生物油轻质组分水相重整制氢的研究

发布时间：2018-07-03 15:44

本文选题：生物油轻质组分 + 水相重整　；参考：《浙江大学》2017年博士论文

【摘要】：对能源需求的快速增长与能源储备的日益枯竭,导致全球面临着严重的能源危机。生物油作为可再生液体燃料,用于替代化石燃料具有十分重要的意义。生物油是一种成分复杂的混合物,含有醇,酸,酮,醛,酚类衍生物和水等。由于其具有热不稳定性,腐蚀性,高粘度和低热值,进一步的提质对其利用是至关重要的。通过减压蒸馏生物原油可获得低沸点组分(LBF)。LBF的含水量可高达70-85wt.%,其中的有机物主要由低沸点的酸,醛和酯等组成。这些组分可与水形成沸点甚至低于水的共沸物,因而难以完全除去LBF中大量的水分。然而,直接丢弃不仅降低了生物质的利用效率,还造成了环境污染。我们课题组前期的研究表明,以LBF为原料通过水相重整(APR)反应制取氢气,可使其得到最充分的利用。此外,还发现Pt/Al_2O_3为该体系中最优单金属催化剂,在催化活性和选择性方面均显示出了优异的结果。本文针对生物油轻质组分水相重整制氢反应,从以下几个方面进行了探索性研究:1.论文研究了 Pt/Al_2O_3催化剂金属颗粒大小对LBF的APR反应催化性能的影响。成功制备了一系列具有不同Pt颗粒尺寸的Pt/Al_2O_3催化剂,发现随着铂金属颗粒粒径的增大,其活性和对氢气的选择性明显降低,即该反应是结构敏感的。通过理论计算得到了不同尺寸的铂颗粒的原子总数,以及面上、顶点和边上原子的数量。发现催化剂的活性与颗粒边上铂原子的数量有顺变关系,其标准转换频率为一常数,说明颗粒边上配位不饱和的原子为该反应的活性位点。原因为这些位点有利于形成相对稳定的Pt-C吸附键,进而促进了 C-C键的断裂,提高了活性和对氢气的选择性。2.实验发现,虽然Pt/Al_2O_3催化剂的APR活性和对氢气的选择性较高,但失活严重,在直接重复使用过程中,第二次反应时催化剂的活性只有新鲜催化剂的40%,因此有必要研究Pt/Al_2O_3催化剂的失活机理。对反应后的催化剂进行的XRD、TEM、SEM和TG等一系列表征结果表明,在反应条件下,γ-Al_2O_3由于水解转化为AlOOH(勃姆石),促进了积碳的形成,伴随着比表面积的下降,以及由于积碳和勃姆石对活性位点的覆盖等因素导致了Pt活性表面积的下降,造成了催化剂的失活。经煅烧再生后,载体晶体结构有所恢复,大部分积碳得以消除,但仍有部分积碳堵塞载体的孔结构且Pt颗粒有所长大。随着循环反应次数的增加,催化剂的催化活性和对氢气的选择性仍持续下降,可见在APR反应体系中,Pt/Al_2O_3的可重复利用性能较差。3.为了探究适用于生物油轻质组分水相重整体系的,具有优异催化活性、选择性和稳定性的铂基催化剂,制备了一系列不同组成的CeO_2-TiO_2,CeO_2-ZrO_2和TiO_2-ZrO_2载体样品。通过BET和XRD表征,比较了其在反应条件下的乙酸溶液中的水热稳定性。结果表明,CeO_2-TiO_2和CeO_2-ZrO_2混合氧化物,特别是C1Z1(CeO_2与ZrO_2摩尔比为1:1)和C1T1(CeO_2与TiO_2摩尔比为1:1),在乙酸溶液中连续处理16h后,没有观察到结构和组成的改变,比表面积略有降低,表现出优异的水热稳定性。4.将这些载体负载铂后,考察了催化剂的还原特性和催化性能。实验观察到Pt/C1Z1和Pt/C1T1分别在相应的三组Pt/CZ和Pt/CT催化剂中,具有最低的还原温度和最佳的催化性能,其原因可能是在还原催化剂过程中,通过"氢溢出"使高度分散在载体表面的CeO_2部分被还原,产生了氧空位,促进了 LBF中极性含氧分子的吸附和转化,进而提高了反应物的转化率。反应后的Pt/C1Z1和Pt/C1T1催化剂经在500℃空气氛中煅烧再生后,用于重复利用性的研究,其催化活性和对氢气的选择性基本得以维持。在重复三次反应后,催化剂的颗粒略微长大,且只形成了微量的积碳。因此,与Pt/Al_2O_3相比,Pt/C1Z1和Pt/C1T1催化剂的催化活性和对氢气的选择性相当,但具有更优异的水热稳定性和可重复利用性。5.以生物油的主要组分:乙酸、乙酸甲酯、羟基丙酮、糠醛和邻甲氧基苯酚为模型化合物,通过单独的模型反应产物结果,推测了可能的反应机理。模型混合物和LBF复杂体系的液相产物中均只检测到了未完全转化的反应物,气相产物的结果与理论值之间也有所不同。本文的实验结果表明,单独的模型反应与实际的LBF复杂体系的反应之间有一定的差距。因此,直接以LBF复杂体系为反应物的研究是非常有意义的。
[Abstract]:The rapid growth of energy demand and the increasing depletion of energy reserves have led to a serious energy crisis in the world. Bio oil, as a renewable liquid fuel, is of great significance in replacing fossil fuels. Bio oil is a complex mixture containing alcohols, acids, ketones, aldehydes, phenolic derivatives and water. Thermal instability, corrosiveness, high viscosity and low heat value, further upgrading is essential to its utilization. The water content of low boiling point component (LBF).LBF can be as high as 70-85wt.% by vacuum distillation. The organic compounds are mainly composed of low boiling acids, aldehydes and esters. These components can form boiling points or even lower than water. The azeotrope of water is difficult to completely remove a large amount of water in LBF. However, direct discarding not only reduces the utilization efficiency of biomass, but also causes environmental pollution. Our previous research group showed that LBF was used as the raw material to make hydrogen through the reaction of water phase reforming (APR), which can make it get the most full use. In addition, it also found Pt/Al_2O_ 3 for the best single metal catalyst in the system, excellent results have been shown in catalytic activity and selectivity. In this paper, an exploratory study was carried out on the reaction of hydrogen production by phase reforming of bio oil light mass group from the following aspects: 1. this paper studied the catalytic performance of the Pt/Al_2O_3 catalyst on the APR reaction of LBF. A series of Pt/Al_2O_3 catalysts with different Pt particle sizes were successfully prepared. It was found that with the increase of the particle size of the platinum metal particles, the activity and the selectivity to hydrogen were obviously reduced. That is, the reaction is structural sensitive. The total number of atoms of platinum particles of different sizes, as well as the surface, vertex and edge are obtained by theoretical calculation. It is found that the activity of the catalyst has a paramagnetic relationship with the number of platinum atoms on the edge of the particle, and the standard conversion frequency is a constant, indicating that the unsaturated atoms on the edge of the particle are the active