分子动力学方法模拟不同温度下铀酰在叶腊石上的吸附和扩散行为

采用分子动力学方法研究了铀酰在叶腊石表面的吸附和扩散。在碳酸根离子存在的情况下,探究了温度对铀酰吸附和扩散的影响。碳酸根离子与铀酰存在较强的作用力,不同数目的碳酸根离子与铀酰结合会形成多种铀酰种态。在不同温度的模拟中,得到了UO_2~(2+)、UO_2CO_3、UO_2(CO_3)_2~(2-)、UO_2(CO_3)_3~(4-)四种铀酰种态和铀酰聚合物。通过原子密度图,观察了粒子在溶液中的分布情况。发现UO_2~(2+)+和UO_2CO_3容易吸附在叶腊石上,而UO_2(CO_3)_2~(2-)和UO_2(CO_3)_3~(4-)主要存在于扩散层中。随着时间的推移,越来越多的碳酸根离子与铀酰配位,使得铀酰在叶腊石上的吸附逐渐减少。本文计算了不同温度下,各铀酰种态的扩散系数。在扩散层中,各种态的扩散系数随温度的变化较为一致,而在吸附层中,UO_2~(2+)和UO_2CO_3的扩散速率随温度的变化较UO_2(CO_3)_2~(2-)和UO_2(CO_3)_3~(4-)慢。但是在同一温度下,同一个吸附层或扩散层中,铀酰种态的扩散系数大小顺序始终保持不变:UO_2~(2+)UO_2CO_3UO_2(CO_3)_2~(2-)UO_2(CO_3)_3~(4-)。说明在碳酸根存在的情况下,UO_2~(2+)可能是主要的扩散形式。     

Metastable Phase Equilibrium in the Reciprocal Quaternary System LiCl+MgCl2+Li2SO4+MgSO4+H2O at 348.15 K and 0.1 MPa

The metastable solubilities and the physicochemical properties including density and pH of the reciprocal quaternary system(LiCl+MgCl₂+Li₂SO₄+MgSO₄+H₂O) at 348.15 K and 0.1 MPa were determined using the isothermal evaporation method. The dry-salt diagram and water-phase diagram were plotted based on the experimental data. There are five invariant points, eleven univariant curves, and seven crystallization zones corresponding to hexahydrite, tetrahydrite, kieserite, bischofite, lithium sulfate monohydrate, lithium chloride monohydrate and lithium carnallite. Comparison between the stable and metastable diagrams at 348.15 K indicates that the metastable phenomenon of magnesium sulfate is obvious, and the crystallization regions of hexahydrite and tetrahydrite disappear in the stable phase diagram. A comparison of the metastable dry-salt phase diagrams at 308.15, 323.15 and 348.15 K shows that with the increasing of temperature the epsomite crystallization zone disappears from the dry-salt phase diagram of 303.15 K, and a new kieserite crystallization zone is presented at 348.15 K. The density and pH in the metastable equilibrium solution present regular change with the increasing of Jänecke index J(2Li⁺), and the calculated densities using the empirical equation agree well with the experimental values.     

Cu/WO3-TiO2光催化剂上丙烯和二氧化碳合成MAA反应性能

研究了Cu/WO₃-TiO₂对CO₂和C₃H₆的吸附特性和光催化性能.结果表明,在Cu/WO₃-TiO₂催化剂表面存在金属位Cu,Lewis酸位W⁶⁺和Ti⁴⁺以及Lewis碱位W-O-Ti的桥氧和WO的端氧三类活性中心;在金属位Cu和Lewis酸位Ti⁴⁺(或W⁶⁺)的协同作用下,CO₂形成活性较高的卧式吸附态Cu-(CO)-O→Ti⁴⁺(或W⁶⁺),C₃H₆的β-H和β-C分别吸附在Lewis碱位WO与金属位Cu上,形成Cu-(CH₂)C(CH₃)-H→OW吸附态;Cu/WO₃-TiO₂催化剂吸收阈值蓝移和光吸收量的提高均有利于其催化活性的提高,担载质量分数为10%的WO₃光催化剂的催化活性优于其它含量的催化剂,光量子效率最高(19.7%);在383K,0.1MPa,空速200h^-1和125W紫外灯辐照下,C₃H₆转化率为7.4%,甲基丙烯酸(MAA)的选择性超过95%.根据实验结果提出了光促表面催化合成反应的机理.     

