No abstract

Alkoxysilanes are silicon compounds containing a Si-OR bond. The applications of tetraalkoxysilanes cover a wide range depending if the Si-OR bond remains intact or is hydrolyzed. Currently, tetraethoxysilane (TEOS) is the most prominent derivative of such silicon compound family. The best known and used method of synthesis of TEOS is the esterification reaction of SiCl4, following the old Von Ebelman’s route (1846). Tetramethoxy- and tetraethoxysilane are obtained by a technology developed in the 1990’s involving the catalyzed direct synthesis of silicon metal and either methanol or ethanol. However, there is few information about novel technologies to produce TEOS, either improved current technology or proposed new approaches. In this work, the reactive distillation (RD) is suggested to produce TEOS as an intensified technology. In general, the concept of process intensification may overcome the traditional process, since it allows design technology with reduction on equipment size, improvement in energy and mass transfer, and reduction in capital cost. Therefore, this work will approach TEOS production by means of two systems, the conventional reaction including the product separation (reaction/separation) and a reactive distillation. In order to evaluate both ways to produce TEOS, the two systems were evaluated considering the total annual cost (TAC) and return of investment (ROI) as economic indexes and the Eco-indicator 99 as an environmental index. As a result, the reactive distillation shows better performance as concern to TAC values; however, when purities above 99.5% wt are obtained, the reaction/separation system overcomes the RD as concern to ROI values. Moreover, when the environmental impact is measured, the RD showed a bigger impact near 30% in comparison with the reaction/separation system.

No abstract

Inherent safety and control properties of a reactive distillation column for the production of tetraethoxysilane are compared with those of a conventional process based in a reactordistillation column. The preliminary design of the reactive distillation column and the analysis of total annual cost and environmental indicator were obtained previously [Sańchez-Ramı ́rez et al. Ind. Eng. Chem. Res. 2018, 57, 5024−5034]. The control properties of the sequences considered were obtained by using the singular value decomposition technique and Nyquist criteria. A complementary closed-loop study using PI controller was carried out. The pairing of the variables in the control loops was carried out by the RGA technique. Process risk quantification was determined through hazard and operability study. The results indicate that reactive distillation columns seem a more appropriated technology for tetraethoxysilane production since its economic and control properties surpass those present by the conventional reaction separation process. Moreover, if the required purity for TEOS is between 98.5% and 99 wt % the profit of the process increases. Even though the inherent safe for the conventional process is slightly better, that difference is not high enough for comparative purposes.

Electrochemical formation of poly(phenylmethylsilane) in a divided cell containing a Teflon R neutral membrane was studied. The electrolysis of dichlorosilanes was carried out in a solution containing tetrahydrofuran + hexamethylphosphoramide as the solvent, tetrabutylammonium perchlorate as the support electrolyte and stainless steel as the cathode, with Pt and graphite as the resistant anodes or stainless steel as the sacrificial anode. Polysilanes with a number-average molecular weight in the range from 2,600 to 130,000 g/mol were obtained, depending on the conditions used.