Adsorption characteristics of metal ions by CO2-fixing Chlorella sp. HA-1

Single and binary metal systems were employed to investigate the removal characteristics of Pb²⁺, Cu²⁺, Cd²⁺, and Zn²⁺ by Chlorella sp. HA-1 that were isolated from a CO₂ fixation process. Adsorption test of single metal systems showed that the maximum metal uptakes were 0.767 mmol Pb²⁺, 0.450 mmol Cd²⁺, 0.334 mmol Cu²⁺ and 0.389 mmol Zn²⁺ per gram of dry cell. In the binary metal systems, the metal ions on Chlorella sp. HA-1 were adsorbed selectively according to their adsorption characteristics. Pb²⁺ ions significantly inhibited the adsorption of Cu²⁺, Zn²⁺, and Cd²⁺ ions, while Cu²⁺ ions decreased remarkably the metal uptake of Cd²⁺ and Zn²⁺ ions. The relative adsorption between Cd²⁺ and Zn²⁺ ions was reduced similarly by the presence of the other metal ions.     

Optimization of the influential factors for the improvement of CO2 utilization efficiency and CO2 mass transfer rate

Microalgae fix CO₂ as energy source and afford biomass and high valued products such as carotenoids, pigments, proteins, and vitamins that can be used for the production of nutraceuticals, pharmaceuticals, animal feed additives, cosmetics, etc. Carbon dioxide is the sole source of carbon and it is supplied continuously for the microalgal cultivation. But undissolved CO₂ is lost by outgassing and sufficient dissolved CO₂ should be provided to avoid carbon limitation. The effect of CO₂ mass transfer with different CO₂ concentrations, aeration rate of gas, bubble size, baffle type and baffle number on the growth of Chlorella sp. AG10002 was investigated and the optimized conditions for the enhancement of biomass productivity were determined. We confirm that these results can be provided as basic data to improve the CO₂ mass transfer ability for the high density culture of Chlorella sp. and some microalgae having commercial value.     

PREDICTION OF CO2 FREEZE-OUT CONDITIONS AND CO2 HYDRATE FORMATION CONDITIONS WITH A SINGLE EQUATION OF STATE

A recent study by Eggeman and Chaffin (2005 Eggeman , T. , and Chafin , S. ( 2005 ). Beware of pitfalls of CO₂ freezing predictions , Chem. Eng. Prog. , 101 ( 3 ), 39 – 44 . [Google Scholar]), which showed large discrepancies in CO₂ freeze-out conditions as predicted by several commercial simulators, prompted a reexamination of using the TBS equation of state for phase equilibrium calculations involving solids. Salim and Trebble (1994 Salim , P. , and Trebble , M. A. ( 1994 ). Modelling of solid phases in thermodynamic calculations via translation of a cubic equation of state at the triple point , Fluid Phase Equilib. , 93 , 75 – 99 .[Crossref] , [Google Scholar]) had previously presented a methodology for extending the Trebble-Bishnoi-Salim (TBS) equation of state (Salim, 1990 Salim , P. ( 1990 ). A modified Trebble-Bishnoi equation of state, M.Sc. thesis , University of Calgary . [Google Scholar]) to calculations involving a solid phase. In this study, the CO₂ freeze-out conditions in CO₂/CH₄ and CO₂/C₂H₆ mixtures are calculated from the TBS equation of state, and it is shown that they provide a better data fit than the traditional Poynting correction method. Furthermore, since the use of an equation of state in SLE/SVE calculations does not require the explicit assumption of a pure solid phase, the model was assessed for its ability to correlate CO₂ gas hydrate equilibrium conditions. Gas hydrates were simply treated as an impure solid phase, and it was seen that the predictions of gas hydrate equilibrium were in very good agreement with the experimental data. Computationally, the use of the TBS equation of state has the advantage, over the model of Yokozeki (2005 Yokozeki , A. ( 2005 ). Methane gas hydrates viewed through unified solid-liquid-vapour equation of state , Int. J. Thermophys. , 26 ( 3 ), 743 – 765 . [Google Scholar]), that it does not require a modifying factor (c_b) in the repulsive term to handle the presence of hydrates; they are instead handled using a unique binary interaction parameter for the hydrate phase.     

