Sorption and Diffusion of Supercritical Carbon Dioxide in a Biodegradable Polymer

A gravimetric method was used to study the sorption and diffusion of supercritical carbon dioxide in a temperature range from 40°C to 80°C and a pressure range from 8.0 to 18.0 MPa in a biodegradable polymer, namely poly(butylene adipate-co-terephthalate) (PBAT). The PBAT presented Fickian behavior and Fick's diffusion model was applied to determine the amount of carbon dioxide present in the samples after a predetermined exposure time as well as the diffusion coefficients. The variations of diffusion coefficients of CO₂ for the sorption under supercritical conditions and desorption at ambient conditions as well as equilibrium sorption amounts of CO₂ with variations of pressure and temperature were determined and compared.     

原位DRIFTS研究CH4部分氧化和CO2重整的耦合

8%Ru-5?/γ-Al2O3催化剂对于甲烷的低温活化具有较好的催化活性,在500℃下甲烷、二氧化碳和氧气的耦合反应中,吸热反应二氧化碳重整和放热反应甲烷部分氧化进行耦合强化,使得耦合反应中的甲烷转化率为38.8%。用原位漫反射傅里叶红外光谱法对钌系催化剂耦合甲烷部分氧化和二氧化碳重整反应体系机理进行研究。CO在8%Ru-5?/γ-Al2O3上吸附,表明CO在催化剂表面上波数为2 167 cm-1(2 118 cm-1)和2031 cm-1(2 034 cm-1)处形成孪生态Ru(CO)2和Ce(CO)2吸附物种,而且高温下CO吸附物种很容易从催化剂表面脱附出来。原位漫反射红外实验结果表明甲烷部分氧化反应时催化剂表面上有吸附物种碳酸根、甲酰基(甲酸盐)和一氧化碳的形成,其中表面的甲酰基和甲酸盐物种是甲烷部分氧化反应的主要活性中间物,这些中间活性中间体由甲烷吸附态CHx和催化剂表面的氧吸附态结合而形成的,随后这种中间物种再分解为CO产物;甲烷和二氧化碳重整反应时没有新的吸附物种产生,由此提出重整反应的机理是吸附态的甲烷和二氧化碳在催化剂活性中心上进行活化解离而生成合成气;甲烷、二氧化碳和氧气耦合反应过程中出现新的羟基物种(桥式羟基Ru-(OH)2),耦合反应机理复杂可能是由部分氧化和重整两类反应机理的复合,其中桥式羟基Ru-(OH)2参与了反应的进行。     

高温二氧化碳气体红外辐射实验研究

主要介绍了依托高频等离子体风洞建立的高温气体辐射测量平台,并在此平台上开展了高温二氧化碳气体红外辐射实验测量。介绍了高频等离子体风洞的运行原理、流场特性及工作介质;介绍了实验测量的条件、装置、标定、数据处理方法和结果分析;通过自建的高温气体发射光谱测量平台实验测量了二氧化碳气体在1 500～3 000 K范围内4个温度点的红外发射光谱;介绍了Abel变换在测量二氧化碳气体红外辐射空间分布中的应用,通过Abel变换获得了高温下二氧化碳气体红外辐射的空间分布结果; 分析了高温二氧化碳气体在4.3 μm附近的红外辐射的强度及其中心波长随温度变化的分布,得到了发射峰中心波长随温度的升高向长波方向展开的结果,并与文献结果进行了对比分析。     

二氧化碳在电解质溶液中的盐溶盐析机制

The solvation of carbon dioxide in sea water plays an important role in the carbon circle and the world climate. The salting-out/salting-in mechanism of CO₂ in electrolyte solutions still remains elusive at molecule level. The ability of ion salting-out/salting-in CO₂ in electrolyte solution follows Hofmeister Series and the change of water mobility induced by salts can be predicted by the viscosity B-coefficients. In this work, the chemical potential of carbon dioxide and the dynamic properties of water in aqueous NaCl, KF and NaClO₄ solutions are calculated and analyzed. According to the viscosity B-coefficients, NaClO₄ (0.012) should salt out the carbon dioxide relative to in pure water, but the opposite effect is observed for it. Our simulation results suggest that the salting-in effect of NaClO₄ is due to the strongly direct anion-CO₂ interaction. The inconsistency between Hofmeister Series and the viscosity B-coefficient suggests that it is not always right to indicate whether a salt belongs to salting-in or salting-out just from these properties of the salt solution in the absence of solute.     

