The continuous solution polymerization process is well known. Y. V. Kissin, in The Kirk-Othmer Encyclopedia of Chemical Technology, in an article titled “Polyethylene, Linear Low Density” briefly describes commercial solution polymerization processes (published on-line 15 Apr. 2005). In the solution process, solvent, monomer(s) and catalyst are continuously fed to a reactor. The reactor can be operated over a relatively wide range of temperatures and pressures; with the goal of producing a single liquid phase containing the desired polymer. Downstream of the reactor, the single liquid phase is phase separated to recover the solvent, unreacted ethylene and α-olefins (if present) from the polymer. In the phase separation step, a vapor/liquid (hereafter V/L) separator operating at lower pressure, relative to the reactor(s), generates: a gaseous overhead stream of solvent, monomers, hydrogen (if present), light-end impurities and possibly some low molecular weight oligomers (“grease”), and; a bottom stream of a polymer rich solution. The gaseous overhead stream is typically treated to separate the components, and various processes have been suggested to accomplish this separation, for example, a distillation process. However, distillation is energy intensive and thus costly. Thus, it is desirable to recycle a major portion of the gaseous overhead stream to the upstream reactor(s), in an energy conserving manner.
In general, the solution polymerization process is an energy intensive process. For example, relative to gas phase polymerization reactors, the solution polymerization reactor(s) run hotter and at higher pressures, consuming more energy, i.e., utilities such as steam and power. A need exits to improve the energy efficiency of the continuous solution polymerization process. This invention describes embodiments of a continuous solution polymerization process that consumes less energy, relative to a base case solution polymerization plant. Because less energy is consumed, manufacturing variable costs are reduced and the environment benefits, e.g., reduced greenhouse gas emissions.