Shelley D. Minteer

Saint Louis University, Missouri

CONTENTS

Introduction………………………………………………………………………………………………………. 1

Methanol…………………………………………………………………………………………………………… 2

Ethanol……………………………………………………………………………………………………………… 3

Butanol……………………………………………………………………………………………………………… 3

Propanol……………………………………………………………………………………………………………. 4

Conclusions………………………………………………………………………………………………………. 4

References………………………………………………………………………………………………………… 4

Abstract Alcohol-based fuels have been used as replacements for gasoline in combustion engines and for fuel cells. The four alcohols that are typically used as fuels are methanol, ethanol, propanol, and butanol. Ethanol is the most widely used fuel due to its lower toxicity properties and wide abundance, but this chapter introduces the reader to all four types of fuels and compares them.

INTRODUCTION

Alcohol-based fuels have been important energy sources since the 1800s. As early as 1894, France and Germany were using ethanol in internal combustion engines. Henry Ford was quoted in 1925 as saying that ethanol was the fuel of the future [1]. He was not the only supporter of ethanol in the early 20th century. Alexander Graham Bell was a promoter of ethanol, because the decreased emission to burning ethanol [2]. Thomas Edison also backed the idea of industrial uses for farm products and supported Henry Ford’s campaign for ethanol [3]. Over the years and across the world, alcohol-based fuels have seen short-term increases in use depending on the current strategic or economic situation at that time in the country of interest. For instance, the United States saw a resurgence in ethanol fuel during the oil crisis of the 1970s [4]. Alcohols have been used as fuels in three main ways: as a fuel for a combustion engine (replacing gasoline), as a fuel additive to achieve octane boosting (or antiknock) effects similar to the petroleum-based additives and metallic additives like tetraethyllead, and as a fuel for direct conversion of chemical energy into electrical energy in a fuel cell.

Alcohols are of the oxygenate family. They are hydrocarbons with hydroxyl functional groups. The oxygen of the hydroxyl group contributes to combustion. The four most simplistic alcoholic fuels are methanol, ethanol, propanol, and butanol. More complex alcohols can be used as fuels; however, they have not shown to be commercially viable. Alcohol fuels are currently used both in com­bustion engines and fuel cells, but the chemistry occurring in both systems is the same. In theory, alcohol fuels in engines and fuel cells are oxidized to form carbon dioxide and water. In reality, incomplete oxidation is an issue and causes many toxic by-products including carbon monoxide, aldehydes, carboxylates, and even ketones. The generic reaction for complete alcohol oxidation in either a combus­tion engines or a fuel cell is

CxH2x+2 O + (~)O2 ^ XCO2 + (X + 1)H2О

It is important to note this reaction occurs in a single chamber in a combustion engine to convert chemical energy to mechanical energy and heat, while in a fuel cell, this reaction occurs in two separate chambers (an anode chamber where the alcohol is oxidized to carbon dioxide and a cathode chamber where oxygen is reduced to water.)