Introduction

Microfiltration is a separation technique for removing micron-sized particles, like bacteria, yeast cells, colloids, and smoke particles, from suspensions or gases. The process uses membrane filters with pores in the approximate size range 0.1 to 10 |im, which are permeable to the fluid, but retain the particles, thus causing separation. Examples of particles with sizes in the microfiltration range are presented in Figure 1.

Microfiltration membranes were first commercialized in the 1920s, and were at that time mainly used for the bacteriological analysis of water. After 1960 the number of successful microfiltration applications grew rapidly, and nowadays microfiltration processes are operated in such different fields as the biotech-nological, automobile, electronics, and food industry. Examples of applications are the harvesting of bacterial and yeast cells, the recovery of latex pigments from paints, and the purification of water for the electronics industry. In the food industry, microfiltration is used in the clarification of fruit juices, wine, and beer, in fat removal from whey and in removal of bacteria from milk.

Microfiltration is the largest industrial market within the membrane field, responsible for about 40% of total sales, both in Europe and in the USA. In 1997, the US microfiltration membrane market amassed revenues worth about $400 million, growing at an average annual growth rate of 6.6%. Microfiltration can be carried out in two different operation modes: dead-end (in line) filtration and cross-flow glass membranes were produced by Corning (Vycor®), Schott, and PPG. Glass membranes are typically made as discs, tubes or hollow-fibres. To produce microporous glass membranes, a homogeneous melt consisting of 70 wt% SiO2, 23 wt% B2O3 and 7 wt% Na2O is formed between 1300 to 1500°C. Phase separation of the initially homogeneous glass melt occurs by lowering the temperature to about 800°C. One phase consists primarily of insoluble silicon dioxide. The other phase, rich in alkali borate, can be leached from the heterogeneous glass by treatment with a mineral acid. After removal of the alkali borate phase, a microporous silica membrane is formed.

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

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