m-Cresol and p-cresol are widely used in medicine and pesticides as important chemical intermediates. They are generally produced as a mixture in industry and are difficult to separate due to the similarities in both chemical structures and physical properties. The adsorption behaviours of m-cresol and p-cresol on zeolites (NaZSM-5 and HZSM-5) with different Si/Al ratios have been compared by static experiments. Selectivity on NaZSM-5(Si/Al = 80) could be greater than 6.0. Adsorption kinetics and isotherms were investigated in detail. The kinetic data was correlated by PFO, PSO, and ID models, the NRMSE of which were 14.03%, 9.41%, and 21.11%, respectively. In the meanwhile, according to the NRMSE of Langmuir (6.01%), Freundlich (57.80%), D-R (1.1%), and Temkin (0.56%) isotherms, adsorption on NaZSM-5(Si/Al = 80) was mainly a monolayer and chemical adsorption process. It was endothermic for m-cresol and exothermic for p-cresol. The Gibbs free energy, entropy, and enthalpy were calculated accordingly. The adsorption of cresol isomers on NaZSM-5(Si/Al = 80) were both spontaneous, and it was exothermic (ΔH = -37.11kJ/mol) for p-cresol while endothermic (ΔH = 52.30kJ/mol) for m-cresol. Additionally, ΔS were respectively -0.05 and 0.20 kJ·mol-1·K-1for p-cresol and m-cresol, which were both close to zero. The adsorption was mainly driven by enthalpy. The result of breakthrough further demonstrated m-cresol and p-cresol could be separated effectively by NaZSM-5(Si/Al = 80). Additionally, the selectivity increased from 7.53 to 14.72 after four cycles regeneration with 9.95% and 53.96% decreases in the adsorption amounts for m-cresol and p-cresol, respectively. In conclusion, NaZSM-5(Si/Al = 80) could be a feasible adsorbent for the separation of m-cresol and p-cresol.
Keywords: Adsorption; Dynamic breakthrough; Kinetics; Regeneration; Thermodynamics.