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离子液体及低共熔溶剂催化醇解PET的应用基础研究
刘博
Subtype博士
Thesis Advisor徐宝华
2019-07-01
Degree Grantor中国科学院大学
Degree Discipline化学工程
Keyword聚对苯二甲酸乙二醇酯,离子液体,低共熔溶剂,醇解,均相催化
Abstract

聚对苯二甲酸乙二醇酯(PET)作为一种性能优异的工程塑料,在生活中有着极为广泛的应用。但伴随着PET消费量的逐年升高,废弃PET带来了严重的环境污染问题,同时PET的生产原料源于不可再生的石油资源,因此无论从保护环境还是节约资源的角度,PET的循环再利用都具有重要意义。醇解法是一种利用PET与醇类反应,将PET降解为小分子单体的方法,是实现PET循环利用的有效途径。目前,醇解法的主要问题在于催化效率低,产物选择性差。离子液体和低共熔溶剂作为新兴的绿色介质和催化剂,在PET醇解领域已经显示出了广泛的应用前景。本论文设计了一系列新型离子液体和低共熔溶剂催化剂用于醇解PET,并提出了一种高效均相乙二醇醇解PET的方法,为PET的高效降解及循环利用提供新思路。本论文的研究内容及成果如下:(1)设计合成了1,3-二甲基脲/过渡金属盐低共熔溶剂并用于催化PET乙二醇醇解反应,结果表明1,3-二甲基脲/醋酸锌低共熔溶剂具有较高的催化活性。优化了反应工艺条件:1,3-二甲基脲/醋酸锌摩尔比4:1、反应温度190 °C、反应时间20 min、催化剂量为PET质量5%、乙二醇质量为PET质量的4倍,此时PET转化率为100%,对苯二甲酸双羟乙基酯(BHET)收率为82.2%。低共熔溶剂催化PET乙二醇醇解的表观反应活化能测定为148.8 kJ/mol。催化剂循环结果表明,催化剂在6次循环后仍能保持较高的催化活性。实验结果证实1,3-二甲基脲中胺基对于催化反应起了重要的作用,基于实验结果提出了Lewis酸-碱协同催化的反应机理。(2)设计合成了4种非金属离子液体,并将其用于催化PET乙二醇醇解反应。研究表明,碱性非金属离子液体1,5-二氮杂双环[4.3.0]-5-壬烯醋酸盐([HDBN]OAc)的催化活性最高,优化了反应工艺条件:在催化剂量为PET质量的5%、190 °C下反应50 min,BHET选择性可达到85.5%,反应速率和产物选择性均高于已报道的其他碱性离子液体。5次循环后催化剂活性没有明显降低。确定了催化剂与乙二醇之间存在氢键相互作用,发现催化剂碱性强弱对于其催化活性存在决定性影响。(3)提出了一种将PET颗粒溶解实现高效均相催化PET乙二醇醇解的方法。选择了二甲亚砜(DMSO)、N-甲基吡咯烷酮(NMP)、苯胺和硝基苯作为PET乙二醇醇解反应的溶剂。加入溶剂形成均相降解体系后,反应时间缩短至5 min以内。该均相降解方法对催化剂具有广泛的适应性,对于不同金属盐、离子液体和低共熔溶剂均能有效提高反应速率。研究了均相降解体系与非均相降解体系的动力学差异,结果表明均相降解体系符合一级反应模型,表观活化能为75.2 kJ/mol,非均相降解体系符合缩核模型,表观活化能为125.0 kJ/mol。PET溶解的机理研究表明π-π相互作用是PET在芳香性溶剂溶解的主要推动力。(4)设计合成了一系列脲类金属盐低共熔溶剂,应用于PET甲醇醇解。其中尿素/醋酸锌低共熔溶剂表现出了最优的催化活性。优化了反应条件:在PET颗粒粒径为40-60目,甲醇和催化剂的质量比为1:4:0.005,反应温度为160 °C,反应时间为60 min时,PET转化率为100%,对苯二甲酸二甲酯(DMT)收率为94.8%。PET甲醇醇解的反应模型符合缩核模型,表观活化能为74.2 kJ/mol。脲类金属盐低共熔溶剂催化PET甲醇醇解机理研究表明,尿素和金属盐在PET甲醇醇解过程中起了协同催化的作用。;As a kind of engineering plastic with excellent performance, polyethylene terephthalate (PET) has a wide range of applications in our life. However, waste PET has caused serious environmental pollution with its increasing consumption. Moreover, PET raw materials are derived from non-renewable petroleum resources. Therefore, the recycling of PET is greatly significant from the purpose of environmental protection and resource saving.The alcoholysis method is a method that PET reacted with alcohol to form monomers, and is an effective way to realize PET recycling. At present, the main problems of the alcoholysis method are low catalytic efficiency and poor product selectivity. As emerging green mediums and catalysts, ionic liquids (ILs) and deep eutectic solvents (DESs) have shown wide application prospects in the fields of PET alcoholysis. In this thesis, a series of new ILs and DESs catalysts were designed. A high efficiency homogeneous glycol alcoholysis method was proposed. The reaction conditions were optimized and the reaction mechanism was obtained, which provides new idea for the efficient degradation and recycling of PET. The main innovative work and results are as follows:(1) 1,3-dimethyl urea/transition metal salt DESs were designed and synthesized to catalyze the PET glycolysis reaction. The reaction activity evaluation result showed that 1,3-dimethyl urea/zinc acetate salt had high catalytic activity. The optimized reaction conditions were obtained: under the conditons of molar ratio between 1,3-dimethylurea and zinc acetate 4:1, reaction temperature 190 °C, reaction time 20 min, the ratio of catalyst 5 wt%, the mass ratio of EG and PET 4:1, the conversion of PET was 100% and the yield of bis(2-hydroxyethyl) terephthalate (BHET) was 82.2%. The apparent reaction activation energy of DESs catalyzed PET glycolysis was 148.8 kJ/mol. The results of catalyst recycling showed that the catalyst maintained high catalytic activity after 6 cycles. The experimental results confirmed that the amine group in 1,3-dimethylurea played an important role in the catalytic reaction. Based on the experimental results, the reaction mechanism of Lewis acid-base synergistic catalysis was proposed.