US2312230A - Catalytic conversion of hydrocarbons - Google Patents

Description

Feb. 23, 1943. A. BELcHx-:Tz

CATALYTIC CONVERSION OF HYDROCARBONS Original Filed June 29, 1940 Patented Feb. 23, 1943 CATALYTIC CONVERSION OF HYDROCARBON S Arnold Belchetz, Kew Gardens, N. Y., assignor to The M. W. Kellogg Company, Jersey City, N. J., a corporation of Delaware Original application .lune 29, 1940, Serial No. 343,222. Divided and this application June 28, 1941, Serial No. 400,253

2 Claims.

The present application'is a divisional application of my co-pending application, Serial No. 343,222, filed June 29`, 1940, the latter application being a continuaticn-in-part application of my co-pending application, Serial No. 274,670, filed May 20, 1939, now U. S.' Patent 2,253,486.

The present Ainvention relates to the catalytic conversion of hydrocarbons into lighter hydrocarbons of lower-boiling point or hydrocarbons otherwise altered in structure. More particularly, my invention relates to the catalytic conversion or cracking of high-boiling petroleum oils to low-boiling products, and the catalytic reforming of petroleum oil fractions such as naphtha and gasoline.`

The catalytic conversion of hydrocarbons involves, in general, two stages, a conversion stage wherein the hydrocarbons undergoing treatment are contacted with the catalyst under conditions adapted to effect the desired conversion, and a regeneration stage wherein the carbonaceous deposit formed on the catalyst during the conversion stage is eliminated. In its preferred aspect, my invention contemplates particularly an improved process involving a conversion stage wherein the hydrocarbons undergoing treatment are passed through the conversion zone in the form of vapor having the catalyst in finely divided condition suspended therein; and a regeneration step wherein used catalyst, after separation from the gaseous conversion products, is suspended in oxygen-containing gas and carried thereby through the regeneration zone to regenerate it by burning off deposited carbonaceous material.

This method of catalytically converting hydrocarbons has certain advantages arising particularly out of the relative intimacy of contact which it affords between the suspended catalyst and the carrier gas both in the conversion and regeneration operations. It exhibits, however, various disadvantages the elimination of which is one of the primary objects of my invention.

One of the objects of this invention is the provision of a procedure for heating and vaporizing the hydrocarbon preparatory to its passage to the conversion zone under such conditions as to avoid undesired thermal decomposition effects and the accomplishment of this result by the direct utilization of the heat of regeneration.

thereof on the catalyst. Various other objects and advantages of my invention will be' evident to those skilled in the art as the description thereof proceeds.

One of the features described and claimed in said co-pending application, Serial No. 274,670 now U. S. Patent 2,253,486, resides in the charging of the catalyst and hydrocarbon feed to the conversion zone in proportions which are markedly different and advantageous compared with those indicated by conventional practice. In such practice, this ratio is determined primarily on the basis of the activity of the catalyst and the extent to which deactivation thereof occurs during the conversion stage, the objective being,

` in general, tolimit the quantity of catalyst em- Another object of the invention is the propioyed to the smallest feasible amount consistent with the production of the desired extent of conversion, both because of thecost of the catalyst and processing costs incidentto its circulation. Limiting factors with respect to the proportion of the catalyst thus employed relative to the hydrocarbon charged, are the total carbonaceous material deposited during the conversion of a given amount of feed to the desired extent, and the quantity of carbonaceous depositwhich the catalyst is capable of carrying before its activity drops to a point Where its continued use is not feasible or desirable.

One feature of this invention involves the mixture of the liquid hydrocarbon feed with preheated catalyst, preferably at a temperature sufflcient to vaporize the feed, the necessary preheating of the catalyst preferably being effected in the regeneration reaction.

Another feature of this invention involves the controlled combustion of the used catalyst in such manner that a predetermined quantity of carbonaceous material is left thereon.

The various features of this invention are interrelated in such manner that their conjoint use is desirable. However, various features thereof are susceptible of application independently of the others, as Iwill be apparent to those skilled in the art.

