Low CO2 Partial Pressure Research Articles

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.

Formation of Calcareous Deposition Layers on AM50 Magnesium Alloy in Presence of Ca2+ in De-Icing Salt Solutions: Immersion Vs. Salt Spray Test

The influence of the presence and absence of de-icing salt ingredient Ca2+ (CaCl2) on the corrosion behavior and morphology of calcareous deposition products on die cast AM50 magnesium alloy was investigated by using an electrolyte close to the de-icing salt composition (NaCl, MgCl2) with and without Ca2+ addition. The aim of the work is to point out the difference of corrosion mechanisms between the presence or absence of Ca2+ and between immersion and salt spray conditions. Electrochemical measurements (OCP, EIS, potentiostatic and potentiodynamic polarization) and several surface analysis techniques (FTIR, XRD, XPS, SEM / EDX) were used. During immersion experiments in the presence of Ca2+, a grey-white, voluminous and open-porous deposition layer has been formed on the surface of magnesium samples, which covered the whole surface after 12 days ­ with layer thicknesses above a tenth of a millimeter. XRD was used to identify Calcite (CaCO3) as a major component in the deposition layer. It has been shown previously by the authors [1, 2] that Ca2+ has an inhibiting effect on Mg alloy corrosion during short time immersion experiments (up to 4.5 h). The inhibiting effect of the Ca2+ in the first 4.5 h cannot be attributed to the incorporation of Ca2+ into the surface layer, which was shown by XPS. Further, an increase of the thickness of the corrosion product layer in presence of Ca2+ seems to be responsible for the inhibiting effect, shown by XPS depth profiling. After several days of immersion in the presence of Ca2+, the element Ca could be detected on the surface by EDX. XRD and FTIR proved the presence of calcite with layer thicknesses up to 155 µm, shown by SEM cross section investigations. The inhibiting effect of Ca2+is not present anymore as Calcite occurs in the surface layers at larger immersion times (> 4,5 h). Furthermore, the influence of the used testing method was investigated. In addition to immersion experiments, salt spray testing was performed up to 13 weeks which resulted in a different morphology of corrosion and deposition products (see Figure 1). Mass gain and mass loss measurements were carried out and showed a 5-times higher mass loss under immersion conditions in comparison to salt spray testing. The presence of a higher amount of carbonates after salt spray testing could be proven. Calcite is present in the surface layers in significant amounts after both testing methods. The increasing OH- concentration during Mg corrosion triggers the deposition of CaCO3 under conditions of low CO2 partial pressure, whilst the carbonate anion derives from the CO2 in the atmosphere.

Carbon Dioxide Conversion to Methanol over Size-Selected Cu4 Clusters at Low Pressures.

The activation of CO2 and its hydrogenation to methanol are of much interest as a way to utilize captured CO2. Here, we investigate the use of size-selected Cu4 clusters supported on Al2O3 thin films for CO2 reduction in the presence of hydrogen. The catalytic activity was measured under near-atmospheric reaction conditions with a low CO2 partial pressure, and the oxidation state of the clusters was investigated by in situ grazing incidence X-ray absorption spectroscopy. The results indicate that size-selected Cu4 clusters are the most active low-pressure catalyst for catalytic CO2 conversion to CH3OH. Density functional theory calculations reveal that Cu4 clusters have a low activation barrier for conversion of CO2 to CH3OH. This study suggests that small Cu clusters may be excellent and efficient catalysts for the recycling of released CO2.

Thermodynamic Modeling for CO2 Adsorption on Activated Carbon at Low Partial Pressure

Abstract The determination of adsorption thermodynamics at low CO2 partial pressure is of great significance. The Langmuir–Freundlich model is used to fit the adsorption isotherms of activated carbon (AC) and amine-modified AC. The isosteric heat and average heat of CO2 adsorption on AC are calculated. The result could benefit the subsequent process development and equipment energy optimization.

