US2326553A - Conversion of hydrocarbons - Google Patents

Description

Aug. 10, 194 3. J. c. MUNDAY CONVERSION OF HYDROCARBON Filed Aug. 26, 1939 Econ/5 HA TING COIL Patented '10, 1943 CONVERSION OF HYDROCARBONS John C. Munday, Baton Rouge, La., assignor to Standard Oil Development Company, a corporation of Delaware Application August 26, 1939, Serial No. 292,025

9 Claims. (01. 196-52) This invention is directed to the catalytic conversion of hydrocarbon and pertains more particularly to a method of maintaining a more uniform degree of conversion throughout the conversion treatment.

The invention is directed morespecifically to a process for carrying out catalytic conversion of hydrocarbons in the presence of a solid contact mass under conditions such that the contact mass more or less gradually becomes contaminated with carbonaceous deposits which reduces the activity thereof.

In many types of catalytic reactions involving the treatment of hydrocarbons, the contact mass becomes coated with carbonaceous deposits which reduce the activity of the catalyst. As a result it catalyst, and other factors. For example some becomes necessary to periodically interrupt the conversion treatment to remove such deposits.

According to present practices these .deposits are usually removed by regenerating the catalyst mass with an oxidizing gas under conditions.

which will burn the carbonaceous deposits from the catalyst.

According to one of the more common processes, the regeneration of the catalyst is carried out in the same chamber in which the conversion treatment is carried out so that the contact mass within the converter is subjected to cycles of alternate reaction and regenerating periods. Whenoperating in such manner the freshly regenerated catalyst at the beginning of the conversion treatment is more highly active than during the final stages of the conversion treatment due to the buiding up of carbonaceous deposits on the catalys In the catalytic conversion of hydrocarbon the amount of hydrocarbon converted during a single passage of the hydrocarbon through the reaction zone, or in other words the conversion per pass, has an important bearing on the economics of the process. For example in the catalytic cracking of hydrocarbon oils, for any given oil to be cracked, there is an optimum range of conversion per pass which will produce the best results. If the conversion per pass is greater than the de sired maximum, excessive amounts of low grade products,v such as low molecular weight gaseous hydrocarbons and coke are formed. If, on the other hand the conversion per pass is below the desired minimum a low yield of desired product is prepared and in order to obtain the same ultimate conversion additional recycling, reheating and repumping is necessary. The optimum conversion penpass will normally vary with the sion per pass than others without involving excessive gas and coke losses. Also, some catalysts are capable of producing lower coke and gas losses for a given conversion per pass than others. The optimum conversion per pass may for example vary between-30% and 60% depending upon the above and other factors.

The conversion per pass is a function of the temperature, time or the contact of the oil vapors with the catalyst and the activity of the catalyst. Since as already mentioned the activity of the catalyst depreciates as the length of the conversion period increases, when operating at a constant temperature and a constant throughput, the conversion per pass will drop as the activity of the catalyst depreciates during the cracking period.

When operating in such manner the conversion I per pass per cycle will be the average conversion nature of the charging stock, the activity of the throughout the period. Consequently the actual conversion per pass during the earlier portion of the period will be greater than the conversion per pass during the final part of the cracking period due to the drop in activity of the. catalyst.

In order to compensate for drop in the activity of the catalyst during the cracking period. it has heretofore been proposed to increase the temperature or decrease the feed rate. However, the depreciation in the activity of the catalyst is not a straight line function of the length of the cracking period. On the contrary the depreciation in activity of the catalyst is much more rapid during the first few minutes of the period than during the final portion of the period. Consequently, as a practical matter it is diflicult, if not impossible to control the feed rate by varying the pump speed or control the furnace temperature to compensate for catalyst depreciation during each cracking period.

The object of the present invention is to provide an improved method of maintaining a more uniform conversion throughout the length of the conversion period. I

A further object of the invention is to provide an improved method for rapidly regulating the temperature and feed rate to maintain a more uniform conversion throughout the conversion period. A further object of the invention is to provide a method for more accurately controlling the extent of conversion at the start of the cracking period and thereby avoid overcracking during this portion of the periodwith the resultant formation of excessive gas and coke.

provided with suitable fractionating elements for fractionally condensing insufficiently cracked constituents as reflux condensate. Condensate formed in the fractionating tower may be withdrawn from the bottom thereof through line 29 and may be rejected from the system through line 30 or a part or all may be recycled through line ii and pump 32 to the inlet side of the vatrol the temperature and contact time of the oil vapors to compensate for catalyst depreciation during the conversion period.

According to a further phase 01 the invention, the diluent gas may consist ofan-inert gas, or it may be a gas capable of bringing about secondary reactions within the reactor such as alkylation, polymerization, dehydrogenation, etc. According to a more specific phase of the invention the diluent gas comprises residual gases formed during the conversion treatment. Such gas may comprise for example hydrogen and low molecular weight hydrocarbons containing from 1 to 4 carbon atoms per molecule. Such gases have the additional advantage in that they tend to suppress the formation of coke and gases.

