Effect of Catalysts on Kinetics of Hydrothermal Processing of Biomass

Abstract

Hydrothermal liquefaction (HTL) of biomass and bio-waste is a promising waste management technology that might produce renewable bio-crude and other valuable aqueous and solid organic products from non-conventional, non-edible biomass and waste sources. The yields and properties of the product phases depend mostly on the biomass composition, reaction temperature, and residence time. However, the current renewable bio-crude is not close enough to the fuel oil properties. Issues such as high acidity, high nitrogen content, and high solid product yields limit the industrial application of HTL. A complete renewable co-solvent and homogeneous catalyst system is investigated as a hydrogen donor co-solvent, alkylation, and esterification agent to reduce the effect of the renewable bio-crude issues, whereas the reaction mechanisms and kinetics models are established and coupled with multiple analytical techniques to understand the synergetic effect of the co-liquefaction conditions. The HTL of the model lipids produced up to 90% renewable bio-crude yield, composed mainly of free fatty acids (FFA). While co-liquefaction produced up to 38% fatty acid ethyl ester (FAEE) known as bio-diesel, with reduced acidity levels. The hydrolysis, transesterification, and esterification are modelled in a loop of forward and reverse reactions to clarify the degrees of equilibrium at the different conditions. Additionally, the activation energies obtained are contrasted with the scientific literature. The HTL of rich in protein biomass produces nearly a quarter mass yield of a high in nitrogen bio-crude and up to 60% nitrogen recovery in the aqueous phase. NOx are environmental pollutant gases from the combustion of rich in nitrogen feedstock, while nitrogen in water is potentially harmful to the aquatic ecosystem and can be complex to treat with biological nutrient removal (BNR). A complete elemental nitrogen balance and kinetic model are developed to understand the migration and transformations of nitrogen under HTL conditions, and a hydrogen donor co-solvent system is tested to enhance renewable bio-crude yields and properties. However, the complexity of protein structure and reactions requires a more in-depth understanding. The HTL of carbohydrates does not produce water-insoluble bio-crude and almost 50% of product yield is char. Solids are undesirable products from the HTL of biomass, as they reduce bio-crude yield and might increase the complexity of the bio-crude recovery due to oil trapping. However, valuable intermediate products such as 5-hydroxymethyl furfural and levulinic acid were found as substantial products in a detailed reaction mechanism and kinetic model from the HTL of glucose, fructose, and cellulose. Additionally, ethanol as a hydrogen donor co-solvent promoted the formation of ethyl levulinate and 5-ethoxymethyl furfural, structures with potential applications as fuel additives and tunable monomers. The interactions between protein and carbohydrate, known as Maillard reactions, are investigated as the second most important pathway contributing to the renewable bio-crude phase. Previous studies with proteins and carbohydrates contribute to the design of experiment and response variables. Where GC-MS of aqueous phases plays a crucial role in providing a new understanding of the Maillard reaction transformation. Proline, as an isomer from glutamic acid and a potential product from the Strecker degradation and Amadori rearrangement of levulinic acid, is the primary candidate to produce pyrrolo-pyrazinedione and piperazinedione intermediates before further degradation into pyrazines and other final products.