A critical transition rule for broadening exponent of fluctuation and its effect on dissipation in chemical reaction-heat conduction coupling systems

A stochastic model of chemical reaction-heat conduction-diffusion for a one-dimensional gaseous system under Dirichlet or zero-fluxes boundary conditions is proposed in this paper. Based on this model,we extend the theory of the broadening exponent of critical fluctuations to cover the chemical reaction-heat conduction coupling systems as an asymptotic property of the corresponding Markovian master equation (ME),and establish a valid stochastic thermodynamics for such systems. As an illustration,the non-isothermal and inhomogeneous Schl-gl model is explicitly studied. Through an order analysis of the contributions from both the drift and diffusion to the evolution of the probability distribution in the corresponding Fokker-Planck equation(FPE) in the approach to bifurcation,we have identified the critical transition rule for the broadening exponent of the fluctuations due to the coupling between chemical reaction and heat conduction. It turns out that the dissipation induced by the critical fluctuations reaches a deterministic level,leading to a thermodynamic effect on the nonequilibrium physico-chemical processes.

Chemical Thermodynamic Analysis of Silicon Doping in MOCVD of GaAs System

With chemical thermodynamic method, enthalpies, entropies and heat capacities of (SiH3)nAsH3-n (1&len&le3), (CH3)4-mSiH4-m (1&lem&le4) and their radicals were calculated. Homogeneous reaction equilibrium of 65 gas phase species in SiH4 (or Si2H6) doped MOCVD GaAs by TMG and AsH3 system was analyzed, the relations of gas phase partial pressures with growth temperatures and input partial pressures were calculated. When the gas phase is saturated with a GaAs: Si solid, the gas phase partial pressures and solid phase silicon impurity (SiGa-As, Ga-SiAs, SiGa-SiAs) concentrations were calculated under different growth temperatures and input partial pressures. With the above results, some of the Si doping behavior in MOCVD of GaAs were explained.

Fluctuation theorem for entropy production in a chemical reaction channel

Fluctuation theorem for entropy production in a mesoscopic chemical reaction network is discussed. When the system size is sufficiently large, it is found that, by defining a kind of coarse-grained dissipation function, the entropy production in a reversible reaction channel can be approximately described by a type of detailed fluctuation theorem. Such a fluctuation relation has been successfully tested by direct simulations in a linear reaction model consisting of two reversible channels and in an oscillatory model wherein only one channel is reversible.

Catalysts and thermodynamic coupling of chemical reactions

The condition of occurrence of the thermodynamic coupling of chemical reactions is analysed from kinetics. It is found that the thermodynamic coupling is impossible for those reactions which obey kinetically the mass action law. The thermodynamic coupling of chemical reactions is further analysed in the case with catalyst. It is found that the thermodynamic coupling which is impossible without catalyst may become possible by introducing proper catalyst into the system. This implies that the catalysts can change not only the rates of chemical reactions, but also the behaviors of thermodynamic coupling of chemical reactions, including the direction of some reactions. Such role of catalysts comes into play not by changing the total free energy of the system, but by changing the reaction mechanism.

Thermodynamics and kinetics of hydriding and dehydriding reactions in Mg-based hydrogen storage materials

Mg-based materials are one of the most promising hydrogen storage candidates due to their high hydrogen storage capacity,environmental benignity,and high Clarke number characteristics.However,the limited thermodynamics and kinetic properties pose major challenges for their engineering applications.Herein,we review the recent progress in improving their thermodynamics and kinetics,with an emphasis on the models and the influence of various parameters in the calculated models.Subsequently,the impact of alloying,composite,and nanocrystallization on both thermodynamics and dynamics are discussed in detail.In particular,the correlation between various modification strategies and the hydrogen capacity,dehydrogenation enthalpy and temperature,hydriding/dehydriding rates are summarized.In addition,the mechanism of hydrogen storage processes of Mg-based materials is discussed from the aspect of classical kinetic theories and microscope hydrogen transferring behavior.This review concludes with an outlook on the remaining challenge issues and prospects.

Research on development of in situ titanium matrix composites and in situ reaction thermodynamics of the reaction systems

The in situ synthesis method for titanium matrix composites （TMCs） has obvious technical and economical advantages over other traditional methods. Ultrafine reinforcement particles were formed in situ by chemical reaction between elements or between elements and compounds. Using the approach, contamination at the composite matrix/reinforcement particle interface did not occur, interface bonding was good, and the reinforcement particle was thermodynamically stable. The stage of development of the preparation process for in situ TMCs as well as the thermodynamic analysis of the possible in situ reaction systems was described.

