Application of nano-and ultrafiltration in sugar industry

Abstract

The separation of non-sucrose compounds in the technological process of sugar production occurs during the process of purification by means of sedimentation and coagulation. Despite all attempts, a great part of the non-sucrose compound remains in solutions from which sucrose is directly crystallized, and makes itself part of the sugar crystals during their formation. One of the current issues to be resolved in the sugar industry is the separation of undesired compounds. Membrane separation processes offer a new range of possibilities that might be technologically fruitful and economically justified, as well as highly desired from the point of view of environmental protection. This chapter will deal with the implementation of ultra-and nanofiltration in the process. The emphasis is laid on understanding the phenomena of the concentration polarization and the membrane fouling by non-sucrose compounds. In order to reduce the mentioned effects and with the aim of achieving a greater permeate flux in the course of ultrafiltration, the usage of static turbulence promoters is considered too. The book chapter will describe the applied equipment which is suitable for the realization of ultraand nanofiltration, the methods of the examination of permeate, retentate and the intermediate products of sugar processing; it lists the types and characteristics of the used membranes, their purification, and it defines the characteristics of the static mixer which is built into the apparatus. It will present the results related to the removing of undesired molecules from some intermediate products of sugar processing by the use of polymer and ceramic membranes (with different pore sizes ranged from 5-20 nm), with and without the presence of a static mixer, under various working conditions. The process efficiency is quantified through the achieved values of permeate flux and also through its colour, purity, turbidity, sugar content, dry substance content, while the working factors were: fluid flow rate (0-400 L/h), temperature (20-80 oC), trans-membrane pressure (0-10 bar), process duration and viscosity. As treated raw sugar syrup (ca. 60% dry substance) belongs to viscous fluids, static mixer was expected to improve the permeate flux as well as the separation process as a whole. Colour decrease of about 50% in permeate can be achieved using ceramic membrane of 5 nm pore sizes at optimal working conditions at flow rate between 100-200 L h-1 and pressure above 6 bar. © 2010 Nova Science Publishers, Inc.