US2150084A

US2150084A - Kefining benzol light oil for

Info

Publication number: US2150084A
Authority: US
Publication date: 1939-03-07
Anticipated expiration: 1956-03-07

Description

A. L. TANNEHILL Filed April 9, 1936 WKN h.

March 7, 1939.

' REFININC- BENZOL LIGHT OIL FOR MOTOR FUEL l il Patented Mar. 7, 1939 STAT ES PAT ENT OF REFINING BENZOL LIGHT OIL FOR MOTOR FUEL 4 Claims.

'I'he present invention relates to fuels for internal combustion engines and-more particularly to the refining of crude benzol light oil, as recovered from coal gas or coke oven gas, to produce motor fuel.

An object of the invention resides in an improved methodof refining crude benzol light oil which will be economical in practice and eicient as to yield of finished product.

A further object of the invention is to provide a method of refining benzo-l light oil as recovered from coal gas or coke oven gas which will conserve certain hydrocarbon constituents of the light oil, thereby increasing the yield of finished product.

A further object is to provide a process of refining benzol light oil Which Will represent an improvement over the present refining process in that both color and sulphur content of the motor fuel can be controlled without sacrifice of any appreciable amount of unsaturated hydrocarbon content.

Crude benzol light oil contains constituents which make it unsuitable for motor fuel without some treatment. These constituents may be classed as acidic compounds, unstable unsaturated compounds, unsaturated compounds which are relatively stable, sulphur compounds which may be washed out by means of sulphuric. acid, a sulphur compound which can not be washed out by sulphuric acid but which may be largely separated into a fraction called forerunning's and small amounts of unsaturated compounds which produce an objectionable color both in the light oil or in a distillate from the light oil.

The treatment necessary to produce a satisfactory motor fuel from'the light oil may vary, depending on the nature of the light oil and on the specification for the finished motor fuel.

The acidic constituents consisting mainly of carbon dioxide, hydrogen sulphide, hydrocyanic acid and small amounts of mercaptans arel all objectionable and should always be removed. Especially objectionable is hydrogen which if present in motor fuel causes the fuel to become corrosive toward metals, due to oxidation to elemental sulphur. Acidic constituents are practically always removed by washing with caustic alkali.

Common practice is to remove the unsaturated hydrocarbons, or at least the more unstable of them, and the color producing compounds, in order to improve the color and prevent the formation of gummy constituents in the fuel by (ci. 19t-38)' these constituents. This isgenerally done by treatment with sulphuric acid.

Some treatment is generally, although not always, necessary to control the sulphur content of thenishd fuel. Sulphur exists in light oil mainly in two forms, as thiophene and as carbon bisulphide;v Thiophene canv be washed out by means of strong sulphuric acid While carbon bisulphide can be removed bydiscarding forerunning's, which isthe 'rst'fraction to distill over when the light oil is distilled. Either or both of these'methods kof reducing the sulphur content may be used. Chemical methods for removing carbonY bisulphide have recently been proposed but as yet vhave had no extensive application.

The older method of refining light oil, and which is still the method generally used, consists of washing the light oil with strong sulphuricv acid in suflicient amount to remove all of the unsaturated hydrocarbons, color produc- E ing compounds and most of the thiophene. The light oil is then washed with caustic alkali, to remove acidic constituents, and distilled. If necessary to further reduce the sulphur content, forerunnings'are discarded. This method of reningby means of strong sulphuric acid is inefcient as `to yield of finished product and expensive because of the large amount of chemicals required.

It is now well known that theunsaturated hydrocarbonsYV are valuable fuel constituents if treated by small amounts of certain substances, known as anti-oxidants or gum inhibitors, and it is therefore highly desirable to leave the unsaturatedhydrocarbons in the fuel.

More recent methods of refining light oil, o

whichY seekfto conserve the unsaturated hydrocarbons, may employ a restricted acid treatment, to remove only the more unstable of the unsaturated hydrocarbons and the color producing constituents, thereby improving the color and reducing the tendency to gum formation. A gum inhibitor may alsobe used. The process is carried out in a manner similar to the one described above except that the sulphuric acid used is restricted as to strength or quantity so as not to remove the unsaturated hydrocarbons which are relatively stable. Thiophene is not' removed by this method in substantial amount and to control the'sulphur it is necessary to discard forerunnings.

