NAMS 2002 Workshop - ICOM 2008

Nanofiltration and Reverse Osmosis III - Applications – 6
Friday July 18, 12:15 PM-12:45 PM, Maui
Purification of Glucose/Sodium Lactate Solutions By Nanofiltration:
Selectivity Improvement By the Addition of a Mineral Salt
C. Umpuch, Suranaree University of Technology, Nakhon Ratchasima, Thailand
S. Galier, Université de Toulouse, Toulouse, France
S. Kanchanatawee, Suranaree University of Technology, Nakhon Ratchasima, Thailand
H. Roux-de Balmann (Speaker), Université de Toulouse, Toulouse, France -
roux@chimie.ups-tlse.fr
Nanofiltration is expected to be adapted to the separation of neutral solutes, like
sugars, from charged ones, like organic acid salts depending on their molecular
weight. This is the case of glucose and sodium lactate for instance. Previous
work was thus devoted to the investigation of NF to purify glucose/sodium lactate
solutions. Indeed, it was considered that such solutions are representative of
those that can be encountered in the frame of the purification of lactic acid
fermentation broths, in which glucose would represent the residual sugar
impurities remaining after the fermentation stage.
The experimental study was carried out with an NF Desal DK membrane and
solutions of increasing complexity, i.e. single solutions of glucose or sodium
lactate on one hand and mixed ones, containing both solutes, on the other hand.
A good selectivity was expected from single solute solutions, since the retention
of glucose and sodium lactate were found to be about 80 and 20% respectively.
On the contrary, it was observed that the retention of glucose in mixed solution
was significantly decreased from 80 to 20%. As a result, the NF selectivity was
found to be very poor. Such an effect of the presence of charged species on the
retention of neutral ones was reported in different situations, with organic as well
as inorganic membranes and with different kind of solutes, like organic acid salts
and PEG for instance.
In this work, we try to investigate to what extend the ionic composition can
influence the selectivity of the glucose/sodium lactate separation by NF. Indeed,
thanks to the former results, one can expect that the addition of a third charged
species, like a mineral salt, affects the sugar and organic acid salt in different
manner. Then, a separation could be achieved for appropriate operating
conditions. An experimental study is thus reported in which the influence of the
fluid composition, and specially the mineral composition, on the selectivity of the
glucose/sodium lactate separation is investigated. This is done by adding
different mineral salts, like NaCl (0.1-1M) and Na2SO4 (0.1- 0.5M). It shows that,
in the lower flux region, the selectivity can be significantly improved by the
addition of a salt. This improvement depends on the mineral salt type and