ESSEN, GERMANY — The decision of Bayer AG (Hall 6/A751-3) to use carbon dioxide as a feedstock is based on sustainability, industrial value creation, market acceptance and climate protection, but not replacement of fossil resources, according to Christoph Gürtle from Bayer's polyurethanes process research department.
Gürtle, who spoke Oct. 9 in Essen at the Nova Institute conference on CO2 as a feedstock for chemistry and polymers, said it is possible to incorporate as much as 43 percent CO2 in aliphatic and cyclic polycarbonate. Bayer is targeting PU as "an all-rounder among plastics."
Use of CO2-based polyol was developed in a joint CAT catalytic center laboratory set up by Bayer and RWTH Aachen University in Aachen, Germany, in 2009, as a step toward implementation in 2010 of a "dream production" project. Bayer opened a CO2-based polyol pilot plant in 2011 and is planning a production plant, scheduled to start up in 2015 in Dormagen, Germany.
The plant should produce "reasonable amounts for industry, several thousand metric tons," Gürtle said. "This is a new chemical process, involving going from a mini plant to several thousand tonnes just to make sure everything is working properly." Gürtle sees great potential for CO2-based polyols in flexible PU foams, because they account for 36 percent of the 2.8 million-metric-ton PU slabstock market.
He described CO2-polyol development as a stage in continuous innovation in PU flexible foams. Gürtle said it took Bayer scientists 40 years to find a sufficiently efficient catalyst to enable production of polyol from CO2.
An RWE AG electricity power station near Cologne supplies scrubbed CO2 flue gas to Bayer Technology Services GmbH in Leverkusen, Germany, which is responsible for CO2 development and conversion. The gas from RWE "is not ideal for direct use for CO2-based polyols used in mattresses, since sulfur and nitrogen have to be removed," Gürtle said. Bayer MaterialScience AG uses the cleaned CO2 to make CO2-polyol, having moved from batches to a continuous process in early 2013. The polyol produced is evaluated in foam mattress trials on Bayer's PU slabstock pilot line.
Gürtle says carbonate groups in CO2 polyols contribute to increased viscosity. This depends on functionality and CO2 content. CO2-polyol based PU foam "looks as good as today's material, maybe even better," Gürtle says, "and it has an intriguing point: heat of combustion is a bit lower."
PU slabstock foam produced from CO2-based polyol shows thermal stability matching PU from conventional polyols. Onset temperature and mass loss are identical and there is no thermal sensitivity difference. Gürtle concludes that the CO2 is fixed inside the PU backbone.
"There is systematic reduction in heat combustion with increasing CO2 content in flexible foam made with CO2-based polyol," Gürtle said.
Niklas van der Assen of RWTH Aachen University continued the presentation, showing life-cycle analysis results based on CO2 capture from lignite power station flue gas, through to production with epoxides into polyol, with the resulting CO2-polyol reacted with isocyanate to produce PU foam.
Production using 1 kilogram of CO2 in conventional polyol involves 3.59 kg of equivalent CO2 emissions; a CO2-polyol with 20 percent CO2 input is just 2.99 kg. For the 0.6 kg reduction, raw material replacement accounts for 0.49 kg, using captured CO2 for 0.14 kg, partly offset by 0.03 kg higher emission due to CO2 transport and the reaction starter used for the reaction to polyol. Polyol with 30 percent CO2 had 2.64 kg of equivalent CO2 emissions.
Van der Assen said using captured CO2 and substituting epoxides results in climate benefits. "The more CO2 used, the better," he said. There also are resource efficiency and other environmental benefits. "It works, very good foam properties are obtained, along with an improved CO2 footprint," van der Assen said.
Major chemical plants making their own ammonia and ethylene oxide produce CO2 that could be supplied via pipeline for CO2-based polyol, van der Assen said, and Gürtle added that steam methane reforming used to produce hydrogen also produces CO2 as a byproduct.
Xiaoqing Zhang of the polymer engineering department at CSIRO Commonwealth Scientific and Industrial Research Organization in Melbourne, Australia, presented opportunities in CO2-based biodegradable polymer materials, focusing on polypropylene carbonate with up to 48 percent CO2 content, as a copolymer of carbon dioxide and propylene oxide.