Design of experiments and optimization of algae bio-crude hydrotreating for biofuel production

Michalski, Karol Michal

4. term

Energy Engineering, Master

2018

2018-06-01

72

Udviklingen af avancerede biobrændstoffer fra ikke-fødevare-biomasse møder stadig barrierer for kommercialisering. Den bio-olie (biokrude) der dannes ved hydrotermisk liquefaktion (HTL) af mikroalger, fungerer som et mellemprodukt, der skal opgraderes, før det kan bruges som et drop-in-brændstof i eksisterende motorer. I dette arbejde blev der gennemført faktorforsøg med to niveauer, hvor hydrobehandling af alge-biokrude blev evalueret, og effekten af driftsbetingelser på iltfjernelse (hydrodeoxygenering, HDO), kvælstoffjernelse (hydrodenitrogenering, HDN) og brintforbrug blev analyseret. Resultaterne viste, at temperaturen er den vigtigste faktor for at fjerne ilt, mens fjernelse af kvælstof afhænger af både brinttrykket og samspillet mellem temperatur og tryk; det samme gælder brintforbruget. Under optimerede betingelser (375 °C, 70 bar, 3 timer) blev ilten fjernet fuldstændigt, mens kvælstofindholdet forblev omkring 3 %, svarende til ca. 60 % reduktion. GC-MS-analyse viste, at det resterende kvælstof findes i forbindelser med højere molekylvægt. Ifølge simuleret destillation (Sim-dis) udgør disse tunge fraktioner cirka en tredjedel af den samlede oliefraktion, så de lette fraktioner, såsom benzin-, jet- eller dieselsnit, forventes at være kvælstoffri. Samlet set blev de mest indflydelsesrige faktorer for hydrobehandling af alge-biokrude identificeret, men der er behov for flere forsøg for at forstå processen i detaljer.

Advanced biofuels made from non-food biomass still face hurdles to commercialization. The bio-oil (biocrude) produced by hydrothermal liquefaction (HTL) of microalgae is an intermediate that must be upgraded before it can behave like a drop-in fuel in existing engines. This study used a set of two-level factorial experiments to evaluate hydrotreating of algae biocrude and to assess how operating conditions affect oxygen removal (hydrodeoxygenation, HDO), nitrogen removal (hydrodenitrogenation, HDN), and hydrogen consumption. We found that temperature is the main driver of oxygen removal, whereas nitrogen removal depends on hydrogen pressure and its interaction with temperature; hydrogen consumption shows a similar dependence. Under optimized conditions (375 °C, 70 bar, 3 h), complete deoxygenation was achieved, while the nitrogen level remained around 3%, corresponding to about a 60% reduction. GC-MS analysis indicated that the remaining nitrogen is contained in higher-molecular-weight compounds. Simulated distillation (Sim-dis) showed these heavy fractions account for roughly one-third of the total oil fraction, so light fractions such as gasoline, jet, or diesel ranges are expected to be nitrogen-free. In sum, the study identifies the key factors that influence hydrotreating of algae biocrude, and highlights the need for more experiments to fully understand the process.

[This abstract was generated with the help of AI]

Biocrude ; Biofuel ; Hydroprocessing ; Algae ; HTL ; Catalytic upgrading

Download
View record in AAU Student Projects