**4.4 Cracking**

These are the upgrading process to convert the oxygen content in the bio-oil to H2O, CO, and CO2 using catalysts. The reaction occurs in a fixed or fluidized bed reactor system under normal pressure. Zeolite catalyst (HZSM-5) is the most common catalyst used in catalytic cracking due to its strong acidity, high reactivity, and stable porous structure [40, 49]. An experiment had proposed that the bio-oil upgradation can be done with two heating units with or without the presence of zeolite catalyst but the characteristics of catalytic cracked bio-oil were better than the non-catalytic cracked bio-oil [47]. During the bio-oil upgrading, the formation of coke can deactivate catalysts and its significant issue. Another experiment conducted with catalytic cracking of bio-oil models such as acetic acid, cyclopentanone and guaiacol had been investigated for the formation of coke using fixed bed reactor. It has found that compared to cyclopentanone and acetic acid, guaiacol produces more coke as it has ring structures that directs polymerization on the catalyst surface to form coke [50]. In **Table 2**, the thermochemical process with its various supported catalyst for the production of biorefinery products have been shown already.


#### *Cyanobacteria – Recent Advances and New Perspectives*

**Table 2.**

*Effect of various thermochemical process on microalgae.*
