NiMo/Al_2O_3-USY催化剂上中低温煤焦油加氢裂化性能研究

采用等体积浸渍法制得一系列NiMo/Al_2O_3-USY催化剂,在200 mL固定床上考察了不同金属负载量对其中低煤焦油加氢裂化催化性能的影响,进一步用NH_4F溶液改性USY以提高催化剂的脱硫性能,并结合XRD、氮气吸附-脱附、XPS、HR-TEM、H_2-TPR和NH_3-TPD等手段对催化剂进行了表征分析。结果表明,NiM o/Al_2O_3-USY催化剂适宜的M oO_3负载量为15%(质量分数);当MoO_3含量超过15%后,MoS_2活性相在载体上团聚,硫化程度趋于稳定,强酸酸量和孔径减少,增加金属负载量对煤焦油加氢裂化转化率影响较小。NH_4F改性USY可增大NiM o/Al_2O_3-USY催化剂的孔径,有利于提高煤焦油加氢裂化转化率。表面强酸酸量减少后,产品中的硫含量明显增加,说明强酸酸量是影响产物硫含量的关键因素。当NH_4F浓度为0.6 mol/L时,NH_4F改性USY制得的NM 0.6催化剂上煤焦油加氢裂化的转化率为87.65%,产品汽油馏分(≤180℃)硫含量为5.96 mg/kg,柴油馏分(180-320℃)硫含量为34.98 mg/kg。

Catalytic performance of NiMo/Al2O3-USY in the hydrocracking of low-temperature coal tar

A series of NiMo/Al₂O₃-USY catalysts with different MoO₃ contents were prepared through incipient wetness method and further modified with NH₄F. The NiMo/Al₂O₃-USY catalysts were characterized by XRD, XPS, HR-TEM, NH₃-TPD, H₂-TPR and N₂ adsorption and their catalytic performance in the hydrocracking of low-temperature coal tar (LTCT) was investigated in a 200 mL fixed-bed reactor. The results indicate that the appropriate MoO₃ content is 15% (mass ratio); higher MoO₃ content may lead to the agglomeration of active metals on the support, although it has little influence on the sulfidation degree of Mo species and the conversion of coal tar upon hydrocracking. In addition, the amount of strong acid sites and pore diameter decrease gradually with a further increase in the MoO₃ content, which is disadvantageous for deep hydrocracking. The modification of USY zeolite with NH₄F solution can enlarge the average pore diameter of resultant NiMo/Al₂O₃-USY catalysts and then improve the residue conversion of coal tar. However, the amount of strong acid sites decreases obviously when the concentration of NH₄F solution exceeds 0.6 mol/L, which may lead to an increase of the sulfur content in the hydrocracking product. Over the NiMo/Al₂O₃-USY catalyst modified with 0.6 mol/L NH₄F solution, the residue conversion of coal tar reaches 87.65%; the sulfur contents in the gasoline fraction (<180 ℃) and diesel fraction (180-320 ℃) are 5.96 and 34.98 mg/kg, respectively.