Mathematical modelling and simulation on the adsorption of Hydrogen Sulfide (H2S) gas

Abstract

Hydrogen sulfide, H2S, a pollutant in biofuel gas, i.e., biohydrogen and biomethane, is produced at concentrations ranging from 100 ppm to 10,000 ppm and is recommended to be removed at the early stage of gas purification because it is known as a problematic compound. In this study, adsorption technologies show a promising technique to remove H2S from biofuel gas, which mainly depends on the operating parameters and adsorbent ability. In this study, the development of the models is important to investigate the fundamentals of H2S adsorption mechanism. The fitted mathematics model was performed by considering several assumptions made for fixed-bed adsorption, leading to the determination of the breakthrough curve by solving a set of partial differential equations (PDEs). The operating parameters were as follows: varied inlet concentration at 1000 ppm to 10,000 ppm, flow rate at 0.2 L/min to 0.6 L/min, length bed used at 10 cm to 30 cm, and pressure at 1.5 atm to 5 atm. The adsorption performance was also studied by using commercial activated carbon such as palm kernel shell (PKS-AC), coconut shell activated carbon (coconut shell-AC), and zeolite ZSM-5. To support the effectiveness of the mathematical models, the adsorption test was performed by loading the adsorbent into the fixed-bed adsorption column at an overall diameter of 6 cm and height of 30 cm. The system operated under room temperature, H2S inlet concentration of 1000 ppm, and varying flow rate as in the modelling for PKS-AC. As a result, in the modelling study, the inlet concentration effect was highest in adsorption capacity, breakthrough time, and exhaustion time. However, the increase of flow rate and length bed used only affected the breakthrough and exhaustion times but not adsorption capacity. The total pressure used did not affect adsorption performance. Coconut shell-AC shows longer exhaustion time compared with other adsorbents due to the less frequent changes of adsorbent. In the experimental study, the 1000 ppm inlet concentration shows the highest flow rate effect on the adsorption performance, which, at 0.2 L/min, took almost 23 h to achieve 30 ppm compared with 0.6 L/min, which only took 13 min to exhaust the same outlet concentration. Hence, the adsorption system with the right choice of operational parameters, adsorbent, and fitted mathematical models can optimize the adsorption efficiency, adsorption capacity, breakthrough time, and exhaustion time.