3D printing of poly(ethyleneimine)-functionalized Mg-Al mixed metal oxide monoliths for direct air capture of CO_(2)

Direct air capture(DAC)of CO_(2)plays an indispensable role in achieving carbon-neutral goals as one of the key negative emission technologies.Since large air flows are required to capture the ultradilute CO_(2)from the air,lab-synthesized adsorbents in powder form may cause unacceptable gas pressure drops and poor heat and mass transfer efficiencies.A structured adsorbent is essential for the implementation of gas-solid contactors for cost-and energy-efficient DAC systems.In this study,efficient adsorbent poly(ethyleneimine)(PEI)-functionalized Mg-Al-CO_(3)layered double hydroxide(LDH)-derived mixed metal oxides(MMOs)are three-dimensional(3D)printed into monoliths for the first time with more than 90%adsorbent loadings.The printing process has been optimized by initially printing the LDH powder into monoliths followed by calcination into MMO monoliths.This structure exhibits a 32.7%higher specific surface area and a 46.1%higher pore volume,as compared to the direct printing of the MMO powder into a monolith.After impregnation of PEI,the monolith demonstrates a large adsorption capacity(1.82 mmol/g)and fast kinetics(0.7 mmol/g/h)using a CO_(2)feed gas at 400 ppm at 25℃,one of the highest values among the shaped DAC adsorbents.Smearing of the amino-polymers during the post-printing process affects the diffusion of CO_(2),resulting in slower adsorption kinetics of pre-impregnation monoliths compared to post-impregnation monoliths.The optimal PEI/MeOH ratio for the post-impregnation solution prevents pores clogging that would affect both adsorption capacity and kinetics.

Defect-rich Mg-Al MMOs supported TEPA with enhanced charge transfer for highly efficient and stable direct air capture

Due to the advantages of low energy consumption and high CO_(2) selectivity, the development of solid amine-based materials has been regarded as a hot research topic in the field of DAC for the past decades.The adsorption capacity and stability over multiple cycles have been the top priorities for evaluation of practical application value. Herein, we synthesized a novel DAC material by loading TEPA onto defect-rich Mg_(0.55)Al-O MMOs with enhanced charge transfer effect. The optimal Mg_(0.55)Al-O-TEPA67% demonstrates the highest CO_(2)uptake of(3.0 mmol g^(-1)) and excellent regenerability, maintaining ~90% of the initial adsorption amount after 80 adsorption/desorption cycles. The in situ DRIFTS experiments suggested the formation of bicarbonate species under wet conditions. DFT calculations indicated that the stronger bonding between Mg_(0.55)Al-O support and solid amine was caused by the abundance of oxygen defects on MMOs confirmed by XPS and ESR, which favors the charge transfer between the support and amine,resulting in intense interaction and excellent regenerability. This work for the first time conducted comprehensive and systematic investigation on the stabilization mechanism for MMOs supported solid amine adsorbents with highest uptake and superior cyclic stability in depth, which is different from the most popular SiO_(2)-support, thus providing facile strategy and comprehensive theoretical mechanism support for future research about DAC materials.

Operating limits and features of direct air capture on K_(2)CO_(3)/ZrO_(2) composite sorbent

