Adiabatic Calorimetric Technique Research Articles

Thermal Stability of Amine Compounds and Dichloromethane

Dichloromethane is employed as a common solvent in the chemical industry. Due to its low boiling point of 39.7 °C it can be used for the extraction of amine compounds. However, caution is advised while handling and storing amine compounds diluted in dichloromethane, since there were incidents with unexpected reactions between amine compounds and dichloromethane in the past (Bretherick’s Handbook of Reactive Chemical Hazards, 2007). For instance, an exothermic reaction occurred during a distillation at 30 °C of a mixture of ethylene diamine and dichloromethane, which subsequently deflagrated (Nolan, 1983). In a later study, the decomposition energy was determined as ?HR = -343 kJ/mol (4.04 kJ/g) based on the amount of dichloromethane (Heskey, 1986). Further incidents in the near past are also known among experts, including the reaction of complex molecules with amine functional groups with dichloromethane are also known among experts (Neuenfeld, 2008).Figure 1: Blown up waste drum with dichloromethane, morpholine, methanol as main components. (Neuenfeld, 2008)This shows that there is largely unknown potential risk, which requires a more detailed investigation. Therefore the reaction between different amine compounds and dichloromethane was investigated, in order to determine the thermal stability and the reactivity of the amine compounds toward dichloromethane. The thermal stability was investigated by DSC (differential scanning calorimetry). For this purpose, different amine compounds and different molar percentages of amine and dichloromethane were selected. The amine compounds in this study were divided in two categories: aliphatic amines, which also include cyclic amines, and aliphatic-aromatic amines. Two main variables were first compared, the onset of the effect and its decomposition energy.The investigations show that for aliphatic-aromatic amines, the decomposition energy decreases with the molecular weight of the compound. Cyclic amines show the highest decomposition energy, which is also related with the lowest onset temperature. The results show significant decomposition reactions in ranges of the boiling of dichloromethane. Such reactions were further investigated using different adiabatic calorimetric techniques such as VSP2 (Vent Sizing Package) and Dewar calorimetry.

Cationic ring‐opening polymerization of hexamethylcyclodisilazane: General aspects and tentative mechanisms

AbstractThe ring‐opening polymerization of hexamethylcyclodisilazane (D2NMe), initiated by methyl triflate in 1,2‐dichloroethane, forms in the first, fast kinetic step both linear polymer and cyclic dimer (D4NMe). Subsequently a slow depolymerization process occurs leading to exclusively cyclotrisilazane (D3NMe). On the basis of kinetic measurements carried out using an adiabatic calorimetric technique and complementary experiments, mechanisms of both propagation, cyclization and back‐biting reactions are proposed. The influence of the reaction temperature was also studied; it is demonstrated that, at low temperature, polymerization does not lead to cyclic oligomer formation. In such conditions, the polymerization presents a ‘living’ character.

The phenol + formaldehyde runaway reaction. Vent sizing for reactor protection

Abstract The purpose of this paper is to demonstrate the use of the experimental techniques of the process safety laboratory to investigate the runaway reaction hazard of the phenol + formaldehyde reaction. A preliminary study of this reaction, using DTA and isothermal calorimetry helps in understanding the various aspects of the runaway reaction hazard and allows us to recognize the worst credible deviation leading to the most severe consequences. A vent is sized to protect the reactor from exploding due to this runaway reaction. The DIERS methodology is applied to determine the vent size: • characterization of the reaction behaviour • acquisition of the data necessary for vent sizing from adiabatic calorimetric techniques. The choice of the best calorimetric technique, to obtain experimental data for vent sizing, is discussed following the results of the various calorimetric methods. • taking into account the system behaviour and the experimental data obtained, a vent size is determined using various vent sizing equations and a relevant two phase flow model. This work demonstrates that a careful study is necessary to obtain reliable expeimental data for vent sizing. A single experiment could be misleading. This supports the conclusion that a good safety level is better achieved by the careful study of a limited number of dangerous reactions than by limited work on a great number of reactions.

