Production of Polycrystalline Silicon in Substantially Closed-loop Processes

Abstract

Production of polycrystalline silicon in a substantially closed-loop process is disclosed. The processes generally include decomposition of trichlorosilane produced from metallurgical grade silicon.

1 . A substantially closed-loop process for producing polycrystalline silicon, the process comprising:
 introducing trichlorosilane and hydrogen to a fluidized bed reactor to produce polycrystalline silicon and an effluent gas comprising silicon tetrachloride, hydrogen and unreacted trichlorosilane;   introducing an amount of silicon tetrachloride and hydrogen from the effluent gas into a hydrogenation reactor to produce trichlorosilane and hydrogen chloride;   contacting hydrogen chloride and silicon to produce trichlorosilane and silicon tetrachloride; and   introducing the trichlorosilane produced by contacting hydrogen chloride and silicon into the fluidized bed reactor to produce polycrystalline silicon.   
     
     
         2 . The process as set forth in  claim 1  wherein hydrogen chloride and silicon are introduced into a chlorination reactor to produce a chlorinated product gas comprising the trichlorosilane and silicon tetrachloride, the process comprising introducing the chlorinated product gas into a purification system to produce a purified trichlorosilane stream and a purified silicon tetrachloride stream, the purified trichlorosilane stream being introduced into the fluidized bed reactor. 
     
     
         3 . The process as set forth in  claim 2  wherein the effluent gas is introduced into an effluent gas separator to separate hydrogen from trichlorosilane and silicon tetrachloride, the trichlorosilane and silicon tetrachloride being introduced into the chlorinated product gas purification system, the purified silicon tetrachloride stream being introduced into the hydrogenation reactor. 
     
     
         4 . The process as set forth in  claim 3  wherein the effluent gas separator is a vapor-liquid separator. 
     
     
         5 . The process as set forth in  claim 2  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 hydrogenated gas separator to separate trichlorosilane and unreacted silicon tetrachloride from hydrogen and unreacted hydrogen chloride, the trichlorosilane and unreacted silicon tetrachloride being introduced into the chlorinated gas purification system. 
     
     
         6 . The process as set forth in  claim 5  wherein the hydrogenated gas separator is a vapor-liquid separator. 
     
     
         7 . The process as set forth in  claim 5  wherein the hydrogen and hydrogen chloride gas are introduced into a separation system to separate hydrogen and hydrogen chloride, the separated hydrogen chloride being introduced into the chlorination reactor, the separated hydrogen being introduced into at least one of the fluidized bed reactor and hydrogenation reactor. 
     
     
         8 . The process as set forth in  claim 2  wherein the chlorinated product gas comprises trichlorosilane, silicon tetrachloride, hydrogen and unreacted hydrogen chloride and wherein the purification system comprises a chlorinated gas separator, a silicon tetrachloride separator and a trichlorosilane purifier, wherein:
 the chlorinated product gas is introduced into the chlorinated gas separator to separate trichlorosilane and silicon tetrachloride from hydrogen and unreacted hydrogen chloride; 
 the separated trichlorosilane and silicon tetrachloride are introduced into the silicon tetrachloride separator to separate silicon tetrachloride from trichlorosilane and produce a trichlorosilane feed gas; 
 the trichlorosilane feed gas is introduced into a trichlorosilane purifier to remove impurities from the feed gas; and 
 the purified trichlorosilane feed gas is introduced into the fluidized bed reactor to produce polycrystalline silicon. 
 
     
     
         9 . The process as set forth in  claim 8  wherein the chlorinated gas separator is a vapor-liquid separator, the silicon tetrachloride separator is a distillation column and the trichlorosilane purifier is a distillation column. 
     
     
         10 . The process as set forth in  claim 8  wherein the separated hydrogen and unreacted hydrogen chloride are introduced into a separation system to separate hydrogen and hydrogen chloride, the separated hydrogen chloride being introduced into the chlorination reactor, the separated hydrogen being introduced into at least one of the fluidized bed reactor and hydrogenation reactor. 
     
     
         11 . The process as set forth in  claim 7  wherein the separation system comprises a hydrogen separator, a hydrogen purifier and a hydrogen chloride purifier, wherein:
 the hydrogen and hydrogen chloride are introduced into the hydrogen separator to produce a hydrogen recycle gas and a hydrogen chloride recycle gas; 
 the hydrogen recycle gas is introduced into a hydrogen purifier to remove impurities from the hydrogen recycle gas; 
 the hydrogen chloride recycle gas is introduced into a hydrogen chloride purifier to remove impurities from the hydrogen chloride gas; and 
 the purified hydrogen recycle gas is introduced into at least one of the fluidized bed reactor and hydrogenation reactor; and 
 the purified hydrogen chloride recycle gas is introduced into the chlorination reactor. 
 
     
     
         12 . The process as set forth in  claim 11  wherein the hydrogen separator is a bubbler, the hydrogen purifier is an adsorber and the hydrogen chloride purifier is a distillation column. 
     
     
         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. 
     
     
         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. 
     
     
         15 . The process as set forth in  claim 1  wherein no hydrogen is added to the process as a make-up stream. 
     
