US2038834A - Process for converting hydrocarbons - Google Patents

Description

April `M28, 1936. F. E. FREY I PROCESS FOR CONVERTING HYDROCARBONS lr'ilewl oct. 6, 1932 WWW# Patented 193s vvr Bartlesville,

n. Frey, `to Phillips Petroleum f'company, Okiasa corporation of Delaware annue-mon ombus, ,1932, serai N9. sscsss s cum. (ci. 19a-1o) 'I'his invention relates to an 'improved process for converting volatile aliphatic hydrocarbons, especially naturaly gas and/or the Agases produced bythe cracking and distilling of petroleum, or

g by the destructive distillation of bituminous ma,-

terials such as coal, into valuable normally liquid hydrocarbons by thermal treatment,

It has been proposed to convert such ,gases into aromatic oils by heating them to elevated l temperatures,12501750 F. for a suillcient time to effect a. substantial conversion into `aromatic oils. 'I'he conversion taires place at atmospheric or-highenpressure lwith the formation ofl aro.v

matic oils, cand, owing to the drastic cracking conditions required, 'the gaseous hydrocarbons are for the most part `destroyed with theexception of methane which is produced in the cracking, and which in itself can be converted into oils by cracking at excessively high temperatures only. Consequently, little material'suitable for 'retreatment is obtained.

lIt has also been proposed to convert gaseous hydrocarbons into normally liquid hydrocarbons 'by heating to a reactionvtemperature under high z5 pressure, above 4500 pounds per square inch. In

, this way 'gaseous oleilnes have been shown to polymerize toliquid hydrocarbons inrgood yield'.l The conversion of the more refractory gaseous vparafiins into'normally liquid products 'has also been proposed. While gases produced by'oil` cracking processes contain both paramns and olenes, natural gases contain only the paraiilns.v v At a temperature of vpreferably 950ll00 F. and

pressure 4o'i preferably 2000 to 3500 pounds per square inch, bltane maybe converted in a single cracking operation into normally liquid hydrocarbons mostly aliphatic and alicylic. in nature to the extent of 8-16 per cent. I have found that propane at such pressuresrequires a higher temperature, while ethaneis inferior to propane.

'In fact, the presence -of propane and ethane, I have foundgis usually undesirable in admixture with butanes or gaseous oleilnes to be converted under such high pressures into liquid hydrocarbons, inasmuch as they detract from the emciency of the conversion unit. In the treatment of the lower boiling paraillns` under heat ,and heavy 'pressure to produce an optimum conversion into aliphatic andalicylic 'hydrocarbons' of higher boiling' point, I have found that when the time of reaction is the minimum necessary to-produce a virtually maximum yield of volatile oils, there survives a great part of the paraiiins -treated unaltered, and some of the unchanged paraiiins may be advantageouslyseparated fromthe products and returned to the vcracking q. operation. The ,Ibutanes and butenes formed, I have found, are

particularly suitable for -retreatment and may' be isolated for this purpose by any suitable means, oo for example, fractional distillation. -Methane,

:ethane, ethylene, lpropane, vand -p'ropyle'ne. I `have vfound to' be formed in'considerable amounts,` in such Ahighpressure thermal treatment, `*that is, in quantities comparable lto the oils formed and -exceeding 5 per cent of the hydrocarbon'treat- 5 ed, and these lower paramns are not as Ysuitable for retreatment as the butanes. A of the `propane and ethane, however, `may be `returned with the Lbutane chiefly for the sake ofthe yield of oils obtainable from the accompanying prllyl- 1u ene or ethylene, but a considerable part of the a hydrocarbons boiling below butane vand butene must be continually discharged from the'system. Consequently, in operating to obtain the best economy, a quantity ofgas containing pro- 15 i pane, ethane, propy'lene, ethylene, methane and hydrogen is obtained as a by-product.' l

