A novel approach to the performic acid pulping of biomass enables effective delignification and fractionation in a time frame not achieved heretofore. An autothermal decomposition reaction was triggered when 100 mg/L Fe-2(SO4)(3) in 4.0 M NaOH was added to 5% or 7.5% H2O2 in aqueous formic acid containing chipped Miscanthus x giganteus. Peroxy-decomposition resulted in pressures of 19 and 35 bar in the 5% and 7.5% peroxide liquors and reduced the lignin content in the resulting pulps to <6% within 140 and 313 min, respectively. Solubilised lignin was available for recovery from the liquor by subsequent dilution with water. Hemicellulose removal to the liquor was 68% and 89% for the 5% and 7.5% peroxide solutions. Crystalline cellulose yields were >99% and >95% and the rate of glucose release from cellulase digestion of the pulps in 24 h was more than 20-fold that for the raw Miscanthus. (C) 2012 Elsevier Ltd. All rights reserved.