Thermal decomposition of strontium oxalate — effect of various atmospheres

Decomposition products have been prepared from strontium oxalate monohydrate by heating for 2 h at 410, 470 and 510 °C in presence of air, water vapour at various pressures, nitrogen, hydrogen or carbon dioxide atmosphere. Structural, textural and morphological changes have been studied by X-ray diffraction and electron microscopy; the influence of various atmospheres is discussed. Differential thermal analysis and thermogravimetry reveal that dehydration of the starting material proceeds in two steps: a main dehydration process takes place at 180 °C, followed by the release of a small amount of water (～5%) at 270 °C. Decomposition of oxalate into carbonate covers the range 400 – 480 °C; a very small endotherm is observed at 450 °C, masked by a strong exotherm (530 °C) due to the release of energy probably accompanying the conversion of the amorphous decomposition product of the oxalate into a crystalline form.     

Thermal decomposition of zinc zirconyl oxalate pentahydrate

Thermal decomposition of zinc zirconyl oxalate (ZZO) has been investigated employing thermogravimetric, differential thermal analysis and differential thermogravimetric techniques and chemical analysis. The decomposition proceeds through three steps. The first step is the dehydration of the zinc zirconyl oxalate pentahydrate in the temperature range 303–473 K. The second stage is the decomposition of the oxalate giving an intermediate residue containing both oxalate and carbonate between 473–613 K. The third and final stage is the decomposition of the intermediate between 613–833 K to give zinc zirconate. The infrared spectral and X-ray data confirm the formation of ZnZrO₃.     

Kinetics of pyrolysis of pure and doped cobalt oxalate

The object of the present work was to illustrate the effect of impurities on the kinetics and energetics of the thermal decomposition of pure cobalt oxalate. Cationic impurities like Mg²⁺, Mn²⁺, Fe²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Pb²⁺, Zr⁴⁺ have been introduced into pure cobalt oxalate dihydrate and differential thermal analysis has been used to determine the enthalpy and energy of activation for the decomposition reaction of pure and doped samples.     

十溴二苯醚热解动力学及在聚苯乙烯中的热解行为

十溴二苯醚(decaBDE)是多种聚苯乙烯(PS)类塑料阻燃添加剂,其热解动力学对开发新型高效的电子塑料安全处置技术具有十分重要的意义,为此采用普适积分法成功关联了氮气中decaBDE的热解动力学参数。结果表明:固体decaBDE在306℃时熔融为液相并在400~450℃进一步汽化为气相,热重/红外(TG/IR)分析表明,其气相产物组成具有与decaBDE相同的红外特征;decaBDE热解过程可用三维扩散模型关联。进而通过对比分析decaBDE、PS和含decaBDE的阻燃PS样品的TG实验结果,发现阻燃塑料样品在热解时存在decaBDE与PS间的相互作用,表现为热解起始温度的降低和终止温度的升高。TG/IR分析表明:阻燃塑料样品的热解气相产物中不存在游离的HBr,decaBDE热解时产生的活性基团改变了PS的降解反应历程,使其气相产物具有与1,3-二苯基丁烷类似的红外特征。     

Variation of the specific surface area and porosity of zinc oxide prepared in various atmospheres

Specific surface area and pore structure studies were carried out on zinc oxide samples prepared from zinc oxalate dihydrate by heating at 330 and 370°C and in various atmospheres of water vapour, oxygen and hydrogen. The variation of S_BET with water vapour pressure for the samples heated at 330°C was found to show a behaviour which can be compared with the Smith-Topley effect. For the samples prepared at 370°C, rapid sintering occurred, and the Smith-Topley effect was not followed in this case. Zinc oxide prepared in an oxygen atmosphere gave higher surface area values than that prepared in a hydrogen atmosphere, which is thought to be due to the oxidation of the carbon impurities on the surface. Analysis of nitrogen adsorption isotherms by the t-method revealed the existence of micropores in the sample prepared at 330°C in vacuo. The rest of the samples have wide pores.     

