钴基催化剂制备及其催化合成汽油类烃的性能

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	钴基催化剂制备及其催化合成汽油类烃的性能
其他题名	Fischer-Tropsch synthesis of gasoline-range hydrocarbons from syngas over cobalt-based catalysts
	李宇萍
导师	吴创之
	2008-12-30
学位授予单位	中国科学院广州能源研究所
学位授予地点	广州能源研究所
学位名称	博士
关键词	Co基催化剂钌费托合成汽油类烃（c5~c12) 生物质合成气
摘要	我国能源资源的基本特点是“富煤、贫油、有气”，特别是今后交通运输的快速发展，必将导致巨大的洁净、高效、液体燃料需求。2000年我国汽油和柴油总消耗量已超过8000万吨，2004年原油的进口量达到1.2亿吨，预计2020年逾2亿吨。而1990～2003期间，我国原油产量从1.4亿吨增长到1.7亿吨，年均增长率仅为1.68％。预计到2030年，中国原油净进口比率将达到74％。根据国民经济持续发展的要求，到2010年我国至少应通过非石油途径解决0.3～0.5亿吨可比原油供应，到2020年，将扩大到0.8亿吨，折合成品油约0.6亿吨。这一巨大缺口，只有通过煤、天然气或生物质等经合成气制备、费托催化技术转化为油品，实现油品供给的多样性，才能解决。以煤或天然气为原料，费托合成油品已在南非和中东开展大规模的运行或正在兴建，但仍摆脱不了对化石能源的依赖。以生物化学或热化学法从“非食用”的生物质原料中获取第二代生物燃料已经引起全世界的关注，该工艺克服了第一代生物燃料（发酵乙醇，生物柴油等）对粮食及耕地的依赖，特别是生物质费托催化合成油品工艺与现有以煤/天然气为原料的工艺相似，且合成油在化学成分和燃烧特性上与车辆技术体系和基础设施兼容程度高，可成为汽/柴油等交通燃料的有效补充，缓解对化石能源生产及供应不确定性的依赖。在费托合成技术应用背景日趋明朗的新能源形势下，开发具有自主知识产权、性能优良的催化剂核心技术和费托合成工艺显得尤为迫切。传统以煤或天然气为原料，进行的费托合成受到Andson-Schultz-Flory（ASF）聚合机理限制，在铁基或钴基催化剂上重质烃选择性高，一般需要对合成产物进一步加氢或异构化处理，以获得中等馏分的汽/柴油燃料。且生物质气化得到的粗燃气中CO2含量高，氢碳比较低，导致催化剂活性低、稳定性差。针对传统费托合成对汽油类烃（特别是异构烃）选择性不高及生物质合成气的气质特点，本论文开展了费托合成汽油类烃（C5~C12）的钴基催化剂制备研究，并将其应用于生物质合成气的催化转化。在采用浸渍法制备Co基催化剂的基础上，考察了SiO2/Zeolite复合载体中SiO2孔径结构和分子筛类型及硅铝比对费托合成产物选择性控制的影响。在Co/SiO2/HZSM-5催化剂上，考察了贵金属Ru的添加对催化活性的影响，对生物质合成气的CO2和H2含量对转化性能影响进行了研究，并对生物质制备汽油类燃料的整体工艺路线进行了分析评价，得出了如下主要结论： 1. 具有大比表面积的中孔SiO2（9nm，SG-2）可均匀分布分子筛并降低其酸性，这种中孔和微孔共存的SiO2/Zeolite复合载体，耦合了中孔结构有利于传质、微孔结构和酸性加强重质烃裂解和异构化等优点，提高了Co/SiO2/Zeolite催化剂的费托合成活性，并使合成产物向汽油类烃偏移，合成气总烃收率均达到150g/Nm3以上。在分子筛类型（USY、Hβ、HZSM-5）和分子筛硅铝比的影响考察中，以HZSM-5（SiO2/Al2O3=38）的改性效果最佳。 2. 少量贵金属Ru的加入即可提高Co/SiO2/HZSM-5催化剂的Co分散度和 Co还原度。当Ru负载量为1～2wt％时，Ru-Co/SiO2/HZSM-5催化剂在150～400℃还原度的提高幅度较大。当Ru添加量高于2wt％时，虽然提高了合成气总烃收率，但快速的CO加氢速率和Ru的氢溢流，使得合成产物向低碳烃方向偏移，降低了汽油类烃的时空产率。Ru的添加还减轻了催化剂的积碳现象。 Ru对H2的解离吸附及Hads从Ru表面溢流到Co表面是催化剂表面积碳降低的主要原因。 3. 一定范围内提高生物质合成气中CO2含量，虽然可提高CO2转化率，但CO和CO2的竞争吸附加氢及低CO2加氢活性，降低了CO转化率及合成气总碳转化率，更多的CO2是作为稀释气体。受共存的CO影响，含CO2的生物质合成气上烃类产物选择性仍呈现典型的费托分布，合成气氢碳比严重影响合成效率。比较三种典型生物质合成气的F-T结果，发现气体中少量的CO2（7.5％），一方面可以使合成气的总碳转化率保持在较高水平，另一方面低CO2加氢活性避免了Co/SiO2¬/HZSM-5催化剂的氧化失活。反应后催化剂中碳物种主要为烃类物质或积碳。合成条件在T=250℃，P=2.0~2.5MPa，WHSV=6.27~12mg/gcat/h范围内，合成气（C）的总烃收率及汽油类烃时空产率较高。 4. 生物质合成气F-T合成液态油品过程采用单程转化结合尾气发电工艺较完全转化工艺具有较高系统效率，维护简单，是比较合理的整体式生物质合成-发电联合系统典范。提高合成气氢气含量始终是合成气组分调变和影响F-T合成效率的关键。根据粗燃气的组成，设计重整或水煤气变换或脱碳工序，均可满足F-T合成对原料气的要求。在提高氢碳比的前提下，采用重整或脱碳工序均可获得较好的整体合成效率。
其他摘要	There is an urgent demand for clean, liquid fuels for transportation. In China, the total consumption amount of gasoline/diesel was more than 80 million ton during 2000. The overall import amount of crude oil will be 0.2 billion ton in 2020. At the same time, the liquid fuel production was less than the actual requirement. It has been expected that at least 0.03~0.05 billion oil fuels is needed from non-oil technology to keep sustainable development of economy in 2010. The only solving method is to find new ways to get liquid fuels, such as catalytic Fischer-Tropsch(F-T) synthesis of synthesis gas from coal/natural gas/biomass. F-T synthesis to get gasoline/diesel has been carried out in South Africa and Middle East from coal or natural gas in large scale. However, this process was still depending on traditional fossil fuels. Second-generation biofuels are usually bio-chemical or thermo- produced from non-edible part of biomass residues as corn stalk or rice husk. That enhances the economic competition, fatally associated with most first-generation biofuels like food-ethanol. Thermo-chemical production of petroleum-gasoline(diesel) substitutes from biomass is more attractive because the catalytic F-T synthesis processes are almost identical to those industrialized ones from coal/natural gas-derived syngas in case biomass syngas is obtained, which is an effect supplement for transportation fuels. While hydrocarbon distribution of traditional F-T synthesis from coal/natural gas over Co- or Fe-based catalyst is determined by the limit of Andson-Schultz-Flory (ASF) law and the selectivity to heavy products is high with low selectivity to gasoline. Usually the following hydrocraking and hydroisomerization