Ethylene Polymerization using Homogeneous Single Site Catalyst

Abstract

FI catalysts (single site catalyst) are capable of providing novel olefin-based materials, with higher catalyst productivity, and greater control over polymer structures such as controlled molecular weight, desired morphology, narrow molecular weight distribution etc. Recently, Reliance R&D has developed a non-cryogenic process i.e. polymerization process at high temperature and high pressure (granted patent) with FI catalyst to produce a specialty type of PE. FI catalyst used in that process was synthesized using standard synthetic procedure as described in the literatures. The synthetic procedure involved severe reaction conditions like very low temperature of -78OC, use of pyrophoric material; use of hazardous solvent, tedious purification step etc. With a view to overcome such process difficulty, a modified synthetic procedure which is cost effective, as developed by Reliance R&D has been followed to prepare FI catalyst. In that process, pentafluoro aniline was reacted with 3-tert butyl salicylaldehyde to produce FI ligand. FI ligand was then converted to its titanium metal-ligand complex or FI catalyst. Both ligand & catalyst were purified and pure ligands and catalysts were characterized by FT-IR and GC-MS. The pure catalyst was evaluated for ethylene polymerization under a different set of polymerization process conditions, which have not been tested before to produce the specialty PE having very high molecular weight. It was found that FI catalyst efficiently polymerize ethylene into PE. Under employed polymerization conditions, MW of resulting PE was as high as 16 million g/mole and it increased with increasing polymerization time from 30 min to 90 min. Further, the performance evaluation of ethylene polymerization with FI catalyst and PMAO/MAO as co-catalyst, in presence of a specific amount of a chain terminating agent (CTA), H2 was studied. It has been found that H2 was an efficient chain regulator in such polymerization. The MW of resulting PE went down to 0.03-0.4 million g/mole from ~ 16.9 million g/mole. Not only that, it significantly narrowed down MWD to 2-3 from ~ 20. The amount of H2 or H2 pressure plays a significant role in lowering down MW of resulting PE. As H2 pressure increases, MW of resulting PE decreases. The above polymerization in presence of a trace quantity of H2 for a certain time period of polymerization results in bimodal PE. There is one important process parameter which can efficiently control high and low molecular weight fractions in resulting PE. The factor is: polymerization time in presence of H2. By varying this parameter, various grades of bimodal PE having a wide range of low and high molecular weight fraction could be achieved, where low -molecular weight fraction falls in the region of HDPE’s molecular weight and high molecular weight fraction in the region of UHMWPE’s molecular weight. Thus the resulting bimodal turns to be a perfect blend of HDPE and UHMWPE.