US2992070A - Steam-stripping of sulfuric acid containing coke-forming impurities - Google Patents

Description

E. J. HENLEY STEAM-STRIPPING 0F' SULFURIC ACID CONTAINING July 11, 1961 COKE-FORMING IMPURITIES Filed Sept. 22, 1958 mrOO .vom @I IOoZ ERNEST J, HENLEY ATTORNEY United States larent 2,992,070 STEAM-STRIPPING F SULFURIC ACID CON- TAINING COKE-FORMING IMPURITIES Ernest J. Henley, New York, N.Y., assignor to American Cyanamid Company, New Y'ork, N.Y., a corporation of Maine Filed Sept. 22, 1958, Ser. No. 7 62,524 3 Claims. (Cl. 23-173) This invention relates to an improvement in processes wherein sulfuric acid containing coke-forming organic impurities is stripped by the injection of superheated steam and more particularly to a method of controlling the particle size and agglomeration of the coke formed during such stripping processes.

Sulfuric acid having a substantial content of polymerizable hydrocarbons and other tarry impurities must be dealt with as a Waste material in a number of industries.

Representative by-products of this character are spent alkylation acids, such as those resulting from the production of high octane gasoline and yfrom the fo-rmation of diarylethanes by the condensation of acetylene with aromatic hydrocarbons. yFor example a typical spent alkylation acid produced in the condensation of butylene with paraffins such as lpropanes and butanes may contain about 83-90% of sulfuric acid, 4-8% of unsaturated hydrocarbons and 5-8% of carbon, the remainder being free oil. A spent sulfuric acid from the production of diarylethanes as exemplified by the process of U.S. Patent No. 2,734,928 may contain about 6575% of sulfuric acid, about l0-25% of arylsulfonic acid, about 36% of tar together with water and metallic mercury liberated from the catalyst. These and other similar spent sulfuric acids are frequently treated by stripping with superheated steam, which decomposes and volatilizes their more volatile impurities -and converts the heavier residues into coke. Thus, the stripping of spent sulfuric acid from the production of diarylet'hanes by means of superheated steam is de scribed in U.S. Patent No. 2,832,810.

When such steam-stripping processes are operated on a commercial scale the formation of large masses of coke in the stripping kettle constitutes a serious problem. Such coke masses, which may reach the size of l -foot or more in diameter, can cause the stalling or breaking of agitators and other damage to the equipment and in smaller sizes may cause the plugging of valves and pipe lines. It is a principal object of the present invention to provide a method of controlling the particle size of the coke formed in such steam-stripping processes and to prevent its agglomeration into large masses.

I have found that this object can be accomplished by mixing finely divided non-reactive solids with the spent sulfuric acid before the superheated steam is injected therein. The presence of such finely divided solids prevents agglomeration of the coke particles into masses and ensures the formation of a granular coke that will not damage or clog the equipment and that can be readily separated from the clarified acid by filtration when the steam-stripping process is completed.

Although agglomeration of the coke into large masses can be prevented by the presence of finely divided solids of almost any character, provided they are not reactive with the sulfuric acid, I have found that the best results are obtained with solids having a porous and absorbent character. Solids of this nature, such as finely divided diatomaceous earth of the ykind used as a filter precoat or filter aid, appear to absorb and adhere to the coke particles as they are formed and thus prevent their agglomeration into larger masses. Coke produced by the process is also absorbent and may be used. The qu-antity of diatomaceous earth or other finely divided solid to be used may vary through a wide range, depending on the charfr ICC acter of the carbonaceous impurities present in the spent sulfuric acid, but will ordinarily be from about 1/2 to 4 times the weight of the tars or other coke-forming impurities in the spent sulfuric acid.

The operating conditions to be maintained during steamstripping of spent sulfuric acid to which diatomaceous earth or other finely divided solids have been added are ordinarily about the same as those employed in the absence of added solids. The spent acid-added solids mixture is heated to stripping temperatures, which are ordinarily within the range of about 140-190 C. depending largely on the strength of the sulfuric acid being stripped. Superheated steam having a temperature higher than the stripping temperature and usually within the range of l300 C. is injected into the acid preferably with mechanical agitation. The injection of steam is continued until the desired degree of decomposition and coking of the impurities has been attained; this may require from about 1 hour to 6 hours or longer and is also dependent to a considerable extent on the strength and temperature of the sulfuric acid. The volatiles removed from the acid may be recovered by condensing the steam if desired.

After completion of the stripping the sulfuric acid containing the suspended solids and coke -is preferably cooled and filtered. It is an important advantage of the invention that this filtration is materially aided by t-he relatively uniform particle size and granular condition of the coke produced in the presence of added solids such as diatomaceous earth. Any suitable type of filter may be used such as a plate and frame filter press or a rotary filter since ordinarily the filter kcake is open and easily drained. A clarified sulfuric acid suitable for fortification and reuse is ordinarily obtained, while the coke may be burned for its fuel value or for recovery of the added finely divided solids.

