Study On Separating Natural Products With Simulated Moving Bed

The simulated moving bed (SMB) is a continuous countercurrent process developed in the 1960s by Universal Oil Products (UOP). Currently, SMB technology has a wide range of applications, including large-scale separations in the sugar and petrochemical industries and recently developed pharmaceutical, chiral, fine chemistry, and bioseparations processes. Compared to preparative chromatography, both the adsorbent inventory and the solvent consumption are much less. In addition, high performance can be achieved even when the selectivity of the adsorbent to the components is rather low.The paper is divided into five chapters. Chapter 1 introduces the character of fixed bed, moving bed and simulated moving bed and their histories, separation theory and application examples.Chapter 2 is modeling of fixed bed and simulated moving bed. A general rate model, which considers axial dispersion, liquid film mass transfer and effective diffusion in particle, was adopted to investigate the chromatography process. The finite element and orthogonal collocation method were used to transfer these equations to ordinary differential equations and to solve them. There are two strategies for modeling SMB operation: the equivalent true moving bed concept and the simulated moving bed concept. The main difference between these two concepts is that the steady state can be obtained only in the asymptotic sense in a SMB whereas it is a definite state in a TMB.Chapter 3 is separation of soybean phosphatidylcholine by fixed bed. A general rate model was adopted to investigate the chromatography process for soybean phosphatidylcholine. The relationship between the film mass-transfer coefficient and the interstitial velocity and the effective diffusion coefficient were measured. Total phosphatidylcholine was isolated from soybean lipids with ethanol-water. The effect of composition and flow rate of mobile phase was investigated. As the water concentration of mobile phase increases, the capacity factor and the resolution decrease. The best water concentration of mobile phase is 20%. On the basis ofmodel, the effects of Pe number, Bi number, r\ number on the chromatographic peak of soybean phosphatidylcholine were studied.Chapter 4 is separation of phosphatidylcholine from soybean phospholipids by simulated moving bed. The effects of flow rate in section 2(Q2) and 3(Q3), switching time, feed flow rate and feed concentration on the operating performance parameters: purity, recovery, productivity and desorbent consumption were studied. Operating conditions leading to more than 90% purity in both outlet streams had been identified, together with those achieving optimal performance. Regimes leading to complete separation were observed and explained theoretically. Due to the mass-transfer effect is not considered, the triangle theory only gives initial guesses for the optimal operating conditions.Chapter 5 is separation of tocopherol homologues by fixed bed. A general rate model was adopted to investigate the chromatography process for tocopherols. The relationship between the film mass-transfer coefficient and the interstitial velocity and the effective diffusion coefficient were measured. The scale-up of the HPLC separation of the tocopherols from analytical to preparative scale was achieved. Total tocopherols were separated with n-hexane-isopropanol as mobile phase using a silica-gel column. The effect of composition and flow rate of mobile phase was investigated. As the isopropanol concentration of mobile phase increases, the capacity factor and the resolution decrease. The best isopropanol concentration of mobile phase is 1%.Chapter 6 is separation of tocopherol homologues by simulated moving bed. A rate model, which considers axial dispersion, external mass transfer, intraparticle diffusion and nonlinear isotherms, and ports periodic switching, was adopted to simulate the SMB process. Adsorption isotherms and mass transfer parameters of the tocopherol homologues were estimated from analytical column. On a laboratory SMB system, the tocopherol homologues were successfully separated and purified into a -tocopherol, Y -tocopherol and 5 -tocopherol component. The experimental results show high purity(>98%) and high recovery(>98%), which closely agree with the rate model simulations and the cyclic steady state was reached. The model predicts the performance of the transient and cyclic steady state behavior to a reasonably good extent. Generally, the model can also be used to direct the separation experiment andto optimize the scale-up design or the industrial production of chromatographic separation process. Muti-component separation is simulated with rate model. Economic analyses and comparisons on batch preparative chromatography and simulated moving bed are achieved.