in the tar.

The treatment of the oil in the tar-acid still may be regulated to recover a desired percentage of its tar-acid content; for example, by recirculating inert gases thru the still at a rate of 200 cubic feet per gallon of tar treated, and if the oil enters the still at a temperature of 150-1'10 C., 'l5-90% of the tar acids in the oil will be recovered. 'Ihe gases and vapors enter the caustic extractor at about -160" C., and are sprayed with caustic soda solution of about 49 Baume.

In carrying out the inert gas distillation, the uncondensed neutral oils resulting from extraction of the tar acids may be recirculated and serve as a part of the inert gas, the balance being largely steam (which may be continuously supplied thru thc pipe |3) or products of decomposition of the oil or air originally present in the system at the start. A bleed condenser 26 is provided to vent any excess of gases to the atmosphere and maintain the inert gas distillation cycle under constant pressure, and to condense oil vapors from the vented gases.

Fig. 2 shows somewhat similar apparatus with a heater Ia and vapor box 2a, a fractionating co1- umn and means for withdrawing condensate from the section 'Ia into the tar-acid still I la, but the cycle for the inert gas distillation includes in addition to the caustic extractor |50, a condenser 30. Both tar acid and neutral oils are distilled in the still I Ia. In the caustic tower 5a tar-acid vapors are extracted and removed from the cycle; The resulting gases include vapors of neutral oils. On cooling in the condenser 30 a portion of the neutral oils is condensed. The condenser is not a total condenser but a partial condenser so that the gases leaving the condenser 30 and returning to the still la include vapors of neutral oils.

Adapting the example recited in connection with Fig. l to the apparatus shown in Fig. 2, with a tar-acid oil with a boiling range of 198 to 270 and tar-acid content of about 10-12% drawn off from the section 'Ia into the oil-treating tower Ila at a temperature of 15G-170 C., and with gases being recycled thru the treating chamber lia at the rate of 200 cubic feet per gallon of tar distilled, neutral oil containing less than 1.5% tar acids may be collected in the condenser 30. The oil drawn on into the receiver |8a will necessarily be of different composition from the oil obtained by the process of Fig. l, because of removal of some of the oils in condenser 30 in addition to removal of tar acid.

Fig. 3 shows apparatus somewhat similar to the apparatus of Fig. l, but instead of a fractionating column in conjunction with Condensers, single oil Condensers are shown at lb, 8b, and 9b connecting with the Vapor box 2b. Condensers of any suitable type may be employed, e. g. heat interchangers in which the tar is preheated, or condensers using water o1' oil as the Vcooling medium. Instead of separate condensers 8b and 9b, a single total condenser may be employed. Fig. 3 differs from Fig. 1 in that the oil from the rst condenser 'Ib is drawn off into the still IIb in which it is treated by inert gas distillation for recovery of tar acids. The arrangement of Fig. 3 is used when a low melting point pitch is produced, since it will be generally found that the first oil condensate contains tar acids of commercial value.

When using the arrangementvof Fig. 3, for example, tar may be heated in the pipe coil heater Ib to a temperature of about 345 C., and flashed in the vapor box 2b so that the vapors pass from the vapor box to the condenser thru the main 5b at a temperature of about 330 C., and the pitch drawn ofl into the receiver 4b has a melting point of about F. The oil fraction drawn 01T section 'Ib thru the line |21)` into the treating tower IIb will have a boiling range of about 230 C. to over 350 C.

The apparatus of Fig. 4 shows a condenser 3| following the oil-treating still I Ic and before the caustic tower I 5c. Part of the oil vapors leaving the tower I Ic are condensed and the gases cooled before being brought into contact with caustic. This arrangement is particularly applicable when the total first oil cut from the vapors leaving the vapor box 2c, which is withdrawn from section 1c, yields vapors during the inert gas distillation which are too hot to be brought into contact with caustic solutions. It is also applicable when it is desired to recover part of the tar acids and the lower boiling oils condensed in 'Ic with the heavy oil as a tar-acid oil condensate withdrawn from 3| into the receiver 3|.

Fig. 5 shows schematically apparatus for passing the vapors from the vapor box 2d, rst thru the condenser 8d from which a high boiling fraction containing little or no Valuable tar acids is recovered, then thru the condenser 'Id from which 9 a fraction containing valuable tar acids 1s recovered, then thru a caustic tower 32 and then thru a condenser 9d. The oil from the condenser 'Id is drawn oli into the tar-acid still d and after vaporizing the tar acids therefrom they are converted to carbolate in the caustic tower |5d. Only a portion of the total Valuable tar acids in the tar is condensed in the condenser ld. Other tar acids pass thru the condenser Id in vapor form and these are extracted in the vapor phase in the caustic tower 32. Any suitable type of gas-liquid-contact apparatus may be employed for bringing the caustic into contact with the tar-acid-containing gases. In Figs. 5 and 6 the caustic towers are shown as packed towers.

