A comprehensive review on the application of aerogels in CO2-adsorption: Materials and characterisation

In recent years, greenhouse gases known as, CH4, N2O, O3, CFC and especially CO2 are released into the atmosphere through activities such as combustion, industrial emission or anaerobic decomposition and they cause an increase in surface temperature and global climate changes due to their high heat absorption capacities. Both political and scientific studies gained momentum as the countries of the world set the priority for the reduction of CO2 emissions. Developing methods for reducing global carbon emissions; are known as carbon capture and storage are known as (CCS) technologies. They are mainly classified as pre-combustion, post- combustion and oxyfuel combustion processes. Adsorption, physical and/or chemical absorption, membrane and cryogenic process can be considered as the most common CCS technologies. Porous solid sorbents can be also used for the physical adsorption of carbon dioxide from flue gases, as well. However, these processes are also known to have weaknesses in terms of both selectivity and cyclic operation. More recently, modification of mesaporous materials with amine groups have been shown to be efficient solid adsorbents for CO2 capture. With this review, current scientific studies on the recent advances in carbon sorption applications of silica aerogels has been investigated. The review consists of three main sections: preparation and modification of silica aerogels, literature studies on CO2 sorption performances and future perspectives. As a result, it has been concluded that amine-modified silica aerogels are promising materials for the carbon capture for the post combustion processes with their superior properties.

The latest development on amine functionalized solid adsorbents for post-combustion CO2 capture: Analysis review

A simple and efficient way to synthesize activated mesoporous biocarbons (AMBs) with extremely high BET surface area and large pore volume has been achieved for the first time through a simple solid state activation of freely available biomass, Arundo donax, with zinc chloride. The textural parameters of the AMB can easily be controlled by varying the activation temperature. It is demonstrated that the mesoporosity of AMB can be finely tuned with a simple adjustment of the amount of activating agent. AMB with almost 100% mesoporosity can be achieved using the activating agent and the biomass ratio of 5 and carbonization at 500 °C. Under the optimized conditions, AMB with a BET surface area of 3298 m2 g-1 and a pore volume of 1.9 cm3 g-1 can be prepared. While being used as an adsorbent for CO2 capture, AMB registers an impressively high pressure CO2 adsorption capacity of 30.2 mmol g-1 at 30 bar which is much higher than that of activated carbon (AC), multiwalled carbon nanotubes (MWCNTs), highly ordered mesoporous carbons, and mesoporous carbon nitrides. AMB also shows high stability with excellent regeneration properties under vacuum and temperatures of up to 250 °C. These impressive textural parameters and high CO2 adsorption capacity of AMB clearly reveal its potential as a promising adsorbent for high-pressure CO2 capture and storage application. Also, the simple one-step synthesis strategy outlined in this work would provide a pathway to generate a series of novel mesoporous activated biocarbons from different biomasses.

Utilizing waste carbon residue from spent lithium-ion batteries as an adsorbent for CO2 capture: A recycling perspective