, The conversion of hydrocarbon gases into aromatic oils previously described may be accomplished lat moderate pressures, sayv below 500 vfr() pounds per square inch, and is applicable to' all simple paraillns and oleilnea'all of which give a substantial yield, of '7 per cent 'or more, of aromatic oils with the exception of methane' which requires prohibitive conversion temperatures. 25

The present invention deals with 'a novel method and'apparatus for combiningthe two methods of cracking above described, andthe subjecting ofthe gaseous by-products of high pressure' oon- .version to low 'pressure cracking and obtaining 3o thereby an additional yield of oils.

lAn object of my invention is to treat hydrocarbon gases in a process which embodies both "-.inethods of conversion above described in sucha manner vthat increase in yield of oils, flexibility '35,

oi' operation as regards relative proportions and qualities of liquid products, and economies in operatioi are obtained which are not realized in the use of either process alone.

,A further object of my invention is to convert 40 volatile normally liquid hydrocarbons having a tendency-to'. detonate, when used as i'uel inA an internal combustion engine,`into other normally liquid hydrocarbonshaving a less tendency to detonate.

Further advantages cf the embodiment to -be described are:

(l) v'lhe cost -of'gas compression is minimized by the use of separating and purifying operations v which deliver charging stock in liquid form to the high pressure conversion operatin. v

2) The low pressure gas cracking operation is M -applied (a) to uncondensed gases and vapors .l

available at -low pressure; (b) propane and other.

constituents which should beI discarded from the -high pressure gasconversion system. v

-l(3) Liqueiled hydrocarbon gases in vthemselves for conversion into normally liquid hydrocarbons are used asan absorbing medium for extracting gases at high pressure.

(4) Absorption of lower gaseous hydrocarbons `are improved by chilling the absorbing medium through the expansion of light hydrocarbon gases formed in the process under high pressure.

(5) Economies are achieved through the use of existing equipment and facilities of a refinery or natural gasoline plant in connection with'the process.

With the `foregoing objects outlined and. with other objects in view,- the invention consists in the novel features hereinafter described in detail in connection with the'accompanying drawing, which shows an elevation of my improved apparatus.

A charging stock consisting predominantly of butane but which may contain gaseous olenes and-limited amounts of ,lower parains is-delivered by pumpsv4 I, 2 and 3 continuously under.' a pressure between 500 pounds and 5000 pounds per square inch lthrough a heating tube 4 positioned within a furnace housing 5 wherein the hydrocarbons are maintained at 'a cracking temperature in a range between '150 F. and 1200 F., butpreferably between 850 and 1100 F., for a time suiilcient to eect the conversion of a substantial portion of the charging stock into normaliy liquid hydrocarbons, together with quantities of paraiiins and oleiines lower than butane and butene. The thermally treated hydrocarbons are discharged into a rprimarycondenser 6 maintained Lunder substantially the same pressure as the coil 4, where the temperature is' reduced by director indirect cooling means to effect condensation of some gasoline and heavier liquid hydrocarbons. The liquid is separated in separator 1 from vapors, and the vapors are discharged into a secondary cooler condenser 8 and a separator 9. A further extraction ot heat takes placein condenser 8 and the greater part of the unconverted butane, together with the remainder of the normally liquid hydrocarbons are .con-

densed. Vapors discharged from 9 enter an absorber or rectier I0, still under such high pressure, and therein undergo further condensation and come into contact with an absorption liquid which, under the conditions existing in the absorber, absorbs ethane, ethylene, and higher hydrocarbons, leaving in the unabsorbed gas the greater part of the methane and any gases oi.' lower boiling point, which gases are discharged from the absorber through a pipe Illa that leads tothe lower portion of a heat exchanger II ofv the' plate and tube type. After passing through the tubes of the heat exchanger, these gases are discharged through a pipe IIa and some ofthe saine may be expanded through an expansion valve IIb and a conduit II c back, into theheat exchanger II. Due to the expansion of this portion of the gases, a very low temperature .will be maintained in the heat exchanger and this will result in the condensation of a portion of the, gases entering the heat exchanger from the pipe I0a. Such condensate is returned to the top of 4the absorber or rectifier through a pipe Ilib. Gas

Should it be desired to crack lthisgas which is high in methane, some of it may be fed from the -pipe II; through pipes IIi and IIk into a low pressure cracking unit I4.

