The vast majority of polycarbonate production relies on phosgene chemistry, notes Garo Vaporiciyan, a venture manager at Westhollow. The phosgene-based process is relatively energy intensive, involves dilute polymer solutions in chlorinated solvents and requires salt removal, he explains. So, there's been a trend to replace toxic phosgene with diphenyl carbonate (DPC). This avoids a safety risk in making the polymer and obviates solvents and washing salt out of the polymer. In addition, co-product phenol can be used to make DPC or bisphenolacetone.
While this approach eliminates phosgene from the polymer step, several companies use phosgene to make DPC. Non-phosgene-based DPC synthesis technology exists but such routes are cumbersome and energy intensive, contends Vaporiciyan, and so investment in phosgene-based DPC production continues.
Shell is developing a process for DPC that he terms a step change improvement in chemistry. In the route, carbon dioxide, phenol and propylene oxide react to form propylene glycol and DPC. Ethylene oxide can replace propylene to give ethylene gyclol instead of propylene glycol.
"…For seven years we've moved from paper to test tubes to pilot plants and now we're smelling commercialization within reach… all while still delivering on this target of making this key material for the polycarbonate industry cheaper with much lower CO2 footprint."
Shell's next step may be commercial production of DPC via the route, says Vaporiciyan.
Meanwhile, the company foresees significant opportunities to improve its OMEGA process. The first-generation version of the technology recently was commercialized. Korea's Lotte Petrochemicals started up a 400,000-metric-ton/year plant at Daesan, in May 2008, while Petro Rabigh, a Saudi Aramco/Sumitomo Chemical joint venture, began production in April 2009 at a 600,000-mt/yr unit at Rabigh. Shell expects to inaugurate a 750,000-mt/yr plant at its Eastern Petrochemicals Complex in Singapore by the end of this year.
The process relies on catalytic conversion of ethylene oxide (EO) to MEG, rather than conventional thermal conversion. It reacts EO and CO2 to form ethylene carbonate, which then reacts with water to yield MEG and CO2. The approach cuts capital investment by about 10%, consumes 20% less steam and produces 30% less wastewater, while obviating di- and tri-ethylene glycol purification, storage and handling, says Dave Van Kleeck, regional technology manager for EO and glycols.
An OMEGA pilot plant at Westhollow set to start up in 2010 will augment an existing pilot plant in Amsterdam and will enable evaluating continuous improvement concepts and their scaling to commercial units. It will permit complete piloting of all recycle streams while its MEG purification capabilities will allow assessing product quality as well as manufacture of drum quantities for customer testing, he says. The new pilot plant will provide more information on EO reactor operation, optimal process conditions, the fate of all impurities and suitable materials of construction, he adds.
The goal, explains Van Kleeck, is to boost EO selectivity to above 90% from today's 88%–90%, while lowering capital and operating expenses.