Separation of glucose, fructose, oligosaccharides and dextran using zeolites / Separação de glicose, frutose, oligossacarideos e dextranas utilizando zeolitas

AUTOR(ES)
DATA DE PUBLICAÇÃO

2003

RESUMO

Dextransucrase from Leuconostoc mesenteroides synthesizes dextran from sucrose in the absence of aceptors, and oligosaccharides with maltose or other sugars as aceptors. Fructose is also produced as a by-product. Among several producer strains Leuconostoc mesenteroides NRRL B-512F is the most studied. The commercial value of these products increases with the purity. Therefore, it is interesting to recover and purifY the products, using chromatographic techniques of separation. Zeolites, crystalline aluminosilicates with elements of the groups IA and lIA, can be used as adsorbents. No modified zeolite (sodium form), Baylith WE-894, was characterized, and its composition, superficial area, pore size distribution and density were determined. Modified zeolite by ion exchanging with different introduced cations (Ba2+, Ca2+, Sr+ and K) was obtained and its equilibrium data for pure fructose and glucose adsorption in finite bath were evaluated. The influence of introduced cation on the adsorption capacity and selectivity in the fructose adsorption, as well as the description of the adsorption equilibrium through adequate isotherm models were studied. The best results were obtained with the zeolite changed with barium ions, whose data fitted well a linear model. This zeolite presented high fructose adsorption capacity (K = 0.82), higher than ion exchange resins according to the literature, and low glucose adsorption capacity (K = 0.12). The adsorption in fixed bed column was studied, using both frontal analysis and pulse response techniques, with glucose-fructose mixtures. Modified zeólita was shown to be more efficient compared to the no-modified zeolite (sodium form), in terms of breakthrough time and separation efficiency. The porosity of the zeolite bed was measured and the properties of the modified zeolite, includiqg composition and particle size distribution, were determined. The separation of synthetic mixtures (glucose-fructose and dextran-fructose) in fixed bed column was evaluated. The influence of parameters such as temperature, components concentration, injected volume to column volume (Vp/Vc) ratio, superficial velocity and molecular weight in the separation efficiency was studied. The temperature has shown to be the most significant parameter in the glucose-fructose separation. An increase on it leads to the improvement of the separation efficiency. In the separation of dextran and fructose, the effect of temperature and injected volume has shown to be significant, whereas the molecular weight of the dextran was considered an important factor in the processo The best results in the separation of glucose and fructose were obtained at 40 °C, 20 g/L of each component, superficial velocity of 0.127 cm/min (flow rate of 0.1 mL/min) and Vp/Vc of 0.1, with a separation efficiency of 1.94. In the dextran-fructose separation the best results were obtained in the same previous conditions and with a dextran molecular weight of9300, with a separation efficiency of2.72. In both cases, the separation efficiencies were better than the ones with ion exchange resins. Also, the separation of the products of dextransucrase action on sucrose, in the absence and presence of aceptors (glucose and maltose), was studied, leading to interesting results. The molecular weight and product concentration are important factors to be considered. The equilibrium, kinetic and transport parameters of fructose, glucose and dextran 9300 in fixed bed column at 40°C were determined. The partition, effective diffusivity and axial dispersion coefficients were estimated and shown to be satisfactory. The values for the partition coefficients were 0.71 for frutose, 0.31 for glucose, with selectivity of 2.33, and 0.13 for dextran 9300, with selectivity of 5.46. The axial dispersion coefficient was dependent on the intersticial velocity. The values for effective diffusivity were 1.02.10-6 cm2/min for fructose, 5.59.10-7 cm2/min for glucose e 7.79.10-8 cm2/min for dextran 9300

ASSUNTO(S)

frutose oligossacarideos glicose

ACESSO AO ARTIGO

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