Development of a green process for poly-α-olefin based lubricants

Abstract

Poly-α-olefin (PAO) based lubricants have a large share of the synlubes market and these are produced in two stages—oligomerisation of α-olefins and hydrogenation. The current industrial processes use AlCl₃ and BF₃ as catalysts for oligomerisation, which are polluting, hazardous and give a very wide molecular weight distribution. This study reports a green synthesis of a PAO synlube by using 1-decene as the starting material with a variety of solid acidic catalysts, mainly based on clays. The activities for oligomerisation were found to be in the following order: K10 montmorillonite clay > 20% w/w ZnCl₂/K10 > 5% w/w (dodecatungstophosphoric acid, DTP)/K10 > 20% DTP/K10 > 10% AlCl₃ + 10% FeCl₃/K10 > S–ZrO₂ > Al-pillared clay > DTP > 20% DTP/carbon. K10 clay gave a conversion of 1-decene of 73% but the selectivities towards the dimer and trimer were 88 and 12%, respectively. 20% ZnCl₂/K10 led to a conversion of 68% with 100% dimer formation. The kinetics of reaction were established by using both K-10 and 20% ZnCl₂/K10. Oligomerisation is controlled by intrinsic kinetics. The catalysts are reusable. Other olefins such as 1-octene and 1-dodecene were also oligomerized in the presence of 20% ZnCl₂/K10. 1-Decene dimer was isolated and then in the next step hydrogenated by employing 20% w/w Ni/SiO₂, 20% w/w Ni–Cu (50:50)/SiO₂ and a clay anchored bipyridine–montmorillonite–PdCl₂ complex as catalysts. Amongst these 20% w/w Ni/SiO₂ was found to be the most active catalyst at 50 atm and 150 °C, whereas the anchored catalyst BM–Pd(II) was active at atmospheric pressure and 30 °C. Effects of various parameters were studied to arrive at a kinetic model with both the catalysts. The reactions are intrinsically kinetically controlled showing zero order in dimer concentration and first order in hydrogen partial pressure. 1-Decene based PAO with a viscosity of about 2 cSt has great many applications The hydrogenated product had a viscosity of 2.22 cSt which was found to be comparable with commercially available sample. High-speed spindle oil used in textile industry was also prepared and its performance tested.