US2088887A - Method of treating cracked hydrocarbon gases - Google Patents

Description

Aug. 3, 1937. c. R.WAG;NER

METHOD OF TREATIG CRACKED HYDROCARBON GASES Filed Feb. 29, 1952 (ZV1/@ller Patented Aug., d, 1937 stares it di s amasar Cary E. Wagner, Chicago, lill., assigner to The Pure Oil Company, @lirica/go, mi., a corporation of Uhio Application February et, iosa, sarai no. starte 8 Claims.

This invention relates to improvements in the art of treating hydrocarbon gases, obtained from cracking processes, to produce therefrom normally liquid hydrocarbon oils having the average boiling range of gasoline and which are characterized by the high percentage of unsaturated hydrocarbons they contain. The low boiling oils, produced ln accordance with the invention, are particularly suitable for direct use as motor fuels lll or as blending agents in lower grade gasolines or motor fuels for the production of an antiknock motor fuel of desired octane number.

In my prior application, Serial No. 354,426, I

have `set forth a process of subjecting cracked hydrocarbon gases, obtained by the conversion oi high boiling hydrocarbon oils in the vapor phase at temperatures of the order of 1000 F.

into low boiling oils, to heat treatment under regulated conditions of temperature and pressure',

2@ wherebyto edect theformation from such gases apparentlyv through polymerization of gasolinelike oils.

It is an outstanding object of the present invention to -obtain similar oils from gases produced by cracking operations other than the lowpressure vapor phase type,v especially cracked gases of the type developed by liquid phase or high pressure vapor-phase cracking operations. The cracked gases. formed by the operation of low-pressure vapor phase cracking processes are rich in ethylene, propylene and butylene and readily lend themselves to polymerization when heated to a temperature of approximately 900 F. and under pressures of the order of 300 to 1000 pounds per square inch, The cracked gases formed by the operation of liquid phase cracking systems, or in some instances high-pressure vapor phase systems, contain relatively smaller quantities of ethylene and its homologues and greater lquantities oi saturated hydrocarbons and, therefore, the gases of such cracking operations are not as adaptable for use in a gas polymerizing l system as the low-pressure vapor phase type and do not form low boiling oils of desired anti-knock value.

The present invention, therefore, provides a system for treating gases formed by the cracking of oils in systems other than low-pressure vapor phase operations` to extract from such gases through an absorption process or by other means the ethylene, propylene and butylene content thereof, whereby these latter hydrocarbons may be separated from the paraiiin hydrocarbons and then` subjected to polymerizing conditions to ef- 55 fect their formation into a high grade motor fuel.

Fora further understanding of the invention, reference is to be had to the following description and the accompanying drawing, wherein:

The figure is a diagrammatic view, partly in section, showing a preferred form of apparatus by which the present out. I

Referring more particularly to the drawing,

the numeral i designates a tank or gas holder which is adapted to receive hydrocarbon gases produced as a result of the cracking or converting of high boiling hydrocarbon oils into lower boiling oils and, especially, the cracked gases discharged as fixed or permanent gas from oil converting systems especially of the liquid phase type. In the cracking of oil in the liquid phase, relatively low temperatures are utilized, such temperatures being commonly oi' the order of from 750 to 875 F. In a typical liquid phase cracking operation, the oils at the temperatures specified by the employment of high pressures are maintained substantially in the liquid phase for the required period of time necessary to effect the molecular decomposition of the high boiling hyl-drocarbons into the desired lower boiling hydro-l carbons. In contrast to this method ofvoperation in the vapor phase vcracking of high boiling hydrocarbon oils, the latter oils are subjected to temperatures of the order of 1050 F. while in the cracking zone, and the pressures on the oils in the cracking zone are not sumciently high to prevent the vaporization ofthe oils. Due to the higher temperatures used in a typical vapor phase cracking system, considerably greater quantities y of unsaturated hydrocarbons are present in the cracked oils and gases than are present in the corresponding constituents of a liquid phase operation and it is to the treatment of these liquid phase cracked gases that the present invention is particularly directed, although in its broader aspect,its general principles have application to I gases resulting from the cracking of oils by any system.

Cracked gases of low olelne content (15 to 25%) are withdrawn from the holder l by way of the pipe line t in which is arranged a pump 3 and these gases are introduced into` the bottom ofan absorption tower fi. The gases passupwardly through the Atower and are brought into intimate contact withl a descending oil, or menstruum such as 'gas oil, solvent naphtha, cresol, high-boiling ketones or esters or other products capable of selectively dissolving olelnes from such a mixture of olenes and paralilns,` the tower being maintained under a pressureb of from invention may be carried l 15 to 350 pounds per square inch, depending upon the solvent used and the concentration of olennes in the raw gas. The oleflne hydrocarbons present in the cracked gas by this operation will be absorbed in the heavy oil to a much greater degree than the paraffin hydrocarbon content or constituents of the gas. These gaseous paramn hydrocarbons may be released from the upper part of the tower by way of a valved outlet line i, while the solvent oil, with the absorbed oleiine hydrocarbons, is withdrawn from the bottom of the tower by way of a valved transfer line 1.

