US1998849A - Process for desulphurizing mercaptan-containing petroleum oil - Google Patents

Description

Patented Apr. 23, 1935 UNITED STATES PROCESS FOR DESULPHURIZING MER- .CAPTAN-CONTAINING PETROLEUM on;

Walter A. Schulze, Bartlesville, Okla, assignor to Phillips Petroleum Company, Bartlesville,

0kla., a corporation of Delaware No Drawing. Application April 11,1932,

Serial No. 604,663

7 Claims.

The present invention relates, generically to a novel and improved method of desulphurization. More specifically, it deals with the removal of mercaptans from petroleum oils, liquefied petro- 5 leum gas, or the like.

A primary object of the invention is the elimination of mercaptans from mercaptan-bearing material by means of a solvent therefor, together with the subsequent regeneration of the solvent from the resultant mercaptide-saturated solution, whereby repeated use may be made of thesame solvent. I

A further object of the present invention is the provision of a continuous process for the removal of mercaptans from petroleum oils or the like, including the step'of oxidizing the mercaptides formed in the Washing material,whereby the latter is freed therefrom and is adapted for re-use to remove additional mercaptans.

Other objects of the invention will become ap-' parent from the detailed disclosure of the invention hereinafter set forth.

t is Well known that sulphur compounds are present in. practically. all unrefined petroleum distillates and, also, that in many cases the sulphur content is so high that the petroleum product must be-subjected to severe refining methods in order to reduce the sulphur content to specific'ations. Strohgsulphuric acid is generally used for this purpose, but there are certain'inherent objections to this method, particularly in the treatment of cracked distillates, which entails enormous losses of unsaturated hydrocarbons due to' polymerization, and the consequent increase of the knocking tendency of the petroleum oil; Other methods have been proposed but none is in general use at the present time.

It is known, also, that the sulphur compounds found. in petroleumdistillates consist'of hydro gen sulphide, mercaptans, alkyl sulphides, alkyl disulphides, and cyclic sulphur compounds. 'Of those named hydrogen sulphide is removed by an alkaline wash during the refining of the oil. Mercaptans are usually converted by some. oxidathe sulphur content of the oil is not lowered there'- by. The other sulphur compounds are not changed or removed during the usual method oi tion method to the corresponding disulphides, but

from certain crudes constitute a relatively large fraction of the total sulphur content or" the distillate and in these cases the reduction in the sulphur content is considerable. There are'rnany other cases where it is desired to'lower the sulphur content only .01 or .02% and this can also be readily accomplished by our process.

Mercaptans can be partially removed from petroleum naphtha, for example, by simple treat,- rnent with sodium hydroxide solution, but'the 1 solution soon reaches a more or less steady state of saturation and fails to remove additional quantities of m'ercaptans. This equilibrium, of course, depends on the distribution coefficients of the mercaptans betweenthe sodium hydroxide and naphtha. The mercaptans show wide diilerences in this respect as their molecular weight increases. 1

In other words, when the sodium hydroxide solution is treated with'consecutive portions of mercaptan-bearing oil, it becomes saturated with butyl mercaptan long. before it is saturated with ethyl mercaptan even' though the two mercaptans are present in equivalent quantities. Therefore, when a' naphtha containing mercap- 2 tans is passed through fresh sodium hydroxide, it is noticed that a largefraction' of the mercaptans is removed from the first-naphtha going through, but that the fraction removed with each successive portion of naphtha decreases rapidly and. the sodium hydroxide becomes saturated when'only a small fraction of the chemical equivalent of mercaptan has been taken up.

The term saturated is used to imply a state of inefiectiveness, i. e., the sodium hydroxide is 3 said to be saturated when it will no longer remove a considerable part of the mercaptans present. The sodium hydroxide, however, cannot be thrown away at this point, as the cost thereof is too great. j

According to the presentinvention, a method is provided for-regenerating the mercaptide-saturated sodium hydroxide, thus making it possible to use it over and'over again. The sodium hydroxide may be used in either a batch or a contin uous method, the latter being preferred. It may be 'commingled with the'oil, preferably in counter current relation to the petroleum oil or gas, and the spent sodium hydroxide removed to a sep arate tank for treatment. Free chlorine'or a r hypochlorite solution may then be added to the spent sodium hydroxide in the amount necessary to'o'xidize the mercaptides to the corresponding disulphides. This reaction is completed almost instantaneously. The disulphides which are 5 formed are not soluble in the sodium hydroxide and will separate as a layer to the top of the sodium hydroxide, from which they may be removed by decanting.

In order to get a complete and rapid removal of the disulphides from the sodium hydroxide, the latter is "thencgiven a Wash with gas oil or the like, the .disulphides being very miscible in such hydrocarbon material. The sodium hydroxide is then ready for re-use. The amount of chlorine which is added to thespent .caustic.de pends naturally on the meroaptide content of the sodium hydroxide. Slightly less than the chemical equivalent of chlorine can be :added but an excess should be avoided.

