A modified FeO/Fe3O4 redox cycle of producing hydrogen from water at a constant temperature of 800 °C is experimentally studied. Instead of solar energy, Fe3O4 was reduced to FeO by CO, the product of carbon gasification. The carbon was from coal carbonization. It was shown that the rate of both oxidation (reaction of FeO with H2O) and reduction (reaction of Fe3O4 with CO) was fast; however, the reduction must stop before formation of metal iron. The addition of 5–10 mol % Mo in iron oxide improved the stability and the reactivity of the latter during reaction cycling. Hydrogen was produced continuously in a process consisting of three reactors that couple the FeO/Fe3O4 redox cycle with carbon gasification (at 900 °C). The residual gas in the reactor and pipeline at the end of reduction may contaminate the hydrogen product; however, an evacuation step complemented to the end of reduction guarantees a hydrogen concentration higher than 95%.

The formation of hydrates in carbon pores was utilized to store natural gas, and ethane is the second major component of natural gas; therefore, ethane hydrate formation in carbon pores is studied in comparison with that of methane. Ethane is a major raw material of ethylene in the petrochemical industry; therefore, its mixture with ethylene is of importance and the formation condition of ethane hydrates was compared also with that of ethylene. The equilibrium isotherms of ethane on wet carbons with different water contents as well as the isotherms for different temperatures were collected, from which the formation pressures of ethane hydrates as well as the enthalpy change of ethane hydrate formation were determined. It was shown that the largest volumetric capacity for ethane storage is observed at the water load that just about fully fills pore spaces. Ethane hydrates were formed in wet activated carbons at about same pressures as in water media and the formation pressure is much lower than that required for methane hydrates formation.

Equilibrium data of ethylene sorption on activated carbon in the presence of water are measured for near-critical temperatures. The isotherms indicate the formation of hydrates. Hydrate is a compressed state of gases and receives interest in gas storage or separation, and the formation in carbon pores may reach complete conversion and show better dynamic behavior. It is presently shown that the hydrate formation pressure at above-critical temperatures observed in carbon pores is considerably less than that reported for water media. Both the molar ratio of water to ethylene at equilibrium and the ratio of formation enthalpies for sub- and supercritical temperatures indicate that the ethylene molecules cannot stay in the small cages of clathrates when the temperature increased to above critical.

The separation between CH4 and N2 bears importance in coalbed methane enrichment, and activated carbon is a major adsorbent for industrial PSA (pressure swing adsorption) separation. However, the adsorption of both gases shows supercritical features, and the physicochemical properties are also similar, which results in similar adsorption behavior and renders the separation difficult. To maximize the separation coefficient, the effect of carbon pore structure on the separation was studied and a series of carbons was prepared at different extent of activation. The effect of specific surface area, pore size and pore volume on the separation coefficient was observed and a linear correlation between the separation coefficient and the small pore (0.7–1.3 nm) volume reduced to unit surface area was shown.

Based on the storage mechanism of methane in wet carbon, the pore size of activated carbon must match the dimension of methane hydrates, and 1.6–2.8 nm was recognized as the optimal pore size. Targeting at the optimal pore size, a progressive activation process was applied on corncob precursors and a carbon possessing abundant pores of the optimal size was prepared. Both gravimetric and volumetric storage capacity of the carbon were experimentally measured, and a theoretical volumetric capacity (TVC) was defined on discussing the transformation from gravimetric to volumetric capacities. It was shown that pore volume and pore size of carbon are decisive factors for the storage capacity, which was greatly raised up through pore size optimization. Sixty three weight percentage of the gravimetric storage capacity, 290 and 204 V/V of the TVC and experimental volumetric storage capacity were reached, which were the highest amounts reported in literature. Compared to CNG (compressed natural gas), the storage method in wet carbon stored same quantity of methane at half storage pressure.