Hydrothermal synthesis of Ag2CO3-TiO2 loaded reduced graphene oxide nanocomposites with highly efficient photocatalytic activity

Abstract

In this work, a growth of Ag₂CO₃-TiO₂ NPs over GO sheets and reduction of GO were simultaneously achieved by the hydrothermal process at 130 °C for 4?h. The photocatalytic activity of the as-prepared Ag₂CO₃-TiO₂ NPs decorated reduced graphene oxide (Ag₂CO₃-TiO₂/rGO) composite was studied by the degradation of methylene blue (MB) solution under visible light irradiation. A remarkable enhancement in the photocatalytic activity of the TiO₂ was achieved after sensitizing with Ag₂CO₃ and loading in rGO sheets which is attributed to the reduced charge recombination, enhanced dye adsorption, and the improvement in the light harvesting capacity of the composite.     

The kinetics of CO2 hydrogenation on a Rh foil promoted by titania overlayers

Submonolayer deposits of titania on a Rh foil have been found to increase the rate of CO₂ hydrogenation. The primary product, methane, exhibits a maximum rate at a TiO _x coverage of 0.5 ML which is a factor of 15 higher than that over the clean Rh surface. The rate of ethane formation displays a maximum which is 70 times that over the unpromoted Rh foil; however, the selectivity for methane remains in excess of 99%. The apparent activation energy for methane formation and the dependence of the rate on H₂ and CO₂ partial pressure have been determined both for the bare Rh surface and the titania-promoted surface. These rate parameters show very small variations as titania is added to the Rh catalyst. The methanation of CO₂ is proposed to start with the dissociation of CO₂ into CO_(a) and O_(a), and then proceed through steps which are identical to those for the hydrogenation of CO. The increase in the rate of CO₂ hydrogenation in the presence of titania is attributed to an interaction between the adsorbed CO, released by CO₂ dissociation, and Ti³⁺ ions located at the edge of TiO _x islands covering the surface. Differences in the effects of titania promotion on the methanation of CO₂ and CO are discussed in terms of the mechanisms that have been proposed for these two reactions.     

Separation of CO2 and N2 on Zeolite Silicalate-1 Membrane Synthesized on Novel Support

This paper reports on the properties of an MFI-type zeolite (silicalite-1) membrane synthesized on a novel tubular support with a 0.45 µm-pore size active layer consisting of zirconium and titanium oxides. Even though the membrane was synthesized by a pore plugging method, apart from penetrating into the support, the silicalite-1 crystals formed a 1.5 µm layer on top of the support. After the zeolite synthesis, the Si constituted more than 35% of the active layer of the support, which implies small size and close packing of the silicalite-1 crystals in the pores of the active layer.

Single gas permeation tests with N₂ and CO₂ revealed comparable N₂ and CO₂ permeances. On the other hand, CO₂/N₂ gas separation tests performed at different total feed pressures and feed compositions lead to CO₂/N₂ permselectivities as high as 26.0, with the corresponding CO₂ permeance of 6 × 10^?8 mol/m² Pa s. The effects of changing the partial pressure gradient of CO₂ across the membrane by means of varying the total feed pressure and the feed composition on the CO₂ permeance and CO₂/N₂ permselectivity are discussed.     

Low Temperature Liquid State Synthesis of Lithium Zirconate and its Characteristics as a CO2 Sorbent

Abstract

In this study, a new preparation method providing greatly improved CO₂ sorption is introduced. Li₂ZrO₃ sorbent was prepared by low temperature co‐precipitation and compared in CO₂ sorption performance with a sorbent prepared by the conventional high temperature solid‐state reaction method. The two sorbents were characterized using scanning electron microscopy, X‐ray diffraction and thermo‐gravimetric analysis. The Li₂ZrO₃ powder prepared by the relatively simple co‐precipitation method showed significantly better performance than the one prepared by solid‐state reaction with respect to both kinetics and CO₂ sorption capacity. Extensive study of the powder prepared by co‐precipitation has been performed at various conditions.     

