Microstructural study on low viscosity poly-α-olefin oils synthesized via AlCl3/H2O cationic system in the present of xylene and heptane solvents

Abstract

It was well established that polyalphaolefin (PAO) synthesis using AlCl3/solvent system can produce low viscosity PAO grades and has potential to be replaced with hazardous BF3 catalyst in commercial scale. The main aim of this research was to study in which extent AlCl3/solvent can produce PAO4 and PAO6 (4 and 6 represent kinematic viscosity of PAO at 100 °C), recognized as the most common PAO grades, and the main characteristic of final products. In this line, first the produced oligomers by AlCl3, AlCl3/xylene and AlCl3/heptane systems and H2O as the co-catalyst (in AlCl3/H2O = 2 M ratio) were fractioned based on their boiling point into 4 samples including low molecular weight byproduct, PAO4, PAO6 and high molecular weight byproduct. Then, the main characteristics of PAO4 and PAO6 fractions were studied by 1H and 13CNMR spectra, Distortion less Enhancement by Polarization Transfer (DEPT, to study CH sub spectra), GPC and viscometry analyses to unravel structure-properties relationships. The results showed using xylene reduces the molecular weight much more than heptane through enhancing the chain transfer reactions. NMR spectra together with viscosity analysis indicated that the oligomers from AlCl3/heptane system had lower short chain branching (SCB) and branching ratio (BR) and higher long chain branching ((CH2)nCH2CH2CH3, with n > 1) and VI values. Furthermore, the microstructural characterization of commercial PAO4 and PAO6 samples revealed slightly lower SCB, BR and VI values than those in the ones produced with optimum amount of xylene. Our obtained results confirmed that 1-decene oligomerization by AlCl3 catalyst in the presence of optimized amount of xylene solvent results PAO4 and PAO6 in good yield (nearly 78%) with the characteristic which is comparable with that of commercial grades.