The concentration of the sodium hydroxide used in the process may vary over wide-limits, although 2 to 5 normal (8 to 20 peroentlispreferred, since the hydroxide ion concentration (and hence mercaptan removal) is greatest'in this range.

The entire ,process can :be carried out at ordinary room or plant temperatures since all the reactions proceed rapidly.

Other alkalies suohasspotassium hydroxide, calcium hydroxide, sodium-zincate, etc., may .be substituted for thesodium hydroxide.

This process is applicable toanypetroleum oil, liquefied petroleum gas, or gas containing mercaptans.

il healkyl disulphides can :be recovered from the absorbent gas oil by either ordinary distillation -or flash evaporation. Large quantities of the disulphides'can thus-be obtained.

What .is claimed and desired to be secured :by Letters Patent is:

1. a process :fordesulphurizing mercaptancontaining petroleum oil, wherein the petroleum oil is subjected to the action ofan alkaline wash whereby mercaptans are removed from the oil and mercaptides are formed in the wash, the steps ofseparating the spent-alkaline wash from the petroleum oil, treating the spent wash with a-ohlorine-yielding oxidizingagent whereby mercap-tides contained in the wash are :converted intowinsoluble 'disulphides, separating the :disulphides from the alkaline wash whereby the wash is regenerated, and returningthe regenerated wash to the system-for re-use.

:2. .A continuous process :for desulphurizing mercaptan-containing ;petroleum oil, comprising-Lintimatelycontacting the oil to be :desulphurized with a anercaptamremoving aqueous sodium hydroxidewash whereby mercaptans .are extracted from the oil and are converted to.sodiumumercaptides soluble in the wash, separating the -merca-ptide-containing wash "from the 'oil, oxidizing-the :mercaptides .in the Wash to the corresponding disulphides-by the :addition of a chlorine-yielding oxidizing agent in anaamount substantially :equivalent to :the meroaptide concentration -in-the 'wash, separating the 'disulphides-from the wash whereby the wash :is regenerated, andreturningthe regenerated 'sodiumihydroxide washto thesystem for're-iuse in further desulphurizing-the petroleum oil.

.3. A continuous process for desulphurizing mercaptan-containing petroleum soil and the like, comprising contacting the oil :with an aqueous alkaline Wash whereby rmercaptans are extracted from the oil andz-are converted to anercaptides which-are'soluble .in the wash, separating the mercaptideecontaining washifrom the oil, oxidizbearingpetroleumoil, comprising contacting the .oil with an aqueouscaustio wash whereby a portion of the mercaptans are removed from the oil by conversion to mercaptides soluble in the wash,

separating 'the meroaptide-containing wash from the'oil, regenerating "the Wash by adding thereto a chlorine-yielding oxidizing agent in an amount substantially equivalent to the meroaptide concentration in the wash, separating the resultant disulphides from the regenerated caustic Wash, and returning the regenerated wash for use in removing additional mercaptans from the-oil.

.5. The process of desulphurizing mercaptanbearing petroleum oil, comprising 'washing the petroleum oil with an aqueous solution of about 8 to 20;per cent sodium hydroxide whereby a portion of the mercaptans are removed from the oil by conversion to mercaptides soluble in the sodium hydroxide solution, separating the meroaptide-containing solution from the oil, reactivating the meroaptide-containing solution by adding thereto a chlorine-yielding oxidizing agent while out of contact with the oil, separating the disulphides from theresultant reactivated sodium hydroxide solution, returning the reactivated solution to the system, and repeating the process until the mercaptans are substantially eliminated from the petroleum oil.

6. A continuous process for desulphurizing mercaptan-containing petroleum oil, comprising intimately contacting the oil tobe desulphurized with a mercaptan-removing aqueous sodium hydroxide wash whereby mercaptans are extracted from the oil and are converted to sodium mercaptides soluble in the wash, separatingthe mercaptide-containing wash from the oil, oxidizing the mercaptides in the wash to-the corresponding disulphides by the addition of a sodium hypochlorite solution in an amount substantially equivalent to the meroaptide concentration in the wash, separating the disulphides from the wash whereby the wash is regenerated, and returning the .regenerated sodium hydroxidewash to the system for re-use in further desulphurizing :the petroleum oil. 7

'7. A continuous process for desulphurizing mercaptan-containing petroleum oil and the like, comprising contacting the oil with anaaqueous alkaline wash whereby mercaptans are extracted from the oil and are converted to mercaptides which are soluble in the wash, separating the meroaptide-containing wash from the oil, oxidizing .the mercaptides in the wash to the corre sponding disulphides by the addition of an alkaline hypochlorite solution in an amountsubstantially equivalent to the meroaptide concentration in the wash, separating the disulphides from the wash whereby the wash is'regenerated, and returning the regenerated alkaline wash to the system for reuse inthe extraction of additional mercaptans from the oil.

WALTER A. SCHULZE.