Chemistry Reference
In-Depth Information
capacity for the component to be bound, though they are still weak enough to be broken by
simple engineering operations such as raising the temperature or decreasing the pressure.
However, the water required for transport must be removed, increasing the cost of process.
An alternative approach is to use solvent-swollen ion-exchange membrane supports [55].
Various petrochemical streams contain a mixture of olefins and saturated hydrocarbons. The
recovery of high-purity olefin gases from paraffins in a petrochemical stream is very
important, since the aliphatic unsaturated hydrocarbons are generally used as intermediate
reactants for industrial chemical syntheses such as the production of polymers.
Another important application is the separation of molecules dissolved in organic
liquids by nanofiltration [56]. Common purification processes (such as distillation,
extraction, chromatography, adsorption and crystallization) determine the energy or
materials consumption and, in some cases, the efficiency. Organic solvent nanofiltration
uses solvent-stable membranes for the separation of molecules of different sizes in
solution. This method is applied to product purification, monomer/dimer separation,
molecular fractionation, room-temperature solvent exchange, catalyst recovery and
recycling, decolouration and solvent recycling. The main advantages are related to
an increase product value, reduced operating cost, reduced processing time and environ-
mental friendliness.
12.3.4 Membrane Operations for the Production of Optically Pure Enantiomers
The importance of enantiopure materials in the pharmaceuticals industry has increased as
technologies for measuring and making enantiopure materials and the production of
enantiomers have become commonplace, with many of the top-selling drugs in the world
now being sold in enantiopure form. Membrane processes are emerging technologies for the
resolution of enantiomers that have recently become widely used in providing rapid access
to enantiopure materials, in order to support pharmaceutical development. Green aspects of
membrane technology include waste reduction, safer solvents and energy efficiency.
Elimination of waste is always a key green chemistry concern and is an important factor
in any separation of enantiomers. The racemization and recycling of the undesired
enantiomer will permit higher yields to be obtained and waste to be reduced. The possibility
of combining membrane operations in the same production system or with traditional
techniques permits the use of process integration capable of pursuing this aim. The green
chemistry principle of a reduction in solvent utilization can be reached using membrane
technology due to the compactness of the plants, control of fluid-dynamic conditions and
recycling of the solvent. Energy efficiency is another advantage of considerable importance.
In this section, enantiocatalytic membrane reactors and enantioselective membrane
processes are described in terms of enantiomer production/separation, a very interesting
field for green chemistry process development in the pharmaceuticals industry. Enan-
tiomers are chemical compounds that are identical to each other in all physical and
chemical properties except optical rotation; therefore, their separation is one of the most
complicated problems in chemical technology.
The chiral nature of living systems has important implications for biologically active
compounds interacting with them. On a molecular level, chirality is an intrinsic property of
fundamental compounds such as amino acids and sugars, and consequently of peptides,
proteins and polysaccarides. Processes mediated by biological systems are very sensitive to
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