The gas released from the top of the tower or .column'is relatively free from oleflnes and theV solvent at the bottom of the column has in solution a mixture of hydrocarbons in which the percentage of oletlnes is very much higher than in the original gas. Depending upon the analysis of the original gas, the solvent used and the pressure employed, this mixture may contain from ..45 to 75% of oleiines.

The mixture from the bottom of the absorption tower is pumped through the transfer line 1 to a suitable form of tire or steam heated still. for example, a conventional tube still, where the mixture is subjected to distillation under temperatures of the order of from 300 F. to 600 F. and pressures varying between 600 and 1500 pounds, a pump 8 being disposed in the line 'I to secure these pressures, the still being designated b y the numeral 9. The heated mixture discharged from the still s is passed into an evaporator III, where gases and solvent separate, the solvent being taken out of the bottom of the evaporator and transferred by means of a line Il, provided with a cooler I2, to the absorption column for reuse in said column.

'Ihe gases released from the top of the evaporator are passed without material pressure reduction through a pipe line Il, which leads to a heating coil il disposed in a polymerizing still Il.`

In order to form liquid oils from the olenne containing hydrocarbons which are thus delivered to the still i5, use is made of the polymerizing system set forth in nLv above identied application and in my continuing application, Serial No. 573,233.' Generally, such polymerization is secured by passing the gases directly from the evaporator Il to the coil Il. In this coil, the gases are heated to temperatures varyins between 600 and 1000 1"., while the same are maintained under pressures of the order specified in connection with the operation of the stili l, namely. 600 to 1500 pounds per square inch. 'Ihese heated products are then delivered to an externally located reaction drum it, in which the polymerizing reactions are permitted to continue for the desired period of time. Since these reactions are highly exothermic in character, I prefer to use the unheated externally located drum, which is removed from the influence of the highly heated furnace gases developed in the setting of the still Il.

It is desirable that the temperatures of the products in the drum It should be carefully observed to maintain strictly polymerizing reactions and to avoid the overheating which would tend to produce cracking conditions and excessive coke formation.

The heated products discharged from the drum It may be cooled in the. cooler I1 and thence conducted to a high pressure accumulator tank I8., The top of the tank vIl is connected with a gas outlet line Il by which the olefine deprived permanent .gases are removed from the system.

The outlet line I9 may be provided with a pressure reducing valve 20 and the so-called permanent gas led to a tank, burner or other zone of storage or utilization.

The liquids formed by polymerization accumulate in the bottom of the tank It and are withdrawn by way oi a pipe line 2 i provided with a pressure releasing valve 22. The end of the line 2i contains a plurality of branches 23, which enter a stabilizing tank 2l, which is adapted to "weather or stabilize the liquids by removing therefrom excessively volatile compounds in the form of vapors or gases, particularly propylene or butylene fractions. These volatile fractions are led from the top of the tank 24 .by way of a pipe line 25 and are conducted back to the gas inlet of the absorption tower 'l for further recovery of their olene content, thus providing for the recirculation of such volatiles through the system and repeated treatment thereof. The bottom of the stabilizing tank 24 may be provided with a valved draw-off line 3| leading to a tank 32 in which the motor fuel distillate is received and stored.

While the system above described sets forth a preferred embodiment of the invention, yet it will be understood that the invention is subject to considerable variation without departing yirom its underlying features. For instance, the system may be operated to distill gases from a solvent obtained from the bottom of the absorption tower at lower pressures than those above specified and use a compressor to place the gases under the pressure necessary in the operation of the polymerizing still I5. In the preferred embodiment of my invention, the use of such a compressor is rendered unnecessary and therefore the system may be operated more economically than ifa compressor were employed.

Another alternative to which I may resort to concentrate the olene content of cracked hydrocarbon gas is to fractionate such gas under high pressure and/or reduced temperatures. In this manner the methane and hydrogen can be removed with the result that the remaining gases contain enough oleilnes to carry on the'desired polymerizing reactions in the still il and its associated drum II.

Still, it is within the scope ofthe invention to.

use solid adsorbents such as silica gel, activated carbon, fullers earth and the like. In .this same manner, partial fractionation is secured and the 1 olenes concentrated sumciently to adapt them to polymerization under the conditions of temperature and pressure specified in connection with the still le.l

The following table sets forth an analysis of various cracked hydrocarbon gases disclosing their relative oleiine contents.

