Transesterification of propylene glycol methyl ether in chromatographic reactors using anion exchange resin as a catalyst.

Reactive chromatography using an anion exchange resin is proposed for a transesterification reaction of propylene glycol methyl ether (DOWANOL™ PM) with ethyl acetate to produce propylene glycol methyl ether acetate (DOWANOL™ PMA). This reaction is studied in batch and chromatographic reactors catalyzed by an anion exchange resin. Several anion exchange resins are tested and compared based on the performance of resin as an adsorbent and a catalyst. A chromatographic column is packed with a selected catalyst, AMBERLITE™ IRA904, and both reaction and chromatographic elution are studied at different temperatures and feed concentrations. The resulting chromatograms are fitted to a mathematical model to obtain adsorption equilibrium and reaction kinetic parameters by the inverse method. Compared to esterification investigated in a previous study, transesterification has advantages such as a higher conversion at lower temperature and easy removal of the byproduct which may lead to higher productivity. Deactivation of anion exchange resins is observed and potential solutions are suggested.

Evaluation of tertiary pyridine resin for the separation of lanthanides by simulated moving-bed chromatography.

Lanthanide separation by simulated moving-bed chromatography was studied as a model system for separating lanthanide fission products and minor actinides from used nuclear fuels. The simulated moving-bed system was modeled for a tertiary pyridine anion-exchange resin supported on silica particles as the stationary phase and a mixture of methanol and 1 M nitric acid as the mobile phase. Pulse injection tests using a single packed column were used to obtain chromatographic parameters for mathematical modeling of the simulated moving-bed system. Higher concentrations of methanol improved the separation, but the chromatograms showed evidence of nonlinearity of the isotherms. The mathematical model of the simulated moving-bed process predicted a production rate of purified samarium and neodymium at 118 g solute/L resin/day and a purity of 99.5%. The optimal methanol ratio for the production rate for various product purities was determined from the model. The excellent separation of Nd and Sm suggests that the simulated moving-bed system could be applied to the separation of minor actinides such as americium and curium.

Optimization of reactive simulated moving bed systems with modulation of feed concentration for production of glycol ether ester.

In this article, we extend the simulated moving bed reactor (SMBR) mode of operation to the production of propylene glycol methyl ether acetate (DOWANOL™ PMA glycol ether) through the esterification of 1-methoxy-2-propanol (DOWANOL™ PM glycol ether) and acetic acid using AMBERLYST™ 15 as a catalyst and adsorbent. In addition, for the first time, we integrate the concept of modulation of the feed concentration (ModiCon) to SMBR operation. The performance of the conventional (constant feed) and ModiCon operation modes of SMBR are analyzed and compared. The SMBR processes are designed using a model based on a multi-objective optimization approach, where a transport dispersive model with a linear driving force for the adsorption rate has been used for modeling the SMBR system. The adsorption equilibrium and kinetics parameters are estimated from the batch and single column injection experiments by the inverse method. The multiple objectives are to maximize the production rate of DOWANOL™ PMA glycol ether, maximize the conversion of the esterification reaction and minimize the consumption of DOWANOL™ PM glycol ether which also acts as the desorbent in the chromatographic separation. It is shown that ModiCon achieves a higher productivity by 12-36% over the conventional operation with higher product purity and recovery.

Systematic optimization and experimental validation of ternary simulated moving bed chromatography systems.

Over the past several decades, many modifications have been proposed in SMB chromatography in order to effectively separate a binary mixture. However, the separation of a multi-component mixture using SMB is still one of the major challenges. Recently, a computational study was performed which compared various existing isocratic ternary separation operating schemes (including the JO process) in terms of the maximum throughput attained, and Generalized Full Cycle strategy was proposed based on a systematic design, which was found to have significant improvement over existing strategies [Agrawal and Kawajiri (2012)]. Nevertheless, the operating strategies were not experimentally validated. In this study, we validate both JO and Generalized Full Cycle SMB systems experimentally. A simultaneous optimization and model correction scheme has been implemented to arrive at the optimal operating condition which satisfies the optimal productivity as well as the desired purity and recovery of products experimentally.

Evaluation of the potential of nonlinear gradients for separating a ternary mixture.

The potential of applying nonlinear gradients in preparative chromatography is evaluated theoretically and experimentally. The second eluting component of a ternary model mixture is considered as the target component. Systematic gradient resolution experiments were conducted for this mixture using reversed phase chromatography. In preliminary experimental investigations the effect of the mobile phase composition on the specific distribution equilibria was quantified. Concave and convex solvent strength gradients were analysed and compared with conventional linear gradients. Main result of the study is the fact that significant improvement in productivity can be achieved if the gradient shapes are designed carefully.

Theoretical study of preparative chromatography using closed-loop recycling with an initial gradient.

Complementing classical isocratic elution, several more sophisticated operating modes have been proposed and are applied in preparative chromatography in order to improve performance. One such approach is gradient elution, where the solvent strength is altered by varying the fraction of a modifier added to the mobile phase to enhance selectivity and to achieve faster elution. Another useful technique is closed-loop recycling, allowing better peak resolution and increased yields. This study focuses on a modified new scheme which incorporates the advantages of both gradient elution and closed-loop recycling for the separation of a ternary mixture where the intermediately eluting component is the target. A parametric study was carried out using typical adsorption isotherm parameters to elucidate the effects of varying loading factors and parameters specific to the two basic operational modes on production rates and yields. A comparison was also made between the proposed scheme and conventional techniques. It was found that the studied scheme could exploit increased column loadings and offers significantly higher production rates.

Preparative separation of multi-component mixtures using stationary phase gradients.

Solvent gradients have been widely applied in analytical and preparative chromatography to enhance selectivity and improve productivity. Recently, an alternative concept using solid phase gradients was introduced in analytical chromatography [Nyiredy, Szucs, Szepesy, Chromatographia 63 (2006) 3; Nyiredy, Szucs, Szepesy, J. Chromatogr. A 1157 (2007) 122]. This concept is based on connecting columns filled with different stationary phases in series, applying a constant mobile phase composition. With the availability of column connecting devices with low dead volumes [K. Bischoff, S. Nyiredy, Z. Szücs, Elements for separating substances by distributing between a stationary and a mobile phase, and method for the production of a separating device. WO/2006/125564; PCT/EP2006/004744, 2006.], the concept can be easily implemented. The application of sequentially connected columns with different properties introduces new degrees of freedom like the type, number, relative lengths and positions of individual segments. In this study, an attempt is made to analyze if such stationary phase gradients could be exploited favorably in preparative chromatography for separating multi-component mixtures. A theoretical study is carried out for a connection of two different types of column segments based on numerical solutions of the equilibrium dispersive model assuming specific adsorption isotherm parameters for each segment. The influence of relative segment lengths and the order of the arrangement are evaluated with respect to the performance of separating intermediately eluting components from multi-component mixtures.