Competitive adsorption

Abstract

UDC 541.183 V. M. Gun'koA review is presented on the multicomponent competitive adsorption, static equilibrium adsorption, and dynamic nonequilibrium adsorption from gaseous and liquid media onto the surface of porous and disperse solids. The state of the theory of multicomponent adsorption is analyzed. Not only traditional methods were used for investigations in this field but also NMR spectroscopy (difference in the spectra of adsorbed and free compounds), FTIR spectroscopy (difference in the spectra of surface groups and bonds in adsorbates), calorimetry, thermally stimulated depolarization, photon correlation spectroscopy, electrophoresis, and cryoporometry.corresponding polymers. We should note that the effect of the conditions of both equilibrium (static) and nonequilibrium (dynamic) adsorption is greater in competitive adsorption since the adsorbates may differ considerably in their rate of diffusion, kinetics and free energy of adsorption, nature of interaction both with the surface (monodentate, bidentate, and polydentate adsorption) and the medium, and in their concentration. On the whole, competitive adsorption leads to a reduced rate of reaching equilibrium. Preadsorption or a higher diffusion rate gives a momentary advantage to the first or more mobile adsorbate, which is most evident in dynamic adsorption and less so in equilibrium adsorption. The time to reach equilibrium in the case of preadsorption or concurrent competitive adsorption may be different but it is greater than in the individual adsorption of the same compounds.There are two approaches to the description of competitive adsorption involving additive and nonadditive models. In the former case, the adsorption of the i-th adsorbate is seen as the adsorption of an individual compound taking account of its partial pressure or concentration, in which the parameters of the adsorbent such as adsorption capacity are redetermined taking account of the adsorption of other adsorbates. We use fitting or additional parameters such as activity coefficients in these models [11]. In the case of nonadditive models, adsorption is described by a system of related equations, determining the corresponding parameters using different variants for uncoupling equations and iterative self-consistency of their solutions. Special program packages have been developed for analyzing the data for multicomponent mixtures. Thus, for example, the TMVOC package [25] (similar to the TOUGH2 or T2VOC packages) was developed at the Berkeley National Laboratory in the United States for modeling systems involving a nonisothermal water flow, soil gas, and a mixture of volatile organic compounds in a heterogeneous porous medium. The 3DHYDROGEOCHEM package was developed by the Environmental Protection Agency in the United States for analogous purposes. These packages are applicable both for "natural" environmental conditions and engineering systems.On the whole, there have been many studies of multicomponent adsorption but nevertheless less than for the adsorption of individual c...

Analysis of Competition between Multicomponent BTX Compounds for the Active Site of Adsorption in a Fixed-Bed Column

“…For competitive adsorption, the time required for the adsorption to occur differs from that for the same monocomponents, this being shorter for the mixture than for the individual compounds. The establishment of the adsorption equilibrium for the multicomponent compounds of lower molar mass occurs more rapidly and requires only minutes or tenths of a minute depending on their concentration in the solution . From Figure it can be noted that the benzene adsorption was inhibited in the presence of different concentrations of toluene and o -xylene, this effect being slightly greater as the contaminant concentrations increase.…”

Analysis of Competition between Multicomponent BTX Compounds for the Active Site of Adsorption in a Fixed-Bed Column

“…For competitive adsorption, the time required for the adsorption to occur differs from that for the same monocomponents, this being shorter for the mixture than for the individual compounds. The establishment of the adsorption equilibrium for the multicomponent compounds of lower molar mass occurs more rapidly and requires only minutes or tenths of a minute depending on their concentration in the solution . From Figure it can be noted that the benzene adsorption was inhibited in the presence of different concentrations of toluene and o -xylene, this effect being slightly greater as the contaminant concentrations increase.…”

Hydroformylation of 1-Hexene over Rh/Nano-Oxide Catalysts

“…In our supported Rh systems, it is likely that the impregnated Rh 3+ is reduced by the syngas, subsequent to which the reaction follows a route similar to that suggested by Zhou et al and Rosales et al for the heterogeneous olefin hydroformylation [34,49]. The hydroxyl groups on metal oxide surfaces are also known to have an impact on the catalytic activity [50,51,52], but their role was not studied in detail in the current work.…”

