Synthesis of Dimer Acid 2‐Ethylhexyl Esters and their Physicochemical Properties as Biolubricant Base Stock and their Potential as Additive in Commercial Base Oils

Abstract

Previously synthesized C36‐dimer acids (DA) have been esterified (97 ± 0.2% conversion at 120 °C for 72 hours) with 2‐ethylhexanol (2‐EH) to produce a new class of C52‐DA 2‐EH esters that have potential application in biolubricant formulations such as base oils and additives. Investigation of physicochemical and lubricant properties showed the bio‐based esters have good solubility in commercial base stocks such as polyalpha olefin (PAO‐6) (>20 w/w) and high‐oleic sunflower oil (HOSuO) (>20 w/w). The neat C52‐DA 2‐EH esters displayed a three‐ to eightfold higher kinematic viscosity and comparable viscosity index (VI = 134) as a commercial base stock, PAO‐6 (VI =137). Both C52‐DA 2‐EH esters, whose parent C36‐DA were synthesized with two different zeolite catalysts, were oxidatively stable above 176 °C. Blending C52‐DA 2‐EH esters in HOSuO improved the pour point (PP) of HOSuO from −18.8 to −21.0 °C at 1% w/w and the cloud point (CP) from −6.3 to −10.6 °C at 8% w/w of C52‐DA 2‐EH ester 1. A similar trend was observed for C52‐DA 2‐EH ester 2, indicating that the esters possess PP depressant (PPD) characteristics in HOSuO blends. Blending C52‐DA 2‐EH esters in PAO‐6 increased the VI of PAO‐6, which is an indication that the bio‐based esters were acting as VI improvers (VII). It was concluded that C52‐DA 2‐EH esters can be employed commercially as bio‐based base oils and as PPD and VII additives in lubricant formulations.

Biolubricant production via esterification and transesterification processes: Current updates and perspectives

“…Researchers have used a variety of catalysts in the synthesis and production of biolubricants as earlier highlighted, as it influences the bioproduct yield and energy efficiency. In this regard, Shehu et al, 20 used a homogeneous acid catalyst (sulphuric acid) to produce a 97% yield of dimer acid 2‐ethylhexyl esters as biolubricant base stock as well as an additive for petroleum and mineral base oils. The reaction conditions employed were 120°C, 72 hours, FAME: ethylhexanol ratio of 1:3 and 1% w/w of H 2 SO 4 .…”

“…Lubricant producers have started a reformulation exercise as well as a redesigning of additives, such as fatty amides, fatty alcohols, fatty amines, propyl gallate, engineered specifically for biolubricants with huge achievements 17,18 instead of the usual mineral‐based additives. These additives act as anti‐foams, anti‐oxidants (AO), anti‐wear agents (AWA), detergents, dispersants, extreme pressure additives (EPA), friction modifiers (FM), pour point depressants (PPD), rust/corrosion inhibitors, and viscosity index improvers (VII) 19,20,21 …”

“…These additives act as anti-foams, anti-oxidants (AO), anti-wear agents (AWA), detergents, dispersants, extreme pressure additives (EPA), friction modifiers (FM), pour point depressants (PPD), rust/corrosion inhibitors, and viscosity index improvers (VII). 19,20,21 It is worth knowing that several recent reviews have been carried out on advancing the production of biolubricants. Mcnutt et al, 8 focused on vegetable oils' different chemical modification pathways and highlighted their respective merits and demerits.…”