US2846357A - Refining of light and heavy petroleum hydrocarbons separately with alkali and cresylic acid followed by regeneration of the alkali solution - Google Patents

Description

Aug. 5, 1958 MCNEILL ETAL 2,846,357 REFINING OF LIGHT AND HEAVY PETROLEUM HYDROCARBONS SEPARATELY WITH ALKALI AND CRESYLIC ACID FOLLOWED BY REGENERATION OF THE ALKALI SOLUTION Filed Nov. 3. 1953 14 15 U10 ii .16 V f-zy f Lr F F INVENTORS ERIC McNEILL RONALD ALFRED DEAN ATTRNEES "United States REFINING F LHGHT AND HEAVY PETROLEUM HYDROCAREQRE SEPARATELY WITH ALKALI AND CRESYLIC ACID FQLLOWED BY REGEN- ERATIQN 0F THE ALKALI SOLUTION Erie Mcbleill and Ronald Alfred Dean, Sunbury-ou- Thames, England, assignors to The British Petroleum Company Limited Application November 3, 1953, Serial No. 390,024

2 Claims. (Cl. 196-32) This invention relates to the refining of petroleum hydrocarbons boiling within the gasoline range and produced by the catalytic cracking of petroleum hydrocarbons boiling within the wax distillate range.

It is known that such cracked gasoline contains acidic bodies, such as thiophenols or aromatic mercaptans, which have or give rise to oxidation products having a harmful effect on the stability of the gasoline, and it is therefore important to remove such acidic bodies from the gasoline and it is also known that this may conveniently be done by treatment with caustic alkali before the cracked gasoline has come into contact with air. The cracked gasoline also contains cresylic acids which would constitute a valuable product. Both thiophenols and the cresylic acids are largely concentrated in the upper part of the boiling range of the cracked gasoline and for this reason it is common practice to divide the cracked gaso line into a light gasoline boiling up to 160 to 170 C. and a heavy gasoline boiling between 160 to 170 and 220 C., since the thiophenols and cresylic acids are thereby concentrated in the relatively small amount of caustic alkali used for treating the heavy gasoline, the caustic alkali used for treating the light gasoline presents no disposal problem, and the light gasoline maybe readily and easily sweetened by known methods.

The principal objects of the present invention are firstly to make use of the cresylic acids present in the heavy gasoline in the refining of the light gasoline, and secondly to recover the cresylic acids as a valuable product after such use.

The present invention provides a process which consists in treating the heavy gasoline with caustic alkali solution in the absence of air for the production of a sweet heavy gasoline and a caustic alkali extract solution containing thiophenols and cresylic acids, treating the extract solution with free oxygen under oxidising conditions to convert the thiophenols into disulphides and yield a cresylic acid-containing caustic alkali solution, treating the light gasoline with said cresylic acid-containing caustic alkali solution in the absence of air to remove mercaptans from said light gasoline and provide a sweet light gasoline and a rnercaptan containing caustic alkali solution, and treating said mercaptan-containing caustic alkali solution with free oxygen under oxidising cOl'lditions to convert the mercaptans into disulphides and yield a cresylic acid-containing caustic alkali solution from which cresylic acid may be recovered in known manner.

