US2348646A - Conversion of hydrocarbon oils - Google Patents

Description

May 9, 1944. E. D. REEVES CONVERSION OE HYDROCARBON OILS Filed July 5, 1941 O O o MMU N M Q W .NQIN it n,

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Patented May 9, 1944 GONVERSION OF HYDROCARBON OILS Edward D. Reeves, Cranford, N. J., assignor to Standard Oil Development Company, a corporation of Delaware Application July 5, 1941, Serial N0. 401,281

3 Claims.

This invention is directed to the conversion of hydrocarbon oils and constitutes a continuation-in-part of my earlier application Serial No. 256,630, iiled February 16, 1939, entitled Conversion of hydrocarbon oils.

In the above-named application I have disclosed an integrated, unitary process for the con- Version of crude oils into gasolines wherein the crude is initially segregated into a plurality of separate fractions and each fraction then subjected to independent conversion treatments in the presence of finely-divided catalysts under conditions selected for the production of maximum yield of gasoline having high anti-knock properties.

The present invention is directed to the combination of catalytic conversion and fractionation of conversion products to segregate the desired constituents therefrom.

In the past it has been the general practice to first separate the powder or iinely-divided catalyst from the conversion products and then to pass the products directly to a fractionating tower wherein they are subjected to fractionation to segregate the desired fraction.

I have found that an overall improvement can be realized particularly in low pressure conversion processes in which substantial amounts of steam are employed in the operation by initially condensing all of the overhead products from the conversion process except for the noncondensible gases formed during the operation, then separating the water condensate phase from the oil condensate before subjecting the latter to fractionation. It has been found that the water phase so segregated contains the bulk of the powdered catalyst which remains entrained in the oil vapors after passing through the separating equipment, and by initially condensing the total conversion stream and separating the water and catalyst, the oil passing to the fractionating equipment will be substantially free of powdered catalyst and can be subjected to fractionation under any desired pressure.

For example, in catalytic cracking it is desirable in most cases to operate at a relatively low pressure level, such as at atmospheric or at a mild superatmospheric pressure. However, in cases Where the cracked products pass directly tothe fractionating equipment, the outlet pressure on the conversion unit must be at least sufcient to overcome the pressure drop through the fractionating and condensing equipment in order to avoid the use of gas compressors vwhich are uneconomical to operate.

Furthermore, it is desirable to operate the fractionating equipment under substantial pressures in order to reduce the size of the fractionating tower for a given capacity and to utilize the cooling medium to the best advantage. The present invention finds particular application in cases where the cracked products contain substantial amounts of inert gases such as steam or other gaseous diluents employed to vaporize the oil. For example, in vapor phase cracking or viscosity breaking ot heavy oils, it is necessary to add considerable amounts of steam or other gas to accomplish the vaporization. This inert gas increases the burden on the fractionating equipment.

In accordance with the present invention, the cracked or conversion `products are rstcooled to a temperature sufficient to condense the normally liquid constituents of the cracked products including the steam used for vaporization or for other purposes. 'I'he condensate is then allowed to separate into a water phase resulting from condensation of the steam and oil phase. The water phase, as previously pointed out, will contain the entrained powder carried over from the conversion process. This mixture of water and powdered catalyst can then berecovered by pumping directly into the cracking or conversion equipment. The oil phase is pumped into-a combined distilling and fractionating tower which may be maintained under any desired pressure independent of the pressure of the cracking process in order to distill and fractionate the motor fuel or other hydrocarbon fractions therefrom.

For a more complete understanding of the invention, reference is now made to the accompanying drawing which is a diagrammatic illustration of an apparatus suitable for carrying the invention into effect. l

Referring to the drawing, the reference character I0 designates a charge line through which the oil to be processed is introduced into the equipment. As illustrated, this oil is preferably a crude petroleum fraction which is to be subjected to initial distillation to segregate the lower boiling hydrocarbons therefrom.

