反应详情

FIG. 1 is a diagram of the invented process using sodium hydroxide and ammonium hydroxide. Terephthalic acid, sodium hydroxide and ammonium hydroxide are metered into reservoir 1 by lines 2, 3 and 4 in ratios of one mole per mole at the beginning of the electrochemical reduction process to form sodium ammonium terephthalate. Added ammonium hydroxide is used as a buffer to raise the pH from approximately 7 to within the range of from about 8.0 to about 11.0. The sodium ammonium salt solution is thereupon pumped by suitable means by line 5 to electrolysis cell 6 wherein the salt of terephthalic acid is reduced to sodium p-hydroxymethylbenzoate (Na p-HMB). The Na p-HMB is thereupon pumped by line 7 back to the reservoir 1 which contains Na p-HMB, NH4OH, and monosodium terephthalate. After optimum levels of Na p-HMB have been reached in the reservoir 1, a portion of the electrolysis cell output of line 7 is pumped by line 8 to reactor 9 to which make-up terephthalic acid and make-up sodium hydroxide are added by lines 10 and 11. Make-up terephthalic acid and sodium hydroxide are required because of the reduction of the sodium ammonium terephthalate to Na p-HMB and to salt out the Na p-HMB. Recycle ammonium salt from reactor 9 is pumped by line 25 to line 18 and thence to reservoir 1. The disodium terephthalate in reactor 9 is pumped with the solution removed from reservoir 1 by line 12 to chill unit 13 wherein the Na p-HMB is salted out by the presence of the disodium terephthalate. The resulting slurry in chill unit 13 is pumped by line 14 to filter 15 wherein solids comprising Na p-HMB are filtered and forwarded by line 16 to be recrystallized in crystallizer 17. Mother liquor from filter 15 is recycled to reservoir 1 by line 18. Mother liquor after dewatering from crystallizer 17 is recycled to reservoir 1 by line 19, which joins line 18. Recycle slurry from filter 15 is returned to chill unit 13 by line 22 if recycle is necessary to obtain sufficient cooling. Make-up terephthalic acid and ammonium hydroxide are added to line 18 by lines 20 and 21 to restore the sodium:ammonium:terephthalate ratio and are reacted in reservoir 1. Sodium p-hydroxymethylbenzoate is removed from crystallizer 17 by line 25 to reactor 23 where it is acidified to obtain p-hydroxymethylbenzoic acid.

1. temperatureto raise the pH from approximately 7 to within the range of from about 8.0 to about 11.0
2. customa portion of the electrolysis cell output of line 7 is pumped by line 8 to reactor
3. additionare added by lines 10 and 11
4. customremoved from reservoir 1 by line 12
5. temperatureto chill unit 13 wherein the Na p-HMB
6. filtrationto filter 15 wherein solids
7. filtrationare filtered
8. customto be recrystallized in crystallizer 17
9. filtrationMother liquor from filter 15
10. filtrationRecycle slurry from filter 15
11. temperatureto chill unit 13 by line 22 if recycle
12. customto obtain sufficient cooling
13. additionare added to line 18 by lines 20 and 21
14. customSodium p-hydroxymethylbenzoate is removed from crystallizer 17 by line 25 to reactor 23 where it