Table 1 Comparison between three kinds of heating for biodiesel production[116, 117]
Characteristic/ parameter | Conventional heating | Supercritical heating | Microwave heating |
|---|---|---|---|
Reaction time | Long (1-2 hr) | Short (<1 hr) | Very short (0.05-0.1 hr) |
Reaction temperature | 40-100°C | 250-400°C | 40-100°C |
Reaction pressure | Atmospheric | High pressure 35-60 MPa | Atmospheric* |
Catalyst required | Yes | No | Yes/No |
Heat losses | High | Moderate | Low |
Form of energy | Electrical energy converted to thermal energy | Electrical energy converted to thermal energy | Electrical energy applied through microwaves |
Process efficiency | Low | Moderate | High |
Catalyst removal | Yes | No | Yes |
Soap removal | Yes | No | Yes |
Advantages | Simple operation, use of low energy source | Short reaction time, easy product separation | Short reaction time, cleaner products, and energy efficient |
Limitations | High energy requirements, saponified products | High capital costs, pressure vessel safety | May not be efficient with feedstock containing solids |