Adsorption has long been used for gas recovery and clean-up applications. The chapter discusses two developed dry adsorption technologies for flue-gas desulfurization: the BF/FW process and the Shell/UOP process. In the BF/FW process activated carbon is used as the adsorbent, and sulfur dioxide removal is achieved by catalytic conversion to sulfuric acid at the char surface. In the Shell/UOP process, copper oxide is used as the adsorbent, and removal of sulfur dioxide is also by chemisorption. The chapter presents what is known about the mechanisms of adsorption and transport of acid gases in ion exchange resins. It discusses fixed-bed contacting protocols for flue-gas treatment. The chapter describes and compares temperature swing and pressure swing adsorption.

The influence of structural interaction between Mn, Ce, and Ti on the elemental mercury adsorption properties of Mn-Ce-Ti sorbents has been investigated. For this purpose, Mn-Ce-Ti sorbents have been synthesized by coprecipitation, codeposition-precipitation, coimpregnation, sequential impregnation, and deposition-impregnation to get different structural properties. All the sorbents were evaluated for elemental mercury capture in the absence and presence of SO2. Among the sorbents tested, the Mn-Ce-Ti sorbent synthesized by coimpregnation exhibits better sulfur resistance. X-ray diffraction measurements show that the samples prepared using impregnation methods exhibit intense reflections due to the cubic fluorite structure of cerium. Temperature-programmed desorption measurements reveal that the type and strength of acid sites depend on the synthesis method. Temperature-programmed reduction measurements suggest that precipitating Mn and Ce together over the surface of titania promotes surface ceria and manganese oxide reduction. However, the simultaneous precipitation of Mn, Ce, and Ti inhibits surface ceria and manganese oxide reduction. X-ray photoelectron spectroscopy (XPS) measurements suggest that the mechanism for Hg adsorption over Mn-Ce-Ti sorbents is the same regardless of the presence or absence of SO2. The Ce 3d XPS spectra show that all the samples exhibit peaks due to both Ce4+ and Ce3+ oxidation states. Surface atomic ratios determined from XPS measurements show that the sorbent synthesized by coimpregnation yields a higher concentration of cerium atoms on the surface and exhibits better sulfur resistance than the other sorbents. The sorbent synthesized by coprecipitation yields more titanium atoms on the surface and exhibits the least sulfur resistance.

Calixarene physisorption onto alkyl-functionalized silica support is presented as an alternative to tethering to reduce synthetic complexity. Three versions of calix[4]arene were synthesized with differing upper rim functional groups: aromatic amine, tert-butyl, and unfunctionalized. Calixarene molecules physisorbed throughout the alkyl layer on the silica following a linear isotherm with a maximum observed loading of 300 μmol g–1. Large exothermic adsorption enthalpies (−60 to −260 kJ mol–1), attributed to van der Waals interactions, were measured for the calixarene physisorption using flow microcalorimetry; large negative entropies were calculated (−140 to −780 J mol–1 K–1). Amine-calix[4]arene was physisorbed onto C18-silica (NCS) through solvent evaporation. The myoglobin uptake on NCS (47 μmol g–1) was twice that on C18-silica; additionally, a greater heat of adsorption (−16.9 ± 2.9 kJ mol–1) was observed on NCS than on C18-support (−12.7 ± 2.2 kJ mol–1).

The laboratory-scale simultaneous removal of elemental mercury (Hg-0) and NO has been investigated using MnOx/TiO2, MnOx/CeO2-TiO2, and CeO2-TiO2 materials in the presence and absence of CO. Remarkably, these materials exhibit excellent NO removal performance and high Hg-0 adsorption capacities both in single-component (NO or Hg-0) tests and in combined NO and Hg-0 removal experiments at 175 degrees C. Interestingly, NO removal increased in the presence of CO due to the selective catalytic reduction (SCR) by CO over 20% MnOx/CeO2-TiO2; Hg-0 adsorption did not inhibit SCR activity. In simultaneous removal tests, 20 wt % MnOx/CeO2-TiO2 effectively removed 9.4 mg Hg-0 g(-1) and 358 mg NO g(-1) at 175 degrees C. The surface areas of the TiO2 and CeO2-TiO2 materials decreased after impregnation with MnOx. CeO2-based materials have more lattice oxygen defects than TiO2, thus enhancing SCR in the presence of CO. Adsorbed Hg-0 reacts with lattice oxygen to form HgO on the surface of the CeO2-based materials.

