Research On Product Design And Large Scale Computation Of Molecular Weight Distribution Of Free Radical Polymerization

Currently 70% of overall polymer products are produced through free radical polymerization, which is very important in industrial application and theoretical research. Typical free radical polymerizations include several coupling elementary reactions, such as chain initiation, chain propagation, chain termination and chain transfer, etc. Within the range of whole conversion, many complicated phenomena such as gel effect, glass effect and cage effect severely influence some key physical quantities (such as viscosity, diffusion coefficients and reaction kinetic coefficients). Consequently, it is very difficult to perform modeling, simulation and optimization of such processes.This work studied the following three aspects of free radical polymerization:1. Dynamic simulation of free radical polymerization processBased on the governing kinetic model of material balance and diffusion controlled reaction rate coefficients model — modified Stickler -Panke -Hamielec Model, after discarding the conventional steady state assumption of the free radicals and analyzing the structure and data flowsheet of the whole mathematical model, this work utilizes the state-of-the-art computing software gPROMS (PSE Ltd.) to perform dynamic simulation of differential algebraic equations(DAEs) using the backward differentiation formula(BDF) and compares the simulation results with the literature reported data and give some discussions.2. Free radical polymerization produced polymer product design using free dynamic optimizationConventional modeling of free radical polymerization used to concentrate on the reaction kinetics and experimental measuring and estimation of reaction rate coefficients and usually neither consider the concept of polymer product design nor introduce the optimization strategy into polymer production. This work proposed a proposition and then solved it from the aspect of process systems engineering, that through dynamic optimization of batch free radical polymerization to design specificmolecular weight distributions by temperature operation control and reaction time adjustment, it is possible to obtain certain required polymer products while other methods couldn't attain such goal. In addition, this work performs productivity maximization and reaction time minimization on the guarantee of specification of polymer product. Such methods should find use for polymer production with processing requirement, terminal user specifications.3. Large-scale simulation of polymer molecular weight distributionConsidering the disadvantage that average molecular weight distributions is incomplete description of molecular weigh distribution which is very important to polymer end-use properties, this work further extends the former modeling aspect to the computation of different length of radicals and dead polymer product. Taking the transfer reaction to polymer and termination both by disproportion and combination into account, and noticing the specific structure of the large scale stiff differential algebraic equations (DAEs) of free radical polymerization model, the author proposed three methods based on the conventional method of moments -simultaneous method, model decoupling sequential method and variable decoupling sequential approach, whose capability of calculating the whole molecular weight distribution of free radicals and polymer products up to chain length of 2000,4×10⁴ and 10⁶ on the DELL^TMPowerEdge^TMSC1425 system with 2.8GHzIntel(?) Xero^TM CPU and 2G memory. Finally this work compares and summarizes the three methods, especially study and discuss the initiative variable decoupling sequential method proposed in this work, which is of bright future in precise prediction of molecular weight distributions and online soft-sensing of polymer product quality and the areas of polymerization kinetics.