Hydrothermolysis of Agricultural Waste

The consumption of petroleum products has been significantly increasing year by year. Petroleum offers a tremendous convenience for our life, and our daily life would be quite different without it. However, the depletion of petroleum is creeping under our foot. Lignocellulosic biomass has unlimited potential because it is possible to substitute for petroleum as energy and chemical sources. Recently, there has been a growing need for development of the decomposition process for lignocellulosic biomass into available chemical compounds. Various decomposition processes of lignocellulosic biomass such as acid hydrolysis and enzymatic hydrolysis have been developed on the pilot plant scale. However, acid hydrolysis has many problems, such as a measure against corrosion, wastewater treatment and so on. Recently, a hydrolysis with hot-compressed water (HCW) has been focused on for nonacid process because of its reactivity of hydrolysis with simple process. 2) We already reported that the saccharification of cellulose with HCW at temperatures ranging from 573 to 673 K using a batch reactor and that hexose (glucose and fructose) could be produced as main components. However, the content of hexose in the water-soluble fraction did not exceed 50 wt % because of the secondary decomposition of the produced hexose in the batch reactor. Therefore, to prevent the secondary reaction going on, we constructed a semi continuous apparatus (HCW-flow reactor) that permits the hot water including the solubilized products to be removed immediately from the reactor by delivering fresh hot water into the reactor continuously and investigated the saccharification of cellulose. As a result of using the HCW-flow reactor, the composition of the products was different from that obtained in the batch reactor, and consequently, secondary decomposition was suppressed and oligoand polysaccharides were the main components. In this paper, we reported the formation behaviors of saccharides from agricultural waste; barley straw, wheat straw, rice straw, rice hull, bagasse, corn cob and kenaf, with HCW-flow reactor. The recovered oligo-and polysaccharides would be used as healthy foods and feedstock of alcohol. For the purpose of recovering saccharides such as free, hemicellulose-derived, and cellulose-derived sugars separately and with minimum sugar-loss from lignocellulosic biomass, the HCW hydrolysis characteristic of above-mentioned biomasses was investigated using a HCW–flow reactor, controlling water temperature stepwise in the range of 393K-573K.