Palligarnai T. Vasudevan, Michael D. Gagnon, and Michael S. Briggs

Abstract Due to diminishing petroleum reserves and the deleterious environmental consequences of exhaust gases from fossil-based fuels, research on renewable and environmentally friendly fuels has received a lot of impetus in recent years. With oil at high prices, alternate renewable energy has become very attractive. Many of these technologies are eco-friendly. Besides ethanol, other alternatives are: biodiesel made from agricultural crops or waste cooking oil that is blended with diesel; biobu­tanol; gas-to-liquids (GTL) from the abundance of natural gas, coal, or biomass; oil trapped in the shale formations such as found in the western United States, and heavy oil lodged in Canadian tar sands. In this chapter, we examine advances made in environmentally friendly fuels such as biodiesel, biobutanol, and cellulosic ethanol in recent years.

Keywords Biodiesel ■ Cellulosic ethanol ■ Biobutanol ■ Lipase ■ Microalgae ■ Microbial ■ Enzymatic

1 Introduction

According to the Energy Information Administration [1], current estimates of world­wide recoverable reserves of petroleum and natural gas are estimated to be 1.33 trillion barrels and 6,186 trillion cubic feet, respectively. The world consumes a total of 85.4 million barrels per day of oil [2] and 261 billion cubic feet per day of natural gas [3]. The US consumes 24.6% of the world’s petroleum (2), 26.7% of the world’s natural gas (3), and 43% of the world’s gasoline (1). At current consump­tion levels, worldwide reserves of oil will be exhausted in 40 years, and reserves of natural gas in 60 years.

P. T. Vasudevan (B)

Department of Chemical Engineering, University of New Hampshire, Durham, NH 03824, USA e-mail: vasu@unh. edu

O. V. Singh, S. P. Harvey (eds.), Sustainable Biotechnology,

DOI 10.1007/978-90-481-3295-9_3, © Springer Science+Business Media B. V. 2010

Along with diminishing petroleum reserves, the price of oil and natural gas has increased dramatically. A barrel of crude oil reached a record high price of $147.27 in July 2008, which is an increase of 1,190% over the $12.38 per barrel price in July 1998 [4]. Due to the rapid increase in the price of oil, the price per gallon of regular unleaded gasoline increased from $1.08 in July 1998 to $4.09 in July 2008 [5], representing an increase of 379%. As the price of petroleum increased, so did corporate profits. Exxon/Mobil reported a second-quarter profit of $11.68 billion in August 2008, when gas prices were the highest [6].

The concentrations of heat-trapping greenhouse gases in the atmosphere have significantly increased over the past century due to the burning of fossil fuels, such as oil and coal, combined with deforestation. As a result, the average temperature of the Earth’s surface is increasing at an alarming rate [7]. The issue of climate change is one of the key challenges facing us and it is imperative that steps are taken to reduce greenhouse gas emission. The combination of diminishing petroleum reserves (it is generally believed that we reached a global “peak” oil or a global Hubbert’s peak in 2006 [8]), and the deleterious environmental consequences of greenhouse gases has led to an urgent and critical need to develop alternative, renew­able and environmentally friendly fuels. Examples include biodiesel, biobutanol, and cellulosic ethanol; the topics of this chapter.

Biodiesel is a renewable, non-toxic [9], biodegradable alternative fuel, which can be used in conjunction with or as a substitute for petroleum diesel fuel. Biodiesel is made entirely from vegetable oil or animal fats by the transesterifi­cation of triglycerides and alcohol in the presence of a catalyst. An advantage is that compression-ignition (diesel) engines, manufactured within the last 15 years, can operate with biodiesel/petroleum diesel at ratios of 2% (B2), 5% (B5), or 20% (B20), and even pure biodiesel (B100), without any engine modifications. Biodiesel contains no polycyclic aromatic hydrocarbons, and emits very little sulfur dioxide, carbon monoxide, carbon dioxide, and particulates, which greatly reduces health risks when compared to petroleum diesel.

Butanol is a four-carbon alcohol that can be produced from petroleum or biomass, and is currently used as an industrial chemical solvent. Biobutanol is an advanced biofuel that has an energy density, octane value, Reid vapor pressure (RVP), and other chemical properties similar to gasoline [10]. Without any engine modifications, it can either be blended at any ratio with standard grade petroleum gasoline or used directly as a fuel. Biobutanol can be produced from the fermenta­tion of sugars from biomass or by the gasification of cellulosic biomass. Compared to gasoline, the combustion of butanol reduces the amount of hydrocarbons, carbon monoxide, and smog creating compounds that are emitted [11].

Cellulosic ethanol is ethyl alcohol, a two-carbon straight-chained alcohol, which is produced from wood, grass, or other cellulosic plant material, particularly the non-edible portions. Ethanol produced from renewable sources can be used as a high-octane biodegradable motor fuel, and is clean burning. It can be used in cur­rent automobile engines in blends up to 10% with gasoline (E10) without any engine modifications, and in higher percentages (E85 and E100) in Flex Fuel Vehicles (FFVs). Biomass consists of cellulose, hemicellulose, and lignin, which requires pretreatment before processing. Enzymatic saccharification followed by fermentation and fermentation using cellulolytic microorganisms are the two main processing techniques used for the production of cellulosic ethanol.

In this chapter, we will examine the current state of the art in the production of biodiesel, biobutanol and cellulose ethanol, respectively.