ConspectusCarbon dioxide (CO2) capture and storage (CCS) is a means to enable the continued use of fossil fuels in the short term. In particular, postcombustion CO2 capture has attracted considerable attention because it can be retrofitted into existing power plants and industrial plants. Among various CO2 capture technologies, the absorption of CO2 using aqueous amines has been industrially employed for decades. However, such amine scrubbing technologies have inherent limitations of environmental and health concerns due to volatile amine loss, corrosion, and high energy demands for regeneration. To overcome these limitations, CO2 adsorption using solid adsorbents has emerged as a promising alternative due to its noncorrosiveness and low energy demand. Various amine-containing adsorbents have been synthesized and investigated for postcombustion CO2 capture. These materials are prepared by physically impregnating low-vapor-pressure amine polymers or by chemically grafting amines onto nanoporous materials. A wide variety of amine guests and nanoporous hosts (e.g., SiO2, Al2O3, zeolites, MOFs, and polymers) have been combined to develop advanced CO2 adsorbents.The design of CO2 adsorbents is a multifaceted puzzle that must ultimately consider integration with large-scale CO2 capture processes. Various engineering aspects need to be carefully considered. Unfortunately, a significant proportion of previous studies has primarily focused on the use of novel materials for improving the CO2 adsorption capacity. In this Account, we describe key challenges and solutions to develop energy-efficient and stable amine-containing adsorbents for postcombustion CO2 capture via temperature swing adsorption (TSA). We found that a high CO2 working capacity, often overemphasized in the literature, does not necessarily guarantee a low energy demand for CO2 capture. Suppressing coadsorption of H2O during the CO2 adsorption in humid flue gas is also a significant factor. Amine-containing adsorbents can be degraded through various pathways, including hydrothermal degradation of nanoporous hosts and chemical degradation of amine guests via urea formation and oxidation. To inhibit such degradation pathways, it is extremely important to properly design the nanoporous structures of the hosts and the molecular structures of the amine guests. By combining macroporous silica hosts, poly(ethylenimine) (PEI) functionalized with various alkyl epoxides, and phosphate-based oxidative stabilizers, we could synthesize adsorbents exhibiting low energy demands for CO2 capture and unprecedentedly high thermochemical stability under TSA conditions. The macroporous silica host synthesized by assembling fumed silica particles via spray-drying exhibited high hydrothermal stability and enabled uniform distribution of bulky amine polymers within its pores. The functionalization of PEI with alkyl epoxides converted its primary amines into hindered secondary amines, leading to a significant reduction in energy demand for TSA cycles and a remarkable improvement in long-term stabilities. The oxidative stability of amines could be drastically improved by adding phosphate metal-binding reagents, which can poison ppm-level metal impurities that catalyze amine oxidation. The present discussions will provide important insights into designing practical adsorbents for CO2 capture from engineering perspectives.

CO2 capture represents the key technology for CO2 reduction within the framework of CO2 capture, utilization, and storage (CCUS). In fact, the implementation of CO2 capture extends far beyond CCUS since it will link the CO2 emission and recycling sectors, and when renewables are used to provide necessary energy input, CO2 capture would enable a profitable zero- or even negative-emitting and integrated energy-chemical solution. To this end, highly efficient CO2 capture technologies are needed, and adsorption using solid adsorbents has the potential to be one of the ideal options. Currently, the greatest challenge in this area is the development of adsorbents with high performance that balances a range of optimization-needed factors, those including costs, efficiency, and engineering feasibility. In this review, recent advances on the development of carbon-based and immobilized organic amines-based CO2 adsorbents are summarized, the selection of these particular categories of materials is because they are among the most developed low temperature (<100 oC) CO2 adsorbents up to date, which showed important potential for practical deployment at pilot-scale in the near future. Preparation protocols, adsorption behaviors as well as pros and cons of each type of the adsorbents are presented, it was concluded that encouraging results have been achieved already, however, the development of more effective adsorbents for CO2 capture remains challenging and further innovations in the design and synthesis of adsorbents are needed.

Biomass derived low-cost microporous adsorbents for efficient CO2 capture

The goal of this research is to develop a low-cost porous carbon adsorbent for selective CO2 capture. To obtain advanced adsorbents, it is critical to understand the synergetic effect of textural characteristics and surface functionality of the adsorbents for CO2 capture performance. Herein, we report a sustainable and scalable bio-inspired fabrication of nitrogen-doped hierarchical porous carbon by employing KOH chemical activation of waste wool. The optimal sample possesses a large surface area and a hierarchical porous structure, and exhibits good CO2 adsorption capacities of 2.78 mmol g−1 and 3.72 mmol g−1 at 25 °C and 0 °C, respectively, under 1 bar. Additionally, this sample also displays a moderate CO2/N2 selectivity, an appropriate CO2 isosteric heat of adsorption and a stable cyclic ability. These multiple advantages combined with the low-cost of the raw material demonstrate that this sample is an excellent candidate as an adsorbent for CO2 capture.

