Selective and efficient separation of biomass hydrolysate levulinic acid and formic acid from aqueous solution

Abstract

The recovery of levulinic acid (LA) and formic acid (FA) from aqueous solutions and actual biomass hydrolysates by using the stepwise adsorption method was investigated for the first time. The carbon molecular sieve was used as the adsorbent for FA and microporous activated carbon was used as the adsorbent for LA according to the steric hindrance effect of the pore channels and the difference in molecular diameter of FA and LA. The adsorption data of LA and FA onto their respective adsorbents were measured and numerically analyzed by adopting batch adsorption experiment and fixed-bed column methods. In the study of static adsorption equilibrium experiment, the Langmuir equation fitted the data of LA adsorption on activated carbon, while the Freundlich equation fitted well the adsorption data of FA adsorption on carbon molecular sieve. In the kinetic study, the LA adsorption on activated carbon and FA adsorption on carbon molecular sieve confirmed the PSO model. Moreover, the effect of various conditions on fixed-bed column adsorption progress was investigated, which indicated that the adsorption property improved with feed flow rate, column length, temperature decreasing and initial concentration increasing. The Yoon-Nelson model was adopted to predict and analyze the whole process of adsorption breakthrough and consistent well with the experimental data. The separation of LA and FA was realized by continuous fractional adsorption.