Hydrothermal carbonization (HTC): Near infrared spectroscopy and partial least-squares regression for determination of selective components in HTC solid and liquid products derived from maize silage

Significance Statement

In the APECS (Anaerobic Pathways to Renewable Energy and Carbon Sinks) group, we are conducting and publishing advanced biogas and biochar research for years. One of the main focuses of our research is to develop interdisciplinary collaboration. This paper is the outcome of such collaboration between the scientists of Leibniz Institute for Agricultural Engineering (ATB), Potsdam, Germany and Fraunhofer Institute for Chemical Technology (Fh-ICT), Pfinztal, Germany. In this paper, we have showed successful use of near infrared (NIR) spectroscopy on hydrothermal carbonization (HTC) products (both solid hydrochar and HTC process liquid) and selective components are determined by partial least squares regressions (PLSR). Lignin, cellulose, hemicellulose, extractives, and ash concentrations were determined by the NIR and PLSR of hydrochar, meanwhile, organic acids, sugars, furfural derivatives, and phenolic compounds were determined of hydrothermal carbonizationprocess liquid. With the evolvement, HTC technology is now applying into various moist waste feedstocks for waste to energy or waste to material production. A robust, simple, but accurate method of determining the quality of hydrothermal carbonization products is very necessary not only for product quality but also for hydrothermal carbonization process design. NIR with PLSR is very promising for fulfilling the purpose and the results from this study backing it up successfully. In the future, we will develop online/inline NIR probe, which collects real time spectra and converts into chemical composition by PLSR.

Figure:  Hydrothermal carbonization reaction system (capacity 5 gal).

Hydrothermal carbonization (HTC) .Renewable Energy Global Innovations

Journal Reference

Bioresource Technology, Volume 161, 2014, Pages 91–101.

Toufiq Reza1,, Wolfgang Becker2, Kerstin Sachsenheimer2, Jan Mumme1


1 APECS Group, Leibniz Institute for Agricultural Engineering (ATB), Max-Eyth-Allee 100, Potsdam 14469, Germany and

2 Energetische Systeme, Fraunhofer Institut für Chemische Technologie (Fh-ICT), Joseph-von-Fraunhoferstr. 7, Pfinztal 76327, Germany.



Near-infrared (NIR) spectroscopy was evaluated as a rapid method of predicting fiber components (hemicellulose, cellulose, lignin, and ash) and selective compounds of hydrochar and corresponding process liquor produced by hydrothermal carbonization (HTC) of maize silage. Several hydrothermal carbonization reaction times and temperatures were applied and NIR spectra of both HTC solids and liquids were obtained and correlated with concentration determined from van-Soest fiber analysis, IC, and UHPLC. Partial least-squares regression was applied to calculate models for the prediction of selective substances. The model developed with the spectra had the best performance in 3–7 factors with a correlation coefficient, which varied between 0.9275–0.9880 and 0.9364–0.9957 for compounds in solid and liquid, respectively. Calculated root mean square errors of prediction (RMSEP) were 0.42–5.06 mg/kg. The preliminary results indicate that NIR, a widely applied technique, might be applied to determine chemical compounds in hydrothermal carbonization solid and liquid.

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