Conversion of CO2 to Multi-carbon Compounds over a CoCO3 Supported Ru-Pt Catalyst Under Mild Conditions

The catalytic hydrogenation of CO₂ to multi-carbon compounds under mild conditions would not only provide value-added products, but also benefit for the reduction of CO₂ emission if hydrogen derives from renewable energy sources. Herein, we report CoCO₃ supported Ru and Pt nano-particles, which could catalyze hydrogenation of CO₂ to produce higher hydrocarbons(C₂-C₂₆) and higher alcohols(C₂OH-C₆OH) at low temperatures of 80-130℃. The selectivity for C₂₊ compounds reached 81.1% at 80℃, which was the highest value reported so far. This work provides a promising catalyst for highly selective converting CO₂ and H₂ to C₂₊ compounds at low temperatures.     

Separation of CO_2–N_2 using zeolite NaKA with high selectivity

The adsorption method based on solid adsorbents is one of feasible ways to capture and store CO_2. Using the ion exchange method, different zeolites Na KA varying in K+content were produced. The adsorption isotherms and kinetic uptakes were measured. The experimental results show that the optimal NaKA could adsorb significant quantities of CO_2 and little N_2. On the zeolite Na KA with 14.7 at.% K+, the adsorption capacity for pure CO_2 is over 3.10 mmol g~(-1) and the CO_2–N_2 selectivity is about 149 at ambient pressure and temperature. The kinetic CO_2–N_2 selectivity could also achieved 200 within 3 min according to the uptake data. To demonstrate the separation effectiveness, breakthrough curves of pure components and binary mixtures were investigated experimentally and theoretically in a fixed bed. It is found that the breakthrough points of CO_2 and N_2 are almost at the same time under the atmospheric pressure at 348 K with the raw gas composition CO_2/N_2(20:80, v/v). If the pressure has been increased higher than 0.1 MPa, CO_2 would break through the bed much slower than N_2. Therefore, the pressure may become the limiting factor for the separation performance of zeolites NaKA.     

Calculation of CO(XΣ) + 0(P) recombination chemiluminescence spectrum

Relative emission spectra for the bent to linear, CO₂(¹B₂)---CO₂(X¹Σ⁺_g) transitions have been calculated using the model: harmonic oscillator, symmetric-top wavefunctions and energy levels for CO₂(¹B₂); first-orer Fermi resonance vibrational wavefunctions and energy levels for CO₂(X¹Σ⁺_g); a Boltzmann distribution of vibrational and rotational states in CO₂(¹B₂); and a constant electronic transition moment. With the literature CO₂(¹B₂) molecular structure, spectra calculated using this model show characteristics similar to the low-temperature chemiluminescence from the combination of atomic oxygen and carbon monoxide. The calculated spectra account for experimental band positions to wavelengths of 570 nm and the weak dependence of the spectra on temperature over the range 206–353 K. The latter result was obtained from a CO₂(¹B₂) bending fundamental of 600 cm⁻¹. The calculated spectra also show a violet-shift in intensity and an attenuated band structure at higher temperatures. The magnitude of these effects depends on the CO₂(¹B₂) force constants and not on the CO₂(¹B₂) molecular structure.     

二氧化碳/甲烷/氮气二元混合物在有序介孔碳材料CMK-3 中的吸附和分离

采用分子模拟与吸附理论研究了天然气成分在有序介孔碳材料CMK-3上的吸附和分离.巨正则系综蒙特卡罗(GCMC)模拟表明,CH4和CO2气体的较优存储条件分别为208 K、4 MPa和298 K、6 MPa,其最大超额吸附量分别为10.07和14.85 mmol· g-1.基于双位Langmuir-Freundlich (DSLF)模型,使用理想吸附溶液理论(IAST)预测了不同二元混合物在CMK-3中的分离行为,发现吸附选择性Sco2/CH4与ScH4/N2比较接近,在298 K和4 MPa下约等于3,而N2-CO2体系中的CO2吸附选择性较高,可达到7.5,说明CMK-3是一种适合吸附和分离天然气组分的碳材料.     

