Since the time of the industrial revolution, the atmospheric CO(2) concentration has risen by nearly 35 % to its current level of 383 ppm. The increased carbon dioxide concentration in the atmosphere has been suggested to be a leading contributor to global climate change. To slow the increase, reductions in anthropogenic CO(2) emissions are necessary. Large emission point sources, such as fossil-fuel-based power generation facilities, are the first targets for these reductions. A benchmark, mature technology for the separation of dilute CO(2) from gas streams is via absorption with aqueous amines. However, the use of solid adsorbents is now being widely considered as an alternative, potentially less-energy-intensive separation technology. This Review describes the CO(2) adsorption behavior of several different classes of solid carbon dioxide adsorbents, including zeolites, activated carbons, calcium oxides, hydrotalcites, organic-inorganic hybrids, and metal-organic frameworks. These adsorbents are evaluated in terms of their equilibrium CO(2) capacities as well as other important parameters such as adsorption-desorption kinetics, operating windows, stability, and regenerability. The scope of currently available CO(2) adsorbents and their critical properties that will ultimately affect their incorporation into large-scale separation processes is presented.

Adsorbent Materials for Carbon Dioxide Capture from Large Anthropogenic Point Sources

In recent years, Carbon Capture and Storage (Sequestration) (CCS) has been proposed as a potential method to allow the continued use of fossil-fuelled power stations whilst preventing emissions of CO2 from reaching the atmosphere. Gas, coal (and biomass)-fired power stations can respond to changes in demand more readily than many other sources of electricity production, hence the importance of retaining them as an option in the energy mix. Here, we review the leading CO2 capture technologies, available in the short and long term, and their technological maturity, before discussing CO2 transport and storage. Current pilot plants and demonstrations are highlighted, as is the importance of optimising the CCS system as a whole. Other topics briefly discussed include the viability of both the capture of CO2 from the air and CO2 reutilisation as climate change mitigation strategies. Finally, we discuss the economic and legal aspects of CCS.

Carbon capture and storage update

In the last few years there has been a rapid growth in governmental funding and research activities worldwide for CO2 capture, storage and utilization (CSU), due to increasing awareness of the link between CO2 accumulation in the atmosphere and global warming. Among the various technologies and processes that have been developed and are emerging for CSU of CO2, solid CO2-adsorbents are widely applied. In this review, these solid CO2-adsorbents are classified into three types according to their sorption/desorption temperatures: low-, intermediate- and high-temperature adsorbents with temperatures ranging from below 200 °C, between 200–400 °C and above 400 °C, respectively. For each type of solid CO2-adsorbent, the synthesis, interaction mechanism with CO2 and sorption performance, potential applications and problems are reviewed. In the last section, several representative CO2-sorption-enhanced catalytic reactions are discussed. It is expected that this review will not only summarize the main research activities in this area, but also find possible links between fundamental studies and industrial applications.

CO2 capture by solid adsorbents and their applications: current status and new trends

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.

/pdf/a-review-of-co2-capture-by-absorption-and-adsorption-5eczh2835p.pdf

A Review of CO2 Capture by Absorption and Adsorption

The increase in the global atmospheric CO2 concentration resulting from over a century of combustion of fossil fuels has been associated with significant global climate change. With the global population increase driving continued increases in fossil fuel use, humanity’s primary reliance on fossil energy for the next several decades is assured. Traditional modes of carbon capture such as precombustion and postcombustion CO2 capture from large point sources can help slow the rate of increase of the atmospheric CO2 concentration, but only the direct removal of CO2 from the air, or “direct air capture” (DAC), can actually reduce the global atmospheric CO2 concentration. The past decade has seen a steep rise in the use of chemical sorbents that are cycled through sorption and desorption cycles for CO2 removal from ultradilute gases such as air. This Review provides a historical overview of the field of DAC, along with an exhaustive description of the use of chemical sorbents targeted at this application. Solv...

