US2353234A - Production of motor fuel - Google Patents

Description

July 11, 1944. K. H. HACHMUTH PRODUCTION OF MOTOR FUEL Filed April l, 1940 BY hun ,www

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ATTORN EY Patented July 1l, 1944 PRODUCTION OF MOTOR FUEL Karl H.

of Delaware Hachmuth. Bartlesville. Okla., assignor to Phillips Petroleum Company,

a corporation Application April l, 1940, Serial No. 327,301

12 Claims.

This invention relates to the manufacture of volatile hydrocarbon oils and more particularly it relates to the production of a suitable charge stock from hydrocarbon conversion processes which can be used in a subsequent conversion process of the polymerization type to produce highly valuable hydrocarbons of higher molecular Weight from hydrocarbons of lower molecular weight. It relates more particularly to the production of hydrocarbons in the motor fuel boiling range from normally gaseous hydrocarbons and especially to the production of a polymerization charge stock from the dehydrogenation of normally gaseous paraffin hydrocarbons having two or more carbon atoms per molecule.

It has been shown that, when used as fuel for internal-combustion engines, c specially those of the spark-ignition type, various hydrocarbons have quite widely different combustion and detonation characteristics. Thus, in many cases, olefin hydrocarbons are less likely to produce or cause detonation when used as a fuel than are the corresponding paraln hydrocarbons. Even among one given class of hydrocarbons such as the parains, for example, the various individual hydrocarbons differ widely among themselves as to their combustion characteristics. This is exemplified by the detonation characteristics of normal heptane and of isooctane (2,2,4-trimethylpentane), the well known standards used for evaluating detonation; the first causing detonation to a considerable extent and having, by denition, a rating of zero octane number, and the latter causing little if any detonation, even in engines having quite high compression ratios, and having by definition a rating of 100 octane number. Even hydrocarbons belonging to the same class and having the same molecular weights have widely diiferent detonation characteristics. This is exemplied by Various heptanes whose octane numbers are as follows:

Octane number Hydrocarbon Normal heptane.

There is considerable advantage to be gained from using fuels with good antidetonating qualities, inasmuch as only fuels which can be so classified can be used in engines with high compression ratios. It is Well known that it is possible to obtain a high thermal efficiency in such an engine, and it has been found that the potential power to be obtained using an engine operating, in each case, at the highest permissible compression ratio may be 50 per cent greaterwith a given hydrocarbon with high antidetonating qualities as a fuel than when using an isomeric hydrocarbon with lower antidetonating qualities. As an example, the maximum possible compression ratio of an engine using normal heptane as a fuel is about 3:1, while with its isomer, 2,2,3- trimethyl butane, the maximumratio is about 13:1. An engine with the latter compression ratio would probably not operate for any length of time if normal heptane were the fuel.

In the preparation of such premium motor fuel, especially when catalytic polymerization is used, it is generally preferable to prepare a charge stock for such polymerization which contains predominantly C3 and C4 hydrocarbons with very little lighter material present. Under ordinary conditions of operation the presence of very much material lighter than C3 hydrocarbons is quite deleterious in that it is generally the practice to p ump such charge stock in the liquid state and if such material is present in Very large amounts the pump will not operate very satisfactorily. Also ethylene is not readily reacted in the presence of a catalyst under the operating conditions which are most favorable for the production of simple olefin polymers, although it is a very desirable material to have in several conversion operations such as thermal alkylation.

f I have now found that the eiiluent of a dehydrogenation step which produces normally gaseous polymerizable olens and hydrogen, and in part lighter and undesirable paraffin hydrocarbons, may be separated into a fraction which contains the desirable polymerizable oleins and into a separate fraction which contains the hydrogen and unclesirably light parafn hydrocarbon by a unique and novel combination of compression-condensation and absorption steps which will be more fully hereinafter described. This separation process and means which comprise my invention permits such a separation without compressing a large portion of the desii-ed material to an excessively high superatmos pheric pressure and without using cooling means or methods which are below atmospheric temperature and which can be obtained only by expensive means. In practicing my invention the eiiiuent of a dehydrogenation step is compressed to a pressure between about 75 and 150 pounds per square inch and is cooled with ordinary cooling water, thus condensing a large proportion of the heavier hydrocarbons which are present. This liquid condensate is suitable for charge stock to a subsequent conversion process. The unl condensed portion of the eiiluent which comprises substantially all of the hydrogen and light parailln hydrocarbon also contains an appreciable proportion of hydrocarbon material which also should be sent to the conversion process.. This uncondensed portion is further compressed and again cooled with ordinary cooling water whereby a further portion of the heavier hydrocarbons are condensed and separated. This condensate is returned and is mixed with the eiiiuent of the dehydrogenation step. The uncondensed material is then contacted with a relatively small amount of absorption oil which absorbs the remainder of the desirable normally gaseous hydrocarbons of higher molecular weight and the hydrocarbons are recovered from this absorption oil and are returned to the process.

My invention will now be more specifically disclosed in connection with the accompanying drawing which forms a part of this specification,

and which is a diagrammatic presentation of the apparatus by which one modification of my invention can be practiced.

