Published April 1997
This Review presents a preliminary evaluation of the Du Pont-DSM technology for producing caprolactam from butadiene. We have derived the design bases primarily from recent patents assigned to DSM; however, the design is based on SRIC's concept of the process and may differ from the manufacturer's scheme.
Our version of the process consists of four stages. In the first stage, butadiene, carbon monoxide, and methanol are reacted in the presence of a carbonylation catalyst consisting of a palladium salt and a bidentate phosphorus ligand. The reaction is carried out in the liquid phase with diphenyl ether as the solvent. The product consists mainly of methyl 3-pentenoate, which is isomerized to methyl 4-pentenoate in a reactor using a palladium-zeolite catalyst. The methyl 4-pentenoate is then hydroformylated using a rhodium compound and tris-(m-sulfonatophenyl) phosphine as the catalyst. The product, consisting of methylformylvalerate isomers, is separated from the unreacted methyl 4-pentenoate, with the latter recycled to the hydroformylation stage. Methyl 5-formylvalerate is reacted with hydrogen and anhydrous ammonia to give methyl 6-aminocaproate in a fixed-bed reactor using a ruthenium-alumina catalyst. The products, along with a recirculating xylene stream, are then sent to a multitublar reactor where they are converted to caprolactam and methanol. Methanol is recycled for reuse.
Our economics are based on a 300 million lb/yr (136,000 t/yr) plant. The process has the potential to produce caprolactam at a somewhat lower cost than existing commercial routes.