Sustainable CO2 capture via adsorption by chitosan-based functional biomaterial: A review on recent advances, challenges, and future directions

In this study, activated carbon and piperazine-modified activated carbon adsorbents were prepared and used for CO2 adsorption. The effect of various parameters including adsorbent particle size, adsorbent amount, piperazine weight percent, pressure, and temperature were investigated on the CO2 adsorption capacity. The adsorbents were characterized using nitrogen adsorption/desorption isotherms and FTIR analyses. The results showed that the adsorption capacity decreases with temperature increasing and increases with pressure increasing. In addition, the surface modification of activated carbon improved the CO2 adsorption capacity more than the unmodified adsorbent, and the highest CO2 adsorption was obtained 203.842 mg/g at 25 °C and 8 bar. Additionally, to determine the adsorbent behavior, CO2 adsorption experimental data were fitted by isotherm and kinetic models. CO2 adsorption isotherm modeling was studied up to 8 bar at 25 °C, and kinetic modeling was investigated up to 85 °C at 6 bar. The results show that Hill isotherm model and Elovich kinetic models have a good agreement with the adsorption data. Finally, thermodynamic modeling was carried out for modified and unmodified adsorbents, and enthalpy, entropy, and Gibbs free energy changes of adsorption for piperazine-modified activated carbon at 25 °C and 6 bar obtained 17.078 kJ/mol, - 0.039 kJ/mol.K, and - 5.318 kJ/mol, respectively.

Porous carbons play an important role in CO2 adsorption and separation due to their developed porosity, excellent stability, wide availability, and tunable surface chemistry. In this chapter, the synthesis strategies of porous carbon materials and evaluation of their performance in CO2 capture are reviewed. For clarity, porous carbons are mainly classified into the following categories: conventional activated carbons (ACs), renewable-resources-derived porous carbons, synthetic polymer-based porous carbons, graphitic porous carbons, etc. In each category, macroscopic and microscopic morphologies, synthesis principles, pore structures, composition and surface chemistry features as well as their CO2 capture behavior are included. Among them, porous carbons with targeted functionalization and a vast range of nanostructured carbons (carbon nanofibers, CNTs, graphene, etc.) for CO2 capture are being created at an increasing rate and are highlighted. After that, the main influence factors determining CO2 capture performance including the pore features and heteroatom decoration are particularly discussed. In the end, we briefly summarize and discuss the future prospectives of porous carbons for CO2 capture.

Adsorbents for the post-combustion capture of CO2 using rapid temperature swing or vacuum swing adsorption

A comparison of the CO2 capture characteristics of zeolites and metal–organic frameworks

Chemically modified carbonaceous adsorbents for enhanced CO2 capture: A review

Adsorption utilising porous solid adsorbent has been considered a feasible option for conventional CO2 absorption over the past few decades. As a preliminary investigation towards obtaining Metal-Organic Frameworks (MOFs) adsorbent for CO2 capture, the CO2 adsorption efficiency using mono- and bimetal-based MOFs was assessed in this study. Among the numerous MOFs, Mg-MOF-74 exhibits the best CO2 uptake at low pressures because of its open metal sites. A strategy to incorporate Zn in Mg-based MOF as a co-metal node is required to enhance the CO2 adsorption performance of solid adsorbent. Selecting Zn as a metal node in MOF synthesis allows for the creation of stable, versatile, and functional materials for CO2 adsorption. Therefore, combining several metals in a structure to develop a new MOF with an improved gas uptake is quite a useful approach to further harness the immense potential of MOFs. This study aims to compare the performance of mono- and bimetallic-MOFs and select the most suitable adsorbent for CO2 capture. The performance of CO2 adsorption was conducted using three parameters: the effect of metal loading on MOFs, pressure (1–5 bar) and adsorbent dosage (0.2–0.5g). Based on the characterisation findings, the studies confirm the formation of Mg-MOF-74, Zn-MOF and 50wt.%Zn/50wt.%Mg-MOF. Overall, it was found that the bimetal adsorbent with 50 wt.%Zn/50wt.%Mg-MOF displayed the highest CO2 adsorption capacity (323 mgCO2/gadsorbent) when compared to the monometallic MOFs (Zn-MOF (134mgCO2/gadsorbent) and Mg-MOF-74) (122 mgCO2/gadsorbent) indicating a 50% increase in adsorption capacity over monometallic MOFs.