**Abstract**

Lignocellulosic biomass as a potential renewable source of energy has a nearzero CO2 emission. Pyrolysis converts biomass to a liquid fuel and increases the energy density and transportability. The pyrolysis bio-oil shows promising properties to substitute the conventional fossil fuels. But, unprocessed biomass is low in bulk and energy density; high in moisture; heterogeneous in physical and chemical properties, highly hygroscopic and difficult to handle. That is why the biomass needs mechanical, chemical and/or thermal pretreatments to turn into a more homogeneous feedstock and minimize the post-treatment fuel upgrading. This chapter explains the effects that various pretreatments such as size reduction, drying, washing and thermal pretreatments have on the quality and quantity of bio-oil. Washing with water or acid/alkali solutions extracts the minerals that consequently reduces the ash and shortens the reactor clean-out cycle. Torrefaction is gaining attention as an effective pretreatment to modify the quality of biomass in terms of physical and chemical properties. Torrefaction produces a uniform biomass with lower moisture, acidity and oxygen contents and higher energy density and grindability than raw biomass. Pyrolysis of torrefied biomass produces bio-oil with enhanced compositional and physical properties such as a higher heating value and increased C (lower O/C ratio).

**Keywords:** pyrolysis, pretreatment, torrefaction, washing, bio-oil, bio-fuel
