An energy-efficient upconcentration of the bio-based carboxylic acids using multiple-effect evaporators

This study proposes an integrated process chain to upconcentrate short-chain carboxylic acids (SCCA) like acetic, propionic, and butyric acid, produced from anaerobic fermentation of the organic fraction of municipal solid waste. The starting point is the residual biogas, which is produced from the anaerobic digestion of the solid fraction obtained after the acid fermentation. Using this biogas energy, integrated multiple-effect evaporator scenarios with varying SCCA initial concentrations from 10 to 40 g/L in the liquid fraction were simulated in Aspen Plus®. Using four-effects and starting from 20 g/L, SCCA can be upconcentrated to 526 g/L with only minor acids loss. This process requires 9.8 kWh energy/kg SCCA produced, which was provided by the biogas generated from the solid residue post-digestion. Also, the accuracy of the simulation results across different pressure ranges has been confirmed through the validation of the input model used in Aspen Plus®. The carbon footprint of this process was 1.24 kg CO₂-eq./kg SCCA produced, which was 50% lower than the existing processes producing fossil-based SCCA. A techno-economic assessment have also been performed for different evaporator configurations.