A hydrocarbon stream comprising predominantly parafilnic, normally gaseous hydrocarbons,

-such as a propane-butane mixture or a mixture of butanes which, in special cases may comprise essentially a pure paralnic hydrocarbon such as lsobutane, enters the system through conduit I and is compressed to a suitable pressure by pump II. In many cases, where such a hydrocarbon stream comes directly from a fractional distillation process or from some other separation step, it may be under a pressure suillciently high to obviate the necessity of the pump II and in such a case, of course, the pump may be omitted. Since a high superatmospheric pressure tends to aifect the subsequent dehydrogeneration adversely, the pressure will generally only be suillcient to overcome the pressure drop through the apparatus up to the compressor 4I to be hereinafter described and to provide a slight superatmospheric pressure at the inlet to this compressor. 'I'his pressure will generally not need to be in excess of about 200 pounds per square inch and in most cases it will be somewhat less than that. The hydrocarbon stream, at the desired pressure, then passes through conduit I2 and then through conduit I3 supplied with a valve I4 to the transferline heat exchanger I5, where it passes in indirect countercurrent heat exchange relationship with the eiliuent of the dehydrogenation to be described. From the heat exchanger I5, the stream passes through conduit I6 supplied with a valve Il to conduit I8, and is sent to the dehydrogenation step. With this arrangement valve 2I in the by-pass 22 is closed, but if desired all or any part of the stream may be diverted from the heat exchanger I through this by-pass by proper control of the valves I4, II, and 2|, as will be readily understood. From conduit I8 the hydrocarbon stream passes through the tube coils 23, located in the furnace or other heating means 24. When the olen hydrocarbons which are charged to the subsequent conversion step are produced from these paraln hydrocarbons by thermal dehydrogenation alone, these coils 23 will be in such a relationship that the hydrocarbon stream is rapidly heated to a dehydrogenation temperature between about 1000 and about 1250 F. and the mixture is then held within this temperature range for a period of time such that from about 10 to about 40 mol per cent of the eilluent material consists of unsaturated normally gaseous hydrocarbons. With this procedure, the eilluent of the coils 23 passes through conduit 25 controlled by valve 26, thence through heat exchanger I5, conduit 21, cooler 23, and conduit 30 to the scrubber 3 I.

At times, however, lt will be more desirable to carry out a catalytic dehydrogenation of the paraffin hydrocarbons, and this may be carried out in this particular modification by opening valve 32 in conduit 33, and valve 34 in conduit 35, thus connecting the catalyst chambers 3l into the system, vand closing valve 26. In the modification illustrated, the catalyst chambers 36 comprise relatively small tubes illled with a suitable dehydrogenation catalyst and they are so located that large amounts of hot combustion gases from the combustion zone of the furnace 24 pass over them. With this modification of operation, the relative volume 'of the coils 23 are such that the hydrocarbon stream is rapidly heated to a desirable reaction temperature, which for catalytic dehydrogenation will generally be between about 850 and 1150 F., and the mixture is then passed directly into contact with the dehydrogenation catalyst in the tubes 36. As the reaction progresses, heat is absorbed and this is supplied by heat transferred from the combustion gases surrounding the catalyst tubes. Although in the diagrammatic showing of the drawing only one source of heat in the furnace 24 has been shown, it will be understood by those skilled in the art that additional burners solely for supplying heat to the catalyst tubes, or other means of supplying heat to the catalyst and to the reactants to maintain the desired temperature level, such as electrical heating means, may also be used. At times also it may be desirable to obtain the production of oleiins by a combination of thermal and catalytic dehydrogenation, with a limited production of desired oleilns by thermal dehydrogenation in the coils 23 followed by a further conversion of the unreacted paraillns to the desirable olens in the catalyst chambers 3l. In any event, the dehydrogenation eilluent passes from the catalyst chambers 36 to a conduit 3l controlled by a valve 34 and thence through conduit 25 to heat exchanger I5, and on through the remainder of the apparatus as has Just been described and will be further described. In place of a feed stock derived by the dehydrogenation of light paraiilns, a suitable mixture for treatment may comprise a low boiling mixture such as a C5, or'Ci, and lighter fraction, including some hydrogen, separated from the eiiluent of a vapor phase oil cracking process, which will contain Cz to C5 or C4 parans and oleilns as well as undesirable light, material. Such a mixture can be readily treated by my process, and can be introduced through conduit 30, controlled by a valve 8|, and leading into the conduit 30, as shown.

In the scrubber 3| any carbon and/or tar is separated from the stream and is removed from the system through conduit 3l controlled by a valve 38. In many cases of operation there will be no tar and/or carbon formed to be separated at this point, which will especially be the case when catalytic dehydrogenation is practiced. However, it has been found to be desirable to have such a piece o1' apparatus in the system when extreme dehydrogenation temperatures are used, or when temporary uctuations of the operating conditions produce small amounts of this undesirable material. In cases where such carbon or tar is present, its removal may be aided by the use of a heavy absorption oil or by other means as will be evident to those skilled in the art, details pertinent to such modiiications not being shown. The elliuent stream then passes through conduit 46 to compressor 4l wherein it is compressed to a pressure of the order of 75 to 150 pounds per square inch. In many instances the pressure at the inlet of this compressor will be only a few pounds above atmospheric such\ as a pressure of to 20 or 25 pounds per square inch gage. The compressed stream passes through conduit 42 to the cooler and condenser 43, wherein it is cooled by indirect heat exchange by a suitable cooling medium which will generally be ordinary cooling water, and the material then passes through conduit 44 to the separator 45.

Under the pressure developed by the compressor 4I and at the ordinary cooling temperatures effected by the cooler and condenser 43, a large portion of the hydrocarbons having 4 and more carbon atoms per molecule, along with an appreciable proportion of lighter hydrocarbons, will be condensed and will be present in separator 45 in the liquid phase, with lighter hydrocarbons being present in the gas phase along with hydrogen. This liquid hydrocarbon mixture contains the hydrocarbons which are to be converted to normally liquid hydrocarbons, and it is passed from the separator 45 through the conduit 46 which is controlled by valve 41 and may be passed through the valve 49 to the poly-feed stripper or separator 50. If desired, additional hydrocarbon material of substantially the same boiling range containing a substantial proportion of olen hydrocarbons may be introduced to the process through conduit 58 controlled by a valve 59 and leading into the conduit 46.