亚临界和超临界二氧化碳-甲醇混合气相及液相区中甲醇核磁弛豫速率比较研究

用核磁共振氢谱测量了不同温度（293.15和308.15 K）及压力高达25 MPa下二氧化碳-甲醇混合气相（超临界）及液相区（亚临界）中甲醇（羟基及甲基）的纵向弛豫时间T_1,exp。本工作的目的是考察近临界区二氧化碳-甲醇混合物的压力、温度及组成对甲醇弛豫速率的影响,揭示混合物不同相区（气相及液相区）中自旋-晶格弛豫（SLR）过程的机理。此外,还对比研究了等温条件下超临界和亚临界混合气相及液相区中甲醇的SLR速率1/T_1,exp随混合物密度的变化规律。研究发现,在本工作所涉及的温度及压力区间,对于纯甲醇或液相区其SLR过程是以偶极-偶极（DD）作用机理为主导,而在气相区SLR过程则是以自旋-转动（SR）作用机理占优势,也即,超临界和亚临界二氧化碳-甲醇混合物的SLR过程在不同相区有不同的作用机理控制。由于甲醇的SLR弛豫速率1/T_1,exp是由甲醇分子间及分子内的DD作用和SR作用三部分共同决定的,所以研究超临界和亚临界二氧化碳-甲醇混合物的SLR弛豫速率随压力、浓度及温度的变化规律有助于提供更多该混合物不同相态区分子间相互作用的动态学信息。     

相变贮热材料四氯合钴酸铵共析物的制备和热性能

在温度353 K的乙醇溶液中, 采用热回流法合成了热致相变化合物四氯合钴酸铵(1-C_nH_2n+1NH₃)₂CoCl₄(n=10, 18)(分别简写为C₁₀Co、C₁₈Co)及其二元混合物. 利用差示扫描量热和X射线法对二元体系进行了表征.根据测定实验数据构筑二元相图, 所得相图结果表明, 在w_C10Co=52.51% (质量分数)处存在中间化合物(1-C₁₀H₂₁NH₃)(1-C₁₈H₃₇NH₃)CoCl₄. 相图还包括两个三相线, 相对应的两个共析温度分别为(347±1)和(343±1) K, 共析点分别在w_C10Co=38.50%和w_C10Co=69.86%处. 并且, 在相图的左右边界存在端际固溶体(α、β)及中间区域存在非化学计量相(γ). 四氯合钴酸铵及其二元混合体系作为相变材料贮热时, 相变温度范围为340-370 K, 相变焓大小范围在2.13到141.12 J·g^-1之间.     

生物油超临界CO_2酯化反应研究

将超临界CO2萃取与酯化反应耦合,研究了萃取酯化提质生物油过程。乙酸(AC)、丙酸(PA)和丙烯酸(AR)在超临界CO2(scCO2)条件下酯化时的平衡转化率显著高于常压酯化时的平衡转化率,表明scCO2对酯化反应具有明显的促进作用。这主要是由于生成的酯不断被萃入scCO2相。在恒温下scCO2的密度随压力升高而增大,因而酯化率随着CO2压力的升高而增加,与有机酸单独酯化时相比,混酸(AC、PA和AR)酯化后各种酸的转化率却比较接近,表明酯化过程中存在着酯交换机制。真实生物油的酯化结果表明,在80℃和28.0MPa下酯化3.0h,总酸的转化率可达86.78%。酯化后生物油的pH值从3.78提高到5.11,萃出生物油在140℃下挥发率接近100%,表明油品质量得到显著提升。     

Carbon dioxide-water phase equilibria results from the Wong-Sandler combining rules

A model based upon the Peng-Robinson equation of state with the Wong-Sandler mixture combining rule (W-S MCR) can correlate phase equilibria in CO₂ + H₂O. The W-S MCR requires two energy parameters for liquid behavior and one interaction parameter for gas behavior, k_ij. In this paper, we present expressions for the energy parameters which cover a wide temperature range, and we use a new procedure to obtain k_ij by relating it to experimental cross second virial coefficients, B_ij. The three-phase pressures calculated for this system using our proposed model agree with the experimental data within a fraction of 1 bar. The correlated phase behavior of CO₂ + H₂O appears to be accurate over the ranges 1 – 1000 bar and 298.15–623.15 K. The proposed model also confirms the advantage of using the W-S MCR for phase equilibrium calculations.     

超临界水中甲酸降解过程实验研究

在550℃~650℃,24 MPa~30 MPa,反应停留16 s~46 s的条件下,对初始浓度0.05 mol/L~0.70 mol/L的甲酸溶液在超临界水中的降解过程进行实验研究。结果表明,甲酸降解的气体产物为H2、CO2和CO,其中H2、CO2为主要产物。高温有利于甲酸降解和H2生成。温度较高(600℃)时,压力变化对甲酸降解无明显影响。在一定范围内延长反应时间可提高气体产物中H2的体积分数和碳气化率。甲酸初始浓度对甲酸降解机理有重要影响,浓度较低(0.1 mol/L)时,甲酸降解主要包含脱羧反应和脱羰反应两条反应路径,其中脱羧反应为主反应路径;浓度较高时则有许多副反应发生。碱性添加剂不利于甲酸降解生成H2。     

