Investigation of Hexamethylenetetramine Adsorption Isotherms on Clay Particles and Investigation of Adsorption Thermodynamics and Mechanism

ABSTRACT This study investigated the adsorption capacity and thermodynamics of hexamethylenetetramine (HMTA) on kaolinite particles. Considering the importance of HMTA in gel injection and clay stabilizing, investigating the adsorption process of these compounds on clay can provide effective solutions for the exact modeling of various processes. First, X‐ray diffraction (XRD) analysis was performed on kaolinite samples, which showed that the particles used have a purity of 97%. These results indicate the appropriate crystal structure of kaolinite particles and their high purity. Behavioral adsorption of solutions with various concentrations of HMTA on kaolinite particles was measured through a UV device, monitoring its concentration in the aqueous solution. The results showed that HMTA tends to be adsorbed by kaolinite particles, and the adsorption capacity reached 112 mg/g in this process. Furthermore, the Langmuir adsorption isotherm model was the most appropriate model for predicting HMTA adsorption behavior compared to other models. Repeating this experiment at higher temperatures and constructing thermodynamic models illustrated that the enthalpy of this process is 9534 J/mole, indicating the endothermic nature of this adsorption. The change in Gibbs free energy (∆G) was minus at every temperature, showing that the adsorption of HMTA on kaolinite particles is spontaneous. 100,000 ppm HMTA solution was injected into various kaolinite sandpacks at different temperatures, confirming the endothermic reaction. Analyzing results disclosed that adsorption capacity in core flooding experiments is much lower than in batch experiments because of the complication of the porous media and the presence of inaccessible sites of particles constructing the porous media.