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1.
采用两体作用势模型和遗传算法对簇合物(p-H2)N-HCCCN的极小能量结构和能量进行了理论研究.结果表明,20个para-H2分子形成HCCCN周围的第一个溶剂层,第一个溶剂层包含三个溶剂环,每个溶剂环都有6个para-H2分子,第19和20个para-H2分子分别聚集在HCCCN分子的N、H原子末端.进一步计算了(p-H2)N-HCCCN的化学势,发现化学势随para-H2分子个数的增加呈震荡变化. 相似文献
2.
The distribution ratio ( DM) of Pd(II) by the extraction with 2-methyl-8-quinolinol (HMQ) was determined using the supercritical carbon dioxide medium (SF-CO 2) and organic solvent media such as perfluoro-methylcyclohexane, heptane, cyclohexane, carbon tetrachloride and benzene. From experimental results of the slopes of log DM versus pH plot and log DM versus HMQ concentration plot, the extracted species both in the SF-CO 2 extraction (SFE) and the solvent extraction (SE) were determined to be Pd(MQ) 2. The distribution constant of HMQ ( KD,HMQ) in the SFE and SE systems were determined from the dependence of the distribution ratio of HMQ ( DHMQ) on the pH. A linear relationship was observed between log KD,HMQ and the solubility parameter ( δ) of the extraction medium based on the regular solution theory in both the SFE using SF-CO 2 at the pressure of 8.5–40 MPa and the SE systems. The difference in the slope of the log KD,HMQ versus δ plot between the SFE and the SE systems is attributable to the extent of the specific interaction of the solute HMQ with the solvent molecules, i.e. CO 2 molecules and the organic solvent molecules. The DM versus δ plot obtained under a given extraction condition using SF-CO 2 (11–40 MPa) and organic solvents showed clear linearity. The DM obtained using SF-CO 2 at relatively low pressure range from 8.5 to 11 MPa was independent of the pressure and the δ of SF-CO 2, which coincides with the experimental fact that the solubility of Pd(MQ) 2 in the SF-CO 2 at 8.5–11 MPa was practically constant. 相似文献
3.
In this study we investigate two alternative pathways to compute the free energy and the entropy of small molecule association (Δ Fassoc and Δ Sassoc) in water. The first route (direct pathway) uses thermodynamic integration as function of the distance R between the solutes. The mean force and the mean covariance of the force with the energy in solution are calculated from molecular dynamics simulation followed by integration of these quantities with respect to the reaction coordinate R. The alternative approach examined (solvation pathway) would first remove the solutes from the solution using thermodynamic integration as function of a solvation coupling parameter λ, change the solute–solute distance in vacuo and then solvate back the solute pair at the new separation distance. The system studied was a pair of CH 4 molecules in water. We investigate the influence of the CH 4–water interaction strength on the obtained Δ Fassoc and Δ Sassoc values by changing van der Waals and Coulomb interaction and evaluated the accuracy and efficiency for the two pathways. We find that the direct route seems more suitable for the calculation of free energies of hydrophobic solutes while the solvation pathway performs better when calculating entropy changes for solutes that have a stronger interaction with the solvent. 相似文献
4.
Counter-current chromatography (CCC) is a form of liquid–liquid partition chromatography. It requires two immiscible solvent phases; the stationary phase is retained in the separation column, generally by centrifugal force, while the mobile phase is eluted. We recently replaced the mobile phase with supercritical fluid carbon dioxide (SF CO 2). Since the solvent strength of SF CO 2 can be varied by changing the temperature and pressure of the system, separation adjustments are thus more versatile. We investigated the pressure and temperature effects on resolution using water and low-carbon alcohol mixtures as the stationary phases. It was demonstrated that these special properties of SF CO 2 were indeed beneficial to the optimization of separations. In addition, the phase retention ratio was examined in terms of separation resolution. The results appeared very similar to those obtained from conventional traditional CCC. This study should be helpful for the future development of SF applications in CCC. 相似文献
5.
