Investigating the potential of Aucoumea klaineana Pierre sapwood and heartwood wastes to produce cellulosic ethanol

Abstract

This work investigates for the first time the different reactivity exhibited by sapwood and heartwood wastes under two conditions: They were pretreated with catalyzed ethanol organosolv in the presence of sulfuric acid and their pulps underwent enzymatic hydrolysis by Trichoderma reesei which causes them to release neutral sugars for the production of cellulosic ethanol. Aucoumea klaineana Pierre (Okoumé) wood wastes were used for the experiment. Organosolv pretreatment was performed to investigate how to harness the benefits of fermentable sugars and lignin, which were reacted at varying defined severity levels as follows: 160°C≤T≤210°C and 0%≤[H₂SO₄]≤2% (w/w). The highest ethanol organosolv lignin content was obtained at T=160°C and [H₂SO₄]=1% for sapwood (18.10%) and heartwood (19.46%) (w/w). Enzymatic hydrolysis of the pretreated wood samples displayed that sapwood and heartwood pulps released their highest sugars content under free acid pretreatment conditions. The maximum neutral sugar released by heartwood pulps pretreated at T=160°C and [H₂SO₄]=0% was 0.126 g/L while that from sapwood pretreated at T=185°C and [H₂SO₄]=0% was 0.125 g/L. It is noteworthy that, the neutral sugars from sapwood and heartwood do not have the same sensitivity to temperature increase. When pretreated at T=160°C and [H₂SO₄]=0%, sapwood pulps yielded the following neutral sugars: Xyl< Ara≈Gal < Man < Glu, while heartwood was: Ara < Gal < Xyl < Man < Glu. However, with increased temperature ( T=185°C and [H₂SO₄]=0%), sapwood yielded the following neutral sugars: Ara < Gal < Xyl < Man < Glu, while heartwood yielded the following: Xyl < Ara≈Gal < Man < Glu. Similar trend was observed in both sapwood and heartwood pulps when sulfuric acid concentration was increased.

Keywords: Aucoumea klaineana Pierre, wood wastes, ethanol organosolv lignin, enzymatic hydrolysis, bioethanol