Artificial sinks

Aresta and Dibenedetto (Chapter 7, this volume) explore the mechanisms by which CO2 may be utilized in industrial chemical synthesis or for technological applications. Although the sink strength represented by the direct incorporation of CO2 into long-lived (>10 years) compounds such as polymers appears rather limited, the indirect reduction in atmospheric CO2 concentrations through reduced industrial energy use makes these 'artificial sinks' a significant component of overall anthropogenic climate forcing.

Currently, industrial use of CO2 is equivalent to ~110 million tonnes CO2/year, which is dominated by urea and carbonate production. Aresta and Dibenedetto identify significant potential for greater use of CO2 in these and other processes, particularly in the production of polymers, methanol and carboxyl-ates. The life cycle analysis (LCA) approach is discussed as a means of assessing the net CO2 reduction achieved by industrial CO2 utilization, with inclusion of both the direct (CO2 incorporation) and indirect (reduced energy use) components highlighted.

Examples with significant potential include the addition of CO2 to CH4 in the production of methanol, an approach that can lead to a net reduction of 200 kg CO2 for each tonne of methanol produced. Likewise, the synthesis of organic carbonates using CO2 can result in both energy savings and the avoidance of toxic compounds like phosgene. Given increased exploitation of these and other processes incorporating CO2, the net CO2 avoidance through such 'artificial sinks' may be increased to between 250 and 300 Tg/year (this is equivalent to offsetting all CO2 emissions arising from aviation in developed countries during 2002).

The wider use of such carbon capture and sequestration (CCS), especially that making use of geological formations to store cap tured CO2 for hundreds or even thousands of years, has huge potential as a strategy to mitigate anthropogenic climate change (see Reay, Chapter 16, this volume).

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