Lubricants—a more than $146-billion market serving numerous applications, automotive among them—are produced from base oils derived from petroleum mineral oils (mineral base oil) or synthetic oils such as poly-α-olefins (PAOs) (synthetic base oil). As such, lubricants have a significant environmental footprint.
A team at the University of Delaware has now synthesized new bio-based base oils with tunable molecular branches and properties at high yields (>80%) from biomass-derived 2-alkylfurans with enals via conjugate addition-hydroxylalkylation/alkylation (CA-HAA) and hydrodeoxygenation reactions. An open-access paper on their work appears in the RSC journal Green Chemistry.
In order to tailor lubricant properties, a significant fraction of additives is employed, increasing cost and environmental footprint. There is increasing need for development of improved energy-efficiency, high performance, durable, and environmentally-acceptable base oils that operate under extreme environmental conditions. Their production from non-food biomass is an attractive alternative to reduce reliance on petroleum and mitigate the environmental footprint.
Bio-ester base oils, produced by chemical modification of fatty acids, have recently been commercialized for this purpose. They have, unlike hydrocarbon-base oils, limited applicability because they lack desired molecular structures and properties and have compatibility issues. … In addition, ester base-oils are hydrolyzed more easily producing corrosive acids. Furthermore, some current commercial additives used in lubricant formulation are not miscible with bio-esters.
A few efforts have been devoted to the synthesis of bio-based hydrocarbons for lubricant base-oils. … We have recently reported the synthesis of bio-based branched hydrocarbons via an atom- and energy-efficient hydroxylalkylation/alkylation (HAA) scheme followed by HDO using biomass-derived 2-alkylfurans and aldehydes. The ASTM specification data for our bio-based C30 branched alkane suggest better viscosity index (VI) and volatility than those of commercially, petroleum-derived synthetic C30 PAOs base-oils. However, the pour point (PP) of our base-oil was higher due to the presence of only one branch on the carbon chain compared to more carbon-branched PAOs.
As more branches on the carbon chain is key for a lower PP, we disclose an efficient catalytic route to synthesize renewable, branched lubricant base-oils in excellent yields.—Liu et al.
The new process consists of tandem conjugate addition (CA) and HAA of biomass-derived 2-alkylfurans with enals to form trifuran compounds over acid catalysts, followed by HDO catalyzed by metal/metal oxide catalysts. This novel concept enables the synthesis of a range of structurally diverse base-oils using different molecular size alkylfurans and enals.
A) Conventional approach to synthesizing base oils and B) the new bio-based approach. Liu et al.
Among several liquid and solid sulfonic acid catalysts tested for the CA-HAA condensation, Aquivion PW79S, a perfluorinated sulfonic acid resin, exhibited the best performance.
The molecular size and number of branches of the products can be tuned by varying the molecular sizes of substrates in the CA-HAA step.
Sibao Liu, Basudeb Saha and Dion Vlachos (2019) “Catalytic Production of Renewable Lubricant Base-Oils from Bio-Based 2-Alkylfurans and Enals” Green Chem. doi: 10.1039/C9GC01044K