甲苯和二甲苯体系固液平衡相图及其低共熔点对比

针对对二甲苯结晶相关由甲苯和二甲苯组成的二元和三元体系,选取固液相平衡计算模型—Van′t Hoff方程简式计算了由甲苯和二甲苯组成的二元和三元体系的液相摩尔分数与低共熔点温度及组成,并绘制了与甲苯有关的对二甲苯-甲苯-邻二甲苯、邻二甲苯-甲苯-间二甲苯、对二甲苯-甲苯-间二甲苯等3个三元体系的固液相平衡相图,对比分析...     

环丁烯砜合成反应的基团贡献法热力学分析

采用基团贡献法对环丁烯砜合成反应进行了热力学分析,计算了300~600 K、0.1~10 MPa反应体系的反应焓变、反应熵变、反应Gibbs自由能变和反应平衡常数,并分析了温度、压力和组成对平衡转化率的影响。结果表明,标准压力下,环丁烯砜合成反应是可逆放热反应,温度小于460 K范围内可以自发进行,降低温度和升高压力有利于反应向正向进行。温度、压力和组成对平衡转化率均有影响,温度影响最为显著。降低温度、升高压力或增大过量比有利于提高平衡转化率,最大平衡转化率接近于1。基团贡献法所得的平衡转化率预测值与实验值吻合较好,相对偏差在10%以内。     

醋酸或醋酸酯加氢制乙醇的热力学计算与分析

对醋酸、醋酸甲酯或醋酸乙酯加氢制乙醇进行了热力学计算和分析。计算了这3个反应的标准摩尔焓变和标准平衡常数,以及温度、压力和反应物配比对平衡转化率的影响。结果表明,3个反应的标准摩尔焓变都小于0,是放热反应;醋酸加氢反应的标准平衡常数较大,而醋酸甲酯加氢反应和醋酸乙酯加氢反应的标准平衡常数都小于0.7;醋酸加氢反应由于标准平衡常数较大,因此其平衡转化率受工艺条件影响较小,而醋酸甲酯加氢和醋酸乙酯加氢反应的平衡转化率受工艺条件的影响较大,醋酸酯加氢制乙醇反应适宜的温度为423~550 K,适宜的压力是2~3 MPa,适宜的氢酯比是10~20。     

碱法合成甲醇钠的热力学分析

氢氧化钠溶解在甲醇中与甲醇反应是制取甲醇钠的主要方法,文中针对该液相反应建立热力学循环,计算了298 K下反应的标准摩尔吉布斯自由能变和标准摩尔焓变,将范特霍夫方程积分后得到化学平衡常数随温度的变化关系式。计算结果表明:该反应的标准摩尔吉布斯自由能变略大于0,说明反应在常温下难以自发进行,需要不断移出生成的水来提高反应转化率;反应微放热,化学平衡常数随温度升高将变小,得到的化学平衡常数与温度的关系式与文献报道的实验结果基本一致,可为工业模拟提供理论计算依据。根据化学平衡常数关系式和汽液平衡模型对生产过程进行分析计算,获得了较适宜的反应温度范围。     

双进料混合二甲苯连续悬浮结晶工艺的优化

甲苯选择性歧化法与传统歧化组合工艺(简称SITDP工艺)得到对二甲苯(PX)含量为90%左右和65%左右的两种混合二甲苯产品,探索将SITDP工艺得到的两种不同浓度PX产品结合成一套分离提纯装置,研究进一步结晶提纯优化方案。通过二甲苯同分异构体三元系固液相平衡实验求取真实二甲苯固液相平衡的模型及数学表达式,结合物料衡算和能量衡算对双进料混合二甲苯连续悬浮结晶工艺进行计算,考察两种含量料液在不同进料比率下的单位质量产品最低能耗QR及其对应的成核区温度T2。计算结果得到最优成核温度的调节范围为248～265K,与实际生产操作工艺中的成核温度调节范围250～266K相当接近。计算结果同时提供了不同进料比率下为获得单位质量产品最低能耗QR时的最优成核区温度T2。     

