Supercritical water gasification of microalgae over a two-component catalyst mixture

Area of Science:

• Biomass Conversion
• Catalysis
• Chemical Engineering

Background:

• Microalgae are a promising feedstock for biofuel production.
• Supercritical water gasification (SCWG) offers an efficient method for converting biomass into gaseous products.
• Catalyst development is crucial for optimizing SCWG efficiency and product selectivity.

Purpose of the Study:

• To investigate the supercritical water gasification (SCWG) of microalga Chlorella pyrenoidosa using a Ru/C and Rh/C catalyst mixture.
• To determine the effects of temperature, water density, and catalyst loading on gasification efficiency and product yields.
• To understand the synergistic effects of the catalyst mixture and the role of hydrogen transfer.

Main Methods:

• SCWG experiments were conducted on Chlorella pyrenoidosa.
• Variables studied included temperature (380-600°C), water density (0-0.197 g/cm³), and catalyst loading (0-20 wt%).
• Gas products (CH₄, H₂, CO, CO₂) and bio-oil composition were analyzed.

Main Results:

• Temperature and water density significantly influenced SCWG, with temperature affecting H₂ yield and water density affecting CO₂ yield.
• Methane (CH₄) constituted approximately half of the gaseous products under most conditions.
• A synergistic effect between Ru/C and Rh/C catalysts enhanced CH₄ production, though this effect diminished at higher temperatures. Hydrogen gasification efficiencies exceeded 100% due to water hydrogen transfer.

Conclusions:

• The Ru/C and Rh/C catalyst mixture shows promise for efficient methane production via SCWG of microalgae.
• Optimizing temperature and water density is key to maximizing gasification efficiency and specific gas yields.
• Nitrogen-containing compounds in bio-oil may act as catalyst poisons, requiring further investigation.