US2187631A - Method of refining hydrocarbons - Google Patents

Description

Jan. 16, 1940. H. c. scHUTT HETHOD 0F REFINING HYDRCCARBONS -Filed June 25',

INVENTOR /MM BY ATTORN EY Patented im. 1s, 1940 UNITED STATES PATENT OFFICE bymeane nts, to American Locomotive Company, New York, N. Y., a corporation or New York,

Application June 25, 1937, Serial No. 150,218

4 Claims.

This invention relates to the art of refining hydrocarbon oil and, more particularly, to the art of rening such oil by thermal conversion to effect changes in the molecular structure.

Hydrocarbon oil, such as, for example, crude petroleum and its fractions has become increasingly important as a source of low molecular weight hydrocarbons of value as raw material for the synthesis of chemical compounds `'having general and specific industrial utility. There may be produced from reduced crude petroleum, for example.,by thermal conversion operations, both liquid and gaseous conversion products. The quantities and the composition of the respective conversion products will be governed generally by the temperature and pressure conditions at which the conversion operations are carried out. Certain of the liquid conversion products produced are hydrocarbons of the aromatic series and are useful as motor fuel and as raw material for the chemical industry. Likewise, certain of the normally gaseous unsaturated hydrocarbons produced, such as, for example, ethylene, propylene, and butylene are of major utility-as a base material for the production of innumerable Ichemical compounds.

An object of this invention is to provide a method for manufacturing from petroleum both unsaturated aliphatic and aromatic hydrocarbons.

Another object of this invention is to provide a method for manufacturing from petroleum an unsaturated normally gaseous hydrocarbon as a product. f

Another object of this invention is to provide a method for manufacturing from petroleum an aromatic hydrocarbon product adapted to be used as motor fuel. 4

Another object of this inventionis to provide a method for manufacturing aromatica from petroleum by thermal conversion at temperatures lower than the heretofore required temperatures.

Other and further objects of .this invention will be apparent from the accompanying description,` accompanying drawing. and the ap pended claims.

'I'he accompanying drawing which forms part oftheinstantspeciilcationisaviewinelevation schematically showing a combination of apparatus with which the method may be carried out.

In general, charge oil suchl as, for example, reduced crude is fractionated to separate the heavy portion which together with recycle oil is subjected to a viscosity-breaking heating opc- (Cl'. ISG-9) ation. There is obtained from the charge oil and the products of this operation, by fractionation and condensation, fuel oil, recycle oil, clean low boiling oil and uncondensable gas. This clean oil is admixed with a carefully selected hydro-4 l carbon fraction comprising mainly C4 and Cs hydrocarbons, i. e., hydrocarbons having four and five carbon atoms per molecule. This selected fraction is preferably rich in unsaturated hydrocarbons, particularly di-olefins and branched 10 chain mono-olens. Unsaturated hydrocarbons illustrative of these groups are, for example, butadiene (1,3) and pentadiene (1,3) being diolens of the C4 and Cs hydrocarbons, respectively, and iso-butylene and 2 methyl butene (1) il being branched chain mono-oleilns of the C4 and Cs hydrocarbons. This hydrocarbon fraction characterized by such constituents functions in admixture with the clean oil to promote the formation of aromatics by thermal conversion 20 at temperatures reduced from the high values heretofore required.

The clean oil admired with the selected hydrocarbon fraction is, subjected to a high temperature-low pressure thermal conversion operation productive of appreciable quantities of desired aromatic and unsaturated hydrocarbons, and the conversion products fractionated. There are obtained as products of this fractionating operation, a heavy fraction forming a synthetic fuel oil, an intermediate fraction containing oil suit# able for recycling and a light gas-vapor fraction containing the unsaturates and aromatics desired as final products. A

The fuel oil is withdrawn from the system and u the intermediate fraction is re-fractionated with the charge oil andl products of the viscosity-- breaking operation. This intermediate fraction through re-fractionation yields clean recycle oil and also assists in more nearly accomplishing the desired substantially complete condensation of the products of this fractionating operation. In addition, the charge oil functions'as an absorption medium to remove free carbon formed by uncondensable gases resulting from the viscosity- `breaking operation are highly compressed in a gas compression plant, preferably in at least two stages coupled with intermediate and final compressed gas cooling and condensate separating stages. i v

The compressed gases are subjected to a selective absorption operation which separates from the gases substantially all of the five carbon atom hydrocarbons and an appreciable percentage of those four carbon atom unsaturated hydrocarbons desired in the so-called selected hydrocarbon fraction. The desired selective absorption is attained through the employment of an aromatic liquid as an absorption oil which. being intended to absorb C4 and Cs hydrocarbons primarily, is substantially free of ve carbon atom hydrocarbons. The aromatic liquid has a greater aillnity for di-olefins and branched chain mono-oleilns of the C4 and Cs unsaturated hydrocarbons, or for saturated hydrocarbons.

