Chemistry Reference
In-Depth Information
Tab. 2.1
(continued)
Patent/Application
Number
Authors
Owner
Main Claims of the Patent
phosgene-forming reaction
is completed. The
phosgene leaving the
second reactor has a
residual chlorine content of
<
50 ppm. The heat
generated during phosgene
formation is used to
produce steam.
US 4231959
04/11/1980
EP 003530 A1
22/08/1979
R. Obrecht
Stauffer Chem.
Co., USA
Reaction of Cl
2
and excess
CO in the presence of an
activated carbon catalyst by
recovering unreacted CO
and recycling it to the
reaction zone
(contaminants:
10 wt%
each of N
2
and HCl; trace
amts.
<
1 wt% each of O
2
and CCl
4
, and
<
<
100 ppm
Cl
2
).
significant ozone depletion and global warming potentials. Therefore, there is an
interest in developing phosgene processes in which the amount of tetrachloro-
methane impurity is minimized.
In the production of polycarbonates from dihydroxylic compounds and phosgene,
tetrachloromethane also causes a yellowing of the material, which is disadvanta-
geous for optical applications of the polymers; a colorless product can only be
achieved when the phosgene has a CCl
4
content
150 ppm [44].
Thus, the development of a process for producing highly pure phosgene has
been one goal of research in this field. On the other hand, extensive industrial re-
search has been dedicated to the quest for new phosgene-free routes to poly-
carbonates. Diphenyl carbonate (DPhC) is used as the key reagent for incorporat-
ing the carbonate functionality into polycarbonates by the so-called non-phosgene
route. One of the di
culties associated with this process, however, is making
the DPhC. Currently, DPhC is made from dimethyl carbonate (DMC) by trans-
esterification with phenol (see, for example, the Enichem process). This reaction is
equilibrium-constrained and requires a fairly complicated processing scheme. The
DMC is in turn prepared by oxidative methylation of carbon monoxide with meth-
anol (as in the Enichem process) as a preferred alternative to obviate the need for
phosgene.
Several efforts have been made to lower the tetrachloromethane content of phos-
gene to below 150 ppm [44-48]. Examining the patent literature, the major tech-
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