Ptfe‐carbon nanotubes and lipase b from candida antarctica—long‐lasting marriage for ultra‐fast and fully selective synthesis of levulinate esters

An effective method for levulinic acid esters synthesis by the enzymatic Fischer esterification of levulinic acid using a lipase B from Candida antarctica (CALB) immobilized on the advanced material consisting of multi‐wall carbon nanotubes (MWCNTs) and a hydrophobic polymer—polytetrafluoroethylene (Teflon, PTFE)—as a heterogeneous biocatalyst, was developed. An active phase of the biocatalyst was obtained by immobilization via interfacial activation on the surface of the hybrid material MWCNTs/PTFE (immobilization yield: 6%, activity of CALB: 5000 U∙L∙kg⁻¹, enzyme loading: 22.5 wt.%). The catalytic activity of the obtained biocatalyst and the effects of the selected reaction parameters, including the agitation speed, the amount of PTFE in the CALB/MWCNT‐PTFE biocatalyst, the amount of CALB/MWCNT‐PTFE, the type of organic solvent, n‐butanol excess, were tested in the esterification of levulinic acid by n‐butanol. The results showed that the use of a two‐fold excess of levulinic acid to n‐butanol, 22.5 wt.% of CALB on MWCNT‐PTFE (0.10 wt.%) and cyclohexane as a solvent at 20 °C allowed one to obtain n‐butyl levulinate with a high yield (99%) and selectivity (>99%) after 45 min. The catalyst retained its activity and stability after three cycles, and then started to lose activity until dropping to a 69% yield of ester in the sixth reaction run. The presented method has opened the new possibilities for environmentally friendly synthesis of levulinate esters.