US1754649A - Sweetening process - Google Patents

Description

Patented Apr. 15, 1930 GENTRY' LLOYD ROWSEY, F AiMARILLO, TEXAS SWEETENING PROCESS N0 Drawing. Application filed April 13,

This invention relates to the refining of hydrocarbon oils; particularly to improvements in the refining of oils of the gasolinekerosene type.

In refining gasolines and kerosenes, it has been common practice .to agitate these oils with solutions containing litharge dissolved in an excess of caustic soda. Such alkaline solutions of sodium'plumbite form' certain colored lead compounds which are oil-soluble but which are precipitated by the addition of free sulphur. To the extent to which the treated oils may contain elementary sulphur, such oil-soluble lead compounds may be precipitated by this sulphur. In practically all cases, however, it is necessary after agitation with the alkaline sodium plumbite solution, to add free sulphur to break up these 011- soluble colored lead compounds and to effect the removal'of lead so combined as lead sulphide. This operation is commonly called sweetening. There are several Well recog nized difficulties incident to the method of sweetening just described. The cost of the reagents is frequently excessive; as much as a pound of litharge per barrel of gasoline or kerosene treated may be consumed 1n the operation. It is diiiicult accurately to regulate the addition of free sulphur to the 011;

usually a slight excess of free sulphur is left in the oil resulting in color instabillty and causing the oil to be corrosg e w th respect to metals such' as copper; brass or bronze.

The precipitate formed in the Oll by the add1- tion of sulphur, largely lead sulphide, is at first extremely flocculent and voluminous and retains a considerable proportion of the oil.

Much time is lost in effecting settling of these pgecipitates in order to permit a reasonably c mplete separation of the ml, and even under favorable conditions there 1s usually a substantial loss of the refined oil product in the precipitate. This precipitate is commonly discarded, although in some instances it 1s treated for the recovery of litharge or sodium plumbite to be used in subsequent operations.

Other sweetening methods have been proposed; for example there have beenproposals to eiiect the purpose of the sweetemngoperation by oxidation'of the objectionable com- 1927. Serial No. 183,624.

pounds, mainly sulphur derivatives, by various oxidizing agents and by absorption of such objectionable compounds on various absorbent materials such as silica gel, bauxite or absorbent precipitates formed in the oil. In general, however, the alkali plumbite method has been most generally used. My invention has several important advantages over this common alkali plumbite sweetening operation.

According to my invention, the gasoline or kerosene is treated with a solution of'caustic alkali containing suspended preformed lead sulphide while subjected to the action of air brought into intimate contact with the oil and treating solution. In carrying out my inven tion, it is advantageous to mix the oil and treating solution together while blowing air therethrough under conditions such that the air is intimately distributed through themixture in the form of fine bubbles. It is also advantageous to employ a treating solution containing suspended a dense pulverulent form of lead sulphide.

Lead sulphide precipitated in the usual sodium plumbite sweetening operation changes from the bulky flocculent form in which it is initially precipitated to a fine, dense powder-like material after standing for some time. This more dense material quickly settles out of oil with which it is agitated. I have found this relatively dense pulverulent form of {lead sulphide, formed when the pre cipitate the ordinary sodium plumbite sweetening operation is permitted to stand, is a particularly advantageous form of lead sulphide for use in-carrying out=my present invention. I

I have found that even extremely malodorous gasolines or kerosenes, containing for example sufficient sulphur containing impurities of the mercaptan type to have a very ob j ectionable odor and topause large consumption of sodium plumbite in the ordinary sweetening operation, "can. be rendered entirely satisfactory as to odor and non-reactive to the sodium plumbite reagent in a very brief. period of treatment by agitation with a suspension of lead sulphide in a caustic alkali solution in the presence of air introduced into and passed through the oil and treating solution in the form of fine bubbles. Subsequent to this treatment, the lead sulphide suspension is settled out of the oil. This settling is easily and quickly effected if the form of lead sulphide described above is used.

The alkaline suspension of lead sulphide separated from the oil after treatment can be used again for treatment of further quantities of the oil, and the activity of the lead sulphide apparently continues for an indefinite time. In the practice of my invention on an industrial scale, I have employed the same alkaline suspension of lead sulphide for periods of three or four weeks in the continuous treatment of successive quantities of raw gasoline without having to replenish the lead sulphide. vantages of my invention; there is no large consumption of the active material, and this affords an important economy as compared to methods hitherto known, in which litharge used for example.

I have found that intimate contacting of air with the lead sulphide suspension is essential, and that the effectiveness and rapidity of the treating operation is to a large extent promoted by promoting intimate contact between the mixture of Oll and the treating solution and the air supplied to the operation.

I have also found that it is advantageous to use treating solutions free from dissolved litharge; otherwise there is sometimes a tendency toward formation of the oil-soluble lead compounds to which I have previously referred. Such compounds, 'if formed, can be decomposed or oxidized by prolonged treatment, but I have found it advantageous to carry the operation out in the substantial absence of sodium plumbite to avoid any formation of such components.

The caustic soda in the treating solution is consumed by the action of any dissolved hydrogen sulphide present in the oil subjected to treatment, and I have also found that the resulting alkali sulphides in the treating solution apparently retard the sweetening operation if present in sufficient amount. Accordingly, I find it advantageous to give oils containing dissolved hydrogen sulphide a preliminary treatment with a caustic olution, for example with a solution containing the minimum proportion of caustic soda sufficient to remove such dissolved hydrogen sulphide.

