Low CO2 Partial Pressure Research Articles

Tailoring of water swollen PVA membrane for hosting carriers in CO2 facilitated transport membranes

Abstract Facilitated transported composite membranes were synthesized for efficient CO2/N2 separation by incorporation surface modified multi-walled carbon nanotubes (CNTs) in polyvinyl alcohol (PVA) and adjusting the pH of the membrane casting solution from acidic to basic. The membranes were developed for post-combustion CO2 capture operating under humidified condition and low CO2 partial pressure. The membrane was tailored by adding different concentrations of surface modified CNTs (0–2%) with respect to PVA and adjusting pH from 5 to 12. An optimal CNT loading along with membrane pH was determined based on experimental results from gas permeation tests. By optimizing the CNT loading and pH of the membrane, the CO2 permeance was increased from 0.18 ± 0.02 m3 (STP)/m2 bar h to 0.44 ± 0.02 m3 (STP)/m2 bar h at a constant CO2/N2 selectivity of 60 ± 1. The membrane swelling degree was also increased from 154 ± 20 to 254 ± 30. The thickness of the selective layer was reduced from ∼0.85 µm to 0.45 µm which resulted in further increase in permeance to 0.48 m3 (STP)/m2 bar h. The developed membrane showed a stable operation over a period of 1 month.

Monitoring instability of linear amine impregnated UiO-66 by in-situ temperature resolved powder X-ray diffraction

Carbon dioxide capture requires stable porous solids like zirconium based metal-organic frameworks (MOFs) in order to make sequestration efforts feasible. Because of the weak binding at low CO2 partial pressures, oligomeric amines are commonly loaded on porous supports to maximize CO2 capture while attempting to keep porosity for enhanced diffusion. Here we show the first temperature resolved stability study of linear-amine impregnated UiO-66 by in-situ monitoring of the PXRD pattern. Our findings show that the crystal structure shows a contraction at temperatures as low as 80 °C and deforms considerably above 120 °C, leading to significant doubts about their applicability in CO2 capture from lean feeds. We confirm that all MOFs need to be thoroughly analyzed at least by means of PXRD at the process relevant temperatures, and reinforced before any plausible plans of application in CO2 capture.

Derivation of Kinetics and Design Parameters for a Carbonator Reactor in a Greenhouse Calcium Looping Process

AbstractThe carbonation/calcination reaction cycle of a limestone sorbent was studied experimentally by using a thermogravimetric analyzer for unique conditions, such as low temperature (400 to 500 °C) and low CO2 partial pressure (0.05 to 0.1 %), pertinent to a novel greenhouse calcium looping process. The kinetic parameters were obtained and compared with those reported in the literature. Various gas–solid reaction mechanisms were considered to determine the best reaction mechanism for the carbonation reaction. The diffusion function, or G(x)=x2, had the best least‐squares linear fit, which resulted in a first‐order reaction for the carbonation reaction in the greenhouse calcium looping process. Moreover, the activation energy and pre‐exponential factor of the carbonation reaction were established to be 19.7 kJ mol−1 and 295.8 min−1 kPa−1, respectively. The derived kinetic parameters were used in Aspen Plus to optimize the carbonator reactor size. The required size of the reactor decreased with increasing operating temperature of the reactor. Exergy analysis revealed that the overall exergetic efficiency of greenhouse calcium looping could be more than 80 %.

Low Hesperian PCO2 constrained from in situ mineralogical analysis at Gale Crater, Mars

Carbon dioxide is an essential atmospheric component in martian climate models that attempt to reconcile a faint young sun with planetwide evidence of liquid water in the Noachian and Early Hesperian. In this study, we use mineral and contextual sedimentary environmental data measured by the Mars Science Laboratory (MSL) Rover Curiosity to estimate the atmospheric partial pressure of CO2 (PCO2) coinciding with a long-lived lake system in Gale Crater at ∼3.5 Ga. A reaction-transport model that simulates mineralogy observed within the Sheepbed member at Yellowknife Bay (YKB), by coupling mineral equilibria with carbonate precipitation kinetics and rates of sedimentation, indicates atmospheric PCO2 levels in the 10s mbar range. At such low PCO2 levels, existing climate models are unable to warm Hesperian Mars anywhere near the freezing point of water, and other gases are required to raise atmospheric pressure to prevent lake waters from being lost to the atmosphere. Thus, either lacustrine features of Gale formed in a cold environment by a mechanism yet to be determined, or the climate models still lack an essential component that would serve to elevate surface temperatures, at least locally, on Hesperian Mars. Our results also impose restrictions on the potential role of atmospheric CO2 in inferred warmer conditions and valley network formation of the late Noachian.

