熔铁催化剂H_(2)-TPR还原动力学和反应模型研究

Study on reduction kinetics of H_(2)-TPR and reaction models of fused iron catalysts

为揭示熔铁催化剂在H_(2)气氛中的还原反应动力学行为,为还原反应器设计和放大提供基础数据,结合H_(2)程序升温还原(H_(2)-TPR)、气固相界面反应模型和谱图分析等方法研究了熔铁催化剂的本征还原反应动力学。熔铁催化剂还原受反应动力学控制,活化能为78.5~82.2 kJ/mol。提高还原温度能显著缩短还原时间,当还原温度不高于480°C时,每提高10°C,还原时间缩短大约31 min。通过4种还原反应动力学模型的比较,发现反应级数模型和几何收缩模型预测的活化能数值与实验值吻合较好(拟合度超过0.99),扩散模型和成核增长模型的预测结果较差。恒温H_(2)-TPR还原结果表明,反应级数模型预测的完全还原所需要的时间和H_(2)-TPR实验误差最小,综合来看,反应级数模型适合用于描述熔铁催化剂的还原过程。通过能量非均匀分布假设,发现活化能在还原过程中的变化较小,最大增幅不超过2.2%,说明熔铁催化剂活性组分的分布比较均匀,还原过程基本遵循能量均匀分布假设。

To reveal the reduction kinetics of fused iron catalyst in H_(2)and provide basic data for the design and scaling up of reduction reactors,the reduction reaction kinetics models of fused iron catalysts were studied by H_(2)temperature programmed reduction(H_(2)-TPR),solid-state reaction model and spectra analysis.The reduction process of fused iron catalysts is controlled by reaction kinetics,and the activation energy is in the range of 78.5 kJ/mol to 82.2 kJ/mol.Increasing the reduction temperature can significantly shorten the reduction time.When the reduction temperature is not higher than 480°C,the reduction time can be shortened by 31 minutes for every 10℃increase.Through the comparison of four reduction kinetic models,it is found that the value of activation energy predicted by reaction-order model and geometric contract model are in good agreement with the experimental data(with a fitting degree exceeding 0.99),While the prediction results of nucleation model and diffusion model are poor.The results of constant temperature H_(2)-TPR show that the time required for complete reduction predicted by the reaction-order model has the smallest error compared to the experimental values of H_(2)-TPR.In summary,reaction-order model is suitable for describing the reduction process of fused iron catalysts.Through the assumption of uneven energy distribution,it is found that the change in activation energy during the reduction process is relatively small with a maximum increase of no more than 2.2%.The above results indicate that the distribution of active components of fused iron catalysts is uniform,and the reduction process basically follows the assumption of uniform energy distribution.