Biocatalytic synthesis of dioctyl sebacate in toluene using an immobilised lipase

Abstract

Abstract Sebacic esters have excellent lubricity, thermal stability, and biodegradability and therefore are widely used as aerospace lubricants, metal working oil, or engine oil. They are mainly produced by chemical synthesis which, however, may cause environmental pollution, its enzymatic synthesis represents a more environmentally friendly alternative. A few reports have described the synthesis of sebacic esters employing immobilised lipases, but these biocatalytic reactions were exclusively carried out in solvent-free systems and thus, could have been limited by slow reaction rates and high reaction temperatures due to poor enzyme dispersion, low substrate solubility, and high viscosity of the reaction mixture. The current study investigated the biosynthesis of dioctyl sebacate in toluene by Novozym 435, a commercial immobilised lipase. The reaction parameters were investigated using the single factor approach and an orthogonal array design. The optimal conditions obtained were as follows: 10 mL toluene, sebacic acid,1 mmol (202.25 mg); molar ratio of sebacic acid to 1-octanol, 1:3; Novozym 435, 0.03 g; 4 Å molecular sieves, 1.5 g; reaction temperature, 40 °C; reaction time, 30 h. A dioctyl sebacate conversion rate of 93% was achieved under these optimal conditions. In particular, the addition of molecular sieves to the reaction mixture markedly improved the product yield. The reaction temperature was low enough to make the operation easy and energy-efficient and therefore, well suited for large-scale production.