Density Functional Theory-Assisted Microkinetic Analysis of Methane Dry Reforming on Ni Catalyst

A comprehensive microkinetic model based on density functional theory (DFT) calculations is constructed to explore the reaction mechanism for dry methane reforming on Ni catalyst. Three low-index facets, namely, Ni(111), Ni(100), and Ni(211), are utilized to represent the contributions from the flat, open, and stepped surfaces. Adsorption energies of all the possible reaction intermediates as well as activation energies for the elementary reactions involved in dry reforming of methane on the three Ni surfaces are calculated through DFT. These results are further employed to estimate the rate constants for the elementary reactions under realistic temperatures and pressures within the framework of transition state theory and statistical mechanics treatments. The dominant reaction pathway is identified as CH4 successive dissociation followed by carbon oxidation by atomic oxygen. The dependence of the rate-determining step on operating conditions is examined. At low CH4 and CO2 partial pressures, both CH4 dis...

On the negative activation energy for limestone calcination at high temperatures nearby equilibrium

The study of limestone calcination under high CO2 pressure and high temperature has gained an extraordinary practical importance due to the recently emerged Ca-looping technology for post-combustion CO2 capture, which uses natural limestone (CaCO3) as precursor of the CO2 solid sorbent (CaO). A critical issue of this promising process is the necessity of producing CaO by calcination of limestone under high CO2 partial pressure. Experimental measurements on the kinetics of limestone calcination usually show that the rate of the endothermic calcination reaction is increased with temperature according to an Arrhenius law with an activation energy similar to the reaction enthalpy change. In situ microscopic observations have demonstrated that the reaction involves a crystallographic structural transformation of CaO. Calcination is started by chemical decomposition leading to the development of metastable CaO⁎ nanocrystals after which CO2 is desorbed while stable CaO cubic crystals grow. In calcination environments with low CO2 partial pressure P (as compared to the equilibrium pressure: P/Peq≪1), desorption of CO2 and the exothermic structural transformation of CaO⁎ to its stable CaO form occur extremely fast and do not play a role on the reaction kinetics, which is just determined by chemical decomposition. However, at high values of P/Peq the reaction rate may be significantly influenced by the structural transformation above a critical temperature. As a main consequence, the reaction mechanism proposed in the present paper shows that, above a critical temperature, limestone calcination is characterized by a negative activation energy in agreement with the experimental results shown.

Butanol and hexanol production in Clostridium carboxidivorans syngas fermentation: Medium development and culture techniques

Clostridium carboxidivorans was grown on model syngas (CO:H2:CO2 [70:20:10]) in a defined nutrient medium with concentrations of nitrogen, phosphate and trace metals formulated to enhance production of higher alcohols. C. carboxidivorans was successfully grown in a limited defined medium (no yeast extract, no MES buffer and minimal complex chemical inputs) using an improved fermentation protocol. Low partial pressure of CO in the headspace, coupled with restricted mass transfer for CO and H2, was required for successful fermentation. In the absence of substrate inhibition (particularly from CO), growth limitation increased production of alcohols, especially butanol and hexanol. Concentrations of butanol (over 1.0g/L), hexanol (up to 1.0g/L) and ethanol (over 3.0g/L) were achieved in bottle fermentations. Minimal medium and controlled supply of CO and H2 should be used in characterizing candidate butanol and hexanol producing strains to select for commercial potential.

