A review on progress made in direct air capture of CO₂

As the concentration of carbon dioxide (CO₂) in the atmosphere continues to rise, and the reality of global warming challenges hits the world, global research societies are developing innovative technologies to address climate change challenges brought about by high atmospheric concentration of CO₂. One of such challenges is the direct removal of CO₂ from the atmosphere. Among all the currently available CO₂ removal technologies, direct air capture (DAC) is positioned to deliver the needed CO₂ removal from the atmosphere because it is independent of CO₂ emission origin, and the capture machine can be stationed anywhere. Research efforts in the last two decades, however, have identified the system overall energy requirements as the bottleneck to the realization of DAC's commercialization. As a result, global research community continues to seek better ways to minimize the required energy per ton of CO₂ removed via DAC. In this work, the literature was comprehensively reviewed to assess the progress made in DAC, its associated technologies, and the advances made in the state-of-the-art. Thus, it is proposed to use traditional heating, ventilation, and air conditioning (HVAC) system (mainly the air conditioning system), as a preexisting technology, to capture CO₂ directly from the atmosphere, such that the energy needed to capture is provided by the HVAC system of choice.