US2278753A - Treatment of petroleum and distillates thereof - Google Patents

Description

Patented Apr. 7, 1942 TREATMENT OF PETROLEUM AND DISTIL- LATES THEREOF Charles Wirth, In, Chicago, 111., assignor to Universal Oil Products Company, Chicago, 111., a

corporation of Delaware Application December 19, 1938,

No Drawing.

Serial No. 246,670 4 Claims. (01. 196-33) This invention relates particularly to the removal of sulfur frompetroleum distillates. Such distillates include natural or absorption gasolines, which are produced by the absorption of liquid hydrocarbons from natural or refinery gases, the so-called straight-run gasoline produced by the primary distillation of crude oils, or gasoline distillates manufactured by the cracking or reforming of high-boiling petroleum oils. Further applications of the process may be to remove sulfur from polymer gasolines or from low-boiling hydrocarbons, such as, butane, butene, propane, propene, etc., which may be liquefied at ordinary temperatures by the application of pressure. Still other distillates which may be treated within the scope of this invention are the kerosene and gas oil fractions of crude oils.

More specifically, the invention is concerned with an improved method of removing sulfur from gasolines which have been sweetened. It is particularly useful as a step in the sodium plumbite or doctor method of sweetening as here-, inafter explained. The treatment is directed toward the elimination of so-called free.sulfur, which is particularly detrimental to the color stability, storage stability, octane number, and susceptibility to introduction of tetra-ethyl lead, of gasolines. used refers to elementary sulfur which may be present in the gasoline as a result of the oxidation of hydrogen sulfide, and/or to the combined or uncombined sulfur which may be present as a result of the use of excessive quantities of elementary sulfur during the doctor sweetening process. The process provides an easy and inexpensive way of salvaging gasolines which contain large amounts of free sulfur and consequently are corrosive to the metal parts of auto-, mobile engines before or after combustion.

In the so-called doctor sweetening method the gasoline is contacted with a solution of sodium plumbite in aqueous sodium hydroxide to produce lead mercaptide which is then converted to the corresponding organic disulfide and lead sulfide by treatment with elementary sulfur, which is usually added to the gasoline in solution in a separate portion thereof. The control of the The term free sulfur as herein I amount of sulfur added is oftentimes difficult because of the variation in mercaptan content of the gasoline and because of the variation in rates of flow through a given equipment. Use of the theoretical amount of sulfur required to cause complete conversion of the lead mercaptide to lead sulfide and. the corresponding alkyl disulfide usually results in a'colloidal suspension of lead sulfide which either does not settle out at all or only after a long period of time. In order to get a reasonably rapid break or separation of the lead sulfide, it has been found necessary to increase the time and degree of contact and also the amount of sulfur added. Thus, the length of time for separation of lead sulfide is ina measure dependent on the amount of excess free sulfur added. However, the addition of this excess sulfur gives rise to undesirable side reactions among which is the formation of alkyl polysulfides.- It has been shown by thework of numerous investi-' gators that the free or polysulfide sulfur remaining in gasoline after doctor sweetening is extremely detrimental to the desirable properties of the gasoline. The antiknock properties and storage stability of the gasoline are particularly sensitive'to the presence of thesesulfur compounds. Furthermore, the color stability is affected and the gasoline may be corrosive. There are inuse at the present time various tests which indicate in a qualitative way the amount of sulfur which can be added'during doctor sweetening without the gasolines becoming corrosive. These tests are used by sweetening plant operators as controls for judging the amount of sulfur to add. One of these tests depends on the amount of precipitate obtained when the sweetened gasoline is shaken with metallic mercury. If the amount of precipitate appears to be less than that obtained with a standard sample, the gasoline is said to be satis-, factory.

Another test involves the use of a solution of butyl mercaptan which is added to the gasoline in known amount together with clear doctor solution, and the mixture shaken. The discoloration which develops in the gasoline upon standing has been found by experience to be related to the amount of sulfur present, and is a measure of the corrosiveness of the gasoline.

However, there is a considerable difference between theamount of sulfur which will give positive corrosion according to these and the standard copper strip tests now in use, and the'amount of sulfur which will result in decreased colorstability and lead susceptibility, and, when dealing with cracked gasolines, lowered storage stability and response to inhibitors. I-Iowever, the addition of a certain amount of excess sulfur is unavoidable and is even considered desirable by treating plant operators in order" to get a clean separation of 'leadsulfide. An object of this invention is to provide a method for removing the 1 excess sulfur after it has served its purpose.

In one specific embodiment the present inven tion comprises treating hydrocarbon distillates with solutions of potassium hydroxide in a mixture consisting of a major proportion of a monohydroxy alcohol containing a minor proportion of a second non-aqueous solvent which is miscible with the alcohol but insoluble in gasoline.

