Separation characteristics of tetrapropylammoniumbromide templating silica/alumina composite membrane in CO<Subscript>2</Subscript>/N<Subscript>2</Subscript>, CO<Subscript>2</Subscript>/H<Subscript>2</Subscript> and CH<Subscript>4</Subscript>/H<Subscript>2</Subscript> systems

Nanoporous silica membrane without any pinholes and cracks was synthesized by organic templating method. The tetrapropylammoniumbromide (TPABr)-templating silica sols were coated on tubular alumina composite support ( γ-Al₂O₃/ α-Al₂O₃ composite) by dip coating and then heat-treated at 550 °C. By using the prepared TPABr templating silica/alumina composite membrane, adsorption and membrane transport experiments were performed on the CO₂/N₂, CO₂/H₂ and CH₄/H₂ systems. Adsorption and permeation by using single gas and binary mixtures were measured in order to examine the transport mechanism in the membrane. In the single gas systems, adsorption characteristics on the α-Al₂O₃ support and nanoporous unsupport (TPABr templating SiO₂/ γ-Al₂O₃ composite layer without α-Al₂O₃ support) were investigated at 20–40 °C conditions and 0.0–1.0 atm pressure range. The experimental adsorption equilibrium was well fitted with Langmuir or/and Langmuir-Freundlich isotherm models. The α-Al₂O₃ support had a little adsorption capacity compared to the unsupport which had relatively larger adsorption capacity for CO₂ and CH₄. While the adsorption rates in the unsupport showed in the order of H₂> CO₂> N₂> CH₄ at low pressure range, the permeate flux in the membrane was in the order of H₂≫N₂> CH₄> CO₂. Separation properties of the unsupport could be confirmed by the separation experiments of adsorbable/non-adsorbable mixed gases, such as CO₂/H₂ and CH₄/H₂ systems. Although light and non-adsorbable molecules, such as H₂, showed the highest permeation in the single gas permeate experiments, heavier and strongly adsorbable molecules, such as CO₂ and CH₄, showed a higher separation factor (CO₂/H₂=5-7, CH₄/H₂=4-9). These results might be caused by the surface diffusion or/and blocking effects of adsorbed molecules in the unsupport. And these results could be explained by surface diffusion. This paper is dedicated to Professor Hyun-Ku Rhee on the occasion of his retirement from Seoul National University.     

Effect of coal blending ratio on CO<Subscript>2</Subscript> coke gasification

Coke gasification is largely influenced by the raw coal, catalyst, and blending ratios, pore structure, and specific surface area of the raw coal. In this study, several properties of cokes related to their reactivity were measured using coke reactivity test apparatus (CRTA), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), Brunauer-Emmet-Teller (BET) surface area analysis, and energy dispersive X-ray spectroscopy (EDS) to investigate the characteristics of coke gasification. The results indicated that the reactivity of coke in the temperature range from 950 to 1,050 °C was affected by the type of coke and its specific surface area rather than the general properties of the coke, although the overall reactivities at the other temperatures were uniform. EDS analysis showed that the catalyst acted on the reactivity of cokes at low temperatures, whereas the BET analysis indicated that the reactivity at high temperature was influenced by the specific surface area.     

CO<Subscript>2</Subscript> methanation and co-methanation of CO and CO<Subscript>2</Subscript> over Mn-promoted Ni/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts

A series of Mn-promoted 15 wt-% Ni/Al₂O₃ catalysts were prepared by an incipient wetness impregnation method. The effect of the Mn content on the activity of the Ni/Al₂O₃ catalysts for CO₂ methanation and the comethanation of CO and CO₂ in a fixed-bed reactor was investigated. The catalysts were characterized by N2 physisorption, hydrogen temperature-programmed reduction and desorption, carbon dioxide temperature-programmed desorption, X-ray diffraction and highresolution transmission electron microscopy. The presence of Mn increased the number of CO₂ adsorption sites and inhibited Ni particle agglomeration due to improved Ni dispersion and weakened interactions between the nickel species and the support. The Mn-promoted 15 wt-% Ni/Al₂O₃ catalysts had improved CO₂ methanation activity especially at low temperatures (250 to 400 °C). The Mn content was varied from 0.86% to 2.54% and the best CO₂ conversion was achieved with the 1.71Mn-Ni/Al₂O₃ catalyst. The co-methanation tests on the 1.71Mn-Ni/Al₂O₃ catalyst indicated that adding Mn markedly enhanced the CO₂ methanation activity especially at low temperatures but it had little influence on the CO methanation performance. CO₂ methanation was more sensitive to the reaction temperature and the space velocity than the CO methanation in the co-methanation process.

