Environmental considerations glycols

Propylene glycols, 12 660-670 economic aspects of, 12 666 environmental considerations related to, 12 667-668... 

Fuels cells are of interest both from energetic and environmental considerations. When methanol is fed directly to an anode, as in Direct Methanol Fuel Cells , electric power is generated, making the devices suitable for small and lightweight uses [53], Alternative fuels such as polyhydric alcohols like ethylene glycol and glycerol are much less volatile and toxic, on the one hand, and electrochemically oxidizable on the other [54]. Therefore, the electrochemical oxidation of various polyhydric alcohols has been investigated in acidic as well as in alkaline conditions. 

Different hydrolytic reactions can lead to different products. 1,2-Dichloroethane hydrolyzes in neutral to acidic solutions by nucleophilic attack of HzO to yield ethylene glycol, but in basic solutions, such as might be found in limestone-rich areas, hydroxyl ions promote the elimination of HC1 and the formation of vinyl chloride, a product of considerably greater environmental concern. 

Several types of diisocyanates (aromatic, aliphatic, cyclo aliphatic) and many different glycol-chain extenders (open-chain aliphatic, cyclo aliphatic, aromatic aliphatic) can be used to produce TPU-elastomer hard segments. In the more conventional and practical formulations only a single diisocyanate component is used to make a TPU, so the diisocyanate is common to both the hard and soft segments. The polymer chemist makes his diisocyanate and glycol-chain-extender component selections based on such considerations as desired TPU mechanical properties, upper service temperature, environmental resistance, solubility characteristics, and economics. 

It is beyond the scope of this publication to delve completely into the nuances of detailed quantitative risk assessments, but a few typical considerations can be presented. As an example, we will consider the risk assessment for ethylene glycol recently carried out by Health Canada (HC) in its second Priority Substance Listing (PSL2) assessment for the chemical, as required under the Canadian Environmental Protection Act (CEPA) of 1999. Ethylene glycol represents an interesting example because humans and the environment can potentially be exposed due to its common use as the active component of anti-freeze and as a component of house paints. 

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