Heats of adsorption measured by flow microcalorimetry (FMC) were used to understand the energetics of biomolecule adsorption on mesostructured cellular foam (MCF) silica. Tryptophan (Trp), lysozyme (LYS), and bovine serum albumin (BSA) were used as probe molecules. The FMC results confirmed that attractive interactions (both electrostatic and van der Walls interactions) between the biomolecules and acid-washed MCF silica were the driving force for adsorption, even when the protein (BSA) and the surface were both negatively charged and repulsion interactions might be expected. Multiple exothermic events occurred, possibly because of multipoint interactions between biomolecules and MCF silica resulting from multiple binding sites on the biomolecule and a curved pore structure. Interestingly, the magnitude of the enthalpy of adsorption (ΔHTotal) increased with increasing biomolecule size at pH 5.2; the number of exothermic peaks corresponded to the number of binding regions on the biomolecule. In addition, standard Gibbs energies of adsorption (ΔG°) and entropy of adsorption (ΔS°) were calculated from batch adsorption isotherms and the measured enthalpy of adsorption. BSA adsorption energetics were significantly affected by changing the pH from 4 to 5.2. This effect was attributed to a dramatic conformational change of BSA as a function of pH. The energetics of adsorption provide invaluable insight into the mechanism biomolecule adsorption.

The heat of lysozyme adsorption on mesostructured cellular foam (MCF) silica was measured using flow microcalorimetry (FMC) to investigate the influence of a neutral salt, sodium sulfate. At concentrations up to 0.5 M sodium sulfate, a complex initial exotherm was followed by an endotherm. Protein surface coverage, the magnitudes of the exothermic heat signals and the magnitudes of the net heat of adsorption increased with sodium sulfate concentration. These observations suggest that electrostatic interactions are the principal driving force at low ionic strengths; van der Waals interactions become dominant at higher salt concentrations. Each exotherm could be deconvoluted into two exotherms, indicating multiple modes of lysozyme attachment to the silica surface. The endothermic peak, associated with protein desorption, disappeared at the highest sodium sulfate concentration (1.0 M), indicating irreversible adsorption of the protein on the MCF silica surface. The data are consistent with an adsorption mechanism in which the initial attachment of lysozyme to the surface is followed by a reorientation and formation of a secondary or stronger attachment to the surface.

Mesostructured cellular foam (MCF) silica was synthesized using a non-ionic surfactant template-directed method without ammonium fluoride; the acid concentration and aging time were varied to determine the effects of these parameters on the final material. Increasing the acid concentration and aging time resulted in larger window size, which is critical in gating of biomolecule access to the interior of the MCF silica. In particular, when the acid concentration was changed from 1.6 to 3.5M the window pore dimension approximately doubled, although the pore size distribution was broader. In this study, the optimal synthesis conditions to produce large, narrowly distributed window pores are 3.5M HCl with an aging time of 20h. The loadings of l-tryptophan (Trp), lysozyme (LYS) and bovine serum albumin (BSA) on the MCF samples were measured using batch adsorption. Adsorption data followed a Type I isotherm. The monolayer adsorption capacity of Trp on acid-washed MCF was several times higher than that of LYS and BSA, because of the smaller size of Trp. Protein adsorption onto MCF silica showed minimal size exclusion until the window size of the silica was barely larger than the largest protein dimension.

