Phosgene-free process cuts polycarbonate costs
8 Sep 2003
Korean chemicals manufacturer LG Chem has developed a new process for making polycarbonate, the plastic used to make CDs and DVDs, in less than half the time and for much lower investment than conventional processes.
Moreover, the process avoids the use of phosgene, the poisonous gas which is used in conventional polycarbonate manufacture.
Polycarbonate is exceptionally tough, with good heat and impact resistance. It can be made extremely clear, and is a very stable carrier of colorants. Its market has expanded rapidly since the 1980s. However, the interfacial polymerisation process used to make it is complicated by its reliance on phosgene.
The process itself is not complex, with polymerisation taking place at the interface between bisphenol-A and phosgene, but the safety and environmental equipment needed to cope with the presence of phosgene makes it costly and hazardous. A safer process exists, but this makes a lower molecular weight polymer than the interfacial process, and expensive high-temperature, high-vacuum equipment is needed to convert this into a high-MW product.
To overcome these problems, LG has developed a condensation process which, like the existing phosgene-free process, uses bisphenol A and diphenyl carbonate as its starting materials. In a two-stage process, the molten starting materials are first trans-esterified to produce a high-quality pre-polymer. The polymerisation process itself is carried out in the solid state in a newly-designed reactor vessel.
LG's chief technology officer and president, Jong-Kee Yeo, claims that the new plants will cost some 70 per cent less than conventional phosgene-based units. 'For instance, the investment for a plant of 60 000tpa can be significantly reduced to less than $100million from $250million,' he says.
Moreover, he says, the new process 'can reduce the total production time by more than half and has enhanced the quality of the resin itself in terms of transparency and colour.' LG intends to offer the technology for licensing overseas, and is also considering seeking a joint venture with a foreign partner.
