Farmers like biodiesel. It's a motor fuel made partly from soybeans or other vegetable oils and it reduces the demand for imported oil. But there's a nearly worthless byproduct of biodiesel production, crude glycerin, which is a financial and environmental liability for the biodiesel industry. Crude glycerin differs significantly from pure glycerin in composition due to the presence of various impurities. Crude glycerin contains 30–40% glycerin (Ooi, et al. 2001). At present, crude glycerin is a low-value byproduct (approximately $0.08/lb) because it contains impurities such as methanol, soap, fatty acid methyl esters, and salts. Currently, it is not economically viable to purify crude glycerin to technical grade glycerin for further applications, and crude glycerin has few feasible uses in its unpurified form.
As worldwide annual output of biodiesel continues to grow, the need for technology to develop commercial applications for crude glycerin has become more pressing. Previous research has concentrated on using both chemical and biological processes to convert crude glycerin to value-added products (Pachauri and He, 2006; Johnson and Taconi, 2007). However, these technologies only use the glycerin fraction (30–40% of the crude glycerin) and impurities can inhibit the microorganisms used in the biological conversion process. Few of these technologies have been proven to be economically viable for further commercialization. Fortunately, new research has demonstrated the potential for using crude glycerin as an alternative to petroleum for production of polyurethane (PU) foam.
Petroleum-based Polyols and PU Foams
Polyurethanes are some of the most versatile polymers in the world because of the flexibility of their structural design. Flexible and rigid foams are two of the most common applications of PU, while coatings, sealants, elastomers, and adhesives are other significant applications. Some of the leading uses of PU foam are found in the automotive, construction, and insulation industries.
Most people are familiar with PU foam as an insulating material. However, flexible and rigid PU foams are also commonly used in the automotive and construction industries. Polyurethanes have become some of the most versatile polymers in the world since they were first developed in 1937. The global market in 2005 was estimated to be a $30–35 billion industry, with approximately 13.7 million tons of total production. North America dominated this production with 3.7 million tons (Petrovic, 2008). This represents a huge potential market for an agriculture-based replacement.
The current PU industry is heavily petroleum dependent because the two major raw materials (polyols and isocyanates) are largely petroleum derived as illustrated in Figure 2. Political instability in the Middle East and growing worldwide demand are causing the price of petroleum to climb. Not only does this affect gasoline prices, but PU products also increase in price. From 2006 to 2008, petroleum-derived polyols for flexible and rigid foam applications increased about 18% and 25%, respectively (Omni 2010).
Figure 2. Production of petroleum-based polyols from crude oil and natural gas (Omni, 2010).
Natural Oil and Biomass-based Polyols and PU Foams
Natural oils, including oil from soybeans, have favorable characteristics when processed into polyols. Currently, polyols from natural oil are commercially available and have prices around $1.25–1.35/lb, which are close to the prices of petroleum-based polyols at $0.95–1.45/lb (Omni, 2010). One challenge with natural oil-based polyols is that high-volume production of natural oil-based polyols would inevitably compete with food supplies. Therefore, despite the extensive research and commercialization efforts relating to development of bio-based polyols or "biopolyols" from natural oil alternatives, petroleum-based polyols still dominate the global polyol market.
Biopolyol production from lignocellulosic biomass has also been studied for more than a decade. Lignocellulosic biomass, such as wood and crop residues, is composed primarily of cellulose, hemicellulose, and lignin. It is renewable, abundantly available at low prices, and does not compete directly with food supplies. The conversion of lignocellulosic biomass to biopolyols is typically achieved by a liquefaction process, during which biopolyols are produced by a series of solvolysis and hydroxyalkylation reactions. Wheat straw (Chen and Lu, 2009), distiller's grain (Yu et al., 2008), and cornstalks (Yan et al., 2008) have been studied for biopolyol and PU foam production. The produced biopolyols and PU foams showed comparable material properties with those produced from petroleum sources. However, this process requires a high-volume of petroleum-based solvents, such as ethylene glycol and ethylene carbonate, with approximately 4 pounds of solvent required for every pound of lignocellulosic biomass (Hassan and Shukry, 2008). This considerably increases processing costs and, consequently, hinders future commercialization efforts. A compelling substitute to natural oil and petroleum-based feedstocks is crude glycerin.
