Adsorption Isotherms of Hydrogen on Granular Activated Carbon Derived From Coal and Derived From Coconut Shell

ABSTRACT

The development of adsorption-based storage systems requires a basic understanding of the isotherms over a wide range of pressure and temperatures for various types of adsorbents. This research is to generate experimental isothermal adsorption data for the adsorption of hydrogen gas on activated carbon. The adsorption apparatus is based on a volumetric method, and the experiments were conducted at temperatures ranging from 273 to 308 K and pressures up to 4 MPa. Two types of activated carbon, (i) a granular coal from Indonesia and (ii) a coconut-shell activated carbon that is produced in the laboratory, were used in the experiments. The experimental data are analyzed using the Langmuir, Toth, and Langmuir–Freundlich isotherm models.     

Enhancement of methane storage on activated carbons in the presence of water

Methane storage was studied on the wet activated carbons by hydrate formation in the mesopore structures. Coconut shell was used as a raw material for preparation of the activated carbon samples. These highly mesoporous samples were prepared by the combination of both physical and chemical activation processes. After wetting the adsorbents with a constant water/carbon weight ratio (R) close to 1, the isotherms were obtained at 2°C up to the pressure of 80 bars. Wetted carbons exhibited stepwise isotherms at the critical pressure in the pressure range of 25–50 bars depending on the activated carbon samples. At this critical pressure, hydrate formation took place slowly. The amounts of methane uptake at 80 bars were obtained ranging from 14.9 to 24.8 mmol.g^–1 based on the dry adsorbent for different samples. By considering the density of activated carbon samples, the amounts of methane storage varied in the range of 185–237 V/V.     

Adsorption Parameter and Heat of Adsorption of Activated Carbon/HFC-134a Pair

This article presents the adsorption isotherms of HFC-134a and activated carbon Maxsorb III measured using the constant-volume–variable-pressure method. The adsorption isotherms cover temperature ranges from 293 to 338 K and pressures up to 0.7 MPa. The trends of the experimental isotherms for activated carbon are found to be identical in all cases with previous studies except that the vapor uptake is slightly higher. The adsorption characteristic of the Dubinin–Ashtakov equation has been regressed from the experimental isotherms data and the maximum specific uptake is 2.15 kg of adsorbate adsorbed per kilogram of activated carbon. The heat of adsorption, which is concentration and temperature dependent, has also been extracted from the experiments.     

The pyrolysis process of biomass by two-stage chemical activation with different methodology and iodine adsorption

Current concerns with the high energy/cost nature of activated carbon production have encouraged research into alternative activated carbon production methods to reduce the environmental impact. The purpose of this study is to produce the activated carbon from biomass (carob bean seed husk, CBSH) by chemical activation with a different methodology using zinc chloride. Two different activation temperature methodologies for the preparation of activated carbons were applied at the ranges of 30–80 and 200–350°C. The effects of the pre-activation and activation temperatures, duration time, and the impregnation ratio on the surface and chemical properties of activated carbon were investigated. Studies were conducted on the adsorption of iodine from the prepared activated carbon. The highest iodine adsorption number was achieved as 874 mg/g. Langmuir surface area was 1544 m²/g. The structural morphology of activated carbons was evaluated with a scanning electron microscope. The surface chemical characteristics of activated carbons were determined by the Fourier transform infrared (FTIR) spectroscopic method.     

Modified potential theory for modeling supercritical gas adsorption

Theoretical modeling of adsorption plays a crucial role in providing better understanding of the adsorption phenomena, isotherms and isosteric heats. However, when modeling the adsorption of gas mixtures containing hydrogen, it is necessary to accommodate a wide temperature range because of hydrogen's low critical temperature. In this work, we extend the multicomponent potential theory of adsorption's (MPTA) capability of predicting adsorption isotherms to a wide temperature range by introducing a temperature dependent Dubinin potential parameter and use it to model adsorption isotherms of supercritical hydrogen, nitrogen and methane on various activated carbons. This extended MPTA can accurately predict the adsorption isotherms when used with NIST equation of state (EOS). The resulting isosteric heats of adsorption of hydrogen agree well with the experimental data for similar volume filling scenarios. Hydrogen's low temperature adsorbed-phase pressure inside the activated carbon's micropore volume reaches the melting pressure of solid hydrogen. This causes the transition of adsorbed hydrogen from supercritical gas to solid-like phase which is clearly observed in our model. Our study, thus, provides a better understanding of physisorption of hydrogen inside the micropores.     

