Phosgene Synthesis Catalysis: The Influence of Small Quantities of Bromine in the Chlorine Feedstream

The effect of relatively low concentrations of Br_2(g) in the Cl_2(g) feedstock for phosgene synthesis catalysis via the reaction of CO_(g) and Cl_2(g) over activated carbon (Donau Supersorbon K40) is explored. Under the stated reaction conditions and in the absence of a catalyst, BrCl_(g) forms from the reaction of Cl_2(g) and Br_2(g). Phosgene synthesis over the catalyst at 323 K is investigated for Br_2(g):Cl_2(g) molar flow ratios in the range 0-1.52% (0-15,190 ppm) and shows enhanced rates of phosgene production. Maximum phosgene production is observed at a Br_2(g):Cl_2(g) molar flow ratio of 1.52% (15,190 ppm), which corresponds to an enhancement in the rate of phosgene production of ∼227% with respect to the phosgene flow rate observed in the absence of an incident bromine co-feed. A reaction model is proposed to account for the experimental observables, where BrCl_(g) is highlighted as a significant intermediate. Specifically, enhanced rates of phosgene production are associated with the dissociative adsorption of BrCl_(g) that indirectly increases the pool of Cl_(ad) available for reaction.