CAS OpenIR
纳滤法分离回收咪唑离子液体研究
钱建国
Subtype博士
Thesis Advisor张香平
2018
Degree Grantor中国科学院大学
Degree Discipline化学工程
Keyword离子液体,团簇,纳滤,溶液环境,溶解扩散模型
Abstract

离子液体作为一种结构可调的绿色试剂已经在许多领域被广泛研究和应用。针对离子液体大规模工业化应用,需要解决的最突出问题之一就是如何高效地回收重复利用,因此,开发离子液体回收方法具有重要现实意义。纳滤作为一种重要的化工分离单元操作,由于其操作简单,低温节能等优点,被广泛应用于多种体系中各组分的分离和提纯。本论文开展了纳滤分离一系列咪唑离子液体的研究。考察了分子大小以及溶液环境对膜分离效果的影响。重点分析了离子液体团簇对膜分离效果,以及膜污染和膜重复使用的影响。同时,基于团簇对溶解扩散模型进行了合理改进,以适用于不同链长的咪唑离子液体水溶液。此外,考察了纳滤耦合蒸馏提纯离子液体的理论经济性,提出了更加高效节能地回收离子液体方法。具体内容如下:(1)使用陶氏纳滤膜分离了一系列1-烷基-3-甲基咪唑盐([Cnmim]X,n表示阳离子烷基侧链数,X表示阴离子)。考察了分子大小对膜通量(Jv)和截留率(Ro)的影响。同时研究了溶液环境对膜分离效果的影响,包括溶液pH,离子强度,大分子有机污染物。实验结果发现,分子大小和大分子有机污染物通过影响孔径筛分效应影响膜分离效果,pH和离子强度通过影响电荷效应影响膜分离效果。此外,溶液环境也对某些离子液体的物化性质产生影响,从而进一步影响膜分离机制及膜分离效果。(2)研究了离子液体团簇对膜分离效果的影响。使用陶氏纳滤膜分离了一系列不同浓度的长碳链离子液体水溶液。通过实验和分子动力学模拟方法,研究了团簇在水溶液中的存在状态。阐述了团簇对膜通量和截留率的影响,以及对膜污染和膜重复利用的影响。实验结果发现,团簇主要通过影响孔径筛分作用影响膜分离效果:离子液体浓度增加,团簇程度提高,团簇的平均大小越大,导致膜通量降低,截留率升高。此外,团簇缓解膜污染程度,其原因是团簇进入孔道的难度更大,空间位阻效应得到了加强,膜孔道被堵塞几率下降。此外,通过调控团簇大小,提高了纳滤分离长碳链离子液体水溶液的分离性能。(3)考察了溶解扩散模型对纳滤分离离子液体水溶液的适用性。使用陶氏纳滤膜分离了不同浓度的长碳链离子液体水溶液,测定了它们的膜通量和截留率。使用溶解扩散模型对截留率进行了预测,并和实验值进行了对比。结果发现,该模型适用于低浓度长碳链离子液体水溶液,而不适用于高浓度长碳链离子液体水溶液。建立了考虑团簇因素的溶解扩散模型,通过分子动力学模拟,对不同浓度的离子液体水溶液中的团簇大小进行了合理地定量计算,并依据团簇大小对该模型中的相关参数进行了合理地修饰。计算结果发现,相比未改进的模型,通过改进后的模型预测地计算值和实验值更加吻合。(4)分析了纳滤耦合蒸馏提纯离子液体的理论经济性。计算了纳滤联合减压蒸馏方法(先经纳滤预浓度,再减压蒸馏)提纯离子液体的成本,并和单纯减压蒸馏方法提纯离子液体的成本进行了对比。实验结果发现,纳滤联合减压蒸馏方法的成本大大低于单一减压蒸馏的成本,其原因是气体做功能耗远远低于加热蒸发的能耗。同时,基于团簇对膜分离性能的影响,提出了更加高效节能地回收长碳链离子液体的方法,即二级纳滤耦合减压蒸馏提纯长碳链离子液体的方法。首先使用孔径较小的纳滤膜进行脱水,随着离子液体浓度升高,团簇生成并逐渐变大,适时改用孔径较大的膜纳滤继续进行脱水,最后经过两步预浓缩的离子液体经减压蒸馏彻底除水。实验结果发现,该方法相比一级纳滤,成本得到进一步降低。;Ionic liquis (ILs) have been extensively studied in many fields as a structurally tunable green reagent. In terms of large-scale application of ILs, one of the most prominent obstacles is how to efficiently recycle ILs. Therefore, it has important practical significance to develop methods to recover ILs. As an important chemical separation unit, nanofiltration is widely used in the separation and purification fields due to its simple operation and energy saving. In this thesis, a series of imidazole-based ILs were filtrated by nanomembranes, and the effects of molecular size and solution environment on membrane filtration have been studied. What’s more, the effect of ion cluster on membrane filtration, membrane fouling and membrane re-use were also investigated. the solution diffusion model was rationally improved based on ion cluster, which makes it suitable for aqueous solutions of ILs with different chain lengths. In addition, the theoretical economic analysis of nanofiltration combined distillation of ILs was studied, and a more efficient and energy-saving method for recovering long-alkyl-chain ILs was proposed. The details are as follows:Firstly, A series of 1-alkyl-3-methylimidazolium-based ILs ([Cnmim]X, n represents the number of cationic alkyl side chains, and X represents anion) were filtrated using Dow nanofiltration membranes. The effect of molecular sizes on volumetric membrane flux (Jv) and observed rejection (Ro) was studied, such as the size of the cationic alkyl side chain and the different halide anions. In addition, the effect of solution environment on membrane filtration was investigated, including pH, ionic strength, and macromolecular organic pollutants. The experimental results showed that the molecular size and macromolecular organic pollutants influence the nanofiltration performance by impacting sieving effect, and the pH and ionic strength influence the nanofiltration performance by affecting charge effect. Besides, the solution environment also impacts the physicochemical properties of certain ILs, thereby influencing the nanofiltration mechanism, and thus the nanofiltration performance.Secondly, the effect of ion cluster on concentration of ILs aqueous solution by nanofiltration