Copper-doped activated carbon from amorphous cellulose for hydrogen,methane and carbon dioxide storage

The transition away from fossil fuel and ultimately to a carbon-neutral energy sector requires new storage materials for hydrogen and methane as well as new solutions for carbon capture and storage. Among the investigated adsorbents, activated carbons are considered especially promising because they have a high specific surface area, are lightweight, thermally and chemically stable, and easy to produce. Moreover, their porosity can be tuned and they can be produced from inexpensive and environmentally friendly raw materials. This study reports on the development and characterization of activated carbons synthesized starting from amorphous cellulose with and without the inclusion of copper nanoparticles. The aim was to investigate how the presence of different concentrations of metal nanoparticles affects porosity and gas storage properties. Therefore, the research work focused on synthesis and characterization of physical and chemical properties of pristine and metal-doped activated carbons materials and on further investigation to analyze their hydrogen, methane and carbon dioxide adsorption capacity. For an optimized Cu content the microporosity is improved, resulting in a specific surface area increase of 25%, which leads to a H₂ uptake (at 77 K) higher than the theoretical value predicted by the Chahine Rule. For CH₄, the storage capacity is improved by the addition of Cu but less importantly because the size of the molecule hampers easy access of the smaller pores. For CO₂ a 26% increase in adsorption capacity compared to pure activated carbon was achieved, which translated with an absolute value of over 48 wt% at 298 K and 15 bar of pressure.     

Upgrading Scrap Tire Derived Oils Using Activated Carbon Supported Metal Catalysts

Abstract

Scrap tire derived oils were upgraded over metal-loaded activated carbon catalysts and commercial catalyst at different operating conditions. Activated carbon support was prepared from the pyrolytic carbon black from pyrolysis of scrap tires. Activated carbon catalysts contained the metal pairs of Co-Ni, Co-Mo, and Ni-Mo. All metal-loaded activated carbon catalysts showed similar catalytic activity for upgrading process at 350°C under hydrogen pressure of 7 MPa. However, Ni-Mo/Ac showed good catalytic activity. Liquid fuels from upgrading oils over Ni-Mo/Ac and commercial catalyst containing 45–55% of naphtha fraction, 20–25% of kerosene fraction was obtained 350°C under hydrogen pressure of 7 MPa.     

Effect of pressure equalization on methane enrichment from stranded natural gas using PSA with amorphous Kenaf and microporous palm kernel shell adsorbents

Improvement of quality fuels has gained traction as a result of growing demand for higher quality fuels because of health concern, environmental issues and tighter emission control by regulatory bodies. Low quality, unprocessed fuels produce household air pollution on burning that can be fatal. In this work, Kenaf and palm kernel adsorbents were used in pressure swing adsorption to enrich methane from stranded natural gas containing extraordinarily high carbon dioxide content of 70 vol%. Microporous palm kernel activated carbon from this work was found effective in methane enrichment process to produce better quality fuel that met the gas pipeline quality standard. Methane with 85.0% purity and 94.2% recovery was achieved at 1 minute of adsorption time due to the methane flow-through and effective carbon dioxide retention. Increased adsorption time of higher than 1 minute resulted in the reduction of both purity and recovery of the gases due to the delayed cross-over of methane. Methane compression at three bars consumed 10.0 kJ/min out of 33.0 kJ/min. Methane expansion released 8.0 and 2.0 kJ/min from methane and carbon dioxide rich stream, respectively during blowdown. The total entropy change from the compression and expansion of the gas was nil, suggesting that the process induced no disorder to the surrounding. Pressure swing adsorption with equalization mode reduced the methane purity to 76% and carbon dioxide recovery to 70% but increased the methane recovery to almost 100% and carbon dioxide purity to 97% in a criss-cross procession.     

