Synthesis,Characterization, and Visible Light Degradation of Rhodamine B Dye by Carbon-Covered Alumina Supported Pd-TiO2/Polysulfone Membranes

Palladium doped titania nanoparticles supported on carbon-covered alumina (CCA/Pd-TiO₂) impregnated polysulfone (PS) membranes were prepared by the phase inversion technique. The nano-sized CCA/Pd-TiO₂ nanoparticles were uniformly dispersed in 18 wt% PS casting solution to synthesize CCA/Pd-TiO₂ polysulfone membranes (PS/CCA/Pd-TiO₂). The amount of the CCA/Pd-TiO₂ was varied between 0.25% and 0.5% to form two types of membranes. These were casted on a non-woven fabric. The nanoparticles were added in order to enhance the photodegradation potential of the PS membranes under visible light. Raman, XRD, SEM, TGA, TGA-FTIR was used to characterize the membranes. The mechanical strength of the membranes was determined with an Instron tensile tester. The SEM results suggested that these membranes had a high degree of porosity and the nanoparticles were distributed on and within the PS membrane. The Raman analysis revealed the presence of the nanoparticles within the membrane matrix while the XRD results exposed the probability of interactions between the polymer and the nanoparticles. The two membranes were then tested for their capability to photodegrade Rhodamine B under visible light illumination. The 0.5% PS/CCA/Pd-TiO₂ membrane photodegraded 80.4% of the dye while the 0.25% PS/CCA/Pd-TiO₂ membrane degraded 70.8% of Rhodamine B over a 270 min period. The photodegradation followed a pseudo first-order reaction rate and the apparent rates were 0.00597 and 0.00448 min^?1 for 0.5% PS/CCA/Pd-TiO₂ membrane and 0.25% PS/CCA/Pd-TiO₂, respectively.     

Effect of H2S on the CO2 corrosion of carbon steel in acidic solutions

The objective of this study is to evaluate the effect of low-level hydrogen sulfide (H₂S) on carbon dioxide (CO₂) corrosion of carbon steel in acidic solutions, and to investigate the mechanism of iron sulfide scale formation in CO₂/H₂S environments. Corrosion tests were conducted using 1018 carbon steel in 1 wt.% NaCl solution (25 °C) at pH of 3 and 4, and under atmospheric pressure. The test solution was saturated with flowing gases that change with increasing time from CO₂ (stage 1) to CO₂/100 ppm H₂S (stage 2) and back to CO₂ (stage 3). Corrosion rate and behavior were investigated using linear polarization resistance (LPR) technique. Electrochemical impedance spectroscopy (EIS) and potentiodynamic tests were performed at the end of each stage. The morphology and compositions of surface corrosion products were analyzed using scanning electron microscopy (SEM)/energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The results showed that the addition of 100 ppm H₂S to CO₂ induced rapid reduction in the corrosion rate at both pHs 3 and 4. This H₂S inhibition effect is attributed to the formation of thin FeS film (tarnish) on the steel surface that suppressed the anodic dissolution reaction. The study results suggested that the precipitation of iron sulfide as well as iron carbonate film is possible in the acidic solutions due to the local supersaturation in regions immediately above the steel surface, and these films provide corrosion protection in the acidic solutions.     

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.     

Oxidative coupling of methane by carbon dioxide: a highly C2 selective La2O3/ZnO catalyst

In the oxidative coupling of methane by carbon dioxide, La₂O₃/ZnO catalysts were found to have high C₂ selectivity and good stability. The coupling selectivity on La₂O₃/ZnO is about 90%, which is much higher than that on pure La₂O₃ or ZnO. The consumption ratio of carbon dioxide to methane is approximately one. X-ray diffraction analysis reveals that the structural forms of the oxides are unchanged during the reaction. The reaction mechanism for C₂ formation is discussed.     

