| 摘要 |
Crude sorbic acid yielded in the polyester decomposition step (1) is submitted to the crystallization step (2) to crystallize the sorbic acid, and the crystallized sorbic acid is separated from the mother liquor (filtrate). This mother liquor is submitted to the extraction step (3) in which a specific extractant is used. The resultant extract (organic phase) is submitted to the back extraction step (4) to treat it with an aqueous alkali solution to extract the sorbic acid as a sorbic acid salt into the aqueous phase. This aqueous phase is neutralized in the neutralization step (6) and the sorbic acid yielded is recovered in the separation step (7). The extractant is an organic solvent which is separable from water and has a solubility in water of 1 wt.% or lower, and in which the solubility of sorbic acid is 0.5 wt.% or higher (e.g., a C6-20 aliphatic alcohol, ketone, ester, aromatic ether, etc.). Thus, sorbic acid can be recovered at a high recovery percentage from the filtrate (mother liquor) yielded in the sorbic acid production step, and the BOD of the waste liquor can be effectively reduced.
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