US2034837A - Method of sweetening hydrocarbon oils with alkali polysulphides - Google Patents

Description

Patented Mar. 24, 1936 2,034,837

UNITED STATES PATENT OFFICE METHOD OF SWEETENING HYDROCARBON OILS WITH ALKALI POLYSULPHIDES Walter A. Schulze and Lovell V. Chaney, Bartlesville, Okla... assignors to Phillips Petroleum Company, Bartlesville, Okla, a. corporation of Delaware No Drawing. Application June 20, 1933,

Serial No. 676,763 I 6 Claims. (Cl. 196-24) This invention relates to a method of treating After 1 minute: Very positive or sour to dochydrocarbon fluids and the like, with particular tor test. reference to sweetening petroleum hydrocarbon 2. One volume of 30 B. NaOH (300 g. of

oils, vapors and gases. NaOH per liter) was added to mixture in (l):

6 It has for its purpose the conversion of cer- After 1 minute agitation: Negative, or sweet, to

tain malodorous sulphur compounds occurring in doctor test. petroleum hydrocarbons into less obnoxious sub- 3. Five volumes of (NH-1); $4.6 solution, constances. This method of treatment is generally taining 377 g. of (NH4)2 Sm per liter, and 5 termed sweetening and the malodorous subvolumes of c. p. NH4OH were agitated with 60 stances sweetened are mercaptans. volumes of n-butyl mercaptan in a petroleum 1 One of the prerequisites of a good motor fuel fraction (0.04 per cent mercaptan sulphur): is that it shall not possess a disagreeable odor. After 10 minutes: Sour, although less posi- This is practically synonymous with saying that tive, or sour, than original. it shall not contain mercaptans. These malodor- 4. Five volumes of 30 B. NaOI-I substituted l5 ous substances at some stage of the refining procfor NH4OH in (3) ess are accordingly usually either completely re- After 1 minute agitation: Sweet. i moved from the petroleum oil being processed or The concentration of excess caustic in the polyare converted by some means to less obnoxious sulphide treating solution may vary within very substances. The latter method is employed in wide limits, the minimum requirement for sweetmany cases and the conversion is accomplished ening being that sufiicient caustic be always pres- 20 by some means of oxidation wherein the mercapent to react with all of the hydrogen sulphidetans are changed principally to disulphides. The formed in the polysulphide-mercaptan reaction usual and accepted method for detecting the presin order to keep the sweetening reaction proceedence of mercaptans is the so-called doctor test, ing to completion. The caustic concentration 5 the details of which are given in most handmay be as high as 300 to 450 g. per liter of NaOH. 2!! books and testing manuals pertaining to petrole- A concentration of the order of 200-225 g. (or um products. A positive doctor test indicates above) per liter is advantageous from the stand the presence of mercaptans. point of producing a product which is non-cor.-

We have discovered that certain alkali polysulrosive to the' well-known copper strip test at 122 phides quickly and completely sweeten such mer- 'F. and also ofmore quickly sweetening higher 80 captan-bearing hydrocarbon oils, vapors and mercaptans and refractory gasolines. gases. This sweetening or oxidizing eflect is ex- As evidence of the efiect of NaOH concentrahibited in a general way by the higher polysultion in producing non-corrosive sweetened prodphides of the alkali and alkaline earth metals and ucts with alkaline polysulphide solutions, the 1'01- most particularly .by the higher polysulphides of lowing data are submitted when an iso-butyl mer- 35 sodium, potassium and ammonium. We have captan stock (0.04 percent mercaptan sulphur) found that this sweetening efiect on mercaptans has been treated with sodium polysulphide soluis very pronounced in the polysulphide range tions containing various concentrations of NaOH. from about the tetrasulphide to the pentasulsix volumes of mercaptan stock were in each case 40 phide or, taking the sodium polysulphides by sweetened with one volume of polysulphide-so- 40 way of illustration, from about NazSas or NazS4 .dium hydroxide solution. to NazSa. Sweetening becomes much less pronounced as the polysulphide composition ap- G 0mm Concmm proaches NazSa. fl f 5m of R f f t d 5 It has been found to be desirable to include a gr perliter 53 53, $Q$R strong base or caustic alkali, such as sodium hyfigj gg liter oi'treatdroxide, in the sweetening solution; and such clemg sirability is demonstrated by the results-of the 438.7 115.7 Negative alter3hours. following tests, conducted at 26 C. (79 F.) in 26 173' 5 Negative after3hom a non-oxidizing atmospher 1914 173.5 Negative afteriiliours.

