| 摘要 |
A process for the recovery and extractive purification of p-aminophenol involving contacting an aqueous feed solution prepared by catalytic reduction of nitrobenzene in acid medium and containing 4,4 min -diaminodiphenyl ether, aniline and other minor amine by-products with a base to adjust the pH of the solution to 4.0-5.0, and then extracting the resulting aqueous feed solution with a mixture of aniline and toluene to selectively dissolve 4,4 min -diaminodiphenyl ether in the aniline-toluene mixture and to produce an aqueous phase containing principally p-aminophenol and an organic aniline-toluene phase containing p-aminophenol, 4,4 min -diaminodiphenyl ether and other amine by-products. The ratio of aniline to toluene is within the range between approximately 4 parts by volume aniline to 1 part by volume toluene and approximately 1 part by volume aniline to 4 parts by volume toluene, preferably a ratio of 1:1.
<??>The volume ratio of aniline-toluene to aqueous feed solution is 0.05 to 1:1, a ratio of 0.2:1 being preferred.
<??>After separation of the aqueous phase from the organic phase, the purified p-aminophenol is recovered from the aqueous phase.
<??>The remaining organic phase may, preferably, be subjected to back extraction by the addition thereto of a potassium or sodium hydroxide solution in excess to obtain an aqueous layer of a pH of more than 12. This aqueous solution can be used to recover p-aminophenol by neutralisation, or to adjust the pH of the original aqueous feed solution to a pH of 4.0-5.0.
<??>In lieu of back-extracting the organic phase with a solution of potassium or sodium hydroxide, the organic phase may also be back-extracted with an ammonium sulfate solution to achieve a greater overall yield of p-aminophenol.
<??>The process may also be carried out by a fractional countercurrent extraction of the aqueous feed solution containing p-aminophenol and the above-mentioned impureties and having a pH of between 4.0 and 5.0 with an aniline-toluene mixture and an ammonium sulfate solution, aniline sulfate or sulfuric acid.
<??>The 4,4 min -diaminodiphenyl ether is again selectively extracted into the aniline-toluene mixture. |
