Melamine-Doped PET-derived Adsorbents for Post-Combustion CO2 Capture

CO2 adsorbents were synthesized from polyethylene terephthalate (plastic water bottle waste), a cheap and abundant plastic waste. Char obtained from polyethylene terephthalate (PET) carbonization was doped with melamine by a wet impregnation procedure. The synthetic route for doping PET-char with melamine for optimal yield and CO2 uptake was assessed. Three synthetic pathway regimes—1 POT, 2 POT, and PAMF—were used to synthesize N-doped PET-derived carbons using 1 g of melamine and a fixed KOH: char ratio of 3. The textural properties and CO2 uptake capacity of the prepared N-carbons were assessed. The surface area of the N-carbons was 2POT (288 m2/g) > 1POT (77 m2/g) > PAMF (26 m2/g). N-carbons synthesized through 2POT, 1POT, and PAMF had dynamic CO2 uptakes of 1.75, 1.06, and 0.75 mmol CO2/g adsorbent, respectively, at 298K and 1 bar. Our results showed that the 2-POT pathway was the best and optimal for doping PET-char with melamine. Using the 2-POT route, we also assess the textural properties and dynamic CO2 uptake of different melamine-doped PET-derived carbons prepared from varying melamine/PET ratios but with a fixed KOH: char ratio of 3. Five N-doped carbons (denoted as NPET-x, where x is the mass ratio of melamine and PET-char) were synthesized and characterized using various analytical protocols. Surface areas, total pore volumes, and the CO2 uptake capacities of the prepared N-doped carbons all decreased with an increasing melamine/PET ratio. Sample NPET-0.5 had the maximum surface area (486 m2/g), total pore volume (0.19 cm3/g), and dynamic CO2 absorption (1.72 mmol/g), while sample NPET-4 had the lowest values. The CO2 adsorption isotherm of sample NPET-0.5 at 273 (low), 298 (moderate), and 323K (high temperature) and 1 bar indicated maximum equilibrium CO2 uptake of 3.28, 2.34, and 1.53 mmol/g, respectively. The total CO2 adsorbed over ten multiple adsorption-desorption cycles for the optimum sample (NPET-0.5) was 17.10 mmol/g, which outperformed that of the commercial adsorbents Norit R (15.78 mmol/g) and Zeolite 13X (14.03 mmol/g), whose dynamic capture capacities were also measured. This research presents a novel method of producing CO2 adsorbents as well as a strategy for managing PET plastic waste.