Operational parameters relevant to the examination of phosgene synthesis catalysis

Abstract

Large-scale phosgene synthesis, as encountered within isocyanate manufacturing chains, is typically performed by the reaction of carbon monoxide and dichlorine over an activated carbon catalyst. A modified micro-reactor arrangement is described that is used to evaluate the effectiveness of different catalyst formulations. The approach adopted is to utilise diluted gas streams and relatively low operational temperatures (300–500 K); arrangements that afford good temperature control of the exothermic reaction. The article addresses the operational constraints concerning gas handling procedures that ensure avoidance of gas mixtures that fall within explosive limits. A methodology to determine mass balance profiles for the hazardous reaction system is additionally described. Following on from previous studies that exclusively investigated the suitability of a particular activated carbon formulation as a phosgene synthesis catalyst, this study concentrates on Norit RX3 Extra as a generic activated carbon that finds wide application in industrial applications. Mass transport issues are assessed and indicate the reaction system to be operating free from diffusion limitations, enabling kinetic measurements to be undertaken. An activation energy for phosgene synthesis of 43.0 ± 1.1 kJ mol⁻¹ is determined, consistent with the reaction being under chemical control.