I. Process Augmentation of Green Technologies
Recent Development of Novel Composite Materials for Carbon Capture: A Green Technology
Introduction
The growing issue of the catastrophic effects of global warming in various regions in the world is contradictory, with the incapability of many countries to reduce the net emissions of greenhouse gases (GHGs) at the prescribed rate as committed to the Kyoto Protocol, which describes the mechanism of reducing carbon (C) emissions by decreasing the concentration of GHGs. These gases can be removed from the atmosphere by sequestrating them in several sinks. C capture or C sequestration is the process through which atmospheric carbon dioxide (CO,) is removed from the atmosphere and stored in soil or other systems, and is generally accepted as the most promising technique for climate change mitigation (Smith et al., 2008).
Soil performs a significant role in maintaining a balanced global C cycle as it is the potential source of GHGs (Jedli et al., 2017). However, soil C sequestration is a relatively slow process in order to meet the requirements of the C removal process in the atmosphere and to mitigate the problems of climate change and global warming. The large size of the soil C pool not only makes it a potential buffer against rising atmospheric CO,, but also makes it difficult to measure changes against the existing background. The main points of CO, capture and storage include effectiveness, capacity of material to sequestrate a large quantity of CO,, stability and cost. Considering the geological sequestration technique, it sequestrates large quantities of CO, at high cost and low economic value, and results in environmentally adverse effects on few occasions. The ocean, which is considered as the major sink for C, has been studied extensively to promote the process of C sequestration. Researchers have shown the potential to store CO, at a depth of 3000 m in the ocean as stable hydrates (Sarv, 1999). Herzog and Adams (1999) also investigated the different forms of C that were sequestered in the ocean after direct injection in liquid state at a depth of 300 m and at a temperature of 8°C. Different types of composite materials, metal- organic framework, nanotechnology-based sponges, membranes and fibrous materials are some of the products being employed for the carbon capture process in recent times (Amutha Rani et al., 2008). In this chapter, we will review the state-of-the-art scenario of utilization of composite materials and novel products that are used to capture atmospheric C02.
Climate Change and Present Scenario
The earth’s climate is subject to altered patterns owing to the intense anthropogenic activities that modify the composition of the atmosphere chemically by the build-up of GHGs, mainly CO,, methane (CH4) and nitrous oxide (N,0). The global atmospheric concentration of CO,, CH4 and N,0 has shown an elevation from their levels of the preindustrial era of about 280 to 387 pmol mol-1, 0.715 to 1.774 pmol mol-1 and 0.270 to 0.319 pmol mol-1, respectively (IPCC, 2007). It is also presumed that elevated concentrations of GHGs would be likely to accelerate the rate of climate change in the future. Climatologists have also predicted that the mean global surface temperature could rise by 1.4-5.8°C with significant variations from region to region by the end of the 21st century (IPCC. 2007). The IPCC has come up with policies to limit the warming to below 1.5°C as well to restrict the concentration of atmospheric GHGs at the level of 589 million tonnes.
Global Carbon Pools and Their Relationship with Climate Change
Carbon is the most important element that influences the climate and its changes. The terrestrial C cycle is presented in Figure 1.1. Soil organic C represents the largest reservoir in interaction with the atmosphere and is estimated at about 6000 pg to 3 m depth. Inorganic C represents around 1700 pg, but it is captured in more stable
FIGURE 1.1 Status of global carbon sinks and associated processes.
forms. The vegetation (620 pg) and the atmosphere (800 pg) store considerably less C than soils. There is a need to understand the biochemical mechanisms regulating C exchanges between the land, oceans and atmosphere and how these exchanges will respond to climate change through climate ecosystem feedback (Heimann and Reichstein, 2008). A slight alteration in the exchange process might result in significant changes in C emissions in the atmosphere rather than its storage in the ecosystem. The basic processes underlying the C cycle are the ‘sources’ and ‘sinks’. The higher the number of ‘sinks’, the greater the rate of C sequestration. Terrestrial ecosystems play a major role in such climate change feedbacks because they release and absorb GHGs while storing large quantities of C in living vegetation and soils, thereby acting as a significant global C sink. The influence of climate change on the soil C sink remains a major area of uncertainty, especially as there is scope for warming-induced liberation of CO, from soil to atmosphere due to enhanced microbial decomposition of soil organic matter (Friedlingstein et ah, 2006). Therefore, it is important to research novel processes or materials that result in sequestration of C.
