US2458777A - Purification of hydrocarbons - Google Patents

Description

Jan. 11,' 1949.

2 Sheets-Sheet 1 Filed D00. 17; 1945 m m a m 0 3 mam 0 VH9 s 7 NW Y I. R E 2 E. N R um 6 o oh n-. w m w 1 7 N T, i m. xmizou but uzHzwm I a FN F Own. 0- a ow .II x v Q Patented Jan. 11, 1949 a UNITED STATES PATENT @FFHCE PURIFICATION OF HYDROCARBQWS Harold J. Hepp and Howard B. Sailors, Bar-tiesville, kla., assignors to Phillips Petroleum Company, a corporation oi Delaware ApplicationDecember 17, 1945, Serial No. 635,590

Claims.

This invention relates to the treatment of hydrocarbons. In one of its more specific aspects it relates to a method for the purification of benzene and its homologues. I

Benzene and its lower alkyl homologues have long been products of commercial importance. The destructive distillation of coal has been and is a major source of such compounds. In more recent years, the cracking of petroleum has provided another source of these compounds, and the products of this operation at least much of the time contain benzene and alkyl benzene compounds in recoverable amounts.

Fractionation, with or without combination with such other process steps as absorption, is used as a means of recovery and separation of these compounds from the cracked products.

Suchmethods, however, do not readily yield pure products. Olefins, produced in large amounts by cracking of petroleum, are especially difllcult to separate from aromatic compounds by such means, and, consequently, the aromatic com- 7 pounds separated from mixtures of aromatics and olefins contain excessive amounts of oleflns for many uses. Treatment with sulfuric acid has been used for removing the olefins from these mixtures, although such side reactions as sulfonation leaves much to be desired in this method. Solid aluminum chloride has also been used asa treating agent in the removal of the olefinicimpurities from benzene and its lower alkyl homologues with satisfactory removal of the olefins.

One object of our invention is to provide a process for the treatment of hydrocarbon stocks containing benzene for the production of a pure benzene product. I

Another object of our invention is to provide a process for the removal of olefins from benzene stocks by the use of aluminum chloride-hydrocarbon complexes. a

Still another object of our invention is to pro- 1 vide a process for the removal of olefins from benzene and its lower alkyl homologues by the companying drawing, forms a part of this specification.

We have discovered that AlCla-hydrocarbon complexes, including those formed and used in from benzene and its lower alkyl homologues; and

that at least a portion of the chlorine in the complex can be recovered as HCl in the process.

Aluminum chloride is widely used as a catalyst in hydrocarbon conversion processes. The AlCla is used much of the time as a hydrocarbon complex, part of the time formed in situ from solid anhydrous AlClz, and part of the time the complex is manufactured outside the reaction zone and then charged to the reaction zone. In the operation of such processes, spent complex is discarded as a waste product, and even the disposal of this waste complex becomes at times a problem. The usual disposition is by burning or hydrolysis in water.

When anhydrous aluminum chloride is used in the treatment of parafilnic, olefinic, cyclic, or aromatic stocks aluminum chloride-hydrocarbon complexes are usually formed. We have found when such complexes are spent as regards further use in said processes that these complexes. are

cess of 40-per cent by weight of AlC13 and react vigorously with evolution of heat when shaken with water. The heat released usually is in excess of 280 calories per gram.

We have found that when such complexes are agitated with aromatic concentrates, as, for example, close-boiling benzene, toluene, xylene, etc.,

fractions separated from the products formed when petroleum fractions are treated by thermal or catalytic cracking processes, or obtained from coke-oven products or other suitable sources, any olefins and diolefins present are caused to polymerize to high-boiling substances readily separated from the aromatics by simple distillation, and/or react with the aromatics to form highboiling alkylated aromatics. To promote the polymerization and minimize the alkylation it is preferred to use AlCla-hydrocarbon complexes which are not too active, for example complexes having a heat of reaction in water of not above about 400 calories per gram. If desired, H01, H20, CHaCl, etc., may be used in amounts of 0.1 to about 5'per cent based on the aromatic concencompounds in the treated concentrate by such means as fractionation. 1

The recovery of HCl is made possible by the fact that the addition of water to AiCla-hydrocarbon complex leads to a hydrolysis reaction in'which HCl is released and oxygen-containing aluminum compounds are formed.