The hydrocarbon stream passing through conduit 46 will generally be essentially composed of hydrocarbons of 3 and more carbon atoms per molecule, but there will be a small amount of hydrocarbons having fewer carbon atoms per molecule along with a still smaller amountl of hydrogen. It has been found to be generally desirable to remove from this mixture the hydrocarbons having fewer than 2 carbon atoms per molecule, and generally also to remove the hydrocarbons having fewer than 3 carbon atoms per molecule, in order that these will not be present in the subsequent conversion process for the production oi normally liquid hydrocarbons. This will generally be true for catalytic polymerization. When such a removal is desired the hydrocarbon stream passing through conduit 46 is passed to a fractionating column or poly-feed stripper 50, which operates as a conventional fraotionating column, with suitable bubble trays not shown,`

and with heating means for the bottom such as is represented by the stream coil 5I and with cooling means for the top as is represented by the cooling coil 52. If it is desired to operate iractionating column 50 at a pressure higher than that existing in separator 45, the stream passing through conduit 46 may have its pressure increased by pump 85. This is accomplished by opening valve 86 in conduit 81 and valve 88 in conduit 89, and closing valve 49, as is readily understood. The undesirable light material passes from the fractionating column 50 as a vapor through the conduit 53 controlled by the valve 54, and may be discharged from the system through conduit 55 controlled by valve 56, or any part or all of this material may be reintroduced into the 'system through valve 51, being mixed with the material passing through the conduit |05 and valve IM which consists of vaporous material passing from the separator 45, hereinbefore described.

A hydrocarbon fraction comprising hydrocarbons of 3 or more carbon atoms per molecule in the liquid state passes from a low point of the fractionating column 50 through conduit 6|! and a valve 6I to a pump 62, which passes the stream to the conversion step at a pressure suitable for the subsequent conversion. In the event that the charge stock to the dehydrogenation process has comprised essentially only butane this material will generally comprise butenes along with butane and may also contain some propene and some propane, and when the subsequent conversion step is to be one of catalytic polymerization of these oleiins to hydrocarbons in the motor fuel boiling range, it will generally be desirable to have this charge stock free of hydrocarbons having two carbons per molecule and less. The material passes at a suitable pressure from the pump 62 through conduit 63 to the polymerization means indicated by the polymerization chamber 64, wherein it undergoes the desired conversion in any manner which is well known to the art. From the conversion chamber 64 the eiliuent passes through conduit 65 controlled by a valve 66 to a separating means such as a fractionating column 61. It may of course be desirable to heat the conversion stock immediately after it leaves the pump 62 and before it undergoes conversion in the chamber 64 and it also may be necessary to cool the latter part of this reaction zone. Means for doing this have not been shown but are well known to those skilled in the art. The separator or' fractionating column 61 may be a conventional fractionating column supplied with suitable bubble trays, not shown, and with a heating means in the bottom indicated by the coil 1| and cooling means in the top represented by the cooling coil 12. Higher molecular weight hydrocarbons produced in the polymerization step pass from the bottom of the separating means 61 through a conduit 13 controlled by a valve 14, and may be subjected to further treatment such as stabilization, fractionation, hydrogenation, and the like, by means well known to the art and not pertinent to the present invention. Light unreacted hydrocarbons may be discharged from the fractionating column and from the process through conduit 15 controlled by a valve 16. This material will generally consist of unreacted hydrocarbons which are suitable as charge stock to the dehydrogenation step, and in case it is desired to charge this material to the dehydrogenation step, it may be effected by passing the stream through conduit 11 controlled by, a valve 18 and introducing it into the conduit I2 with suitable control of the valve 16 in the conduit 15. In those cases where the only material charged to the process enters the system through the conduit 58 controlled by the valve 59, the paraffin hydrocarbons passing through the conduit 11 will constitute the only charge stock to the dehydrogenation step. It will of course also be possible to remove hydrocarbons through the valve 16, subject them to further treatment, such as additional fractionation, or further polymerization of unreacted, residual oleilns, before reintroducing a desired part of the hydrocarbons into the system through the conduit |0.

It may at times be more desirable to operate the conversion means represented by the chamber 64 as a thermal conversion process, in which case it will not be always desirable or necessary to remove the hydrocarbons having fewer than 3 carbon atoms per molecule, and in many such cases the hydrocarbon fraction passing through the conduit 46 fromthe bottom of the separator 45 is suitable in composition for charging directly to such a thermal conversion process. In such a case the fractionating column 50 may be bypassed by allowing the stream to pass from conduit 46 through conduit 68 controlled by a valve 69, after closing the valve 49, and introducing the stream into the conduit 60 immediately before the pump 62. Other modifications of these operations will be readily appreciated by those skilled in the art. A very desirable method of operating the polymerization process represented by the means 64 has been described by F. E. Frey in his copending application Serial Number 305,549, iiled November 21, 1939. With certain modications of such an operation the cooling means represented by the coil 52. in the top of the fractionating column 50 may be very advantageously one of propylene cooling by using recycled unreacted propylene such as has been described by Hays et al. in their copending application Serial Number 336,250, led May 20, 1940, which can be also readily adapted to my process.

