Renewable glycoaldehyde isolation from pyrolysis oil by reactive extraction with primary amines

The transition to a sustainable bio-based economy has rapidly increased the interest to obtain renewable platform chemicals from biomass. Glycolaldehyde is one of potential future platform chemicals, which is present in high quantity (5–13 wt%) in wood-derived pyrolysis oil. Water addition to pyrolysis oil isolates glycolaldehyde and other polar compounds, nearly quantitatively in the aqueous phase. In order to apply extraction for the subsequent glycolaldehyde recovery a water-insoluble solvent is required. This work was done to identify a suitable solvent. Firstly, several long chain alkanes and alcohols were evaluated by extracting an aqueous solution of 6.2 wt% glycolaldehyde. The results demonstrated that alkanes cannot extract glycolaldehyde whereas the distribution coefficient of glycolaldehyde in alcohols decreases with chain length, from 0.23 for 1-octanol to 0.04 for oleyl alcohol. Due to low distribution coefficients, primary amines were considered extractants since they can form reversible imines with aldehydes. A solution of 1 M Primene JM-T in 1-octanol and pure Primene JM-T increases the distribution coefficient of glycolaldehyde in 1-octanol by a factor of 10 and 75, respectively. The extraction factors are 0.46 for 1-octanol, 3.79 for 1 M Primene JM-T in 1-octanol and 30.87 for pure Primene JM-T. Another alternative is aniline derivatives. At a concentration of 1 M, 4-ethylaniline gives more than two orders of magnitude higher distribution ratio than 2-ethylaniline and Primene JM-T. The extraction capability of amines is: octylamine >4-ethylaniline >phenylethylamine >>Primene JM-T >2-ethylaniline. In conclusion, highly branched primary amines and orthoalkylanilines are promising extractants, taking into account the reversibility of the Schiff base formation. The final selection of the most suitable extractant/diluent combination will depend on the actual selectivity towards glycolaldehyde and back-extraction yield.