Solid/Gas Synthesis of Isobutyl Propionate Catalyzed by Packed-Bed CalB Cross-Linked Enzyme Aggregates (CLEA)

This research examines the viability and effectiveness of cross-linked enzyme aggregates (CLEA) ofCandida antarctica lipase B (CalB)/bovine serum albumin (BSA) for the green synthesis of isobutyl propionate (isoPro) from propionic acid (aciP) and isobutyl alcohol (isoB). Solid/gas (S/G) biocatalysis is proposed as a more sustainable alternative to chemical synthesis, which involves toxic catalysts and harsh conditions, or plant extraction compounds, which are economically unfeasible for bulk production. A formulation containing 10 mg mL^-1 BSA and 3% glutaraldehyde (GA) was selected based on CalB-CLEA's demonstrated catalytic efficiency in n-heptane as solvent, along with its thermal and operational stability. Using 600 mg of the selected CalB-CLEA in the S/G bioreactor yielded 91.71% isoPro at a water activity (a _w) of 0.52, with a nitrogen flow rate of 62 mL min^-1 and a 1:4 acid/alcohol molar ratio, operating at 55 °C and 585 mmHg. Although 1.0 g of commercial CalB ImmoPlus achieved a higher yield (98.9%), its total turnover number (TTN) (mol product mol^-1 enzyme) and specific space-time yield (STY_spe) (g product L^-1 h^-1 mg^-1 CalB) under steady-state conditions were 6- and 4-fold lower, respectively, than those of CalB-CLEA. Additionally, CalB-CLEA eliminates resin disposal costs, yielding similar outputs with lower enzyme loads while achieving comparable productivity. Ultimately, the S/G system incorporating CalB-CLEA outperforms both CalB ImmoPlus (in S/G) and CalB-CLEA (in n-heptane) in green, mass-based sustainability metrics, underscoring its strong potential for industrial-scale applications.