Modeling, Simulation and Optimal Control of Ethylene Polymerization in a High-Pressure Tubular Reactor

Low-density polyethylene (LDPE) is a very important material for the manufacture of engineering and commodity plastics. The products are usually produced in high-pressure free  radical polymerization either by autoclave or by tubular processes. This study presents a kinetic model based on a postulated reaction mechanism to describe the evolution of monomer, initiator consumption and the average molecular weights of ethylene polymerization in a high-pressure polymerization tubular reactor. The variations in the density and viscosity of the reacting mixture along multiple injection points for an initiator are used along reactor length is explicitly taken into account. A simulation program is developed to solve the mathematical model and the results are compared with those reported earlier. Further, the optimal control of the LDPE reactor is carried out using genetic algorithms to maximize monomer conversion using the jacket temperature of heat-exchange fluid as a control  function  along  reactor  length.  The  results  indieate  a 22-40%  increase  in the reduction of monomer concentration.