CAS OpenIR
离子液体修饰多孔材料协同催化合成二元醇的研究
苏倩
Thesis Advisor成卫国
2018-07
Degree Grantor中国科学院研究生院
Degree Name博士
Degree Discipline化学工程
Keyword离子液体,氮化碳,介孔二氧化硅,乙二醇,协同催化
Abstract

二元醇,主要包括乙二醇(EG)和丙二醇(PG),是化工行业重要原料和中间体。EG是最简单的二元醇也最受关注,成为乙烯下游第二大衍生物。我国是EG消费第一大国,传统工艺水比大、能耗高、收率低,迫于能源危机及高需求的压力,技术革新成必然趋势。基于CO2为原料的碳酸乙烯酯(EC)法及环氧乙烷(EO)催化水合法是可替代传统工艺的最具工业前景的新工艺路线,也是目前国际学术研究前沿。两条技术路线中最关键的是催化剂的开发。针对目前羰基化反应催化剂稳定性与活性不能兼具以及催化水合反应活性及选择性不能兼具的难题,本课题基于离子液体高活性和聚集特性,通过修饰组装多孔材料,有效结合二者优势,针对特定反应定向制备活性位点与孔道结构协同作用的新型催化材料。围绕离子液体调控多孔材料修饰与限域组装方法、复合材料结构性质与催化性能关系以及复合材料催化反应机理三方面的内容,开展了以下五项具体工作。为EG工艺中高效催化剂的研发开辟了新的思路,为二元醇催化剂的研究奠定了基础。本论文取得的创新性成果如下:(1)以离子液体同时用作模板剂与掺杂剂实现氮化碳材料的调控制备并用于高稳定性催化环氧化合物羰基化。结合分析表征与活性评价,获得离子液体浓度对氮化碳材料结构性质与催化性能的影响规律,优化得到最佳离子液体添加浓度(模板剂与前驱体比为0.01)和B掺杂量(<1.59 atm%),在130℃反应条件下,可催化环氧丙烷(PO)合成碳酸丙烯酯(PC)收率达95.7%。通过DFT计算,获得氮化碳材料边缘缺陷调控规律并提出B增强型不饱和氨基协同催化反应机理。(2)揭示了离子液体浓度对介孔二氧化硅(mSiO2)骨架结构与限域作用的调控规律,获得低浓度离子液体添加下高分散度高稳定性复合材料。最优离子液体浓度(6.9 wt.%)下催化PO转化获得1.7倍于体相的高转化频率TOF(112.6 h-1)。揭示出高活性位点分散度(Si/Br=25)及强限域作用(Si-OH/Br=8)是催化活性和稳定性的主要影响因素,提出Si-OH与Br负离子协同催化羰基化反应机理。(3)获得离子液体阳离子结构对mSiO2限域离子液体材料结构性能的影响规律。针对环氧化合物羰基化反应,得出碳链较长(碳数>8)不适合于mSiO2限域催化羰基化反应的结论。结合XPS分析,提出4个碳链最优原理,即含4个碳链对称性离子液体具有适当的限域作用(Si-OH/Br=23)与较高的循环稳定性,循环使用三次PO转化率仍达87.0%。主要是由于四个方向烷基链的支撑作用,既保证稳定性又使阴离子活性位点更具催化空间。(4)优化CO2功能化的羧酸内盐离子液体的结构,筛选最优离子液体作为后续限域研究的活性组分。通过离子液体自身的链长控制,实现对活性位点的最强束缚,得出对称性短链长离子液体DMIC适合于高效催化EO转化生成EG的结论。实现仅离子液体自身短时间(0.5 h),低水比(5:1)下的高催化性能,EO转化率及EG选择性均接近100%。结合分析表征及活性评价,提出脱碳离子交换碱催化反应机理。(5)采用溶胶凝胶法,以所筛选的最优离子液体作为模板剂,实现硅胶对离子液体的限域,通过离子液体浓度/结构对硅胶复合材料尺寸进行调制,在低离子液体限域量(5.5 wt.%),低水比(5:1)下,以较少量的离子液体(体相的10%)实现了EO转化率及EG选择性均高达99.9%的高催化性能。通过对羧酸类非内盐型离子液体限域硅胶复合材料的结构-性能关系研究,发现4个碳链对称性离子液体(N(Et)4Ac)具有较好的限域催化性能。初步揭示微孔利于选择性、介孔利于转化率的微-介孔协同催化作用机制,为后续相关催化剂的开发奠定了基础。;Diols, including ethylene glycol (EG) and propylene glycol (PG), are important raw materials and intermediates in chemical industry. As the most concerned and simplest diol, EG becomes the second major derivative of ethylene. China is the largest consumer of EG. The traditional technology has some disadvantages, such as large water ratio (H2O/EO), high energy consumption and low EG yields. Under the pressure of energy crisis and high demand, technological innovation has become an inevitable trend. There are two most promising alternative processes, including CO2 based process via ethylene carbonate (EC) and catalytic hydration process of ethylene oxide (EO). All the two new technologies become international research frontiers, of which the most important is catalyst development. To overcome the disadvantages of current catalysts, including uncombined activity and stability of carbonylation catalysts in EC process, as well as scarce activity and selectivity of EO hydration catalysts, new catalysts would be designed by combining the feature of ionic liquids and porous materials. With the good activity and clustering effect, ionic liquids could be used to modify and assemble with stable porous materials to function synergistically in efficient catalytic synthesis of EG. In this work, investigations were conducted around three aspects, including ionic liquids adjusting methods on formation and assembly of porous materials, the structure-activity relationship between composite materials and catalytic performance, and synergistic catalytic mechanisms by ionic liquids and materials. The study will open a new approach for development of highly efficient catalysts in EG synthesis process and provide the basis for catalyst development of other diols. The innovative achievements of the thesis are as follows:(1) Ionic liquids were used as both templates and dopants for the preparation of carbon nitrides for epoxides carbonylation. Based on characterization and catalytic evaluation, the structure-activity relationship with varying ionic liquids concentration was obtained and the optimal addition of ionic liquids (BmimBF4/Melamine=0.01) and boron doping amount (<1.59 atm%) was achieved. With the optimal catalyst, the propylene carbonate (PC) yield could reach 95.7% under 130 oC. By DFT calculation, the regulation law for more exposed edge defects is obtained and the corresponding boron enhanced catalytic mechanism is proposed.