Study On Nanofiltration Separation Performance Of Amino Monosaccharides

As chitin derivatives, amino monosaccharides have many important physiological and medicinal functions. However, there exist many precursor amino monosaccharide residues during amino monosaccharides preparation. Nanofiltration (NF) is a potential efficient technology to separate amino monosaccharide mixtures. To explore nanofiltration separation performance of amino monosaccharides, this project aims to study the effects of different physical conditions on NF performance of single glucosamine hydrochloride (GAH), N-acetyl glucosamine (NAG) and glucosamine sulfate (GAS) systems and their mixed systems separation. The study can provide theoretical basis for molecular structure analogues NF separation and useful supplement for nanofiltration separation mechanisms.Firstly, the separation performance for three kinds of single amino monosaccharide was studied through negatively charged organic NF membrane with the molecular weight cut-offs of 500 Da. The NF process was adjusted by pressure (4-22 bar), feed concentration (5-25 g/L for GAH and GAS,30-70 g/L for NAG), temperature (15-35?) and ionic strength (NaCl, MgCl2 and MgSO4). The results showed that the membrane fluxes increased linearly with the pressure increasing from 4 to 22 bar. Simultaneously, rejections of GAH and NAG both increased and then decreased while GAS rejection went up to 48% with pressure increasing to 22 bar. When the feed concentration rose, NAG rejection declined to 35% while GAH and GAS rejections increased to 42%?49%, respectively. With operation temperature increasing from 15? to 35?, the membrane volume fluxes increased continuously while three monosaccharides rejections decreased by 10%?15%?12% due to membrane swelling. By adjusting ionic strength, both GAH and GAS rejections increased with MgSO4 addition while they were influenced least with MgCl2 addition. Meanwhile, NAG rejection was the highest with MgSO4 addition. Compared with NaCl, MgCl2 is better for NAG permeat, thus NAG retention was the lowest with MgCl2 addition.In the following research, the NF process for three mixed systems including GAH and NAG, GAH and GAS, GAS and NAG was characterized by a series of mathematical models. And the NF separation performance was analyzed in detail. The results showed that GAH separation factor depended slightly on pressure and it was aboutl.2. Due to steric hindrance and charge effects, GAH rejection was lower than NAG rejection. When the concentration ratio of GAH to NAG increased to 1:2, GAH separation factor increased up to 1.23. With operation temperature increasing from 15? to 35?, GAH separation factor reduced from 1.37 to 1.07, thus, higher temperature was not beneficial for GAH and NAG separation. At the same time, polarities of GAH and NAG increased to 3.74?5.94 Debye, respectively. And the calculated molecular diameters of GAH and NAG increased to 0.62% 0.68 nm, respectively. Both GAH and NAG rejections by calculating were consistent with those by fitting, which made useful supplement for NF separation mechanisms. In addition, GAH separation factors were influenced evidently by ionic strength. GAH separation factors reduced nearly to 1 with MgSO4 addition. Electrostatic repulsion and Donnan equilibrium were the main mass transfer mechanisms for GAH and solute diffusion was the main mass transfer mechanism for NAG. For the mixed system of GAH and GAS, due to Donnan repulsion, GAH separation factor increased to 1.35 withMgSO4 addition and reduced to 1.05 withMgCl2 addition. What's more, the results were consistent with the mathematical models. Therefore, the models used in this paper can be applied to NF separation of GAH and GAS. For the mixed system of GAH and GAS, NAG separation factor increased with GAS concentration increase. And the results were consistent with the mathematical models. Thus, the models used in this paper can also be applied in NF separation of NAG and GAS.The results showed that rejections difference among three amino monosaccharides can be expanded by regulating physical conditions. The study provides technical support for large-scale amino monosaccharides nanofiltration separation.