Membrane Gas Separation

14.4
New Metrics for Gas Separation Applications 
For measuring progress towards sustainability, many efforts are being made for defi ning 
indicators of industrial process and, in particular their impact on three specifi c areas 
[72,73] : 
• environmental indicators, which refer to the resource exploitation and the emission, 
effl uents and waste related to the production
• economic indicators, which take into account the investments profi ts, values and 
taxes
• social indicators, that consider the employment situation, health and safety at work and 
the benefi ts/troubles for the community.
Most of these indicators are calculated in form of appropriate ratios. Ratio indicators, in 
fact, can provide a measure of impact independent of the scale of the operation, or to 
weigh cost against benefi ts and, in some cases, they can allow comparison between 
different operations
[74] 
. Membrane operations are well 
- 
known for their modularity, 
compactness and fl exibility, therefore they can be considered as new operations developed 
in the logic of PI. Recently, new metrics for comparing membrane performances with 
that of conventional units have been introduced [72,75] . With respect to the existing 
indicators, these new metrics take into account the size, the weight, the fl exibility, the 
yield and the modularity of the plants. They are useful for having an immediate indication 
of the eventual gain that a membrane operation can offer with respect to a traditional 
one. In this sense, they are useful also for indicating which of a membrane or traditional 
operation is more suitable for a specifi c process. 

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Membrane Engineering: Progress and Potentialities in Gas Separations
301
14.4.1