The vapors enter condenser ld at such a high temperature that it is not practical to extract tar acids from them in the vapor phase; therefore, they are cooled in this condenser to a temperature such that when they pass into the extractor 32 they can be extracted by direct contact with concentrated caustic. This invention, however, offers a means of reconverting into vapors the valuable tar acids which have been condensed in the oil from section 'Id and recovering them as carbolate simultaneously with the recovery of the tar acid vapors in extractor 32. From the caustic extractor 32 the gases pass to the condenser 9d, which may be a total condenser as shown, or several separate condensers. In this condenser neutral oils are recovered.

As an example of carrying out the process, cokeoven tar with a tar-acid content of 3% may be heated in the heater Id to a temperature of 400 C., and flashed inthe vapor box 2d. The vapors leave the vapor box at a temperature of about 380 C., and are cooled in the condenser Ed to about 300 C. In the condenser 'Id the gases are cooled to a temperature of about 200 C., or lower, and the oil condensate is drawn off into the taracid still ||d in which it is treated for the recovery of tar acids. The vapors pass thru the caustic tower 32 without substantial cooling and are sprayed with a concentrated solution of caustic. This converts the tar acids tov carbolate, which is collected in the tank 33 and the extracted oil Y aolrtvcaA vapors passaonto the condenser 9d. Under these conditions about.4045% of the tar acids lin the tar is condensed with the oil withdrawn from the condenser ld and of this asA much as Sil-% may be recovered as oarbolate in the tower l5d. About 30-35% more of the tar acids in the tar may be recovered as carbolate in the extractor 32. The proportion of tar acids recovered in the condenser ld may be varied and the proportion ren covered Vas carbolate in the caustic tower 32 will Vary accordingly, depending upon the conditions of operation.

In most respects the apparatus of Fig. 6 is the same as that shown in Fig. 5 but the operation is changed in that the carbolate from the caustic tower 32e is sprayed into the caustic tower |5e instead of being separately collected. Caustic is added to the tower 32e in excess over that required for extracting the tar acids in the vapors leaving le, and this excess is used for extracting tar acids from the gases and vapors in the caustic tower I 5e. However, fresh caustic may be added to the tower 15e, if desirable.

In Figs. '7, 8 and 9 an ordinary tank still or simple still is shown. The still comprises a metal tank 5I which is heated from a hre-box 52.

Fig. 7 shows ap-paratus designed for recovering tar acids from a batch distillation process. As the tar in the still is gradually heated, higher and higher boiling oils are given olf. Until the temperature ofthe vapors reaches 200 C. the vapors may be passed thru the causticY extractor 53 and there extracted directly with hot concentrated caustic to produce carbolate. The vapors remaining after this extraction of tar acids may then be passed to condensers to recover the remaining neutral oils. As the distillation progresses and the vapors leave the still at a temperature around 200 C. or higher, the vapors will no longer be passed thru the extractor 53 but will be passed to condensers. Two condensers 54 and 55 are shown inthe drawings. The oil which condenses in the condenser 54 is first extracted for tar acids and then as the temperature of the vapors goes still higher it may be desirable to rst cool the vapors in the condenser 54 to condense high boiling oils which are substantially free from valuable tar acids and then on further cooling in the condenser 55 throw down a tar acid oil. Both of the condensers 54 and 55 are connected with the tar-acid still Hf. Both of the condensers are also connected with oil storage tanks 54' and 55. The oilfrom the condensers may be run to these storage tanks or the oil from either of these condensers may be run to another oil storage tank, or if it is a tar-acidcontaining o-il it is run into the tar-acid still I lf. In the taracid still it is subjected to inert gas distillation while it is still hot 'and tar acids are extracted in the caustic extractor I5j. During the early stages of the distillation, when tar acids are extracted inthe extractor 53, neutral oils may be condensed in the condensers 54 and 55 and be drawn 0E into suitable storage tanks. It is not necessary that the tar acid be extracted from the vapors given off during the early stages of the process, but :these vapors may be cooled to produce a tar-.acid oil.

As the recovery of tar acids does not take place simultaneously in caustic towers 53 and 51, one caustic tower can be employed to make both extractions.v In this case by making suitable pipe connections vapors from the still would run directly through caustic tower 53 until the vapor temperature reached 200 C.,- then the vapors would be made to bypass caustic tower 53 and oil condensed in condensers 54 and 55 would be run intol inert gas still Ilf and the vapors from the inert gas still passed through caustic tower 53 for extraction.