Titanium Dioxide/Carbon Fabric Prepared by a Controlled Pyrolysis Method

Titanium dioxide/carbon fabrics were prepared through pyrolysis of cellulosic fabrics in the presence of titanium ions. The influence of sintering temperature on the characteristics of the TiO₂/carbon fabrics was investigated. The properties of the samples were characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The photocatalytic efficiency was evaluated by degradation of methylene blue (MB) solution. The results showed that the sample sintered at 300°C exhibits high photocatalytic efficiency.     

Effect of thermobaric conditions in a uniform bed on the displacement of low-viscosity oil by supercritical carbon dioxide

An experimental setup was constructed that makes it possible to study oil displacement over wide pressure (up to 20 MPa) and temperature (up to 373 K) ranges under conditions reproducing the thermobaric, geological, and physicochemical conditions in real oil beds, as well as the parameters of displacing agents. Experiments on the displacement of kerosene from a model oil bed with supercritical carbon dioxide at temperatures of 313–353 K and pressures within 7–12 MPa were performed. The results are indicative of a high efficiency of recovery of low-viscosity oils with supercritical carbon dioxide.     

Effect of temperature and high pressure on Mn2+ EPR spectra in K3H(SO4)2 fast-proton conductor

The linewidth ΔH _pp and spin-Hamiltonian parameters under temperature and high hydrostatic pressure by X-band continuous wave electron paramagnetic resonance in the K₃H(SO₄)₂ crystal were studied. Spin-Hamiltonian parameters, direction cosines and coordination of Mn²⁺ ion were determined at room temperature. The pressure at 300?MPa leads to the change of hydrogen bond potential and the transition from double well to single well potential moves about 10?K towards a higher temperature.     

Carbon Dioxide Measurement Based on Multimode Diode Laser Correlation Spectroscopy Employing Wavelength Modulation Techniques

The use of a tunable multimode diode laser system based on correlation spectroscopy and wavelength modulation spectroscopy to measure the concentration of the carbon dioxide in ambient air through the 2 υ₁ + 2υ₂ + υ₃ absorption lines around 1570 nm is reported. The carbon dioxide concentrations are derived from the relationship between the normalized second-harmonic signal peak heights of the measurement and reference signals. The validation of the system is conducted by a set of experiments with controlled carbon dioxide and nitrogen mixtures. The correlation and standard deviation between the measured and actual carbon dioxide concentrations are 0.9973 and 4.03%, respectively, over the tested range. A detection limit of 340 ppm m was achieved using 30 successive measurements during 30 min. All these results demonstrated potential utility of the system for carbon dioxide sensing.     

Thermal Reaction Characteristics of Nano/Micron-Sized Aluminum Mixtures in Carbon Dioxide

Thermal reaction characteristics of nano/micron-sized aluminum mixtures in a carbon dioxide atmosphere were investigated by thermogravimetry that aimed to examine the interactions between nanosized aluminum powder and micron-sized aluminum powder. Thermal reaction characteristics of nano/micron-sized aluminum mixtures at different ratios were studied. The synergistic effect mechanism was discussed by comparing experiment result and theoretical calculation. The morphologies and compositions of products were obtained by scanning electron microscopy and X-ray diffraction technologies. Results indicated that there were three weight gain stages for nano/micron-sized aluminum mixtures at different ratios. Although the temperature range of synergistic effect of nano/micron-sized aluminum mixtures with various ratios had somewhat differences, there was a significant synergistic effect from about 900 to 1040°C. The products analyses indicated that the products morphologies of nano/micron-sized aluminum particles showed molten and stuck together, and products contained aluminum and α-Al₂O₃.     

