The UNIPOL Polyethylene (PE) Process produces the widest array of linear low-density polyethylene (LLDPE), medium-density polyethylene (MDPE) and high-density polyethylene (HDPE) having unimodal or bimodal molecular weight distribution (MWD) using a single, lowpressure, gas-phase reactor.
The UNIPOL PE Process provides licensees proven flexibility to use a single process with the capability to produce a broad product mix that can be adapted to changing market needs.
Ethylene, comonomer, hydrogen and nitrogen enter the circulation loop that delivers reactants, cooling and mixing in a fluidized bed gas phase reactor (1). Ziegler-Natta, chromium-based or metallocene catalyst is fed into the reactor, which operates at low pressure (< 25 bar) and low temperature (approximately 90°C) and is capable of producing products with either unimodal or bimodal MWD. Adjusting and controlling gas composition and temperature allows for a broad product range to be made with each catalyst. A second reaction system is not required for bimodal products. The reactor dome efficiently separates the solids from the circulating gas, and the robust design of all equipment avoids the complexity and fouling risk of secondary separation devices such as cyclones or filters. The low head compressor (2) sends the circulation gas through a single conventional external cooler, removing the heat of reaction and compression. The UNIPOL PE Process pioneered the use of “Condensing Mode” and now “Super Condensing Mode” where a portion of the heavier components of the circulation are condensed and carried into the reactor bed as well-dispersed droplets without the need for separators or pumps. The evaporative cooling allows for higher production rates and smoother operation using smaller reactors. The product discharge system (3) uses the effect of solids displacing gas to minimize reactant discharge and avoid a costly recycle compressor. The granular PE powder is conveyed up to a settled bed purge bin where a drying gas removes the residual reactants. The mixed gas from the purge bin is compressed and cooled in the vent recovery system (4) so condensed reactants can be easily pumped back to the reactor without any distillation or purification. The drying and recovery is inherently simple since no diluent or solvent is used in the process. In one low-investment configuration, the granular powder from the purge bin flows by gravity to the pelletizing system (5) where additives are incorporated. Low gel pelletizing is achieved across the product slate. Univation Technologies’ attention to process design provides a simple and cost effective process for polyethylene manufacture. Products: A broad range of LLDPE, MDPE and HDPE products can be produced using butene or hexene comonomer with a density range of 0.915 g/cm to 0.970 g/cm and a narrow, broad or bimodal MWD. Melt index varies from less than 0.1 to greater than 200. Grades produced are suitable for film, blow molding, pipe (PE-100), injection molding, rotational molding and extrusion applications. Economics: The simplicity of the UNIPOL PE Process offers low investment and operating costs while providing the flexibility to quickly adapt product mix to changing market needs. The manufacture of bimodal products in a single reactor reduces investment when compared against multiple reactor processes. With a low operating pressure and no diluent or solvent, the gas-phase process has low usage of steam and electricity, and provides efficient use of monomer, nitrogen and water. Licensor: Univation Technologies, LLC