Syngas production from chemical looping reforming of ethanol over iron-based oxygen carriers: Theoretical analysis and experimental investigation

Chemical looping reforming(CLR)is a recent trend for syngas production,which has several merits compared to the conventional manner.One of the most important issues for CLR is to find low-cost material as oxygen carriers,so iron is a promising candidate.This paper contributes to testing the thermodynamic ability of iron-based oxygen carrier for chemical looping reforming of ethanol(CLRE).Iron thermodynamically investigated in temperature 100–1300℃and excess oxygen number(φ)0–4.It was found that the temperature andφhave an apparent effect on the gaseous composition produced from the process.Increases in temperature within the range of 100–1300℃enhanced syngas generated and reduced coke formation and CH4.Whereas,increasedφ,particularly at higher temperatures,had also enhanced syngas production as well as reduced coke formation.However,increasingφfor values beyond one had decreased syngas and not significantly reduced coke deposition.Moreover,an experimental investigation was carried out in a fixed bed reactor for more in-depth verification of iron ability as an oxygen carrier through using magnetite ore(mainly Fe3O4).It found that the effect of temperature on syngas production was consistent with that calculated thermodynamically,as syngas increased with raising the temperature through the CLRE.

Thermodynamic Analysis of Formation of Low-carbon Olefins via Coal Gasification Coupling C_1 Reaction

The complex reaction system of the coal gasification coupling C1 reaction was analyzed based on the principles of thermodynamics. The results show that an increase in the temperature is beneficial to the generation of hydrocarbons with high carbon-atom contents, in which the alkane yield is higher than the alkene yield. The complex reaction system consisting of C, H20, CO, CO2, H2, C2H4, C3H6 and C4Hs was studied, and the obtained results indicated that when the maximum mole fraction content of C2-C4 olefins was regarded as the optimized objective function, the optimum temperature was approximately 648 K, the pressure was 0.1 MPa, the feed ratio was approximately 0.6, and the maximum mole fraction content of C2-C4 olefins was approximately 28.24%. The thermodynamic simulation and calculation of the complex reaction system can provide a basis for the determination and optimization of actual process conditions and are therefore of great theoretical and practical significance.

Interface reaction and thermodynamic analysis on Al_2O_3-SiO_(2(sf))/AZ91D composite

Al2O3-SiO2(sf)/AZ91D composite was fabricated by squeezing infiltration using preform made of crystallized aluminum silicate short fibers as reinforcement and aluminum phosphate as binder. The interfacial reaction products were investigated by optical microscopy, X-ray diffractometry, scanning electron microscopy, and the thermodynamics was discussed. It is shown that alumina silicate fibers are ideal candidates for the reinforcement of the Mg alloy matrix composites, and the perfect strong interfaces were formed by the chemical reaction between Mg in the magnesium alloy matrix and aluminum phosphate binder through generation of MgO particles. In addition, brittle Mg2Si phase was precipitated at the interface through the reaction between amorphous SiO2 and Mg in the magnesium alloy matrix, which affects the mechanical property of the composite.

Reaction mechanisms of low-grade molybdenum concentrate during calcification roasting process

The effects of Ca-based additives on roasting properties of low-grade molybdenum concentrate were studied. The resultsshow that calcium-based additives can react with molybdenum concentrate to form CaSO4 and CaMoO4. The initial oxidationtemperature of MoS2 is 450℃, while the formation of CaMoO4 and CaSO4 occurs above 500℃. The whole calcification reactionsare nearly completed between 600 and 650℃. However, raising the temperature further helps for the formation of CaMoO4 but isdisadvantageous to sulfur fixing rate and molybdenum retention rate. Calcification efficiency of Ca-based additives follows theorder： Ca（OH）2〉CaO〉CaCO3. With increasing the dosage of Ca（OH）2, the molybdenum retention rate and sulfur-fixing rate rise, butexcessive dosages would consume more acid during leaching process. The appropriate mass ratio of Ca（OH）2 to molybdenumconcentrate is 1：1. When roasted at 650 ℃ for 90 min, the molybdenum retention rate and the sulfur-fixing rate of low-grademolybdenum concentrate reach 100% and 92.92%, respectively, and the dissolution rate of molybdenum achieves 99.12% withcalcines being leached by sulphuric acid.

Thermodynamic study and methanothermal temperature-programmed reaction synthesis of molybdenum carbide

Nanostructured molybdenum carbide （Mo2C） was successfully prepared from molybdenum trioxide （MoO3） using methanothermal temperature-programmed reaction. Thermodynamic analysis indicated that in presence of methane, the formation of Mo2C from MoO3 occurs through the path of MoO3 → MoO2→ Mo2C. The carburized MoO3 was characterized using X-ray diffraction （XRD）, CHNS/O analysis, Brunauer-Emmett-Teller （BET） analysis, and field-emission scanning electron microscopy （FESEM）. At final carburization temperatures of 700 and 800℃ and at methane contents ranging from 5vol% to 20vol%, Mo2C was the only solid product observed in the XRD patterns. The re- suits indicated that the effect of methane content on the formation of the carbide phase is substantial compared with the effect of carburization time. Elemental analysis showed that at a final temperature of 700℃, the carbon content of carburized MoO3 is very close to the theoretical carbon mass percentage in Mo2C. At higher carburization temperatures, excess carbon was deposited onto the surface of Mo2C. High-surface-area Mo2C was obtained at extremely low heating rates; this high-surface-area material is a potential electrocatalyst.