High pressure viscosity and density measurements of the binary mixture tridecane + 2,2,4,4,6,8,8-heptamethylnonane

Abstract

The dynamic viscosity η of the binary mixture tridecane + 2,2,4,4,6,8-heptamethyl-nonane has been measured in the temperature range 293.15-353.15K (in progressive 10 K steps) at pressures 0.1,20,40,60,80 and 100 MPa. The system is described by 9 molar fractions (0 to 1 in 0.125 progressive steps). The density ρ has been measured at pressures from 0.1 to 65 MPa in progressive 5 MPa steps. The whole set of experimental data represents 378 points for η and 882 for ρ. The measurements of η allow to determine the excess viscosity η^E and the excess activation energy of viscous flow ΔG^E versus pressure, temperature and composition.     

Low temperature high-pressure crystallization and fluid phase equilibria in the systems Ar + CHF3 and N2 + CHF3

Abstract

An optical autoclave for phase studies on mixtures in the temperature range from 80 to 373 K and for pressures up to 200 MPa is described. The cell is fitted with sapphire windows and employs magnetic stirring. Measurements are performed according to the synthetical (e.g. by visual observation) or analytical method (e.g. by sampling and online gaschromatography). Results for the crystallization and fluid phase equilibria of the binary systems nitrogen + trifluoromethane and argon + trifluoromethane from 110 K to 230 K and up to 200 MPa are presented and discussed in comparison with other N₂- and CHF₃-systems.     

Drying and Impregnation of Wood with Propiconazole Using Supercritical Carbon Dioxide

The process of wood drying is studied in supercritical (SC) CO₂ and SC-CO₂ containing 5 vol % ethanol at temperatures of 323, 343, and 353 K and pressures of 10, 20, and 30 MPa. It is established that 40–87% of moisture is removed from wood in the first cycle of drying. An increase in the duration of the decompression stage of the drying process decreases the number of cracks in the wood samples. The solubility of propiconazole is studied in SC-CO₂ at 323, 343, and 353 K in the pressure range of 10–30 MPa using a dynamic method. Rather high saturation concentrations of (3–5) × 10^–3 mol/mol CO₂ are obtained, which indicates the potential benefits of using SC-CO₂ as a solvent in wood impregnation with propiconazole. Continuous impregnation is achieved when impregnating wood with propiconazole from SC-CO₂. The impregnation efficiency increases with increasing pressure and duration of the process.     

The determination of the parameters of sub- and supercritical extraction of plant raw materials

The extraction of biologically active substances by carbon dioxide from various plant raw materials (amaranth seeds, Sophora japonica flower buds, Stephania rotunda stems, and Stevia rebaudiana leaves) was studied at sub- and supercritical parameters. A laboratory unit for the extraction of plant raw materials by liquefied gases and supercritical fluids at 5–35 MPa pressures and 285–350 K temperatures was developed. The maximum yield of the extracted substances from plants specified was obtained at temperature and pressure exceeding the critical parameters of CO₂ (320–330 K, 28–30 MPa).     

Features of Propene Oxidation in Argon,Carbon Dioxide and Water Vapor Media at a High Density of Reagents

The features of propene oxidation in high-density mixtures of C₃H₆/O₂ ([C₃H₆]₀ = 0.23–0.25 mol/dm³, [O₂]₀ = 0.76–0.82 mol/dm³), diluted with argon, carbon dioxide and water vapor at uniform heating (1 K/min) to T ≤ 620 K are investigated for the first time. From the time dependences of reaction mixtures temperature it is found that propene self-ignition occurs at 465 K and does not depend on the nature of the diluent. Using mass spectrometry analysis it is demonstrated that in the composition of the products of propene oxidation in the Ar and CO₂ medium predominate methanol, acetaldehyde, acetone, acetic acid and formaldehyde; in the oxidation in the H₂O medium, only small amof O₂ in the oxidation of propene increases in ounts of these substances were registered. Degree of consumption the following order: CO₂ ? Ar < H₂O, which is a consequence of the involvement of CO₂ and H₂O molecules in chemical transformations. Mechanisms of the observed processes are discussed.     

