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1.
《Solid State Sciences》2012,14(2):250-257
CO2 adsorption properties on Mg modified silica mesoporous materials were investigated. By using the methods of co-condensation, dispersion and ion-exchange, Mg2+ was introduced into SBA-15 and MCM-41, and transformed into MgO in the calcination process. The basic MgO can provide active sites to enhance the acidic CO2 adsorption capacity. To improve the amount and the dispersion state of the loading MgO, the optimized modification conditions were also investigated. The XRD and TEM characteristic results, as well as the CO2 adsorption performance showed that the CO2 adsorption capacity not only depended on the pore structures of MCM-41 and SBA-15, but also on the improvement of the dispersion state of MgO by modification. Among various Mg modified silica mesoporous materials, the CO2 adsorption capacity increased from 0.42 mmol g−1 of pure silica SBA-15 to 1.35 mmol g−1 of Mg–Al–SBA-15-I1 by the ion-exchange method enhanced with Al3+ synergism. Moreover, it also increased from 0.67 mmol g−1 of pure silica MCM-41 to 1.32 mmol g−1 of Mg–EDA–MCM-41-D10 by the dispersion method enhanced with the incorporation of ethane diamine. The stability test by 10 CO2 adsorption/desorption cycles showed Mg–urea–MCM-41-D10 possessed quite good recyclability.  相似文献   

2.
The molar heat capacities of GeCo2O4 and GeNi2O4, two geometrically frustrated spinels, have been measured in the temperature range from T=(0.5 to 400) K. Anomalies associated with magnetic ordering occur in the heat capacities of both compounds. The transition in GeCo2O4 occurs at T=20.6 K while two peaks are found in the heat capacity of GeNi2O4, both within the narrow temperature range between 11.4<(T/K)<12.2. Thermodynamic functions have been generated from smoothed fits of the experimental results. At T=298.15 K the standard molar heat capacities are (143.44 ± 0.14) J · K−1 · mol−1 for GeCo2O4 and (130.76 ± 0.13) J · K−1 · mol−1 for GeNi2O4. The standard molar entropies at T=298.15 K for GeCo2O4 and GeNi2O4 are (149.20 ± 0.60) J · K−1 · mol−1 and (131.80 ± 0.53) J · K−1 · mol−1 respectively. Above 100 K, the heat capacity of the cobalt compound is significantly higher than that of the nickel compound. The excess heat capacity can be reasonably modeled by the assumption of a Schottky contribution arising from the thermal excitation of electronic states associated with the CO2+ ion in a cubic crystal field. The splittings obtained, 230 cm−1 for the four-fold-degenerate first excited state and 610 cm−1 for the six-fold degenerate second excited state, are significantly lower than those observed in pure CoO.  相似文献   

3.
A novel cation exchanger (TFS-CE) having carboxylate functionality was prepared through graft copolymerization of hydroxyethylmethacrylate onto tamarind fruit shell (TFS) in the presence of N,N′-methylenebisacrylamide as a cross-linking agent using K2S2O8/Na2S2O3 initiator system, followed by functionalisation. The TFS-CE was used for the removal of Cu(II) from aqueous solutions. At fixed solid/solution ratio the various factors affecting adsorption such as pH, initial concentration, contact time, and temperature were investigated. Kinetic experiments showed that the amount of Cu(II) adsorbed increased with increase in Cu(II) concentration and equilibrium was attained at 1 h. The kinetics of adsorption follows pseudo-second-order model and the rate constant increases with increase in temperature indicating endothermic nature of adsorption. The Arrhenius and Eyring equations were used to obtain the kinetic parameters such as activation energy (Ea) and enthalpy (ΔH#), entropy (ΔS#) and free energy (ΔG#) of activation for the adsorption process. The value of Ea for adsorption was found to be 10.84 kJ · mol?1 and the adsorption involves diffusion controlled process. The equilibrium data were well fitted to the Langmuir isotherm. The maximum adsorption capacity for Cu(II) was 64 · 10 mg · g?1 at T = 303 K. The thermodynamic parameters such as changes in free energy (ΔG°), enthalpy (ΔH°), and entropy (ΔS°) were derived to predict the nature of adsorption process. The isosteric heat of adsorption increases with increase in surface loading indicating some lateral interactions between the adsorbed metal ions.  相似文献   