are needed to obtain gasoline/diesel fuels. At the same time biomass syngas is generally CO2-rich with low H2/C ratio, which is unfavorable for F-T synthesis directly over Co- or Fe-based catalyst. In the present work, the hybrid support of mesoporous SiO2 and microporous zeolite were used to prepare multifunctional catalysts. The support features of the impregnated Co-based catalysts, such as the texture properties of SiO¬2, the types of zeolite with different SiO2/Al2O3 ratio were evaluated to synthesize gasoline-range hydrocarbons（C5~C12）. Noble metal (Ru) was loaded to modify the catalytic activity of Co/SiO2/HZSM-5 catalysts. The F-T synthesis performance of biomass syngas was also investigated over Co/SiO2/HZSM-5 by activity test and catalyst characterization, where H2 and CO2 content in the syngas were the main influence factors. And the whole route of biomass to liquid fuels(BTL) was roughly analyzed to optimize the efficiency of F-T synthesis from biomass. The results obtained are listed below 1. The high dispersion degree of cobalt particles resulted from high surface area of the supports, but the strong acidity of zeolite decreases this tendency. When the zeolite（USY、Hβ、HZSM-5）with different SiO2/Al2O3 ratio was used along with mesoporous SiO2 (9nm)as hybrid supports, the large surface area of SiO2 dispersed zeolite particles and reduced the acidity of zeolite without meso-pore structure destruction. The meso- and micro-pore structure of tailor-made Co/SiO2/Zeolite catalysts combined the advantage of quick diffusion rate and high shape selectivity to C5~C12, which increased the hydrocarbon yield to 150 g/Nm3. HZSM-5(38) was better than the other two zeolites during F-T synthesis. 2. Loading small amount of noble metal(Ru) increased the dispersion degree and reduction of Co/SiO2/HZSM-5 catalysts by H2 spillover. When Ru content was 1~2wt% on Co/SiO2/HZSM-5 catalyst, the increase degree of reduction degree at 150-400℃ was high. Although the hydrocarbon yield was increased when Ru loading amount was higher than 2wt%, the accelerated CO hydrogenation rate derived from high Co dispersion degree and reduction resulted in low space-time yield of C5-C12. The characterization of the used catalyst implied the carbon species deposited were hydrocarbons from F-T synthesis. And the decreased carbon depositing amount was due to the dissociative adsorption of H2 on Ru surface and Hads spillover from Ru to Co surface. 3. Proper amount of CO2 in biomass syngas increased CO2 conversion, but decreased CO conversion and total carbon conversion because of relatively slow hydrogenation rate of CO2 and the competing adsorption of Hads between CO and CO2. But CO2 conversion would be debased when quite amount of CO2 played as diluting gas without being catalyzed. While the product selectivity still showed typical F-T distribution model, resulted from CO hydrogenation in CO and CO2-containing biomass syngas. The proper H2/C ratio also affected the total synthesis results. 7.5% CO2 in the biomass syngas(C) inhibited WGS reaction and decreased the re-oxidation of Co-based catalysts, which kept the carbon usage and F-T performance at high level. The carbon species in the used catalysts were mainly hydrocarbons and carbon deposition. The favorable hydrocarbon yield and space-time yield of C5~C12 were achieved at T=250℃，P=2.0~2.5MPa， WHSV=6.27~12mg/gcat/h 4. For liquid fuel synthesis, the “Once-through” route combined with power generation from unconverted tail gas has higher efficiency with easier maintenance than 100% syngas conversion. And to increase H2 content is the primary task for stoichiometic adjustment of syngas composition and the key factor that affect efficiency of biomass to liquid technology. Both reformation and decarbonization of crude biomass gas can get fine BTL results.
页数	127
语种	中文
文献类型	学位论文
条目标识符	http://ir.giec.ac.cn/handle/344007/5772
专题	中国科学院广州能源研究所
推荐引用方式 GB/T 7714	李宇萍. 钴基催化剂制备及其催化合成汽油类烃的性能[D]. 广州能源研究所. 中国科学院广州能源研究所,2008.

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