US2410891A - Process for improving naphtha - Google Patents

Description

Nov. 12, 1946. R. N. MEINERT E'rAL PROCESS FOR IMPROVING NAPHTHA Filed Dec. 8, '1944 Richard mez'nerf '3ra doruzn .und

Y venters ze Jr l ,f Clbbotneq bq'lt Patented Nov. 12,1946

rRocEss Fon IMPRovrNG NAPHTHA- Richard N. Meinen, Westfield, and Pnuetus n.

Holt, 2nd, Summit, N. J., assg'nors to Standard il Development Company, a corporation of Delaware Application December 8, 1944, Serial No. 567,278

Our present invention relates to improvements in the catalytic-reforming of naphthas in a ilud" catalyst process in which a heat .balance is maintained in the system by controlling coke formation and the ratio of hydrogen which is recycled with respect to the naphtha fed to the system, all of which will more fully appear hereinafter.

In catalytic cracking in a system involving a reaction zone and a regeneration zone, it has been proposed to supply the amount of heat necessarir for the endothennic reaction of cracking by burning the cokev formed during cracking in a regeneration zone. It is not possible to maintain such a system in heat balance without the use of coolers and/or heaters, because there is no variable at a given conversion of oil to gasoline, since the amount of coke formed is fixed by conditions.

In catalytic reforming we have found that the reforming (endothermic) reaction may be maintained in heat balance with the regeneration phase (exothermic) by adjusting a variable, namely, the quantity of hydrogen used in the process, thereby increasing or decreasing the amount of coke formed. To illustrate, suppose that for a given degree of reforming it developed that more coke was formed on the catalyst than that required when burned in the regeneration phase to sustain the reaction phase, then the coke formation may be reduced by increasing the quantity of hydrogen feed to the reaction zone f which has the e'ect of reducing the amount of y productive phase, then the quantity of coke being formed may be increased by reducing the quantity of hydrogen feed to the reaction zone.

'I 'he object of our invention is to operate with catalytic reforming of naphthas in the process in which there is a productive phase and a catalyst regeneration phase under operating conditions such that the system is rendered internally heat compensating without resort to the use of coolers and/or heating means.

A more specific object of our invention has reference to controlling the amount of coke which is formed on the catalyst during the catalytic reforming of naphthas in the presence of added hydrogen.

We have found that the catalyst best suited for reforming naphthas is one consisting of a zinc alumina composition commonly called zinc spinel and molybdenum oxide or chromium oxide. The molybdenum oxide or the chromium oxide which comprises 8 to 12 per cent of the total composition is the active component whereas the zinc spinel is the carrier or spacing agent. We have found that this catalyst, particularly when employed in the process maintained under relatively low pressures, not only converts naphthenes to the corresponding aromatic by dehydrogenation but also converts parafiins to aromatics. Hence, it is possible by our process to convert a virgin naphtha having an octane number of, say, 40 CFR to a product having an octane number of from 85 to 100 on the same scale, in good yields.

In the accompanying drawing we have shown diagrammatically apparatus elements in which a preferred modification of our invention may be carried into practical eiect. Similar reference characters refer to similar parts.

Referring in detail to the drawing, a West Texas virgin naphtha, in the example we have chosen to illustrate our invention, is introduced into the system through line I. This naphtha is at a temperature of around 400 F., having been pre-heated by heat exchange with hot products in a subsequent portion of the system according to known means (not shown). The feed is mixed with a hydrogen-containing gas as its enters the system, the .purpose of the hydrogen being to direct the course of the reaction as previously indicated, particularly with regard to the formation of coke which is unavoidably formed in an operation of the type here involved. 3 is a catalyst regenerator andl from 3 we withdraw through a standpipe 4 controlled by a valve V a quantity of powdered catalyst which is discharged into line- I, where it admixes with the naphtha feed and the hydrogen, and due to the fact that it is at a temperature of about 1100 F. it causes vaporization and super-heating of the naphtha. to a temperature of about 950 F. The catalyst is carried in suspension by the vaporized naphtha in the hydrogen into a delayed settler reactor 5. Within the reactor the gas or vapor velocity is main'- tained within the limits of from about 1/2 to i0 the weight ratio of catalyst to oil in the reactor,

or the amount maintained therein, because as will subsequently appear, catalyst is being continuously withdrawn from the reactor to be regenerated. containing operating conditions within the reactor.

