QIBEBT-IR  > 热化学转化团队
MCM-22分子筛上甲醇制烯烃反应研究
张雷
学位类型博士 ; 学位论文 ; 博士 ; 学位论文
导师吴晋沪
2016-05
学位授予单位中国科学院大学
学位授予地点北京
学位专业化学工程
关键词Mto Mcm-22分子筛 硅铝比 多级孔道 稳定性
摘要乙烯、丙烯等低碳烯烃是现代化学工业中重要的原料。随着石油资源的日益枯竭,采用甲醇制烯烃(methanol to olefins,MTO)技术取代传统的石脑油制烯烃技术受到关注。近年来,丙烯需求增加迅速,在传统烯烃生产技术中,丙烯只是作为主产物乙烯的副产物存在,随着乙烯生产原料的多元化和轻质化,在甲醇转化反应中获得高选择性的丙烯产物更具经济价值和现实意义。 ZSM-5沸石和SAPO-34分子筛是公认的两种性能卓越的甲醇制烯烃催化剂,并应用于商业化的MTP (methanol to propylene)和MTO工艺中。虽然SAPO-34在MTO工艺中具有高的低碳烯烃选择性,但极易失活,需要频繁再生,能耗投资费用高。ZSM-5沸石虽然稳定性好,但丙烯选择性低,大分子烃副产物多,这些大分子副产物需进一步回炼生成丙烯,工艺复杂。因此,当前MTO反应研究的挑战仍在于高效催化剂的开发。 MCM-22分子筛是一种结构独特的层状分子筛,其酸性与ZSM-5类似,它的两个10元环孔道孔径大于SAPO-34的8元环孔径,而略小于ZSM-5的10元环孔径,因此较ZSM-5会具有更高的丙烯选择性。而且MCM-22分子筛的正弦孔道结构具有较高的稳定性,因此被认为一种很有潜力的MTO反应催化剂。 本论文以MCM-22分子筛作为研究对象,通过对其结构、形貌和酸性的调节来调变其对MTO反应的催化性能。主要研究内容及结论如下: (1)首先采用水热合成法制备了不同硅铝比的(Si/Al在10-50之间)的MCM-22分子筛,表征及评价结果显示,硅铝比对其酸性和催化性能影响很大,随着硅铝比的提高,其在MTO反应中的稳定性和烯烃选择性都增加。但是硅铝比过高(Si/Al=49.8时)会导致所合成的MCM-22分子筛结晶度降低,并使其在MTO反应中的稳定性和烯烃选择性降低。在450 oC和1 h-1反应条件下,Si/Al=35.1的MCM-22分子筛在MTO反应正具有最好的催化性能,催化剂寿命(即保持甲醇100%转化的时间)可达48 h,C2=-C4=选择性为68.1%,丙烯选择性为39.9%,产物中丙烯/乙烯(P/E)比为7.6。 (2)在上述研究基础上,为提高MCM-22分子筛的硅铝比及催化性能,采用硝酸、草酸和氟硅酸铵对其进行脱铝处理。元素分析表征结果表明相比于硝酸和草酸,氟硅酸铵能够脱除更多的铝元素。27Al MAS NMR表征结果表明,不同的脱铝方法所脱除的铝的种类不同,硝酸倾向于脱除骨架铝(framework Al, AlF),氟硅酸铵倾向于脱除非骨架铝(extraframework Al, AlEF),而草酸能以相似比例脱除骨架铝和非骨架铝。MTO催化性能评价结果表明,MCM-22分子筛的AlF/ AlEF比与总酸量共同影响其在反应中的稳定性,而丙烯选择性与脱铝量的多少有关,适当的脱铝有利于丙烯选择性的提高,而过度脱铝会导致丙烯选择性的降低。其中0.01 mol/L的氟硅酸铵溶液脱铝后的MCM-22分子筛(Si/Al=100.9)在MTO反应中具有最长的寿命,最高的C2=-C4=选择性、丙烯选择性,分别为54 h, 74.6%,46%,此时产物中的P/E比为10.9。 (3)为了进一步提高MCM-22分子筛上MTO反应的催化性能,以炭黑为硬模板合成了具有多级孔道结构的MCM-22分子筛,并考察了不同硬模板加入量对MCM-22分子筛性质和催化性能的影响。表征结果表明,多级孔道MCM-22分子筛具有中空巢状结构,含有3-150 nm之间的晶间介孔-大孔结构,硬模板加入量的增加有利于中空巢状结构的形成并能够增加晶间的介孔-大孔结构。催化性能评价结果表明,多级孔道MCM-22分子筛较普通MCM-22分子筛能够提高其在MTO反应中的稳定性,最高C2=-C4=选择性和丙烯选择性,但会降低反应产物中的P/E比。H-MCM-22(2C)(m(SiO2):m(炭黑)=4:2)在MTO反应中具有最长的寿命、最高的C2=-C4=选择性和丙烯选择性,分别为108 h,70.6%和39.8%。产物中的P/E比为5.6。多级孔道MCM-22分子筛能够降低积碳速率,MCM-22(2C)具有最低的积碳速率。最后对多级孔道MCM-22分子筛采用氟硅酸铵进行脱铝处理,0.02 mol/L氟硅酸铵溶液脱铝处理的多级孔道MCM-22分子筛(Si/Al=81.5)具有最长的催化剂寿命(124 h)、最高的C2=-C4=选择性(74.2%)和丙烯选择性(44.3%),。此时产物中的P/E比为8.5。
其他摘要Light olefins, such as ethylene and propylene, are very important raw materials in modern chemical industry. As the foreseeable depleting of world oil reserves, MTO (methanol to olefins) technology draws more and more attention for the production of light olefins instead of the traditional production of light olefins from naphtha. In recent years, demand of propylene increases rapidly, ethylene is the main product in the traditional production of light olefins from naphtha, with the production of propylene as by-product. As the ethylene feedstock becomes more and more light and diverse, conversion of methanol with high propylene selectivity has more economic value and practical significant. ZSM-5 zeolite and SAPO-34 molecular sieve are regarded as the most valuable MTO catalysts