The foregoing and various other features of the invention will be apparent from the following description thereof, given with reference to the appended drawing which illustrates diagrammatically suitable apparatus for its practice.

The drawing is a diagrammatic illustration of suitable form of apparatus for the practice of the embodiment of the invention involvingthe feature of the use of preheated catalyst to vaporize the feed stock.

Referring to the drawing. the feed to the system, for example, a reduced petroleum crude, enters from any convenient source indicated by the numeral I and is pumped by pump 2- to a heater or furnace 8 wherein-it is preheated I-to a suitable temperature and then flash evaporated in evap-v" cumulator 8 through line I8. The gas oil con-v densate is pumped by pump IIl through line I8 to heat exchanger 8 and into line I2. Part of the gas oil is returned as reflux to the evaporator through line I4.

The apparatus described above is merely illustrative of conventional apparatus forsupplying the gas oil or other treated hydrocarbon at a suitable temperature for the following conversion operation.

'I'he preheated fresh feed in transfer line I2 may be advantageously combined with a hot recycle oil introduced through line I4, the combined streams passing to the conversion stage through line I5. The oil passes through line I5 into pipe I 8 constituting an extension of the conversion reactor I1. Hot preheated catalyst is supplied from drum I8 by helical feeder I8 and mixed with the oil in pipe I8. Line 88 indicates the upper level of the catalyst collected in drum I8. The temperature of the catalyst and quantity of catalyst used are such as to cause vaporization of the oil thereby forming a suspension of the catalyst in the vapors. Sufficient steam or other suitable gas to initially disperse the catalyst as discharged from feeder I9 is preferably introduced through -line 20. Steam or other suitable gas may be supplied in greater quantities through line 28 when required to supplement the vapors resulting from the vaporization of the feed stock to produce the required volume of gas to carry the catalyst through the conversion reactor Il. The ratio by weight of the catalyst to fresh feed stock is preferably maintained and regulated as set forth in detail hereinafter. The gaseous mixture of feed stock, catalyst and steam flows upwardly through reactor II during which flow conversion or cracking of the oil to the desired extent occurs.

Reaction products pass from the top of reactor I1 to a suitable separator system to separate the catalyst from the vaporous reaction products. That shown comprises a settling tank 2I in which the major proportion of the suspended catalyst is separated, the separated catalyst flowing by gravity from the bottom of tank 2I through conduit 22 to the top of a steam stripper tower 28 and the vapors containing a relatively small fraction of fine catalytic material are withdrawn at the top through line 24. These vapors pass through line 24 to a suitable separator such as a cyclone type of dust collector 25 wherein most of the remaining suspended catalyst is separated and then passed to tower 28 by gravity flow from the bottom of the separator through line 28. Tower 28serves to displace hydrocarbon vapors contained in the voids between theparticles of catalyst and is suitably provided with bailies 2lV to eectively expose the catalyst passing downwardly therethrough -to the displacing action of.v 75,

used catalyst, is Passed through line 8| to a suitable type of fractionator 82 wherein a low-boiling fraction such as gasoline and fixed gases may be separated from the high-boiling products such as light and heavy cycle gas oils. Infractionator 82 the rconversion products may, for example, be fractionated into a low-boiling fraction including gasoline and ilxed gases withdrawn as the overhead product from the fractionator through line 88, an intermediate product such as light gasoil withdrawn as a side cut through line 84, and a residual high-boiling fraction such as heavy recycle gas oil withdrawn through line 85, cooled in cooling coil 8|, and pumped to storage through line 88.V i

In the bottom of fractionator 82 suitable means may be provided for separating residual catalyst present in the vapors introduced through line 8|. Asshown, these means comprise a line 8lv through which a portion of the high-boiling frac- A tion withdrawn through line 85 is returned to the fractlonator over bames 88 which deflect the vapors from line 8l into intimate contact with the returned fraction which consequently adsorbs or scrubs out residual catalyst present in the vapor. After passing over baiiles 88 the scrubbing liquid collects in the bottom of fractionator 82 from whichit is withdrawn through line 88 and pumped by pump 48 into line I4 for utilization as a re-u cycle oil,v as previously described.

