US2281369A - Treatment of gasolines - Google Patents

Description

Ap 8. 19 2 J. c. MoR ELL 2,281,369

TREATMENT OF GASOLINE Filed April 50, 1938 TBEATER FRACTIONATOR TREATER COOLER RECEIVER FURNACE FRACTIONATOR FURNACE INVENTOR JACQUEVC. MORRELL atented Apr. 28, 1942 TREATMENT or oasotnvas .lac ue C. Morrell, Chicago, EL, asslor-to Universal 01! Products Company, Chicago, ill a corporation of Delaware Application April 30, 1938, Serial No. 205,36

(Cl. MiG-=50) 2 Claims.

This invention relates more particularly to the treatment of gasolines produced by cracking the relatively heavy portions of petroleum oils or similar products produced by thermally decomposing' primary tars produced by the distillation of solid hydrocarbonaceous materials such as coal, and shales. It is specifically directed to improving the properties of cracked gasolines with respect to color, gum content, and antiknock value. Substantially all cracked gasolines are characterized by improved antiknock value over their straight run counter parts, but they contain undesirably high amounts of colored compounds and potential gum forming materials, the last named class being generally of the character of conjugated di-oleflns which become readily polymerized into high molecular weight resins and gummy products through the agency of accidental oxygen and catalytic con tacts.

It is recognized that many processes are in practical operation which eliminate to a greater or lesser extent the undesirable properties of cracked gasoline, the oldest of which is sulfuric acid treatment, and some of the more recent of which are characterized by the use of adsorbent material such as fullers earth which may contain in addition special chemical treating reagents or catalytic materials which tend to selectively remove gum-forming compounds as polymers which are retained mechanically. The present process is a contribution to the art of eliminating the undesirable properties ofgasoline while improving and stabilizing the more desirable properties.

In one specific embodiment the present invention comprises a process'for improving the quality of primary cracked gasolines and particularly unstabilized cracked gasolines containing material percentages of readily polymerized olefins which consists in separating said gasoline by fractionation into a light and a heavy fraction, the light fraction being subjected to controlled contact with phosphoric acid-containing catalyst and the heavy fraction being reformed by pyrolysis. The products of these two separate treatments are blended'to form the final product of the process.

In order to indicate the combination of cooperative steps which characterize the present process, a description of a characteristic process flow will be given in connection with the attached drawing which shows by the use of conventional figures in general side elevation an arrangement of interconnected units which may be employed. I

Referring to the drawing, a primary cracked naphtha of approximate gasoline-boiling range may be introduced through a line i containing a valve 2 to a charging pump 3 which discharges through a line i containing a valve 5 into and through a heating element t arranged to be heated by a furnace i. The function of this primary heating and vaporizing coil 6 is to raise the charge to the temperature necessary for separating it by fractionation into a light and heavy fraction, the heated products passing through line 8 containing a valve 9 into a primary fractionator ill. The exact point of division of difierent cracked gasolines will depend upon a variety of factors such as the amount and character of its oleiins, its boiling range, the stock from which it was produced by cracking, and various other factors. In some cases only a 25% fraction may be taken overhead for the succeeding catalytic polymerizing treatment while in other cases as high as may be thus treated. Those skilled in the refining of petroleum will appreciate the fact that only approximate rules can be given in such processes as the one at present under discussion.

The overhead vapors comprising the lighter portion of the cracked gasoline charged and the dissolved normally gaseous constituents which will ordinarily includeprincipally 3 and 4 carbon atom hydrocarbons both saturated and unsaturated pass through vapor line H containing valve It to a system of treaters containing granular material whose active constituent is an acid of phosphorus. These materials are generally known as solid phosphoric acid catalysts and are made by the general steps of incorporating a major amount of a phosphoric acid with a due principally, however, to the tendency to formpolymers from the primary esters formed by the a combination of olefins with phosphoric acid.

According to the present invention it has been determined that not only the color and gum forming properties of the lighter portions of cracked naphthas improved by the solid phosphoric acid treatment but the normally gaseous oleflns are concurrently polymerized to form additional yields of gasoline boiling range compounds having a high antiknock value so that in eflect the treatment of the light ends of the gasoline and the polymerization of the normally gaseous oleflns is effected concurrently.

The drawing shows a very simple arrangement of treaters in series although any number may be employed either in series or parallel connection. The vapors pass downwardly through treater l8 which contains a bed or a number of separate beds of granular material and thence through line I4 containing control valve l5 through a second treater I6 which represents the last in any series which may be employed. The temperature employed will vary somewhat with the relative amounts of gaseous olefins and vapors of gasoline respectively but in general they may be varied from 350-550 F. under pressures of approximately 100 to 500 lbs. per square inch. In the case of highly oleflnic mixtures there will be a tendency for a temperature rise in the first units of a series of treaters owing to the exothermic character of polymerizing and treating reactions so that it is usually best to start with a relatively low temperature and allow for the rise although cooling of the treaters or intermediate cooling between treaters may be employed.

