氯甲烷尾气综合回收工艺设计与优化

发布时间：2018-06-25 17:00

  本文选题：氯甲烷 + 二甲醚　； 参考：《大连理工大学》2015年硕士论文

【摘要】：氯甲烷是丁基橡胶合成的重要溶剂。在溶剂循环精制过程中,以尾气排放掉的氯甲烷约占溶剂总量的十分之一,进一步回收尾气中的氯甲烷,已成为企业重点考虑的问题。排放的三股尾气中钝化尾气与其他尾气组成存在显著差异,组成中含有大量二甲醚(25mo1%),且与氯甲烷沸点极为接近,难以通过常规手段分离,所以将其单独处理；而另两股尾气氯甲烷浓度(其一：3.5 mo1%；其二：20 mmo1%)差异较大,根据这一特点,进行梯级回收处理。因此,本文的工作主要分为以下两个部分：(1)氯甲烷与二甲醚的沸点非常接近,难以精馏分离,工业上通常利用浓硫酸与二甲醚的反应来提纯氯甲烷,分离费用高,且存在安全隐患。根据两种气体与H+形成氢键能力的差别,提出以水为吸收剂脱除氯甲烷中的二甲醚。为了吸收过程的准确模拟与优化,利用二甲醚-氯甲烷、二甲醚-水、氯甲烷-水三个二元体系的相平衡数据比较了UNIQUAC、NRTL 和 NRTL-RK三种组分活度系数评估模型的准确性。结果表明,NRTL-RK模型的评估结果与实验数据吻合度更高,平均相对偏差小于2.5%。在此基础上,使用NRTL-RK模型预测三元体系的气液相平衡,分析了不同温度和压力条件下水对氯甲烷和二甲醚的分离系数和溶解度影响,发现随着液相中二甲醚含量的增加,水溶液性质逐渐偏向二甲醚,增加了氯甲烷溶解度,导致分离系数不断降低,尤其是低温时较为明显,并从热力学角度给出水吸收二甲醚适宜的温度、压力范围。在以上研究的基础上,设计以水为吸收剂的吸收-解吸工艺,对钝化尾气中氯甲烷进行回收处理。采用Aspen Plus模拟软件对工艺进行模拟优化,考察了吸收塔压力、吸收剂温度、解吸塔压力对二甲醚吸收率、氯甲烷损失率及再生能耗的影响,优化结果表明,氯甲烷回收率达到95.7%,纯度为99.1 mo1%,单耗仅为0.016￥·kg-1。此外,水吸收工艺避免了腐蚀性吸收剂浓硫酸的使用,更加安全清洁高效。(2)针对于浓度差异的常规氯甲烷尾气,直接混合回收,使得物料返混,分离能耗增加。因此,设计压力梯级利用、氯甲烷梯级浓缩的压缩冷凝-膜-PSA耦合回收流程。其工艺特点：膜分离装置浓缩低浓度氯甲烷,压缩冷凝回收高浓度氯甲烷,PSA深度脱除氯甲烷。对工艺进行模拟优化,考察了冷凝温度对氯甲烷吸收率的影响以及膜面积对压缩冷凝装置和PSA装置负荷的影响。结果表明：膜面积增大,有利于减少PSA装置负荷,同时可增加压缩冷凝进气氯甲烷流量。通过经济效益核算,优选膜面积80 m2、冷凝温度-35℃,可实现回收率为99.25%,放空气中氯甲烷含量小于40 g/m3,创造经济效益近111万元。
[Abstract]:Chloromethane is an important solvent in the synthesis of butyl rubber. In the process of solvent recycling refining, the amount of chloromethane emitted from tail gas is about 1/10 of the total solvent, and it has become an important problem for enterprises to recover chloromethane from tail gas. There is significant difference between passivation tail gas and other tail gas components, which contains a large amount of dimethyl ether (25mo1%), and is very close to the boiling point of chloromethane, so it is difficult to be separated by conventional means. However, the concentration of chloromethane (1: 3.5 mo1; 2: 20 mmo1%) in the other two streams of tail gas varies greatly. According to this characteristic, cascade recovery is carried out. Therefore, the work of this paper is divided into the following two parts: (1) the boiling point of chloromethane and dimethyl ether is very close, it is difficult to be separated by distillation. In industry, the reaction of concentrated sulfuric acid and dimethyl ether is usually used to purify chloromethane, and the separation cost is high. And there are hidden safety problems. According to the difference of hydrogen bonding ability between two gases and H, water is used as absorbent to remove dimethyl ether from chloromethane. In order to accurately simulate and optimize the absorption process, the accuracy of the evaluation models for the activity coefficients of UNIQUACU NRTL and NRTL-RK were compared using the phase equilibrium data of three binary systems: dimethyl ether-chloromethane, dimethyl ether-water and chloromethane water. The results show that the evaluation results of NRTL-RK model are more consistent with the experimental data, and the average relative deviation is less than 2.5. On this basis, the NRTL-RK model was used to predict the vapor-liquid equilibrium of the ternary system. The effects of water at different temperatures and pressures on the separation coefficient and solubility of chloromethane and dimethyl ether were analyzed. It was found that with the increase of the content of dimethyl ether in liquid phase, The properties of aqueous solution gradually deviate to dimethyl ether and increase the solubility of chloromethane, which leads to the constant decrease of separation coefficient, especially at low temperature. The suitable temperature and pressure range for water absorption of dimethyl ether are given from the point of view of thermodynamics. On the basis of the above research, an absorption-desorption process with water as absorbent was designed to recover chloromethane from passivation tail gas. The process was simulated and optimized by Aspen Plus simulation software. The effects of absorber pressure, absorbent temperature and desorption column pressure on dimethyl ether absorption rate, loss rate of chloromethane and regeneration energy consumption were investigated. The recovery rate of chloromethane was 95.7%, the purity was 99.1 mol ~ (-1), and the unit consumption was only 0.016 kg ~ (-1). In addition, the water absorption process avoids the use of corrosive absorbent concentrated sulfuric acid, and is safer, cleaner and more efficient. (2) aiming at the conventional chloromethane tail gas with different concentration, the material is remixed and recovered directly, and the separation energy consumption is increased. Therefore, the compression condensing-membrane-PSA coupling recovery process with pressure cascade utilization and chloromethane cascade concentration is designed. The characteristics of the process are as follows: low concentration chloromethane is concentrated in membrane separator, and high concentration chloromethane is recovered by compression condensation. The effects of condensation temperature on the absorption rate of chloromethane and the effect of film area on the load of compression condenser and PSA unit were investigated. The results show that the increase of membrane area is beneficial to reduce the load of PSA unit and increase the flow rate of compressed condensate inlet chloromethane. The optimum film area is 80m2, the condensation temperature is -35 鈩，

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