A study on optimal pore range for high pressure hydrogen storage behaviors by porous hard carbon materials prepared from a polymeric precursor

In this study, activated polymer-based hard carbons were prepared using various steam activation conditions in order to enhance their hydrogen storage ability. The structural characteristics of the activated carbons were observed by X-ray diffraction and Raman spectroscopy. The N₂ adsorption isotherm characteristics at 77 K were confirmed by Brunauer-Emmett-Teller, Barrett-Joyner-Halenda and non-local density functional theory equations. The hydrogen storage behaviours of the activated carbons at 298 K and 10 MPa were studied using a Pressure-Composition-Temperature apparatus. From the results, specific surface areas and total pore volume of the activated carbons were determined to be 1680–2320 m²/g and 0.78–1.39 cm³/g, respectively. It was also observed that various pore size distributions were found to be dependent on the functions of activation time. In the observed result, the hydrogen adsorption of APHS-9-4 increased about 30% more than that of as-prepared hard carbon. This indicates that hydrogen storage capacity could be a function not only of specific surface area or total pore volume, but also of micropore volume fraction in the range of 0.63–0.78 nm of adsorbents.     

Development research on composite adsorbents applied in adsorption heat pump

A novel adsorbent design technique base on the concept of Kelvin equation was proposed to develop hydrophilic adsorbent applicable to water vapor adsorption heat pump (AHP) for high performance. In the process, the composite adsorbent was prepared after silica gel was synthesized in the pores of activated carbons by impregnating activated carbons in sodium silicate solution. Two kinds of activated carbons were tested to produce composite adsorbent and to investigate the performance by measuring the adsorption isotherms of water vapor and pore structure characteristics. All adsorption isotherms of the silica impregnated activated carbons prepared shifted to a lower region of water vapor pressure compared to those of the raw activated carbons. The volume-based amount of adsorption in the AHP operation range (φ = 0.1–0.4) for the adsorbents prepared at sodium silicate solution concentration of 10 wt.% and impregnating time of 48 h are 5.88 and 2.62 times that of the raw activated carbons (AC1 and AC2), respectively. Based on the Kelvin equation, it is clarified that the contact angle and the volume of pore radius greater than 1.2 nm decrease with the increase of sodium silicate solution concentration for the novel composite adsorbents, which contributes the isothermals shift to lower relative pressure range.     

A sieverts apparatus for measuring high-pressure hydrogen isotherms on porous materials

A high-pressure Sieverts apparatus, specifically designed to investigate carbon and other low-density materials for hydrogen storage, has been constructed and used to investigate potential storage materials for which the volume of the sample is uncertain or difficult to define. The apparatus can be managed from a computer via a graphical interface and used to measure gas sorption isotherms from 77 K to 873 K, utilising a computer driven piston pressure booster to compress the gas to 340 bar. Based on measurements of activated carbons and graphene-like samples, this article demonstrates the low sensitivity of the apparatus to uncertainty in the sample volume and the quality of data obtained for H₂ adsorption isotherms measured at 296 K and 77 K at pressures up to 300 bar.     

Environmentally benign working pairs for adsorption refrigeration

This paper begins from adsorption working pairs: water and ethanol were selected as refrigerants; 13x molecular sieve, silica gel, activated carbon, adsorbent NA and NB, proposed by authors, were selected as adsorbents, and the performance of adsorption working pairs in adsorption refrigeration cycle was studied. The adsorption isotherms of adsorbents (NA and NB) were obtained by high-vacuum gravimetric method. Desorption properties of adsorbents were analyzed and compared by thermal analysis method. The performance of adsorption refrigeration was studied on simulation device of adsorption refrigeration cycle. After presentation of adsorption isotherms, the thermodynamic performance for their use in adsorption refrigeration system was calculated. The results show: (1) the maximum adsorption capacity of water on adsorbent NA reaches 0.7 kg/kg, and the maximum adsorption capacity of ethanol on adsorbent NB is 0.68 kg/kg, which is three times that of ethanol on activated carbon, (2) the refrigeration capacity of NA–water working pair is 922 kJ/kg, the refrigeration capacity of NB–ethanol is 2.4 times that of activated carbon–methanol, (3) as environmental friendly and no public hazard adsorption working pair, NA–H₂O and NB–ethanol can substitute activated carbon–methanol in adsorption refrigeration system using low-grade heat source.     

