SYNTHESIS METHOD OF ALKOXYSILANES

摘要

The direct depolymerization of biogenic and other high surface area silica sources uses both simple and hindered diols to produce alkoxysilanes in one or two steps that can be separated and purified directly from the reaction mixture by distillation, extraction or filtration followed by solution modification and distillation or extraction. The alkoxysilanes can take the form of spirosiloxanes or simple alkoxysilanes or oligomers thereof. Thereafter they can be treated with acid to produce colloidal or precipitated silica or aerosolized and combusted to provide fumed silica without the intervention of SiCl4.

主权项

1. A synthesis method of alkoxysilanes, comprising:
a first step, in which freshly produced or aged biogenically concentrated silica in a milled or un-milled form is mixed with a liquid polyol including ethylene glycol, 1,2-diol, 1,3-diol, 2,3-diol, 1,4-diol, triols, triethanolamine, trishydroxy-methylamine, or a mixture thereof; a second step, in which sufficient base including LiOH, NaOH, KOH, CsOH, RbOH or a mixture thereof in a catalytic amount ranging from 0.25-50 mol % is added so that a mixture is heated to a temperature where water and a by-product of a dissolution process distill out; a third step, in which addition of a diol that forms a 4,5 or 6 member ring with silicon forms an alcoholate and a spirosiloxane that is distilled out directly from the polyol solution before or after filtration to remove undissolved biogenic silica to recover the solution of alkoxysilane and the alcoholate substantially free of solids followed by distillation, extraction, or separation through a semipermeable membrane that selectively removes the spirosiloxane leaving anionic and polyol species to remain in the original reaction mixture followed by addition of simple ROH alcohols including MeOH and EtOH and stirred to effect exchange with the chelating diol to produce Si(OR)4 which can be separated, being also possible to slightly acidify the solution using an organic acid or acid anhydride or non-aqueous inorganic acid or acid anhydride or ion exchange resin or HCl to catalyze the exchange reaction followed by purification, said recovered spirosiloxane or alkoxysilane then being combusted to produce fumed silica or treated with sufficient acid to produce colloidal dispersions of or precipitated silica; and a fourth step, in which any residual base present as alcoholate in the recovered alkoxysilane or rice hull ash is neutralized by adding a non-aqueous acid including HCl gas and NH4Cl to eliminate the residual alkali metal base present in the form of a salt that can be removed by filtration or precipitation leaving a pure alkoxysilane or spirosiloxane free of metal impurities; alternately these impurities can be removed using ion exchange materials.