1. Five volumes of aqueous Na2S4.5 solution, 150 0 173 5 gy ig q gg iggg f fggg n ini 278 g. of Nazsm per li er, w 65:8 11315 Positive in less than lminute tated with 60 volumes of a synthetic solution of .2717 New! afteflhours n-butyl mercaptan (0.04 per cent mercaptan sulphur) in a petroleum fraction: It is desirable to have the polysulphide concentration fairly high for highly eflicient sweetening, but again this may vary over a wide range depending on the characteristics of the stock treated, degree of contact between treating solution and stock treated, throughput of plant, etc. A preferred, very effective and relatively inexpensive treating solution comprises NazSus and NaOH in the following concentrations:

NazSu, 180 g; per liter NaOH, 225 g. per liter While we prefer the concentration of Nassau, for instance, in our treating solutions to be around 180 g. per liter, or of Nazsat to be about g. per liter, good results are obtained with concentrations varying from 25-75 g. per liter of Nags-rs to 400 or 450 g. per liter; and from 20-60 g. per liter of Nazsas to 350 or 400 g. per liter.

Similarly to the practicability of maintaining. ammonium polysulphide solutions substantially alkaline (with strong bases, as sodium hydroxide) when they are utilized as sweetening agents, we have found that it is also necessary from a practical viewpoint to maintain a substantially high alkalinity in treating solutions comprising the readily hydrolyzable alkaline earth polysulphides. We have found, for example, that calcium polysulphides approximating CaS4 very quickly sweeten mercaptans when an excess of solid Ca(OH)2 is present.

The sweetening effect of alkali and alkaline earth polysulphides on mercaptan-bearing hydrocarbon oils is further exemplified and substantiated by the data submitted in the table below. All polysulphide solutions contain a substantial amount of the corresponding hydroxide or of sodium hydroxide and are reacted in the approxi mate volume ratio of 1:6, treating solution to stock treated. The latter is a synthetic solution of n-butyl mercaptan (0.04 per cent mercaptan sulphur) in a light petroleum fraction.

In preparing polysulphide solutions as above, elementary sulphur (precipitated or the usual flowers) was added to aqueous solutions of the simple or mono-sulphides which had been prepared with concentrations of approximately 145 g. of Nags, 205 g. of K25 and g. of (NH4) 28 per liter. With the desired amountof elementary sulphur added, solution of the sulphur was permitted to take place at atmospheric temperature, which readily occurred with occasional agitation of the mixture. Elevating the temperature of the mixture,tohasten solution of the sulphur is inadvisable in certain cases, especially if air is prescut, and was not practiced since it causes decomposition of the polysulphides. A minimum access of air during thestorage of the solutions and during the treating operation is advantageous in sulphur to 1 part of Ca(OH) 2, by weighareacted in this manner produces an effective sweetening agent when employed underalkaline conditions.

In addition to n-butyl and the lower mercaptans, higher polysulphides in similar concentrations to those solutions in the aforementioned illustrations quickly and completely sweeten hy drocarbon solutions of secondary and tertiary butyl and isoand n-amyl mercaptans. In the case of n-heptyl mercaptan, as an example of the higher mercaptans, and some types of refractory petroleum naphthas, the time required for complete sweetening is quite long. We have found that a small quantity of alcohol (as little as 1 or 15 per cent by volume) added to the polysulphide treating solution causes the most diflicult gasolines and the higher mer'captans to be completely sweetened in one to three minutes of agitation. For example, a very sour cracked naphtha which was still slightly sour after 10 minutes agitation with an alkaline Nags solution, was sweet in less than 1 minute when a fresh portion of the naphtha was agitated with the same polysulphide solution to which had been added 3 per cent by volume of ethyl alcohol. Potassium polysulphides more effectively sweeten refractory mercaptans than do the corresponding sodium polysulphides. For example, a very refractory naphtha required the addition of alcohol to an NazSu treating solution for rapid sweetening, whereas a solution comprising K2843 and a caustic alkali sweetened the naphtha in slightly over 2 minutes. The particular alcohol added to the treating solutions is relatively unimportant, cost of such being the principal factor involved. The utility of the alcohol appears to reside in its property of aiding in bringing the mercaptans in the hydrocarbon solvent into more intimate contact with the active sweetening substances in the aqueous treating solution. We prefer to incorporate methyl or ethyl alcohol in our treating solutions when necessary, although propyl and butyl alcohols, while much less effective, may also be employed.

