US2222276A - Apparatus and a process for the recovery of gasoline from cracked petroleum hydrocarbons - Google Patents

Description

Nov. 19, 1940. D. F. BABCOCK 2.2223 5 APPARATUS AND A PROCESS FOR THE RECOVERY OF GASOLINE FROM CRACKED PETROLEUM HYDROCARBONS Filed Oct. 14, 1957 2 Sheets-Sheet l INVENTOR.

- ATTORNEY Nov. 19, 19 40. F. BABCOCK 2 222,276

D. v APPARATUS AND A PROCESS FOR THE RECOVERY OF GASOLINE FROM CRACKED PETROLEUM HYDROCARBONS Filed 0012. 14, 1957 2 Sheets-Sheet 2 IN V EN TOR.

BY Q6 Mole/V53 I ations, produces both liquid and gaseous-products.

Patented Nov. 19, 1940 2,222,276 PATENT OFFICE APPARATUS AND A PROCESS FOR THE RIB- COVERY OF GASOLINE FROM CRACKED PETROLEUM HYDROCARBONS Dale F. Babcock, Wilmington, DeL, assignor to E. I. du Pont de Nemours & Company, Wilmington, Del., a. corporation of Delaware Application October 14, 1937, Serial No. 168,891

2 Claims.

This invention relates to a process for the separation of mixtures of gaseous hydrocarbons by liquefaction and fractionation, and more particularly to the recovery of hydrocarbons containing in excess of three carbon atoms per molecule from a complex gas mixture.

The pyrolysis of petroleum materials, as practiced in commercial vapor phase cracking oper- These cracked gases are usually saturated with materials boiling in the gaseous range which must be recovered prior to use of the gas in other processes or for fuel. a

In the gasoline refining industry this recovery of gasoline is often effected by compressing the cracking gas to a moderate pressure, cooling and thereby liquefying a portion of its gasoline content. The uncondensed gases, still under pressure, are then forced up through a scrubbing tower, countercurrent to a light oil which scrubs the remaining gasoline from the fixed gases. The low-boiling gasoline is then distilled from the fat oil, which is then recycled to the scrubbing operation. The distillate is joined with the liquid fraction separated after compression, and the mixture is introduced into a stabilizing column where the low-boiling components which are too volatile to be used in gasoline are distilled 0.1. I have found it much more expedient to recover and to stabilize the gasoline content of the cracked gas in a diflerent manner.

the separation of the gasoline fraction from a.

mixture of gases obtained by cracking petroleum products. apparatus for the accomplishment of the above ends. Other objects will appear hereinafter.

These objects are accomplished by the following invention which comprises compressing the gas mixture, cooling and separating the liquid formed, which comprises principally gasoline, rectifying the liquid fraction so'that the more volatile gases are separated from the materials boiling in the gasoline range, combining the gaseous fraction from the gas and liquid separation step with the gaseous fraction from the rectification step andfurther compressing same to a higher pressure, cooling the thus compressed gases and rectifying the resultant fluid so as to A furtherobject is the provision of an separate all of the fraction boiling within the gasoline range as a liquid and the more volatile components as a gas, reducing the pressure on this second liquid fraction to the pressure of the first part of the system and combining the resulting fluid with the efliuent from the first compression step. I

The accompanying drawings represent diagrammatically complete apparatuses for the separation of the components of this fluid mixture. Figure I is the simplest modification of the apparatus and embodies a process which has but two compression stages. Figure II is a modification of the apparatus in which three compression stages are used. It is understood that the details of this apparatus, whichare well known to those skilled inthe art, have been omitted for the sake of clarity and that modifications in the details of construction and in arrangement of parts may be made without departing from the spirit of the invention. The following represents a description of the processes and apparatuses shown in the two figures of the drawings.

In the modification represented by Figure I the crude gas enters the first stage of compressor & via conduit 2 under substantially atmospheric pressure. The gas is compressed to about 6 atmospheres and passes to water cooler 8 and separator I2 via conduits 6 and Ill. The condensed liquid is passed by gravity fiow from separator 12 through .conduit H into the middle of rectifylng column l8. Reflux is provided in this column,

cooled to room temperature by means of water;

cooler 25 and pass to rectifier 30 via conduit 28:?

