Influence of impregnation with lactic acid on sugar yields from steam pretreatment of sugarcane bagasse and spruce, for bioethanol production

Lignocellulosic biomass can be utilized to produce ethanol, a promising alternative energy source produced through fermentation of sugars. However, in order to achieve high sugar and ethanol yields, the lignocellulosic material must be pretreated before the enzymatic hydrolysis and fermentation. Dilute acid pretreatment, using SO2, is one of the most promising methods of pretreatment for softwood and agricultural residues. However, handling the high acidity of the slurry obtained from pretreatment and difficulty in recycling/degradation of the impregnating agent are some of the drawbacks of the dilute acid processes. In the present study the influence of utilization of a weak organic acid (lactic acid), as impregnating agent, on the sugar yield from pretreatment, with and without addition of SO2, was investigated. The efficiency of pretreatment was assessed by enzymatic hydrolysis of the slurry obtained by pretreatment, using sugarcane bagasse and spruce, stored for one and two months in the presence of lactic acid separately, as feedstocks. Pretreatment of bagasse after storage with 0.5% lactic acid resulted in an overall glucose yield, i.e. after enzymatic hydrolysis, of 79% of theoretical based on the amount available in the raw material. This was as good as pretreatment using SO2 as impregnating agent. However, storage of spruce with lactic acid before pretreatment, with and without addition of SO2, was not efficient and resulted in lower sugar yields than pretreatment using SO2 only.

► Dilute acid pretreatment is a leading pretreatment process for conversion of forest and agricultural residues to ethanol.
► Storage of feedstock with lactic acid, i.e. similar to ensiling, was used as a pre-pretreatment method.
► Steam pretreatment of sugarcane bagasse merely stored with lactic acid resulted in high overall sugar yields.
► Pretreatment of spruce chips requires strong acid catalyst (SO2).