(2) Four non-metal ionic liquids were designed and synthesized and used to catalyze the PET glycolysis reaction. Studies have shown that the alkaline non-metal ionic liquid 1,5-diazabicyclo[4.3.0]-5-decene acetate ([HDBN]OAc) has the highest catalytic activity, and optimized reaction conditions are obtained: under the conditions of catalyst amount 5 wt%, 190 °C and 50 min, the selectivity of BHET can reach 85.5%, and the reaction rate and product selectivity are higher than other alkaline ionic liquids reported. There was no significant decrease in catalyst activity after 5 cycles. The hydrogen bond interaction between the catalyst and ethylene glycol was determined. It was found that the basic strength of the catalyst had a decisive influence on its catalytic activity.(3) A method for dissolving PET particles to achieve efficient homogeneous glycolysis of PET was proposed. Dimethyl sulfoxide (DMSO), N-methylpyrrolidone (NMP), aniline and nitrobenzene were selected as solvents for the PET glycol alcoholysis reaction. After adding a solvent to form a homogeneous degradation system, the reaction time was shortened to within 5 min. The homogeneous degradation method has wide adaptability to the catalysts, and can effectively increase the reaction rate for different metal salts, ionic liquids and eutectic solvents. The kinetic differences between homogeneous degradation system and heterogeneous degradation system were studied. The results show that the homogeneous degradation system accords with the first-order reaction model, the apparent activation energy is 75.2 kJ/mol. The heterogeneous degradation system conforms to the shrinking-core model, and the apparent activation energy was 125.0 kJ/mol. Mechanism studies of PET dissolution indicate that the π-π interaction is the main driving force for the dissolution of PET in aromatic solvents.(4) A series of ureas/metal-salt DESs were designed and synthesized, which were used in the PET methanolysis reaction. Urea/Zinc acetate showed the best catalytic activity. Optimized reaction conditions were obtained: under the conditions of PET 40-60 mesh, the ratio of PET, methanol and catalyst 1:4:0.005, 160 °C, 60 min, the PET conversion was 100%, the yield of dimethyl terephthalate (DMT) was 94.8%. The reaction kinetics of PET methanolysis was studied. PET methanolysis kinetics model was consistent with the shrinking core model, and the apparent activation energy was 74.2 kJ/mol. The mechanism of methanolysis of PET catalyzed by urea metal salt eutectic solvent was showed that urea and metal salt played a synergistic catalytic role in the methanolysis of PET.

Language中文
Document Type学位论文
Identifierhttp://ir.ipe.ac.cn/handle/122111/40635
Collection中国科学院过程工程研究所
Recommended Citation
GB/T 7714
刘博. 离子液体及低共熔溶剂催化醇解PET的应用基础研究[D]. 中国科学院大学,2019.
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