Study of methane and carbon dioxide adsorption capacity by synthetic nanoporous carbon based on pyrogallol-formaldehyde

Nanoporous carbons were synthesized at certain conditions by sol–gel method combined with furnace firing in inert atmosphere from pyrogallol-formaldehyde (PF) mixtures in water using perchloric acid as catalyst. Their morphology was studied experimentally to examine their adsorption capacity for greenhouse gases. The preparation conditions of the nanoporous carbons were explored by changing the pyrolysis temperature. The effect of this factor on determining the pore structures and the adsorption capacities were evaluated. The synthesized xerogels were characterized by X-ray diffraction, nitrogen adsorption–desorption isotherms, thermogravimetric analysis (TGA), differential thermal analysis (DTA), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results showed that surface areas and nitrogen adsorption capacity are dependent completely on the pyrolysis temperature. Equilibrium and enthalpies studies for the CO₂ and CH₄ adsorption on PF were measured at room temperature and up to 25 bar. The adsorption capacity on PF was highest for CO₂ and then CH₄. The best sample shows maximal adsorption capacities as follows 5.50 mmol g^?1 of CH₄ and 7.62 mmol g^?1 of CO₂ at 25 bar and 30 °C.     

Effect of contaminants from flue gas on CO2 sequestration in saline formation

Deep saline aquifers are reported to have the largest estimated capacity for CO₂ sequestration. Most geochemical studies on CO₂ storage in saline formations are focused on the interactions of pure CO₂ and do not consider the potential impacts of contaminants such as SO₂ found in typical post‐composition flue gas streams. This paper reports on results of a combined CO₂–co‐contaminant–brine–rock experimental and a simple modeling study of the potential impact of flue gas contaminants on saline formations. Chemical reactions of the sandstone from Mount Simon formation exposed to CO₂ mixed with other gas species under sequestration conditions were studied (i.e. solid material — representative Mount Simon sandstone; liquid — synthetic Illinois Basin brine; T and P — 50 °C, 110 bar; gas composition — 1% SO₂, 4% O₂, 95% CO₂). The experimental study indicates that the co‐injection of 1% SO₂ would lead to substantially reduced brine pH due to the formation of sulfuric acid and the formation of bassanite (major) and anhydrites. Preliminary equilibrium computational modeling yielded similar results. Copyright © 2013 John Wiley & Sons, Ltd.     

Hydrogen adsorption on natural and sulphuric acid treated sepiolite and bentonite

In this study, hydrogen (H₂) adsorption on sepiolite and bentonite and those of acid treated forms were studied at 77 K using volumetric apparatus up to 100 kPa. Both clay minerals were treated with 100 ml of 0.5, 1.0, 2.0 and 4.0 M H₂SO₄ solutions at 80 °C for 5 h. Differences in the structures of the sepiolite and bentonite samples before and after the acid treatments were determined by XRD, XRF, TG, DTA and N₂ adsorption methods. The level of H₂ adsorption of original and acid treated sepiolite samples (1.332–2.252 mmol/g) was higher than those of the bentonite samples (0.341–1.003 mmol/g). The variation in the H₂ adsorption capacities during the acid treatment was also discussed.     

Comprehensive evaluation of a CO2‐capturing high‐efficiency power generation system for utilizing waste heat from factories