The widely applied desulfurization technologies for flue gas are based on the acidic property of SO2. However, CO2 is also acidic, and the content of CO2 in flue gas is several orders higher than that of SO2; therefore, the interference of CO2 on desulfurization is a problem and an origin of secondary pollution. A reaction-enhanced sorption method is presented and tested in the present work. CO2 remained unchanged while the detrimental acidic species are oxidized and captured by adsorbent. The irreversibility of reactions and the large surface area of adsorbent guaranteed a complete capture of SO2. A breakthrough capacity of adsorbent as large as 323 mg/g was observed on a SBA-15 mesoporous adsorbent. The by-products produced at regeneration are of market value, and the desulfurization technique does not yield secondary pollution.

Flue gas desulfurization technology is important for coal-fueled power plants, and adsorptive separation of SO2 is a potential method applicable in practice. Large pore SBA-15 with surface modified by TEA (triethanolamine) showed excellent performance for the selective adsorption of SO2 from flue gas. The SO2 capacity reached 177 mg/g at 80% TEA loading ratio, while the adsorption of CO2 was negligible. The adsorbent also showed good tolerance to moisture existing in flue gas, and the moisture showed a positive effect on the desulfurization. The saturated adsorbent was regenerated when heated to 120 °C, and the SO2 capacity was almost retained in consecutive adsorption/regeneration cycles.

Progress in natural gas storage with wet adsorbents is presented. The storage mechanism switched from adsorption for adsorbed natural gas (ANG) to hydrate formation when wet adsorbents were used. The activated carbon with a pore size of 1.6−3 nm was shown more suitable for the wet storage method, and a larger than 40 wt % gravimetric storage capacity and a deliverable capacity of more than 150 (v/v) were experimentally observed under conditions of 273−283 K and pressure ca. 8 MPa. The stored amount in wet carbon is 2 times higher than that of adsorbed and 1.5 times than that of compressed at the indicated conditions. All of the inherent technical drawbacks of ANG were overcome, and the storage pressure reduced more than half compared to compressed natural gas (CNG). Both investment and energy costs of fuel are expected to reduce, and the safety of the natural gas (NG) vehicle will improve radically.

High-pressure adsorption attracts research interests following the world’s attention to alternative fuels, and it exerts essential effect on the study of hydrogen/methane storage and the development of novel materials addressing to the storage. However, theoretical puzzles in high-pressure adsorption hindered the progress of application studies. Therefore, the present paper addresses the major theoretical problems that challenged researchers: i.e., how to model the isotherms with maximum observed in high-pressure adsorption; what is the adsorption mechanism at high pressures; how do we determine the quantity of absolute adsorption based on experimental data. Ideology and methods to tackle these problems are elucidated, which lead to new insights into the nature of high-pressure adsorption and progress in application studies, for example, in modeling multicomponent adsorption, hydrogen storage, natural gas storage, and coalbed methane enrichment, was achieved.

The adsorption amount of methane on 16 different kinds of materials at 3.5 MPa and 298 K holds a linear relation with the specific surface area. The linear relationship implies that gases are adsorbed monolayerly on the surface of adsorbents at above-critical temperatures. Determination of surface area and calculation of storage capacity of a material are explicitly discussed. It is indicated that methane storage is different from natural gas storage and the difference affects the development of storage material. Natural gas is a mixture and all components other than methane cannot be desorbed when the tank pressure released to atmospheric at ambient temperature, therefore, a storage mechanism other than adsorption might be more suitable.

The sorption isotherms of CO2 + CH4 mixtures on an activated carbon were collected in the presence of water at a temperature suitable for hydrate formation. The equilibrium composition of both phases was determined. The initial concentration of CO2 in mixtures was set at 33, 38 and 42%, and the total pressure was up to 10 MPa. CO2 hydrates were firstly formed following the increase of total pressure, and CO2 dominates the sorbed phase composition. CO2 concentration in the sorbed phase begins to decrease when the partial pressure of methane allows for the formation of methane hydrates. Competition for hydrate cavities was observed between CO2 and CH4 as reflected in the isotherm shape and phase composition at equilibrium. The formation pressure of hydrates is lower for mixtures than for pure gases, and the highest sorption capacity of each gas decreased in the mixture sorption either.Sorption isotherms of CH4 + CO2 mixture on wet activated carbon.

