Gow-Jen Tsai

Enhancement of in situ adsorption on the acetone-butanol fermentation by Clostridium acetobutylicum

Abstract An integrated process of the acetone-butanol batch fermentation coupled with in situ toxic products removal was developed. It was found that the in situ adsorption process using polyvinylpyridine as the adsorbent enhanced the fermentation rates and the reactor productivity by Clostridium acetobutylicum. In a typical traditional acetone-butanol fermentation process, only about 60.0 g/L of glucose could be used in a batch operation mode and thus at maximum only 21 g/L of the total final products concentration could be achieved. In the adsorption-coupled system, an initial glucose concentration of 94.0 g/L was fermented when a weight ratio of the adsorbent to the fermentation broth of 3/10 was used. An overall product concentration of 29.8 g/L and a productivity of 0.92 g/L · h were achieved in the adsorptive batch fermentation system. Compared with the controlled traditional batch acetone-butanol fermentation, the integrated process increased the final product concentration by 54% and the productivity by 130%.

MODELING OF GRADIENT ELUTION IN MULTICOMPONENT NONLINEAR CHROMATOGRAPHY

Gradient elution in nonlinear chromatography is a very powerful tool for the separation of components having a wide range of retentivity. It is not only used for chemical analysis, but also used in preparative- and large-scale chromatography for the separation of many macromolecules, such as proteins. In this work, a general rate model has been presented for the study of gradient elution in nonlinear chromatography. The model considers axial dispersion, external film mass transfer, intraparticle diffusion and kinetic effects. The modulator-eluite relationship used in the model accounts for both electrostatic and hydrophobic interactions. Examples of simulations have been given to demonstrate the efficiency and robustness of a computer code based on a numerical procedure for the general rate model, which uses the finite-element, the orthogonal-collocation and Gears stiff methods. The examples also show the advantage of gradient elution over isocratic elution in multicomponent elutions, and the comparisons among linear, nonlinear and stepwise linear gradients.

Multicomponent adsorption and chromatography with uneven saturation capacities

In chromatographic separations involving elutes with large differences in the molecular size, the adsorption saturation capacities of the elutes may differ because of the differences in the degree of size exclusion. With uneven saturation capacities, isotherm crossovers may occur, which often results in selectivity reversal. In this work, a new multicomponent isotherm has been developed for this kind of system. The isotherm is an extension of the common multicomponent Langmuir isotherm and introduces no or a very limited number of new parumeters for its construction. The isotherm crossover conditions have also been derived. Simulations based on a general rate model using the new isotherm have successfully demonstrated the phenomena of peak reversal and crossover of breakthrough curves.

A theoretical study of multicomponent radial flow chromatography

A theoretical study of radial flow chromatography was carried out based on a general nonlinear multicomponent rate model which considers radial dispersion. external mass transfer, intraparticle diffusion. and nonlinear multicomponent isotherms. Radial dispersion and mass transfer coefficients were treated as variables which are dependent on the radial coordinate of the radial flow column. The model was solved numerically by using the finite element method and the orthogonal collocation method for the discretization of partial differential equations and Gears stiff method for the solution of the resulting ordinary differential equation system. Computer simulations were carried out for various multicomponent chromatographic operations. Dispersion and mass transfer effects were investigated. The question of whether radial dispersion and mass transfer coefficients should be treated as variables was discussed. The difference between inward flow and outward flow in radial flow chromatography and the comparison between conventional axial flow chromatography and radial flow chromatography were studied. Langmuir isotherms were used in this work.

Analysis of chromatography by plate theory

Abstract Recent advances in the plate theory for the analysis of chromatography are reviewed in this article. It can be seen that through a proper definition of height equivalent to a theoretical plate, both plate model and mass-balance model can be closely related. The plate height expressions resulting from various approaches are almost the same in linear chromatography. The emphasis of this article is placed on the extension of plate theory to the configurations of chromatography other than the conventional axial-flow column and to the nonlinear chromatography. The concept of volume equivalent to a theoretical stage has been developed to overcome the problem of design and scale-up of chromatography other than axial-flow configuration. In nonlinear chromatography used for the purification of biomolecules, the retention behavior and the band broadening could be significantly affected by concentration and volume overloads and slow adsorption kinetics. Works on the derivation of thermodynamic and kinetic contributions to plate height owing to nonlinear isotherm and volume overload are reviewed and compared. To conclude this review, future prospects of the application of the plate theory is also presented.

