Membrane glucose demudding by a decanter-membrane synergy process: A development update

Rotary vacuum filters (RVFs) with adiatomaceous earth (kieselguhr) coatings as filter aid are the most established technology for the removal of the so-called mud fraction after liquefaction and saccharification in the production of starch-based sweeteners. The RVFs is an open process which is further associated with the use of filters resulting in an increasing disposal challenge. Based on this there is a demand from the industry for alternative demudding solutions.
Since about 2005 Alfa Laval is working on development and introduction of a new concept for demudding – a synergy process consisting of a decanter and a membrane unit. The initial large scale pilot tests were carried out in 2008 focusing on low DE wheat-based sweetener - DE45 and maltose. These tests proved that the basic principles of the concept were working and were in line with previous experience on starch-based sweetener demudding using decanters and membranes independently. The decanter before the ultrafiltration unit removed over 95% of the mud fraction and the subsequent ultrafiltration unit polished the sweeteners to a quality higher than achieved by existing RVFs with regard to turbidity and colour removal. Hence, this concept was found to be not only suitable to replace the RVFs but also to have the potential to lower downstream processing costs. Based on these tests and previous experience two full-scale demudding systems were installed for corn-based sweetener in 2011. The first system operates on low DE sweetener - DE40 – 45 and maltose - and the second system works on higher DE sweetener - DE95. Both systems operate 24h/7days per week. In order to achieve this the membrane systems are operating with sequential cleaning – one of the five loops of the membrane plant is in cleaning/maintenance mode, while the other four loops are in production mode. The membranes installed in the plant are dedicated ultrafiltration membranes for demudding with a high hydrophilicity. Compared to conventional membranes used for demudding, this particular membrane has a relatively low MW cut-off which provides a high removal of turbidity and colour without significant impact on the Brix in polished permeate stream compared to the original feed stream plus a resistance against retrograded starch. Further, in order to improve increase plant capacity the module design was optimised to the requirements of the application. Most recently Alfa Laval optimised the performance of the synergy process for DE96 wheat-based sweeteners on large pilot-scale.
Overall, Alfa Laval has developed over the years a comprehensive knowledge base covering wheat- and corn-based sweeteners from low DEs (40+) to high DEs (95/96). Current development work is focusing on the optimisation of the performance parameters and the extrapolation of the achieved to other starch sources.