Water Removal in Direct Diphenyl Carbonate Process

Water Removal In Direct Diphenyl Carbonate Process 

As already mentioned, water removal in the oxidative carbonylation of phenols to make diaryl carbonates is a necessary process since it greatly enhances the productivity of the reaction and thus reduces reactor cost per unit mass of product. The use of 3 or 4 A molecular sieves, effectively removing water in laboratory-scale runs [8d], is impractical at an industrial scale. 

The use of an inert stripping agent such as pentane vapor for the removal of water from a direct DPC process was claimed [85]. Pentane was condensed to separate from the water stripping step and recycled back to the water stripping step [85]. 

About 2.5 times improvement in DPC yield for a batch process catalyzed by PdBr2 in combination with Mn(acac)2, TBAB, and NaOPh was achieved if the generated water was removed continuously from a partial flow of the reaction under reduced pressure at isothermal conditions, and the dehydrated partial flow is returned to the reaction [86]. It was proposed to perform water removal during continuous process by removing a portion of liquid stream from a reactor to a flash vessel subjecting to reduced pressure and returning a portion of dried liquid stream to the reactor [87]. The DPC yield obtained with this procedure was comparable with that obtained with the use of 3 A molecular sieves as a desiccant. 

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