Exploring the potential of eversa transform 2.0 to produce high-performance biolubricants: from biocatalyst design to tribological studies

Abstract

Biolubricants are a sustainable alternative to mineral-based lubricants. Similarly, biocatalysts are a sustainable alternative to chemical catalysts. Eversa Transform 2.0 (ETL) is a low-cost biocatalyst engineered from the lipase from Thermomyces lanuginosus (TLL). ETL was designed to produce biodiesel; however, the specificity scope of ETL is herein explored by employing branched alcohols and polyols to produce high-performance biolubricants. Firstly, free ETL was employed in the esterification of 2-ethyl-1-hexanol with the free fatty acids (FFAs) from castor oil. Some process parameters were evaluated by the Taguchi method, reaching over 95% of conversion under optimized reaction conditions (15 wt.% of biocatalyst, 1:4 molar ratio (acid/alcohol), 30 °C, 180 rpm, 96 h). The 2-ethyl-1-hexanol-esters exhibited improved oxidative stability compared to the feedstock (0.18 h to 16.83 h); and, compared to a 20W-50 lubricant, the 2-ethylhexanol-esters exhibited a lower friction coefficient (FC) (0.052 versus 0.078). In another study, ETL and TLL were immobilized on a methacrylate macroporous resin containing octadecyl groups (C18) by interfacial activation; then, ETL@C18 and TLL@C18 were compared to their free counterparts and to commercially immobilized TLL (Lipozyme® TL IM) in the esterification of neopentylglycol (NPG) with the FFAs from soybean oil. ETL@C18 surpassed all tested biocatalysts, reaching a conversion up to 98% (3 wt.% of biocatalyst, 2:1 (acid/alcohol), 45 °C, 180 rpm, 6 h). ETL@C18 retained approximately 90% of conversion after 10 reuses. The NPG-esters presented higher viscosity index (190.84 versus 215.86) and oxidative stability (0.10 h versus 1.34 h) than the feedstock; and lower FC (0.049 versus 0.064) and wear scar diameter (139.03 μm versus 151.43 μm) than a 20W-50 lubricant. ETL@C18 also surpassed free ETL as well as free and C18-immobilized lipase from Candida antarctica (CALA@C18) in the hydrolysis of residual coconut oil (RCO), reaching full hydrolysis under optimized reaction conditions (9 wt.% of biocatalyst, 1:2 (oil/water, w/w), 50 °C, 180 rpm, 3 h) and maintaining up to 85% of hydrolysis yield after 10 reuses. Finally, ETL@C18, CALA@C18 and their combi- lipases were evaluated in the hydroesterification of RCO with trimethylolpropane (TMP). The combi-lipases outperformed the single biocatalysts, reaching full hydrolysis (99.63%) under optimized reaction conditions (9 wt.% of biocatalyst content, 1:2 (oil/water), 40 °C, 240 rpm and 2 h) and full conversion (99.82%) under optimized reaction conditions (5 wt.% of biocatalyst content, 3:1 (acid/alcohol), 50 °C and 180 rpm and 8 h). The 0.75ETL@C18 + 0.25CALA@C18 combi-lipases maintained 83% of hydrolysis whereas the 0.5ETL@C18 + 0.5CALA@C18 combi-lipases maintained 94% of esterification after 10 reuses. The TMP-esters presented a higher viscosity index than the feedstock (162.66 versus 126.90) and a lower FC than a 20W-50 lubricant (0.066 versus 0.074). Overall, ETL@C18 presented a suitable performance in the preparation of FFAs to produce biolubricants as well as in the production of high- performance biolubricants from different feedstocks – from hydroxyl to saturated fatty acid; from branched alcohols to triols.