Sometimes the'light oil or a fraction of the light oilmay be merely washed with caustic alkali, to remove acidic constituents, followed by a distillation and the 'addition of an inhibitor. Sulphur content may be controlled by discarding forerunnings but color is not controlled byY this y method.

All of the refining methods heretofore Apracticed which aim to conserve the unsaturated hydrocarbons have the disadvantage that thiophene sulphur cannot be removed, the acid treatment, if any, being insufficient to remove thiophene. Forerunnings are generally discarded when necessary to reduce the sulphur content.

Actual tests have proven that most of the unsaturated hydrocarbons are found in the forerunnings if the light oil is distilled before these constituents are removed. Therefore, since acid treatment drastic enough to remove thiophene also removes the unsaturated hydrocarbons, and since most of the unsaturated hydrocarbons are found in the forerunnings of the untreated light oil, prior methods fail to conserve the unsaturated hydrocarbons to the full extent if the sulphur content is to be controlled. Furthermore, if

- either sulphur or coloris to be controlled by methods practiced heretofore, unsaturated hydrocarbons must be sacrificed. Y

The present invention furnishes a method whereby the sulphur content of the fuel can be reduced by removing thiophene and without destroying a substantial amount of the unsaturated hydrocarbons.` This is a great advantage. In many cases it will offer sufcient control of the sulphur to obviate the necessity for removing carbon bisulphide and'in other cases the amount of carbon bisulphide which'must be removed will be reduced. Furthermore, even though chemical methods for removing carbon bisulphide, now being proposed, and inspired by a desire to conserve the unsaturated hydrocarbons, should prove successful, there still remains a great advantage in the present method of removing thiophene, as often the removal of carbon bisulphide alone will not give suiiicient reduction in the sulphur content. The process of this invention can be employed in conjunction with chemical methods for removing carbon bisulphide. Y

The invention also furnishes a method for controlling the color of the motor fuel without loss of a substantial amount of the unsaturated hydrocarbon content.

The method of this invention also provides an improved method of removing acidic constituents, which saves most of the chemicals required for this purpose by former methods.

A still further advantage of the new process of refining light oil is that where only a portion of the light oil is converted to motor fuel, the remainder being worked up into pure aromatic hydrocarbons, such as pure benzol, pure toluol etc., the rening is accomplished with the use of a greatly reduced quantity of strong sulphuric acid.

By the process of the invention the forerunnings are rst separated from the light oil by distillation. The forerunnings, containing most of the unsaturated hydrocarbons and carbon bisulphide, are treated to remove acidic compounds and after adding an inhibitor may become a finished product. The color of the forerunnings is controlled by aging the light oil for a suitable length of time before distillation. Actual tests have proven that by aging the light oil for a suitable length of time a water white distillate is obtained. The time of aging may vary from a few hours to two days or even more. The distillation is preferably conducted in a continuous manner, as by so doing the separation of the forerunnings is more easily and cheaply accomplished and small auxiliary apparatus can be used. A further and more important advantage of continnous distillation is that by this process the distillate is easily kept out of contact with air until the acidic gases are removed. Contact with air for any extended time in the presence of hydrogen sulphide will cause the distillate to become corrosive. Batch distillation can, however, be managed so as to avoid harmful oxidation by treating the distillate continuously, as it comes from the still, for the removal of acidic constituents. A column still for the distillation is contemplated.

By the process of the invention, two alternative methodsY for removing acidic compounds from the forerunnings have been provided. I have found that by condensing the vapors at the top of the column, returning the condensate to the top of the column and withdrawing the condensate a few rings below the top, the acidic gases are mostly expelled as bent gases and the con-- densate may easily be washed free of the remaining acid compounds with a very small quantity of caustic alkali. An alternative method to the caustic alkali washing is to pass the forerunnings through an auxiliary column having a boiler at the bottom and a condenser at the top. The acidic gases are entirely expelled as vent gases and the product is withdrawn from the boiler, cooled and an inhibitor added.

