セルロースナノファイバーを基盤としたバイオ燃料製造技術

摘要

In recent years, growing attention has been devoted to the development of new technology for efficiently converting wood-related biomass resources into bio-ethanol. The method of enzymatic saccharification of cellulose and hemicellulose in wood before ethanol fermentation using yeast goes mainstream. However, since the wood is a stiff and stable material, it is necessary to pretreat it in order to improve its enzymatic reactions. Although various kinds of pretreatment technologies have been researched, none of them are commercialized. We started the research for finding out the key factor in order to improve enzymatic saccharification by reverifying highly effective fine grinding treatment although it is a classical and high-cost treatment. Lower crystallinity and removal of the wood cellulose lignin had been the key factor. However, as a result of reverification, we found that even refined pulp with high crystallinity has high saccharification, and that the correlation between particle size of the wood powder produced by dry grinding and cellulose crystallinity is low. As a result of various analyses, we found the ground product consisted of a nano-scale domain of about 5nm. Then we tried the saccharification test on the micro-fibrillated wood fiber between 20 and 100nm produced by wet grinding, and found that even the wood fiber with high crystallinity showed high saccharification. We tried to find other wet grinding methods for the purpose of improving pretreatment efficiency, and found the disc-type crusher or stone-mill-type crusher was effective. In order to reduce variability caused by the kinds of material, we produced a pretreated product with high enzymatic saccharification from various materials, whose strong tissue had been weakened by the wet grinding treatment using a disc-type crusher after it was treated by the preliminary wet grinding and hot water autoclave. We found enzymes can easily adhere to and approach the cellulose since the wood raw material is softened and loosened to the nano-size micro-fibrillated fibers in this pretreated product and they have very large surface area. At present we are developing a large-scale demonstration project where the further developed enzymatic saccharification technologies and advanced paper manufacturing technologies are applied. Since micro-fibrillated fibers (cellulose nanofibers) produced from the wood have high potentiality as a material, their application to composite materials is also researched.%近年，地球温暖化対策やエネルギーセキュリティーの観点からバイオ燃料が注目されている．現在，米国やブラジルでは大量のバイオエタノールが製造されているが，食料系バイオマスであるトウモロコシ（米国）やサトウキビ（ブラジル）が原料であるため，さまざまな弊害も引き起こしている．そのため，非可食系バイオマスである木材や稲ワラなどの利用技術が重要になっている．木材や草本等からのバイオエタノール製造は研究開発途上であり商業化はされていないが，でんぷん系と比較してLCA的にも炭酸ガス削減効果は高いと言われている．