Separation Of C₆H₆ From Waste Gas By Using Membrane-based Gas Absorption Technique

In this paper , The aqueous solution of n-Formyl morpholine (NFM) was used as absorbent .This works focuse on a membrane based gas absorption process for the separation benzene (C₆H₆) from N₂ and on vacuum membrane distillation(VMD) process for the absorbent regeneration.In the membrane based gas absorption process,effect of various factors, including flowrate of absorbent and feed gas, concentration of absorbent and feed gas, differences of membranes modules on the removal efficiency 7 and overall mass transfer coefficient k_ovwere investigated. The model of mass transfer resistance model was presented and the prediction value was compared with experimental value. It was found that the characteristics of separation of C₆H₆/N₂ by membrane contactor are of quicker mass transfer velocity and higher efficiency of separation. The overall mass transfer coefficient K_ov achieves 0.8×10^-6m·s^-1-2.5×10^-6m·s^-1, when following conditions were used: volume ratio of NFM, 40 %; flowrate of absorbent, 20 mL·min^-1-100 mL·min^-1; flowrate of feed gas, 100 mL·min^-1-200 mL·min^-1. Prediction value is in better agreement with experimental value, the maximal error is 20.2 %, the average error is 7.9 %, it is proved that the model mass transfer resistance layer can be used to simulate the process of membrane-based gas absorption for the removal of C₆H₆, and provide theory for the enlarging experiment of membrane contactor. In the cacuum membrane distillation process, effect of various factors, including concentration of absorbent ,flowrate of absorbentand and temperature of absorbent were investigated, the result shows that VMD has higher efficiency of regeneration in separation of C₆H₆ from the aqueous solution of n-Formyl morpholine.and the regeneration efficiency should be higher than 80 % .The regeneration efficiency and the flux will increase when increase the concentration of absorbent,flowrate of absorbent and temperature of absorbent; The flux achieves 0.5×10^-3-5.5×10^-3mg·cm^-2·min^-1, when following conditions were used: volume ratio of NFM, 40 %; flowrate of absorbent, 20 mL·min^-1-100 mL·min^-1; concentration of absorbent, 0.18 g·L^-1-0.45g·L^-1; temperature of absorbent, 15℃-40℃.