Steady-state simulation of a novel extractive reactor for enzymatic biodiesel production

Intensification of the biodiesel production process may offer significant capital and operating cost benefits due to fewer unit operations. In addition, the continuous removal of co-product glycerol from the reactive phase during transesterification promises higher biodiesel yield relative to conventional batch reactors. As a result, this paper investigates the application of a novel liquid-liquid extractive reactor with basket-like mixing impellers containing enzyme particles for biodiesel production. Steady-state modelling using commercial process simulation software coupled with an iterative method for estimation of holdup was carried out. Models considered countercurrent flow of vegetable oil and aqueous ethanol solution in a multistage, mixer-settler type extractive reaction column (XRC), catalysed by immobilised lipase. Simulation results revealed that the conversion was insensitive to solvent to feed ratios beyond stoichiometric ratio of ethanol-to-triglycerides, thus making the XRC superior to batch process which uses excess alcohol. Increasing number of stages, stirring speed and raffinate recycle ratio improved conversion over the respective ranges studied. Optimum ethanol content in the solvent (water) was located at 46%v/v. In all simulations, glycerol recovery in the extract stream exceeded 99.9%, while biodiesel was retained almost exclusively in the product raffinate stream, illustrating exceptional product quality associated with the novel XRC.

► Novel extractive reactor column (XRC) offers superior performance to batch reactor.
► XRC was modelled using Aspen Plus coupled to iterative holdup calculation.
► Conversion increases with number of stages and with square of stirring speed.
► Optimum aqueous ethanol concentration is 46 vol%.
► Greater than 99% glycerol recovery achieved in extract stream.