Thus, although substantially all of the saturated and unsaturated Cs hydrocarbons will be' absorbed by the aromatic absorption medium, desired unsaturatedhydrocarbons of the C4 hydrocarbons will be concentrated in the aromatic liquid, from which the selected hydrocarbon fraction to be mixed with the clean oil for subsequent thermal conversion is to be separated. The

y the four and five carbon atom hydrocarbons as a selected fraction for admixture with the clean oil. A portion of the aromatic product thus recovered is employed as the lean absorption oil previously referred to, the remaining portion being removed from the system. The four and five carbon atom hydrocarbons forming the selected fraction are admixed with the clean oil andy subjected therewith to the high temperature zthermal conversion operation as has previously been described.

The 4uncondensed products of the fractionating iperation together with gases, unabsorbed'by the aromatic absorption liquid and substantially freed of di-oleilns and other unstable hydrocarbons readily polymerlzable to gums at a high pressure are preferably first freed of any water and carbon dioxide present and then fractionated under high pressure and at low temperature without danger of gum formation and deposition to recover unsaturated gaseous hydrocarbon desired as a finished product, fromgaleousconstituents of both higher and lower molecular weight, the lower molecular weight oonstituents being removed from the system.

'Ihe higher molecular weight gaseous constituents are subjected to a separate high tempera-- ture thermal conversion operation productive of additional quantities of desired unsaturated and aromatic hydrocarbons and are then fractionated with the products of the clean oil thermal conversionV operation serving in this fractionating operation, by reason of their high heat content and stripping capacity, to promote a better separation of aromatic hydrocarbons from the combined products of the respective thermal conversion operations.

As an example of carrying out this invention, reference may be had to the following descrip- 5 tion wherein the application of the method o f this invention to the manufacture of liquid ethylene and an aromatic liquid as desired products from a reduced crude petroleum is decribed.

Referring now lmore Vparticularly to to the drawing, a reduced crude of 2030 A. P. I. gravity and at a temperature of from about 70 F. to about 400 F., preferably 400 F., is charged through a pipe I by means of a pump 2 into a heavy oil fractionator 3. The fractionator 3 is 15 divided by means of a member l forming a com- -bined collecting pan and vapor riser into intercommunicating fractionating sections 5 and 8, each of which is provided with suitable .fractionating elements (not shown).

The fractionating section 5 is preferably suitably retluxed to provide a temperature gradient ranging from a temperature at the bottompf the section of from. about 600 F. to about 650 F., preferably 625 F., to a temperature at the -top of the section of from about 450 F. to about 550 F., preferably about 500 F.

The fractionating section 6 is preferably suitably reiluxed to provide a temperature gradient therein rangingfrom a temperature at the bottom of the section of from about 750 F. to about 850 F., preferably about 800 F., to a temperature at thetop of the sectionof from about 750 F. to 800 F., preferably about 775 F.

Liquidbottoms accumulating on the member 4 are withdrawn from the fractionating section l through a pipe I by means of a pump Il and charged serially through a pipe .0, through a viscosity breaking heating coil I0' positioned in a suitable furnace ll provided with one or more 40 burners I2, and through a pipe` I3 having a pressure reducing valve I4, into the fractionating section 6 of the fractionator 3.

'Ihe liquid bottoms in passing through the coil I0 are heated to a temperature at the coil outlet of from about 875 F. toabout 925 F., preferably about 900 F., under a coil outlet pressure of from about 100 lbs. per square inch gage to about 300 lbs. per square inch gage, preferably about 200 lbs. per square inch gage. These' pressure and temperature conditions are such as to effect a preliminary viscosity breaking cracking operation on the liquid bottoms productive of relatively low boiling hydrocarbons from which may be extracted a light clean oil more suitable asachargingstockforthesubsequenthightemperature cracking operation. The pressure on the-heated bottoms issuing from the viscosity breaking cof'. Il is reduced by means of the valve il to a pressure of from about 5 lbs. per square inch gage to about 40 lbs. per square inch gage, preferably about 20 lbs. per square inch gage, which is the pressure maintained in the fractionator 3. y

The conversion products of the viscosity break-I m8 operation are steam stripped in the fractionating section 3 with steam entering the fractionating section through a pipe il controlled by a valve I3 and the unvaporizod fuel oil resid-ue is withdrawn through a pipe I1 by means of a pump i3 which discharges the residue liquid serially through a pipe Il and cooler 20 to storage. lThe cooler 33 is provided with cooling liquid inlet and outlet pipes 2l and 22 respectively.