4.
Some heterogeneous reactions of oxide ion exchange (carbonate ion dissociation and magnesium oxide dissolution) in the molten {KCl + LiCl} eutectic at temperatures of (873, 973 and 1073) K were studied using an electrochemical cell with an oxygen membrane electrode Pt(O2)|ZrO2(Y2O3). The dissociation constant of the CO32− was found to increase with increasing temperature: pK (873 K)=(2.39 ± 0.05); pK (973 K)=(1.81 ± 0.09); pK (1073 K)=(1.53 ± 0.08). Removal of CO2 from the gas above the melt allows the complete transformation of CO32− to O2−. pPMgO values decrease more from (6.99 ± 0.08) to (5.41 ± 0.04). The oxobasicity indices, pI(KCl+LiCl), were calculated from the solubility data to be 3.2 at 873 K, 3.4 at 973 K, and 3.6 at 1073 K. This trend suggests an increase in acidity with increasing temperature of {KCl + LiCl}.  相似文献   

5.
We report a theoretical study to predict the phase-equilibrium properties of ozone-containing clathrate hydrates based on the statistical thermodynamics model developed by van der Waals and Platteeuw. The Patel–Teja–Valderrama equation of state is employed for an accurate estimation of the properties of gas phase ozone. We determined the three parameters of the Kihara intermolecular potential for ozone as a = 6.815 · 10−2 nm, σ = 2.9909 · 10−1 nm, and ε · kB−1 = 184.00 K. An infinite set of εσ parameters for ozone were determined, reproducing the experimental phase equilibrium pressure–temperature data of the (O3 + O2 + CO2) clathrate hydrate. A unique parameter pair was chosen based on the experimental ozone storage capacity data for the (O3 + O2 + CCl4) hydrate that we reported previously. The prediction with the developed model showed good agreement with the experimental phase equilibrium data within ±2% of the average deviation of the pressure. The Kihara parameters of ozone showed slightly better suitability for the structure-I hydrate than CO2, which was used as a help guest. Our model suggests the possibility of increasing the ozone storage capacity of clathrate hydrates (∼7% on a mass basis) from the previously reported experimental capacity (∼1%).  相似文献   

6.
The Knudsen mass-loss effusion technique was used to measure the vapour pressures at different temperatures of the following six compounds: 2-methyl-3-nitrobenzoic acid, between T =  357.16 K and T =  371.16 K; 2-methyl-6-nitrobenzoic acid, between T =  355.16 K and T =  369.16 K; 3-methyl-2-nitrobenzoic acid, between T =  371.16 K and T =  385.14 K; 3-methyl-4-nitrobenzoic acid, between T =  363.21 K and T =  379.16 K; 4-methyl-3-nitrobenzoic acid, between T =  363.10 K and T =  377.18 K; 5-methyl-2-nitrobenzoic acid, between T =  355.18 K and T =  371.08 K. From the temperature dependence of the vapour pressure, the standard molar enthalpies of sublimation were derived by the Clausius–Clapeyron equation and the molar entropies of sublimation at equilibrium pressures were calculated. Using estimated values for the heat capacity differences between the gas and the crystal phases of the studied compounds the standard, po =  105Pa, molar enthalpies ΔcrgHmo, entropies ΔcrgSmoand Gibbs energies ΔcrgGmoof sublimation at T =  298.15 K, were derived:  相似文献   

7.
The thermodynamic properties ofZn5(OH)6(CO3)2 , hydrozincite, have been determined by performing solubility and d.s.c. measurements. The solubility constant in aqueous NaClO4media has been measured at temperatures ranging from 288.15 K to 338.15 K at constant ionic strength (I =  1.00 mol · kg  1). Additionally, the dependence of the solubility constant on the ionic strength has been investigated up to I =  3.00 mol · kg  1NaClO4at T =  298.15 K. The standard molar heat capacity Cp, mofunction fromT =  318.15 K to T =  418.15 K, as well as the heat of decomposition of hydrozincite, have been obtained from d.s.c. measurements. All experimental results have been simultaneously evaluated by means of the optimization routine of ChemSage yielding an internally consistent set of thermodynamic data (T =  298.15 K): solubility constant log * Kps 00 =  (9.0  ±  0.1), standard molar Gibbs energy of formationΔfGmo {Zn5(OH)6(CO3)2 }  =  (  3164.6  ±  3.0)kJ · mol  1, standard molar enthalpy of formation ΔfHmo{Zn5(OH)6(CO3)2 }  =  (  3584  ±  15)kJ · mol  1, standard molar entropy Smo{Zn5(OH)6(CO3)2 }  =  (436  ±  50)J · mol  1· K  1and Cp,mo / (J · mol  1· K  1)  =  (119  ±  11)  +  (0.834  ±  0.033)T / K. A three-dimensional predominance diagram is introduced which allows a comprehensive thermodynamic interpretation of phase relations in(Zn2 +  +  H2O  +  CO2) . The axes of this phase diagram correspond to the potential quantities: temperature, partial pressure of carbon dioxide and pH of the aqueous solution. Moreover, it is shown how the stoichiometric composition{n(CO3) / n(Zn)} of the solid compoundsZnCO3 and Zn5(OH)6(CO3)2can be checked by thermodynamically analysing the measured solubility data.  相似文献   

