【作者】 王刚；

【导师】 李钢； 郭洪臣；

【作者基本信息】 大连理工大学 ， 工业催化， 2022， 博士

【摘要】 以钛硅沸石TS-1为催化剂的丙烯-H₂O₂液相环氧化生产环氧丙烷（PO）技术是近年来实现工业化的一种环境友好PO生产新工艺（HPPO）。然而,目前HPPO工艺还存在着循环甲醇溶剂的微量杂质种类多,对TS-1环氧化催化剂性能影响大的突出问题,亟待解决。迄今为止,尚未见到国内外文献中报道过与该问题有关的研究工作。为此,本文开展了以下系统性研究工作,并得到了有重要价值的结果:（1）借助于气-质联用（GC-MS）技术和标准样品标定,建立了定性和定量分析甲醇溶剂中微量杂质的气相色谱分析方法。从一个HPPO工艺的工业循环甲醇溶剂样品中分析鉴定出5类（杂醇、醛酮、酯类、缩醛、有机胺）14种有机物微量杂质。同时,用长达500多小时的固定床反应对比实验,表明工业循环甲醇溶剂中的微量杂质对丙烯液相环氧化反应的主要危害是加快TS-1催化剂失活速度和降低环氧丙烷产品的选择性。在此基础上,通过配制含有单一杂质的模拟甲醇溶剂开展环氧化反应研究和微量杂质的竞争吸附研究,揭示出甲醇溶剂中的微量杂质导致TS-1沸石催化剂失活和降低环氧丙烷选择性的主要原因。前者是由于微量杂质在TS-1沸石骨架钛活性中心上的竞争吸附占位,后者是由于一些微量杂质在环氧化反应中促进环氧丙烷开环副产物和其他微量杂质生成。（2）通过用新鲜甲醇作溶剂开展丙烯液相环氧化反应研究,发现在没有外来杂质参与的情况下丙烯环氧化反应过程中主要生成乙醛、丙醛、丙酮、羟基丙酮、一缩二丙二醇和二丙二醇单甲醚六种微量杂质。降低环氧化催化剂的表面酸性和反应介质酸性（p H值）、降低反应温度和提高进料空速（缩短反应时间）,有利于抑制环氧化反应过程中生成上述微量杂质。通过甲醇溶剂向丙烯环氧化反应中逐一引入1,2-丙二醇或醛、酮、有机酸等微量杂质,推测出环氧化反应中醛、酮、缩醛和酯类微量杂质的生成路径,以及丙烯-H₂O₂液相环氧化反应的主-副反应网络。研究表明,在环氧化反应中生成缩醛和酯类微量杂质的主要原因是外来醛、酮和羧酸类微量杂质与甲醇溶剂反应所致。这一重要发现进一步说明了限制工业循环甲醇溶剂中微量杂质含量的重要性。（3）通过用异丙醇胺溶液对TS-1沸石进行适度的水热改性,发现了TS-1沸石改性对于抑制微量杂质在丙烯液相环氧化反应中生成的重要作用。在170℃、液固比10:1（m L/g）、异丙醇胺溶液浓度0.03 mol/L和改性时间24 h条件下制得的改性TS-1催化剂,在间歇釜反应中的H₂O₂转化率比母体降低约7%,但PO选择性提高约20%,微量杂质丙醛、羟基丙酮、二丙二醇单甲醚、一缩二丙二醇和乙醛的生成量与母体相比降幅达31%、38%、67%、67%和68%。催化剂表征结果说明,异丙醇胺溶液水热改性导致了TS-1沸石骨架溶解脱硅,改性效果与TS-1沸石表面酸性减弱、四配位骨架钛上出现Ti-OH和微环境发生改变以及环氧丙烷在TS-1上的强吸附减少有密切关系。（4）在开展吸附脱除模拟甲醇溶剂中微量杂质的探索研究中,发现TS-1沸石、椰壳活性炭和001×7凝胶型阳离子交换树脂对吸附脱除模拟甲醇溶剂中含有的缩醛、醛、酮、酯类和有机胺类微量杂质有较好效果。当把三种吸附剂按照树脂、活性炭和沸石的顺序装于三根串联吸附柱中进行动态吸附实验时,可将模拟甲醇溶剂中的多种微量杂质的总含量从24700 ppm降至约1900 ppm。上述探索研究结果预示着高性能微量杂质吸附剂的研制对于解决HPPO工艺循环甲醇溶剂中微量杂质含量高的问题有重要意义。更多还原

