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1.
The International Measurement Evaluation Programme (IMEP) is an interlaboratory comparison scheme, founded, owned and coordinated by the Institute for Reference Materials and Measurements (IRMM) since 1988. IMEP-9 is the third round of trace elements in water evaluation following IMEP-3 and IMEP-6. Reference values for 15 elements stating total concentrations and combined uncertainties (according to GUM) were established. The reference values were established mainly by isotope dilution mass spectrometry (IDMS) as a primary method of measurement, and values traceable to the SI were obtained. The four elements that could not be certified by IDMS were assigned values by means of other measurement techniques. Results from 201 laboratories from 35 countries and four continents were evaluated against the reference values and the comparability between the laboratories is presented graphically. 相似文献
2.
Diana Paola Vargas Liliana Giraldo Joaquín Silvestre-Albero Juan Carlos Moreno-Piraján 《Adsorption》2011,17(3):497-504
A series of activated carbon monoliths have been prepared by chemical activation of two lignocellulosic precursors, coconut
shell (CACM) and African palm stones (PACM). The incorporation of a conforming step between the impregnation with H3PO4 and the activation step allows the successful development of disc-shape monoliths without the use of a binder. Textural characterization
results using N2 adsorption at 77 K show that the effect of the activating agent highly depends on the nature of the carbon precursor used.
While chemical activation with phosphoric acid has mainly no effect when using coconut shell, a large development of both
micro- and mesoporosity is observed for African palm stones. Large concentrations of the activating agent produce the partial
shrinkage of the narrow microporous structure independently of the precursor used. Concerning the adsorption of CO2 at atmospheric pressure and 273 K, both series of activated carbon monoliths exhibit an improved adsorption behaviour with
the activation degree up to an optimum value around ∼164 mg CO2/g, for sample CACM-32, and ∼162 mg CO2/g, for sample PACM-28, the amount adsorbed decreasing thereafter. Apparently, the total amount of CO2 adsorbed under these experimental conditions is defined by the volume of narrow micropores (V
n
). 相似文献
3.
Jhulimar M. Celedonio Jong Hyun Park Young Soo Ko 《Research on Chemical Intermediates》2016,42(1):141-154
The stability of amine-functionalized silica sorbents prepared through the incipient wetness technique with primary, secondary, and tertiary amino organosilanes was investigated. The prepared sorbents were exposed to different gaseous streams including CO2/N2, dry CO2/air with varying concentration, and humid CO2/air mixtures to demonstrate the effect of the gas conditions on the CO2 adsorption capacity and the stability of the different amine structures. The primary and secondary amine-functionalized adsorbents exhibited CO2 sorption capacity, while tertiary amine adsorbent hardly adsorbed any CO2. The secondary amine adsorbent showed better stability than the primary amine sorbent in all the gas conditions, especially dry conditions. Deactivation species were evaluated using FT-IR spectra, and the presence of urea was confirmed to be the main deactivation product of the primary amine adsorbent under dry condition. Furthermore, it was found that the CO2 concentration can affect the CO2 sorption capacity as well as the extent of degradation of sorbents. 相似文献
4.
5.
Yanlou Wang Tiantian Meng Dongdong Jia Yongyue Sun Naixuan Li 《Journal of solution chemistry》2017,46(1):70-88
Solubilities of two calcium channel blockers, nifedipine and lacidipine, were measured in supercritical carbon dioxide at T = (313, 323, and 333) K over the pressure range (12.0–36.0) MPa using a dynamic-analytical apparatus. The solubility values obtained are in the range of (0.18–7.05) × 10?5 mol·mol?1. The solubilities of the two solids show similar trends with a crossover region of the respective isotherms in the range 18.0–21.0 MPa. The experimental solubility data were correlated with several different models. The semi-empirical density-based models provided satisfactory correlation results with AARD values lower than 10%. According to the results of the Méndez-Santiago and Teja models, the measured solid solubility data are quite consistent at all experimental conditions, which indicates the reliability of the data. The compressed gas model of the Peng–Robinson equation of state, combined with the two parameter van der Waals mixing rule (PR-EoS-VDW2) model, gives better correlation results than the PR-EoS-VDW1 model. The expanded liquid model based on Scatchard–Hildebrand regular solution theory can be used for solubility prediction, but the correlation results for nifedipine and lacidipine by the model are inferior to the compressed gas models in this work. 相似文献
6.
