Avoiding Carbothermal Reduction: Distillation of Alkoxysilanes from Biogenic, Green, and Sustainable Sources

Abstract

The direct depolymerization of SiO 2 to distillable alkoxysilanes has been explored repeatedly without success for 85 years as an alternative to carbothermal reduction (1900 8 8C) to Si met ,followed by treatment with ROH. We report herein the base-catalyzed depolymerization of SiO 2 with diols to form distillable spirocyclic alkoxysilanes and Si(OEt) 4 .T hus,2methyl-2,4-pentanediol, 2,2,4-trimethyl-1,3-pentanediol, or ethylene glycol (EGH 2 )r eact with silica sources,s uch as rice hull ash, in the presence of NaOH (10 %) to form H 2 Oa nd distillable spirocyclic alkoxysilanes [bis(2-methyl-2,4-pentanediolato) silicate,bis(2,2,4-trimethyl-1,3-pentanediolato) silicate or Si(eg) 2 polymer with 5-98 %c onversion, as governed by surface area/crystallinity.S i(eg) 2 or bis(2-methyl-2,4-pentanediolato) silicate reacted with EtOH and catalytic acid to give Si(OEt) 4 in 60 %y ield, thus providing inexpensive routes to high-purity precipitated or fumed silica and compounds with single SiÀCb onds.

Silicon carbide (SiC) derived from agricultural waste potentially competitive with silicon anodes

“…The detailed extraction of SiO 2 from RHA (Wadham Energy Inc.) to recover SDRHA and distill spirosiloxane was reported elsewhere. 36,97,98 Synthesis of SiC via carbothermal reduction of the SDRHA with various SiO 2 : C ratios was detailed recently. 41 In brief, (60 wt% SiO 2 ) powders were placed in a covered graphite crucible.…”

“…We previously described a method of directly extracting SiO 2 from RHA to produce silica depleted RHA (SDRHA) using an environmentally-and economically-friendly approach. 36 In principle, this approach valorizes RHA as a practical precursor to solar grade silicon (99.999% pure); 37 high surface area fumed and precipitated silicas for vacuum insulation panels; 38 high-performance electrodes for hybrid Li + supercapacitors; 39 and precursors for solid Li + electrolytes. 40 In particular, SDRHA with controllable SiO 2 :HC ratios allows more efficient use of the intimately mixed nano-SiO 2 and HC as natural starting materials for carbothermal reduction to high surface area SiC, Si 2 N 2 O, or Si 3 N 4 , without need for external carbon sources.…”

“…We previously described a method of directly extracting SiO 2 from RHA to produce silica depleted RHA (SDRHA) using an environmentally- and economically-friendly approach. 36 In principle, this approach valorizes RHA as a practical precursor to solar grade silicon (99.999% pure); 37 high surface area fumed and precipitated silicas for vacuum insulation panels; 38 high-performance electrodes for hybrid Li + supercapacitors; 39 and precursors for solid Li + electrolytes. 40…”

Avoiding Carbothermal Reduction: Distillation of Alkoxysilanes from Biogenic, Green, and Sustainable Sources

“…If we only consider precipitated silica, then our process does not produce CO 2 or Na 2 SO 4 by‐products, thus making it a green, low carbon footprint, low‐temperature, and low‐cost route to high‐purity ppt SiO 2 . Finally, the resulting carbon‐enriched RHA, when treated with dilute HCl, provides a high‐purity starting material for direct carbothermal reduction to produce silicon metal with 99.9999 % purity without further purification …”

Reactive Distillation Column Design for Tetraethoxysilane (TEOS) Production. Part II: Dynamic Properties and Inherent Safety

“…In order to avoid the carbothermic process to produce silicon from quartz and the chlorosilane route, recently Laine et al reported that TEOS could be manufactured by means of the reaction of SiO 2 and diols. In such a report, biogenic SiO 2 from rice-hulls is the starting material.…”