US2088216A - Process of refining a hydrocarbon oil - Google Patents

Description

July 27,V 1937..

E. R. P. E. RETAILLIAU PROCESS OF REFINING A HYDROCARBON OIL Filed May 13, 1935 Patented July 27, 1937 PROCESS 0F REFINHE A HYDROCARBON Edmond R. P. E. Retailliau, Wood River, Ill., as-

signor to Shell Development Company, San Francisco, Calif., a corporation of Delaware Application May 13, 1935, Serial No. 21,147

8 Claims.

This invention relates to the improvement of hydrocarbon oils containing small proportions of esters. In particular it relates to the treatment of oils which, in the course of their refinement, have been in contact with sulfuric acid.

It is an object of my invention to provide means for reducing the content of objectionable esters in hydrocarbon oils to a concentration at which they no longer are harmful in any way. Another object is to neutralize acidulated mineral oils by means of water and without the use of chemicals; and it is a further object to provide a process, whereby acid treated hydrocarbon oils can be produced which have a better color, color stability and other improved properties, than were obtainable heretofore by related methods, and whereby the treating cost is reduced.

It has been recognized in the past that instability of sulfuric acid treated hydrocarbon oils is often due to the presence of sulfuric acid esters, such as dialkyl sulfuric esters or monoalkyl sulfuric acids and their salts. These esters are unstable; they slowly decompose, forming free sulfuric acid and/or sulfur dioxide. Both sulfuric acid and sulfur dioxide, if present in a finished oil, are exceedingly harmful. vIn minute traces they l cause general instability of the oil and in slightly larger proportions they induce corrosion.

Previous practice of reducing the content of esters consisted of treating the acidulated oil with caustic, ammonia, clay, etc., in the belief that these reagents either by chemical reaction or physical absorption would effect such reduction. I have found that such old methods of treatment are not as effective as may have been expected. Hydrolysis of certain dialkyl sulfuric esters to monoalkyl sulfuric acids proceeds readily, while monoalkyl sulfuric acids are quite stable, and hydrolysisunder ordinary conditions progresses exceedingly slowly. Metallic oxides or hyl droxides instead of promoting hydrolysis, form salts with alkyl vsulfuric acids, many of which are soluble to some degree in hydrocarbon oils. The effector caustic, for instance, is largely that of converting Vcli-alkyl sulfuric esters to oil soluble sodium monoalkyl sulfates. If an oil containing the above type of salts is subjected to a distillation, breakdown occurs with resulting formation of sulfur dioxide. The overhead distillate is sour, unstable and corrosive, due mostly to the presence of sulfur dioxide. The residue of the distillation often turns dark, probably because of a slight cracking.

Alkyl sulfates also prove troublesome in refining of mineral oils owing to' their property of emulsifying. When, forinstance, sulfuric acid and alkali treated cracked distillates are washed with water, emulsions cause frequent difficulties, which may upset plant operation or result in actual losses of distillates.

(Cl. ISG- 147) Acid treated heavy oils, which are not subjected to distillation, present a somewhat different condition, which, however, is no less troublesome. In modern refining practice such oils are usually neutralized with clays, all of which contain more or less readily ionizable metallic constituents, such as sodium, magnesium, aluminum, etc., which form corresponding salts when brought in contact with the oil containing esters. Small amounts of alkyl sulfuric acid salts of these metals may remain in the oil and as a result of their spontaneous breakdown during subsequent heat treatment or slow hydrolysis at atmospheric temperatures the re-acidication and darkening of the finished oil in storage occurs. Contributory to the hydrolysis is the peculiar property of many of the sulfuric acid salts to enable the dissolution of an amount of water about equal to their own volume.

Besides sulfuric acid esters, other esters have been found in mineral oils, the most frequent being those of the naphthenic and fatty acids. Depending upon the relining process to which the oil has been subjected, esters of mineral acids other than sulfuric may also be present.

