Mathematical Modelling of a Tubular Reactor for Continuous Production of Synthetic Resins

Abstract

Synthetic resins have, so far, been universally produced
by batch processes, A continuous process however is shown to
have some general advantages which make it desirable in
commercial production.

The physical properties of the resin systems have
resulted in the choice of a tubular reactor for continuous
operation and the urea-formaldehyde resin system is selected
for detailed examination.

To account theoretically for the performance of the
tubular reactor two mathematical models are developed, The
first model, which ignores all but the bulk transports, is
a plug-flow model catering for good radial mixing in the
reactor, The second model, involving a parabolic velocity
profile with inclusion of radial and axial diffusion is a
complex model and caters for laminar flow in the reactor
tubes. The physical data necessary for the solution of the
models are estimated using standard procedures. The chemical
kinetic data available are shown to be inadequate for use at
the elevated temperatures employed in the reactor. A novel
technique is therefore developed for evaluation of the high
temperature urea-formaldehyde reaction data, The data are
then described mathematically with postulation of chemical
reaction mechanisms, followed by optimisation of the rate
constants for the proposed reaction schemes to give good
mathematical fits.

To test the models, an available rig is modified. The
problems of sampling under reactor conditions are overcome
by the introduction of a novel design of a sampling valve
and sample collection technique which avoids physio-chemical
change to the resin, The experimental results are discussed
with regard to the performance of the reactor as affected
by various parameters, The best conditions for production
of the addition products of the urea-formaldehyde reaction
with a minimum formation of the condensation products are
shown to be high formaldehyde to urea molar ratios, high
temperatures, low concentrations and low residence times.

The plug-flow and complex models are solved using both
a Honeywell 316 and an ICL 1904S computer. A novel numerical
solution technique, in conjunction with the use of computers,
is introduced for the solution of the complex models.

The simulation results show excellent predictions by
the plug-flow models, and poor accuracy of prediction by the
complex models. The reason for the good plug-flow predictions,
at comparatively low Reynolds numbers, is attributed
to the shape of the reactor which also explains the shortcomings
of the complex models.

Date of Award	1977
Original language	English