' The solubilities of complex in benzene and benzene in complex are rather high. For example, at room temperature, an AlCla-hydrocarbon com plex withdrawn from an ethylene-isobutane alkylation process increases in volume to about 2.5 to 3 times its original volume upon treating olefincontaining benzene. The benzene, in turn, will dissolve between about one to three per cent of its own volume of complex. It is, therefore, necessary to consider these mutual solubilities in designing apparatus for carrying out the process of this invention with best results.

Referring now to the drawing and specifically to Figure 1, a raw aromatic stock such as a benzene stock containing olefins is conducted through a pipe ill to a mixer I I, the mixer operating in substantially liquid phase between the temperatures of about 40 F. and 250 F., preferably between about 100 F. and 175 F., the pressure being at least sufficient to maintain the benzene stock in the liquid phase. Aluminum chloride-hydrocarbon complex from a subsequent step may be introduced to the mixer ll through a pipe l9. HCl, water to generate H], or other activator from any source may be introduced to the mixer H through a pipe, not shown. The raw benzene and complex are thoroughly mixed by a mechanical agitator. The reaction mixture of complex and hydrocarbon may be conducted from the mixer ll through a pipe l2 to a settler l3. In this settler the hydrocarbon and complex are allowed to separate by gravity, the hydrocarbon phase being the upper phase. The hydrocarbon phase is removed from the separator I3 .through a pipe I 4 and passed to a second mixer l6. Fresh complex, from a source not shown, for treating the benzene, is added through pipe IE to pipe I and carried to mixer i6. In this mixer the hydrocarbon and added complex are thoroughly mixed, the temperature and pressure limitations of mixer ll applying also to this mixer. In this mixer substantially complete reaction of olefin and partial spending of the newly added complex is obtained. Reaction mixture of complex and hydrocarbon are withdrawn through a pipe I! to a gravity settler [8, operating in the same mannet as the settler IS. The settled complex from this settler is recycled through pipe l9 to the mixer H, as mentioned herein before.

The hydrocarbon phase from settler I8 is passed through a pipe 29 to a pump 2|, then through a discharge line 22 into a tank 23. Water may be added through a pipe 24 to this tank 23 and/or through a pipe 25 to the transfer pipe 20. Settlings from the bottom of the settler tank 23 are withdrawn through a recycle pipe 26 and added to line 20. Spent complex is removed from the settler tank 13 through a pipe'2l and added to this pipe 26, thereby joining the recycle stream from the tank 23. In this tank and pump system the aluminum chloride complex reacts with the water and is decomposed, the amount of water added being such that it is substantially completely consumed in the complex decomposition, and the complex is intended to be decomposed substantially completely. We prefer to use not more than about three moles of water per mole of active AlCla. It is preferred that the recirculation stream carried by pipe 26 be comparatively large so that the heat evolved by the reaction of the water and complex does not lead to a large localized temperature rise as in pump 2|. Cooling of the tank 23, though not shown, may if necessary be accomplished by a heat exchanger in line 22 or by internal cooling within the tank itself. From the tank 23 the mixed product is removed through a pipe 30 to a stripper 32, this product containing the oils from the complex, benzene, and alkylated benzene as the major portion of its hydrocarbon constituents, and hydrogen chloride and some aluminum compounds from the hydrolysis of the aluminum chloride in the complex. Solids may be removed if desired by any conventional means, for example,

