Technoeconomic and Environmental Assessment for Design and Optimization of Tetraethyl Orthosilicate Synthesis Process

Biobased Silicon and Biobased Silica: Two Production Routes Whose Time has Come

This study offers an updated bioeconomy perspective on biobased routes to high-purity silicon and silica in the context of the societal, economic and environmental trends reshaping chemical processes. We summarize the main aspects of the green chemistry technologies capable of transforming current production methods. Coincidentally, we discuss selected industrial and economic aspects. Finally, we offer perspectives of how said technologies could/will reshape current chemical and energy production.

Design and assessment of an energy self-supply process producing tetraethyl orthosilicate using rice husk

Combusting rice husk (RH) generates energy and rice husk ash (RHA) containing high amount of silica. Recent studies showed RHA can directly react with ethanol for producing tetraethyl orthosilicate (TEOS), an important substance for different industries. Nevertheless, this process requires an intensive energy supply. This study aims to design and evaluate an energy self-supply process producing TEOS using RH for feasibility. A process simulator was used to design the target process. The simulation results revealed that RH combustion can completely meet the RHA and high energy demands of TEOS production. The economic and environmental benefits were thoroughly evaluated and compared with processes using conventional raw materials (i.e., Si_mg and silica). The evaluation results showed that using RH for TEOS production could reduce CO₂ emissions substantially. Large economic benefit was gained when renewable electricity was co-generated and sold to the power grid as a surplus.

From SiO2 to Alkoxysilanes for the Synthesis of Useful Chemicals

The transformation of silica (SiO₂) to useful chemicals is difficult to explore because of the strength of the Si-O bond and thermodynamic stability of the SiO₂ structure. The direct formation of alkoxysilanes from SiO₂ has been explored as an alternative to the carbothermal reduction (1900 °C) of SiO₂ to metallic silicon (Si_met) followed by treatment with alcohols. The base-catalyzed depolymerization of SiO₂ with diols and monoalcohols afforded cyclic silicon alkoxides and tetraalkoxysilanes, respectively. SiO₂ can also be converted to alkoxysilanes in the presence of organic carbonates, such as dimethyl carbonate. Alkoxysilanes can be further converted to useful chemicals, such as carbamates, organic carbonates, and chlorosilanes. An interesting and highly efficient pathway to the direct conversion of SiO₂ to alkoxysilanes has been discussed in detail along with the corresponding economic and environmental implications. The thermodynamic and kinetic aspects of SiO₂ transformations in the presence of alcohols are also discussed.

Let's Make White Phosphorus Obsolete

Industrial and laboratory methods for incorporating phosphorus atoms into molecules within the framework of Green Chemistry are in their infancy. Current practice requires large inputs of energy, involves toxic intermediates, and generates substantial waste. Furthermore, a negligible fraction of phosphorus-containing waste is recycled which in turn contributes to negative environmental impacts, such as eutrophication. Methods that begin to address some of these drawbacks are reviewed, and some key opportunities to be realized by pursuing organophosphorus chemistry under the principles of Green Chemistry are highlighted. Methods used by nature, or in the chemistry of other elements such as silicon, are discussed as model processes for the future of phosphorus in chemical synthesis.