SOLUBILITY OF CO2AND H2S IN A MIXED SOLVENT

Mixed solvents are a combination of chemical and physical solvents and have some advantages over traditional treating solvents for the removal of acid gases from gas streams. The solubility of H₂S and CO₂in a mixed solvent consisting of AMP (2-amino-2-methyl-l-propanol), sulfolane, and water has been measured at 40 and 100°C at partial pressures of the acid gas to 6000 kPa. The solubility in the mixed solvent was compared with the solubility in an aqueous solution of equivalent amine concentration. At solution loadings less than 1 mol acid gas/mol amine, the solubility of the acid gas is lower in the mixed solvent than in the corresponding amine solvent. At higher loadings, the trend is reversed and the solubility is greater in the mixed solvent. The results are rationalized in terms of the effect of the physical solvent component on the chemical reaction and physical vapor-liquid equilibria. The solubility model of Deshmukh and Mather was used to correlate the data.     

EFFICIENT DESULFURIZATION IN O2/CO2 COMBUSTION: DEPENDENCE ON COMBUSTION CONDITIONS AND SORBENT PROPERTIES

Based on experiments on desulfurization, CaSO₄ decomposition, and a system approach using theoretical analysis, efficient in-furnace desulfurization in O₂/CO₂ combustion was investigated. The influence of combustion conditions and sorbent properties on system desulfurization efficiency was clarified. The global desulfurization efficiency was found to increase with O₂ purity. The global desulfurization efficiency in a dry recycle was higher than that in a wet recycle. The global efficiency of in-furnace desulfurization decreased with initial O₂ concentration. As the temperature increased, the global desulfurization efficiency increased first and then decreased due to the decomposition of CaSO₄. In the temperature range investigated, the global desulfurization efficiency in O₂/CO₂ coal combustion was much higher than that of conventional coal combustion in air. The global desulfurization efficiency decreased with sorbent size. When the particle radius decreased to one quarter, the global desulfurization efficiency doubled, becoming as high as 80%. The global desulfurization efficiency was very different among the three sorbents investigated, whether in O₂/CO₂ combustion or in conventional air combustion. The global desulfurization efficiency increased in the order of Ca(OH)₂, scallop, and limestone in O₂/CO₂ combustion, but in the order of scallop, Ca(OH)₂, and limestone in conventional air combustion. Nevertheless, all three sorbents demonstrated much higher desulfurization efficiency in O₂/CO₂ combustion than in conventional air combustion.     

A Fourier-transform infrared study of CO2 and CO2/H2 interactions with caesium-doped copper catalysts

FTIR spectra are reported of CO₂ and CO₂/H₂ on a silica-supported caesium-doped copper catalyst. Adsorption of CO₂ on a “caesium”/silica surface resulted in the formation of CO₂ ⁻ and complexed CO species. Exposure of CO₂ to a caesium-doped reduced copper catalyst produced not only these species but also two forms of adsorbed carboxylate giving bands at 1550, 1510, 1365 and 1345 cm⁻¹. Reaction of carboxylate species with hydrogen at 388 K gave formate species on copper and caesium oxide in addition to methoxy groups associated with caesium oxide. Methoxy species were not detected on undoped copper catalyst suggesting that caesium may be a promoter for the methanol synthesis reaction. Methanol decomposition on a caesium-doped copper catalyst produced a small number of formate species on copper and caesium oxide. Methoxy groups on caesium oxide decomposed to CO and H₂, and subsequent reaction between CO and adsorbed oxygen resulted in carboxylate formation. Methoxy species located at interfacial sites appeared to exhibit unusual adsorption properties.     