8.
A new apparatus based on a static–analytic method assembled in this work was utilised to perform high-pressure (vapour + liquid) equilibria measurements of aqueous ternary systems. This work includes values of isothermal partition coefficients between CO2 and water of two apple aroma constituents, (E)-2-hexenal and hexanal. Additionally, this work reports new experimental (vapour + liquid) equilibria measurements for the ternary systems (CO2 + (E)-2-hexenal + water) and (CO2 + hexanal + water), at fixed liquid phase composition (600 mg · kg−1), at temperatures of (313, 323 and 333) K and at pressures from (8 to 19) MPa. Vapour liquid interphase was checked and monitored visually for all the systems studied in this work. No liquid immiscibility was observed at the composition, temperatures and pressures studied. In order to suggest reasonable operation conditions for fractionation of aromas with dense carbon dioxide, partition coefficients of the aroma compounds between CO2 and water along with their separation factors from water were calculated. Partition coefficients of (E)-2-hexenal between CO2 and water were in the range of (6 to 91) and where found to be near six times higher than those of hexanal (9 to 17). Very high separation factors from water were observed (∼104) especially for (E)-2-hexenal. The highest separation factor, for both compounds, was found at a temperature of 313 K and pressures from (12 to 14) MPa.  相似文献   

9.
10.
A magnesium-based metal organic framework (MOF), also known as Mg-MOF-74, was successfully synthesized, characterized, and evaluated for adsorption equilibria and kinetics of CO2 and CH4. The Mg-MOF-74 crystals were characterized with scanning electron microscopy for crystal structure, powder X-ray diffraction for phase structure, and nitrogen adsorption for pore textural properties. Adsorption equilibrium and kinetics of CO2 and CH4 on the Mg-MOF-74 adsorbent were measured in a volumetric adsorption unit at 278, 298, and 318 K and pressures up to 1 bar. It was found that the Mg-MOF-74 adsorbent prepared in this work has a median pore width of 10.2 Å, a BET specific surface area of 1174 m2/g, CO2 and CH4 adsorption capacities of 8.61 mmol g?1 (37.8 wt.%) and 1.05 mmol g?1 (1.7 wt.%), respectively, at 298 K and 1 bar. Both CO2 and CH4 adsorption capacities are significantly higher than those of zeolite 13X under similar conditions. The pressure-dependent equilibrium selectivity of CO2 over CH4 (qCO2/qCH4) in the Mg-MOF-74 adsorbent showed a trend similar to that of zeolite 13X and the intrinsic selectivity of Mg-MOF-74 at zero adsorption loading is 283 at 298 K. The initial heats of adsorption of CO2 and CH4 on the Mg-MOF-74 adsorbent were found to be 73.0 and 18.5 kJ mol?1, respectively. The adsorption kinetic measurements suggest that the diffusivities of CO2 and CH4 on Mg-MOF-74 were comparable to those on zeolite 13X. CH4 showed relatively faster adsorption kinetics than CO2 in both adsorbents. The diffusion time constants of CO2 and CH4 in the Mg-MOF-74 adsorbent at 298 K were estimated to be 8.11 × 10?3 and 4.05 × 10?2 s?1, respectively, showing a modest kinetic selectivity of about 5 for the separation CH4 from CO2.  相似文献   

11.
Measurements of compressed liquid densities for 1-pentanol and for {CO2 (1) + 1-pentanol (2)} system were carried out at temperatures from 313 K to 363 K and pressures up to 25 MPa. Densities were measured for binary mixtures at 10 different compositions, x1 = 0.0816, 0.1347, 0.3624, 0.4651, 0.6054, 0.7274, 0.8067, 0.8573, 0.9216, and 0.9757. A vibrating tube densimeter was used to perform density measurements using two reference calibration fluids. The uncertainty is estimated to be better than ±0.2 kg · m?3 for the experimental density measurements. For each mixture and for 1-pentanol, the experimental densities were correlated using an explicit volume equation of six parameters and an 11-parameter equation of state (EoS). Excess molar volumes were determined for the (CO2 + 1-pentanol) system using 1-pentanol densities calculated from the 11-parameter EoS and CO2 densities calculated from a multiparameter reference EoS.  相似文献   