Experimental study on CO2 hydrate formation in the presence of TiO2, SiO2, MWNTs nanoparticles

ABSTRACT

A series of experiments on CO₂ hydrate formation were carried out in the presence of titanium dioxide (TiO₂), silicon dioxide (SiO₂), multi-walled carbon nanotubes (MWNTs) nanoparticles. The effects of these nanoparticles on induction time, final gas consumption, and gas storage capacity have been investigated at the temperature of 274.15 K and the initial pressure of 5.0 MPa.g. The induction time of CO₂ hydrate formation was remarkably shortened to 12.5 min in the presence of 0.005 wt% MWNTs nanoparticles. The high thermal conductivity and heat capacity of MWNTs nanoparticles presented better heat transfer, and large surface area provided more suitable sites for heterogeneous nucleation of CO₂ hydrate.     

Photocatalytic reaction of H2O+CO2 over pure and doped Rh/TiO2

In the photocatalytic reduction of carbon dioxide to formic acid, formaldehyde and methanol in aqueous suspensions of TiO₂ and Rh/TiO₂, the effects of doping the TiO₂ with W⁶⁺ were investigated.This laboratory is a part of the Center for Catalysis, Surface and Material Science at the University of Szeged.     

A two-step depressurization batch process for the formation of bi-modal cell structure polystyrene foams using scCO2

A two-step depressurization batch process is developed to produce bi-modal cell structure polystyrene (PS) foams by using supercritical carbon dioxide (SC-CO₂) as the blowing agent. Bi-modal cell structure foams can be achieved by depressurization in two distinct steps and can be significantly affected by the process parameters. The process conditions at the holding stage between the two steps are the key to controlling the bi-modal cell structure. The findings of this study can help predict the bi-modal cell morphology of PS and other polymers prepared by a two-step depressurization bath process.     

Synthesis of vicinal diamines via Zn–H2O–CO2-induced reduction of aromatic imines in supercritical carbon dioxide

Zn–H₂O–CO₂ is a good reducing reagent for the reduction of imines in supercritical carbon dioxide (scCO₂). They provide the corresponding vicinal diamines in moderate to good yields. The results showed that carbon dioxide plays an important role as both solvent and reagent.     

Transport and stability enhancement in interfacially and dimensionally constrained CO2 selective polymers embedded in nanoporous sieve membranes

Nanocomposite polymer and ultrathin film membranes have shown great promise in enhancing gas permeation and selectivity properties by interfacially straining polymer matrices, yielding structures of higher free volume. However, undesired particle aggregation and short temporal stability remain a big challenge. In the present study, an “inverse” architecture to conventional polymer nanocomposites was investigated, in which the polymer phase poly(l-trimethylsilyl-1-propyne) (PTMSP) was interfacially and dimensionally constrained in nanoporous anodic aluminum oxide (AAO) membranes. While with this architecture the benefits of nanocomposite and ultrathin film membranes could be reproduced and improved upon, also the temporal stability could be enhanced substantially. Gas permeabilities of helium, nitrogen and carbon dioxide were increased over five-fold, and selectivities of CO₂/He and CO₂/N₂ could be enhanced by 40% compared to the pristine bulk phase, while physical aging, caused by free-volume collapse, was reduced twenty-fold compared to ultrathin membranes.     

Absorption of carbon dioxide in aqueous MDEA solution coupling dust suppression under atomization

ABSTRACT

Large amounts of CO₂ and dust particles coming from power plant flue need to be captured and removed before flue is discharged into the air. In present work, absorption of carbon dioxide in aqueous N-methylidiethanolamine (MDEA) solution coupling dust suppression has been studied in an atomization absorption column, with MDEA concentrations ranging from 0.1 to 0.5mol/L, and with atomization frequencies ranging from 50 to 80 HZ. The obtained experimental results show that absorption rate of CO₂ in aqueous MDEA solution can be enhanced when the absorption process couples a dust suppression one under the condition of atomization. The reason for it is attributed to the adsorption of droplets on the solid particles which restrains the amount of entrainment and makes more droplets contact with gas so as to increase effective mass transfer area, thus resulting in the increase of CO₂ absorption rate. The range of obtained enhancement factor is from 1.1 to 1.7. Mass transfer enhancement factor increases with the increase of MDEA concentration and atomization frequency at a certain range. Effective mass transfer areas and entrainment ratios suppressed have been calculated based on theoretic research. The results calculated agree with our experimental phenomena, and support the enhancement mass transfer mechanism proposed.     

