Oxidative torrefaction of microalgae Chlorella sorokiniana: Process optimization by central composite design

Area of Science:

• Biomass energy
• Thermochemical conversion
• Biofuels technology

Background:

• Microalgae possess unfavorable raw fuel properties, limiting their use as solid biofuels.
• Torrefaction, particularly under oxidative conditions, presents a cost-effective and energy-efficient method to improve biomass fuel characteristics.

Purpose of the Study:

• To investigate the impact of oxidative torrefaction parameters on microalgae fuel properties.
• To determine optimal conditions for enhancing microalgae's solid biofuel potential.

Main Methods:

• A central composite design experiment was employed to study temperature, time, and oxygen concentration effects.
• Thermogravimetric analysis was used to determine solid yield, energy yield, higher heating value, and carbon conversion temperatures.

Main Results:

• Temperature and time significantly influenced all measured responses (yield, energy value, conversion temperatures).
• Oxygen concentration impacted higher heating value, energy yield, and 90% carbon conversion temperature.
• Optimal conditions identified: 200°C, 10.6 min, 12% O2, yielding 98.73% energy yield and 1.08 enhancement factor.

Conclusions:

• Oxidative torrefaction significantly improves microalgae's solid biofuel properties.
• Optimized oxidative torrefaction offers a viable pathway for producing high-quality microalgae-based biofuels.
• Microalgae exhibit enhanced reactivity under oxidative conditions compared to inert torrefaction.