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

Conversion to biochar may be a value-added approach to recycle defatted cottonseed meal, 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 cottonseed meal into biochar products. Elemental analysis, attenuated total reflection Fourier transform infrared (ATR FT-IR) spectroscopy and quantitative solid state 13C nuclear magnetic resonance (NMR) spectroscopy were applied to characterize raw meal 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 cottonseed meal were retained during pyrolysis and became enriched in biochar as a result of the decreased mass yield. The spectral data showed that pyrolysis removed the functional groups of biopolymers in cottonseed meal, producing highly aromatic structures in biochars. With increasing 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 the values of a simple 3-band (1800,1700, and 650 cm-1)-based R reading of the biochars were linearly related to the pyrolysis temperature, and showed strong correlations with decreasing aromaticity and increasing alkyl, aliphatic C-O/N and carbonyl signal intensities in the 13C NMR spectra. Therefore, the cheaper and faster FT-IR measurement could be used as a routine conversion indicator of pyrolysis of lignocellulosic biomass instead of the more expensive and time-consuming NMR spectroscopy.