Potassium carbonate-based sorbents are prospective materials for direct air capture(DAC).In the present study,we examined and revealed the influence of the temperature swing adsorption(TSA)cycle conditions on the CO_(2) sorption properties of a novel aerogel-based K_(2)CO_(3)/ZrO_(2) sorbent in a DAC process.It was shown that the humidity and temperature drastically affect the sorption dynamic and sorption capacity of the sorbent.When a temperature at the sorption stage was 29℃ and a water vapor pressure P_(H2O) in the feed air was 5.2 mbar(1 bar=105 Pa),the composite material demonstrated a stable CO_(2) sorption capacity of 3.4%(mass).An increase in sorption temperature leads to a continuous decrease in the CO_(2) absorption capacity reaching a value of 0.7%(mass)at T=80℃.The material showed the retention of a stable CO_(2) sorption capacity for many cycles at each temperature in the range.Increasing PH2O in the inlet air from 5.2 to 6.8 mbar leads to instability of CO_(2) sorption capacity which decreases in the course of 3 consecutive TSA cycles from 1.7%to 0.8%(mass)at T=29℃.A further increase in air humidity only facilitates the deterioration of the CO_(2) sorption capacity of the material.A possible explanation for this phenomenon could be the filling of the porous system of the sorbent with solid reaction products and an aqueous solution of potassium salts,which leads to a significant slowdown in the CO_(2) diffusion in the composite sorbent grain.To investigate the regeneration step of the TSA cycle in situ,the macro ATRFTIR(attenuated total reflection Fourier-transform infrared)spectroscopic imaging was applied for the first time.It was shown that the migration of carbonate-containing species over the surface of sorbent occurs during the thermal regeneration stage of the TSA cycle.The movement of the active component in the porous matrix of the sorbent can affect the sorption characteristics of the composite material.The revealed features make it possible to formulate the requirements and limitations that need to be taken into account for the practical implementation of the DAC process using the K_(2)CO_(3)/ZrO_(2) composite sorbent.

Thermodynamic analysis on direct air capture for building air condition system:Balance between adsorbent and refrigerant

Direct air capture(DAC)is one of the most potential technologies to mitigate CO_(2) emission.Adsorption technol-ogy is recognized as a promising CO_(2) capture method in view of its desirable characteristics including reusability of adsorbents and low capital investment.To further improve thermal performance,evaporation/condensation heat of vapor compression refrigeration(VCR)cycle in air condition system of buildings is adopted for adsorp-tion/desorption process of DAC.Thermal performance of a 4-step temperature swing adsorption process(TSA)is analyzed at various adsorption/desorption temperatures by using different adsorbents.Analysis on Coefficient of Performance(COP)of VCR cycle is also conducted in search for a balance between adsorbent and refrigerant.Taking both real working capacity and COP into consideration,Mg-MOF-74&R134a is the best choice for more amounts of CO_(2).Real working capacity of Mg-MOF-74 is up to 0.38 mol•kg−1 at 70°C,which is twice as much as that of zeolite 13X.While zeolite 13X&R134a shows the best performance of two cycles in view of exergy efficiency and COP,which could reach 81.9%and 7.21,respectively,at 35°C.These matches will provide some guidelines for the practical application of the combination of DAC with heating,ventilation and air conditioning(HVAC).

Challenges in engineering the structure of ionic liquids towards direct air capture of CO_(2)

1.Introduction Man-made perturbations over emissions of greenhouse gas(GHG)bring tremendous negative impacts on the survival environment[1].CO_(2)accounts for~75%of global GHG impacts with others mainly composed of N_(2)O,CH_(4),and small fluorinated gas molecules[2].Deployment of“negative emission”technologies via direct air capture(DAC)of CO_(2)by engineered chemical reactions represents one of the most promising and distinct pathways to limit and alleviate the global warming trend[3].

Cost analysis of air capture driven by wind energy under different scenarios

Reducing the concentration of carbon dioxide(CO2) in the air can effectively alleviate climate change.Air capture,which captures CO2 directly from the air in an industrial process,is an alternative option to address climate change.The results of recent studies on the energy demand in CO2 capture process and the costs of CO2transport and CO2 storage in air capture are analyzed in this paper.Considering renewable energy will not produce additional CO2 in the process of utilization,the electric energy in CO2 capture process of air capture driven by wind energy is different from that of carbon capture and storage.Taking externalities of renewable energy intoaccount,the trading price of CO2 emission is taken to assess the cost of electric energy in CO2 capture of air capture driven by wind energy.Finally,the total cost and the total cost savings of air capture driven by wind energy under different scenarios are analyzed.