QUALIDADE DE PERAS ‘ROCHA’ ARMAZENADAS EM ATMOSFERA CONTROLADA

RESUMOO objetivo deste trabalho foi avaliar o efeito de diferentes condições de atmosfera controlada (AC) e da indução de perda de massa (IPM) sobre a qualidade de peras ‘Rocha’. Frutos provenientes do município de São Joaquim-SC, foram armazenados por oito meses e quinze dias a -0,5±0,1 ºC e UR de 96±1%. Os tratamentos foram constituídos em armazenamento refrigerado (AR; 21,0 kPa de O2 + &lt;0,03 kPa de CO2), bem como de cinco condições de AC: 1,0 kPa de O2 + &lt;0,03 kPa de CO2; 2,0 kPa de O2 + 1,0 kPa de CO2; 1,0 kPa de O2 + 1,0 kPa de CO2; 1,0 kPa de O2 + 2,0 kPa de CO2; e 1 kPa de O2 + 2,0 kPa de CO2 + IPM de 2,6%. O AR propiciou frutos com casca mais amarela, menor teor de sólidos solúveis, menor acidez titulável e baixa aceitação nos testes sensoriais para os atributos de textura e equilíbrio doçura/acidez. Os frutos mantidos em AR e em AC, com pressão parcial de CO2 de &lt;0,03 kPa, apresentaram maior firmeza de polpa e de força para penetração da polpa após sete dias de exposição dos frutos em condições ambiente, não desenvolvendo textura amanteigada, própria para o consumo. Não houve incidência de escurecimento de polpa em nenhuma das condições avaliadas. A IPM de 2,6% não apresentou efeito na qualidade dos frutos. As condições de AC de 1,0 kPa de O2 + 1,0 kPa de CO2 e 1 kPa de O2 + 2,0 kPa de CO2 proporcionam melhor manutenção da qualidade de peras ‘Rocha’, permitindo o amadurecimento normal dos frutos após o armazenamento prolongado.

Low CO2 permeability of cholesterol-containing liposomes detected by stopped-flow fluorescence spectroscopy.

Here we ask the following: 1) what is the CO2 permeability (Pco2) of unilamellar liposomes composed of l-α-phosphatidylcholine (PC)/l-α-phosphatidylserine (PS) = 4:1 and containing cholesterol (Chol) at levels often occurring in biologic membranes (50 mol%), and 2) does incorporation of the CO2 channel aquaporin (AQP)1 cause a significant increase in membrane Pco2? Presently, a drastic discrepancy exists between the answers to these two questions obtained from mass-spectrometric (18)O-exchange measurements (Chol reduces Pco2 100-fold, AQP1 increases Pco2 10-fold) vs. from stopped-flow approaches observing CO2 uptake (no effects of either Chol or AQP1). A novel theory of CO2 uptake by vesicles predicts that in a stopped-flow apparatus this fast process can only be resolved temporally and interpreted quantitatively, if 1) a very low CO2 partial pressure (pCO2) is used (e.g., 18 mmHg), and 2) intravesicular carbonic anhydrase (CA) activity is precisely known. With these prerequisites fulfilled, we find by stopped-flow that 1) Chol-containing vesicles possess a Pco2 = 0.01cm/s, and Chol-free vesicles exhibit ∼1 cm/s, and 2) the Pco2 of 0.01 cm/s is increased ≥ 10-fold by AQP1. Both results agree with previous mass-spectrometric results and thus resolve the apparent discrepancy between the two techniques. We confirm that biologic membranes have an intrinsically low Pco2 that can be raised when functionally necessary by incorporating protein-gas channels such as AQP1.

The effects of river inflow and retention time on the spatial heterogeneity of chlorophyll and water–air CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; fluxes in a tropical hydropower reservoir

Abstract. Abundant research has been devoted to understanding the complexity of the biogeochemical and physical processes that are responsible for greenhouse gas (GHG) emissions from hydropower reservoirs. These systems may have spatially complex and heterogeneous GHG emissions due to flooded biomass, river inflows, primary production and dam operation. In this study, we investigated the relationships between the water–air CO2 fluxes and the phytoplanktonic biomass in the Funil Reservoir, which is an old, stratified tropical reservoir that exhibits intense phytoplankton blooms and a low partial pressure of CO2 (pCO2). Our results indicated that the seasonal and spatial variability of chlorophyll concentrations (Chl) and pCO2 in the Funil Reservoir are related more to changes in the river inflow over the year than to environmental factors such as air temperature and solar radiation. Field data and hydro\\-dynamic simulations revealed that river inflow contributes to increased heterogeneity during the dry season due to variations in the reservoir retention time and river temperature. Contradictory conclusions could be drawn if only temporal data collected near the dam were considered without spatial data to represent CO2 fluxes throughout the reservoir. During periods of high retention, the average CO2 fluxes were 10.3 mmol m−2 d−1 based on temporal data near the dam versus −7.2 mmol m−2 d−1 with spatial data from along the reservoir surface. In this case, the use of solely temporal data to calculate CO2 fluxes results in the reservoir acting as a CO2 source rather than a sink. This finding suggests that the lack of spatial data in reservoir C budget calculations can affect regional and global estimates. Our results support the idea that the Funil Reservoir is a dynamic system where the hydrodynamics represented by changes in the river inflow and retention time are potentially a more important force driving both the Chl and pCO2 spatial variability than the in-system ecological factors.

