(117c) Determining Kinetics and Mechanisms of Model Compounds to Understand Chemistry of Algae Liquefaction In High Temperature Water

Hydrothermal liquefaction refers to the process of converting biomass to bio-oil by contacting the biomass with water at high temperatures (>200°C) and sufficient pressures to maintain water in the liquid state. Hydrothermal liquefaction of algae producing bio-oil has the advantage of energy efficiency and capability of dealing with wet biomass^1-3. Although few studies exist, the exact chemistry for bio-oil formation during algae liquefaction is not quite clear. In this project, we try to overcome this gap by studying ethyl oleate (triglyceride), phenylalanine (protein) and phytol (chlorophyll) as model compounds, representing different classes of biomacromolecules in algae. Our ultimate aim is to use the principles of reaction engineering and develop a unique model based on the understanding of these pure model compounds and their mixtures that is capable of predicting conversions given a starting composition of algae.

Recently, we determined the kinetics for ethyl oleate hydrolysis in high-temperature water and for the reverse reaction, oleic acid esterification, in near- and supercritical ethanol⁴. Hydrolysis was clearly autocatalytic. A phenomenological kinetics model is proposed using our experimental data that has thermodynamically and thermochemically consistent Arrhenius parameters. We also developed a unified mechanism for this system. We suggest that hydrolysis of ester is catalyzed by both H⁺ and fatty acid, while esterification is only specific acid catalyzed. Both the phenomenological and the mechanistic model provide a good correlation of the data and also exhibit the ability to make quantitatively accurate predictions within and outside the parameter space investigated. This study, a first of its kind for hydrolysis and esterification kinetics in tandem, is especially useful for a multicomponent system that will occur during algae liquefaction. For instance, hydrolysis of proteins in algae can generate organic acids, in turn catalyzing the hydrolysis of triglycerides. Our model can be extended to understand and predict this type of behavior.

References

1)      Brown,T.M.; Duan,P.; Savage,P.E. Energy Fuels, 24 (6) (2010) 3639-3646.

2)      Dote,Y.; Sawayama,S.; Inoue,S.; Minowa,T.; Yokoyama,S. Fuel, 73 (1994) 1855 -1857

3)      Inoue,S.; Dote,Y.; Sawayama,S.; Minowa,T.; Ogi,T.; Yokoyama,S. Biomass and Bioenergy, 6 (4) (1994) 269-274

4)      Changi,S.; Pinnarat,T.; Savage,P. Ind. Eng. Chem.Res, 50 (2011) 3206-3211