Ultrafiltration of Whole Milk

Tubular ultrafiltration membranes were used to concentrate and fraetionate whole milk. Fresh, pasteurized, homogenized whole milk was concentrated to 21.5% total solids and 8.6% protein (40% in dry matter). At all flow rates and temperatures an asymptotic permeate flux was reached at a pressure of about 100 kPa, indicating that whole milk ultrafiltration is limited by concentration-and gelpolarization. The permeate flux increased with fluid velocity to the 1.66 i .16 power. The positive effect of temperature on the permeate flux, particularly at high flow rates, generally followed the Arrhenius form with an average activation energy of 6.8 .8 kcal/gmole. The logarithmic decrease of the permeate flux with increasing concentration factor further indicated the importance of concentration polarization in whole milk ultrafiltration. The rejection coefficients for milk proteins, fat, lactose, and ash did not vary with temperature, pressure, or fluid velocity. A four-parameter model adequately described the observed variation of permeate flux with process variables.