焙烧温度对含Mg助剂的铁基催化剂F-T合成反应性能的影响

Effect of calcination temperature on magnesium promoted iron-based catalyst for Fischer-Tropsch synthesis

采用连续共沉淀和喷雾干燥技术相结合的方法制备了Mg助剂的Fe/Cu/K/SiO2 催化剂,采用N2 物理吸附、XRD、MES和H2 -TPR等表征手段,考察了焙烧温度对催化剂比表面积、体相结构和还原性能的影响。结果表明,随着焙烧温度的升高,催化剂的比表面积降低,平均孔径增大,体相中α-Fe2O3 晶粒逐渐增大,催化剂变的越来越难还原,其结构更加稳定。在H2 /CO(摩尔比) = 2. 2、250℃、2. 0MPa和2 000h-1于固定床反应器考察了焙烧温度对该催化剂F-T合成反应性能的影响,结果表明,随着焙烧温度的升高,催化剂的F-T合成反应活性降低,在运行过程中反应活性逐渐增加直至达到平稳,但达到平稳所需的诱导期越来越长;提高焙烧温度使烃产物分布向重质烃方向转移,有利于降低CH的选择性,促进重质烃的生成。

Magnesium-promoted Fe/Cu/K/SiO2 catalyst for Fischer-Tropsch synthesis (FTS) was prepared using spray-dried technology. The structures of the catalysts after calcination at different temperatures were characterized by means of N2 physisorption, X-ray diffraction (XRD), Mossbauer spectroscopy (MES), and H2 temperature-programmed reduction (TPR). It showed that increasing calcination temperature decreased the BET surface area and increased the average pore diameter and the size of α-Fe2O3 crystallite for the catalyst, leading to a difficult reduction of the active phase. The Fischer-Tropsch performance of the catalysts after calcination was tested in a fixed bed reactor under the conditions of 250°C, 2.0 MPa and 2000 h-1. With the increase of the calcination temperature, the initial activity of the catalyst decreased, and the activity gradually approached to a stable value with time on stream, depending on the induction period which prolonged with increasing calcination temperature. Additionally, the increase of the calcination temperature also favored the formation of heavy hydrocarbons and declined the CH4 selectivity.