Search

For the calculation of kinetic parameters from thermal data files numeric optimization has been well introduced. But suitable starting values near the global minimum of the sum of deviation squares are needed for a successfully parameter estimation. Namely the search for starting values requires a lot of time and diminishes the effectiveness of the total procedure. Therefore we have developed an algorithm of the automatic search of starting values for the optimization of activation energy end frequency factor of a chemical reaction. This search procedure uses the knowledge of the specific course of the corresponding SDS surface in the near of its global minimum. In this area the SDS describes two plateaus separated by a narrow valley. The search procedure avoids starting values at one of these plateaus. This PC program is part of the complex software package TA-kin v3.3 for kinetic evaluation of thermal measurements.

Adiabatic calorimetry is a suitable method for investigations of reactions because the generated heat remains completely in the reactor. For the investigation of organic reactions, the adiabatic precision calorimeter ACTRON 5 is used. The alcoholyses of phenyl isocyanate and 1,2-butyleneoxide were investigated. The temperature-time course was estimated by means of the nonlinear program TA-kin. Inclusion of the concentration-time course in the estimation procedure led to an increase in the reliability of the parameters. Probes were taken during isoperibolic measurements and were analysed by means of HPLC.

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.

All temperature sensors have a finitely time constant. The influence of the sensor time constant gts on the results of kinetic evaluation is demonstrated at four reaction types. The ignorance of the sensor indolence gives incorrect activation parameters. Therefore the determination of Τs is necessary.

The method of computer-experiments can be applied successfully on the radical depolymerization under inclusion of initiation, depropagation and termination. The comfortable PC-program ‘TA-kin’ for the non-linear estimation of parameters for TG- or DSC-experiments was applied to the determination of activation parameters of depropagation and termination. Therefore the overall-evaluation of three or more data sets is a prerequisite. The determination of kinetic parameters runs satisfactory if the measured curves are strongly different, e.g. by varying the heating rate, including acceptable experimental errors. Several recommendations for laboratory experts are given. A great support for a very sufficient estimation is the inclusion of simultaneous analysis of the radical concentration.

Four computer programs as well as one demo-version for non-linear evaluation of kinetic data in thermal analysis and calorimetry, were presented. The multi-task program TA-kin meets all mathematical requirements for solving the numerical assignments. It is shown that the so-called compensation effect is due to the mathematical structure of the Arrhenius equation. Several applications of TA-kin to a lot of DSC- and TG-measurements and isoperibolic batch experiments as well as adiabatic semi batch experiments realized by precision calorimetry have been discussed.

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.

The investigation of the hazardous potential of reaction courses is very important for the chemical industry. Compared with the isoperibolic the adiabatic calorimetry has essential advantages for kinetic evaluations, because corrections of heat flux are not necessary. With the adiabatic precision calorimeter ACTRON 5 is the investigation of reaction courses in small volumes possible. The possibilities of the nonlinear investigation program TA-kin are shown with examples of Semi-Batch-Measurements. With this program the change in heat capacities whilst encoring the second component is included.

Reactions with large negative enthalpy changes are often encountered in the chemical industry. Sometimes they give rise to technical dangers and hazards, including explosions. This investigation concentrates on examination of adiabatic temperature-time-curves and gives non-linear optimization procedures for obtaining kinetic parameters of simple decompositions,e.g. o-nitrobezaldehyde, two types of autocatalysis, consecutive reactions and competitive consecutive reactions. The advantage of this computing method is that only differential kinetic equations are needed.

A computer-aided calorimeter for the region of −15° to 180°C and with a resolution 2·10−5 K is described. The reactive volume may be varied from 10 to 100 ml.

For kinetic evaluation by TG and DSC of simple and complex reactions we used a direct fit on the basis of TG differential equations and DSC non-linear equations. The advantages of an overall evaluation, i.e. the simultaneous inclusion of all data sets at different heating rates, are described. TG and DSC measurements of the dehydration of calcium oxalate monohydrate and the decomposition of calcium oxalate are used as examples.

Telomerization of isoprene is characterized by intense thermal effects. The reaction system di-μ-chlorobis(η3-allyl)-dipalladium(II): tri-n-butylphosphine: sodium methylate: isoprene=1∶2∶3∶200 in a solvent-mixture of methanol∶benzene=1∶3 is used as a model. It is concluded that reaction of the catalyst combined with reduction of Pd(II) is followed by the telomerization reaction. There is a marked influence of Pd and phosphine concentration in the catalyst as well as concentration of isoprene. Results are available to optimize technical applications.

The alcoholysis of triethylaluminium can be investigated by DTA in the liquid phase. The reaction enthalpy of the alcoholysis with primary alcohols is from −150 to −170 kJ mole−1 in tetrahydrofuran/toluene as solvent. The reaction rate in pure hydrocarbons is higher than in the presence of Lewis bases. The reaction mechanism is probably ofSE2 type and the reactivity decreases in the sequence primary, secondary, tertiary alcohol. In the second step of substitution the diethylaluminium alkoxides are less reactive than triethylaluminium because of the stronger association of the alkoxides. For the turnover of two moles of alcohol with one mole of triehylaluminium two DTA peaks appear in accordance with consecutive reactions.

Das Problem der rationellen Losung des Zeitintegrals stand bei der kinetischen Auswertung nichtisothermer Prozesse haufig zur Diskussion. Nun werden fur lineare und nichtlineare Aufheizung gemas dT/dt=Q·Tb mitb von 4 bis −2 Auswerteverfahren vorgestellt, die in jedem Fall eine vollstandige Korrektur derjenigen kinetischen Parameter gestatteten, die durch linearisierte Auswertung erhalten worden sind. Diese Methode der vollstandigen Exponentialintegrale zeigt, das eine klare Abstufung nach dem Typ der Aufheizung besteht. Die notwendigen Korrekturen furb=1, 2 und 3 sind kleiner als furb=0 d.h. fur lineare Aufheizung. Die vier Korrekturtabellen sind fur Verfahren der kinetischen Analyse anwendbar, denen ein Aktivierungsansatz nach Arrhenius bzw. Eyring zugrunde liegt. Die Realisierung nichtlinearer Aufheizprogramme wird empfohlen.

An exact kinetic evaluation is practicable in homogeneous systems if no gradients of concentration or temperature appear. With permanent stirring, the measurement of the real difference temperature and absolute temperature at a suitable heating rate allows the application of liquid-phase DTA in the range between 170 and 380 K. For the examination of air — and moisture-sensitive substance too, equipment has been developed, that operates under inert conditions.

The conditions and premises of the kinetic evaluation of thermoanalytical curves on the basis of chemical kinetics are demonstrated, and the limits of their availability are pointed out. For reactions with an unclear structural and chemical course, some appropriate definitions of terms are proposed.

Formfaktoren fur DTA- und TG-Kurven (S T undS x) mussen unbedingt getrennt behandelt werden. Nur furS x kann man uberschaubare Beziehungen zur Reaktionsordnungn gewinnen. Im rationellen Bereich vonn zwischen 0.5 und 3 werden bei linearer, exponentielle und hyperbolischer Temperaturfuhrung folgende Funktionen gefunden $$S_x = an^{0,5} + b$$ Da bei linearem Temperaturprogramm eine geringe Abhangigkeit vom Frequenzfaktork 0 festgestellt wird, konnen durch Formfaktoranalyse sowohln als auchk 0 ermittelt werden.