Having set forth the general nature and objects, the invention will now be described in more detail, in which reference will be made to the accompanying drawing which is a diagrammatic illustration of an apparatus which is capable of carrying the invention into effect.

Referring to the drawing the numeral llldesignates a charge line through which the hydrocarbons to be converted are introduced into the system. For illustrative purposes the invention will 'be described with reference to the catalytic cracking of hydrocarbonoils, it being understood that the invention'in its broader phases has application to other types of catalytic reaction wherein the catalytic mass becomes contamiporizing coil l2 and be subjected to further catalytic treatment along with the fresh oil. If desired the cycle stock withdrawn from the system through line 30 may besubjected to separate and independent cracking treatment.

Vapors remaining uncondensed in the fractionating tower 28 pass overhead through line 33 to a condenser 34 wherein the desired distillate is condensed. Products from the condenser 34 pass to a receiver 35 wherein the liquid distillate separates from uncondensed normally gaseous constituents. The raw distillate collected in receiver 35 is withdrawn therefrom'through line 38 and may be sent to suitable stabilizing and refining equipment not shown. If desired, a part,

of the raw distillate. may be returned to the top of the fractionating tower through line 31 as reflux therefor. Normally gaseous constituents separatedin the receiver 35 are removed therefrom through line 39.

As the cracking operation proceeds within the reaction chamber 20 or 2 I the catalyst contained therein gradually becomes contaminated with carbonaceous deposits. As a. result the activity of the catalyst depreciates. When the activity of the catalyst has depreciated to a point where it is no longer capable of bringing about the desired degree of cracking, the cracking operation is discontinued in and reactor and transferred to the other andthe-contaminated catalyst is regenerated. As shown in the drawing the regeneration is accomplished by introducing a mixture of air and inert gas by means of blower 40 taking nated with carbonaceous deposits during the revaporize a substantial portion of said oil.

Products from the heating coil l2 pass through transfer line l4 to a-separator I! wherein vapors separate from unvaporized residue. The residue is withdrawn from the separator II through line II and may be rejected from the system.

Vapors liberated in the separator 15 pass overhead through line I! and, after being combined with a suitable diluentv gas introduced through line it as hereinafter described, are passed through line I! and branch line 22 and 23 respectively to either of the two catalytic converters Ill-and 2|. One of the two converters is adapted to be on the cracking operation while the other is undergoing regeneration. I

- When employing a clean condensate stock which is completely 'vaporizablethe separator ll may be omitted-or the product from the vaporizing coil l2 by-passed through line 24 around the separator ll.

Cracked products after passing through chamhere 24 or 2| asthecasemaybepassthroughline suction on an air inlet 4! and a regenerating gas recycle line 42. The blower 40 forces the regencrating gas through a manifold line 43 having branch lines 44 and 45 leading to the reaction chambers 20 and 2| respectively. Products of regeneration are withdrawn from the converters 20 and 2| through outlet lines 46 and 41 respectively merging with a manifold line 48. The

products of regeneration from the manifold line 48 may be rejected from the system through line 49 or a part after passing through a cooler 50 may be returned to the suction side of the blower 40 through line 42 and be employed as a diluent for the air introduced through line 4|. In lieu of using recycle gases as a diluent extraneous gas such as steam, or-spent combustion gases may be introduced into the regenerating system through line ll.

In accordance with the present invention the per cent conversion throughout the cracking period' is controlled by introducing variable amounts of a diluent gas through line [8 into the feed vapors passing through the converters. According to the preferred embodiment of the invention the diluent gas comprises the residual gases produced during the cracking operation. To this end the normally gaseous constituents withdrawn from the receiver 35 through line 39 may be passed through line 62 and blower 53 to a heat ing coil 54 wherein they are heated to the desired temperature. After passing through the heating coil 54. the gas passed through transfer line ll having a valve 55 for controlling the vol-- II or 24 and line H to afractionating' tower I! it ume of gases introduced into the feed stream.

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asaacts the oil in the reaction chamber can be increased by decreasing the volume of diluent introduced into the stream. Thus during the initial portion of the cracking period wherein the activity of the catalyst is greatest-the volume of diluent gases introduced will be greater than during the final period when the activity ofthe catalyst is at its lowest. Thus by reducing the volume of diluent gases during the cracking period by simple manipulation of the valve 55 the contact time of the oil may be accurately and rapidly controlled to maintain a constant conversion throughout the operating period.

As a further aspect of the invention the temperature of the oil stream passing through the reaction chamber may be modified by regulating the temperature to which the diluent gases are heated during their passage through the heating coil 54. The diluent gases may be utilized for example to 'raise the temperature of the oil stream from a vaporizing temperature to the desired reaction temperature and for maintaining the desired reaction temperature throughout the cracking operation.