' by a sand filter a prior to stripping. Tank 23 should preferably be of such size that the stream carried by pipe 30 is low in solids, the major portion of the solids in the tank being carried in suspension in the lower part of the tank to be removed through pipe 26.- From the pipe 26 a part of the material passing therethrough is removed through a pipe 20 to a gravity settler 29 where at least a part of the solids and heavy materials is allowed to settle. The upper phase from this settler 29 is carried by a pipe 3| to pipe 30, thence through sand filter 301:, into the stripper 32. In this stripper 32 HCl is removed as an overhead product through pipe 33 while the hydrocarbons are removed through the bottoms line 34 and passed to further purification steps such as, for example, a water and/or a caustic wash and fractionation steps. From the settling tank 29 the lower phase containing the major portion oi the solids is removed through a drawofl line 35 and added to the contents of pipe 34. The hydrogen chloride from the overhead line 33 may be treated for removal of hydrocarbons and other contaminants by oil absorption, adsorption in charcoal or silica gel or by other means.

The reactions taking place in the two mixers I i and I8 and system of pump 2! and tank 23 are exothermic and it is therefore desirable to provide some means of temperature control at these points. Numerous methods of temperature control, for example, recirculation through a heat exchanger or internal cooling are well known and need not be, discussed in detail.

Figure 2 of the drawing shows a second embodiment of our invention. Olefin containing benzene stock is charged through a charge line 36 to a mixing pump 31, thence through a line 38 into a settling tank 39, operating in substantially liquid phase. This tank 39 contains substantially spent catalyst and hydrocarbon and is sufllciently large to serve as a gravity separator. The aluminumchloride containing complex is withdrawn from tank 39 and passed through a pipe 40 to the charge line 38 up stream of the pump 31, at which point the complex is contacted with the fresh benzene olefin containing stream.

as described.- Tlie hydrocarbon phase in Partially spent complex' from a subsequent source passesthro'ugh pipe 41 to pipe llandiscontacted with fresh benzene charge in-the "pump 81. In this pump 31 the aluminum chioride'complex is substantially completely spent in reacting with oleilns from the raw benzene stock. From tank 3! the hydrocarbon or upper phase, still containing a substantial amount of oleilns, is removed through a pipe ll and conductcdto a mixing pump 42. Fresh aluminum chloride'complex from a drier 88 ispassed through a pipe II and added to the partly treated benzene stream in line H these materials being thoroughly mixed or contacted in the mixing pump 12. The mix;- ture is passed through a pump discharge line '4: to 'a' second settling tank 44 which operates in about the same manner as tank". Settled complex from the lower portion of tank 44 is withdrawn through a pipe 45 and returned to pipe 4| at a point up stream of the pump 4!. The amount of this recycled stream should preferably be sufllciently large to prevent an excessively I large temperature rise due to reaction'oi olenns and complex in the pump 42. In this portion of the system, that is, pump -42 and tank 44, the

olefins remaining from the previous contacting are substantially completely removed and the complex partially spent. This double operation of the two mixers and their respective settling tanks is substantially a countercurrent operation.

A portion oi the recycled complex stream from pipe 45 is withdrawn therefrom and passed through a pipe .41, previously mentioned, topipe 40, this recycled complex then following a. path and led by a pipe 53 to a gravity settler SI. the

hydrocarbons separating and forming an upper phase in this settler and being conducted by a pipe 55 back to the benzene charge stock line It as a recycle stream. The complex phase in the settler 54 is withdrawn and passed through a pipe 58 to a mixing pump 80. when desired, at least a portion of this latter stream may be by-passed from pipe I6 through a pipe 51 to a pipe I and to join a hydrocarbon stream in pipe idjust prior to passage of the hydrocarbon stream into the water or caustic washer 5|. The settler 54 may also be by-passed by passing the substantially spent complex from pipe 53 through a pipe 5! to pipe" and thence to the mixing pump 8!. Water from a line 59 is introduced into the complex passing through pipe 56 and this mixture thoroughly mixed and contacted in the mixing pump 80. The water is added in such proportion that the active complex is at least'partially decomposed, and the water is substantially completely consumed in the decompositionreaction. As in the previous illustration, that is, the embodlment of Figure 1, the water is added at'the rate of about 1 to 3 moles per mole of active v rating tank 82- which is operating in such man- -ner as'to provide a vapor space in the upper portion or the tank. We prefer to operate this tank at temperatures above about 100 F. in order to reduce the solubility of the hydrogen chloride in the liquid hydrocarbons. The hydrocarbon liquid from this tank is withdrawn through a pipe and added to the complex in pipe 56 as a recycle stream prior topassage of the complex through the pump 00 so that any Water remaining in thetank a: will be consumed. A sufllciently large volume of the liquid in the tank 62 is recycled to absorb heat released by the hydrolysis reaction in pump 80 to prevent an excessive temperature rise at this point.

