Production of polycrystalline silicon in substantially closed-loop processes that involve disproportionation operations
View Patent ↗Production of polycrystalline silicon in substantially closed-loop processes and systems is disclosed. The processes and systems generally involve disproportionation of trichlorosilane to produce silane or dichlorosilane and thermal decomposition of silane or dichlorosilane to produce polycrystalline silicon.
1. A substantially closed-loop process for producing polycrystalline silicon, the process comprising:
a) introducing an amount of hydrogen chloride and silicon into a chlorination reactor to produce a chlorinated gas comprising trichlorosilane, silicon tetrachloride and hydrogen;
b) separating hydrogen from the chlorinated gas produced from the chlorination reactor to obtain a remaining stream comprising trichlorosilane and silicon tetrachloride;
c) introducing the remaining stream comprising trichlorosilane and silicon tetrachloride to a disproportionation system to produce silicon tetrachloride and dichlorosilane;
wherein the disproportionation system comprises a first distillation column, a second distillation column and a disproportionation reactor,
wherein:
the remaining stream comprising trichlorosilane and silicon tetrachloride and a disproportionation reactor product stream are introduced into the first distillation column to separate silicon tetrachloride into a bottoms fraction and to separate dichlorosilane and trichlorosilane into an overhead fraction;
introducing the overhead fraction produced from the first distillation column into the second distillation column to separate trichlorosilane into a bottoms fraction and dichlorosilane into an overhead fraction; and
introducing the bottoms fraction produced from the second distillation column into the disproportionation reactor to produce the disproportionation reactor product stream comprising dichlorosilane and silicon tetrachloride;
d) introducing (1) dichlorosilane from the second distillation column of the disproportionation system and (2) hydrogen as a carrier gas into a fluidized bed reactor to produce polycrystalline silicon and an effluent gas comprising hydrogen and unreacted dichlorosilane, the fluidized bed reactor being separate from the disproportionation system,
wherein an amount of hydrogen separated from the chlorinated gas is used as the carrier gas;
e) introducing an amount of silicon tetrachloride from the first distillation column of the disproportionation system and an amount of hydrogen from the effluent gas into a hydrogenation reactor to produce a hydrogenated stream comprising trichlorosilane and hydrogen chloride; and
f) separating hydrogen chloride from the hydrogenated stream and returning an amount of the separated hydrogen chloride to the chlorination reactor in step a).
2. The process as set forth in claim 1 wherein the hydrogenated stream further comprises unreacted hydrogen and unreacted silicon tetrachloride, the hydrogenated stream being introduced into a separation system to separate the remaining stream comprising trichlorosilane and unreacted silicon tetrachloride from hydrogen and unreacted hydrogen chloride.
3. The process as set forth in claim 2 wherein the separation system comprises:
a chlorosilane separator for separating the remaining stream comprising trichlorosilane and silicon tetrachloride from hydrogen and hydrogen chloride; and
a hydrogen separator for separating hydrogen from hydrogen chloride.
4. The process as set forth in claim 3 wherein the chlorosilane separator is a vapor-liquid separator.
5. The process as set forth in claim 3 wherein the hydrogen separator is a vapor-liquid separator or a bubbler.
6. The process as set forth in claim 2 wherein the chlorinated gas discharged from the chlorination reactor further comprises unreacted hydrogen chloride and wherein the chlorinated gas is introduced into the separation system.
7. The process as set forth in claim 1 wherein the remaining stream of step b) is introduced into a stripper column to remove light end impurities prior to introduction into the disproportionation system.
8. The process as set forth in claim 1 comprising adding chlorine as a make-up, wherein the molar ratio of hydrogen chloride added as a make-up to the amount of hydrogen chloride circulating within the substantially closed-loop process is less than about 1:10.
9. The process as set forth in claim 1 comprising adding hydrogen as a make-up, wherein the molar ratio of hydrogen gas added as a make-up to the amount of hydrogen circulating in the substantially closed-loop process is less than about 1:10.
10. The process as set forth in claim 1 comprising adding chlorine as a make-up, wherein the molar ratio of chlorine added as a make-up to polycrystalline silicon product that is produced is less than about 2:1.
11. The process as set forth in claim 1 comprising adding hydrogen as a make-up, wherein the molar ratio of hydrogen added as a make-up to polycrystalline silicon product that is produced is less than about 1:1.
12. The process as set forth in claim 1 wherein the first distillation column and the disproportionation reactor are separate units.
13. The process as set forth in claim 1 wherein the effluent gas from the fluidized bed reactor comprises hydrogen chloride, the process further comprising:
separating the hydrogen chloride from the effluent gas; and
introducing an amount of separated hydrogen chloride from the effluent gas into the chlorination reactor to produce the chlorinated gas.
14. The process as set forth in claim 1 wherein an amount of hydrogen separated from the chlorinated gas is introduced into the hydrogenation reactor to produce trichlorosilane.
15. The process as set forth in claim 1 wherein hydrogen is directed toward a reactor wall of the fluidized bed reactor.
16. The process as set forth in claim 1 wherein hydrogen is added to the fluidized bed reactor as a make-up stream for hydrogen.