【Abstract】 The recently commercialized technology of liquid-phase epoxidation of propylene and H₂O₂ over titanium silicalite-1（TS-1）zeolite catalyst,HPPO process,is an eco-friendly route for the production of propylene oxide（PO）.However,this process is now still encumbered by the prominent issue of many kinds of trace impurities involved in its recycled methanol solvent,which negatively impacts on the performance of TS-1 catalyst and should be settled urgently.Up to now,research work related to this issue has not been reported in the literature.Therefore,this dissertation carried out systematical studies and obtained significant results as follows.Firstly,a gas chromatographic method for qualitative and quantitative analysis of the trace impurities in methanol solvent was established with the aid of gas chromatography-mass spectrometry（GC-MS）and standard sample calibration.Fourteen organic impurities of five types of substances,i.e.,fusel,aldehyde and ketone,ester,acetal,and amine,were identified in an industrial recycled methanol solvent from a HPPO unit.At the same time,comparative experiments were carried out continuously on a fixed-bed reactor for more than 500 hours with fresh methanol solvent and the industrial recycled methanol solvent,respectively.Experimental results show that the main negative effects of the trace impurities in the industrial recycled methanol solvent on the liquid-phase epoxidation of propylene were the acceleration of TS-1 deactivation and the reduction of PO selectivity.On this basis,by using simulated methanol solvents containing single trace impurity,the liquid-phase epoxidation and competitive adsorption experiments of trace impurities have been carried out,aiming to reveal the fundamental reason of TS-1 deactivation and PO selectivity reduction.Results show that deactivation of TS-1 catalyst was caused by the competitive adsorption of trace impurities on the framework Ti of TS-1 and the occupancy of the active sites.Reduction of PO selectivity,however,was resulted in by some of the trace impurities in methanol solvents,which promoted the formation of ring-opening byproducts,as well as some trace impurities during the liquid-phase epoxidation of propylene.Secondly,by using fresh methanol as solvent for the liquid-phase epoxidation of propylene,acetaldehyde,propionaldehyde,acetone,hydroxyacetone,dipropylene glycol and dipropylene glycol monomethyl ether have been found to be the primary trace impurities during the liquid-phase epoxidation.Formation of the above-mentioned trace impurities can be suppressed by decreasing the acidities of both catalyst and reaction medium（p H）,lowering the reaction temperature,and increasing the feed velocity（shortening the reaction time）.Through introducing 1,2-propylene glycol,aldehydes,ketone or carboxylic acids into the epoxidation system with methanol solvent one by one,the formation paths of aldehydes,ketones,acetals and esters trace impurities during the liquid-phase epoxidation were concluded,and thus an entire HPPO reaction network including main and side reactions were also proposed.Results demonstrated that the formation of acetals and esters trace impurities were mainly attributed to the reactions of methanol solvent with the inputted aldehydes,ketone and carboxylic acids.This finding highlights the significance of strict control of the trace impurities content in industrial recycled methanol solvent for HPPO process.Thirdly,hydrothermal modification of TS-1 by amino-2-propanol（MIPA）is capable of inhibiting the formation of trace impurities during the liquid-phase epoxidation of propylene.A MIPA hydrothermally modified TS-1 catalyst obtained under the conditions of 170℃,liquid-solid ratio 10:1（m L/g）,MIPA concentration 0.03 mol/L and modification time 24 h,exhibited a H₂O₂conversion of 7%lower than that of the parent TS-1,but a PO selectivity of20%higher than that of the the parent TS-1 catalyst.Especially,the amounts of produced propionaldehyde,hydroxyacetone,dipropylene glycol monomethyl ether,dipropylene glycol and acetaldehyde trace impurities by using the modified catalyst,compared to those with the parent catalyst,were reduced by 31%,38%,67%,67%and 68%,respectively.Catalyst characterization results showed that the MIPA hydrothermal modification of TS-1 zeolite proceeded with the dissolution and desilication of TS-1 framework,which resulted in the reduction of TS-1 surface acidity,the modification of framework Ti local environment（generated Ti-OH）,and the decrease of strong adsorption of PO on TS-1 zeolite.Inhibition of trace impurities during the liquid-phase epoxidation may be attributed to regulations of these physicochemical properties.Finally,in the exploratory research of adsorption removal of trace impurities from the simulated methanol solvent,it was found that TS-1 zeolite,coconut shell activated carbon and001×7 gel cation exchange resin had excellent performance concerning the adsorption revomal of acetals,aldehydes,ketone,esters and amines trace impurities from the simulated methanol solvents.Packing three columns with the above-mentioned adsorbents one by one in the sequence of resin,activated carbon and zeolite,the total content of various trace impurities in a simulated methanol solvent was reduced from 24700 ppm to 1900 ppm during the dynamic adsorption experiment.These results indicate that the development of high-performance adsorbents for removal of trace impurities is of great signicance for solving the problem of impurities in recycled methanol solvent for HPPO process.更多还原