Optimization of the Sodium Hydroxide–Assisted Hydrogen Sulfide Selective Removal from Natural Gas

Scrubbing of hydrocarbon-based gases such as natural gas or biogas is essential prior to its use. These gas mixtures when contaminated with hydrogen sulfide cause safety, environmental, and corrosion problems in pipelines. There are several methods of reducing the content of hydrogen sulfide in sour gases, but few of these are selective as well. Selectivity is important to avoid unnecessary chemical usage. Chemisorption in sodium hydroxide solution by applying a special spray technique appears to be an efficient and selective method for hydrogen sulfide removal. This study aims to determine the characteristic of system and thereby facilitating the design of gas-cleaning parameters. The studied parameters include the contact time, concentration of sodium hydroxide, absorbent volumetric flow rate, and gas composition. Model gas mixtures of hydrogen sulfide, carbon dioxide, and nitrogen were used for experiments. To define the optimal experiment setup, the Box-Behnken design (BBD) method was applied. Based on the method, the number and the condition of necessary absorption experiments were constructed. To rank the operating parameters of the absorption process from the point of view of which effect is more significant on the scrubbing performance, statistical analysis of variance (ANOVA) was done. The analysis shows contact time and concentration of sodium hydroxide as the two most influential factors in the absorption process. Carbon dioxide content of sour gas as influencing factor was examined for efficiency and order of priority parameters of process. An extended model has been created to support the optimization of operating conditions in the investigated removal system.