I-Ieretofore the acidic compounds have been removed solely by washing with caustic alkali, which however consumes a considerable amount of reagent. An advantage of the present method is therefore a saving in caustic alkali requirements.

The inhibitor treated forerunings containing most of the unsaturated hydrocarbons of the light oil, may be a satisfactory motor fuel providing the sulphur content is not too high. It will generally happen, however, that the sulphur content will not be low enough, in which case the forerunnings are blended with a fraction of the light oil which is low in sulphur. This is best prepared by rening the residual light oil from the forerunnings distillation by means of strong sulphuric acid, used in sumcient quantity to remove a major portion of the thiophene. This part of the process therefore consists in blending a portion of the light oil which has been rened by means of strong sulphuric acid with a portion or'fraction which has not been so refined. An inhibitor, which must be added to prevent gumming, may be added either to the forerunnings or to the acid rened portion before blending or to the blend, the order of the blending being immaterial. It is generally best, however, to add the inhibitor to the portion which has not been rened with strong acid since this portion is unstable and must be treated with inhibitor very soon after it is made. Low sulphur benzol is blended with the forerunnings fraction in such proportion as is desired or as is required to meet the sulphur content requirements for the motor fuel. In case the sulphur content of the finished fuel can not be sufficiently reduced by blending, it may be desirable to treat the forerunnings by chemical methods for the removal of carbon bisulphide. In this case it will be so treated before adding an inhibitor. The reiining of the residual light oil is accomplished with very little acid, since it contains very little unsaturated hydrocarbons.

Thus, in accordance with the process of the invention, an improved method is provided for rening benzol light oil for motor'fuel which affords-means of controlling the color and sulphur content of the finished motor fuel and at the same time conserves a major portion of the unsaturated hydrocarbon content; also, an improved method is provided for removing acidic compounds from the crude benzol light oil.

The drawing illustrates diagrammatically one preferred arrangement of apparatus for refining crude benzol light oil according to the invention.

Numeral I indicates a receiving and storage tank for crude benzol light oil. The invention controls the color of the finished product by aging the light oil a suflicient length of time before distillation. The time of aging may vary from a few hours to two days or even more, depending on the color required, and is governed by the Volume maintained in the tank. The oil is drawn by pump Il from said storage tank and delivered through pipe l2 to the continuous column still I3. From this still considerable amounts of acidic gases such as hydrogen sulphide, carbon dioxide and hydrocyanic acid are removed, being expelled from a vent at the top of the still as at lli. The light oil is continuously distilled and the forerunnings are Withdrawn from the still near the top. The still may comprise a column of fifteen to thirty plates. At the top the column is provided with a condenser p of a size to condense practically all the hydrocarbon vapors and return them to the top of the column. The liquid forerunnings are continuously Withdrawn from about the fourth plate from the top. The oil passes through boiler l5 thereof through the cooler l@ and is eventually delivered to tank l'l. From tank l1 the oil is drawn through pipe I8 by the pump i9 and is forced through pipe 2li to an agitator 2l Where the oil is Washed with strong sulphuric acid and neutralized. The oil is then charged into a iinishing still 22 having a boiler 23. From the still the refined fractions desired for use as motor fuel are draWn oii and delivered through pipe 2li to tank 25. Said tank 25 therefore contains an acid Washed distillate and has connection through pipe 26 with the blending tank 2l. Interposed in said pipe is a pump 28 for Withdrawing the contents of tank 25 and delivering the same to the blending tank.