If preferred, some of the gas which is high in methane may be vented from the system through the line I3 by passing the same through a valved pipe I3a which connects pipes II! and I3.

By reason of the high pressure existing in a portion of the system, liquefied hydrocarbon gas, preferably butane, may be used as an absorption or reux medium in I0. This medium extracts the valuable hydrocarbons more effectively at -a reduced temperature. Accordingly, butane from 'a pipe I 3b is mixed with the cold condensate from the heat exchanger II before said condensate enters the absorbency or rectifier.

The liquid separated in I0 contains the absorption medium, thev butane and butene not previously condensed, 4,and the greater part of the propane, propylene, ethane and ethylene formed by the high pressure conversion operation. This liquid is discharged by pipe I5 through a pressure regulator I5a into a rectier and condenser IB and I1 in which the butaneand butene mixed with a controlled limited proportion of propane and lighter hydrocarbons are separated under a pressure of about 500 pounds-per'square y inch, and returned by pump 3 through pipeIB to be retreated in the high pressure conversion-coil 4. Hydrocarbons lighter than butane, in gaseous and liquid'- condition, pass respectively from coner I1, through pipes Ilb and I1c to an ex-- -hausting or rectifyingcolumn I9 ,iny which -lighter hydrocarbons, chiefly methane may be separated under a pressure of about 500 pounds per square 5 in ch and discharged through pipe 20,'leaving the system at I`3. The liquefied hydrocarbons discharged at 22 `are chiefly ethane and ethylene, propane and propylene, and are led through a pressure reducing valve 22a to the low pressure cracking unit I4` for conversion into aromatic oils under a pressure between atmospheric and 500 pounds per square inch, but preferably about pounds per square inch. If the quantity of methane is not large, 'it need not be separated and discarded, and by opening valve 23, all the vapors from I6 may pass directly to the cracking unit I4.

The normally liquid hydrocarbons formed in f pressure conversion coil, while lighter vapors may be allowed to pass through a pressure regulator 3| and into the cracking unit I4. The normally liquid hydrocarbons are fractionated in the rectifler 21 together with the condensate from 1, which enters through pipe 2 9, and the vaporsfrom the rectifier 21 are condensed in a condenser' 21a and such condensate becomes the motor-fuel distillate which is collected in a receiver 30. A less volatile residue is discharged from the still 28. l A conventional reflux .condenser 21h is positioned between the rectifier 21 and condenser 21a.

Normally liquid hydrocarbons, as for example,

the higher boiling fractionsof natural gasoline,

of low anti-knock value, may be introduced, preferably mixed with'other charging stock, to the conversion into liquid hydrocarbons of higher anti-.knock value, which are recovered at 30. Or such material, as well as gases ofhigh olene content, may be charged into an intermediate point of the high pressure conversion zone at a point 33 nearer the exit to avoid excessive reaction in casea refractory charging stock requiring a high temperature, such as butano, is at the same time undergoing treatment and entering from pipe i8.

The gaseous hydrocarbons lighter than butano,

produced by the pressure conversion operation and separated as described, are passed into a common conduit 35 into which also may be led other hydrocarbon gases of limited methane content, which may be available at amoderate pressure. These gases pass into' theV low pressure cracking unit I4 in which they are heated to a temperature of 1250-1750 F., for a time sufficient to produce a substantial yield of aromatic oils. The reaction products are discharged from i4 through a conduit lla into a primaryl cooler 36 in which by either direct or indirect cooling means, the temperature is reduced and tar separated; thence into an extraction plant 31 in which the remainder of the oils, which are largely aromatic, are separated and a small amount of lighter oleiinic hydrocarbons may be isolated and returned to either conversion zone through valved pipes 39 or 40. The dry gas is then discharged from the system through pipes 38 and I3. The gases discharged from the system, owing to their high hydrogen-carbon ratio, are particularly suitable for the production of hydrogen.