No more than 1 to 5 per cent by volume of the treating solution need usually consist of alcohol, although more may'be used if desired. Depending upon the solubility of the alcohol in the hydrocarbon liquid treated, some alcohol will be lost in the hydrocarbon phase, and it is accord the requirements.

' We have also found that alkaline solutions of polysulphides lower than NazSa or Na'rSas, for example, readily sweeten mercaptan-bearing petroleum hydrocarbon 'oils if elementary sulphur-is dissolved in the oil, either naturally existent therein or purposely added, in quantity suiiicient to increase the sulphur ratio in the polysulp hide up to the composition for rapid sweetening.

- A preferred method for utilizing our, process for sweeteninghydrocarbon oils comprises intimately contacting the sour hydrocarbon fluids with sodium polysulphide solutions containing about g. per liter (1.5 lb. per gallon) of polysul-' phides of the approximate composition represented by'the formula Na2S4.5 and approximately 225 g. per liter (1.88 lb. per-gallon) of NaOH. Preftion of the treating mixture or to maintain a non-oxidizing atmosphere in the system duringthe treating operation, or during preparation of the polysulphide solutions and their storage. We prefer to treat the hydrocarbon fluids at ordinary atmospheric temperatures, or from about 40 to 90 F., although the process may be operated at temperatures from 32" F. to 130-140 F. If the material to be treated arrives at the polysulphide treating stage at a temperature in excess of 100 F. we prefer to let the material cool to, or artificially decrease the temperature to or F. before subjecting it to the polysulphide treatment.

After intimately contacting the hydrocarbon fluid with the alkaline polysulphide solution, the 'former is separated from the treating solution by settling and decantatiomor by other separating means.

A good commercial grade of elementary sulphur may be used to prepare the sodium polysulphide stock, weighing the required-amount of sulphur for an NazSu solution, for example, into a stock solution of sodium monosulphide prepared by dissolving NazS in a minimum amount of water and adjusting the resulting solution (by analysis or calculation) so that it contains approxi mately 145 g. of NazS per liter (1.2 lb. per gallon) While this concentration of NazS in the base or stock sodium mono-sulphide solution is preferable, the concentration may vary over quite a wide range without materially affecting the resulting polysulphide treating solutions. It may be increased up to 200 g. per liter or a stock solution may be employed with NazS concentrations of approximately '75 to g. per liter.

By way of definition, ammonium compounds are classed with those of the alkali metals, sodum, potassium, etc. See page 657, Mellor, Modern Inorganic Chemistry, Longmans, Green and Co., 1925. Alkali hydroxides, caustic alkali, strong bases and sodium hydroxide, .for instance, are used as synonymous terms. While the first definition above classes ammonium hydroxide as an alkali hydroxide, it is not so considered in the present method or treating agent for it is a wea base, is usually termed such, and is insuflibiently strong for best utility in the process just described.

From the foregoing it is believed that the various steps of the process may be readily understood by those skilled in the art, and it is apparent that changes may be made in the details disclosed, without departing from the spirit of the invention, as expressed in the claims.

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

1. A process of sweetening sour hydrocarbon oils without the aid of lead compounds, which comprises as the initial step agitating the oil while at atmospheric temperature with an aqueous' solution consisting of a strong base and a polysulphide higher than the trisulphide of an element of the group consisting of the alkali and alkaline earth metals, and separating the oil from the treating solution.

2. A process of sweetening sour hydrocarbon oils without the aid of lead compounds, which comprises as the initial step subjecting the oil while at atmaspheric temperature to the action of an aqueous treating solution consisting of a strong base and a sodium polysulphide higher than the sodium trisulphide, and separating the oil from the treating solution.

,3. In a process of oxidizing mercaptans to the disulphide form without the aid of lead compounds, the step which consists in initially subjecting a sour hydrocarbon oil containing the said mercaptans while at atmospheric temperature, to the action of an aqueous treating solution consisting of a strong base and a sodium polysulphide higher than the trisulphide, and separating the oil from the treating solution.

4. A process of sweetening sour ga-solines without the aid of lead compounds, which comprises as the initial step agitating the gasoline while at atmospheric temperature with an aqueous solution consisting of sodium hydroxide and sodium polysulphide higher than sodium trisulphide, and separating the oil from the treating solution.

5. A process of sweetening mercaptan-bearing petroleum oils without the aid of lead compounds, which comprises as the first step intimately contacting the oil in a non-oxidizing atmosphere at substantially atmospheric temperature with an aqueous solution consisting of sodium hydroxide and sodium polysulphide higher than the trisulphide, and separating the oil from the treating solution.

6. A method of sweetening sour gasolines which