US1968842A - Treatment of hydrocarbons - Google Patents

Description

Patented Aug. 7, 1934 UNITED STATES TREATMENT F HYDROCARBONS William M. Mallsoi'l, Philadelphia, Pa., assigner to The Atlantic Refining Company, Philadelphia, Pa., a corporation oi' Pennsylvania Application November 3, 1930, Serial No. 493,064

4 Claims.

The present invention relates to the refining of hydrocarbon oils, and more particularly to the removal of sulfur from hydrocarbon oils such as petroleum oils or fractions thereof.

5 Of the many types of sulfur compounds which occur in hydrocarbon oils, particularly petroleum oils and their fractions, the mercaptans are perhaps one of the most objectionable due to their odor, and the removal of this type of sulfur compounds constitutes a primary object of my invention. The term "mercaptans is used herein and in the appended claims to describe sulfur compounds having one or more SH groups, including alkyl and aromatic mercaptans.

Whereas mercaptans are objectionable in substantially any hydrocarbon oil, their presence in light petroleum fractions, such as lamp oil, gasoline and naphtha, is most undesirable. My process is particularly effective in removing mercaptans from these light fractions, but it isequally applicable to the treatment of higher boiling fractions, for instance, for the removal of mercaptans from gas oil prior to cracking, or from the product resulting subsequently thereto. It appears however, that it is of advantage to eii'ect removal of sulfur from an oil prior to cracking.

Of the many proposed methods for treating hydrocarbon oil to affect itsl sulfur content, per haps the most commonly applied process is the well known f doctor treatment which involves treating the sulfur-containing oil with a weak solution of sodium plumbite to convert at least a portion of the mercaptans to lead mercaptides. Certain of the low-molecular weight lead mercaptides are insoluble in oil, and, if formed by the reaction of low molecular -weight mercaptans andl sodium plumbite, either precipitate or remain in suspension in the oil.l The remainder of the lead mercaptides, which after the aforesaid reaction ordinary constitute the maj or portion of the total mercaptide content, go into solution in the oil. Elementary `sulfur is added to oxidize these remaining soluble lead mercaptides into organic disulfides which are also soluble in the oil, and insoluble lead sulfide. the doctor treatment, therefore, the sulfur content of the oil is reduced only to the extent of the insoluble lead'mercaptides formed and this reduction is generally more than offset by the addition of an unavoidable excessof elementary sulfur which is oil soluble, and therefore remains in solution therein. The prior art also suggests that the doctor treatment" be modified by washing the sulfur-containing oil with an alcohol solution of sodium plumbi'te, but in this process ele- As the ultimate result of mentary sulfur likewise is added to effect a reaction somewhat similar to that which occurs in the parent process, and like disadvantages result.

The doctor treatment" is objectionable theree0 fore, in that there is very little if any actual removal of the sulfur compounds, the majority of the mercaptans present merely being converted into other organic sulfur compounds of a less objectionable nature which remain dissolved in the e5 oil. An oil which does not react with the doctor solution is said to be sweet. Consequently oils which have been subjected to the "doctor treatment are of this nature. However, when a sulfur-containing oil which has been subjected to the doctor treatment for sweetening, is re-run or redistilled, it is usually noticeable that the oil is no longer sweet to the doctor solution, indicating a regained content of mercaptan compounds. Also the difiiculties caused by the ior- 'n' mation of insoluble metal-sulfur compounds are always encountered when lead salts are employed.

A primary object of the present invention is to eiect removal of mercaptans from hydrocarbon 30 oils containing the same. In accordance with this and other objects of my invention, it is contemplated to effect an actual removal of sulfur, particularly mercaptan sulfur. as contrasted with a mere conversion of the mercaptans into 35 other compounds which remain in the oil, certain of which upon redistillation of the oil may cause souring. It is also my object to render a sulfur-containing oil sweet regardless of whether it is redistilled, without incurring the disadvantages incident to prior processes. In addition, my process is simple in operation and relatively inexpensive. These and other objects and advantages will appear from the following description.

I have found that mercaptans may be removed by treating the sulfur-containing oil with a solution of an alkali substance in an organic solvent. As the alkali component of my treating reagent I may use an alkali hydroxide or carbonate, al- 10o koxides of the alkali or alkaline earth metals, ammonia, onium bases, equivalent alkaline substances, or mixtures of two or more of these yarious substances. It is necessary that the alkali substance be soluble to an appreciable extent in oneL or more of the organic solvents hereinafter described. The function of the alkali substance to beused in my treating solution is to react with mercaptans contained in the oil to form sulfur compounds such as mercaptides which will preferentially dissolve in the solvent employed. The term alkali substance will be used to denote one or a mixture of two or more compounds from the groups indicated, and will comprehend compounds of sodium, potassium, and ammonium, and also, though less desirable, compounds of the alkaline earth metals, which are capable of effecting the desired reaction with mercaptans. In most instances, it is desirable to use hydroxides of the alkali metals, as sodium and potassium hydroxides, and my invention may be considered as primarily, although not exclusively, contemplating the use of these specific substances.