The hydrogen chloride accumulating in the vapor space of tank 82 is conducted through a pipe- II -to the drier 88 in which the I-ICl is dried by countercurrent contacting with fresh complex -added"to the drier through a complex charge line H. Dry hydrogen chloride is removed through a pipe 10 and conducted to suitable storage or utilization. notshown. A portion of the hydrogen chloride may be passed through -a pipe I3 and recycled to the pipe 40 as an activator for the substantially spent complex for treating the raw benzene charge stock. From the drier 68 complex is removed and passed through the pipe H and added to pipe M which is up stream oi the mixing pump 42.

A portion of the hydrolyzed complex from settling tank tl-whichis carried by recycle line 63 thesettler 65 may be by-passed by the use of a by-pass l4 and the hydrolyzed materials passed therethrough are then passed directly to pipe 50 prior to the water and/or caustic wash treatment in the treater 5|.

Figure 3 shows an alternative treatment of the aluminum chloride complex phase without hydrogen chloride recovery. In this embodiment our inventionis shown with reference to such a. mixer system as mixers I i and I6 of Figure 1. Substanti'ally spent complex is withdrawn from the settler i3 and passed through a pipe 15 to a mixing pump". In this pump water added through a line I1 and complex from the line 15 are contacted and the complex substantially completely decomposed. The products of this decomposition are then passed through a pump discharge line 82 into a settling tank 16 in which the oils and aqueous phases are separated by gravity settling. The lower or aqueous phase from this tank passes through a draw-oil line 18 back through pump 8| for recycle. As the aqueo s phase .in tank I6 builds up, a portion may be discarded through a discard line 83 to such disposal as desired. The amount of aqueous pha withdrawn through line 83 and the amount of 'water' added from line 11 are proportioned in such a manner as to maintain an HCl concentration in the aqueous phase in the settler 16 between the approximate limits of 1' to 8 per cent to minimize emulsifying and precipitation of the aluminum compounds. The upper hydrocarbon phase separating in settler 16 may be withdrawn page? through an overhead line 19 and passed into the hydrocarbon stream in line 20, then to a suitable water and/or caustic wash and fractionating system, not shown in this figure.

In some cases a single contacting of hydro carbon and complex will sumce and in this case the separator l3 may be omitted, water being added directly to the contactor eilluent.

The following examples will give a better understanding of the operation of our invention. In these examples the aluminum chloride hydrocarbon complex used was discarded catalyst from an ethylene-isobutane alkylation process and received no special treatment prior to use according to our invention. The heat of hydrolysis of the complex was about 325 calories per gram. The olefin-containing benzene stock was recovered fromthe efliuent of a low pressure high temperature thermal cracking operation in which the charge stock was propane. The benzene concentrate contained about 7 mole per cent olefins as determined by bromine titration.

Example I Five hundred cc. of the olefin-containing benzene was shaken with 100 cc. of the above described AlCla-hydrocarbon complex, the temperature kept at 160 F. or less during the treatment. The two liquid phases were separated. The upper phase, or hydrocarbon phase, was washed with water and caustic solution, and 331 cc. of

washed hydrocarbon recovered substantially free of olefins. The lower phase, or'complex phase, was poured on ice and decomposed, 190 cc. of oils being recovered after water and caustic washing.

By fractionation, 88-volume per cent of the hydrocarbon phase was recovered as 96 to 98 per cent benzene free of olefins. From the oils of the complex phase, 55 volume per cent was recovered by fractionation as 96 to 98 per cent benzene free of olefins. This result shows 79 volume per cent of the original olefin-containing benzene charged recovered as 96 to 98 per cent benzene free from olefins. This amounts to about 85 per cent recovery of the benzene charged.

