Metal modified fluorapatite (metal = Co, Ni, Cu, Zn): a new type of efficient catalyst for methyl N-phenyl carbamate direct synthesis from urea, methanol and aniline

Abstract

The application of metal modified fluorapatite (metal-FAP, MCa9(PO4)6F2, M = Ca, Co, Ni, Cu, Zn) as highly efficient catalysts for the synthesis of an important intermediate methyl N-phenyl carbamate (MPC) for non-phosgene isocyanate production, from urea, methanol and aniline is reported firstly. The catalysts metal-FAP powders were synthesized by co-precipitation method and their properties were identified by ICP-AES, XRD, BET, TEM, EDS and NH3-TPD. Zn modified fluorapatite (ZnCa9(PO4)6F2, ZnFAP) with the strongest acidity among the metal-FAP (metal = Ca, Co, Ni, Cu, Zn) catalysts exhibited the highest catalytic activity to MPC formation. The effects of reaction temperature, time, molar ratio of raw materials, dosage of catalyst and reusability of the catalyst on the process were investigated. The optimal reaction parameters were determined as follows: aniline 20 mmol, the molar ratio urea/aniline 5:1, the molar ratio of methanol to aniline 20:1, ZnFAP 8.0 mmol, 6 h, 180 °C, with 94.4% aniline conversion and 75.8% selectivity to methyl N-phenyl carbamate. ZnFAP catalyst showed little catalytic activity loss after five times repeated use. The reaction mechanism is proposed and discussed.