Siemens Reloaded: Chloride‐Assisted Selective Hydrodechlorination of SiCl₄ to HSiCl₃

Abstract

Trichlorosilane is the key intermediate for the large-scale production of polycrystalline silicon in the Siemens and Union Carbide processes. Both processes, however, are highly inefficient, and over two thirds of the trichlorosilane employed is converted to unwanted silicon tetrachloride accumulating in millions of tons per year on a global scale. In this combined experimental and theoretical study we report an energetically and environmentally benign synthetic protocol for the highly selective conversion of SiCl 4 to HSiCl 3 using organohydridosilanes as recyclable hydrogen transfer reagents in combination with onium chlorides as efficient catalysts. We put the same protocol to further use demonstrating the quantitative conversion of higher oligosilane residues, which form as another unwanted and potentially hazardous byproduct of Siemens processes, to HSiCl 3 in a low-temperature recycling step.

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

“…Said production will not be abandoned, we forecast in conclusion, whereas the supply of HSiCl 3 will grow thanks to the recently discovered catalytic conversion of SiCl 4 by‐product of the Siemens and Union Carbide processes [19] . The major driver for change in polysilicon production occurred since 2004, when dramatic expansion of polysilicon production started in China, is that now the solar cell production rate and installation of solar modules has reached the the 300 GW/a threshold, making PV a crucially important technology for the energy security of most world's countries.…”

“…However, both are atomically inefficient as they respectively afford 11-14 and 22-27 tons of unwanted SiCl 4 per ton of solar-grade Si through the disproportionation of trichlorosilane (Eq. ( 3)): [19] 2HSiCl 3ðgÞ ! SiH 2 Cl 2 þ SiCl 4…”

“…[6] Said production will not be abandoned, we forecast in conclusion, whereas the supply of HSiCl 3 will grow thanks to the recently discovered catalytic conversion of SiCl 4 by-product of the Siemens and Union Carbide processes. [19] The major driver for change in polysilicon production occurred since 2004, when dramatic expansion of polysilicon production started in China, is that now the solar cell production rate and installation of solar modules has reached the the 300 GW/a threshold, making PV a crucially important technology for the energy security of most world's countries. This requires to start (or to re-start) polysilicon production for domestic solar cell manufacturing in all major economies: both in the economically developed countries, where it was once produced at small rate for the microelectronic industry, and in rapidly developing large countries in the global South including India, Brazil, the Philippines, Indonesia, South Africa, Nigeria, and Vietnam.…”

“…However, both are atomically inefficient as they respectively afford 11–14 and 22–27 tons of unwanted SiCl 4 per ton of solar‐grade Si through the disproportionation of trichlorosilane (Eq. ): [19] $$$\vcenter{\openup.5em\halign{$\displaystyle{#}$\cr {\rm 2HSiCl}{_{3({\rm g})}}\rightarrow {\rm SiH}{_{2}}{\rm Cl}{_{2}}+{\rm SiCl}{_{4}}\hfill\cr}}$$$ …”

Biobased silicon and biobased silica: two production routes whose time has come

“…Both (optimized) industrial processes employed for the production of solar-grade silicon (the Siemens process uses 90% of the global output, and the Union Carbide process), however, are atomically inefficient as they respectively afford 11-14 and 22-27 tonnes of unwanted SiCl4 per tonne of solar-grade Si [19].…”