Carbon capture and storage (CCS) is broadly recognised as having the potential to play a key role in meeting climate change targets, delivering low carbon heat and power, decarbonising industry and, more recently, its ability to facilitate the net removal of CO2 from the atmosphere. However, despite this broad consensus and its technical maturity, CCS has not yet been deployed on a scale commensurate with the ambitions articulated a decade ago. Thus, in this paper we review the current state-of-the-art of CO2 capture, transport, utilisation and storage from a multi-scale perspective, moving from the global to molecular scales. In light of the COP21 commitments to limit warming to less than 2 °C, we extend the remit of this study to include the key negative emissions technologies (NETs) of bioenergy with CCS (BECCS), and direct air capture (DAC). Cognisant of the non-technical barriers to deploying CCS, we reflect on recent experience from the UK's CCS commercialisation programme and consider the commercial and political barriers to the large-scale deployment of CCS. In all areas, we focus on identifying and clearly articulating the key research challenges that could usefully be addressed in the coming decade.

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Carbon capture and storage (CCS): the way forward

Global warming resulting from the emission of greenhouse gases, especially CO2, has become a widespread concern in the recent years. Though various CO2 capture technologies have been proposed, chemical absorption and adsorption are currently believed to be the most suitable ones for post-combustion power plants. The operation of the chemical absorption process is reviewed in this work, together with the use of absorbents, such as the ionic liquid, alkanolamines and their blended aqueous solutions. The major concerns for this technology, including CO2 capture efficiency, absorption rate, energy required in regeneration, and volume of absorber, are addressed. For adsorption, in addition to physical adsorbents, various mesoporous solid adsorbents impregnated with polyamines and grafted with aminosilanes are reviewed in this work. The major concerns for selection of adsorbent, including cost, adsorption rate, CO2 adsorption capacity, and thermal stability, are compared and discussed. More effective and less energy-consuming regeneration techniques for CO2-loaded adsorbents are also proposed. Future works for both absorption and adsorption are suggested.

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A Review of CO2 Capture by Absorption and Adsorption

Global concentration of CO2 in the atmosphere is increasing rapidly. CO2 emissions have an impact on global climate change. Effective CO2 emission abatement strategies such as Carbon Capture and Storage (CCS) are required to combat this trend. There are three major approaches for CCS: post-combustion capture, pre-combustion capture and oxyfuel process. Post-combustion capture offers some advantages as existing combustion technologies can still be used without radical changes on them. This makes post-combustion capture easier to implement as a retrofit option (to existing power plants) compared to the other two approaches. Therefore, post-combustion capture is probably the first technology that will be deployed. This paper aims to provide a state-of-the-art assessment of the research work carried out so far in post-combustion capture with chemical absorption. The technology will be introduced first, followed by required preparation of flue gas from power plants to use this technology. The important research programmes worldwide and the experimental studies based on pilot plants will be reviewed. This is followed by an overview of various studies based on modelling and simulation. Then the focus is turned to review development of different solvents and process intensification. Based on these, we try to predict challenges and potential new developments from different aspects such as new solvents, pilot plants, process heat integration (to improve efficiency), modelling and simulation, process intensification and government policy impact.

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Post-combustion CO2 capture with chemical absorption: A state-of-the-art review

Sustainable solvents are a topic of growing interest in both the research community and the chemical industry due to a growing awareness of the impact of solvents on pollution, energy usage, and contributions to air quality and climate change. Solvent losses represent a major portion of organic pollution, and solvent removal represents a large proportion of process energy consumption. To counter these issues, a range of greener or more sustainable solvents have been proposed and developed over the past three decades. Much of the focus has been on the environmental credentials of the solvent itself, although how a substance is deployed is as important to sustainability as what it is made from. In this Review, we consider several aspects of the most prominent sustainable organic solvents in use today, ionic liquids, deep eutectic solvents, supercritical fluids, switchable solvents, liquid polymers, and renewable solvents. We examine not only the performance of each class of solvent within the context of the...

Green and Sustainable Solvents in Chemical Processes

This Review details the structural and chemical features of state-of-the-art metal–organic frameworks for their application in the entire carbon cycle of capturing, purifying and transforming CO 2 into valuable products.

The chemistry of metal–organic frameworks for CO 2 capture, regeneration and conversion

This study successfully demonstrated the hydrogenolysis of benzylic alcohols and their derivatives over a Pd/C catalyst by using CO2-expanded methanol (CX-methanol) and compressed CO2/water as two green reaction media. It was found that with the addition of low-pressure CO2 (1 MPa), the reaction conversions of benzylic alcohols and their derivatives could all be increased in the CO2 promoted systems. For example, the conversion of 1-phenylethanol could be elevated from 23% to 63% in CX-methanol and the conversion of benzyl alcohol could be elevated from 75% to 92% in compressed CO2/water. The positive effects of CO2 could be attributed to the decrease of mass transfer resistance and the increase of hydrogen solubility. CO2 could also form methylcarbonic acid and carbonic acid in methanol and water, respectively. Therefore, it could enhance the departing ability of the protonated hydroxyl leaving groups by providing a more acidic environment. In addition, the hydrogenolysis (or deoxygenation) of aromatic aldehyde and ketone by using compressed CO2/water as the solvent were also studied in this work. The results suggested that both CX-methanol and compressed CO2/water could be used as two efficient solvents for the hydrogenolysis reactions.

