| Summary: | 碩士 === 中原大學 === 化學工程研究所 === 105 === Concentration of liquid foods generally can significantly reduce the transport, packaging and storage costs and also make it has a greater stability in storage. Among the membrane technologies widely used in food industry, osmotic distillation (OD) which can be operated at room temperature and atmospheric pressure to preserve the nutritious characteristics of the food will have high potential in concentrating the liquid foods. In this study, OD with tube-based membrane modules for concentrating glucose solution was analyzed by experiments and simulation to investigate the effect of feed concentration, feed temperature and module characteristics on the flux and concentration factor.
A comparison between the OD flux simulated in the study and that measured from literatures was made first and showed the relative difference between both is only 0.2~2 %. Experiments using the self-assembly tubular PVDF module for batchwise concentration of 16.8 wt% glucose solution with draw solution of 34 wt % CaCl2 showed that average fluxes for 10 hrs operation increase from 0.7 to 2 kg/m2hr as temperature operated from 25 to 45℃. The fluxes simulated are about 2~7 % relative difference compared with the experimental data. Simulation results of the PVDF module with 45 wt % CaCl2 and at 35 ℃ showed that the flux decrease 9 % as glucose concentration of feed increases from 10 to 40 wt%. The flux simulated for 25 wt % glucose concentration showed 2% decrease as module length increase from 10 to 30 cm. With respect to the effect of flow in the module, simulation showed that the countercurrent flow has about 0.7 % higher flux that that with cocurrent flow.
Batchwise concentration experiments using Liqui-Cel® PP module with 10 L, 19.1% glucose solution and 11L , 34 % CaCl2 solution showed that the average flux is about 0.22 kg/m2hr for 10 hrs operation at 45℃. Since the PP module has an area of 1.4 m2, the glucose solution was concentrated to 23.9 wt% after 10 hrs of treatment. The simulation showed that glucose solution was concentrated from 19.1 to 60.6 wt% after 40 hours of continuous operation with periodical replacement of draw solution every 10 hrs. However, only 41.0 wt% concentrated solution was obtained without the replacement of draw solution.
Finally, osmotic membrane distillation (OMD) with PVDF module for concentrating glucose solution was also investigated. It appeared that the increase of feed temperature can result in an obvious increase of flux.
Experiments using Liqui-Cel® PP module showed that flux about 0.22 kg/m2hr at 45℃. However, the effect area of Liqui-Cel® PP module is 1.4m2, 10 liter glucose solution was concentrated from 19.1 to 23.9 wt% after 10 hours of treatment.
Batch experiments for concentrating glucose solution by osmotic membrane distillation (OMD), only 3~10 % error. The simulated results also indicated that more than 90% of mass transport resistance in the OD process is contributed from membrane layer.
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