Energetic Characterization of Faujasite Zeolites Using a Sensor Gas Calorimeter

In addition to the adsorption mechanism, the heat released during exothermic adsorption influences the chemical reactions that follow during heterogeneous catalysis. Both steps depend on the structure and surface chemistry of the catalyst. An example of a typical catalyst is the faujasite zeolite. For faujasite zeolites, the influence of the Si/Al ratio and the number of Na+ and Ca2+ cations on the heat of adsorption was therefore investigated in a systematic study. A comparison between a NaX (Sodium type X faujasite) and a NaY (Sodium type Y faujasite) zeolite reveals that a higher Si/Al ratio and therefore a smaller number of the cations in faujasite zeolites leads to lower loadings and heats. The exchange of Na+ cations for Ca2+ cations also has an influence on the adsorption process. Loadings and heats first decrease slightly at a low degree of exchange and increase significantly with higher calcium contents. If stronger interactions are required for heterogeneous catalysis, then the CaNaX zeolites must have a degree of exchange above 53%. The energetic contributions show that the highest-quality adsorption sites III and III’ make a contribution to the load-dependent heat of adsorption, which is about 1.4 times (site III) and about 1.8 times (site III’) larger than that of adsorption site II

Energetic Characterization of Faujasite Zeolites Using a Sensor Gas Calorimeter

In addition to the adsorption mechanism, the heat released during exothermic adsorption influences the chemical reactions that follow during heterogeneous catalysis. Both steps depend on the structure and surface chemistry of the catalyst. An example of a typical catalyst is the faujasite zeolite. For faujasite zeolites, the influence of the Si/Al ratio and the number of Na+ and Ca2+ cations on the heat of adsorption was therefore investigated in a systematic study. A comparison between a NaX (Sodium type X faujasite) and a NaY (Sodium type Y faujasite) zeolite reveals that a higher Si/Al ratio and therefore a smaller number of the cations in faujasite zeolites leads to lower loadings and heats. The exchange of Na+ cations for Ca2+ cations also has an influence on the adsorption process. Loadings and heats first decrease slightly at a low degree of exchange and increase significantly with higher calcium contents. If stronger interactions are required for heterogeneous catalysis, then the CaNaX zeolites must have a degree of exchange above 53%. The energetic contributions show that the highest-quality adsorption sites III and III’ make a contribution to the load-dependent heat of adsorption, which is about 1.4 times (site III) and about 1.8 times (site III’) larger than that of adsorption site II

Investigation of Mechanical, Chemical and Adsorptive Properties of Novel Silicon-Based Adsorbents with Activated Carbon Structure

In this article, for the first time the chemical and mechanical properties of novel adsorbents based on the coating of activated carbons with silicon carbide are reported. The adsorbents are prepared by chemical vapor infiltration (CVI) of activated carbons with tetramethylsilane (TMS) as a precursor. A comparison of two different modified types of activated carbon, C40/4 Extra and A35/4 Extra, each infiltrated with 25%-mass at infiltration temperatures of 973.15 and 1098.15 K, respectively, is presented. Adsorption properties were characterized by measuring nitrogen isotherms and volatile organic compounds (VOC) isotherms in gas phase and excess isotherms in liquid phase. In addition, the physico-chemical properties including the bulk density, ash content, particle hardness, abrasion, conductivity, water-soluble components, and pH value were determined. Furthermore, the first experiments in a fluidized bed adsorber are presented. The results show that the adsorption properties of the modified adsorbents are mainly maintained. The particle hardness and the abrasion resistance increases with increasing infiltration temperature, which leads to an overall increasing of mechanical stability. A modification of the chemical stability as a result of the infiltration experiments is not observed

Adsorptive Water Removal from Primary Alcohols and Acetic Acid Esters in the ppm-Region

Dry organic solvents are important for many industrial sectors. Adsorptive water removal is one technique to obtain highly pure solvents. However, in-depth knowledge of the parameters influencing adsorption behavior is still fragmentary. This paper presents a systematic investigation of water adsorption from alcohols (C1 to C6) and acetic acid esters (methyl acetate to <i>n</i>-butyl acetate) of different chain lengths. Zeolites of types 3A and 4A are used as adsorbents. The impact of size exclusion on adsorption properties is analyzed. The water adsorption isotherms on zeolite 3A from solvents with a large critical molecular diameter are similar to the water vapor isotherm as expected from literature data. In case of smaller solvent molecules (methanol, ethanol, 1-propanol) a significantly lower water adsorption capacity is found on zeolite 3A. In case of all solvents on zeolite 4A water adsorption is lower than water vapor adsorption even if the estimated molecular diameter is larger than the reported window aperture of the zeolite cage. It is discussed to what extent water and solvent are capable to coadsorb and compete for adsorption sites

Impact of Na+ and Ca2+ Cations on the Adsorption of H2S on Binder-Free LTA Zeolites

