Optimization of the operating conditions for the removal of alcoholic insoluble compounds contained in sugar beet vinasse

The purification of sugar beet distillery vinasse, a by-product of bioethanol manufacturing, was studied with a view to removing the insoluble compounds by precipitation in ethanol. Two influential operating parameters, i.e. temperature and ethanol:vinasse (w/w) ratio of the precipitation, were optimized by a simplex method. An optimum was reached for a weight ratio of 4.6 at 21 °C, that allowed 52.4% of the vinasse dry matter to be separated. Additional experiments were then carried out to establish a second-order polynomial model from a Doehlert design and measure the weight of solid removed as a function of temperature and ethanol:vinasse (w/w) ratio used. In the experimental domain studied, results showed the very weak positive influence of temperature and the weak negative influence of ethanol:vinasse (w/w) ratio on weight of precipitate obtained. In addition, the statistical model enables to determine the response surface in order to predict the variation in response when the values of variables are modified. Lastly, the sugar beet precipitation was successfully scaled up, enabling a mass balance of the process to be established. Results showed that a large proportion of proteins and pectins were separated during the process.