Investigation of the chirality dependence of thermal properties in chiral-racemic mixtures of the cholesteric ester CE6

Abstract A scanning adiabatic calorimetric technique has been used to study the thermal properties of the chiral and racemic liquid crystal CE6 and the phase diagram covering the cholesteric phase, the three blue phases and the isotropic phase. The purpose of this investigation is to study thermal properties of liquid crystals as a function of chirality, while all other parameters remain constant. Results for the temperature and the chirality dependence of the enthalpy and of the heat capacity are reported. The latent heats between the cholesteric phase and BPI and between the different blue phases change slightly as a function of the chirality. The total heat of transition at the isotropic phase boundary is independent of the chirality, but with decreasing chirality, we observe a large increase in the latent heat and, correspondingly, a decrease in the pretransitional contribution. These experimental facts are in qualitative agreement with the predictions of a Landau–de Gennes theory for blue phases.

Cationic polymerization of N-vinyl carbazole by trityl salts—I. : Reactivity of propagating species

The cationic polymerization of N-vinyl carbazole, initiated by Ph 3C + AsF 6 − and Ph 3C + PF 6 − in methylene dichloride at 20 and 0°, has been studied in some detail. Reactions were very fast and rates of monomer consumption were measured using an adiabatic calorimetric technique. Initiation was relatively “slow” but complete, and termination was deduced to be insignificant during kinetic lifetimes. Values for k p were found to vary with the initial initiator concentration; this dependence is discussed in terms of current theories regarding equilibria between ion pairs and free ions in non-aqueous solvents. k p + values estimated from two methods of extrapolation are 9.5 · 10 5 M −1 sec −1 at 20° and 4.8 · 10 5 M −1 sec −1 at 0°. Finally, it has been found that ion pairs are much less reactive than free ions in this system.

Reactivity and mechanism in the cationic polymerization of p-methoxystyrene initiated by cycloheptatrienyl hexachloroantimonate

The cationic polymerization of p-methoxystyrene initiated by cycloheptatrienyl hexachloroantimonate in dichloromethane solution has been studied in some detail. Reactions proved to be highly exothermic, and rates of monomer consumption were measured using an adiabatic calorimetric technique. Termination was deduced to be insignificant during kinetic lifetimes, and M ̄ n values in the range 10000–50000 showed chain breaking to occur by transfer mechanisms. Appropriate analysis of conversion/time curves allowed computation of enthalpies of polymerization and rate coefficients for propagation, k p (obs), under various conditions. Data for k p (obs) were found to vary with the initial concentrations of initiator and monomer employed, and these dependences are discussed in terms of current theories regarding ion pair/free ion equilibria in nonaqueous solvents. In particular values of 3.6 × 10 3 M −1s −1 and 4.8 × 10 3 M −1s −1 at 0° and +10°C respectively for the rate constant for propagation by free poly ( p-methoxystyryl) cation have been deduced, and a tentative value of 450 M −1s −1 at 0°C has been estimated for the rate constant for propagation by the corresponding hexachloroantimonate ion pairs. These data and the related activation parameters are compared with independent results in the literature. Polymerizations carried out in the presence of excess common ion salt, dimethyl benzyl phenyl ammonium hexachloroantimonate, showed rate depressions far in excess of those predicted by a simple mass law effect, arising possibly as a result of a more dramatic ionic association than simple ion pairing.