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Efficient pressure swing adsorption for improving H<Subscript>2</Subscript> recovery in precombustion CO<Subscript>2</Subscript> capture

An efficient design for pressure swing adsorption (PSA) operations is introduced for CO₂ capture in the pre-combustion process to improve H₂ recovery and CO₂ purity at a low energy consumption. The proposed PSA sequence increases the H₂ recovery by introducing a purge step which uses a recycle of CO₂-rich stream and a pressure equalizing step. The H₂ recovery from the syngas can be increased over 98% by providing a sufficient purge flow of 48.8% of the initial syngas feeding rate. The bed size (375m³/(kmol CO₂/s)) and the energy consumption for the compression of recycled CO₂-rich gas (6 kW/(mol CO₂/s)) are much smaller than those of other PSA processes that have a CO₂ compression system to increase the product purity and recovery.     

Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and CeO<Subscript>2</Subscript>-promoted MgO sorbents for CO<Subscript>2</Subscript> capture at moderate temperatures

A series of Al₂O₃ and CeO₂ modified MgO sorbents was prepared and studied for CO₂ sorption at moderate temperatures. The CO₂ sorption capacity of MgO was enhanced with the addition of either Al₂O₃ or CeO₂. Over Al₂O₃-MgO sorbents, the best capacity of 24.6 mg- CO₂/g-sorbent was attained at 100 °C, which was 61% higher than that of MgO (15.3 mg-CO₂/g-sorbent). The highest capacity of 35.3 mg-CO₂/g-sorbent was obtained over the CeO₂-MgO sorbents at the optimal temperature of 200 °C. Combining with the characterization results, we conclude that the promotion effect on CO₂ sorption with the addition of Al₂O₃ and CeO₂ can be attributed to the increased surface area with reduced MgO crystallite size. Moreover, the addition of CeO₂ increased the basicity of MgO phase, resulting in more increase in the CO₂ capacity than Al₂O₃ promoter. Both the Al₂O₃-MgO and CeO₂-MgO sorbents exhibited better cyclic stability than MgO over the course of fifteen CO₂ sorption-desorption cycles. Compared to Al₂O₃, CeO₂ is more effective for promoting the CO₂ capacity of MgO. To enhance the CO₂ capacity of MgO sorbent, increasing the basicity is more effective than the increase in the surface area.

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N<Subscript>2</Subscript>O fluxes and CO<Subscript>2</Subscript> exchange at different N doses under elevated CO<Subscript>2</Subscript> concentration in boreal agricultural mineral soil under <Emphasis Type="Italic">Phleum pratense</Emphasis>