It is becoming more important to realize CO₂‐capturing power generation systems (PGSs) for drastically decreasing an amount of CO₂ emission into the atmosphere. However, net power generation efficiency (NPGE) of a CO₂‐capturing system has been considered to be greatly deteriorated, since capturing CO₂ requires extra energy. This paper proposes a new CO₂‐capturing PGS that has a high‐efficient NPGE by utilizing waste heat from factories. As an example of a waste heat, exhaust gas with temperature 200°C from refuse incinerator plants is adopted. In the proposed system, the temperature of saturated steam produced by utilizing the waste heat is raised by combusting fuel with the use of pure oxygen in a combustor, and is used as the main working fluid of a gas turbine PGS. It is estimated that the proposed system has a fuel‐to‐electricity NPGE of 59.3%, when turbine inlet temperature (TIT) is assumed to be 1000°C. The economics of the proposed system is also evaluated and the CO₂ reduction cost is estimated to be small; 4.16 U.S. $ t⁻¹ CO₂ compared with 32.1 U.S. $ t⁻¹ CO₂ for a conventional steam turbine PGS. It is shown that CO₂‐capturing is not cost consuming but becomes to be profitable owing to improved power generation characteristics, when its TIT is increased from 1000 to 1200°C. Copyright © 2009 John Wiley & Sons, Ltd.     

Structural and textural control of high-pressure hydrogen adsorption on expandable and non-expandable clay minerals in geologic conditions

Both natural and anthropogenically-generated hydrogen gas occurs in sedimentary rocks and geotechnical barriers. Due to high-pressure conditions, a significant portion of H₂ can be physisorbed in available micropores of clay minerals, which have been proven to control the gas adsorption properties of rocks. This study investigates H₂ adsorption on clay minerals naturally occurring in rocks, by combining the high-pressure H₂ experiments with sample characterization analyzed using low-pressure adsorption of N₂ and CO₂, and structural analysis using X-ray diffraction. We found that H₂ adsorption depends strongly on the mineral texture, which is not related directly to its structure. Most of H₂ is adsorbed in the micropores accessible to CO₂. H₂ intercalates in the smectitic interlayers with a basal spacing larger than 10.8 Å. The density of adsorbed H₂ is about double that of free H₂ gas under given pressure and temperature, effectively increasing the gas storage capacity of rocks.     

Evaluation of Mg‐MOF‐74 for post‐combustion carbon dioxide capture through pressure swing adsorption

This paper presents a computational study of an energy‐efficient technique for post‐combustion CO₂ capture using novel material, namely, Mg‐MOF‐74, using pressure swing adsorption (PSA) processes. A detailed one‐dimensional, transient mathematical model has been formulated to include the heat and mass transfer, the pressure drop and multicomponent mass diffusion. The PSA model has been further extended by incorporating a heat regenerating process to enhance CO₂ sequestration. The heat dissipated during adsorption is stored in packed sand bed and released during desorption step for heating purpose. The model has been implemented on a MATLAB program using second‐order discretization. Validation of the model was performed using a complete experimental data set for CO₂ sequestration using zeolite 13X. Simulation of the PSA experiment on fixed bed has been carried out to evaluate the capacity of Mg‐MOF‐74 for CO₂ capture with varying feed gas temperature of 28 and 100 °C, varying pressurization and purge times and heat regeneration. It was discovered that the PSA process with heat regeneration system might be advantageous because it achieves equivalent amount of CO₂ sequestration in fewer PSA cycles compared with PSA without heat regeneration system. Based on the simulated conditions, CO₂ recovery with Mg‐MOF‐74 gives high percentage purity (above 98%) for the captured CO₂. Copyright © 2015 John Wiley & Sons, Ltd.     

Novel LaNi intercalated Egyptian bentonite clay for direct conversion of methane using CO2 as soft oxidant

Natural Egyptian bentonite clay intercalated with both La and Ni having different molar ratio (La: Ni = 2:1, 1:1 & 1:2) were prepared, saving 5mmole pillar/gm clay, using ultrasonic assistance method. The prepared catalysts were calcined at 450 and then reduced at 400 °C & 600 °C.Characterization of the prepared LaNi-PILC was achieved by X-ray diffraction (XRD), Furrier transform infrared spectroscopy (FTIR), N₂ adsorption desorption isotherm (BET) and H₂-temperature programmed reduction (H₂-TPR). The data confirm the success of intercalation process for both La & Ni in the lamellar structure of bentonite clay. The La: Ni molar ratio affected the specific surface area, Ni crystal size, dispersion and reducibility of the prepared catalyst. The reduction temperature had a great effect on the reactivity and product selectivity during CO₂/CH₄ reforming at different reaction temperatures (600–800 °C). Where, reduction at 400 °C gives rise to CH₄ oxidation reaction (MOR) with formaldehyde as a main product. While reduction at 600 °C enhances the activity and stability for CO₂ reforming of methane (CRM) and syngas production (H₂/CO ~ 1.19). The most active and stable LaNi_1:2-PILC₅ catalyst (CO₂ and CH₄ conversions reached 85% and 90% respectively) is superior with respect to the performance of PILC based catalysts reported in the literatures.     