Absolute reactivity in the cationic polymerization of methyl and other alkyl vinyl ethers

The cationic polymerizations of methyl-, 2-chloroethyl-, ethyl-, cyclohexyl- and t-butyl- vinyl ethers initiated by cycloheptatrienyl hexachloroantimonate in methylene chloride solutions have been studied in detail. Reaction rates were measured by an adiabatic calorimetric technique and rate constants for propagation of each of the monomers, k p (obs), were determined by appropriate kinetic analysis of the experimental curves. The results obtained are discussed in terms of current theories regarding ion pair/free ion equilibria in non-aqueous solvents. Although ethyl-, cyclohexyl- and t-butyl- vinyl ethers behave very similarly to isobutyl vinyl ether, and their reactivities are comparable [ k p (obs) ∼ 3 × 10 3M −1sec −1 at 0°C] both methyl- and 2-chloroethyl- vinyl ethers show markedly different characteristics to the others, and in particular exhibit a reactivity approximately one order of magnitude less [ k p (obs) ∼ 2 × 10 2M −1sec −1 at 0°C]. These variations in reactivity are discussed in terms of preferred monomer conformations, and the resulting differences in activation energy which are likely to arise when such conformers are approached by an electrophile.

The heat of adsorption of hydrogen on platinum

Abstract The heat of adsorption ( q ) of hydrogen on clean polycrystalline platinum filaments has been determined as a function of the coverage (θ), temperature and method of preadsorption using UHV adiabatic calorimetric techniques. Adsorption at 273 °K results in a stepped shape q -θ curve with q ( θ =0)= 24.7 kcal mole −1 . At 77 °K, the form of the curve depends on the temperature of preadsorption. The relative roles of a priori and induced heterogeneity are discussed and while both must play a part, the temperature dependence of the form of the q -θ curves suggest that the latter is the more important of the two in these experiments.

Absolute reactivity in the cationic polymerization of N-vinylcarbazole

The cationic polymerization of N-vinylcarbazole initiated by tropylium hexachloroantimonate and tropylium perchlorate has been studied in detail. Initiation was rapid and complete and conversion to polymer was quantitative in all cases. Reaction rates were measured by an adiabatic calorimetric technique and half lives were of the order of 1–2 s. Catalyst concentrations employed were sufficiently low (< 10 −5 M for essentially complete dissociation into free ions, as indicated by the ion-pair dissociation constants. The rate coefficient for propagation by free cations in dichloromethane at 0°C is estimated as ∼3 × 10 +5 M −1 s −1, approximately five orders of magnitude greater than that for the corresponding free radical polymerization. Molecular weights were higher when SbCl 6 − was the counter-ion than with ClO 4 − and it is suggested that monomer transfer reactions occur more readily with the small equilibrium concentrations of ion pairs (allowing an effect of counter-ion), whereas propagation occurs predominantly via free cations. Initiation is shown to occur by addition of tropylium ion to the monomer double bond and detailed mechanisms for this, together with propagation and transfer reactions, are considered.

Reactivity and mechanism in the cationic polymerization of isobutyl vinyl ether

The cationic polymerization of isobutyl vinyl ether initiated by triphenyl methyl and tropylium hexachloroantimonates, and by triphenyl methyl tetrafluoroborate, has been studied in detail. Initiation was rapid and complete, termination was shown to be insignificant, polymerization half lives were of the order of 5–10 s and reaction rates were measured by an adiabatic calorimetric technique. Catalyst concentrations employed were sufficiently low that essentially complete dissociation into free ions is indicated by ion-pair dissociation constants, and this permits estimation of the rate coefficient for propagation by free cations ( k p ). At 0°C in methylene dichloride k p ∼ 5 × 10 3 M −1 s −1, in substantial agreement with values obtained by radiation induced polymeirzation of bulk monomer. Molecular weights of the poly( isobutyl vinyl ether) samples fell in the range 2000–5000 on account of monomer transfer processes. Detailed mechanisms for initiation, propagation, transfer and termination reactions are considered.

The magnetic phase diagram of deuterated manganese chloride

The magnetic phase diagram of MnCl 2·4D 2O. from 1°K to the Néel temperature, has been traced out, using an adiabatic calorimetric technique. The triple point was located at T = 1.19° K and H c = 7550 Oe.