【作者】 盛清涛；

【导师】 凌开成；

【作者基本信息】 太原理工大学 ， 化学工程与技术， 2012， 博士

【摘要】 木文以HZSM-5分子筛为基础进行了多种改性方法的研究,对各种改性催化剂进行了XRD、SEM、ICP-AES、NMR、BET、NH3-TPD及IR等表征,并利用连续固定床反应器探讨了改性催化剂对乙醇脱水制乙烯反应的催化性能。得出如下主要结论：一、制备了一种新的乙醇脱水制乙烯的HZSM-5/SAPO-11复合分子筛催化剂。考察了原料比、模板剂和晶化时间对样品结构及乙醇脱水催化性能的影响,得出以下主要结论。1、在本实验条件卜合成了HZSM-5/SAPO-11复合分子筛,该分子筛催化剂在乙醇脱水制乙烯反应中表现出良好的催化性能,最佳乙醇转化率和乙烯选择性分别达到99.8%和99.5%;连续反应150h,乙醇转化率和乙烯选择性均保持在95％以上,表明其具有较好的活性和稳定性2、通过复合分子筛HZSM-5/SAPO-11合成条件的优化实验,确定了最佳制备条件为：原料比DPA:HZSM-5:Al2O3=8:4:1,模板剂为二正内胺,晶化时问为24h,晶化温度为185℃3、通过对合成的复合分子筛的一系列分析表征,发现其结构为以HZSM-5为核SAPO-11为壳的核壳式分子筛。孔结构的变化、强酸量的减少,是复合分子筛催化性能得到改善的内在原因。二、对HZSM-5分子筛进行了水热改性和高温热处理改性研究,对改性催化剂进行了详细的分析农征及催化活性评价实验,探讨不同处理温度和时间对催化剂结构、酸性及催化性能的影响,得到了如卜结论：1、对HZSM-5分子筛进行了一系列水热和高温热处理改性的研究。发现水热处理和高温热处理改性催化剂的催化性能得到进一步改善,水热改性催化剂最佳乙醇转化率和乙烯选择性分别为99.5%和99.4%,比原HZSM-5分子筛略有提高。但其稳定性得到明显改善,连续反应350h,乙醇转化率和乙烯选择性仍可达到94.4%和96.0%;高温热处理改性催化剂副反应减少、乙烯选择性增大,800℃热处理催化剂的乙醇转化率和乙烯选择性分别达到99.5%和99.6%,260℃时连续反应300h,乙醇转化率和乙烯选择性均保持在95%以上2、通过对改性催化剂酸量表征可知,改性对HZSM-5分子筛表面酸量及酸强度有很大影响,尤其对强酸中心影响较大。NH3-TPD分析表明强酸量明显减少,酸强度减弱;Py-IR表明B酸中心及总酸量减小,B/L值减小。由低温氮吸脱附表征可知：水热和高温热处理过程都发生了骨架脱铝形成了大量的介孔,增大分子筛的外表而积和介孔孔容,将分子筛单一的微孔结构变成了介-微孔道结构。适度的酸量和酸分布以及介-微孔道结构都是脱铝改性催化剂催化胜能提高的原因。3、适度的水热和高温热处理可提高乙醇脱水反应的活性和稳定性。但过度处理会使HZSM-5分子筛酸量明显减小,既不利于催化剂微孔结构的保持,也不利于形成新的介孔,从而使催化活性明显降低。三、通过碱处理改性制备了一系列碱脱硅改性催化剂,并对改性催化剂进行了详细的表征及催化活性评价,探讨了碱处理浓度和温度对HZSM-5分子筛酸性、孔结构及乙醇脱水制乙烯催化性能的影响,得到了如下主要结果：1、通过碱改性HZSM-5催化剂的催化活性研究,结果表现碱改性催化剂活性和寿命都得到进一步的提高。不同条件下处理的HZSM-5分子筛低温活性增大;NaOH溶液浓度为0.2M,65℃,搅拌120min时的催化在乙醇脱水制乙烯反应中表现出优异的催化性能,乙醇转化率和乙烯选择性均都达到99.6%,连续反应350h,乙烯选择性仍保持在95%以上。2、通过对碱改性催化剂的表征及催化实验可知：碱改性催化剂催化性能的提高与碱处理过程中表而酸性变化及形成的介孔有关。3、对改性分子筛催化剂的一系列表征可知,碱处理可以选择性的脱除分子筛骨架上的硅原子,在微孔结构基本不被破坏的情况下改性分子筛均不同程度地产生介孔结构;碱改性对分子筛酸性造成一定的影响,碱浓度较低时HZSM-5分子筛强酸量及总酸量基本不变化,碱浓度增大时强酸量及总酸量降低;碱处理温度对分子筛的酸性影响作用小于碱浓度的影响。4、通过对反应后的分子筛催化剂进行BET分析,可得出在脱水反应中形成的积炭更容易沉积在分子筛的介孔中,而微孔中的积炭相对较少,因此碱处理过程中脱硅形成的介孔有利于催化剂寿命的提高。5.通过正交实验和乙醇脱水催化实验得到碱处理条件对分子筛催化性能的影响,碱溶液浓度>碱处理温度>碱处理时间。四、通过三种改性方法制备了一系列改性催化剂,并对改性催化剂进行了表征及催化活性评价,比较了三种改性方法对HZSM-5分子筛酸性、孔结构及乙醇脱水制乙烯催化性能的影响,并对较为理想的碱改性催化剂进行了再生研究,得到了如卜主要结果：1、通过对三种改性催化剂催化性能的研究可知,改性催化剂的催化性能都得到进一步的改善,催化活性和稳定性得到提高。相比较未处理HZSM-5分子筛,改性催化剂乙烯选择性都略有升高,而稳定性则得到大大提高,高温热处理、水热处理、碱处理催化剂稳定性分别提高到300h、350h、350h。2、通过对改性催化剂一系列表征可知：三种改性方法都减少了分子筛表面强酸中心数量,这抑制了强酸中心上积炭等副反应的发生;同时都不同程度形成了介孔,这有利于反应物和产物分子在分子筛孔道内扩散,减少了积炭的发生,大大提高了分子筛的稳定性。3、通过对碱改性催化剂进行了再生研究,发现程序升温再生能够保证积炭的烧除井且再生后微孔恢复程度比恒温再生好。再生后的碱改性催化剂催化活性得到恢复,反应250h,其乙醇转化率和乙烯选择性均保持95%以上。综合考虑催化剂的活性、稳定性及再生性,碱改性催化剂更适合乙醇脱水制乙烯反应。更多还原

