旋轉填充床之高黏度系統中氣提甲醇

Abstract

旋轉填充床是程序強化的重要項目之ㄧ，係以離心力取代重力場而使得系統操作範圍變廣，質傳效果也大幅提升。本實驗即是使用旋轉填充床的高質傳係數特質，來解決從甘油中氣提甲醇遇到之質傳效率不佳的瓶頸；文中探討了氣量、液量、轉速、黏度、溫度及濃度等變數對氣提百分比和氣膜質傳係數的影響。 實驗結果顯示，於重量百分濃度為2%及8%實驗中，隨著轉速增加(1200至2400rpm)、氣體流量增加(40至50L/min)、溫度升高(30至60℃)，氣提百分比會有約3.4倍之增加；於重量百分濃度為0.5%實驗中，液體流量減少(200至100mL/min)而使氣量/液量比例增加，亦讓系統有較大的能力帶出大量甲醇，進而提升了氣提效率約2倍，另外設定溫度由30℃升至60℃可使氣液平衡常數增加約3倍，因此升溫可有效提升2-3倍的氣提效率。 於本研究中提出一可適用於高黏度系統及水相系統之所有醇類迴歸式如下，實驗數據包含本研究、本實驗室及公開文獻資料。

在高溫、高濃度之系統下實驗所得之氣液進口溫度以及氣液出口溫度之變化極大，其中系統溫度變化來自於空氣中的水由氣相進入甘油而產生放熱現象，以及甲醇由液相氣提至氣相的吸熱現象，也因此造成系統設定溫度會高於實際氣液質傳時之溫度，故部分高溫高濃度所求得KGa屬保守估計值，實際KGa應高於計算結果。

A so-called rotating packed bed (RPB) which substitutes the centrifugal force for gravitational force plays an important role in the field of “process intensification.” With the help of centrifugal force, a wider operating range and better mass transfer efficiency could be expected. As a result, in this research, with the trait of high mass transfer coefficient in an RPB, the bottle neck of stripping methanol from viscous glycerol solution could be improved. The gas flow rate, liquid flow rate, rotor speed, liquid viscosity, temperature, and liquid concentration were taken into consideration as the operating variables to pursue better stripping ratio and mass transfer coefficient in the system. According to the experimental results of 2% and 8% (methanol/glycerol) data sets, as the rotor speed increased from 1200 to 2400 rpm, gas flow rate increased from 40 to 50 L/min, and temperature increased from 30 to 60℃, the stripping ratio could be raised to 3.4 folds. As considering the ratio of (gas flow rate/liquid flow rate) in 0.5% data, we could find that while the liquid flow rate decreased from 200 to 100 mL/min, there would be a higher ratio of (gas flow rate/liquid flow rate) and a higher capacity to remove methanol from the liquid phase to gas phase. Thus the stripping efficiency could be found to be doubled. On the other hand, equilibrium constant became triple by increasing temperature from 30 to 60℃, and 2~3 times of stripping efficiency was obtained. In this research, a correlation applicable to both aqueous and viscous systems is presented as:

It was found that a significant temperature variation might be noted within the packed bed, especially with high temperature and concentrated cases. This might be due to the exothermic phenomena of methanol evaporation and the endothermic process of water (humidity) moving from gas phase to liquid (glycerol) phase. Therefore, because of choosing the oven temperature as a reference one, the KGa estimated from the correlation shown above would be a conservative one.