Designing a device to separate water from water-ethanol mixture using dry ice baths
One suggestion: try cooling the alcohol-water mixture more slowly. Slower crystal growth may produce larger ice crystals that occlude less of the ethanol and are easier to separate by filtration. How to do it? Place the steel beaker in the outer bath before adding dry ice to the outer bath, then add the dry ice incrementally to gradually bring the temperature down to where you first observe ice crystals, then keep the temperature constant for a while as crystals form. Then lower the temperature a degree or two and repeat the cycle. Probably better not to stir the inner mixture. It will probably help to use a thermometer to carefully monitor the temperature of the alcohol mixture.