Integrated ethanol and biogas production from pinewood

Abstract

Ethanol and biogas production from softwood pine was maximized by dilute acid pretreatment. Pretreatment was performed with 0.25 and 0.5% w/w H₂SO₄ at 100, 140 and 180 °C for 5–30 min. Untreated wood and the solid fraction of the pretreatments, mainly containing cellulose, were used for ethanol production. The liquid fraction of the pretreated materials, mainly containing hemicellulosic sugars, was detoxified and subjected to anaerobic digestion for biogas production. The highest methane production yield was obtained by pretreatment with 0.5% H₂SO₄ at 140 °C for 5 min, resulting in methane yield of 162 m³ per ton of pinewood, whereas the highest ethanol yield of 53% was achieved by treatment with 0.5% H₂SO₄ at 180 °C for 30 min. Pretreatment at high temperature, i.e., 180 °C, increased the production of inhibitory compounds. These compounds had more significant inhibitory effects on biogas production than ethanol production. The highest gasoline equivalent, 61.5 gallons per ton, was obtained after wood pretreatment with 0.5% acid at 140 °C for 5 min, whereas the gasoline equivalent was only 4.9 gallons per ton for untreated wood. The reason for the improvements was followed by compositional and structural changes made by the pretreatment.