苯酚羟基化合成苯二酚反应产物分离过程酚焦油的形成原因

Phenolic Tar Formation during Products Separation of Diphenols Synthesis by Phenol Hydroxylation

对苯酚羟基化合成苯二酚产物分离过程酚焦油的形成原因进行了研究。模拟研究表明,在含有邻苯二酚和对苯二酚的混合溶液中,邻苯二酚比对苯二酚更易氧化缩合生成酚焦油。苯酚羟基化反应液中催化剂残留和催化剂被溶解形成的金属离子对酚焦油的形成具有促进作用;对苯醌的存在对酚焦油的生成具有促进作用;泄漏进入的氧或空气可加速苯二酚的氧化缩合反应;酚焦油生成量随常压脱水和减压精馏过程操作温度的升高、操作时间的延长而增加。醋酸能溶解催化剂活性组分,存在醋酸和金属离子残留问题,从而增加了羟基化反应产物分离过程酚焦油的生成量。在羟基化反应产物中加入Na2HSO3,使羟基化反应产物中的对苯醌还原,同时减少羟基化反应产物中的溶解氧含量,从而起到了抑制脱水和精馏过程中酚焦油生成的作用。

Formation of phenolic tar during separation of products from diphenols synthesis by phenol hydroxylation was studied. Phenolic tar was formed when dehydration of products under atmospheric pressure and successive vacuum distillation. In mixed solution of catechol and hydroquinone, the former condensated to phenolic tar more easily than hydroquinone. Residue of catalyst,presence of dissolved metal ions,leaked in oxygen and benzoquinone, would all accelerate formation of phenolic tar in hydroxylated liquid. High temperature and long operation time would also favoured amount of phenolic tar produced. Active components of composite oxides catalysts could be partly dissolved by acetic acid in hydroxylation system and increased amount of phenolic tar. Residual acetic acid and metallic ions could be avoided by modification of composite oxides catalyst, using solid acid instead of acetic acid as assistant catalyst. Na2HSO3 could inhibit formation of phenolic tar during dehydration and distillation of hydroxylated products.