High activity Ni/MoS2 catalysts obtained from alkylthiometalate mixtures for the hydrodesulfurization of dibenzothiophene

An efficient method for improving the catalytic properties of unsupported Ni/MoS₂ catalysts is mixing thiometalate precursors applying the appropriate precursors and thermal conditions. High active catalysts for the hydrodesulfurization (HDS) of dibenzothiophene (DBT) are prepared by the controlled decomposition of physical mixtures of Ni(diethylentriamine)₂MoS₄ (NDTA-TM) and [(Propyl)₄N)]₂MoS₄ (TPA-TM). The catalysts with a higher content of NDTA-TM are very active with a high selectivity for the direct desulfurization pathway (DDS) due to the synergistic effect of nickel. In addition the presence of a large amount of carbon may produce single-slabs of nickel promoted carbon containing molybdenum sulfides. The activity enhancement is attributed to an increased number of NiMoS active sites originated by the chemical interaction between the precursors NDTA-TM and TPA-TM during the mixing procedure. Furthermore, the carbon content in the final products is related to the enhancement of the activity and the preference of the DDS pathway. The controlled decomposition of mixtures of NDTA-TM + TPA-TM yields catalysts which are about twofold more active than an industrial NiMo/Al₂O₃ catalyst. This improvement may be attributed to an intense interaction of the precursors during the synthesis causing a re-dispersion of nickel atoms from NDTA-TM over the surface of carbon containing molybdenum sulfide provided by the precursor TPA-TM, increasing the amount of active sites. The catalysts from mixtures of (NH₄)₂MoS₄ (A-TM) and NDTA-TM behave similarly to the pure precursors.     

Design and operation of pilot plant for CO2 capture from IGCC flue gases by combined cryogenic and hydrate method

This project is a trial conducted under contract with CO₂CRC, Australia of a new CO₂ capture technology that can be applied to integrated gasification combined cycle power plants and other industrial gasification facilities. The technology is based on combination of two low temperature processes, namely cryogenic condensation and the formation of hydrates, to remove CO₂ from the gas stream. The first stage of this technology is condensation at −55 °C where CO₂ concentration is expected to be reduced by up to 75 mol%. Remaining CO₂ is captured in the form of solid hydrate at about 1 °C reducing CO₂ concentration down to 7 mol% using hydrate promoters. This integrated cryogenic condensation and CO₂ hydrate capture technology hold promise for greater reduction of CO₂ emissions at lower cost and energy demand. Overall, the process produced gas with a hydrogen content better than 90 mol%. The concentrated CO₂ stream was produced with 95-97 mol% purity in liquid form at high pressure and is available for re-use or sequestration. The enhancement of carbon dioxide hydrate formation and separation in the presence of new hydrate promoter is also discussed. A laboratory scale flow system for the continuous production of condensed CO₂ and carbon dioxide hydrates is also described and operational details are identified.     

Development and characterization of silica-based membranes for hydrogen separation

The method of chemical vapor deposition (CVD) in the counter current configuration was employed in the present study for the development of composite silica membranes. The experiments were carried out in a horizontal CVD reactor under controlled temperature conditions and at various reaction times and differential pressures across the substrate sides. Tetraethylorthosilicate (TEOS) and ozone were used as deposition precursors. Two types of substrates were employed: a porous Vycor tube and an alumina (γ-Al₂O₃) nanofiltration (NF) tube. Measurements with a novel mercury intrusion technique showed that significant reduction of the initial pore size of the γ-Al₂O₃ substrates was achieved, which reached 76% in the cases of extended silica deposition. Additionally, by appropriately interpreting the Knudsen type O₂ permeance results, acquired during the CVD treatment of Vycor tubes, a pore radius reduction even down to the 30% of the initial value was concluded. The permeance of Η₂ and other gases (Ηe, Ν₂, Αr, CO₂) on the developed membranes was measured in a home-made apparatus. The separation capability of the composite membranes was determined by calculating the selectivity of hydrogen over helium, nitrogen, argon and carbon dioxide.     