The overhead products of the fractionating 1| alsmaar the-lighter constituents is made.

The fractionator 3 discharges its well fractionated overhead products serially through a trans fer pipe 23, a heat exchanger 25, and a water cooler 26 into a gas separator 24. 26 is provided with cooling liquid inlet and outlet pipes 21 and 28, respectively. The uncondensed constituents in the separator 24 are ventedtherefrom through a pipe 29 for further processing as will be more fully pointed out hereinafter and any water as may accumulate in the separator 24 is drained therefrom through a pipe 30 controlled by a Valve 3|.

.'I'he condensate in the separator 24 may be characterized as a clean oil and consist primarily of hydrocarbons having boiling points generally within the boiling range of gasolineand gas oil. 'I'his oil is withdrawn from the separator 24 through a pipe 32 by'a pump 33 and discharged thereby througha pipe 34 from which pipes 35 and 36 having s uitable control valves 31 and 38 respectively conduct the oil in suitable quantities to the' fractionating sections 5 and 6 respec- The clean oil is also conducted from the pipe' 34 by a pipe 39 through the heat exchanger 25 wherein it is heated, into a pipe 40 feeding a high temperature thermal conversion coil 4| positioned in a furnace 42 having a suitable burner 43. It is to be understood that the arrangement of the coil 4| in the furnace 42 as shown is by way of example only as the coil 4| may comprise any, suitable number of convectively and/or radiantly heated sections for heating and/or thermally converting the oil. This will obvious to those skilled in the art.

'I'he oil, before entering thecoil 4|, is preferably admixed with a selected hydrocarbon fraction comprising mainly hydrocarbons having four and ve carbon atoms. from the conversion products by subsequent steps This fraction is recovered of the method, as will hereinafter be pointed out, and is added to the oll in the feed pipe 40 through a pipe |34.

It is preferred that the high temperature thermal conversion coil 4| be operated with an outlet temperature of from about 1250 F. to about 13.50 F., preferably about 1300 F., and at an outlet pressureof from, about 10 lbs, per square inchgage to about 50 lbs. per squareinch gage, preferably about 30 lbs. per square inch gage, although the exact temperatures and pressures employed will obviously be'chosen so as to effect the optimum production of the products desired.

The conversion products are conveyed by the transfer pipe 44 into a main fractionatorl 45 having an upper fractionating section 46 and a lower fractionating section 41 separated from each otherby means of a member 48 forming a combined vapor riser and collecting pan. Each preferably about 400`F., and -a temperature at The cooler.

the top of the section of from about F. to about 225 F., preferably about 200 F.

The fractlonating section 41 is preferably suitably reiluxed to provide a temperature at the hottom of the section of from about 500 F. to about 600 F., preferably about 550 F., and a tempera-v ture at the top of the section ranging from about 400 F. to about 500 F., preferably about 450 F.

Synthetic fuel oil is separated from the conversion products in the fractionating section 41 and is withdrawn therefrom through a pipe 49 by means of a pump 5|) and discharged thereby serially through a pipe 5| and cooler 52 to storage. Cooling liquid is caused to be circulated through the cooler 52 through the cooling liquid inlet and outlet pipes 53 and 54, respectively.

