Strategy For CO2 Capture Research Articles

CO2 sorption on surface-modified carbonaceous support: Probing the influence of the carbon black microporosity and surface polarity

The use of solid sorbents is a convenient option in post-combustion CO2 capture strategies. Sorbents selection is a key point because the materials are required to be both low-cost and versatile in typical post-combustion conditions in order to guarantee an economically advantageous overall process. This work compares strategies to tailor the chemico-physical features of carbon black (CB) by surface-modification and/or coating with a CO2-sorbent phase. The influence of the CB microporosity, enhanced by chemical/thermal treatments, is also taken into account. Three CB surface modifications are performed and compared: (i) oxidation and functionalization with amino-groups, (ii) coating with iron oxides and (iii) impregnation with an ionic liquid (IL). The CO2 capture performance is evaluated on the basis of the breakthrough curves measured at atmospheric pressure and room temperature in a lab-scale fixed bed micro-reactor. Most of tested solids adsorb a CO2 amount significantly higher than a 13X zeolite and DARCO FGD (Norit) activated carbon (up to 4 times more in the best case). The sorbents bearing basic functionalities (amino-groups and IL) exhibit the highest CO2 sorption capacity. The use of a microporous carbonaceous support limits the accessibility of CO2 toward the adsorbing phase (IL or FM) lowering the number of accessible binding sites for CO2.

Effect of operating conditions on the CO2 recovery from a fine activated carbon by means of TSA in a fluidized bed assisted by acoustic fields

CO2 temperature swing adsorption (TSA), consisting in adsorbing the CO2 and, then, inducing the sorbent regeneration and CO2 recovery by a temperature increase and gas purge, is a promising strategy for CO2 capture. With reference to the sorbent, commercially available adsorbent materials are generally available in the form of fine powders. A sound-assisted fluidized bed is capable of fully exploiting the potential and properties of fine sorbents, due to large gas–solid contact efficiency, high rate of mass/heat transfer and low pressure drops. This work is focused on the CO2 desorption process by TSA in a sound-assisted fluidized bed of fine activated carbon. The effect of desorption temperatures and N2 purge flow rate on the regeneration efficiency has been assessed in terms of CO2 recovery level and purity and desorption time. Both of them positively affect the desorption process in terms of enhanced desorption kinetics. Increasing temperatures also yield higher CO2 purities, whereas, no remarkable dilution effect has been observed when increasing the N2 flow rate. Finally, the activated carbon keeps its performances over 16 adsorption/desorption cycles, due to the stability of the regeneration process under sound-assisted fluidization conditions.

Magnetite loaded carbon fine particles as low-cost CO2 adsorbent in a sound assisted fluidized bed

CO2 adsorption with solid sorbents is one of the most promising options for post-combustion CO2 capture strategies. Typical post-combustion flue-gas conditions are CO2 1–15%vol. and atmospheric pressure and the performances of solid sorbents under typical flue gas conditions have been poorly investigated. In that condition the CO2 uptake capacity is influenced primarily by material functionality effects rather than material pore metrics so materials with a distinctive surface chemistry (presence of activated surface atoms or sites) could find applications in adsorption technologies. Hence the sorbent selection became a key point because the materials should be convenient from the economic point of view but versatile in post-combustion conditions. Recent studies of CO2 adsorption on low-cost iron metal oxide surfaces strongly encourage the possible use of metal oxide as sorbents, but the tendency of magnetite particles to agglomerate causes a lowering of CO2 uptake capacity. The dispersion of magnetite nanoparticles on carbonaceous matrix appears to be a promising strategy to overcome this shortcoming. This work investigates the adsorption behavior of CO2 on composite materials prepared coating a low-cost commercial carbon black (CB) with magnetite fine particles. The CO2 capture capacity of composites produced at different CB load was evaluated on the basis of the breakthrough times measured at atmospheric pressure and room temperature in a lab-scale fixed bed micro-reactor. A CB–FM composite has been selected to verify the possibility of carrying out a two-stage operation and the thermochemical stability in a sound assisted fluidized bed. To this aim the reactor has been firstly operated for CO2 adsorption and then for regeneration. The effect of multiple cycles of adsorption and desorption steps has been also quantified.

Effect of light supply on CO2 capture from atmosphere by Chlorella vulgaris and Pseudokirchneriella subcapitata

Carbon dioxide (CO2) is one of the primary greenhouse gases that contribute to climate change. Consequently, emission reduction technologies will be needed to reduce CO2 atmospheric concentration. Microalgae may have an important role in this context. They are photosynthetic microorganisms that are able to fix atmospheric CO2 using solar energy with efficiency ten times higher than terrestrial plants. The objectives of this study were: (i) to analyse the effect of light supply on the growth of Chlorella vulgaris and Pseudokirchneriella subcapitata; (ii) to assess the atmospheric CO2 capture by these microalgae; and (iii) to determine the parameters of the Monod model that describe the influence of irradiance on the growth of the selected microalgae. Both microalgae presented higher growth rates with high irradiance values and discontinuous light supply. The continuous supply of light at the highest irradiance value was not beneficial for C. vulgaris due to photooxidation. Additionally, C. vulgaris achieved the highest CO2 fixation rate with the value of 0.305 g-CO2 L−1 d−1. The parameters of the Monod model demonstrated that C. vulgaris can achieve higher specific growth rates (and higher CO2 fixation rates) if cultivated under higher irradiances than the studied values. The presented results showed that microalgal culture is a promising strategy for CO2 capture from atmosphere.

