Decomposition behavior of rice (Oryza sativa) straw, as one of the monocotyledonous angiosperms, was investigated under the two-step semi-flow hot-compressed water at 230°C/10 MPa/15 min (1st stage) and 270 °C/10 MPa/30 min (2nd stage). Prior to the hot-compressed water treatment, cold-water extraction at 20°C/10 MPa/30 min was performed. It was consequently found that some inorganic constituents and free neutral sugars such as xylose, arabinose, glucose and mannose, which would not be chemically bonded with the plant cell wall, were recovered in the cold-water extractives. On the other hand, in the 1st stage, hemicellulose, pectin and para-crystalline cellulose, whose crystalline structure is somewhat disordered, were selectively hydrolyzed, as well as lignin being partially decomposed. In addition, protein was found to be hydrolyzed and formed into various amino acids. Hydrolysis of crystalline cellulose was, however, observed in the 2nd stage. Some additional decomposition of lignin and protein was revealed at this stage as well. In total, 97.9% of oven-dried extractives-free rice straw sample could be solubilized into cold and hot-compressed water. Various products in the water-soluble portion were primarily recovered as saccharides (hydrolyzed products of the polysaccharides), which were partially isomerized and then dehydrated and fragmented. The 2.1% of residue after the treatment was composed mainly of lignin and a trace of silica.
Rapid pyrolysis experiments using a fluidized bed reactor, FBR, were carried out for various biomass species. Alumina particles used as bed particles adhered on the surface of the produced char. This phenomenon may cause serious operational problems of FBR such as agglomeration, clogging and so on. The effects of various conditions including heating rate and pyrolysis temperature, together with type of biomass were observed on the adhesion behavior of the bed particles. Among the samples of Japanese cypress, Eucalyptus camaldulensis, bagasse, and switchgrass, while all samples showed the phenomenon in case of rapid pyrolysis, no adhesion was observed in case of slow (10°C/min) pyrolysis, excepting that switchgrass showed the phenomenon at 400-1000°C (mainly 300-600°C). By rapid pyrolysis, softwood samples showed the adhesion phenomenon between 600 and 1200°C and hardwood, between 800 and 1000°C. Much more particles adhered on softwood char than on hardwood char. Among the herbaceous plant and agricultural residue samples, the adherability and temperature range strongly depended on the species. To investigate the effects of biomass type on the adhesion phenomenon, biomass model materials were pyrolyzed. Adhesion behavior was not observed for lignin only, however, it was observed with cellulose or hemicellulose and was also affected by their kind.