Kaufmann A., Kunihs S., Häcker L. and Kienberger M.
The aromatic acids p-hydroxybenzoic acid (HBAC), vanillic acid (VANAC), and syringic acid (SYRAC) are important chemicals applied in food, cosmetics, and pharmaceuticals. One possible production route is the wet oxidation of the macromolecule lignin, resulting in an acidic aqueous solution of aromatic acids, that can be recovered by a solvent extraction procedure.
In this work, 14 solvents that can be produced from renewable resources grouped by ethers, esters, fatty alcohols, terpenes, and terpenoids, including Hydrophobic Deep Eutectic Solvents (HDES) are screened for their extraction efficiency of the components HBAC, VANAC, and SYRAC. The experiments consisted of solvent extractions with a model solution, followed by a back-extraction with 0.1 M NaOH, to determine the overall extraction efficiency. Analyte concentrations were determined by High Performance Liquid Chromatography. Mutual solubility was measured by Total Organic Carbon analysis and Karl-Fischer titration. The number of theoretical separation stages for a counter-current extraction was calculated applying the solvent 1-octanol.
The highest extraction efficiency for HBAC and VANAC was achieved by the ether 2-methyl tetrahydrofuran with 99.00 %, and 98.06 % at a value of 94.87 % for SYRAC, facing drawbacks of high mutual solubility. The terpenoid geraniol yielded the highest extraction efficiency for SYRAC with 96.57 % at numbers of 97.76 % for HBAC, and 97.89 % for VANAC. The highest and nearly complete recovery of HBAC and VANAC was achieved by the solvents 1-octanol and geraniol at a SYRAC-recovery of 85.67 %, and 85.47 %, respectively. The highest recovery of SYRAC was reached by the HDES, consisting of 80 mol.% fenchol and 20 mol.% 1-dodecanol with 87.15 %. In general, investigated HDES face drawbacks when contacted with 0.1 M NaOH, which led to problems such as hydrolysis or the establishment of a third phase. The number of theoretical separation stages to extract 99 % of aromatic acids at a solvent to feed ratio of 1:1 applying 1-octanol was calculated to be 1.67 for HBAC, 1.78 for VANAC, and 1.87 for SYRAC.
Separation and Purification Technology, 2025
DOI: doi.org/10.1016/j.seppur.2025.134130