In this example, more complex was used than absolutely necessary; There is a lower limit to the'amount of complex necessary to remove the olefins from the benzene, and is determined by the composition of the hydrocarbon to be treated and the nature of the AlCla-hydrocarbon complex.

Example II A two-stage countercurrent treatment of the olefin-containing benzene with AlCla-hydrocarbon complex was carried out using complex in the amount of five volume per cent of the hydrocarbon treated.

One hundred fifty cc. of the benzene concentrate was treated with complex to reduce its olefin content to about 3-4 per cent, and the complex discarded. Then this hydrocarbon was water several times, and the washed hydrocarbons distilled; 125 cc. of saturated benzene was recovered in this distillation. Based on the benzene content or the benzene concentrate, this is per cent recovery, thus indicating better results from multistage countercurrent treating. This benzene concentrate had a bromine No. of 0.1, thus indicating a product of good quality.

As a comparative example, a. batchwise singlestage treatment with five volume per cent complex reduced the unsaturation of the benzene concentrate from 7 to 3.5 per cent. 4

Equipment for use in our process should possess such corrosion resistant properties as not to be corroded unduly during operational or standby periods. Since water is added to aluminum chloride catalyst, or rather spent catalyst materials, hydrogen chloride is of course produced and this material in the presence of water is quite corrosive. Corrosion resistant equipment to withstand such action is readily available in commerce and of course, should be used where needed.

Many valves, pressure and temperature indi-' cating devices have not been shown in the drawing nor mentioned in the written description for purposes of simplicity. The installation and use of such equipment is well understood by those skilled in the art.

It will be obvious to those skilled in the art that many modifications of our process may be made and yet remain within the intended spirit and scope of our invention.

Having described our invention, we claim:

1. A continuous countercurrent process for the purification of a hydrocarbon stock containing an aromatic hydrocarbon selected from the group consisting of benzene, toluene and the xylenes, and containing olenfinic impurities, for the removal of this olefinic impurity and wherein the hydrocarbon stock remains otherwise substantially unaltered, comprising contacting in a first zone with respect to the flow of complex an aluminum chloride hydrocarbon complex and partially treated hydrocarbon stock containing said aromatic hydrocarbon and olefinic impurities in the ratio of a maximum of about 20 parts by weight of complex to parts by weight of hydrocarbon stock, separating, the so treated stock as a product of the process from the contacted aluminum chloride hydrocarbon complex, further contacting this latter complex in a second zone with the first mentioned hydrocarbon stock and with dry hydrogen chloride as an activator wherein the complex is substantially fully degraded and the hydrocarbon stock is partially purified, separating said partially purified hydrocarbon stock from the substantially fully degraded complex and passing said partially purifled hydrocarbon stock to the first contacting zone as the partially purified stock; adding water to the substantially iully degraded complex to libtreated with 7.5 cc. of fresh complex, and the hyerate hydrogen chloride, said liberated hydrogen chloride containing some moisture, and treating said liberated hydrogen chloride containing some moisture with a fresh aluminum chloride hydrocarbon complex to remove said moisture from said hydrogen chloride and passing this dried hydrogen chloride into said second zone as the first mentioned dry hydrogen chloride, and passing said aluminum chloride hydrocarbon complex "from the moisture removal step to said first contacting zone. 1

