E. Adair Johnson, Zhanfei Liu, Elodie Salmon, and Patrick G. Hatcher

Abstract We describe a new procedure for conversion of algal biomass into biodiesel using a single step process through the use of tetramethylammonium hydroxide (TMAH). The dried algae is placed in a laboratory-scale reactor with TMAH reagent (25% in methanol) under a blanket of flowing nitrogen gas and converted to a con­densable gas-phase product (biodiesel) at temperatures ranging from 250 to 550°C. The condensed biodiesel is freed of methanol and analyzed by gas chromatography/ mass spectrometry. Fatty acid methyl esters (FAME) are the main products of the reaction at all temperatures studied. Residues from the one-step conversion exhibit varying levels of transformation which may likely affect their end use.

1 Introduction

Because of increases in crude oil prices, limited resources of fossil fuels, and the growing concern of greenhouse gases, there has been a renewed interest in convert­ing biomass, vegetable oils, and animal fats to biodiesel fuels [5, 9, 19] . There are many forms of biodiesel from biomass, but one form is commonly produced from vegetable, plant, and animal-based oils that are converted to fatty acid methyl esters (FAMEs) by a transesterification process [8, 22]. The traditional biological sources of biomass oils are soybean, sunflower, and rapeseed. A drawback to using these

E. A. Johnson • E. Salmon • P. G. Hatcher (*)

Department of Chemistry and Biochemistry, Old Dominion University, Norfolk, VA 23529, USA e-mail: PHatcher@odu. edu

Z. Liu

Department of Chemistry and Biochemistry, Old Dominion University, Norfolk, VA 23529, USA

Marine Science Institute, The University of Texas at Austin,

Port Aransas, TX 78373, USA

J. W. Lee (ed.), Advanced Biofuels and Bioproducts, DOI 10.1007/978-1-4614-3348-4_29, 695

© Springer Science+Business Media New York 2013

biomass sources for producing biofuel is that they compete for land with agricultural crops used as food sources. Algae as a renewable biomass, however, eliminate many of the problems associated with traditional biomass sources.

The use of microalgae as a source of biodiesel is not a new concept and was a focus of the Department of Energy’s “Aquatic Species Program” commenced in 1978 [28]. Although great progress was made, the program was discontinued in 1996 because of decreasing federal budgets and low petroleum costs [25]. With cur­rent higher petroleum costs and overall interest in biodiesel, the interest in algal — derived biofuel has increased significantly. Algae are an attractive form of biomass for biodiesel because they do not compete for land needed for food crops. They are an inexpensive and vast renewable resource, and some species are highly enriched with lipids [5]. The main advantage of microalgae is that they can exhibit doubling rates of once or twice a day, making them among the most efficient organisms at converting sunlight and atmospheric CO2 into biomass. They can grow photosyn­thetically so that no carbon source other than CO2 is required for growth. The com­bustion of any fuel from this biomass source will yield CO2 previously fi xed from existing atmospheric CO2 so that the energy supply will be regarded as CO2 neutral [27]. In comparison with other more traditional biomass fuel sources, algae have the potential to yield more energy per acre per unit time and appear to be the only source of biodiesel that has the potential to replace fossil diesel if used exclusively [5]. Weyer et al. [29] calculated the theoretical maximum for algal oil production to be on the order of 354,000 Lha-1year-1 of unrefined oil, with best cases examined ranging from 40,700 to 53,200 L ha-1year-1 of unrefined oil.

Finding an economical process to convert algae to biodiesel is one of the major challenges of producing algal biofuel on an industrial scale. The transesterification of oils to FAMEs through a base-catalyzed process is a common commercial tech­nique known for about 100 years [4]. This chemical process converts the triglycer­ides from vegetable oils and animal fats into FAMEs via a multistep synthesis at temperatures less than 60°C [22]. There have been recent attempts to develop cata­lysts and processes to perform this conversion of the oil through a single-step pro­cess; however, we are unaware that anyone has demonstrated direct conversion to FAMEs by a one-step treatment of the biomass [4, 24, 30]. We report here a pro­posed method in which the conversion of algae to biodiesel involves only a one-step methylation/transesterification and simultaneous distillation of FAMEs at high temperature (e. g., 250°C) using the alkylation reagent Tetramethylammonium hydroxide (TMAH) and shown in (1) [7, 16, 17].

This reagent has previously been used for conversion of cooking oils to FAMEs at temperatures of less than 60°C as its strongly alkaline properties make it ideal for the conventional transesterification process [1, 4] in the presence of methanol.

The one-step thermal conversion of algae to biodiesel with TMAH was carried out in a reactor we consider only as a prototype for larger, more commercial units. Analysis of the collected liquid product was carried out using GC-MS to confirm the presence of FAMEs and other products. The unconverted residue was analyzed for use as a potential fertilizer by elemental analysis and solid-state 1 3C nuclear magnetic resonance (NMR) to evaluate the extent of the transformation brought about by elevated temperatures in the reactor.