生物质低温强化脱氧与催化热解共耦合制备单环芳烃的机理研究

It is of great importance for the development of biomass based liquid fuels to produce mononuclear aromatics, a main vehicle fuel additive, from biomass thermal-chemical conversion. Recently it is indicated that monocylic aromatics can be produced by catalytic cracking from lignin and cellulose, and it will be very promising if the raw biomass with a relatively cheap price can be as the pyrolysis material. Biomass which consists by hemicellulose, cellulose and lignose, is relatively cheap than pure lignose and cellulose, and becomes a promising resource for mononuclear aromatics production. However, how to strengthen the deoxidization of biomass to promote the conversion from cellulose and lignin to monocylic aromatics and how to reduce the probability of catalyst deactivation are the two key problems for the development of produce of mononuclear aromatics directly from biomass catalytic pyrolysis. As a sequence, this project proposed a novel process combined with intense deoxygenation with catalytic pyrolysis to make mononuclear aromatics from biomass. Firstly biomass is pre-pyrolysised under the temperature range from 200 to 320℃ with Mg(OH)2 additive to absorb CO2. Thus more carbonyl groups will be removed with the present of MgO. Then the formation of aldehyde, acid and furan will be reduced theoretically in the following pyrolysis process, which is helpful for the alleviation of catalyst deactivation. Secondly the mixture is pyrolysised with on-line HZSM-5 catalytic under the temperature from 450 to 600℃ to produce mononuclear aromatics directionally. Meanwhile the Mg-based additive will be regenerated. Finally relatively high content of mononuclear aromatics will be produced. This project will also used in-situ infrared spectrometry and isotopic tracing measurements, the generalized two-dimensional correlation spectroscopy analytical method, and quantum chemistry simulation tool to deeply describe the mechanism of the mentioned processes, and to form a new craft, which will realize to make relative high content mononuclear aromatics directly from biomass pyrolysis, which will be significant for the development of biomass oil products.

生物质制取单环芳烃类化合物对生物质液体燃料具有重要意义。研究表明木质素和纤维素是催化热解生成单环芳烃产物的主要来源，目前生物质热解原料相对便宜，且可同时利用纤维素和木质素，极具前景。然如何强化脱氧促进纤维素和木质素向单环芳烃转化，及如何降低催化剂失活成为关键性问题。针对上述问题，本项目首先在低温脱氧（200~320℃）过程中采用Mg(OH)2添加剂吸收CO2，促进羰基脱除，减少后续热解过程中醛、酸和呋喃类物质的生成，降低后续过程催化剂结焦失活；接着对脱氧后混合物进行在线分子筛催化热解（450~600℃），定向制备单环芳烃并再生镁基添加剂，最终实现生物质热解高效制备单环芳烃。本研究同时利用原位红外和同位素示踪等试验方法，广义二维相关光谱分析方法和量子化学模拟计算最终建立生物质强化脱氧和催化热解共耦合制备较高浓度单环芳烃的理论和方法，形成一种新的工艺，将为车用燃料芳香族添加剂提供新的来源。

生物质是重要的可再生能源，是未来化学品和清洁燃料的重要来源。但生物质存在含氧量高、水含量高和能量密度低等特点，不利于直接催化热解制备车用燃料添加剂BTX。本研究采用了低温强化脱氧和ZSM-5催化热解相联合的方式制取BTX，主要是研究了基于镁基添加剂下的生物质低温强化脱氧特性及对后续的热解和催化热解的影响；对于ZSM-5这种催化剂，详细探讨了起酸性和孔结构对于BTX生成路径和产率的影响；最后探究了生物质洗涤烘焙两级处理对生物质特性和热解的影响，以期寻求更好的生物质前处理方式。研究发现镁基添加剂MgO-K2CO3脱氧效果最好，其在促进氧元素脱除的同时还能降低氢元素的损失，并显著降低液体产物中酸类物质的相对含量，并提高酚类、酮类的相对含量。低温脱氧段引入的镁基添加剂可在热解过程中起催化剂的效果，提高了芳香烃和烃类化合物相对含量，但低温脱氧预处理温度在260-290℃为宜。在添加剂作用下低温脱氧预处理过程与快速热解进行耦合可有效提高热解生物油中芳香烃类化合物的相对含量，并降低除酮类化合物外的其他典型含氧化合物的相对含量，在260-320℃范围内，添加剂与棉秆质量比为0.5:1时，能够更好的促进芳烃类化合物的产生。基于不同种类金属改性ZSM-5的生物质催化热解产物分布有较大的差异性，其中Zn/ZSM-5催化剂的催化性能相比ZSM-5有较大提升。这是因为BTX的产率与催化剂的强酸含量呈正相关，Zn提高了催化剂的强酸含量，促进了BTX的生成。同时，高浓度的Zn负载会使导致催化剂孔道堵塞和酸性降低，从而降低催化剂的催化效率。ZSM-5催化剂的介孔量与生物质催化热解BTX产率呈正相关。微介孔复合型ZSM-5催化剂中的介孔对生物质热解中的大分子酚类物质有较强的裂解作用，因为产生的小分子物质可以更好的匹配催化剂中的微孔。水洗和酸洗对AAEMs有很好的脱除效果，但是酸洗效果要优于水洗效果，轻质油水相部分和5%醋酸对AAEMs脱除的差异性很小。酸洗烘焙两级预处理对热解油的化学组成起到了明显的改善作用：主要是促进了糖类含量的提升，而酚类、酸类、呋喃类、酮类的含量都有所降低。本研究对于生物质催化转化为化学品和燃料的应用做了很好的铺垫，具有较好的应用前景。