**1. Introduction**

High strategic risk of dependence on imported energy sources is attracting profoundly alarming concerns as indicated by recent international trend and past experience. Self-sufficient energy supply system is at least needed to maintain a certain minimum living standard in a nation in general and the society in particular so that easy access to domestic and neighboring energy sources is a key factor to maintain. Alcohol fuels are very promising alternative energy sources from this point of view.

Worldwide demand for liquid fuels will increase steadily at least through the mid-twenty-first century, but not in the form of CO2-emitting scheme, rather in a renewable and sustainable way. Actually, there had been many options that can use locally plentiful energy resources, typically in a biomass type.

The major energy source nowadays is most certainly (hydrocarbon) gas, electricity, and liquid fuel, which is almost unanimously agreed upon. Current energy infrastructure has already been solidly established with (hydrocarbon-based) gas, electricity, and liquid fuel as convenient energy sources and such energy infrastructure appear to get more and more solidly implemented. Inconvenience related to the utilization of solid fuels is no longer tolerable, and rapid commercialization of electric vehicle is also foreseen in the near future. Liquid fuel gets replaced to the ultra-clean fuel that meets the ever-stringent environmental regulations. Electricity is produced from atomic energy, coal, natural gas, and petroleum oil products, but safety, environmental friendliness, and global warming issues must also be comprehensibly considered. Many Asian countries almost exclusively depend on imported liquid natural gas for energy source. This raises dual issues on the feasibilities of steady supply in energy sources and of reasonably affordable cost. In fact, natural

gas that emits 40–55% level of reduced CO2 evolution compared to coal is surely a promising source of energy. Ethanol produced from sugarcane is one of the most carbon-efficient biofuels available globally, with life cycle greenhouse gas emissions around 70% lower than conventional hydrocarbon transport fuels [1]. Current worldwide trend of shifting to alternative clean, sometimes ultra-clean, gas/liquid fuel from more conventional liquid fuel of gasoline/light oil necessitated a new definition of role and position of alcohol fuels in the emerging picture.

Alcohol fuels were originally regarded as an alternative energy sources for petroleum oil to realize energy independence during oil crisis of the 1970s. A brief look into the history of bio-ethanol shows Ford Motor Company's development of ethanol-fueled car in 1899, which was terminated by low-priced gasoline then. Oil crisis of the 1970s revived similar interest in the form of gasohol by mixing ethanol, which was developed and commercialized mainly in Brazil.

The first starting point on alcohol fuels in the 1970s tells the basic background at that time. It is prompted by concerns about reliance on foreign sources of oil and a desire to support domestic agriculture. In the United States, in particular, E10 gasohol was implemented during the oil crisis of 1970s to reduce petroleum oil dependence and simultaneously to utilize surplus farm crops. At present, E15 product with 15% ethanol content is distributed for consumer market.

In the twenty-first century, alcohol fuels are again becoming a frequent keyword for clean fuel utilization in connection with mitigation of climate change and clean fuel technology suitable for less-used local energy sources. As a matter of fact, demand for alcohol fuels is mainly derived from socioeconomic and political motivations rather than from consumer conscious reasons and economic viability.

The centralized energy system that emphasizes cost-effectiveness had diminished the key driving force for technological advances in alcohol fuels. Petroleum-based liquid fuel has dominated the transportation area till now. Also, low petroleum oil cost lessened the motivation for further technology development for alcohol fuels. Global oil shock of the 1970s are not expected to break out again within the foreseeable future, and the prospect for alcohol fuel as a remedy to soaring petroleum price is not a plausible picture either. On the other hand, clean energy generation policy by utilization of locally acquired biomass or sea algae will be emphasized to replace local consumption of liquid fuel and to produce electricity or pure alcohols for fuel cells or other means, as a rather cleaner way.

For the future energy sources, renewable-based energy society must be the final goal to reach, but unfortunately it takes a long time to reach the economics and technological easiness to be a common practice, which appears to take at least one or two decades. In order to bring the technology in earlier time, there exist many hurdles and require efforts in scientific and societal side.

All in all, future energy generation direction had been solidly established as "to be clean, renewable, and sustainable," but low petroleum cost lessened the necessity of alternative clean energy source development, e.g., alcohol fuels.

Recently, global warming is becoming a central social issue attracting worldwide attention and provides a kind of consensus that society should be changed to deal with alleviating the prime causes of CO2 evolution in addition to pollution-related issues such as fine dust. The utilization of alcohol fuels reduces carbon dioxide contents in the atmosphere, thus significantly alleviating global warming potential.

Alcohol fuels have been known as a good replacement of fossil-based liquid fuels [2]. Brazil and the United States consume alcohol fuels in the most significant proportions, and such trend will not easily change. In particular, bio-ethanol are well known for its use in Brazil as a gasoline supplement (**Figure 1**).

When we say alcohol fuels, they comprise of methanol, ethanol, ethers (MTBE, ETBE, TAME, TAEE, and DME and DEE), and esters (biodiesels: methyl and

#### **Figure 1.**

*Worldwide ethanol production by country and year 2007–2015 [3].*

ethyl esters of fatty acids derived from vegetable oils and animal fat), in a broad sense. Most widely used alcohol fuels typically include methanol, ethanol, and bio-butanol. Ethanol that is produced through yeast-based fermentation using corn or sugarcane is the most well-known. Bio-butanol is capable of overcoming technological limitations surrounding bio-ethanol, and it is currently becoming another promising focal issue of clean energy.

The chapter deals with the current status of alcohol fuels and tries to elaborate the future direction for more wider utilization and the possible roles of alcohol fuels in attaining the far-reaching goal of low-carbon economy using sustainable energy resources.
