Monitoring Polymerization Reactions by Wayne F. Reed & Alina M. Alb

Author:Wayne F. Reed & Alina M. Alb
Language: eng
Format: epub
Publisher: Wiley
Published: 2013-11-29T16:00:00+00:00

11.2 ACOMP INSTRUMENTATION

11.2.1 The ACOMP “Front End”

This refers to the ensemble of pumps, mixing stages, and conditioning elements that ultimately produce the diluted, conditioned stream, which continuously feeds the detection train. Extraction of liquid from the reactor typically ranges from 0.010 to 0.500 ml min−1, depending on the application. Many different approaches have been taken for the front end. One system uses two high-performance liquid chromatography (HPLC) pumps, one for reactor extraction, the other for dilution, and a high pressure mixing chamber. This arrangement supplies a reliable, diluted, conditioned stream up to reactor viscosities of only about 300 centipoise (cP).

To deal with very high reactor viscosities, up to 106 cP, a two-stage mixing system was introduced, which consists of (i) a reactor extraction pump capable of withdrawing high viscosity fluids, such as a gear pump; (ii) a mixing stage at atmospheric pressure, which also allows any bubbles created by exothermicity or other processes in the reaction to be exhaled and excluded from the detector stream; and (iii) a high pressure mixing stage, which allows for further dilution after the low pressure stage. This normally involves five pumps [5].

Another popular front-end style uses a recirculation loop from a reactor outlet back into an inlet, powered by a gear pump or other suitable type. A mass flow controller (MFC) is introduced in a T-junction in the loop and the desired flow rate through the MFC can be set to a small fraction of the recirculation flow rate; for example, extracting 0.10 ml min−1 through the MFC from a 20 ml min−1 flow through the recirculation loop is common. The MFC itself has a feedback controlled valve for regulating the amount of reactor content that passes through it. Recirculation ensures that fresh reactor liquid is continuously sampled and reduces possible problems of spatial inhomogeneity from intermittent dip-tube sampling in a batch reactor.

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