MEMBRANE CARBON DIOXIDE STERILIZATION, OF LIQUID FOODS: SCALE UP OF A COMMERCIAL CONTINUOUS PROCESS

摘要

The objective of this work is to provide guidelines for scaling up a commercial continuous process. Sims proposed such a process with partial recycle of carbon dioxide. It is most important to recognize that the kinetics of carbonation and of kill are separate and need to be optimized individually. The process sequence is shown in Figure 1. It was shown by Sims that the highest microbial killing rate is achieved when the concentration of dissolved carbon dioxide is at saturation at a particular operating pressure and temperature in the holding tube. The solubility of carbon dioxide in water, Figure 2, shows why an operating pressure of about 75 bar is near optimum. Solubility increase rapidly with increasing pressure up to 50 - 75 bar, but an increase of pressure beyond 75 bar gives little additional increase in solubility or of microbial killing rate. The minimum operating temperature in the holding tube is set by the degree of sterility required and the type of microorganisms. Most pathogenic and spoilage microorganisms in their vegetative state are killed at 40℃, and their spores at 45℃, Optimizing the holding tube is simply a matter of choosing tubing size so that a residence time of about one minute and a plug flow velocity profile is achieved, i.e. a Reynolds Number of greater than 3000. Because the cost of a membrane contactor is based on its active surface area ($/m~2), the optimized membrane carbonator achieves the following criterion: flowrat/area = > maximum The optimum membrane contactor achieves the highest flux of carbon dioxide. The flux in a hollow fiber membrane increases with feed liquid velocity as shown in Figure 3.