Fractionated vapors from the' fractionating section 41 pass through the vapor riser of the member 48 intoV the upper fractionating section 46 from which liquid oil which collects on the collecting pan of the member 48 is withdrawn through a pipe 55 by means of a pump 56 and charged thereby through a pipe 51 to a suitably located tray in the fractionating section 5 for re-fractionation and recovery as recycle stock which, when discharged with the fractionator overhead products, aids in the approachment to the desired substantially complete condensation of the overhead products. Y

Liquid oil for refluxing the fractionating sections 46 and 41 is also withdrawn from the collecting pan of the member 48 serially through a pipe 58 and heat exchangers 59 and 60, by means of a pump 6|, the oil being cooled in transit in heat exchangers 59 and 60 'by indirect heat exchange With'cooler liquid, as will be more fully pointed out hereinafter. 'I'he pump 6| discharges cooled bymeans of cooling liquid caused to be circulated through the cooler through liquidinlet and outlet pipes 262 and 263, respectively. The cooled oil flows from .the pipe 62 through the pipe 64 in regulated quantities controlled by a valve 65 into the upper fractionating section 46 of the fractionator 45 and refluxes this section to' maintain the temperature range desired therein. Similarly, cooled 'cil flows from the pipe 62 through the pipe 66 in regulated quantities controlled by a valve 61 into the lower fractionating section 41 of the fractionator 45 and reiluxes this section to maintain the temperature range desired therein. d.

There is performed concurrently with the performance of the high temperature thermal conversion operation on thel clean oil 4and selected hydrocarbon fraction a separate high tempera- .i

ture thermal conversion operation on a gaseous charging stock recovered vfrom conversion products of the respective thermal conversion opera'- tions, as will be more particularly pointed out hereinafter. 'Ihis gaseous charging stock which` on recovery is preferably accumulated as a liquid in a feed tank 68 under a pressure of from about f 350 lbs. per square inch gage to about550 lbs. per

square inch gage, maintained therein, is caused`v to flow under the existing pressure serially through a pipe 69, a pressure reducing valve 10 positioned therein, heat exchanger 60 and pipe 1| to the inlet of a high temperature thermal gas conversion coil 12 positioned in a suitable furnace 13 having one or more suitableburners 14. The liquefied gas is -caused to expand in owing through the valve 10 and in doing so abstracts heat from the oil flowing? through the heat exchanger 58.

, The gaseous charging stock is heated in transit through the coil 12 to a coil outlet temperature of from about 1300 F. to about 1500 F., preferably from l400 F., under a coil outlet pressure of from about 10 lbs. per square inch gage to about 50 lbs. per square inch gage, preferably about 30 lbs. per square inch gage.

The temperature and pressure conditions maintained in the thermal gas conversion coil 12 will effect the formation of additional quantities of ethylene (and aromatic hydrocarbons) from the gaseous charging stock and the resultant conversion products are conveyed by a transfer pipe 15 into the lower part of theupper fractionating sectionv 46v of the fractionator 45 wherein their heat content and stripping capacity aid the fractionation being performed therein, thus promoting a better recovery of aromatic hydrocarbons in the overhead products of the fractionator.

The overhead products. of the fractionator 45 'are conveyed therefrom serially through a transfer pipe 16 and cooler 11 into a gas-liquid separator 18. Cooling liquid is'caused to be circulated through the cooler 11 by means of cooling liquid inlet and outlet pipes 18 and88, respectively..

The overhead products passing through the cooler 11 are cooled to the lowest possible temperature with theavailable cooling water to eifect the condensation of the greatest possible amount of the overhead products and a portion of the liquid accumulating in the separator 18 is withdrawn therefromthrough a pipe 8| by means of a pump 82 and discharged thereby through a pipe 88 to the top of the fractionator 45 for reiluxing the vapors and assisting in the maintenance of the desired temperature range therein.

The-separator 18`is maintained at substantially the pressure existing within the fractionator 45, namely, a pressure of from about 5 lbs. per square inch gage to about 45 lbs. per square inch gage, preferably about 25 lbs. per square inch gage, and constituents of the overheadproducts remaining uncondensed in the separator 18 under these temperature and pressure conditions are.

discharged therefrom through a pipe 84.

These uncondensed constituents, together with those vented from the separator 24 through the pipe 28, vare conveyed by means of pipe 85 to a .v

gas compression plant diagrammatically shown as 86. The net liquid product in the separ" tor 18 is withdrawn therefrom through a pipe 8 by means of a pump 88 and charged thereby through a pipe 88 into the gas compression plant 88-where it is combined with condensate formed therein and discharged from the plant through a pipe 85.

In the gas compression plant 88, the uncondensed constituents are compressed, preferably in two or more successively higher pressure stages coupled with intermediate cooling and gas-liquid separating operations all in a manner well understood by those well skilled in the art. The constituents uncondensed in the gas compression a, plant under a final pressure of from about 108 lbs. per square inch gage to about 400 lbs. per square inch gage employed therein are conveyed atthis pressure by the pipe 88 to an absorber 8|, preferably equippedy with fractionating trays (not shown).