The Importance of Stabilizing PaCO2 during Long-term Non-invasive Ventilation in Subjects with COPD.

In subjects with chronic obstructive pulmonary disease (COPD), the effect of partial pressure of CO2 (PaCO2) alterations during long-term non-invasive ventilation (NIV) on continuance remains uncertain. We herein investigated the utility of PaCO2 stability during long-term NIV as a prognostic outcome. We retrospectively assessed data from 54 subjects with COPD who received long-term NIV. The annual alteration in PaCO2 during NIV was determined using a simple linear regression method for each subject who had at least two 6-month intervals of PaCO2 data. Annual alterations in PaCO2 during long-term NIV and probable confounders were examined, and long-term NIV discontinuation was the major outcome. Data from 37 subjects who met the criteria were analyzed. PaCO2 during long-term NIV increased slightly in 19 subjects (group 1, <2 mm Hg/y), and increased greatly in 18 subjects (group 2, >2 mmHg/y). In the multivariate modality model, smaller annual alterations in PaCO2 (p=0.009) and lower PaCO2 6 months after the start of long-term NIV (6 m-PaCO2) (p=0.03) were associated with a significantly higher probability of continuing NIV. The 2- and 5-year probabilities of continuing NIV were 89% and 66% for group 1 and 78% and 32% for group 2, respectively. A lower 6 m-PaCO2 and a lower annual alteration of PaCO2 during long-term NIV are significant predictive variables for patients with COPD.

Nickel Nanoparticles for Enhancing Carbon Capture

Hydration reaction of CO2 is one of the rate limiting steps for CO2 absorption (in aqueous solutions) and aqueous CO2 mineralization. The catalytic activity of nickel nanoparticles (NiNPs) for CO2 hydration is studied at different temperatures, pH, and low CO2 partial pressures to mimic the true flue gas conditions. Results show that NiNPs can work as active catalyst for hydration of CO2 in applications such as CO2 separation and CO2 mineralization. The NiNPs display optimum activity within 20–30°C and at pH value &lt;8. NiNPs show catalytic activity even at low CO2 partial pressures (12 vol%). In 50 wt% K2CO3 solution, an enhancement of 77% is observed in the rate of CO2 absorption with NiNPs. Commercially, CO2 saturated K2CO3 solutions are usually regenerated at 150°C; at these conditions, NiNPs show no considerable surface oxidation. They still exhibit catalytic activity for hydration reaction of CO2. CO2 absorption and mineralization (as CaCO3) in DI water are three times higher in presence of NiNPs. Calcite (CaCO3) particles precipitated in presence of NiNPs are spherical in morphology.

Novel scrubbing system for post-combustion CO2 capture and recovery: Experimental studies