An Experimental Study of the Formation of Talc through CaMg(CO3)2–SiO2–H2O Interaction at 100–200°C and Vapor-Saturation Pressures

The metamorphic interaction between carbonate and silica-rich fluid is common in geological environments. The formation of talc from dolomite and silica-rich fluid occurs at low temperatures in the metamorphism of the CaO–MgO–SiO2–CO2–H2O system and plays important roles in the formation of economically viable talc deposits, the modification of dolomite reservoirs, and other geological processes. However, disagreement remains over the conditions of talc formation at low temperatures. In this study, in situ Raman spectroscopy, quenched scanning electron microscopy, micro-X-ray diffraction, and thermodynamic calculations were used to explore the interplay between dolomite and silica-rich fluids at relatively low temperatures in fused silica tubes. Results showed that talc formed at ≤200°C and low CO2partial pressures (PCO2). The reaction rate increased with increasing temperature and decreased with increasingPCO2. The major contributions of this study are as follows:(1)we confirmed the formation mechanism of Mg-carbonate-hosted talc deposits and proved that talc can form at ≤200°C;(2)the presence of talc in carbonate reservoirs can indicate the activity of silica-rich hydrothermal fluids; and (3) the reactivity and solubility of silica require further consideration, when a fused silica tube is used as the reactor in highP–Texperiments.

Photosynthetic induction and its diffusional, carboxylation and electron transport processes as affected by CO2 partial pressure, temperature, air humidity and blue irradiance.

Plants depend on photosynthesis for growth. In nature, factors such as temperature, humidity, CO2 partial pressure, and spectrum and intensity of irradiance often fluctuate. Whereas irradiance intensity is most influential and has been studied in detail, understanding of interactions with other factors is lacking. We tested how photosynthetic induction after dark-light transitions was affected by CO2 partial pressure (20, 40, 80 Pa), leaf temperatures (15·5, 22·8, 30·5 °C), leaf-to-air vapour pressure deficits (VPDleaf-air; 0·5, 0·8, 1·6, 2·3 kPa) and blue irradiance (0-20%) in tomato leaves (Solanum lycopersicum). Rates of photosynthetic induction strongly increased with CO2 partial pressure, due to increased apparent Rubisco activation rates and reduced diffusional limitations. High leaf temperature produced slightly higher induction rates, and increased intrinsic water use efficiency and diffusional limitation. High VPDleaf-air slowed down induction rates and apparent Rubisco activation and (at 2·3 kPa) induced damped stomatal oscillations. Blue irradiance had no effect. Slower apparent Rubisco activation in elevated VPDleaf-air may be explained by low leaf internal CO2 partial pressure at the beginning of induction. The environmental factors CO2 partial pressure, temperature and VPDleaf-air had significant impacts on rates of photosynthetic induction, as well as on underlying diffusional, carboxylation and electron transport processes. Furthermore, maximizing Rubisco activation rates would increase photosynthesis by at most 6-8% in ambient CO2 partial pressure (across temperatures and humidities), while maximizing rates of stomatal opening would increase photosynthesis by at most 1-3%.