Experimental results on the interaction of Cr atoms with various oxygen-containing molecules (NO, N2O, CO2, NO2, and SO2) at high temperatures (>1000 K) are presented. It is demonstrated that activation barrier for spin-forbidden reactions is
higher, all other things being equal. For the reaction of Cr atoms with N2O, an interpolated temperature dependence of the rate constant, based on the high-temperature measurements conducted in the
present work and the published low-temperature data, is proposed. 相似文献
7.
Zhong-Suo Liu Qi Wang Zong-Shu Zou Guang-Lei Tan 《Journal of Thermal Analysis and Calorimetry》2011,104(3):1091-1096
Experiments of carbon (graphite) gasification in CO2 have been carried out by thermal analysis techniques (TG-DTG-DSC) under non-isothermal conditions. The results indicate that
the entire carbon gasification process can be divided into an exothermic slow gasification stage during the initial period
and an endothermic fast gasification later. The analyses of energy conservation and non-isothermal kinetics arrive at the
following conclusions; (1) The exotherm of the initial stage is caused by the combined effect of the exothermic chemisorption
and the endothermic chemical reaction. The gasification reaction may be expressed by the series of chemisorption and chemical
reaction and the overall process is controlled by interface reaction via chemisorption. (2) The endothermic effect of fast
gasification stage is almost equal to the reaction heat of carbon gasification, which implies that the chemisorption step
disappears. The gasification process can be expressed by a simple interface reaction. 相似文献
8.
Yu. V. Kokunov Yu. E. Gorbunova V. V. Kovalev 《Russian Journal of Inorganic Chemistry》2008,53(12):1885-1892
Coordination polymers [AgCF3CO2(2,3-Et2Pyz)](I)(2,3-Et2Pyz-C8H12N2) and [AgCF3CO2(Bpeta)] (II) (Bpeta is 4′4-bipyridylethane, C12H12N2) are synthesized. Their structures are determined. The crystals of compound I are monoclinic, space group P2(1)/n, a = 7.185(1), b = 14.754(1), c = 12.317(1)Å, β = 97.09(1)°, V = 1295.7(2) Å3, ρcalcd = 1.831 g/cm3, Z = 4. Structure I consists of infinite chains of doubled polymeric chains joined by silver carboxylate dimers [[Ag2(CF3CO2)2(Et2Pyz)2]∞. The coordination polyhedron of Ag+ is a distorted tetrahedron. The crystals of compound II are orthorhombic, space group Pbca, a = 13.555(3), b = 13.991(3), c = 16.449(3) Å, V = 3119.5(11) Å3, ρcalcd = 1.725 g/cm3, Z = 8. Doubled polymeric chains with the Ag…Ag bond (3.16 Å) are also formed in structure II. Supramolecular layers are formed in the structure due to the weak π-π-stacking interaction between the aromatic groups of chains. The CF3CO 2 ? anion is weakly bound to Ag+ (Ag-Oavg 2.790 Å). 相似文献
9.
Andres Trikkel Merli Keelmann Tiit Kaljuvee Rein Kuusik 《Journal of Thermal Analysis and Calorimetry》2010,99(3):763-769
In the present research, CO2 and SO2 binding ability of different oil shale ashes and the effect of pre-treatment (grinding, preceding calcination) of these ashes
on their binding properties and kinetics was studied using thermogravimetric, SEM, X-ray, and energy dispersive X-ray analysis
methods. It was shown that at 700 °C, 0.03–0.28 mmol of CO2 or 0.16–0.47 mmol of SO2 was bound by 100 mg of ash in 30 min. Pre-treatment conditions influenced remarkably binding parameters. Grinding decreased
CO2 binding capacities, but enhanced SO2 binding in the case of fluidized bed ashes. Grinding of pulverized firing ashes increased binding parameters with both gases.
Calcination at higher temperatures decreased binding parameters of both types of ashes with both gases studied. Clarification
of this phenomenon was given. Kinetic analysis of the binding process was carried out, mechanism of the reactions and respective
kinetic constants were determined. It was shown that the binding process with both gases was controlled by diffusion. Activation
energies in the temperature interval of 500–700 °C for CO2 binding with circulating fluidized bed combustion ashes were in the range of 48–82 kJ mol−1, for SO2 binding 43–107 kJ mol−1. The effect of pre-treatment on the kinetic parameters was estimated. 相似文献
10.
