Reductive catalytic fractionation of wheat straw biomass



Reductive catalytic fractionation (RCF) is a promising method for the development of so-called “lignin-first” biorefineries. Apart from the widely investigated virgin woody biomass, it is essential to explore the potential of waste biomass feedstocks. Herein, the RCF of wheat straw is examined, to produce lignin mono-/oligomers along with a processable carbohydrate pulp. The use of different catalysts (Ru/C and Ru/Al2O3) and catalyst loadings (0 – 20% w/wbiomass) revealed the superior performance of Ru/C, which resulted in the largest yield of phenolic monomers (up to ~25 wt% of initial acid insoluble lignin) and in the lowest formation of high-molecular weight fragments in the extracted lignin oil. Furthermore, the operating temperature was shown to substantially affect both lignin extraction-depolymerization and polysaccharides preservation-processability. For a reaction time of 3 hours, an increase of the temperature from 200 to 250 °C resulted in a > 2-fold boost of the yields of lignin oil and monophenolics, while the recovery of polysaccharides decreased by about 30 wt% (with ~20% lower enzymatic digestibility). An economic assessment highlighted that the high-temperature treatment becomes the most profitable configuration as the market price of lignin products increases. Overall, this work provides insight into the adoption of RCF for the upgrading of lignocellulose from inexpensive and widely available wheat straw biomass.


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Supplementary material

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Supporting information
A complete description of the materials used in this work, of the experimental procedures adopted for carrying out fractionation experiments and for the analysis of the obtained product streams is given. Details of the calculations are provided. The supporting figures include pictures of the experimental setup and of the fractionation products, FTIR spectra, XRD profiles, GPC, GC, and HPLC chromatograms, 1H-13C HSQC NMR spectra of lignin oils, SEM images of isolated pulps, OM mass balances, a flow diagram of RCF, and an economic sensitivity analysis. The supporting schemes show the proposed reaction pathways for the formation of monophenolics and carbohydrate derivatives. The supporting tables provide details about the compositional analysis of wheat straw biomass, ATR-FTIR bands assignments, 1H-13C HSQC NMR cross signals assignments and quantification, and the calculations and the data used for the economic assessment.