苯和二甲苯体系固液相平衡的数据预测与相图

针对对二甲苯装置结晶单元中由苯和二甲苯组成的相关体系,选取了固液相平衡计算模型—Van′t Hoff方程简式,利用与苯和二甲苯有关的二元和三元体系固液相平衡文献数据对该模型进行考察,利用该模型预测由苯和二甲苯组成的二元和三元体系的固液相平衡数据,并绘制三元体系的固液相平衡相图。结果表明：采用Van′t Hoff方程简式计算,苯和二甲苯有关体系的液相摩尔分数的平均相对偏差为2.69%,低共熔点温度的偏差最高为0.59℃,最低为0.01℃,表明所选模型适用于由苯和二甲苯组成的体系固液相平衡计算;利用该模型预测苯-间二甲苯、苯-邻二甲苯二元体系及对二甲苯-间二甲苯-苯、对二甲苯-邻二甲苯-苯、间二甲苯-邻二甲苯-苯三元体系的固液相平衡数据,绘制了对二甲苯-间二甲苯-苯三元体系的固液相平衡相图,这些新的相平衡数据和相图均未见有文献报道,可为对二甲苯结晶相关体系的固液相平衡研究提供理论指导和依据。     

丙酮与甲醛合成4-羟基-2-丁酮的热力学分析

采用Benson基团贡献法对丙酮与甲醛合成4-羟基-2-丁酮反应进行热力学分析。计算了反应中各组分的标准摩尔生成焓、标准摩尔熵、摩尔定压热熔以及反应平衡常数,并讨论了反应温度对该反应热力学平衡的影响。结果表明,生成4-羟基-2-丁酮反应是放热反应,反应平衡常数随温度的升高而降低,适当提高反应温度有利于反应的进行,最佳反应温度应在550K左右。     

生物质气催化合成甲醇的热力学分析

由生物质气合成甲醇是一复杂反应系统,本文计算了其中各个反应的反应热和平衡常数与温度的关系.并以CO 21.5%、CO₂ 22.8%、H₂ 52.5%、N₂ 3.2%的气体模拟生物质气,用平衡常数法计算了在473.15～553.15 K、3～6 MPa下的平衡组成、碳的平衡转化率和所得甲醇的浓度.计算结果表明,这一体系中,主要是CO+H₂生成甲醇.低温和高压有利于提高碳的平衡转化率和甲醇的浓度.并用工业C306催化剂验证了上述规律的正确性.由于反应既受热力学控制,又受动力学控制,在3 MPa时碳的转化率在533.15 K时达到最大,接近平衡转化率.随压力升高,甲醇产率及液相产物中的浓度逐渐升高.     

Al_2O_3含量对ITSOFC用SrO-La_2O_3-Al_2O_3-B_2O_3-SiO_2玻璃性能的影响(英文)

采用高温熔融法制备了中温固体氧化物燃料电池用系列硼硅酸盐玻璃,玻璃摩尔组成为40SrO-5La2O3-xAl2O3-(25-x)B2O3-30SiO2(x=0,2.5,5.0,10.0)。结果表明:随着Al2O3含量的逐渐增多,玻璃转变温度和析晶峰温度逐渐升高,而热膨胀系数(CTE)均在9.8×10-6/K左右,这与电极材料8%(摩尔分数)Y2O3稳定ZrO2(8YSZ)在相同温度范围内的CTE相接近。Al2O3摩尔含量为5%的硼硅酸盐玻璃在700℃热处理100h后未能检测到明显的析晶和CTE变化,同时与8YSZ电极材料在700℃保温100h没有观测到明显的界面反应,表明该玻璃具有良好的化学相容性。     

混合C_4芳构化反应的热力学研究

利用混合C4生产芳烃,对于提高混合C4综合利用利用水平和企业经济效益均具有重要意义。简要描述了混合C4芳构化的反应过程,并利用热力学原理计算了各反应的标准摩尔反应焓、标准摩尔吉布斯自由能和标准平衡常数。计算结果表明,温度是影响混合C4芳构化反应热力学的重要因素,高温有利于大部分芳烃生成反应的进行;为了促进混合C4中丁烷、丁烯最大限度地转化成芳烃,其反应温度应控制在655 K以上。     

催化氧化邻羟基甲苯制备邻羟基苯甲醛的热力学分析

引言邻羟基苯甲醛(o-hydroxybenzaldehyde,OHBA)是重要的有机合成中间体,广泛应用于医药工业[1-2]、农药[3-5]、食品香料与香精、电镀[6]、石油化工和合成纤维等领域。目前合成邻羟基苯甲醛的方法很多,从原料的角度主要可以分为以邻羟基苯甲醇、邻羟基苯甲酸、苯酚和邻羟基甲苯为原料的合成方法[7]。其中由于邻羟基甲苯廉价易得,且以其为原料的空气/氧气直接氧化法[8-12]环境污     

Effect of different additives on the phase separation behavior and thermodynamics of p-tert-alkylphenoxy poly (oxyethylene) ether in absence and presence of drug