Crude Glycerin-based Polyols and PU Foams
Yebo Li and his colleagues at The Ohio State University–OARDC in Wooster have developed a one-pot catalytic process that produces a biopolyol from crude glycerin and lignocellulosic biomass (patent pending) (Figure 3). In this process, the reactor is loaded with crude glycerin, biomass, and a catalyst and is heated at atmospheric pressure. During the reaction process, methanol, which can be reused for biodiesel production, is recovered with a distillation system at temperatures of around 100°C. After the reactor reaches the designated temperature, the crude glycerin (both glycerin and impurities) reacts with biomass in the presence of the catalyst to create the biopolyol. After the reaction, the crude biopolyol is pumped through a filter to remove impurities and is ready to be shipped to end-users for the production of rigid and flexible PU foams and products. The biopolyol yield ranges from 80 to 95% percent. The exact yield is affected by the methanol content of crude glycerin and the ratio of biomass to crude glycerin.
Figure 3. Process for producing biodiesel, plus polyols from the crude glycerin by-product.
This Ohio State University technology has been licensed to Poly Green Technologies, LLC, for commercial production of biopolyols from crude glycerin. Poly Green's current biopolyol product can be used to make rigid foam or blended with petroleum-based polyols to produce flexible foam.
Factors to Be Considered
Figure 4. Polyurethane samples produced from crude glycerin and lignocellulosic biomass.
Because crude glycerin is a byproduct of the biodiesel production process, its composition varies substantially based on the feedstocks and processes that are used to produce the biodiesel. The inconsistent composition of crude glycerin makes it difficult to produce biopolyols with consistent quality and performance, creating a major technical barrier for commercialization. By working to overcome the inconsistency of crude glycerin-based biopolyols, Poly Green and its collaborators have the potential to displace the petroleum domination of the PU market with a sustainable, environmentally friendly bio-based polymer material.
The use of crude glycerin in the production of biopolyols will have two benefits for biodiesel producers: eliminating disposal fees and creating a new revenue stream. For an industry with very low profit margins, this reduction in cost and increase in revenue will make the biodiesel industry more viable.
Chen, F., & Lu, Z. (2008). Liquefaction of wheat straw and preparation of rigid polyurethane foam from the liquefaction products. J. Appl. Polym. Sci., 111(1), 508–516.
Hassan, E. M., & Shukry, N. (2008). Polyhydric alcohol liquefaction of some lignocellulosic agricultural residues. Ind. Crop Prod., 27(1), 33–38.
Johnson, D. T., & Taconi, K. A. (2007). The glycerin glut: Options for the value-added conversion of crude glycerol resulting from biodiesel production. Environ. Prog., 26(4), 338–348.
Li, Y., Zhou, Y., & Lubguban, A. (2009). Methods for producing polyols and polyurethanes. Ohio State University Research Foundation.
Omni Tech International. (2010). A survey of recent chemical price trends: The potential impact of rising petrochemical prices on soy use for industrial applications. United Soybean Board.
Ooi, T. L., Yong, K. C., Dzulkefly, K., Wangyunus, W. M. Z., & Hazimah, A. H. (2001). Crude glycerine recovery from glycerol residue waste from a palm kernel oil methyl ester plant. J. Oil Palm Res., 13(2), 16–22.
Pachauri, N., & He, B. (2006). Value-added utilization of crude glycerol from biodiesel production: A survey of current research activities. ASABE.
Petrovic, Z. (2008). Polyurethanes from Vegetable Oils. Polym. Rev., 48, 109–155.
Yan, Y., Pang, H., Yang, X., Zhang, R., and Liao, B. (2008). Preparation and characterization of water-blown polyurethane foams from liquefied cornstalk polyol. J. Appl. Polym. Sci., 110, 1099–1111.
Yu, F., Le, Z., Chen, P., Liu, Y., Lin, X., & Ruan, R. (2007). Atmospheric pressure liquefaction of dried distillers grains (DDG) and making polyurethane foams from liquefied DDG. Appl. Biochem. Biotechnol., 148, 235–243.
Reviewed by Mary Wicks, Dr. Harold Keener, and Lindsay Kilpatrick.
This fact sheet is based on "Development of Polyurethane Foam and Its Potential within the Biofuels Market" by Yebo Li, published in Biofuels, July 2011.