When considering the devolatilization
in fluidized bed, three resistances in series can be identified: the interphase resistance to oxygen transfer from the bubble phase to the particulate phase; the resistance to oxygen diffusion from the particulate phase to the surface of the particle; the resistance to the combustion reaction at the surface of the particle .
The phenomenon of bubble nucleation and growth in non-Newtonian liquids as well as polymer melt devolatilization
are still not too well understood, even though there is a considerable body of literature in these areas, for instance, Arefmanesh et al.
Hands-on demonstrations at the Leistritz New Jersey process laboratory will include co-rotating and counter-rotating twin screw extruders; devolatilization
via extrusion, including ambient, vacuum assist and multi-stage; downstream addition of fillers, fibers and additives; direct sheet/film extrusion with gear pump front-end; and foam extrusion via supercritical injection.
The point of incipient stable-bubble formation is an important design variable for two-stage bulk polymerizations (PMMA, polystyrene, etc.) since it would be a good point to switch from the first reactor to the second and possibly avoid the devolatilization
Figure 2 also illustrates that thermal stress fragmentation and devolatilization-induced fragmentation have little effect on small-size particles (<0.6 mm) because of uniform temperature distribution in little time and rapid mass transfer during devolatilization
. Thus, the fragmentation on small particles may be mainly caused by secondary fragmentation and attrition during the later period of fluidized bed combustion .
The polymer devolatilization
(DV) in screw extruder mainly includes the following three contents: flash DV, stripping-agent-added DV and surface renewal DV (SRDV).
In one polyetherimide example, the resin after devolatilization
was free of solvent (meaning less than 1000 parts per million of residual solvent).
Topics will include high speed, energy input (HSEI) twin screw extruder theory and design; comparison to low speed, late fusion (LSLF) designs; screw design and process techniques; techniques for dispersive and/or distributive mixing; sequencing of multi-stage process operations; devolatilization
process techniques and practices; scale-up of the twin screw extrusion process; feeder and materials handling for pellets, powders and liquids; gear pumps and screen changers; pelletizing, including strand cut, water ring and underwater; direct extrusion for sheet, film, fibers and profiles; reactive processing; process troubleshooting; control and monitoring options; screw assembly and disassembly; and machine maintenance.
These finishing trains contained devolatilization
units, gear pumps, extruders, screen systems, and pelletizing dies.
For example, during the last three decades in coal science there has been a shift from simple kinetic models to more complex "network" devolatilization
Their investigation on foam-enhanced devolatilization
indicates that the supersaturation alone was insufficient to generate a new bubble phase when the solvent level is low.
Charlie Martin is president and general manager of Leistritz, a leading supplier of twin-screw extrusion equipment for compounding, devolatilization
, direct extrusion, pharmaceutical, and other applications.