High surface area ceria-titania materials were used as supports for manganese oxide for both warm-gas mercury capture and low temperature selective catalytic reduction. These materials exhibited excellent mercury capture capability at 175 degrees C. Increasing manganese loadings improves the mercury capacities. In the presence of SO(2), only a small decrease in mercury capacity was observed for the CeO(2)-TiO(2) adsorbents. CeO(2)-TiO(2) adsorbents similarly showed excellent stability in the presence of CO and NO. It was also found that the CeO(2)-TiO(2) support can capture Hg(0) and Hg(2+) simultaneously from nitrogen at 175 degrees C; the total mercury capacities were high. Brunauer-Emmentt-Teller surface area measurements suggested that increasing manganese loading reduced the surface area due to pore blockage. X-ray diffraction measurements showed that MnOx is in an amorphous state on CeO(2)-TiO(2) materials. X-ray photoelectron spectroscopy (XPS) results indicate that the adsorbed mercury is present as both Hg(0) and Hg(2+) on these ceria-based materials. The XPS observations also suggest that the incorporation of titanium into the cubic lattice of ceria leads to the formation of more lattice oxygen atoms, leading to greater formation of Hg(2+) on the CeO(2)-TiO(2) support.

The energetics of lysozyme adsorption on aminopropyl-grafted MCF silica (MCF-NH2) are compared to the trends observed during lysozyme adsorption on native MCF silica using flow microcalorimetry (FMC). Surface modification on MCF silica affects adsorption energetics significantly. All thermograms consist of two initial exothermic peaks and one later endothermic peak, but the heat signal trends of MCF-NH2 are opposite from those observed for adsorption onto native MCF silica in salt solutions of sodium acetate and sodium sulfate. At low ionic strength (0.01 M), LYS adsorption onto MCF-NH2 was accompanied by a large exotherm followed by a desorption endotherm. With increasing ionic strength (0.1 and 3.01 M), the magnitude of the thermal signal decreased and the total process became less exothermic. Also a higher protein loading of 14 μmol g(-1) was obtained at low ionic strength in batch adsorption isotherm measurements. Taken together, the FMC thermograms and batch adsorption isotherms reveal that MCF-NH2 has the nature of an ion exchange adsorbent, even though lysozyme and the aminopropyl ligands have like net charges at the adsorption pH. Reduced electrostatic interaction, reduced Debye length, and increased adsorption-site competition attenuate exothermicity at higher ionic strengths. Thermograms from flow microcalorimetry (FMC) give rich insight into the mechanisms of protein adsorption. A two-step adsorption mechanism is proposed in which negatively charged surface amino acid side chains on the lysozyme surface make an initial attachment to surface aminopropyl ligands by electrostatic interaction (low ionic strength) or van der Waals interaction (high ionic strength). Secondary attachments take place between protruding amino acid side chains and silanol groups on the silica surface. The reduced secondary adsorption heat is attributed to the inhibitory effect of the enhanced steric barrier of aminopropyl group on MCF silica.

The adsorption of bovine serum albumin (BSA) and lysozyme (LYS) on siliceous SBA-15 with 24 nm pores was studied using flow microcalorimetry; this is the first attempt to understand the thermodynamics of protein adsorption on SBA-15 using flow microcalorimetry. The adsorption mechanism is a strong function of protein structure. Exothermic events were observed when protein-surface interactions were attractive. Entropy-driven endothermic events were also observed in some cases, resulting from lateral protein-protein interactions and conformational changes in the adsorbed protein. The magnitudes of the enthalpies of adsorption for primary protein-surface interactions decrease with increased surface coverage, indicating the possibility of increased repulsion between adsorbed protein molecules. Secondary exothermic events were observed for BSA adsorption, presumably due to secondary adsorption made possible by conformational changes in the soft BSA protein. These secondary adsorption events were not observed for lysozyme, which is structurally robust. The results of this study emphasize the influence of solution conditions and protein structure on conformational changes of the adsorbed protein and the value of calorimetry in understanding protein-surface interactions.