The oil introduced through line I0 is pumped by means of pump Il through a preheating coil or distilling coil l2 located in furnace i3 wherein the oil is subjected to a temperature which would vaporize a substantial portion of the oil passing therethrough. The outlet temperature of the vaporizing coil may be, for example, of the order of from 700 F. to 900 F.

Products from the vaporizing coil vl2 pass through transfer line l into a combined separating and fractionating tower I6 wherein the vapors separate from unvaporized residue and the vapors are fractionated to condense higher boiling constituents thereof. Unvaporized liquid and condensate formed in the bottom section of the tower i6 are withdrawn therefrom through line I1 and may he rejected from the system through line i8. However, this reduced crude or residual stock.

is preferably subjected to further treatment as hereinafter described.

A lower boiling condensate stock formed in the intermediate section of the fractionating tower I6 is collected in trap-out tray I9 and is withdrawn therefrom through line 2U. This fraction may be treated according to the parent application hereinbefore referred to, or it may be subjected to treatment asherein'after described.

A'still lower boiling condensate fraction which may comprise heavy naphtha, kerosene, or the like may be collected in the upper portion of the fractionating tower I6 in trap-out tray 2I and may be withdrawn therefrom through line 22. This fraction may be treated as described in the parent application or subjected to any further treatment outside of the present invention.

Vapors`remaining uncondensed in the fractionating tower I6 pass overhead through line 22 to a condenser 23 wherein they are cooled further to condense normally liquid hydrocarbons. Products from the condenser 23 pass to a receiver 24 wherein the liquid condensate formed in condenser 23 separates from any normal gases liberated during the distilling process. The liquid distillate is withdrawn from receiver 24 through line 25 and may be further treated as described in the parent application. Gases segregated in the receiver 24 may be removed therefrom through line 26.

Returning to the fractionating tower I6, the residual fraction withdrawn through line I1 or the gas oil fraction withdrawn through line 20, or a mixture thereof, may be passed through line 21 to a preheating and vaporizing coil 28. The oil during its passage through the vaporizing coil 28 is subjected to further heating to vaporize an additional fraction of said oil. To assist in the vaporization, water or steam is introduced through line 29 or to other points in the vaporizing coil. The amount of steam so introduced may range, for example, from 5 mol per cent to 50 or more mol per cent, depending upon the character of the oil to be vaporized.

The heated oil after passing through the vaporizing coil 28 passes through transfer line 3| to a separator 32 wherein vapors formed in the heating coil 28 are segregated from any unvaporized residue. If desired, additional steam for assisting in the separation may be introduced into the separator through line 33. Liquid residue separated in the separator 32 is withdrawn therefrom through line 34.

Vapors liberated in the separator 32 pass overhead through line 35 to a dispersion chamber 36 in which they are admixed with powdered contact material introduced into the dispersion chamber 36 through line 31. This powdered contact material may be any cracking catalyst such as activated clays, synthetic gels of silica and alumina or silica having other cracking catalysts combined therewith. The amount of powdered catalyst introduced into the vapors in the dispersion chamber 36 may vary over an extended range, depending upon a number of factors, such as the activity of the catalyst, composition of the feed, temperature of the cracking operation, and per cent conversion desired. In general, this amount will be between 0.5 and l0 parts of catalyst per part of oil by weight. The ternperature of the oil vapors introduced into the dispersion chamber 36 may be of the order of from 700 F. to 950 F.

The dispersion of oil vapors and powdered catalyst formed in the dispersion chamber 36 passes through line 38 to a. cracking or reaction zone 39 wherein the oil vapors are retained for a period sufficient to obtain the desired conversion into motor fuel. For illustrative purposes, the reaction zone has been shown in. the form of a vertical tower through which the dispersion passes in an upward direction. When employing this type of reaction chamber, 'the velocity of the oil vapors may be regulated so that the time of residence of the catalyst within the tower may be materially longer than the time of residence of the oil vapors.

It will be understood, however, that the present invention is not restricted to the particular type of reactor illustrated, since other types of cracking chambers, such as coils, horizonta1 drums and the like, may be employed in lieu thereof.