Dynamic response and parameter estimation in a two-phase continuous flow stirred tank reactor

Abstract Based on a three-parameter model, the dynamic response of an isothermal two-phase continuous flow stirred tank reactor with a first-order chemical reaction occurring in uniform spherical catalyst particles was obtained analytically by using the method of Laplace transforms. Three modes of input perturbation are specifically considered in the solution: step change, impulse, and the sudden introduction of catalyst into the reactor. In all cases, it was found that the time domain solution can be divided into three cases by a critical Thiele modulus. This critical Thiele modulus also divides the reactor dynamics into two different responses when the catalyst particles, which are filled with inert liquid initially, are introduced into the reactor at time zero. In terms of the dimensional form, this critical Thiele modulus relates the rate constant with the inlet liquid flow rate and other parameters except for the liquid—solid mass transfer coefficient and intraparticle coefficient. This makes it possible to determine the rate constant directly from the experiments, even though mass transfer resistances are coexistent, by simply manipulating the inlet liquid flow rate.

Multicomponent affinity radial flow chromatography

Abstract Radial flow chromatography can provide high volumetric flow rates with small bed pressures. It is advantageous for use in affinity chromatography in which resolution requirements can be easily achieved because of highly selective biospecific binding. In this work a general multicomponent kinetic rate model has been formulated for the simulation of various aspects of radial flow affinity chromatography. The model accounts for radial dispersion, external mass transfer, intraparticle diffusion, second-order kinetics, and reactions between soluble ligands and the macromolecules in the elution stage of affinity chromatography. The model is solved with an efficient and robust numeric procedure that uses the finite element, the orthogonal collocation, and the Gears stiff methods. Kinetic effects have been studied and compared with mass transfer effects. The three stages of affinity chromatography—frontal adsorption, wash, and elution—have been simulated. The effects of the concentration and the affinity of the soluble ligands used in the elution stage have been discussed.

Ultraviolet difference spectroscopic study on the interactions of cellulase fromTrichoderma reesei with cellodextrins

The formation of cellodextrin-cellobiohydrolase complex was studied by ultraviolet difference spectroscopy. Upon the binding of cellodextrins (G7‐G3), cellobiohydrolase (EC 3.2.1.91) purified fromTrichoderma reesei produced difference spectra having maxima at 289‐293 nm and 283‐286 nm. These spectra are consistent with prior observations reported for lysozyme and amylase. In this case, water soluble cellulose oligomers (i.e., cellodextrins) are shown to interact with tryptophan residue(s) on cellobiohydrolase. The difference spectral maxima observed at acidic or alkaline pH were shifted. This was accompanied by a marked decrease of binding ability of cellobiohydrolase for cellodextrins. The standard free energy change for the association of cellodextrins to the cellobiohydrolase was an order of 4 kcal/gmol. The association constant of enzyme for substrate decreases by 15‐20% as temperature increases from 20 to 48°C. At 25°C, the dissociation constants for the enzyme with respect to cellohexose and cellotriose were estimated to be 1.19 and 1.37 mM, respectively. A decrease in dissociation constants was observed with an increase in the number of glucosyl units from 3 to 6. This suggests that there may be six or more subsites in the active center of cellobiohydrolase.

Characterization of glucoamylase immobilized on celite

Immobilization of glucoamylase (EC 3.2.1.3) on Celite R649 bio-catalyst carrier for hydrolysis of maltose and maltodextrin has been investigated in both packed bed and recirculated batch reactors. The kinetics parameters on the hydrolysis of maltose were estimated from the packed bed reactor. It is found that this immobilized enzyme is as efficient as the soluble enzyme in catalyzing hydrolysis of maltose. However, it is less efficient than the soluble enzyme in hydrolyzing 30% (w/v) maltodextrin, giving a maximum dextrose equivalent (DE) value of 96.0% instead of 98.2%.

Dynamic response of an isothermal three-phase slurry reactor. I, The PM-PM-HS/ID model : analytical solutions for continuous and semi-batch operations

Abstract Based on the PM-PM-HS/ID model, the dynamic response of an isothermal three-phase catalytic reactor with a first order reaction in uniform spherical catalyst particles was presented analytically. The solution is valid for any mode of input perturbation with non-negative and constant initial conditions, and for continuous and semi-batch operations. Two critical Thiele moduli divide the solution into five cases and the dynamic response depends on the magnitude of the Thiele modulus. For the semi-batch operation with a sudden introduction of catalyst into the reactor, there exists two types of response for the effluent reactants in both gas and liquid phases, and the responses are distinguished by the first critical Thiele modulus. Based on the difference of the responses, a method which is able to determine the rate constant directly from the experiments was also proposed. For the continuous operation, two types of response always exist if the inlet liquid stream is pre-equilibrated with a gas which has the same composition as the inlet gas stream. The criterion to distinguish these two responses was also given. However, if there is no gas reactant dissolved in the inlet liquid stream, it is possible to have only the decay type response as the liquid flow rate is larger than some critical value.