Background/purpose: The water content of skin has a significant impact on skin properties; sufficient hydration is necessary to keep the skin supple, flexible, and smooth. To understand more completely the water retention properties of the human skin barrier, physical macroscopic properties must be related to the structural organization of the stratum corneum (SC). Water, lipids, and natural moisturizing factor (NMF) influence the molecular structures that affect the properties of SC, including water sorption and binding enthalpy. In the research reported here, isothermal microcalorimetry was used to study the interaction of water vapor with isolated human SC in intact, delipidized, and water‐washed delipidized forms to identify the influences of the principal components of SC on water sorption. The calorimetric data are interpreted in conjunction with spectroscopic results to identify the conformational changes in keratins induced by lipid and NMF removal and to assess the influence of these changes on water binding in SC.Methods: Isothermal calorimetry was used to measure the integral heat of water vapor sorption on intact, delipidized, and water‐washed delipidized human SC at 32 °C as a function of relative humidity using back and thigh skin from three donors. Calorimetric measurements were combined with water vapor sorption measurements to determine the differential thermodynamic properties of these systems. Attenuated total reflection–Fourier transform infrared spectroscopy was used to investigate effects of extraction on protein secondary structure.Results: The magnitudes of the differential enthalpy, entropy, and free energy were greatest for intact SC and least for water‐washed delipidized SC. Water sorption followed a similar trend. Delipidization led to a significantly reduced binding enthalpy at low water content; water washing the delipidized SC had only a small additional effect on binding enthalpy. Delipidization converts a fraction of keratin α‐helixes to turns and random coils, while water sorption converts a fraction of keratin α‐helixes to β‐sheets, turns, and random coils.Conclusions: The results of this study are consistent with a water sorption model in which keratin–keratin hydrogen bonds are replaced by keratin–water hydrogen bonds. Delipidization reduces the fraction of dry keratin that is in the α‐helix conformation, suggesting that lipids hold the keratins in a conformation conducive to optimal hydration.

A new class of adsorbents for direct capture of mercury from warm-gases has been developed. In these adsorbents, a dicarboxylic acid (DCA) is dissolved in a selective ionic liquid (IL) layer; the DCA + IL solution is coated on a mesoporous support. Mercury is absorbed by the IL and reacts with the DCA to form a halatopolymer, immobilizing the captured mercury. A prototype adsorbent was prepared by coating the IL [bmim]Cl and azelaic acid on mesoporous silica. Thermogravimetric analysis indicates that the adsorbent is thermally stable at the target operating temperature. Fixed-bed adsorption tests of elemental mercury capture from nitrogen at 160 degrees C show that this adsorbent can capture 44 mg Hg-0/g adsorbant. Leaching tests indicate that the captured mercury is held tightly by the adsorbent. The high mercury capacity and high adsorption temperature suggest that the prototype adsorbent is competitive with modified carbons currently used in integrated gasification combined cycle applications.

The present study was focused on elucidating the effects of nanopore diffusional resistance on the activity of Burkholderia cepacia (BC lipase) lipase immobilized in ordered mesoporous silica hosts. BC lipase was immobilized in ordered SBA-15 hosts possessing 55 and 240A˚ diameter pores by physical adsorption. A colorimetric assay of p-nitrophenyl acetate was employed to determine the lipase catalytic activity. The effect of diffusional resistance on catalytic activity of lipase immobilized in SBA-15 hosts was investigated by determining the effective substrate diffusivity as a function of pore size of the SBA-15 host and enzyme loading. Lipase immobilized in SBA-15-55A˚ exhibited 20–30% of free lipase activity and the activity was further reduced with enzyme loading due to limited accessibility of substrate to the enzyme active sites. Lipase immobilized in SBA-15-240A˚ hosts showed catalytic activity similar to free lipase activity suggesting that diffusional limitations were minimal. Large pore SBA-15 hosts provided an improved environment for BC lipase to retain its catalytic activity.

