Conversion of Microalgae to Fuels or Fuel Components

DGMK Research Report 777 Published

Subject of the DGMK project 777 was the scientific penetration of a two-stage process for the conversion of the entire moist algae biomass into high-quality fuels or fuel components. In the first stage, the moist biomass is thermochemically converted into a heavy oil-like product - so-called biocrude (hydrothermal liquefaction). This process already eliminates a large proportion of the heteroelements contained in the biomass without the use of hydrogen. Finally, in the second stage, the upgrading to usable fuel components takes place by means of hydrogenating processes (hydrotreating). In the project, fundamental investigations were carried out both on the influence of parameters on both stages and on the dependence of the product yield and properties after hydrotreating on the reaction conditions during hydrothermal liquefaction. The aim was to optimise the process chain as a whole with regard to product yield and quality as well as hydrogen consumption. 

By using various methods of instrumental analysis, the very complex educts and products could be comprehensively characterised materially/chemically and the understanding of the reactions taking place could be deepened. The investigations have shown that about one third of the algae biomass can be converted into almost heteroatom-free naphtha and middle distillate fractions. The energy yield in terms of the energy chemically bound in the microalgae is approx. 60 %, even taking into account the necessary hydrogen supply. An economic analysis based on the experimental results showed that for a production plant (capacity 100 kt of hydrogenation product per year) at a realistic future biomass price of 0.30 €/kg, fuel could be produced at a price of less than 2 €. These costs are in the same magnitude as those currently being discussed for power-to-liquid technologies.