Since methane is the only gaseous hydrocarbon unsuitable for conversion into aromatic oils, all available hydrocarbon gases except those ccntaining excessive amounts of methane may be treated in the low pressure cracking unit i4 to produce aromatic oils, includinggases predominating in butane and butene, which, while suitable for conversion in higher yields into oils by high pressure conversion, may be available in excessive quantities or under pressures so low as to unfit them for conversion in the high pressure unit 4. For the high pressure conversion operation, hydrocarbons higher than propane are most Y suitable, but when propylene or ethylene are present in substantial concentrations in lighter gases, they are suitable for conversion in the high pressure unit, whether or not a high concentration of butane accompanies them. The operating conditions giving best results depends on the composition of charging.V stock. The ccnversion of butanes containing olenes in small amounts may be conducted at 100G-5000 pounds' per square inch pressure, and 9 50-1200 F., the

higher temperatures within'the range being. the more eiective if ethane and propane are presentin substantial amount. Lower temperatures are preferable when a high olefine content accompanics the parains, temperatures as low as 750 and pressures as low as 500 pounds per square inch giving good results when olenes predominate in the charging stock. A particularly suitable charging stock is the more easily liqueed gases produced in cracking petroleum, which gases predominate in butanesgandbutenes. gases may be converted to the extent of 50%,and

even more, into normally liquid hydrocarbons,

-"-Gases from various sources, subject to the above limitations, may be treated in the high Such' direct compression, and in some cases direct compression with or without the use of a liquid pump for further increasing the pressure may be profitably employed. Y

In conjunction with a natural gasoline extraction plant or a refinery, additional economies can be effected. The products of the high pressure conversion operation conducted in coil 4, can be cooled in heat exchange relation with oils and gases of lower temperature', thereby effecting heat economies, and the products of the low pressure cracking step, formed at a higher temperature, may bev used to elect cracking as well, both in contact and out of contact with oil to be cracked. Condensing and distilling units may likewise beused to perform a dual role in effecting separations of hydrocarbon constituents in connection with both the process for gas conversion and renery gasoline plant operations, and many other obvious advantages can be gained from such combination.

Both the high pressure and low pressure conl version operations yield a substantial amount of ,normally liquid hydrocarbons when, in accordance with the foregoing disclosure, the appropriate hydrocarbons are heated to the proper temperature for a time sufficient to effect the desired conversion. Heat may be introduced continuinapplicable. The low pressure conversion is preferably conducted in accordance with U. S.

Patent 1,847,238, March 1, 1932, and the high,

pressure conversionmay be conducted in either one or two stages.

As an example of the process, a mixture of the butanes containing 70% n-butane and 30% isobutane was converted at 975 F.' and 3100 pounds pressure for a period of approximately 10 minutes, thenmaintained for a shorter time at a somewhat lower temperature to further synthetic reactions. Carbon formation was slight.

'40% of the butano was discharged unconverted of .'12sl at 20 c. The remainder consisted of gaseous products. The analysis of the gases involume percent was as follows:

Hydrogen-- Methane- 40.5 Ethane.4 16.6 Ethylene .2 Propane 11.1 .fPropylene 1.3 Butanes 27.7 Butylenes f 1.6

