Polyolefins Unipol process

In 1979, the UNIPOL process for gas-phase production of LLDPE was introduced by the Union Carbide Corp. Since the new resins were difficult to process on the lines designed for LDPE, by 1982 several patents were issued for improvement of LLDPE processability by blending it with other polyolefins, viz., LDPE, PP, and olefinic rubbers. Ethylene copolymers, rubbers, EPDM, EVAc, maleated polypropylene, EPR, etc., have also been used (Cowan 1983 Turtle 1983 Fukui et al. 1983 Haas 1983 Hert 1983). Thus, blends LLDPE/LDPE were found miscible at low LDPE contents, then immiscible at high LDPE. Addition of HDPE as cosolvent resulted in miscible tertiary blends (Lee and Denn 2000). 

In 1979 UNIPOL process for gas-phase production of LLDPE was introduced by the UCC. Since the new resins were difficult to process on the LDPE processing lines, several patents were issued for LLDPE blends with, e.g., LDPE or PP, which had better processability In 1982 a number of patent applications for blends of LLDPE, with other polyolefins, co-polyolefins, and olefinic elastomers, for example, ethylene copolymers and thermoplastic elastomers (e.g., TPO, EPDM, EPR, EVAc, PP-MA,), have been filed... 

Gaseous polymerization of polyolefins is carried out in fluidized-hed reactors. The conversion per pass is kept rather low (order of 2%) so that the heat of polymerization is removed via convection by the unconverted reactants, which are cooled externally and recycled to the reactor. In some cases, an inert liquid is added to the feed so that its evaporation helps remove some of the heat of the reaction. The Unipol process is one of the most common processes used to carry out this gaseous polymerization. Other processes for producing polyolefins include Hypol, Novolen, Catalloy and Spheriline. 

Gas Phase Fluid Bed Processes. These processes are of particular commercial importance with polyolefin production. A prominent example of this technology is the Unipol process, first commercialized in 1975. A flow sheet is shown in Fig. 19.16. A gaseous monomer, such as ethylene or propylene, along with comonomers and chain transfer... 

Fig. 19.16. Unipol process for polyolefin manufacture. Courtesy Union Carbide.)...

Keywords metallocene catalyst, Ziegler-Natta catalyst, olefin polymerization, polyolefins, homogeneous catalysts, supported catalysts, stereoregularity, molecular weight distribution (MWD), chemical composition distribution, Unipol , Novolen , stereoselectivity, single site catalyst, multiple site catalyst, gas phase process, slurry process, homopolymerization, copolymerization. 

FIGURE 12.4 UNIPOL gas-phase polyolefin process. Reprinted with permission from CHEMTECH 13(4), 225 (1983). Copyright 1983 American Chemical Society. 

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