The material passing in the gaseous phase from the separator 46 through conduit |00 controlled by valve which may be used to slightly reduce the pressure down stream if the stream from conduit 53 is introduced, contains substantial quantitles of hydrogen, and generally also contains appreciable quantities of methane along with considerable amounts of heavier hydrocarbons which will include appreciable proportions of hydrocarbons having 3 or more carbon atoms per molecule which are desirable as a part of the charge stock to the conversion means 64. To this gaseous mixture is added another gaseous mixture passing from the top of the fractionating column 50 through the conduit 53 if such operation is desired and used. The combined mixture passes to the compressor |02 wherein it is compressed further to a pressure which is generally appreciably above 150 lb./sq. in. From the compressor |02 the mixture passes through conduit |03 to :the cooler and condenser |04 where it is cooled by indirect heat exchange with a cooling medium, which may very advantageously be ordinary cooling water. From the cooler and condenser |04 the mixture, now containing some material in the liquid phase, passes through the conduit |05 to the separator |06. The material which has been liqueed by the compression and cooling step collects in the bottom of the separator |06, and is passed through conduit |01 controlled by a valve |08 to the conduit 44 and thus is reintroduced into the separator 45 in part as a liquid which may be removed therefrom and passed along with other liqueed hydrocarbons to the conversion step. Although an appreciable proportion of the desirable material is recovered in this manner it will often be desirable to submit the material in the vapor state to further separation, and this may be done by passing these vapors from the separator |06 through a conduit ||0 controlled by a valve through valve |24 to the compressor ||2 wherein the gaseous material is still further compressed and passes through conduit ||3 to the cooler and condenser |4 which is similar to the hereinbefore described cooler and condenser |04. From the cooler ||4 the material, which also contains some liquefied hydrocarbons, passes through the conduit ||6 to the separator ||6. The liquid material is separated from the contents of the separator ||6 and passes through conduit |I1 controlled by a. valve ||8 to the conduit |05 and is thus introduced :to the separator |06. Uncondensed material passes from the separator ||6 through the conduit |20 controlled by a valve |2| and is introduced into the bottom of the absorber |30. It may be desirable to eliminate the last described separation step which includes the separator ||6, in which case the gaseous eflluent of the separator |06 may be passed from the conduit |0 through a conduit |22 controlled by a valve |23 and the mixture is introduced into conduit |20 and sent directly into the bottom of the absorber |30. In such a case the valve |24 in the conduit ||0 will be closed, as will be valve |2| in the conduit |20. In other cases it may not only be desirable to use all of the separators illustrated, but it is to be understood that in certain conditions additional compressors and separators may also be used, although I have found that in most cases such is not necessary. I! desired, any part or all of the material passing through conduit |20 may be discharged from the system through conduit |26 controlled by valve |21, with proper control of valve |28 in conduit |20.

The material which remains in the gaseous phase and enters the absorber |30 through the conduit |20 comprises an appreciable concentration of hydrogen and methane and contains only small amounts of heavier hydrocarbons, but in most cases contains suillcient portion or propene and butenes to justify their removal in the subsequent absorption step. This removal is accomplished by passing the gaseous mixture in countercurrent, direct contact with an absorption oil which is introduced at the top of the absorption column |30 through a conduit |45. A gas comprising principally hydrogen and methane, along with small 'portions of C: hydrocarbons if these are eliminated from the charge to the conversion step 64, passes from the absorber |30 by conduit |3|, and may be eventually discharged from the system through the valve |60. If desired this material may be used to hydrogenate any part or all of the polymer fraction which passes from the separator 61 through the conduit 13, in an operation such as is disclosed in the copending application of Frey et al., Serial Number 745,348, filed September 24, 1934, which has issued as Patent No, 2,227,639.

The rich absorption oil, which contains absorbed propene' and butenes, passes from the absorber |30 through a conduit |32 controlled by a valve |33 and is heated in a heater |34 before passing through conduit |35 to the top of the stripper column |36. The absorption in the absorption oil takes place at pressures in excess of about 300 lb./sq. in., which may be as high as 850 lb./sq. in or more and which will generally be in the range of 500 to 750 lb./sq. in., and at temperatures which may ordinarily be obtained by ordinary cooling water.

The rich absorption oil is heated in the heater |34 to a temperature which is preferably in excess of 200 F. and which may be as high as 250 to 275 F., and is introduced into the stripper |36 at a pressure which should not be in excess of about 50 pounds per square inch and which is preferably between about 10 and 30 pounds per square inch. The absorbed hydrocarbons pass from the absorption oil and from the stripper |36 in vapor phase through conduit, |53, which is controlled by a valve |54, and are introduced to the conduit 30, which contains the dehydrogenation effluent, by being passed through the valve |55. In this manner these desirable hydrocarbons are reintroduced into the system and may be eventually recovered for use in the conversion step. The denuded absorption oil passes from the bottom of the stripper |36 through a conduit |31 controlled by a valve |38 and is cooled to ordinary temperatures in the cooler |39 before it passes through a conduit |40 to the absorption oil accumulator |4|. From the accumulator |4| the oil may be withdrawn as desired through conduit |42 controlled by a valve |43 and passed by pump |44 through a conduit |45 controlled by a valve |46 t the top of the absorber |30. It will generally be desirable to aid the desorption of the absorbed hydrocarbons in the stripper |36 by means of a lean gas. This may be accomplished by diverting a part of the gases which are passing through conduit |3|, by opening valve |52 in the conduit I| and allowing a part of these gases to enter the bottom of the stripper. It will take only a small portion of these gases to accomplish the desired result and effectively remove the last traces of the absorbed hydrocarbons having 3 and more carbon atoms per molecule from the absorption oil which isin the lower portion of the stripper |36. This method of operation will cause, of course, a slight increase in the amount of hydrogen and light undesirable hydrocarbons in the subsequent steps of the process, but it will not affect the final material which is charged to the conversion step in any appreciable manner. The operation will in a short time after being started reach a steady state, so that the amount of hydrogen and light hydrocarbon material discharged through the conduit |3| ywill be equal in amount to that produced by the dehydrogenation step.

