alkahalic fuels 1

8/10/2019 Alkahalic Fuels 1

1/3

1

1Alcoholic Fuels: AnOverviewShelley D. MinteerSaint Louis University, Missouri

CONTENTS

Introduction ...........................................................................................................1

Methanol................................................................................................................2

Ethanol ..................................................................................................................3

Butanol ..................................................................................................................3

Propanol ................................................................................................................4

Conclusions ...........................................................................................................4

References .............................................................................................................4Abstract

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 forfarm products and supported Henry Fords 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 2006 by Taylor & Francis Group, LLC

Alcoholic Fuels: An Overview3

ETHANOL

Ethanol (also known as ethyl alcohol) is the most common of alcohols. It is the

form of alcohol that is in alcoholic beverages and is easily produced from corn,sugar, or fruits through fermentation of carbohydrates. Its chemical structure is

CH3

CH2

OH. It is less toxic than methanol. The LD50

for oral consumption by a

rat is 7060 mg/kg [5]. The LD50


2/3

for inhalation by a rat is 20,000 ppm for 10

hours [6]. The NIOSH recommended exposure limit is 1000 ppm for 10 hours

[7]. Ethanol is available in a pure form and a denatured form. Denatured ethanol

contains a small concentration of poisonous substance (frequently methanol) to

prevent people from drinking it. Ethanol is a colorless liquid with a melting point

of144C and a boiling point of 78C. It is less dense than water with a density

of 0.789 g/ml and soluble at all concentrations in water. Ethanol is frequently

used to form blended gasoline fuels in concentrations between 1085%. More

recently, it has been investigated as a fuel for direct ethanol fuel cells (DEFC)

and biofuel cells. Ethanol was deemed the fuel of the future by Henry Ford

and has continued to be the most popular alcoholic fuel for several reasons: (1)

it is produced from renewable agricultural products (corn, sugar, molasses, etc.)

rather than nonrenewable petroleum products, (2) it is less toxic than the other

alcohol fuels, and (3) the incomplete oxidation by-products of ethanol oxidation

(acetic acid (vinegar) and acetaldehyde) are less toxic than the incomplete oxidation

by-products of other alcohol oxidation.

BUTANOL

Butanol is the most complex of the alcohol-based fuels. It is a four-carbon alcohol

with a structure of CH3

CH2

CH2

CH2

OH. Butanol is more toxic than either methanol

or ethanol. The LD50

for oral consumption of butanol by a rat is 790 mg/kg.

The LD50

for skin adsorption of butanol by a rabbit is 3400 mg/kg. The boiling

point of butanol is 118C and the melting point is 89C. The density of butanol

is 0.81 g/mL, so it is more dense than the other two alcohols, but less dense than

water. Butanol is commonly used as a solvent, but is also a candidate for use asa fuel. Butanol can be made from either petroleum or fermentation of agricultural

products. Originally, butanol was manufactured from agricultural products in a

fermentation process referred to as ABE, because it produced Acetone-Butanol

and Ethanol. Currently, most butanol is produced from petroleum, which causes

butanol to cost more than ethanol, even though it has some favorable physical

properties compared to ethanol. It has a higher energy content than ethanol. The

vapor pressure of butanol is 0.33 psi, which is almost an order of magnitude less

than ethanol (2.0 psi) and less than both methanol (4.6 psi) and gasoline (4.5

psi). This decrease in vapor pressure means that there are less problems with

evaporation of butanol than the other fuels, which makes it safer and more

environmentally friendly than the other fuels. Butanol has been proposed as a

replacement for ethanol in blended fuels, but it is currently more costly than

ethanol. Butanol has also been proposed for use in a direct butanol fuel cell, but 2006 by Taylor & Francis Group, LLC.

4

Alcoholic Fuels

the efficiency of the fuel cell is poor because incomplete oxidation products easily

passivate the platinum catalyst in a traditional fuel cell.

PROPANOL

Although propanols are three carbon alcohols with the general formula C3

H


3/3

8

O,

they are rarely used as fuels. Isopropanol (also called rubbing alcohol) is frequently

used as a disinfectant and considered to be a better disinfectant than

ethanol, but it is rarely used as a fuel. It is a colorless liquid like the other alcohols

and is flammable. It has a pungent odor that is noticeable at concentrations as

low as 3 ppm. Isopropanol is also used as an industrial solvent and as a gasoline

additive for dealing with problems of water or ice in fuel lines. It has a freezingpoint of89C and a boiling point of 83C. Isopropanol is typically produced

from propene from decomposed petroleum, but can also be produced from fermentation

of sugars. Isopropanol is commonly used for chemical synthesis or as

a solvent, so almost 2M tons are produced worldwide.

CONCLUSIONS

In todays fuel market, methanol and ethanol are the only commercially viable

fuels. Both methanol and ethanol have been blended with gasoline, but ethanol

is the current choice for gasoline blends. Methanol has found its place in the

market as an additive for biodiesel and as a fuel for direct methanol fuel cells,

which are being studied as an alternative for rechargeable batteries in small

electronic devices. Currently, butanol is too expensive to compete with ethanol

in the blended fuel market, but researchers are working on methods to decrease

cost and efficiency of production to allow for butanol blends, because the vaporpressure difference has environmental advantages. Governmental initiatives

should ensure an increased use of alcohol-based fuels in automobiles and other

energy conversion devices.

REFERENCES

1. Ford Predicts Fuel From Vegetation,

The New York Times, Sept. 20, 1925, p. 24.2.

National Geographic

, 31, 131, 1917.3. Borth, C.,Chemists and Their Work, Bobbs-Merrill, New York, 1928.

4. Kovarik, B., Henry Ford, Charles F. Kettering and the Fuel of the Future,Automot.Hist. Rev., 32, 727, 1998.

5.Toxicology and Applied Pharmacology, Academic Press, Inc., 16, 718, 1970.6.

Raw Material Data Handbook, Vol. 1: Organic Solvents, Nat. Assoc. Print. InkRes. Inst., 1, 44, 1974.7.

National Institute for Occupational Safety and Health, U.S. Dept. of Health,Education, and Welfare, Reports and Memoranda

, DHHS, 92100, 1992.

2006 by Taylor & Francis Group, LLC

alkahalic fuels 1

Documents