Total 100.0

Owing to the low oleiine content, the gases lighterthan butaneand butene would decrease the throughput of the plant when added to the butane, which is recycled. The gaseous products of the above composition, exclusive of butane and butene, may be cracked at 1475 F. with an exposure time of 0.2 minutes to produce 0.7 gallons of benzol per thousand cubic feet or, when the methane is separated andiethane, ethylene, propane, and propylene are cracked, 1.6 gallons per thousand cubic feet. In the complete conversion of this butane mixture by the combination process in which all unconverted butane and butene formed are returned to the pressure conversion, a yield of about 30' percent by weight of gasoline is obtained, together with 7 percent by weight of benzene. Heavy oil andta-r amounting to about 7 and 4 percent respectively, are formed. About 52 percent of the original hydrocarbon survives the conversion steps as a gas suitable for fuel, containing chiefly, methane, but the gas produced by high temperature cracking contains about 16 percent of ethylene and 4 percent propylene and butylene by volume, which may be extracted under favorable conditions for treatment in either conversion step. The yields of normally liquid hydrocarbons Will be augmented when gases containing oleflnes are availablefor treatment.

It will be noted that the combination is flexible??? in that the relative proportions of products from -the high pressure and low pressure process can be varied within certain limits, ard thereby render the combination process capable of operation under the most advantageous conditions. In other words, the yield of benzol from the low pressure cracking unit 14 could be increased at the expense of a decrease in yield of liquid products from the high pressure conversion zone 4.`

'I'his mode of operation could be followed when the market price of benzol was considerablyhigher ,than the market price of high octane motor fuel.

While I have disclosed preferred ways of practicing the process, it will be understood by those skilled in the art that changes in procedure may be resorted to without departing from the spirit of the invention, as set forth in the claims.

What I claim and desire to secure by Letters Patent is:

1. A process for the conversion of normally' gaseous hydrocarbons, composed chiefly of hydrocarbon mixtures consisting,r largely of butanes,

Vt"al part of said hydrocarbons into normally liquid hydrocarbons essentially aliphatic in character, separating from the thermally treated hydrocarbons said normally liquid hydrocarbons, also separating from said thermally treated hydrocarbons higher gaseous hydrocarbons predominating in butane and gaseous hydrocarbons lighter than said butane returning the higher gaseous hydrocarbons to said heating zone, then passing said lighter gaseous thermally treated hydrocarbons, while under a pressurc between atmospheric and 500 pounds persquare inch, through a second heating zone and heating them therein to a temperature between 1250 F. and 1750 F. for a suflicient period of time to produce a substantia1 yield of aromatic oils, and thereafter separating the aromatic oils so produced from the mixture resulting from the last mentioned thermal treatment.

' 2..A process for converting hydrocarbons consisting largely of butanes into higher boiling hyhydrocarbons and drocarbons predominantly of the boiling range of gasoline, which comprises continuously passing the aforesaid lower boiling hydrocarbons Athrough a heating zone under a pressure of from pheric and below 500 pounds per square inch for a sufficient period of time to produce a substantial yield of aromatic oils, and separating the aromatic oils so produced from the products of the last mentioned'pyrolysis.

3. A process for converting hydrocarbons consisting largely of butanes into higher boiling hydrocarbons, which comprises subjecting the first mentioned hydrocarbons to conversion in a heating zone at temperatures of '750 to 1200 F. and pressures of 500 to 5000 pounds per square inch, separating the eilluents from the said heating zone into a gasoline and heavier fraction, a recycle fraction of approximately the boilng range of the original charging stock, a lower boiling fraction predominantly methane, and a fraction containing principally hydrocarbons intermediate in boiling point between methane and the recycle fraction, returning the recycle fraction to the inlet of the aforesaid heating zone for re-l processing, discarding the high methane fraction, and cracking the aforesaid intermediate fractio-n at temperatures between 1250 F. and 1750 F. and under pressure between atmospheric and 500 pounds per square inch for a sumcient period of time to produce a substantial yield of aromatic oils.

