Process for the controlled production of polyethylene and its copolymers

The present invention relates to a process for the controlled production of high density polyethylene (HDPE) or of linear low density polyethylene (LLDPE) in one or more gas phase reactors, in the presence of either chromium or Ziegler-Natta catalysts, said process possessing an on-line control of certain process variables as well as the control of certain physical properties of the final resin product. More specifically, such process comprises: i) the use of models for inferring the physical properties as well as the process variables which are not measured continuously and ii) models which are relevant for the control of said properties and operating conditions of the process under study. The control of the process variables provides further the maximization of the production rate as well as of the catalyst yield in the polymerization reaction. A process for producing high density polyethylene (HDPE) or linear low density polyethylene (LLDPE) in gas phase reactors, isolated or combined, using chromium or Ziegler-Natta catalysts, provided with on-line control of certain process variables as well as physical properties of the produced resin is described. Such process comprises the use of models for the inference of the physical properties and of the process variables that are not continuously measured as well as models which are relevant for the control of said properties and of the operating conditions of the process. The control of the process variables provides further the maximization of the production rate and of the catalyst productivity in the polymerization reaction.