Joint control and operation design for alkyd resin polyesterification reactors

Conference Dates

May 10-15, 2015


The production of many alkyd resins is carried out in conventional semi-batch polyesterification reactors. These systems display the following features: (i) the need for continuous removal of water for the completion of the corresponding reversible reaction, usually performed at high temperatures, (ii) the high interaction among process variables, (iii) the exponential increase of viscosity, and (iv) the need for cooking the batch until a sufficiently large viscosity is attained, implying the need of a timely measurement or estimate of viscosity. However, viscosity is difficult to measure on-line, i.e., and only discrete-delayed acid number (AN) and/or cold-dilute (μ) viscosity measurements can be available for monitoring and control. The preceding issues, in conjunction with the lack of detailed mechanistic models for analysis and control design preclude the consistent batch-to batch operation, as well as the standardization of processing time and final product quality indices. In this work, the standardization of the state-trajectories for semi-batch polyesterification processes is addressed. The combination of polymer reaction engineering notions and tools with conventional feedforward- feedback (FF-FB) control techniques yields a joint operation - control design methodology that includes: (i) a FF-FB controller that enforces the reactor to follow a prescribed temperature policy, and (ii) a pair of feedback event controllers that set the raw material addition policy, and the water removal. The proposed methodology has been tested with several experimental runs at the lab-scale and at the industrial scale. Figure 1 compares the temporal trajectories of viscosity and acid number for several batches, performed under the conventional procedure (left) and under the proposed operation (right). It can be seen that, by applying our control methodology to the polyesterification process, the viscosity and acid number curves evolve inside a narrower tube in the state space than the one for the conventional previous approach. In other words, the proposed joint operation - control design methodology yields standardized trajectories of process variables like cold-dilute viscosity, acid number, and total processing time. The rather simple methodology improves the performance obtained with previous conventional control and advanced estimation techniques.

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