In order to more effectively control the temperature of the diluent gases introduced into the vapor line l9 a-by pass line 56 around the furnace 54 may be provided whereby any desired portion or all of the diluent gases may be by-passed around the heating furnace. By introducing the diluent gas at a temperature below the temperature'of the oil vapors the temperature of the oil stream passing to the converters will rise as the volume of diluent is reduced. As a result both contact time and temperature can be readily controlled by simple manipulation of valve 55.

In lieu of recycling residual gases from the cracking operation through line 52, diluent gases from an extraneous source, such as nitrogen, hydrogen, steam, carbon dioxide or the like may be introduced to the suction side of the blower 53 through line 51 and employed in part or all as a diluent for the oil vapors to be cracked.

While I have described in the foregoing it catalytic cracking operation it will be understood that the invention in its broader phases will have an application to other types of hydrocarbon reactions wherein the activity of. the catalyst gradually decreases as the reaction continues due to the carbonaceous deposits therein.

Having described the specific embodiment of the invention it will be understood that it embraces other variations and modifications that come within the spirit and scope thereof. It will be further understood that it is not my intention to unnecessarily restrict the invention or dedicate any novel phases thereof.

I claim:

1. In catalytic decomposition of hydrocarbons wherein the hydrocarbon to be converted is passed in vapor form through a reaction zone containing a solid catalyst mass, the activity of comprises combining a substantial volume of diluent gas with the hydrocarbon vapors passing through the reaction zone at the start of the decomposition period and thereafter reducing the volume of diluent gas while maintaining the vol- -ume of' hydrocarbon vapors substantially constant as the length of the decomposition period increases to thereby compensate in loss for catalytic activity during the operating period.

which diminishes as the length of the decompog ."a'. substantially constant decomposition ghout the length of the operating period den spitejreduction in activity or the catalyst which bons wherein the catalyst mass is periodically regenerated to remove carbonaceous deposits thereon and wherein the freshly regenerated catalyst at the start of. the decomposition period is overactive in that it produces excessive amounts of low molecular weight gases and coke; a method of avoiding over decomposition during the initial part of the decomposition period which comprises combining with the hydrocarbons to be converted a relatively large volume or diluent gases at the start of the decomposition period and thereafter reducing the volume of diluent gases as the ace tivity of the catalyst depreciates during the'operating period.

3. In the catalytic-cracking of hydrocarbon oils wherein the oil-to be cracked is passed in vapor form through a reaction zone containing a catalyst mass, the activity of which depreciates as the length of cracking period increases whereby the amount of cracking decreases as the 4. In the catalytic cracking of hydrocarbon.

oils wherein the oil to be cracked is passed in vapor form. through a reaction zone containing a solid catalyst mass and wherein the cracking operation is interrupted at the end of predetermined periods to regenerate the catalyst and wherein activity of the catalyst depreciates with the length of cracking period; the method of controlling the degree of cracking throughout the cracking period which comprises introducing into the oil vapors to be cracked prior to passing through the reaction zone a diluent gas in an amount sufficient to maintain the degree of cracking below a predetermined maximum during the start of the cracking period and thereafter reducing the volume of diluent combined with said oil vapors to maintain said degree of cracking at said predetermined maximum throughout the cracking period.

5. In the catalytic'cracking of hydrocarbon oil wherein the oil in vapor form is passed through a reaction zone containing a cracking catalyst maintained at a temperature sufiicient to crack said oil, the oil vapors maintained in contact with said catalyst for a period sufiicient to effect the substantial cracking thereof, the cracked products thereafter fractionated to separate a desired distillate product and a normally gaseous fraction therefrom and wherein the activity of the catalyst depreciates as the length of the cracking period increases; a method controlling the amount of cracking throughout the cracking period which comprises combining with the oil vapor to be cracked prior to passing to the 2. The catalytic decomposition of hydrocarreactlon zone a diluent ga in an amount sufficient to maintain the degree of cracking at a predetermined maximum at the start of .the cracking operation, thereafter reducing the volume of diluent gases combined with said hydrocarbon vapors to maintain the degree of cracking at said predetermined maximum.

6. In the invention defined in claim 5 the further improvement which comprises employing normally gaseous products separated from the cracked products as said diluent gas.

7. In the process defined in claim 5 the further improvement which comprises independently heating said diluent gas prior to combining with said hydrocarbon 'vapors and regulating the temperature oi the combined products by the heatmg of said diluent gas.

8. In the method according to claim5 the further improvement which comprises using normally gaseous hydrocarbons separated from the cracked products as the diluent gas.

9. In the method according to claim 5 the further improvement which comprises using low molecular weighthydrocar'cons as the diluent gas.

JOHN C. MUNDAY.

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