Additives enhancing supported amines performance in CO_(2)capture fromair

The utilization of supported amines as adsorbents in direct air capture(DAC)has been demonstrated to be a promising strategy for the reduction of CO_(2)emissions.To improve the performance of amine-based adsorbents,the incorporation of additives has been widely adopted.In the present study,we conduct a comprehensive comparison of seven additives on tetraethylenepentamine-impregnated mesoporous silica as a representative amine-based adsorbent.The results indicate thatminor molecularweight additiveswith hydroxyl groups show improved adsorption-desorption performance and increase oxidative stability.A proposed mechanism for these improvements is the combined physical and chemical promotion effects of hydroxyl groups.Through a comprehensive review of existing literature,it is found that the effects of additives on amine-based adsorbents are dependent on factors,such as additive type,pristine adsorbent properties,incorporation method,and testing conditions.Based on these findings,it is recommended that future DAC systems prioritize the use of hydroxyl-containing additives,whereas higher CO_(2)concentration and temperature capture may benefit from the incorporation of additives without hydroxyl groups.These conclusions are expected to contribute to the design of efficient adsorbents for CO_(2)capture.

Combating Climate Change and Global Warming for a Sustainable Living in Harmony with Nature

As humanity has been polluting the atmosphere with greenhouse gases,the planet is getting warmed up which is triggering the frequency and the intensity of extreme events like heat waves,dry conditions,wildfires,cyclones,tornadoes,lightning,and massive flooding all over the planet Earth.There is considerable evidence that the concentration of greenhouse gases,especially that of CO_(2) has steadily increased in the atmosphere as a result of the indiscriminate use of fossil fuels around the world particularly during the last 70 years.The glaciers in the high mountain and polar regions are diminishing fast,sea levels are rising,and food production is being affected severely in certain parts of the world.In fact,the changing climate has currently become one of the major threats to the survival of civilization.The world scientific communities are warning of a climate emergency and requesting the decision makers to promptly respond and act to sustain life on planet Earth.To deliver net zero emissions by the year 2050,the whole world must phase out the technologies such as coal-powered thermal plants and diesel/petrol/gasoline-powered vehicles which release abundant amounts of CO_(2) and other greenhouse gases into the atmosphere and invest in the development of clean energies such as hydel,wind,solar,space-solar,and nuclear energies.This transition to a low-carbon economy with the help of these technologies together with other technologies such as hydrogen fuel,fuel cells,electric vehicles,and massive plantations is expected to take our planet Earth to a safe zone in the coming 20-30 years.

Low-cost preferential different amine grafted silica spheres adsorbents for DAC CO_(2)removal

DAC CO_(2)capture is gaining wide attention as one of the most difficult carbon approaches to tackle climate change.In this work,different pore-size silica spheres were grafted using different amine groups such as APTES,APTMS,and Diamine.Herein,all samples based on the wet and dry grafting method were used for CO_(2)adsorption isotherm at room temperature and pressure(298 K and 1 bar).The sample based on the wet grafting(Silica-APTES-W)sample shows the highest CO_(2)uptake 1.67 mmol/g.Also,the adsorption isotherm of the Silica-APTES-W sample was showed a high capacity of CO_(2)1.2 mmol/g at 25℃,which describes the strong physical interaction between CO_(2)and amine.The isosteric adsorption of Silica-APTES-W also confirmed that the physical adsorption was dominant because of low adsorption heat ranging from 23 to 37 k J/mol.Also,the fixed bed experiment was conducted with 2000 ppm CO_(2)that obtains the optimal working capacity 4.5 m L/g with the lowest regeneration temperature 90℃.It was shown that Silica-APTES-W sample was superior performance for DAC CO_(2)capture in practical applications.