4. A process for the conversion of normally gaseous hydrocarbons composed of hydrocarbons higher than methane and principally of hydrocarbons of three and four.carbon atoms per molecule into normally liquid hydrocarbons, which comprises continuously passing the hydrocarbons while maintained under superatmospheric pressure between 500 and 5000 pounds per square inch through a heating zone and heating the hydrocarbons to a temperature between 750 F. and 1200" F. to effect conversion of a substantial part thereof into normally liquid hydrocarbons comprising motor fuel, separating normally liquid hydrocarbons from normally gaseous separating the normally gaseous hydrocarbons into a fraction consisting principally of hydrocarbon gases lighter than the.

principal constituent of the charging stock and another fraction consisting principally of hydrocarbon gases of substantially the same boiling range as the charging stock, returning the lastmentioned fraction to the heating zone for fur.-

ther treatment, passing the fraction consisting principally of hydrocarbon gases lighter than the principal constituent of the charging stock through another heating zone and heating it during its passage therethrough to a temperature of from about 1250 F. to 1750 F. for a suilcient period of time and while being maintained under a pressure between atmospheric and about 500 pounds per square inch to produce a substantial 2,038,884 yield of aromatic oils, and*l recoveringsaid aromatic oils.

5. A process for converting hydrocarbons consisting largely of hydrocarbons having'four carbon atoms per molec'ule into high boiling hydrocarbons predominantly of the 'motor fuel boiling range which comprises continuously passing said hydrocarbons while being maintained under a superatmospheric pressure between 500 and 5000 pounds per square inch through a heating zone and heating the hydrocarbons to alhigh temperature between 750 F. and 1200"` F. to eect polymerization of a substantial part thereof into normally liquid hydrocarbons comprising motor fuel, separating under said pressure, normally liquid hydrocarbons from normally gaseous hydrocarbons and separating the normally` gaseous 'hydrocarbons into a fraction consisting principally of hydrocarbon gases lighter than the principal constituent of the charging stock and another fraction consisting principally of hydrocarbon gases of substantially the same boiling range as the charging stock,returning the lastmentioned fraction to the heating zone lfor further treatment, passing the fraction consisting principally of hydrocarbon gases lighter than the principal constituent of the charging stock in a confined stream through another heating zone and heating it during its passage therethrough to a temperature of from about 1250 F. to 1750 F. for a sucient period of time and while being maintained under a pressure between atmospheric and about 500 pounds per square inch to produce a substantial yield of aromatic oils, and

recovering said aromatic oils. A

6. A process for converting hydrocarbons consisting largely of hydrocarbons having four carbon atoms per molecule into high boiling hydrocarbons predominantly of the motor fuel boiling range which comprises continuously passing said hydrocarbons while being maintained under a 'superatmospheric pressure between 500 and 5000 pounds per square inch through a heating zone and heating the hydrocarbons to a high tem-V perature between '150 F. and 1200 F. to effect polymerization of a substantial part thereof into normally liquid hydrocarbons comprising motor fuel, separating normallyv liquid hydrocarbons from normally gaseous hydrocarbons and separating the normally gaseous hydrocarbons into a fraction consisting principally of hydrocarbon gases lighter than the principal constituent of the charging stock and another fraction consistqlng principally of hydrocarbon gases of substan- Jtially the same boiling range as the charging stock, returning the last-mentioned fraction to the heating zone for further treatment, separating methane from the fraction consisting principally of hydrocarbon gases lighter than the principal constituent of the charging stock and dis'" charging it from the process, and subsequently passing the remaining portion of thelast-mentioned lighter fraction through another heating zone and heating it during its passage therethrough to a temperature of from about 1250 F.

