Polypropylene Membrane Advantages

The uses of membranes for the filtration of beverages are well accepted today. With this, wine clarification by microfiltration has rapidly grown in recent decades.

However, it is well-known from most of the applications of membranes in fluid filtration that fouling of the membrane surface is the reason for a major loss of membrane permeability and, therefore, of volume through put. The key to success in the clarification of wine is the membrane selection with regard to fouling behavior and the specific membrane surface area respective of pore size.

Higher through put and longer service life

Field test results demonstrate this finding in a direct comparison of two microfiltration membranes with 0.2 µm nominal pore size made from either polyethersulfone (PES) based polymers or polypropylene (PP). When filtering the same white wine, the 3M™ Liqui-Flux™ Beverage Membrane Modules, using 3M’s unique Accurel PP hollow fiber membrane, revealed a much higher through put and service life compared to modules utilizing PES membranes.

Taking into account that the membrane area of the 3M™ Liqui-Flux™ Beverage Membrane Modules B22 beverage modules with Accurel PP membrane was about half of the area of the polyethersulfone modules and that the filtrate volume flow was about twofold higher after 4 hours of filtration, the superior performance of the Accurel PP membranes is obvious. The mean transmembrane pressures were about 1.3 bar for the 3M™ Liqui-Flux™ Beverage Membrane Modules B22 modules and about 2 bar for the modules with polyethersulfone membrane.

The smaller pores also have an influence on the adsorbed amounts of wine ingredients, especially for high-molar mass solutes*

Membrane Specific surface area (m²/g) Pore volume (dp < 80 nm)(mL/g)
PES 3.6 0.010
Accurel PP 300/1200 17.3 0.036

This table indicates the specific surface area and available pore volume of the tested membranes pointing out the markedly different pore structure. The specific surface area of the PP membrane is significantly larger than for the PES membrane.

It was found that different membranes (based on PP or PES) exhibit different adsorption levels of typical foulants in wine such as polyphenols, polysaccharides and tannin*. Furthermore, it can be stated that smaller pores hinder the accumulation of high-molar mass polysaccharides. The low adsorption tendency of wine ingredients with Accurel PP membranes also results in higher fluxes and longer service life of the respective filtration modules in wine clarification.

 

The adsorption of polyphenols seems to be governed by polar interactions which are much stronger with PES than with PP, and multiple hydrogen bonds towards the additive Polyvinylpyrrolidone (PVP) - used to manufacture PES membranes - increase the adsorption tendency.

In contrast, PP is far less prone to adsorption effects resulting in higher measurable flux rates and longer service life of the respective filtration modules in wine clarification.