ABSTRACT
Based on the molecular sieving and solution-diffusion effect in nanofiltration separation, the correlation between initial concentration and mass transfer coefficient of three typical phenolic acids from Salvia miltiorrhiza was fitted to analyze the relationship among mass transfer coefficient, molecular weight and concentration. The experiment showed a linear relationship between operation pressure and membrane flux. Meanwhile, the membrane flux was gradually decayed with the increase of solute concentration. On the basis of the molecular sieving and solution-diffusion effect, the mass transfer coefficient and initial concentration of three phenolic acids showed a power function relationship, and the regression coefficients were all greater than 0.9. The mass transfer coefficient and molecular weight of three phenolic acids were negatively correlated with each other, and the order from high to low is protocatechualdehyde >rosmarinic acid> salvianolic acid B. The separation mechanism of nanofiltration for phenolic acids was further clarified through the analysis of the correlation of molecular weight and nanofiltration mass transfer coefficient. The findings provide references for nanofiltration separation, especially for traditional Chinese medicine with phenolic acids.
ABSTRACT
Objective To explore the enhanced separation behavior of ferulic acid in organic solution by nanofiltration. Methods In the experiment, molecular weight cut-off (MWCO) of nanofiltration membrane, ethanol concentration, and solution pH were selected as influencing factors to find the sensitive region of ethanol concentration and pH on the retention rate of ferulic acid with Box-Behnken central composite experiment design. And then, the separation rule of ferulic acid with organic solution was analyzed, the correlation between mass transfer coefficient and concentration of organic solvent was fitted with the changed organic solution by nanofiltration mass transfer mathematical model. Results Experiments indicated that the enhanced separation behavior appeared and the mass transfer coefficient decreased as the ethanol concentration increased from 20% to 40% with MWCO 450 and pH 8.0. Under the same condition, the enhanced separation behavior happened as the solvent was changed into methanol and acetonitrile, and the enhanced effect was positively correlated with the concentration of the three common organic solvents, the effect rule was ethanol ≈ methanol > acetonitrile material. Conclusion The enhanced separation effect of nanofiltration was related to the type and concentration of organic solvent. And taking ferulic acid as an example, the mechanism of nanofiltration separation in the environment of organic solution was studied, and the results provided references for nanofiltration concentrate for heat-sensitive traditional Chinese medicine of phenolic acid in organic solution.
ABSTRACT
Objective To explore the correlation of molecular state of caffeic acid from Perilla frutescens and its nanofiltration mass transfer process. Methods The pH value of solution was changed and the free-dissociation ratio was adjusted with caffeic acid as an index, the rejection and membrane flux of the corresponding initial concentration and operating pressure in different existence conditions were collected. Based on the solution-diffusion effect and charge effect in nanofiltration separation, the linear equations between the rejection and mass transfer coefficient was constructed, the correlation between mass transfer coefficient and initial concentration was established, the mathematical models which based on the operating pressure and initial concentration to predict the rejection of caffeic acid was developed and used to verify its applicability by aqueous extract of P. frutescens. Results Experiments indicated that there was a linear relationship between operation pressure and membrane flux. Besides, mass transfer coefficient and initial concentration of caffeic acid were positively correlated with each other by solution-diffusion effect and charge effect. The mass transfer coefficient of dissociated caffeic acid was less than those of free state and free-dissociation. Moreover, on the basis of power function relationship between mass transfer coefficient and initial concentration, the results showed that the predicted rejections of caffeic acid from P. frutescens water extract using mathematical model approximate well to real ones. Conclusion The mass transfer coefficient of caffeic acid is associated with existential state and initial concentration. The predicted model of nanofiltration separation has a preferable applicability to caffeic acid and provides references for nanofiltration separation, especially for heat-sensitive traditional Chinese medicine.