Friday, August 8, 2008

Developing clean energy technologies: Role for green chemistry?

From the ACS Green Chemistry website:
"Green chemistry consists of chemicals and chemical processes designed to reduce or eliminate negative environmental impacts. The use and production of these chemicals may involve reduced waste products, non-toxic components, and improved efficiency."
If we consider that the production of fuels is a chemical process, with the energy in the fuel being the output of the process, applying the twelve principles of green chemistry could potentially impact the way fuels are produced. Three of the twelve principles of green chemistry that can be applied to clean energy technologies are the use of renewable feedstocks, maximizing atom economy, and designing chemicals to degrade after use. Some of the important challenges for developing clean energy technologies from a green chemistry perspective are:
  • How can we better use renewable materials to produce fuels or industrial feedstocks?
  • How can we maximize atom efficiency the above conversions?
  • How can we plan for chemical degradation/CO2 sequestration after use?
To better illustrate the above questions, consider the case of producing fuels/petrochemical feedstocks from natural materials/fossil fuels. The production of fuels and petrochemicals from crude oil is highly atom-efficient (but significant improvements can still be made in the energy requirements), compared to technologies such as coal-to-liquids (CTL). Additionally, the production of renewable polymers from natural materials (corn, cellulose, etc.) also involves breaking them down to sugars, followed by fermentation and polymerization to produce the desired polymer. [As an example, see the NatureWorks(TM) polylactic acid (PLA) production from corn.] Similarly, CTL technologies also involve breaking down the complex organic compounds in coal to simpler compounds and further processing to obtain fuels with desirable properties. From a green chemistry perspective, it is much more efficient to maximize the atom economy in these conversions. (This is probably easier to implement in the case of polymers compared to fuels, because the fuels have to match a given specification, while a polymer's specifications can be changed by controlling various process conditions).

Additionally, planning for the end-of-life means that we should have effective means to recycle/reuse products derived from natural sources, and we that we should have strategies to mitigate CO2 emissions while using CTL. I do not advocate that we only use CTL technologies, but only that if we do, we should have some means to mitigate CO2 emissions in place.
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