1. An extraction process for a pure plant mother liquor (PPML) formed during pure terephthalic acid (PTA) production, the process comprising:
combining the PPML with a solution comprising an organic entrainer to form a mixture wherein the temperature of the PPML is at least about 20\xb0 C. less than the azeotropic temperature of the solution comprising an organic entrainer;
separating the mixture into an organic stream comprising residual aromatic carboxylic acids and an aqueous stream;
heating the organic stream via heat exchange with effluent from a distillation column to form a heated organic stream;
heating the aqueous stream via heat exchange with effluent from a recovery column to form a heated aqueous stream;
feeding the heated organic stream to the distillation column; and
feeding at least a portion of the heated aqueous stream to the recovery column.
2. The process of claim 1, further comprising feeding a second portion of the heated aqueous stream to the distillation column.
3. The process of claim 1, wherein the organic entrainer is selected from the group consisting of toluene, xylene, ethylbenzene, methyl butyl ketone, chlorobenzene, ethyl amyl ether, butyl formate, n-propyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate, amyl acetate, methyl acetate, n-butyl propionate, isobutyl propionate, propanol, water, and mixtures thereof.
4. The process of claim 1, wherein the temperature of the PPML is at least about 25\xb0 C. less than the azeotropic temperature of the solution comprising the organic entrainer.
5. The process of claim 1, wherein the temperature of the PPML is less than about 60\xb0 C.
6. The process of claim 1, wherein the temperature of the PPML is less than about 50\xb0 C.
7. The process of claim 1, further comprising cooling the PPML stream prior to the combining step.
8. The process of claim 7, further comprising filtering the PPML stream after cooling but prior to the combining step to recover a solids fraction therefrom.
9. The process of claim 8, further comprising directing the recovered solids fraction into the PTA production.
10. The process of claim 1, further comprising recovering at least a portion of the residual aromatic carboxylic acids for reuse in the PTA production by extracting them into acetic acid in the distillation column, removing the acetic acid comprising residual aromatic carboxylic acids from the distillation column, and directing the acetic acid comprising residual aromatic carboxylic acids into the PTA production.
11. A process for producing pure terephthalic acid (PTA) by oxidizing a paraphenylene compound in acetic acid to give crude terephthalic acid and purifying the crude terephthalic acid to give PTA and a pure plant mother liquor (PPML) comprising water and residual aromatic carboxylic acids, the process comprising:
combining the PPML with a solution comprising an organic entrainer to form a mixture wherein the temperature of the PPML is at least about 20\xb0 C. less than the azeotropic temperature of the solution comprising the organic entrainer;
separating the mixture of PPML and solution comprising an organic entrainer into an organic stream comprising the residual aromatic carboxylic acids and an aqueous stream;
feeding the organic stream to a second distillation column; and
feeding at least a portion of the aqueous stream to a recovery column.
12. The process of claim 11, wherein the temperature of the PPML is at least about 25\xb0 C. less than the azeotropic temperature of the solution comprising an organic entrainer.
13. The process of claim 11, wherein the temperature of the PPML is less than about 60\xb0 C.
14. The process of claim 11, wherein the temperature of the mixture is less than about 50\xb0 C.
15. The process of claim 11, further comprising cooling the PPML stream prior to the combining step.
16. The process of claim 15, further comprising filtering the PPML stream after cooling but prior to the combining step to recover a solids fraction therefrom.
17. The process of claim 16, further comprising directing the recovered solids fraction into the PTA production.
18. The process of claim 11, further comprising heating the aqueous stream via heat exchange with effluent from the recovery column prior to feeding the aqueous stream to the recovery column.
19. The process of claim 11, further comprising heating the organic stream via heat exchange with effluent from the distillation column prior to feeding the organic stream to the distillation column.
20. A system for extracting a pure plant mother liquor (PPML) formed during pure terephthalic acid (PTA) production, the system comprising:
a mixing device adapted for mixing a stream comprising the PPML with a stream comprising an organic entrainer;
at least one of a cooling device adapted for cooling the PPML stream to ensure that temperature of the PPML is at least about 20\xb0 C. less than the azeotropic temperature of the stream comprising an organic entrainer;
a separating device adapted for separating the mixture of organic entrainer and PPML into an organic stream and an aqueous stream;
an azeotropic distillation column adapted to receive the organic stream and to output an acetic acid-containing stream and the stream comprising an organic entrainer;
a heat exchanger adapted to heat the organic stream via heat exchange with the acetic acid-containing stream;
a recovery column adapted to receive the aqueous stream and to output a stripped aqueous stream; and
a heat exchanger adapted to heat the aqueous stream via heat exchange with the stripped aqueous stream.
