Separation From Inorganic Electrolyte/Sugar Mixtures Solution By Nanofiltration Membrane

Nanofiltration (NF) is a pressure-driven membrane separation technique lying between ultrafiltration (UF) and reverse osmosis (RO), which has typically pore size about1nm. Similar to RO membrane, NF membrane can effectively retention multivalent ions and low molecular organic compounds. In industrial production, the compositions in feed solution are complex, usually containing organic compounds and inorganic salts. There is an increasingly importance to carry out effective separation from low molecular organic and electrolyte salt mixtures in feed. Nanofiltration separation research is still inadequate for low molecular organic (sugar, amino acid, dye, PEG and so on) and salt mixtures solution, relative literatures mainly focus on sugar and salt mixtures. The NF experiments mainly focus on glucose and NaCl mixtures, and there is a relatively lean literature on the separation of mixtures containing other sugar and salt. According to the situations, it is essential to expand the solute types and different conditions to run tests.In this work, the separation experiments by using two NF membranes (DK1812and NF90) were carried out for single solute solutions of electrolyte salts (NaCl, MgCl2, Na2SO4and MgSO4) and sugars (glucose, fructose, xylose and lactose) and mixtures solution of salt and sugar. The aim of this study was to evaluate the mutual effects between sugar and salt in mixed-solute solutions. Solute concentration, operating pressure and different compositions on the separation performance (observed rejection and flux) were investigated for single and mixtures solution, respectively. The main findings may be summarized as follows:1. The first series of experiments were done with single solutions of each solute as function of applied pressure. The rejections to sulfates were higher than those to hydrochlorides for DK1812and NF90, and NF90performed better (especially for NaCl, rejection>90%). The rejection to lactose was obviously higher than those to monosaccharide for DK1812, and NF90were almost all reject sugars. The flux of single solute solution all increased linearly with the increasing pressure.2. A second series of experiments, carried out with single salt and sugar mixtures by DK1812. The increase of sugar rejections in the presence of salts were attributed to diffusion effect, which had not been widely reported in previous literatures and was considered a novel observation. The glucose rejection curves were in accordance with fructose, it is because that glucose and fructose is a pair of isomer. The effects of the sugar addition on hydrochlorides and sulfates rejections were found to be quite different. The rejections to hydrochlorides were diminished when sugar was present, but those to sulfates were unaffected. The flux was less in mixed-solute solutions than in single-solute solutions.3. Further experiments at different glucose concentrations (2000to16000mg/L) and NaCl (2000mg/L) were also performed by DK1812. The rejection of glucose all reduced at the variation of glucose concentration, and the decrease slowed down gradually at the same time. The rejection of NaCl decreased with the increasing glucose concentration.