12.
The low-temperature heat capacity of NiAl2O4 and CoAl2O4 was measured between T = (4 and 400) K and thermodynamic functions were derived from the results. The measured heat-capacity curves show sharp anomalies peaking at around T = 7.5 K for NiAl2O4 and at T = 9 K for CoAl2O4. The exact cause of these anomalies is unknown. From our results, we suggest a standard entropy for NiAl2O4 at T = 298.15 K of (97.1 ± 0.2) J · mol?1 · K?1 and for CoAl2O4 of (100.3 ± 0.2) J · mol?1 · K?1.  相似文献   

13.
In this work, new experimental results for the (vapour + liquid) equilibrium (VLE) of CO2 in piperazine (PZ)-activated concentrated aqueous 2-amino-2-methyl-1-propanol (AMP) are presented for the temperature range of (303 to 328) K and PZ concentration range of (2 to 8) wt.%, keeping the total amine concentration in the solution at 40% and 50 wt.%. The partial pressures of CO2 are in the range of (0.2 to 1500) kPa. The electrolyte non-random two-liquid (ENRTL) theory has been used to develop the VLE model for the quaternary system (CO2 + AMP + PZ + H2O) to describe the equilibrium behaviour of the solution. The CO2 cyclic capacity of these solvents is determined between the rich and lean CO2 loadings. It is found that the CO2 cyclic capacity increases with the addition of PZ in aqueous AMP and also with the increase in AMP concentration in the aqueous solution. However, solid precipitation has been observed for 50 wt.% total amine concentration below T = 318 K for all relative compositions of AMP and PZ in the solvent at higher CO2 loading. The model results of equilibrium composition, pH of the loaded solution and amine volatility of the mixed solvent system, are also presented.  相似文献   

14.
《Fluid Phase Equilibria》2006,239(2):172-177
Phase behavior of β-d galactose pentaacetate–carbon dioxide binary system is investigated by dew-point and bubble-point measurements conducted in a high pressure variable volume sapphire cell. The phase envelope for solutions of β-d galactose pentaacetate in supercritical CO2 is obtained for β-d galactose pentaacetate concentrations between 2 and 26 wt%, and for the temperature range of 308–323 K. The system exhibits lower critical solution temperature (LCST) behavior and high solubility of β-d galactose pentaacetate is observed. The densities of the system are also measured, and liquid-like densities (near 1 g/cm3) are observed for single-phase solutions of β-d galactose pentaacetate in supercritical CO2 at concentrations of 18 wt% and higher. Viscosity is measured for solutions of 18 and 25 wt% β-d galactose pentaacetate in the single-phase region at 313 K and 17 MPa and the viscosity values, 0.095 and 0.103 cp, respectively, are similar in magnitude to the viscosity of pure carbon dioxide.  相似文献   

15.
The molar heat capacity of Zn2GeO4, a material which exhibits negative thermal expansion below ambient temperatures, has been measured in the temperature range 0.5⩽(T/K)⩽400. At T=298.15 K, the standard molar heat capacity is (131.86 ± 0.26) J · K−1 · mol−1. Thermodynamic functions have been generated from smoothed fits of the experimental results. The standard molar entropy at T=298.15 K is (145.12 ± 0.29) J · K−1 · mol−1. The existence of low-energy modes is supported by the excess heat capacity in Zn2GeO4 compared to the sums of the constituent binary oxides.  相似文献   

