A new reaction calorimeter and calorimetric tools for safety testing at laboratory scale

Calorimetry combined with thermal analysis is an essential tool for the evaluation of thermal risks linked with chemical reactions at industrial scale. The energies of synthesis reactions or decomposition reactions as well as the heat capacities of reaction masses can be measured using such techniques. The capacity of the SETARAM differential reaction calorimeter (DRC) to determine essential safety data has been demonstrated with the measurement of heat capacities of cyclohexane and propanoic acid. Results of an industrial reaction are also presented.     

Estimation of kinetic parameters from thermochemical data

A method is described by which kinetic parameters may be calculated from the measured temperature changes caused by the heat produced during a chemical reaction. An isoperibol titration calorimeter with an ampoule-breaking facility is used to obtain the temperature data. The temperature changes resulting from the reaction between tri-isopropyl phosphite and sulphur (S(8)) are used as an example to demonstrate the effectiveness of the method. The temperature changes are used to calculate an enthalpy of reaction. From the enthalpy of reaction and intermediate heats, instantaneous concentrations of the reactants may be calculated.     

On-line reaction calorimetry optimization of safety parameters

When chemical reactions are performed in semi-batch mode and the reaction rate is relatively low, the reactant added may be accumulated. The resulting thermal accumulation is of major concern regarding process safety, as a fault in the cooling system may lead to a run-away reaction. The feed rate in semi-batch processes is usually constant, but this paper discusses methods of optimizing the feed rate interactively, based on the measured heat flow and the calculated amount of compound that has actually reacted. The prerequisite of such procedures is to run the experiments in a reaction calorimeter in which the heat flows can be measured accurately and continuously. For this purpose a ChemiSens reaction calorimeter CPA202, which is calibration free and gives stable, flat ‘zero-line-type’ baselines, was employed.     

Using the Transfer Function of an Isoperibolic Reaction Calorimeter for Thermo-kinetic Analysis

It is an aim of the present work to determine the chemical heat flow rate of a reaction without explicitly solving the heat balance equations. Therefore, it is necessary to calculate the heat flow rate directly from the temperature course of an experimentally determined reaction. For this transformation the transfer function of the calorimeter is needed 1 . An isoperibol reaction calorimeter was used for the experiments. With different calibrations and gained transfer functions, it is shown that the chemical heat flow rate can be determined from the temperature course of a reaction. The evaluation is fast and easy to use, which improves automation and prevents possible input errors.     

A constant heat-flux calorimeter for measuring heat transfer data

A new isothermal calorimeter, designed especially for simultaneously measuring the heat of reaction and the heat transfer data in a reaction solution, is described. The system, called a Constant Heat-Flux Calorimeter, is similar to a differential scanning calorimeter in terms of direct calorimetric measurement of the energies of reaction, but differs from the conventional calorimeters described in the literature. With this device, one recorded output in a temperature control circuit is a linear function of change in energies of reaction, and second in a differential temperature control circuit is found to be proportional to a resistance to heat transfer in a solution. The performance of the calorimeter was evaluated on the basis of some results on heat transfer data of aqueous solution of polyethylene glycol and on solution polymerization of styrene at constant temperatures.     

Communication between calorimetric experiment and continuous data evaluation during the incomplete reaction run

The kinetic control of exothermic reactions plays an important role in chemical safety technology. Predictions of thermal explosions by runaway, e.g. redox reactions, poly reactions, and decompositions, are required in case of simple as well as of complex reactions. Activation parameters of chemical reactions are often stressed by systematic errors which are caused by failures in accuracy of measurement and calibration. The influence of systematic errors for some selected reactions has been investigated by the software package TA-kin. The coupling between continuous data evaluation software and the precision calorimeter ACTRON 5.0, including a safety scenario equipment, was established to test the validity of calculated runaway predictions under practical conditions. Measured data are applied for kinetic evaluations by nonlinear optimization methods in real time. In this way, the experimental investigations of reaction systems become possible beyond the point of no return without any danger for the laboratory.     

Thermische Analyse der Reaktivität vono- undp-Chlornitrobenzen

Because there is risk of autocatalytic reduction, the conversion of chloronitrobenzene with alkaline alcohol is important in safety management. The influence of several parameters on the reaction will be described. The experiments were realized in a non commercial calorimeter, equipped with for the precision calorimeter ACTRON developed hard- and software. For the non-linear kinetic evaluation of the experiments the program TA-kin was used.It could be ascertained, that the calorimetry is applicable for the investigation of the influence of parameters on the conversion of chloronitrobenzene.

