Oleh Kutowy

Membrane-based separation scheme for processing sweeteners from stevia leaves.

In existing processes, extraction and refining of glycoside based sweeteners from stevia leaves involves many process steps including extraction by organic solvents. The purpose of the present study was to develop a process of extraction and refining of sweeteners with reduced number of unit operations and minimization and/or elimination of chemical usage including organic solvents. It was found that water was very effective for extracting glycosides at selected pH and temperatures. It was also shown that a multi-stage membrane process was successfully able to concentrate the glycoside sweeteners. Based on the preliminary results, it appears that bitter-tasting components were washed out from the sweetener concentrate in the nanofiltration process. This work also has demonstrated that a membrane-based separation process for refining glycoside-based sweeteners could be viable and needs to be investigated further.

Functional group polysulphones by bromination-metalation

Abstract A variety of functional groups can be substituted on aromatic polysulphones by a process of bromination followed by metalation. Both Udel polysulphone and Radel polyphenylsulphone were brominated at room temperature using bromine without a catalyst. Repeat units containing two bromine atoms at the electrophilic site in the bisphenol portion were obtained when excess reagent was used. These polymers readily undergo metal-halogen exchange with n-butyllithium. The resulting polyanionic lithiated polysulphones are reactive to a variety of electrophiles and give polymers containing functional groups such as carboxyl and hydroxyl. These polymers are useful as membrane materials.

Polysulfone membranes II. Performance comparison of polysulfone-poly-(N-vinyl-pyrrolidone) membranes

Abstract The characteristic behaviour of the polysulfone (PSF), poly-(N-vinyl-pyrrolidone) (PVP), N-methyl-2-pyrrolidinone (NMP) ultrafiltration membrane casting solution system was investigated. Solutions containing different weight percentages of PSF and PVP were prepared. Zero-shear casting solution viscosities were determined. Membranes were then cast using the phase inversion technique and characterized by a series of separation experiments using polyethylene glycols of varying molecular weights as test solutes. A simple pore flow model was fitted to the resulting separation data to provide estimates of the average pore radius. The resistance to fluid transport for a given membrane pore radius was described by the ratio of the number of pores per unit membrane area to the effective pore length. These two parameters were used to compare the performance of laboratory cast polysulfone membranes with data for several commercial products.

Membrane separation of low volatile organic compounds by pervaporation and vapor permeation

Abstract Pervaporation of dilute benzyl alcohol solutions was studied using polydimethylsiloxane (PDMS) membranes. The membrane performance was investigated under various temperatures, downstream pressures and feed concentrations. The benzyl alcohol concentration in the permeate decreased dramatically by increasing the downstream pressure, but increased by increasing the operating temperature. The separation and recovery of benzaldehyde from nitrogen was also investigated. Polyetherimide flat sheet membranes were prepared and then coated with silicone material. The performance of membranes in both coupon form and spiral-wound configuration was studied. When the experimental results from both configurations were compared, it was found that for the same material the membrane coupons had higher separation efficiency than the spiral-wound prototype modules. The ratio of benzaldehyde mole fraction in the permeate to the feed reached 500 for a small membrane coupon of effective surface area 10.2 cm 2 . This ratio was only 26 for the prototype modules, which can be attributed to some limitations of the membrane system design. These limitations are discussed and some recommendations to improve the performance are given.

High flux cellulose acetate ultrafiltration membranes

Abstract Conditions for casting high flux tubular and flat cellulose acetate ultra-filtration membranes are given. The usefulness of some of the tubular membranes cast under the above conditions for ultrafiltration applications in industrial water purification and reuse is illustrated. Using ethanol-water mixture as the gelation medium in the temperature range-20° to 30°C, ultrafiltration membranes giving water fluxes in the range 400 m3/m2 day at the operating pressure of 689.5 × 103 Pa (100 psig) have been obtained.

Use of membranes for energy efficient concentration of dilute streams

In the chemical-process industries, dilute streams containing valuable ingredients are generated in several unit operations. Mechanical vapor-recompression is the best available technology for vaporization that may be used for concentrating such dilute solutions. Energy consumption for vaporization by compression and membrane technology is 350 and 90 kJ/kg, respectively. In order to save additional energy by recycling water, this study explored the use of membranes for processing a hot feed (70-80°C) containing small amounts of food ingredients. Pilot tests report the effects of experimental parameters on membrane performance. The impact of pretreatment of the feed and membrane-cleaning procedures to maintain performance will also be discussed. Initial results indicate that the use of a membrane to pre-concentrate, prior to the final concentration with mechanical vapor recompression, has the potential to save significant amounts of energy. Furthermore, the use of membranes would increase plant capacity by reducing the load on the vapor-compression unit. In this study, it was estimated that a plant processing 15 metric tonnes of feed every day and using membrane technology for concentrating to twice the concentraiton would save about 2 GJ of energy.

Separation of Humic Acids from Bayer Process Liquor by Membrane Filtration

Abstract Humic acids of high molecular weight were removed from spent Bayer liquor by polymeric ultrafiltration membranes. Among the commercial and laboratory-cast membranes tested, Radel-R polyphenylsulfone on a polypropylene backing material was found to be the most promising candidate for this separation. However, the maximum separation of humic acids obtained at operating conditions of 50°C and 0.34 MPa, as measured by spectrophotometric analysis, was only in the 50 to 55% range. In order to explain this limited membrane separation of humic acids in spent Bayer liquor, a synthetic alkaline solution of humic acids was treated using the same membranes. These tests indicated much higher separation of humic acids (92%). Humic substances in Bayer liquor appear to be hydrolyzed and degraded to low molecular weight fractions (molecular weight < 1000 daltons) by the combined action of the strongly alkaline Bayer liquor and high digestion temperatures. These low molecular weight fractions cannot be retained by...