基于CO2捕集的秸秆低温催化气化制氢过程机理研究

Organic combination of CO2 capture enhanced hydrogen production from biomass steam gasification and the low temperature catalysis of potassium salts, a new technology of CO2 capture enhanced hydrogen production from low-temperature (600-700℃) catalytic gasification of straw is proposed in this project. Through experimental research, theoretical analysis and simulation, from the mechanism of the key unit processes including enhanced straw pyrolysis, enhanced volatile reforming and CaO cyclic carbonation, the process mechanism of this technology will be studied in-depth. The research will focus on the special and common key issues of this process such as potassium salts and calcium oxide cooperative enhancement and key unit process coupling, thereby to further reveal the mechanism of the effects of potassium salts and calcium oxide cooperation on the rout of straw pyrolysis and product selectivity and the enhancement mechanism of volatile reforming for hydrogen production, grasp the effect of potassium salts on the performance of CaO carbonation and the upgrading methods, and build the kinetic mechanism model of the whole system of CO2 capture enhanced hydrogen production from low-temperature catalytic gasification of straw, thus comprehensively answer the mechanism of the cooperative effect of potassium salts and calcium oxide and its enhancement mechanism to the hydrogen production process, and achieve the efficient, clean and one step conversion of agricultural straw to hydrogen. The research achievements of this project could provide theoretical foundation and scientific basis for practical application of this new hydrogen production technology, and it could also give a new method and way for the high efficient conversion and high value utilization of the abundant agriculture straw resources in China.

本项目将基于CO2捕集的生物质强化制氢工艺与K盐低温催化有机结合，提出一种基于CO2捕集的秸秆低温(600-700℃)催化气化制氢新工艺。针对该工艺，采用实验研究、理论分析与模拟相结合的方法，从秸秆强化热解、热解挥发分强化重整和CaO循环碳酸化等关键过程机理入手，对其进行深入研究，并把研究重点放在K、Ca协同强化、关键过程耦合这些特性与共性关键问题上，以期深入揭示K、Ca协同对秸秆热解路径与产物选择性的影响机制和对热解挥发分重整制氢的强化作用机理，掌握K盐对CaO循环碳酸化性能影响及其改性途径，建立基于CO2捕集的秸秆低温催化气化制氢系统动力学机理模型。从而全面解答K、Ca协同反应机理及其对制氢过程的强化作用机制，实现在较低温度下农业秸秆高效、清洁、一步转化制氢。本项目的研究成果可为该制氢工艺实际应用提供理论基础与科学依据，并为我国秸秆资源高效转化与高值化利用提供一条新的方法与途径。

根据研究计划考察了高CaO添加量下生物质热解特性及其动力学，发现CaO添加吸收CO2使得生物质热重热解在高温段出现了一个新的CaCO3煅烧分解失重峰，且CaO添加使得生物质热解活化能降低。考虑到CaO的碳酸化性能，其反应温度不宜过高，以避免生成的CaCO3重新分解。较低温度下（700℃），CO2被大量固定在固相中使得热解气的产率显著下降，而热解焦的产率上升，同时CaO还可催化热解过程，使得热解气和热解油的组成和分布特性均发生了显著变化。研究了CaO添加对水汽变换（WGS）反应和挥发分重整制氢特性的影响，确定了CaO原位吸收CO2促进平衡移动是产气中H2浓度和产率升高的一个重要原因。同时，CaO活化H2O分子，促进其在表面解离生成H*和OH*，是CaO催化WGS反应（羧基化机理）生成更多H2的另一重要原因。CaO还可催化挥发分的裂解与水蒸气重整反应，从而进一步提高H2的产率。K2CO3和CH3COOK在高温及碳存在下会分解为K2O，其经过K2O-C↔K2O2-C氧化/还原反应机理可显著强化麦秆的水蒸气气化制氢性能，而KCl和K2SO4的添加则在一定程度上抑制H2的生成，而促进中间产物聚合生成更多焦炭。将K盐负载在CaO上，考察两者同时添加对麦秆热解气化制氢特性的影响，发现当K盐负载量为0.25%时，0.25%KCl/CaO相较其他K盐表现出更好的制氢性能，KCl的添加可一定程度强化CaO的CO2吸收性能，提高产气中H2浓度和产率。煅烧石灰石、煅烧碳酸钙和煅烧白云石的添加均可大幅提高产气中的H2浓度和产率。且煅烧白云石中的MgO组分还可进一步催化气化过程，并强化CO2的吸收，从而获得更高的H2浓度和产率。在CaO基础上进一步引入活性组分NiO，NiO/CaO催化吸收剂对玉米秆热解气化过程显示出比煅烧白云石更好的催化性能。而NiO/γ-Al2O3和煅烧白云石同时添加则可进一步增加产气中H2的浓度和产率，在NiO负载量为15%时，产气中的H2浓度可达到最大值85.1%。最后，在流化床气化试验台上进一步验证了基于CO2捕集的生物质低温催化气化制氢工艺，并利用ASPEN PLUS软件建立了该制氢工艺的系统模型，并进行了模拟预报与工艺优化。本项目的研究结果可为我国生物质高效转化与高值化利用提供一条新的可行路径，具有很好的应用前景。