Bhaskar Singh

Department of Applied Chemistry Indian Institute of Technology (BHU)

Varanasi, India

Yun Liu

College of Life Science and Technology Beijing University of Chemical Technology Beijing, China

Yogesh C. Sharma

Department of Applied Chemistry Indian Institute of Technology (BHU) Varanasi, India

CONTENTS

8.1 Introduction………………………………………………………………………………………………… 99

8.2 Esterification/Transesterification……………………………………………………………… 101

8.3 Thermochemical………………………………………………………………………………………. 103

8.4 World Scenario on Production and Application of Biodiesel……………………. 108

8.5 Biofuel/Biodiesel from Microalgal Oil as a Potential Alternative to

Other Fuels………………………………………………………………………………………………. 109

8.6 Conclusion………………………………………………………………………………………………… 110

Acknowledgments……………………………………………………………………………………………… 110

References…………………………………………………………………………………………………………. 110

8.1 INTRODUCTION

Microalgae have emerged as a potential feedstock for the production of biodiesel. The steps involved in the production of bio-oil and biodiesel from microalgae include cul­tivation, harvesting, dewatering and concentrating microalgae, extraction of oil/lip — ids from the microalgae, and separation of triglycerides and free fatty acids from the crude lipids (for the synthesis of biodiesel). The final step consists of pyrolysis or ther­mochemical catalytic liquefaction for the production of bio-oil and esterification or transesterification for the synthesis of biodiesel. The species of microalgae employed for the production of biofuel include Chlorella vulgaris, Chlorella sorokiniana, Sargassumpatens C., and Spirulina. The method of biodiesel production from algal biomass can be done either by direct transesterification or in two steps involving the extraction of oil from algae followed by transesterification. Economic in situ transesterification of the microalgae has been adopted that involves combining the two steps of lipid extraction and transesterification into a single step. Direct trans­esterification of the microalgae after cell disruption by sonication resulted in a high conversion of biodiesel (97.25%). The fuel properties of the biodiesel synthesized from the microalgal oil derived from Chlorella protothecoides showed high fuel quality with a cold filter plugging point of -13°C. A high composition of unsaturated fatty acid methyl ester content in the microalgal oil methyl esters (MOME) (i. e., 90.7 wt%) led to a low oxidation stability of the fuel (4.5 h). The chemical treatment, pyrolysis, or thermochemical catalytic liquefaction of microalgal oil for the synthe­sis of bio-oil eliminates the dewatering and drying steps. The major constituents of bio-oil obtained from brown microalgae Sargassum patens C. Agardh by hydrother­mal liquefaction consist of carbon (64.64%), followed by oxygen (22.04%), hydrogen (7.35%), nitrogen (2.45%), and sulfur (0.67%).

The alga belongs to the third-generation feedstock for the synthesis of a renewable fuel, biodiesel, or bio-oil. The first generation of feedstock was the crop species, and second-generation feedstock consisted of grasses and trees, which principally consisted of lignocellulosic biomass. With the limited availability of crop species, the focus of recent research has been on second — and third-generation feedstocks (Stephenson et al., 2011). Second-generation feedstocks have certain constraints that involve breaking the complex structure of lignin and converting the crystalline cellulose to amorphous cellulose. The process involved in second-generation biofuels makes it quite energy intensive. Hence, the focus of the research to a large extent in recent years has been on third-generation feedstocks, that is, microalgae (Lam and Lee, 2012). The conversion of microalgal lipids into biodiesel is a holistic approach that begins with the identifica­tion of an appropriate microalgal species that has a high potential to accumulate oil within the cells. The oil consists of crude lipids and neutral lipids. Neutral lipids con­sist of triglycerides, free fatty acids, hydrocarbons, sterols, wax and sterol esters, and free alcohols. Among these, only triglycerides and free fatty acids are saponifiable, and hence can be converted to biodiesel by esterification or transesterification. Crude lipids consist of neutral lipids along with pigments (Sharma et al., 2011). The triglycerides and free fatty acids are the part of microalgal lipids that can be converted to biodiesel or bio-oil. The microalgal biomass can be used for the production of biofuel, either by pyrolysis or through direct combustion or thermochemical liquefaction in which bio­oil is produced. Alternatively, the lipid can be derived from microalgal biomass and converted to biodiesel via transesterification (Kao et al., 2012).

In general, microorganisms that accumulate more than 20% to 25% of their weight as lipid are called oleaginous species (Kang et al., 2011). As these oleaginous micro­organisms can accumulate a large amount of oil within their cells, they can be very good feedstocks from which to extract oil and lipids that can be converted to biofuel (bio-oil or biodiesel). In some of the algae, the lipid content may be as high as 75% of their dry biomass. Most species of algae produce triglycerides (that can be utilized for biofuel production) and alkanes. A few algal species may also contain long-chain hydrocarbons that are formed via the terpenoid pathway (Sivakumar et al., 2012). Hence, the characterization of the algae is prerequisite to assessing the potential of the microalgae extract to be converted to biofuel. Once the triglyceride content in the microalgal species is determined, depending on their feasibility, the microalgae extract can be utilized for its conversion to either bio-oil or biodiesel. This chapter deals with the conversion of microalgal lipids into biodiesel or bio-oil, taking into account the following aspects: esterification/transesterification, and chemical method.