Recovery of xanthan from fermentation broths by precipitation in a stirred tank

Precipitation of xanthan gum with isopropanol from dehydrated-reconstituted fermentation broths was carried out in a stirred tank (0-014 m³) with four impeller types (D/T ≈ 0·5). The effects of xanthan concentration, stirring speed and broth feeding rate on precipitation yields and power drawn, were evaluated. The xanthan concentration in the broth was the most important parameter in determining precipitation yields and power consumption. When working with a 30 kg m^-3 broth, yields, higher than 85% were obtained with the marine propeller and with minimal energy expenditure. Similar yields were reached with the Lightnin A-310 and Rushton turbines but at higher energy inputs. Curved blade impeller (marine propeller and Lightnin A-310) showed decreased yields as the impeller speed was higher. Flat blade impellers (Rushton and 45° pitched blade turbines) showed an opposite although less pronounced trend.