Ethanol production from hazelnut shells through enzymatic saccharification and fermentation by low-temperature alkali pretreatment

- Hazelnut shells pretreated with NaOH at low temperature for long pretreatment time.
- Effect of pretreatment conditions on the glucose recovery and ethanol production is studied.
- An energy balance is established and thermal energy consumption and pretreatment energy efficiency are determined.

Low-temperature sodium hydroxide (NaOH) pretreatment, enzymatic saccharification and ethanol fermentation were evaluated for hazelnut shell cellulose to fermentable sugars and ethanol. Maximum glucose recovery (48.33 g/100 g cellulose) was achieved with 6% NaOH for 72 h and at 1/10 solid/liquid ratio. At these conditions, 41.18% of lignin was removed. The theoretical ethanol yield (ethanol produced/potential glucose in biomass) was 40.71%, overall process efficiency was 37.73 g/kg biomass, ethanol productivity and fermentation efficiency were 0.115 g/(L h) and 96.7%, respectively. Total energy consumed for the low-temperature-long-residence-time alkali process was 34.8 MJ/kg untreated hazelnut shells. Pretreatment time has a significant effect on thermal energy consumption for the low-temperature alkali process.