**3. Bio oil properties and its applications**

In general, biomass is composed essentially of three organic components: cellulose, hemicellulose and lignin. Besides these there is also an inorganic fraction (ash) and the water associated with the structure of the material in the form of moisture. The composition of these fractions is an important reference in the quality of bio-oil to be obtained. **Table 2** shows a general summary of the lignocellulosic composition of various biomasses.

During the pyrolysis process these three polymers decompose at virtually the same time, however each has different thermal decomposition kinetics [21], which can lead not only to different yields of bio-oil and its sub products (biochar and gas) but also generate a variation in the distribution of organic functions that make up the bio-oil [22].

Due to the different physicochemical properties of cellulose, hemicellulose and lignin, they tend to produce different products. While cellulose tends to contribute to higher bio-oil yields, higher lignin concentration contributes more significantly to biochar formation [20, 23, 24]. The organic composition of bio-oil is extremely variable and presents several classes of organic composts. **Figure 2** shows a deviation map of these organic functions that typically compose the pyrolysis bio-oil in relation to the thermal reactivity of cellulose, hemicellulose and lignin [25].

In addition, the inorganic fraction of biomass (ash) can also influence the characteristics of bio-oil. Some studies show that biomasses with alkali rich ash, such as potassium (K), and phosphorus can exhibit catalytic properties and alter the distribution of organic compounds present in bio-oil [26]. A number of other characteristics of bio-oil can be described to assess its quality, such as appearance, typically characterized by a dark brown or reddish color; odor, which is characteristic of acidic flavors and can even cause airway and visual irritation upon prolonged exposure; and miscibility, which is a complex factor as it is not miscible with petroleum fuels due to the large presence of polar and oxygenated compounds,


### **Table 2.**

*Lignocellulosic composition of various biomasses.*

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

### **Figure 2.**

*Thermal decomposition of lignocellulosic compounds and their products (adapted from [25]).*

and is not water soluble as excessive addition can lead to the formation of two liquid phases [19, 20].

Due to its varied composition, a number of applications have been attributed to bio-oil. **Figure 3** illustrates some of the main applications.

The pyrolysis bio-oil presents compounds in high concentrations such as phenols, guaiacs, acetic acid among others and with the advancement of separation techniques, such as liquid–liquid extraction, with the addition of solvents (hexane, chloroform etc.) has allowed the recovery of fractions with high concentrations of these compounds that have high added value for the industry, production phenolic resins, organic acids among others [27–30]. In addition, the greatest potential for use of bio-oil is in its use for the production of biofuels, being necessary, firstly, the application of upgrading steps to improve its properties.

Bio-oil can also be used in combustion or co-combustion systems with other fuel oils to obtain heat in industrial processes. However, the applications of bio-oil in these combustion systems are traditional for combustion of heavy or

**Figure 3.** *Bio-oil applications.*

mineral oils due to their physical–chemical characteristics completely different and their instability that can impact on essential parameters for a quality combustion of oil as the quality of atomization, ignition, tendency to coke formation, vaporization rate of drops, clogging among others. However, having a good understanding of the properties of the bio-oil used and the ratio some benefits are reported in co-combustion operations such as the reduction of SO2 and thermal NOx emissions [27–30].

### **4. Reactors to fast pyrolysis**

The design of a fast pyrolysis process has at its core the reactor where the appropriate heat and mass transfer conditions will be provided for the thermochemical processing of the material. In general, a fast pyrolysis process consists of a biomass fitting unit (1) to fit the required particle size and moisture conditions, the pyrolysis reactor (2) where the bio-oil (vapors) and by-products (biochar and noncondensable gases) are formed, cyclone(s) and/or particulate removal systems (3), condensation unit and bio-oil collection (4) and finally a thermal energy conversion and integration system in the system (5) as illustrated in **Figure 4**.

The pyrolysis is an endothermic process, as the goal of fast pyrolysis is to obtain higher yields in liquids, the other by-products (biochar and gas) can be used as fuels in the thermal energy generation unit providing the necessary entapia, to perform the pyrolysis reactions. Fast pyrolysis reactors in general can be separated into those that use a gaseous agent for heat transfer in the reactor and those that do not use gas as a fluid, and most of them are already in commercial scale. A **Table 3** mostra um resumo dos principais reatores utilizados nos processos de pirólise dus prncipais características e seu status comercialização.

### **5. Pyrolysis and bio-oil improvement strategies**

Bio-oil obtained from lignocellulosic feedstock with fast pyrolysis has many disadvantages in front of fossil fuels such as high water content, presence of small particles of coal and alkaline ash, acidity, low calorific value and thermal stability that make it difficult to application of bio-oil in the power system such as


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

### **Table 3.**

*Description of the main fast pyrolysis reactors and their characteristics.*

### **Figure 5.**

*Different processes and strategies to improve the fast pyrolysis of bio-oil quality.*

engines [40]. The currently technological research shows that there are basically three ways to improve the performance of the fast pyrolysis and the quality of the obtained bio-oil. The **Figure 5** shows these deferments strategies.

### **5.1 Pre-treatment**

Several authors have already reported the effect of physical treatments (i.e. treatments that do not alter the chemical composition or chemical structure of biomass) of biomass on pyrolysis processes. The most relevant one reported is the biomass grinding aiming at its particle size reduction, which has a positive impact on all fast pyrolysis reactors, providing an increase in the bio-oil yield [41].

The washing (or leaching) it's a process used to remove or modified inorganic compounds of the biomass or modified the lignocellulosic complex. The H2O washing it's a simple and low cost process able to remove mainly alkalis (K, Ca), Cl and S [42, 43]. The Acid washing it's a more complete but expensive kind of washing with (organic or inorganic) acid diluted, this process its able to remove near all components (alkalis, halogens, heavy metals etc) found in biomass ashes promoting the complete demineralization [42, 44]. In addition to these effects, the acid treatment of biomass (washing and acid infusion) can lead to the formation of bio-oil rich in sugars [45, 46]. Studies have pointed out [46] showed that there is considerable enrichment in sugars, especially levoglusan (up to 55% of cellulose) during the acid infusion of corn stover. These results were mainly attributed to the catalysis of the decomposition of the cellulose structure.

Another process considered a pre-treatment of biomass for fast pyrolysis is Dry Torrefaction. This process is like mild pyrolysis; occurring in the range of 200–280°C and in an inert atmosphere, it promotes a thermal pre-degradation of lignocellulosic polymers, generating a biomass with the potential to produce a bio-oil with better quality [47, 48]. In parallel, the Wet Torrefaction (WT) process can also qualitatively improve the biomass properties for the fast pyrolysis process. It occurs in aqueous phase and ambient to moderate pressures, with water at high temperatures it removes alkalis, carbonates and halogens. Research shows that biooil produced from biomass pre-treated with WT produced bio-oil with less phenols, ketones, furans and richer in sugar, especially levoglucosan. However, in addition to energy consumption, this process generates a biomass with high water content [46, 49–52].

The process of acid treatment and torrefaction of biomass can be combined to improve the performance of fast pyrolysis both quantitatively (higher bio-oil yield) and qualitatively (bio-oil with better properties) as shown in **Figure 6**. Studies showed that the coupling of acid washed with acetic acid (1% wt) and

### **Figure 6.**

*A combination of acid treatment and dry torrefaction to improve the fast pyrolysis process performance (adapted from [53]).*

dry torrefied (270°C) in the pretreatment of *P. radiata* allowed achieving 57.8% of bio-oil yield and improving the quality of bio-oil with low H2O and organic acids content [54].