Cloud point(CP) determinations of 4-(1,1,3,3-tetramethylbutyl)phenyl-polyethylene glycol(TX-100(nonionic surfactant)) was carried out in aqueous as well as in the attendance of drug(ceftriaxone sodium trihydrate(CFT))/(CFT + different inorganic salts) and discussed thoroughly. Nonionic surfactants are employed extensively in different formulations. In aqueous solution, the values of CP of TX-100 are obtained to increase by means of enhancing of their concentration in the solution. The CP values of TX-100 solutions were found to decrease in the presence of drug and their values decrease more with rising concentrations of the drug. The values of CP of CFT and TX-100 mixtures were found to further decrease in the attendance of inorganic salts in comparison to their absence. The effect of different sodium salts in decreasing CP values of TX-100 was achieved in the following order: NaCO_3 Na_2SO_4 Na Cl. However, in the case of potassium and ammonium salts, the decreasing order obtained is K_2SO_4 KCO_3 KCl and(NH4)2 SO_4 Na_2CO_3 NH_4Cl respectively. Various thermodynamic parameters for example standard free energy(ΔG_c~Θ), standard enthalpy(ΔH_c~Θ) as well as standard entropy(Δ Sc?)changes of phase separation were also evaluated and discussed in detail on the basis of their behavior.     

Analysis of the thermodynamic feasibility of NOx decomposition catalysis to meet next generation vehicle NOx emissions standards

Free energy minimization calculations are used to determine the thermodynamic equilibrium concentrations of NO_x and other species in stoichiometric and lean gas mixtures over a range of temperatures and compositions. Under lean (excess N₂ and O₂) conditions, the NO decomposition (NO↔(1/2)N₂+(1/2)O₂) and NO oxidation (NO+(1/2)O₂↔NO₂) equilibria impose lower bounds on the NO_x concentrations achievable by thermodynamic equilibration or NO_x decomposition, and these equilibrium NO_x concentrations can be practically significant. Assuming a perfect isothermal catalyst acting on a representative diesel exhaust stream collected over the federal test procedure (FTP) cycle, equilibrium NO_x levels exceed upcoming California Low Emission Vehicle II (LEV-II) and Tier II NO_x emissions standards for automobiles and trucks at temperatures above approximately 800 K. Consideration of a perfect adiabatic catalyst acting on the same diesel exhaust shows that equilibrium NO_x values can fall below NO_x emissions standards at lower temperatures, but to achieve these low concentrations would require the catalyst to attain 100% approach to equilibrium at very low temperatures. It is concluded that NO_x removal based on a thermodynamic equilibrating catalyst under lean exhaust conditions is not practically viable for automotive application, and that to achieve upcoming NO_x standards will require selective NO_x catalysts that vigorously promote NO_x reactions with reductant and do not promote NO decomposition or oxidation. Finally, the ability of a selective NO_x catalyst system to reduce NO_x concentrations to or below thermodynamic equilibrium values is proposed as a useful measure for selective catalytic reduction (SCR) activity.     

An Evaluation of Vaporizing Rates of SiO2 and TiO2 As Protective Coatings for Ultrahigh Temperature Ceramic Composites

For temperatures >1973 K, the thermodynamic and kinetic analyses of the major gaseous species for a liquid titanate layer would vaporize significantly less than a silicate layer, when considering these layers as a protective barrier for ultrahigh temperature ceramic composites. At 2500 K, the major species is TiO( g ) with p _{TiO( g )}=0.1 kPa compared with SiO( g ) with p _{SiO( g )}=1.3 × 10³ kPa at the Ti/TiO₂ and Si/SiO₂ equilibrium, respectively. The SiO( g ) attains a partial pressure greater than ambient pressure at 2500 K even with a thermodynamic activity of 0.01 considering equilibration with a silicide (e.g., TiSi _x ). In addition, at 2500 K the TiO₂ layer would vaporize at a rate of 0.23 mm/s compared with the SiO₂ layer's loss rate of 207 mm/s. Although the oxygen diffusivity and permeability through titanate solutions must be further analyzed, the thermodynamic and kinetic analyses for vaporization indicate a longer duration for a liquid titanate than for a liquid silicate layer at ultrahigh temperatures.     

Thermodynamic Activities in B2O3-SiO2 Melts at 1475 K

Eight glass samples in the B₂O₃-SiO₂ system with compositions from 20 to 90 mol% B₂O₃ were prepared. The equilibrium vaporization was studied by Knudsen effusion mass spectrometry at temperatures between 1450 and 1500 K. B₂O₃ ( g ) was the most abundant boron-containing species in the vapor; no silicon-containing gaseous species were detected. Thermodynamic activities of B₂O₃ in the liquid were determined at 1475 K. Thermodynamic activities of SiO₂ and integral excess Gibbs energies were estimated from the thermodynamic activities of B₂O₃. The thermodynamic data support the results obtained by other methods indicating the existance of a miscibility gap in the metastable liquid.     