The absorber'8l is preferably operated under a pressure of from about 100 lbs. per square inch gage to about 400 lbs. per square inch gage, preferably about 200 lbs. persquare inch gage, using2 an aromatic vliquid product of the method as an absorption medium. The rate of circulation o the absorption medium is preferably maintained at s uch levels in conjunction with the pressure in the absorber as to extract from the gas fed to the absorber approximately 68% of the hydrocarbons having four carbon atoms and substantially 100% of the hydrocarbons having five carbon atoms.

The hydrocarbons having four carbon atoms produced by the high temperature thermal con`- version operation on the clean oil and selected 1 hydrocarbon fraction include about 5% butadiene and about 45% iso-butylene, each having a greater afilnity for the armoatic liquid than normal butylene or normal butane has. Thus,

under the conditions existing in the absorber 8|, 1

substantially all of the butadiene and iso-butylene will be absorbed in the aromatic distillate in effecting `a separation from the gas feed to the absorber of approximately 60% of the hydrocarbons having four carbon atoms. i

Unabsorbed gas is vented from the absorber as an overhead product through a. pipe 88 and enriched aromatic liquid is removed from the absorber 8| through a pipe 84. The enriched aromatic liquid, together with the liquid product 5 of the gas compression plant 88 removed therefrom through the pipe 85, is conducted by means of a pipe 86 to the suction side of a pump 81 which discharges the liquid serially through a pipe 88 and heat exchanger 88 into a fractionator i |88 equipped with suitable fractionating elements (not shown).

The fractionator |88 is operated at a pressure from about 200 lbs. per squareinch to about 400 lbs. per square inch, preferably about 300 lbs. per 1 square inch, and at a corresponding equilibrium temperature effective to secure a separation from vthe liquid feed of mainlythose hydrocarbons having less than four 'carbon atoms. 'Ihese hydrocarbons which form the overhead product of 4 the fractionator are conducted by means of a pipe |8| through a cooler |82 provided with cooling liquid inlet and outlet pipes |88 and |84, respectively, into acombined reflux accumulator and gas separator |85. the cooler |82 and collected in the accumulator |85 will consist mainly of three carbon atom hydrocarbons and is withdrawn from the accumulator through a pipe |88 by means of a pump |81 and returned in whole or in part to the fracil tionator |88 as reflux liquid through a pipev |88v to maintain the desired temperature gradient. i

The uncondensed products in the accumulator |85 will consist mainly of hydrocarbons having less than three carbon atoms, together with some l hydrogen, and are vented from the accumulator for further processing through a pipe |88 at a suitable pressure controlled by a valve ||8 posi- .'fractionating elements (not shown) and is oper- 'i ated at a pressure reduced somewhat from that ,maintained in the fractionator |88. Expansion h occurringv during the passage of the reboiled bottoms from reboiler throughl the reducing valve ||l causes heat to be abstracted yfrom the liquid I The condensate formed in 4 ing the desired aromatic product. 'I'he fractionator ||1 is preferably operated at a pressure of from about 100 lbs. per square inch gage to about 200 lbs. per square inch gage, preferably about 150 lbs. per square inch gage,- and at a corresponding equilibrium temperature eective to secure the desired separation.

Heat is supplied to the fractionator |I1 in conjunction with a reboiling operation performed in a conventional reboiler ||9 through which a reboiling medium is caused to be circulated through iluid inlet and outlet pipes ||9 and |20 respec-v tively.

The aromaticproduct substantially free of four and five carbon atom hydrocarbons is conducted as a finished product from the reboiler Ill to storage through a pipe |2| being cooled in transit by indirect heat exchange with the feed to fractionator ||.1 passing through the exchanges ||5. A portion of the cooled aromatic product is conducted from thepipe |2| by a pipe |22 serially. through a cooler |24 into the.pipe92 by which it is conducted into the top of the absorber 9|. The flow of the aromatic product through the pipes |22 and 92 iseffected by means of a pump |23 and the liquid is cooled in transit by means of a coole'r |24 through which cooling uid is caused to be circulated by means of cooling fluid inlet and outlet pipes |25 and |25, respectively.

