US2308001A - Process for refining cracked gasoline - Google Patents

Description

Jan. l2, 1943. w. E. FORNEY VPROCESS FR REFINING CRACKED GASOLINE Original Filed Feb. 19, 1936 ATTORNEY Patented Jan. 12, 1943 PROCESS FOR REFINING CRACKED GASOLIN William E. Forney, Merchantville, N. J., assigner, by mesne assignments, to Cities Service Oil Company, New York, N. Y., a corporation of Pennsylvania Original application February 19, 1936, Serial No. o

Divided and this application December 8, 1939, Serial No. 308,105

6 Claims.

This invention relates to the manufacture of an improved motor fuel product and more particularly to a blending composition adapted to improve the anti-knock qualities of motor fuels or gasolines poor in this respect.

This application is a division of the applicants pending application Serial No. 64,671, led February 19, 1936, and which has issued as Patent 2,263,266, November 18, 1941, for Motor fuel product and process of manufacture.

For a number of years past, the demand for high anti-knock motor fuels has been increasing and the petroleum refiner has been constantly improving the octane value of the gasolines produced. However, in almost every instance an improvement in the anti-knock character of the gasoline has resulted in the lowering of its end point. The higher boiling parain vhydrocarbons have been found to have lower octane ratings than the lower boiling paraffin hydrocarbons. It has therefore been necessary to eliminate higher boiling fractions from the gasolines marketed because of the necessity of obtaining a certain speciiied octane rating.

'Ihe rening of cracked gasoline has also materially changed in recent years because of the necessity of avoiding the lowering of the octane rating of the gasoline through treating. Formerly it was usual practice to refine cracked gasolines with concentrated sulfuric acid, but it is now a recognized fact that sulfuric acid treatment, particularly in the old type agitators, materially lowers the octane value of the resulting gasoline. Cracked gasolines are therefore n ow refined to a large extent by treating them with certain agents such as fullers earth and similar adsorptive materials to avoid as far as possible the destruction of the desirable anti-knock constituents which in most cracked gasoline depends upon its content of unsaturated olelinic hydrocarbons.

The higher boiling hydrocarbon fraction however, which formerly went into the motor fuel product is now eliminated by a fractionating oper ation and either returned to the cracking unit or used as fuel oil.

The primary object therefore of the present invention is to provide a methed of rening cracked gasolines in order to avoid the necessity of eliminating the heavier constituents which normally` should be in the gasoline in order to give it a reasonably high B. t. u. value.

A further object of the invention is to provide a process for producing a gasoline motor fuel product having a relatively high end point and at the i I same time a higher octane rating than the crude gasoline as received from the cracking unit.

A still further object oi the invention is to provide an improved blending material or fraction of relatively high octane value suitable for blending with straight run gasoline or other relatively low octane motor fuel.

Accordingly the present invention relates to certain improvements designed to renne the crude cracked gasoline received from the cracking unit by bringing the same into intimate contact With concentrated phosphoric acid under such temperature and pressure conditions as to eliminate e undesirable gum-forming constituents and at the same time actually increase the octane rating of the gasoline. The invention also includes the production of a relatively high octane blending product of high boiling point which is particularly adapted for blending with straight run gasoline or natural gasoline to increase the octane rating of the linal blend. A further feature of the invention involves the contacting of unsaturated hydrocarbon gases with concentrated phosphoric acid under controlled temperature and pressure conditions to produce a polymerized product of unusual value as a motor fuel, or for blending with relatively low octane gasolines.

Other features and objects of the present invention will be apparent to those skilled in the art from the following more detailed description taken in connection with the accompanying drawings in which:

The single figure is a diagrammatic flow sheet showing a combination of apparatus elements particularly adapted for carrying out the improved process of the present invention to produce the improved product herein disclosed.

