(764e) Structure Function Relationship between Catalyst Hydrophobicity and Water Tolerance of Alkyl-Modified SBA-15-Supported Propylsulfonic Acid Catalysts

Upgrading of fast pyrolysis-derived bio-oils via acid-catalyzed esterification is hindered by high water content of the bio-oil. This study focused on understanding the relationship between catalyst hydrophobicity and water tolerance using SBA-15-supported propylsulfonic acid catalysts on a model esterification reaction. In addition to the propylsulfonic acid surface moiety, alkyl modifiers of varying lengths were introduced to the surface to change the hydrophobicity of the catalyst active site. The catalysts were tested under dry and wet reaction conditions on the esterification of acetic acid with methanol in the liquid phase. A structure function relationship between hydrophobicity and water tolerance was determined via calorimetry and reaction studies. The degree of hydrophobicity of the catalyst was probed using solution calorimetry. The hydrophobically modified catalysts were immersed in water and the heat evolved was used to quantify the level of hydrophobicity of the catalyst surface. Water tolerance was quantified by measuring reaction rates at varying initial concentrations of water up to 5 M and calculating the water reaction order. Apparent activation energies were determined at increasing wate­­r concentrations between 30 °C and 70 °C. The importance of considering non-ideal thermodynamics (i.e. activity coefficients) in solutions was addressed in this system.