'I'he organic solvent used in accordance with my invention acts to carry the alkali substance in solution and to exert a preferential solubility for the reaction product of the alkali substance and the mercaptans contained in the oil. Since it is necessary to free the oil from the treating solution in order to obtain the desired oil product, it is essential that the organic solvent be of a type which'may be satisfactorily separated from the oil. In most instances the immiscibility of the 'treating solution and the oil is depended upon when separation of the two liquids is effected. Among the organic solvents which are suitable for my process, are members of the groups comprising monohydric alcohols, polyhydric alcohols, ketones, halogen hydrins, or mixtures of two or more members of the several groups. More specically, I have found it desirable to use methyl, ethyl, propyl, and isopropyl alcohols; glycols and glycerine; acetone, ethyl methyl ketone and diethylketone; and epichlorhydrin. Of the subv stances named methyl alcohol, ethyl alcohol, glycol and glycerine are of particular utility. The term organic solvent is used herein and in the appended claims to designate one or a mixture of two or more of the solvents above mentioned or their equivalents.

Thus, the sulfur-containing oil is treated with a solution of an alkali substance in an organic solvent, and the alkali substance reacts with mercaptans contained in the oil to form sulfur compounds which are more soluble in the organic solvent than in the oil. The removal of these sulfur compounds is completed by the separation and removal of the treating solution from the oil. y

As before stated, it is necessary that the organic solvent be capable of being separated from the oil. That is,- the solvent and oil must be mutually immiscible or capable of being rendered so. It is not essential that the solvent be initially immiscible with the oil. The treating solution may be substantially miscible with the oil, but in such case it is necessary to render the two liquids immiscible before their separation may be effected. Only those oil miscible treating solutions may be used which are capable of being rendered immiscible with the oil subsequently. For instance, anhydrous methyl alcohol is appreciably miscible with the oil. 'Ihe oil miscible solution of an alkali substance in anhydrous meth- -yl alcohol may be used to effect removal of mercaptans from hydrocarbon oils since it is possible to render the treating solution immiscible with the oil by adding a small amount of water. In general, when oil miscible organic solvents within the classes or groups listed above are employed, the necessary immiscibility may be obtained by having an immiscible rendering substance present in the treating solution, and examples of such substances are water, inorganic salts. such. as,

calcium nitrate, or even organic compounds such as urea. 'Ihe alkali substance itself may have some immiscible rendering effect. These tend to inhibit miscibility between the oil and the treating solution employing an oil miscible solvent. The term immiscible rendering, substance will be used herein and in the appended claims to denote one or more substances which are soluble in the treating solution, which will not materially interfere with the reaction between the alkaline substance and the mercaptans contained in the oil, n'or with the removal by the treating solution of the products of this reaction, and which will cause the oil miscible solvent of the treating solution to be or become immiscible with the oil. Although I prefer to use a treating solution which is initially immiscible with the oil, good results may be obtained by adding to the mercaptan-containing oil an oil miscible treating solution. 'Ihe two liquids go into solution, and 'afford an excellent contact between the alkali substance and mercaptans and thereafter upon adding an lm miscible' rendering substance to the solution of oil and treating-solution the latter becomes immiscible with and separable from the oil. Certain of the solvents indicated, for instance, glycol, glycerine and certain esters and ethers of these solvents are substantially immiscible with hydrocarbon oils, even when anhydrous, and in their use it is not necessary that water or other immiscible rendering substance be present. In any case the amount of immiscible rendering substance needed to regulate immiscibility will demiscible rendering substance presentinmy treating solution is to render the latter immiscible with and therefore separable from the oil. Dilute alcohol solution of alkali substances have been employed according to the well-known processes for various purposes, such as the removal of color-i'orming bodies from hydrocarbon oils, and for neutralization of acid treated oils. However, I have found that for the purpose of freeing hydrocarbon oils from mercaptans, there is a limit to the amount of water which may be present in my treating solution. When mercaptan-containing oil is treated with an alkali solution, the mercaptans react with the alkali to form mercaptides. It is my theory that the presence of water Will cause hydrolysis of the mercaptides to reform mercaptans. These mercaptides are soluble in the organic solvent, but the mercaptans are more soluble in oil than in the solvent. Thus, in the presence of an undesirable amount of water, the purpose of my process may be' defeated by the hydrolysis resulting. In addition to effecting hydrolysis of the extracted mercaptides, increasing amounts of water in the treating solution decrease the preferential solubility of the treating solution for the mercaptides. Therefore, when an oil miscible solvent is employed. and when water is used to render the treating solution immiscible with the oil, it is desirable .to confine the water content to only an amount suiiicient to render the solution immiscible with the oil. Although, in general, itis possible to employ a treating solution containing 15 percent or sometimes even more of las its

water, preferred results are obtained by employing a treating solution containing not more than substantially 10 percent of wat`er. A

