| Rice husks, which represent 20% dry weight of the harvested rice, are of a lignocellulosic nature, contain 15-20wt% silica and a number of organic constituents. At the present time, rice husks are the raw biomaterials for the production of a series of silicon-based materials,such as silica, silicon carbide,silicon nitride,silicon tetrachloride, pure silicon and zeolite.Any number of reports have been published on the component, application and intended uses of rice husks since at least as early as 1871.The exploit and utilization of biomass wnergy is an effective method for relieving the pressures of energy crisis and environmental pollution. Cellulose hydrolysis technology which can convert biomass energy to reducing sugars, and with the fermentation of reducing sugars, we can get ethanol and other high add-value chemical material.Silicon probably as a silicate or monosilicate acid, which in a soluble form, enters into the rice plant through its root and then moves to the outer surface of the rice plant, where it comes into being a cellulose silica membrane by evaporation and polymerization. This is in accord with that the silica play the leading role in inorganic linkages basically, but some of the silica is also bonded covalently to the organic compounds. It is reported that rice husks are admirable source of high-grade amorphous silica and lots of authors studied production of silica from rice husks.The residue of rice husk hydrolyzed with concentrated acid is thought to have advantages for use in some manufacturing processes as a silicon source because the concentrated-acid-hydrolysis seems to lower the impurity level apparently. For instance, metallurgical silicon is usually produced by a carbothermic process, which reduces silica in a furnace.Therefore, the silica of rice husk obtained by the concentrated acid hydrolysis process should have a extensive future as a raw biomaterial for metallurgical silicon. In brief, the low impurity content is advantageous for industrial applications of rice husk silica in the production processes of various silicon-based materials, such as ceramics, synthesized zeolites and metallurgical silicon. Kapur77 designed a tube-in-basket (TiB) setup use for combusting rice husks.Moreover, it is observed that the silica of rice husk was noncrystalline up to 600℃.Rice husk used in this study were pretreated with 6% H2SO4 and 75% ethanol solution to eliminate hemicellulose and lignin respectively.Hydrolysis method was evaluated for conversion of rice husk cellulose to monomeric sugars(glucose).After the pretreatment,no measurable furfural and hydroxymethyl furfural were produced during the acid hydrolysis progress. Dilute H2SO4 hydrolysis at varied temperature (185-230℃) and varied acid-concentration(0.5-2.0%, v/v) were evaluated for conversion of rice cellulose to monomeric sugars. The maximum yield of monomeric sugars from rice husk by dilute H2SO4 (1.0%, v/v) hydrolysis(215℃,80min,1:15) was 22.4g/100gRH.The almost complete conversion (99%) of rice husk cellulose to sugars was achieved by two-stage hydrolysis(72% H2SO4, 10min,50℃and 30-40% H2SO4,20min,90℃).While without the second hydrolysis,the maximum yield of monomeric sugars was 26.4g/100gRH. The other objective of this work is to extract silica from concentrated-acid hydrolysis rice husk.The residue of rice husk after hydrolyzation, due to being rich in silica, has a wide application prospect. However, there is no better commercial utilization yet. Therefore, the ecological and economical point of view are necessary to discover reasonable utilization of this material. This experimental design methods to optimize various factors such as acid concentration, hydrolysis time, hydrolysis temperature and the liquid/solid ratio which can affect the yield, size and appearace of the silica. Changes in the physical characteristics and morphology of silica were studied by using scanning electron microscopy (SEM).It is observed that the silica yield was decreased by increasing acid concentration and hydrolysis time. The SiO2 bearing uniform sphericity particles about 100nm with the narrow particles size distribution with optimum conditions (72 wt.% H2SO4,50℃,5min and burnt at 800℃for 3h).
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