测定了CO2在复合溶液N-甲基二乙醇胺(MDEA)+2-氨基-2-甲基-1-丙醇(AMP)中的溶解度,研究了气相CO2浓度、温度和复合溶液的组分对溶解度的影响。实验获得了温度分别为25℃、30℃和40℃时,CO2在复合溶液MDEA-AMP中的溶解度。实验表明,溶解度随气相中CO2浓度升高或随AMP在复合溶液中的摩尔分数升高而升高,随温度升高而降低。 相似文献
6.
The solubility of CH 4 and CO 2 in cellulose 2.4-acetate membranes was measured at temperatures between —10° and 30°C, and at pressures of up to 40 atm. Pre-exposure of the membrane samples to high-pressure CO 2 caused an increase in the solubility of CH 4, as well as of CO 2 [2]. In contrast, pre-exposure of the samples to high-pressure CH 4 did not alter the solubility of either CH 4 or CO 2. A similar “conditioning effect” by high-pressure CO 2 was also observed with other glassy polymers by Paul et al. [9-11], who reasonably attributed it to the non-equilibrium nature of the glassy state. The solubility isotherms for CH 4 and CO 2 in cellulose 2.4-acetate can be fitted to the “dual-mode” sorption model [1], but a consideration of the heats of solution suggests that a “two Langmuir sites” model [16] may offer a more satisfactory representation of the data. The cellulose acetate samples employed in this study were prepared by drying reverse osmosis membranes and are believed to have contained a large amount of free volume. 相似文献
7.
Two types of poly(phenylene oxide) (PPO) membranes were prepared: one by chemical modification through sulfonation using chlorosulfonic acid and another by physical incorporation with a heteropolyacid (HPA), viz., phosphotungstic acid. These membranes were tested for the separation of CO 2/CH 4 mixtures. Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction techniques were used to confirm the modified structure of PPO as well as to understand its interactions with gaseous molecules. Scanning electron microscopy (SEM) was used to investigate the membrane morphology. Thermal stability of the modified polymers was assessed by differential scanning calorimetry (DSC), while the tensile strength was measured to evaluate their mechanical stability. Both chemical and physical modifications did not adversely affect the thermally and mechanical stabilities. Experiments with pure CO 2 and CH 4 gases showed that CO 2 selectivity (27.2) for SPPO increased by a factor of 2.2, while the PPO–HPA membrane exhibited 1.7 times increase in selectivity with a reasonable permeability of 28.2 Barrer. An increase in flux was observed for the binary CO 2/CH 4 mixture permeation with an increasing feed concentration (5–40 mol%) of CO 2. An enhancement in feed pressure from 5 to 40 kg/cm 2 resulted in reduced CO 2 permeability and selectivity due to the competitive sorption of methane. Both the modified PPO membranes were found to be promising for enrichment of methane despite exhibiting lower permeability values than the pristine PPO membrane. 相似文献
8.
为了准确分析高浓度SF 6中痕量的CO及CO 2,发展了可靠的气相色谱-火焰离子化检测器(GC-FID)方法。通过双Porapak Q色谱柱结合阀切换将SF 6从待测样品中分离并排出检测系统,从而避免SF 6可能造成的在线转化柱中毒现象,同时实现CO和CO 2的完全分离;通过在线镍催化将CO和CO 2的检测转化为对CH 4的检测,极大地提高检测灵敏度。结果显示,该方法对CO和CO 2的检测互不干扰,两者都可在2~500 μL/L范围内呈现良好的线性相应,测定重复性好(RSD小于2%),准确度高。建立的GC-FID方法可直接用于SF 6高压断路器中痕量CO及CO 2的检测,为SF 6相关电气设备潜伏性故障诊断提供了研究手段。 相似文献
10.
