Abstract
The effect of relatively low concentrations of Br2(g) in the Cl2(g) feedstock for phosgene synthesis catalysis via the reaction of CO(g) and Cl2(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 Cl2(g) and Br2(g). Phosgene synthesis over the catalyst at 323 K is investigated for Br2(g):Cl2(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 Br2(g):Cl2(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.
Highlights
This communication is rooted in the production of phosgene for use in large-scale isocyanate production facilities, where the phosgene is produced in the vapor phase by combining carbon monoxide and dichlorine over an activated carbon catalyst, eq 1
Industrially led research has resulted in process operational practices that have resulted in favorable outcomes in terms of product quality, little is known about how small quantities of bromine in the chlorine feedstream affect the surface chemistry that controls the actual catalysis of phosgene production
A series of UV−visible spectra for individual Cl2 and Br2 feeds and Cl2/Br2 mixed feeds that were passed over quartz powder located in the reactor bypass line at 295 K
Summary
This communication is rooted in the production of phosgene for use in large-scale isocyanate production facilities, where the phosgene is produced in the vapor phase by combining carbon monoxide and dichlorine over an activated carbon catalyst, eq 1. The present article considers a contemporary issue experienced in the operation of large-scale phosgene production units when Cl2 has been generated from NaCl that has been isolated from sea water or has been mined In this case, small quantities of dibromine or bromochlorine impurity may be present in the dichlorine feedstream that could affect the catalytic performance. Industrially led research has resulted in process operational practices that have resulted in favorable outcomes in terms of product quality, little is known about how small quantities of bromine in the chlorine feedstream affect the surface chemistry that controls the actual catalysis of phosgene production Against this background, it is opportune to apply the recently acquired awareness of phosgene synthesis catalysis over a specified substrate (Donau Supersorbon K40)[3−5] to determine how relatively small quantities of dibromine or bromochlorine could affect aspects of the phosgene synthesis process. The article links an established industrial problem to specific issues within the surface chemistry of phosgene synthesis catalysis that, results in modified process kinetics
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