In carrying out my process, I have obtained particularly desirable results by using a solution of sodium hydroxide in methyl alcohol which contains no more water than an amount sumcient to render it substantially immiscibie with the oil. I have found that solutions of an alkoxide, such as sodium methylate, in solvents such as glycol, for instance, are effective treating solutions, since their use is accompanied by a decreased tendency for hydrolysis to take place.

The manual operation of my process is quite simple. It may be carried out in batch washes, or as a semi-continuous or continuous operation. The oil is intimately contacted with the treating solution, for instance, by agitation. Upon settling after completion of the washing operation the immiscible liquids form divisible layers which are easly separated, as for example, by decantation. In this manner the oil may be treated several times with fresh batches oi' the treating solution. The oil then may be subjected to further purifying treatment, such as washing with water to remove traces of the treating solution; and the expended treating vsolution may be worked up into valuable products.

In most cases the solution will be heavier than the oil and so will sink to the bottom of the container upon allowing the mixture of oil and treating solution to settle. This lower layer is found to contain the organic solvent, unexpended alkali materials, mercaptides. and a certain amount of tarry materials probably formed by secondary reactions.

The figure in the drawing is a diagrammatic representation of suitable apparatus in which my process may be effected continuously.

Oil from which mercaptans are to be extracted is pumped from an oil supply tank 2 into the treating chamber l at a point somewhat above the bottom thereof. The oil progresses upwardly and is passed from approximately the top of the chamber into oil storage tank 3.

Treating solution is passed from supply tank 4 into the treating chamber at a point somewhat below the top of the chamber, and due to the differences in specific gravity passes downwardly therethrough countercurrent to the upwardly flowing oil. Intimate contact between the two liquids is provided by agitation eiected by means of stationary agitator blades 6 coacting with rotating agitator blades 7. The spent treating solution. settles out of the cil at the bottom of the treating chamber below dotted line b and is drawn olf into tank 5.

Suflicient space is provided above the treating solution inlet for instance, above dotted line a to allow a substantial separation of the oil from the treating solution. Likewise, the oil inlet is sufficiently above the bottom of the chamber to allow separation of the spent treating solution from the oil.

From the following specific examples, my 1nvention will be more clearly understood.

`% methyl alcohol with anhydrous sodium hydroxide. This solution was used to treat a previously untreated, sour cracked distillate obV tained from a Gulf Coast crude. The distillate before treatment had a sulfur content of 0.36

percent. The treatment was effected by mixing with the distillate 2 percent by volume of the treating solution, agitating the mixture for about ve minutes, settling, and removing the resultant lower layer of treating solution. This operation was repeated four times with fresh portions of the treating solution. After final separation of the treating solution, the oil was found to contain 0.22 percent sulfur. Also, the treated oil was sweet to the doctor test, and remained sweet even after subsequent distillation. The boiling range of the treated oil showed no appreciable change from that of the untreated oil.

Example II A gas oil from a West Texas crude was treated by proceeding as in Example I with five 2 percent by volume washes of a solution of five parts by weight of sodium hydroxide-in one hundred parts by weight of 90 percent methyl alcohol. The gas oil was thus sweetened and remained sweet after being distilled, its sulfur content was reduced from 1.12 percent to 0.96 percent, and its boiling range was substantially unchanged by the treatment.

Example III ,A sour compression blend gasoline derived from refinery gases which had an original sulfur content of 0.20% was contacted with three 2% by volume batches of a substantially saturated anhydrous solution of caustic potash in glycol, the treating solution and gasoline being separated after each contacting. After the last contacting and separation the gasoline was found to be sweet to the doctor test and remained so even after redistillation, and to contain .08% of sulfur, while the boiling range thereof remained substantially unchanged.

Example IV A sour low boiling fraction of a cracked distillate from a West Texas crude containing .24% sulfur was washed with four 2% by volume batches of a saturated solution of ammonia in a substantially anhydrous mixture of 75 parts of glycerine and 25 parts of methanol. After the last washing, the sulfur content of the distillate was .07%, the distillate was sweet and remained so after distillation, and the boiling range thereof remained substantially unchanged.

Eample V A sour sample of crude benzene was freed of merceptans and rendered sweet evenafter subsequent distillation. by washing with two 2% by volume batches of a substantially anhydrous 50% saturated. solution of caustic soda in glycerine. l

Example VI A sour lubricating oil distillate having a sulfur content of 1.12% was treated by washing with three 2% batches of a substantially anhydrous saturated solution of NaOH in a 50-50 mixture of acetone and methyl alcohol. Its sulfur content after treating was .88%, it remained sweet after redistillation, and its boiling range remained substantially unchanged.

