The influence of ferrous sulfate utilization on the sugar yields from dilute-acid pretreatment of softwood for bioethanol production

By employing metal salts in dilute-acid pretreatment the severity can be reduced due to reduced activation energy. This study reports on a dilute-acid steam pretreatment of spruce chips by addition of a small amount of ferrous sulfate to the acid catalyst, i.e., either SO₂, H₂SO₃ or H₂SO₄. The utilization of ferrous sulfate resulted in a slightly increased overall glucose yield (from 74% to 78% of the theoretical value) in pretreatment with SO₂ and H₂SO₃. Impregnation with ferrous sulfate and sulfuric acid did not give any improvement compared with pretreatment based solely on H₂SO₄.