Establishment Of A Nanofiltration Rejection Sequence Spectrum Of Neutral Monosaccharides

Monosaccharides are important food materials or medicinal ingredients and have great demand in food and pharmaceutical industries. However, due to the existence of mix monosaccharides or derivatives, it is difficult to obtain high puritied monosaccharides with the process of preparation, extraction and purification of monosaccharides. This research is focused on establishing a nanofiltration rejection sequence spectrum of available monosaccharides by series of nanofiltration experiments of eight commercial available monosaccharides. Researching the law of monosaccharides rejection systematically and obtaining the nanofiltration rejection sequence spectrum of monosaccharides that can supply referenced datum for separation of monosaccharides nanofiltration. Finally, applications and theories of isomers or structural analogs will be enriched in the aspect of nanofiltration.Firstly, the important properties of nanofiltration membrane were measured. The results indicated that the molecular weight cut-offs (MWCO) of DK was 180-200 Da. The pure water permeability (Lp) was 0.2132×10-10m.pa-1.s-1 at 25℃, membrane pore radius (rp) was 0.39 nm, and the effective membrane thickness (Ax/Ak) was 0.9849×0-6m. Based on the AMF images of DK membrane under trans-membrane pressure (TMP), pH, temperature, salt, et al different conditions, the results showed that high pressure, high pH, high temperature and high salt solution had significantly effect on membrane surface depth. However, those conditions almost had no effect on membrane roughness (Ra).Secondly, the rejected characteristics of nanofiltration of eight monosaccharides were studied. In addition, the influences of TMP, pH, temperature, concentration and salt on rejected characteristics of nanofiltration were investigated. The results showed that membrane fluxes would increase linearly with the increase of TMP and the rejection reached the maximum at 11.0 bar. pH did not have significantly effect on fluxes and rejections of monosaccharides. However, temperature and concentration had adverse effect on pH. Salts did not have significantly effect on rejections of monosaccharides whether Na2SO4 or MgSO4 solution were existed or not, but fluxes would be changed obviously. Under the same experimental condition, certain regularity of eight monosaccharides rejections can be presented, i.e, the rank of monosaccharides rejections according to the size of value:fructose (83.3%-93.5%), glucose (81.9%-93.7%), mannose (81.7%-93.2%), galactose (81.3%-92.0%), sorbose (80.0%-90.6%), arabinose (59.9%-81.2%), xylose (54.5%-75.6%), ribose (49.8%-59.2%). The difference of hexose rejections was rather small, about 2%, while pentose was more obvious than that of hexose, above 5%. Besides, temperature would expand the difference of monosaccharides rejections. For hexose, the difference would arrive 4% at 40 ℃.Finally, Hyperchem software was used to stimulate monosaccharides molecules that kept at constant temperature stable statue. The 3D structures parameters of molecules were obtained and then computational molecular sizes (rs) were calculated by a mathematical formula. Differences of rs and Stokes radii or other calcualted ways were compared. The results showed that values of rs were smaller than those of Stoke radius. The rs values of fructose, glucose, mannose, sorbose, galactose, arabinose, xylose and ribose were 0.3235, 0.3156,0.3113,0.3012,0.2804,0.2748,0.2677 and 0.2599 nm respectively. The Donnan steric pore model and the Steric hindrane pore model were used to obtain the rejections (Real) of monosaccharides as a function of rs. The results showed that the values of Rcai obtained from DSPM were more accurate than those obtained from SHP. According to the size of value of Real, the rank was:fructose (85.4%-96.3%), glucose (82.6%-95.4%), mannose (80.9%-94.8%), sorbose (73.5%-93.0%), galactose (52.2%-86.7%), arabinose (46.9%-83.9%), xylose (41.4%-80.3%) and ribose (30.0%-68.8%). Concentration polarization was also taken into account to calculate Rreal and their Rcal agreed well with their Rreal. Therefore, differences in Robs are mainly due to differences in the molecular structures of monosaccharides, and the novel way of calculating monosaccharides molecules sizes is feasible, which provides tool for monosaccharides rejection and separation effect by predicting and regulating solutes physical properities.