In an embodiment, a method of producing a carbonate comprises reacting carbon monoxide and chlorine in a phosgene reactor in the presence of a catalyst to produce a first product comprising phosgene; wherein carbon tetrachloride is present in the first product in an amount of 0 to 10 ppm by volume based on the total volume of phosgene; and reacting a monohydroxy compound with the phosgene to produce the carbonate; wherein the phosgene reactor comprises a tube, a shell, and a space located between the tube and the shell; wherein the tube comprises one or more of a mini-tube section and a second tube section; a first concentric tube concentrically located in the shell; a twisted tube; an internal scaffold; and an external scaffold.

A process according to the invention is a process to separate an initial fluid stream comprising phosgene and hydrogen chloride in at least a first and a second fluid stream, said first fluid stream being a hydrogen chloride enriched and phosgene depleted gaseous stream, said second fluid stream being a hydrogen chloride depleted and phosgene enriched stream. The separation is performed by feeding said initial fluid stream to a membrane separation unit, said membrane separation unit separating said initial fluid stream in a first and a second fluid stream.