The reactants pass through the dense phase of catalyst into the space S above L where the amount of catalyst suspended in the vapors decreases sharply upward due to the settling out of the catalyst and then the vapors pass through one or more centrifugal separators C disposed in the top of the reactor where entrained catalyst nes are substantially separated from the feed vapors and returned by-a dip pipe D (or dip pipes) to the main bulk of the catalyst. 'I'he reaction products and hydrogen eventually exit We shall set forth, hereinafter, tables from the reactor through line i0 and then pass to a purication and hydrogen recovery system (not shown) for recovery of desired products and return of hydrogen to the reaction zone. It is deemed unnecessary to describe the purification `recovery of the desired products since that is well' understood by those who are familiar with the art.

As previously pointed out, .during the reforming of the naphthas, coke is unavoidably deposited on the catalyst and therefore it is necesv sary to remove this coke to maintain the catalyst in an active condition. To this end, therefore, we withdraw catalyst continuously through the standpipe I2 carrying taps t and controlled by valve V. As is well known the taps t are disposed in the standpipe I2 for the purpose of injecting a small amount of gas which may be hydrogen, steamor other inert gas, into the downfiowing catalyst for the purpose of maintaining the same in a fluidizedv condition. The catalyst discharges into an air stream I4 in which it forms a suspension which is conveyed to regenerator 3. The catalyst forms in the regenerator 3 a dense suspension having` an upper level at L in the regenerator by maintaining the gas flow rate therein of the same order as those previously mentioned in connection with the description of the operation in reactor 5. The catalyst entering the regenerator 3 is at a temperature at around 900 F. but during the regeneration wherein the coke on the catalyst is burned, the temperature is increased to about 1100 F. As in the case of the reactor above L there is a sparse phase S1 wherein the concentration of catalyst in gas sharply decreases upward due to settling out of catalyst so that eventually it contains only theflner portions of the catalyst. The

gas containing the fines is then passed through one or more cyclone separators C1 wherein the catalyst fines are substantially removed, permitting the issuance of the regeneration fumes from regenerator 3' through line 20 substantially freed of catalyst. Of course, it will be understood that the sensible heat contained in the regeneration fumes is preferably, in at least part, recovered by causing the passage of the hot f es through heat exchangers, waste heat-boilers, and the like. This is accomplished in equipment not shown. Thus, for example, as previously indicated, the cold oil entering the system may bepre-heated by heat interchanging with these fumes or with the hot vapors in line I0 according to known means. vThe regenerator is provided with a dip pipe D1 which serves to return catalyst separated from the gas in separator C1 and returned to the main body of catalyst below L1. The space S1 between L1 and the top of the regenerator is, as in the case of the reactor, a catalyst disengaging space.

The regenerator catalyst issues through drawoff pipe 4 as previously indicated and the cycle is repeated.

We have thus described generally a method of carrying our improvements into enect. We do not claim novelty in the iluidized type of operation we have described but as previously indil'cated in the manner of maintaining the system in heat balance without the aid of extraneous equipment and utilities. To illustrate this proposition, we direct attention to the fact that where, say, the temperature of the catalyst in the regenerator is 1100 F. and that in the reactor 900 F. it is desired to convert virgin naphtha to gasoline having an octane number of 85, we nd that about 2000-3000 lbs. of catalyst must be circulated to the reaction zone per lbs. of oil fed Where the incoming feed is at a temperature of 400 F. (that is, feed in line l about to be mixed with hot catalyst). This means We must Benerate in the regenerator l 36500 B. t. u.'s. It will be understood that this is a specific example il lustrating our invention and is not to be taken as limiting thereon for, obviously, different conditions will require a different amount of coke to be deposited on the catalyst for burning to supply the heat for the system. However, we set forth inthe below tables a full statement of conditions in the reactor which we have found to give the desired results.

Table I Conditions giving good results: Temperature F 8501l00 Pressure lbs. per square inch-- 0-400 Lbs. of catalyst per 100 lbs. of oil per hour fed to the reactor 500-4000 Table II The preferred conditions are: Temperature F 920-980 Pressure lbs. per square inch..- 15-50 Lbs. of catalyst per 100 lbs. of oil per hour fed to the reactor 2000--3000` In addition to the conditions set forth above, the real gist of the present invention as previously indicated has to do with controlling the quantity of coke which is formed on the catalyst during the reaction. If the temperature in the reactor 5 tends to be decreased below the desired value, immediately the quantity of hydrogen feed to the reactor is reduced, thereby permitting the formation of additional coke on the catalyst, which additional coke when burned in regenerator 3 will, of course, supply an additional quantity of heat which would be absorbed by the catalyst and returned to the reactor to correct the unfavorable temperature condition therein tending to take place. Of course, the actual amount of hydrogen which is fed to the reactor per barrel of oil in order to maintain the desired conditions herein enumerated will depend on the feed stock. Generally speaking, the amount of hydrogen is within the range of from about 1000 to 4000 cubic feet measured under standard conditions per barrel of oil. But as previously pointed out, it may be and often is necessary to change the ratio of hydrogen to oil to accommodate a particular feed stock, or the same feed stock as a catalyst gradually decreases in activity during long-continued use. It is, of course, impossible to set forth numerical values defining every possible set of conditions but we may indicate the amount of hydrogen necessary by reference to the following guide:

Let us assume that the plant is operating in the reforming of a West Texas virgin naphtha under conditions generally specied in the above tables and that for every 100 lbs. of oil fed to the system there is formed 4 lbs. of coke, that is to say, the system is producing high octane gasoline, same gasoline having an octane rating of 85; that the temperature inthe reaction zone is 950 F. and that in the regenerator 1100 F.; that there is fed to the reactor 30 lbs. of catalyst per pound of oil; and nally, that there is fed to the reactor.2000 cubic feet of hydrogen per barrel of oil. It then develops that the temperature in the reactor tends to decrease. In that situation, the amount of hydrogen fed to the reactor is immediately lowered, say, to 1500 cubic feet of hydrogen per barrel of oil, which lowered hydrogen feed will 'be reected in a greater amount of coke formation so that the coke rate rises, say, to 5 per cent by weight on feed. When this catalyst is withdrawn from the reactor and regenerated, it will of course liberate a greater quantity of heat than the preceding portions and when this additional increment ofvheat contained in the catalyst is delivered back to the reaction zone it will counteract the tendency of the temperature therein to decrease. As previously indicated, it is diilicult to give numerical values for all possible types of feed, for they may include virgin naphthas, cracked naphthas, or mixtures of the two. However, our experience has been that the coke formed on the catalyst should amount to from 3 to 7 weight per cent of the oil feed with the coke formation amounting to 4 per cent based on feed giving good results.

Numerous modifications of our invention may be made by those familiar with this art Without departing from the spirit thereof.

What we claim is:

1. A continuous method for reforming naphthas which comprises charging a mixture of a hydrogen-containing gas and a petroleum naphtha to a reaction zone containing a lower dense phase suspension and an upper dilute phase suspension of powdered catalyst in gasiiorm reactants comprising the naphtha undergoing reforming, the said catalyst consisting essentially of a zinc spinel carrier supporting one of the class of group VI oxides consisting oi molybdenuml 6. oxide and chromium oxide, maintaining a temperature of from 850 to 1100 F. and a pressure of from about 15-50 pounds per square inch within said reaction zone, permitting the reactants to remain resident in the reaction for a suffi-- cient period of time to effect the desired conversion, continuously withdrawing a reformed naphtha. from an upper portion-of said reaction zone, continuously withdrawing the catalyst fouled during the reaction from said reaction zone at a lower point thereof, mixing said withdrawn catalyst with an oxygen-containing gas and conducting it to a regeneration zone where it is formed into a lower dense phase suspension and an upper dilute phase suspension of said powdered catalyst in said oxygen-containing gas, permitting the catalyst to remain resident in the regeneration zone for a suflicient period of time to eiect the desired regeneration, continuously withdrawing catalyst from a lower portion of said regeneration zone, returning said regenerated catalyst directly to the reaction zone and maintaining the reaction zone at reaction temperatures without employing extraneous utilities by increasing the amount of hydrogen fed to the reaction zone as the temperature therein tends to rise and, conversely, decreasing the amount of hydrogen fed to the reaction zone as the tem-1l perature therein tends to recede, thus forming that amount of carbonaceous material on the catalyst during the reaction so that when the catalyst is regenerated in the regeneration zone, the heat released and absorbed by the catalyst is adapted to maintain the reaction. zone at the desired temperature when the regenerated catalyst is returned to the reaction zone.

2. 'Ihe method set forth in claim 1 in which 2000 to 3000 pounds of heated catalyst per one hundred pounds of oil are fed to the reaction zone each hour, where the temperature of the incoming oil is about 400 F. a'nd further, in which the amount of carbonaceous material formed on the catalyst in the reaction zone is between about 4 to 5 pounds per one hundred pounds of oil fed to the reaction zone.

3. The method set forth in claim 1 in which the catalyst consists of a major portion of zinc4 spinel and a minor portion of chromium oxide.

RICHARD N. MEUIIERT. PHILEI'US H. HOLT, 2nd.

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