It is important that the treatment of the heavy gasoline with caustic alkali solution be carried out so that the proportions of caustic alkali and cresylic acid in the extract solution are such as to adapt the extract solution, after removal of the thiophenols therefrom, for the removal of mercaptans from the light gasoline. This heavy gasoline treatment is advantageously carried out in a twostage countercurrent plant using suflicient caustic alkali solution of 20 to 30% w./v. concentration to remove both the thiophenols and the cresylic acids. Precau- 2,846,357 Patented Aug. 5, 1958 tions are taken to avoid contact with air during this treatment since this would lead to oxidation of the thiophenols rather than their extraction. The subsequent oxidation of the thiophenols and mercaptans in the caustic alkali extract solution after removal from the heavy gasoline may be eflfected by stirring the solution vigorously in an atmosphere of oxygen at atmospheric temperature and pressure. The reaction mixture rises in temperature during this process to a value of 50 to C. and the reaction is complete in a few hours. No catalyst is required although the presence of materials such as tannin increases the rate of oxidation. Alternatively, the oxidation may be carried out using air in place of oxygen in which case the air must be blown through the solution. The oxidation is not so rapid under these conditions but the method is quite practicable either with or without a catalyst. The best results are achieved when the air is passed in a very fine stream through the well-stirred extract solution, but other wellknown methods of securing the necessary intimate contact etween the. oxygen and the extract solution may be used. The disulphides formed are then separated and the caustic alkali treated with a hydrocarbon solvent such as kerosine to remove the last traces of disulphide. The caustic alkali solution obtained is relatively odourless but contains cresylic acid to the extent of between 5 and 10% w./v. and may therefore be used with advantage for the extraction of rnercaptans from the light gasoline. This operation should be carried out in the absence of air when a light gasoline is produced which, suitably inhibited, is relatively stable. Any cresylic acid partitioned into the light gasoline might assist in making the gasoline gum stable if a similar type of antioxidant were employed.

The oxidation of the mercaptans in the spent caustic alkali solution from treatment of the light gasoline may be carried out in a similar manner to the previous oxida tion step, with or-without the aid of a catalyst, whereby a mercaptan free sodium cresylate solution is produced. Well-known methods can be used to produce saleable cresylic acids from this solution. For example, by treating with flue gas, the cresylic acids can be made to separate leaving a soda ash solution which can :be used for such purposes as the removal of H 8 in the refinery.

The following experiment was carried out to demonstrate that cresylic acids contained in the heavy gasoline are substantially as effective in assisting the extraction of mercaptan by caustic alkali solution as cresylic acids derived from coal tar.

A casutic soda solution from the treatment of heavy catalytically cracked gasoline of l80220 C. boiling range was treated with oxygen in a well stirred vessel until all traces of mercaptans had disappeared. The super-natant disulphide layer was removed and the caustic soda-cresylic acid solution washed free of traces of disulphide with isopentane. The resulting solution was odourles s and contained about 7 percent by weight of cresylic acid and 20 percent by weight of sodium hydroxide. A similar solution was acids of coal tar origin but of the same boiling range as those recovered from the catalytically cracked gasoline, i.r. ZOO-225 C.

A litre of straight-run gasoline from Qatar crude which contained 0.623 percent of mercaptan sulphur was charged to a well stirred closed flask and all air was swept out. The gasoline was then agitated for five minutes with successive 200 ml. amounts of de-aerated caustic soda-cresylic acid solution made from the catalytically cracked gasoline. The experiment was repeated with the solution containing coal tar cresylic acid. The results are shown below and indicate little difference bemade using cresylic tween the two types of cresylic acid in the power of assisting mercaptan extraction.

' The process according to the invention may advantageously be carried out in an apparatus as diagrammatically illustrated in the accompanying drawing.

Tanks 1 and 1A are part of acontinuously operating two stage countercurrent treating unit operating on the pump and tank system. In this alight gasoline frompump 3, containing no material boiling above 160 to 170 C., is contacted with caustic soda solution; Care is taken to exclude oxygen from the gasoline prior to" and during treatment and the caustic soda solution in tank is preferably stripped of oxygen by a slow stream of inert gas free from CO from line 7. Tanks 2 and 2A and 6 and pump 4 are parts of a similar treating. plant for the gasoline boiling in the range 160 to 220 C. Similar precautions to exclude oxygen are also taken in this equipment.

The process is started by charging unused caustic soda solution from 20 to 30 percent w./v. of sodium hydroxide to the tanks 5 and 6. This is then pumped countercurrent to the gasolines at rates determined by their mercaptan contents. In general, the whole of the very high aromatic mercaptan content of the heavy gasoline can be removed but the mercaptans in the light gasoline are less easily extracted. The quantity of soda supplied to 1A should therefore be as large as possible, e. g. of the order of 20 percent by volume on the gasoline. The amount supplied to tank 2A will depend on the combined mercaptan and phenol content of the untreated heavy gasoline but sufficient caustic soda solution must be used to retain all extracted acid oils in solution in the soda leaving tank 2. A convenient quantity would be about 3 percent by volume on the gasoline.

