Development of a carbon-based adsorbent from biogenic waste for carbon capture

Abstract

Anthropogenic carbon dioxide emission into the atmosphere is over 36 billion tons annually, equivalent to around 1100 metric tons each second. The atmospheric CO2 concentration surpassed 400 parts per million permanently in 2016. Reducing CO2 emissions is the only solution to improve the climatic conditions in the future. A long-term solution in the current scenario is switching to CO2-free energy sources. At the same time, there is a need to cut emissions in the short and medium term through carbon capture. Carbon, as a material, has excellent potential as an adsorbent to remove CO2 from flue gas. The present trend in the ocean of carbon is the functionalization of porous carbon, which is now making history through minor modifications and outstanding improvements worldwide. In addition, production of carbon-based adsorbents from biogenic waste is an alternative to diminish the environmental problems related to agro-industrial waste disposal and the emission of hazardous materials to the environment. Consequently, there exists a plethora of applications of waste derived carbon across diverse sectors. In peruse of this situation, to contribute to CO2 mitigation objectives of this research were standardized. To develop an eco-friendly adsorbent material of higher adsorption capacity using biogenic waste, that performs efficiently in carbon capture applications. To replace traditional carbon sources, for this study wastewater generated from the biomass pretreatment (denoted as PHWW) used as precursor to produce solid carbon through hydrothermal carbonization (HTC). Carbon recovered from the waste utilized as the raw material to develop solid adsorbent for carbon capture. Adsorbent developed for this study used in gas-phase application possess several significant additional characteristics. These include a notable adsorptive capacity per unit volume, a substantial retention capacity, a pronounced preference for adsorbing gases even in the presence of moisture, a minimal resistance to the flow of gases, and a complete release of adsorbates as temperatures increase. Within the design range of HTC, 220°C shows a promising carbonization temperature according to the recovered amount of carbon as hydrochar. In order to get higher surface area and micropore volume activation of HTC char was carried out by both physical and chemical methods with nitrogen flow. For chemical activation KOH was used as activating reagent. After going through several characterizations’ adsorbent produced by chemical activation showed higher surface area 1047.46 m2/g and pore volume 0.6 cm3/g activated at temperature 800°C. However, adsorbents activated at temperature 700°C for 1h showed maximum adsorption capacity 5.34 mmol/g at adsorption temperature 0°C and CO2 partial pressure 0.15 bar. Narrow microporosity and surface area seemed to work together to control this CO2 physisorption. Conversely, surface functionalities were essential for encouraging selective chemisorption of CO2 at higher temperatures and lower partial pressures. Nitrogen functional groups were introduced onto the carbon surface using hydrothermal treatment to boost the adsorption capability at higher temperatures. To see how the nitrogen concentration of the adsorbent changed following treatment, two distinct modifiers- a 25% NH4OH solution and solid CO(NH2)2 were utilized separately. Urea treated adsorbent showed 7.36 mmol/g adsorption capacity at 0°C for partial pressure 0.15 bar which was ~38% greater than the untreated adsorbent. It also provided good performance for cyclic operations. At temperature 80°C, adsorption capacity was found 3.71 mmol/g at partial pressure 0.5 bar of CO2 which was ~488% greater than untreated adsorbent. The adsorbent developed for this research exhibits comparable adsorption capability at critical condition’s application in comparison to previously reported findings. Even for cyclic operation it showed better performance and only 7% capacity was lost after five complete operations. Its superior adsorption capacity, even in humid conditions, makes it a viable option for post-combustion CO2 capture from flue gas as an adsorbent. Compared to conventional processes, there is a huge potential of solid carbon-based adsorbents to remove CO2 from flue gas, especially for regeneration energy and significant cost reduction. Overall, the development of HTC char into CO2 adsorbent from biogenic waste represents a promising step towards a more sustainable and environmentally sustainable future.