As a specific example of the practice of my invention. I give below an operation carried out upon a very sour gasoline obtained from crude petroleum from the Panhandle field in Texas, commonly known as Panhandle crude:

The gasoline treated had a particularly high content of sulphur compounds of the mercaptan type, and when treated by the usual sodium plumbite method required about one pound of litharge and a correspondingly large proportion of sulphur per barrel (42 This is one of the important adgallons). In a batch operation, in accordance with my invention, 1,000 barrels of this gasoline were treated with 100 barrels of a solution of caustic soda, about 15 B., containing about 1,500 pounds of previously prepared precipitated lead sulphide in suspension. This mixture was agitated by blowing air through it, and the air was introduced so as to form fine bubbles producing a froth which was carried up into and through the oil. After fifteen minutes agitation, the treating solution and suspended lead sulphide was allowed to settle out of the oil, and the oil separated from the settled alkaline mixture. The separated oil was of entirely satisfactory odor and was non-reactive to sodium plumbite.

In the treatment of such gasoline in the manner just described, it is not unusual to find that there has also been a substantial improvement in color, for example as much as one to two points on the Saybolt color scale.

I have observed, in *arrying out my inven tion, that the bubbles of air when in a sufficiently line state of sub-division, become filmed over with lead sulphide, the lead sulphide thus being carried up through the oil. And I find it advantageous in carrying out my invention to promote sub-division of the air introduced into the mixture of oil and treating solution. For this purpose, I have employed various forms of apparatus. For example, in the treatment of successive batches of oil, I have employed cone bottom agitators of conventional design and have introduced the air in very fine streams of bubbles through a plurality of small orifices arranged close to the bottom of the cone. I have also introduced the air in relatively small streams beneath mechanical agitating devices such as a propeller or a propeller arranged to operate within a sleeve. The air may also be introduced by forcing it into the mixture of oil and treating solution through porous material, for example through a tube or plate of alundum or porous baked silica, forming very fine bubbles or a fine froth. In continuous operation, the oil and treating solution may be supplied to the lower end of a vertically arrange-d orifice mixer into the low-er part of which the necessary air is also introduced.

I am not certain as to the exact relationship of the effect of'the air and the metallic sulphide in the calistic soda solution in causing the sweetening action. The air and lead suI- phide apparently react to a considerable extent to form sodium thiosulphate, which then reacts with the sulphur compounds in the oil to assist in the sweetening action. There also appears to be a direct oxidation of the sulphur compounds by the air when intimately admixed with the oil being treated, the lead sulphide promoting the reaction. In any event I do know that the action of the air on the lead sulphide suspended in the caustic soda solution or on the oil in the presence of the lead sulphide suspension is such that the desired result is accomplished in a period of time in which there seems to be very little if any improvement in the absence of lead sulphide. However, I do not intend to predicate my invention upon any particular explanation. I may also note that the treatment of gasolines and kerosenesin accordance with my invention does notusually involve any large reduction in sulphur content.

In commercial practice, I have found that, even in extreme cases, the use of inordinately large volumes of air is unnecessary. In many cases, for example, I have found the total volume of air required is not much more than about ten times the total volume of the oil treated, and frequently the proportion required is less than this. The proportion of air used, of course, is dependent upon the efficiency with which it-is used, and this is another respect in which fine sub-division of the air assists in making the operation economical.

My invention also lends itself to continuous operation. In continuous operation, gasoline or kerosene is pumped continuously through a zone where it is intimately mixed and agitated with the treating solution containing lead sulphide and caustic soda and with air and is then conducted through one or more settling receptacles where the rate of flow is adjusted to promote separation of the oil from the treating solution. The facility with which the treating solution can be caused to separate from the oil in carrying out my in vention makes it particularly valuable for continuous operation. ikewise, in continuous operation in accordance with my invention, the treated solution'containing lead sulphide may be pumped directl from the bottom of the settling tanks bac to the mixing apparatus. The treating solution, in such an operation, may be replaced from time to time, or a part of it may be continuously discharged and this part replaced by fresh treating solution.

In order to reduce any loss of gasoline or kerosene by evaporation, the air employed is advantageously recirculated, in whole or in part, until due to consumption of oxygen it becomes ineffective for the purposes of the treatment. Likewise, escaping air may be subjected to treatment for the recovery of any hydrocarbon vapors it may contain, for

example by absorption treatment with active charcoal or with an absorbent oil, or-by cooling and compression. Although the lead sulphide m be used repeatedly, an indefinite number of times, its activity may be promoted by treatment, from time to time, with steam to remove any absorbed or entrained oils or oily impurities.

Such treatment assists in making it ossible to use a minimum of the lead sulphide or to reduce the time of treatment or to reduce the amount of air required.

I claim:

1. An improved method of sweetening gasolines and .kerosenes which comprises agitating the oil With a suspension of preformed lead sulphide in a caustic soda solution while bringing air into intimate contact with the mixture.

2. .An improved method of sweetening gasolines and kerosenes which comprises agitating the oil with a suspension of dense pulverulent lead sulphide in a solution of caustic soda while bringing air into intimate contact with the mixture.

3. An improved method of sweetening gasolines and kerosenes which comprises agitating the oil with a suspension of preformed lead sulphide in a caustic soda solution while passing air through the mixture in the form of line bubbles.

4. An improved method gasolines and kerosenes which com rises agi tating the oil with a suspension 0 lead sulphide in a solution of caustic soda substantially free from dissolved litharge while bringing air into intimate contact with the mixture.

In testimony whereof I afiix my signature.

GENTRY LLOYD ROWSEY.

of sweetening