| Pharmaceuticals are indispensable for human being. However, large amounts oforganic solvents are used for the production of pharmaceuticals, some of them may berejected into air and water, causing severely environmental pollution. Meanwhile, theenergy consumption of vacuum evaporation utlized to concentrate the dilutepharmaceutical solution is high. Furthermore, owing to the heat sensitivity, thepharmaceuticals may be damaged to some extent by vacuum evaporation, thusresulting in a low product purity and the destruction of antibacterial activity.Therefore it is urgent to develop a new separation and concentration technology. Most pharmaceutical molecular weights are smaller than 1000 Dalton, which liein the nanofiltration molecular weight cut-off range. It is promising to utilizenanofiltration for pharmaceutical organic solution or aqueous organic solutionseparation and concentration. However, the application in organic solution or aqueousorganic solution is relatively scarce. Based on the above background, the feasibility of NF concentration of thepharmaceutical aqueous organic solution was carried out using clindamycin phosphate(CLP) ethanol aqueous solution as model solution. The most suitable membrane wasscreened out and the effects of various factors on the performance of NF membranewere investigated, the characteristics of mass transfer and the mechanism and cure ofmembrane fouling were also studied. The difference between the permeate flux of ethanol-water mixture and the purewater was experimentally studied, the result shows that the former is quite small thanthe latter. And then DL and DK membrane, which are screened out experimentally,have high rejection of more than 99% while remaining a high permeate flux, thepermeate flux of DL is even higher than DK. Using DL membrane, the effects ofpressure, temperature, bulk velocity in the channel, and the concentration of the feedsolution on the separtion process were experimentally investigated. The suitableoperating pressure range is in the range of 1.2 to 1.6MPa, the suitable temperaturerange is 40~50?C. Bulk velocity has much effect on the performance of the membrane.Higher Bulk velocity is preferred in the nanofiltration process. Feed concentrationalso has great effect on the performance of DL membrane. At higher feedconcentration, CLP may form surface crystallization, resulting in the decrease of thepermeate flux. IIIThe anti-solvent property of DL membrane was investigated. DL can withstandethanol-water mixture at temperature higher than 65?C, while remaining a rejection of96%. The nanofiltration concentration of CLP aqueous ethanol solution by DLmembrane was investigated, the solution was concentrated from 40g/L up to 90 g/L.With the increase of the concentration of the pharmaceutical, the permeate fluxdecreases gradually. However, the rejection is higher than 99%. the permeateconcentration remains lower than 0.5g/L, which was suitable for serving as desorptingsolvent. Pilot scale experiment was performed in the pharmaceutical factory with DL2540 membrane to concentrate CLP resin desorption solution, the rejection of CLPwas higher than 99%. The mass transfer phenomena outside and inside the membrane wereinvestigated. A parallel plate crossflow filtration model -modified WZY model, wasestablished. The permeate flux predicted by the modified WZY model agrees with theexperimental value quite well at concentration lower than 60g/L. However, itoverestimated the permeate flux at concentration higher than 60g/L which is due tothe surface crystalization. The nanofiltration separation process of CLP aqueousethanol solution was predicted using the modified WZY model, and the effects ofpressure, temperature, bulk velocity, and length and width of the channel on theprocess were predicted. Higher feed flow rate and feed concentration of CLP,narrower membrane cell channel and shorter channel length, will cause...
|
PDF Full Text Request