Variation of the specific surface area and porosity of zinc oxide prepared in various atmospheres

Specific surface area and pore structure studies were carried out on zinc oxide samples prepared from zinc oxalate dihydrate by heating at 330 and 370°C and in various atmospheres of water vapour, oxygen and hydrogen. The variation of S_BET with water vapour pressure for the samples heated at 330°C was found to show a behaviour which can be compared with the Smith-Topley effect. For the samples prepared at 370°C, rapid sintering occurred, and the Smith-Topley effect was not followed in this case. Zinc oxide prepared in an oxygen atmosphere gave higher surface area values than that prepared in a hydrogen atmosphere, which is thought to be due to the oxidation of the carbon impurities on the surface. Analysis of nitrogen adsorption isotherms by the t-method revealed the existence of micropores in the sample prepared at 330°C in vacuo. The rest of the samples have wide pores.     

Catalytic pyrolysis of biomass in inert and steam atmospheres

The objective of this study was to investigate thermal conversion of a perennial shrub, Euphorbia rigida biomass sample with catalyst in inert (N₂) and steam atmospheres. Experimental studies were conducted in a well swept fixed bed reactor with a heating rate of 7 °C/min to a final pyrolysis temperature of 550 °C and with a mean particle size of 0.55 mm in order to determine the effect of different atmospheres with various catalyst ratios on pyrolysis yields and characteristics. The catalyst ratios were 5%, 10% and 20% (w/w) under nitrogen atmosphere with flow rates of 50, 100, 200 and 400 cm³/min and steam atmosphere with well-swept velocities of 12, 25 and 52 cm³/min. The optimum oil yield was obtained as 32.1% at the nitrogen flow rate of 200 cm³/min, while it was obtained as 38.6% at steam flow rate of 25 cm³/min when a 10% catalyst by weight according to the biomass was used. Higher oil yields were observed when biomass sample was treated in steam atmosphere than in inert (N₂) atmosphere. The oil composition was then analysed by elemental analyses techniques such as IR and GC-MS. The oil products were also fractionated by column chromatography. The bio-oils obtained at both atmospheres contain mainly n-alkanes and alkenes, aromatic compounds; mainly benzene and derivatives and PAHs, nitrogenated compounds and ketones, carboxylic acids, aldehydes, phenols and triterpenoid compounds. More oxygenated compounds and less substituted alkanes and alkenes were obtained in catalytic pyrolysis of E. rigida in the steam atmosphere. The experimental and chemical characterisation results showed that the oil obtained from perennial shrub, E. rigida can be used as a potential source of renewable fuel and chemical feedstock.     

Thermal decomposition of pure and rhodium impregnated cerium(III) carbonate hydrate in different atmospheres

The thermal decomposition of pure and rhodium impregnated cerium(III) carbonate hydrate in oxidising, reducing and inert atmospheres has been studied using combined thermogravimetry/mass spectrometry (TG/MS) and X-ray photoelectron spectroscopy (XPS). In oxygen, the decomposition of the pure carbonate proceeds in two steps, yielding H₂O,CO₂, and cerium(IV) oxide. In inert or reducing atmospheres, the second decomposition step is shifted towards higher temperatures and is divided into two parts. In the second part, CO₂ evolved is partly reduced by Ce(III) to CO and to elemental carbon, and non-stoichiometric CeO_2–x is formed as the solid product. In the presence of rhodium as a reduction catalyst, decomposition in helium yields hydrogen and less carbon monoxide than that of the pure carbonate, due to the water-gas shift activity of the solid. In hydrogen, quantitative reduction of the carbon dioxide evolved to methane and water is observed when rhodium is present.     

Thermal decomposition of a blackband ironstone. II. Kinetics

Blackband ironstone and siderite have been separately decomposed in a fluidised bed of sand in an atmosphere of nitrogen and the progress of reaction followed by a ‘volatile matter’ test. For the ironstone in the temperature range 370–570°, the residual volatile matter (V_R) after a time (t) between 10 sec and 60 min. was given by the expression V_R = A – B log t, where A and B are constants for a given temperature. The kinetics of decomposition of siderite at 455 and 485° were first-order with an activation energy of 51 kcal. /mole. It is concluded that blackband ironstone appears to decompose by a large number of independent first-order reactions having a range of activation energies showing a peak frequency near 50 kcal.     