In Fig. 8 the still is equipped for continuous distillation, the tar being fed continuously to the still and pitch being continuously drawn off from it. The vapors pass thru the condensers El, 62 and 53 in series in which they are fractionally cooled. If a high melting point pitch is produced heavy oil from the condenser 6| and possibly alsoI the oil from the condenser 52 will be drawn off into separate storage tanks and will not be extracted for tar-acid content. The heavy oil may all be condensed in the condenser 0l and taracid oils may then be condensed in the condensers 52 and E53. The tar-acid oils that are to be extracted may be drawnV off in separate tar-acid stillsfor the separate recovery of tar acids of different boiling range or they may be drawn off into thev same tar-acid still, Hg, as shown.

In Fig. 9 a plurality of tar stills 1|, 12, 13 and 14 are shown with the tar flowing thru them in series in cascade. The tar is subjected to progressive distillation inthe variousstills and pitch of the desired melting point is drawn off from the last still of the series. Light oils are distilled offI in the still 'll and condensed in the condenser 15. These light oils are drawn 01T to a suitable storage tank. If high melting point pitch is produced the heaviest oils vaporized in the still 'i4 and condensedin the condenser 'i6 are likewise advantageously drawn off into separate storage tank. One or both of the intermediate fractions distilled in the stills 'l2 and 'i3 and condensed in the condensers 71 and'l are drawn off into the tar-acid still l lh and treated for the recovery of tar acids.

Different types of condensing means may be employed in connection with the different stills shown. Tar acid extractors of various types may be employed. In the tar-acid cycle in which the tar acids are vaporized in inert gases and then extracted in a caustic extractor, condensers may be employed either before or after the caustic extractor, as indicated in Figs. 4 and 2, respectively, and the apparatusshown in any one of the figures may be modified or added to in this or other ways all within the scope of this invention.

Although the invention is described more particularly as applied to the distillation of coke-oven tar, it may be applied to the treatment of other tar-acid-containing tars such as vertical retort tar, gas-retort tar and other coal tars, and also to the treatment of distillate such as coal-tar distillate.

I claim: l

1. The method of treating Vliquid tar-acidand neutral-oil containing hydrocarbon material, which comprises distilling tar acids and'neutral oils therefrom, cooling the vapors resulting from the distillation to condense both tar acids and neutral oils, and then distilling tar acids from this condensate by the self-contained heat thereof.

2. The method of treating a batch of tar-acidand neutral-oil-containing hydrocarbon material, which comprises distilling the same, cooling vapors which distill oir at a temperature above 200 C. so as to condense tar acids and neutral oils therefrom, and then distilling tar acids from the condensate in a current of inert gases while the condensate is still at an elevated temperature.

3. The method of treating tar-acidand neutral-oil-containing hydrocarbon material, which comprises distilling the same by a process of continuous distillation according to which the vapors leave the still at a temperature of at least 200 C., cooling the vapors to condense tar acids and neutral oils therefrom and vaporizing tar acids from the condensate in a current of inert gases while the condensate is still at an elevated temperature.

4. The method of treating liquid tar-acidand neutral-oil-containing hydrocarbon material, which comprises distilling tar acids and neutral oils therefrom by a process according to which the vapors leave the still at a temperature of at least 200 C., cooling the vapors resulting from the distillation to condense both tar acids and neutral oils and then distilling tar acids from the resulting condensate in a current of inert gases by the self-contained heat of the condensate.

5. The method of distilling tar, which comprises distilling tar acids and neutral oils therefrom at a temperature of at least 200 C., cooling the resulting oil vapors to produce a tar-acid-containing distillate, distilling tar acids from the distillate, using the self-contained heat of the distillate in effecting the distillation, and extracting tar acids from the resulting vapors by direct contact with a caustic alkaline reagent.

6. The method of treating liquid tar-acidand neutral-oil-containing hydrocarbon material, which comprises heating the material to a temperature such that, on flashing, distillate comprising tar acids will distill therefrom, flashing the heated material, condensing from the resulting vapors an oil fraction comprising tar acids, and distilling tar acids from this fraction in a current of inert gases while the fraction is still at an elevated temperature.

7. 'I'he method of treating liquid tar-acidand neutral-oil-containing hydrocarbon material, which comprises distilling tar acids therefrom at a temperature above 200 C., condensing from the resulting vapors an oil fraction comprising tar acids, distilling tar acids from this fraction in a current of inert gases including neutral oil vapors, spraying a caustic alkaline solution into the vapors resulting from the inert gas distillation soas to extract tar acids, and recycling at least a portion of the gases and resulting neutral oil vapors into contact with the oil fraction.

8. The method of distilling coal tar, which comprises distilling tar acids and neutral oils from the tar, cooling the resulting vapors to condense neutral oils and part of the tar acids therefrom leaving uncondensed tar acid vapors, vaporizing tar acids from this condensate and extracting tar acids from the vapors by direct contact with an alkaline reagent, and extracting tar acids from the uncondensed vapors by bringing them into direct contact with a caustic alkaline reagent, thereby removing tar acids from uncondensed vapors in the form of their alkaline salts.

