颗粒内部毛细凝聚对气体有效扩散系数影响的研究
发布时间：2018-10-08 12:09
【摘要】：多相放热反应中低沸点易挥发的物质容易在催化剂孔内发生毛细凝聚从而降低气体扩散速率,本研究试图测量内部润湿分率和有效扩散系数来表征毛细凝聚现象对气体在催化剂孔内扩散的影响,这可为催化剂制备、载体的选择、优化反应条件等提供重要依据。采用重量法在373K～413K及0.4 MPa～1.0MPa条件下测量了环己烷、丙酮和甲醇三种吸附质在某工业催化剂Ni/γ-Al2O3催化剂床层上的吸附等温线,结果表明：在一定的相对压力范围内,吸附等温线存在多重滞后环；随着温度的升高,滞后环宽度变窄；在相同的条件下,随着吸附质分子极性的增强,吸附等温线滞后环起点朝着吸附质蒸气相对压力减小的方向移动。利用D-R吸附模型来模拟三种吸附质在催化剂上吸附量,通过实验数据的线性拟合,可以确定其中的待定参数n,证实了实验条件下模型的适用性和准确性。采用改进型Wicke-Kallenbath稳态扩散池,在与吸附实验相同的条件下测定了氢气通过催化剂颗粒的有效扩散系数。实验采用逐步增加吸附质流量至某最大值而后逐步降低回到初始点的方法,测得了三种吸附质在催化剂孔内发生毛细凝聚时氢气的有效扩散系数随吸附质蒸气相对压力的变化关系。结果表明：气体的有效扩散系数滞后环宽度随着温度的升高而变窄,并且出现多重滞后环。根据内部润湿分率定义,结合吸附实验和有效扩散系数实验的数据得到有效扩散系数与内部润湿分率关系曲线。发现对于同一种吸附质,催化剂内部润湿分率越小,氢气的有效扩散系数对操作条件的变化越敏感。建立了催化剂部分润湿时氢气的有效扩散系数与内部润湿分率的关联式,与实验测量值符合较好。
[Abstract]:In the multiphase exothermic reaction, the volatile matter with low boiling point is easily condensed by capillary in the pore of the catalyst, thus reducing the gas diffusion rate. This study attempts to measure the internal wetting fraction and effective diffusion coefficient to characterize the effect of capillary condensation on the gas diffusion in the pore of the catalyst, which can provide an important basis for the preparation of catalyst, the selection of support, and the optimization of reaction conditions. The adsorption isotherms of cyclohexane, acetone and methanol on the bed of a commercial catalyst Ni/ 纬 -Al _ 2O _ 3 were measured by gravimetric method at 373K~413K and 0.4 MPa~1.0MPa. The results showed that the adsorption isotherms of cyclohexane, acetone and methanol on the bed of a commercial catalyst Ni/ 纬 -Al _ 2O _ 3 were obtained. There are multiple hysteresis rings in the adsorption isotherm, the width of the hysteresis rings becomes narrower with the increase of temperature, and under the same conditions, with the increase of the polarity of adsorbate molecules, The starting point of the adsorption isotherm hysteresis ring moves towards the direction of the decrease of the relative pressure of the adsorbed vapor. The D-R adsorption model is used to simulate the adsorption capacity of three adsorbents on the catalyst. By linear fitting of the experimental data, the undetermined parameters n can be determined, which proves the applicability and accuracy of the model under the experimental conditions. The effective diffusion coefficient of hydrogen through the catalyst particles was measured under the same conditions as the adsorption experiment by using the modified Wicke-Kallenbath steady diffusion cell. In the experiment, the adsorption mass flow rate was gradually increased to a certain maximum and then gradually decreased back to the initial point. The relationship between the effective diffusion coefficient of hydrogen and the relative pressure of adsorbed vapor was measured when the capillary condensation of three adsorbates occurred in the pore of the catalyst. The results show that the width of the effective diffusion coefficient hysteresis ring becomes narrower with the increase of temperature, and there are multiple hysteresis rings. According to the definition of internal wetting fraction, the relationship curve between effective diffusion coefficient and internal wettability is obtained by combining the data of adsorption experiment and effective diffusion coefficient experiment. It is found that for the same adsorbate, the smaller the wetting fraction of the catalyst is, the more sensitive the effective diffusion coefficient of hydrogen is to the change of operating conditions. The correlation formula between the effective diffusion coefficient of hydrogen and the internal wetting fraction was established, which is in good agreement with the experimental results.
【学位授予单位】：华东理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TQ021.4
本文编号：2256697
[Abstract]:In the multiphase exothermic reaction, the volatile matter with low boiling point is easily condensed by capillary in the pore of the catalyst, thus reducing the gas diffusion rate. This study attempts to measure the internal wetting fraction and effective diffusion coefficient to characterize the effect of capillary condensation on the gas diffusion in the pore of the catalyst, which can provide an important basis for the preparation of catalyst, the selection of support, and the optimization of reaction conditions. The adsorption isotherms of cyclohexane, acetone and methanol on the bed of a commercial catalyst Ni/ 纬 -Al _ 2O _ 3 were measured by gravimetric method at 373K~413K and 0.4 MPa~1.0MPa. The results showed that the adsorption isotherms of cyclohexane, acetone and methanol on the bed of a commercial catalyst Ni/ 纬 -Al _ 2O _ 3 were obtained. There are multiple hysteresis rings in the adsorption isotherm, the width of the hysteresis rings becomes narrower with the increase of temperature, and under the same conditions, with the increase of the polarity of adsorbate molecules, The starting point of the adsorption isotherm hysteresis ring moves towards the direction of the decrease of the relative pressure of the adsorbed vapor. The D-R adsorption model is used to simulate the adsorption capacity of three adsorbents on the catalyst. By linear fitting of the experimental data, the undetermined parameters n can be determined, which proves the applicability and accuracy of the model under the experimental conditions. The effective diffusion coefficient of hydrogen through the catalyst particles was measured under the same conditions as the adsorption experiment by using the modified Wicke-Kallenbath steady diffusion cell. In the experiment, the adsorption mass flow rate was gradually increased to a certain maximum and then gradually decreased back to the initial point. The relationship between the effective diffusion coefficient of hydrogen and the relative pressure of adsorbed vapor was measured when the capillary condensation of three adsorbates occurred in the pore of the catalyst. The results show that the width of the effective diffusion coefficient hysteresis ring becomes narrower with the increase of temperature, and there are multiple hysteresis rings. According to the definition of internal wetting fraction, the relationship curve between effective diffusion coefficient and internal wettability is obtained by combining the data of adsorption experiment and effective diffusion coefficient experiment. It is found that for the same adsorbate, the smaller the wetting fraction of the catalyst is, the more sensitive the effective diffusion coefficient of hydrogen is to the change of operating conditions. The correlation formula between the effective diffusion coefficient of hydrogen and the internal wetting fraction was established, which is in good agreement with the experimental results.
【学位授予单位】：华东理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TQ021.4
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