Desulfurization of a Turkish lignite at various gas atmospheres by pyrolysis. Effect of mineral matter

An investigation was made of the removal of pyritic and organic sulfur by pyrolysis at ambient pressure of a Turkish lignite under nitrogen and carbon dioxide atmospheres and the effect of mineral matter on the sulfur removal in pyrolysis of HCl and HCl/HF-treated coal under carbon dioxide atmosphere. Results obtained indicated that both pyritic and organic sulfur removal increased with increasing pyrolysis temperature. The pyrolysis in carbon dioxide atmosphere had more effect on the organic sulfur removal at high temperatures. As a consequence of treatment of coal with HCl, pyritic sulfur removal increased but organic sulfur removal decreased. This implies that the removal of carbonates from coal negatively affects the organic sulfur removal. The observed decrease in organic sulfur removal may be related to the decrease in pyrolytic conversion. It was observed that HCl/HF treatment has an increased effect on the pyritic removal and organic sulfur removal during pyrolysis. The increase in organic sulfur removal after HF-treatment therefore might be due to the removal of clay minerals in the raw coal structure. In addition, it may be said that the presence of silicate minerals in the coal matrix can be induced that the easily removable organic sulfur compounds are converted to thermally stable and non-removable organic sulfur compounds (thiophenic or condensed thiophenic compounds) at these temperatures. Increase in the pyritic sulfur removal of HCl-treated and HCl/HF-treated coal samples may be attributed to the fact that increase of mass and/or heat transport in comparison with untreated coal as a result of elimination of mineral matter.     

The pyrolysis of a Wyoming coal in different nonreactive atmospheres

This study investigated how differing nonreactive atmospheres affected the properties of chars produced by coal pyrolysis. Samples of a Wyoming subbituminous coal were first heated at 586°C in helium for 6 hr. They were then heated for another 6 hr at 300°C higher in helium, argon or nitrogen. Weight losses in the chars during the second step were apparently unaffected by the choice of inert environment. Surface characteristics, pore structures, and reactivities of the resulting chars were, however, significantly different as shown by the results of scanning electron microscopy, nitrogen adsorption, carbon dioxide adsorption, and reactivity of the chars in carbon dioxide. Smoothness of the surface, adsorption capacities, N₂ and CO₂ surface areas, and reactivity during gasification all decreased in the direction (in order of inert atmospheres employed) He >Ar >N₂. In addition, there were strong indications that trace contaminants in the inert gases could alter the characteristics of the resulting char markedly.     

Oil-shale pyrolysis: Kinetics and mechanism of oil production

Literature data on the thermal decomposition of the organic material in Colorado oil shale are analysed. Inclusion of a thermal induction period in the data analysis results in a concise interpretation of the kinetics of oil production in terms of a simple mechanism involving two consecutive first-order reactions. The rate constants and activation energies for these two reactions are deduced.     

Isothermal oil shale pyrolysis. 2. Kinetics of product formation and composition at various pressures

A rich (250¦t^?1) Green River oil shale was retorted in a helium atmosphere. Isothermal, isobaric retort runs were conducted over a temperature range of 648–773 K (375–500 °C) and a pressure range of 78–765 kPa (11.3–111 psia). Oil was collected as a function of time. A deasphaltened, dry whole oil product (DDWO) was then separated into five fractions: polars (P), ‘weak’ polars (WP), saturates (S), aromatics (A), and olefins (O). One objective of this work was to determine the effect of pressure on the kinetic rate expressions for product oil and oil fraction formation. As the system pressure increased the kinetic rate constants, and, consequently, the product yield decreased. A second objective of the experimental programme was to determine kinetic rate constants for the five oil fractions. A first-order kinetic rate expression was utilized and kinetic parameters were determined for the product oil and oil fractions at each temperature and pressure studied. The kinetic rate constants flow an Arrhenius temperature dependence in the region 688–773 K (415–500 °C); at lower temperatures a change in the activation energy is observed.     