The caustic soda solution from tank 2 is allowed to flow by means of pipe 8 to vessel 10 which is one of several" batch oxidisers. These are vessels fitted with hot water jackets and are agitated by vertical spindle centrifugal pumps. These pumps are so designed that in addition to circulating the contents of the tanks at least four times each hour, they serve as gas dispersers. Oxygen is preferably supplied by a pipe 14 into the suction line and the issuing gas is dispersed as minute bubbles by the high speed of the rotating impellor. These bubbles may be further sheared by suitable design of the stator. It has been found that a very high rate of oxidation is possible by this means and by careful control of the oxygen gas rate, 100 percent utilisation can be obtained. This is important as objectionable fumes are entirely eliminated. It may be necessary to heatthe contents to 100" F. initially but thereafter the heat of reaction will maintain the temperature and it may even be necessary to employ cooling water to avoid exceeding 150 P. which is considered as high a temperature as is expedient. If air is used,]an oxygen utilisation as high as 40 to 60 percent may be obtained but the disposal of the gases may give rise to a nuisance.

The oxidation step is carried out as a batch operation at the conclusion of which the disulphidesformed are allowed to settle on the surface. The caustic soda solution now containing phenolic compounds but no mercaptans is: pumped by pump 12 back to tanks 5 and-6 for reuse for light and,- if desired, heavy gasolines. The disulphides, which float as a well definedea'sily separablelayeron, the.

surface of the mercaptan free caustic soda solution, may be disposed of by line 16. These compounds at present require to be burned in refinery fuel but it is also possible by further oxidation to produce sulphonic acid derivatives which are potentially valuable as cheap detergents.

The used soda from tank 1 flows by line 9 to another series of batch oxidisers 11, similar to 10 already described. Here the mercaptans are oxidised by oxygen or air from line 15 and the disulphides eliminated by line 17. The caustic soda solution is returned by pump 19 either to tank 5 or 6.

It must be made clear that the caustic soda solution V passing through the light gasoline washery does not inare oxidised to disulphides. *necessity in orderto replace such sodium hydroxide as crease in phenol content while that passing through the heavy gasoline washery increases in phenol content each time it is used. It is quite common for regenerated caustic soda solutions of the type described and which have been contacted with heavy catalytically cracked gasoline to contain from 5 to 10 percent w./v. of alkyl phenols.

By suitable allocation of the caustic soda solution between the two treating units, it is possible to operate the light gasoline washery with between 10 and 20 percent phenols in the caustic soda solution thereby securing very eifectiveextracting of the mercaptans present. Care must be taken that the heavy gasoline treater is at all times supplied with enough caustic soda solution with sufficient power of taking up all the mercaptans present so that all the easily extracted aromatic mercaptans are removed. For example, if the caustic soda solution supplied for this purpose is saturated with respect to phenols, complete removal of mercaptans may not be possible. It is therefore necessary to discard from the system the phenols taken up from the heavy gasoline; this is done by turning a. portion of the caustic soda solution into a third series of vessels 22 by means of pipe 21. In these vessels, carbon dioxide is dispersed by similar means to those already described and the phenolic bodies separated as a floating layer. The sodium carbonate solution is disposed of by line-24 for use as a general purpose neutralising agent in the refinery. The phenolic layer is disposed of through line 23 and may be sold as a valuable by-product.

Itwill at all times be necessary to supply make up fresh caustic soda from tank 29 as a very concentrated solution. This may be conveniently pumped by pump 19 intotank 6. By this means it is possible to counteract the dilution caused by the water formed when mercaptans Such addition is also a may combine with aqueous oxidation products of disulphides and phenols which may unavoidably be formed.