Phase behaviour of the thermotropic cubic mesogen 1,2-bis(4-n-decyloxybenzoyl)hydrazine under pressure

The phase transition behaviour of an optically isotropic, thermotropic cubic mesogen 1,2-bis(4-n-decyloxybenzoyl)hydrazine, BABH(10), was investigated under pressures up to 300 MPa using a high pressure differential thermal analyser, a wide angle X-ray diffractometer and a polarizing optical microscope (POM) equipped with a high pressure optical cell. The reversible change in structure and optical texture between the cubic (Cub) and smectic C (SmC) phases was associated with a change from a spot-like X-ray pattern and dark field for the Cub phase to the Debye-Sherrer ring pattern and sand-like texture for the SmC phase under both isobaric and isothermal conditions. The Cub phase was found to disappear at pressures above about 11 MPa. The phase transition sequence, low temperature crystal (Cr₃)-intermediate temperature crystal (Cr₂)-high temperature crystal (Cr₁)-Cub-SmC-isotropic liquid (I) observed at atmospheric pressure, is maintained in the low pressure region below 10 MPa. The transition sequence changes to Cr₃-Cr₂-(Cr₁)-SmC-I in the high pressure region. Since the Cub-SmC transition line determined by POM has a negative slope (dT/dP) in the T-P phase diagram, a triple point is estimated approximately at 10-11 MPa, and 143-145°C for the SmC, Cub and Cr₁ phases, giving the upper limit of pressure for the observation of the cubic phase.     

Vapor-liquid equilibria for binary mixtures of carbon dioxide and fatty acid ethyl esters

Vapor-liquid equilibria were measured and correlated using the Peng-Robinson equation of state for five binary systems of carbon dioxide and fatty acid ethyl esters (ethyl stearate, ethyl oleate, ethyl linoleate, ethyl eicosapentanoate, ethyl docosahexanoate) at 313.15 K, 323.15 K and 333.15 K. Solubility in CO₂ of fatty acid ethyl esters of equal chain length but of various degrees of unsaturation was compared. Although there was no distinct difference in solubility at lower pressures, at higher pressures (more than 15 MPa), those with a higher degree of unsaturation showed a slightly higher solubility. When the solubility in CO₂ of methyl esters and the corresponding ethyl esters were compared, it was noted that the former showed a slightly higher solubility at all system pressures measured in this work.     

High-pressure phase studies on fluid mixtures of low-volatile organic substances with supercritical carbon dioxide

Two high-pressure phase equilibrium cells working according to the analytical method in the temperature range 300 to 450 K and up to 200 MPa have been developed. In the first cell p,T,x,y equilibrium data can be determined by sampling and GC analysis. With this cell the gas-liquid phase behaviour of the ternary systems carbon dioxide + tridecane + hexadecane and carbon dioxide + tridecane + 1-hexadecanol were determined at 423.4 K and between 8 and 35 MPa. For the second apparatus a spectroscopic high-pressure cell fitted with two pairs of sapphire windows was developed. Molar absorptivities are obtained from calibration runs in the homogeneous region. Gasliquid phase equilibria in the system decane + CO₂ were investigated from 342.8 to 400.2 K and between 10 and 20 MPa; here absorption data were measured in the NIR region.     

Ca掺杂的CeO2模型催化剂的形貌和电子结构及其与CO2分子的相互作用

利用扫描隧道显微镜、X射线光电子能谱和同步辐射光电子能谱研究了CeO₂(111),部分还原的CeO_2-x(111) (0＜x＜0.5)以及Ca掺杂的CeO₂模型催化剂的形貌、电子结构以及它们与CO₂分子间的相互作用。CeO₂(111)和部分还原的CeO_2-x(111)薄膜外延生长于Cu(111)单晶表面。不同Ca掺杂的CeO₂薄膜是通过在CeO₂(111)薄膜表面室温物理沉积金属Ca及随后真空退火到不同温度而得到的。不同的制备过程导致样品具有不同的表面组成,化学态和结构。CO₂吸附到CeO₂和部分还原的CeO_2-x表面后导致表面羧酸盐的形成。此外,相比于CeO₂表面,羧酸盐物种更易在部分还原的CeO_2-x表面生成,而且更加稳定。而在Ca掺杂的氧化铈薄膜表面,Ca²⁺离子的存在有利于CO₂的吸附,且探测到碳酸盐物种的形成。     