2. A continuous countercurrentprocess for the purification of a. hydrocarbon stock containing benzene and olefinic impurities for the removal 9 of said olefinic impurities and wherein the hydrocarbon stock remains otherwise substantially unchanged comprising contacting an aluminum chloride hydrocarbon complex in a first zone with respect to flow oi complex and partially treated hydrocarbon stock containingsaid benzene and some olefinic impurity in the ratio of a maximum of about 20 parts by weight of complex to 100 arts by weight of hydrocarbon stock, separating the so treated stock as a product of the process from the contacted aluminum chloride hydrocarbon complex, further contacting this latter complex in a second zone with the first mentioned hydrocarbon stock and with dry hydrogen chloride as'an activator wherein the complex is substantially iully degraded and the hydrocarbon stock is partially purified, separating said partially purified hydrocarbon stock from the substantially fully degraded complex and passing said partially purified hydrocarbon 7 stock to the first contacting zone as the partially purified stock; adding water to the substantially fully degraded complex to liberate hydrogen chloride, said liberated.hydrogen-chloride containing some moisture, and treating said liberated hydrogen chloride containing some moisture with a fresh aluminum chloride hydrocarbon complex to remove said moisture from said hydrogen chloride and passing this dried hydrogen chloride into said second zone as the first mentioned dry hydrogen chloride, and passing said aluminum chloride hydrocarbon complex from the moisture removal step to said first contacting zone.

3. A continuous countercurrent process for the purification of a hydrocarbon stock containing toluene and oleflnic impurities for the removal 01 said oleflnic impurities and wherein the hydrocarbon stock remains otherwise substantially unchanged comprising contacting an aluminum chloride hydrocarbon complex in a first zone with respect to fiow of complex and partially treated hydrocarbon stock containing said tolu- 10 drogen chloride into said second zone as the first mentioned dry hydrogen chloride, and passing said aluminum chloride hydrocarbon complex from the moisture removal step to said first con tacting zone.

4. A continuous countercurrent process for the purification of a hydrocarbon stock containing xylene and oleflnic impurities for the removal of said olefinic impurities and wherein the hydrocarbon stock remains otherwise substantially unchanged comprising contacting an aluminum chloride hydrocarbon complex in a first zone with respect to flow of complex and partially treated hydrocarbon stoclrcontaining said xylene and some oleflnic impurity in the ratio of a maximum of about 20 parts by weight of complex to 100 parts byweight of hydrocarbon stock, separating ,the so treated stock as a product of the process from the contacted aluminum chloride hydrocarbon complex, further contacting this latter complex in a second zone with the first mentioned hydrocarbon stock and with dry hydrogen chloride as an activator wherein the complex is substantially fully degraded and the hydrocarbon stock is partially purified, separating said partially purified hydrocarbon'stock from the substantially fully degraded complex and passing said partially purified hydrocarbon stock to the first contacting zone as the partially purified stock; adding water to the substantially fully degraded complex to liberate hydrogen chloride, said liberated hydrogen chloride containing some moisture,

. and treating said liberated hydrogen chloride ene and some oleflnic impurity in the ratio of a maximum of about 20 parts byweight of complex to 100 parts by weight of hydrocarbon stock, separating the so treated stock as a product of the process from the contacted aluminum chloride hydrocarbon complex, further contacting this latter complex in a second zone with the first mentioned hydrocarbon stock and with dry hydrogen chloride as an activator wherein the complex is substantially fully degraded and the hydrocarbon stock is partially purified, separating said partially purified hydrocarbon stock from the substantially fully degraded complex and passing said partially purified hydrocarbon stock to the first contacting zone as the partially purified stock; adding water to the substantially fully degraded complex to liberate hydrogen chloride, said liberated hydrogen chloride containing some moisture, and treating said liberated hydrogen chloride containing some moisture with a fresh aluminum chloride hydrocarbon complex to remove said moisture from said hydrogen chloride and passing this dried hycontaining some moisture with a fresh aluminum chloride hydrocarbon complex to remove said moisture from said hydrogen chloride and pass-' ing this dried hydrogen chloride into said second zone as the first mentioned dry hydrogen chloride, and passing said aluminum chloride hydrocarbon complex from the moisture removal step to said first contacting zone.

5. The process of claim 1 wherein the aluminum chloride hydrocarbon complex and the partially purified hydrocarbon stock containing said a aromatic hydrocarbon and olefinic impurities are REFERENCES CITED The following references are of record in the file oi this patent:

UNITED STATES PATENTS Soday Dec. 24. 1946

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