Pyrolyzed Rice Husk–Mg/Al LDH for Efficient MDEA Chloride Removal

This research introduces a new adsorbent designed for cost efficiency and environmental sustainability to eliminate chloride ions from methyldiethanolamine solutions, a critical process for enhancing the sustainability and operational efficiency of natural gas sweetening. The adsorbent was produced by co-pyrolyzing rice husk. and a magnesium–aluminum layered double hydroxide at temperatures ranging from 400 to 700 °C. A factorial design of experiments was applied to investigate how various factors—including the initial chloride concentration, solution temperature, pyrolysis temperature, and the magnesium-to-aluminum molar ratio—influence adsorption performance. ANOVA results revealed that all variables significantly influenced the adsorption capacity. Statistical comparisons showed optimal chloride adsorption at a pyrolysis temperature of 500°C and an Mg/Al ratio of 3. Adsorption kinetics conformed to a pseudo-second-order model, with equilibrium data aligning with the Freundlich isotherm, indicating multilayer adsorption. Under optimal conditions, the peak adsorption capacity was attained at 105 mg/g. Surface analyses indicated that the material exhibited a surface area of 891.4 m²/g, a mesoporous framework with a mean pore diameter of 3.18 nm, and surface functional groups, including hydroxyl and silicate moieties. Spectroscopic and microscopic techniques confirmed the presence of these features. Additionally, XRD patterns indicated the formation of a hydrotalcite-like structure, alongside magnesium oxide and spinel phases, which likely contributed to the enhanced chloride uptake by facilitating ion exchange and interlayer trapping. These results indicate that the rice husk–based composite is a highly efficient and eco-friendly adsorbent for chloride removal in natural gas processing.