Thermochemical Conversion of Algal Based Biorefinery for Biofuel

*Arosha Vaniyankandy, Bobita Ray, Subburamu Karthikeyan and Suchitra Rakesh*

### **Abstract**

Algae being the photosynthetic organism, currently considered as underexplored species for biofuel production in the entire global region and yet need to be explored more. In presence of algal based theory regarding the thermochemical process, though many researchers have been proceeding with the experiment but have got to stretch it further. This process aims to produce energy and bioactive compounds using algal biomass as a raw material. The current study relates with the thermochemical conversion process and mainly reflects about the algal biomass conversion into biorefinery production, in a short time with easier and economically viable points, unlike other biochemical and chemical conversion processes. In thermochemical process, high temperatures used during the process produces different biofuels including solid, liquid, gaseous biofuels. This thermal decomposition process of algal biomass can be categorized into Gasification, Pyrolysis, Direct combustion, Hydrothermal process, and Torrefaction. Hence, in this study, it briefs on different type of processes for better production of biofuel as well as its significant merit and demerit comparisons of each process.

**Keywords:** algae, biomass, thermochemical conversion, biorefinery, liquefaction

### **1. Introduction**

Algae, grouped among the photosynthetic organism, are sustained in the diverse form of habitats. It can flourish in freshwater, marine water as well as wastewater. Algae are a suitable biomass resource for renewable energy production because of the rapid growth rate, high content of lipids, and tremendous biomass productivity [1]. The algal biorefinery concept integrates various processes for converting algal biomass into biofuels and other bioactive products [2]. They aim to produce energy and bioactive compounds using algal biomass as a raw material. The conversion process for biorefinery production includes biochemical, chemical, and thermochemical conversion processes.

The thermochemical conversion process is considered an efficient method for producing biofuel from algal biomass. During the process, molecules in algal biomass are broken down to release their potential energy. It transforms the entire algal biomass to the respective fuel in a shorter time, unlike other conversion processes. The process uses high temperatures to degrade the algal biomass to produce different biofuels, including solid, liquid and gaseous biofuels [3]. It is the best option to process algae with low lipid content or residues after extraction of the algae with high lipid content. The process is direct, easy, and fast compared to biochemical and chemical conversion processes and is economically viable [4]. This thermal decomposition process of algal biomass can be categorized into Gasification, Pyrolysis, Direct combustion, Hydrothermal process, and Torrefaction.

Gasification is an excellent process to convert algal biomass to gaseous fuels. In contrast, pyrolysis and hydrothermal liquefaction (HTL) processes give bio-oil low molecular weight and bio-crude high energy density [5]. In the gasification process, the partial oxidation of algal biomass occurs at high temperatures. Combustible fuel gases like CH4 and H2 are produced. The actual process of gasification involves the reaction with the carbon-containing compound in the algal biomass and the air, oxygen or steam present at high temperatures in the gasifier, resulting in the production of syngas and mixtures of other combustible gases like CO, H2, CO2, N, CH4 [2]. These studies indicated the promising role of steam gasification in hydrogen production. Pyrolysis is an anaerobic heating process that produces medium to low calorific value liquid fuels on a large scale. The significant products obtained after pyrolysis are bio-oil, biochar, and charcoal [4, 6].

Hydrothermal processes such as liquefaction is emerged to be the most promising method to convert wet algal biomass to liquid fuel with the use of high temperature and pressure. It consists of evolving technique that can connect biomass with high moisture content and low energy and can convert into heat, hydrogen, biochar, electricity and other type of synthetic fuels. It is more efficient and favorable in converting wet algal biomass to biofuel than pyrolysis [7]. Combustion is the easiest and most traditional method among all thermochemical processes. The direct combustion process involves burning or incinerating the algal biomass and converting the stored chemical energy in the biomass into gases in the presence of excess air [4, 8]. Whereas pyrolysis and combustion characteristics of *Chlorella vulgaris* are under different heating rates found compared to pyrolysis, combustion produces higher biomass, and the faster heating rate leads to the quicker and higher conversion [9]. The torrefaction process is introduced to overcome the demerit of low calorific values of algae. These upgrading methods involve the thermal degradation of algal Sbiomass in an inert or N2 environment [2].

Biofuel generated from algae will be environmentally friendly, non-toxic, and highly biodegradable. So these are considered a better alternative to fossil fuel as it has many disadvantages like environmental degradation, climate change, rising price, and depletion. The algal biorefinery approach is an excellent way to produce biofuels and other value-added products from algae. Many review papers reviewed different processes and steps involved in algae-based biorefinery. Since solid, liquid, and gaseous fuels can be produced via thermochemical strategies, these are emerged as the viable option to recover energy from algal biomass. The thermochemical conversion process can recover highly efficient and economically valuable biofuels. The thermochemical conversion process provides a simpler route of conversion. Various thermochemical approaches are widely explored because of their huge advantage over other methods. This chapter describes the different types of thermochemical conversion process for various biorefinery productions as well as it also emphasizes the influence of catalysts in thermochemical process for upgrading of biofuels. For a brief understanding of this chapter a figure have been shown below mentioned as **Figure 1**.

*Thermochemical Conversion of Algal Based Biorefinery for Biofuel DOI: http://dx.doi.org/10.5772/intechopen.106357*

**Figure 1.** *Algal biomass to biofuel conversion techniques.*