Used catalyst is fed from drum 88 by screw feeder 4I to pipe 42 and carried therein by a current of oxygen-containing gas such as air injected through line 48 to regeneration or combustion chamber 44 wherein combustion of the carbonaceous deposit on the spent catalyst occurs during the passage of the catalyst therethrough. Steam may be introduced when desired through line 45. Line 82 indicates the upper level of the catalyst in drum `88. 'I'he proportion of oxygencontaining gas injected relative to the quantity of used catalyst is preferably maintained and resulated, as described hereinafter in detail.

Combustion gases bearing the regenerated catalyst pass from chamber 44 into a suitable recovery system for separating the catalyst. As'

shown, this system comprises a settling tank 48 wherein most ofthe catalyst is' separated and flows downwardly therefrom through conduit 41 l to surge drum I8. The separated gases containing a small residual amount of catalyst ilnes leave separator 48 at the top through line 48 and pass to a cyclone type of dust collector 48, wherein substantially complete separation of the catalyst is eifected. The separated catalyst from collector 48 then flows downwardly through line 58 and is combined with the initially separated catalyst'in drum 'I8 from which it is fed to the conversion stage by feeder I8, as previously de-4 m, scribed. Drum I8 and feeder I8 may be suitably provided with heat insulation material to obviate loss of heat by the regenerated catalyst in its passage therethrough.

The range of catalyst-to-on-reed ratio suitably' and preferably employed land other preferred:

The gaseous suspension withdrawn from septhe folprocessing conditions, is illustrated by lowing examples.

In one example, a petroleum gas oil having a gravity of 31.4 A. P. I. was used as the feed stock to be catalytically converted or cracked by the process to a low-boiling stock having a required amount of hydrocarbon within the gasoline boiling range. This particular gas oil was produced by the flash evaporation of a reduced crude and constituted the volatile portion thereof amounting to about 901% of the crude charged to the evaporator. In the process of converting this particular oil to the desired extent. it was determined that coke or carbonaceous material appearing as a deposit on the catalyst would be produced to the extent of 3.5% by weight of the charged gas oil. A temperature of 865 F. was chosen as representing a suitable mean temperature for the reaction which, since the conversion reaction is endothermic, corresponded to an inlet temperature to the reactor of about 880 F., and an outlet temperature of 850 F. The deactivationu temperature of the particular catalyst employed was ascertained to be approximately 1000 F., this temperature being the maximum temperature to which the catalyst could be safely subjected under the regeneration conditions without undue impairment of its catalytic ac- Vcatalyst in sufiicient amount to absorb a definite minimum amount of the heat of regeneration, this ratio R being determinable by the application of a generalized formula derived by the application of the principles of my invention, as follows:

CH K

Rian-T2) In this formula, R represents the catalyst-to-oil weight ratio; the vsymbol C, the fraction of the gas oil or other hydrocarbon charged, converted to coke or oarbonaceous material and deposited on the catalyst during the conversion; H, the heat of combustion of the coke or carbonaceous material expressed in B. t. u.s per lb.; S, the specific heat of the. catalyst; T1, the deactivation temperature in degrees Fahrenheit of the catalyst; T2, the temperature in degrees Fahrenheit of the catalyst on entering the regeneration zone; and K, a fractional coeiilcient having a lower limit determined by the extent to which expedients other than the heat absorption capacity of the catalyst may be employed to dissipate the heat of regeneration.