to l'750 F. for a suflicient period of time and while being maintained under a pressure between atmospheric and about 500 pounds per square inch to produce a substantial yield of aromatic comprises continuously passing the hydrocarbons while maintained under pressure between 500 and l5000 pounds per square inch through a heating zone and heating the hydrocarbons to atemperaturel between 750 F. and 1200 F. to eect 5 conversion of a substantial'part thereof into normally liquid hydrocarbons comprising motor fuel, separating normally liquid hydrocarbons from normally gaseous hydrocarbons, separating the normally gaseous hydrocarbons into a fraction 10 consisting principally of hydrocarbons lighter than the principal constituent of the charging stock and another fraction consisting principally of hydrocarbon gases of substantially the same boiling range as the charging stock, subjecting 15 the last-mentioned fraction while under a pressure between 500 and 5000 pounds per quare inch to a temperaure between '150 F. and 1200 F. to eifect further conversion thereof, passing the fraction consisting "principally of hydrocarbon 20 gases lighter than the principal constituent ofthe charging stock through another heating zone and heating it during its passage therethroughl to a temperature of from about 1250 F. to 1750 F.

for a sufcient period of time and While being 2'5v maintained under a pressure between atmospheric and about 500 pounds per square inch to produce a substantial yield of aromatic oils, and recovering said aromatic oils.

8. A process for the conversion of normally 30 gaseous hydrocarbons composed of hydrocarbons higher than methane and principally of hydrocarbons of three and four carbon atoms per molecule into normally liquid hydrocarbons, which comprises continuously passing the hydro- 35 carbons while maintained under pressure between 500 and 5000 pounds per square inch through a heating zone and heating the .hydrocarbonsl to a temperature between 750 F. and 12009 F. to effect conversion of a substantial part thereof into 40 normally liquid hydrocarbons comprising motor lfuel, separating normally liquid hydrocarbons from normally gaseous hydrocarbons, separating the normally gaseous hydrocarbons into a fraction consisting principally of hydrocarbon gases 45 lighter than the principal lconstituent of the charging stock and another fractionA consisting of hydrocarbon gases of substantially the same fboilingrange. as the charging stock, subjecting the last-mentioned fraction while under pressure 5o between 500 and 5000 pounds persquare inch to a temperature between 750? F. and 1200 F. to effect further conversion thereof, passing the fraction consisting principally 'of hydrocarbon gases lighter than the principal constituent of the 55 charging stock through a second heating zone and .heating it during its passage therethrough to a temperature from about 1250 F. to 1750 F. for a sunicient period of time and while being main-4 tained under a pressure between atmospheric and 60 aboutv 500 pounds per square inch to produce a substantial yield of aromaticoils, separating normally gaseous hydrocarbons from said aromatic oils and returning at least a part of the lastmentioned gaseous hydrocarbons to the mst-,65

mentioned heating zone for further treatment.

9. A process for the conversion of normally gaseous hydrocarbons composed of hydrocarbons higher than methane and principally of hydrocarbons' 'of three and four carbon atoms per 70 molecule j into normally lliquid hydrocarbons, which comprises continuously passing the hydrocarbons while maintained under pressure between 500 and 5000 pounds per square inch through a heating' zone and heating the hydrocarbons to a 75 temperature between '150 F. and 1200 F. to effect conversion of a substantial part thereof into normally liquid hydrocarbons comprising motor fuel, separating normally liquid hydrocarbons from normally gaseous hydrocarbons, separating the normally gaseous hydrocarbons into a fraction consisting principally of hydrocarbon gases lighter than the principal constituent of the charging stock and another fraction consisting of hydrocarbon gases o! substantially' the same boiling range as the charging stock, subjecting the last-mentioned fraction while under pressure between 500 and 5000 pounds per square inch to a temperature between 750 F. and 1200 F. to effect further conversion thereof, passing the fraction lconsisting principally of hydrocarbon gases lighter than the principal constituent of the charging stock through a second heating zone and heating it during its passage therethrough to a temperature from about 1250 F. to 1750 F. for a suillcient period of time and while being maintained under a pressure between atmospheric and about 500 pounds per square inch to produce a substantial yield of aromatic oils, separating normally gaseous hydrocarbons from said aromatic oils and returning at least a part oi the last-mentioned gaseous hydrocarbons to the second heating zone for further treatment.

FREDERICK E. FREY.

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