The Experimental Study On Concentration Of Grape Juice Through Vacuum Membrane Distillation

Vacuum Membrane Distillation(VMD), which has the advantages of low operating temperature and high efficiency, is an innovative membrane separation technology developed in recent years. The vacuum membrane distillation method was used for experimental investigation on the concentration of grape juice. The testing equipment was installed by ourselves, with the hollow fiber as the membrane material. The single factor method and orthogonal test were applied to study the relationship between feed temperature, feed velocity and vacuum degree to get the largest water flux. The flavor index and aroma compounds were experimentally examined for original, once-concentrated and twice-concentrated juice respectively, which was intended to get the retention rate of main components of grape juice. The mechanism of heat and mass transfer for VMD and the membrane fouling were also investigated. The main research contents were as flows:(1) The single factor method showed that the fluxes of membrane will increase as the outlet temperature and vacuum degree increase and that as the flow rate of feed increases, the fluxes increase quickly at first, and then become slow.(2) The orthogonal test showed that.the best process conditions of this experiment are when the fluid rate is 50L/h, the inlet temperature is 52℃and the vacuum degree is 685mmHg.(3) After the grape juice was treated with VMD, the flavor index increased proportionally with the concentration times, the retention rates of the total sugar and total acid were higher than 90 percent while the aroma compounds decrease.(4) On the basis of the above experiment and theory analysis, in order to simulate industrialproduction, a new equipment for juice concentration was designed, with the heat pump principle applied for energy saving.(5) The method of recoil gas, which was used in membrane cleaning, was experimental studied. The mechanism of heat and mass transfer for VMD and the membrane fouling were also discussed.As the experimental investigation of the concentration of grape juice with VMD was carried out under the normal temperature, the retention rates of the total sugar and total acid were high while the aroma compounds decreased, it was indicated that VMD is feasible for grape juice concentration. It may also be feasible for industrial production if the scale-up test is taken.