Raney-Ni催化生物油轻质组分加氢制备含氧燃料

摘要

鉴于生物油的高含氧量，将其轻质组分在温和条件下转化为以饱和醇为主要成分的含氧燃料可能成为生物油利用的新思路。该文以自制Raney-Ni为催化剂，研究在高压反应釜中反应温度（100～180℃）、氢气冷压（4～8 MPa）、催化剂用量（0.5～2 g）对生物油轻质组分催化加氢改质的影响；对Raney-Ni催化剂进行N2吸附脱附、X射线衍射（X-ray diffraction）、扫描电镜（scanning electron microscope）表征，分析催化剂失活机理，研究催化剂的重复使用性能。试验结果表明：反应温度和反应初压对生物油加氢产物分布的影响较大，在反应温度为140℃、氢气初压为6.0 MPa 时，产物中饱和醇的相对含量（以GC峰面积百分比计算）最高可达53.51%；当催化剂用量从0.5 g增加到1 g时，产物中饱和醇的含量显著提升，由25.42%提高到51.89%，进一步提高催化剂用量对饱和醇含量的提高影响不大；一次与二次催化剂催化生物油加氢反应产物中饱和醇含量由53.51%降为29.20%，活性显著降低可能与催化剂孔道内部及表面的活性中心被覆盖进而降低反应效率有关。加氢过程中，除有酮醛酚类化合物的加氢反应和酸与醇的酯化反应外，存在醇脱水成醚的反应发生。与烃类液体燃料相比，含氧燃料以其优异的燃烧性能逐渐被人们所青睐。将生物油的轻质组分加氢制备含氧燃料有望成为生物油的应用提供新思路。%Bio oil, for its simple preparation and low cost, had the potential to be one kind of substitute liquid fuel. In view of its high temperature, H2 pressure, and high oxygen content, hydrodeoxygenation (HDO) is very critical for hydrocarbon fuel. Upgrading the light phase of bio-oil might be a potential method and stable oxygenated compounds might be a kind of potential fuel for the application of bio-oil. In this paper, a Raney Ni catalyst was used for hydrogenating bio oil to saturated alcohols in the high pressure reaction kettle. The influences of temperature (100-180℃), initial pressure of hydrogen (4-8 MPa), the dosages and the recycle usage of the catalyst on the hydrogenation of bio-oil over the self-made Raney-Ni catalyst were discussed. X-ray Diffraction, Brunauer Emmett Teller, and a scanning electron microscope were used to investigate the deactivation mechanism. The results indicated that the reaction temperatures and the initial pressures of the hydrogen gas had an obvious effect on the conversion of the light composition of the bio oil. With the increasing of the reaction temperature to 140℃and the initial pressure to 6 MPa, the yield of saturated alcohols increased and reached the highest point of 53.51%. Meanwhile, the total content of stable alcohols and esters reached 64.62%. At this condition, there was no aldehyde detected in the product, and nearly 40%of the ketones were hydrogenated to alcohols. And also there was 1.77%of ether detected in the products which accounts for the dehydration happening from alcohols. With the increasing of temperature, the conversion of phenol increased. When the dosage of the catalyst increased from 0.5 g to 1 g, the content of saturated alcohols in the product increased from 25.42% to 51.89%. Over 0.5 g of Raney Ni catalyst, there were some unstable ketone compounds such as 1-hydroxy-butanone, 3-hydroxy-butanone, and hydroxyl-acetone in the products. When the dosage of Raney Ni catalyst increased, the content of saturated alcohols in the upgraded bio oil was little changed. Over fresh and once-used Raney Ni catalysts, the content of saturated alcohols decreased from 53.51%to 29.20%. The XRD results showed that the three characteristics of the diffraction peak intensity decreased significantly, and the heterogeneous metal skeleton crystal structure of the Raney Ni catalyst collapsed after use. The SEM results showed that after the hydrogenation reaction, the catalyst presented a black honeycomb solid surface and the activity on the surface was covered by coking. The deactivation of the catalyst may relate to the covering of the catalyst pore and the coking on the catalyst channel, which leads to a decrease of the catalyst’s activity and a reduction of the reaction efficiency. During the upgrading process, the ketones and the aldehydes compounds could be hydrogenated to alcohols, and the phenols could be hydrogenated to cyclohexanol and its derivatives. Apart from the hydrogenation reaction, the esterifications existed during the process, and the contents of acids decreased after hydrogenation to some extent. Compared with hydrocarbon fuel, oxygenated fuel for its good combustion performance becomes more popular. It might be a potential and novel way of upgrading bio-oil to oxygenated fuel.