Sustainable Polyurethanes and the Bio Economy? Sustainability has become a key concern in polyurethane industry. Reducing the environmental impact of polymers by replacing fossil derived carbon, using more environmental friendly processes and reducing and recycling the carbon used either directly or indirectly is a corporate goal of many producers.
The use of biomass to produce value added chemicals for polymer synthesis is a major focus of the effort to replace fossil carbon. The theory is that these products can lead the way in developing the bio-economy until it reaches the scale where fuel production becomes more economical. It is believed that profits from the value-added products can be used to fund future construction and justify infrastructure improvements.
The development of polyurethanes made using renewable biomass carbon from natural oils, sugars or waste carbon dioxide provides an excellent example of the replacement of petroleum derived products. The question is if these new materials can play an important economic role and impact the bio-economy and environment as a whole?
Sustainable polyurethanes are a fast growing segment of the polymer market and represent a success story for the investment by government and industry in products with a lower carbon footprint. They are the result of 100s of millions of dollars of research and development efforts. Their success is clearly tied to their lower costs and equivalent or better performance compared to petroleum derived products. This makes them attractive even without the bonus of being able to be marketed as a “green” alternative.
Polyurethanes were invented by Otto Bayer in the 1930s. They are formed by reacting a polyol (a compound with more than two reactive hydroxyl groups per molecule) with a diisocyanate or a polymeric isocyanate in the presence of suitable catalysts and additives. Because a variety of diisocyanates and a wide range of polyols can be used to produce polyurethane, a broad spectrum of materials can be produced to meet the needs of specific applications. They are used in products ranging from coatings and adhesives to shoe soles, mattresses and foam insulation. Global demand for polyurethane products approximated 20 million tons in 2014. Total revenues from the market are expected to reach $54.2 billion by 2019. The renewable polyols have been available for about a decade, and market for these and other renewable polyurethanes is anticipated to grow to $10.3 billion in 2023.
The wide variety of polyurethane applications provides many appropriate size niche markets for introduction of new products. It is possible for modest size first generation plants to provide sufficient product to be considered a trusted supplier by end users.
Polyols can be made from a number of biomass derived materials including natural oils like: castor, palm and soy oil; and sugars like: adipic and succinic acids, and even captured waste CO2. Materials with a performance rivaling or exceeding petroleum-based products are available Sustainable polyols are currently capable of replacing 33-55% of the petrochemical in polyurethanes. Several companies are blending the natural oils with recycled materials to produce materials with significantly higher “green” carbon contents. Substituting biomass derived cyanates allows the production of 100% renewable polymers.
What is the impact on environmental carbon of renewable polyurethane? In 2014, 12 million tons of polyurethanes were produced worldwide as compared to 4,700 million tons of crude oil. A complete shift to renewable polyols would have less than 0.3% impact on crude oil use. Clearly, the major drivers for moving to biomass derived materials has to be their low cost and performance; although government regulation and consumer preference are playing an increasing role for some applications like automobile interiors and footwear.
Polyols from Natural Oils.
Renewable polyols made from natural oils were developed in the early 2000s and began to be offered commercially soon after. The global natural oil polyols (NOP) market was valued at 5.03 billion USD in 2015. There are several large suppliers and specialty companies marketing natural oil based renewable polyols listed in adjoining table. Natural oil polyols are attractive in agricultural economies where oil supplies are limited. Commercial polyols have been made from sawgrass oil, soybean oil, castor, rapeseed oil, palm oil (kernel and mesocarp), and coconut oil. Some formulations were found to have a price advantage over petroleum derived polyols particularly during a period of high oil prices. However, they are price competitive even in at the current price levels of $45 per gallon. They have a significant advantage in that they already contain oxygen and do not require oxygen addition like petroleum products. The chemistry used to make them from the base oils is not complex and does not require large capital investments.
The characteristics of natural oil polyols can be varied by the selection of appropriate base oils. It is also possible to graft additional groups on to the base oils. Differences and modifications in the process conditions and methods can also change the properties of materials made with the same base oil. A significant effort has been made formulating products for specific applications. This effort needs to considered a significant barrier to the adoption of any non-drop-in replacement for existing products. However, the results of these efforts has been products with some superior properties including less odor, improved durability, more controlled hydrophobicity, foam density and others.
The use of natural oils for polyols raises some concerns among sustainability advocates because of the competition for land use with food and protected natural areas. The argument made for natural oils is that the total amount used for polyurethane is a small fraction of the worldwide production, and that this use provides higher value for producers than other current uses.
The success of the natural oils in the marketplace provides some guidance for how to gain acceptance for biomass based products. At the time of their introduction oil prices were soaring and large companies were looking for some stability in their raw material costs. There was already an infrastructure for harvesting and extracting the oil at scales significant larger than those required for the polyurethane application. There were significant investments by large established commercial companies and natural oil suppliers which funded the required application development and capital funding for required plants.
Polyurethanes from Sugars
Approximately 250,000 tons of synthetic adipic acid was used to prepare polyurethanes in 2014. However, the main use of Apidic acid is to produce nylon. Apidic acid production has a high environmental cost and alternative routes to this material have been desired for a long time.