The effects of elevated atmospheric CO₂ concentration on N₂O fluxes, instant CO₂ exchange and the biomass production of timothy (Phleum pratense) were studied in the laboratory. Three sets of 12 farmed sandy soil mesocosms sown with Phleum pratense were fertilised with a commercial fertiliser in order to add 5, 10 and 15 g N m⁻², and equally distributed in four thermo-controlled greenhouses. In two of the greenhouses, the CO₂ concentration was kept at atmospheric concentration (360 μmol mol⁻¹), and in the other two at double the ambient concentration (720 μmol mol⁻¹). Forage was harvested and the plants fertilised twice during the N₂O measurements. This was followed by an extra fertilisation and harvesting. After the third harvest, the growth of P. pratense was maintained at a height of 18 cm for measurements of instant CO₂ exchange, performed in two growth chambers. N₂O exchange was monitored using a closed chamber technique and a gas chromatograph. Instant CO₂ exchange was monitored using an infrared gas analyser. N₂O was emitted from the soil in the low, moderate and high N treatments at both CO₂ concentrations when the moisture content was low, the N₂O probably being mainly derived from nitrification. The highest flux (3303 μg N₂O m⁻² h⁻¹) occurred in the highest N treatment before thinning the stand of P. pratense under elevated CO₂ concentration. P. pratense was acclimated to the elevated CO₂ concentration: the NEE and P _G of the elevated growth of P. pratense decreased, in contrast to the fluxes of the normal ambient growth, when measured at the changed CO₂ concentration (ambient). The rate of respiration (R _TOT) in the agroecosystem did not increase due to the elevated CO₂ concentration, but instead the results indicated decreased R _TOT (on average 2049 and 1808 mg CO₂ m⁻² h⁻¹ at ambient and elevated CO₂ concentration, respectively) when there was an abundant N supply. This infers the possibility of enhanced C accumulation in agriculture mineral soil via P. pratense under an increased atmospheric CO₂ supply.     

Simplified synthesis of K<Subscript>2</Subscript>CO<Subscript>3</Subscript>-promoted hydrotalcite based on hydroxide-form precursors: Effect of Mg/Al/K<Subscript>2</Subscript>CO<Subscript>3</Subscript> ratio on high-temperature CO<Subscript>2</Subscript> sorption capacity

Hydrotalcite was synthesized from hydroxide-form precursors to prepare a novel high-temperature CO₂ sorbent, and the effect of Mg/Al ratio on CO₂ sorption was studied. To enhance the CO₂ sorption capacity of the sorbent, K₂CO₃ was coprecipitated during the synthetic reaction. X-ray diffraction analysis indicated that the prepared samples had a well-defined crystalline hydrotalcite structure, and confirmed that K₂CO₃ was successfully coprecipitated in the samples. The morphology of the hydrotalcite was confirmed by scanning electron microscopy, and N₂ adsorption analysis was used to estimate its surface area and pore volume. In addition, thermogravimetric analysis was used to measure its CO₂ sorption capacity, and the results revealed that the Mg: Al: K₂CO₃ ratio used in the preparation has an optimum value for maximum CO₂ sorption capacity.     

Ni-Co bimetallic catalyst for CH<Subscript>4</Subscript> reforming with CO<Subscript>2</Subscript>

A co-precipitation method was employed to prepare Ni/Al₂O₃-ZrO₂, Co/Al₂ O₃-ZrO₂ and Ni-Co/Al₂O₃-ZrO₂ catalysts. Their properties were characterized by N₂ adsorption (BET), thermogravimetric analysis (TGA), temperature-programmed reduction (TPR), temperature-programmed desorption (CO₂-TPD), and temperature-programmed surface reaction (CH₄-TPSR and CO₂-TPSR). Ni-Co/Al₂O₃-ZrO₂ bimetallic catalyst has good performance in the reduction of active components Ni, Co and CO₂ adsorption. Compared with mono-metallic catalyst, bimetallic catalyst could provide more active sites and CO₂ adsorption sites (C + CO₂ = 2CO) for the methane-reforming reaction, and a more appropriate force formed between active components and composite support (SMSI) for the catalytic reaction. According to the CH₄-CO₂-TPSR, there were 80.9% and 81.5% higher CH₄ and CO₂ conversion over Ni-Co/Al₂O₃-ZrO₂ catalyst, and its better resistance to carbon deposition, less than 0.5% of coke after 4 h reaction, was found by TGA. The high activity and excellent anti-coking of the Ni-Co/Al₂O₃-ZrO₂ catalyst were closely related to the synergy between Ni and Co active metal, the strong metal-support interaction and the use of composite support.     

