Melt condensation polymerization techniques are used in the polymer industry for the synthesis of thermoplastics and specialty polymers. For example, saturated polyesters (such as poly(ethylene terephthalate) - PET and poly(butylene terephthalate) - PBT), polyamides, polyarylates, and polycarbonates are manufactured in either semi-batch or continuous polycondensation reactors. Many of these processes are characterized by multiple reaction stages and complex reaction networks that give rise to various unwanted side products. The pure molten monomers are polymerized in the absence of added solvents - a more environmentally friendly process than other industrial polymerization processes. The process is also advantageous because the polymers can be directly pelletized or spun into fibers. A common feature of industrial melt polycondensation processes is that multiple reaction stages are employed using several reactors in series. For PET production, the sequential reaction procedure includes: (a) monomers, low molecular weight oligomers, and low molecular weight prepolymers are synthesized in continuous stirred tank reactors, and (b) the prepolymers are then polymerized to higher molecular weight polymers in finishing polymerization reactors (often rotating disc reactors) where large vapor-liquid surface areas are provided. The final polymer product properties are mostly regulated in this finishing polymerization stage, therefore the optimal design and operation of this reactor is important and is the objective this research. Specifically, the PI will address the following questions: (1) What are the major factors that affect the formation of polymer films on a rotating disc? What are the quantitative relations between the disc design/operating variables and film thickness? (2) What is the role of gas bubbles of condensation byproducts in the mass transfer process? How can one quantify the effect of gas bubbles on the total vapor- liquid mass transfer rate? (3) What interactions occur between the neighboring discs and what will be the optimal layout of multiple discs on the agitator shaft? What will be the optimal angle of disc immersion in the liquid pool? (4) What is the overall liquid (polymer melt) flow pattern in the reactor? (5) How does the continuous finishing reactor behave under various reactor operating conditions and feed conditions at steady state and transient state? What polymer properties are most strongly influenced by what reactor variables? How should one pair the polymer property parameters with reactor operating conditions for the design of product quality control systems? Both experimental work and reactor modeling will be done.***//

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University of Maryland College Park
College Park
United States
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