Effect of sodium houttuyfonate on symptom pattern of lung-Qi deficiency in rats induced by bacterialbiofilm infection

OBJECTIVETo investigate the in vivo inhibitory effects of sodium houttuyfonate (SH) on symptom pattern of Qi-deficiency in rats induced by infection of bacterial biofilm on rat respiratory tract. METHODSSymptom pattern is a term used in Traditional Chinese Medicine (TCM) to define a cluster of symptoms in a medical condition. Based on the pattern, TCM therapies are administered. The symptom pattern used in this study was lung-Qi deficiency pattern identified in rats, which was induced by nasal intubation drip of Pseudomonas aeruginosa (P. aeruginosa) (two strains) to form bacterial biofilm on airway combined with stimulation of cold and fatigue. We measured the variations of the symptoms of the pattern, weight, spleen and thymus index, blood gas, lung bronchial tissue pathology and cytokine of rat in different treatments and control groups. RESULTSThe rats of SH-treatment groups had not showed typical symptoms comparing with model group in the early stage of infection. The weight, spleen and thymus index of the SH-treatment groups were significantly higher comparing with untreated model group. The SH-treatment groups also showed higher O2 partial pressure and lower CO2 partial pressure than model group. Furthermore, we found that the bronchopulmonary section of SH-treatment groups not showed typical pathogenic variation in model group. The comparison of cytokine concentration in different groups indicated that SH could prevent the over-production of cytokine to reduce the inflammation occurrence. CONCLUSIONIn the early stage of airway infection by biofilm of P. aeruginosa, application of SH can prevent the occurrence of lung-Qi deficiency pattern.

Supported lithium hydroxide for carbon dioxide adsorption in water-saturated environments

Rebreather-type personal protective equipment requires efficient removal of CO2 from the air that the user exhales. The required operating conditions of low CO2 partial pressure, low temperature, and water saturation create a challenging environment for developing high capacity CO2 adsorbents. Biphasic adsorbents of lithium hydroxide supported on high surface area carbons were synthesized and tested for CO2 capacity under water-saturated conditions. The LiOH phase provides high CO2 capacity through chemisorption while the porous carbon structure helps prevent the formation of diffusion barriers that limit the effectiveness of pure LiOH pellets. Several carbons with different pore morphology were tested, and it was determined that the ideal support has a high degree of mesoporosity that balances the need for high surface area without excess blockage of pore volume upon deposition of LiOH. The activated carbon Norit SX Ultra was chosen based on this criterion. It was found that the maximum achievable loading of LiOH on Norit SX Ultra was 30 wt%, and the highest CO2 capacity under water-saturated conditions at atmospheric pressure with one mole percent CO2 in the gas phase was 3.4 mol/kg.

Oxidation of P700 in Photosystem I Is Essential for the Growth of Cyanobacteria.

The photoinhibition of photosystem I (PSI) is lethal to oxygenic phototrophs. Nevertheless, it is unclear how photodamage occurs or how oxygenic phototrophs prevent it. Here, we provide evidence that keeping P700 (the reaction center chlorophyll in PSI) oxidized protects PSI. Previous studies have suggested that PSI photoinhibition does not occur in the two model cyanobacteria, Synechocystis sp. PCC 6803 and Synechococcus elongatus PCC 7942, when photosynthetic CO2 fixation was suppressed under low CO2 partial pressure even in mutants deficient in flavodiiron protein (FLV), which mediates alternative electron flow. The lack of FLV in Synechococcus sp. PCC 7002 (S. 7002), however, is linked directly to reduced growth and PSI photodamage under CO2-limiting conditions. Unlike Synechocystis sp. PCC 6803 and S. elongatus PCC 7942, S. 7002 reduced P700 during CO2-limited illumination in the absence of FLV, resulting in decreases in both PSI and photosynthetic activities. Even at normal air CO2 concentration, the growth of S. 7002 mutant was retarded relative to that of the wild type. Therefore, P700 oxidation is essential for protecting PSI against photoinhibition. Here, we present various strategies to alleviate PSI photoinhibition in cyanobacteria.

Reduced plant water status under sub-ambient pCO2 limits plant productivity in the wild progenitors of C3 and C4 cereals.