Recasens, P., Velo, E., Larrayoz, M.A. and Puiggené, J., 1993. Endothermic character of toluene adsorption from supercritical carbon dioxide on activated carbon at low coverage. Fluid Phase Equilibria, 90: 265-287. Heat effects and volumetric properties are analyzed for the adsorption of toluene from supercritical carbon dioxide onto activated carbon at the limit of zero coverage, based on existing data for the system. Using values of the adsorption equilibrium constant at different temperatures as a function of fluid density, large, negative partial molar volumes for toluene in the fluid were obtained, which were previously unavailable. Numerical integration of the differential equation that expresses the isobaric temperature dependence of the equilibrium constant, coupled with parameter optimization, enabled us to estimate the differential enthalpy of toluene adsorption onto the surface from the ideal gas at the same pressure and temperature, in addition to the enthalpy of transfer from the fluid to the surface. This is found to be large and positive near the critical conditions. Using the thermodynamic analysis of Kelley and Chimowitz, our results show that in terms of the enthalpy of transfer, the isothermal adsorption from a supercritical fluid is an endothermic process, thus explaining the retrograde behavior experimentally observed for the regeneration of carbon with supercritical CO2 at conditions not far from the solvent's critical point. 相似文献
11.
Since flow injection (FI) is a dilution technique, efforts have been undertaken to minimize online dilution or dispersion. Solutes in supercritical fluids exhibit increased diffusion coefficients which have been shown to decrease dispersion of the sample zone. This work investigates the use of supercritical fluids (or CO 2 modified fluids) as carrier streams for FI. Both a non-reacting tracer and an online chemical reaction were employed to investigate the behavior of solutes in supercritical and near critical systems. Further, these results are compared to those obtained in the system studied with a conventional carrier stream. Plots of peak response vs% CO 2 modifier increase with a sharp break at moderate modifier composition (20–30%). Plots of peak variance vs% CO 2 modifier show decreased variance with increasing % modifier. The system was also optimized with regards to temperature and pressure. The optimized system displayed improved limits of detection and decreased variance relative to 0% CO 2 modifier carrier streams. 相似文献
12.
Solvation of both tautomeric forms of 2-oxopyrimidine by carbon tetrachloride has been investigated using the Monte Carlo method for a cluster consisting of 50 molecules at T=300 K. The results indicate that, in oposition to hydration, this solvation shifts the tautomeric equilibrium a little towards the lactim form, in agreement with experiment. The structure of the solvation shell in both tautomers closely resembles that of the pure solvent. Local minima of the interaction energy between n = 1, 2, 3, 4, 6 and 8 CCl 4 molecules and 2-oxopyrimidine have been examined. The results shed some light on the nature of the poor solubility of purines and pyrimidines in carbon tetrachloride. 相似文献
13.
选用非质子型有机溶剂聚乙二醇二甲醚(NHD)与 N, N-二甲基乙酰胺(DMAC), 分别与BmimFeCl 4复配, 构建了BmimFeCl 4/NHD和BmimFeCl 4/DMAC复合铁基离子液体体系. 考察了温度、 BmimFeCl 4/溶剂的质量 比以及压力对CO 2在复合铁基离子液体体系中溶解行为的影响. 结果表明, 高压低温的吸收条件更利于CO 2 的溶解, 当BmimFeCl 4/DMAC质量比为7∶3时, CO 2在BmimFeCl 4/DMAC复合体系中的亨利系数为0.9181 MPa·L·mol -1, 低于同等条件下BmimFeCl 4/NHD体系的亨利系数. 在常压、 363.2 K条件下进行再生, 经5次循环后, CO 2在BmimFeCl 4/NHD和BmimFeCl 4/DMAC中的溶解度分别为初次吸收量的92.53%和99.04%. 傅里叶变换红外光谱(FTIR)结果表明, 铁基离子液体复配体系吸收CO 2为物理吸收过程. 密度泛函理论(DFT)计算与IRI分析的结果表明, 在复配DMAC的体系中, CO 2更倾向与阳离子和溶剂分子作用, 而在复配NHD的体系中, CO 2则更容易与阴离子和溶剂分子作用. 相似文献
14.