Kinetic study on carbonation of crude Li<Subscript>2</Subscript>CO<Subscript>3</Subscript> with CO<Subscript>2</Subscript>-water solutions in a slurry bubble column reactor

Investigations were conducted to purify crude Li₂CO₃ via direct carbonation with CO₂-water solutions at atmospheric pressure. The experiments were carried out in a slurry bubble column reactor with 0.05 m inner diameter and 1.0 m height. Parameters that may affect the dissolution of Li₂CO₃ in the CO₂-water solutions such as CO₂-bubble perforation diameter, CO₂ partial pressure, CO₂ gas flow rate, Li₂CO₃ particle size, solid concentration in the slurry, reaction temperature, slurry height in the column and so on were investigated. It was found that the increases of CO₂ partial pressure, and CO₂ flow rate were favorable to the dissolution of Li₂CO₃, which had the opposite effects with Li₂CO₃ particle size, solid concentration, slurry height in the column and temperature. On the other hand, in order to get insight into the mechanism of the refining process, reaction kinetics was studied. The results showed that the kinetics of the carbonation process can be properly represented by 1−3(1−X)^2/3+2(1–X)=kt+b, and the rate-determining step of this process under the conditions studied was product layer diffusion. Finally, the apparent activation energy of the carbonation reaction was obtained by calculation. This study will provide theoretical basis for the reactor design and the optimization of the process operation.     

Techno-economic assessment of pulverized coal boilers and IGCC power plants with CO<Subscript>2</Subscript> capture

The current studies on power plant technologies suggest that Integrated Gasification Combined Cycle (IGCC) systems are an effective and economic CO₂ capture technology pathway. In addition, the system in conventional configuration has the advantage of being more “CO₂ capture ready” than other technologies. Pulverized coal boilers (PC) have, however, proven high technical performance attributes and are economically often most practical technologies. To highlight the pros and cons of both technologies in connection with an integrated CO₂ capture, a comparative analysis of ultrasupercritical PC and IGCC is carried out in this paper. The technical design, the mass and energy balance and the system optimizations are implemented by using the ECLIPSE chemical plant simulation software package. Built upon these technologies, the CO₂ capture facilities are incorporated within the system. The most appropriate CO₂ capture systems for the PC system selected for this work are the oxy-fuel system and the postcombustion scheme using Monoethanolamine solvent scrubber column (MEA). The IGCC systems are designed in two configurations: Water gas shift reactor and Selexol-based separation. Both options generate CO₂-rich and hydrogen rich-gas streams. Following the comparative analysis of the technical performance attributes of the above cycles, the economic assessment is carried out using the economic toolbox of ECLIPSE is seamlessly connected to the results of the mass and energy balance as well as the utility usages. The total cost assessment is implemented according to the step-count exponential costing method using the dominant factors and/or a combination of parameters. Subsequently, based on a set of assumptions, the net present value estimation is implemented to calculate the breakeven electricity selling prices and the CO₂ avoidance cost.     

Effect of CO<Subscript>2</Subscript> concentration on the performance of different thermodynamic models for prediction of CH<Subscript>4</Subscript>+CO<Subscript>2</Subscript>+H<Subscript>2</Subscript>O hydrate equilibrium conditions

Accurate prediction of phase equilibria regarding CH₄ replacement in hydrate phase with high pressure CO₂ is an important issue in modern reservoir engineering. In this work we investigate the possibility of establishing a thermodynamic framework for predicting the hydrate equilibrium conditions for evaluation of CO₂ injection scenarios. Different combinations of equations of state and mixing rules are applied and the most accurate thermodynamic models at different CO₂ concentration ranges are proposed.     

Dye sensitized CO<Subscript>2</Subscript> reduction over pure and platinized TiO<Subscript>2</Subscript>

TiO₂ thin and thick films promoted with platinum and organic sensitizers including novel perylene diimide dyes (PDI) were prepared and tested for carbon dioxide reduction with water under visible light. TiO₂ films were prepared by a dip coating sol–gel technique. Pt was incorporated on TiO₂ surface by wet impregnation [Pt(on).TiO₂], or in the TiO₂ film [Pt(in).TiO₂] by adding the precursor in the sol. When tris (2,2′-bipyridyl) ruthenium(II) chloride hexahydrate was used as sensitizer, in addition to visible light activity towards methane production, H₂ evolution was also observed. Perylene diimide derivatives used in this study have shown light harvesting capability similar to the tris (2,2′-bipyridyl) ruthenium(II) chloride hexahydrate.     

