【作者】 张志华；

【导师】 杜朕屹；

【作者基本信息】 太原理工大学 ， 化学工程， 2018， 硕士

【摘要】 生物质气化技术能有效地将低品位的生物质能转化为高品质的燃气,但是焦油问题一直是气化技术的主要瓶颈问题。焦油不仅降低了气化效率,而且还会造成管道堵塞和环境污染等问题。利用水蒸气重整工艺可以降低焦油含量,改善产气品质,被普遍认为是一种具有良好工业化应用前景的焦油处理方法,该工艺的关键问题是高效催化剂的开发。考虑到成本因素,价格低廉的可弃型催化剂更可能被用到实际工业应用中。半焦具有孔隙结构发达、价格低廉、可利用生物质原料“原位”制得等特点,被广泛用于焦油重整研究中。但是,半焦作为一种碳材料,在高温下会迅速被水蒸气气化消耗,而在低温下催化能力不足,这成为半焦作为焦油重整催化剂存在的主要问题。由于过渡金属Ni对焦油具有很强的裂解/重整作用,因此,本文通过构筑Ni/半焦催化剂,在相对较低温度下（本文指600 ^o C）,实现生物质焦油水蒸气重整高效转化。本文首先探究了碳热还原条件下半焦上Ni纳米颗粒的形成过程,在此基础上,以甲苯作为生物质焦油模型化合物,进行了一系列实验探究,重点考察催化剂制备参数（热解制备温度和Ni负载量）对活性组分Ni颗粒大小和催化活性的影响,并对比研究了不同催化剂的本征催化活性（转化频率:TOF）;进一步将最佳Ni/半焦催化剂与两种传统金属氧化物负载Ni催化剂（Ni/ZrO₂和Ni/γ-Al₂O₃）进行100 h稳定性评价实验;最后将性能最佳Ni/半焦催化剂用于真实生物质焦油催化重整反应。通过对以上工作的研究,揭示了半焦上Ni纳米颗粒碳热还原形成过程,确定了调控半焦载体上形成高分散（小尺寸）Ni纳米颗粒的方法,优化了Ni/半焦催化剂的设计,建立了活性较高和稳定性较好的Ni/半焦催化剂制备方法。主要结果和结论如下:1.当Ni/半焦催化剂热解制备温度高于400 ^o C时,半焦上会发生碳热还原反应,生成活性组分Ni纳米颗粒。2.降低热解制备温度和Ni负载量有利于制备高分散的Ni纳米颗粒,提高催化剂的催化活性。Ni负载量为5%,热解温度为600 ^oC的Ni/BC（5Ni-600/BC）催化剂较其他催化剂具有较大的比表面积和较高的Ni颗粒分散。甲苯水蒸气重整在具有较多边和角位点的小颗粒Ni上更容易进行,因此,5Ni-600/BC催化剂在本征催化活性和稳定性较其他催化剂表现良好的催化性能。3.100 h稳定性评价实验表明反应后大量积碳和Ni颗粒烧结导致5Ni-600/BC逐渐失活,但5Ni-600/BC催化剂具有较大的比表面积,使其具有更高的容碳能力。因此,5Ni-600/BC催化剂在100 h内表现出较高的催化活性和较好的稳定性。4.与BC催化剂相比,5Ni-600/BC催化剂用于真实生物质焦油水蒸气重整反应不仅能有效降低焦油总量,而且也能促进大分子焦油裂解生成小分子,改变焦油组成,提高有效气体含量。更多还原

【Abstract】 Biomass gasification technology can effectively convert low-grade biomass into high-quality gas,and tar has always been the most critical issue for gasification technology.Tar not only reduces the gasification efficiency,but also causes pipeline clogging and environmental pollution problems.Steam reforming can reduce the tar content and improve the gas production quality.It is generally considered as a tar treatment method with a good industrial application prospect.The key issue for steam reforming is development of high-performace catalyst.Considering the factor of cost,low-cost and disposable catalysts are more likely to be applied in practical gasification plants.Char with high specific surface area,low-cost,and can be prepared in-situ from biomass itself,is widely used in tar reforming.However,char,as a carbon material,can be consumed by steam during reforming at high temperatures and has poor catalytic activity at low temperatures,which is the key problem char as catalyst in tar steam reforming.However,the transition metal Ni shows an excellent activity on tar cracking and reforming.Therefore,this study develops biochar supported nickel（Ni/BC）catalysts,which can be realized efficient conversion in tar steam reforming under relatively low temperatures（600 ^oC）.In this paper,the formation process and regulation method of Ni nanoparticles in char matrix during carbothermal reduction were explored firstly.On this basis,a series of experimental were investigated using toluene as a biomass-derived tar model compound.The influence of preparation parameters（pyrolysis preparation temperature and Ni loading amount）on the Ni particle size and catalytic activity was examined and the initial activity（TOF）of different catalysts was explored comparatively.Then two conventional metal oxides supported Ni catalysts（Ni/ZrO₂ and Ni/γ-Al₂O₃）were selected for comparison with high performance Ni/BC in100 hours long-term stability tests.Finally,high performance Ni/BC was further examined for its performance in steam reforming of real biomass tar.By studying the above studies,this work illustrates the formation process of Ni nanoparticles during carbothermal reduction,the regulation method for the dispersion of Ni nanoparticles and the preparation method of Ni/BC catalyst with high catalytic activity and stability.The main results and conclusions are as follows:1.Ni metal is the main active site of toluene steam reforming.When the Ni/BC catalyst pyrolysis preparation temperature is higher than 400 ^oC,the carbothermal reduction occurs on the char matrix,with generation of Ni nanoparticles.2.Lower pyrolysis preparation and Ni loading amount,which is benefit to the higher dispersion of Ni nanoparticles（i.e.lower particle size）.Ni/BC pyrolyzed at 600 ^oC with a Ni loading of 5%（5Ni-600/BC）catalyst displayed higher specific surface areas and higher Ni dispersion than other catalysts.Toluene steam reforming priority is carried out on small particles Ni with more steps and edge sites.Therefore,5Ni-600/BC catalyst showed superior catalytic performance in terms of initial activity（TOF）and stability than other catalysts.3.The 100h long-term stability tests showed that the spent 5Ni-600/BC catalyst experienced severe coke deposition and metal sintering resulted in the gradual deavtivation,but the 5Ni-600/BC catalyst has a larger specific surface area,which makes it have a higher carbon content ability.Therefore,the 5Ni-600/BC catalyst showed higher catalytic activity and better stability activity within 100 h.4.Compared with BC catalyst,5Ni-600/BC catalysts for real biomass tar steam reforming not only reduced the overall amount of tar,but also changed the composition of tar by cracking large molecules into smaller ones and usable gases.更多还原