Chemometrics to connect feedstock quality, process settings and calorific value of hydrochar through infrared spectra

The current urgent need for clean energy has sparked interest in hydrothermal carbonization (HTC) as a sustainable avenue to convert high moisture biomass wastes into an efficient bioenergy source. Without destructive methodologies and offering distinct advantages (e.g. real-time analysis) over traditional assessments, chemometric methods coupled to Fourier Transform Infrared Spectroscopy (FTIR) is presented as an innovative approach for a rapid assessment of the higher heating value (HHV) of hydrochars. With the help of advanced chemometric techniques such as Partial Least Squares (PLS) or Sequentially Orthogonalized PLS (SO-PLS) further insights are gained into the underlying chemical transformations during HTC treatment of a wide variety of biodegradable wastes. Our model predicts the HHV of the diverse hydrochars with an impressive R² value of 0.961 and an RMSE of 0.845 MJ/kg. The scores and loading plots point out the pivotal functional groups that distinguish the various hydrochars, while also unveiling the inherent similarities among them. A second model has been further devised to predict the HHV of hydrochar as a function of feedstock composition and HTC operation conditions, thus allowing process optimization. This challenging approach can be extrapolated to quickly evaluate other physicochemical parameters of hydrochars designed for various applications.