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AbstractDuring the past 15 years, increasing application of microwave heating to polycondensation reactions has been witnessed. Experiments have been carried out at laboratory scale using widely different experimental procedures. The use of microwaves has often led to significant benefits compared to conventional heating experiments in terms of multi-fold decrease in reaction times and energy consumption and production of polymers with increased molecular weight and improved mechanical properties. In other cases, microwaves do not appear to 2 produce any significant benefits compared to conventional heating. At present, guidelines to experimentalist as to the process conditions and experimental design that should be applied are missing and experimentation seems to be based on an empirical trial-and-error approach.In view of the very different experimental protocols that have been applied and the contradictory trends that are frequently reported, we aim in this review to shed light on the role of important process parameters, such as the presence and type of solvent, the dielectric properties of the mixture and the individual phases, the use of heterogeneous catalysts, pressure, stirring, reflux conditions, temperature measurement method and microwave absorbing fillers, which all seem to determine the occurrence and magnitude of the benefits enabled by microwaves during polycondensation reactions.
This paper presents a comparison of microwave swing regeneration (MSR) and temperature swing regeneration (TSR) of acetone and toluene from 13X molecular sieves in terms of desorption kinetics and desorption efficiencies. The experiments were performed for two forms of the adsorbent: adsorbent bed consisting of spherical beads and adsorbent pressed in the shape of pastilles to allow for precise temperature measurement of the solid adsorbent. In TSR the adsorbent is heated by means of a hot inert gas stream whereas in MSR the adsorbent dissipates microwave energy into heat. It was found that MSR runs faster even when the adsorbent temperature is much lower than the gas temperature in TSR. This implies more efficient desorption due to less energy waste in the form of heat losses and less sensible enthalpy of purge gas stream since the total gas consumption is considerably decreased. The observed enhancement of microwave-driven desorption is more pronounced for the polar adsorbate (acetone) or high heat transfer resistances (pastilles). Finally, it was verified that microwaves do not affect the adsorption capacity of the molecular sieves after several consecutive adsorptionÀdesorption cycles.
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