1. A substantially closed-loop process for producing polycrystalline silicon, the process comprising:
introducing trichlorosilane into a disproportionation system to produce silicon tetrachloride and at least one of silane and dichlorosilane;
introducing silane or dichlorosilane produced from the disproportionation system into a fluidized bed reactor to produce polycrystalline silicon and an effluent gas comprising hydrogen and unreacted silane or dichlorosilane;
introducing an amount of silicon tetrachloride produced from the disproportionation system and an amount of hydrogen from the effluent gas into a hydrogenation reactor to produce trichlorosilane and hydrogen chloride;
introducing an amount of hydrogen chloride produced from the hydrogenation reactor and silicon into a chlorination reactor to produce a chlorinated gas comprising trichlorosilane and silicon tetrachloride; and
introducing trichlorosilane produced from the chlorination reactor to the disproportionation system to produce silicon tetrachloride and at least one of silane and dichlorosilane.
2. The process as set forth in claim 1 wherein:
trichlorosilane is introduced into a disproportionation system to produce silicon tetrachloride and silane;
silane produced from the disproportionation system is introduced into a fluidized bed reactor to produce polycrystalline silicon and an effluent gas comprising hydrogen and unreacted silane; and
introducing trichlorosilane produced from the chlorination reactor is introduced into the disproportionation system to produce silicon tetrachloride and silane.
3. The process as set forth in claim 2 wherein the disproportionation system comprises a first distillation column, a second distillation column, a third distillation column, a first disproportionation reactor and a second disproportionation reactor, the process comprising:
introducing trichlorosilane and silicon tetrachloride produced from the chlorination reactor and dichlorosilane produced from the first disproportionation reactor 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;
introducing the bottoms fraction produced from the second distillation column into the first disproportionation reactor to produce a first disproportionation reactor product gas comprising dichlorosilane and silicon tetrachloride, the first disproportionation reactor product gas being introduced into the first distillation column;
introducing the overhead fraction produced from the second distillation column into the second disproportionation reactor to produce a second disproportionation reactor product gas comprising silane and trichlorosilane;
introducing the second disproportionation reactor product gas into the third distillation column to separate silane into an overhead fraction and trichlorosilane into a bottoms fraction;
introducing the bottoms fraction produced from the third distillation column into the second distillation column; and
introducing the overhead fraction produced from the third distillation column into the fluidized bed reactor to produce polycrystalline silicon.
4. The process as set forth in claim 3 wherein the bottoms fraction produced from the first distillation column is introduced into the hydrogenation reactor to produce trichlorosilane and hydrogen chloride.
5. The process as set forth in claim 1 wherein silicon tetrachloride and hydrogen are introduced into the hydrogenation reactor to produce a hydrogenated gas comprising trichlorosilane, hydrogen chloride, unreacted hydrogen and unreacted silicon tetrachloride, the hydrogenated gas being introduced into a separation system to separate trichlorosilane and unreacted silicon tetrachloride from hydrogen and unreacted hydrogen chloride, the trichlorosilane and unreacted silicon tetrachloride being introduced into the disproportionation system.
6. The process as set forth in claim 5 wherein the separation system comprises:
a chlorosilane separator for separating trichlorosilane and silicon tetrachloride from hydrogen and hydrogen chloride; and
a hydrogen separator for separating hydrogen from hydrogen chloride, the separated hydrogen chloride being introduced into the chlorination reactor, the separated hydrogen being introduced into at least one of the hydrogenation reactor and the fluidized bed reactor.
7. The process as set forth in claim 5 wherein the chlorosilane separator is a vapor-liquid separator.
8. The process as set forth in claim 5 wherein the hydrogen separator is a vapor-liquid separator or a bubbler.
9. The process as set forth in claim 5 wherein the chlorinated gas comprises trichlorosilane, silicon tetrachloride, hydrogen and unreacted hydrogen chloride and wherein the chlorinated gas is introduced into the separation system.
10. The process as set forth in claim 1 wherein the chlorinated gas is introduced into a stripper column to remove light end impurities prior to introduction into the disproportionation system.
11. The process as set forth in claim 1 wherein the 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, less than about 1:20, less than about 1:50, less than about 1:100, from about 1:250 to about 1:10 or from about 1:100 to about 1:20.
