Devolatilization and reactive extrusion in a counter-rotating twin screw extruder.

摘要

This work concerns the reaction enhancement in reactive extrusion (REX) when accompanied by devolatilization (DV) of inert solvents.; A model of locally enhanced mass transfer has been developed to describe chemical reaction acceleration in boiling polymer solutions. The mass transfer model suggests that the concentrations of reactants and catalyst increase significantly at the bubble interface during the bubble growth, due to the rapid diffusion of the inert solvent into the vapor bubbles. After the bubble rupture, the bubble interface film containing higher reactant concentrations contracts quickly into a droplet, tending to preserve this concentration difference and continue affecting the reaction rate. The model has been successfully used to explain the reaction enhancement in a flask reactor with a boiling polymer solution and in a batch reactor with devolatilization of an inert solvent. The model reactions used were the transesterification reaction of ethylene-vinyl acetate copolymer with 3-phenyl 1-propanol and the monoesterification reaction of styrene-maleic anhydride copolymer with octanol.; A statistical method for the relationship between the overall residence time distribution (RTD) function and the RTD functions in appropriately divided elements of the screw was introduced to establish RTD models for the non-intermeshing counter-rotating twin screw extruder. Assuming that the flow is sufficiently rearranged at the boundaries between the elements, the overall RTD is related to the RTDs in the elements by a convolution integral. The latter can be determined from first principles. The RTDs in the extruder and in individual vent zones were also measured using tracer technique. Good agreements were found between the measured RTDs and those predicted from the RTD model developed in this work; The RTD in fully-filled and partially-filled parts in all the individual vent zones have been determined by both RTD models and experimental measurements. With the detail RTD information, the apparent reaction rate in the REX accompanied by (DV) has been investigated using the monoesterification reaction. Significant reaction enhancement has been observed and it has also been explained by the mass transfer model developed.