Investigation on kinetics of carbon dioxide absorption in aqueous solutions of monoethanolamine + 1, 3-diaminopropane

ABSTRACT

Environmental concerns from global warming and climate change demand carbon dioxide separation from post-combustion gases. Important parameters are involved in choosing the suitable solvent for carbon dioxide separation, including the reaction rate of carbon dioxide and the solvent. In this paper, the kinetics of carbon dioxide (CO₂) absorption in aqueous solutions of Monoethanolamine (MEA) + 1,3-Diaminopropane (DAP), a diamine containing two primary amino group, was developed. The measurements were performed in a stirred cell with a horizontal gas-liquid interface in the temperature range of 313.15–333.15 K and aqueous solutions of 10 wt% MEA + 5 wt% DAP and 12.5 wt% MEA + 2.5 wt% DAP. Experiments were conducted in an isothermal batch reactor with a horizontal gas-liquid interface under pseudo-first-order conditions, enabling the determination of the overall kinetic rate constant from the pressure drop method. Second-order reaction rate constants of CO₂ absorption in amine solutions were estimated using the calculated initial absorption rate. It was found that the rate constants in MEA+ DAP solutions were greater than in MEA solutions which means that DAP increases the reaction rate.     

Improving SAPO-34 performance for CO2/CH4 separation and optimization of adsorption conditions using central composite design

ABSTRACT

SAPO-34 molecular sieves have a high adsorption capacity in separation of CO₂ from CO₂/CH₄ mixture. In this study, SAPO-34 was modified by different solutions at various operating conditions to enhance the removal of carbon dioxide from the methane gas. Modifications can change pore size and also Si/Al ratio in SAPO-34 and make changes in the acidity of the adsorbent via the ion exchange process. The effects of temperature and pressure on the separation were studied using the design of experiments. Finally, based on the results of the experimental optimization process applying central composite design (CCD) method, the highest yield of CO₂ separation from the methane gas (95%) was obtained when using P-SAPO-34 sample at 17.4°C and 4.6 bar.     

CO2 Hydrogenation to Methanol Over Cu/ZnO/Al2O3 Catalysts Prepared by a Novel Gel-Network-Coprecipitation Method

A novel gel-network-coprecipitation process has been developed to prepare ultrafine Cu/ZnO/Al₂O₃ catalysts for methanol synthesis from CO₂ hydrogenation. It is demonstrated that the gel-network-coprecipitation method can allow the preparation of the ultrafine Cu/ZnO/Al₂O₃ catalysts by homogeneous coprecipitation of the metal nitrate salts in the gel network formed by gelatin solution, which makes the metallic copper in the reduced catalyst exist in much smaller crystallite size and exhibit a much higher metallic copper-specific surface area. The effect of the gel concentration of gelatin on the structure, morphology and catalytic properties of the Cu/ZnO/Al₂O₃ catalysts for methanol synthesis from hydrogenation of carbon dioxide was investigated. The Cu/ZnO/Al₂O₃ catalysts prepared by the gel-network-coprecipitation method exhibit a high catalytic activity and selectivity in CO₂ hydrogenation to methanol.     