Hydrogeochemistry of Damt thermal springs,Yemen Republic

The Damt thermal springs (40–45°C) flowing through travertine deposits belong to the Na–HCO₃ type of water and have higher pCO₂ ( from −118 to −058=PCO₂ from 007 to 026 atm) relative to cold Ca–SO₄− (Cl) groundwaters The cold waters have pCO₂ ranging from −186 to −250 (=PCO₂ from 0014 to 00035 atm) The chemical composition of the cold springs is controlled by evaporite deposits present in the Tawilah sandstone and Amran limestone formations while simple crustal dissolution coupled with CO₂-rich fluid–rock interaction control the chemical signature of the hot spring waters. The temperature of the feeding system based on the K ²/Mg geothermometer varies between 80 and 120°C Damt thermal springs appear to be related to a 10 000 year-old volcanic activity that led to the appearance of several craters in the area.     

Effect of NaOH addition on the thermochemical heat storage capacity of nanoporous molecular sieves

The water vapor sorption capacity and corresponding generated heat amount are the most important properties for adsorbents in thermochemical heat storage systems. In order to understand the adsorption/desorption behavior of three nanoporous molecular sieves such as 5A, mordenite and natural clinoptilolite (with different structures, Si/Al ratios and balancing cations), the pure zeolites and their composites (obtained by depositing NaOH onto the molecular sieves) were characterized in their structural and surface properties by using appropriate techniques (N₂ adsorption isotherms at ?196 °C, XRD and (MAS) NMR). The adsorption of water was performed using a Setaram TG‐DSC 111 apparatus. Three successive cycles of hydration (at 20 °C)/dehydration (at 150 °C) were carried out to check the stability of the system in conditions close to those used in adsorption heat pumps. The measured heats of dehydration vary in the 183–614 kJ kg^?1_sample range for the various samples that present also different water vapor sorption capacities (from ≈ 0.08 to ≈ 0.14 kg_H2O kg^?1_sample). The water adsorption/desorption behavior of the zeolites was mainly related to the porous structure and to the Si/Al ratio, that drive the affinity of zeolite to water. The experimental results showed that the impregnation of the three kinds of nanoporous zeolites with different amounts of sodium hydroxide negatively affects the sorption characteristics of the composites. The blockage of zeolite pores (that limits the access to water molecules), the slight amorphization of the zeolite structure and the formation of carbonates are some of the phenomena identified to influence the water sorption onto NaOH‐containing composites. Copyright © 2016 John Wiley & Sons, Ltd.     

Theoretical performance analysis of heat pump water heaters using carbon dioxide as refrigerant

The aim of this paper is to simulate the performance of an air source heat pump water heater using carbon dioxide (CO₂) as a working fluid. The heat pump water heating system consists of a compressor, a gas cooler, an expansion device and an evaporator. The computer simulation model has been developed by using the heat transfer data and the thermodynamic properties of CO₂. The effects on the heat pump performance by the operating parameters such as the compressor rotational speed, the inlet water temperature at the gas cooler, the inlet air temperature at the evaporator and the mass flow rate ratio of water to refrigerant were presented. For rated capacities of a 4 kW compressor with a 10 kW gas cooler and a 6 kW evaporator, the coefficient of performance is found to be between 2.0 and 3.0. The mass flow rate ratio of water and CO₂ between 1.2 and 2.2 is the most suitable value for generating hot water temperature above 60°C at 15–25°C ambient air temperature. Copyright © 2007 John Wiley & Sons, Ltd.     