Isotherms and thermodynamics for the adsorption of n-butane on pitch based activated carbon

The adsorption isotherms of n-butane on pitch based activated carbon (type Maxsorb III) at temperatures ranging from 298 to 328 K and at different equilibrium pressures between 20 and 300 kPa have been experimentally measured by a volumetric technique. The porous properties such as, the density, Brunauer–Emmett–Teller (BET) surface area, pore size, pore volume along with pore size distribution (PSD) of Maxsorb III have been determined. The Dubinin–Astakhov (DA) adsorption isotherm model describes all of the isotherm experimental data within the acceptable error ranges. The present isotherm data are compared with other published data of activated carbon (AC)/n-butane and showed the superiority of the present findings in terms of uptake capacity. The isosteric heat of adsorption (ΔH_ads) of n-butane on Maxsorb III is calculated for different loading. Using the adsorption isotherms and ΔH_ads, the thermodynamic property maps as a function of pressure, temperature and adsorbate amount are also presented.     

Prediction of CO2 adsorption on different activated carbons by hybrid group method of data-handling networks and LSSVM

CO₂ is a ubiquitous species that has received much attention recently. The adsorption of CO₂ by means of activated carbons is a well-tried technology that can be used on a large scale. Improvements of the prediction models with more accurate results and lower error are necessary for future development of the projects and the economic dispatch sector. The least square support vector machine, a relatively unexplored neural network known as group method of data handling (GMDH), were implemented to forecast the CO₂ adsorption on different activated carbons. This work aims to provide new methods to predict the adsorption equilibrium of pure CO₂ on a set of commercial activated carbons and to express it regarding textural properties such as Brunauer–Emmett–Teller (BET) surface area, total pore volume, and micropore volume. Results indicated that the utilized models are very accurate in predicting CO₂ adsorption on different activated carbons. Comparison of the outcomes of the two models shows that the GMDH model is more accurate with R² and mean squared error values of 0.8915 and 0.0001425, respectively.     

Carbon materials for H2 storage

In this work a series of carbons with different structural and textural properties were characterised and evaluated for their application in hydrogen storage. The materials used were different types of commercial carbons: carbon fibers, carbon cloths, nanotubes, superactivated carbons, and synthetic carbons (carbon nanospheres and carbon xerogels). Their textural properties (i.e., surface area, pore size distribution, etc.) were related to their hydrogen adsorption capacities. These H₂ storage capacities were evaluated by various methods (i.e., volumetric and gravimetric) at different temperatures and pressures. The differences between both methods at various operating conditions were evaluated and related to the textural properties of the carbon-based adsorbents. The results showed that temperature has a greater influence on the storage capacity of carbons than pressure. Furthermore, hydrogen storage capacity seems to be proportional to surface area, especially at 77 K. The micropore size distribution and the presence of narrow micropores also notably influence the H₂ storage capacity of carbons. In contrast, morphological or structural characteristics have no influence on gravimetric storage capacity. If synthetic materials are used, the textural properties of carbon materials can be tailored for hydrogen storage. However, a larger pore volume would be needed in order to increase storage capacity. It seems very difficult approach to attain the DOE and EU targets only by physical adsorption on carbon materials. Chemical modification of carbons would seem to be a promising alternative approach in order to increase the capacities.     

Posidonia Oceanica and Wood chips activated carbon as interesting materials for hydrogen storage

The goal is to investigate the feasibility to use a local biomass (Posidonia Oceanica and Wood chips), as a raw precursor, to the production of activated carbons (AC) with a high surface area and remarkable hydrogen (H₂) adsorption properties.Biomasses (particle size of 0.3–0.4 mm) were pyrolyzed at 600 °C with a heating rate of 5 °C/min under an argon atmosphere. The biochar obtained from the carbonization step was chemically activated with KOH. The activation methodology induces a considerable improvement of the properties of the porous carbon in terms of carbon content (from 58 to 69 wt% to 93–96 wt%), surface area (from 41 to 425 m²/g to 2810–2835 m²/g) and H₂ adsorption in cryogenic condition (from 0,1 wt% to over 5 wt%).All porous carbons were characterized in terms of elemental analysis (CHNS–O), textural properties and H₂ adsorption measurements.     

