BACKGROUND: The organosolv process promotes biomass delignification at relatively high temperatures using a wide variety of organic solvent solutions. Nevertheless, previous studies on organosolv processes have not dealt with the use of ethyl lactate as organic solvent. Thus the aim of the present contribution was to determine and to validate if the use of ethyl lactate has a positive influence on lignin recovery for organosolv processes whose feedstock is the solid waste from a wheat straw-based biorefinery. The effect of operating conditions (temperature and time) on lignin recovery was also studied. RESULTS: A mixed design of experiments was proposed as the strategy to maximize lignin recovery. The mathematical model derived from a multiple linear regression applied to the mixed design results indicates that 190 ∘ C and a non-aqueous solution containing ethyl lactate and ethanol (81.2% w/w ethyl lactate) could provide a maximum lignin recovery of 75.9% w/w. This theoretical maximum was validated. Thus the proposed model adequately describes the behavior of lignin recovery. Moreover, Fourier transform infrared (FTIR) characterization of the resultant lignin suggested that its structure is a function of the organic solvent solution used during the organosolv process.CONCLUSION: The evidence from this study indicates that lignin recovery from the solid waste of a wheat straw-based biorefinery in an organosolv process depends on temperature and ethyl lactate presence in the reaction medium. These findings enhance the understanding of organosolv processes and could be applied if eventual lignin valorization is desired.Corrections added on 24 January 2020, after first online publication: the second occurrence of the term "m residue " in Equation 1 has been changed to "m sample ". Also the term "m sample " has been included in the sentence "In summary, 300.0 ± 10.0 mg of the solid waste was weighed in a pressure tube" under the section "Washings and lignin content quantification in solid waste".

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