Vaporization Studies of the La2O3–Ga2O3 System

The vaporization of the samples of the compositions Ga₂O₃+ LaGaO₃, LaGaO₃+ La₄Ga₂O₉, and La₄Ga₂O₉+ La₂O₃ was investigated using Knudsen effusion mass spectrometry in the temperature range 1494–1937 K. The partial pressures of the gaseous species O₂, Ga, GaO, Ga₂O, and LaO were determined over the samples investigated. The equilibrium partial pressures were used for the calculation of the thermodynamic activities of the components at 1700 K. Gibbs energies of formation of LaGaO₃( s ) and La₄Ga₂O₉( s ) at 1700 K from the component oxides were derived from the thermodynamic activities as −46.4 ± 4.7 and −99.2 ± 7.9 kJ·mol⁻¹, respectively. The results were compared with the literature data obtained using other methods.     

Interaction of cetyltrimethylammonium bromide with cefixime trihydrate drug at different temperatures and compositions: Effect of different electrolytes

Herein,conductivity measurements have been carried out to explore the interaction between cetyltrimethylammonium bromide(CTAB,a cationic surfactant) and antibiotic drug(cefixime trihydrate(CMT)) in water and also in occurrence of inorganic salts(NaCl,Na_2 SO_4 and Na_3 PO_4) over the temperature range of 303.15-323.15 K with an interval of 5 K.In all cases,two critical micelle concentrations(c~*) were achieved for the CMT-surfactant system.Addition of CMT drug to CTAB solution decreases the values of c~*which indicates the interaction between CMT and CTAB.Both values of c~*for CMT-CTAB mixture in the presence of salts are lower in magnitude compared to the aqueous medium which indicates that micellization of the CMT-CTAB mixed system is favorable in salt solution.The values of △G_m~0 were obtained to be negative indicating the spontaneity of the micellization process and the extent of spontaneity further increases by means of rising temperature.The obtained outcomes from the ΔHm0 and ΔSm0 values disclose that the interactions between CMT and CTAB are mostly electrostatic along with hydrophobic in nature.The thermodynamic parameters of transfer and enthalpy-entropy compensation phenomenon were also determined and discussed in detail.     

Gibbs Energy Change of Carbothermal Nitridation Reaction of γ-AlON and Its Thermodynamic Stability

In order to determine the standard Gibbs energy change of carbothermal nitridation reaction of γ-aluminum oxynitride spinel, γ-AlON, the equilibrium N₂–CO gas compositions coexisting with γ-AlON, aluminum nitride (AlN), and graphite have been measured by means of gas chromatography at elevated temperatures. From the results obtained, the standard Gibbs energy change has been determined at temperatures ranging from 1912 to 2002 K , where γ-AlON is expressed as Al_{(64+ x )/3} V _{(8− x )/3}O_{32− x} N _x ( V : vacancy). Moreover, the thermodynamic stability in the homogeneous phase region of γ-AlON has been evaluated by a thermodynamic model of γ-AlON together with the experimental results.     

Phase Relations in the System La-Rh-O and Thermodynamic Properties of LaRhO3

Phase relations in the system La-Rh-O at 1223 K have been determined by examination of equilibrated samples by optical and scanning electron microscopy, powder X-ray diffraction (XRD), and energy-dispersive analysis of X-rays (EDAX). Only one ternary oxide, LaRhO₃, with distorted orthorhombic perovskite structure ( Pbnm, a = 0.5525, b = 0.5680, and c = 0.7901 nm) was identified. The alloys and intermetallics along the La-Rh binary are in equilibrium with La₂O₃. The thermodynamic properties of LaRhO₃ were determined in the temperature range 890 to 1310 K, using a solid-state cell incorporating yttria-stabilized zirconia as the electrolyte. A new four-compartment design of the emf cell was used to enhance the accuracy of measurement. For the reaction
The compound decomposes on heating to a mixture of La₂O₃, Rh and O₂. The calculated decomposition temperatures are 1843 (± 5) K in pure O₂ and 1728 (± 5) K in air at a pressure of 1.01 × 10⁵ Pa. The phase diagrams for the system La-Rh-O at different partial pressures of oxygen are calculated from the thermodynamic information.