Capturing CO2 from ambient air using a polyethyleneimine–silica 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)–silica 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 PEI–silica 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 gas–solid 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 PEI–silica adsorbent to capture CO2 from ambient air at a large scale of capturing 1 Mt-CO2 per year. The proposed novel “PEI-CFB air capture system” 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 $108/t-CO2 captured and$152/t-CO2 avoided with an avoided fraction of 0.71. Further research on the proposed 40 t-CO2/day ‘PEI-CFB Air Capture System’ 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 PEI–silica adsorbent

Association between Organochlorine Pesticides and Vitamin D in Female Subjects

In human population studies, organochlorine pesticides (OCPs) have been linked to vitamin D deficiency. Therefore, this study examined the association between OCPs, vitamin D3 (cholecalciferol, 25(OH)D3), and the active metabolite 1,25-dihydrovitamin D3 (1,25(OH)2D3) in a cohort of non-obese women. The serum samples of 58 female participants (age—31.9 ± 4.6 years; body mass index (BMI)—25.7 ± 3.7 kg/m2) were screened for 10 indicator OCPs. 25(OH)D3 and 1,25(OH)2D3 levels were determined via isotope dilution liquid chromatography tandem mass spectrometry. In this cohort, the 25(OH)D3 and 1,25(OH)2D3 levels were 22.9 ± 11.2 ng/mL and 0.05 ± 0.02 ng/mL, respectively, with 28 participants classified as 25(OH)D3-deficient (<50 nmol/L). In the study cohort, no correlations were found between individual or total OCPs (ƩOCPs) and 25(OH)D3. p,p′-dichlorodiphenyldichloroethylene (DDE) and ƩOCPs correlated positively with 1,25(OH)2D3, with the latter being negatively correlated with estimated glomerular filtration rate (eGFR). In women with sufficient 25(OH)D3 levels, p,p′-dichlorodiphenyltrichloroethan (DDT) was positively correlated with 1,25(OH)2D3, whilst in the deficient group, hexachlorobenzene (HCB) and p,p′-(DDE) were positively correlated with 1,25(OH)2D3, β-Hexachlorocyclohexane (HCH) was positively correlated with 25(OH)D3, and none of the OCPs were associated with measures of renal function. Overall, OCPs and ƩOCPs were not associated with 25(OH)D3, suggesting that they are unrelated to vitamin D deficiency, but p,p′-DDE and ƩOCPs correlated positively with active 1,25(OH)2D3, while ƩOCPs correlated negatively with eGFR, suggesting a possible renal effect. Analysis of vitamin D deficiency revealed an association between β-HCH and 25(OH)D3, and between HCB and p,p′-DDE and 1,25(OH)2D3, suggesting that OCP effects may be enhanced in cases of vitamin D deficiency

Serum polychlorinated biphenyl levels and circulating miRNAs in non-obese women with and without polycystic ovary syndrome

IntroductionPolychlorinated biphenyls (PCBs), organic lipophilic pollutants that accumulate through diet and increase with age, have been associated with polycystic ovary syndrome (PCOS) and shown to affect microRNA (miRNA) expression. This work aimed to determine if PCBs were associated with circulating miRNAs and whether there were any correlations with serum PCB/miRNA levels and hormonal changes.Methods29 non-obese PCOS and 29 healthy control women, with similar age and body mass index (BMI), had their serum miRNAs measured together with 7 indicator PCBs (PCB28, PCB52, PCB101, PCB118, PCB138, PCB153, PCB180) using high resolution gas chromatography coupled with high resolution mass spectrometry.ResultsIn the combined study cohort, four miRNAs (hsa-miR-139-5p, hsa-miR-424-5p, hsa-miR-195-5p, hsa-miR-335-5p) correlated with PCBs, but none correlated with metabolic parameters. hsa-miR-335-5p correlated with FSH. When stratified, 25 miRNAs correlated with PCBs in controls compared to only one (hsa-miR-193a-5p) in PCOS; none of these miRNAs correlated with the metabolic parameters of BMI, insulin resistance, or inflammation (C-reactive protein, CRP). However, of these 25 miRNAs in controls, hsa-miR-26a-5p, hsa-miR-193a-5p, hsa-miR-2110 and hsa-miR-195-5p positively correlated with luteinizing hormone (LH), hsa-miR-99b-5p and hsa-miR-146b-5p correlated with estradiol, hsa-miR-193a-5p correlated with progesterone, hsa-miR-195-5p correlated with follicle stimulating hormone (FSH), and hsa-miR-139-5p and hsa-miR-146b-5p negatively correlated with anti-müllerian hormone (AMH) (all p&lt;0.05). hsa-miR-193a-5p in PCOS cases correlated with estradiol.ConclusionIn this cohort of women, with no difference in age and BMI, and with similar PCB levels, the miRNAs correlating to PCBs associated with menstrual cycle factors in healthy menstruating controls versus the anovulatory PCOS subjects. The PCB-associated miRNAs did not correlate with non-reproductive hormonal and metabolic parameters. This suggests that PCB effects on miRNAs may result in changes to the hypothalamo-ovarian axis that may thus affect fertility