Referring again to the continuous column still i3 the forerunnings are Withdrawn from the top of said still by pipe Sil Which delivers said forerunnings to a cooler 3l having connection through pipe 32 with the caustic Washer 33. Said washer 33 comprises a vessel lled with packing material such as broken brick of about one-half inch in size and containing caustic solution of about twenty-five per cent strength. The caustic alkali solution removes the remaining acidic gases and mercaptans and the product obtained passes the corrosion and doctor test. The forerunnings are withdrawn from the Washer 33 by pipe 3G and delivered to tank 35 forming a receiver for the forerunnings Where an inhibitor is added thereto. The addition of an inhibiting substance, which may comprise cresol or benzol-amino-phenol prevents the formation of gummy substances in the product. The receiving tank for the forerunnings is connected by pipe Sii with the blending tank 2i, the contents being Withdrawn from the receiving tank by pump 3l. Thus in the blending tank the distillate from the residue oil which has been refined by means of strong sulphuric acid is mixed in the proper proportions With the forerunnings which have not-been refined by sulphuric acid to form the motor fuel.

As an alternative to the caustic alkali Washing of the forerunnings it is possible to continuously distill the forerunnings in an auxiliary column, taking-the finished product from thevbottom cf the column. The apparatus for continuously distilling the forerunnings would therefore eliminate the soda washer.

In accordance with the process of the invention the objectionable compounds, namely, hydrogen sulphide, carbon dioxide and hydrocyanic acid, all of Which may be termed acidic gases, are removed by distillation at the continuous column still I3 Without the loss of appreciable amounts of hydrocarbons. Heretofore these objectionable compounds have been removed by Washing the light oil With caustic soda solution, Which however, consumes a considerable amount of caustic soda. An advantage of the present method is therefore a saving in caustic soda since the acidic gases are largely removed as vent gases. Therefore the forerunnings may be Washed free of the remaining objectionable compounds including mercaptans, using only a very small quantity of caustic soda.

rIhe strong-acid refined fractions removed from the still 23, which are of loW sulphur content, are blended in tank 21 With the inhibitor treated forerunnings fractions in such proportion as is desired or as is required to give a finished motor fuel of satisfactory sulphur content. Accordingly, the present process conserves the major portion of the unsaturated hydrocarbons and at the same time provides a means of controlling the color and sulphur content of the product. The process also greatly reduces the amount of chemicals required for refining light oil.

What is claimed is:

1. The method of producing motor fuel from benzol light oil, which comprises distilling forerunnings from said light oil in such manner as to expel the bulk of the acidic gases as vent gases, Washing said forerunnings with caustic alkali to further remove objectionable compounds, Washing the residue oil with sulphuric acid to remove sulphur compounds, distilling said acid Washed residue oil, blending the distillate with said Washed forerunnings, and adding an inhibitor.

2. The process of refining benzol light oil for motor fuel, which comprises aging said light oil for a period ranging from several hours to several days depending on the volume of oil and the color required, distilling the forerunnings from said light oil in such manner as to expel the bulk of the acidic gases as vent gases, washing said forerunnings with caustic alkali to further remove objectionable compounds, washing the residue oil with sulphuric acid to remove sulphur compounds, distilling said acid Washed residue oil, blending the distillate With said Washed forerunnings and adding an inhibitor.

3. The process of refining benzol light oil for motor fuel, which comprises continuously distilling forerunnings from said light oil in such a manner as to expel the bulk of the acidic gases as vent gases, Washing said forerunnings With a caustic alkali solution of approximately 25 per cent strength to remove the remaining objectionable acidic compounds, adding an inhibitor thereto to prevent gumming, Washing the residue oil With strong sulphuric acid to remove sulphur compounds, distilling said acid Washed residue oil and blending the Washed forerunnings with said last mentioned distillate.

4. The process of refining benzol light oil from motor fuel, which consists in continuously distilling said light oil in a column still, condensing substantially all of the hydrocarbon vapors at the top of the column while Venting the acidic gases, returning the condensate to4 the top of the column, withdrawing the condensate from the column at a point intermediate between the light oil inlet and the condenser, washing the condensate so withdrawn with caustic alkali to remove the remaining objectionable acidic compounds, washing the residue oil with sulphuric acid to remove sulphur compounds, blending said condensate with a distillate of said acid washed residue oil, and adding thereto a gum inhibitor.

ARTHUR L. TANNEHILL.