Integrated rice and wheat straws processing for high value chemicals and materials.
A project undertaken at the Department of Chemical Engineering, Monash University, and supervised by P Webley.Rice husk, the by-product of the rice milling industry, is produced in large quantities as a waste, creating environmental problems. The high silica content of rice husk (20 wt%) makes it unsuitable for use as cattle feed and also bestows very low fuel value to this biomass. In this project, we examine if high-value chemicals can be made from rice husk and under what conditions this is possible. The salient features of this study are the sequential depolymerisation of rice husk with organic acids (of increasing severity) to remove alkali, hemicellulose, lignin and cellulose from rice husk. This pre-treatment will alter the rice husk carbon/silica ratio since the organic component (mostly cellulose) will be removed and the silica component left unaffected. This treatment has a large influence on evolution of pore structure, surface area, and pore volume. Subsequent pyrolysis of the treated rice husks was also examined to understand the improvements possible with this treatment.
Figure 1. Autoclave used for leaching.
Figure 2. TEM micrograph showing the highly disordered and non-graphitic structure of the material before leaching out of the silica. The insets in the left-hand side are two enlargements of the areas marked A and B. Also inset is an EDX spectrum of the region. Quantitative analysis indicated the presence of SiO2 and C according to a ratio of approximately 8:3.
Figure 3. TEM micrograph showing the open structure of the material after leaching out of the silica. The two enlargements of the areas marked A and B (see insets in the left-hand side) are examples of the graphitic vesicles present. The EDX spectrum inset confirms the very low SiO2 content.