9. The method of treating coal tar, which comprises heating the tar to such a temperature that, on ashing, tar acids will vaporize, flashing the heated tar, cooling the resulting vapors so as to obtain a tar acid oil, vaporizing tar acids from the resulting condensate by the self-contained heat of the condensate, and extracting tar acids from the vapors by bringing a caustic alkaline reagent into direct contact therewith.

10. The method of treating tar, which comprises distilling tar acids from the tar, cooling the resulting vapors to condense only a part of the tar acids, extracting the resulting vapors with an excess of caustic alkali solution thereby forming a caustic-carbolate solution, drawing the tar acid oil from the condenser off into a tar acid still, vaporizing tar acids from the tar acid oil in the tar acid still while the tar acid oil is still hot, and bringing the caustic carbolate solution from the caustic extractor into contact with the resulting vapors to extract tar acids therefrom.

11. Apparatus for the distillation of tar cornprising a pipe coil, a Vapor box, means for heating the pipe coil, means for passing tai` through the pipe coil to the vapor box, a condenser, means for passing vapors from the vapor box thru the condenser, a tar-acid still, av caustic extractor adapted to contact caustic alkali with the tar acid vapors and means for passing vapors and gases from the tar-acid still to the caustic extractor, and means for drawing oil off from the condenser to the tar-acid still.

12. Apparatus for the distillation of tar comprising a pipe coil, a vapor box, means for heating the pipe coil, means for passing tar through the pipe coil to the vapor box, a condenser, means for passing vapors from the vapor box to the condenser, a tar-acid still, a caustic extractor adapted to contact caustic alkali with the tar acid vapors, means for repeatedly recirculating vapors serially thru the tar-acid still and the caustic extractor, and means for passing condensate from the condenser to the taracid still.

13. Apparatus for the distillation of tar cornprising a tar still, at least two condensers, means for passing vapors from the still thru a first condenser and then thru the other condensers in series, a tar acid, means for conveying condensate from at least one of the condensers, not the rst condenser, to the tar acid still, a caustic extractor adapted to contact caustic alkali with the tar acid vapors, means for repeatedly recycling vapors serially thru the tar acid still and the caustic extractor.

14. Apparatus for the distillation of tar comprising a tar still, a condenser, means for passing vapors from the still to the condenser, a tar acid still, means for passing condensate from the condenser to the tar acid still, a caustic extractor adapted to contact caustic alkali with the tar acid vapors, a second condenser, means for repeatedly recycling gases thru the tar acid still thru the caustic extractor and then thru the second condenser in series.

15. Apparatus for the distillation of tar comprising a tar still, a condenser, means for passing vapors from the still to the condenser, a tar acid still, means for passing condensate from the condenser to the tar acid still, a secondu condenser, a caustic extractor adapted to contact caustic alkali with the tar acid vapors and means for repeatedly recycling gases thru the tar acid still, the second condenser and the caustic extractor in series.

16. Apparatus for the distillation of tar comprising a tar still, a condenser, a caustic extractor adapted to contact caustic alkali with the tar acid vapors, means for passing vapors from the still thru the condenser and then thru the caustic extractor, a tar-acid still, means for drawing condensate off from the condenser to the tar-acid still, a second caustic extractor, and means for passing vapors from the tar-acid still to the second caustic extractor.

1'7. Apparatus for the distillation of tar comprising a tar still, a condenser, a caustic extractor adapted to contact caustic alkali with the tar acid vapors, means for passing vapors Afrom the still thru the condenser and then thru the caustic extractor, a tar-acid still, means for drawing condensate 01T from the condenser to the tar-acid still, a second caustic extractor, means for passing vapors from the tar-acid still to the second caustic extractor and means for conveying carbolate from th e first caustic eX- tractor to the second caustic extractor.

18. Apparatus for the distillation of tar comprsing a tar still, three condensers, means for passing vapors from the still thru the condensers in series, an inert gas still, a caustic extractor adapted to Contact caustic alkali with the tar acid vapors, means for recycling gases thru the inert gas still and the caustic extractor, means forconveying condensate Without substantial reduction in temperature from the second condenser of the series to the inert gas still and means for separately collecting condensate from the rst and third condensers.

19. The method of recovering tar acids fro-rn tar, which comprises distilling the tar, cooling the resulting vapors to condense part but not all of the tar acid vapors thereby producing taracid-containing condensate, vaporizing tar acids from the condensate While still hot in a current of inert gases containing neutral oil vapors, cooling the resulting gases and vapors to condense a part of the tar acid oil vapors and then extracting remaining gases and vapors for tar acids by contact with an alkaline reagent.

WILFRED M. BYWATER.

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