In this particular example, the regeneration was effected in accordance with the preferred mode of practising my invention wherein thev 0.035; 16,400; 0.22; and 1000. Since the used catalyst may be advantageously transferred directly from the conversion zone to the regeneration zone without substantial intermediate cooling in accordance with my invention, which procedure was followed in this instance, the value of T2 corresponded approximately to the outlet temperature of the conversion zone, namely, 850. Accordingly, substituting these values for the corresponding symbols in the above formula it is evident that the maintained catalyst-to-oil weight ratio, R, is equivalent to the ratio,

By the maintenance ofthe catalyst-to-oil ratio at the relatively high value of 14.5, as determined above, the absorption of the heat of regeneration at a temperature below the deactivation temperature of the catalyst, was readily and effectively accomplished solely through the medium of the heat absorption capacity of the catalyst and the combustion gases without the use of extraneous cooling means.

It is to be noted that the ratio as above determined, is not sharply critical and may be increased or decreased. these variations in general corresponding to permissible variations in the numerical limits of the coeillcient K. In the above specific example, for instance, the catalystto-oil ratio may be maintained at a larger figure than 14.5, thereby assuring the circulation of a quantity of catalyst not only sufficient but in excess of that needed for the desired minimum absorption of heat by the catalyst during the regeneration reaction. The amount of such surplus catalyst will normally be controlled by economic considerations dependent upon the cost of the surplus catalyst and the processing expense incident to its circulation. Since these factors will normally outweigh any advantage to be gained by the circulation of surplus catalyst, it is contemplated that the practice of my invention will usually and preferably be practised with an oil-to-catalyst ratio wherein K has a value not very greatly in excess of that employed in the above example.

The oil-to-catalyst ratio, as above determined, may also be decreased to some extent, such changes corresponding to the lower limiting value of the coefficient K. For example, thev use of a lower ratio and corresponding lower K value may be feasible through the use to a limitedr extent of cooling coils or similar extraneous cooling means in the regeneration zone. It is contemplated, however, that in the practice of my invention in its preferred aspect wherein the heat of regeneration is largely absorbed by the catalyst that the value of K, will be greater than 0.2 and preferably greater than 0.5.

In the conversion of the gas oil used in the above example, the procedure followed was that previously described in connection with the appended drawing, the catalyst-to-oil ratio being maintained at a minimum of 14.5 to 1, as above determined, and air being introduced through line 43 in quantity suiiicient to supply only the theoretically required amount of oxygen to burn oil or reduce the concentration of the carbonaceous deposit to the desired extent; also the hot regenerated catalyst was' withdrawn from drum I8 and thereafter mixed with the feed stock Without any substantial intervening cooling, and

.. contained sufiioient heat to vaporize the feed stock introduced at a temperature of about 550 with a minimum amount of carbonaceous material thereon mounting to 1.5% by weight of the catalyst. In passing through the conversion zone the carbonaceous material concentration on the catalyst under the conditions of this particular example increased to 1.74% and accordingly, in the regeneration stage, the carbon concentration of the catalyst was reduced from 1.74% to 1.5%.

'I'he average velocity of the vapors through the reactor may be of the order of about 10 feet per second and the vapor contact time of the order of about 6 seconds; such conditions correspond to an average catalyst concentration in therel actor of about 6 pounds per cubic foot.

The maintenance of a definite minimum concentration of carbonaceous material on the catalyst as exemplified by the above example, has

important and distinctive advantages. It assists in the regeneration reaction since the rate of combustion is accelerated and more readily controlled by the presence of an amount of carbonaceous material in excess of that which is to be removed by combustion. The retention of, residual carbonaceous material also makes it possible to discharge the regeneration combustion gas with a relatively low percentage or in some cases, entirely free of oxygen, and the gas is thus better adapted for use for various purposes. Also, in certain'instances, particularly in catalytic cracking in the presence of alumina-silica type of cracking catalyst such as Super-Filtrol, the conversion reaction is faciiltated by the presence of a small amount of residual carbon and in most instances the advantages obtained in regeneration by the maintenance of a residual carbon concentration will outweigh the disadvantages, if any, resulting in the conversion stage. The residual carbon concentration maintained may depart-somewhat from the value of 1.5% regarded as the approximate optimum in the foregoing example wherein a Super-Filtrol type of alumina-silica cracking catalyst was ernployed.' Preferably, this permissible range is confined to about 0.5% to 2.0%, by weight of the catalyst, ror the narrower range of about 0.8% to 1.5%.