Tackling increased CO2 concentration in feeds for existing acid gas removal units: A simulation study based on a customized CO2 kinetics model

A Middle East-based amine sweetening unit, with an overall capacity of about 2.2 BSCFD of gas, is among the world’s largest process plants and currently processes sour gas with 10 mol% of hydrogen sulfide (H₂S) and carbon dioxide (CO₂) put together. Current expectation is that acid gas contents in the feed may increase beyond the design limit of the plant. The present work is an effort to quantify the effects of the feed gas CO₂ increase on the plant and to proffer solutions to handle these effects efficiently. We revised the kinetics of amine-based CO₂ absorption correlation of an existing model using real-data-driven parameters re-estimation. Evolutionary technique that employs particle swarm optimization algorithm is used for this purpose. The new CO₂ kinetic model is inserted in a first-principle process simulator, ProMax® V4.0, in order to analyze various solutions necessary to mitigate the operational challenges due to increased feed CO₂. The process plant with present design and operating conditions is determined to handle up to 8.45 mol% CO₂ contents in the sour gas feed. Further results revealed that methyldiethanolamine, diethanolamine, and dimethyl ether propylene glycol (DEPG) could not handle this high feed CO₂ challenge, even at maximum (design) steam and solvent usage. However, diglycolamine exclusively renders the solution as it treats high CO₂ feed gas efficiently with allowable utility consumption, while satisfying the constraints imposed by product gas specifications.     

Biodegradation ofVernonia galamensis seed Oil byAcinetobacter andPseudomonas sp.

The biodegradability ofVernonia galamensis seed oil (VO) has been demonstrated with two environmental bacterial strains,Acinetobacter Iwoffi (HU 3955), andPseudomonas sp. (HU 4020). A time-dependent increase in the degradative activities of both bacteria species was apparent. There wasca. 60% decrease in the amount of VO over an eightday incubation period. Additionally, lipolytic activity was evident from the amount of free fatty acid (FFA) that was generated. The percent FFA of the residual oil were 82% for thePseudomonas strain, and 62% for theAcinetobacter strain. The weight per epoxy value of the VO in the fermentation medium remained relatively constant over the incubation period, suggesting the lack of preference for either the epoxidized or nonepoxidized acids present in VO.     

Transcritical CO2 Heat Pump Dryer: Part 1. Mathematical Model and Simulation

In this study, a mathematical model and simulation code has been developed to investigate the performance of a transcritical CO₂ heat pump dryer. The model takes into account detailed heat and mass transfer and pressure drop phenomena occurring in each component of the system. To take care of the variable heat transfer properties, the heat exchanger components were divided into several infinitesimal segments to examine the state, heat and mass balance and pressure drop for both refrigerant and air, and hence accurate results are expected. In Part 2 of the article, the model developed has been validated with experimental data and then the model was used to investigate effects of important operating parameters on the performance.     

Floral CO2 Reveals Flower Profitability to Moths

The hawkmoth Manduca sexta (Lepidoptera: Sphingidae), an experimentally favorable Lepidopteran that is highly sensitive to carbon dioxide (CO2), feeds on the nectar of a range of flowering plants, such as Datura wrightii (Solanaceae). Newly opened Datura flowers give off dramatically elevated levels of CO2 and offer ample nectar. Thus, floral CO2 emission could indicate food-source profitability. This study documents that foraging Manduca moths prefer surrogate flowers that emit high levels of CO2, characteristic of newly opened Datura flowers. We show for the first time that CO2 may play an important role in the foraging behavior of nectar-feeding insects.     

Hydrotalcites for adsorption of CO2 at high temperature

Adsorption of carbon dioxide by hydrotalcites was investigated by using a gravimetric method at 450 ‡C. Hydrotalcites possessed higher adsorption capacity of CO₂ than other basic materials such as MgO and Al₂O₃. Two different preparation methods of hydrotalcite with varying Mg/Al ratio were employed to determine their effects on the adsorption capacity of CO₂. In addition, varying amounts of K₂CO₃ were impregnated on the hydrotalcite to further increase its adsorption capacity of CO₂. The hydrotalcite prepared by the high supersaturation method with Mg/Al=2 showed the most favorable adsorption-desorption pattern with high adsorption capacity of CO₂. K₂CO₃ impregnation on the hydrotalcite increased the adsorption capacity of CO₂ because it changed both the chemical and the physical properties of the hydrotalcite. The optimum amount of K₂CO₃ impregnation was 20 wt%. The hydrotalcite prepared by the high supersaturation method with Mg/Al=2 and 20 wt% K₂CO₃ impregnation has the highest adsorption capacity of CO₂ with 0.77 mmol CO₂/g at 450 ‡C and 800 mmHg.     

