SUBJECT: MEMBRANE TECHNOLOGY: BASIC PRINCIPLES OF REVERSE OSMOSIS AND ULTRAFILTRATION

Theories of the process of ultrafiltration and reverse osmosis, that involve permeation of solvent through a membrane in a sense opposite to that which obtains in osmosis, are considered. Factors that affect rates of permeation of solute and of solvent, and hence the selectivity of the membrane, are discussed.
The physical structure and chemical composition of membranes are discussed, and the effect of processing variables on structure and composition, and hence on permeation rates and selectivity, are considered. The formation of boundary layers of high solute concentration at the surface of the membrane exposed to the solution has an appreciable effect on permeation; techniques for preventing their formation are mentioned. Some basic considerations relating to the power requirements of membrane processes are defined.     

USE OF ULTRAFILTRATION/REVERSE OSMOSIS SYSTEMS FOR THE CONCENTRATION AND FRACTIONATION OF WHEY

SUMMARY– Existing ultrafiltration/reverse osmosis technology provides a means of fractionating and concentrating cheese whey into liquid fractions containing a variety of protein: lactose ratios. These ratios may range from about 1:8 (raw whey) through 3:5 (a "skim milk equivalent") to 2:1 or higher. If a two- or three-stage ultrafiltration system were used with water injection between stages, a product with a protein:lactose ratio of 20:1 could be obtained. The exact protein:lactose ratio in the concentrate stream is a function of the permeability and selectivity characteristics of the membrane, and the system design and operating conditions. Some of the sanitation problems associated with the introduction of these new unit operations in the dairy and food processing industries are also treated at length.     

EFFECT OF PROCESSING METHOD AND pH OF PRECIPITATION ON THE YIELDS AND FUNCTIONAL PROPERTIES OF PROTEIN ISOLATES FROM GLANDLESS COTTONSEED

SUMMARY— Glandless cottonseed meals were prepared under controlled conditions in a pilot plant by three different processing methods. These meals along with a glandless cottonseed meal produced at a commercial oil mill were used as source meals for protein isolates. Two protein fractions differing in composition and characteristics were isolated from each type meal using a two-step, two-solvent isolation procedure developed at the USDA Southern Utilization R & D Div. yields of each isolate precipitated at three different pH levels were determined on the pilot plant meals. Isolate yields from the commercial meal were determined near the respective isoelectric points of the two fractions. Functional properties including whippability, heat gelation, solubility and foaming properties, were measured on all isolates. Variation in measured values due to meal processing method and precipitation pH was statistically assessed in some instances. Meal processing method was found to significantly affect the yield of Isolate I, the minor isolate. pH of precipitation was found to significantly affect the yield of Isolate II, the major isolate. Also, it was shown that the pH-solubility profiles of both Isolates I and II could be altered by changing the pH at which they were precipitated. The functional properties of isolates from meals processed without heat were superior to those of isolates from heated meals. Data collected indicated the need for a new practice in evaluating the extent of denaturation of cottonseed protein products. The present practice of determining nitrogen solubility at one point was shown to be inadequate.     

反渗透膜及其应用

概述了反渗透膜类型、原理、分离技术,同时介绍了反渗透膜的用途及目前存在的问题.     

DYNAMIC TURBULENCE PROMOTION IN REVERSE OSMOSIS PROCESSING OF LIQUID FOODS

SUMMARY– The phenomenon of concentration polarization operates to reduce the efficiency of solvent-solute separation in the processing of foods by reverse osmosis. The viscous nature of most food concentrates aggravates the problem. Disrupting the boundary layer by mechanically inducing turbulence in the fluid stream improves the permeation efficiency. Flux improvement of up to 3-fold is possible with dynamic turbulence promotion involving plastic spheres moving randomly with the orange juice concentrate. Concentrate (and sphere) movement is pulsed alternately from one end of the membrane flow channel to the other. The spheres are confined within the flow channel to avoid the problem of moving them through the recycling pumps. A net movement of concentrate results when the pump volume is greater in one direction than the other. The permeation rate with dynamic turbulence promotion does not drop off significantly with time. The long-term effects of sphere movement on the membrane surface are not known but are believed not to be serious.     

棉籽蛋白的开发利用

介绍棉籽蛋白的用途和棉籽的去毒方法,侧重介绍乙醇－轻汽油混合溶剂一次浸出棉仁脱酚工艺。     

ULTRAFILTRATION OF WHOLE MILK WITH HOLLOW FIBER MEMBRANES

Whole milk was concentrated using Romicon PM50 membranes. Rententate and permeate were analyzed for total solids, protein (TKN) and fat at five concentration levels. The effects of pressure, concentration, fiber length and several milk pretreatments on flux were examined. A 5X concentrate was prepared containing 37.2% solids, 13.3% protein and 17.8% fat. The highest initial and 4X fluxes were obtained using a pressure differential of 1.4 kg/cm² - 2.11/0.7 (20 psig - 30/10). Flux declined slowly with concentration to 3X (20% loss) and decreased more rapidly thereafter. Higher fluid velocities were deemed responsible for 27% higher initial flux and 47% higher 4X flux when a shorter module was employed (63.5 versus 109.2 cm). Clarification, pasteurization and/or homogenization had little effect on flux at either level.