Thermodynamic analysis of combined reforming process using Gibbs energy minimization method: In view of solid carbon formation

Thermodynamic analysis was applied to study combined partial oxidation and carbon dioxide reforming of methane in view of carbon formation. The equilibrium calculations employing the Gibbs energy minimization were performed upon wide ranges of pressure （1-25 atm）, temperature （600-1300 K）, carbon dioxide to methane ratio （0-2） and oxygen to methane ratio （0-1）. The thermodynamic results were compared with the results obtained over a Ru supported catalyst. The results revealed that by increasing the reaction pressure methane conversion decreased. Also it was found that the atmospheric pressure is the preferable pressure for both dry reforming and partial oxidation of methane and increasing the temperature caused increases in both activity of carbon and conversion of methane. The results clearly showed that the addition of O2 to the feed mixture could lead to a reduction of carbon deposition.

Physical-Chemical Characterization of Nanodispersed Powders Produced by a Plasma-Chemical Technique

This article presents a review on the physical-chemical properties and characteristics of plasma-chemically produced nanodispersed powders （NDP）, such as metals, oxides, nitrides, carbides, and catalysts. The plasma-chemical preparatior~ of the powders was carried out in thermal plasma （TP） created by means of high-current electric arcs, plasma jets, high-frequency （HF） discharges, etc. We also discuss certain properties and characteristics of the NDPs, which are determined largely by the conditions of preparation.

Ternary phase diagrams and solvate transformation thermodynamics of omeprazole sodium in different solvent mixtures

Omeprazole sodium(OMS), a typical non-hydrogen bond donors API, is only available in solvates so far, including monohydrate, ethanol solvate and methanol solvate. The methanol solvate was found for the first time. Solvate transformation thermodynamics of OMS was studied in this paper. First, the ternary phase diagrams forming two solvates for OMS in binary solvent mixtures including methanol + water, ethanol + water, and methanol+ ethanol were measured at temperature ranging of T =(278.15 to 313.15) K under atmospheric pressure. Further, the standard equilibrium constants of the solvate transformation reactions were evaluated according to the chemical reaction isothermal equation. The standard molar Gibbs free energy, the standard molar enthalpy, and the standard molar entropy of solvate transformation reactions were then calculated based on van't Hoff equation. Moreover, the thermodynamic stability of the OMS solvate was analyzed based on phase diagram. The results are of great importance to develop a crystallization process for manufacturing OMS solvate, and could be helpful to other solvate transformation research.

负温度系数区域内RP-3喷气燃料表征燃料化学反应动力学分析

为探究喷气燃料(RP-3)在不同条件下负温度系数(NTC)区域内的反应路径、敏感反应以及小分子基元团的影响规律,以CRECK小分子详细机理为核心,基于解耦法耦合正十二烷、正丁基环己烷、正丁基苯简化机理,构建得到RP-3多组分表征燃料化学反应动力学详细机理;并在不同压力、燃料/空气质量比工况下对其NTC区域内的燃烧过程进行了敏感性分析、组分含量变化分析以及组分间交互作用路径分析。结果表明:NTC区域内反应H_(2)O_(2)(+M)=2OH(+M)(M为反应中第三体)是最重要的着火促进反应;不同反应条件下O_(2)、CH_(4)、C_(2)H_(4)的陡降时刻与CO_(2)的激增时刻均与燃料的着火延迟期表现出极高的吻合度;压力与燃料/空气质量比的改变仅会影响反应路径的占比。