The following data are given as an illustration of the principles of operation of one modification of my process, but it is not intended that the restrictions proposed by these data should limit the scope of my invention in any way. A hydrocarbon mixture containing over 90 per cent of butane, with a small proportion of propane, was

passed through conduit |0 and the heat exchanger I5. after being raised by the pump to a pressure of about 150 pounds per square inch. It was thermally dehydrogenated in the coils 23 at a temperature of between 1100 and 1200 F. for a period of time such that the effluent comprised about mol per cent of normally gaseous olefin hydrocarbons, which comprised substantially entirely propene and butenes. The effluent entered the compressor 4| with a gage pressure of about 20 pounds per square inch and was boosted in pressure by the compressor to a pressure of about 135 pounds per square inch, and was passed to the separator at a temperature of about '75 F. The liquid separated at the bottom of the separator 45 contained over 95 per cent of hydrocarbons having 3 and more carbon atoms per molecule with less than l per cent of hydrogen and about 2 per cent of methane. This material was passed through the conduit 46 to the fractionator 50. wherein the undesirably light material was removed and returned to the process through the conduit 53. The liquid passing from the bottom of the fractionating column 50 to the conduit 60 was completely freed of methane and hydrogen and contained over 98 per cent of hydrocarbons having 3 and more carbon atoms per molecule, This material was sent to an olefin conversion step, which comprised polymerizing the oleflns to polymers boiling mainly below 400 F. in the presence of a silica-alumina catalyst under a pressure of 500 to 1500 pounds per square inch at a temperature between 100 and 500 F., and which produced a premium motor fuel in high yield. The unreacted normally gaseous parafin hydrocarbons were recirculated, after being separated from the effluent Aof the conversion step, to the dehydrogenation step. The gaseous material which passed from the separator 45 to the conduit |00 contained about 50 per cent of C3 hydrocarbons and heavier along with a high proportion of methane and hydrogen. This material was compressed by the compressor |02 to a pressure of about 275 pounds per square inch and was passed to the separator |06 under this pressure and at a temperature again of about '75 or F. The liquid from the bottom of the separator |06 contained about 80 per cent of C3 and heavier hydrocarbons and was passed to the inlet of the separator 45. The vapors from the separator |06 contained only about 35 per cent of hydrocarbons having 3 and more carbon atoms per molecule and was again compressed by the compressor ||2 which produced a pressure in excess of 700 pounds per square inch. The compressed material was then cooled to about 75 to F. by the cooler I4 whereby a further amount of C3 and C4 hydrocarbons was condensed. 'I'his mixture was passed to the separator |l6, and a liquid hydrocarbon fraction containing about 75 per cent of hydrocarbons of 3 and more carbon atoms per molecule was separated and passed through the conduit ||1 to the inlet of the separator |06. The vapor passing from the separatoi` ||6 contained only about 20 per cent of hydrocarbons having 3 and more carbon atoms per molecule, and contained over 70 per cent by volume of methane and hydrogen. This gaseous mixture, while still under a pressure of about 700 to pounds per square inch, was passed at the prevailing temperature of about 'l5 to 80 F. to the bottom of the absorber |30.

In the absorber |30 an absorption oil with a molecular weight of about 200 was used, with about l gallon of oil charged for every 50 to 60 cubic feet of gas charged. The rich absorption oil passed from the bottom of the absorber |30 through conduit |32 at a temperature 125 F, and this temperature was raised to about to 210 F. by the heater |34, and the oil was introduced into the top of the stripper at a pressure of'about 35 pounds per square inch. About 11s of the lean gas passing through the conduit |3| was diverted through the valve |52 and conduit |5| to the bottom of the stripper to aid in freeing the oil of the absorbed hydrocarbons. The denuded oil passed from the bottom of the stripper through the conduit |31 and was eventually returned to the absorber |30 through the conduit |45. The absorbed gases which were separated from the absorption oil, were passed from the stripper through conduit |53, contained about 50 per cent of hydrocarbons having 3 and more carbon atoms per molecule and were reintroduced into the absorption and separation system by being passed through conduit |53 to conduit 30 where they were mixed with the dehydrogenation effluent. The residue gas from the absorber |30 which was discharged from the system through conduit I3| and valve |50 contained a very large portion of hydrogen and methane and less than per cent of hydrocarbons having 3 and more carbon atoms Cil As has been previously mentioned hereinbeiore.

the dehydrogenation step of this process may be either thermal or catalytic, or a combination ot both. Any such dehydrogenation is preferably carried out at a low pressure, such as below 200.

pounds per square inch and preferably lower, under temperature and time conditions which are well known in the art for individual hydrocarbons for thermal dehydrogenation, and which may be readily determined by trial by one skilled in the art when using known dehydrogenation catalysts. As examples of some such catalysts there may be mentioned chromium oxide, especially dried gels comprising chromium oxide as disclosed in U. S. Patents 1,905,383 and 2,098,959, bauxite, bauxite and chromium oxide, and other metal oxide catalysts. The low pressure, vapor phase cracking of heavier oils produces considerable amounts of light hydrocarbons which comprise polymerizable olens, and such mixtures may be readily freed of accompanying hydrogen and methane, and Cz hydrocarbons if desired also, by practicing my process.

The subsequent conversion process whereby the C2 to C5 hydrocarbons are converted to higher boiling hydrocarbons may be any known conversion process suitable for the hydrocarbon fraction so produced. Present day practice is to convert this material into motor fuel, by thermal or catalytic conversion, either oi! which may be only for the polymerization oi' oletlns, or may involve a polymerization of oleilns and paramns to form volatile, higher boiling paraillns. However, these light hydrocarbons may be converted to other higher boiling hydrocarbons, such as lubricating oils or additives for lubricating oils, or the olefins may be processed to produce ne chemicals such as alcohols, or may be reacted with sulfur dioxide to produce resins, or some other known conversion process may be employed.

As a catalyst to use in the conversion of these light hydrocarbons to motor fuel wherein olens and paraffins are joined, a. catalyst of the double salt type such as sodium chloroaluminate is very desirable, with reaction temperatures of 100 to 550 F. and pressures of 200 to 1500 pounds per square inch or more. A very effective catalyst for the simple polymerization oi' the oleflns is a silica-alumina catalyst, such as is disclosed in U. S. Patents 2,142,324 and 2,147,985, used under similar conditions. Any so-called "solid phosphoric acid catalysts may also be used, or liquid catalysts such as alcoholic solutions of ferric chloride or aqueous sulfuric acid. Non-catalytic thermal conversion processes may also be used, as has been previously mentioned. Suitable conditions for any particular hydrocarbon mixture, using any of these methods, may be readily determined by trial by following the teachings of the art.

