A porous activated carbon (AC) was synthesized from cotton black liquor, and the synthesis process was optimized using response surface method (RSM). The AC prepared under the optimal condition was applied to the direct H2S catalytic oxidation. Complete parametrical computational fluid-dynamic (CFD) model, coupling stoichiometric reaction with variation of porosity as the user-defined scalars (UDS), was developed to simulate the removal process. Various experiments, including breakthrough, pressure drops, and H2S conversion at different experimental conditions, were carried out. The CFD model was validated by results from the experiments, as the experiment results were found to adequately match model predictions. Hence, the model developed in this study can be a useful tool for studying the fluid dynamics of H2S oxidation by AC catalyst at investigated experimental conditions. Graphical abstract A porous carbon was synthesized from cotton black liquor. The carbon produced at the optimal condition was used for H2S oxidation at 423K at different experimental conditions. The H2S oxidation was modeled by a novel CFD approach by coupling the stoichiometric reaction with variation of porosity as the user-defined scalars (UDS). The established model can be a useful tool for studying the fluid dynamics of H2S oxidation by AC catalyst at experimental conditions in this work. (C) 2019 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.