顆粒內(nèi)部毛細凝聚對氣體有效擴散系數(shù)影響的研究
發(fā)布時間：2018-10-08 12:09
【摘要】：多相放熱反應(yīng)中低沸點易揮發(fā)的物質(zhì)容易在催化劑孔內(nèi)發(fā)生毛細凝聚從而降低氣體擴散速率,本研究試圖測量內(nèi)部潤濕分率和有效擴散系數(shù)來表征毛細凝聚現(xiàn)象對氣體在催化劑孔內(nèi)擴散的影響,這可為催化劑制備、載體的選擇、優(yōu)化反應(yīng)條件等提供重要依據(jù)。采用重量法在373K～413K及0.4 MPa～1.0MPa條件下測量了環(huán)己烷、丙酮和甲醇三種吸附質(zhì)在某工業(yè)催化劑Ni/γ-Al2O3催化劑床層上的吸附等溫線,結(jié)果表明：在一定的相對壓力范圍內(nèi),吸附等溫線存在多重滯后環(huán)；隨著溫度的升高,滯后環(huán)寬度變窄；在相同的條件下,隨著吸附質(zhì)分子極性的增強,吸附等溫線滯后環(huán)起點朝著吸附質(zhì)蒸氣相對壓力減小的方向移動。利用D-R吸附模型來模擬三種吸附質(zhì)在催化劑上吸附量,通過實驗數(shù)據(jù)的線性擬合,可以確定其中的待定參數(shù)n,證實了實驗條件下模型的適用性和準確性。采用改進型Wicke-Kallenbath穩(wěn)態(tài)擴散池,在與吸附實驗相同的條件下測定了氫氣通過催化劑顆粒的有效擴散系數(shù)。實驗采用逐步增加吸附質(zhì)流量至某最大值而后逐步降低回到初始點的方法,測得了三種吸附質(zhì)在催化劑孔內(nèi)發(fā)生毛細凝聚時氫氣的有效擴散系數(shù)隨吸附質(zhì)蒸氣相對壓力的變化關(guān)系。結(jié)果表明：氣體的有效擴散系數(shù)滯后環(huán)寬度隨著溫度的升高而變窄,并且出現(xiàn)多重滯后環(huán)。根據(jù)內(nèi)部潤濕分率定義,結(jié)合吸附實驗和有效擴散系數(shù)實驗的數(shù)據(jù)得到有效擴散系數(shù)與內(nèi)部潤濕分率關(guān)系曲線。發(fā)現(xiàn)對于同一種吸附質(zhì),催化劑內(nèi)部潤濕分率越小,氫氣的有效擴散系數(shù)對操作條件的變化越敏感。建立了催化劑部分潤濕時氫氣的有效擴散系數(shù)與內(nèi)部潤濕分率的關(guān)聯(lián)式,與實驗測量值符合較好。
[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/ 緯 -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/ 緯 -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.
【學位授予單位】：華東理工大學
【學位級別】：碩士
【學位授予年份】：2015
【分類號】：TQ021.4
本文編號：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/ 緯 -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/ 緯 -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.
【學位授予單位】：華東理工大學
【學位級別】：碩士
【學位授予年份】：2015
【分類號】：TQ021.4
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