12. The process as set forth in claim 1 wherein the 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, less than about 1:20, less than about 1:50, less than about 1:100, from about 1:250 to about 1:10 or from about 1:100 to about 1:20.
13. The process as set forth in claim 1 wherein the molar ratio of chlorine added as a make-up to polycrystalline silicon product that is produced is less than about 2:1, less than about 1:1, less than about 1:1.2, less than about 1:1.5, less than about 1:2, less than about 1:2.5, from about 2:1 to 1:5 or from about 1:1 to about 1:5.
14. The process as set forth in claim 1 wherein the molar ratio of hydrogen added as a make-up to polycrystalline silicon product that is produced is less than about 1:1, less than about 1:2, less than about 1:3, less than about 1:5, less than about 1:10, from about 1:1 to 1:20 or from about 1:2 to about 1:10.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. A flame-resistant garment having an outer shell fabric comprising:
5 to 50 parts by weight of a polypyridobisimidazole fiber having an inherent viscosity of greater than 20 dlg and
50 to 95 parts by weight of polybenzimidazole fiber.
2. The flame-resistant garment of claim 1 where the polypyridobisimidazole fiber has an inherent viscosity of greater than 25 dlg.
3. The flame-resistant garment of claim 1 where the polypyridobisimidazole fiber has an inherent viscosity of greater than 28 dlg.
4. The flame-resistant garment of claim 1 comprising
35 to 50 parts by weight of a polypyridobisimidazole fiber, and
50 to 65 parts by weight of polybenzimidazole fiber.
5. The flame-resistant garment of claim 1 where the polypyridobisimidazole and polybenzimidazole fibers are present as staple fibers.
6. The flame-resistant garment of claim 5 where the polypyridimidazole polymer is poly2,6-diimidazo4,5-b:4,5-e- pyridinylene-1,4(2,5-dihydroxy)phenylene).
7. The blend of fibers of claim 1 where the polybenzimidazole fiber comprises polybibenzimidazole polymer.
8. The blend of fibers of claim 9 where the polybibenzimidazole polymer is poly(2,2\u2032-(m-phenylene)-5,5\u2032-bibenzimidazole) polymer.
9. The flame-resistant garment of claim 1 where the polypyridobisimidazole and polybenzimidazole fibers are present as continuous filaments.
10. A flame-resistant garment comprising in order
a) an inner thermal lining,
b) a liquid barrier, and
c) an outer shell fabric,
the outer shell fabric comprising:
5 to 50 parts by weight of a polypyridobisimidazole fiber having an inherent viscosity of greater than 20 dlg and
50 to 95 parts by weight of polybenzimidazole fiber.
11. The flame-resistant garment of claim 10 where the polypyridobisimidazole fiber has an inherent viscosity of greater than 25 dlg.
12. The flame-resistant garment of claim 10 where the polypyridobisimidazole fiber has an inherent viscosity of greater than 28 dlg.
13. The flame-resistant garment of claim 10 where the outer shell fabric comprises:
35 to 50 parts by weight of a polypyridobisimidazole fiber, and
50 to 65 parts by weight of polybenzimidazole fiber.
14. The flame-resistant garment of claim 10 where the polypyridobisimidazole and polybenzimidazole fibers are present as staple fibers.
15. The flame-resistant garment of claim 14 where the polypyridimidazole polymer is poly2,6-diimidazo4,5-b:4,5-c- pyridinylene-1,4(2,5-dihydroxy)phenylene).
16. The blend of fibers of claim 10 where the polyberizimidazole fiber comprises polybiberizimidazole polymer.
17. The blend of fibers of claim 16 where the polybibenzimidazole polymer is poly(2,2\u2032-(m-phenylene)-5,5\u2032-bibenzimidazole) polymer.
18. The flame-resistant garment of claim 10 where the polypyridobisimidazole and polybenzimidazole fibers are present as continuous filaments.
19. A method of producing a flame-resistant garment having an inner thermal lining, a liquid barrier, and an outer shell fabric, by incorporating into the garment an outer shell fabric comprising
5 to 50 parts by weight of a polypyridobisimidazole fiber having an inherent viscosity of greater than 20 dlg and
50 to 95 parts by weight of polybenzimidazole fiber.
20. The method of claim 19 where the polypyridobisimidazole fiber comprises poly2,6-diimidazo4,5-b:4,5-e- pyridinylene-1,4(2,5-dihydroxy)phenylene).