Decarbonization as a Route Towards Sustainable Circularity

The ability of certain gases i.e., greenhouse gases (GHGs) to absorb energy (radiative efficiency), during their effective time in the atmosphere (lifetime) causing a warming effect known as Global Warming Potential (GWP) is described in this chapter. GHGs include carbon dioxide (CO₂), methane (CH₄), water vapor (H₂O), nitrogen oxides (NO_x), chlorofluorocarbons (CFCs), perfluorocarbons (PFCs), sulfur hexafluoride (SF₆) and ozone (O₃) Among them, CO₂ is the most abundant with its concentration growing at a rate of more than 2 ppm/y. Another concept considered regarding climate change is Radiative Forcing (RF), which was introduced to explain the net change in the energy balance of the Earth system due to some imposed perturbation, such as the increase of GHGs atmospheric concentration. The effort of countries represented in the United Nations Framework Convention on Climate Change (UNFCCC), to achieve a temperature increase that does not exceed 1.5 °C by 2050 defined within an initiative known as the “Net-Zero” is introduced, as well as the rising of sea level and its possible effect on climate change. Emphasis is placed on the need for CO₂ emission reductions. CO₂ is a rather inert compound that can be either stored or utilized in the production of (longer lifecycle) products and/or in applications for its continuous recycle/reuse. This chapter includes the description of its properties, supporting uses or applications that will be discussed in Chap. 2.

This chapter describes the pathways to convert emitted (or otherwise wasted) CO₂ into more valuable products or chemical feedstock (CU) as means for adding value or creating revenues through CO₂ utilization, which might contribute to attaining economic sustainability while solving energy and environmental issues. Emphasis is given on the need of implementing R&D processes for the conversion of CO₂ (using low-carbon energy sources) to warrant a green future. Thus, inorganic as well as organic valorization routes are described, together with other more aspirational and inspirational routes, such as artificial photosynthesis, keeping in mind that CO₂ abatement cannot rely on natural photosynthesis as the unique process to reduce CO₂ concentration in the atmosphere. Process conditions, economic and energy limitations, or incentives are also incorporated in the discussion. The issues faced and addressed by the end-users and the challenges of marketing the end-products are included in a separate section. Another section of the chapter introduces the net-zero initiative, approaches, and pathways to the 1.5 °C goal, to finally reach a section dealing with the potential of the different sources of energy, as well as with the decarbonization ambitious targets.

This chapter discusses different aspects of a sustainable circular economy, by reviewing the cumulative knowledge on strategies, approaches, and business models developed to close the cycle involving C-bearing compounds and materials. Some approaches, such as the role of the bioeconomy and of the renewable resources, as well as the introduction of the eco-design, eco-efficiency, and eco-effectiveness concepts, are discussed. A Circular Economy (CE) conceived as a way of minimizing, even avoiding waste generation is most appropriate in a decarbonizing scenario. However, circularity per se is not a warrant for sustainability and other measures need to be in place, to accomplish a sustainable circular economy. Within a decarbonization strategy, closing the carbon cycle becomes a circularity challenge. Unless the electric sector firstly passes through a drastic decarbonization, any electrification strategy will fail or be too slow to achieve the sustainability goals. The difficulties in assessing, monitoring, and measuring advances of circularity are also part of this chapter. Other required changes, such as business model, policies and regulations, social behavior, and product uses, for instance, are also discussed.

In this chapter, the discussion of the importance of a change in social behavior that needs to be guided, by the principles developed through the scientific investigation and findings to analyze the environmental threat is presented. The difference in magnitude between emissions (Gton) and utilization (Mton) is a measure of the required efforts for developing solutions. In previous chapters, the basis to claim that there is no universal/single solution to the emissions problem was set. Multiple technologies are required and need to be developed, within a holistic set of criteria. The needs, challenges and existing gaps identified in the CU advances discussed in Chap. 2 are collected in this chapter. Implementation of technologies should take place, by circular integration, within CBMs. A vision of the aspirational (better) future is also offered in this chapter.