Referring to the drawing, the cracked gasoline to be rened is passed in Vapor phase either directly from the cracking unit or from a Vaporizing unit at a temperature of from 300 to 475 F. through a valved line 2 into a rening column 4 and passed upwardly therethrough in intimate contact with concentrated phosphoric acid. The column 4 may comprise the usual bubble cap tower of conventional design, in which the concentrated phosphoric acid ows downwardly over the trays while the cracked hydrocarbon vapors pass upwardly in intimate contact with the phosphoric acid maintained in each tray. The concentrated phosphoric acid used in the tower 4 is introduced through a valve line 6, preferably after being heated to a temperature equal to that of the incoming vapors. The refined gasoline vapors treated in the tower 4 are discharged through a vapor line 8 and conducted through one or more valved connecting lines I0, into the lower midportion of a bubble plate fractionating tower l2, in which the vapors are fractionated for the purpose of eliminating any undesired high boiling constituents and to give the gasoline the desired end boiling point according to market specifications.

The hot phosphoric acid which is preferably about 85% acid in passing downwardly through the treating column 4 polymerizes the extremely unsaturated hydrocarbons such as diolefines, as well as some of the normal oleiines. The resulting polymers have been found to comprise not only the aliphatic hydrocarbons, but to include substantial proportions of naphthenic and aromatic hydrocarbons. The higher boiling polymers produced in column 4 are condensed and flow downwardly through the tower with the phosphoric acid, The phosphoric acid also reacts with olefines contained in the gasoline vapors to form certain amounts of alkyl phosphate compounds. The liquid mixture reaching the bottom of the tower 4 is withdrawn therefrom through a valved line i4 into a separator I6, in which the oil constituents are separated from the phosphoric acid and dissolved alkyl phosphates. If the acid mixture in the tower '4 should become too viscous because of the concentration of the phosphoric acid, a small proportion of steam may be introduced through the line 2. However, at the temperatures used in the tower 4, very little Water is lost from the acid and in no case has the acid mixture been concentrated enough to affect its flow downwardly through the tower.

The partially spent phosphoric acid and dissolved alkyl pho-sphates are withdrawn from the separator I 5 through a line I8 and all or any desired portion thereof may be withdrawn to storage through a valved line 2U, or passed to a suitable apparatus for recovering the alkyl phosphates, or used for the manufacture of alcohols or other organic compounds. A portion of the partially spent acid withdrawn through the line I8 may be conducted through a line 22, a pump 24, and a valved line 2tl which serve to reintroduce the partially spent acid back into the tower 4 through the line 6. The acid may be introduced into the mid-portion of the tower instead of the top of the tower by using the valve connecting line 2B. Dilute recovered acid may be used in the top of the tower since the excess water will be removed with the vapor.

Certain gasolines may contain abnormally high proportions of unsaturated hydrocarbons or for some other reason may require a milder treatment than other gasolines. Therefore the phosphoric acid introduced through the line B may be modified by adding thereto some of the spent acid from separator l. It has been found that alkyl phosphates (both the acid and the neutral phosphates) are very effective refining agents for certain types of cracked gasoline. Byr reintroducing these constituents into the top of the tower the refining agent in the tower 4 may be controlled very accurately. In the treatment of some gasolines, it is particularly desirable to give it a mild initial treatment in order to polymerize, react with, or stabilize very unstable compounds, and therefore provision is made for reintroducing the alkyl phosphates into the mid-portion of the tower Il so as to independently control the composition of the treating material in the tower 4 and particularly in the lower half of the tower where it first contacts the fresh raw gasoline vapors.

The separator I6 may comprise any suitable type of apparatus such as a gravity separator or a centrifugal separator. The partially spent acid and alkyl phosphates conducted through the lines i8 and 22 may be brought to any desired temperature for reintroduction into the column 4 by passing all or any portion thereof through a valved line and conducting it through a heat exchanger 32 and back into the line 26. Ordinarily the acid passing through the line 30 may need to be heated in order to bring it to the desired temperature, but on the other hand, it may be cooled if for any reason the temperature of the acid discharged from the bottom of tower 4 has been heated too highly by the hot vapors introduced through the line 2.

