Dehydrogenation of paraffins

#This invention relates to a process for the dehydrogenation of paraffinic hydrocarbons to the corresponding monoolefins. More particularly, this invention relates to the dehydrogenation of paraffins containing 3 to 6 carbon atoms to the corresponding monoolefin in the vapor phase in the presence of oxygen and an improved oxidative dehydrogenation catalyst.

#Oxidative dehydrogenation of paraffinic hydrocarbons has been previously described in U.S. Pat. No. 3,697,614 wherein paraffins of from 2 to 12 carbon atoms are dehydrogenated to olefins with molecular oxygen in a molten alkali-metal hydroxide containing aluminum metal, and in solution, a transition metal oxyanion, preferably consisting of dichromate, molybdate, tungstate, manganate, permanganate, ferrate and metavanadate. Canadian Patent 912,051 describes a vapor phase process for the dyhydrogenation of paraffins and olefins with oxygen and halogen in the presence of a solid catalyst containing an alkali metal or an alkaline earth metal compound and a promoter which may be a transition metal of Groups 1 and 4 to 8, or a rare earth metal compound, particularly a halide or oxide of Zr, Ti, V, Cr, Mo, Mn, W, Fe, Co, Ni, Pd, Cu or Ag.

#In the production of olefins by the catalytic dehydrogenation of paraffins, it is of course desirable to obtain as high a yield of olefin as possible in a single passage of the paraffin through the dehydrogenation zone. It is also desirable to conduct the reaction under such conditions and in the presence of such catalysts wherein a minimum amount of coke is formed on the catalyst. The advantage of the present process resides in the use of certain catalysts which maintains a high olefin selectivity in the presence of oxygen and wherein the oxygen is used to consume the coke. The required frequency of catalyst regeneration with the catalysts of this process is thereby greatly reduced or virtually eliminated.

#12.86 g. of NH.sub.4 VO.sub.3 and 90.0 g. of Dispal M Al.sub.2 O.sub.3 were combined in 500 mls. of water. The mixture was evaporated to a thick yellow paste, dried at 115.degree. C. and calcined for 4 hours at 427.degree. C C. 4 hours at 593.degree. C.

#The catalyst was placed in a 20 cc standard fixed bed reactor constructed of 1/2 inch O.D. stainless steel tubing. A 1/8 inch O.D. thermocouple well, located axially, allowed for temperature profile measurement. The reactor and a pre-heat loop were immersed in a controlled temperature salt bath, and temperatures recorded were the maximum temperatures reached in the catalyst bed. The catalyst volume was 20 cc and the catalyst mesh size was 10 to 30 mesh per linear inch (U.S.A. Standard Sieve Series). The hydrocarbon feed employed in the examples was propane. A mixture of air and propane in a molar ratio of air to propane of 2.5 was passed over the catalyst at a temperature of 538.degree. C. and at a rate so that the contact time was equivalent to 3 seconds. The reactor effluent passed through an air-cooled condensation pot and a "Drierite" tube before sampling and metering. Hydrogen in the effluent stream was determined by gas chromatography, using a 3-foot molecular sieve column at ambient temperature with an argon carrier gas. Other components of the effluent were analyzed by the Fisher Partitioner, using the standard HMPA-molecular sieve column combination.

#The percent conversion obtained as shown in the tables represents the total propane converted to propylene and other products (total propane converted per pass); per pass conversion to propylene represents percent of propane converted to propylene in a single pass; and selectivity to propylene is the percent of propylene obtained based on the propane converted, all percents being calculated on a molar basis.