It is likely that when certain high sulphur waxy distillates, such as those obtained from Kuwait crude, provide "the feed stocks for cracking operations, the mercaptan contents by I. P. Method 104 of the gasolincs after treatment such as has been described might be of the order:

Heavy gasoline--0.003 percent weight mercaptan sulphur The gasolines may be sweetened by means of antioxidants of the paraphenylene diamiue type and facilities for doing this are shown in the diagram. Antioxidant dissolved in a suitable solvent is supplied by a proportioning pump 25 at a rate not exceeding that required to promote gum stability (0.005 percent w./v.) to the combined treated light and heavy gasolines. It is also advantageous to have present a metal deactivator to suppress the effects of gasoline-soluble metallic contaminants whichare likely to be present in a gasoline still containing mercaptans. Proportioning pump 28 supplies small quantities (0.0005 percent) of these materials. Before enteringtank 27 enough air or oxygen is admitted through line 26-to saturate the gasoline. Tank 27 is one of a series of storage tanks of such capacity that the gasoline can remain'there undisturbed for; about a week; this is usually time enough for sweetening to be completed without loss of gum stability of the gasoline.

If desired, unit 1, 1A may be used for sweetening a proportion of other gasolines provided these gasolines are free from H S. In this case it may be necessary to provide more time in tank 27 for sweetening to be completed.

The following is a detailed example of the process according to the present invention.

A wax distillate of boiling range BOO-550 C. obtained from Kuwait crude oil was processed over a powdered silica-alumina cracking catalyst. The reaction products were passed through the necessary distillation steps and a debutanized gasoline of 240 C. end point and free from H S was produced. This was continuously distilled in the absence of oxygen in such a way as to produce a light gasoline of 150 C. end point and a heavy gasoline boiling between that temperature and 220 C. Both these gasolines were distillates so that it was necessary for a residual product in the boiling range above motor spirit to be taken from the bottom of the column. This material can be disposed of in marine, diesel, or tractor fuel. The heavy gasoline fraction so produced contained 0.1 percent by weight of mercaptan sulphur and gave an intense lemon yellow precipitate when doctor solution was added without sulphur. This gasoline was treated in a Scheibel type stirred column with 2 /z% by volume of caustic soda solution. The countercurrent extraction was conducted with strict exclusion of oxygen and resulted in complete removal of the mercaptans. The resulting gasoline, suitably inhibited, was 'gurn stable without further treatment. The caustic soda solution resulting from this operation was freed from oil, and placed in a well stirred vessel into which oxygen was admitted. Absorption took place readily and was accomplished by a rise in temperature, and after several hours agitation all the mercaptans had disappeared. The disulphides produced were removed from the caustic soda and the latter washed free from the last traces of disulphide by treatment with kerosene.

The caustic soda solution now free of mercaptans and disulphide was found to contain about 7% of cresylic acid and this solution was used for extraction of the mercaptans present in the light gasoline. When this treatment was conducted in the absence of air in a Scheibel column, a mercaptan content of less than 0.001% was obtained in the product.

The caustic solution leaving this operation was oxidised in the same way as previously and the last traces of disulphides removed by washing with kerosine. A stream of CO gas was then admitted and caused the liberation of the cresylic acid. The aqueous solution, though smelling of cresylic acid, contained very small amounts of these bodies and could be used in the refinery for the removal of H S.

We claim:

1. A process for the refining of catalytically cracked gasoline produced by the catalytic cracking of petroleum hydrocarbons boiling within the wax distillate range, which comprises separating the cracked gasoline into a heavy gasoline boiling between -220 C. and containing the thiophenols and cresylic acids present in the cracked gasoline, and a light gasoline boiling up to 160 C., treating the heavy gasoline with caustic alkali solution free from a solutizing agent and in the absence of air for the production of a sweet heavy gasoline and a caustic alkali extract solution containing thiophenols and cresylic acids, treating the extract solution with free oxygen under oxidising conditions to convert the thiophenols into disulphides and yield a cresylic acid-containing caustic alkali solution, treating the light gasoline with a cresylic acid-containing caustic alkali solution derived solely from the heavy gasoline treatment and in the absence of air to remove mercaptans from said light gasoline and provide a sweet light gasoline and a mercaptan-containing caustic alkali solution, and treating said mercaptan-containing caustic alkali solution with free oxygen under oxidising conditions to convert the mercaptans into disulphides and yield a cresylic acidcontaining caustic alkali solution from which cresylic acid may be recovered in known manner.