Removal of carbon dioxide from gas mixtures by wollastonite

Wollastonite synthesis and decomposition were analyzed from the viewpoint of thermodynamics (using the TERRA software). It is shown that wollastonite synthesis from limestone and silica takes place at a minimum content of nitrogen (10^?5 N₂) with a release of carbon dioxide. The synthesis temperature is T ≥ 560 K. Wollastonite is decomposed in the presence of flue gas (4N₂) with limestone and silica formation and burial of carbon dioxide in the form of CaCO₃(c). Wollastonite decomposition temperature is T ≤ 420 K. The cyclic reciprocating process for complete removal of carbon dioxide by wollastonite is suggested. Four strokes of the reciprocating system with the fixed temperatures of wollastonite decomposition (T=300 K) and wollastonite synthesis (T=560 K) are presented. Total energy consumption (T = 560 K) is ΔI ≈ 130 kJ/mole, 30 % of energy is spent for heating and 70 % of energy is spent for chemical reaction. This is comparable with the heat of CO₂ solution in ethanolamin.     

Effects of pressure and temperature on the solubility of monosodium L-glutamate monohydrate in water

Abstract

The solubility of monosodium L-glutamate monohydrate (MSG.H₂O) in water was measured at pressures in the range of 0.10-300MPa and 298.15K. The density of MSG solution at high concentrations and heat of solution at saturated concentration were also measured at atmospheric pressure. The solubility, m_s, increased with increasing pressure and the pressure coefficient, Θ_p, [?(? In m_s,? p)_T] at 0.10 MPa was (2.0 ± 0.1) × 10-¹⁰Pa-1. It agrees well with (2.1 ±0.2)× 10-¹⁰ Pa-¹ thermodynamically estimated using the partial molar volume, the activity coefficient of the solute in solution, and the molar volume of the crystal. The excellent agreement at 0.10MPa gives us confidence in the solubility data at higher pressures. The heat of solution data and other pertinent values were used to calculate the temperature coefficient of solubility, Θ_T [? (? In m_s/?(1/T))_p], by a thermodynamic equality. The resulting Θ_T compares well with the data directly measured by Ogawa.     

春季南黄海表层海水中二氧化碳的分布特征及其影响因素

根据2007年4月南黄海区块(SYS)表层海水中二氧化碳分压(pCO₂)的连续走航数据,结合水温(T)、盐度(S)、叶绿素 (Chla)以及pH的同步观测资料,对该海域pCO₂分布特征及其主要影响因素进行了初步探讨。分析结果表明：春季南黄海pCO₂的范围在365.2~734.9 μatm之间,平均值为548.0 μatm;最高值出现在121.5°E,33.4°N海域,最低值出现在123°E,32.3°N海域。受海水中物理、化学和生物因素的综合影响,pCO₂的分布存在较大的不均匀性,总体上表现为西部高于东部,中间高于南北两边;在苏北浅滩和鲁南海区,pCO₂与水温的变化呈正相关关系,与盐度的大小呈明显的负相关关系,而在长江入海口变化趋势则相反;此外,在整个调查海区pCO₂与叶绿素、pH基本上呈负相关关系。研究将两台检测器串联进行互校,同时利用二氧化碳标准气体对其中一台仪器进行全程校准,可连续不间断观测海水和大气中的pCO₂。该方法操作简单,获得的数据准确可靠,可为节能减排能力建设提供技术支持。     

