Adsorption of water vapor and carbon dioxide at carboxylic functional groups on the surface of coal

Adsorption of water vapor and carbon dioxide at carboxylic functional groups on the surface of coal

The simultaneous adsorption of carbon dioxide and water vapour by fixed beds of molecular sieves

According to the present data, KA zeolite, which can adsorb only water vapor, helium, and hydrogen, has the greatest selectivity in drying. The feasibility of using this zeolite in devices for selective drying of gases used in gas-analysis systems was studied. The results of the experiments were approximated by the thermal equation of the theory of bulk filling of micropores. The limiting value of the adsorption depends on the temperature, and it can be calculated according to the density of the adsorbed phase and the adsorption volume. The critical diameters of the water and carbon dioxide molecules are close to the dimensions of the KA-zeolite pores, something that determines the activated nature of the adsorption of these substances. Experiments on coadsorption of water vapor and carbon dioxide by a fixed bed of KA-zeolite under dynamic conditions showed that the adsorption of these substances has a frontal nature. The time of the protective action of the layer of zeolite during adsorption af water vapor exceeded by more than an order the time of the protective action during adsorption of carbon dioxide. The results showed that this adsorbent can be used for selective drying of gas mixtures containing carbon dioxide in batch-operationmore » devices. Beforehand, the adsorbent should be regenerated with respect to moisture, and then it should be saturated with carbon dioxide by blowing the adsorbent with a gas mixture of the working composition until the equilibrium state is reached.« less

Structural modelling of silicon carbide-derived microporous carbon and its application in CO2 capture and separation of volatile gases from moist streams

Energy storage through adsorption and desorption of water vapour in raw Saudi bentonite

In-situ silver-modification of Silicalite-1 for trace ethylene capture under humid conditions

A diverse pool of six semiconductor GaN nanopowders was synthesized by the thermally-driven pyrolysis of gallium imide at various temperatures. The XRD-derived average crystallite sizes for the nanopowders were in the range 1-17 nm. Standard nitrogen adsorption measurements at 77 K yielded the basic characteristics of the powder pore structures including the BET surface areas that spanned 23-287 m2/g. Rare studies of adsorption of water vapor, carbon dioxide, and hydrogen on the nitride nanopowders were carried out. The data on water vapor adsorption at 295 K supported chemisorption of water molecules on the primary adsorption centers and physisorption on the secondary centers. The data on carbon dioxide adsorption at 273 K and hydrogen adsorption at 77 K were used to determine the selectivity of adsorption for these gases defined as the ratio of the respective Henry's constants calculated from the Langmuir equation. The GaN nanopowders showed remarkably diverse pore structure characteristics and adsorption properties that could be linked to the nitride's average crystallite size and crystallite agglomeration, the latter supported by helium density data.

The simultaneous adsorption of water and hydrocarbon vapor from natural gas bythree grades of alumina has been studied at atmospheric pressure andtemperature. Results of this investigation reveal that the presence of watervapor in the gas inhibits the adsorption of hydrocarbon vapor, although thepresence of the latter does not have a pronounced effect upon the adsorption ofwater vapor. Adsorption of water-hydrocarbon mixtures from gas is divided intothree phases. In the first, both water and hydrocarbon vapor are adsorbed; inthe second, adsorption of water vapor proceeds while desorption of hydrocarbontakes place; in-the third phase, the adsorbent approaches complete saturationwith respect to both water and hydrocarbon vapors. Both theory and experimentaldata can be applied to design and operation of commercial dehydration plants, and an illustration is presented. Introduction Dehydration of natural gas becomes increasingly important as the operatingpressures employed in gas processing and transmission are increased above 500lb. per sq. in. Gas produced from high-pressure wells is saturated with watervapor when it leaves the reservoir and it continues into the processing plantor transmission system in a saturated condition because of the substantialdecrease in temperature due to expansion at the wellhead. Usually this gas isaccompanied by liquid water and hydrocarbons that have condensed with thechange in temperature and pressure. Without dehydration, gas temperatures must be held at relatively high levels toprevent solidification of gas hydrates. According to Hammerschmidt's data onthe relationship of pressure to the freezing point of natural-gas hydrates, theminimum safe operating temperatures range from 55? to 90?F for pressuresranging from 500 to 3000 lb. per sq. in., respectively. Often it is difficultto maintain gas temperatures above the hydrate-freezing temperature because ofclimatic conditions, unless flow-line heaters are installed. Also, inprocessing gas for its gasoline content at high pressures, it is desirable toemploy operating temperatures lower than the hydrate-freezing point. Indistributing high-pressure gas, the large pressure drop from line pressure totown-gate pressure often produces sufficient cooling to freeze the regulatorsand disrupt consumer service. Therefore, it is highly essential to dehydratehigh-pressure natural gas if smooth and economical operation is to bemaintained at all times. Few published data are available on the simultaneous adsorption of water andhydrocarbon vapors. T.P. 1628

The adsorption of water vapor on a highly microporous carbon derived from the carbonization of coconut shell has been studied. This material was characterized by the adsorption of nitrogen at 77 K and carbon dioxide at 273 K. The micropore size distribution was determined using probe molecule vapors at p/p0 = 0.5 and 301 K. The adsorption and desorption characteristics of water vapor on the activated carbon were investigated over the pressure range 0−2.41 kPa (p/p0 0−0.9) in a static water vapor system. The adsorption and desorption kinetics were studied with different amounts of preadsorbed water for changes in vapor pressure of 0.303 kPa. The adsorption rate constants were also studied for three relative humidities for a dynamic flow system at a constant temperature. In these experiments the changes in vapor pressure were much higher than in the static vapor pressure experiments. The kinetic results for both the static atmosphere and dynamic flow systems are discussed in relation to their relative position on the equilibrium isotherm and the adsorption/desorption mechanism.