16.
Standard values of Gibbs free energy, entropy, and enthalpy of Na2Ti6O13 and Na2Ti3O7 were determined by evaluating emf-measurements of thermodynamically defined solid state electrochemical cells based on a Na–β″-alumina electrolyte. The central part of the anodic half cell consisted of Na2CO3, while two appropriate coexisting phases of the ternary system Na–Ti–O are used as cathodic materials. The cell was placed in an atmosphere containing CO2 and O2. By combining the results of emf-measurements in the temperature range of 573⩽T/K⩽1023 and of adiabatic calorimetric measurements of the heat capacities in the low-temperature region 15⩽T/K⩽300, the thermodynamic data were determined for a wide temperature range of 15⩽T/K⩽1100. The standard molar enthalpy of formation and standard molar entropy at T=298.15 K as determined by emf-measurements are ΔfHm0=(−6277.9±6.5) kJ · mol−1 and Sm0=(404.6±5.3) J · mol−1 · K−1 for Na2Ti6O13 and ΔfHm0=(−3459.2±3.8) kJ · mol−1 and Sm0=(227.8±3.7) J · mol−1 · K−1 for Na2Ti3O7. The standard molar entropy at T=298.15 K obtained from low-temperature calorimetry is Sm0=399.7 J · mol−1 · K−1 and Sm0=229.4 J · mol−1 · K−1 for Na2Ti6O13 and Na2Ti3O7, respectively. The phase widths with respect to Na2O content were studied by using a Na2O-titration technique.  相似文献   

17.
The heat capacity of a 13 nm hematite (α-Fe2O3) sample was measured from T = (1.5 to 350) K using a combination of semi-adiabatic and adiabatic calorimetry. The heat capacity was higher than that of the bulk which can be attributed to the presence of water on the surface of the nanoparticles. No anomaly was observed in the heat capacity due to the Morin transition and theoretical fits of the heat capacity below T = 15 K show a small T3 dependence (due to lattice contributions) with no T3/2 dependence. This suggests that there are no magnetic spin-wave contributions to the heat capacity of 13 nm hematite. The use of a large linear term to fit the heat capacity below T = 15 K is most likely due to superparamagnetic contributions. A small anomaly within the temperature range (4 to 8) K was attributed to the presence of uncompensated surface spins.  相似文献   

18.
A flow mixing calorimeter followed by a vibrating-tube densimeter has been used to measure excess molar enthalpies HmE and excess molar volumesVmE of {xC3H8 +  (1   x)SF6}. Measurements over a range of mole fractionsx have been made at the pressure p =  4.30 MPa at eight temperatures in the rangeT =  314.56 K to 373.91 K, in the liquid region at p =  3.75 MPa andT =  314.56 K, in the two phase region at p =  3.91 MPa andT =  328.18 K, and in the supercritical region at p =  5.0 MPa andT =  373.95 K. The measurements are compared with results from the Patel–Teja equation of state which reproduces the main features of the excess function curves as well as it does for similar measurements on{xCO2 +  (1   x)C2H6} ,{xCO2 +  (1   x)C2H4} and{xCO2 +  (1   x)SF6} reported previously.  相似文献   

19.
The Knudsen mass-loss effusion technique was used to measure the vapour pressures at different temperatures of the following compounds: 3-phenylpropionic acid, between T =  305.17 K and T =  315.17 K; 3-(2-methoxyphenyl)propionic acid, between T =  331.16 K and T =  347.16 K; 3-(4-methoxyphenyl)propionic acid, between T =  341.19 K and T =  357.15 K; 3-(3,4-dimethoxyphenyl)propionic acid, between T =  352.18 K and T =  366.16 K. From the temperature dependence of the vapour pressure, the standard molar enthalpies of sublimation ΔcrgHmowere derived by the Clausius–Clapeyron equation and the molar entropies of sublimation at equilibrium pressures were calculated. On the basis of estimated values for the heat capacity differences between the gas and the crystal phases of the studied compounds the standard, p   =  105Pa, molar enthalpies, entropies and Gibbs energies of sublimation at T =  298.15 K, were derived:  相似文献   

20.
The forming of surface species during the adsorption of carbon monoxide (CO) and CO/O2 on a CeO2/Co3O4 catalyst was investigated by in situ Fourier transform infrared (FT-IR) spectroscopy and temperature programmed desorption-mass spectroscopy (TPD-MS). When CO was adsorbed on the CeO2/Co3O4 catalyst, two types of surface species were distinguishable at room temperature: carbonate and bicarbonate. Surface carbonate was adsorbed on the cerium and cobalt, while the surface bicarbonate absorbed on the CeO2/Co3O4 catalyst at 1611, 1391, 1216 and 830 cm−1. Furthermore, the TPD-MS profiles revealed that the CeO2/Co3O4 catalyst showed a greater amount of CO2 than CO at 373 K. The CO desorption from the CeO2/Co3O4 catalyst with increasing temperature showed that the order of thermal stability was surface bicarbonate < surface carbonate < interface carbonate species. Interestingly, the residual carbonate species could remain on the interface up to 473 K. The results revealed that surface bicarbonate could promote the conversion of CO into CO2 for CO oxidation below 50 K.  相似文献   

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