US 2399678 A
Description (OCR text may contain errors)
May 7', 1946.
E. J. HOUDRY EI'AL CATALYSIS Filed July 27, 1943 Q 3 Q 20 i 2% z 0 E u 2 Q.
1/00 1200 1300 Mp0 150a 1600 "00 TEMPE ATURE "F INVENTOR EUGENE a. Hove/2v ATTORNEY Patented May 2, i946 CATALYSIS Eugene J. Houdry, Ardmore, and Hubert A. Shebaker, Media, Pa... asslgnors to Houdr'y Process Corporation, Wi of Delaware ngton, Del., a corporation Application July 27, 1943, Serlal'No. tildfldt 4 Claims. (G11. zoo-sac) The present invention relates to improvements in catalytic dehydrogenation of hydrocarbons,
such as parafiinic, olefinic or alkyl aromatic hydrocarbons which contain a carbon chain of less than 6 carbon atoms.
Catalytic dehydrogenation of the type to which the present invention relates proceeds with the formation of coke or coke-like material which is deposited in the catalyst and the formation of hydrogen in addition to the production of unsaturated or aromatic products. This coke-like material is, of course, formed from the hydrocarbon being dehydrogenated and therefore represents a loss of material. Any reduction in losses, in general, is an advantage. Reduction of coke is of particular advantage in these dehydrogenation processes in facilitating temperature control, and, in the case of adiabatic operation, in improving the conditions of operation.
in modern gas dehydrogenation procedures the heat produced. by burning of this coke-like matelit rial during regeneration is stored in'the catalyst mass and is employed to maintain the temperature during the endothermic dehydrogenation, processes of this type being termed adiabatic dehydrogenations. In these processes a limiting factor on the extent of the dehydrogenation, and therefore the eihciency of the process is the amount of coke produced in relation to the amount of dehydrogenation effected. Thus, as the temperature of the operation increases, the extent of the dehydrogenation in general also in creases; likewise, the amount of coke deposited increases. As, the temperature is increased, the increase in the amount of coke deposited is more than proportionate to the increase in dehydrogenation. Therefore, under fixed operating conditions, the condition at which the heat of dehydrogenation is cqual to the heat of regeneration is a special case. If the ratio of coke dcposited to dehydrogenation efiected can be decreased, the temperature is increased at which the heat of dehydrogenation is equal to the heat of regeneration. This, according y, allows oper-- ation of adiabatic operation at higher temperatures, with resultant increase in the extent of dehydrogenation. likewise, plants operating at high temperatures and using extraneous means to dissipate heat such as an air blow can be run at a substantial saving by areduction in the ratio of coke to dehydrogenation.
The present invention is of particular application to dehydrogenation processes for the production of butadiene. Dehydrogenation catalysts treated in accordance with this invention not only produce less coke but, additionally, when employed under the same conditions, produce a till a slight increase results in major savings in the cost ofrecovery of butadiene from mixed dehydrogenation product.- T
Objects of the present invention are to provide improved processes for the manufacture of dehydrogenation catalysts, to provide improved dehydrogenation processes wherein the losses are decreased, to provide for the use of more favorable operating conditions, and to provide processcs for the production of dienes, in particular butadiene, in which, under like conditions, the concentration of diene in the reaction mixture is increased. Other and more specific objects will become apparent as the following description proceeds.
The improvements here involved are applic able in the dehydrogenation of parafiinic hydrocarbons. as in the dehydrogenation of propane or isobutane to propylene or isobutene, or the product, alternatively, may contain dlenes, as in the dehydrogenation of paratfins and olefins to olefins and dienes. Further, the product may contain unsaturated aromatic derivatives, as in the dc-- hydrogenation of allryl aliphatics in which the allryl group is a carbon chain containing less than six carbon atoms in the chain. In the latter type of process, the charge may be relatively pure, such a technical ethyl-benzene or it may be a naphtha cut. V
This invention involves the treatment of dehydrogenation catalysts oi the type which contains a polyvalent, multivalent heavy metal oxide, for example, chromium, molybdenum, vanadium or iron, carried by surface active support comprising a refractory metal oxide, non-reducible under the reaction conditions employed for the dehydrogenation, such as alumina, zirconia, magnesium oxide, and cerium oxide. This treatment of the dehydrogenation catalysts of the type stated is efiected at elevated temperature in the presence of steam. The treatment is eflected at a temperature between 1200 and 1600 F. at a partial pressure of steam in pounds per square inch above 1 lb. and above and at a partial pressure or steam in pounds per square inch below 30 lbs. and below T-1630 where '1 equals the temperature of treatment in degrees Fahrenheit. The treatment is continued for over two hours and for a time sufficient that the ratio of percent dehydrogenation to per cent coke is increased at least 50% per cent dehydrogenated being calculated as the per cent of dehydrogenated product times one hundred divided is of realand substantial importance since even by the total of dehydrogenated product plus un- The product may be principally olefins,
. The pellets were divided into three lots.