The reduction of plant productivity by low atmospheric CO2 partial pressure (pCO2) during the last glacial period is proposed as a limiting factor for the establishment of agriculture. Supporting this hypothesis, previous work has shown that glacial pCO2 limits biomass in the wild progenitors of C3 and C4 founder crops, in part due to the direct effects of glacial pCO2 on photosynthesis. Here, we investigate the indirect role of pCO2 mediated via water status, hypothesizing that faster soil water depletion at glacial (18 Pa) compared to post-glacial (27 Pa) pCO2, due to greater stomatal conductance, feeds back to limit photosynthesis during drying cycles. We grew four wild progenitors of C3 and C4 crops at glacial and post-glacial pCO2 and investigated physiological changes in gas exchange, canopy transpiration, soil water content and water potential between regular watering events. Growth parameters including leaf area were measured. Initial transpiration rates were higher at glacial pCO2 due to greater stomatal conductance. However, stomatal conductance declined more rapidly over the soil drying cycle in glacial pCO2 and was associated with decreased intercellular pCO2 and lower photosynthesis. Soil water content was similar between pCO2 levels as larger leaf areas at post-glacial pCO2 offset the slower depletion of water. Instead the feedback could be linked to reduced plant water status. Particularly in the C4 plants, soil-leaf water potential gradients were greater at 18 Pa compared with 27 Pa pCO2, suggesting an increased ratio of leaf evaporative demand to supply. Reduced plant water status appeared to cause a negative feedback on stomatal aperture in plants at glacial pCO2, thereby reducing photosynthesis. The effects were stronger in C4 species, providing a mechanism for reduced biomass at 18 Pa. These results have added significance when set against the drier climate of the glacial period.

Electrochemical and Surface Analysis Studies on the Carbon Dioxide Corrosion of X‐65 Carbon Steel

AbstractA comprehensive study of the CO2 corrosion of carbon steel (X‐65) at low partial pressures of CO2 is reported in this paper. Field emission scanning electron microscopy (FESEM), Raman spectroscopy (RS), synchrotron radiation‐grazing incidence X‐ray diffraction (SR‐GIXRD), and electrode kinetic studies have confirmed that chukanovite, magnetite and siderite are the main corrosion products at low partial pressures of CO2. Chukanovite forms predominantly in the presence of CO2, while magnetite was found to be the major corrosion product in the absence of CO2, although the majority of previous work based on conventional ex‐situ materials characterization techniques has implied that siderite is the main corrosion product. Here, it is shown that the nature of corrosion products is strongly dependent on the experimental conditions at low pressures of CO2, which has not been elucidated in previous studies. Accordingly, this study has made a significant contribution to identifying the true nature of corrosion scales formed at low partial pressures of CO2 allowing the development of effective anti‐corrosive agents for the control and prevention of carbon steel corrosion at low CO2 partial pressures.

Trolox-equivalent antioxidant capacity and composition of five alpine plant species growing at different elevations on the Qinghai–Tibetan Plateau

Background: Alpine plants on the Qinghai–Tibetan Plateau are exposed to an extremely harsh environment, namely severe cold, strong ultraviolet radiation, hypoxia and low CO2 partial pressure. These conditions are sources of oxidative stress, which increase in severity with increasing elevation.Aims: To examine whether antioxidant capacity and chemical composition of alpine plants change with increasing elevation.Methods: We measured the Trolox-equivalent antioxidant capacity (TEAC) and chemical composition of five alpine plant species at 3016, 3814 and 4621 m a.s.l.Results: With increasing elevation: (1) the TEAC increased and total phenols and tannins tended to increase in two forb and two shrub species but not in a sedge species; (2) concentrations of protein and fat increased in all five plant species; (3) polyunsaturated fatty acids (PUFA) increased and (4) mineral concentrations tended to decrease, but trends were inconsistent.Conclusions: We conclude that with increasing elevation, TEAC and total phenols and tannins increased which we interpreted as an adaptation to higher oxidative stress; and protein and fat contents increased to support high metabolic activity. The increase in PUFA and the trend for minerals to decrease with increasing elevation require further investigation.

Direct Evidence of CO2 Capture under Low Partial Pressure on a Pillared Metal-Organic Framework with Improved Stabilization through Intramolecular Hydrogen Bonding.

