Biomethanol Production from Forage Grasses, Trees, and Crop Residues

Hitoshi Nakagawa et al.*

Biomass Research and Development Center National Agriculture and Food Research Organization (NARO)

Japan

1. Introduction

About 12 billion tons of fossil fuels (oil equivalent) are consumed in the world in 2007 (OECD 2010) and these fuels influence the production of acid rain, photochemical smog, and the increase of atmospheric carbon dioxide (CO2). Researchers warn that the rise in the earth’s temperature resulting from increasing atmospheric concentrations of CO2 is likely to be at least 1°C and perhaps as much as 4°C if the CO2 concentration doubles from pre­industrial levels during the 21st century (Brown et al. 2000). A second global problem is the likely depletion of fossil fuels in several decades even though new oil resources are being discovered. To address these issues, we need to identify alternative fuel resources.

Stabilizing the earth’s climate depends on reducing carbon emissions by shifting from fossil fuels to the direct or indirect use of solar energy. Among the latter, utilization of biofuel is most beneficial because; 1) the solar energy that produces biomass is the final sustainable energy resource; 2) it reduces atmospheric CO2 through photosynthesis and carbon sequestration; 3) even though combustion produces CO2, it does not increase total global CO2; 4) liquid fuels, especially bioethanol and biomethanol, provide petroleum fuel alternatives for various engines and machines; 5) it can be managed to eliminate output of soot and SOx; and 6) in terms of storage, it ranks second to petroleum and is far easier to store than batteries, natural gas and hydrogen.

Utilization of biomass to date has been very limited and has primarily included burning wood and the production of bioethanol from sugarcane in Brazil or maize in the USA. The necessary raw materials for bioethanol production by fermentation are obtained from crop plants with high sugar or high starch content. Since these crops are primary sources of human nutrition, we cannot use them indiscriminately for biofuel production when the

demand for food keeps increasing as global population increases. Although fermentation of lignocellulosic materials, such as wood of poplar (Populus spp.) (Wyman et al. 2009), switchgrass (Panicum virgatum) (Keshwani and Cheng 2009) and Miscanthus (Miscanthus spp.) (Sorensen et al. 2008), straw of rice (Oryza sativa) (Binod 2010), old trunks of oil palm (Elaeis guineensis) (Kosugi et al. 2010) are being attempted by improving pre-treatment of the materials, yeast and enzymes, establishment of the technology with low cost and high ethanol yield will be required. Recently, a new method of gasification by partial oxidation and production of biomethanol from carbohydrate resources has been developed (Sakai 2001). This process enables any source of biomass to be used as a raw material for biomethanol production. We report on the estimated gas mixture and methanol yield using this new technology for biofuel production from gasification of diverse biomass resources, such as wood, forages, and crop residues etc. Data obtained from test plant operation is also provided.

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