Creosote Wood Valorization Coupled with Simultaneous Extraction of Embedded Hydrocarbons

Abouelela, A.R.; Hallett, J.P.

This study investigates the use of the protic ionic liquid (IL) N,N,N-dimethylbutylammonium hydrogen sulfate [DMBA][HSO₄] to effectively valorize and decontaminate hazardous creosote-treated timber. We found that [DMBA][HSO₄] mixed with 20 wt % water is capable of fractionating creosote-treated timber into a cellulose-rich pulp and lignin stream at a high solid loading of 1:5 g g^–1. Pretreatment severity plays an essential role in the process fractionation performance with delignification reaching 60% and enzymatic saccharification of cellulose-rich pulps, exceeding 70% of the theoretical maximum achieved under the highest investigated pretreatment severity conditions (170 °C, 45 min, and 20 wt % water content as a cosolvent). We report that the nonhydrophobic protic IL [DMBA][HSO₄] is highly effective in extracting polycyclic aromatic hydrocarbons (PAHs) from the creosote embedded in the timber, producing a highly digestible, PAH-free cellulose-rich pulp. Analysis of the fate of PAH compounds in the process streams (feedstock, IL liquor, cellulose pulp, and lignin) showed the high tendency of the PAHs to precipitate with lignin upon the addition of water as an antisolvent. The study demonstrates a novel application of protic [HSO₄]-based ILs in fractionating and decontaminating creosote-treated, unutilized hazardous biomass waste to produce inexpensive highly digestible cellulose substrates for second-generation biofuel production.