21. The system of claim 20, wherein the mixing device comprises a static mixer.
22. The system of claim 20, wherein the cooling device is adapted for cooling the PPML stream to a temperature of less than about 65\xb0 C.
23. The system of claim 20, further comprising a filter device adapted for filtering a solids fraction from the PPML stream.
24. An extraction process for a pure plant mother liquor (PPML) formed during pure terephthalic acid (PTA) production, the process comprising:
combining the PPML with a solution comprising an organic entrainer to form a mixture having a temperature of at least about 20\xb0 C. less than the azeotropic temperature of the mixture;
separating the mixture into an organic stream comprising residual aromatic carboxylic acids and an aqueous stream;
heating the organic stream via heat exchange with effluent from a distillation column to form a heated organic stream;
heating the aqueous stream via heat exchange with effluent from a recovery column to form a heated aqueous stream;
feeding the heated organic stream to the distillation column; and
feeding at least a portion of the heated aqueous stream to the recovery column.
25. A process for producing pure terephthalic acid (PTA) by oxidizing a paraphenylene compound in acetic acid to give crude terephthalic acid and purifying the crude terephthalic acid to give PTA and a pure plant mother liquor (PPML) comprising water and residual aromatic carboxylic acids, the process comprising:
combining the PPML with a solution comprising an organic entrainer to form a mixture having a temperature of at least about 20\xb0 C. less than the azeotropic temperature of the mixture;
separating the mixture of PPML and solution comprising an organic entrainer into an organic stream comprising the residual aromatic carboxylic acids and an aqueous stream;
feeding the organic stream to a second distillation column; and
feeding at least a portion of the aqueous stream to a recovery column.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
What is claimed is:
1. A nonvolatile semiconductor memory device including a memory cell, comprising:
a semiconductor substrate;
a semiconductor layer, located above said semiconductor substrate, including a source region, a channel region and a drain region of said memory cell; and
a lower insulator film located between said semiconductor substrate and said semiconductor layer.
2. The nonvolatile semiconductor memory device according to claim 1, further comprising an insulator film on said channel region, wherein
said insulator film includes a first charge trap insulator film capable of trapping charges.
3. The nonvolatile semiconductor memory device according to claim 2, further including a gate electrode of said memory cell on said insulator film for applying a potential to said first charge trap insulator film for trapping charges.
4. The nonvolatile semiconductor memory device according to claim 3, wherein
said insulator film has a multilayer structure of a first insulator film, said first charge trap insulator film and a second insulator film, and
said lower insulator film has a multilayer structure of a third insulator film, a second charge trap insulator film for trapping charges and a fourth insulator film.
5. The nonvolatile semiconductor memory device according to claim 4, wherein
at least either said first charge trap insulator film or said second charge trap insulator film is made of a nitride film.
6. The nonvolatile semiconductor memory device according to claim 4, wherein
the electric capacitance of at least one of said first, second, third and fourth insulator films is different from the electric capacitances of remaining said insulator films.
7. The nonvolatile semiconductor memory device according to claim 4, further comprising a lower electrode for applying a potential to said second charge trap insulator film for trapping charges.
8. The nonvolatile semiconductor memory device according to claim 7, wherein
said lower electrode includes a polysilicon film or an impurity diffusion region.
9. The nonvolatile semiconductor memory device according to claim 4, having first charge trap regions trapping charges in a region including a portion corresponding to the boundary between said source region and said channel region and a region including a portion corresponding to the boundary between said drain region and said channel region in said first charge trap insulator film while having second charge trap regions trapping charges in a region including a portion corresponding to the boundary between said source region and said channel region and a region including a portion corresponding to the boundary between said drain region and said channel region in said second charge trap insulator film.
10. The nonvolatile semiconductor memory device according to claim 9, capable of storing information of four bits in one said memory cell.
11. The nonvolatile semiconductor memory device according to claim 1, wherein
said lower insulator film includes a charge trap insulator film capable of trapping charges.
12. The nonvolatile semiconductor memory device according to claim 11, wherein
said lower insulator film has a multilayer structure of a first insulator film, said charge trap insulator film and a second insulator film.
13. The nonvolatile semiconductor memory device according to claim 12, wherein
said charge trap insulator film is a nitride film.
14. The nonvolatile semiconductor memory device according to claim 12, further including a lower electrode applying a potential to said charge trap insulator film for trapping charges.
15. The nonvolatile semiconductor memory device according to claim 14, wherein
said lower electrode includes a polysilicon film or an impurity diffusion region.
16. The nonvolatile semiconductor memory device according to claim 12, including charge trap regions trapping charges in a region including a portion corresponding to the boundary between said source region and said channel region and a region including a portion corresponding to the boundary between said drain region and said channel region in said charge trap insulator film.