规整填料塔中离子液体吸收CO_2的传质与流体力学性能

Mass transfer and hydraulic performance of CO_2 absorption by ionic liquids over structured packings

在规整填料塔中采用离子液体吸收二氧化碳气体,利用计算流体力学(CFD)软件建立可靠的数学模型,系统考察了离子液体结构及规整填料几何参数对吸收过程的传质特性和流体力学性能的影响规律。结果表明,床层压降随气体流速增大而增大,液相传质系数随液体流速的增大而增大。相同阴离子时,随着阳离子碳链长度的增长,吸收过程压降增大,同时液相传质系数减小。相同阳离子时,不同阴离子的离子液体压降大的同时传质系数也大。但离子液体的结构对压降影响不明显。离子液体筛选主要考虑传质系数和溶解度因素,但二者与离子液体结构表现出相反的规律。两种折线结构的规整填料传质性能优于传统的X型和Y型结构。

In this work, ionic liquids （ILs） were proposed for the capture of CO2 over the structured packings. The pressure drop and mass transfer coefficient were investigated using computational fluid dynamics （CFD）. The relationship among the structure of ILs, performance of pressure drop and mass transfer coefficient, as well as the relationship among the corrugation angles of structured packings, performance of pressure drop and mass transfer coefficient were identified. The results showed that under the same operating conditions with same anion, the increase of carbon number in the alkyl chain on the cation of ILs leads to the increase of the pressure drop （i.e., [HMIM][Tf2N] 〉 [BMIM][Tf2N] 〉 [EMIM][Tf2N]）, and decrease of the mass transfer coefficient （i.e., [EMIM][Tf2N] 〉 [BMIM][Tf2N] 〉 [HMIM][Tf2N]）. Thus, the cation [EMIM] is the optimum choice with regard to the pressure drop and mass transfer performance. Moreover, for ILs with different anions the pressure drop and mass transfer coefficient show the same trend,i.e., [EMIM][BF4] 〉 [EMIM][TFA]≈ [EMIM][TfO] 〉 [EMIM][Tf2N]. There is an inverse relationship between the mass transfer coefficient and solubility of CO2 for different ILs. Thus, there is a tradeoff when choosing IL for the capture of CO2. In addition, four types of structured packings with different corrugation angles （X type, Y type, and two transition types） were compared. From the viewpoint of mass transfer performance the two transition types structured packings are superior to thetraditional X or Y types.