The polymer oil separated out in the separator I6 which may comprise from 1% to 5% of the gasoline treated in the tower 4 is passed through a valved line 34 into a washer 35 in which the oil may be washed with water oran alkaline solution introduced through a valved line S8. An alkaline solution is preferred since it effectively removes any occluded acid constituents. The wash water or alkaline solution is withdrawn from the washer 36 through a valved line 4i),

r while the refined oil is withdrawn through a line 42. This polymer oil withdrawn through the line 42 has been found to be a very unusual product because according to known practices it would have a relatively low octane rating and be entirely unsuited for use as a motor fuel. However, it was found on testing this product that it contained substantial proportions of aromatic hydrocarbons and that it had a relatively high octane value. In one particular instance, this polymer oil had a boiling range of from 310 to 486 F., a gravity of 34.7 A. P. I., and when blended in equal parts with Seminole straight run gasoline having an octane number of 50, it raised the octane number of the blend to 6l.

The above described operation may be modified to the extent that hydrocarbon gases, preferably gases comprising principally propylene, the butylenes and pentenes, are introduced into column 4 through a line 44, and subjected to the treatment of phosphoric acid along with the gasoline vapors.

However, these and similar gases may be treated alone in column 4 with phosphoric acid, but the yield of polymer withdrawn with the phosphoric acid will be substantially lower. The contact of the unsaturated gaseous hydrocarbon with phosphoric acid and alkyl phosphates in column 4, particularly under pressures of from 250 to 350 pounds per square inch effects a substantial polymerization to normally liquid constituents containing appreciable quantities of aromatic and naphthenic hydrocarbons. Most of these normally liquid constituents however will remain in vapor state in the column 4 and pass through the lines 8 and I0 into the tower l2. The same thing is true in the treatment of cracked gasoline in column 4, since substantial polymerization of the lower molecular weight hydrocarbons in the gasoline increases the proportion of aromatic and naphthenic constituents which pass over with the vapors through the line 8. These results have been verified by the fact that the gasoline taken overhead through the line 8 has a substantially higher octane rating than the gasoline introduced into the tower 4 through the line 2. In a particular instance, it was noted that the' aromatic hydrocarbon con- -tent of the gasoline treated in tower 4 had increased approximately '7%.

Where the gasoline constituents discharged from the column 4 through the line 8 have the proper end point desired for the gasoline, the use of the column I2 may be entirely dispensed with, but ordinarily the gasoline must be made for a particular market condition or for a particular season, so that in order to give it the proper desired end point it is subjected to fractionating in column l2. This column is provided with the usual bubble cap trays and with a steam heating coil 46 for maintaining the desired bottom temperature and temperature gradient in the column. The desired gasoline fraction is taken overhead from the column I2 through a vapor line 48 together with any uncondensible gases. This mixture is passed through a condenser S in which the gasoline is condensed and thereafter conducted through a line 52 to a receiver and gas separator 54. The uncondensible gases separated out are discharged from the receiver 54 through a valved line 56. In order to maintain the proper cut temperature on the column l2 a portion of the final product from the receiver 54 is withdrawn and passed through a line 58, a pump 60, and a line 62 onto the top tray in the column. The amount of such product returned t-o the column I2 may be automatically regulated in accordance with welleknown practices. A pressure substantially equal to that in tower 4 may be held in tower l2 but 50 pounds is usually suilicient.

