**Abstract**

The reduction of environmental impacts caused by emissions of greenhouse gases has become an internationalized goal. In this context the development of technologies capable of producing energy from clean or renewable sources has gained broad prominence, among them the fast pyrolysis is a type of thermochemical process capable of converting biomass and agroindustrial waste into a liquid product called bio-oil that has a wide range of applications in the bioenergy scenario. For this type of technology to be consolidated as an alternative source of renewable energy, economic, political and environmental incentives are necessary, as well as research development to improve the conversion processes, such as reactor types, logistics in obtaining and pre-treating potential biomass, improvement and conversion routes for bio-oil obtained in renewable biofuels or chemicals with higher added value. This chapter covers the fundamentals of thermal conversion of biomass into bio-oil and the most studied processes to convert bio-oil into a product with better properties, such as deoxygenation and energy densification.

**Keywords:** biomass, fast pyrolysis, bio-oil, bioenergy, environmental

### **1. Introduction**

The demand for clean energy sources and the accompanying reduction in greenhouse gas emissions have gained increasing emphasis on environmental policy agendas around the world. One of the current portraits of these discussions was in 2021, when the Climate Summit was promoted, in which the political leaders of each nation set social, technological and political goals for the coming years in order to mimic the agents causing natural and climate changes. Among the most discussed measures, mainly by countries in the northern hemisphere, is the attack on the consumption of fossil fuels such as diesel, gasoline and mineral coal.

Biomass, urban and agricultural waste have great potential to be converted into products with added energy value. Although there are several routes for converting biomass into fuels (biological, thermal and physical–chemical), most of them, as biological, are highly selective, offering little variability of the final product. In thermal processing there is the possibility of producing a range of complex products such as chemicals, advanced biofuels and integrated electrical energy. Although the production of charcoal, through the carbonization process, is an old and wellknown process, it was during the oil crisis in the 1970s that research was directed towards obtaining renewable fuels from lignocellulosic materials, where fast

pyrolysis stood out. In this process, the carbonaceous material is subjected to moderate temperatures (in the range of 500°C) at high heating rates and in the absence of oxygen, thus, the release of organic vapors and gases occurs at low resistance times in the reactor, in addition to the formation of a char fraction [1, 2].

The biomass pyrolysis process in general can be understood as a thermal fractionation of the lignocellulosic complex into three predominant fractions: char, gases and liquids (condensable vapors). The greater or lesser yield of each of these fractions is adjusted according to the input parameters and adjustment of process variables such as temperature, reactor type, biomass composition, biomass physical properties and so on. In the fast pyrolysis process, all these parameters are conditioned in such a way as to provide low residence times in the vapor phase reactor. When being condensed, these vapors form a liquid phase composed of a variety of organic compounds called bio-oil.

Bio-oil has a wide range of applications. Due to its varied composition (alcohols, organic acids, sugars, phenolic aromatics, etc.) it can be used to obtain chemical species through refining and extraction, raw material for obtaining advanced biofuels, in addition to liquid biofuels for processes of direct burning of biomass is not possible. In addition, as it is a liquid product, its handling and transportation are facilitated in relation to solid biomass. Finally, bio-oil can have its quality improved by modifications directly in the pyrolysis process such as downstream upgrading processes.

Thus, this work presents an overview of the fast pyrolysis of biomass for bio-oil production, the properties of bio-oil and its general application, showing the main processes (reactors) developed and new trends for the improvement of the pyrolysis process aiming to obtain more efficient bioenergy sources.

### **2. Fast pyrolysis: general aspects**

Thermochemical processes have by their nature the conversion of raw materials into products that have greater added energy value. These processes occur having heat as the agent of transformation, either by release or demand of the process. **Figure 1** shows a summary of the main endothermic processes [3–9].

### **Figure 1.**

*Diagram showing the main characteristics of the most conventional thermochemical processes.*


### *Advances in the Pyrolysis Process and the Generation of Bioenergy DOI: http://dx.doi.org/10.5772/intechopen.99993*

### **Table 1.**

*Main properties of bio-oil from different feedstock compared to heavy fuel oil.*

During the fast pyrolysis process, the lignocellulosic structure of the biomass is degraded and converted mostly under specific reaction conditions, generating a main product called bio-oil. **Table 1** shows an overview summary of the main physical–chemical properties of a typical bio-oil compared to a heavy fuel oil.

In order to quantitatively obtain organic products in the form of bio-oil in an expressive way, it is necessary to maintain some parameters and variables in an essential way during fast pyrolysis.


By carefully following these parameters, it is possible to obtain bio-oil yields of up to 75% on a dry basis depending on the technology (reactor type) employed and the nature of the material. Moreover, depending on its composition and the way it is collected, the bio-oil can form two phases, a lighter one with a higher presence of water and a heavier one with a higher concentration of organic fraction.
