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

The effect of relatively low concentrations of Br in the Cl feedstock for phosgene synthesis catalysis via the reaction of CO and Cl over activated carbon (Donau Supersorbon K40) is explored. Under the stated reaction conditions and in the absence of a catalyst, BrCl forms from the reaction of Cl and Br. Phosgene synthesis over the catalyst at 323 K is investigated for Br:Cl 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:Cl 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 is highlighted as a significant intermediate. Specifically, enhanced rates of phosgene production are associated with the dissociative adsorption of BrCl that indirectly increases the pool of Cl available for reaction.