The effect of the number of fibers in hollow fiber membrane modules for NOx absorption

As a type of gas that contributes to air pollution, nitrogen oxide (NO_x) has harmful effects on humans and the environment. Among several types of NO_x, nitric oxide (NO) and nitrogen dioxide (NO₂) are most commonly found in air. The utilization of membranes as reactors is a system that combines chemical reactions with the separation process through membranes to increase the conversion of the reaction. This study investigated the absorption process by utilizing a hollow fiber membrane module (polysulfone) as a bubble reactor with H₂O₂ (0.5 wt. %) and HNO₃ (0.5M) as the absorbent. NOx feed gas was flown into the tube side of the membrane; the shell side was filled with static H₂O₂ and HNO₃ and the shell input and the tube output flow were closed to create gas bubbles. The experimental results showed that the absorption efficiency increased, but the mass transfer coefficient and flux decreased as the number of fibers in the membrane module increased at the same feed gas flow rate. The NO_x loading is relatively constant as the amount of fiber in the membrane module increased at the same feed gas flow rate. The experimental results also showed that the mass transfer coefficient, flux, and NO_x loading increased with increasing feed gas flow rate, but the absorption efficiency decreased when using the same number of fibers in the membrane module. The maximum NO_x absorption efficiency achieved in this study was 94.6% at the feed gas flow rate of 0.1 L/min, using a membrane module with 48 fibers.