A number of companies including Verdezyne, BioAmber, Celexion, and Genomatica have been developing fermentation based processes for the production of adipic acid. The complexity and environmental costs of the chemical route to adipic acid through cyclohexane oxidation provides a significant margin that can justify the cost of fermentation.
Rennovia is commercializing a process that starts with C-6 sugars and converts them to adipic acid and other compounds via chemical methods. The process is reported to be economical using non cellulosic market priced sugars and is likely lower in cost than fermentation processes. They expect to start production in 2018.
Carbion, Myriant and Reverdia are developing bio mass derived succinic acid. Recent work has shown that polyurethanes prepared with succinic acid have some attractive properties when compared with those made with adipic acid and other polyols. It is possible that succinic acid based polyurethanes could compete with adipic acid materials. However, there of other markets for the succinic acid and polyurethane use will not be major driver for developing the biosynthetic route to the chemical.
The use of cellulosic sugars is a key enabler of these processes by lowering the raw material costs. The use of cellulosic sugar would also open up environmental motivated financing and regulators who are concerned with the use of food products as petroleum replacements.
Polyurethanes from CO2
The continued increase in the use of carbon dioxide capture technology has created a new source of concentrated waste streams that can be tapped if methods are developed for using the captured wastes. Preparing polyols from CO2 is one way of using this resource. These new polyols may more economical than those made from natural oils due to the use of a lower cost feedstock.
The development of new catalysts has facilitated the reaction CO2 and epoxides to form polycarbonates. These polycarbonates can be used to form polyurethane. Using CO2 to manufacture polyurethane can partially replace raw material. It also captures the CO2 in a nonvolatile form.
Covestro (formally Bayer Material Science) announced that a commercial plant is now producing polyurethanes from CO2 and propylene oxide using a proprietary Zn catalyst. The plant with a 5000 ton per year capacity started production in 2016. The Cardyon® polymer line is reported to have lower production costs than conventional polyurethanes.
Similarly, Novomer, a startup company, has developed catalysts for activating a CO2 to polymer technology. They recently sold their polyol for polyurethane technology, Converge®, to Saudi Aramco for $100 million. Aramco is building a commercial plant that should start production by 2018. Production costs are again estimated to be below that of convention polyols. The plant is being located close to a newly started carbon dioxide capture unit.
Both the Cardyon® and the Converge® product lines have been prepared in a number of different forms and shown to be effective for use a wide variety of products. Using CO2 avoids the issue of competition with food production. Life cycle studies have shown that their adoption leads to a real decrease in the polyurethane carbon footprint. Both technologies are seeking certifications that will allow them be eligible for environmental credits in the future.
Other Biomass Derived Polyurethane Components
There are a number of other biomass derived polyurethane components being marketed. Dupont is marketing Susterra® Propanediol for polyurethane applications. Covestro is developing the first biobased disocynate, DESMODUR®, made by chemical modification of the fermentation produced pentamethylene diamine. Cabolite is marketing aromatic polyols derived from cashew shells.
Impact on the Bio-Economy & the Environment
Production of polyols from biomass provides an example of how to gain acceptance of biomass derived materials. It was critical to demonstrate lower costs to drive the development of the technologies required for production and applications. Good performance in a variety of applications was demonstrated by partnerships between producers, formulators, and end users. The quantities of materials required for specific applications is modest and can be easily produced in smaller first generation plants. The cache of being environmental friendly allowed them to gain government funding during the initial research and development phase.
The volume of petroleum carbon that can potentially be replaced by renewable polyurethanes is less than 1% of the total worldwide carbon emissions. The positive environmental impact was used to garner initial interest but almost certainly it was not enough to push the technology into commercialization, however it is a useful marketing tool.
Recycling of the polyurethanes is still considered a viable alternative to meeting future environmental regulations and has an advantage of reducing the volume of wastes. The effect of the use of the biomass derived polyols on this recycling effort still needs to be determined. This same problem has been a concern for other biomass derived plastics.
While sustainable polyols would contribute to the overall growth of biomass use and therefore, will help support infrastructure development, their contribution will be small. The producers acknowledge that the environmental impact is small but correctly mention that every little bit helps. Their main benefit will be to provide a net profit to their producers which is why they will be successful. Given this, the investment of public funds needs to be justified on the same economic basis.
About the Author
Dr. Lorenz Bauer (deceased) was a member of Lee Enterprises Consulting, the world’s premier bioeconomy consulting group, with more than 150 consultants and experts worldwide who collaborate on interdisciplinary projects, including the types discussed in this article when first published in 2017. The opinions expressed herein are those of the author, and do not necessarily express the views of Lee Enterprises Consulting. Dr. Bauer had a doctorate from Washington University. He was one of the catalysis, oil refining and biomass conversion experts, an inventor with over 20 patents, and whose projects ranged from food additives, off gas treatment, upgrading unconventional feeds and waste recycling. Most recently, he was working of developing renewable chemicals, the fast pyrolysis of biomass and upgrading products to fuels and chemicals. RIP Larry. See also: Polyurethane Expert;