废旧镍基高温合金浸出液中铬铝的分离与回收

采用共沉淀法从镍基高温合金的硫酸浸出液中提取分离铬和铝,在热力学分析基础上,研究确定了铬铝沉淀分离的最佳工艺流程及技术参数。热力学分析表明,pH值在4.6~5.4范围内,溶液中的Cr^(3+)和Al^(3+)能够完全沉淀,而Ni^(2+)和Co^(2+)不会发生沉淀。氢氧化钠调节浸出液pH值为4.76,80℃反应20 min的条件下,Cr^(3+)、Al^(3+)、Co^(2+)及Ni^(2+)均会发生氢氧化物沉淀,沉淀率分别为99.95%、99.99%、17%及18.3%。Me-OH^(-)系Eh-pH分析表明,pH>13时,E(CrO_(4)^(2-)/CrO_(2)^(-))≈—0.4 V<0,即Cr^(3+)易被氧化为CrO_(4)^(2-),此时Al(OH)3溶解生成AlO_(2)^(-),镍和钴氢氧化物不会溶解。沉淀物在pH=14,H_(2)O_(2)添加量为0.2 mol/L的条件下溶解,铬和铝分别以CrO_(4)^(2-)和AlO_(2)^(-)的形式进入溶液,镍、钴仍然以沉淀的形式存在;溶液中CrO_(4)^(2-)与氯化钡反应形成BaCrO_(4)沉淀,沉淀率为99.83%。随后用氢氧化钠调节溶液pH值为7,析出Al(OH)_(3)沉淀,达到铬和铝分离回收的目的。本研究为镍基高温合金中有价金属的回收提供了一种高效可行的工艺方法。

乙烯基醚系列产品合成过程的热力学研究

乙烯基醚是一类重要的聚合单体,但针对其合成过程的系统热力学分析尚未见报道。分别采用Benson法、Joback法等方法,以经典热力学公式为基础,计算了乙炔与不同醇(甲醇、乙醇、丁醇、异丁醇以及叔丁醇)合成对应乙烯基醚类化合物(乙烯基甲醚、乙烯基乙醚、乙烯基丁醚、乙烯基异丁醚以及乙烯基叔丁醚)的热力学参数,包括在反应温度为283~363 K下的焓变(△_(r) H^(θ))、熵变(△_(r) S^(θ))、吉布斯自由能(△_(r) G^(θ))和反应平衡常数(K)。系统分析和总结了不同结构的醇与乙炔发生亲核加成反应过程的难易程度,以及热力学反应参数的变化规律。结果表明,所有反应均为强放热反应且均可自发进行,反应温度越低反应进行得越彻底。即使在近室温(283 K)条件下,乙烯基醚类化合物仍可顺利合成,且反应温度越低,安全性越高。本研究结果可为乙烯基醚工业化生产提供理论指导。

化学反应焓变实验中误差分析及实验设备改进

化学反应焓变的测定是大学化学实验中的一个经典实验。本文对选取的60名学生的实验报告数据进行了分析,并结合教师在预备实验中发现的问题,对实验数据的误差进行了分析,并提出了实验设备的改进方法。

Study on the mechanism and reaction characteristics of metal-supported phosphogypsum as oxygen carrier in a chemical looping gasification application

This study aimed to explore the chemical looping gasification(CLG)reaction characteristics of the metal-supported composite phosphogypsum(PG)oxygen carriers(OCs)and the thermodynamic mechanism.The FactSage 7.1 thermodynamic simulation was used to explore the oxygen release and H_(2)S removal mechanisms.The experimental results showed that the syngas yield of CLG with PG-CuFe_(2)O_(4)was more than that with PG-Fe_(2)O_(3)20/CuO40 or PG-Fe_(2)O_(3)30/CuO30 OC at 1023 K when the water vapor content was 0.3.Furthermore,the maximum syngas yield of the CO selectivity was 70.3% and of the CO_(2)selectivity was 23.8%.The H_(2)/CO value was 0.78,and the highest carbon conversion efficiency was 91.9% in PG-CuFe_(2)O_(4)at the gasification temperature of 1073 K.The metal-supported PG composite oxygen carrier was proved not only as an oxygen carrier to participate in the preparation of syngas but also as a catalyst to catalyze coal gasification reactions.Furthermore,both the experimental results and FactSage 7.1 thermodynamic analysis revealed that the trapping mechanism of H_(2)S by composite OCs was as follows:CuO first lost lattice oxygen as an oxygen carrier to generate Cu_(2)O,which,in turn,reacted with H_(2)S to generate Cu_(2)S.This study provided efficient guidance and reference for OC design in CLG.

以重油加氢实例展示化工过程分析与合成课程中稳态模拟的正、逆问题求解

本文采用了一种基于数值计算的稳态模拟方法,结合实验获取的重质油加氢脱硫实验数据和模型假设,使用数学模型进行“正、逆问题”求解。通过对重油加氢实例的研究,首先实现了重质油加氢脱硫模型的建立,进而基于实验数据求解了稳态模拟的“逆问题”;其次又基于所建立模型及拟合得到的参数完成了稳态模型“正问题”的求解。“正、逆问题”的求解逻辑,不仅是一种有效的科研手段,更是一项脱胎于工程实际案例的教学素材。通过深入探讨重油加氢实例,并结合正、逆问题求解方法,我们可以为学生提供更全面、系统的化工知识和能力培养。