【作者】 刘鹏程；

【导师】 李殿卿；

【作者基本信息】 北京化工大学 ， 应用化学， 2007， 硕士

【摘要】 合成各种聚合物的乙烯单体，通常是由烃类蒸汽裂解制得。在裂解气中除了乙烯单体以外常常含有少量的乙炔等杂质，为了提高聚合物的性能，通常需要对裂解气进行精制，以使乙炔含量降至10ppm以下，最好小于5ppm。工业上一般采用催化选择性加氢的方法将乙烯原料中的乙炔除去。球形氧化铝作为催化剂或催化剂载体使用时，以点相互接触，堆砌均匀，因而大大提高了传质和催化效果。油柱成型法制备的氧化铝不仅外观呈球形，而且具有比表面大、强度高、孔结构优良等优点，是理想的C2选择性加氢催化剂载体。针对油柱成型法制备的球形氧化铝在作为C2选择性加氢催化剂载体应用时存在选择性较差、绿油生成量偏高的缺点，本论文对油柱成型法制备的球形氧化铝表面性质进行改性，对制备结构和性能可控的C2选择性加氢催化剂载体开展了系统研究。以铝粉和盐酸为原料合成铝溶胶，利用过程还原—磁性分离技术和装置精制铝溶胶，再以其为原料用油柱成型法制备了系列球形氧化铝。通过水洗法、氨水洗涤法和焙烧法对球形氧化铝进行改性。分析结果表明，水洗法和氨水洗涤法可有效降低球形氧化铝载体的氯含量，在一定程度上提高了球形氧化铝载体的水热稳定性和降低了表面酸量。焙烧法对球形氧化铝的性质影响显著，600℃、960℃、1050℃、和1200℃下焙烧的球形氧化铝晶型分别为γ-Al₂O₃、δ-Al₂O₃、θ-Al₂O₃和α-Al₂O₃，随焙烧温度的提高，球形氧化铝载体的比表面积、孔容和表面酸量逐渐减少，平均孔径逐渐增大。采用油柱成型法成功制备了一系列La、Si和Ti元素改性的球形氧化铝样品。在La改性的球形氧化铝中，当La／Al摩尔比等于0.02或更高时，La元素在前体中以LaCO₃OH的形式出现，经过高温焙烧形成LaAlO₃。La改性球形氧化铝样品酸中心的数量则先随La／Al摩尔比增加而增大，并在La／Al摩尔比为0.01时达到最大值，当La／Al摩尔比继续增大时，酸中心的数量迅速减小并低于纯氧化铝。添加SiO₂对氧化铝具有热稳定性作用，SiO₂含量越高，球形SiO₂-Al₂O₃的比表面积和孔容增加越显著，热稳定效果越明显，并且酸中心数量随SiO₂含量的增加而增加。添加TiO₂会降低的氧化铝的晶型转变温度，使氧化铝的热稳定性降低，在焙烧温度高于960℃的情况下，Ti元素以晶红石型的TiO₂晶型出现，球形TiO₂-Al₂O₃的比表面积、孔容和平均孔径随TiO₂含量的提高而减少，酸中心数量随TiO₂的引入稍有增加。C2选择性加氢评价实验表明，经过1150℃焙烧的空白球形氧化铝载体在负载了活性组分后，在反应中表现出良好的活性和选择性，并且绿油生成量低，性能优于国内现有催化剂，在实际乙烯工业生产过程中具有良好的应用价值。更多还原

【Abstract】 Ethylene is a monomer that is used in preparing a number of olefin polymers. Ethylene is generally made by the pyrolysis or catalytic cracking of refinery gas, ethane, propane, butane, and the like. Ethylene so produced usually contains small proportions of acetylene. In polymer grade ethylene, it is generally preferred that the acetylene content be less than about 10 ppm, most preferably less than about 5 ppm. One of the techniques that has been used in the past for reducing the amount of acetylene in an ethylene stream has involved selective hydrogenation using a catalyst.When used in fixed beds, spherical alumina facilitates uniform packing of the bed, whereby variations in the pressure drop through the bed are minimized and channeling of the feed stream of reaction components is substantially reduced. Spherical alumina prepared by oil-drop method can be employed in the selective hydrogenation reaction on account of high activity, high specific surface area, high intensity, fine pore volume and pore distribution maintaining the advantage of spherical form. The said support could not perform both said excellent performance and high purity, pore properties and high thermalstability together. In the thesis, preparing spherical alumina with controlling of structure and properties has been studied.The alumina hydrosol was firstly synthesized using aluminum powder and hydrochloric acid. The amount of impurity in alumina hydrosol was decreased during the synthesis of alumina hydrosol using reduction-magnetic separation process. Spherical alumina granules are prepared by the oil-drop method using the purified alumina hydrosol as starting material. Spherical alumina granules are modified by hot water, hot ammonia and calcining at different temperature. The analysis results show that the amount of Cl of spherical alumina modified by hot water and ammonia was highly reduced. The hydrothermal stability has been improved and the surface acidity has been decreased. The crystal types of alumina calcined at 600℃, 960℃, 1050℃and 1200℃areγ-Al₂O₃,δ-Al₂O₃,θ-Al₂O₃ andα-Al₂O₃ respectively. The specific surface area, pore volume, and surface acidity are decreased and average pore diameter is enlarged with the increase of calcining temperature.Spherical alumina modified by La, Si, and Ti was prepared. The sample prepared by La modified with 0.02 or higher of La/Al mole ratio shows LaCO₃OH in precursor and LaAlO₃ after calcined at 600℃or higher. With the increase of La/Al mole ratio, the La modified alumina’s acid sites increase at the beginning, reach maximum value with 0.01 of La/Al mole ratio, and then decrease rapidly and lower than normal alumina. SiO₂ can improve the thermalstability of the spherical alumina, specific surface area, pore volume and surface acidity increase with the increase of SiO₂ content. TiO₂ can weaken the thermalstability of the spherical alumina, when calcined at 960℃or higher, there is rutile TiO₂ crystal in spherical alumina, specific surface area, pore volume and average pore diameter decrease with the increase of TiO₂ content.The catalyst prepared by spherical alumina calcining at 1150℃and loaded with active ingredient shows good activity and selectivity and a low production level of green oil in selective hydrogenation for acetylene action test. The result is better than that of exiting products. There’s good prospect of the catalyst being employed in the ethylene industry.更多还原