Cloud-point measurement of the biodegradable poly(d,l-lactide-co-glycolide) solution in supercritical fluid solvents

Experimental data of high pressure phase behavior between 35 °C and 105 °C and pressures up to 2,200 bar is presented for poly(d,l-lactic acid)(d,l-PLA) and poly(lactide-co-glycolide)₁₅ (PLGA₁₅), PLGA₂₅, and PLGA₅₀ in supercritical carbon dioxide, trifluoromethane (CHF₃), chlorodifluoromethane (CHClF₂), dichloromethane (CH₂Cl₂), and chloroform (CHCl₃). d,l-PLA dissolves in carbon dioxide at pressures of 1,250 bar, in CHF₃ at pressures of 500 to 750 bar, and in CHClF₂ at pressures of 30–145 bar. As glycolic acid (glycolide) is added to the backbone of PLGA, the cloud point pressure increases by 36 bar/(mol GA) in carbon dioxide, 27 bar/(mol GA) in CHF₃, and by only 3.9 bar/(mol GA) in CHClF₂. PLGA₅₀ does not dissolve in carbon dioxide at pressures of 2,800 bar, whereas it is readily soluble in CHClF₂ at pressures as low as 95 bar at 40 °C. Cloud point behavior of d,l-PLA, PLGA₁₅, and PLGA₂₅ in supercritical carbon dioxide shows the effect of glycolide content between 35 °C and 108 °C. Also, the phase behavior for poly(lactic acid) — carbon dioxide-CHClF₂ mixture shows the changes of pressure-temperature slope, and with CHClF₂ concentration of 6 wt%, 19 wt%, 36 wt% and 65 wt%. The cloud-point behavior shows the impact of glycolide content on the phase behavior of PLA, PLGA₁₅, PLGA₂₅ and PLGA₅₀ in supercritical CHClF₂. A comparison was made between the phase behaviors of d,l-PLA and poly(l-lactide)(l-PLA) in supercritical CHF₃. The phase behavior of CHF₃ as a cosolvent for 5 wt% d,l-PLA-supercritical carbon dioxide system is presented for the effect being added 10 wt% and 29 wt% to CHF₃ content.     

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.     

CO2 reforming of methane over vanadia-promoted Rh/SiO2 catalysts

The reforming of methane with carbon dioxide over rhodium dispersed on silica, Rh/SiO₂, and vanadia-promoted silica, Rh/VO_x/SiO₂, was studied by kinetic test reactions under differential conditions in a temperature range from 723 to 773 K. Transmission infrared spectroscopy was applied to observe the interaction of CO₂ with the catalysts and the formation of surface intermediates during the CO₂–CH₄ reforming reaction. To analyze carbon deposition XP spectroscopy and TPO was carried out. It has been shown that the promotion of Rh/SiO₂ catalysts with vanadium oxide enhances the catalytic activity for CO₂ reforming of methane and decreases the deactivation by carbon deposition. This is attributed to the formation of a partial VO_x overlayer on the Rh surface, which reduces the size of accessible ensembles of Rh atoms required for coke formation and creates new sites at the Rh–VO_x interfacial region that are considered to be active sites for the activation/dissociation of carbon dioxide. This revised version was published online in June 2006 with corrections to the Cover Date.     

Solid-phase photocatalytic degradation of polystyrene with modified nano-TiO2 catalyst

A novel photodegradable polystyrene-grafted-TiO₂ (PS-g-TiO₂) nanocomposite was prepared by embedding the grafted-TiO₂ into the commercial polystyrene. Solid-phase photocatalytic degradation of the PS-g-TiO₂ nanocomposite was carried out in ambient air at room temperature under ultraviolet lamp and/or sunlight irradiation. The properties of composite film were compared with those of the pure PS film by methods such as weight loss measurement, scanning electron microscope (SEM), gel permeation chromatogram (GPC), X-ray photoelectron spectroscopy (XPS), FT-IR spectroscopy, and UV-vis spectroscopy. The results show that the photo-induced degradation of PS-g-TiO₂ composite film is significantly higher than that of pure PS film. The weight loss of composite film reached 31.9%, average molecular weight (M_w) of composite film decreased by 53.1%, and the number average molecular weight (M_n) decreased by 73.2% after 396 h of UV-light irradiation. FT-IR analysis and weight loss indicated that the benzene rings in PS-matrix of composite film were cleaved during UV-light irradiation. The photocatalytic degradation mechanism of the films is briefly discussed.