This study presents using zeolitic imidazolate framework-8 (ZIF-8) as porous filler dispersed phase and polyurethane (PU) as continuous phase to synthesis mixed matrix membranes (MMMs). ZIF-8 nanoparticles were synthesized using centrifugal method. The synthesized nanoparticles were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and thermal gravimetric analysis (TGA). In order to investigate the effect of ZIF-8 loading on the membrane performance in CO2/CH4 separation, different membranes were prepared with various amounts of ZIF-8 (0–50 wt%). Membranes properties were characterized by SEM, XRD, TGA, differential scanning calorimetry (DSC), and tensile analysis. SEM images exhibit that the ZIF-8 is dispersed uniformly in cross section of membrane. Thermal stability of membranes increases with addition of the ZIF-8 nanoparticles into the polymer matrix. Both tensile strength and strain at break in the MMMs increase with the ZIF-8 loading. To study the effect of feed pressure on CO2 and CH4 transport properties of the membranes, single gas experiments were conducted at 4, 8, and 12 bar feed pressures. Incorporation of ZIF-8 crystals into continuous PU matrix resulted in high-performance gas separation membranes. Increasing feed pressure, significantly, increased separation performances in all the membranes. 相似文献
11.
V. S. Savenko 《Russian Journal of Inorganic Chemistry》2007,52(3):465-467
Be2(OH)2CO3 solubilities at 25°C in 0.7 M NaClO4 solutions containing variable NaHCO3 and Na2CO3 concentrations has been experimentally determined. The solubilities increase with increasing carbonate alkalinity. The results of the experiments do not contradict the suggestion that the mixed hydroxocarbonate complex Be2(OH)2CO 3 2? is the major beryllium solute species. At fluoride concentrations higher than 250 μmol/L, the Be2(OH)2CO3 solubilities noticeably increase as a result of the formation of beryllium fluoride complexes. 相似文献
12.
V. A. Neves M. V. Costa J. D. Senra L. C. S. Aguiar L. F. B. Malta 《Journal of Thermal Analysis and Calorimetry》2017,130(2):689-694
Cu/Al layered double hydroxide (LDH) can be used as a catalyst for important processes such as cross-coupling reactions. This property may be improved by adding palladium by either impregnation or intercalation. Therefore, the LDH matrix and its composites with Pd0 or [PdCl4]2? have been prepared. By powder X-ray diffraction, FT-infrared spectroscopy, thermogravimetric and elemental analysis it was determined the LDH formula Cu4Al2(OH)12CO3.4H2O, with malachite as the second phase. The LDH thermal decomposition occurs between 120 and 600 °C, having as intermediates the double oxi-hydroxide and the mixed oxide phases. At 800 °C the residue is composed of CuO and CuAl2O4. The composites were obtained employing [PdCl4]2? and Pd2(dba)3 as precursors, and the solvent choice for this process was shown to be of significant importance: the materials obtained using DMF had Pd impregnated in the surface, while the usage of water promoted the intercalation of [PdCl4]2? in the LDH matrix. The thermogravimetric analysis was able to distinguish the mode of supporting palladium between the composites being a reliable characterization for such task. 相似文献
13.
Zh. A. Kochkarov M. V. Khubaeva Z. L. Khakulov 《Russian Journal of Inorganic Chemistry》2011,56(5):783-786
This is the first study of the NaBO2-Na2CO3-Na2MoO4-Na2WO4 quaternary system by differential thermal analysis. Na2[MoO4(x)WO4(1 − x)] solid solutions in the quaternary system are found to not decompose. 相似文献
14.
At present, carbon dioxide is considered the largest contributor among greenhouse gases. This review covers the current state
of problem of carbon dioxide emissions from industrial and combustion processes, the principle of photocatalysis, existing
literature related to photocatalytic CO2 reduction over TiO2 based catalysts and the effects of important parameters on the process performance including light wavelength and intensity,
type of reductant, metal-modified surface, temperature and pressure.
Presented at the 34th International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 21–25 May
2007. 相似文献
15.
The phase diagrams of the ternary reciprocal systems Na,K||BO2,CO3 and Na,K||BO2,Cl were studied for the first time by a calculation-experimental method and by differential thermal analysis. Analytical models of phase equilibrium states were derived, and the coordinates of eutectics were found to be (680°C, 32 mol % NaBO2, 68 mol % KCl) and (648°C, 9 mol % NaBO2, 45.5 mol % NaCl, 45.5 mol % KCl). Binary solid solutions based on metaborates and carbonates of sodium and potassium were shown to be stable. The possibility of synthesizing tungsten oxide bronzes in a eutectic melt in the ternary system NaBO2–NaCl–КCl was revealed. 相似文献
16.