sites of the reaction. The reason is that these sites are beneficial to the formation of a relatively stable Pt-C adsorption bond, and thus promote the fracture of the C-C bond and improve the activity. The selective.2. experiments on hydrogen and hydrogen have found that, although the APR activity of the Pt/Al_2O_3 catalyst and the selectivity to hydrogen are higher, the deactivation is serious. In the process of direct reuse, the activity of the catalyst is only 40% of the fresh catalyst during the second reaction. Therefore, it is necessary to study the deactivation mechanism of the Pt /Al_2O_3 catalyst. A series of characterization results, such as XRD, TEM, SEM and TG, showed that, under the reaction conditions, the conversion of gamma -Al_2O_3 to AlOOH (boehmite) promoted the formation of carbon accumulation, decreased the specific surface area, and the reduction of the active surface area of Pt due to the carbon deposition and the coverage of the boulite to the active site, resulting in the catalyst. After calcining, the crystal structure of the carrier was recovered and most of the carbon was eliminated, but some carbon deposited the pore structure of the carrier and Pt particles grew up. The catalytic activity of the catalyst and the selectivity for hydrogen continued to decline with the increase of the number of cyclic reactions. In the APR reaction system, Pt/Al_2O_3 could be seen. A series of platinum based catalysts with excellent catalytic activity, selectivity and stability were used to prepare a series of CeO_2-TiO_2, CeO_2-ZrO_2 and TiO_2-ZrO_2 carrier samples with excellent catalytic activity, selectivity and stability in order to explore the poor performance of.3., which was suitable for the biologic oil light mass fraction water phase reforming system. The reaction conditions were compared by BET and XRD. The hydrothermal stability in the acid solution shows that the mixed oxides of CeO_2-TiO_2 and CeO_2-ZrO_2, especially C1Z1 (CeO_2 and ZrO_2 molar ratio 1:1) and C1T1 (CeO_2 and TiO_2 mole ratio of 1:1), are not observed to change the structure and composition after continuous treatment in the acetic acid solution, and the surface product is slightly lower than the surface product, showing excellent hydrothermal stability. After loading platinum by sex.4., the reduction and catalytic properties of the catalyst were investigated. It was observed that Pt/C1Z1 and Pt/C1T1 had the lowest reduction temperature and the best catalytic performance in the corresponding three groups of Pt/CZ and Pt/CT catalysts, which may be caused by the "hydrogen overflow" in the process of reducing the catalyst. The CeO_2 part of the carrier surface is reduced and the oxygen vacancy is produced, which promotes the adsorption and transformation of polar oxygen molecules in LBF, and thus improves the conversion rate of the reactant. After the reaction, the Pt/C1Z1 and Pt/C1T1 catalysts are calcined in the air of 500 degrees centigrade and are used for reutilization, and their catalytic activity and selectivity to hydrogen are basic. It was maintained. After repeated three reactions, the particles of the catalyst grew slightly and only formed a small amount of carbon deposition. Therefore, compared with Pt/Al_2O_3, the catalytic activity of the Pt/C1Z1 and Pt/C1T1 catalysts was equal to the selectivity for hydrogen, but it had better hydrothermal stability and heavy compound.5. as the main component of the bio oil: acetic acid, B Acid methyl ester, hydroxy acetone, furfural and O methoxy phenol are model compounds. The possible reaction mechanism is speculated by the result of a single model reaction product. The reactant in the liquid product of the model mixture and the LBF complex system is only detected, and the results of the gas phase are also different from the theoretical values. The experimental results show that there is a gap between the single model reaction and the reaction of the actual LBF complex system. Therefore, it is very meaningful to study the reactant directly with the complex system of LBF.
【学位授予单位】：浙江大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：O643.36;TQ116.2

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