【作者】 李小松；

【导师】 朱爱民； 石川；

【作者基本信息】 大连理工大学 ， 应用化学， 2007， 博士

【摘要】 甲烷无氧芳构化可同时产生作为洁净能源的氢气和作为有机化工基本原料的芳烃。本论文通过等离子体—催化两段式或一段式的结合，实现了甲烷在无氧和较低的温度条件下向芳烃的转化。1)本论文首先考察了产生大气压非平衡等离子体几种典型的放电方式对甲烷无氧转化的影响。在四种不同放电（脉冲流光放电、脉冲火花放电、交流介质阻挡放电、单极性脉冲介质阻挡放电）方式下，甲烷无氧转化的主要产物都是C₂烃和氢气，仅有极少量的芳烃生成。在这几种放电方式下，转化甲烷、生成乙炔（脉冲流光和脉冲火花放电时）或乙烷（介质阻挡放电时）和生成氢气所需的能耗均随着甲烷转化率的增加而增加。在脉冲火花放电时，当甲烷转化率从18％增加到69％，相应的比能耗为：转化每个甲烷分子14～25 eV，生成每个乙炔分子35～65 eV，生成每个氢分子10～17 eV。在脉冲流光放电时，当甲烷转化率从19％增加到41％，相应的比能耗为：转化每个甲烷分子17～21 eV，生成每个乙炔分子38～59 eV，生成每个氢分子12～19 eV。在介质阻挡放电方式中，乙烷是主要的产物；相应地，应该考察生成乙烷的比能耗。对脉冲介质阻挡放电，随着甲烷转化率从6％增加到13％，转化每个甲烷分子需38～57eV，生成每个乙烷分子为137～227 eV，生成每个氢分子为47～75 eV。对交流介质阻挡放电，随着甲烷转化率从5％增加到8％，转化每个甲烷分子需116～175eV，生成每个乙烷分子为446～637 eV，生成每个氢分子为151～205 eV。脉冲流光和脉冲火花放电发射光谱的研究表明乙炔的高选择性应该与C₂自由基有关。在脉冲流光放电和介质阻挡放电的放电区引入载体会促进甲烷的转化和C₂烃的生成。2)本论文首次开展了在等离子体—催化两段式反应器内甲烷无氧转化为芳烃和氢的研究，即甲烷先经等离子体转化后的产物再经过催化剂区进一步转化。采用脉冲火花放电等离子体与Ni／HZSM-5催化剂相结合的两段方式，实现了甲烷在较低的催化剂温度（300～400℃）下转化为芳烃和氢；并且考察了Ni的担载量、反应温度和反应时间等条件对芳烃选择性的影响。当脉冲火花放电的比输入能量为68.6 kJ／L和n_H2／n_CH4为1时，在Ni（1 wt．％）／HZSM-5催化剂上400℃和反应300 min内，甲烷转化率、芳烃和氢收率的平均值分别为72.1％、32.7％和41.2％。另外，程序升温反应的结果表明，HZSM-5催化剂上的Bronsted酸位对乙炔转化为芳烃起了关键的作用，Ni的引入明显地促进了乙炔的转化和芳烃的生成。3)本论文探索了在等离子体—催化一段结合方式下甲烷无氧转化为芳烃的过程。采用介质阻挡放电和Mo／HZSM-5催化剂一段式结合的结果表明，介质阻挡放电对甲烷芳构化的促进作用非常有限。采用脉冲流光放电和Ni／HZSM-5催化剂一段式结合的方式，可以实现甲烷在较低的温度下（250～350℃）向芳烃的转化。芳烃的选择性与Ni的担载量、反应温度和反应时间等条件有关。当脉冲流光放电比输入能量为50.0 kJ／L和n_H2／n_CH4为1时，在Ni（0.5 wt．％）／HZSM-5催化剂上300℃和反应300 min内，甲烷转化率和芳烃收率的平均值分别为41.4％和15.0％。更多还原

【Abstract】 The aromatization of methane under oxygen-free conditions can produce CO_x-free hydrogen for clean energy and aromatics for chemical feedstocks. The two-stage plasma-followed-by-catalyst （PFC） process and one-stage plasma-over-catalyst （POC） process were used for oxygen-free conversion of methane to aromatics and hydrogen at lower temperatures in this paper.Oxygen-free conversions of methane in atmospheric non-thermal plasma generated by using different discharge techniques, pulsed streamer discharge, pulsed spark discharge, unipolar-pulsed dielectric barrier discharge （DBD） and AC DBD were investigated. Of the four electric discharge techniques, C₂ hydrocarbons and hydrogen were the major products, with only extremely small amount of aromatic product.Energy costs for methane conversion, acetylene （for pulsed streamer discharge and pulsed spark discharge） or ethane （for DBD processes） formation, and H₂ formation increase with methane conversion percentage, and were found to be: in pulsed spark discharge （methane conversion 18-69%）, 14-25, 35-65 and 10-17 eV/molecule; in pulsed streamer discharge （methane conversion 19-41%）, 17-21, 38-59, and 12-19 eV/molecule; in unipolar-pulsed DBD （methane conversion 6-13%）, 38-57, 137-227 and 47-75 eV/molecule; in AC DBD （methane conversion 5-8%）, 116-175, 446-637, and 151-205 eV/molecule, respectively. The results of optical emission spectroscopy in pulsed streamer discharge and pulsed spark discharge showed that high selectivity of acetylene could be related to C₂ radicals. Supports immersed in pulsed streamer discharge and DBD enhanced the methane conversion and C₂ hydrocarbons production.This study investigated the oxygen-free conversion of methane to aromatics and hydrogen for the first time in a two-stage plasma-followed-by-catalyst （PFC） reactor. By using pulsed spark discharge plasma at the first stage and Ni/HZSM-5 catalyst bed at the second stage, conversion of methane to aromatics and hydrogen has been achieved at lower temperatures of 300～400℃. The effect ofNi loadings, reaction temperatures and on-stream time on aromatics selectivity was investigated. The methane conversion percentage and yield of aromatics and hydrogen on the average during 300 rain were 72.1%, 32.7% and 41.2% over Ni（1 wt.%）/HZSM-5 at 400℃with 68.6 kJ/L of specific input energy. Furthermore, the results of temperature-programmed reaction showed that the Bronsted acid sites played a key role in conversion of acetylene to. aromatics and that Ni promoted acetylene conversion and aromatics production.The conversion of methane to aromatics in a plasma-over-catalyst （POC） reactor was explored in this paper. The results of the one-stage combination of DBD with Mo/HZSM-5 catalyst showed that DBD had a slightly positive effect on methanearomatization. By using pulsed streamer discharge plasma over Ni/HZSM-5 catalysts process, conversion of methane to aromatics has been achieved at lower temperatures of 250～350℃. The effects of Ni loadings, reaction temperatures and on-stream time on aromatics selectivity were investigated. The average methane conversion percentage and aromatics yield during 300 min were 41.4% and 15.0% over Ni（0.5 wt.%）/HZSM-5 at 300℃with 50 kJ/L of specific input energy.更多还原