Method for inhibiting polymerization during the recovery and purification of unsaturated mononitriles
View Patent ↗Economical processes are disclosed for recovery and refining of valuable nitrogen-containing organic compounds formed by catalytic oxidation of least one feed compound selected from the group consisting of propane, propylene, isobutane and isobutylene in the presence of ammonia to produce a gaseous. Processes of the invention include quenching the gaseous reactor effluent with an aqueous quench liquid; forming an aqueous solution comprising the corresponding unsaturated mononitrile, hydrogen cyanide and other organic co-products; and using an integrated sequence of distillations and phase separations to recover for recycle of a useful aqueous liquid, and obtain the desired nitrogen-containing products. According to the invention aqueous solutions are fractionated in an integrated system of multi-stage columns while an effective polymerization inhibiting amount of at least one member of a preselected class of p-phenylenediamine compounds is maintained therein.
1. A process for manufacturing an unsaturated mononitrile which process comprises:
reacting at least one feed compound selected from the group consisting of propane, propylene, isobutane and isobutylene, with ammonia and a source comprising dioxygen in the presence of a catalyst in a reactor to produce a reactor effluent containing the corresponding unsaturated mononitrile;
transferring the reactor effluent containing the unsaturated mononitrile to a quench/absorption section wherein the reactor effluent containing the unsaturated mononitrile is contacted with at least a first aqueous stream to cool the reactor effluent, and thereafter the cool effluent is contacted with at least a second aqueous stream in an absorption column to separate and recover the unsaturated mononitrile in an aqueous solution;
transferring the aqueous solution containing the unsaturated mononitrile to a recovery and purification section where the unsaturated mononitrile is recovered and purified in at least a first distillation column and a second distillation column; and
maintaining within one or more of the distillation columns an effective polymerization inhibiting amount of at least one phenylenediamine compound represented by the formula:
wherein Ph is a phenylene group, and R 1 and R 2 are the same or different and are hydroxyl free organic moieties having about 2 to about 10 carbon atoms with the proviso that neither R 1 nor R 2 is a phenyl group.
2. The process according to claim 1 wherein the effective polymerization inhibiting amount is no less than about 5 parts per million parts of unsaturated mononitrile present in the aqueous solution.
3. The process according to claim 2 which further comprises admixing a liquid source of the phenylenediamine compound with an aqueous solution containing the unsaturated mononitrile which is being transferred into the first distillation column and/or second distillation column.
4. The process according to claim 1 wherein the unsaturated mononitrile is acrylonitrile or methacrylonitrile, and the feed compound is a corresponding olefin selected from the group consisting of propylene and isobutylene.
5. The process according to claim 1 wherein the organic moieties R 1 and R 2 are members of a group consisting of ethyl, propyl, butyl, phenyl, hexyl, heptyl, octyl, nonyl and decyl straight and branched-chain hydrocarbon groups.
6. The process according to claim 1 wherein the phenylenediamine compound is selected from of a group consisting of N,N′-dialkyl-p-phenylenediamine compounds.
7. The process according to claim 1 wherein the unsaturated mononitrile is acrylonitrile, and the feed compounds are members of a group consisting of propane and propylene.
8. The process according to claim 7 wherein the phenylenediamine compound is selected from a group consisting of N,N′-di-sec-propyl-p-phenylenediamine, N,N′-di-sec-butyl-p-phenylenediamine, N,N′-di-isobutyl-p-phenylenediamine, and N,N′-di-tert-butyl-p-phenylenediamine.
9. The process according to claim 8 wherein the compound is N,N′-di-sec-butyl-p-phenylenediamine.