What I claim is:

1. In a process for the production of normally removing from the eiiluent ot a iirst hydrocarbon conversion process a normally gaseous mixture containing hydrocarbons to be converted in a second conversion process to higher molecular weight hydrocarbons and having not less than two nor more than tlve carbon atoms per molecule along with material lower boiling than C: hydrocarbons, cooling said mixture to condense at least a portion of the higher boiling constituents and passing said cooled mixture to the iirst ot a series of at least two vapor-liquid separatori, removing uncondensed vapors from said rst separatorand compressing and cooling said vapors to condense at least a portion of the higher boiling fconstituents and passing said compressed and cooled material to a second vapor-liquid separator, separating the condensed liquid from saidsecond separator and introducing it into liquid hydrocarbons, the steps which comprise said first separator, removing uncondensed vapors from the last of said series o! separators and passing said vapors in an absorption step in countercurrent direct contact with an absorption oil to i'orm a rich oil and a lean gas comprised substantially or said material lower boiling than Cs hydrocarbons, passing said rich oil at a higher temperature and a lower pressure to a vaporf liquid separator to 'remove therefrom absorbed hydrocarbons, mixing absorbed hydrocarbons so removed with said normally gaseous mixture passed to said ilrst separator, removing the condensed liquid from said nrst separator and passing said liquid to a. conversion step to convert hydrocarbons contained therein into hydrocarbons of higher molecular weight.

2. In a process for the production oi.' normally liquid hydrocarbons from hydrocarbons of lower molecular weight, the steps which comprise dehydrogenating predominantly paraillnic hydrocarbons having not less than-two nor more than iive carbon atoms per molecule to form free hydrogen and polymerizable oleilns, cooling the eiiiuent to condense at least a portion oi the higher boiling material and passing said cooled eilluent to a ilrst vapor-liquid separatonremoving uncondensed vapors from said ilrst separator and compressing and cooling said vapors to condense at least a portion of the higher boiling material and passing said cooled material to a second vapor-liquid separator, separating the condensed liquid from said second separator and introducing it into said ilrst separator, removing uncondensed vapors from said second separator and passing said vapors in an absorption step in counter-current direct contact with an absorption oil to form a rich oil and a lean gas, passing the said rich oil at a higher temperature and a lower pressure in countercurrent direct contact with a portion of said lean gas to form a lean oil and to recover absorbed hydrocarbons, mixing said recovered hydrocarbons with the eiliuent of said dehydrogenation, removing a condensed liquid from said first separator, and converting hydrocarbons contained therein to higher molecular weight hydrocarbons.

3. In a process for the production of normally liquid hydrocarbons from normally gaseous hydrocarbons, the steps which comprise removing from the eilluent .of a rst hydrocarbon conversion process a normally gaseous mixture containing hydrocarbons to be converted in a second conversion process and having not less than two nor more than ilve carbon atoms per molecule along with material lower boiling than Cz hydrocarbons, compressing and cooling said mixture to condense at least a portion of the higher boiling constituents and passing said mixture to the rst of a series of at least two vapor-liquid separators, from cach of said separators except the last removing uncondensed vapors and further compressing and subsequently cooling the same to condense at least a portion of the higher boiling constituents thereof and passing each said compressed and cooled mixture to a subsequent separator in said series, from each of said separators except the rst removing a condensed liquid, and introducing each liquid into the immediately previous separator, removing uncondensedvapors from the last of said series .of separators and passing said vapors in an absorption step without substantial reduction in pressure in countercurrent direct contact with an absorption oil to form a rich oil and a lean gas comprised substantially of said material lower boiling than Cz hydrocarbons, passing said rich oil at a higher temperature and a lower pressure to a vaporliquid separator to remove therefrom absorbed hydrocarbons as vapors, mixing vapors so formed with said normally gaseous mixture passed to said first separator, removing from said first separator the condensed liquid and passing said liquid to a fractionating column, removing vapors from the top of said fractionating column and mixing said vapors with the vapors passing from the aforesaid first separator, removing from a low point in said fractionating column a normally gaseous hydrocarbon fraction and passing said fraction to a conversion step to convert normally gaseous hydrocarbons to normally liquid hydrocarbons.

4. The process of claim 3, wherein a part of said lean gas is used to aid in separating absorbed hydrocarbons from said rich oil.

5. In a process for the production of higher molecular weight hydrocarbons from 'normally gaseous hydrocarbons, the steps which comprise dehydrogenating predominantly paraiiinic hydrocarbons having not less than two nor more than five carbon atoms per molecule to form free hydrogen and polymerizable olens. cooling the eilluent to condense at least a portion of the higher boiling material and passing said cooled material to a first vapor-liquid separator, removing uncondensed vapors from said first separator and compressing and cooling said material to condense at least a portion of the higher boiling material and passing said cooled material to a second vapor-liquid separator. separating the condensed liquid from said second separat-or and introducing it into said rst separator, removing uncondensed vapors from said second sepa- Vrator and compressing and cooling said material to condense at least a portion of the higher boiling material and passing said cooled material to a third vapor-liquid separator, separating lthe condensed liquid from said third separator and introducing it into said second separator, removing uncondensed vapors from said third separator and passing said vapors without substantial reduction in pressure in an absorption step in countercurrent direct contact with an absorption oil to absorb a part of said vapors in said oil, passing the resultant rich oil at a lower pressure and higher temperature in countercurrent contact with a part of the unabsorbed gases from said absorption step to remove absorbed hydrocarbons, mixing the resulting vaporous mixture with the aforesaid dehydrogenation eilluent,`separating the condensed liquid from said first separator and passing said liquid to a fractionating column, removing vapors from the top of said fractionating column and mixing said vapors with the uncondensed vapors passing from said first separator, separating from a. low point of said fractionating column a hydrocarbon fraction and passing said fraction to an olen polymerization step.

