在旋轉填充床內吸收親疏水性有機揮發物之研究

Abstract

本研究為錯流式旋轉填充床內同時吸收甲苯與異丙醇的質傳程序，甲苯為疏水性揮發有機物，而異丙醇為親水性揮發有機物，分別使用水、矽油以及矽油加水混合物作為吸收劑進行吸收程序。單獨用水時，異丙醇最高吸收分率可達到0.99，而甲苯最高吸收分率只有0.1，顯示對於親水性揮發有機物水是一個適當的吸收劑；單獨使用矽油時，甲苯最佳吸收分率為0.78，而異丙醇只有0.33，明顯可看出矽油適合作為疏水性揮發有機物的吸收劑。 接著，使用矽油加水混合物吸收甲苯與異丙醇實驗，其結果顯示，甲苯與異丙醇皆可達到0.9以上的吸收分率。為了探討矽油加水混合物對於甲苯與異丙醇的吸收是正向或負向幫助，透過E factor(enhancement factor)的計算進行分析。甲苯的E值在矽油流量為0.1L/min時，隨水流量增加而上升到最大值為2.5，當矽油流量越大，能提昇的E值幅度就越小，而異丙醇的E值在水流量為0.01 L/min與0.03L/min時皆小於1，隨著水量的增加回逐漸上升到1左右。以上的結果主要來自碰撞包覆效應與總液體流量效應兩個因素所影響，碰撞包覆效應會使得矽油包覆在水的外面，造成矽油與氣體接觸面積增加，但讓水與氣體接觸面積減少，因此有利於甲苯的吸收，卻不利於吸收異丙醇；總液體流量效應可藉由水使得黏度高的矽油均勻分布於床體中，使得甲苯與矽油接觸面積大幅提升，使得甲苯的質傳效果變好。

This work presented a mass transfer process of absorbing toluene and isopropanol in a cross-flow rotating packed bed (RPB) at the same time. Toluene is a hydrophobic volatile organic compound (VOC) while isopropanol is a hydrophilic VOC. Water, silicone oil, as well as the mixture of silicone oil and water were used as absorbents for these absorption processes. When using water as the only absorbent, the best absorption fraction of isopropanol was 0.99, but it was only 0.1 for toluene. It obviously indicated that water is a suitable absorbent for hydrophilic VOCs. When silicone oil was the absorbent alone, the best absorption fraction for toluene was 0.78, and 0.33 for isopropanol. It suggested that silicone oil is a appropriate absorbent for hydrophobic VOCs. Then, we implemented the absorption processes of toluene and isopropanol by the mixture of silicone oil and water. Both absorption fractions for these two compounds could reach more than 0.9. We calculated the enhancement factor (E) to evaluate the impacts on absorptions of toluene and isopropanol by this mixed absorbent. As the silicone oil flow rate was 0.1, the E value of toluene rose significantly to 2.5 with increasing water flow rate. Higher the silicone oil flow rate resulted in less enhancements. However, the E value of isopropanol was less than 1 when the water flow rate were 0.01 and 0.03 L/min, and it would gradually increase to about 1 with the increase of water flow rate. The “insertive merging effect” and the total liquid flow rate effect could be used to explain the results above. The insertive merging effect means that the water droplet inserted into silicone oil droplet. This effect increased the effective gas-liquid contact area of oil but hindered that of water. Thus it was favorable for absorption of toluene but not for isopropanol. The total liquid flow rate effect means that water lead silicone oil of high viscosity to distribute better inside the RPB, and it causes higher gas-liquid contact area between toluene and silicone oil. Therefore, it could enhance mass transfer for hydrophobic VOCs.