. My method of ridding oils of dissolved esters, and in particular sulfuric acid esters, consists of `treating the oil with water at a temperature above 250 F. for a predetermined length of time and under a pressure sufficient to keep the reactants substantially in the liquid state. The water may be `slightly alkaline to avoid corrosion of the equipment; or if desired, it may be slightly acidic to `accelerate the hydrolytic decomposition. However, I prefer to use water alone without the addition of chemicals. This not only reduces the expense of the treatment, but also results in a neutral oil at a fair rate of hydrolysis. My method enables in many instances neutralization as well as removal of esters. This is so, because` most oil soluble acids or their esters not originally contained in the oil, if not soluble in water to begin with, are made water soluble by my treatment. It is of course understood that in the presence of acids which are insoluble in water but soluble in oil, neutralization of the oil can not take place. i

Neutrality of the treated oil is easily ascertained by shaking a sample first with phenolphthalein and then with methyl-orange indicator solution. Phenolphthalein must remain colorless and methyl-orange must stay orange. The test can be made more sensitive` by distilling or heating a sample of oil until the liquid reaches about 400 F., cooling, and then applying the indicators to the residue. If the oil is substantially free from mineral acid esters, it will satisfactorily i tralizing agent may be added to the water. Too high a content of neutralizing agent should be avoided because of the danger of formation of oil soluble alkali monoalkyl sulfate salts, which hydrolyze less readily than the free acids. Dilute solutions of approximately 1% alkali or less are suitable.

When hydrolizing in the presence of mineral acids, such as hydrochloric acid, precautions should be taken to avoid secondary reactions. Evidence has been found of the formation of substituted products by the action of the catalyst acid on some of the oil constituents. Such byproducts may be as harmful as the primary esters. In accordance with the above explanations I prefer to limit the pH value of my treating water for practical purposes from to l0.

The removal of esters by my treatment, although normally not altogether complete, is sufcient to increase stability of oils well above present day general requirements. I have found that the harmful eiTect of esters is in a large measure dependent on their concentration. To illustrate this phase I refer to the figure which represents a diagram showing the effect of sulfurie acid ester concentration in a distillate on the amount of SO2 evolved upon distilling under a standardized set of conditions. Esters are expressed in milligrams as dibutyl sulfate, and SO2 evolved in cubic centimeters of a 1/20 normal solution, both per 100 cubic centimeters of distillate. As will be noted the trend of the curve indicates that practically no sulfur dioxide is evolved at concentrations of esters lower than 80 mg. dibutyl sulfate per 100 cc. From this it can be readily seen that it is enough to reduce the concentration of esters to a point at which they will not cause harm, as may be evidenced by instability, sludge and gum formation, and development of corrosiveness in standing, and which in many cases corresponds to a maximum of about 80 mg. dibutyl sulfate per 100 cc.

The higher the temperature of treatment and the longer the time of contact, the more completely are the esters removed. For practical purposes 250 F. represents the lower temperature limit. An upper limit is only imposed by the safe operation of the pressure vessels required in the treatment. The time of contact may vary from several hours to only a few minutes. It depends primarily on the temperature, quicker and more complete hydrolysis taking place at a higher temperature. The amount of water used in the operation is relatively unimportant, as long as the minimum for complete hydrolysis is present and is kept in thorough contact with the oil. In practice I have found that about one volume of water is reacted with nine volumes of oil to give satisfactory results. During the hydrolysis free acid and alcohol are evolved according to the general formula which is shown below, and which summarizes the final result of the reaction.

Actually the reaction proceeds in two stages in the course of which a mono ester and an alcohol are formed in the rst stage, the mono ester further decomposing to sulfuric acid and alcohol in the second stage.

If the water to oil ratio is not greatly lower than indicated above, the acid released in the reaction is sufficiently diluted, so as not to cause secondary reactions to any extent. The reaction, in other words, is substantially one of straight hydrolysis. The process can be carried out in batch, in closed vessels equipped with stirrers, or in continuous mixers, as long as the requisite time-temperature combination is observed, and as long as the equipment is built to withstand the pressures.

At the end of the reaction period, water is allowed to separate and is removed. This may be done at the temperatures and pressures of the treatment, or else the mixture may be cooled and separated at atmospheric pressure. Settling or centrifugal separation may be applied.

Acids and lower alcohols are removed with the water and, if desired, can be concentrated and recovered therefrom. Higher alcohols remain in the oil, and in the case of gasoline contribute to its anti-knock value.

Before subjecting the acid treated oil to my treatment it is good practice to remove as much as possible of insoluble esters or suspended sludge. This can be done by settling, centrifuging, filtering through absorbent material, contacting with solid adsorbents or by simple water or caustic wash. The quantities of esters remaining in the oil thereafter are usually below 1/%, and in rare instances only above 1%.