Reflux is produced in this rectifier by heating calandria 32 with steam and cooling condenser 38 with water. The non-condensable 'gas leaving the top of rectifier 30 via conduit 40 passes to a low temperature separation system where pure ethylene and propylene are'recove'red. The liquid from the base of rectifier 3|! is expanded through valve. 34 and conduit 36 into conduit 6 where it mixes 'with the vapors leaving compressor'l.

In Figure II the crude gasenters the first stage of compressor I04 by conduit I02, the gas is compressed to about 3 atmospheres and passes to water cooler I08 and separator III via conduits I06 and H0. The condensed liquid is passed by gravity flow from separator II2 through conduit II4 into the middle of rectifying column H6. The reflux is.provided in the rectifying column 5 H6 by heating the calandria I42 with steam and cooling the condenser I44 with water. The stabilized gasoline produced at the base of the rectifying column I I6 is removed from the system by way of conduit I46 and valve I48. The 10 non-condensable vapors leaving the top of rectifier II6 are passed to the second stage of the compressor I22 via conduit I20. The gase lus fractions from the separator II2 are combined with the non-condensable vapors from the rectifler II6 by introducing via conduit II8 into conduit I20. These combined vapors are compressed by compressor I22 to a pressure of about 10 atmospheres, cooled to room temperature by means of water cooler I26 and passed into rectifier I30 90 via conduits I24 and I28. Reflux is produced in rectifier I30 by heating calandria I32 with steam and cooling condenser I38 with water. The liquid from the base of rectifier I30 is expanded through valve I34 to 3 atmospheres pressure and conducted via conduit I36 to conduit I06 where it is mixed with the vapors leaving compressor I04.

The non-condensable gas leaving the top of rectifler I30 is conducted via conduit I 40 to the third stage of the compressor I50 where it is compressed to 33 atmospheres. The thus compressed gas is then conducted by conduit I52 through water cooler I54 and conduit I56 into the rectifying column I58. Reflux liquids in rectifying column I58 are produced by heating calandria I60 with steam and cooling condenser I66 with water. The liquid from the base of rectifier I58 is expanded through expansion valve I62 to a pressure of 10 atmospheres and then via conduit I64 is introduced into I24 where it mixes with the vapors leaving compressor I22. Non-condensable gas leaves the rectifier I58 via conduit I68, at the top thereof.

The process described herein is an improvement over the process described in the copending application Serial No. 30,031, of C. H. Greenewalt, in that the liquid in the process herein is essentially free of low boiling materials. It is therefore more advantageously employed as an m absorption oil to promote the condensation of high boiling components from the intermediate -pressure gas.

Example A gas of the following composition that had 56 been produced by the vapor phase cracking of petroleum was processed according to the modification of the invention as shown by Figure I.

Mole per cent 60 Hydrogen 8 Methane Ethylene Ethane l0 Propylene and propane 17 65 C4 hydrocarbons 10 C5 and heavier hydrocarbons 10 This gas was compressed to six atmospheres, 70 combined with the expanded liquid from the high pressure rectifier, cooled to C., the liquid separated from the vapor and the liquid processed in the intermediate pressure rectifier. The base of this rectifier was heated with steam to 117 C., at which temperature essentially all of the butylene contains only two stages.

and more volatile components were expelled from the. liquid producing gasoline containing essentially only C6 and heavier hydrocarbons. The condenser of the intermediate pressure rectifier was cooled to 30 C. The vent gas from this Propylene and propane 5 .04 hydrocarbons '26 C5 and heavier hydrocarbons 69 The vapors leaving the top of the high pressure rectifier at 25 C. contained essentially all of the butylene and lighter components originally contained in the crude gas together with about of l mole per cent of C5 hydrocarbons.

