熱氣化生物質制氫催化劑及熱力學分析研究

黃建兵 朱超

摘 要：在反應過程中加入催化劑可在更溫和的水熱條件下實現生物質高效氣化制氫。在眾多催化劑中，Ni系催化劑因其廉價并在反應中表現出較高的活性等優點而被認為是很有發展前景的制氫催化劑。該課題組針對Ni/Al2O3酸性位易于積碳引起催化劑失活的弱點，通過金屬助劑的輔助作用對Al2O3為載體的負載Ni催化劑進行改性。選用Cu、Co、Sn、Ce和堿性Mg，通過共浸漬、分步浸漬和共沉淀等方法制備雙金屬Ni-M或者復合氧化物載體催化劑。結果表明，金屬助劑Ce的引入有效提高了Ni系催化劑的催化產氫活性，催化劑的抗積碳性能亦得到有效改進，表明金屬Ce是非常合適的金屬助劑。MgAl2O4使催化劑水熱穩定性得到改善，堿性Mg助劑可以有效抑制Ni-Al催化劑的表面結晶碳的形成。較低的熱處理溫度，或者分步浸漬制備Ni-Mg-Al催化劑能獲取更多有效的活性位。堿性Mg助劑可以改善Ni-Al催化劑的催化活性及水熱穩定性。對于溶膠-凝膠法制備的Rutile TiO2負載Ni催化劑，降低催化劑熱處理溫度可以獲取分散性更高的Ni晶粒，從而提供較多的活性位，以促進生物質在水熱條件下C-C鍵的斷裂，水汽轉化反應和甲烷化反應，從而提高生物質轉化率。通過利用Aspen Plus軟件根據Gibbs自由能最小化原理采用PR狀態方程，以MHV2混合規則建立熱力學模型來模擬水熱條件下氣化生物質及其模型化合物產氫的過程，對水熱氣化生物質及模型化合物進行了理論分析，計算出在一定溫度和壓力條件下達到平衡時系統的產氣量，提供了催化氣化生物質的方向和限度的數據。

關鍵詞：制氫 水熱氣化 生物質 催化劑 熱力學模型

Abstract：Highly efficient hydrogen production from biomass can be realized by using catalysts in the reaction process under more mild hydrothermal conditions. Among various catalysts， Ni based catalysts are considered as the most promising catalyst for hydrogen production due to its low cost and good catalytic activity. In order to solve the problem of catalyst deactivation caused by carbon deposion at the acid site of Ni/Al2O3，the additives were studied to modify the Ni based catalysts loaded on Al2O3 in our research group. Cu， Co， Ce and Mg were chosed as additive and bimetal Ni-M or complex oxide catalysts were prepared by co-impregnation， impregnation by step， and co-precipitation， etc. The results show that the introduction of metal Ce can effectively improve the catalytic activity of hydrogen production， and the resistance of carbon deposition can also be improved， indicating that metal Ce is a suitable additive. Mg additive can restrain the formation of crystalline carbon on the surface of Ni-Al catalyst. Much lower heat-treating temperature or impregnation by step in preparation can obtain more effective active sites for Ni-Mg-Al catalyst. Moreover， Mg additive can improve the catalytic activity and hydrothermal stability of Ni-Al catalyst. As to the Ni catalyst loaded on rutile TiO2 prepared by sol-gel process， Ni crystals with much higher dispersity can be achieved by lowering the heat-treating temperature， which provide more active sites and promote the C-C bond breaking of biomass under hydrothermal conditions as well as water gas shift reaction and methanation reaction， thus improving the conversion efficiency of biomass. The thermodynamic analysis was performed with Aspen Plus V7.3.2. The thermodynamic models was built using the P-R equation of state and the MHV2 mixing rule to predict the gas yields in the hydrothermal gasification process. Hydrothermal gasification of biomass and its model compounds was theoretically analyzed. The equilibrium state of hydrothermal gasification reaction was obtained by calculating the gas production under certain temperature and pressure， which points out the direction and limitation of hydrothermal gasification reaction.

Key Words：Hydrogen production；Hydrothermal gasification；Biomass；Catalyst；Thermodynamic model

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