Hierarchical porous polystyrene-based activated carbon spheres for CO2 capture

Recent Progress on Porous Carbons for Carbon Capture

High emission of carbon dioxide (CO2) has caused CO2 levels to reach more than 400 ppm in air and led to a serious climate problem. In addition, in confined spaces such as submarines and aircraft, the CO2 concentration increase in the air caused by human respiration also affects human health. In order to protect the environment and human health, the search for high-performance adsorbents for carbon capture from high and low concentration gas is particularly important. Porous carbon materials, possessing the advantages of low cost and renewability, have set off a boom in the research of porous adsorbents, which have the opportunity to be utilized on a large scale for industrial carbon capture in the future. In this review, we summarize the recent research progress of porous carbons for carbon capture from flue gas and directly from air in the last five years, including activated carbon (AC), heteroatom-modified porous carbon, carbon molecular sieves (CMS), and other porous carbon materials, with a focus on the effects of temperature, water content, and gas flow rate of industrial flue gas on the performance of porous carbon adsorbents. We summarize the preparation strategies of various porous carbons and seek environmental friendly porous carbon materials preparation strategies under the premise of improving the CO2 adsorption capacity and selectivity of porous carbon adsorbents. Based on the effects of real industrial flue gas on adsorbents, we provide new ideas and evaluation methods for the development and preparation of porous carbon materials.

Household mixed plastic waste derived adsorbents for CO2 capture: A feasibility study

The feasibility of producing activated carbon (AC) from real Household Mixed Plastic Waste (HMPW) comprising of LDPE, HDPE, PP, PS, and PET for carbon capture via direct carbonisation followed by microwave-assisted or conventional thermally assisted chemical activation was investigated. A microwave-assisted activation procedure was adopted to assess the impact on the CO2 capture capacity of the resulting AC using both a lower temperature (400 °C vs. 700 °C) and a shorter duration (5 vs. 120 mins) than that required for conventional activation. The results obtained showed that the AC yield was 71 and 78% for the conventional and microwave-assisted samples, respectively. Microwave activation consumed five-fold less energy (0.19 kWh) than the conventional activation (0.98 kWh). Thermal stability results indicated total weight loss of 10.0 and 8.3 wt%, respectively, for conventional and microwave-activated samples over the temperature range of 25-1000 °C, with ACs from both activation routes displaying a type 1 nitrogen isotherm. The dynamic CO2 uptake capacity at 1 bar and 25 °C was 1.53 mmol/g, with maximum equilibrium uptake ranging between 1.32 and 2.39 mmol/g at temperatures (0-50 °C) and 1 bar for the conventionally activated AC. The analogous microwave-activated sample showed a higher dynamic CO2 uptake of 1.62 mmol/g and equilibrium uptake in the range 1.58-2.88 mmol/g under equivalent conditions. The results therefore indicate that microwave activation results in enhanced carbon capture potential. To the best of our knowledge, this is the first-time microwave heating has been employed to convert household mixed plastic wastes directly into ACs for carbon capture applications. This report therefore demonstrates that the management of mixed plastics could lead to the development of a circular economy through the conversion of waste into value-added materials.

Preparation of CPVC-based activated carbon spheres and insight into the adsorption-desorption performance for typical volatile organic compounds

Chlorinated polyvinyl chloride (CPVC)-based activated carbon spheres with smooth surfaces, good sphericity, interconnected hierarchical porous structure and high porosity have been synthesized by non-solvent induced phase separation method, followed by successive treatments of stabilization, carbonization at 450 °C in N2 atmosphere, and activation with CO2 as an agent at 900-1000 °C. The effect of activation temperatures on the textural properties of activated carbon spheres and their adsorption potential for volatile organic compounds (VOCs) under dynamic conditions is investigated. CO2 activation improves the hierarchy in the microporous range by stimulating the formation of supermicropores and significantly expands the specific surface area and pore volume of activated carbon spheres. The textural properties of adsorbents play a vital role in the adsorption performance of different VOCs. The adsorption capacity of VOC molecules can be greatly promoted by elevating specific surface area and pore volume. Due to the compatibility difference between the VOC molecules and the pore structure of adsorbents, the adsorption capacity follows the order of toluene > m-xylene > n-hexane. The adsorption isotherm of toluene on CPVC-AC1000 can be generally expressed by the Langmuir model. The adsorbents with larger average pore diameters possess a lower activation energy of desorption, which is beneficial for desorption. The carbon sphere activated at 1000 °C is a high-performance adsorbent with good reusability. Thus, the present study provides a synthesis process to produce the activated carbon spheres with high porosity from low-cost CPVC for its application in VOC adsorption.

