Fabrication and extraction of silicon-containing products from rice husks

To isolate silicon-containing products from plant materials, the reaction of interaction of rice husks with triethanolamine and ethylene glycol have been investigated. The effect of pretreatment of raw materials and the reaction conditions on the yield of soluble products containing silicon has been studied. It has been shown that the highest enrichment of rice husks with silicon occurs upon its treatment with concentrated hydrochloric acid and the Schweitzer's reagent. The highest degree of silicon extraction (69%) was achieved at using native rice husks and vanadyl acetylacetonate as a catalyst. The resulting solution contained silicon in the form of silatrane fragments. In order to isolate a silicon-containing product from the ethylene glycol solution, which would have the prospect of practical use and the maximum silicon yield, the heterofunctional polycondensation method was applied. It has appeared to be possible to isolate solid products using acetylacetonates of trivalent and tetravalent metals, which formed metal siloxanes. The structure of the obtained compounds has been confirmed by the element and X-ray diffraction analysis, as well as by the IR spectroscopy. When using rice husk chaffs as a silicon source, the product of the reaction with ethylene glycol and triethanolamine has appeared to be an irregular copolymer comprising amorphous silicon dioxide fragments and cyclic fragments similar in structure to that of silatranes. The application of metal acetylacetonates has made it possible to isolate silicon derivatives in the form of organometallic siloxanes. Тhe yield of metalsiloxanes increased in the sequence Zr < Fe < Al. Apparently, this was due to formation of lattice structures in the case of trivalent aluminum and iron, while zirconium had two remaining acetylacetonate groups and, in this case, its functionality was lower than for trivalent metals, which was confirmed by the spectral data.