By Jinfeng Lai
A novel two-step ex situ hydropyrolysis vapor upgrading (HPVU) process can generate tailored oxygenated hydrocarbon products from lignocellulosic biomass by adjusting vapor upgrading temperature. Such products, containing varied oxygen contents (ranging from 2 to 17 wt%), are different from traditional petroleum hydrocarbons and conventional biomass-derived pyrolysis oil. Elucidation of the comprehensive structural motif of these unconventional products is critical for development and deployment of the HPVU process.
To this end, two-dimensional heteronuclear 1H–13C NMR techniques were employed to first provide single- and multiple-bond correlations between proton and carbon characteristic of different organic functional groups. The distribution of carbon functional groups was further determined by quantitative 13C NMR spectroscopy with full relaxation and well-defined chemical shift regions obtained from diverse NMR methods. Phenols and ketones were identified as the main oxygenate species in these renewable products. For products obtained from higher vapor upgrading temperatures, a decrease in oxygenate species and an increase in alkylation on aromatic rings were observed. Of particular importance, compared to pyrolysis oil, the amounts of active oxygenate species, such as aldehyde, carboxylic acid, and carbohydrate, were found to be minimal, suggesting good stability of these renewable hydrocarbon products.