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Research paper : Bioethanol production from woods with the aid of nanotechnology (T. Endo)−272−Synthesiology - English edition Vol.2 No.4 (2010) remove the lignin component that may inhibit the enzymatic activity. The pretreatments according to these rules include milling, cooking, and steam explosion[3], but all methods have issues (table in lower part of Fig. 2). In the milling treatment, equipments such as the ball mill are used. The operation is simple and the enzymatic saccharification degree of the pretreated material is high. However, the power consumption is high and processing efficiency is low since it is batch processed. In many cases and the cost turns out high. Cooking treatment is a method where the lignin and hemicellulose in the wood are decomposed and removed using chemicals and water. It is similar to the pulping process of papermaking. Although the saccharification degree of the treated material is high, the dependency on certain wood species and the waste liquid are issues. In the steam explosion treatment, the material is placed in high-temperature high-pressure steam for a certain time, exposed to atmospheric pressure immediately, and the wood is broken down into fibers by the rapid volume expansion of steam. The need for high-pressure resistant facilities, heat recovery, and dependency on wood species are issues. Recently, hydrothermal treatment using pressurized hot water over 100 ºC has drawn attention. This method uses the hydrolysis action of hot-compressed water, but like in the acid saccharification, over-decomposition tends to occur at high temperature of 200 ºC or over.Therefore, we conducted re-experiments for the milling treatment, which is a simple yet highly effective operation, and analyzed and evaluated the mechanism for increased saccharification from the perspectives of wood chemistry and cellulose chemistry. Moreover, based on the findings, we attempted the development of the optimal pretreatment technology by combining several technologies.4 Mechanochemical treatment technologyWe conducted R&D on technologies to pulverize the cellulose materials such as pulp, and technologies to composite pulp or wood powder with resin, by controlling the aggregation of particles produced by milling (control of formation of hydrogen bonds)[4]-[7]. In the process of pulverization of materials in the milling process, reactions such as breaking of chemical bonds occur. Also, the pressure and shearing force of milling can form bonds and synthesize new materials. Since milling causes the chemical reaction by the mechanical process, it is called the mechanochemical treatment. We consider the formation and breaking of bonds including weak bonds such as the hydrogen bond and the hydrophobic bond (intermolecular force) as part of the mechanochemical treatment. The mechanochemical treatment was developed originally as the technology for compositing of inorganic substances and metals, and as alloy technology. It is possible to form covalent bonds such as esterification reaction in organic substances. However, there is a “threshold value” for the change of substance to occur in milling, and breakdown and compositing will not occur even if milling is done for a long time unless enough milling energy that can set off the chemical reaction is applied.As explained so far, the mechanochemical treatment is a relatively simple mechanical process, and has been known to improve the enzymatic saccharification of cellulose[8]. The important points were considered to be milling the wood Fig. 2 Characteristics of acid saccharification and enzymatic saccharification methods.× Theoretically difficult× Acid-resistant facility× Increased influence due to property of substrate (cellulose, etc.)◎ High yieldCharacteristics of pretreatment methodsOccurrence of over-decompositionWood type dependency yesHigh-pressure resistant facility, heat recoveryWood type dependency highRecovery of chemicalsWood type dependency yesPower consumption highIssuesMedium used is water onlyMonosaccharification is possibleRelatively simple treatmentApplication of pulping technologySimple treatmentWood type dependency lowAdvantagesMediumHigh ~ mediumHighDegree of saccharificationHydrothermal treatmentSteam explosion treatmentCooking treatmentMilling treatmentPretreatment method× Long reaction time◎ Short reaction time◎ No side reaction× Occurrence of side reaction (over-decomposition)Selective hydrolysis by enzymeRandom hydrolysis due to acid catalyst reaction (lignin undergoes polycondensation)・Milling treatment・Cooking treatment・Steam explosion treatment・Hydrothermal treatmentPretreatmentFermentationSaccharificationEnzymatic saccharificationAcid saccharificationBioethanolMonosaccharides・Cellulose・Hemicellulose・LigninMain components of woodHigh ~ medium

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