Levulinate and Formate Salt Reactions during Thermal Deoxygenation (TDO)

Thermal deoxygenation (TDO) refers to a biochemical-thermochemical reaction scheme for the removal of oxygen from biomass carbohydrates.   First, the carbohydrate is pre-treated via acid hydrolysis to yield levulinic and formic acids.  These acids are then neutralized using a base, such as calcium or magnesium hydroxide, to form a salt.  Slow heating of the salt mixtures to 450°C yields chars, carbonates, condensable products (crude bio-oil and water), and non-condensable gases.   The crude TDO-oil has physical properties similar to a light petroleum crude which phase separates from water and has low total acid number (<2 mg KOH/g) and oxygen content (< 4 wt.%).    

In this presentation, the conversion of solid-phase species is followed during heating in a tube furnace under inert atmosphere over the temperature range of 100-700°C.  H¹ and C¹³ Nuclear Magnetic Resonance (NMR) and Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) is used to monitor the solid-phase chemical composition of levulinate/formate salt mixtures. GC-MS is used to both monitor levulinate and formate conversion and identify volatile compounds captured during salt decomposition.  TDO reactions are found to begin at temperatures above 200°C and further reactions initiate above 375°C.  These reactions predominately yield dehydration and decarboxylation products, respectively.  TDO reactions above 400°C begin to show a complex mixture of reaction products.