Integration of Membrane Processes for Decolourization of Starch Hydrolysates

Abstract

The decolourization during the production of starch hydrolysates involves removing impurities to obtain a brilliant, light-coloured, transparent syrup. However, conventional processes in the industry result in low yield and quality, wasting energy and high-value chemicals. Therefore, starch hydrolysate production requires new separation techniques, such as membrane separation technology, which have overcome traditional methods in different applications. This technology used for product decolourization can reduce chemicals and benefit the subsequent evaporation and crystallization processes, increasing product recovery. Nevertheless, a single membrane step is sometimes impractical in achieving high colour removal, desalination, and sugar permeation due to their limited selectivity in complex solutions and low permeate flux. Consequently, integrating different membrane processes is necessary to improve separation selectivity and decolourization while ensuring high operational flux. In this study, three commercially available membranes (70 kDa, 5 kDa and 150-300 Da) were selected to investigate the colour removal, sugar permeation and conductivity change from a diluted glucose syrup obtained from saccharified starch hydrolysates. The experiments were conducted with a lab-scale crossflow membrane module and constant temperature (60°C). Depending on the maximum capacity of each membrane unit, different operating conditions were considered (feed concentration and transmembrane pressure). The most colour removed was achieved with the 5 kDa membrane with 36 %, followed by the 70 kDa membrane with 27.5 %. Besides, a considerable portion of salts can be removed during NF or 150-300 Da membrane, with an approximated 56 % conductivity change. This study proposed an integrated membrane system and using a theoretical balance was found that the colour of starch hydrolysates could be reduced to 53.6 % using three different steps of membrane filtration. These results will be helpful in the future as a starting point to evaluate in more detail the integration of varying membrane separation techniques and possible process scale-up. The new integrated system is expected to improve the separation of non-sugar compounds and operating conditions during starch hydrolysates' decolourization.