Simulation and Investigation of H2S Adsorption Effects by 4A Molecular Sieve for Separation from Natural Gas

One of the widely used methods to remove acid gas is surface adsorption using solid molecular sieves. The advantages of H2S adsorption with molecular sieves can be seen in reversibility of the process, chemical and thermal stability, no secondary product, and high selectivity of H2S in these adsorbents. Therefore, in this study, Aspen-Adsim software was used to investigate the effect of various parameters on adsorption of H2S on 4A molecular sieve adsorbent. The desired bed is considered vertical and one-dimensional. The results related to the breakthrough curves and saturation time showed that maximum amount of adsorption occurred in early times. As the adsorption time increases, the rate of H2S adsorption decreases. The results of investigating the effect of operating parameters showed that increasing the tower pressure from 90 to 104 bar reduces the output H2S content by 21 ppm. Also, reducing the feed temperature showed significant results on amount of H2S absorption and the reduction of the output H2S content, so that for every one degree of temperature reduction in the feed gas temperature, the dew point temperature of the output was reduced by 1.6°C. Due to high amount of absorbent and its heat capacity compared to the amount of H2S in the gas phase, a slight temperature increase occurs along the tower so that the difference between inlet and outlet temperatures does not exceed 1˚C. According to the breakthrough curve, it was also determined that after 7920 seconds, the entire bed of the tower is saturated with H2S molecules.