Transesterification of oil to biodiesel in a continuous tubular reactor with static mixers: Modelling reaction kinetics, mass transfer, scale-up and optimization considering fatty acid composition

Abstract

Simulations of the methanolysis of lipids in a mixer-packed bed heterogeneous flow process were performed based on the thermodynamics (equilibrium) as well as mechanism and chemical kinetics of glycerides and fatty acid methyl esters (FAME) containing different combinations of gadoleic (G), linoleic (L), linolenic (Ln), oleic (O), palmitic (P) and stearic (S) acids, bonded as glycerol (alcohol) substituents. Transport phenomena and fluid dynamics were established for emulsion interface films and through axial dispersion coefficients (Péclet number) in a fixed bed for both transient and stationary operation. Alcoholysis was also studied experimentally within a broad range of temperatures, hydrodynamic conditions in terms of volumetric flow rates, phase ratios and base catalyst concentrations. Diffusion resistance proved to be negligible, temperature was proven as a prevalent factor, while steady state was reached only after a few residence times elapsed. Process economics were finally evaluated in terms of cost and price breakdown, allowing methodology extension to other waste oil resources. Sensitivity analysis revealed high LLL triglyceride content in oil having the greatest positive, and OOL negative effect on FAME yield. Process intensification with static mixers was proven feasible upon scaling-up from 5 to 10mm internal diameter with no deterioration in overall process progression.