Effect of SDBS on Crystallization Behavior of Pseudoboehmite

“…In the actual system, several different adsorbates exist at the interface. Different adsorbents compete for adsorption sites with the smallest adsorption energy characteristics . Ji et al found that there was an adsorption behavior between the pseudoboehmite crystal face and water molecules.…”

“…In addition, with the exception of the (002) crystal plane, SDBS was at a disadvantage with respect to competitive adsorption with water molecules based on the positive values of E adp(SDBS‑H2O) . The predominant adsorption of one of the adsorbates on certain sites causes selective adsorption . The (200) crystal plane exhibits the highest adsorption energy due to the surface structure collapse of pseudoboehmite caused by molecular adsorption.…”

Analysis of Competition between Multicomponent BTX Compounds for the Active Site of Adsorption in a Fixed-Bed Column

“…For competitive adsorption, the time required for the adsorption to occur differs from that for the same monocomponents, this being shorter for the mixture than for the individual compounds. The establishment of the adsorption equilibrium for the multicomponent compounds of lower molar mass occurs more rapidly and requires only minutes or tenths of a minute depending on their concentration in the solution . From Figure it can be noted that the benzene adsorption was inhibited in the presence of different concentrations of toluene and o -xylene, this effect being slightly greater as the contaminant concentrations increase.…”

Hydroformylation of 1-Hexene over Rh/Nano-Oxide Catalysts

“…In our supported Rh systems, it is likely that the impregnated Rh 3+ is reduced by the syngas, subsequent to which the reaction follows a route similar to that suggested by Zhou et al and Rosales et al for the heterogeneous olefin hydroformylation [34,49]. The hydroxyl groups on metal oxide surfaces are also known to have an impact on the catalytic activity [50,51,52], but their role was not studied in detail in the current work.…”

Effect of SDBS on Crystallization Behavior of Pseudoboehmite

“…In the actual system, several different adsorbates exist at the interface. Different adsorbents compete for adsorption sites with the smallest adsorption energy characteristics . Ji et al found that there was an adsorption behavior between the pseudoboehmite crystal face and water molecules.…”

“…In addition, with the exception of the (002) crystal plane, SDBS was at a disadvantage with respect to competitive adsorption with water molecules based on the positive values of E adp(SDBS‑H2O) . The predominant adsorption of one of the adsorbates on certain sites causes selective adsorption . The (200) crystal plane exhibits the highest adsorption energy due to the surface structure collapse of pseudoboehmite caused by molecular adsorption.…”

Analysis of Competition between Multicomponent BTX Compounds for the Active Site of Adsorption in a Fixed-Bed Column

“…For competitive adsorption, the time required for the adsorption to occur differs from that for the same monocomponents, this being shorter for the mixture than for the individual compounds. The establishment of the adsorption equilibrium for the multicomponent compounds of lower molar mass occurs more rapidly and requires only minutes or tenths of a minute depending on their concentration in the solution . From Figure it can be noted that the benzene adsorption was inhibited in the presence of different concentrations of toluene and o -xylene, this effect being slightly greater as the contaminant concentrations increase.…”

Hydroformylation of 1-Hexene over Rh/Nano-Oxide Catalysts

“…In our supported Rh systems, it is likely that the impregnated Rh 3+ is reduced by the syngas, subsequent to which the reaction follows a route similar to that suggested by Zhou et al and Rosales et al for the heterogeneous olefin hydroformylation [34,49]. The hydroxyl groups on metal oxide surfaces are also known to have an impact on the catalytic activity [50,51,52], but their role was not studied in detail in the current work.…”

Effect of SDBS on Crystallization Behavior of Pseudoboehmite

“…In the actual system, several different adsorbates exist at the interface. Different adsorbents compete for adsorption sites with the smallest adsorption energy characteristics . Ji et al found that there was an adsorption behavior between the pseudoboehmite crystal face and water molecules.…”

“…In addition, with the exception of the (002) crystal plane, SDBS was at a disadvantage with respect to competitive adsorption with water molecules based on the positive values of E adp(SDBS‑H2O) . The predominant adsorption of one of the adsorbates on certain sites causes selective adsorption . The (200) crystal plane exhibits the highest adsorption energy due to the surface structure collapse of pseudoboehmite caused by molecular adsorption.…”