Direct Capture of CO2 from Ambient Air

The use of calcines of natural limestones as CO2 regenerable sorbents is investigated in this work by studying the decay of the maximum carbonation conversion during many carbonation/calcination cycles. New experimental information is complemented with a compilation of previously published data on this subject. The observed conversion limits in the reaction of CO2 with lime are interpreted in terms of a certain loss in the porosity associated with small pores and a certain increase in the porosity associated with large pores. In the carbonation part of every cycle, the CaCO3 fills up all the available porosity made up of small pores plus a small fraction of the large voids, limited by the thickness of the product layer that marks the onset of the slow carbonation rate. A simple model based on textural changes, observed by scanning electron microscopy, fits equally well all the data from this work and from other authors. The two model parameters are consistent with known mechanism occurring during calcinat...

Conversion Limits in the Reaction of CO2 with Lime

Experiments in a pilot-scale fluidized-bed reactor have been carried out to investigate the carbonation reaction of CaO, as a potential method for CO2 capture from combustion flue gases at high-temperatures. Results show that CO2 capture efficiencies are very high, while there is a sufficient fraction of CaO in the bed reacting in the fast reaction regime. The total capture capacity of the bed decays with the number of carbonation-calcination cycles. The experimental CO2 concentration profiles measured inside the bed during the fast reaction period are interpreted with the KL fluid bed model, by supplying information on sorbent deactivation from laboratory tests. It is concluded that a fluidized bed of CaO can be a suitable reactor to achieve very effective CO2 capture efficiencies from a combustion flue gas. © 2004 American Institute of Chemical Engineers AIChE J, 50:1614–1622, 2004

Capture of CO2 from combustion gases in a fluidized bed of CaO

Calcium oxide can be an effective CO2 sorbent at high temperatures When coupled with a calcination step to produce pure CO2, the carbonation reaction is the basis for several high-temperature separation systems of CO2 The formation of a product layer of CaCO3 is known to mark a sudden change in the reaction regime, from a very fast CO2 uptake to very slow carbonation rates The critical thickness of this product layer of CaCO3 has been measured in this work on real sorbent materials, using different limestone precursors and submitting them to many repeated carbonation calcination cycles (up to 100) Mercury porosimetry curves of the calcines and their carbonated counterparts have been obtained and their differences interpreted with a simple pore model, from which the thickness of the product layer is derived An average value of 49 nm (±19% standard deviation) has been obtained, which is quite insensitive to the type of limestone and to the texture of the calcine as long as the model is fulfilled The i

Determination of the Critical Product Layer Thickness in the Reaction of CaO with CO2

Phase-mineral and chemical composition of coal fly ashes as a basis for their multicomponent utilization. 1. Characterization of feed coals and fly ashes☆

The use of carbonation/calcination cycles of CaO/CaCO3 is emerging as a viable technique for the capture of CO2 generated in the combustion of coals for power generation. Specifically, the choice of natural limestones as CO2 carriers is an attractive option because they are cheap and abundant materials, although previous studies indicate that the reactivity of the calcines toward CO2 rapidly drops with cycling. This paper reports on the effects of the internal morphology of CaO particles on their capability of absorbing CO2. Calcines of a natural limestone with different initial textures were repeatedly submitted to carbonation/calcination conditions (up to 100 cycles). The textural evolution, as well as the carbonation conversion, of the calcined and recarbonated samples was followed along the experiments. In addition to the known mechanisms of deactivation due to grain growth and limited diffusion of CO2 through the product layer, we have found that pore closure is also taking place in our samples, toge...

Diego Alvarez

Papers

Conversion Limits in the Reaction of CO2 with Lime

Capture of CO2 from combustion gases in a fluidized bed of CaO

Determination of the Critical Product Layer Thickness in the Reaction of CaO with CO2

Phase-mineral and chemical composition of coal fly ashes as a basis for their multicomponent utilization. 1. Characterization of feed coals and fly ashes☆

Pore-Size and Shape Effects on the Recarbonation Performance of Calcium Oxide Submitted to Repeated Calcination/Recarbonation Cycles