Adsorption of CO2, N2, CH4 and H2 on triamine-grafted pore-expanded MCM-41 mesoporous silica (TRI-PE-MCM-41) was investigated at room temperature in a wide
range of pressure (up to 25 bar) using gravimetric measurements. The material was found to exhibit high affinity toward CO2 in comparison to the other species over the whole range of pressure. Column-breakthrough dynamic measurements of CO2-containing mixtures showed very high selectivity toward CO2 over N2, CH4 and H2 at CO2 concentrations within the range of 5 to 50%. These conditions are suitable for effective removal of CO2 at room temperature from syngas, flue gas and biogas using temperature swing (TS) or temperature-pressure swing (TPS) regeneration
mode. Moreover, TRI-PE-MCM-41 was found to be highly stable over hundreds of adsorption-desorption cycles using TPS as regeneration
mode. 相似文献
17.
Matthias Weil Franz Werner Frank Kubel 《Monatshefte für Chemie / Chemical Monthly》2002,133(3):267-275
Summary. Single crystals of MgAl2F8(H2O)2 have been obtained under hydrothermal conditions (250°C, 14 d) from a starting mixture of AlF3 and MgAlF5(H2O)2 in a 5% (w/w) HF solution. The crystal structure has been determined and refined from single crystal data (Fmmm (#69), Z = 4, a = 7.2691(7), b = 7.0954(16), c = 12.452(2) ?, 281 structure factors, 27 parameters, R(F
2 > 2σ (F
2)) = 0.0282, wR(F
2 all) = 0.0885). The obtained crystals were systematically twinned according to (010/100/001) as twinning matrix, reflecting
the pseudo-tetragonal metric. The crystal structure is composed of perowskite-type layers built of corner sharing AlF6 octahedra with an overall composition of AlF4
− which are connected via common fluorine atoms of [MgF4/2(H2O)2/1] octahedra. Group-subgroup relations of MgAl2F8(H2O)2 to WO3(H2O)0.33 and to other M(II)M(III)2 F8(H2O)2 structures are briefly discussed. Above 570°C, MgAl2F8(H2O)2 decomposes under elimination of water into α-AlF3, β-AlF3, and MgF2.
Received October 29, 2001. Accepted (revised) December 6, 2001 相似文献
18.
Five-component reciprocal systems Na,K∥Cl,CO3,MoO4,WO4 and Na,K∥F,CO3,MO4,WO4 have been studied by differential thermal analysis (DTA) and X-ray powder diffraction (XPD). The systems have been triangulated to phase simplexes. The main reciprocal and complex-formation reactions have been revealed. The stability of [Na,K]2CO3, Na2[Mo,W]O4, and K2[Mo,W]O4 binary solid solutions and the nonexistence of quintuple invariant points in the title systems have been verified. 相似文献
19.
U. Örnemark L. Van Nevel P. D. P. Taylor P. Robouch P. De Bièvre A. Uldall M. Loikkanen M. M. Müller J.-C. Libeer H. Steensland K. Hellsing A. Squirrell L. A. Penberthy D. Schiel T. Tamberg T. Walczyk J. W. H. Lam 《Accreditation and quality assurance》1999,4(11):463-472
In the seventh round of the Institute for Reference Materials and Measurements' International Measurement Evaluation Programme,
277 clinical laboratories from 17 countries participated. The measurands consisted of inorganic components, present at minor
and trace level, in a human liquid serum. Results for calcium, chloride, copper, magnesium, sodium, selenium and zinc are
reported and are compared to reference values established mainly by isotope dilution mass spectrometry and neutron-activation
analysis. The overall conclusion is that routine measurements of total concentrations of the components by clinical laboratories
are of high quality. The fraction of significant errors is small (0.5%) and the self-declared uncertainty values are generally
fairly realistic. Results are further commented on with respect to the recent development in metrology in chemistry.
Received: 5 March 1999 / Accepted: 24 July 1999 相似文献
20.
As a base-promoted Kolbe–Schmitt carboxylation reaction, the mechanism of synthesis of salicylic acid derivatives from phenols with CO2 in the industry is still unclear, even up to now. In this paper, synthesis of 3,6-dichloro salicylic acid (3,6-DCSA) from 2,5-dichloro phenoxide and CO2 was investigated in the presence of K2CO3. We show the reaction can proceed by itself, but it goes at a slower rate as well as a lower yield, compared to the case with the addition of K2CO3. However, the yield of 3,6-DCSA is only minorly affected by the size of K2CO3, which cannot be explained from the view of catalytic effect. Therefore, K2CO3 may on one hand act as a catalyst for the activation of CO2 so that the reaction can be accelerated, while on the other hand, it also acts as a co-reactant in deprotonating the phenol formed by the side reaction to phenoxide, which is further converted to salicylate. 相似文献