Example VII 14 A solution of a hydrocarbon oil containing 1.42

grams of phenyl mercaptan, 0.71 grams of p-tolyl mercaptan and 1.06 grams of n-amyl mercaptan per cc, was treated 5 times with 2% by volume batches ot a substantially anhydrous solution of methanol saturated with caustic soda. 'I'he resulting oil product was mercaptan free, and contained sulfur equal only to the original sulfur' the solution and the oil, the amount of water,

present being not more than substantially 15%, and thereafter separating the treating solution from the oil.

2. In the process i'or removing mercaptans from hydrocarbon oils containing the same, the step which consists in contacting fthe oil at ordinary temperatures with a solution of sodium hydroxide in at least one of the solvents from the group consisting of methyl alcohol, ethyl alcohol,

propyl alcohol, iso-propyl alcohol, glycol, glycerol,

acetone, ethyl-methyl ketone, diethyl ketone and epichlorhydrin, said solution containing sutcient water substantially to inhibit the mutual solubility ot the'solution and the oil, the amount ofwater present being not more than substantially 15%, and hereafter separating the treating solution from the oil.

3. In the process for removing mercaptans from hydrocarbon oils containing the same, the step which consists in contacting the oil with a solution of sodium hydroxide in methyl alcohol, said solution containing sufficient water to inhibit the mutual solubility of the solution and the oil, the amount of water present in the solution being not more than substantially 10%, and thereafter separating the solution from the oil.

4. In the process for removing mercaptans from hydrocarbon oils containing the same, the step which consists in contacting the oil with a solution of alkali metal hydroxide in methyl alcohol, said solution containing water suflicient substantially to inhibit the mutual solubility oi.'

the solution and the oil, Vthe amount of water present in the solution being less than substantially 15%, and thereafter separating the solution from the oil.

WILLIAM M. MALISOFF.

CERTIFICATE 0F coaRECTIoN.

Patent No. l, 968, 842.

August 7, 1934.

WILLIAM M. MALISOFF.

lt is hereby certified that error appears in the printed specification of the 'above numbered patent requiring correction as follows: Page l, line 40, for "ordinary" read ordinarily; page 3, line 2l, for "easly" read easily; and page 4,

line 81, claim 2, for "hereafter" read thereafter; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Office.

Signed and sea-led this 11th day oi September, A. D. 1934.

(Seal) Leslie Frazer Acting Conunissioner of Patents.

methanol saturated with caustic soda. 'I'he resulting oil product was mercaptan free, and contained sulfur equal only to the original sulfur' the solution and the oil, the amount of water,

present being not more than substantially 15%, and thereafter separating the treating solution from the oil.

2. In the process i'or removing mercaptans from hydrocarbon oils containing the same, the step which consists in contacting fthe oil at ordinary temperatures with a solution of sodium hydroxide in at least one of the solvents from the group consisting of methyl alcohol, ethyl alcohol,

propyl alcohol, iso-propyl alcohol, glycol, glycerol,

acetone, ethyl-methyl ketone, diethyl ketone and epichlorhydrin, said solution containing sutcient water substantially to inhibit the mutual solubility ot the'solution and the oil, the amount ofwater present being not more than substantially 15%, and hereafter separating the treating solution from the oil.

3. In the process for removing mercaptans from hydrocarbon oils containing the same, the step which consists in contacting the oil with a solution of sodium hydroxide in methyl alcohol, said solution containing sufficient water to inhibit the mutual solubility of the solution and the oil, the amount of water present in the solution being not more than substantially 10%, and thereafter separating the solution from the oil.

4. In the process for removing mercaptans from hydrocarbon oils containing the same, the step which consists in contacting the oil with a solution of alkali metal hydroxide in methyl alcohol, said solution containing water suflicient substantially to inhibit the mutual solubility oi.'

the solution and the oil, Vthe amount of water present in the solution being less than substantially 15%, and thereafter separating the solution from the oil.

WILLIAM M. MALISOFF.

CERTIFICATE 0F coaRECTIoN.

Patent No. l, 968, 842.

August 7, 1934.

WILLIAM M. MALISOFF.

lt is hereby certified that error appears in the printed specification of the 'above numbered patent requiring correction as follows: Page l, line 40, for "ordinary" read ordinarily; page 3, line 2l, for "easly" read easily; and page 4,

line 81, claim 2, for "hereafter" read thereafter; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Office.

Signed and sea-led this 11th day oi September, A. D. 1934.

(Seal) Leslie Frazer Acting Conunissioner of Patents.

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