Fourier transform infrared and solid state 13C nuclear magnetic resonance spectroscopic characterization of defatted cottonseed meal-based biochars

Authors: He, Zhongqi; GUO, MINGXIN - Delaware State University; Fortier, Chanel; CAO, XIAOYAN - Brandeis University; SCHMIDT-ROHR, KLAUS - Brandeis University

Submitted to: Modern Applied Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/12/2021
Publication Date: 1/15/2021
Citation: He, Z., Guo, M., Fortier, C., Cao, X., Schmidt-Rohr, K. 2021. Fourier transform infrared and solid state 13C nuclear magnetic resonance spectroscopic characterization of defatted cottonseed meal-based biochars. Modern Applied Science. 15(1):108-121. https://doi.org/10.5539/mas.v15n1p108.
DOI: https://doi.org/10.5539/mas.v15n1p108

Interpretive Summary: While cotton is a cash crop and provides a major fiber source for the textile industry, exploration of other cotton biomass as sustainable industrial feedstock are environmentally and economically feasible for cotton industry. Given its relatively high energy density, defatted cottonseed meal (CSM) could be a good feedstock for producing biochar and bio-oil via pyrolysis. While there are several reports from Turkey and India on pyrolysis of defatted cottonseed cake (equivalent to the meal product in USA) mainly for bio-oil production, no pyrolysis of defatted cottonseed product CSM in USA had been conducted. In this work, complete slow pyrolysis of CSM at seven temperatures from (300 to 600°C ) in batch reactors was implemented to convert the raw material into biochar products. Elemental analysis, attenuated total reflection Fourier transform infrared spectroscopy (FT-IR) and solid state C-13 nuclear magnetic resonance (NMR) spectroscopy were applied to characterize CSM and its biochar products. Comparative data analysis indicated that a simple 3-FT-IR-band (1800,1700, and 650 cm-1)-based algorithm (R readings) of the biochars was linearly related to the pyrolysis temperature, indicating pyrolysis temperature as a key factor affecting the readings. Furthermore, the readings showed a negatively linear regression with the relative intensity of NMR-identified aromatic structures, and positively linear regressions with 1MR-identified functional groups of alkyl, aliphatic C-O/N and carbonyl. If further confirmed, the more affordable and faster FT-IR R measurement could be used as a routine conversion indicator of pyrolysis of lignocellulosic biomass rather than the expensive and time-consuming solid state C-13 NMR spectroscopy.

Technical Abstract: 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.