2. A process according to claim 1 wherein the heavy gasoline is treated with a caustic alkali-solution of 20 to 30% w./v. concentration.

References Cited in the file of this patent UNITED STATES PATENTS 2,270,667 Caselli et al J an. 20, 1942 2,297,537 Craig et al. Sept. 29, 1942 2,316,966 McNamara Apr. 20, 1943 2,556,438 Parker et al June 12, 1951 2,574,122 Ryder Nov. 6, 1951 2,589,663 Bond Mar. 18, 1952 2,693,442 Tom et a1. Nov. 2, 1954 UNITED STATES PATENT OFFICE CERTIFICATION OF CORRECTIGN Patent 2,846,357 August 5, 1958 Eric McNeill et a1.

It is hereby certified that error appears in the above numbered pat ent requiring correction and that the said Letters Patent should read as corrected below.

Column 2, line 21, for "etween" read between column 5, line 34, for "accomplished" read accompanied Signed and sealed this 6th day of June 1961.

(SEAL) Attest:

ERNEST W. SWIDER DAVID L. LADD Attesting Officer Commissioner of Patents

Claims (1)

1. A PROCESS FOR THE REFINING OF CATALYTICALLY CRACKED GASOLINE PRODUCED BY THE CATALYTIC CRACKING OF PETROLEUM HYDROCARBONS BOILING WITHIN THE WAX DISTILLATE RANGE, WHICH COMPRISS SEPARATING THE CRACKED GASOLINE INTO A HEAVY GASOLINE BOILING BETWEEN 160-220*C. AND CONTAINING THE THIOPHENOLS AND CRESYLIC ACIDS PRESENT IN THE CRACKED GASOLINE, AND A LIGHT GASOLINE BOILING UP TO 160*C., TREATING THE HEAVY GASOLINE WITH CAUSTIC ALKALI SOLUTION FREE FROM A SOLUTIZING AGENT AND ION THE ABSENCE OF AIR FOR THE PRODUCT OF A SWEET HEAVY GASOLINE AND A CAUSTIC ALKALI EXTRACT SOLUTION CONTAINING THIOPHENOLS AND CRESYLIC ACIDS, TREATING THE EXTRACT SOLUTION WITH FREE OXYGEN UNDER OXIDISING CONDITIONS TO CONVERT THE THIOPHENOLS INTO DISULPHIDES AND YIELD A CRESYLIC ACID-CONTAINING CAUSTIC ALKALI SOLUTION, TREATING THE LIGHT GASOLINE WITH A CRESYLIC ACID-CONTAINING CAUSTIC ALKALI SOLUTION DERIVED SOLELY FROM THE HEAVY GASOLINE TREATMENT AND IN THE ABSENCE OF AIR TO REMOVE MERCAPTANS FROM SAID LIGHT GASOLINE AND PROVIDE A SWEET LIGHT GASOLINE AND A MERCAPTAN-CONTAINING CAUSTIC ALKALI SOLUTION, AND TREATING SAID MERCAPTAN-CONTAINING CAUSTIC ALKALI SOLUTION WITH FREE OXYGEN UNDER OXIDISING CONDITIONS TO CONVERT THE MERCAPTANS INTO DISULPHIDES AND YIELD A CRESYLIC ACIDCONTAINING CAUSTIC ALKALI SOLUTION FROM WHICH CRESYLIC ACID ANY BE RECOVERED IN KNOW MANNER.

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