Cost-effective FTIR and 1H NMR spectrometry used to screen valuable molecules extracted from selected West African trees by a sustainable biochar process
Abstract
This study focused on wood extractives by a slow pyrolysis thermal extraction technique and screening of potentially valuable compounds from three African trees: Lophira lanceolata Tiegh. ex Keay., Dialium guineense Willd. and Afzelia africana Sm. The primary objective of the thermal treatment was biochar production but also liquids were collected and analyzed. Raw materials were cut into sizes of about 25 cm in length and then processed with slow pyrolysis from 20°C up to 400°C; the slow pyrolysis process included two stages, drying and pyrolysis. Five end-point temperatures were used in the range of 250°C–400°C. Raw distillates were collected at three temperatures (120°C, 60°C and 25°C) and their composition screened by either cost-effective FTIR or benchtop 80 MHz 1H NMR methods. HR-NMR and 2D GC–MS were used to confirm some findings. Results from the drying stage indicated that all distillates contained mostly water >90%, acetic acid, methanol and some other compounds at very low levels. The percentages of acetic acid were 3.5% for L. lanceolate, 2.8% for D. guineensis and 3.8% for A. africana (% with respect to the identified peaks). Results from the pyrolysis stage revealed the presence of bioactive compounds such as ketones, methanol, hydrocarbons, acetic acid, esters, alkenes and phenolic compounds at higher quantities than in the drying stage. The quantity of phenols in certain runs and distillate fractions using NMR was 1%–20% for L. lanceolata, 7–17% for D. guineensis and 10%–17% for A. africana (% with respect to the composition of the identified peaks). The percentage of hydrocarbons was 1%–48% for L. lanceolata, 1%–34% for D. guineensis and 2%–33% for A. africana. The percentage of ketones was 7%–19% for L. lanceolate, 4%–27% for D. guineensis and 19%–22% for A. africana. In general, the results indicated the presence of potential valuable compounds at relatively high concentrations. By optimizing the slow pyrolysis process parameters, it is possible to collect distillates with high concentrations of valuable biomolecules.
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