Direct structural observation of CO2 -loaded MOFs is helpful for revealing the specific binding interactions to allow the design of better CO2 sorbents, but such direct structural evidence is almost always observed for pure-component CO2 under a pressure of 1 atm or more, which does not really represent practical CO2 capture and separation under low partial pressure (≤1 atm) in the presence of other gases. Herein, a series of isoreticular MOFs [Zn(Trz)(R-BDC)1/2 ] (FJU-40-R, R=H, NH2 , Br, or OH) are synthesized. Among them, FJU-40-NH2 exhibits the highest robustness, and good heat and water resistance, attributed to its intramolecular hydrogen-bonding interactions. A CO2 /N2 (15:85, v/v) mixture can be separated efficiently through a column packed bed of FJU-40-NH2 solid. The structures of CO2 -loaded FJU-40-NH2 at 1 atm under various atmosphere conditions, including pure CO2 , CO2 /N2 (15:85, v/v), and air, are observed, and it is found that: 1) the mechanism for CO2 loading into the cages depends on the CO2 partial pressure; 2) FJU-40-NH2 can capture CO2 directly from air, and CO2 will have priority to occupy hydrophobic cage-I, whereas hydrophilic cage-II containing the amino group is occupied by H2 O molecules; 3) the triazolate C-H groups, rather than the amino groups in past observations in dry ice, act as predominant functional sites here under low CO2 partial pressure.

Enhanced CO2 Adsorption Using MgO-Impregnated Activated Carbon: Impact of Preparation Techniques

The development of a facile and sustainable approach to produce magnesium oxide (MgO) activated carbons impregnated through a single-step activation of biochar is reported. In a single-step activation process, biochar is impregnated with 3 and 10 wt % of magnesium salt solutions followed by steam activation. In a two-step method, activated carbon, the product of steam activation of biochar, is impregnated with magnesium salt using the incipient wetness and excess solution impregnation process and calcined. The impacts of activation method, impregnation method, and metal content are evaluated, and the product qualities are compared in terms of porosity and surface chemistry. The sorbents are then used for CO2 capture in low partial pressure of CO2 at 25 and 100 °C from a feed containing 15% CO2 in N2 in a fixed-bed reactor. The incipient wetness of activated carbons results in the highest CO2 uptake (49 mg/g) at 25 °C, while single-step impregnation of biochar with rinsing step yields the largest surface a...

Experimental testing of a sorbent reactivation process in La Pereda 1.7 MWth calcium looping pilot plant

Calcium looping for post-combustion CO2 capture with low-cost natural sources of CaO as CO2 regenerable sorbent has already demonstrated its high technical and economic viability in several large-scale pilot plants. However, there is still scope for reducing the energy requirements of these systems by increasing the modest CO2 carrying capacity of highly cycled particles without compromising the equipment and sorbent costs. This work presents the results obtained from a series of experimental campaigns carried out in La Pereda 1.7 MWth pilot plant to test a novel reactivation process based on the “recarbonation” principle, where the CO2 carrying capacity of the sorbent is enhanced by placing the carbonated solid stream coming from the carbonator reactor in contact with concentrated CO2. For this purpose, several modifications were introduced into the pilot plant so that an existing loop seal could operate as the new recarbonator reactor. In the experiments carried out under the new operating regime, a clear improvement in CO2 carrying capacity was observed with respect to tests conducted without recarbonation. The effect of the recarbonator reactor temperature and CO2 partial pressure on the performance of the reactor was found to be critical: negligible levels of sorbent improvement were achieved at recarbonation temperatures below 750°C and low partial pressures of CO2. In contrast, the CO2 carrying capacity increased by up to 10 net percentage points under strong recarbonation conditions, providing that the solids were allowed sufficient residence time inside the loop seal acting as recarbonator reactor.

AltitudeOmics: Resetting of Cerebrovascular CO2 Reactivity Following Acclimatization to High Altitude.