The nal gasoline product recovered in receiver 54 is withdrawn through a valved line 64 into a washer 66 in which it is washed with water oralkaline solution introduced through a valved line 68. The spent solution is withdrawn from the washer through a valved line 1i), while the final product is withdrawn through a valved line 12. This product may be sent directly to storage or market, or blended with some of the higher boiling products produced in the process by passing it through valved lines 14 or 14 and 16, which respectively discharge into blending tanks 18 and The heavy naphtha recovered in the base of the tower I2 is not returned to the cracking unit in accordance with the usual practice. It is very valuable blending stock because of its relatively high content of naphthenic and aromatic hydrocarbons. It particularly contains substantial proportions of branched chain aliphatic and aromatic hydrocarbons which were produced in the column 4 by the action of the phosphoric acid. This heavy blending naphtha is withdrawn from the tower I2 through a valved line 82 and washed in a washer 84 with water or alkaline solution introduced through a valved line 85. The wash liquor`is discharged through a valved line 88 while the finished heavy naphtha is discharged through a valved line 9i). This'product may be passed to storage and used directly as a motor fuel, or it may be introduced through valved connecting lines 92 and 94 respectively, into blending tanks 80 and 18.

In a similar manner the nished polymer product discharged from the washer 36 through the line 42 may be used as a heavy motor fuel or conducted through valved lines 4lili or 96 and S8 respectively, into blending tanks 18 and 85. Straight run gasoline or natural gasoline may be introduced into the blending tanks 18 and 89 respectively through valved lines |60 and |02 to give the desired blends having the proper initial boiling point and octane number.

In the treatment of unsaturated hydrocarbon gases such as cracking still gases and coke oven gases, a recovery of from 3 to '7 gallons of condensate per thousand cubic feet of gas is obtained, depending upon the unsaturated hydrocarbon content of the gas. Some of the material polymerizes to relatively high boiling constituents in the treating column 4, while the lower boiling polymers pass on to the column l2 and condenser 5d. All of the liquid products obtained from the treatment of gases with the phosphoric acid in the tower 4 contain appreciable quantities of aromatic and naphthenic hydrocarbons. The gas discharged from the receiver 54 through the line `56 usually contains a relatively low proportion of unsaturated hydrocarbons, but the wet gases from the usual stabilizing apparatus where cracked gasolines are stabilized, have been found to give high yields when subjected to treatment in the tower 4.

As an example of the difference in character of untreated cracked gasoline and of the treated gasoline made in accordance with the process of the present invention, a cracked gasoline containing l8.2% unsaturates; 22.5% aromatics; 36.8% naphthenes; and 22.5% paraftins, when treated with phosphoric acid in accordance with the present invention showed an increase in the aromatic hydrocarbon content to 29.5% and a decrease in the unsaturates to 12.3%.

As a further example of the anti-knock character of the polymer product recovered from the tower 4 a vapor `phase gasoline was treated in this column and the residue oil was recovered from the base of the column. This residue or polymer oil was redistilled and a heavy naphtha distillate having a gravity of 29.5 A. P. I., and a boiling range of 252 F. to 540"` F. was recovered. This distillate was blended in equal proportions with a 350 F. end point straight run Pennsylvania gasoline of 5l. octane number (by C. F. R. motor method). The resulting blend by the same test engine had `an octane number of 63.7.

In the treatment of cracked gasolines in the tower 4, it is unnecessary to use high pressures, but pressures of approximately 50 lbs. have given satisfactory results. In the treatment of unsaturated hydrocarbon gases however, a high pressure of from 250 to 350 lbs. per square inch gives a longer time reaction and facilitates the polymerization or reactions taking place in the tower d. The term polymerization may not accuratelydefine the reactions taking place between the unsaturated hydrocarbons and the phosphoric acid, because .it is undoubtedly 'true that the acid enters into the reaction in many instances to form an intermediate product which in the presence of other unsaturated hydrocarbons produces constituents such as naphthenes, branched chain aliphatic and aromatic hydrocarbons, and other products which have superior anti-knock properties.

The reactions carried out in the tower 4 may be effected in the liquid phase by suitably ad- .justing the temperature and pressure relation-4 -stituents used to make up the heavy blending stock will be separated and withdrawn through the line 82.