A number of highly advantageous results are secured by mixing the liquid feed stock with the regenerated catalyst while the latter retains the heat imparted to it in the regeneration reaction.

Conventional methods for vaporizing and preheating the oil to the required conversion temperature would frequently result in substantial thermal decomposition or crackingf which is undesirable because of the low quality of products thus obtained, particularly with respe'ct to octane number and ultimate amount of coke formed, compared with those produced b'y complete catalytic conversion. Due to the intimate contact between the hot catalyst and feed stock and resultant rapid and emcient vapcrization, undesired thermal cracking" is largely obviated. Substantial savings are further secured by the resulting direct use of the major proportion of heat evolved during the regeneration stage.

Any type of catalyst suitable for effecting the desired conversion may be employed in the pract-ice of rnv invention. For the conversion or cracking of high-boiling fractions such as gas oil to low-boiling fractions such as gasoline, I regard cracking catalysts of the alumina-silica type as especially suitable, this term lbeing inclusive of cracking catalysts such as certain types of activated clays or synthetically produced mixtures or compounds of alumina and silica. The circulated catalyst may be composed entirely of the active catalytic material and is preferably pre dominantly composed thereof. However, the active catalyst material may be associated with supports, extenders or solid diluents which for the purpose of my invention are to be considered as part of the catalyst, since such solid diluents. etc., will function in a manner similar to the active part of the catalyst relative to the absorption of heat in the regeneration zone and the transfer of this heat to the hydrocarbons undergoing treatment. When alumina-silica type of cracking catalysts are employed, the practice oi' my invention will* usually involve catalyst-to-oil weight ratios greater than 2.5 to 1, and preferably greater than 5.0 to 1.

From the foregoing it will be apparent that the process therein described accomplishes the objects of my invention, and that various features thereof may be utilized to advantage either conjointly or separately. It will further be readily apparent to those skilled in the art that while the invention has been illustrated and described with respect to a preferred operation and examples, and with references to suitableapparatus for its practice, the invention is not limited to such exempliiications but may variously be practised and embodied within the scope of the claims hereafter made.

I claim: i

1. In a process for the catalytic conversion of high-boiling hydrocarbons into low-boiling hydro carbons within the gasoline boiling range involving passing a stream of the high-boiling hydrocarbons having a solid, incombustible cracking catalyst suspended therein through a conversion zone for a time and at a temperature adapted to eilect the required degree of conversion to lowboiling hydrocarbons and also resulting in acarbonaceous deposit on the catalyst, separating the used catalyst from the vaporous conversion products, suspending the Iused catalyst in an oxygencontaining gas and passing the suspension through a regeneration zone to burn oi! carbonaceous material deposited on the catalyst,- and returning the catalyst for reuse in the conversion reaction, the improvement which consists in introducing the used catalyst into the regeneration zone and burning oil. the carbonaceous material in said zone under such conditions as to leave a residual quantity of carbonaceous material on the catalyst amounting to about 0.5% to 2.0% of the weight of the regenerated catalyst as discharged from said regeneration zone and reused in the conversion zone, withdrawing the regenerated catalyst from said regeneration zone and admixing it with liquid hydrocarbon feed. stock while retaining suiilcient heat to vaporize the feed stock, and returning said catalyst in suspension in the vapors thus produced to said conversion zone.

2. A process for the catalytic conversion of tion products and regenerating it by passage 10 through a regeneration zone, while suspended in an oxygen-containing gas, withdrawing the regenerated catalyst frorn said regeneration zone and admixing it with liquid hydrocarbon feed stock while retaining sufcient heat to vaporize the feed stock, and returning said catalyst'in suspension in the vapors thus produced to said conversion zone.

ARNOLD BELCHE'IZ.

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