was investigated. A series of long-alkyl-chain ILs aqueous solutions with different concentrations were filtrated using Dow nanofiltration membranes. The existential state of ion cluster in aqueous solution was studied by experiments and molecular dynamics simulation. The effect of ion cluster on Jv, Ro, membrane fouling and membrane recycling were investigated. The experimental results showed that ion cluster mainly influences the nanofiltration performance by affecting sieving effect: with the increasing of concentration of ILs, the degree of ion cluster increases, and thus the larger average size of ion cluster, which leads to the decrease of the Jv and the increase of the Ro. In addition, ion cluster alleviates the degree of membrane fouling, It is more difficult for ion cluster to enter membrane pores, because the steric hindrance effect is enhanced, and the probability of the membrane pores being blocked is decreased. What’s more, according to the influence of the cluster on the membrane filtration, the filtration performance was enhanced by adjust the molecular size of ion cluster in long-alkyl-chain ILs aqueous solutions.Third, The applicability of the solution-diffusion model to the nanofiltration of ILs aqueous solutions was investigated. A series of long-alkyl-chain ILs aqueous solutions with different concentrations were filtrated using Dow nanofiltration membranes, and their Jv and Ro were measured. Using the solution-diffusion model, Ro was predicted by the experimental value Jv. As a result, it was found that the model is suitable for long-alkyl-chain ILs aqueous solutions with low concentrations, but not for long-alkyl-chain ILs aqueous solutions with high concentrations. The solution-diffusion model was reasonably modified based on ion cluster. The molecular size of ion clusters in different concentrations of ILs was quantitatively calculated by molecular dynamics simulation. The relevant parameters in the model were calculated according to the size of ion cluster. The calculation results showed that compared with the unmodified model, the calculated values predicted by the improved model agreed better with the experimental values.Fourth, The theoretically economic investigation of nanofiltration combined with distillation to recover ILs was investigated. The costing of nanofiltration combined with vacuum distillation (pre-concentration by nanofiltration and followed by reduced pressure distillation) for recovering ILs aqueous solutions was calculated. The experimental results showed that the costing of the nanofiltration combined with vacuum distillation method is much lower than that of simple vacuum distillation. The reason for the reduction in costing is that the gas work is much lower than the energy consumption of heating and evaporation. In addition, based on the influence of ion cluster on membrane filtration, a more efficient and energy-saving method for recovery of long-alkyl-chain ILs was proposed, which is a method of two-stage nanofiltration combined with vacuum distillation to purify long-alkyl-chain ILs. Firstly, the membrane with smaller pore size is used for filtration. As the concentration of ILs increases, the ion clusters are formed and the size gradually becomes larger, and the membrane with a larger pore diameter is used at the appropriate moment. Finally, the pre-concentrated ILs was completely purified by reduced pressure distillation. The experimental results show that the costing of the method is further reduced compared to the one-stage nanofiltration. 

Language中文
Document Type学位论文
Identifierhttp://ir.ipe.ac.cn/handle/122111/40731
Collection中国科学院过程工程研究所
Recommended Citation
GB/T 7714
钱建国. 纳滤法分离回收咪唑离子液体研究[D]. 中国科学院大学,2018.
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