Effects of freeze storage of bark-containing larch on pretreatment efficiency

Bark-containing lignocellulosic biomass for production of bio-ethanol is generally hard to deconstruct its structure by pretreatment process and demands large energy. Therefore, the studies of stronger pretreatment methods have been carried out and various catalysts for pretreatment efficiency have been extensively researched in recent years. In this study, we tried to overcome this recalcitrance of bark-containing lignocellulosic biomass using a physical property of H₂O during the biomass storage step. The purpose of this study is to evaluate the effect of freeze storage on deconstruction of bark-containing lignocellulosic biomass and on liberated reducing sugar yield after pretreatment. Small diameter log of larch (Larix kaempferi) including bark was obtained from Seoul National University Forest (Seoul, South Korea). Larch (glucan: 46.4%, mannan: 11.5%, xylan: 5.1%, galactan: 4.8%, arabinan: 2.0%) was ground into powder (40 mesh), mixed with distilled water (solid:liquid=1:2(w/v)), and stored at -15°C until the pretreatment process. The pretreatment was conducted in 20 mL-reactor, which was loaded with 0.3 g of larch and 3 ml of 1% sulfuric acid in several conditions (reaction temperature: <150°C, reaction time: <20 min). After pretreatment, liberated reducing sugars in the liquid fraction were analyzed by HPLC and water insoluble solid recovery rate was calculated. As a result, degradation rate of larch stored in freezer increased 8.4-41.9%, compared with larch stored at room temperature. Liberated reducing sugar yield of larch stored in freezer was also slightly higher than untreated sample, suggesting that the change of H₂O volume in biomass might have accelerated the deconstruction of lignocellulosic structure.