【Abstract】 The reaction of ethanol dehydration to ethylene was studied over modified catalyst in this thesis. HZSM-5/SAPO-11composite was synthesized by embedding methods. Micro/mesoporous HZSM-5zeolites was prepared using dealumination and desilication method. The activity and stability of the catalysts were tested in a continuous flow fixed-bed reactor. The modified catalysts were characterized by XRD、SEM、ICP-AES、NMR、BET、NH3-TPD and IR. The reason of improved stability of modified catalysts was investigated by catalytic performance. The main conclusions are as following:1、A new catalyst HZSM-5/SAPO-11composite for ethanol dehydration to ethylene was synthesized. The influence of ratios of raw materials, template and crystallization on catalytic performance was studied. The main conclusions are as following:Micro/microporous HZSM-5/SAPO-11melecular sieve was synthesied in the best synthesis conditions. HZSM-5/SAPO-11composite molecular sieve exhibted better catalytic performance for ethanol dehydration to ethylene. Ethanol conversion and ethylene selectivity were99.8%and99.5%. They were above95%after150hours run. The optimum synthesis condition was determined by varing the synthesis parameters. The optimum synthesis condition was as follow:ratios of raw materials was DPA:HZSM-5:Al2O3=8:4:1. DPA as template agent, crystalliza-tion time was24h and temperature was185℃Characterizations indicated that the composite zeolites existed in a form of a core-shell structure, with the HZSM-5phase as the core and the SAPO-11as the shell. Results indicated that the improved catalytic performance was related not only to the pore structure, but to the catalyst acid number.2、The modified catalysts were characterized and the catalytic performance were tested. The effect of hydrothermal and high temperature treatment on HZSM-5catalysts was analyzed during dehydration of ethanol to ethylene. The main conclusions are as following:Modified zeolites showed good catalytic performance. Ethanol conversion and ethylene selectivity of hydrothermal teated catalyst were99.5%and99.4%. they were94.4%and96.0%after350hours run at280℃. High temperature treated zeolite suppressed the formation of carbon deposit and improved ethylene selectivity. Ethanol conversion and ethylene selectivity were99.8%and99.5%and were still above95%after300hours run at260℃.Hydrothermal and high temperature treatment adjusted surface acidic distribution of HZSM-5zeolites. The total acidic amount decreased and the strength of acid sites weakened. BrOnsted acid sites and the strong acid sites were decreased; more Lewis acid sites were produced. Some of A1was removed from the framework of zeolite and extracted out of the zeolite channels after hydrothermal and heat treatment. Mesopores were formed after high temperature heat and hydrothermal treament. The improvement of catalytic performance can be attributed to suitable acidity and new complex meso/microporous structure.Moderate hydrothermal and high temperature treatment improved the catalytic performance. However, the severe treatment led