Development of composite amine functionalized polyester microspheres for efficient CO2 capture

In order to reduce the impact of greenhouse gases on the environment, the development of various new CO2 capture materials has become a hot spot. In this work, a novel composite amine solid adsorbent was prepared by simultaneously using tetraethylenepentamine (TEPA) and 2-[2-(dimethylamino) ethoxy] ethanol (DMAEE) for amine functionalization on the polyester microsphere carrier. The introduction of methyl methacrylate (MMA) with high glass transition temperature into the polyester carrier makes the carrier microspheres have high hardness. At the same time, the carrier also contains active epoxy groups and hydrophobic glycidyl methacrylate (GMA, which can undergo ring-opening reaction with composite amines to achieve high-load and low-energy chemical grafting of amines on the carrier. The composite aminated polyester microspheres were used as an efficient adsorbent for CO2 in simulated flue gas. The results show that the synergistic effect of TEPA-DMAEE composite amine system in the adsorbent is beneficial to the improvement of CO2 capture capacity. When the total amine content in the impregnating solution is 45 wt% and the composite amine ratio is TEPA: DMAEE = 6: 4, the CO2 adsorption capacity can reach the optimal value of 2.45 mmol/ g at 70 °C. In addition, the composite amine microsphere adsorbent has cyclic regeneration performance. Importantly, through kinetic fitting, the Avrami kinetic model fits the CO2 adsorption better than the quasi-first-order and quasi-second-order kinetic models, which proves that physical adsorption and chemical adsorption coexist in the adsorption process. This simple, long-term stable and excellent selective separation performance makes amine-functionalized adsorbents have potential application prospects in CO2 capture.

On the use of plastic precursors for preparation of activated carbons and their evaluation in CO2 capture for biogas upgrading: a review

In circular economy, useful plastic materials are kept in circulation as opposed to being landfilled, incinerated, or leaked into the natural environment. Pyrolysis is a chemical recycling technique useful for unrecyclable plastic wastes that produce gas, liquid (oil), and solid (char) products. Although the pyrolysis technique has been extensively studied and there are several installations applying it on the industrial scale, no commercial applications for the solid product have been found yet. In this scenario, the use of plastic-based char for the biogas upgrading may be a sustainable way to transform the solid product of pyrolysis into a particularly beneficial material. This paper reviews the preparation and main parameters of the processes affecting the final textural properties of the plastic-based activated carbons. Moreover, the application of those materials for the CO₂ capture in the processes of biogas upgrading is largely discussed.

Intensification of CO2 absorption and desorption by metal/non-metal oxide nanoparticles in bubble columns

In this study, four different metal/non-metal oxide nanoparticles including CuO, Fe₃O₄, ZnO, and SiO₂ were employed to improve CO₂ absorption and desorption in methyl diethanolamine (MDEA)-based nanofluid. CO₂ absorption experiment with various nanofluids was done in a bubble column reactor at ambient temperature. Also, CO₂ stripping experiments for all nanofluids were done at 60 and 70 °C. The influence of nanoparticles type, nanoparticle concentration, and the stability of nanoparticles were studied on both CO₂ absorption and stripping. The obtained results revealed that Fe₃O₄ nanoparticles at 0.01 wt.% concentration had the best influence on CO₂ absorption and it improved the CO₂ loading up to 36%. Also, CO₂ stripping experiments for all nanofluids were done at 60 and 70 °C. The desorption experiments illustrated that metal oxide nanoparticles can be more efficient in improving CO₂ desorption. In CO₂ desorption, the CuO nanoparticles at 0.05 wt.% had higher efficiency, and enhanced CO₂ concentration at outlet gas phase up to 44.2 vol.% at 70 °C. Finally, as an indication, the chemical stability of Fe₃O₄ NPs under optimum operational conditions was studied using XRD analysis and the result showed that the proposed operational condition did not have any negative effect on the chemical nature of Fe₃O₄ NPs.