Phosgene catalyst deactivation

Phosgene synthesis from CO and Cl2 in a multitubular reactor (Fig. 19-225). The activated carbon catalyst is packed inside the tubes with water on the shell side. Reaction by-products include CCl4. The temperature profile in a tube (shown in the figure) is characterized by a hot spot. The position of the hot spot moves toward the exit of the reactor as the catalyst deactivates. 

A similar type of mechanism was also proposed for carbon tetrachloride oxidation, important steps in both mechanisms were the adsorption of the chlorinated hydrocarbon on the Br-nsted acid sites and dissociative adsorption of molecular oxygen on Co cation sites. The formation of CO and CO2 products were via parallel reaction pathways, with little or no CO2 formed by sequential CO oxidation. The formation of phosgene as a reaction intermediate has been identified during CCL, oxidation at space velocities above 15,000 h 4n a wet feed stream and as low as 2,400 h Mn a dry stream. The selectivity of phosgene also increased with time on line as the catalysts deactivated from 99% conversion to ca. 10% conversion after 22.5 h use. 

Another reaction of significance involving methanol is the direct synthesis of dimethyl carbonate (DMC) by carbonylation of methanol with CO which offers a potentially green chemical replacement for phosgene which is used for polymer production and other processes. The direct synthesis of dimethyl carbonate has been pursued over a variety of carbon supported cuprous chloride catalysts, but these catalysts deactivate due to loss of chloride and as such require reactivation by drying and contact with gaseous HCl. King et discovered that the chloride is not necessary to catal-... 

With respect to the synthesis from amines, C02 and alkyl halides, the synthesis of carbamates from amines, C02 and alcohols (Equation 6.10) is not only a phosgene-free, but also a halogen-free process. Moreover, water forms as the only reaction coproduct. Whilst these features make the route very attractive from the point of view of environmental sustainability, unfortunately the reaction suffers from both thermodynamic and kinetics limitations. Kinetic impediments make necessary the use of a suitable catalyst which, moreover, must be water-tolerant in order to avoid deactivation by cogenerated H20. Several strategies have been explored to overcome these restraints, based mainly on the use of alcohols in a dehydrated form (for instance, as ortho esters or ortho carbonates) [63], or on the use of dehydrating agents [64, 65]. 

The use of zeolite-based catalysts for VOC oxidation, in particular chlorinated VOCs, has been demonstrated at low temperatures, however, they deactivate relatively quickly and will therefore require regular regeneration, which may prove impractical for commercial operation. The very low selectivity towards CO2 and the formation of potentially hazard by-products such as phosgene also needs to be addressed. 

Method and device for preparing phosgene from diphosgene and/or triphosgene, by reaction on a catalyst comprising compounds with one or several N atoms with a pair of deactivated electrons. 

---