CO2 promoted hydrogenolysis of benzylic compounds in methanol and water

The regeneration of supercritical carbon dioxide from a mixture containing caffeine by the prepared mesoporous silica and microporous silicalite membrane filters was studied. The mesoporous silica layer, with an average pore opening of 2.5 nm, was deposited on a tubular α-alumina filter. The experimental data showed that a caffeine rejection as high as 0.98 in the first 6 h and a supercritical carbon dioxide permeation flux of 0.074 mol/m 2 /s could be obtained at 35 °C and 13.79 MPa. The mass transfer resistance in the coated mesoporous silica layer was found to be negligible and the adsorption in the silica layer to be the major mechanism in the separation. Because of the occurrence of adsorption, a steady state operation was hard to achieve and caffeine rejection would drop when the adsorption equilibrium was approached. For the prepared microporous silicalite membrane with pore openings of 0.5–0.6 nm, a caffeine rejection of 1.0 was observed at a temperature of 35 °C and a pressure equal to or lower than 12 MPa. The separation under these pressures was based on the molecular sieving mechanism. Due to the presence of some defects, mainly resulting from inter-grain porosity in the coated layer, a high caffeine rejection but not 1.0 could be achieved when the pressure was larger than 12 MPa. At these pressures, adsorption also occurred in the microporous silicalite layer. The mass transfer resistance in a thin silicalite layer was not significant, resulting in a CO 2 permeation flux sufficiently close to that of the parent filter.

Separation of supercritical carbon dioxide and caffeine with mesoporous silica and microporous silicalite membranes

In this study, rhodium–nickel bimetallic nanoparticles loaded on aluminated silica (RhNi/Al-SBA-15) were used as catalysts for the hydrogenation of phthalate in water to produce environmentally acceptable non-phthalate plasticizers. Chemical fluid deposition (CFD) was used to dope metals onto the aluminated silica support, which helped to create a uniform structure of RhNi on Al-SBA-15. The introduction of Ni helped to reduce the use of expensive Rh and increase the number of metal active sites by reducing the bimetallic nanoparticle size. Aluminated SBA-15 not only acted as the support for the RhNi bimetallic catalyst but also enhanced the reaction efficiency by introducing Bronsted and Lewis acid sites and the absorption of phthalates on the catalyst in water. The physicochemical properties of prepared catalysts were characterized by N2 adsorption–desorption isotherm, X-ray diffraction (XRD), in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), Scanning electron microscopy (SEM), and Transmission electron microscopy (TEM). The catalytic performance of the synthesized catalysts was evaluated with the hydrogenation of dimethyl phthalate (DMP). Despite the low solubility of DMP in water, the hydrogenation using Rh0.5Ni1.5/Al-SBA-15 was carried out with an 84.4% reaction yield (cis- : trans- = 97.5 : 2.5) at 80 °C using 1000 psi of H2 after 2 h.

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Synthesis of phthalate-free plasticizers by hydrogenation in water using RhNi bimetallic catalyst on aluminated SBA-15

A simple and green method of depositing monometallic (Ru, Rh, Pd) and bimetallic nanoparticles (Ru-Rh, Ru-Pd and Rh-Pd) on an ordered mesoporous silica support (MCM-41) in supercritical carbon dioxide (scCO2) is described. Metal acetylacetonates were used in the experiments as CO2-soluble metal precursors. Suitable temperature and pressure conditions for synthesizing each kind of nanoparticles were applied in this study. The characterizations of these nanocomposites were performed by transmission electron microscopy (TEM), X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDS). The nanoparticles had average sizes varying from 2 nm to 8 nm. The Ru nanoparticles were clearly shown to be inside the mesopores of MCM-41 from the TEM image. These nanocomposites used as catalysts for hydrogenation was demonstrated. The efficiency of the scCO2 prepared Ru/MCM-41 catalyst was nearly 8 times than that of a Ru/MCM-41 catalyst prepared by conventional impregnation method.

Chemical fluid deposition of monometallic and bimetallic nanoparticles on ordered mesoporous silica as hydrogenation catalysts.

Supercritical propane (SC-propane) was found to be a promising solvent for grafting (3-aminopropyl)triethoxysilane (APS) onto synthesized SBA-15 for CO2 capture. The influence of operating conditions in SC-propane for CO2 adsorption at different pressures (8.3–13.8 MPa), temperatures (85–120 °C), and periods of time (4–16 h) were evaluated. The CO2 adsorption conditions under different partial pressures, temperatures and moisture were evaluated. The results showed a reduction in pore characteristics and an increased amount of grafted APS with increasing pressure and temperature after grafting. After grafting in SC-propane at 11.0 MPa and various temperatures for 16 h, a 3–20% increase in the amount of grafted APS and a 6–49% increase in the CO2 adsorption capacity over the toluene refluxing was observed. The time required for grafting in SC-propane could be reduced while maintaining higher nitrogen content and CO2 adsorption capacity compared with grafting in toluene refluxing.

Chung-Sung Tan

Papers

CO2 promoted hydrogenolysis of benzylic compounds in methanol and water

Separation of supercritical carbon dioxide and caffeine with mesoporous silica and microporous silicalite membranes

Synthesis of phthalate-free plasticizers by hydrogenation in water using RhNi bimetallic catalyst on aluminated SBA-15

Chemical fluid deposition of monometallic and bimetallic nanoparticles on ordered mesoporous silica as hydrogenation catalysts.

SBA-15 grafted with 3-aminopropyl triethoxysilane in supercritical propane for CO2 capture