converted charge. It is in general unnecessary to treat for over thirty hours to obtain the desired change in catalyst characteristics and accordingly it is preferred that the treatment be not extended beyond that time.
It appears that in the preliminary stages of treatment the selectivity of the catalyst is somewhat improved with respect to side reactions which give gas and low boiling hydrocarbons of a number of carbon atoms to the molecule other than contained in the charge. However, upon continued treating, and in accord with this invention, the coke is also reduced. Both of these changes reduce losses. The second one appears to be a permanent change in the catalyst, the results of which are in no way similar to the deposition of a transitory molecular film of water. As an incident of the reduction in coke as stated it'has been found that there is an increase in the extent of dehydrogenation.
It should be noted in connection with the mathematical expressions employed to define the treating conditions that these expressions are purely empirical and define the curved lines BC and EF, respectively in the accompanying drawing. Thus, along the the line BC the partial pressure of steam is equal to and along th line EF the partial pressure is equal to In this drawing the zone of treating is outlined in heavy lines and consists of the zone ABCDEF. This invention is illustrated in the following examples which should be taken as indicative of the character of the invention but not definitive of the scope thereof.
EXAMPLE 1 & drained off and the pellets were dried in circulating air at 210 F. By analysis the pellets contained 18.5% by weight CraOa on ignited basis. One of the lots employed as a blank was heat treated at 1400 F. for 10 hours in dry air, the other two lots were steam treated in accordance with this pressure of 3 lbs.'and the other at 1400 F. for
20 hours at a steam pressure of 1.5 lbs. The 3 lb. and 1.5 lb. steam pressures were obtained by maintaining the pellets in contact respectively with a 20% steam, 80% air mixture and a 10% steam, 90% air mixture. both of which were maintained at atmospheric pressure. The heat treated catalysts were subjected to reduction by contacting at elevated temperature with hydrogen prior to use for dehydrogenation.
The conditions employed for dehydrogenation were as follows: A mixture of 24.5% n-butane, 75.0% n-butene and 0.5% butadiene was contacted with the catalyst at a temperature of 1075 F., at a pressure of 5 inches mercuryabsolute and a rate of about 20 grams of charge per liter of catalyst per minute. Each run on a catalyst was conducted for minutes and the catalysts were reduced with hydrogen before each run following regeneration.
e Percent dehydrogenated 1 Percent dehydrogenated/eoke.. Percent increase in ratio gomuoooolel l use 1 Percent dehydrogenated- EXAMPLE 2 Six parts by volume of Activated Alumina" pellets were allowed to stand in four parts by volume of a solution of chromic acid of specific gravity 1.025. After standing for 30 minutes the solution was drained from the pellets. There was recovered 1.995 parts by volume of solution of specific gravity 1.018. The pellets were dried at 200 to 210 F. in circulating air and were found to contain 3.28% CrzOa on ignited basis.
The dried alumina pellets containing chromic acid were divided into 3 portions, one of which for control purposes was heat treated in dry air for 10 hours at 1400 F. The remaining two portions were steam treated at 1400 F. for 10 hours, one of them at a partial pressure of steam of 1.5 and the other of 3 lbs. per square inch. This steam treat was effected in the first instance by maintaining an atmosphere of 10% steam, 90% air at' atmospheric pressure in contact with the catalyst, and in the second instance, 20% steam, air, at atmospheric pressure. After reduction the three catalysts were employed for dehydrogenation under the conditions stated in Example 1. The results tabulated below were obtained:
Table 2 Temp., F Time in ho r Steam pressure Percent dehydrogenated Percent dehydrogenated/coke Percent increase in ratio ExAmPLz 3 Six parts by volume of Activated Alumina pellets were soaked for 30 minutes in four parts by volume of a 1.268 specific gravity chromic acid solution, following which residual solution was drained from the pellets. There were 2.15 liters of residual solution of specific gravity 1.285. The pellets were dried in circulating air at 200 to 210 F. The pellets were found by analysis to contain 13.68% CrzOa on ignited basis.