The cracked products and catalyst after passing through the cracking zone 39 are transferred through line 4I to a separator such as a cyclone separator 42 for separation of the powdered catalyst from the cracked vapors. The powdered catalyst separated from the cracked vapors in the cyclone separator 42 discharges into a vertical column 43 into which is introduced an inert stripping gas through line 44. If desired, the column 43 may be provided with suitable bailles for intermixing the stripping gas with the catalyst. The catalyst after passing through the co1- umn 43 discharges into a hopper 45.

Cracked vapors after being treated to separate the powdered catalyst therefrom are removed from the cyclone separator 42 through line 46.

In accordance with the present invention, these cracked vapors are passed tol a condenser 41 wherein they are cooled to a temperature sutilcient to condense all the normally liquid constituents present in the product. While an indirect heat exchanger 41 has been shown for effecting this cooling, it will be understood that other types of cooling devices, such as a spray chamber for effecting direct contact between the cracked vapors and cooling agent, may be employed in lieu thereof. Productsfrom the cooler 41 pass through line 48 to a receiver 49 wherein liquid formed in the cooler 41 separates from uncondensed gases. Furthermore, the water condensate formed by condensation of the steam used in the process and containing any entrained catalyst carried over from the separator 42 will co1- lect as a bottom layer in the separator 49 and may be withdrawn therefrom 'through line 50 and returned by means of a suitable pump to the inlet side of the preheating coil 28 and there combined with fresh oil lfor the process.

Gases separated from the liquid condensate in the receiver 49 are withdrawn therefrom through line 5I and may be subjected to further treatment for the recovery of gasoline constituents therefrom. The line 5I may be provided With suitable release valves 52 for maintaining the desiredpressure on the cracking'system. In accordance with the present invention, the cracking system is operated at relatively low pressure. For example, the inlet pressure on the oil vapors passing to the cracking zone may be only sumcient to overcome the pressure drop through the cracking and separating equipment.

The liquid oil comprising gasoline and higher boiling fractions collected in receiver 49 is withdrawn therefrom through line 53 and is forced by means of pump 54 to a heating coi1 55 wherein the oil is heated to a temperature suicient to distill the lower boiling motor fuel constituents therefrom. Products from the 4heater 55 then pass to a combined distilling and fractionating tower 56 wherein the oil is subjected to distillation and fractionation to separate the same into the desired fractions. Such fractionation may consist, for example, in the distillation or liberation of motor fuel from the higher boiling constituents. If desired, additional heat may be added to the fractionating tower 56 through heating coil 51. Vapors liberated in the distilling and fractionating tower 56 pass overhead through line 58 to a condenser 59 wherein the normally liquid products are condensed. This product may consist, for example, of a gasoline fraction of the desired end point. Products from the condenser 59 then pass to a second receiver 6I wherein the uncondensed gases liberated during the distiliing and fractionating treatment are separated from the liquid condensate. The gases so liberated are removed from receiver 8| through line 62 having a release valve 63 for imposing the desired pressure on the fractionating system. For example, the fractionating tower 55 may be operated under a substantial superatmospheric pressure, such as from 100 to 500 pounds per square inch. The gasoline or naphtha formed in the process collects in receiver 6I and is withdrawn from the bottom thereof through line 64 from which it may be passed to other purifying and refining treatment outside the scope of the present invention.

