Membrane Separations for Green Chemistry - Process Intensification for Green Chemistry - page 306

improving the performance of reactive processes and providing reliable options for
sustainable industrial growth.
Membrane processes are actually the most effective separation processes and their
increasing development promotes new and alternative strategies for their application in
green technology. Their intrinsic characteristics of efficiency, selectivity, modularity,
reduced energy consumption and waste production, decreased equipment size/productivity
ratio, increased safety, remote control and automation fit the requirements of green and
intensified processes well. In the last 45 years, membranes have been the subject of increasing
interest at the industrial level, passing from lab to large scale in different application fields,
with high technical and economical impact as clean, selective and efficient technologies.
In the first part of this chapter, some basic aspects of membranes and membrane
processes are briefly described. In the second part, some relevant case studies are
illustrated. Finally, water purification from heavy metal ions, hydrocarbons and organic
and inorganic acids will be considered together with some examples of integrated
membrane processes in water desalination and fruit juice concentration.

12.2 Membranes and Membrane Processes

In the most general sense, a membrane can be defined as a discontinuous phase that separates
and/or contacts two adjacent compartments/phases and promotes exchange of matter, energy
and information between the compartments under the action of a driving force (Figure 12.1).
Membranes show a great variety in their physical structures and the materials they are
made from. In Table 12.1 a membrane classification according to materials, structures and
configurations is reported.
Separation in membrane processes is the result of the different transport rates of different
components through the membrane. Transport rates of individual chemical components
through the membrane are determined by the driving force acting on them, their mobility
and their concentration within the membrane.

Membrane

Phase 2

Phase 1

a

a

X a' X a''

Driving forces

Xa' > Xa''

Flux of component a

Figure 12.1 Schematic representation of mass transport through a synthetic membrane.