Adsorption of benzene and water vapors on activated carbons of various microporous structure was studied. The values of the characteristic energy of adsorption of benzene and water vapors were compared and the affinity coefficients βH2O for carbons with various degrees of activation were calculated. The values of the βH2O coefficient for carbons with the same degrees of oxidation remain constant. This makes it possible to use the experimental data on benzene adsorption for prediction of the behavior of microporous activated carbons towards adsorption of water vapor.

Understanding the interactions between jet engine soot and exhaust plume vapor components, such as water vapour and benzene, is crucial for assessing post-combustion soot modification and the resulting impact on the environment and human health. This study focuses on the adsorption and desorption of single component exhaust plume species, namely, water vapor and volatile organic compounds (VOCs) with varying physicochemical properties, on soot particles derived from different combustion conditions, thus providing fundamental insights into the vapor-solid partitioning process and, therefore, the thermodynamic and kinetic mechanisms governing soot aging in jet exhaust plumes.Model jet soot particles were synthesized by two methods: (1) enclosed spray combustion using Jet-Al fuel, which contains surface-adsorbed organic compounds, and (2) controlled oxidation of carbon black to mimic the physicochemical properties of jet soot without any adsorbed organic compounds to separate the role of soot core-shell structure, porosity, and surface chemistry on the solid-vapour partitioning process. Water vapor and VOCs adsorption isotherms, including components relevant to jet exhaust (e.g., toluene and benzene), were measured on soot powders using gravimetric dynamic vapor sorption under precisely controlled temperature and partial pressure conditions. Preliminary results indicated Type II isotherms for VOCs, driven by soot’s functional groups and particle surface area. Thermodynamic analysis of adsorption isotherms showed a moderate enthalpy of adsorption (31.8–45.4 kJ/mol) at low surface coverage and ambient temperature, consistent with a physisorption mechanism. Kinetic modeling using the linear driving force (LDF) and stretched exponential (SE) diffusion models showed that single aromatic species followed the LDF mechanism, displaying rapid adsorption kinetics (average k=0.016 s-1), indicative of interparticle void filling. In contrast, water vapor adsorption mainly followed the Fickian diffusion mechanism and was much slower (average k=0.001 s-1), possibly due to intraparticle diffusion of water vapor to oxygen functional groups on the edges of graphitic planes.This study highlights how soot's physicochemical properties, such as pore size distribution, surface area, and surface chemistry, govern adsorption characteristics that control solid-vapor partitioning. By investigating the fundamental sorption mechanisms, these findings could advance our understanding of atmospheric jet soot aging and provide a foundation for modeling multicomponent vapor interactions in complex, real-world environments. The results could also inform strategies for mitigating the environmental and health impacts of aviation emissions through modifications to the combustion process.

The article gives considerations to issues dealing with systems for separation and purification of gas mixtures containing methane. A method of pressure swing adsorption is suggested for biogas purification. The present results show the use of natural zeolite (Izhberdinskoye field, Orenburg region) to improve biogas quality by adsorption of water vapor, hydrogen sulphide and carbon dioxide.

A non-activated carbon ‘D’ was obtained by carbonizing date pits at 773 K in a limited supply of air. Activated carbons were obtained by gasifying portions of ‘D’ with air at 773 K, carbon dioxide at 1123 K, or steam at 1173 K, all to different burn-offs between 15% and 60%. The adsorption of nitrogen at 77 K and of carbon dioxide at 298 K was investigated using a volumetric adsorption apparatus of a conventional type. The adsorption of water vapour at 298 K and the chemisorption of pyridine at 423 K was followed by means of quartz spring balances. Gasification with oxidizing gases increased the surface area and total pore volume, as measured by nitrogen or carbon dioxide adsorption. In most cases, comparable surface areas were measured by nitrogen and carbon dioxide. The adsorption of water vapour depended on the percentage burn-off and the gasification conditions. Chemisorption of pyridine at 423 K was found to be related to the chemistry of the surface rather than to the surface area or total pore volume.

The specific surface areas of ten soil samples (clay content 1—72 %, organic carbon content 0.8—11.5 %) were determined by water vapor and nitrogen gas adsorption. The surface areas obtained by application of the BET equation to water vapor sorption at p/po 0.12—0.42 (21—195 m2/g) were, on the average, 80 % of the areas determined by water vapor sorption at p/po 0.20, range 27—229 m2/g. A BET water monolayer coverage was formed on the soil surface at p/po 0.12—0.20. The BET water area correlated closely with the one-point water area (p/po 0.20). The surface area determined by nitrogen gas adsorption ranged from 0.3 to 21 m2/g and did not correlate closely with water areas. The water surface areas were closely related to soil organic carbon content, while the nitrogen area was primarily related to soil clay content.

Preparation of niobium oxide films as a humidity sensor