The dried pellets were divided into four lots and heat treated under the following conditions: The first at 1400 F. for 10 hours in dry air for a blank, the second at 1400 for 10 hours at a steam pressure of 1.5, the third at 1400" F. for 10 hours at 3 lbs. steam pressure, and the fourth at 1400 F. for hours at lbs. steam pressure. After reduction the catalyst was employed for dehydrogenation under the conditions in Example 1. The results are shown in the followin tabulation:
32 liters of "Activated Alumina pellets were soaked for minutes in 28.6 kilograms of a chromic acid solution of specific gravity 1.142.
The remaining solution was then drained off and upon measurement there was obtained 13.05 liters of residual solution of specific gravity 1.146. The pellets were dried at 210 F. in circulating air.
'''The pellets were found by analysis to contain 9.12% CrzOa on ignited basis.
The catalyst was divided into four lots and heat treated as stated in Example 3 and employed for dehydrogenation under the conditions in Example 1. The resultsareshown in the following tabulation Table 4 Temp., F 1, 400 l. 400 1,400 Time in hours.- 10 10 10 Steam ressure 1. 5 3 15 Ca, Cs 3. 5 2. 7 0.8 1.0 Total 04....... 90. 6 92.3 94.8 96.0 Butadiene 16. 3 19. 7 19. 9 18. 4 Coke 3. 4 2. 5 2. 4 2. 1 Percent dehydrogenated 18. 0 2i. 4 21 19. 1 Percent dohydrogenated/coke. 5. 30 8. 57 8. 75 9. 10 Percent increase in ratio 62 65 72 Preferred catalysts employed in the present invention contain a minor portion generally in the .sran e between 2% and or the heavy metal oxide and a mojor proportion generally in the range from 60% to 98% of the refractory surface active support.
We claim as our invention:
1. The process of dehydrogenating a selected hydrocarbon containing an aliphatic chain of less than 6 carbon atoms which comprises subjecting said hydrocarbon to contact with a dehydrogenation catalyst of the type which contains a polyvalent, multivalent heavy metal oxide carried by a surface active refractory metal oxide support, said catalyst having been preconditioned by contact with steam at a temperature between 1200 and 1600 F. at a partial pressure of steam in pounds per square inch between 1 pound and 30 pounds and above and below where '1 equals the temperature of preconditioning in degrees Fahrenheit, the preconditioning being continued for more than two hours and for a time sufllcient that the ratio of percent dehydrogenation to percent coke is increased at least over the results obtained with no preconditioning.
2. The process of dehydrogenating a selected hydrocarbon gas which comprises subjecting said gas to contact with a dehydrogenation catalyst of the type which contains a polyvalent, multivalent heavy metal oxide carried by a surface active refractory metal oxide support. said catalyst ha ing been preconditioned by contact with steam at a temperature between 1200 and 1600 F. at a partial pressure of steam in pounds per square inch between 1 pound and 30 pounds, the partial pressure of steam being correlated with the temperature to lie within the zone ABCDEF in the accompanying drawing, the preconditioning being continued for more than two hours and for a time suilicient that the ratio of percent dehydrogenation to percent coke is increased at least 50% over the results obtained with no preconditioning.
3. The process of dehydrogenating a selected hydrocarbon gas which comprises subjecting said gas to contact with a dehydrogenation catalyst which contains a minor portion of chromium,
oxide carried by a major portion of a surface active alumina, said catalyst having been preconditioned by contact with steam at a temperature between 1200 and 1600 F. at a partial pressure of steam in pounds per square inch between 1 pound and 30 pounds, and above and below where T equals the temperature of the preconditioning in degrees Fahrenheit, the preconditioning being continued for more than two hours and for a time sufficient that the ratio of percent dehydrogenation to percent coke .is increased at least 50% over the results obtained with no preabove and below where T equals the temperature of the preconditioning in degrees Fahrenheit, the preconditiom ing being continued for more than two hours and for a time sumcient that the ratio of percent dehydrogenation to percent coke is increased at least 50% 'over the results obtained with no pre- EUGENE J. HOUDRY. HUBERT L 41m conditioning.