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固体酸碱催化剂催化酯化改质提升生物油的研究

Upgrading Bio-oil over Solid Acid and Base by Catalytic Esterification

【作者】 张琦

【导师】 常杰;

【作者基本信息】 中国科学技术大学 , 工程热物理, 2006, 博士

【摘要】 国际原油价格上涨,燃油供应紧张,液体代用燃料的研究广泛开展。生物质热解液化技术得到的燃料产率很高,是高效率的生物质转化过程,并使生物质成为最有可能部分代替化石能源的可再生能源。然而生物油粘稠、稳定性差、腐蚀性强、化学组成复杂等缺点给生物油部分替代传统石油产品的进程带来极大阻碍,成为生物油工业化利用的瓶颈。对生物油进行精制,提高生物油的品质势在必行。因而本文对改质与酯化反应相结合的提升生物油新方法进行探索,具有重要的应用价值和现实意义。 目前生物油精制主要方法中,生物油加氢脱氧得到烃类物质的方法成本,设备复杂,操作过程中经常遇到反应器堵塞和催化剂失活的现象;利用催化裂解将生物油中含氧有机物转化为轻质组分的方法成本低廉,但是由于此方法结焦率高,得到的精制油质量较差;水蒸气重整制氢的工艺比较复杂,对设备要求较高,需要开发成熟、稳定、与反应器相适合的催化剂;乳化方法无需过多的化学转化操作,但不可忽视乳化的成本和乳化需要的能量投入,而且作为汽车用油,乳化油对发动机的腐蚀效应比较严重。针对生物油内含有的多种有机羧酸物质、羧酸总含量较高(10-20wt%)的特点,本研究筛选具有高效酯化活性的固体酸和碱催化剂,探索改质与酯化反应相结合的生物油改质提升的新方法,与传统精制方法比较,提高生物油品质的同时,降低了设备及操作成本。 首先利用模型反应在众多固体酸催化剂体系中筛选了高酯化活性的固体酸催化剂,试制开发了固体酸mix 40STS400高效催化酯化催化剂,结合物理表征手段发现mix 40STS400的高酯化活性与Ti的结合方式、形态和SiO2含量有关,一定量的四方晶锐钛矿型TiO2、正交晶硫酸氧钛、少量立方晶金属钛加上高分散、高比表面积的SiO2组成了具有高酯化活性的催化剂。添加的SiO2形成Ti-O-Si键,它帮助mix 40STS400与SO42-在样品表面形成强相互作用,增强了催化剂与SO42-的结合,使SO42-不易脱除,结合的SO42-主要以无机螯合状双配位和有机硫酸酯两种结构形式存在。固体碱的催化酯化研究表明添加K2CO3的γ-Al2O3酯化效果最好,30%K2CO3-γ-Al2O3/NaOH比30%K2CO3-γ-Al2O3耐水性强,但活性略低。

【Abstract】 The research on alternative liquid fuel development has been carried out extensively as s result of rising price of international crude oil and tension of oil supply. Biomass pyrolysis is an efficient process of biomass conversion with high yield of liquid fuel, which makes biomass the most promising renewable energy to substitute the conventional fossil fuel. But the negative properties of bio-oil, such as the high viscosity, instability, severe corrosiveness and complicated composition put a lot of obstacles for its replacing process consequently, and have become a bottle-neck in its full applications. An urgent necessity to upgrade bio-oil is demanding. So the study in this dissertation combining bio-oil upgrading and catalytic esterification deserves great value and realistic significance.Among present bio-oil upgrading techniques, hydrodeoxygenation process needs complicated equipments, superior techniques and excessive cost and usually is halted by catalyst deactivation and reactor clogging. Although catalytic cracking is regarded as a cheaper route by converting oxygenated feedstocks to lighter fractions, the results seem not promising due to high coking and poor quality of the fuels obtained. Emulsification does not demand redundant chemical transformations, but the high cost and energy consumption input cannot be neglected. The accompanying corrosiveness to the engine and the subassemblies is inevitably serious. Based on the characteristic of high total amount (10-20wt%) and multi-organic acids existence, solid acid and solid base catalysts with high esterification activity were screened out and put into bio-oil upgrading investigation by esterification in order to lower the operation cost and improve the bio-oil quality.Solid acid "mix 40STS400" was chosen and accepted for its high esterification activity by model reaction of ethanol and acetic acid esterification. The physical characterization proved that the connection between high activity and crystalline phase composition, crystallographic state of Ti and existence of SiO2. And the combination of tetragonal anatase TiO2, orthorhombic crystal titanium oxide sulfate and cubic crystal titanium with highly-scattered and amorphous SiO2 ensured the

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