CO<Subscript>2</Subscript> capture using aqueous solutions of K<Subscript>2</Subscript>CO<Subscript>3</Subscript>+2-methylpiperazine and monoethanolamine: Specific heat capacity and heat of absorption

The specific heat capacity, heat of CCO₂ absorption, and CCO₂ absorption capacity of aqueous solutions of potassium carbonate (K₂CO₃)+2-methylpiperazine (2-MPZ) and monoethanolamine (MEA) were measured over various temperatures. An aqueous solution of K₂CO₃+2-MPZ is a promising absorbent for CCO₂ capture because it has high CCO₂ absorption capacity with improved absorption rate and degradation stability. Aqueous solution of MEA was used as a reference absorbent for comprison of the thermodynamic characteristics. Specific heat capacity was measured using a differential scanning calorimeter (DSC), and heat of CCO₂ absorption and CCO₂ absorption capacity were measured using a differential reaction calorimeter (DRC). The CCO₂-loaded solutions had lower specific heat capacities than those of fresh solutions. Aqueous solutions of K₂CO₃+2-MPZ had lower specific heat capacity than those of MEA over the temperature ranges of 303-353 K. Under the typical operating conditions for the process (CCO₂ loading=0.23mol-CCO₂·mol^?1-solute in fresh solution, T=313 K), the heat of absorption (?ΔHabs) of aqueous solutions of K₂CO₃+2-MPZ and MEA were approximately 49 and 75 kJ·mol-CO₂, respectively. The thermodynamic data from this study can be used to design a process for CCO₂ capture.     

Photoreduction of CO<Subscript>2</Subscript> into CH<Subscript>4</Subscript> using Bi<Subscript>2</Subscript>S<Subscript>3</Subscript>-TiO<Subscript>2</Subscript> double-layered dense films

Nano-sized bismuth sulfide (Bi₂S₃) and titanium dioxide (TiO₂) with the orthorhombic and anatase tetragonal structures, respectively, were synthesized for application as catalysts for the reduction of carbon dioxide (CO₂) to methane (CH₄). Four double-layered dense films were fabricated with different coating sequences—TiO₂ (bottom layer)/Bi₂S₃ (top layer), Bi₂S₃/TiO₂, TiO₂/Bi₂S₃: TiO₂ (1 : 1) mix, and Bi₂S₃: TiO₂ (1 : 1) mix/Bi₂S₃: TiO₂ (1 : 1) mix—and applied to the photoreduction of CO₂ to CH₄; the catalytic activity of the fabricated films was compared to that of the pure TiO₂/TiO₂ and Bi₂S₃/Bi₂S₃ doubled-layered films. The TiO₂/Bi₂S₃ double-layered film exhibited superior photocatalytic behavior, and higher CH₄ production was obtained with the TiO₂/Bi₂S₃ double-layered film than with the other films. A model of the mechanism underlying the enhanced photoactivity of the TiO₂/Bi₂S₃ double-layered film was proposed, and it was attributed in effective charge separation.     

Self-Metathesis of 1-Octene Using Alumina-Supported Re<Subscript>2</Subscript>O<Subscript>7</Subscript> in Supercritical CO<Subscript>2</Subscript>

In this contribution we describe the use of heterogeneous catalysts for the liquid-phase self-metathesis of 1-octene in supercritical CO₂. Our work aims at addressing the mass-transfer problems associated with such reaction systems. By coupling a heterogeneous supported Re₂O₇ catalyst with the use of scCO₂, the self-metathesis of 1-octene takes place by and large much more rapidly than in traditional solvent media, and furthermore, by using scCO₂ the overall efficiency and sustainability of the transformation can be improved.