     
         16 . A substantially closed-loop process for producing polycrystalline silicon, the process comprising:
 introducing trichlorosilane and hydrogen to a first fluidized bed reactor to produce polycrystalline silicon and a first effluent gas comprising silicon tetrachloride, hydrogen and unreacted trichlorosilane;   introducing silicon and an amount of silicon tetrachloride and hydrogen from the effluent gas into a second fluidized bed reactor to produce a second effluent gas comprising trichlorosilane and unreacted hydrogen and unreacted silicon tetrachloride;   contacting hydrogen chloride and silicon to produce trichlorosilane and silicon tetrachloride; and   introducing the trichlorosilane produced by contacting hydrogen chloride and silicon into the first fluidized bed reactor to produce polycrystalline silicon.   
     
     
         17 . The process as set forth in  claim 16  wherein hydrogen chloride and silicon are introduced into a chlorination reactor to produce a chlorinated product gas comprising the trichlorosilane and silicon tetrachloride, the process comprising introducing the chlorinated product gas into a purification system to produce a purified trichlorosilane stream and a purified silicon tetrachloride stream, the purified trichlorosilane stream being introduced into the first fluidized bed reactor. 
     
     
         18 . The process as set forth in  claim 17  wherein the first effluent gas is introduced into a first effluent gas separator to separate hydrogen from trichlorosilane and silicon tetrachloride, the trichlorosilane and silicon tetrachloride being introduced into the chlorinated gas purification system, the purified silicon tetrachloride stream being introduced into the second fluidized bed reactor. 
     
     
         19 . The process as set forth in  claim 18  wherein the first effluent gas separator is a vapor-liquid separator. 
     
     
         20 . The process as set forth in  claim 17  wherein the second effluent gas is introduced into a second effluent gas separator system to separate trichlorosilane and unreacted silicon tetrachloride from hydrogen, the trichlorosilane and unreacted silicon tetrachloride being introduced into the chlorinated gas purification system. 
     
     
         21 . The process as set forth in  claim 20  wherein the second effluent gas separator is a vapor-liquid separator. 
     
     
         22 . The process as set forth in  claim 20  wherein the second effluent gas comprises hydrogen and hydrogen chloride, wherein trichlorosilane and unreacted silicon tetrachloride are separated from hydrogen and hydrogen chloride, the hydrogen and hydrogen chloride being introduced into a separation system to separate hydrogen and hydrogen chloride, the separated hydrogen chloride being introduced into the chlorination reactor, the separated hydrogen being introduced into at least one of the first fluidized bed reactor and the second fluidized bed reactor. 
     
     
         23 . The process as set forth in  claim 17  wherein the chlorinated product gas comprises trichlorosilane, silicon tetrachloride, hydrogen and unreacted hydrogen chloride and wherein the purification system comprises a chlorinated gas separator, a silicon tetrachloride separator and a trichlorosilane purifier, wherein:
 the chlorinated product gas is introduced into the chlorinated gas separator to separate trichlorosilane and silicon tetrachloride from hydrogen and unreacted hydrogen chloride; 
 the separated trichlorosilane and silicon tetrachloride are introduced into the silicon tetrachloride separator to separate silicon tetrachloride from trichlorosilane and produce a trichlorosilane feed gas; 
 the trichlorosilane feed gas is introduced into a trichlorosilane purifier to remove impurities from the feed gas; and 
 the purified trichlorosilane feed gas is introduced into the first fluidized bed reactor to produce polycrystalline silicon. 
 
     
     
         24 . The process as set forth in  claim 23  wherein the chlorinated gas separator is a vapor-liquid separator, the silicon tetrachloride separator is a distillation column and the trichlorosilane purifier is a distillation column. 
     
     
         25 . The process as set forth in  claim 23  wherein the separated hydrogen and unreacted hydrogen chloride are introduced into a separation system to separate hydrogen and hydrogen chloride, the separated hydrogen chloride being introduced into the chlorination reactor, the separated hydrogen being introduced into at least one of the first fluidized bed reactor and the second fluidized bed reactor. 
     
     
         26 . The process as set forth in  claim 22  wherein the separation system comprises a hydrogen separator, a hydrogen purifier and a hydrogen chloride purifier, wherein:
 the hydrogen and hydrogen chloride are introduced into the hydrogen separator to produce a hydrogen recycle gas and a hydrogen chloride recycle gas; 
 the hydrogen recycle gas is introduced into a hydrogen purifier to remove impurities from the hydrogen recycle gas; 
 the hydrogen chloride recycle gas is introduced into a hydrogen chloride purifier to remove impurities from the hydrogen chloride gas; and 
 the purified hydrogen recycle gas is introduced into at least one of the first fluidized bed reactor and the second fluidized bed reactor; and 
 the purified hydrogen chloride recycle gas is introduced into the chlorination reactor. 
 
     
     
         27 . The process as set forth in  claim 26  wherein the hydrogen separator is a bubbler, the hydrogen purifier is an adsorber and the hydrogen chloride purifier is a distillation column. 
     
     
         28 . The process as set forth in  claim 16  wherein the molar ratio of chlorine added as a make-up to polycrystalline silicon product that is produced is less than about 2:1. 
     
     
         29 . The process as set forth in  claim 16  wherein the molar ratio of hydrogen added as a make-up to polycrystalline silicon product that is produced is less than about 1:1. 
     
     
         30 . The process as set forth in  claim 16  wherein no hydrogen is added to the process as a make-up stream.