René B. Madsen

Effect of hydrothermal liquefaction aqueous phase recycling on bio-crude yields and composition.

Hydrothermal liquefaction (HTL) is a promising thermo-chemical processing technology for the production of biofuels but produces large amounts of process water. Therefore recirculation of process water from HTL of dried distillers grains with solubles (DDGS) is investigated. Two sets of recirculation on a continuous reactor system using K2CO3 as catalyst were carried out. Following this, the process water was recirculated in batch experiments for a total of 10 rounds. To assess the effect of alkali catalyst, non-catalytic HTL process water recycling was performed with 9 recycle rounds. Both sets of experiments showed a large increase in bio-crude yields from approximately 35 to 55wt%. The water phase and bio-crude samples from all experiments were analysed via quantitative gas chromatography-mass spectrometry (GC-MS) to investigate their composition and build-up of organic compounds. Overall the results show an increase in HTL conversion efficiency and a lower volume, more concentrated aqueous by-product following recycling.

Analysis of organic gas phase compounds formed by hydrothermal liquefaction of Dried Distillers Grains with Solubles

This work provides a comprehensive characterization of the gas phase from hydrothermal liquefaction of Dried Distillers Grains with Solubles (DDGS) collected during a 24-h continuous experiment. The gas consisted mainly of CO2, CO, H2, CH4 and C2H6 accounting for 96 v/v% while further analysis by gas chromatography coupled to mass spectrometry (GC-MS) showed additionally 62 compounds of which 54 were tentatively identified. These products included methanethiol, dimethyl sulfide, various olefins and several aromatic compounds. The composition provided clear indication of the steady state of the system. Apart from CO2, olefins were the most abundant compound class and could provide a source of revenue.

Hydrothermal co-liquefaction of biomasses – quantitative analysis of bio-crude and aqueous phase composition

Hydrothermal liquefaction (HTL) is a promising technology for conversion of wet biomasses to liquid fuels, but considerable amounts of oxygen and nitrogen remain in the bio-crude, while large amounts of water-soluble organics are displaced to the aqueous phase (AqP). In this study the bio-crude and AqP from HTL of 11 different feedstocks of lignocellulosics, residues, macroalgae, microalgae, and their mixtures were analyzed for elemental composition, total acid number, total organic carbon (TOC), total nitrogen, and pH. Quantitative analysis of major compound classes present in both bio-crudes and AqPs was achieved using gas chromatography coupled to mass spectrometry employing prior derivatization of authentic standards. A wide range of biochemical content was obtained through mixing of biomasses and quantitative analysis showed particular interaction between carbohydrates and proteins with extended effect on lipids. The ability of ammonia and amines to form Schiff bases was the key factor affecting elemental distribution and the direction of reaction pathways involved in the formation of cyclic oxygenates, hydroxypyridines, oxygenated aromatics, diols, and fatty acids in bio-crudes. Similarly, Schiff base formation accounts for increased formation of nitrogen-containing compounds in the AqP, leading to a decrease in TOC and total nitrogen in products from HTL of mixed biomasses. This work highlights the quantitative differences in bio-crude and AqP composition from HTL of varying biomasses and provides new knowledge of the effect of mixing biomasses on elemental distribution and composition of product fractions. The results provide valuable information for optimizing the feedstocks used for HTL based on biochemical composition.

Qualitative characterization of solid residue from hydrothermal liquefaction of biomass using thermochemolysis and stepwise pyrolysis-gas chromatography-mass spectrometry

Hydrothermal liquefaction (HTL) produces solid residue (SR) as a side-product with an organic fraction of char highly dependent on the feedstock. In this work the char from batch HTL of poplar, Spirulina, and their 1 : 1 mixture was characterized for the first time using stepwise thermal desorption and pyrolysis-gas-chromatography-mass spectrometry (py-GC-MS) along with thermochemolysis. Three distinct compound fractions were identified in the form of trapped or strongly adsorbed compounds, residual lignin, and repolymerized phenolics. The trapped or adsorbed fraction resembled the compounds in the bio-crude and aqueous phase from both poplar and Spirulina. Residual lignin was only found from poplar while repolymerized phenolics were predominantly observed from poplar through ortho and para-directed polymerization. Multiple aliphatic hydrocarbons and some alkylated pyrroles were observed from Spirulina. Co-liquefaction of biomasses led to a markedly different SR from the individual biomasses with multiple alkylated pyrroles and indoles, both volatile and non-volatile, while repolymerized phenolics diminished due to imine formation. This work demonstrates that potential bio-crude is present in the SR from both poplar and Spirulina while co-liquefaction hinders repolymerization of phenolics but also produces a vast number of volatile and non-volatile pyrroles. The work shows that additional information on the reaction pathways of HTL may be found by the characterization of the SR and provides researchers investigating biomass conversion with a method to evaluate the effects on SR formation.