Effect of supercritical CO2 as the organic solvent on cap rock sealing performance for underground storage

Supercritical CO₂ fluid is capable of extracting organic matter from rocks. Although the sealing performance of cap rock is essential for CO₂ underground storage, typical cap rock such as shale or mudstone usually contains organic matter. To determine how well cap rocks can seal supercritical CO₂, cap rock samples from the Nagaoka injection test site were treated with supercritical CO₂, and then the porosity and pore radius distribution of the samples were measured by mercury porosimetry. The results showed that the pore radius distributions slightly shifted to a larger size after treatment, while the porosity and permeability changed less than 1%.     

Electrochemical performance of different carbon fuels on a hybrid direct carbon fuel cell

In this work, three processed carbon fuels including activated carbon, carbon black and graphite have been employed to investigate influence of the chemical and physical properties of carbon on the HDCFC performance in different anode atmospheres at 650–800 °C. The results reveal that the electrochemical activity is strongly dependent on crystalline structure, thermal stability and textural properties of carbon fuels. The activated carbon samples demonstrate a better performance with a peak power density of 326 mW cm^?2 in CO₂ at 750 °C, compared to 147 and 59 mW cm^?2 with carbon black and graphite samples, respectively. Compared to the ohmic resistance, the polarization resistance plays a more dominated role in the cell performance. When replacing N₂ by CO₂ purge gas, the power density is the strongly temperature dependent due to the Boudouard reaction.     

Catalytic performance of CH4–CO2 reforming over metal free nitrogen-doped biomass carbon catalysts: Effect of different preparation methods

A series of nitrogen doped biomass carbon catalysts were prepared through two different nitrogen doped methods by using soybean meal as the raw material, melamine as nitrogen source and KOH as the activators. The catalysts were characterized by BET, SEM, CO₂-TPD, EA, FTIR, XPS and Raman. The catalytic performances of CH₄–CO₂ reforming over different samples were also studied. The results show that the preparation method of the catalyst significantly affects the structural characteristics, N content and N species type of the catalyst. The characterization results also show the proportion of pyrrolic-N in the catalyst prepared by in-situ nitrogen doped method (Y-NC) is higher than that in prepared by the post-treatment method (H-NC). Pyrrole-N is more conducive to the adsorption and activation of CO₂. So, the catalyst prepared by in-situ nitrogen doped method has good catalytic activity and stability. The conversion of CH₄ and CO₂ were respectively 40% and 65% at 900 °C after 50 h of CH₄–CO₂ reforming reaction.     

Effect of different activated carbon support on CH4CO2 reforming over Co-based catalysts

CH₄CO₂ reforming to syngas was investigated over three different activated carbon catalysts. To better understand the influence of the supports on the catalytic properties, catalysts were analyzed by some characterization methods, such as nitrogen adsorption–desorption isotherms, XRD, H₂-TPR, NH₃-TPD, CO₂-TPD, FTIR, TEM and EDX. The results showed that the catalyst with AC₂ as the support provided the best catalytic activity. The CH₄ conversion and CO₂ conversion were 92% and 98% at 900 °C, respectively; best selectivity with the H₂/CO ratio was close to 1 among the three supports used. It also showed a better stability at 900 °C. H₂-TPR analysis showed that Co species in Co/AC₂ catalyst were strong interaction with the support. It was observed that active metals were well dispersed on the AC₂ support by the TEM. In addition, the ratio of CH₄/CO₂ also had great influence on the CH₄ and CO₂ conversion.     

