| As a functional oligosaccharide, raffinose has the excellent properties of promoting the proliferation of bifidobacterium, and could be used in the protection solution of organ transplantation and as the moisturizing ingredient in cosmetics, which bring raffinose high economic values and broad application prospects in food, cosmetics and pharmaceutical industries. Raffinose has a relatively high content in cottonseed meal, therefore, the extraction and purification of raffinose from cottonseed meal could make full use of residual resource and bring positive social, economic and environmental benefits.Raffinose solution extracted from cottonseed meal has impurities such as protein, pigments, salts and similiar carbohydrates like sucrose and stachyose. Therefore, a purification process for preaparing high purity of raffinose was explored in this dissertation using the combined steps including decoloration with macroporous resin followed by desalination with electroosmosis, and separation of raffinose and sucrose by fixed bed packed with activated carbon, as well as separation of raffinose and stachyose with simulated moving bed.HZ-818 was determined as the best macroporous resin for decoloration among different kinds of macroporous resins. Decoloration ratio of 77.1% was gained in 17 h at 30℃ with a loss ratio of raffinose within 2.4%.2.0 g resin/10 mL solution was recognized as the optimized resin dosage and 9 h was the best equilibrium time. Resins desorbed by 60% aqueous ethanol solution showed a satisfing decoloration ratio up to 94%, indicating a good regeneration performance. Salts were removed by electroosmosis, and results showed that the desalination ratio increased with the increasing voltage ranged from 10 V to 20V, and decreased with the increased flow rate in the range of 20-60 L/h. Desalination rate of 91.2% was obtained in 120 min at the voltage of 30 V and flow rate of 20L/h with the raffinose recovery of 94.5%.Adsorption isotherms and kinetic curves of raffinose and sucrose on activated carbon were determined. Thermodynamics and kinetics models were applied to fit the experimental data. Freundlich and pseudo-second-order model, respectively, fit the thermodynamic and kinetic data well. The saturated adsorption amount of raffinose and sucrose was 0.60-0.65 g/g and 0.40-0.45 g/g, respectively. Adsorption capacity decreased with the increased temperature, indicating an exothermal process of adsorption. Adsorption equilibrium could be reached in 8 h. The effects of inlet concentration, flow rate and activated carbon bed height on the breakthrough curves of mixed solution of raffinose and sucrose in the fixed bed were investigated. Aqueous ethanol solution (20 v%) was used to desorb the saturated activated carbon, and fraction of raffinose with purity above 90% was obtained with a recovery rate of 79.2%. Both breakthrough and desorbed curves of real extract solution after decoloration and desalination agree the simulated’s curves well, and the purity of raffinose reached 73.9% with the recovery of 69.3%.Retention times of raffinose and stachyose on strong acid ion exchange resin (Dowex 50W) of different cross-linking degrees, ion-forms and particle sizes were determined. Cross-linking degree of 4, ion-form of Na+, and mesh number of 200-400 was chosen as the best resin for separation by comparing resolution and selectivity. The effects of flow rate, inject volume, inject concentration and temperature were investigated with HPLC, and results showed that lower flow rate and higher temperature are beneficial for improving selectivity. The influences of Q2/Q3, ts, QF, and feed concentration have been investigated via the process simulation using SMB_Guide, and optimized operation conditions are suggested. |
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