Separation of m-cresol and p-cresol by NaZSM-5 with different Si/Al ratios

ABSTRACT

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.

GRAPHICAL ABSTRACT

KEYWORDS:

• Adsorption
• Kinetics
• Thermodynamics
• Dynamic breakthrough
• Regeneration

Acknowledgement

This study did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data accessibility

The data used to support the findings of this paper are accessible from the corresponding author upon request.