Palladium-catalyzed Heck coupling reactions using different fluorinated phosphine ligands in compressed carbon dioxide and conventional organic solvents

Palladium-catalyzed Heck reaction of iodobenzene and styrene was investigated in compressed CO₂ using different fluorinated phosphine compounds as ligands at a temperature of 70 °C. The reaction mixture is a single phase at 12 MPa but biphasic at 8 MPa, a little higher than the critical pressure of pure CO₂ under the reaction conditions used. Although the solubility of fluorinated ligands is very high in dense CO₂, they have marginal improvements in Heck conversion in this medium compared with a non-fluorinated ligand of triphenylphosphine. The activity of palladium complexes strongly depends on the kind of phosphine compound used, in the order of bis(pentafluorophenyl)phenylphosphine (III)>triphenylphosphine (I), tris(pentafluorophenyl)phosphine (IV)>diphenyl(pentafluorophenyl)phosphine (II), tris(p-fluorophenyl)phosphine (V)>tris(p-trifluoromethyl phenyl)phosphine (VI), 1,2-bis[bis(pentafluorophenyl)phosphino]ethane (VII), for the homogeneous reaction at 12 MPa. This order of effectiveness of these ligands is different from those obtained in conventional organic solvents. Hexane, toluene, ethanol, and N-methylpyrrolidone (NMP) showed maximum conversions with the ligands VI, IV, V and VII, respectively. The conversion in CO₂ with the ligand III is comparable with those in polar solvents of ethanol and NMP, and larger than those in hexane and toluene in the presence of the best ligands. The dense CO₂ may affect the specific activity of palladium complex catalysts and/or the reactivity of reacting species. Small quantities of fluorinated products were observed to form at high pressure of CO₂ and this is direct evidence of P–C bond cleavage during Heck reaction in dense CO₂. The activity of palladium complexes with those ligands is higher in more polar solvent.     

CO2在非质子溶剂与铁基离子液体复合体系中的吸收

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BmimFeCl₄复配, 构建了BmimFeCl₄/NHD和BmimFeCl₄/DMAC复合铁基离子液体体系. 考察了温度、 BmimFeCl₄/溶剂的质量 比以及压力对CO₂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CO₂ 的溶解, 当BmimFeCl₄/DMAC质量比为7∶3时, CO₂在BmimFeCl₄/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BmimFeCl₄/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, CO₂在BmimFeCl₄/NHD和BmimFeCl₄/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CO₂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, CO₂更倾向与阳离子和溶剂分子作用, 而在复配NHD的体系中, CO₂则更容易与阴离子和溶剂分子作用.     

New p–ρ–T measurements up to 70 MPa for the system CO2 + propane between 298 and 343 K at near critical compositions

The vibrating tube densimeter method along with the Forced Path Mechanical Calibration model, is used to measure the high pressure isothermal p–ρ behavior of the CO₂+propane system along 17 isotherms between 293 and 343 K, at pressures up to 70 MPa. The compositions cover the range of mole fractions from x_CO2=0.45 to 1.0. The uncertainty in temperatures is ±0.015 K. The uncertainties in pressures are ±0.0013 MPa from 0.1 to 15.0 MPa and ±0.010 MPa from 5.0 to 70.0 MPa. The precision of the density measurements is ±0.014 kg m⁻³. The minimum global uncertainty is ±0.204 kg m⁻³, based on the calibration of the densimeter with pure water. A generalized Helmholtz energy model for mixtures is used to check the consistency of the new data with respect to previous p–ρ–T studies of this mixture. The average absolute deviation of our data with respect to the model is 0.64% which is fully consistent with the assessed accuracy.     

新型类沸石金属-有机骨架材料用于天然气中CO2的分离

研究了在usf型类沸石金属-有机骨架材料(usf-ZMOF)中不同金属离子(Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, Mg²⁺, Ca²⁺, Sr²⁺, Al³⁺)对天然气分离(以CO₂/CH₄, CO₂/H₂, CO₂/N₂为研究对象)的不同影响. 结果表明, 此类材料对于3种体系的分离选择性均高于现有材料. 其中性能最好的是Al-usf-ZMOF, 其对CO₂/CH₄, CO₂/N₂和CO₂/H₂的分离选择性分别为290, 1700和16800. 同时, 对于经不同的离子交换后的usf-ZMOF, 吸附选择性随着离子电荷值的增加而增大; 对于同一主族的离子, 选择性随着原子序数的增加而减小. 而上述现象的产生是由阳离子和CO₂间的强静电作用所致.