Vpob Gn Cracked Cracked phase moved ld nl cracked from q und gas low stabiliser lm Bubu pressure tank m b' presen l1. 4 7 n. n 15. 6 L 9 4. 12. 3 19. 4 lo 44. 0 12; 5 u 2 5. 0 l. 6. 2 I. l I. 0 l 4 2. 0 3. 1 l.

From the above table, it will be noted that gas produced by low pressure vapor phase crackin gmethodsisparticularlyrichintheoleiinu represented by ethylene and its homologues, whereas the corresponding compounds in gases produced by the operation of standard liquid phase cracking operations set forth have Values considerably lower. However, by the use of the present invention, cracked gas obtained from such liquid phase operations may be treatedso that prior to polymerization, it will contain oleines varying in quantity from 60 to 70%.

In view of the foregoing, it will be seen that the present invention provides a practical and economical method and means for treating cracked hydrocarbon gases, of the type produced particularly in the liquid phase cracking of oils, to obtain therefrom high yields of liquid oils suitable for use as improved motor fuels. The present invention renders ticable to utilize these liquid phase cracked gases for use in a gas polymerizing system and thus transform them into hydrocarbons of greater economic value. It has been customary in the past to employ cracked gases resulting from liquid phase operations merely as fuel for use in oil refinery processes. The present invention however enables a large percentage of these low value gases toflbe transformedfinto a superior grade of motor fuel.

What is claimed is:

1. The process of obtaining polymerized lowboiling liquid products of the gasoline boiling range'from a gas mixture containing methane, hydrogen, and gaseous oleiinic hydrocarbons which comprises compressing said mixture to 100-350 pounds/square inch above atmospheric pressure, contacting said compressed gasmixture with a petroleum hydrocarbon solvent having an average boiling range higher thanthat of gasoline and having-a relatively low solvent power for methane and non-hydrocarbon gases under the working conditions, separating methane and other undissolved gases fromsaid solvent charged with dissolved hydrocarbon gases, separating said dissolved hydrocarbon gases from said charged solvent, injecting said separated gases into la polymerization system maintained at a pressure vof 600-,1500 pounds/square inch above atmospheric, heating said gases in said system to a temperature about 7001000 F. and maintaining themat said temperature to eiect conversion, cooling conversion products and separately recovering gasoline gases. f

2. The process of obtaining polymerized lowboiling liquid products of the gasoline boiling .f

range from a gas mixture containing methane, hydrogen and gaseous olenic hydrocarbons which comprises contacting said mixture while under pressure of 100.to 350 pounds per square inch with a petroleum hydrocarbon solvent havno ing an average boiling range higher than that of gasoline and having la relatively low solvent power for methane and non-hydrocarbon gases it feasible and pracand unconverted under the working conditions, separating methane and other undissolved gases from said solvent charged with dissolved hydrocarbon gases, separating said dissolved hydrocarbon gases from said charged solvent, injecting said lastmentioned separated gases into a polymerization' system maintained under superatmospheric pressure, heating said gases in said system to a temperature suitable for effecting polymerization of the olenic constituents' of said gases to gasoline boiling hydrocarbons at the pressure to which the gases are subjected, cooling conversion products and separately recovering gasoline boiling range constituents and unconverted gases.

3. Process in accordance with claim,2 in which the undissolved gasesare withdrawn from the system without being processed.

4. Process in accordance with claim 1 in which the conversion products are cooled While under superatmospherc pressure, the uncondensed gases separated from the condensed products,

the normally gaseous constituents separated the undissolved gases, after separation from the charged solvent, are withdrawn from the system.

7. In a process for polymerizing rich olencontaining gases, to gasoline boiling constituents at pressures of 600-1500 pounds/square inch and at temperatures suitable for converting the gases to gasoline boiling constituents at the aforesaid pressures, the steps of cooling the conversion products and separating the gaseous from liquid components without substantial reduction in pressure, then materially reducing the pressure on the liquid components and separating the normally gaseous constituents therein from the normally liquid constituents, contacting under `pressure of -100 to 350pounds per square inch, the normally gaseous constituents with a petroleum hydrocarbon solvent having an average boiling range higher than that of gasoline and having a relatively low Solvent power for methane and non-hydrocarbon gases under the working conditions, separating undissolved gases from the system. separating dissolved gases from the solvent and charging the latter gases to the polymerization process.

8. Process in accordance with claim 7 in which the temperature ranges from approximately 700 to 1000 F. and the gaseous constituents are contactedwith the solvent at pressures of 15 to 300 pounds/square inch.

CARY R. WAGNER.

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