Previous studies reported enhanced cerebrovascular CO2 reactivity upon ascent to high altitude using linear models. However, there is evidence that this response may be sigmoidal in nature. Moreover, it was speculated that these changes at high altitude are mediated by alterations in acid-base buffering. Accordingly, we reanalyzed previously published data to assess middle cerebral blood flow velocity (MCAv) responses to modified rebreathing at sea level (SL), upon ascent (ALT1) and following 16 days of acclimatization (ALT16) to 5260 m in 21 lowlanders. Using sigmoid curve fitting of the MCAv responses to CO2, we found the amplitude (95 vs. 129%, SL vs. ALT1, 95% confidence intervals (CI) [77, 112], [111, 145], respectively, P = 0.024) and the slope of the sigmoid response (4.5 vs. 7.5%/mmHg, SL vs. ALT1, 95% CIs [3.1, 5.9], [6.0, 9.0], respectively, P = 0.026) to be enhanced at ALT1, which persisted with acclimatization at ALT16 (amplitude: 177, 95% CI [139, 215], P < 0.001; slope: 10.3%/mmHg, 95% CI [8.2, 12.5], P = 0.003) compared to SL. Meanwhile, the sigmoidal response midpoint was unchanged at ALT1 (SL: 36.5 mmHg; ALT1: 35.4 mmHg, 95% CIs [34.0, 39.0], [33.1, 37.7], respectively, P = 0.982), while it was reduced by ~7 mmHg at ALT16 (28.6 mmHg, 95% CI [26.4, 30.8], P = 0.001 vs. SL), indicating leftward shift of the cerebrovascular CO2 response to a lower arterial partial pressure of CO2 (PaCO2) following acclimatization to altitude. Sigmoid fitting revealed a leftward shift in the midpoint of the cerebrovascular response curve which could not be observed with linear fitting. These findings demonstrate that there is resetting of the cerebrovascular CO2 reactivity operating point to a lower PaCO2 following acclimatization to high altitude. This cerebrovascular resetting is likely the result of an altered acid-base buffer status resulting from prolonged exposure to the severe hypocapnia associated with ventilatory acclimatization to high altitude.

Modified atmosphere generated during storage under light conditions is the main factor responsible for the quality changes of baby spinach

Minimally processed products are generally exposed to low temperature and uncontrolled light conditions during the supply chain. The positive effect of low temperature on quality of baby spinach is widely reported, but there is little information available about the light effect. The objective of this study was to obtain insight about the cause-effect of light exposure of baby spinach on leaf quality and senescence parameters. Minimally processed baby spinach was stored in passive Modified Atmosphere Packaging (MAP) and in Controlled Atmosphere (CA) under different light conditions. In passive MAP, three very different headspace gas compositions within the bags due to photosynthesis and respiration reactions were generated that strongly affected the quality characteristics. To isolate the light effect from the atmosphere composition influence, and thus understand the mechanisms causing the quality changes, baby spinach was stored under two CA of 0.5kPa O2+10kPa CO2 (low O2+high CO2 levels) and air combined with 2 light conditions (continuous light and darkness). The changes observed under the different light conditions were mainly caused by the differences in gas composition. Under light, MAP with high O2 partial pressure (pO2) and low CO2 partial pressure (pCO2) was detrimental because of the growth of Pseudomonas spp. and the progress in tissue senescence due to oxidative stress, increasing cell damage, lipid peroxidation and chlorophyll degradation. Under darkness, MAP with low pO2 and high pCO2 was also detrimental because of the intense off-odour developments, the increase in pH and electrolyte leakage and the reduction in chlorophyll fluorescence. Our results showed that the modified atmosphere generated with exposure to the different light conditions affects the quality of baby spinach mainly because of the high pO2 under light and high pCO2 under darkness.

Pd Nanoparticle Formation in Ionic Liquid Thin Films Monitored by in situ Vibrational Spectroscopy.