Recent Advances of Porous Solids for Ultradilute CO_(2) Capture

The urgency of dealing with global climate change caused by greenhouse gas(GHG) emissions is increasing as the carbon dioxide(CO_(2)) concentration in the atmosphere has reached a record high value of 416 ppm(parts per million). Technologies that remove CO_(2) from the surrounding air(direct air capture, DAC) could result in negative carbon emissions, and thus attracts increasing attention. The steady technical progress in adsorption-based CO_(2) separation greatly advanced the DAC, which largely relies on advanced sorbent materials. This review focuses on the latest development of porous solids for air capture;first discussed the main types of sorbents for air capture, which include porous carbons, zeolites, silica materials, and metal-organic frameworks(MOFs), particularly their modified counterparts. Then, we evaluated their performances, including uptake and selectivity under dry and humid CO_(2) streams for practical DAC application. Finally, a brief outlook on remaining challenges and potential directions for future DAC development is given.

Assessment of the carbon abatement and removal opportunities of the Arabian Gulf Countries

The Arabian Gulf Countries(AGC)are strongly reliant on the economic export of fossil fuels,while being vulnerable to climate change that is resulting in temperature increase,air pollution and sea-level rise,and threatening the health of the population and ecosystem.In agreement with the Paris Accords,most of the AGC have published short-term goals to reduce their carbon emissions in the coming decades.In relation to these goals,this study explores the potential CO_(2)reduction,avoidance and removal in the region,by comparing a business-as-usual(BAU)scenario to three decarbonization scenarios for the power sector.In 2018,the total greenhouse gas(GHG)emissions in the AGC were~1333 MtCO_(2)/yr and are expected to rise to 1568 MtCO_(2)/yr in 2030 following a BAU scenario,which is likely to be reduced to 1522 MtCO_(2)/yr in 2030 by following the countries’planning.Countries issued plans for the coming decades that focus on increasing the share of renewable energy in their grid mix.The three decarbonization scenarios presented in this study focus on supply-side technological solutions.The retirement of the oldest natural-gas and oil power plants could lead to a total emissions reduction of~75 MtCO_(2)/yr,without accounting for the embodied carbon emissions associated with renewable energy.In addition,the implementation of point-source capture at power plants expected to retire in>10 years’time could avoid emissions of~240 MtCO_(2)/yr,provided the CO_(2)is permanently sequestered in appropriate geological formations.The region also shows high-quality solar resources and large CO_(2)-storage potential that could couple to direct air-capture plants to offset difficult-to-avoid emissions.This last scenario has the potential to ultimately result in net negative emissions.

Development of a hybrid photo-bioreactor and nanoparticle adsorbent system for the removal of CO2,and selected organic and metal co-pollutants

Fossil fuel combustion and many industrial processes generate gaseous emissions that contain a number of toxic organic pollutants and carbon dioxide（CO_2） which contribute to climate change and atmospheric pollution.There is a need for green and sustainable solutions to remove air pollutants,as opposed to conventional techniques which can be expensive,consume additional energy and generate further waste.We developed a novel integrated bioreactor combined with recyclable iron oxide nano/micro-particle adsorption interfaces,to remove CO_2,and undesired organic air pollutants using natural particles,while generating oxygen.This semi-continuous bench-scale photo-bioreactor was shown to successfully clean up simulated emission streams of up to 45% CO_2 with a conversion rate of approximately 4%CO_2 per hour,generating a steady supply of oxygen（6 mmol/hr）,while nanoparticles effectively remove several undesired organic by-products.We also showed algal waste of the bioreactor can be used for mercury remediation.We estimated the potential CO_2 emissions that could be captured from our new method for three industrial cases in which,coal,oil and natural gas were used.With a 30% carbon capture system,the reduction of CO_2 was estimated to decrease by about 420,000,320,000 and 240,000 metric tonnes,respectively for a typical 500 MW power plant.The cost analysis we conducted showed potential to scale-up,and the entire system is recyclable and sustainable.We further discuss the implications of usage of this complete system,or as individual units,that could provide a hybrid option to existing industrial setups.