From the foregoing description of the present invention, it is apparent that certain modifications may be made in the operation without departing from the scope thereof. For example, the blended products formed in the blending tanks T8 and i) may be varied to suit particular conditi-ons, according to the demands of the market or the particular motor in which the fuel is to be used. In any case, it is apparent that considerable advantage is obtained from the process and that normally waste .products or substantially valueless products Vare converted into products of superior quality.

Original claims of application Serial No. 54,671 referred to above included the steps of passing gasoline hydrocarbons containing a substantial proportion of unsaturated olenic and aromatic constituents in intimate contact with concentrated phosphoric acid maintained at a temperature of approximately from 300 to 475 F'. in a reaction zone whereby a liquefied polymer oil product is formed, and of discharging the treated gasoline vapors as a refined gasoline product. Slightly different language included the use of a series of Zones maintained at a temperature of approximately 375 F. for intimate contact of hydrocarbons with phosphoric acid, converting portions of the hydrocarbons into constituents condensable under the conditions obtaining in the Zones, and withdrawing partially spent phosphoric acid and oily product produced in the zones.

Having thus described the invention in its preferred form, what is claimed as new is:

l. The improvement in the liquid phase refining of a cracked motor fuel product for the elimination of gum-forming constituents by refining the product with a reagent consisting of phosphoric acid, which comprises passing the cracked motor fuel product to be refined in liquid phase into intimate contact with concentrated phosphoric acid in a series of contact Zones, passing concentrated phosphoric acid through said zones countercurrent .to the motor fuel passed therethrough, effecting the contact in said Zones at a temperature of from 300 to 475 F. and at a superatmospheric pressure suficient to maintain the motor fuel in the liquid phase, passing the treated motor fuel product from said series of contact zones into a fractionating tower and therein fractionally distilling the motor fuel product to recover overhead from the tower a refined motor fuel of desired end point, and removing the high boiling constituents of the treated motor fuel product from the lower portion f of the tower.

2. The improvement in the liquid phase refining of a cracked motor fuel product as defined by claim 1 in which .the phosphoric acid passed through said series of zones is withdrawn therefrom together with any oily reaction products dissolved therein, and in which the withdraw phosphoric acid is separated from any such oily reaction products and then returned to said series of zones and passed through at least some of them in intimate contact with the cracked motor fuel product under treatment.

3. The improvement in the liquid phase renin-g of a cracked motor fuel product as defined by claim 1 in which unsaturated hydrocarbon gas is passed into the said series of zones along with the motor fuel product to be rened whereby higher boiling normally liquid constituents are produced therefrom.

4. The process of refining cracked gasoline for the elimination of gum-forniing constituents by refining the cracked gasoline with a reagent consisting of phosphoric acid While at the same time preventing the destruction of anti-knock constituents of the cracked gasoline, which comprises passing the gasoline through a series of contact zones in intimate contact with concentrated phosphoric acid at a temperature of from 300 to 475 F., passing concentrated phosphoric acid through said zones countercurrent to the passage of the cracked gasoline therethrough, maintaining a, superatmospheric pressure of at least lbs. per square inch on the constituents in said zones, passing .the treated gasoline from the final zone into a fractionating tower and therein fractionally distilling the gasoline to produce overhead a. refined gasoline of desired end point, and withdrawing the high boiling constituents of said treated gasoline from the lower portion of said fractionating tower.

5. The process as defined by claim 4 in which the contact between the cracked gasoline and the phosphoric acid is effected in a bubble cap tower in which the concentrated phosphoric acid flows downwardly through the tower over the trays while the cracked gasoline flows upwardly through the tower and passes in intimate contact with phosphoric acid on each tray.

6. The process of refining cracked gasoline as defined by claim 4, in which the phosphoric acid passed through said series of zones is withdrawn therefrom together with any olly reaction products dissolved therein, and in which the withdrawn phosphoric acid is separated from any such oil reaction products and then returned to said series of Zones and passed through at least some of them in intimate contact with the cracked gasoline under treatment therein.

WILLIAM E. FORNEY.

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