It is desirable to heat the base of rectifiers 30 l and I58 to such a temperature that essentially all of the butylene and more volatile components are driven from the liquid. However, many crude gases contain such a quantity of polymer and gum-forming materials that this procedure is impractical. of rectiflers 30 or I58 may be heated to a temperature below that at which polymerization takes place allowing the liquid which is expanded from the base of this rectifier to contain appreciable quantities of butylene andpropylene.

The compression system outlined in Figure I The compression system may contain three stages as shown by Figure 11 or'even a larger number of stages maybe used. In every case it is obvious additional rectiflers will be required with the. liquid from the highest pressure rectifier being expanded back into the discharge line from the next highest pressure compressor exactly as shown herein.

In my experiments I desired to produce a stabilized gasoline at the base of rectifiers I6 or II6 which was essentially free of "butylene and more volatile components. In the gasoline industry it is oftentimes desirable to leave up to 5% of butylene in the liquid. This may be accomplished in the process herein described by reducing the temperature in calandrias 42 or I42 to say 100 instead of 115 as mentioned in the above example.

This process has the advantage of recycling a minimum quantity of intermediate boiling material and thereby reducing the power used for operating the compressors. Also in the present invention no liquid or gaseous product attains a temperature lower than that of cooling water, thus eliminating troublesome freeze-ups that might occur if temperatures are used below the freezing point of water, in view of the fact that the incoming gas contains a small amount of water. A further power savings is accomplished by expanding the high pressure liquid from the rectifier into the 'ei'fluent from the next lower compressor. This liquid acts as an absorbing oil condensing from the eiiluent certain of the heavier fractions that would normally remain in the gas and be recompressed to the higher pressure.

Under such a condition the base As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that I do not limit myself to the specific embodiments thereof except as defined in the appended patent claims.

I claim:

l. The process which comprises compressing a gaseous mixture from cracked petroleum hydrocarbons containing a gasoline fraction and gases that are lower boiling than said gasoline fraction, cooling the compressed gases to effect liquefaction of said gasoline fraction, separating said gasoline fraction therefrom, rectifying the separated gasoline fraction by counter-current flow of reflux liquors andby boiling the liquid at the base of the rectifying column in order to establish refluxing conditions and expel the lower boiling hydrocarbons from the liquid gasoline, combining the gaseous fraction obtained from the rectification step and the gaseous traction obtained from the gas and liquid separation step, compressing said gaseous fraction in a plurality of compression stages, said stages being characterized in that there is a cooling and rectifying step between each stage of compression, said rectifying steps being operated by counter-current flow of refluxing liquors and by boiling the liquid at the base of the rectifying column in or-- der to establish refluxing conditions and separate as a liquid gasoline andexpel the lower boiling I hydrocarbons therefrom, said process being further characterized in that the gasoline fraction from the higher pressure stage is expanded to the pressure of the next lower pressure stage and combined with the efliuent from the next lower pressure stage.

2. An apparatus for separating the components of a fluid mixture which comprises the following elements in combination: a gas and liquid separator and a multi-stage compressor. together with a cooler and a rectifier for each compression stage, means for introducing .the fluid mixture into the first compression stage, means for passing the fluid mixture from the first compression stage through the cooler connectedtherewith into the gas and liquid separator, means for passing the liquid from the gas and liquid separator into the rectifying column adapted for operation with the first compression stage, means for withdrawing the gaseous fraction from the gas and liquid separator and the gaseous fraction from the rectifying column and combining same and introducing said combined gaseous fractions into the second compression stage, means for removing the liquid fraction from the bottom of the rectifying column; separate means for withdrawing the gases from the top of the rectifier in each compression stage except the first and last and introducing said gases into the next higher compression stage,

separate means for passing the compressed gases from each compression stage above the first through the cooler for each compression stage into the rectifying column for each compression stage, separate means for withdrawing the gases from the rectifier of the last compression stage, and separate means for withdrawing the liquid from each of the rectifying columns for each of the compression stages except'the first and for combining said liquid with the efiluent from the compression stage ,next lower in pressure.

DALE F. BABCOCK.

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