Bio-oil upgrading and second-generation processes

The liquid or bio-oil produced by pyrolysis is a complex mixture of products oxygenated and nitrogenous hydrocarbons with water and residual carbon. The pyrolysis vapors are seasoned and intermediate products are frozen, producing bio-oil. The composition of these products varies with temperature as evidenced by Toft (1998), the 

The second generation of physical processes occurs in homogeneous phase, but they depend on the processing mode and reaction temperature. At the hot filtration, one can reduce the presence of residual carbon. However, carbon can act as a catalyst, allowing the breaking of the molecules with molecular weights smaller, increasing the selectivity and quality of the final product. It also depends on the filtration mode and the type of cyclone. 

The process reduces the viscosity by addition of solvents, especially methanol, which stabilizes the bio-products. During the emulsion process, through the addition of surfactants, it permits the formation of micro-emulsions and stabiUzes the bioproducts, and facilitates its transport. 

The catalytic processes are of great interest and can produce different compounds. When used directly, the bio-oil is pretreated to remove carbon and ash residuals, because both contain oxides or materials which can act as promoters or inhibitors. 

In catalytic processes, the reactors are generally fixed-bed or three-phase (trickle bed), where the catalyst is used in the form of pellets (5 mm), being careful with the effects of mass transfer and hot spots inside the reactor. 

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