Tuning the selectivity of methanol-to-hydrocarbons conversion on H-ZSM-5 by co-processing olefin or aromatic compounds
Tuning the selectivity of methanol-to-hydrocarbons conversion on H-ZSM-5 by co-processing olefin or aromatic compounds
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DOI：
10.1016/j.jcat.2012.03.016
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发表时间：
2012-06-01
影响因子：
7.3
通讯作者：
Bhan, Aditya
中科院分区：
文献类型：
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作者：
Ilias, Samia;Bhan, Aditya
在548 K、等转化率（20.8-22.7 C%）条件下，通过共进料少量C-13-丙烯和C-13-甲苯（4 kPa）与C-12-DME（70 kPa），系统地调节了二甲醚（DME）在H-ZSM-5上转化为烃的产物选择性。对乙烯（14.5-18 C%）和芳族化合物（7.1-33.7 C%）的选择性增加，而对C-4-C-7芳族化合物（42.8-16.9 C%）的选择性随着共进料中甲苯量（0-4 kPa）的增加而降低。在548 K和较高温度（623 K）下在较低转化率（4.6-5.1 C%）下也观察到类似的趋势，表明烯烃与芳族化合物的比率可用作参数，以在本工作中研究的条件范围内将烯烃和芳族化合物基碳池传播到不同程度。C-13-丙烯与C-12-DME的共反应表明，C-5-C-7烯烃几乎完全由甲基化反应形成，而丁烯由烯烃裂解和甲基化反应两者形成。具有至少一个C-12的丙烯的高分数（55.1%）表明大部分丙烯是烯烃裂化反应的产物。在芳族基循环占主导地位的条件下（共进料中甲苯的量增加），乙烯和丙烯都含有约10%的C-13原子，表明当烯烃基循环被抑制时，这些轻质烯烃主要源自芳族基循环。流出物中甲苯的C-13含量与C-13-甲苯进料中的含量相比没有变化，这意味着甲苯没有作为重要产物形成。此外，至少9.8%的对二甲苯、1，2，4-三甲基苯和1，2，4，5-四甲基苯同位素异构体完全是C-12标记的，而小于2%的甲苯和邻二甲苯同位素异构体完全是C-12标记的，这表明在本工作中研究的条件下，环化反应主要发生在C8+芳烃上，以形成对二甲苯和更大的芳烃。因为烯烃和芳族基循环不是彼此隔离的，所以理解两个循环之间的连通是控制MTH在H-ZSM-5上的选择性的重要步骤。(c)2012 Elsevier Inc. All rights reserved.
The product selectivity of dimethyl ether (DME) conversion to hydrocarbons on H-ZSM-5 was systematically tuned by co-feeding small amounts of C-13-propene and C-13-toluene (4 kPa) with C-12-DME (70 kPa) under isoconversion conditions (20.8-22.7 C%) at 548 K. The selectivity to ethene (14.5-18 C%) and aromatics (7.1-33.7 C%) increased while selectivity to C-4-C-7 aliphatics (42.8-16.9 C%) decreased with increasing amounts of toluene (0-4 kPa) in the co-feed. Similar trends were also observed at lower conversions (4.6-5.1 C%) at 548 K and at higher temperatures (623 K), showing that the olefin-to-aromatic ratio can be used as a parameter to propagate the olefin- and aromatic-based carbon pools to varying extents within the range of conditions studied in this work. The co-reaction of C-13-propene with C-12-DME showed that C-5-C-7 olefins are formed almost exclusively from methylation reactions while butenes are formed from both olefin cracking and methylation reactions. The high fraction of propene (55.1%) with at least one C-12 indicated that a large fraction of propene is a product of olefin cracking reactions. Under conditions in which the aromatic-based cycle is dominant (increasing amounts of toluene in the co-feed), both ethene and propene contained approximately 10% C-13 atoms, showing that when the olefin-based cycle is suppressed, these light olefins primarily originate from the aromatic-based cycle. The C-13 content of toluene in the effluent was unchanged compared to that in the C-13-toluene feed, implying that toluene is not formed as a significant product. Additionally, at least 9.8% of p-xylene, 1,2,4-trimethylbenzene, and 1,2,4,5-tetramethylbenzene isotopomers were entirely C-12-labeled, while less than 2% of toluene and o-xylene isotopomers were entirely C-12-labeled, showing that under the conditions studied in this work, cyclization reactions occur predominantly for C8+ aliphatics to form p-xylene and larger aromatics. Because the olefin- and aromatic-based cycles are not isolated from one another, understanding communication between the two cycles is an important step in controlling selectivity of MTH on H-ZSM-5. (c) 2012 Elsevier Inc. All rights reserved.