Understanding the significance of in situ coal properties for CO2 sequestration: An experimental and numerical study

Over the years, there has been a rapid increase in atmospheric CO₂ concentrations, from 280 ppm in 1850 to 360 ppm in 1998. Therefore, mitigation methods such as carbon sequestration in subsurface reservoirs have been suggested. CO₂ sequestration is attractive, especially in relation to coal, with the additional potential benefit of CH₄ recovery. However, the potential of CO₂ sequestration is not well understood for various types of coals due to important in situ properties of coal. In this study, data from previous studies for coal permeability, density, moisture content, mineral content, vitrinite reflectance, compressive strength and temperature are compared with the CO₂ adsorption results to understand the significance of these in situ coal properties on CO₂ sequestration. To verify the findings, a custom‐designed advanced core flooding apparatus is used to simulate the effects of various in situ properties on CO₂ sequestration. This apparatus can test samples of 203 mm in diameter and up to 1000 mm in length. Hence, heterogeneity effects can be understood, as previous CO₂ sequestration‐related formulae have been based on coal samples of sizes ranging up to only about 100 mm. However, initially, a reconstituted coal core sample has been used to simplify the heterogeneity effects. Flow rates are estimated by analysing the lag of downstream pressures over time. With the use of a 203‐mm‐diameter and 816‐mm‐long reconstituted Victorian brown coal sample, flow rate reductions of 70% and 98% are observed for injection pressures of 2 and 4 MPa, respectively, due to CO₂ injection. This study highlights the appropriateness of a candidate coal reservoir for CO₂ storage in terms of in situ properties. Copyright © 2013 John Wiley & Sons, Ltd.     

Ceria and zirconia modified natural clay based nickel catalysts for dry reforming of methane

Ce and Zr promoted Fe/Cu-modified natural clay based catalysts were prepared and tested in dry reforming of methane (DRM) at temperatures from 600 to 800 °C. The physicochemical properties of these catalysts were analyzed by means of N₂ adsorption, X-ray diffraction (XRD). H₂-temperature programmed reduction (H₂-TPR) and CO₂-temperature programmed desorption (TPD). Ce and Zr promotion resulted in a considerable increase of the catalytic activity. This increase can be mainly ascribed to an improved reducibility of Ni species, together with slightly higher Ni⁰ crystal size, that, on the other hand, also catalyze undesired parallel reactions resulting in carbon formation, such as direct methane decomposition. Both Ce and Zr presence also promoted the presence of weak and medium strength basic sites, which are thought to favor CO₂ adsorption and desorption on the catalyst surface, leading to enhanced catalytic activity.     

Insight into the effect of In addition on hydrogen generation behavior and hydrolysis mechanism of Al‐based ternary alloys in distilled water—A new active Al‐Ga‐In hydrolysis hydrogen generation alloy

(Al2Ga)‐xIn (x = 0, 2, 4, 6, 8 wt%) ternary aluminum (Al) alloys with different weight ratio of In for hydrolysis H₂ generation were prepared by melting‐casting technique. The phase compositions and microstructures of Al‐rich alloys were investigated by X‐ray diffraction (XRD) and high resolution scanning electron microscope (HR‐SEM) equipped with an energy dispersive spectrometer (EDS). The effect of In addition ratio on microstructures and H₂ generation performance were investigated, and the hydrolysis mechanism for Al‐Ga‐In ternary Al‐based alloys has been proposed. Al phase as matrix phase in the Al‐Ga‐In ternary alloy mainly determines the hydrolysis behavior, and the second phase In strongly promotes the hydrolysis process. The increase of In content can accelerate the H₂ generation rate as well as the final capacity and generation yield in neutral water. The generation yields for (Al2Ga)‐x In (x = 2, 4, 6, 8 wt%) alloys at 50°C are 0.56, 0.59, 0.62, and 0.66, respectively. The raising hydrolysis temperature can elevate the initial hydrolysis rate, final H₂ generation capacity, and yield. The H₂ generation capacities of (Al2Ga)‐8In alloy at 50°C, 60°C, and 70°C are 262, 290, and 779 mL·g^?1, respectively.     