Hydrogen sulfide is removed from natural gas via adsorption on zeolites. The process operates very effectively, but there is still potential for improvement. Therefore, in this article, the adsorption of hydrogen sulfide was investigated on eight LTA zeolites with different cation compositions. Starting with the zeolite NaA (4 A), which contains only Na+ cations, the Ca2+ cation content was gradually increased by ion exchange. Equilibrium isotherms from cumulative breakthrough curve experiments in a fixed-bed adsorber at 25°C and 85°C at 1.3 bar (abs.) were determined in the trace range up to a concentration of 2000 ppmmol. From a comparison of the isotherms of the different materials, a mechanistic proposal for the adsorption is developed, taking into account the specific positions of the cations in the zeolite lattice when the degree of exchange is increased. The shape of the isotherms indicates two energetically different types of adsorption sites. It is assumed that two mechanisms are superimposed: a chemisorptive mechanism with dissociation of hydrogen sulfide and covalent bonding of the proton and the hydrogen sulfide ion to the zeolite lattice and a physisorptive mechanism by electrostatic interaction with the cations in the lattice. As the degree of exchange increases, the proportion of chemisorption sites seems to decrease. Above an exchange degree of 50%, only evidence of physisorption can be found. It is shown that this finding points to the involvement of weakly bound sodium cations at cation position III in the chemisorption of hydrogen sulfide

Amtsblatt des Großherzoglich Hessischen Oberschulraths No 41. Darmstadt am 25. May 1842

75. Die Zeit der Entlassung der israelitischen Kinder aus der Volksschule

Mercury Adsorption on Phosphoric Acid- and Nitric Acid-Modified Activated Carbon

In this work, the influence of phosphoric groups on the surface of activated carbon on the adsorption of elemental mercury (Hg0) is systematically investigated for the first time. The influence of functional oxygen groups–controversially discussed in the literature–on the single-component adsorption of Hg0 as well as the co-adsorption of water and Hg0 are thoroughly analyzed, leading to a new mechanistic proposal. Single-component adsorption of Hg0 and co-adsorption of mercury and water on modified activated carbons are investigated by breakthrough curves as well as by coupled adsorption and temperature-programmed desorption (TPD) experiments. The modification of a basic activated carbon with phosphoric acid evolves phosphoric acid esters on the surface, which significantly increase the chemisorptive capacity for Hg0. TPD experiments reveal that only a single chemisorptive mechanism is involved. Based on these findings, a schematic mechanism for the chemisorptive attachment of Hg0 is proposed. In contrast to this, physisorptive interactions between Hg0 and surface groups dominate at the basic activated carbon and at the activated carbon modified with nitric acid. Oxygen-containing functional groups formed by nitric acid do not significantly enhance the one-component adsorption of elemental mercury. The experiments on the co-adsorption of mercury and water prove that the surface complexes of oxygen functional groups and Hg0 are strongly stabilized by water from the gas phase. A schematic chemisorptive mechanism is also proposed here. The chemical reaction of Hg0 with phosphoric acid esters, on the other hand, is not influenced by water from the gas phase in the concentration range investigated

Trace Level Adsorption of Toxic Sulfur Compounds, Carbon Dioxide, and Water from Methane

This paper presents breakthrough curves and isotherms of the adsorption of sulfur compounds, carbon dioxide, and water from a carrier gas (methane) on a fixed solid bed at 298 K and 1.3 bar. For the investigation two industrial adsorbents (silica–alumina gel, zeolite 5A) were used. The adsorptives were prepared in trace level concentrations up to 2000 mol-ppm. Common isotherm equations were fitted to the adsorption capacities which were obtained from breakthrough curves by mass balances. Binary systems (one adsorptive in methane) and ternary systems (two adsorptives in methane) are included. Methane is used to duplicate conditions of industrial scale natural gas treatment as far as possible. Though methane is a very weak adsorptive on oxidic adsorbents the reported adsorptive capacities might be slightly lower than pure component loadings accessible from a volumetric or gravimetric method. The adsorption isotherms of the binary systems show distinctly different capacities depending on the polarity of the adsorptive and the structure of the adsorbent. The investigation of the ternary systems reveals significant coadsorption and displacement as well as kinetic effects due to the presence of competing adsorptives

Temperature Dependent Adsorption of Sulfur Components, Water, and Carbon Dioxide on a Silica–Alumina Gel Used in Natural Gas Processing

Adsorption is one of the key technologies for the removal of sulfur compounds in trace levels from natural gas prior to a technical utilization. To improve the design of these coupled adsorption–desorption processes a profound insight into the thermodynamics of adsorption is necessary. Therefore, this article provides adsorption isotherms of ethyl mercaptan, methyl mercaptan, hydrogen sulfide, water, and carbon dioxide on a commercial silica–alumina gel used in natural gas purification. The experimental data spans a temperature range between 25 and 300 °C at concentrations between 0 and 2000 mol-ppm at total pressure of 1.3 bar. Equilibrium capacities and isosteric heats of adsorption are compared and discussed based on an analysis of specific interactions between the adsorptives and the adsorbent’s chemical surface functionality