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- Author or Editor: S. Cavallaro x
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Abstract
Chemical polymerization of pyrrole (Py) was carried out in a reaction calorimeter by using FeCl3 or CuCl2 as an oxidant in an acetonitrile medium. The formation heat of polypyrrole (PPy), determined under a wide range of reactant concentrations and reaction temperatures, is directly related to the PPy yields and to the degree of polymerization. Due to the negative values of both the entropy and enthalpy of the reaction the gravimetric yield is inversely related to the temperature and directly to the Py concentration. The yields to the PPy and the related reaction heats, are close to zero when the 
ceiling temperatures
are reached (T
ceil=348 K for Fe-doped and T
ceil=313 K for Cu-doped PPys). It was observed that a ceiling concentration corresponds to each ceiling temperature and only light oligomers are formed if Py concentration is too low. The electric conductivity values of the products were also determined and a direct relationship to the yields was found as well. The highest electric conductivity value (C=0.6 S cm–1) was related to the PPy fresh synthesized from a 0.017 M Py solution.
Carbon dioxide absorption by MEA
A preliminary evaluation of a bubbling column reactor
Abstract
Biogas generally contains significant quantities of carbon dioxide in addition to methane. A bubbling column reactor operating at atmospheric pressure is proposed for cheap separation and a Mettler RC1 reaction calorimeter was used to build a simplified empirical model for measuring the molar heat of solubility of CO2 in aqueous solutions of monoethanolamine (MEA). Determinations were performed in 12 mass% MEA solutions regenerated at atmospheric pressure and reflux temperature for 3 h. Flows of CO2 from 174 to 917 mL min−1 were used at a reactor temperature of 283 to 353 K.
Oxidative chemical polymerization of pyrrole
Calorimetric and kinetic measurements
A reaction calorimeter has been used to determine at three different temperatures the enthalpy values for the polymerization of pyrrole dissolved in acetonitrile, by using FeCl3 as the oxidative agent. From the calorimetric data it has been found that the reaction is first-order with respect to the pyrrole. The rate constants at the same temperatures have also been determined. By using the Arrhenius equation we have obtained the activation energy for the formation of this electroconducting polymer.
The calorimetric determination of the ceiling temperature for the chemical polymerization of pyrrole
Implications on the electrical conductivity
Abstract
The previously found strong dependence of the polymerization enthalpy on the reaction temperature has been rationalized. The temperature dependence is to be ascribed to the existence of a ‘ceiling temperature’ for the polymerization process of the pyrrole monomer. The determined ceiling temperature has beenT≊350 K when FeCl3 was used as the oxidizing agent in CH3CN solution. The existence of a ceiling temperature together with its already determined exoenthalpic nature allows to classify the polymerization reaction as an exoentropic one. From the dependence of the yield of insoluble polymer on the reaction temperature, the trend of the relative mean numeral molecular massM n for the different obtained polymers has been determined. Measurements of electrical conductivity on pressed pellets of the different polymers allowed to establish a correlation between theM n value and the conductivities The dependence of the conductivity on the exposition time to the air allowed to do some essays on the aging behaviour of the obtained polypyrrole. By making some assumptions, an absolute calorimetric determination of the value ofM n of polypyrrole was tempted together with that of the related poly-N-vinilpyrrole.
Abstract
Waterlogged archaeological woods Pinus pinaster and Fagus sylvatica L. were analyzed by using TG technique. Degradation processes ascribable to the holocellulose decay were evidenced at nearly the same temperature for sound and archaeological samples. The residual matters at 600 and 900 °C of the sound woods are much lower than those of archaeological waterlogged woods in agreement with the presence of inorganic materials encapsulated during the burial into the marine environment. It was proposed a new protocol to rapidly calculate the maximum water content parameter, which is related to the wood degradation state. TG experiments at variable heating rates were performed to obtain kinetic parameters for the degradation process. The Flynn–Wall–Ozawa and Friedman approaches allowed us to calculate the activation energy, which is significantly different for the sound and the archaeological woods.
Abstract
Catalytic reactions of the steam reforming (SR) of dimethyl ether (DME) and (bio)ethanol to hydrogen-rich gas were compared in a fixed-bed continuous-flow reactor at temperatures of 550–650 °C under atmospheric pressure over Rh/Al2O3 catalysts in terms of product distribution. Rh/Al2O3 catalysts are able to catalyze the high-temperature SR of both EtOH and DME, but in the latter case, higher H2 yields are obtained and the catalyst is less prone to coking. The aim of this work is to optimise the hydrogen production. Differences in reaction pathways over DME/H2O and EtOH/H2O are indicated.