6. In a process for the production of normally liquid hydrocarbons from normally gaseous hydrocarbons, the steps which comprise dehydrogenating at a Alow pressure a propane-butane mixture to form polymerizable normally gaseous olens along with free hydrogen and lighter hydrocarbons, compressing and cooling said mixture to condense at least a portion of the higher boiling constituents and passing said mixture to the first of a series of at least two vapor-liquid separators, from each of said separators except the last removing an uncondensed vaporous mixture and compressing and cooling each said mixture to condense at least a portion of the higher boiling constituents thereof and passing each said mixture to the immediately subsequent separator in said series, from each of said separators except the first removing a' condensed liquid and introducing each liquid into the immediately previous separator, removing uncondensed vapors from the last of said series of separators and passing said vapors in an absorption step without substantial reduction in pressure in countercurrent direct contact with an absorption oil to form a rich oil and a lean gas comprised substantially of said free hydrogen and lighter hydrocarbons, passing said rich oil at a higher temperature and a lower pressure to a vaporliquid separator to remove therefrom absorbed hydrocarbons as vapors, mixing vapors so formed with the eluent of said dehydrogenation, removing from said first separator the condensed liquid and passing said liquid to a fractionating column, removing vapor from the top of said fractionating column and mixing said vapors with the vapors passing from the aforesaid first separator, removing from a low point in said fractionating column a hydrocarbon fraction comprising polymerizable olens produced by said dehydrogenation, and passing said fraction to an olefin polymerization step.

'7. In a process for the production of higher molecular weight hydrocarbons from normally gaseous hydrocarbons, the steps which comprise thermally dehydrogenating at a low pressure a hydrocarbon material comprised predominatly of isobutane to form isobutene and propene along with free hydrogen and methane, compressing and cooling the efuent of said dehydrogenation to condense at least a portion of the higher boiling constituents and passing the resultant mixture to the rst of a series of at least two vaporliquid separators, removing from each of said separators except the last an uncondensed vaporous mixture and further compressing and subsequently cooling each said mixture to condense a portion of the higher boiling hydrocarbons and passing each resultant mixture to the immediately subsequent separator in said series, removing from each of said separators except the rst a. condensed liquid and introducing each liquid into the immediately previous separator, removing an uncondensed gaseous mixture from the last of said series of separators, passing said gaseous mixture at an elevated pressure to an absorption step and contacting said mixture with an absorption cil to form a rich oil and a lean gas comprised substantially of free hydrogen and methane, passing said rich oil at an elevated temperature and a low pressure to a stripping step and introducing a part of said lean gas to said stripping step to aid in vaporizing absorbed hydrocarbons from said absorption oil, mixing the gaseous mixture evolved from said stripping step with the effluent of said dehydrogenation. removing the condensed liquid from the aforesaid first separator and introducing said liquid into a fractionating column, mixing vapors evolved from the top of said fractionating column with vapors evolved from the aforesaid first separator, and removing from a low point of said fractionating column a liquid hydrocarbon fraction comprising propene and isobutene and substantially free of lighter hydrocarbons.

8. In a process for the production of normally liquid hydrocarbons from normally gaseous hydrocarbons, the steps which comprise dehydrogenating at a low pressure and a dehydrogenating temperature a hydrocarbon material comprised predominantly of butanes to form normally gaseous olefins along with free hydrogen and lighter hydrocarbons, compressing the effluent of said dehydrogenation to between about '75 and 150 pounds per square inch and cooling the compressed eflluent to condense at least a portion of the higher boiling constituents thereof and passing the resultant mixture to the first of a series of at least two vapor-liquid separators, removing from each of said separators except the last an uncondensed vaporous mixture and further compressing and subsequently cooling each said mixture to condense at least a portion of the higher boiling constituents thereof and passing each resultant mixture to the immediately subsequent separator in said series, removing from each of said separators except the first a condensed liquid and introducing each said liquid into the immediately preceding separator of said series, removing an uncondensed gaseous mixture from the last of said series of separators, passing said gaseous mixture at a pressure between about 300 and 850 pounds per square inch to an absorption step and contacting said mixture with an absorption oil to form a rich oil and a lean gas comprised essentially of free hydrogen and said lighter hydrocarbons, passing said rich oil at a temperature between about-150 and 250 F. and at a pressure not substantially in excess of about 50 pounds per square inch into a vaporliquid separator to remove therefrom absorbed hydrocarbons as vapors, mixing the vapors so produced with the eluent oi' said dehydrogenation, removing the condensed liquid from the first separator of said series and introducing said liquid into a fractionating column, mixing vapors evolved from the top of said column with vapors passing overhead from the aforesaid first separator, removing from a low point of said fractionating column a liquid hydrocarbon fraction substantially free of lighter hydrocarbons and passing said hydrocarbons to an olefin pdlymerization step.