DECOMPOSITION BEHAVIOR AND MECHANISM OF CALCIUM SULFATE UNDER THE CONDITION OF O2/CO2 PULVERIZED COAL COMBUSTION

The decomposition behavior and mechanism of calcium sulfate in O₂/CO₂ pulverized coal combustion were studied in an entrained flow reactor. A reaction rate expression correlating the influence of various factors was proposed for CaS0₄ decomposition and it is able to predict CaS0₄ decomposition satisfactorily. Under the conditions investigated, the decomposition of CaS0₄ was found to be a regime of chemically controlled shrinking core reaction. A CO₂-rich atmosphere enhances CaSO₄ decomposition in absence of oxygen. CaSO₄ particles have catalytic effect on formation of CO from CO₂. A high SO₂ concentration inhibits CaSO₄ decomposition. The kinetics of CaSO₄decomposition has obvious dependence on experimental facilities and conditions, whereas the activation energy has much lower dependence. The kinetics derived in this work is more appropriate for investigating desulfurization in O₂/CO₂ pulverized coal combustion because an entrained flow reactor has a much closer condition to that in O₂/CO₂ pulverized coal combustion than a TGA.     

Effects of potassium on the chemisorption of CO2 and CO on the Mo2C/Mo(100) surface

The interaction of CO₂ with K-promoted Mo₂C/Mo(100) has been studied with high-resolution electron energy loss spectroscopy, work function measurements and temperature-programmed desorption. Pre-adsorbed potassium dramatically affects the adsorption behavior of CO₂ on the Mo₂C/Mo(100) surface. It increases the rate of adsorption, the binding energy of CO₂ and it induces the dissociation of CO₂ through the formation of negatively charged CO₂. Potassium adatoms also promote the dissociation of adsorbed CO over Mo₂C. This revised version was published online in July 2006 with corrections to the Cover Date.     

Investigation of CO2 Reaction with CaO and an Acid Washed Lime in a Packed-Bed Reactor

In this work, a mathematical model was developed for the prediction of packed-bed reactor behavior for CaO+CO₂ reaction based on the random pore model. A natural limestone and a modified sorbent using acetic acid washing were used for the experiments. The performances of these sorbents were initially determined using a thermogravimeter analyzer. Then, the reaction was accomplished in a packed-bed reactor for obtaining CO₂ breakthrough curves and investigation of model predictions. This model was able to successfully predict the effect of process conditions and solid texture on the breakthrough curves of the packed-bed reactor.     

Role of support in reforming of CH4 with CO2 over Rh catalysts

The reforming of CH₄ with CO₂ over supported Rh catalysts has been studied over a range of temperatures (550–1000 K). A significant effect of the support on the catalytic activity was observed, where the order was Rh/Al₂O₃>Rh/TiO₂>Rh/SiO₂. The catalytic activity of Rh/SiO₂ was promoted markedly by physical mixing of Rh/SiO₂ with metal oxides such as Al₂O₃, TiO₂, and MgO, indicating a synergetic effect. The role of the metal oxides used as the support and the physical mixture may be ascribed to the promotion in dissociation of CO₂ on the surface of Rh, since the CH₄ + CO₂ reaction is first order in the pressure of CO₂, suggesting that CO₂ dissociation is the rate-determining step. The possible model of the synergetic effect was proposed.     

Low temperature oxidation of CO over supported PdCl2-CuCl2 catalysts

PdCl₂-CuCl₂ catalyst supported on activated carbon was examined for the low temperature oxidation of CO. The catalyst developed in the present study was active and stable at ambient conditions if water were existing in the feed gas stream. The addition of Cu(NO₃)₂ into the PdCl₂-CuCl₂ catalyst significantly enhanced the CO oxidation activity. X-ray diffraction study revealed that the role of Cu(NO₃)₂ was to stabilize active Cu(II) species, Cu₂Cl(OH)₃, on the catalyst surface which maintains the redox property of palladium. When HC1 and SO₂ were also existing in the feed, they easily inactivated the catalyst. It was found that HC1 and SO₂ inhibited the formation of active Cu(II) species on the catalyst surface.