熱氣化生物質(zhì)制氫催化劑及熱力學(xué)分析研究

黃建兵 朱超

摘 要：在反應(yīng)過程中加入催化劑可在更溫和的水熱條件下實(shí)現(xiàn)生物質(zhì)高效氣化制氫。在眾多催化劑中，Ni系催化劑因其廉價(jià)并在反應(yīng)中表現(xiàn)出較高的活性等優(yōu)點(diǎn)而被認(rèn)為是很有發(fā)展前景的制氫催化劑。該課題組針對(duì)Ni/Al2O3酸性位易于積碳引起催化劑失活的弱點(diǎn)，通過金屬助劑的輔助作用對(duì)Al2O3為載體的負(fù)載Ni催化劑進(jìn)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(fù)合氧化物載體催化劑。結(jié)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(chǎn)氫活性，催化劑的抗積碳性能亦得到有效改進(jìn)，表明金屬Ce是非常合適的金屬助劑。MgAl2O4使催化劑水熱穩(wěn)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(jié)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(wěn)定性。對(duì)于溶膠-凝膠法制備的Rutile TiO2負(fù)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(jìn)生物質(zhì)在水熱條件下C-C鍵的斷裂，水汽轉(zhuǎn)化反應(yīng)和甲烷化反應(yīng)，從而提高生物質(zhì)轉(zhuǎn)化率。通過利用Aspen Plus軟件根據(jù)Gibbs自由能最小化原理采用PR狀態(tài)方程，以MHV2混合規(guī)則建立熱力學(xué)模型來模擬水熱條件下氣化生物質(zhì)及其模型化合物產(chǎn)氫的過程，對(duì)水熱氣化生物質(zhì)及模型化合物進(jìn)行了理論分析，計(jì)算出在一定溫度和壓力條件下達(dá)到平衡時(shí)系統(tǒng)的產(chǎn)氣量，提供了催化氣化生物質(zhì)的方向和限度的數(shù)據(jù)。

關(guān)鍵詞：制氫 水熱氣化 生物質(zhì) 催化劑 熱力學(xué)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

閱讀全文鏈接（需實(shí)名注冊(cè)）：http：//www.nstrs.cn/xiangxiBG.aspx？id=49183&flag=1