Fractionation of lignocellulosic biomass via organosolv pretreatment: Valorization of cellulose and lignin fractions

The demand for sustainability is rapidly increasing in the world due to the rapid increase in population and constantly developing industry. Incorporating sustainable resources into the life cycle plays an important role in ensuring sustainability. Among these resources, biomass is the only resource that allows the production of fuel, energy, materials, and chemicals by using different conversion methods. Among various types of biomasses, lignocellulosic biomass is the most promising raw material because it is abundant in nature, easily available and low cost. In order to obtain maximum benefit from the structural components of lignocellulosic biomass, pre-treatment must be applied to lignocellulosic biomass. The type of biomass, the desired final product and its cost are important in the selection of pretreatment. Among the pre-treatments, the organosolv method provides the recovery of high purity lignin, minimal degradation of cellulose and a very low amount of ash. Studies on the organosolv process in the literature were generally carried out under pressurized conditions. However, the cost of high-pressure systems and the risk of high pressure limit the use of low-boiling point solvents. Solvents with high boiling points, such as ethylene glycol (EG) and γ-valerolactone (GVL), can be used under milder conditions without the need for pressurized reactors. Additionally, although delignification with high-boiling point solvents has been studied in the literature, the precipitation and recovery of lignin has rarely been investigated. Since EG and GVL solvents have high boiling points, they are suitable for operation in atmospheric conditions. Additionally, since both EG and GVL are green solvents, they will contribute to a sustainable economy. In the literature, phosphoric acid (FA), acetic acid (AA) and sodium hydroxide (NaOH) as catalysts have never been tested under atmospheric conditions. Therefore, the results obtained will make a significant contribution to organosolv studies, biorefining methods and bioeconomy. This thesis consists of three stages. Firstly, pre-treatments are mentioned, in the second part, information about organosolv process experiments is given and experimental findings are discussed, and finally, information is given about the usage areas of the lignin and celluloses obtained. In the study, two different lignocellulosic biomass, hazelnut shells and spruce wood sawdust, were examined separately under different conditions with organosolv pretreatment. The obtained lignin and cellulose-rich bagasse were analyzed and the findings were discussed. The EG-FA solvent-catalyst system had the highest delignification efficiency in both hazelnut shells and spruce wood sawdust. It was observed that the AA system was not an effective catalyst when compared to FA and NaOH catalysts. In the process performed with GVL, delignification efficiency was observed to be in hazelnut shells (<26%) and spruce sawdust (~39%), and lignin could not be precipitated in hazelnut shells in the GVLAA solvent-catalyst system. EG and GVL solvents are promising as an effective solvent when used under different conditions.