Introduction

In 1990, the prognosis for the annual marked growth of membrane technology was 12-15%. A particularly high growth potential was predicted for newly developed membrane processes such as gas separation and pervap-oration.1 However, these high expectations were fulfilled only by seawater desalination using reverse osmosis. This application field has still the highest annual growth together with hemodialysis, at 12%. All other membrane processes have shown less than 10% growth, far below all expectations. The annual turnover for membranes and membrane modules for the food industry is shown in Table 11.1.

The reasons for this unexpected development are diverse: (1) the rate of development of membrane materials has not been as rapid as expected; (2) the established membranes do not fulfill the needs of industry; (3) the membranes in use are generally sensitive to organic solvents and to traces of chlorine; (4) membrane fouling is still an unsolved problem that leads to a decrease in membrane efficiency and durability. In fact, due to the loss of yield caused by microbial growth and related fouling issues, membrane processes are usually unprofitable for low-value products. Regarding high-value products the selectivity of current membrane material is not sufficient to fulfill the high demands concerning product quality and cleanliness. For these reasons, membrane technology has been successfully implemented in relatively few application areas on a large scale. These areas are mainly:

• reverse osmosis for seawater and brackish water desalination;

• microfiltration for sterile filtration;

• dialysis and ultrafiltration for hemodialysis and hemofiltration.

Table 11.1 Annual turnover of membrane and membrane modules, after Strathmann12

Application

Turnover 1990 (Million US$)

Turnover 1996 (Million US$)

Turnover 2000 (Million US$)

Predominant applied membrane process

Haemodialysis,

1020

1400

2250

Dialysis,

haemofiltration

ultrafiltration

Water

90

250

430

Reverse osmosis

desalination

Reprocessing of

75

250

400

Micro-, ultrafiltration

industrial

process water

Biotechnology

20

150

250

Micro-, ultrafiltration

Food and beverage

169

150

250

Micro-, ultrafiltration

industry

Purification of

n/a

100

160

Micro-, ultrafiltration

surface water

Chemical

115

160

300

Gas separation,

industry

electro-dialysis

Diagnostic,

n/a

90

130

Micro-, ultrafiltration

analytical

applications

Other applications

n/a

230

380

In spite of these limitations, membrane users predict a further growth potential for this industry. Due to the development of new membranes and especially new membrane processes such as perstraction and vapor permeation the membrane market is set to expand. Additionally the inclusion of membrane processes in hybrid processes is expected to stimulate further growth.3,4 It is considered that membrane processes should not replace established technologies, but augment them.

Current research in membrane technology is therefore focused on the following areas:5,6

• new application fields such as electro-chemistry and biotechnology;

• development of new membrane techniques such as perstraction;

• development and characterization of membrane materials;

• the combination of a number of processes to create hybrid processes;

• modeling and simulation of membrane processes.

In order to address these points, this chapter will describe established and sophisticated membrane processes and their applications. Established processes include ultra- and microfiltration for the purification of proteins, and sterile filtration as well as reverse osmosis for seawater desalination. New processes to be described include organophilic pervaporation and perstraction.

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