Capacity ratios k have been determined for phenyl myristate, phenyl palmitate and phenyl stearate from supercritical fluid chromatography (SFC) at 35 to 56°C and 85 to 190 bar using supercritical CO 2 as mobile phase and Perisorb A and Perisorb RP8 as stationary phases. For the esters used a rise in pressure from 90 to 190 bar produces a drop of k by about two orders of magnitude giving evidence of the rapidly increasing solvent power of supercritical CO 2 with increasing density. At a constant CO 2 density, k decreases with increasing temperature. The separation of the esters was found to be the better the lower the pressure was. An apparatus for the chromatographic determination of binary diffusion coefficients in supercritical gases is described. D12 values for some organic compounds in carbon dioxide at 40°C and in the pressure range from 80 to 160 bar are presented. With an improved electronic flow regulator an overall precision of the D12 values of ±3% is obtained. 相似文献
15.
New measurements have been made of rate constants for the vibrational deactivation of N 2(ν = 1) by CH 4 in liquid Ar/liquid N 2 mixtures. The ratio of the liquid phase rate constants, kL,M for the liquid mixture over kL,Ar for liquid argon solution, varies non-linearly with composition. The results imply a saturation effect which occurs when one solvent N 2 molecule is present in the first solvation shell of the excited molecule. It is proposed that this is due to the formation of a N 2(ν = 1) … N 2 collision complex. 相似文献
16.
The mechanism of CO 2-exchange between the atmosphere and sea-water was re-examined by simultaneously measuring pH and pO 2 in artificial sea-water exposed to CO 2 and air atmospheres. The data were fitted to an exchange model by using both the differential and integral forms of the diffusion equation. It was found that the pH and pO 2 data support the assumption that the exchange for these gases is driven by the gradient of the partial pressure of the gas across the imaginary solution-gas boundary layer (the z layer) and is not affected by chemical reaction or hydration rate under the experimental conditions used, viz. 1–100 meq/ l., alkalinity, pH 4.5–8.3 and z-layer thickness 2–500 μm. It is concluded that the rate of hydration of CO 2 plays an insignificant role in the exchange mechanisms between the atmosphere and the oceans. 相似文献
17.
Isothermal pressure (p)-mass fraction (w) phase diagrams were measured for CO 2 + tetradecanoic acid at six temperatures from 328.2 K to 373.2 K and for CO 2 + docosane at four temperatures from 343.2 K to 393.2 K as well as isobaric temperature (T)-mass fraction (w) phase diagrams for both systems at 34.5 MPa. In addition the isothermal and isobaric Gibbs phase prisms at 373.2 K and 34.5 MPa respectively were determined for the ternary system CO 2 + tetradecanoic acid + docosane, and and isobaric miscibility window was found between 333 K and 385 K at 34.5 MPa. 相似文献
18.
A novel channel-wall engineering strategy of the porous materials cationic covalent organic frameworks(COFs)is established based on rapid microwave-assisted anion exchange reaction and utilized to prepare a set of new COFs.Due to the interaction between the carbon dioxide(C02)and the acetate anion,the resulting SJTU-COF-AcO shows greatly enhanced carbon dioxide capacity up to 1.7 times of the pristine COF.The effect of the counteranions to CO2 capacity in the cationic COFs is investigated for the first time,which demonstrates that our channel-wall engineering strategy is a promising way to tailor the property of COFs for high CO2 capacity. 相似文献
19.
页岩气革命为低碳经济发展提供了重要契机.在低碳烷烃(甲烷和乙烷)催化转化过程中,以二氧化碳作为氧化剂参与反应,通过C-H键的选择性活化可将页岩气转化为优质化工原料——合成气和乙烯,是一种低碳烷烃转化与二氧化碳资源化利用的工艺路线.本文总结了近年来甲烷干重整与乙烷和二氧化碳反应中与C-H键活化相关的研究进展,分析了甲烷干... 相似文献
20.
采用柠檬酸法制备了钙钛矿镍酸镧,并将其作为催化剂的前躯体用于二氧化碳甲烷化反应中。催化剂在400℃~700℃温度下反应气中进行活化处理。活化过程中生成了金属镍颗粒和碳酸氧化镧。金属镍呈高度分散状并被碳酸氧化镧包裹,这种现象有助于反应在400℃和500℃的高温下仍保持高活性和稳定性。XRD、XPS、TEM和H 2-TPD等表征测试表明,在活化过程中生成的碳酸氧化镧对反应起到了至关重要的作用。 相似文献
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