Power plant emissions of flue gas to the atmosphere releases considerable CO2 which is considered to be the main contributor to global warming. Several gas absorption techniques are being investigated to reduce the capital and operating costs for CO2 capture from post-combustion flue gas. Conventional method of CO2 capture by an aqueous solution of monoethanolamine (MEA) and its subsequent stripping in a separate tower with steam at 120°C is highly energy intensive. The low partial pressure of CO2 in the flue gas inhibits the application of CO2-selective membranes unless methods are employed to increase the CO2 partial pressure in the flue gas to be treated. An absorption–stripping technique to potentially bypass the shortcomings of many existing approaches is described here. Bench-scale CO2 capture and recovery from simulated flue gas with and without moisture was demonstrated using an advanced hollow fiber membrane contactor. This was achieved by the use of a novel non-volatile absorbent, consisting of the ionic liquid [bmim][DCA] containing 20wt% polyamidoamine (PAMAM) dendrimer Gen 0. We have employed a simulated humidified flue gas containing around 14% CO2 and demonstrated successful removal of bulk of the CO2 and its recovery in a CO2-concentrated stream; the CO2 concentration achieved in the stripper out stream was ~92vol%. An estimate of the overall volumetric mass transfer coefficient (Kla) for the current CO2-IL-PAMAM Gen 0 system has been obtained.

Effect of Heat Pretreatment/Recarbonation in the Ca-Looping Process at Realistic Calcination Conditions

Even though an increasing number of pilot-scale plants are demonstrating the potential efficiency of the Ca-looping technology to capture CO2 at a commercial level, a still standing matter of concern is the loss of carbonation reactivity of the regenerated CaO by calcination, which is expected to be particularly marked at realistic conditions necessarily implying a high CO2 partial pressure in the calciner. In this work, we address the effect of previously reported strategies for sorbent reactivation, namely heat pretreatment and the introduction of a recarbonation stage before regeneration. Both techniques, either combined or separately, are shown to favor the carbonation reactivity, albeit CaO regeneration is usually carried out at low CO2 partial pressure in lab-scale tests. Novel results reported in this paper show the opposite when the sorbent is regenerated by calcination at high CO2 concentration, which is arguably due to the diverse mechanisms that rule decarbonation depending on the CO2 concentra...

Calcium-looping for post-combustion CO2 capture. On the adverse effect of sorbent regeneration under CO2

The multicyclic carbonation/calcination (c/c) of CaO solid particles at high temperature is at the basis of the recently emerged Calcium-looping (CaL) technology, which has been shown to be potentially suitable for achieving high and sustainable post-combustion CO2 capture efficiency. Despite the success of pilot plant projects at the MWth scale, a matter of concern for scaling-up the CaL technology to a commercial level (to the GWth scale) is that the CaO carbonation reactivity can be recovered only partially when the sorbent is regenerated by calcination at high temperatures (around 950°C) as required by the CO2 high concentration in the calciner. In order to reactivate the sorbent, a novel CaL concept has been proposed wherein a recarbonator reactor operated at high temperature/high CO2 concentration leads to further carbonation of the solids before entering into the calciner for regeneration. Multicyclic thermogravimetric analysis (TGA) tests demonstrate the feasibility of recarbonation to reactivate the sorbent regenerated at high calcination temperatures yet at unrealistically low CO2 partial pressure mainly because of technical limitations concerning low heating/cooling rates. We report results from multicyclic c/c and carbonation/recarbonation/calcination (c/r/c) TGA tests at high heating/coling rates and in which the sorbent is regenerated in a dry atmosphere at high CO2 partial pressure. It is shown that at these conditions there is a drastic drop of CaO conversion to a very small residual value in just a few cycles. Moreover, the introduction of a recarbonation stage has actually an adverse effect. Arguably, CaCO3 decomposition in a CO2 rich atmosphere is ruled by CO2 dynamic adsorption/desorption in reactive CaO (111) surfaces as suggested by theoretical studies, which would preclude the growth of the regenerated CaO crystal structure along these reactive surfaces, and this effect would be intensified by recarbonation. Nevertheless, the presence of H2O in the calciner, which is also adsorbed/desorbed dynamically in CaO reactive planes, would shield CO2 adsorption/desorption thus mitigating the deeply detrimental effect of CO2 on the carbonation reactivity of the regenerated CaO structure. Oxy-combustion, which produces a significant amount of H2O, is currently used in pilot-scale plants to raise the temperature in the calciner. Auxiliary techniques are being explored to help heating the partially carbonated solids since oxyxombustion represents an important penalty to the CaL technology. Our study suggests that steam injection would be necessary in a dry calciner environment to avoid a sharp loss of CaO conversion if the sorbent is regenerated at high CO2 partial pressure.