It is a well-known fact that solutions of potassium hydroxide in absolute alcohol will remove sulfur from gasoline. However, the process as taught in the prior art has certain disadvantages which have prevented its widespread use. cording to the previous methods it is necessary to remove the alcohol from the gasoline in which it is soluble, and this is usually done by water washing. The use of water inalcoholic solutions of potassium hydroxide is not practical, since such solutions do not remove the free sulfur. As a consequence, the alcohol which is recovered must 7 4 be purified and rendered absolute, or nearly so, before it can be used again in the process. This step requires the installation of expensive equipment, which from the standpoint of cost makes the process impractical of use.

The present process, however, utilizes only nonaqueous solutions, or solutions containing minor amounts of water, for example, less than 5%. Glycerine or other similar substances, such as ethylene glycol and the mono methyl ether of diethylene glycol otherwise known as methyl carbitol have a selective solvent effect on the alcohol such that solutions of potassium hydroxide in alcohol and glycerine are immiscible with gasoline. This does not, however, result in the loss of the activity of the potassium hydroxide for removing sulfur.

The alcohol-glycerine-potassium hydroxide solution is agitated with a sulfur-containing gasoline by any of the known efficient means until the reaction between the sulfur and the potassium hydroxide is complete. Such methods include countercurrent contacting in packed towers, mechanical agitation, passage through orifices and mixing nozzles, and many other devices well known to the art. When the reaction is complete the mixture is permitted to settle and the gasoline is decanted from the spent solution. The

to permit crystallization of the major portion of the reaction products between potassium hydroxide and sulfur, followed by filtration to remove the glycerine. While this may result in a small amount of the salts going back into solution, the amount is, so small that it does not interfere with the operation of the process. The recovered alcohol and glycerine are blended together, additional KOH is dissolved and the operation repeated. As a result of this method of treating, it has been found possible with but small expense to the refiner, to continuously reduce the free sulfur content of distillates below a point where it exerts harmful effects on the desirable, properties of the gasoline.

The following examples are given to indicate the efficiency of the proposed process, although they should not be construed as limiting the scope of the invention to the exact procedure described.

Example 1 A sour Midcontinent-West Texas cracked gasoline was sweetened by the sodium plumbite method in the usual manner by agitating with doctor solution and adding sufficient excess of sulfur to bring about rapid settling of the lead sulfide. As a result of this treatment the gasoline was found to be corrosive to the copper strip test at 122 F. Instead of blending the corrosive gasoline back with the sour gasoline and sweetening the mixture with a reduced amount of sulfur,

which is a standard procedure for the recovery of corrosive gasolines but which is expensive and troublesome, the gasoline was treated in the following manner:

The gasoline and 10% by volume of a solution consisting of 10% potassium hydroxide, methanol and 10% glycerine were blended thoroughly by passage through a series of orifice mixers and then permitted to settle. The alkaline solution which was by no means spent was withdrawn and recirculated. The gasoline which had originally contained 0.02% excess free sulfur and was corrosive, was found at this point to be non-corrosive to the copper strip and to contain 0.0006% of elementary sulfur. The properties of the gasoline before and after treatment by this process are shown in the following table:

The results show that the octane number of the gasoline was improved, the tetraethyl lead susceptibility increased by a substantial amount, and that the induction period of the gasoline containing inhibitor was improved. The quantity of tetraethyl lead required to arrive at a given octane number, and the inhibitor necessary for a 240-minute induction period was materially reduced, thus resulting in considerable savings.

Example 2 A straight-run gasoline from Midcontinent crude oil was sweetened by the conventional doctor-sweetening method after which it was found to be highly unstable to light. The gasoline developed a pronounced color and became cloudy upon exposure to. sunlight. Furthermore, when blended with a sweetened cracked gasoline the blend. was made unstable both as to color and storage stability so that it was impossible to market theblend having the characteristics produced. As a consequence, the refiner was forced to resort to. various expensive means, such as acid treatment of the straight-run prior to sweeteningin order to market a satisfactory final blend.

The doctor sweetened straight-run gasoline was treated by means. of 1.0% by volume of a solution similar to that described in Example. 1, with a result that said gasoline was stable to sunlight, did not develop haze, and could be used in the final blend with the cracked gasoline with no further treatment. It" was further found that by treating both the cracked and straight-run gasoline after plumbite'sweetening a still greater said second solvent being selected from the group consisting of glycerine, ethylene glycol and mono methyl ether of diethylene glycol.

2. The method as defined in claim 1. further characterized in that said second solvent is glycerine. Y

3. The method as defined in claim 1 further characterized in that said second solvent is ethylene glycol. I

4. The method as defined in claim 1 further characterized in that said second solvent is mono methyl ether of diethylene glycol.

CHARLES WIRTH, III.