Kinetic modeling of liquid phase catalytic alkylation of guaiacol with cyclohexene

Abstract

The kinetics of the liquid-phase alkylation of guaiacol (G) with cyclohexene (CH) over Amberlyst 36 resin was studied using Langmuir–Hinshelwood–Hougen–Watson (LHHW) heterogeneous kinetic models. Catalytic tests were performed in a batch reactor, in solvent-less conditions, at 363 K, 1 bar, 600 RPM, using a G:CH molar ratio equal to 5 with a total volume of 30 ml and 1.5 g of solid catalyst. The alkylation of G with CH formed cyclohexyl-2-methoxyphenylether (CHMPE) by O-alkylation and cyclohexyl-2-methoxyphenol isomers (CHMP) by C-alkylation. Furthermore, CHMPE isomerizated into CHMP. A negligible amount of cyclohexylcyclohexene (CHC) was observed by dimerization of CH. Among these products, CHMP are important intermediaries for the production of resins, antioxidants, drugs, polymeric additives, agrochemicals, etc. Several LHHW kinetic models, varying the rate limiting step of reactions, were proposed in order to elucidate a reaction mechanism. The fitting of experimental data was performed consecutively by: (1) a stochastic optimization method and (2) by nonlinear regression, using the Levenberg–Marquardt algorithm, reducing the probability of reaching local minima in the objective function. The selected kinetic model considers that: (a) the rate limiting step for both the O-alkylation and C-alkylation is the surface chemical reaction between adsorbed G and adsorbed CH; (b) the adsorption of the O-alkylated products is the rate limiting step for the isomerization into C-alkylated products. Finally, this kinetic model that fits experimental data appreciably well from both physical and statistical point of view, suggests that CH adsorbs stronger than G over Amberlyst 36 catalyst.