The invention will be further described with reference to the accompanying drawing, the single figure of which is a flow sheet illustrating its application in the recovery of a spent sulfuric acid obtained in the alkylation of toluene with acetylene. On this drawing an alkylator indicated generally by reference numeral 1 is charged with toluene, sulfuric acid and mercuric sul-fate catalyst and with acetylene gas -at the rates indicated in the following specific example and is maintained at 0-10 C. by a coolant such as liquid ammonia introduced through line 2. The resulting mixture of ditolylethane, excess toluene, mercury, spent sulfuric acid and toluene sulfonic acid together with the tars formed during the reaction is discharged through line 3 into a settling tank or decanter 4, where it separates by gravity into `an upper alkylate layer and a lower layer of spent sulfuric acid. The spent acid, which contains the toluene sulfonic acid and much olf the mercury and tarry impurities, is discharged through line 5 into an acid stripper 6 Where it is mixed with diatomaceous earth and stripped by the injection of superheated steam. During the stripping much of the toluene sulfonic acid is decomposed into toluene and oxides of sulfur which are volatilized along with the mercury and volatile components of the tar. The steam and vapors pass through line 7 into a scrubber 8 where they are Washed with a recirculating stream of cold aqueous sodium hydroxide solution. The uncondensed gases escape through a vent 9, the mercury is recovered from the base of the scrubber in a mercury pot 10, and the toluene is separated in a separator 11 and returned to the toluene supply tank. The oxides of sulfur react with the aqueous caustic solution and are recovered as sodium sulfate.

When stripping of the spent acid is complete the contents of the acid stripper are cooled, preferably by vacuum cooling, and are discharged through line 12 to a filter 13. Because of the granular condition of the colze a continuous rotary lter of the type illustrated diagrammatically on the drawing may be used. The claried sulfuric acid obtained as filtrate from this lter is collected in a storage tank 14 while the coke is discharged for combustion or other disposal.

The quantities of materials and operating conditions in a preferred embodiment of this process are given in the following specific example. It should be understood, however, that this example is given primarily for the purpose of illustrating the invention, and should not be construed as a limitation thereof.

Example The alkylator 1 was operated continuously for a time such that 1500 lbs. of acetylene were reacted with a mixture of 37,400 lbs. of toluene, 4766 lbs. of sulfuric acid, 250 lbs. of water and 13 lbs. of mercurio sulfate while maintaining a reaction temperature of 5 C. The resulting mixture was discharged -into the decanter 4 where it separated into an upper layer containing the ditolylethane product and excess toluene and a lower acid layer. This layer weighed about 6500 lbs. and contained about 65% of H2504, about 22% of toluene sulfonic acid, 7% of water, 6% of tar land about 5 lbs. of mercury.

The lower layer was drawn off and charged into the acid stripper 6 and agitated as 780 lbs. of diatomaceous earth of a grade used as a lter aid were added and mixed. Superheated steam having a temperature of about 200 C. was then introduced, While continuing the agitation, until a temperature of 171-173 C. was reached, after which the batch was stripped by continuing the steam addition for 2 hours while maintaining this temperature. A total of 1440 pounds of steam was used. The toluene, oxides of sulfur, mercury and steam were passed through line 7 into the scrubber 8 where they were recovered by contact with a recirculating stream of aqueous 10% sodium hydroxide solution. The mercury settled by gravity into the mercury pot 10 while the oxides 4l of sulfur reacted with the alkali. About 1000 lbs. of toluene were recovered as an upper layer in the separator 11 and returned to the toluene storage tank.

During the stripping process there was no agglomeration of the coke into large masses. A granular mixture of coke and diatomaceous earth particles having a small and uniform particle size was suspended in the stripped acid. This was readily separated from the acid by liltration on the rotary filter 13.

What I claim is:

l. A method of decomposing and removing tarry impurities in a spent al'kylation sulfuric acid while preventing the formation of agglomerated coke masses therein which comprises mixing finely divided non-reactive solids with said acid and then injecting Superheated steam there- 2. A method of decomposing and removing tarry impurities in a spent alkylation sulfuric acid while preventing the formation of agglomerated coke masses therein which comprises mixing diatomaceous earth with said acid and then injecting Superheated steam therein.

3. A method according to claim 2 in which the spent alkylation acid is obtained by reacting an Ialkylbenzene with acetylene in the presence of a dispersion of a mercury salt in strong sulfuric acid, settling the resulting alkylate mixture into layers, and drawing off the bottom layer containing the spent acid.

References Cited in the file of this patent UNITED STATES PATENTS 2,624,697 Clouse et -al Jan. 6, 1953 2,709,676 Krebs May 3l, 1955 2,832,810 Sm-olin Apr. 29, 1958 2,863,823 Moser Dec. 9, 1958 2,886,514 Gn'fn et al May 12, 1959 2,895,904 Jones et al July 2l, 1959

Claims (1)

1. A METHOD OF DECOMPOSING AND REMOVING TARRY IMPURITIES IN A SPENT ALKYLATION SULFURIC ACID WHILE PREVENTING THE FORMATION OF AGGLOMERATED COKE MASSES THEREIN WHICH COMPRISES MIXING FINELY DIVIDED NON-REACTIVE SOLIDS WITH SAID ACID AND THEN INJECTING SUPERHEATED STEAM THEREIN.

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