and applied in commercial MTP (methanol to propylene) and MTO technology, respectively. Although SAPO-34 molecular sieve gives high light olefins selectivity, it deactivates rapidly due to coke deposition and necessitates to be regenerated frequently with high consumption of energy and investment. ZSM-5 zeolite is more resistant to deactivation, but its medium channel dimension leads to a low propylene selectivity and forms a large amount of C5+ hydrocarbons which is necessary to be recycled and cracked to produce propylene. At present, the greatest challenge for MTO research is still the development of effective catalyst. MCM-22 molecular sieve has a unique lamellar structure, its acidity is similar to ZSM-5 zeolite, both of the dimensions of 10MR channels are wider than that of SAPO-34 molecular sieve and slightly narrower than that of ZSM-5 zeolite, therefore, MCM-22 molecular sieve is more selective to produce propylene than ZSM-5 zeolite. Moreover, the sinusoidal channels of MCM-22 molecular sieve is more resistant to deactivation, thus, it is a potential catalyst for MTO reaction. In this thesis, MCM-22 molecular sieve was used as catalyst in MTO reaction. Morphology and acidity of MCM-22 molecular sieve was adjusted to improve its catalytic performances. The main contents and conclusions in this study are as follow: (1) First MCM-22 molecular sieve with different Si/Al (silicon/aluminum) ratios (ranging from 10 to 50) was hydrothermally synthesized, the results from characterization and catalytic tests showed that the acidity of MCM-22 molecular sieve and its catalytic performances in MTO reaction were strongly affected by its Si/Al ratio. The stability and light olefins selectivity of MCM-22 molecular sieve in MTO reaction increased with its Si/Al ratio. However, high Si/Al ratio (Si/Al=49.8) gave rise to low crystallinity of MCM-22 molecular sieve, which led to the decrease of its stability and light olefins selectivity in MTO reaction. MCM-22 molecular sieve with Si/Al=35.1 gave the best catalytic performance, its catalytic life, defined as the time in which methanol was completely converted, light olefins selectivity, propylene selectivity and P/E ratio in the reaction products were 48 h, 68.1%, 39.9% and 7.6, respectively. (2) Based on the results above, in order to increase the Si/Al ratio of MCM-22 molecular sieve and improve its catalytic performances in MTO reaction, MCM-22 molecular sieve was dealuminated with nitic acid, oxalic acid and ammonium hexafluorosilicate (AHFS). The results from ICP AES and 27Al MAS NMR showed, comparing with nitric and oxalic acid, AHFS could effectively decrease the content of aluminum in MCM-22 molecular sieve. Nitric acid is selective to eliminate framework aluminum (AlF), while AHFS is selective to eliminate extra-framework aluminum (AlEF), and for oxalic acid, framework aluminum and extra-framework aluminum are eliminated proportionally. The results from MTO reaction proved the lifetime of MCM-22 molecular sieve was affected by total acid sites and AlF/AlEF ratio, propylene selectivity was related to the amount of aluminum eliminated, proper dealumination was benefit for the increase of propylene selectivity and excess dealumination led to the decrease of propylene selectivity. MCM-22 molecular sieve dealuminated with 0.01mol/L AHFS solution (Si/Al ratio=100.9) had the longest lifetime, the highest light olefins selectivity and propylene selectivity, which were 54 h, 74.6% and 46%. The P/E ratio in reaction products was 10.9. (3) For the further improvement of catalytic performances of MCM-22 molecular sieve in the MTO reaction, hierarchical MCM-22 molecular sieve was synthesized with carbon black used as the hard template and effects of the content of carbon black in the synthetic gel on the properties of hierarchical MCM-22 molecular sieve and its catalytic performances were investigated. The results from characterization proved that hierarchical MCM-22 molecular sieve was hollow nest-like aggregates and possessed exotic meso/macropores of 3-150 nm in diameter. Increasing the content of carbon black in the synthetic gel was benefit for the formation of the hollow nest-like aggregates and increased its meso/macropores. Comparing with the conventional MCM-22 molecular sieve, hierarchical MCM-22 molecular sieve gave longer lifetime and higher light olefins selectivity and propylene selectivity in the MTO reaction, but decreased P/E ratio in the products. Hierarchical MCM-22 molecular sieve synthesized with m(SiO2):m(carbon black)=4:2 gave the longest lifetime and highest light olefins selectivity and propylene selectivity, which were 108h, 70.6% and 41.6%, respectively. P/E ratio was 5.6. Hierarchical MCM-22 molecular sieve could decrease the coking rate in MTO reaction and among them, MCM-22(2C) gave the lowest coking rate. After dealuminated with 0.02mol/L AHFS solution, the lifetime, light olefins selectivity and propylene selectivity of hierarchical MCM-22 molecular sieve (Si/Al=85.1) in the MTO reaction increased, which were 124h, 74.2% and 44.6%, respectively. P/E ratio was 8.5.
作者部门热化学转化
学科领域工学
公开日期2016-07-01
学位类型博士 ; 学位论文 ; 博士 ; 学位论文
语种中文
文献类型学位论文
条目标识符http://ir.qibebt.ac.cn/handle/337004/9766
专题热化学转化团队
作者单位中国科学院青岛生物能源与过程研究所
推荐引用方式
GB/T 7714
张雷. MCM-22分子筛上甲醇制烯烃反应研究[D]. 北京. 中国科学院大学,2016.
条目包含的文件 下载所有文件
文件名称/大小 文献类型 版本类型 开放类型 使用许可
MCM-22分子筛上甲醇制烯烃反应研究.(4813KB)学位论文 开放获取CC BY-NC-SA浏览 下载
个性服务
推荐该条目
保存到收藏夹
查看访问统计
导出为Endnote文件
谷歌学术
谷歌学术中相似的文章
[张雷]的文章
百度学术
百度学术中相似的文章
[张雷]的文章
必应学术
必应学术中相似的文章
[张雷]的文章
相关权益政策
暂无数据
收藏/分享
文件名: MCM-22分子筛上甲醇制烯烃反应研究.pdf
格式: Adobe PDF
此文件暂不支持浏览
所有评论 (0)
暂无评论
 

除非特别说明,本系统中所有内容都受版权保护,并保留所有权利。