to partial destruction of the zeolite framework, which was disadvantageous not only for the micropores but also for the formation of mesopores.3、A series of mesoporous HZSM-5were synthesized by desilication and the effects of the alkali treatment conditions on catalytic dehydration of ethanol to ethylene were investigated. The main conclusions are as following:The experiment of catalytic dehydration of ethanol showed that alkali-treated HZSM-5zeolites improved not only the catalytic activity but the stability. Ethanol conversion and ethylene selectivity were99.6%and the ethylene selectivity remained above95%after350hours run.The experiment of catalytic dehydration of ethanol indicated improved catalytic activity and excellent catalytic stability of alkali-treated HZSM-5catalyst was related not only to the catalyst acid number and strength, but to the created mesopores by desilication.The complexed meso/microporous HZSM-5zeolites were formed owing to alkali-treatment desilication. The amount of strong acid sites of modified zeolites decreased and weak acid sites increased. The coke produced in the reaction procedure tended to deposit in the mesopores of the zeolites. So, the newly created mesoropores by desilication led to the improvement of catalytic stability.The effects of several alkali-treatment parameters on the catalytic performance of HZSM-5zeolite were investigated by orthogonal and dehydration of ethanol. The results was concentration> alkali treatment temperature> alkali treatment time.4、A series of modified HZSM-5were prepared by hydrothermal treatment, high temperature treatment and desilication. The effects of the treatment conditions on pore structure, surface acidity and catalytic dehydration of ethanol to ethylene were investigated. Regeneration of alkali-treated catalyst was studied. The main conclusions are as following:Modified zeolites showed good catalytic performance. Ethylene selectivity of modified catalysts was improved. The lifetime of hydrothermal treated catalyst, high temperature treated catalyst and alkali-treated catalyst was350h,300h and350h.The improvement of catalytic performance can be attributed to suitable acidity and new complex meso/microporous structure.Temperature programming regeneration would obtain a better coke burning and microporous recovery than constant temperature regerneration. The regenerated catalyst showed good catalytic stability. Ethanol conversion and ethylene selectivity remained above95%after250hours run. Considering the activity, stability and regerneration of alkali-treated HZSM-5zeolites catalyst comprehensively, the alkali-treated mesoporous HZSM-5zeolites was the suitable catalyst in the dehydration of ethanol to ethylene.更多还原