Fourier Transform Infrared and Solid State 13c Nuclear Magnetic Resonance Spectroscopic Characterization of Defatted Cottonseed Meal-Based Biochars

Conversion to biochcar may be a value-added approach to recycle defatted cottonseed meal (CSM), a major byproduct from the cotton industry. In this work, complete slow pyrolysis at seven peak temperatures ranging from 300 to 600°C in batch reactors was implemented to process CSM into biochar products. Elemental analysis, attenuated total reflection Fourier transform infrared (ATR FT-IR) spectroscopy and solid state 13C nuclear magnetic resonance (NMR) spectroscopy were applied to characterize raw CSM and its derived biochar products. The biochar yield and organic C and total N recoveries decreased as the peak pyrolysis temperatures was elevated. However, most of the mineral elements including P in CSM were retained during pyrolysis and became enriched in biochar as a result of the decreased mass yield. The spectral data showed that pyrolysis removed signatures of the biopolymers in CSM and produced highly aromatic structures in biochars. With increasing the pyrolysis temperature, alkyl structures decreased progressively in the biochar products and became negligible at higher temperatures (550 and 600°C). Quantitative analysis of FT-IR data revealed that simple 3-band (1800, 1700, and 650 cm-1)-based R readings of the biochars were linearly related to the pyrolysis temperatures. The 13C NMR spectra further validated that the decreasing aromatic structures and increasing alkyl, aliphatic C-O/N and carbonyl groups in CSM-derived biochars were highly correlated with the increasing pyrolysis temperature. Therefore, the cheap and faster FT-IR measurement could be used as a routine conversion indicator of pyrolysis of lignocellulosic biomass rather than the more expensive and time-consuming NMR spectroscopy.