(660c) Reactive Extraction of Acetic Acid from Liquid Phase Pyrolysis Oil and Solvent Regeneration By Distillation

Biomass is also considered as an alternative to fossil resources for fuel production. To improve efficiency of biobased processes, complete utilization of biomass is essential. Therefore, also side streams are investigated for usage. Exemplarily in liquid phase pyrolysis, like the bioCRACK process, two liquid product phases are formed. The nonpolar phase, the bioCRACK oil, can directly be processed in a refinery. The polar phase, the liquid phase pyrolysis oil (LPP), has a high water fraction containing carboxylic acids and long-chain molecules. For upgrading of LPP oil to fuel grade, a hydrodeoxygenation step is necessary for removing the high oxygen content. Before hydrodeoxygenation, the carboxylic acids shall be removed by liquid-liquid extraction with the aim of generating an additional product and for increasing the catalyst stability in hydrodeoxygenation.

Carboxylic acid extraction from aqueous phase is well investigated using organophosphorus compounds, enabling distillation for solvent regeneration. Therefore, Cyanex^®923, a mixture of trialkylphosphine oxides, in n-undecane was chosen for LPP oil extraction. To obtain sufficient separation of the acids and simultaneously minimize the loss of other organic components to the solvent phase, the concentration of the reactive extractant was optimized. The molar ratio of Cyanex^®923 to acids in the LPP oil of 0.75 showed the highest selectivity towards acids of 30 %, and an acid extraction efficiency of 47 % was achieved in one equilibrium stage.

For solvent regeneration, the laden solvent was distilled at a pressure of 200 mbar in a Dean-Starck apparatus. n-undecane forms a heterogeneous azeotrope with water which also transfers the acids to the distillate. The aqueous distillate is collected in the product funnel, while the organic phase, the upper layer in the product funnel, is recycled to the reboiler. The acid recovery from the laden solvent to the distillate was 78 %. 89 % of water was transferred from the refined solvent to the distillate. The distillate also contained small amounts of methyl acetate, propanoic acid, butanoic acid, n-undecane and 1-hydroxy-2-propanone.

In a three-stage process with extraction followed by distillation for solvent regeneration, an overall acid extraction efficiency of 81 % was achieved without loss of reactive extractant to the LPP oil.