Ionic liquids (ILs) are flexible reaction media and solvents for the synthesis of metal nanoparticles (NPs). Here, we describe a new preparation method for metallic NPs in nanometer thick films of ultraclean ILs in an ultrahigh vacuum (UHV) environment. CO-covered Pd NPs are formed by simultaneous and by sequential physical vapor deposition (PVD) of the IL and the metal in the presence of low partial pressures of CO. The film thickness and the particle size can be controlled by the deposition parameters. We followed the formation of the NPs and their thermal behavior by time-resolved IR reflection absorption spectroscopy (TP-IRAS) and by temperature-programmed IRAS (TR-IRAS). Codeposition of Pd and [C1C2Im][OTf] in CO at 100 K leads to the growth of homogeneous multilayer films of CO-covered Pd aggregates in an IL matrix. The size of these NPs can be controlled by the metal fraction in the co-deposit. With increasing metal fraction, the size of the Pd NPs also increases. At very low metal content, small Pd carbonyl-like species are formed, which bind CO in on-top geometry only. Upon annealing, the [OTf](-) anion coadsorbs at the NP surface and partially displaces CO. Co-adsorption of CO and IL is indicated by a strong red-shift of the CO stretching bands. While the weakly bound on-top CO is mainly replaced below the melting transition of the IL, coadsorbate shells with bridge-bonded CO and IL are stable well above the melting point. Larger three-dimensional Pd NPs can be prepared by PVD of Pd onto a solid [C1C2Im][OTf] film at 100 K. Upon annealing, on-top CO desorbs from these NPs below 200 K. Upon melting of the IL film, the CO-covered Pd NPs immerse into the IL and again form a stable coadsorbate shell that consists of bridge-bonded CO and the IL.

THEORETICAL STUDY OF CO2:N2 ADSORPTION IN FAUJASITE IMPREGNATED WITH MONOETHANOLAMINE

Many efforts have been made to develop amine-based solid adsorbents for capture of CO2 by adsorption. Compared with the traditional process of absorption in aqueous solutions of amines, the adsorbents with amine immobilized in solids generally result in processes with lower capital and energy costs. The literature contains some experimental studies of CO2 adsorption in impregnated materials; however, few studies are devoted to the theoretical interpretation of this system in terms of CO2 capture for post-combustion (N2 mixture with a low partial pressure of CO2). Therefore, this study investigates the adsorption of a CO2:N2 mixture on zeolite NaX impregnated with monoethanolamine (MEA), using molecular simulation. A model of NaX impregnated with MEA was proposed and the adsorption of a 15:85 (CO2:N2) mixture was investigated based on the Monte Carlo method. The simulation of the MEA impregnated zeolite at 25 ˚C predicted higher CO2 selectivity and significant improvement in the heat of adsorption. Unfortunately, the adsorption heat improvement did not translate into corresponding increases in the amount of adsorbed CO2. Moreover, MEA concentrations higher than 12 wt% hindered the adsorption of CO2 molecules. An explanation for the results in terms of occupied volumes and interaction energies is presented.

Development of sodium/lithium/fly ash sorbents for high temperature post-combustion CO2 capture

CO2 capture from combustion processes faces several challenges including high energy penalty, low CO2 partial pressure, high flow rates and presence of water vapours. Absorption of CO2 at high temperature is recently attracting increasingly attention. Alkali metal based sorbents present clear advantages compared to other high temperature sorbents, such as high CO2 capture capacity, lower regeneration temperatures (<750°C) and excellent stability. In this work, Na/Li-silicates prepared by mixing Na/Li carbonates with fly ash (FA) in various molar ratios were evaluated for their capacity to chemisorb CO2 at 500–700°C and in presence of H2O (2–12vol%), diluted CO2 (14vol%) and CO2 sorption promoters.The results indicate that the carbonate:silica ratio used in the sorbents synthesis significantly affects the CO2 sorption capacity and regeneration temperature. The presence of steam enhances the diffusion of Li and Na ions resulting in higher CO2 uptake. CO2 chemisorption follows a double layer mechanism with formation of carbonate layer on the surface. The simultaneous presence of Li and Na (and K when used as additive) in the formed carbonate layer results in an eutectic melt between 600 and 700°C, which facilitates the diffusion of the ionic species. Li–Na–FA with molar ratio of 0.5:0.5:1 was the best prepared sorbent with a capacity of 2.54 mol CO2/kg sorbent (12% H2O, 14% CO2 at 700°C). Absorption/desorption was completed in 15min with reaction kinetics comparable to that of pure Li4SiO4 sorbents. The tested materials maintained their capacity and absorption/desorption rates after 10 cycles at 700°C. Overall, the Na/Li materials showed a CO2 capture capacity, stability over time and sorption–desorption kinetics comparable to those of other high-temperature sorbents, such as Li–FA (Li4SiO4 prepared using fly ash), and higher stability than CaO and hydrotalcites.