A commercial low-density polyethylene (LDPE) which is produced by the
polymerization process of ethylene in the presence of initiators in a long
tubular reactor is the most widely used in polymer industry. The highly
exothermic nature of the LDPE polymerization process and the heating-cooling
prerequisite in tubular reactor can lead to various problems particularly
safety in term of thermal runaway and productivity, i.e. decreasing monomer
conversion. Therefore, model based optimization of an industrial LDPE
tubular reactor under thermal safety consideration is required to be
implemented. A first principle model for this process is developed and
validated using industrial data. Mass and energy balances have been derived
from kinetics of LDPE polymerization. Thereafter, an expression of reactor
temperature under critical condition is developed and incorporated in the
reference model for the thermal safety study. In order to ensure the process
is thermally safe and meet the desired product grade, the constrained
dynamic optimization is proposed to maximize the conversion of monomer using
orthogonal collocation (OC). The dynamic optimization result shows that the
maximum reaction temperature under critical condition constraint can be
satisfied by optimizing reactor jacket. Moreover, it is achieved without
jeopardizing the monomer conversion and the product grade.
Effect of initiator concentration to low-density polyethylene production in a tubular reactor
