Negative emission technologies

Abstract

Carbon dioxide (CO2) is an important greenhouse gas (GHG), which concentration in the atmosphere has been rising since the Industrial Revolution due to emissions from anthropogenic activities (mainly burning of fossil fuels). The continuous CO2 emissions may lead to a potentially irreversible climate change (global warming) and ocean acidification. Even if CO2 emissions could be cut to zero today, the environmental impacts would persist in the future due to the long residence time of this GHG. Therefore an international agreement was signed, aiming to limit the increase of the global temperature at 2°C. In this context, CO2 capture from large point sources is gaining the attention of the scientific community as a mitigation option. The pure stream obtained can be transported and stored, avoiding the emission of high amounts of CO2. However, since half of the CO2 emissions come from diffuse sources, capturing CO2 from the atmosphere may be also needed to fulfill the mitigation targets. Despite the higher costs when compared to CO2 capture from large sources, negative emission technologies (NETs) present several advantages: (1) it can capture CO2 emitted from different sources at different locations and time, and (2) the sequestration site can be placed anywhere, avoiding infrastructures transportation. NETs can be divided into two routes: (1) direct air capture-using physicochemical processes and (2) indirect air capture-using biological processes. This chapter aims to present an overview of the main NETs, demonstrating their advantages and drawbacks. Currently, there is no single process that can be considered the only solution to achieve the mitigation goals. Research efforts should be made to completely assess the environmental impacts and reduce its costs, possibly through a process integration.