Paper to the Institution of Chemical Engineers Research Event/First European Conference, Edinburgh, 104, 4th-6th January 1995.

S F Bush, with O K Ademosu

Abstract

Process Pathways Analysis generalizes the familiar concept of reaction pathway to allow changes in physical state to be described in broadly the same way as chemical changes. While applicable to all chemical processes, the approach is particularly relevant to polymerization, where the product is required in specific physical as well as chemical forms, and where the phases in which reactions may be carried out – solution, suspension, melt, liquid, gas – greatly affect the viability of candidate processes. Five processes for making Styrene-Maleic Anhydride copolymers have been explored using the PPA approach. Experimental and predicted results are compared for key chemical and physical properties.

Paper to the Institution of Chemical Engineers Conference, Process Intensification, 18th-19th April 1983.

S F Bush

Introduction

The relatively low growth rates, around 3% per annum or less, projected for the next ten years, contrasted with those obtaining when most of the current chemical processes were designed, prompts a re-examination of the economies of scale for a number of reasons.  In the last few years, under the spur of sharply increased energy prices, much effort has naturally been devoted to increased energy utilization efficiency.  A number of such endeavours have, by occasioning a re-examination of existing designs, enabled savings in capital as well as energy to be made. None-the-less, when design inefficiencies have been stripped out, energy is the resource we use to achieve intensification or volumetric compactness. The relationship between energy efficiency and intensity rules in an approximate way in all industries, including Man’s oldest industry, agriculture, as has been pointed out by Green (1), (Table 1):

While the detailed figures depend on precise definition, the trend is clear. Equally clear for optimal design is the need to determine the fundamental limiting relationship between energy efficiency (including availability) and intensity, for the generality of chemical processes. Le Goff (2) has recently addressed this problem in connection with the design of heterogeneous reactors.

There is additional reason to examine the design fundamentals of polymerization reactors in particular and that is because the products (i.e. polymers) are now demanded in ever-increasing variety. The period 1950-1970 of rapid scale increases has been followed to-date by a period of adaptation of the processes and modification of the basic polymers (polyethylene, PVC, polystyrene, etc) designed and introduced in the former period under basically different assumptions. Additionally a number of second-generation polymers (e.g. polycarbonates, poly(phenylene oxide)) have become fully commercial during the current period. As will be indicated, there are thus both significant similarities and differences with the general class of chemical processes and both general and particular principles to apply.

References

(1) M B Green (1976), Lecture to the Society of Chemical Industry.

(2) P Le Goff (1980), Chemical Engineering Science, 35, 2029-2063.

(3) K G Denbigh (1957), “Principles of Chemical Equilibrium”, pp 71-72.

(4) H Brauer (1982), Institute of Chemical Engineers Symposium, 78, T5/11-19.

(5) P J Tail (1980), Macromolecular Chemistry, 1, SPR, Roy. Soc. Chem. 3-21.

(6) K H Laidler (1965), “Chemical Kinetics”, p 70 ff.

(7) G I Taylor (1954), Proc. Roy. Soc. A220, 446-467.

(8) S F Bush (1969), “The Design and Operation of Jet-stirred Reactors for Chemical Kinetic Studies”, Trans. I. Chem. E. 47, 59-72.

(9) R S Brodky (1966), in Uhl and Grey “Mixing”, p 52.