Methanol as a fuel source

Methanol is manufactured by the oxidation of natural gas or the reaction of carbon dioxide with hydrogen. It has numerous chemical uses and has potential as a partial replacement for gasoline.

Background

Methanol (also called methyl alcohol and wood alcohol) is a colorless liquid with little taste or odor. It boils at 64.51° Celsius and has a melting point (and triple point) of -97.56° Celsius. At 20° Celsius it has a vapor pressure of 97.60 torrs, a of 0.7913 gram per milliliter, and an index of refraction of 1.3284. Its molar mass is 32.04 grams. Methanol is completely soluble in water and most organic solvents. It has a flash point of only 11° Celsius and is thus highly flammable. Methanol forms numerous binary and ternary azeotropic combinations with a variety of compounds, so it is difficult to purify.

Methanol is of considerable importance: It has long been considered a major industrial organic chemical, and it has more recently been identified as a likely automotive fuel source. The world production capacity for methanol is more than 22 million metric tons per year. By 2013, worldwide of methanol is estimated to reach 58 million metric tons, more than one-half of which will be consumed in China, the world’s largest producer and consumer of methanol.

Primary Uses

A major portion of the methanol produced is used for the production of methyl esters such as methyl acrylate, methyl methacrylate, and methyl terephthalate, which are used in the manufacture of high-volume polymers. Methanol has been used to prepare formaldehyde, but now more direct formaldehyde synthetic methods have somewhat reduced that usage. Because formaldehyde is used in enormous quantities for the production of synthetic water-based polymers, such as the phenolic and urea resins (employed in plywood manufacture, for example), even the reduced formaldehyde production from methanol is important. A growing use for methanol is its reaction with isobutene (2-methylpropene) for the synthesis of methyl tertiary-butyl ether, a gasoline additive that is used in winter in many large cities to reduce air pollution. Methanol is also used for the chemical synthesis of acetic acid, methyl chloride, vinyl acetate, vinyl chloride, ethylene glycol (antifreeze), and other compounds. Methanol is also used as a solvent and extracting medium. Some methanol is used for the preparation of synthetic protein.

Methanol has an octane number value of 100; therefore, fuel uses for methanol have been proposed repeatedly. During the 1970s, as prices skyrocketed, a number of processes for producing methanol for fuel purposes from wood or other biomass sources were considered. Vehicles capable of using methanol or a gasoline-methanol mix were developed. As gas prices softened in the late 1990s, automakers shifted attention to ethanol, which is more economical to produce, as methanol prices rose. Methanol continues to be used as a fuel for drag race cars, and it is widely used in China as an automobile fuel. Even though methanol combustion products (almost entirely carbon dioxide and water) are nonpolluting and automobile engines can be easily modified to burn methanol, US automakers have shifted their attention from methanol to hybrid and electric vehicles.

Methanol Production

Before 1930 the most common production method was the anaerobic destructive distillation of hardwoods at temperatures below 400° Celsius. However, this method produced low yields (about 21 liters per metric ton of wood) of very impure methanol. Small amounts of relatively impure methanol produced in this manner are added to commercial ethanol to “denature” it and prevent the commercial alcohol’s use as a beverage. Fermentation processes used to produce other alcohols have not been successful for methanol. However, because methanol is found in both plants and animals and is utilized by bacteria, fermentation appears to be a likely method if appropriate microorganisms could be identified or if genetically engineered bacteria could be developed for that purpose.

The most often used synthetic processes involve reactions of carbon monoxide and hydrogen (called synthesis gas), using catalysts such as copper, zinc, and chromium oxides at elevated pressures (above 300 atmospheres) and at temperatures higher than 300° Celsius. The high-pressure process is sometimes replaced with a lower-pressure one (below 100 atmospheres) at a somewhat lower temperature. The lower-pressure process requires more purified reactants and a more complex catalyst system but allows the reaction to proceed in simpler reactors. The synthesis gas is obtained by treating (methane) or petroleum fractions with high-pressure steam. Synthesis gas can also be obtained directly from coal, and if carbon dioxide is easily available, it may be more economically desirable to produce the synthesis gas from the prior reaction of the carbon dioxide with hydrogen.

Toxicity

Methanol, even in minute quantities, is a powerful poison, acting on many parts of the nervous system, particularly the optic nerves. Blindness, at least temporary, often results from its ingestion. Methanol is oxidized in the body to formaldehyde and formic acid, which are the major direct culprits in methanol poisoning. Coma and death frequently occur as a result of methanol consumption.

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