By taking this precaution my hydrolytic water treatment can usually displace treating of acid treated oils with chemicals entirely. For instance, in the manufacture of high anti-knock crack-ed gasoline, a cracked distillate may be treated with two or more dumps of diluted sulfurie acid of increasing strength. Sludge is separated as completely as possible by any of the known means, and the sludge-free oil is then subjected to my hydrolytic treatment. After separation of the water layer, the oil is fedistilled. The overhead product has a good color and color stability, is neutral, and has a lower gum, actual as well as potential, than has the same distillate after a conventional acid and neutralizing treatment.

As intimated, my process is not limited to any particular type of oil. The entire range of liquid hydrocarbon products, naphthas, kerosenes, lubricating oils, etc., are equally well applicable. It is understood, of course, that certain oils will show greater improvement than others, particularly since the conventional methods produce fairly stable oils from certain stocks. My method is particularly advantageous in cases in which the old methods of neutralizing are not satisfactory. But even where comparatively stable oils are produced, my treatment results in some improvement regardless, in addition to a reduction of treating cost.

The most decided gain is obtained in the treatment of highly cracked distillates, or in the production of oils which during their use are subjected to enormous strains, such as, for instance, transformer oils. The latter not only gain resistance to sludging, but also show a marked improvement in electrical resistance.

I claim as my invention:

1. In the process of treating a substantially sludge-free hydrocarbon` oil containing mineral acid esters, the step of contacting said oil with water substantially free of active chemicals at a temperature of at least 256 F. and under a superatmospheric pressure sufficient to maintain the oil and the water in the liquid phase.

2. In the process of treating a substantially sludge-free liquid hydrocarbon oil containing mineral acid esters, the stepof contacting saidl liquid oil with Water substantially free of active chemicals at a temperature of at least 250 F. under a superatmospheric pressure suflicient to maintain the oil and Water in the liquid state for a period suicient to hydrolyze a substantial fraction of said esters.

3. In the process of treating a substantially s1udge-free liquid hydrocarbon oil containing sul.

furic acid esters, the step of contacting said liquid oil with Water substantially free of active chemicals at a temperature of at least 250 F. under a superatmospheric pressure suicient to maintain the oil and Water in the liquid state.

4. In the process of treating a hydrocarbon oil the steps of contacting said oil With a mineral acid, capable of forming esters with hydrocarbons under conditions to produce an ester-containing oil and acid sludge, separating the oil from the sludge, and then contacting the liquid acid-treated oil with Water substantially free of active chemicals at a temperature not less than 250 F. under a superatmospheric pressure sufficient to maintain the oil and water in the liquid state.

5. In the processy of refining a substantially sludge free liquid hydrocarbon oil containing mineral acid esters, the steps of contacting said liquid oil with Water substantially free of active chemicals at a temperature of at least 250 F.

under a superatmospheric pressure surlicient to' maintain the oil and Water in the liquid state for a period suicient to hydrolyze a substantial portion of said esters, thereby dissolving some of the products of hydrolysis in the hot Water, and separating the aqueous solution of said dissolved products of hydrolysis from the treated hydrocarbon oil.

6. In the process of rening a hydrocarbon oil the steps of treating said oil with a mineral acid capable of forming esters With hydrocarbons under conditions to produce a sludge and oil soluble esters, separating the sludge from the oil, and then contacting the latter with Water substantially free from active chemicals at a temperature of not less than 250 F. under a superatmospheric pressure suicient to maintain the oil and the water in the liquid phase for a time suflicient to reduce the ester content of l the oil to below that which corresponds to about 80 milligrams dibutyl sulfate per hundred milliliters of oil.

'7. The process of claim 5 in which the oil to water ratio is approximately 9 to l.

8. In the process of rening a hydrocarbon oil the steps of treating said oil With a mineral acid capable of forming esters with hydrocarbons under conditions to produce a sludge and oil soluble esters, reducing the ester content to not more than about 1/2% by removing sludge from the treated oil, and then contacting the latter with Water substantially free from active chemicals at a temperature of not less than 250 F. under a superatmospheric pressure suiiicient to maintain the oil and the Water in the liquid phase for a suiiicient time to hydrolyze a substantial portion of the said esters to free acid and alcohol.

EDMOND R. P. E. RETAILLIAU.

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