Promotion of microalgal biomass production and efficient use of CO2 from flue gas by monoethanolamine

AbstractBACKGROUNDFlue gas as carbon source for microalgae culture has been applied to reduce the high cost of production. However, low mass transfer efficiency owing to the low CO2 partial pressure in flue gas limited its utilization. In this work, monoethanolamine was proposed to enhance CO2 utilization and microalgal biomass production.RESULTSIn abiotic absorption experiments, the total inorganic carbon concentration in the medium increased with the increase of monoethanolamine concentration and the CO2 absorptivity remained above 60% for a considerable pH range (6.5–10.0). The biomass productivity and lipid productivity of Scenedesmus dimorphus were enhanced with monoethanolamine ranging from 0 to 100 mg L−1. When 100 mg L−1 monoethanolamine was added, the CO2 utilization efficiency reached 76.1%, which was much higher than the 44.5% obtained in routine culture. The growth of cells was inhibited with monoethanolamine concentration exceeding 150 mg L−1. The changes of net photosynthetic activity revealed that the oxygen evolving complex might be injured by the higher concentration of monoethanolamine.CONCLUSIONSThese results indicated that the incorporation of monoethanolamine could be a promising solution to the problem of low CO2 utilization efficiency and low biomass productivity in the microalgae culture system. © 2014 Society of Chemical Industry

Reaction Mechanism for the Aqueous-Phase Mineral Carbonation of Heat-Activated Serpentine at Low Temperatures and Pressures in Flue Gas Conditions

Mineral carbonation is known as one of the safest ways to sequester CO2. Nevertheless, the slow kinetics and low carbonation rates constitute a major barrier for any possible industrial application. To date, no studies have focused on reacting serpentinite with a relatively low partial pressure of CO2 (pCO2) close to flue gas conditions. In this work, finely ground and heat-treated serpentinite [Mg3Si2O5(OH)4] extracted from mining residues was reacted with a 18.2 vol % CO2 gas stream at moderate global pressures to investigate the effect on CO2 solubility and Mg leaching. Serpentinite dissolution rates were also measured to define the rate-limiting step. Successive batches of gas were contacted with the same serpentinite to identify surface-limiting factors using scanning electron microscopy (SEM) analysis. Investigation of the serpentinite carbonation reaction mechanisms under conditions close to a direct flue gas treatment showed that increased dissolution rates could be achieved relative to prior work, with an average Mg dissolution rate of 3.55 × 10(-11) mol cm(-2) s(-1). This study provides another perspective of the feasibility of applying a mineral carbonation process to reduce industrial greenhouse gas (GHG) emissions from large emission sources.

Theoretical investigation on CO2 absorption into DEAB solution using hollow fiber membrane contactors

4-Diethylamino-2-butanol (DEAB) is a novel amino alcohol, which has been synthesized to incorporate the advantages of amine blends such as low regeneration energy as well as high CO2 pick up. In this study, the absorption of carbon dioxide by monoethanolamine (MEA), diethanolamine (DEA), methyldiethanolamine (MDEA) and DEAB solutions was compared theoretically in a hollow fiber membrane contactor. A numerical analysis was performed to solve the applied partial differential equations for the liquid, gas and membrane phases simultaneously. The model results were validated using the available experimental data in the literature for MEA, DEA and MDEA. The effects of different operating conditions including DEAB concentration, system temperature, liquid and gas velocities and CO2 partial pressure on the removal behavior of CO2 were investigated. The simulation results indicated that the CO2 absorption flux into DEAB solution was lower than MEA solution, however much higher than MDEA solution in all range of CO2 partial pressures. DEAB had almost the same absorption flux compared to DEA solution at low partial pressures of CO2, and a better performance at higher CO2 partial pressures. Increasing the system temperature, DEAB concentration, gas and liquid flow rates enhanced the absorption flux.