A modified method for production of hydrogen from methane

The steam–methane‐reformation (SMR) reaction has been modified by including sodium hydroxide in the reaction. It is found that the reaction: 2NaOH+CH₄+H₂O = Na₂CO₃+4H₂ takes place at much lower temperatures (300–600°C) than the SMR reaction (800–1200°C). The reaction rate is enhanced with a nickel catalyst. We have studied the effect of variously ball‐milled nickel on the reaction rate and determined the optimum particle size of the catalyst. Best results were achieved by grinding the catalyst for 2 h. Prolonged ball milling caused the nickel platelets to coalesce and grow in size decreasing the reaction rate. Copyright © 2011 John Wiley & Sons, Ltd.     

Adsorption behavior and kinetics of H2S on a potassium-promoted hydrotalcite

Adsorption of H₂S and the influence of steam on its adsorption capacity and kinetics were studied on a commercial potassium-promoted hydrotalcite. The sorbent shows a very high cyclic working capacity for H₂S compared to CO₂ and H₂O, even at lower partial pressures and at different operating temperatures ranging between 300 and 500 °C. The operating temperature does not significantly influence the cyclic working capacity for half-cycle times of 30 min. The adsorption mechanism, however, changes at higher temperatures. At lower temperatures (300 °C) a fast adsorption with a fast approach to steady state was observed. At higher operating temperatures, H₂S reacts with the hydrotalcite structure, forming strongly bonded sulfuric species on the sorbent. When using dry regeneration conditions, the first cycles in cyclic operation at higher temperatures show a significantly higher adsorption of H₂S (especially the first cycle), which cannot be desorbed during regeneration with N₂. After the first fast initial adsorption rate a continuous slow adsorption of H₂S occurs, probably caused by a surface reaction between H₂S and the hydrotalcite structure. This reaction is, however, reversible if steam is used.The adsorption mechanism for H₂S and H₂O was determined using multiple cyclic experiments comparable to previous studies performed for CO₂ and H₂O adsorption. It is evident that the adsorption mechanism developed for CO₂ on the same sorbents is also valid for H₂S, indicating that the developed mechanism is consistent for sour gas adsorption on this type of sorbents. The cyclic working capacity can be significantly increased if steam is used during the regeneration step of the sorbent. The mechanistic model developed for the adsorption of CO₂ and H₂O was successfully validated with more than 160 different TGA experiments. An operating temperature of 400 °C seems to be optimal to achieve a high cyclic working capacity for H₂S, because at higher temperatures the regeneration of the formed sulfuric species seems to be hindered resulting in a significant decrease in the cyclic working capacity.     

Enhanced specific heat and thermal conductivity of ternary carbonate nanofluids with carbon nanotubes for solar power applications

Specific heat and thermal conductivity are important thermal properties of high-temperature heat transfer fluids and thermal storage materials for supercritical solar power plants. In the present work, nanofluids composed of ternary carbonate Li₂CO₃-K₂CO₃-Na₂CO₃ (4:4:2, mass ratio) and 1.0 wt.% carbon nanotubes (CNT) were prepared to obtain high-temperature heat transfer and storage media with enhanced specific heat and thermal conductivity. The dispersion of CNTs in the nanofluids was tuned by changing the evaporation temperature (100, 140, 180 and 220 °C) and adding surfactants such as sodium dodecyl benzene sulfonate (SDBS), sodium dodecyl sulfate (SDS), or gum Arabic (GA). The results showed that GA and SDS facilitate good dispersion of CNT in nanofluids at the evaporation temperatures of 140 °C and 180 °C, resulting in the formation of more needle-like nanostructures. The higher increase in the specific heat and thermal conductivity of the nanofluids with SDS at 500 °C was 78.3% and 149.2%, respectively. Additionally, the specific heat of as-prepared ternary carbonate nanofluids exhibits a good thermal stability after 30 cycles of thermal shock experiments.