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.
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.
Zhang referred to rare earth tertiary complex and double metal cyanide complex catalysts, saying the catalyst is key to polymerization efficiency and also to competitive pricing.
PPC compounds are typically 63.3 percent biodegraded within 95 days, meeting Australian six-month biodegradability standards, but not more stringent requirements. Zhang said "it depends on additives, chain length, degree of cross-linking, etc. A Chinese PPC producer has blended PPC with other biopolymers for shopping bags passing the U.S. requirement of 95 percent biodegradability within six months."
Zhang said industrial PPC products from China, Germany and the United States are dimensionally stable between minus 5° C and 50° C, have the same 85 percent transparency as PE and offer better moisture barrier properties than polylactic acid and PVC. But these amorphous-structure PPCs have glass transition temperature and mechanical strength lower than that of PLA.
He said that with PLA typically costing $3,000 per tonne, Chinese-made PPC has been offered at the same price. At some future time, Zhang expects the PLA price to fall to $1,400-$1,500, but PPC to drop to $950-$1,100 per metric ton.
To increase PPC molecular weight for a 40°C Tg PPC (compared 55-60°C for PLA), Zhang suggests end capping, use of 1-2 percent of bifunctional epoxide and a high amount of multifunctional epoxide, to encourage cross-linking. CSIRO has made fine-wood-flour-reinforced PPC compounds with such high-molecular-weight PPC, compounding it at 170°C, followed by compression molding.
PPC compounds have ductile failure, PLA ones brittle failure. Zhang said PPC can be foamed, extruded and compression molded. Further work will focus on blending and grafting of high-molecular-weight PPC, use of chain extension agents and cross-linking of low-molecular-weight PPC.
In a paper on sustainability of CO2 sources, Dietmar Wechsler of Wuppertal Institute advocated production of polymers from hydrogen derived from electrolysis, run by renewable energy and captured CO2 from fossil power plants, blast steel furnaces and cement kilns. Wechsler warned, however "you will not always have coal plants in the future." Conventional energy costs for electrolysis are still too high, so politicians should seek renewable energy storage solutions, Wechsler said.
Algae have 20-60 percent oil content and can produce 20,000-50,000 liters of oil per hectare per year, compared with annual palm oil production of 6,000 liters per hectare, Barbosa said. Algae grow in freshwater and seawater, using residual nutrients, and produce valuable co-products such as starch and proteins.
She said the global micro-algae market is below 10,000 tonnes per year. In the SPLASH project, algae allow in-situ extraction and isolation of sugars and hydrocarbons for further processing into polymers. These include innovative polyesters and copolyesters from sugars, as well as polyolefins.
Algae production in industrial plants uses blue-tinted transparent ultraviolet-resistant PVC pipes. Georg Fischer Piping systems received a SolVin innovation award at K 2010 for algae processing plants with such pipes. In 2011 the company acquired Harvel Enviroking in the U.S., a company that was also producing blue-tinted, UV-resistant, transparent pipes for algae production, now operating as Georg Fischer Harvel LLC in Easton, Pa.
In her presentation, Barbosa referred to polyethylene furanoate bottle development as a bio-based alternative to PET. Although not mentioned by Barbosa, Avantium Chemicals BV announced in May its intention — with Alpla Werke Alwin Lehner GmbH & Co KG, Coca-Cola Co. and Danone — to introduce a PEF bio-based PET bottle by 2016, using YXY catalyst technology to convert furan dicarboxylic acid to PEF through reaction with ethylene glycol.
Avantium said it was supplying its development partners with PEF made in a Geleen, Netherlands, pilot plant and planning a 50,000-tonne-per-year commercial plant, scheduled for 2016 start up to enable the full commercial launch of PEF bottles.
In a paper on CO2 as a substrate for a sustainable biotech industry, Klaas Hellingwert of Amsterdam University in the Netherlands, referred to various means of photosynthesis, including use of cyanobacteria. He recommended photosynthesis based on three-dimensional illumination with light-emitting-diode lights. Based on 70 percent LED efficiency and 50 percent photovoltaic efficiency, it would be possible to achieve conversion into fuel with 35 percent efficiency using 700 nanometer photons. Overall 10 percent efficiency with 0.1 MW per acre would mean "a field of solar panels on non-fertile soil would drive natural photosynthesis more efficiently than plant photosynthesis on its own."
Hellingwert said this solution does not compete with food supply or create a minerals problem and needs little water. But "designer organisms" should be developed for maximum efficiency.
Mathias Reckers of the LIKAT Leibniz institute for catalysis in Rostock, Germany, and I. Peckermann of Bayer Technical Services GmbH promoted carbon capture and utilization rather than carbon capture and storage, saying CO2 should be considered as an economical and abundant raw material rather than waste.
Jeanette Hilf of Johannes-Gutenberg University in Mainz, Germany, said use of CO2 as a direct building block for aliphatic PC "may eventually enable elimination of toxic reactants such as phosgene" by using appropriate catalysts for CO2 copolymerize with epoxides. Functionality distributed randomly at the polymer backbone could provide for tailored hydrophilic and hydrophobic properties, as well as biodegradability.