Development of Liquefaction Technique of Pulverized Ligneous Biomass Powder

The wood biomass was liquefied by the pressurized hydrothermal method. The wood biomass powder in the different particle size, which was pulverized by a vibration mill, cutter mill and grinder, was used for the liquefaction. The liquefaction material was biomass slurry, which was prepared by mixing the wood biomass powder and water together (1:9). After filling the biomass slurry in a pressure vessel, the vessel was heated up around 423 to 573 K. The pressure of the vessel was as same as the water vapor pressure of that temperature. After the reaction, the vessel was cooled down to room temperature immediately to prevent secondary reaction. As the result, around 60 % of the wood biomass powder was soluble in water and around 40 % was remained in the bottom of the vessel as residual. The dissolved liquid was sugars that were decomposed components of cellulose, hemi-cellulose or lignin. Depend on the reaction temperature and particle size of the biomass powder, the ratio between dissolved liquid and residual changed dramatically. INTRODUCTION Of recent years, the utilization of unused ligneous biomass has been attracted attention as the environmental-friendly resource for the development of resource cycling society in Japan, because of the environmental issues, such as CO2 emissions. Although the wood biomass exists abundantly, those were not considered as rescues for the energy or chemical for a long time, they were used as the pulp material partially or dumped to a landfill. Recently, the biomass has been expected as alternative resource and the various technological research and developments on wood biomass utilization has been encouraged for the electric generation by the gasification [1] and bio-fuel production or chemical production by the liquefaction. However, there were still lots of issues for commercialization, because of low efficiency and productivity and bad economical efficiency. The liquefaction was the one of methods to produce chemicals from wood biomass and this method was one of the component fractionation techniques of wood constituent called hydrothermal process. There were a lot of liquefaction methods, such as steam explosion method and supercritical water method, but the liquefaction in a hot compressed water was mild reaction condition and simple operation condition rather than the other liquefaction method. Therefore, it was possible to simplify the total system and cut down energy consumption. For such reasons, liquefaction by a hot compressed water was considered as the effective method for the efficient ligneous biomass utilization [2]. For the effective liquefaction by a hot compressed water, pretreatment such as pulverization could be effective on operations and reactions. The liquefaction technique used pulverized fine powder as materials started developing, because reactivity of the materials may enhance [3]. However, there were few papers considering the effect of the particle size on the liquefaction efficiency. In this study, in order to develop the efficient liquefaction technique of wood biomass, the wood biomass pulverized into micron order particle by a vibration mill was liquefied in a hot compressed water and measured the liquefaction productivity. In the experiment, the effects of reaction temperature, pulverizing method of wood biomass and size of wood particles on the yield of liquefied substance were discussed. EXPERIMENTAL Pretreatment of liquefaction material The pulverized biomass was used for the liquefaction material. The liquefaction material was prepared by pulverizing the shaving dust of Oregon pine (conifer). The shaving dust size was distributed widely, and it was a few millimeters in thickness and a few centimeters in length. The moisture content of biomass was controlled around 10% dried in air for several days before pulverization. Three pulverization machine, vibration mill, cutter mill and grinder were used for the pulverization in this study. Cumulative particle size distribution was measured by laser diffraction / dispersion particle diameter distribution analyzer (Shimadzu Co. Ltd.). The particle size distributions in the different pulverization method were shown in Figure 1. The 50 % particle diameter pulverized by the vibration mill was about 35 μm and that of the cutter mill was around 200 μm, respectively. The 50 % particle diameter of grinder mill was around 500 μm, but the particle size distribution pulverized grinder mill was too broad to be shown in the figure. Over the 10 % of the particle pulverized by the vibration mill was less than 10 μm. Specific surface area of the pulverized powder was also measured by an automated mercury porosimeter (Shimadzu Co. Ltd.). The specific surface area of wood powder in each pulverization method sieved between 212 μm and 500 μm was summarized in Table 1. The surface are was not include the nano-order pore area. Even the same particle size range, the powder pulverized by the vibration mill had the biggest surface area and it was around two times bigger than that of grinder mill. The shape of wood particles was observed by the Scanning Electron Microscopy (SEM). The SEM micrographs of the particles pulverized by the different methods were shown in Figure 2. In the case of using the vibration mill, the structure of wood fiber was completely broken down, the shape of the particles was almost round and homogeneous in each particle, and the surface of the particle was smooth. On the other hand, the particle shape pulverized by the cutter mill was rectangle and the wood fibers could be observed clearly. The particle shape pulverized by the grinder mill was irregular and the wood fibers were branch off at the end of each particle.