(102d) Catalytic Dehydration of Levoglucosan and Cellulose to Levoglucosenone Using Brønsted Solid Acid Catalysts in Tetrahydrofuran
The production of levoglucosenone (LGO) via levoglucosan (LGA) and cellulose dehydration was studied using Brønsted solid acid catalysts in tetrahydrofuran (THF). We evaluated the use of propylsulfonic acid functionalized SBA-15 (PS-SBA-15), commercial acid functionalized SiO2 and zeolite catalysts for the dehydration of LGA. PS-SBA-15 showed the best catalytic performance to produce LGO from LGA. The highest LGO yield obtained from LGA using PS-SBA-15 was 58.6%. That yield is more than two times higher to that obtained using sulfuric acid, which was 24.5%. We showed that the conversion of cellulose to LGO using a solid acid catalyst must be assisted by a homogeneous acid catalyst such as sulfuric acid (H2SO4), to promote the depolymerization of cellulose into LGA. The main role of the solid Brønsted acid catalyst is the dehydration of LGA to LGO during the cellulose conversion to LGO. We identified that surface properties such as acid-surface interactions and hydrophobicity are important variables to explain the catalytic behavior of the solid acid catalysts evaluated. We also studied the stability of PS-SBA-15 in THF and 1.2 mM H2SO4 in THF. The physicochemical properties of the silica catalysts change for different treatment times in THF. However, these changes do not have a significant effect on the acidity and mesostructure of the silica catalysts. On the other hand, adding H2SO4 to the THF causes a decrease in the acidity of the PS-SBA-15 after treatment. We demonstrated that solid Brønsted acid catalysts produce higher yields to produce LGO from LGA and cellulose than sulfuric acid. Also, we identified that the catalysts surface properties are a crucial parameter for the dehydration of LGA to LGO.