Development of isocratic and solvent-gradient simulated moving bed processes for optimal separation of the following three systems: (1) sugar-acid mixture, (2) amino acid mixture, and (3) organic acid mixture

Abstract

In this study, a simulated moving bed process for continuous separation and purification of highly valuable bioproducts has been developed in a systematic way. First, a solvent-gradient simulated moving bed (SG-SMB) process for separation of two useful amino acids, phenylalanine and tryptophan, has been studied, which revealed that the SG-SMB outperformed the corresponding isocratic SMB for the same separation task. However, most of the previous studies on the SG-SMB for separation of the two amino acids have been limited to process simulation and optimization, including some batch-chromatography tests. The development of a SG-SMB process was attempted in this study for the first time. This task was started by assembling the experimental unit of the SG-SMB process. Its operating conditions were determined from the SG-SMB optimization tool based on up-to-date genetic algorithm, in which the mass-transfer parameters as well as the adsorption isotherm parameters of the feed components (two amino acids) were entered as the mathematical models expressed as a function of liquid-phase composition (i.e., modifier concentration in the liquid phase). Based on the determined operating conditions, the relevant SG-SMB experiment was conducted until a cyclic steady-state was reached. The assay of all the resultant product samples verified that the SG-SMB separation of interest was performed as successfully as designed. The experimental data were also found to agree closely with the model predictions. Next, one of the important steps in the application of biomass to producing sugars, which can be converted into bio-ethanol and other valuable chemicals by fermentation, is to hydrolyze the biomass components by sulfuric acid. It was reported that such a hydrolysis entailed the generation of acetic acid, which has been recognized as a key impurity to be surely removed from the biomass hydrolyzate for ensuring high fermentability of the hydrolyzed sugars. Regarding such a removal task, there has been a previous application of a SMB chromatographic process based on the Dowex99 adsorbent, whose performance, however, was limited by low selectivity between acetic acid and sugars. To overcome such a limitation, another adsorbent alternative to Dowex99 was searched in this study. It was found that Amberchrom-CG161C allowed higher selectivity between acetic acid and sugars than Dowex99. In addition, the development of such an Amberchrom-CG161C SMB process, including its optimal design, was attempted. This task was started by assembling the experimental unit of the SMB process with three zones. Its operating conditions were then optimized by using genetic algorithm. Under the optimized operating conditions, the relevant three-zone SMB experiment was conducted. The assay of all the product samples verified that the SMB separation of interest was performed successfully as designed. Experimental data were also found to agree closely with the model predictions. A partial-discard strategy was applied to maintain the sugar product concentration as high as possible. To investigate the relative superiority of Amberchrom-CG161C over Dowex99 as the adsorbent of an SMB process for removing acetic acid from the biomass hydrolyzate, the two SMB processes based on Amberchrom-CG161C and Dowex99 were optimized using the SMB optimization tool based on standing wave design (SWD) method. From optimization results, the Amberchrom-CG161C SMB outperform was revealed to the Dowex99 SMB by a wide margin. Finally, the issue of separating succinic acid and lactic acid in a continuous mode has been a major concern in the biotechnological process for production of succinic acid. In regard to this issue, it has recently been revealed that the Amberchrom-CG300C resin could function well as the adsorbent of a SMB process for continuous separation of succinic acid and lactic acid. However, a previous research on the Amberchrom-CG300C SMB for such separation has been limited to only a theoretical work. The experimental validation of such an Amberchrom-CG300C SMB process, including its optimal design, was attempted in this study using a self-assembled SMB unit with three zones. First, the intrinsic parameters of the two organic acids were estimated at 40 C and then used to optimize the operating conditions of the three-zone SMB unit. Based on the optimized conditions, the relevant SMB experiment was conducted at 40 C and all the resultant samples from the product ports and column outlets were assayed, which verified that the continuous separation of succinic acid and lactic acid was successfully. The experimental data for the product concentration profiles and the internal concentration profiles were also in reasonable agreement with the model predictions. The developed design methods and SMB processes for optimal separation of sugar-acid, amino-acid and organic acid mixtures in this thesis are expected to contribute to marked improvement in the productivity of other continuous processes for bioproducts separation.