Sustainable nanoporous carbonaceous adsorbents for carbon dioxide capture

Abstract

Adsorption onto nanoporous activated carbons arises as a sustainable, efficient, and versatile alternative to remove and capture CO2 from process gaseous streams, among current technologies. These adsorbents, obtained from lignocellulosic biomass such as forestry, agricultural and agroindustrial residues, in addition to fulfill their function of capturing CO2, contribute to the abatement of emissions avoiding the accumulation of these residues and immobilizing, with a high degree of mineralization, the carbon removed from the atmosphere during the life time of plant growth. The present chapter attempts to get better insight about the relationship between the process variables involved in activated carbons preparation and their CO2 removal performance, trying to find the key features associated to the efficient CO2 adsorption. The biomassic precursors employed were Parkinsonia aculeata wood sawdust, Pouteria sapota seeds, from the popular tropical fruit locally known as “mamey”, and cones from Pinus canariensis evergreen tree. Chemical activation of the precursors employing KOH as activating agent was applied under pre-established experimental conditions. For the cones, the influence of the impregnation ratio and thermal treatment was additionally investigated. Chemical, textural and morphological characteristics of the adsorbents developed were evaluated in relation with the type of precursor and experimental conditions applied. The resulting adsorbents showed well developed, predominantly microporous, structures with specific surface areas ranging from 1000 to 2000 m2 g -1 , as assessed by gas physisorption techniques. CO2 adsorption capacities mimicking postcombustion conditions, were evaluated from thermogravimetric assays and experimental breakthrough curves obtained in a packed-bed column. The results indicated a good CO2 adsorption performance reaching values between 1 and 2 mmol of CO2 per gram of adsorbent. Simulation of the breakthrough curves by well known models enabled to obtain data for the scale up and industrial application of these materials to remove CO2 from post-combustion streams, thus supplying valuable information for designers of air purifying systems. Regeneration by thermal desorption of the activated carbons studied was also assessed. The CO2 removal capacity was not noticeably affected after five adsorption-desorption cycles. The samples almost kept their initial CO2 adsorption capacity, pointing to their potential use as storage material and further utilization of the desorbed CO2.