A novel catalyst for low temperature selective catalytic reduction (SCR) using CO as reductant, MnOx supported on titania, has been shown to be effective for both elemental mercury capture and low temperature SCR. In low temperature (200 degrees C) SCR trials using an industrially relevant space velocity (50 000 h(-1)) and oxygen concentration (2 vol %), nearly quantitative reduction of NO, was obtained using CO as the reductant. Fresh catalyst used as an adsorbent for elemental mercury from an inert atmosphere showed remarkable mercury capture capacity, as high as 17.4 mg/g at 200 degrees C. The catalyst effectively captured elemental mercury after use in NO, reduction. Mercury capture efficiency was not affected by the presence of water vapor. Mercury capacity was reduced in the presence Of SO2. Manganese loading and bed temperature, which influence surface oxide composition, were found to be important factors for mercury capture. X-ray photoelectron spectroscopy (XPS) results reveal that the mercury is present in its oxidized form (HgO) in spent catalyst, indicating the participation of lattice oxygen of the catalyst in the reaction. These results suggest that a single-step process integrating low temperature SCR and mercury capture from flue gas might be feasible.

Studies of adsorption on biologically derived materials typically include direct measurement of either the adsorption isotherm or the heat of adsorption, but not both. Simultaneous measurement of adsorption and heat of adsorption should provide a more reliable description of the material under study. In this context, an analysis of the thermodynamics of water sorption is presented and a multilayer heat of sorption equation is derived within the framework of the Guggenheim–Anderson–deBoer (GAB) model. This model is applied to the previously published data for water vapor sorption and heat of water vapor sorption on stratum corneum (SC) over a range of relative humidities. The GAB models effectively characterize both heat evolution and equilibrium mass uptake over a broad water activity range. The thermodynamic results suggest significant restructuring of the SC during the sorption process; the sorption data alone are not sufficient to identify this effect. The results of this study emphasize first, the importance of incorporating a multilayer approach with variable energies of interaction in modeling of water uptake by SC and second, the utility of correlating sorption and calorimetric data simultaneously.

Six room temperature ionic liquids (RTILs) were synthesized and tested as coatings for adsorbents for mercury capture from nitrogen at 160 degrees C. All six RTILs were thermally stable to temperatures above 160 degrees C. These RTILs were coated oil mesoporous silica gel, and the fixed-bed mercury capture characteristics of these adsorbents were observed at 160 degrees C. Hg-0 capture appears to result from the formation of a complex involving Hg-0 and ions in the RTIL complex, and not from oxidation by the RTIL. The high observed oxidized mercury capacity for Cl--based RTILs is believed to be due to greater dissociation of HgCl2 in the RTILs that incorporate chloride anion. The higher hydrogen-bond basicity and dipolarity of these RTILs might underlie improved HgCl2 dissociation. [bmim]Cl was identified as a promising RTIL for the simultaneous capture of elemental and oxidized mercury from the gas phase. A nanostructured chelating adsorbent with a coating of 25 wt % [bmim]Cl has an elemental mercury capacity of 10 mg/g and an oxidized mercury capacity of at least 38 mg/g.

Thermally robust chelating adsorbents for the capture of vapor-phase mercuric chloride (HgCl2) have been developed, to address the issue of mercury removal from flue gases from coal-fired power plants. The adsorbents are mesoporous silica substrates functionalized with a chelating agent and coated with an ionizing surface nano-layer. This architecture enables selective, multi-dentate adsorption of mercury directly from the gas phase with high capacity. The capture efficiency of the adsorbents was evaluated in the fixed-bed mode for oxidized mercury at 160°C. Two chelating adsorbents, one functionalized with 3-mercaptopropyltrimethoxysilane (MPTS) and the other with 2-mercaptobenzothialzole (MBT), were studied. For both adsorbents a high mercury uptake capacity was observed, several times higher than that of commercial activated carbon. The mechanism for mercury uptake in the two adsorbents is different. The effect of pore size on uptake was also evaluated. It was found that pore size does not have a significant effect on the mercury adsorption, and mercury diffusion through the ionic coating is believed to be the rate-limiting step for capture.