9. A process for the separation of a liquid hydrocarbon material from a normally gaseous mixture, which comprises passing a normally gaseous mixture containing a substantial proportion both of heavier hydrocarbons and of lighter material to the first of a series of at least two vapor-liquid separators at a pressure and temperature such that a substantial portion of heavier normally gaseous hydrocarbons are in liquid phase, from each of said separators except the last removing uncondensed vapors and further compressing and subsequently cooling the same to condense at least a portion o1' the higher boiling constituents thereof and passing each said compressed and cooled mixture to a subsequent separator in said series, from. each of said separators except the first removing a condensed liquid and introducing each liquid into the immediately previous separator, removing uncondensed vapors from theA last of said series of separators and passing said vapors in an absorption step without substantial reduction in pressure in countercurrent direct contact with an absorption oil to form a rich oil and a lean gas comprisedsubstantially of said material Ilower boiling than C2 hydrocarbons, passing said rich oil at a. higher temperature and a lower pressure to a vapor-liquid separator to remove therefrom absorbed hydrocarbons as vapors, mixing vapors so formed with said normally gaseous mixture passed to said first .seporator, removing from said first separator condensed liquid and passing said 1iquid to a fractionating column, removing vapors from the top of said fractionating column and mixing said vapors with vapors passing from the aforesaid first separator, and removing from a low point of said fractionating column a liquid hydrocarbon material as a product of said separation.

10. A process for the separation of a 1iquid hydrocarbon material from a normally gaseous mixture, which comprises passing a normally gaseous mixture containing a substantial proportion both of heavier hydrocarbons and of lighter material through a conduit to the first of a series of at least two vapor-1iquid separators at a pressure and temperature such that a substantial portion of heavier normally gaseous hydrocarbons are in liquid phase, from each of said separators except the last removing uncondensed vapors and further compressing and subsequently cooling the same to condense at least a portion of the higherboiling constituents thereof and passing each said compressed and cooled mixture through a conduit to a subsequent separator in said series, from each of said separators except the first removing a condensed liquid and introducing each said 1iquid into the conduit entering the immediately previous separator at such a point in said conduit that substantially complete mixing of said liquid with the fluids in said conduit results prior to the expansion of the mixture in said separator, removing uncondensed vapors from the last of said series of separators and passing said vapors in an absorption step Without substantial reduction ln pressure in countercurrent direct contact with an absorption oil to form a. rich oil and a lean gas comprised substantially of said material lower boiling than C2 hydrocarbons, passing said rich oil at a higher temperature and a lower pressure to a vapor-liquid separator to remove therefrom absorbed hydrocarbons as vapors, mixing vapors so formed with said normally gaseous mixture passed to said first separator, removing from said first separator condensed 1iquid and passing said liquid to a fractionating column, removing vapors from the top of said fractionating column and mixing said vapors with vapors passing from the aforesaid first separator, and removing from a low point of said fractionating column a liquid hydrocarbon material as a product of said separation.

11. In a process for the production of normally liquid hydrocarbons, the steps which comprise removing from the effluent of a rst hydrocarbon conversion process a normally gaseous mixture containing hydrocarbons to be converted in a second conversion process to hydrocarbons having higher molecular weights and having not less than two nor more than ve carbon atoms per molecule together with material lower boiling than C2 hydrocarbons, cooling said mixture to condense at least a portion of the higher-boiling constituents and passing said cooled mixture through a conduit to the rst of a series of at least two vapor-liquid separators, removing uncondensed vapors from said first separator and compressing and cooling said vapors to condense at least a portion of the higher-boiling constituents and passing said compressed and cooled material to a second vapor-liquid separator, separating the condensed liquid from said second separator and introducing it into the conduit entering said rst separator at such a point in said conduit that substantially complete mixing of said liquid with the fluids in said conduit results prior to the expansion of the mixture in said first separator, removing uncondensed vapors from the last of said series of separators and passing said vapors in an absorption step in countercurrent direct contact with an absorption oil to form a rich oil and a lean gas comprised substantially of said material lower boiling than Cz hydrocarbons, passing said rich oil at a higher temperature and a lower pressure to a vaporliquid separator to remove therefrom absorbed hydrocarbons, mixing absorbed hydrocarbons so removed with said normally gaseous mixture passed to said first separator, removing the condensed liquid from said rst separator and passing said liquid to a conversion step to convert hydrocarbons contained therein into hydrocarbons having higher molecular weights.

12. In a process for the production of normally liquid hydrocarbons from normally gaseous hydrocarbons, the steps which comprise dehydrogenating at a low pressure and at a dehydrogenating temperature a hydrocarbon material comprised predominantly of butanes to form normally gaseous oleflns along with free hydrogen and lighter hydrocarbons, compressing the effluent of said dehydrogenation to between approximately '75 and approximately 150 pounds per square inch and cooling the compressed eluent to condense at least a portion of the higher-boiling constituents thereof and passing the resultant mixture through a conduit to the first of a series of at least two vapor-liquid separators, removing from each of said separators except the last an uncondensed vaporous mixture and further compressing and subsequently cooling each said mixture to condense at least a portion of the higherboiling constituents thereof and passing each resultant mixture to the immediately subsequent separator in said series, removing from each of said separators except the first a condensed liquid and introducing each said liquid into the conduit entering the immediately preceding separator of said series at such a point in said conduit that substantially complete mixing of said liquid with the fluids in said conduit results prior to the expansion of the mixture in said separator, removing an uncondensed gaseous mixture from the last of said series of separators, passing said gaseous mixture at a pressure between approximately 300 and approximately 850 pounds per square inch to an absorption step and contacting said mixture with an absorption oil to form a rich oil and a lean gas comprised essentially of free hydrogen and said lighter hydrocarbons, passing said rich oil at a temperature between approximately 150 and approximately 250 F. and at a pressure not substantially '1n excess of approximately pounds per square inch into a vaporliquid separator to remove therefrom absorbed hydrocarbons as vapors, mixing the vapors so produced with the eilluent of said dehydrogenation, removing the condensed liquid from the first separator of said series and introducing said liquid into a fractionating column, mixing vapors evolved from the top of said column with vapors passing overhead from the aforesaid first separator, removing from a low point of said fractionating column a liquid hydrocarbon fraction substantially free of lighter hydrocarbons and passing said hydrocarbons to an olen poly'- merization step.

KARL H. HACHMUTH.

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