Table 7.

Brief description of bio-oil upgrading techniques.

Upgrading Techniques	Process Conditions	Pros.	Cons.
Extraction	Mild conditions, solvents	Extracts valuable chemicals from bio-oil	Low cost separation and refining techniques are still needed
Solvent addition	Mild conditions, polar solvents	Simple	No chemical reaction to convert or remove undesired compound within bio-oil
Emulsification	Mild conditions, surfactant	Simple	High energy consumption, no chemical reaction to convert or remove undesired
Esterification/alcoholysis	Mild conditions, alcohol	Relatively simple, mild conditions, low cost of alcohol if methanol is used	Not effective to remove nitrogen-containing compounds
Supercritical fluids (SCFs)	Relatively high pressure and temperature, organic solvents	Effective to increase HHV and reduce viscosity	Needs high pressure equipment, some solvents are expensive
Hydrotreating	Relatively high pressure and temperature, catalysts	Removes N, O, and S as NH3, H2O, and H2S, and increase HHV, commercialized already	Needs high pressure equipment, high cocking and catalyst deactivation
Catalytic cracking	Relatively high temperature, atmospheric pressure, catalysts,	Produces large amounts of light products	Needs high pressure equipment, catalyst deactivation
Steam reforming	High temperature, catalyst	Produces H2 as a clean energy resource	Needs high temperature equipment