Perspectives on local government’s place in federal systems and central–local relations

To expand on the themes identified by Tomas Hachard’s paper 'Capacity, voice and opportunity: advancing municipal engagement in Canadian federal relations', the Journal commissioned six personal ‘perspectives’ from a diverse group of other Commonwealth countries – Australia, India, New Zealand, Nigeria, South Africa and the United Kingdom. This replicated the model adopted in Issue 26 for Zack Taylor’s paper on 'Regionalism from above: intergovernmental relations in Canadian metropolitan governance'. Similarly, the purpose was to establish a broader picture of issues and trends across the Commonwealth, rather than ‘review’ Hachard’s work

Performance of polyethyleneimine–silica 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 PEI–silica adsorbent under different working conditions including with/without the presence of moisture, different gas–solid 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 10.6–11.1% 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 7.6–8.2% w/w with the gas–solid 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 PEI–silica 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 PEI–silica adsorbent is found to be 2360 kJ/kgCO2 assuming 75% recovery of sensible heat which is well below the values of 3900–4500 kJ/kgCO2 for a typical MEA scrubbing process with 90% recovery of sensible heat

Preparation of carbon dioxide adsorbents from the chemical activation of urea–formaldehyde and melamine–formaldehyde 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 adsorbent–adsorbate interaction for CO2. Nitrogen enriched carbons were produced from urea–formaldehyde and melamine–formaldehyde 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 urea–formaldehyde 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

Parametric study on the regeneration heat requirement of an amine-based solid adsorbent process for post-combustion carbon capture

The thermal energy required for regeneration of CO2-rich adsorbents or absorbents is usually regarded as the most important criterion to evaluate different materials and processes for application in commercialscale CO2 capture systems. It is expected that the regeneration heat can be greatly reduced by replacing the mature aqueous monoethanolamine (MEA) technology with amine-based solid adsorbents capturing systems, due to the much lower heat capacity of solid adsorbents comparing to aqueous MEA and the avoidance of evaporating a large amount of water in the regenerator. Comparing to the MEA technology, the regeneration heat for solid adsorbent based systems has not received adequate attention especially on the impacts of process related parameters. Further, the methodologies used in previous investigations to calculate the regeneration heat may have deficiencies in defining the working capacities, adopting proper heat recovery strategies and/or evaluating the effect of moisture co-adsorption. In this study, an energy equation to calculate the regeneration heat has been revised and proposed to systematically evaluate the most important parameters affecting the regeneration heat, including the physical properties of the adsorbents and process related variables including the heat of adsorption, specific heat capacity, working capacity, moisture adsorption of the polyethyleneimine (PEI)/silica adsorbent, the swing temperature difference and the degree of heat recovery. Based on the parametric analysis, the calculated regeneration heat for the PEI/silica adsorbent based system is found to be around 2.46 GJ/tCO2, which is much lower than the value of 3.9 GJ/tCO2 for a typical aqueous MEA system and is also lower than 3.3 GJ/tCO2 for an advanced MEA system. Sensitivity analysis of all the parameters has also been conducted and the results have shown that working capacity, moisture adsorption and heat recovery ratios are the most influential factors. With more proficiency and development in the energy efficient process designs, the advantages of a solid adsorbent based capturing system over typical MEA systems will be justified