     

The cis-trans Isomerization of Azobenzene in the Molten State: A useful test reaction for the kinetic evaluation of DSC measurements

Contrary to the situation in the field of temperature, heat and heat flow rate calibration, so far no generally accepted and easily practicable chemical reaction exists with regard to a kinetic evaluation. A possible reaction would be the well-known first-order cis-trans isomerization of subcooled liquid azobenzene. Surprisingly, the evaluation of measurements performed with a power compensated calorimeter yields activation parameters, which are dependent on the heating rate. The desmearing of the curves does not produce any improvements. However, constant activation parameters are obtained, if a small self-heating of the sample during the exothermic reaction is taken into account.This revised version was published online in November 2005 with corrections to the Cover Date.     

Investigation of run-away reactions by precision calorimetry

Investigations in chemical safety are necessary in case that the reaction course depends on changes of the reaction conditions sensitively. To break off a conversion in a hazardous situation, the precision calorimeter ACTRON 5 is equipped with two safety pumps. They empty and rinse the reactor with cold solvent. The pumps will be activated automatically. For testing the calorimeter the complex reaction of chloronitrobenzene with alkalined alcohol was used and break off at predefined conditions. The possibility of the kinetic estimation of these break-off files is shown.     

Continuous gradient method in flow microcalorimetry: Part II: Application to solution equilibria

A flow microcalorimeter operating in mixing mode generates a type of “continuous titration” when one of the feeding pumps is connected to a continuous gradient generating device. The proper correction of the instrumental signal for the thermal lag of the calorimeter can be performed by chemical calibration, through an evaluation of the parameters of Tian's equation, modified for the microcalorimeter. This equation relates the instrumental signal to the actual power developed by the reaction. This paper shows how a continuous exponential gradient method can be applied to the determination of the enthalpy changes of metal-ligand-proton equilibrium reaction in solution. The enthalpies obtained for the protonation of D-cycloserine and for the formation of CuL and CuL₂ complexes in the Cu(II)-Glycine system are in substantial agreement with published values. The computer programs, in BASIC language on an IBM-XT PC, used to process gradient data, are presented.     

Calorimetry and potentiometry of chemical oscillations in Briggs-Rauscher reactions with simultaneous measurements of the produced oxygen volume

The Briggs-Rauscher reaction is known as a nonlinear and non-equilibrium chemical oscillation reaction. The reaction solution is composed of malonic acid as organic substrate, hydrogen peroxide and iodate in sulphuric acid as oxidizing agent, and manganese (II) as metal catalyst. The calorimetric behaviour, in terms of the total heat Q and the heat evolving rate q for each chemical oscillation, was followed with the use of a heat exchange calorimeter of the batch type assembled by the authors. Simultaneously, the concentration of iodide ions produced as the intermediate species was measured as the potential difference E by the common potentiometric cell incorporated in the calorimeter and the released oxygen volume G was also observed by a simple flowmeter. The starting point of the peak on the curve of q against time t coincided with that in the curve of E against t. The switching concentration of iodide between radical and nonradical paths was calculated from literature values of rate constants. The heat evolving period of Q coincided with the period in the radical path. The curve of Q against t also coincided with that of G against t. The total volume of released oxygen was larger than that calculated from the stoichiometric reaction formula.     

Assessing thermal hazards of reaction mixtures

A strategy for assessing thermal hazards of chemical manufacturing processes is presented with an emphasis on new developments in the areas of the desired and decomposition reaction research. In the case of the desired reaction, the application of a computer program, CAMEO, for assessing synthetic reaction pathways, and enthalpies, and for evaluating the chemistry of specific failure modes is demonstrated. For the decomposition reaction, an unexpected decomposition destabilization phenomenon in mixtures was observed, which clearly demonstrated the need for chemical/solvent mixture testing to provide reliable thermochemical data for reaction hazard assessment. An application of the reaction mixture hazard evaluation strategy to a chemical process is presented.The authors would like to thank P. R. Kingsley for carrying out the experimental work necessary to complete this project. The authors also wish to acknowledge the support of Eastman Kodak Company in the preparation of this study.     

