| dc.description.abstract | Purpose of the PhD thesis was to develop a novel microencapsulation process, designing and
building a single-pot semi-continuous bench scale apparatus. The novel process is based on the
coupling of two emerging techniques, involving ultrasound and microwave, used in atomization and
heating operations, respectively. The process has been designed to respond to the needs for process
intensification, i.e. improvement of process efficiency and cutting down of energy consumption.
With this aim, a review of the main processes used for microencapsulation was first performed:
conventional processes showed a number of drawbacks, such as high energy consumption, batch
configuration, use of solvents and long times of production. On the basis of the state of the art, the
idea of an intensified apparatus for particles production, exploiting alternative resources, such as
ultrasound and microwave, was formulated. The apparatus was composed of three main sections:
feeding, atomization, separation/stabilization. The feeding and atomization sections were built
connecting a double channel ultrasonic atomizer to a system for feeding solutions in a purposely
designed separation/stabilization section, thus realizing a semi-continuous apparatus. Separation
section consisted of a wet-collector, i.e. a sort of hydrocyclone, which allowed a uniform
distribution of the hardening solution and the consequent contact with the atomized drops, a
filtering device, and a microwave oven. The wet-collector was placed into the microwave oven to
obtain an “on-line” drying. Recirculation of the hardening solution, to renew contact surface
between droplets and cross-linker, was guaranteed by a system of centrifugal pumps. In this
configuration, when atomization occurred, drops were harvested in the wet-collector. After
atomization, the obtained suspension was collected in the cross-linker tank, then the filtering device
was inserted in the lower part of the wet-collector, so that hardening solution was recovered and
particles settled on the filter, when the suspension was brought again to the wet-collector and after
its complete emptying. An eventual following washing step can be done in a similar way to the
previous hardening step. Finally, particles were stabilized by microwave drying, and then
recovered.
The steps for building the microencapsulation apparatus were accurately shown. Then, criteria used
for components selection, in order to obtain the best performances from the plant, were highlighted.
After building the plant, the process parameters were defined. First, the research for the best
combination of feeding parameters, such as type of materials, composition, concentration and feed
rate, that assure the encapsulation of the core material in the shell, was carried out. Then, the
parameters of the ultrasonic atomizer (atomization section), essentially power, were tuned. Finally,
for stabilization/separation section, fundamental was the relevant stabilization step, where
microwave power was set to avoid too high temperatures that could degrade molecules... [edited by Author] | it_IT |
