Patent ID: 8080686

Claim:
A process for producing an unsaturated carboxylic acid or an unsaturated nitrile from the corresponding C 3 -C 4 alkane, said process comprising the steps of: A) contacting a C 3 -C 4 alkane and oxygen with an oxidative dehydrogenation catalyst in an exothermic reaction zone, wherein the upstream catalyst is catalytically active for the exothermic conversion of the C 3 -C 4 alkane to its corresponding C 3 -C 4 alkene, in the presence of oxygen; and B) exothermically converting a portion of the C 3 -C 4 alkane to the corresponding C 3 -C 4 alkene, in the exothermic reaction zone, to produce a heated mixed product gas which comprises the corresponding C 3 -C 4 alkene, unreacted C 2 -C 4 alkane, and heat produced by said exothermically converting step; C) contacting the heated mixed product gas and a weak oxidant comprising carbon dioxide with a endothermic dehydrogenation catalyst in an endothermic reaction zone, wherein the downstream catalyst is catalytically active for the endothermic conversion of the unreacted C 3 -C 4 alkane to the corresponding C 3 -C 4 alkene, in the presence of the weak oxidant comprising carbon dioxide; D) endothermically converting at least a portion of the unreacted C 3 -C 4 alkane to the corresponding C 3 -C 4 alkene, in the endothermic reaction zone, to produce a cumulative product stream which comprises at least the corresponding C 3 -C 4 alkene produced in each of the reaction zones; E) cooling and drying the cumulative product stream; F) separating C 3 -C 4 alkene, unreacted C 3 -C 4 alkane and unreacted carbon dioxide from the cooled cumulative product stream by absorption with a solvent to produce an organic-rich solvent stream comprising the separated C 3 C 4 alkene, unreacted C 3 -C 4 alkane and unreacted carbon dioxide, and a stream comprising non-absorbed constituents; G) separating the C 3 -C 4 alkene, unreacted C 3 -C 4 alkane and unreacted carbon dioxide from the organic-rich solvent stream to produce a recovery stream comprising recovered C 3 -C 4 alkene, C 3 -C 4 alkane and carbon dioxide; H) oxidizing the C 3 -C 4 alkene of the recovery stream to produce an oxidation product stream comprising the corresponding unsaturated carboxylic acid or nitrile, in the presence of at least one catalyst capable of facilitating the oxidizing reaction; I) separating the oxidation product stream to form an aqueous oxidation product stream comprising the corresponding unsaturated carboxylic acid or nitrile, and a gas stream comprising unreacted C 3 -C 4 alkane and unreacted carbon dioxide; J) drying the gas stream and separating the unreacted C 3 -C 4 alkane and unreacted carbon dioxide therefrom; and K) recycling the separated unreacted C 3 -C 4 alkane and unreacted carbon dioxide to the exothermic converting step.