25 research outputs found
Capturing CO2 from ambient air using a polyethyleneimineâsilica adsorbent in fluidized beds
Carbon Capture and Storage (CCS) uses a combination of technologies to capture, transport and store carbon dioxide (CO2) emissions from large point sources such as coal or natural gas-fired power plants. Capturing CO2 from ambient air has been considered as a carbon-negative technology to mitigate anthropogenic CO2 emissions in the air. The performance of a mesoporous silica-supported polyethyleneimine (PEI)âsilica adsorbent for CO2 capture from ambient air has been evaluated in a laboratory-scale Bubbling Fluidized Bed (BFB) reactor. The air capture tests lasted for between 4 and 14 days using 1 kg of the PEIâsilica adsorbent in the BFB reactor. Despite the low CO2 concentration in ambient air, nearly 100% CO2 capture efficiency has been achieved with a relatively short gasâsolid contact time of 7.5 s. The equilibrium CO2 adsorption capacity for air capture was found to be as high as 7.3 wt%, which is amongst the highest values reported to date. A conceptual design is completed to evaluate the technological and economic feasibility of using PEIâsilica adsorbent to capture CO2 from ambient air at a large scale of capturing 1 Mt-CO2 per year. The proposed novel âPEI-CFB air capture systemâ mainly comprises a Circulating Fluidized Bed (CFB) adsorber and a BFB desorber with a CO2 capture capacity of 40 t-CO2/day. Large pressure drop is required to drive the air through the CFB adsorber and also to suspend and circulate the solid adsorbents within the loop, resulting in higher electricity demand than other reported air capture systems. However, the Temperature Swing Adsorption (TSA) technology adopted for the regeneration strategy in the separate BFB desorber has resulted in much smaller thermal energy requirement. The total energy required is 6.6 GJ/t-CO2 which is comparable to other reference air capture systems. By projecting a future scenario where decarbonization of large point energy sources has been largely implemented by integration of CCS technologies, the operating cost under this scenario is estimated to be 152/t-CO2 avoided with an avoided fraction of 0.71. Further research on the proposed 40 t-CO2/day âPEI-CFB Air Capture Systemâ is still needed which should include the evaluation of the capital costs and the experimental investigation of air capture using a laboratory-scale CFB system with the PEIâsilica adsorbent
Preparation of carbon dioxide adsorbents from the chemical activation of ureaâformaldehyde and melamineâformaldehyde resins
10 pages, 4 figures, 3 tables.-- Available online Aug 14, 2006.Adsorption is considered to be one of the more promising technologies for the capture of CO2 from flue gases. In general, nitrogen enrichment is reported to be effective in enhancing the specific adsorbentâadsorbate interaction for CO2. Nitrogen enriched carbons were produced from ureaâformaldehyde and melamineâformaldehyde resins polymerised in the presence of K2CO3 as a chemical activation agent, with activation undertaken over a range of temperatures. CO2 adsorption capacity was determined to be dependent upon both textural properties and more importantly nitrogen functionality. Adsorbents capable of capturing above 8 wt.% CO2 at 25°C were produced from the chemical activation of ureaâformaldehyde resin at 500°C. Chemical activation seems to produce more effective adsorbents than CO2 activation.The authors are grateful for support for this work provided by the Research Fund for Coal and Steel (RFC-CR-03008) and for CP a grant from Plan I + D + I Gobierno del Principado de Asturias.Peer reviewe
Performance of polyethyleneimineâsilica adsorbent for post-combustion CO2 capture in a bubbling fluidized bed
The high performance of polyethyleneimine (PEI)-based solid adsorbent for CO2 capture has been well recognized in thermogravimetric analysis (TGA) and small-scale fixed bed reactors through the measurements of their equilibrium capacities but has not been really demonstrated on larger scales towards practical utilization. In the present study, a laboratory-scale bubbling fluidized bed reactor loaded with a few kg adsorbent is used to evaluate the adsorption performance of PEIâsilica adsorbent under different working conditions including with/without the presence of moisture, different gasâsolid contact times, initial bed temperatures, and CO2 partial pressures. The adsorption capacities have shown a clear degradation tendency under dry condition. However, they can be stabilized at a high level of 10.6â11.1% w/w over 60 cycles if moisture (ca. 8.8 vol%) is present in the gas flow during adsorption and desorption. Breakthrough capacities can be stabilized at the level of 7.6â8.2% w/w with the gasâsolid contact time of 13 s. The adsorption capacities for the simulated flue gases containing 5% CO2 are only slightly lower than those for the simulated flue gases containing 15% CO2, indicating that the PEIâsilica adsorbent is suitable for CO2 capture from flue gases of both coal-fired and natural gas-fired combined cycle power plants. The exothermal heat of adsorption is estimated by the energy balance in the fluidized bed reactor and found to be close (within 10%) to the measured value by TG-DSC. The regeneration heat for the as prepared PEIâsilica adsorbent is found to be 2360 kJ/kgCO2 assuming 75% recovery of sensible heat which is well below the values of 3900â4500 kJ/kgCO2 for a typical MEA scrubbing process with 90% recovery of sensible heat
Preparation and CO2 adsorption of amine modified Mg-Al LDH via exfoliation route
