RESUMO
Kinetics and thermodynamics of esterification by a cation-exchange resin in an intensified fixed-bed reactor was studied systematically. The resin type, catalyst loading, volume flow rate, initial molar ratio, temperature, and catalyst reusability were studied and optimized. The nonideality of the reaction system was corrected by the UNIFAC group contribution method. The Δr H 0, Δr S 0, and Δr G 0 of the reaction were acquired by two methods. The pseudo-homogeneous (PH) model and the Langmuir-Hinshelwood-Hougen-Watson (LHHW) model were adopted to simulate the kinetic process. The result indicated that the LHHW model was better suited to simulate the kinetic process than the PH model.
RESUMO
Based on the inhibition effect of methimazole (MMI) on the reaction of luminol-H(2)O(2) catalyzed by gold nanoparticles, a novel chemiluminescence (CL) method was developed for the determination of MMI. Under the optimum conditions, the relative CL intensity was linearly related to MMI concentration in the range from 5.0 × 10(-8) to 5.0 × 10(-5) mol L(-1). The detection limit was 1.6 × 10(-8) mol L(-1) (S/N=3), and the RSD for 6.0 × 10(-6) mol L(-1) MMI was 4.83 (n=11). This method has high sensitivity, wide linear range, inexpensive instrumentation and has been applied to detect MMI in pharmaceutical tablets and pig serum samples. Furthermore, a possible reaction mechanism is discussed.