Interpretation of the mechanism of 3,3′-dichloro-4,4′-diamino diphenylmethane synthesis over HY zeolites

Abstract

Catalytic activities of zeolites HY, Hβ and HZSM-5 in the heterogeneous synthesis of 3,3′-dichloro-4,4′-diaminodiphenyl methane (MOCA) from o-chloroaniline and formaldehyde were pre-screened in an autoclave, and HY demonstrated better performance than others. Kinetic behaviors of MOCA synthesis over HY(11) were further investigated in a fixed bed continuous flow reactor, and under the conditions of the catalyst bed volume = 20 mL (8.14 g), n(o-chloroaniline) : n(HCHO) = 4 : 1, LHSV = 3.5 h⁻¹, 0.5 MPa and 443 K, HCHO conversion and MOCA selectivity steadily fluctuated at high levels of 90–92% and 75–77% during 16 h, respectively. Catalysts were characterized by BET, NH₃-TPD and XRD, products analyzed by HPLC, and reaction intermediates identified by LC/MS and ¹H NMR. The mechanism of MOCA synthesis has been interpreted in detail, which also suggested that deposition of basic intermediates on active sites and accumulation of polymeric by-products in pore channels of the catalyst could cause significant decay of HY(11) activity and selectivity under severe conditions. Supplementary tests on catalyst regeneration confirmed that the acidity and surface area of spent HY(11) could be well recovered after burning off the deposited by-products.