Engineered Nanocomposites for Capturing and Converting Carbon Dioxide into Useful Chemicals

ABSTRACTWe describe a simple drop-cast processing method to synthesize multicomponent polymer-based nanocomposites for carbon dioxide (CO2) capture and conversion into stable carbonates. These multicomponent nanocomposites are made of combination of different metal oxide nanoparticles and catalysts in a porous polymer matrix. The formulation includes the combination of titanium dioxide and magnesium oxide, ruthenium oxide, and iron oxide where each metal oxide exhibits its own catalytic function of trapping carbon dioxide. Such a material system provides numerous localized catalytically active hot reaction spots generated by the dispersed multifunctional oxide nanoparticles that react with CO2 when exposed to the gas stream and instantaneously convert the captured carbon into carbonates. Finally, we discuss our ongoing work on the possibility of converting captured-carbon-formed-carbonate into useful products/commodities such as methane, methanol and formic acid. The integration of polymer materials with catalytically active nanomaterials shows a promising strategy for CO2 capture and conversion into useful products towards achieving a sustainable energy future.

A superstructure‐based optimal synthesis of PSA cycles for post‐combustion CO2 capture

AbstractRecent developments have shown pressure/vacuum swing adsorption (PSA/VSA) to be a promising option to effectively capture CO2 from flue gas streams. In most commercial PSA cycles, the weakly adsorbed component in the mixture is the desired product, and enriching the strongly adsorbed CO2 is not a concern. On the other hand, it is necessary to concentrate CO2 to high purity to reduce CO2 sequestration costs and minimize safety and environmental risks. Thus, it is necessary to develop PSA processes specifically targeted to obtain pure strongly adsorbed component. A multitude of PSA/VSA cycles have been developed in the literature for CO2 capture from feedstocks low in CO2 concentration. However, no systematic methodology has been suggested to develop, evaluate, and optimize PSA cycles for high purity CO2 capture. This study presents a systematic optimization‐based formulation to synthesize novel PSA cycles for a given application. In particular, a novel PSA superstructure is presented to design optimal PSA cycle configurations and evaluate CO2 capture strategies. The superstructure is rich enough to predict a number of different PSA operating steps. The bed connections in the superstructure are governed by time‐dependent control variables, which can be varied to realize most PSA operating steps. An optimal sequence of operating steps is achieved through the formulation of an optimal control problem with the partial differential and algebraic equations of the PSA system and the cyclic steady state condition. Large‐scale optimization capabilities have enabled us to adopt a complete discretization methodology to solve the optimal control problem as a large‐scale nonlinear program, using the nonlinear optimization solver IPOPT. The superstructure approach is demonstrated for case studies related to post‐combustion CO2 capture. In particular, optimal PSA cycles were synthesized, which maximize CO2 recovery for a given purity, and minimize overall power consumption. The results show the potential of the superstructure to predict PSA cycles with up to 98% purity and recovery of CO2. Moreover, for recovery of around 85% and purity of over 90%, these cycles can recover CO2 from atmospheric flue gas with a low power consumption of 465 k Wh tonne−1 CO2. The approach presented is, therefore, very promising and quite useful for evaluating the suitability of different adsorbents, feedstocks, and operating strategies for PSA, and assessing its usefulness for CO2 capture. Published 2009 American Institute of Chemical Engineers AIChE J, 2010

Microalgal removal of CO2 from flue gases: Changes in medium pH and flue gas composition do not appear to affect the photochemical yield of microalgal cultures

Our research objectives are to determine under what conditions microalgal-based CO2 capture from flue gases is economically attractive. Specifically, our objective here was to select microalgae that are temperature, pH and flue gas tolerant. Microalgae were grown under five different temperatures, three different pH and five different flue gas mixtures besides 100% CO2 (gas concentrations that the cells were exposed to ranged 5.7–100% CO2, 0–3504 ppm SO2, 0–328 ppm NO, and 0–126 ppm NO2). Our results indicate that the microalgal strains tested exhibit a substantial ability to withstand a wide range of temperature (54 strains tested), pH (20 strains tested) and flue gas composition (24 strains tested) likely to be encountered in cultures used for carbon sequestration from smoke stack gases. Our results indicate that microalgal photosynthesis is a limited but viable strategy for CO2 capture from flue gases produced by stationary combustion sources.