In response to the recent focus on reducing carbon dioxide emission, the preparation and characterization of organically functionalized materials for use in carbon capture have received considerable attention. In this paper the synthesis of amine modified layered double hydroxides (LDHs) via an exfoliation and grafting synthetic route is reported. The materials were characterized by elemental analysis (EA), powder x-ray diffraction (PXRD), diffuse reflectance infrared Fourier transform spectrometer (DRIFTS) and thermogravimetric analysis (TGA). Adsorption of carbon dioxide on modified layered double hydroxides was investigated by TGA at 25â80 °C. 3-[2-(2-Aminoethylamino) ethylamino]propyl-trimethoxysilane modified MgAl LDH showed a maximum CO2 adsorption capacity of 1.76 mmol gâ1 at 80 °C. The influence of primary and secondary amines on carbon dioxide adsorption is discussed. The carbon dioxide adsorption isotherms presented were closely fitted to the Avrami kinetic model
Templated polymeric materials as adsorbents for the postcombustion
Increasing awareness of the influence of greenhouse gases on global climate change has led to recent efforts to develop strategies for the reduction of carbon dioxide (CO2) emissions. The strategy that is
receiving the most attention involves the capture of CO2 from large point sources (such as fossil fuelfired power plants) and long-term storage underground or in the ocean. Aqueous solutions of amines have long been used by industry as absorbents for acid gas (CO2, H2S) removal. However, they have
a number of shortcomings for treating flue gases. As an alternative, adsorption is considered to be a promising technologies for capturing CO2 from flue gases, with the potential to overcome the problems
associated with liquid amines.The EPSRC Advanced Research Fellowship EP/C543203/1Peer reviewe
Developing strategies for the regeneration of polyethylenimine based CO2 adsorbents
Adsorption is considered to be one of the more promising technologies for capturing CO2 from flue gases. The efficient adsorption of CO2 at low partial pressures, associated with post-combustion capture, require chemical type adsorbents containing basic amine functional groups. It has been
demonstrated that amine polymers, for example polyethylenimine (PEI), immobilised on various porous substrates, silica, zeolites and fly ash, are effective adsorbents for CO2. When considering the use of adsorption for large scale CO2 capture, the ease of regeneration and the lifetime of the adsorbents are critical factors in determining their efficiency, cost and therefore feasibility for use. In this paper two approaches, thermal swing adsorption (TSA) cycles over a range of temperatures and time in an atmosphere of CO2 and thermally assisted pressure swing desorption, are explored for the regeneration of the PEI based adsorbents.The Carbon Trust and EPSRC (Advanced
Research Fellowship EP/C543201/1)Peer reviewe
Silica-templated melamineâformaldehyde resin derived adsorbents for CO2 capture
11 pages, 4 figures, 4 tables.-- Printed version published Sep 2008Adsorption on porous solids is an emerging alternative for CO2 capture that seeks to reduce the costs associated to the capture step. The enhancement of a specific adsorption capacity may be carried out by increasing the affinity of the adsorbent surface to CO2. Nitrogen enrichment is reported to be effective in introducing basic functionalties that enhances the specific adsorbentâadsorbate interaction for CO2. In this work a templating technique was used to produce highly porous nitrogen enriched carbons from melamineâformaldehyde resins. Nitrogen incorporated into the polymer matrix results in the greater stability of the adsorbents in terms of volatile and thermal loss of nitrogen. CO2 capture performances were evaluated between 25°C and 75°C in a thermobalance. CO2 adsorption capacities up to 2.25 mmol gâ1 of CO2 at 25°C were achieved. Both texture and surface chemistry influence the CO2 capture performance of the adsorbents. The carbonisation temperature used during the synthesis step controls the nitrogen functional groups present, as determined by XPS, with the loss of triazine nitrogen with increasing carbonisation temperature proposed to account for the decreased CO2 affinity.CP acknowledges a postdoctoral fellowship from the Plan I+D+I â Gobierno del Principado de Asturias. TCD would like to thank the EPSRC for funding this research (EPSRC Advanced Research Fellowship EP/C543203/1). The authors would also like to thank Emily Smith for the XPS analysis.Peer reviewe
Bark decay by the white-rot fungas Lentinula edodes : polysaccharide loss, lignin resistance and the unmasking of suberin
The chemical composition of oak bark during growth of Lentinula edodes was studied to assess the transformation of lignin, suberin, tannin and structural polysaccharides. Oak logs (Quercus alba) were decayed by L. edodes over 8 years, during which time they were sampled at five intervals (30, 40, 66, 77, 101 months). Elemental analysis (C, H, N and O), solid-state 13C NMR as well as off-line thermochemolysis in the presence of tetramethylammonium hydroxide (TMAH) with gas chromatography-mass spectrometry were used in the characterization of fresh and degraded barks. Solid-state 13C NMR analysis showed that cellulose and xylans were the main structural components of fresh bark but that L. edodes caused a 46% decrease in polysaccharide content and that loss of crystalline and non-crystalline cellulose regions occurred in parallel. The decrease in cellulose content was accompanied by a relative increase in the proportion of methylene carbon from suberin. The aromatic region of the spectra revealed a loss of a shoulder at 145 ppm attributed to tannins after 30 months decay; in contrast the aromatic content remained unaltered, suggesting that highly structured tannins were degraded in preference to lignin. Chemolytic treatment with TMAH confirmed moderate changes in guaiacyl and syringyl acid-aldehyde ratios with growth indicating that the fungus had not caused extensive oxidative side chain alterations. The ratio of syringyl to guaiacyl units (S/G) in fresh oak bark was lower at 0.6 than that previously reported for oak sapwood (S/G>1) and a slight decrease in S/G values was observed with fungal decay. The resistance of bark lignin as compared to sapwood lignin is attributed in part to the inhibiting effect of tannins and suberin on fungal growth