**4. Conclusions**

The energy produced from lignocellulosic biomass is renewable, environmentally friendly and carbon-neutral. Characteristics of bio-oil produced in fast pyrolysis showed that it is capable to substitute conventional petroleum-based fuels. This chapter explained the fast pyrolysis process and the pretreatments that contribute to acquiring a transportation bio-oil with enhanced physical and chemical properties. The modification of biomass feedstock properties through available pretreatment techniques plays a key role in the pyrolysis process. Pretreatments change the biomass feedstock's size, shape, mineral content, composition, hygroscopic properties, homogeneity, grindability, stability and transportability.

Torrefaction as a mild pyrolysis of biomass feedstock is a promising pretreatment that modifies the structure and chemical composition of biomass by removing hemicelluloses, dehydrating and enriching biomass in cellulose and lignin. Torrefaction makes the structure of biomass more brittle that make it more grindable. Grinding torrefied biomass produces more uniform particles with smaller and narrower particle size distribution. Pyrolysis of torrefied material enhances the properties of produced bio-oil. This enhancement is consistent with the DOE MYPP's target that "additional processing of the bio-oil is required to enable it to become a feedstock suitable for use in a petroleum refinery at several entry points." However, this is penalized with a liquid yield reduction.

With all the opportunities of renewable biomass energy, some important issues are still needed to be solved to commercialize the process. To find the least-cost combination of torrefaction along with biomass fast pyrolysis, further testing of the two along with economic analysis are required.
