Hydrogen production by the steam reforming and partial oxidation of methane under the dielectric barrier discharge
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摘要: 构建了CH4-O2-N2-H2O反应体系，对介质阻挡放电条件下甲烷水蒸气重整和部分氧化制氢反应过程进行了研究，考察了H2O/CH4物质的量比、O2/N2物质的量比、气体总流量、放电电压及放电频率等参数对制氢效率的影响，并基于发射光谱原位诊断法分析了反应机理。结果表明，甲烷转化率和氢气产率随着H2O/CH4物质的量比、O2/N2物质的量比和放电电压的增加而增加，而随着反应气体总流量的增加而减小，随着放电频率的增加先增大后减小，在9.8 kHz处取得最大值。在H2O/CH4物质的量比1.82、O2/N2物质的量比2.1、总流量136 mL/min、放电电压18.6 kV及放电频率9.8 kHz的条件下，甲烷转化率与氢气产率分别达47.45%和21.33%。甲烷和水蒸气等反应物分子通过电子解离产生CHx·、H·、OH·、O·等自由基，进而通过自由基间的碰撞反应生成H2；H·自由基一方面来源于CH4的电子解离；另一方面来源于水蒸气一次解离以及OH·的进一步离解。部分氧化反应主要表现为O2电子解离形成的O·自由基以及水蒸气一次反应产物OH·自由基进一步离解形成的O·自由基对CH2·自由基的氧化。Abstract: The steam reforming and partial oxidation of methane to produce hydrogen under dielectric barrier discharge were conducted in the CH4-O2-N2-H2O reaction system; the effects of H2O/CH4 molar ratio, O2/N2 molar ratio, total gas flow, discharge voltage and discharge frequency on the hydrogen production were investigated and the reaction mechanism was analyzed on the basis of the in-situ diagnostic emission spectroscopy. The results indicate that the conversion of methane and the yield of hydrogen increase with the increase of H2O/CH4 molar ratio, O2/N2 molar ratio, and discharge voltage, but decrease with the increase of the total gas flow rate and show an volcano-shape trend with the increase of discharge frequency (peaked at 9.8 kHz). Under the conditions with an H2O/CH4 molar ratio of 1.82, O2/N2 molar ratio of 2.1, total flow rate of 136 mL/min, discharge voltage of 18.6 kV and discharge frequency of 9.8 kHz, in particular, the conversion of methane and the yield of hydrogen reach 47.45% and 21.33%, respectively. During the reaction, methane and water vapor may dissociate by the action of high energy electrons to generate CHx ·, H·, OH·, O· and other free radicals and hydrogen is then produced through the collision between the free radicals. H· may come from the electronic dissociation of CH4 as well as the dissociation of OH· formed primarily from the water vapor dissociation. The partial oxidation of methane is mainly manifested by the oxidation of CH2· with O·, where O· is produced by the electronic dissociation of O2 as well as the further dissociation of OH·.
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Key words:
- methane /
- dielectric barrier /
- steam reforming /
- partial oxidation /
- hydrogen
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图 1 实验系统示意图
Figure 1 Schematic diagram of the reaction system for the hydrogen production by methane steam reforming and partial oxidation under the dielectric barrier discharge
图 2 H2O/CH4物质的量比对甲烷转化率及主要产物产率的影响
Figure 2 Effect of H2O / CH4 molar ratio on the conversion of methane and the yields of main products for the steam reforming and partial oxidation of methane under the dielectric barrier discharge
图 3 反应气体总流量对甲烷转化率及主要产物产率的影响
Figure 3 Effect of total reactant gas flow rate on the conversion of methane and the yields of main products
图 4 放电电压对甲烷转化率及主要产物产率的影响
Figure 4 Effect of discharge voltage on the conversion of methane and the yields of main products
图 5 放电频率对甲烷转化率及主要产物产率的影响
Figure 5 Effect of the discharge frequency on the conversion of methane and the yields of main products
图 6 O2/N2物质的量比对甲烷转化率及主要产物产率的影响
Figure 6 Effect of the O2/N2 molar ratio on the conversion of methane and the yields of main products
图 7 CH4-O2-N2-H2O反应体系最佳氢气产率下的发射光谱谱图
Figure 7 Emission spectrum of the CH4-O2-N2-H2O system under the dielectric barrier discharge with the highest yield of hydrogen
图 8 发射光谱检测到的各添加气体系中主要自由基的相对强度
Figure 8 Relative intensity of major free radicals in each additive gas system detected by emission spectroscopy
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