The' overhead products of the fractionator ||1, consisting mainly of hydrocarbons having four and tlve carbon atoms, are conducted, together with whatever lower boiling hydrocarbons may be present, by a pipe |21 through a cooler |29 into an accumulator-separator |29. Cooling liquid is caused to be circulated through the cooler |29 by means of cooling liquid inlet and outlet pipes |30 and |3|, respectively. Substantially all the hydrocarbons of four and iive carbon `atoms are condensed inthe cooler |23 and a portion of thev condensate is returned through a pipe |32 bymeans of a pump |33 to the fractionator ||1 as "reilux liquid for maintaining the desired temperature range therein;

'I'he balance of the condensate'is conducted by means of a pipe |34 serially through a pressure reducing valve |35 and heat exchanger 59 into the feed pipe of the clean oil thermal conversion coil 4| wherein, due to its presence, the. light distillate produced by this conversion op eration will contain a much higher percentage of pure aromatcs than it would were the clean oil not admixed therewith.

The condensate in passing through the valve |35 expands and is thus sufiiciently cooled to reduce i the temperature of reflux oil in the heat exchanger 59. Where the coil 4| is operated at a high outlet pressure, it may be desirable to substitute a pump for the valve |35.

-Any uncondensed constituents in thehseparator |29 may be vented therefrom .through a pipe |35 and a pressure reducing valve |31, and recycled I through the recovery system into which they may be fed at a suitable'point of lower pressure..

tively small portion of the total gaseous conversion products are conducted by the pipe 93 into suitable treating apparatus, diagrammatically shown at |33, for removing carbon dioxide and water therefrom. Suitable agents and operations well known inI the art, such as for example, calcium chloride, silica gel, water washing and the like, may be employed toy accomplish the desired separation. Y

Carbon dioxide and water is discharged from the treating apparatus |38 through a pipe |39 and the gaseous constituents are conducted by a pipe |40 serially through a compressor |4| and a cooler |42 into a low temperature fractionator |43`equipped with suitable fractionating elements l(not shown). i Thev ncondensed constituents are compressed in the compressor |4| to a pressure of from about 500 lbs.' per square inch gage to about 900 ibs. per square inch gage, preferably about 700 lbs. per square inch gage, and are then cooled in the cooler |42 to remove the heat of compression.

The fractionator |43 is operated at a pressure of from about 500 lbs. per square inch gage to about 900 lbs. per square inch gage, preferably about 700 lbs. per square inch gage, and at a corresponding equilibrium temperature at the top of the tower, for examplefrom about F. to about F., preferably about 125 F. Reiluxing of the fractionator |43 is accomplished by cooling and 'condensing a portion of the overhead products such as methane in a reflux condenser |43 through which a refrigerant at a suitably low temperature is caused to be ex panded through uid inlet and outlet pipes |44 and |45, respectively. The refrigeration may be l obtained, for example, by expanding a liquefied The, overheadproducts issuing from the re-I flux condenser |43 are conducted by means of a pipe |46 through a pressure reducing value |41 and the cooler |42 either to the atmosphere, to a fuel gas main, or to storage, as may be desired.

The overhead products, inpassing through the pressure reducing valve |41, are preferably expanded and thereby furthercooled. The cooled gases, inpassing through the heat exchanger |42. remove the heat of compression from compressed gases passing /to the fractionator |43.

Heat is supplied Ato the fractionator |43 in conjunction with a reboiling operation performed in a conventional reboiler |48 through which a reboiling fluid such as, for example, water at a normal temperature, is caused to be circulated through fluid inlet and outlet pipes |49 and |50, respectively. 'I'he bottoms product is conducted from the reboiler |43 by a pipe |5| serially through a pressure reducing valve |52 and heat exchanger |53 wherein it is heated to 'a second low temperature fractionator |54 equipped with suitable fractionating elements (not shown).

The fractionator |54A is operated to separate ethylene as an overhead product from the ethylene and higher molecular weight hydrocarbons forming the liquid feed to the fractionator. In effectingv this desired separation, the tower is operated at a pressure of fromabout 400 lbs. per square inch gage to about 600 lbs. per square inch gage, preferably about 5,00 lbs. per square inch gage, at a corresponding top tower equilibrium temperature of from about 25 F. to about +25 F., preferably about 0 F. Refiuxing of the tower to provide the desired low top tower temperature is' accomplished by cooling and condensation of 'l5 a portion oi' the overhead products in a reiiux condenser |55 through which a suitable refrigerant is caused to be expanded by means of fluidinlet andvapor outlet pipes |56 and |51, respectively. f

'I'he ethylene -issuing from the reflux condenser |55 as an overhead product is conducted by a pipe |58 through a cooler |59 to an accu- 'I'he refrigerant employed in the reflux condenser |55 and the cooler |59 may advantageously be propane, carbon dioxide, ammonia and the like, 20 although any other suitable refrigerant by which the desired low temperature maybe attainedl may be employed.