中红外二氧化碳传感器的研制及在农业中的应用

利用二氧化碳气体分子在4.25μm处的基频吸收带,研制了一种差分式中红外二氧化碳检测系统.系统的光路部分由热辐射红外光源、双通道热释电探测器和球面反射镜构成,电路部分主要包括信号处理、光源驱动及主控模块.采用Tracepro软件对气室结构进行仿真和优化设计,使气体吸收光程达到30cm,改善了系统的性能.实验研究了系统对不同浓度二氧化碳气体样品的传感特性.实验结果表明,由拟合曲线得到的浓度与实际浓度误差较小,在0~5 000ppm范围内,测得二氧化碳浓度的标准差小于45ppm,而在500ppm以下,测量浓度的标准差小于5ppm;对浓度为0ppm的二氧化碳气体样品连续测量2h,测量结果的标准差约为2.8ppm;根据Allan方差分析得到系统的1σ检测下限为2.5ppm.在每个二氧化碳传感器上增加无线模块nRF24L01,构成传感器节点,在选定的日光温室大棚中构建了无线传感器网络,采集了温室大棚中的二氧化碳浓度信息,验证了所研制的传感器性能.     

EPR observation of phase transitions in calcium cadmium acetate hexahydrate: Using Mn2+ and Cu2+ ions as probe

Results of temperature dependence of EPR spectra of Mn²⁺ and Cu²⁺ ions doped calcium cadmium acetate hexahydrate (CaCd(CH₃COO)₄·6H₂O) have been reported. The investigation has been carried out in the temperature range between room temperature (～ 300 K) and liquid nitrogen temperature. A I-order phase transition at 146 ± 0.5 K has been confirmed. In addition a new II-order phase transition at 128 ± 1 K has been detected for the first time. There is evidence of large amplitude hindered rotations of CH₃ groups which become frozen at ～ 128 K. The incorporation of Cu²⁺ and Mn²⁺ probes at Ca²⁺ and Cd²⁺ sites respectively provide evidence that the phase transitions are caused by the molecular rearrangements of the common coordinating acetate groups between Ca²⁺ and Cd²⁺ sites. In contradiction to the previous reports of a change of symmetry from tetragonal to orthorhombic below 140 K, the symmetry of the host is concluded to remain tetragonal in all the three observed phases between room temperature and liquid nitrogen temperature.     

High pressure ignition delay times of H2/CO mixture in carbon dioxide and argon diluent

Ignition Delay Time (IDT) plays a significant role in combustion process of advanced power cycles such as direct-fired supercritical carbon dioxide (sCO₂) cycle. In this cycle, fuel and oxidizer are heavily diluted with carbon dioxide (CO₂) and autoignite at a combustor inlet pressure range of 10–30 MPa and a temperature range of 900–1500 K. A fuel candidate for sCO₂ power cycle applications is syngas (H₂/CO mixture); however, its ignition properties at these conditions are not studied. Moreover, the existing chemical kinetics models have not been evaluated for H₂/CO mixtures applications relevant to elevated pressure conditions and under large dilution levels of CO₂. Therefore, two tasks are performed in this study. First, IDTs of a H₂/CO=95:5 mixture at stoichiometric and rich (Φ=2) conditions are measured in a high-pressure shock tube under 95.5% CO₂ dilution level and at 10 MPa and 20 MPa for a temperature range of 1161–1365 K. For the experimental conditions considered in this work, Aramco 2.0, FFCM-1, HP-Mech and USC Mech II kinetic models are capable of capturing IDT data. Second, similar experiments are conducted by replacing the CO₂ dilute gas with Argon (Ar) to understand the chemical effect of CO₂ on IDT globally. Sensitivity analysis results reveal that for both diluents, reaction H + O₂(+M)=HO₂(+M) is the most important reaction in controlling ignition. Further, a rate of production analysis shows that CO₂ has a competing effect on OH radical production. On one hand, CO₂ accelerates the consumption of H radicals through H + O₂+CO₂→HO₂+CO₂ therefore hindering HO₂+HOH+OH reaction for OH production. On the other hand, CO₂ is shown to enhance OH production through H₂O₂+M=OH+OH+M. These kinetic effects from CO₂ cancel out, therefore CO₂ does not significantly alter the IDT globally when compared to the Ar bath case. This is confirmed by both experimental results and simulation.