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摘要: 在反应温度550℃、空速5000h-1和1.2% H2S浓度下，考察了反应气中添加CO2对负载型Mo基催化剂甲烷化活性的影响。结果表明，添加CO2会促进逆水煤气变换反应，从而降低MoO3/Al2O3催化剂的耐硫甲烷化活性。与MoO3/Al2O3催化剂相比，添加CO2对铈铝复合载体负载的Co-Mo双组分催化剂的影响较小。通过表征发现，添加CO2引起催化剂活性下降的主要原因是由于其增强了逆水煤气变换反应过程，使甲烷化过程可用氢气量减小。另外，逆水煤气变换反应生成的水会影响催化剂表面结构和组成。在连续加入10% CO2 20h后停止加入CO2，催化剂的耐硫甲烷化活性可以得到恢复，因此，认为CO2加入量低于10%时，对催化剂及甲烷化反应的影响是可逆的；但CO2加入量大于10%后由于生成的水量增大会破坏催化剂的结构并减少活性位，从而造成催化剂的不可逆失活。Abstract: The methanation of synthesis gas is the key process of coal to natural gas. Considering the existence of CO2 in the synthesis gas, it is important to investigate the influence of CO2 on the sulfur-resistant methanation. In this paper, the effect of CO2 on methanation activity of Mo-based catalysts was investigated at the reaction temperature of 550℃ and the gas space velocity of 5000h-1 with the syngas containing 1.2% H2S (volume ratio). The results show that the promoter Co and the cerium-aluminum composite support can improve the stability of the catalyst and reduce the deactivation. The CO2 is proved to promote the reverse water gas shift reaction, which would inhibit the activity of MoO3/Al2O3 catalyst more heavily than MoO3-CoO/CeO2-Al2O3 catalyst. When the CO2 adding to the inlet gas is less than 10% for 20h, the catalyst activity could be restored to its original activity after stopping the addition of CO2. However, as the added CO2 in inlet gas is over 10%, more H2O will be generated through reverse water gas shift reaction to damage the catalyst structure and decrease the active component, resulting in an irreversible loss of catalyst activity.
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Key words:
- sulfur-resistant methanation /
- Mo-based catalyst /
- carbon dioxide /
- deactivation /
- water-gas shift
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图 1 10% CO2对Al2O3负载催化剂耐硫甲烷化活性的影响
Figure 1 Effect of 10% CO2 on the activity of Mo-based catalysts
(a): Mo/Al; (b): Co-Mo/Al
图 2 10% CO2对Mo/CeAl催化剂的影响
Figure 2 Effect of 10% CO2 on the activity of Mo/CeAl catalyst
图 3 不同含量CO2对Co-Mo/CeAl催化活性的影响
Figure 3 Effect of various CO2 concentrations on Co-Mo/CeAl catalyst activity
(a): 10%CO2; (b): 20%CO2; (c): 30%CO2
■: x(CO); ○: s(CH4)
图 4 CO2浓度对CO平衡转化率的影响
Figure 4 Effect of CO2 concentrations on CO equilibrium conversion
图 5 添加CO2反应后Mo基催化剂的XRD谱图
Figure 5 XRD patterns of Mo-based catalysts after reaction
(a): different catalysts with 10% CO2 added; (b): Co-Mo/CeAl catalyst at different CO2 concentrations
图 6 10%CO2对Mo基催化剂影响的TEM照片
Figure 6 TEM image of Mo-based catalysts with 10% CO2 added
(a): Mo/Al; (b): Co-Mo/Al; (c): Mo/CeAl; (d): Co-Mo/CeAl
图 7 不同CO2含量对Co-Mo/CeAl催化剂影响的TEM照片
Figure 7 TEM image of Co-Mo/CeAl catalysts with different CO2 contents
(a): 10% CO2; (b): 20% CO2; (c): 30% CO2
表 1 Lurgi炉、GE (Texaco) 炉、Shell炉气化产品对比[9]
Table 1 Comparion of gas composition from Lurgi, GE (Texaco) and Shell gasifier
Gasifier type Composition of gas φ/% H2 CO CO2 CH4 Lurgi 38-41 17-21 28-32 10-12 GE (Texaco) 36-39 43-46 16-18 ＜0.01 Shell 26-30 65-69 2-4 ＜0.01 
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表 2 甲烷化反应前后Mo基催化剂的织构性质
Table 2 Textural properties of Mo-based catalysts before and after reaction
Mo-based catalyst BET surface area A/(m2·g-1) Pore volume v/(cm3·g-1) Pore size d/nm BR ARN AR BR ARN AR BR ARN AR Mo/Al 204 154 156 0.25 0.26 0.14 6.0 6.0 4.4 Co-Mo/Al 165 133 135 0.27 0.20 0.19 5.0 6.0 5.3 Mo/CeAl 118 102 88 0.28 0.35 0.16 7.8 13.0 5.8 Co-Mo/CeAl 125 115 111 0.18 0.19 0.19 5.4 5.9 6.0 BR: before reaciton; ARN: after reaction without CO2; AR: after reaction at 10% CO2 concentration
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表 3 添加不同含量CO2经甲烷化反应前后Co-Mo/CeAl催化剂的织构性质
Table 3 Textural properties of Co-Mo/CeAl catalyst before and after reaction with CO2 added
Co-Mo/CeAl catalyst BET surface area A/(m2·g-1) Pore volume v/(cm3·g-1) Pore size d/nm ARN 115 0.19 5.9 AR10 111 0.19 6.0 AR20 100 0.26 8.2 AR30 103 0.28 8.3 ARN：after reaction without CO2; AR10：after reaction at 10% CO2 concentration; AR20：after reaction at 20% CO2 concentration; AR30：after reaction at 30% CO2 concentration
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