Evaluation of activated carbons based on olive stones as catalysts during hydrogen production by thermocatalytic decomposition of methane

Catalytic decomposition of methane over carbon materials has been intensively studied as an environmental approach for CO₂-free hydrogen production without further by-products except hydrogen and valuable carbon. In this work, we will investigate the catalytic activity of activated carbons based on olive stones prepared by two different processes. Additionally, the effect of three major operational parameters: temperature, weight of catalyst and flow rate of methane, was determined. Therefore, a series of experiments were conducted in a horizontal-flow fixed bed reactor. The outflow gases were analysed using a mass spectrometer. The textural, structural and surface chemistry properties of both fresh and used activated carbons were determined respectively by N₂ gas adsorption, X-Ray Diffraction and Raman and Temperature Programmed Desorption. The results reveal that methane decomposition rate increases with temperature and methane flow however it decreases with catalyst weight. The two carbon samples exhibit a high initial activity followed by a rapid decay. Textural characterization of the deactivated carbon presents a dramatic drop of surface area, pore and micropore volumes against an increase of average pore diameter confirming that methane decomposition occurs mainly in micropores. XRD characterization shows a turbostratic structure of fresh samples with more graphitization in deposed carbon explaining the lowest activity at the end of reaction. Raman spectra reveal the domination of the two bands G and D which varying intensities affirm that the different carbons tend to organise in aromatic rings. Finally the surface chemistry qualitatively changes greatly after methane dissociation for CAGOC unlike CAGOP but quantitatively a small difference is observed which indicates that these functionalities may have a role in this heterogeneous reaction but cannot be totally responsible. Among the two catalysts tested, CAGOC has the highest initial methane decomposition rate but CAGOP is the most stable one.     

Hydrogen Production by Thermocatalytic Methane Decomposition

This article reports on the use of mesoporous carbons as catalysts for hydrogen production by thermocatalytic decomposition of methane. The prepared ordered mesoporous carbons (OMCs) and commercial carbon materials (including disordered microporous carbon, mesoporous carbon, and carbon nanotube) were tested for their catalytic activities for methane decomposition in a fixed-bed reactor. Characterizations by different techniques including gas adsorption, x-ray photoelectron spectroscopy, and transmission electron microscopy were carried out for the pristine and used catalysts. Results showed that the initial activity was related to the chemical structure of the catalysts such as defects, while the long-term activity was related to the physical characteristics such as the BET surface area and pore volume. Unlike disordered carbons, OMCs with relatively larger uniform pores could maintain a steady catalytic activity for a longer time, followed by a sharp activity decline due to the blockage of most of the pores. It is conceived that by designing and preparing carbon materials with ideal pore systems using the replication method, it is possible to enhance the catalytic activity and stability of the reaction.     

Influence of ethylene on carbon-catalysed decomposition of methane

Catalytic decomposition of methane is a much promising pro-ecological method of hydrogen production. However, the drawback of this method is fast deactivation of the catalyst by deposition of a low-active methane-originated carbon on its surface. In this study an attempt has been made to reduce the process of catalyst deactivation by adding admixture of ethylene to methane directed to the reactor. The study has been performed on the activated carbon obtained by Na₂CO₃ activation of pine wood and two commercial types of activated carbons. All the carbon types have been subjected to ultimate analysis, determination of the surface area and pore structure. It has been shown that ethylene also forms a carbonaceous deposit but in contrast to the methane-originated deposit the ethylene-originated one shows good catalytic properties in the reaction of methane decomposition. The addition of 20% ethylene seems to be optimum for ensuring high yield of hydrogen for a long time. The ethylene admixture addition is the more effective the higher the temperature of the process.