Twenty-two compositional characterizations and theoretical energy potentials of extensively diversified China's crop residues

Knowledge of the compositional properties of crop residues feedstocks is important for process control and handling of co-products and waste from energy utilization. In this study, 1076 crop residues were collected from 326 sites across China. Chemical analysis of five organic chemical compositions, four proximate compositions, five ultimate compositions and eight mineral elements were conducted. Energy potentials of crop residues in China were quantified based on their compositional characterization. Results showed that the compositional characteristics of wheat straw, rice straw, corn stover, rape stalk and cotton stalk were shown to be significant different (p < 0.05) and highly variable. The coefficients of variation were negatively correlated with the means of crop residues compositions. Principal component analysis reflected that the compositions could explain several variations and clustering rules of the five crop residues. The correlations among parameters could be briefly summarized as hemicelluloses/ash-cellulose/lignin/water soluble carbohydrates/crude protein/P, water soluble carbohydrates-crude protein, crude protein-N-P-Mg-Cu, volatile matter-ash-fixed carbon, C-H-O-N-S, P-K-Na-Ca and ash-C/H/O/K (p < 0.01). The energy potentials of the five substrates were also significantly different (p < 0.05). The higher heating values, theoretical ethanol yields, and theoretical biomethane yields of the crop residues were 12.97-18.58 MJ/kg, 336.69-658.25 g/kg, and 151.48-288.45 L/kg, respectively.