Maxwell-Stefan modeling of mass transfer effects in reactive chromatography.

摘要

A rigorous dynamic theoretical model was developed and implemented for simultaneous diffusion, reaction, and adsorption inside porous solids for the fixed bed chromatographic reactor (FBCR), true moving bed chromatographic reactor (TMBCR), and simulated moving bed chromatographic reactor (SMBCR). It takes into account multicomponent inter-particle and intra-particle mass-transfer effects using the Maxwell-Stefan approach. In all the simulation results, this model proved to be robust and in all cases predicted very accurately the experimental data for several chromatographic reactor case studies from the recent literature with nonlinear multicomponent adsorption isotherms catalyzed by the acid resin Amberlyst 15. They included the synthesis of diethylacetal from ethanol and acetaldehyde; the production of triacetine, from glycerol and acetic acid; the production of dimethylacetal from methanol and acetaldehyde; the synthesis of ethyl lactate, from ethanol and lactic acid; and the synthesis of methylacetate from methanol and acetic acid.;The model based on the Maxwell-Stefan approach was found to predict the behavior of the FBCR, TMBCR, and SMBCR significantly better than the previous linear driving force (LDF) and Fickian diffusivity approximations. It was also used to compare the predictions of the TMBCR and SMBCR for any given application. It was found that, for some applications, the TMBCR approximation of the SMBCR performance is not justified.;The influence of feed composition, switching time, and reaction separation region on the performance of a SMBCR for diethylacetal synthesis was analyzed by simulation. The best operational point in terms of productivity (24.29 kg of acetal/L of adsorbent-day) and desorbent consumption (5.15 L ethanol/kg acetal) for 97% purity of both raffinate and extract was found to be a switching time of 3.75 min, feed concentration of 80% mol of acetaldehyde, and fluid/solid flow ratios in sections II and III of gammaII = 2.625, gamma III = 3.5, respectively. The numerical solution of all model equations was obtained for transient (in the FBCR, TMBCR, and SMBCR) and steady state (in the TMBCR) using MATLABRTM7.