The sorption behavior of CO2 and CH4 on activated carbon in the presence of water was comparatively studied. The equilibrium sorption data of CO2 and CH4 on an activated carbon with a wide pore-size distribution were collected at the temperature of hydrate formation in the presence of different amounts of water. Differently from methane, the sorption behavior of CO2 was remarkably affected by pore dimension of activated carbons no matter the carbon is wet or dry. It affects the isotherm shape and the molar ratio of water to the fixed CO2 in wet carbon. This effect of pore dimension and the difference in the sorption behavior between CO2 and CH4 were explained based on the possibility of condensation and dissolution. The enthalpy change was evaluated on the basis of the sorption data at different temperatures for the formation of CO2 and CH4 hydrates in the pore spaces of the tested carbon.

An ordered mesoporous carbon was synthesized using SBA-15 as the template. The sorption isotherms of methane on the synthesized carbon material were collected. Its ordered structure was confirmed by the XRD, SEM and TEM examinations. The BET surface area is 1100–1200 m2/g, the total pore volume is 1.24–1.30 cm3/g, and the pore size distribution is very narrow and centered at 2–5 nm. As high as 41.2 wt.% of methane was stored per unit mass of carbon at 275 K and pressures less than 7 MPa in the presence of 3.86 times more water. This sorption amount is 31% higher than the largest sorption capacity reached by activated carbon in the presence of water, which was equal to or higher than the storage capacity of compression till 20 MPa. The enthalpy change corresponding to the sudden change of isotherms was equal to the enthalpy change of methane hydrate formation; therefore, the mechanism of the enhanced methane storage was considered due to the formation of methane hydrate in the porous carbon material.

The sorption/desorption equilibrium of methane onto/from silicon gel loading different quantity of water were measured with a volumetric method at 275 K for the pressure range of 0–11 MPa. The observed isotherms are similar to that for wet active carbons, and the quantity of the pre-adsorbed water showed a considerable influence on the sorption capacity. However, there is some difference in the variation trend of the sorption isotherms between the wet silica gel and the wet active carbon. Both pore size distribution and pore volume were changed after contacting water for different periods of time. Such changes might be caused by hydrolysis of the silicon-hydroxyl groups of the silicon surface and might be responsible for the peculiar behavior of isotherms observed at the wet silica gel.

The dynamic behavior of charging/discharging methane onto/from water-preloaded activated carbon was studied at different conditions. It was shown that methane hydrate could form quickly in the porous space of carbon at the condition of 275 K and pressures beginning with 4.12 MPa. The stored methane could be continuously released at a constant flowrate for the whole discharging process. The packing density of 0.6 g cm−3 seemed optimal for the wet carbon tested, which yielded 152 V/V of released methane at charging pressure of 8 MPa. The thermal effect observed on the charging/discharging process was low and did not affect the effective storage capacity.

Experiments were made for the adsorption of CO2 and N2 on typical adsorbents to investigate the effects of porous structure and surface affinity of adsorbents as well as those of adsorption temperature and pressure that might cause the variation of adsorption mechanism. It is shown that polar surface tends to enlarge the adsorption difference between CO2 and N2, and the difference is more sensitive to temperature than the adsorbents with non-polar surface. The adsorbents with non-polar surface are not much sensitive to the effect of water vapor, though the water vapor interferes the separation remarkably. The separation coefficient linearly increases with the micropore volume per unit surface area of activated carbons, but no rule is shown on mesoporous silicon materials. The function of adsorption mechanism on the separation is not as much as expected.