Glycols recovery using reactive extraction with boronic acid derivatives

Important bulk chemicals like alcohols, glycols and organic acids can be produced from renewable sources through fermentation processes where the product has to be recovered from diluted fermentation broths. The recovery of these products by distillation or multiple effect evaporation is associated with high-energy consumption. Low molecular weight diols, such as mono ethylene glycol (MEG) are particularly difficult to separate because of their high affinity to water. Liquidliquid extraction (LLE) is a technology that can be interesting because it is energy efficient. Unfortunately, with conventional solvents the distribution is too low to achieve efficient extraction at low broth concentrations. Therefore, novel extractants are needed that improve MEG distribution. Boronic acids are known because their good ability to form complexes with cisdiols. In an approach to efficiently extract MEG from water, Naphtalene-2- Boronic Acid (NBA) was tested experimentally. NBA is a hydrophobic boronic acid that was dissolved in 1-ethyl-hexanol and octanol. 1-ethyl-hexanol worked better than octanol, which is in agreement with previous research. NBA requires a counterion for the complexation with MEG, hereto Aliquat 336 (trialkylmethyl ammonium) was selected. The partition coefficient of MEG in 1-ethyl-hexanol is 0.0025. It was found that the distribution can be increased by addition of NBA and Aliquat 336 in equal amounts. The distribution was pH dependent; the best results were obtained with pH 11. Distribution coefficients up to 0.026 at 25 °C in a single stage extraction were found, which is about 10 times better than the conventional solvent. In order to improve the extraction of MEG from water, the effect of temperature will be investigated further, as well as the effect of the structure of the boronic acid on the distribution coefficient of MEG.