Kinetics of coke deposition in naphtha pyrolysis

The effect of run time, surface area, reaction temperature and inlet naphtha partial pressure on the rate of coke formation during naphtha pyrolysis has been investigated in a jet-stirred reactor. The pyrolysis products could be predicted by a model developed earlier for naphtha pyrolysis. Various simplified models for the coke formation involving either the reactant or products were postulated and the kinetic parameters determined by a statistical analysis. The rate of coke formation was best modelled by an approximately second order reaction involving the aromatics.     

Photochemical decomposition of oxalate precipitates in nitric acid medium

This work has been performed as a part of the partitioning of minor actinides. Minor actinides can be recovered from high-level wastes as oxalate precipitates, but they tend to be co-precipitated together with lanthanide oxalates. This requires another partitioning step for mutual separation of actinide and lanthanide groups. Accordingly, the objective of this study was to decompose and dissolve oxalate precipitates into a dilute nitric acid solution by using a photochemical reaction. In order to do this, oxalic acid and neodymium oxalate precipitate were used in this study. Neodymium oxalate was chosen as a stand-in element representing americium, curium and lanthanides. As a result, decomposition characteristics of oxalic acid were first investigated and then on the basis of these results, the decomposition of neodymium oxalate precipitates was evaluated. From results using oxalic acid, the oxalate decomposition appeared to take place due to the reaction between the oxalate ion and hydroxyl radical generated from the nitric acid by photo-radiation. And the oxalate decomposition rate was measured in the experiments for various nitric acid contents when a mercury lamp (λ=254 nm) was used as a light source. The maximum decomposition rate was obtained when the nitric acid concentration was around 0.5 M, while the decomposition rate was reduced with an increase in the nitric acid concentration at more than 0.5 M. The photo-decomposition rate of neodymium oxalate precipitates was found to be 0.0034 M/h at the condition of 0.5 M HNO₃.     

不同气氛下磷石膏热脱水特性及动力学比较研究

为研究不同气氛对磷石膏热脱水特性及动力学影响,分别测定了动态空气气氛和N2气氛下,不同升温速率时磷石膏热脱水反应的TG-DTG-DTA同步热分析数据.采用Kissinger法、FWO峰值转化率近似相等法和FWO等转化率法分别计算了磷石膏的热脱水动力学参数.结果表明,两种气氛下,磷石膏的热脱水温度都随升温速率的加快而升高...     

邻苯二甲酸镁的流变相合成及其热稳定性研究

用流变相反应法合成了二水邻苯二甲酸镁。通过元素分析、X-射线粉末衍射、红外光谱确定了它的组成和晶体结构,它为层状结构,属单斜晶系。用TG和DTA研究了它在氮气中的热稳定性,并用GC—MS、XRD表征了热分解产物。二水邻苯二甲酸镁在氮气中热分解分为两步：先失去两个结晶水,最终产物为氧化镁。生成的气相凝聚物成分比较复杂,主要是二苯甲酮、蒽醌。     

Kinetics of xylose dehydration into furfural in acetic acid

In this paper kinetics of xylose dehydration into furfural using acetic acid as catalyst was studied comprehensively and systematical y. The reaction order of both furfural and xylose dehydration was determined and the reaction activation energy was obtalned by nonlinear regression. The effect of acetic acid concentration was also investi-gated. Reaction rate constants were galned. Reaction rate constant of xylose dehydration is k1 ? 4:189 . 1010 ?A.0:1676 exp ?108:6.1000RT . ., reaction rate constant of furfural degradation is k2 ? 1:271 . 104?A.0:1375 exp?63:413.1000RT . and reaction rate constant of condensation reaction is k3 ? 3:4051 . 1010?A.0:1676 exp?104:99.1000RT .. Based on this, the kinetics equation of xylose dehydration into furfural in acetic acid was set up according to theory of Dunlop and Furfural generating rate equation is dd?F.t ? k1?X.0e?k1t?k2?F.?k3?X.0e?k1t?F.. ? 2015 The Chemical Industry and Engineering Society of China, and Chemical Industry Press. Al rights reserved.