The total products from the polymerizing and treating units pass through line H containing a valve l8, through a cooler i9 and thence through a run-down line containing a valve 2| to a receiver 22 with a conventional gas release line 23 containing. a valve 24 and a liquid draw line 25 containing valve 26. The material in receiver 22 is later blended with the cracked products separately produced by thestep to be presently described.

The treating materials may be employed in any way which effects the best overall results in the process. They will gradually become carbonized and require reactivation which may be brought about by the careful use of low oxygen content combustion gas mixtures to oxidize and remove the carbonaceous deposits at temperatures below those which have been found to be capable of causing permanent impairment of the treating reagent properties. After oxidation, steam contact may be utilized for rehydration to an optimum activity as in the case of the catalyst preparation.

The heavier fractions of the gasoline appearing as a bottoms from fractionator I0 pass through line 21 containing a valve 28 to a pump 29 which discharges through line 30 containing a valve 3| to a reforming unit which comprises a heating element 32 arranged to receive heat from a furnace 83 as its first unit. Pressures and temperatures used in reforming the heavier portions of cracked gasolines to further improve their antiknock value are relatively high, of the order. of 925-1050 F. and relatively high pressures are also employed within the safe capacity of the apparatus. The heated and partially cracked heavy fractions pass through line 34 containing valve 35 to a reaction chamber 38 which is of suitable design and capacity for permitting time for completion of the desired conversion reactions, the total cracked products following line 31 containing valve 38 to a separating chamber for further processing on account of their coke forming tendencies, these products being withdrawn through line 40 containing valve 4| to any suitable use such as fuel or a charge to a coking plant. a

The vapors from separator 38 flow through line 42 containing valve 43 and enter a final fractionator 44 which is so operated that the overhead vapors contain all components of gasoline boiling range and the total fixed gases, these overhead products following a line 45 containing a valve 48 to a condenser 41, cooled and partly condensed products flowing through run-down line 48 containing a valve'49 to receiver 50 which again has a gas vent line 5| containing a valve 52 and a liquid draw line 63 containing a valve 54. The gas mixture withdrawn from this receiver may be returned in its entirety by means of line 5| provided with valves 52' and 53' and pump 54', to the primary polymerizing and treating step to utilize its oleflnic content for the production of further yields of, good antiknock gasoline or it may be subjected to fractionation and the three and four carbon atom fraction returned. The liquid products are preferably blended with the polymerized and treated lighter fraction to form the final product of the process.

The bottoms from fractionator 44 comprising the intermediate products from the reforming step heavier than gasoline but essentially nonknocking in character pass through line 55 containing valve 66 to a recycling pump 51 and are returned by way of line 58 containing valve 59 at the inlet of heating element 52 to undergo further conversion with the primary charge.

The following example of operation is given to indicate the type of results to be expected from the practical application of the present process although its scope is not intended to be thereby precisely limited.

The gasoline treated was produced by the cracking of a mixed Mid-Continent-West Texas residuum. This gasoline had a color of approximately 4 on the Saybolt colorimeter, a gum content of mg./ cc. by the copper dish method, and an octane number of 68 before stabilization.

The gasoline was fractionated into approximately equal portions and the lighter vaporized products were passed through a series of three treaters containing solid phosphoric acid catalyst at an average temperature of 400 F. under a pressure of 250 lbs. per square inch.

The heavier 50% was reformed at a temperature of 975 F. and a pressure of 500 lbs. per square inch with a loss of approximately 15% in heavy bottoms and fixed gases.

The final products obtained by blending the stocks produced by the combined polymerizing and treating and the reforming operations respectively equalled 92% of the original gasoline and had an octane number of .73. It was found that the gum content was approximately 40 mgs. which was readily reduced to 5 mgs. by the addition of 0.01% of commercial inhibitor. The color of the final blended product was 25 on the Saybolt scale.

I claim as my invention:

1. A process which comprises separating cracked gasoline into a light fraction and a with a polymerizing agent under polymerizing conditions to produce gasoline boiling hydro= carbons from the gaseous oleiins and to free said light gasoline fraction of objectionable gum= head product containing the gaseous olefins and a substantial portion of the normally liquid fractions of the gasoline, contacting the overhead product with a polymerizing agent under poly merizing conditions to convert normally gaseous olefins contained therein into normally liquid hydrocarbons and to free said liquid fractions of the gasoline of objectionable gum-forming olefins, subjecting the bottom product of approximately gasoline end point to reforming conditions of temperature and pressure for enhancement of its anti-knock value under conditions such that a portion thereof is decomposed into normally gaseous olefins, and supplying normally gaseous olefins produced in the reforming step to the aforesaidv polymerizing step.

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