A study on the carbonaceous deposition on Ni-Al2O3 catalyst in CO2-CH4 reforming on the basis of temperature-programmed hydrogenation characterization
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摘要: 采用水热沉积法制备Ni-Al2O3催化剂，用于CO2-CH4重整反应；基于程序升温氢化（TPH）表征，研究了反应时间、温度、原料气CO2/CH4比例和空速等因素对CO2-CH4重整反应过程中Ni-Al2O3催化剂上表面积炭行为的影响。结果表明，表面积炭是导致催化剂重整反应失活的重要原因。随反应时间的延长，催化剂表面积炭量增多，虽未成比例增加，但其TPH峰温有向高温方向移动的趋势，表明所积之炭的石墨化程度增加。反应温度和空速对催化剂表面积炭也有一定影响，且空速的影响更大。另外，由于CO2消炭反应（CO2+C=2CO）的存在，CO2/CH4比例对表面积炭的影响也很大。CO2/CH4比例太低，不能明显抑制积炭；随着CO2/CH4比例增加，积炭将得到有效抑制，但CO2/CH4比例过高，CO2在产物中的分离和回收再利用将使成本增加。
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关键词:
- Ni-Al2O3催化剂 /
- CO2-CH4重整 /
- 积炭 /
- 程序升温氢化
Abstract: Ni-Al2O3 catalyst was prepared by hydrothermal deposition method and used in the reaction of CO2-CH4 reforming. The effect of reaction time, temperature, CO2/CH4 ratio and feed space velocity on the carbonaceous deposition on the Ni-Al2O3 catalyst surface in CO2-CH4 reforming was investigated, on the basis of temperature-programmed hydrogenation (TPH) characterization. The results indicate that the carbonaceous deposition is an important factor for the deactivation of Ni-Al2O3 catalyst in CO2-CH4 reforming. The amount of deposited carbon increases with the prolongation of reaction time; meanwhile, the hydrogenation peak in the TPH profiles shifts towards higher temperature, indicating that the graphitization degree of the deposited carbon also increases with prolonging the reaction time. The reaction temperature and feed space velocity, especially the later one, also have an influence on the carbon deposition. In addition, due to the carbon elimination reaction by CO2 (CO2+C=2CO), the ratio of CO2/CH4 in the feed shows a great influence on the type and amount of carbon deposited on the Ni-Al2O3 catalyst. A low CO2/CH4 ratio may not achieve a significant inhibition on the coke formation; with the increase of CO2/CH4 ratio, the carbon deposition can then be increasingly inhibited; however, a higher CO2/CH4 ratio also means higher cost for CO2 separation and recovery in the product. -
图 2 固定床空反应管CO2-CH4重整性能
Figure 2 Conversions of CO2 and CH4 for the CO2-CH4 reforming in the empty fixed bed reactor without loading any catalyst at 800 ℃, 0.1 MPa, GHSV = 14400 h-1, and CO2/CH4 =1
图 3 重整反应CO2和CH4转化率随时间的变化
Figure 3 Conversions of CO2 and CH4 for the CO2-CH4 reforming over the Ni-Al2O3 catalyst for different reaction times at 800 ℃, 0.1 MPa, GHSV = 14400 h-1, and CO2/CH4 =1
图 4 不同时间重整反应试样的TPH谱图
Figure 4 TPH profiles of various spent Ni-Al2O3 catalysts after carrying out the CO2-CH4 reforming reaction for different times
图 5 催化剂反应10 h后表面积炭实物示意图
Figure 5 Photos of the carbon deposited after carrying out the CO2-CH4 reforming reaction for 10 h
(a): carbon deposited on the thermocouple tube;
(b): carbon on the Ni-Al2O3 catalyst;
(c): carbon on the wiping paper from thermocouple tube
图 6 反应10 h后催化剂的热重分析曲线
Figure 6 TG curves of the fresh Ni-Al2O3 catalyst and the spent one after carrying out the CO2-CH4 reforming for 10 h
图 7 不同反应时间下催化剂表面积炭的TEM照片
Figure 7 TEM images of various spent Ni-Al2O3 catalysts after carrying out the CO2-CH4 reforming reaction for different times
(a): fresh; (b): 0.5 h; (c): 1 h; (d): 2 h; (e): 5 h; (f): 10 h
图 8 不同温度下重整反应的转化率随温度的变化
Figure 8 Conversions of CO2 and CH4 for the CO2-CH4 reforming over the Ni-Al2O3 catalyst under different temperatures after reaction for 10 h at 0.1 MPa, GHSV = 14400 h-1, and CO2/CH4 =1
图 9 不同温度下重整反应后试样的TPH谱图
Figure 9 TPH profiles of the spent Ni-Al2O3 catalysts after carrying out the CO2-CH4 reforming reaction under different temperatures
图 10 不同空速下重整反应转化率和选择性随空速的变化
Figure 10 Conversions of CO2 and CH4 for the CO2-CH4 reforming over the Ni-Al2O3 catalyst under different GHSVs after reaction for 10 h at 800 ℃, 0.1 MPa, and CO2/CH4 =1
图 11 不同空速下重整反应后试样的TPH谱图
Figure 11 TPH profiles of the spent Ni-Al2O3 catalysts after carrying out the CO2-CH4 reforming reaction under different GHSVs
图 12 不同CO2/CH4比例下试样重整反应的活性评价
Figure 12 Conversions of CO2 and CH4 for the CO2-CH4 reforming over the Ni-Al2O3 catalyst under different CO2/CH4 ratios after reaction for 10 h at 800 ℃, 0.1 MPa, and GHSV=14400 h-1
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