熔融结晶法回收硝基氯苯精馏废液的研究

Study on the recovery of nitrochlorobenzene from rectification waste by means of melt crystallization

采用熔融结晶法对精馏塔处理过的硝基氯苯废料回收进行了研究。考察了指定进料组成下,降温速率、结晶终温、结晶时间等操作条件对对硝基氯苯(p-NCB)和间硝基氯苯(m-NCB)结晶过程的影响,以及对位结晶与间位结晶的差异。给出了2种典型进料组成的最优操作分离条件:进料质量分数w(p-NCB)=89.31%、w(m-NCB)=10.69%时,降温速率0.049 1℃/min、结晶时间480 min、结晶终温60℃;进料质量分数w(m-NCB)=76.03%、w(p-NCB)=23.97%时,降温速率0.015 8℃/min、结晶时间440 min、结晶终温27℃。实验表明,硝基氯苯间位结晶提纯比对位结晶提纯困难得多,采用实验中获得的最佳分离条件,w(p-NCB)≥90%的原料经单级结晶就可以得到纯度99%以上的产品,w(m-NCB)≥90%的原料通过二级结晶也可得到纯度99%以上的产品,而进料质量分数较低时经过多级结晶也能得到纯度99%以上的产品。

The p-nitrochlorobenzene （p-NCB） and m-nitrochlorobenzene （m-NCB） in rectification waste of nitrochlorobenzene were recovered by means of melt crystallization. Crystallizations with different composition of p-NCB and m-NCB were studied. The crystalline difference between p-NCB and m-NCB and also the effects of operating parameters, such as cooling rate, final temperature, crystallizing time on crystallization were investigated. The optimum operating conditions for the two kinds of typical material composition were found out by synthesizing all operation conditions： ω （p-NCB）= 89. 31%, ω （m-NCB）= 10. 69%, cooling rate 0. 049 ℃/min, crystallizing time 480 min, final temperature 60 ℃ ; ω （m-NCB） = 76.03 %,ω （p-NCB） = 23.97 %, cooling rate 0.015 8℃/min, crystallizing time 440 min, final temperature 27 %. The results show that crystallization of ω-NCB is more difficult than that ofp-NCB, the crystalline products with a purity of more than 99% can be got from the original of ω（p-NCB） ≥90% by one-stage crystallization at the optimum operating conditions, but by two-stage crystallization for the original of ω（m-NCB） ≥90%, and may have to be crystallized by multistage for that of low mass fraction of p-NCB or m-NCB.