Returning to the catalyst hopper 45 receiving catalyst separated from the cracked vapors, the catalyst collected therein may be discharged through line 65 having a suitable feeding device such as a valve 66 from which it may be fed at a controlled rate into a dispersion chamber B1 into which a regenerating or carrier gas may be introduced through line 68. The catalyst-gas dispersion formed in the dispersion chamber 61 is transferred through line 69 to a regenerating chamber 11 wherein the catalyst is subjected to regenerative treatment for removal of carbonaceous deposits formed during the cracking operation. This regenerative treatment may be used by maintaining an oxidizing atmosphere in the regenerating chamber 11. To this end, the carrier gas introduced through line 68 may consist of air or a mixture of air and inert diluent gases, or it may consist of an inert diluent gas and the air or other oxidizing gas may be separately introduced into the regenerating chamber. For illustrative purposes, the regenerating chamber 11 is also shown in the form of a vertical tower through which the dispersion passes in an upward direction. It will be understood, however, that the invention is not restricted to the particular type of regenerating chamber employed for this purpose. The velocity of the carrier gas passing through the regenerator 11 may be regulatedso as to maintain the catalyst within the regenerating chamber for a period suflicient to remove at least the major portion of the carbonaceous deposits contained on the catalyst material. The dispersion of regenerating gas and regenerated catalyst after passing through the regenerating chamber 11 passes through line 18 to a cyclone separator 19 or other equivalent device for separation of the regenerated catalyst from the regen- 1 erating gas. The regenerating gas after passing through the cyclone separator or other suitable separating and purifying device may be rejected from the system through line 8l. The regenerated catalyst separated in the separator 19 discharges into a vertical column 82 into which an inert stripping gas may be added through line 83 for removing any absorbed oxygen retained in the catalyst. The regenerated catalyst discharges from column 82 into a catalyst hopper 84 from which it is fed by means of a suitable feeding device such as a worm screw 85 into a mixing chamber 88 in which it is admixed with a gaseous carrier introduced through line 81. This gaseous carrier is preferably a non-hydrocarbon gas such as steam, nitrogen, hydrogen, or the like. The dispersion or mixture of gas and regenerated catalyst discharges from a chamber 85 through line 31 into the initial dispersion chamber 38 where it again admixes with oil vapors to be cracked It will be understood that makeup catalyst may be introduced at any desired point in the system for maintaining the desired amount of catalyst in circulation.

Having described the preferred embodiment of the invention, it will be understood that it embraces such other variations and modifications as ,come within the' spirit and 'scope thereof.

What is desired to be protected by Letters Patent is:

1. In a process for converting higher boiling hydrocarbons into lower boiling hydrocarbons suitable for motor fuel wherein a substantial volume of steam is employed to vaporize the oil to be cracked; the improvement which comprises passing oil vapors and steam through a cracking zone in admixture with a powdered cracking catalyst, maintaining said cracking zone at cracking temperature, thereafter separating the catalyst from the cracked products, cooling the total cracked products to a temperature sumcient to liquefy al1 normally liquid hydrocarbon constituents and steam, separating the steam condensate containing powdered catalyst from the oil condensate, returning said steam condensate to the cracking zone, and distiliing and fractionating said last-named condensate under a pressure materially above the pressure maintained in the -cracking zone to separate the desired motor fuel fraction therefrom.

2. In a process for converting higher boiling hydrocarbons into lower boiling hydrocarbons suitable for motor fuel wherein a substantial volume of steam is employed to vaporze the oil; the improvement which comprises passing the oil vapors and steam through a cracking zone in admixture with a powdered cracking catalyst, maintaining said cracking zone at active cracking temperature, thereafter separating the catalyst from the cracked products, cooling the total cracked products to a temperature sumcient to iiquefy-all of the normally liquid constltuents and steam, separating the steam con densate containing powdered catalyst from the oil condensate, returning said steam condensate to the cracking zone and distiliing and fractionating the last-named condensate to separate a desired motor fuel fraction therefrom.

3. A method of cracking hydrocarbon oils which comprises vaporizing the oil to becracked in the presence of a. substantial amount of steam,

, forming a mixture of oil vapors, steam, and pow.

10 ing process.

steam to a temperature suiiicient to condense all normally liquid hydrocarbon constituents and steam, separating the oil condensate substantially free of entrained catalyst from the steam condensate containing a substantial portion of entrained catalyst, distilling and fractionating the oil condensate to separate el. desired motory fuel fraction therefrom, and returning the water condensate containing said catalyst to the crack- EDWARD D. REEVES.

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