Hydrolysis of a two-membered silica ring on the amorphous silica surface

We have combined density functional theory (DFT) with classical interatomic potential functions to model hydrolysis of amorphous silica surfaces. The water-silica interaction is described by DFT with incorporation of a long-range elastic field described by classical interatomic potentials. Both physisorption and chemisorption of water on a surface site, known as the two-membered silica ring, are studied in detail. The hybrid quantum-mechanical and classical mechanical method enables more realistic treatment of chemical processes on an extended surface than previous methods. We have studied cooperative events in the hydrolytic reactions and discovered a new reaction pathway that involves a double proton transfer process. In addition, the evaluation of the total energy in a hybrid quantum-mechanical and classical mechanical system is discussed.     

RD-I型热导式自动量热计的研制

在文献[10]、[12]的基础上,研制了一种能在常温到150°C的较大温度范围内工作的“RD-Ⅰ型热导式自动量热计”。本文报导了仪器结构和工作原理。通过电能测定,证明仪器设计合理,工作正常。其性能完全符合Tian氏方程的要求。而且重现性好(相对精度为0.5%-1%左右),灵敏度高(对1卡以上的热效应能够准确地进行测量)。量热计通过光笔记录仪实现了测量记录的自动化。     

A direct isoperibol aneroid calorimeter

An aneroid isoperibol calorimetric apparatus is described which is particularly suitable for measurement of the reaction heat among solids. Such an apparatus contains four calorimeters and allows to carry out differential measurements. Each calorimeter includes two small electric furnaces employed for heating the solid mixture until the reaction begins and for the successive electric calibrations, respectively. The temperature trend of each calorimeter is followed by 80 thermocouples in series. The instrument characteristics are briefly discussed. Examples of its employment in the alloy thermochemistry are given.     

Thermoanalytische methoden in der chemischen verfahrensentwicklung

Thermal analysis methods are used in process development for the investigation of chemical kinetics, for the evaluation of thermal hazards and for the determination of caloric design data. For these applications heat-flow methods are preferably used.This paper gives a survey of methods and instruments, and then presents a new “bench scale heat-flow calorimeter”. The use of this new instruments is illustrated by investigations on the formation of a Grignard compound and on the isomerisation of trimethyl-phosphite.     

Application of a new type of safety calorimeter

Safety production in chemical plants is a high-priority task, especially as concerns reactions which can change mechanism suddenly under defined conditions, e.g. from a simple well-defined to an undesired autocatalytic reaction. An example of this kind, the reaction of chloronitrobenzene with alkaline alcohol, was investigated with the new adiabatic precision calorimeter ACTRON 5, designed with a safety concept. It is shown that the reaction can be interrupted safely under predicted conditions.     

Fitting isoperibolic calorimeter data for reactions with pseudo-first order chemical kinetics

The non-linear least squares fitting of the chemical heat flow and the reactor temperature are compared for reactions with pseudo-first order chemical kinetics carried out in an isoperibolic calorimeter operating quasi-isothermally. Both methods give very similar results for the reaction rate constant and enthalpy of reaction but fitting the reactor temperature appears to have some advantages especially when there is an enthalpy of mixing of the reagents.     

热导式热量计冷却常数的化学标定法

热导式热量计是热力学研究的重要工具,其量热体系之仪器常数的标定目前所广泛采用的方法是电能标定法,有时也采用化学标定法．前者简单、方便,能满足热静力学与热动力学研究中的需要,但电能标定所得仪器常数与化学反应时的仪器常数不一定完全相同［１］,特别是有些热...     

Performance validation of step-isothermal calorimeters

Isothermal calorimetry is becoming indispensable as a tool for the study of a wide variety of systems. As with all scientific instruments it is essential that robust calibration routines be developed in order to validate the data obtained. Chemical test reactions offer many advantages over (the traditionally used) joule effect heating methods, not least because they have the potential to validate instrument performance (i.e. they can be used to assess all aspects of calorimeter operation). In this work the results of a validation exercise, conducted by Thermal Hazard Technology as part of an installation routine, using the base catalysed hydrolysis of methyl paraben are discussed. In the case described, a systematic misreporting of the reported temperature of a calorimeter was identified, caused by an upgrade to the calorimeter's firmware, a discrepancy which may not have been noted using traditional electrical calibration methods and one which highlights the importance of both manufacturers and end-users adopting chemical test reactions into their test and validation routines.