| Tubular reactors are attractive for polymerization due to their continuous nature. Continuous processes are generally cheaper in terms of initial investment as well as operating costs and are easier to run. Tubular reactors are often used in industrial production of polymers but typically not from the monomer. Precautions need to be taken to guard against the practical problems of hydrodynamic and thermal instabilities. The high molecular weight polymer typically produced causes high viscosities and possible plugging of the tubes in the reactor.; The modeling of molecular weight distributions by a lumping technique for the anionic polymerization of styrene in tubular reactors was undertaken. Diffusion coefficients which depend in various ways upon the polymer's chain length were investigated as a contributing factor to the build up of high molecular weight polymer on the walls of these reactors. Two methods for arbitrarily assigning individual diffusion coefficients to an unlimited number of components while maintaining a mass balance, the proportional flux and pairwise flux methods, were devised. High molecular weight polymer with number average chain lengths of about 2100 was formed. For all cases, chain length dependent diffusion coefficients increased the average chain lengths and polymer concentration at the tube wall, but not to any great extent. Results depended upon the particular diffusion coefficient model when the proportional flux method was used, but results were identical for all diffusion coefficient models with the pairwise flux method. Only small amounts of velocity elongation and temperature increases were found. The size of polymer molecules will always hinder transport within the reacting mass, but stable operation of tubular reactors was predicted, especially with the high solvent levels used in this study. |
