Study On Characteristics Of Mixing System In High Viscosity Fermentation Of Microbial Polysaccharides Xanthan Gum

The microbial polysaccharides characterized by high viscosity are new products using modern industrial biotechnology in recent years. They have broad application in the food, oil, medicine and other industries. Although China has become the third largest country producing Xanthan gum, the production of high quality and performance microbial polysaccharides has still basically been monopolized by the well-known foreign enterprises. The main reason is that in high viscosity fermentation technology, there is a gap between China and foreign countries: the mass transfer and mixing efficiency of conventional impeller can not meet the needs of high-viscosity fermentation, gas dispersed is not effective, and the energy consumption is huge. Therefore, there is an urgent need to establish the independent innovation technology and equipment to overcome the key issues happened in the high-viscosity fermentation process.Four impeller combinations of new radial flow type impeller and axial flow type impeller, namely Rushton Turbine, Asymmetric Blade Impeller and A315 have been tested in a laboratory bioreactor. The liquid phase physical-chemical properties have been varied using Xanthan gum solutions in different concentration and water. There are some results which are as followed:First of all, the rheological properties of microbiology polysaccharides Xanthan gum have been studied, and the result showed that it was typical pseudoplastic fluid having good performance of the shear diluted. Meanwhile, the flow-behavior index n, fluid-consistency index k and shear stress, which associated with the apparent viscosity, have been tested to get the microbial polysaccharides apparent viscosity in the mixing system.Secondly, an experimental investigation was performed of four impeller combinations in water and Xanthan gum solution, the characteristics of oxygen transfer, fractional gas hold-up and power dissipation were studied. It has been observed that the impeller combination of MBTD-MA315-MA315 used the lowest power (Np≈1.7) and gave highest values of gas-liquid mass transfer coefficient and fractional gas hold-up, which were 45% and 35% higher than the impeller combination of DT-DT-DT, in the non-Newtonian fluid. Therefore, the impeller combination of BTD-A315-A315 has high effective in the non-Newtonian fluid.The last but not least, reached and analysis four factors which impact the oxygen transfer effect in non-Newtonian fluid and carried on the variance analysis to compare the impact of various factors using volumetric oxygen mass transfer coefficient per volumetric power. Correlations have been developed for the prediction of the mass transfer coefficient for the above media. It offers the gist to magnify the impeller combination.