(2) Ionic liquids adjusting law for one-step assembly of mesoporous silica (mSiO2) and confinement of ionic liquids is revealed. The composite materials owning high dispersity and stability were obtained under low ionic liquids concentration. Under the optimal confined content of EmimBr (6.9 wt.%), a higher TOF (112.6 h-1), nearly 1.7 times of bulk phases, is achieved. The high dispersity of active sites (Si/Br=25) and the strong confining effect (Si-OH/Br=8) of mSiO2 skeleton are the main factors affecting the catalytic performance, and the catalytic mechanism based on synergistic function of Si-OH and Br anion is proposed.(3) The influence law of ionic liquid cations on mSiO2 skeletons and confining effect is obtained. It was found that ionic liquids with long carbon chain (carbon number >8) were not suitable for confined catalysis of epoxides conversion, and the symmetric ionic liquids with four carbon chains functioned best both in stability (Si-OH/23) and recyclability with PO conversion up to 87.0% after three runs. Analyzed by XPS, the reason leading to the higher stability of four carbon chains is explained, which is mainly due to a propping effect in four directions, both to ensure stability and create more space for mobility of active anions.(4) CO2 functionalized carboxylic ionic liquids were designed to catalyze the EO hydration. By adjusting the chain lengths of ionic liquids, the strongest restraining effect from cation is observed with the shortest chain length. The ionic liquids with symmetric shortest chain length (DMIC) could catalyze EO hydration with nearly 100% EO conversion and EG selectivity under low water ratio (H2O/EO=5:1) and short reaction time (0.5 h). Through characterization and catalytic evaluation, the possible catalytic mechanism, based on CO2 leaving,anion transformation and base catalysis, was proposed finally.(5) With ionic liquids as the template and directing agents, ionic liquids were confined during the formation of silicagels via sol-gel way. By tailoring the concentration and structures of ionic liquids, the pore sizes of silicagels were selectively modulated for efficient catalytic conversion of EO and selectivity of EG. With low ionic liquids confined (5.5 wt.%), both 99.9% of EO conversion and EG selectivity were achieved under low water ratio (H2O/EO=5:1) and short reaction time (0.5 h). Compared with bulk phases, only 10% of ionic liquids were used. The structure-activity relationship and catalytic performance of confined ionic liquids was preliminarily studied. Ionic liquids with four symmetric carbon chains (N(Et)4Ac) were found to be most suitable for confined catalysis of EO hydration due to the cooperative effect of the suitable micropore sizes for high EG selectivity and large quantities of mesopores for high EO conversion. This study laid the foundation for the subsequent development of similar catalyst systems.

Language中文
Document Type学位论文
Identifierhttp://ir.ipe.ac.cn/handle/122111/26891
Collection中国科学院过程工程研究所
研究所(批量导入)
Recommended Citation
GB/T 7714
苏倩. 离子液体修饰多孔材料协同催化合成二元醇的研究[D]. 中国科学院研究生院,2018.
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