Heat is supplied to the fractionator |54 in conjunction With a reboiling operation performed in 25 a conventional reboiler |65 through which a suitable reboiling medium is caused to be circulated through. the fluid inlet and outlet pipes |66 and |61, respectively. 'Ihe bottoms product comprising liquid ethane and hydrocarbons of higher 50 molecular weight particularly saturated and unsaturated three and four carbon atom hydrocarbons recovered therewith, is r'conducted from the reboiler |65 by a pipe |66 serially through the heat exchanger |53 and aflow control valve |69 66 for controlling the liquid level in the reboiler |65,

into the feed tank 68 supplying the high temperature gas conversion coil 12.

It will be understood that although there has beendescribed the application of the method to the manufacture and recovery of ethylene as a nished product, that such description is by way of example only as other normally gaseous hy-y or the like, and liquid hydrocarbon products) containing a high percentage of pure aromatica;

It will be observed that certain features and sub-combinations are of `utility and may be employed without reference to other features and sub-combinations. This is contemplated by and 60 is within the scope of the appended claims. It

is further obvious that various changes may be made in details within the scope of the appended claims without ydeparting from the 4spirit of this invention. It is, therefore, to be understood that this invention is not to be limited to the specic details shown and described.

Having thus described this invention, what-is claimed is: t

1. The method comprising mixing a selected hydrocarbon fraction with a low boiling hydrocarbon oil; subjecting the mixture-to a high temperature' thermal conversion operation; separating a normally gaseous unsaturated hydrocarbon from the conversion products as a desired product; separating an aromatic liquid from the conversion products as a desired product; separating mainly hydrocarbons having four and five carbon atoms from the conversion products by an absorption operation and employing them as the selected hydrocarbon fraction; and, employing a portion of the aromatic liquid as lean oil in the absorption operation.

2. The method comprising mixing a selected hydrocarbon fraction with a low boilinghydrocarbon oil; subjecting the mixture to a thermal conversion operation; separately subjecting a normally gaseous hydrocarbon charging stock to a higherv temperature thermal conversion operation; separating a normally gaseous unsaturated hydrocarbon as a desired product from the conversion products of both said conversion operations; separating 'an aromatic liquid from these conversion products as a desired product; separating mainly hydrocarbons having four and five carbon atoms from these conversion products by an absorption operation and employing them as the selected hydrocarbon fraction; employing a portionl of the aromatic liquid as lean oil in the absorption operation; and, recovering the normally gaseous hydrocarbon chargingstock fromv conversion products not absorbed by the lean oil during the absorption operation.

3. The method 'comprising mixing a selected hydrocarbon fraction with a low boiling hydrocarbon oil; subjecting the mixture to a high temperature thermal conversion operation procarbons, and aromatics; separately subjecting a normally gaseous hydrocarbon charging stock to a high ,temperature thermal conversion operation productive of normally gaseous unsaturated hydrocarbons and aromatics; dephiegmating the conversion products of both conversion operations and recovering as products an aromatic liquid and uncondensed hydrocarbon gas; com

.pressing the gas to obtain additional aromatic liquid; subjecting the lcompressed gas to an absorption operation with an aromatic absorption medium; subjecting 'the rich absorption medium ,together 'with aromatic liquid previously recovered to a series'pf fractionating operations and and the normally gaseous chargingstock.

4. Method comprising subjecting a clean hydrocarbon oil admixed with a selected hydrocarbon fraction comprising mainly C4 and C5 hydrocarbons to a thermal conversion operation at a temperature of from about 1250 F. to about' 1350 F.; subjecting mainly normally gaseous -Cz hydrocarbons vto a separate thermal l'conversion operation. at a temperature of from about 1300 F. to about 15 0O F.; dephlegmating conversion productsof both conversion' operations in a common dephlegmating zone; and; recovering a normally gaseous unsaturated hydrocarbon and an aromatic liquidfrom dephlegmated gas-vapor 'products of the dephlegmating opration.

HERMANN C. SCHUTT.

ductlve of normally gaseous unsaturated hydro-

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