**8. Reaction of biodiesel in situ**

The biodiesel production process usually involves the extraction of oils or lipids from biomass, which will later be processed to produce biodiesel; thus called a twostage process. Currently, industries still require new technologies in the oil extraction and purification of the biodiesel, which are estimated to impact 70 to 80% on production costs [48].

Direct or "in situ" transesterification, an expression of the Latin that means "on the spot", is the most prominent to perform lipid extraction and the transesterification reaction concurrently, in a single step of the process. Currently, the process has been called a Reactive Extraction Process. Therefore, the direct processing of biomasses seems to be an economically viable alternative as it results in a more economical use of resources in the production process. This direct use of biomass in the reactor is called Direct Transesterification or "In Situ". The "In situ" Transesterification process emerges as a viable alternative to this problem as it makes direct use of the raw material without the need to prioritize oil extraction (**Figure 7**) [49].

The TEIS of microalgae biomass is shown as a potential alternative in reducing the costs of microalgal biodiesel production by eliminating the pre-treatment of biomass, enabling lipid extraction and purification, which has been the main factor in preventing the advancement of this industry; it minimizes the high consumption of solvents and uptime [49]. The elimination of the lipid extraction step not only reduces production steps but also results in a lower initial investment cost, equipment installation and maintenance, and energy [50].

**395**

*Microalgae Cultivation in Photobioreactors Aiming at Biodiesel Production*

As reported by Skorupskaite et al. [50], in situ technology can be applied to almost any raw material of plant origin or waste. However, attention should be focused on the biomass characteristics such as humidity, particle size, oil composition, acid content and reaction conditions (characteristics of reagents and catalyst,

*The "In situ" Transesterification process use of the raw material without the need to prioritize oil extraction.*

The reaction system for the TEIS process is suitable if the agitation of the reaction medium is effective enough to keep the biomass suspended [42]. This implies that there is a homogeneous dispersion of the liquid solvent and the solid biomass in the TEIS process [50]. that is, a perfectly agitated reactor. However, several authors have proposed different reaction systems to produce biodiesel in situ from

The high rate of cell growth, the high content of lipids in the biomass and the non-competition in the food chain place microalgae as sources of raw material suitable in the production of biodiesel. To maximize biomass productivity, photobioreactors are key equipment in the success of a microalgal biodiesel production chain, as the photobioreactors allow an accelerated growth of microalgae, making more lipids available to be converted in biodiesel. In this sense, different configurations of photobioreactors can be used to produce microalgae biomass, with raceways and

We thank Coordenação de Aperfeiçoamento de Pessoal de Ensino Superior

tubular photobioreactors being the most used configurations.

(CAPES) for financial support to conduct this work.

*DOI: http://dx.doi.org/10.5772/intechopen.93547*

reaction time, temperature, etc.).

microalgae.

**Figure 7.**

**9. Conclusion**

**Acknowledgements**

*Microalgae Cultivation in Photobioreactors Aiming at Biodiesel Production DOI: http://dx.doi.org/10.5772/intechopen.93547*

#### **Figure 7.**

*Biotechnological Applications of Biomass*

and allow recycling, but at high costs.

*Catalysts used in biodiesel reactions for Chlorella microalgae.*

**8. Reaction of biodiesel in situ**

catalysis [45].

*Source: authors.*

**Table 3.**

glycerol [24].

production costs [48].

(**Figure 7**) [49].

advantages of alkaline catalysts are high catalytic activity, low cost and moderate operating conditions. However, it requires a low acidity index to prevent soap formation. Acid catalysts have the advantage of preventing soap formation. However, these catalysts corrode the equipment and require long reaction times. Heterogeneous catalysts (enzymes and metallic compounds) are highly selective

**Microalgae Catalyst Condition Reference** *Chlorella minutissima* H2SO4 molar ratio (alcohol:lipid) 9:1, 90°C e 8 h Loures et al. [45]

*Chlorella sp.* H2SO4 Molar ratio (alcohol:lipid) 30:1, 60°C and 4 h Amaral et al. [47]

Miao, Wu [46]

*Chlorella protothecoides* H2SO4 Molar ratio (methanol:lipid) 56:1, 30 °C and 4 h

The oil extracted from marine microalgae has a high acidity index, indicating acid catalysis as the most suitable for biodiesel production, as can be seen in **Table 3** which highlights the research done in the process of biodiesel synthesis via acid

The synthesis of biodiesel from microalgal oils is carried out in a reactor. The mixture of alcohol and catalyst reacts with the triglyceride and/or fatty acids present in the microalgal oil. After the reaction, the mixture is transferred to a separation tank to guarantee the formation of the upper layer consisting of methyl ester, excess of alcohol and catalyst (acid or base) and the lower layer, predominantly

The biodiesel production process usually involves the extraction of oils or lipids from biomass, which will later be processed to produce biodiesel; thus called a twostage process. Currently, industries still require new technologies in the oil extraction and purification of the biodiesel, which are estimated to impact 70 to 80% on

Direct or "in situ" transesterification, an expression of the Latin that means "on the spot", is the most prominent to perform lipid extraction and the transesterification reaction concurrently, in a single step of the process. Currently, the process has been called a Reactive Extraction Process. Therefore, the direct processing of biomasses seems to be an economically viable alternative as it results in a more economical use of resources in the production process. This direct use of biomass in the reactor is called Direct Transesterification or "In Situ". The "In situ" Transesterification process emerges as a viable alternative to this problem as it makes direct use of the raw material without the need to prioritize oil extraction

The TEIS of microalgae biomass is shown as a potential alternative in reducing the costs of microalgal biodiesel production by eliminating the pre-treatment of biomass, enabling lipid extraction and purification, which has been the main factor in preventing the advancement of this industry; it minimizes the high consumption of solvents and uptime [49]. The elimination of the lipid extraction step not only reduces production steps but also results in a lower initial investment cost,

equipment installation and maintenance, and energy [50].

**394**

*The "In situ" Transesterification process use of the raw material without the need to prioritize oil extraction.*

As reported by Skorupskaite et al. [50], in situ technology can be applied to almost any raw material of plant origin or waste. However, attention should be focused on the biomass characteristics such as humidity, particle size, oil composition, acid content and reaction conditions (characteristics of reagents and catalyst, reaction time, temperature, etc.).

The reaction system for the TEIS process is suitable if the agitation of the reaction medium is effective enough to keep the biomass suspended [42]. This implies that there is a homogeneous dispersion of the liquid solvent and the solid biomass in the TEIS process [50]. that is, a perfectly agitated reactor. However, several authors have proposed different reaction systems to produce biodiesel in situ from microalgae.

### **9. Conclusion**

The high rate of cell growth, the high content of lipids in the biomass and the non-competition in the food chain place microalgae as sources of raw material suitable in the production of biodiesel. To maximize biomass productivity, photobioreactors are key equipment in the success of a microalgal biodiesel production chain, as the photobioreactors allow an accelerated growth of microalgae, making more lipids available to be converted in biodiesel. In this sense, different configurations of photobioreactors can be used to produce microalgae biomass, with raceways and tubular photobioreactors being the most used configurations.

#### **Acknowledgements**

We thank Coordenação de Aperfeiçoamento de Pessoal de Ensino Superior (CAPES) for financial support to conduct this work.
