Properties and Historical Background

Methanol, also called methyl alcohol or wood alcohol, is a colorless, water-soluble liquid with a mild alcoholic odor. It freezes at -97.6 °C, boils at 64.6 °C, and has a density of 0.791 at 20 °C. Methanol in its (relatively) pure form was first isolated in 1661 [106] by Robert Boyle, who called it "spirit of the box" because he produced it through the distillation of boxwood. Its chemical identity or elemental composition, CH3OH, was described in 1834 by Jean-Baptiste Dumas and Eugene Peligot. They also introduced the word methylene to organic chemistry, from the Greek words methu and hyle, meaning respectively wine and wood. The term methyl, derived from this word was then applied to describe methyl alcohol, which was later given the systematic name methanol. Containing only one carbon atom, methanol is the simplest of all alcohols. Methanol is commonly referred to as wood alcohol because it was first produced as a minor byproduct of charcoal manufacturing, by destructive distillation of wood. In this process, one ton of wood generated, along other products, only about 10-20 L of methanol. Beginning in the 1830s, methanol produced in this way was used for lighting, cooking and heating purposes, but was later replaced in these applications by cheaper fuels, especially kerosene. Up until the 1920s, wood was the only source for methanol, which was needed in increasing quantities in the chemical industry. As hard as it may be to believe today, all the methanol required during World War I for example, was derived from charcoal furnaces along with acetone and other essential chemicals [107]. With the industrial revolution, wood was largely replaced by coal in many applications. Coal and coke gasification processes through the action of steam and heat were developed, by which gases containing carbon monoxide and hydrogen could be obtained to supply cities with town gas. Using hydrogen produced with this technology, Fritz Haber and Carl Bosch developed the technical hydrogenation of molecular nitrogen N2 to ammonia at very high temperature and pressure. This breakthrough resulted in the development of a number of other chemical processes, necessitating similar severe conditions and feedstock, including methanol synthesis. In fact, from the earliest days, the synthesis of methanol and ammonia were so interrelated that they are often produced in the same plant. The synthetic route to methanol production, by reacting carbon monoxide with hydrogen, was first suggested in 1905 by the French chemist Paul Sabatier [108]. In 1913, the Badische Anilin und Soda Fabrik (BASF), based on the investigations of A. Mittasch and C. Schneider, patented a process to synthesize methanol from syn-gas, produced from coal, over a zinc/chromium oxide catalyst at 300-400 °C and 250-350 atm [108, 109]. After World War I, BASF resumed its research into synthetic methanol and built, in 1923, the first commercial high-pressure synthetic methanol plant in Leuna, Germany. Between 1923 and 1926, F. Fischer and H. Tropsch reported from the Muhlheim Coal Research Laboratory their extensive studies of the production of hydrocarbons, including that of methanol, from syn-gas, a mixture of carbon monoxide and hydrogen, which was the basis of what is known as the Fischer-Tropsch synthesis [110, 111]. In 1927, in the United States, Commercial Solvents Corporation used the high-pressure technology to produce methanol from CO2/H2 mixtures obtained as fermentation byproduct gases [112]. At the same time, the DuPont company began the production of both methanol and ammonia in the same plant using syn-gas produced from coal. In the 1940s, steam reforming of natural gas began in the United States, based on developments of BASF in the 1930s. From then on, coal was slowly abandoned as a feedstock for syn-gas in favor of the cleaner, cheaper and plentiful natural gas. Over the years, other feedstock including heavy oil and naphtha have also been used, albeit at much lesser extent. The steam reforming process of methane, because of the very high purity of the syn-gas, opened the way to the technical realization of the low-pressure methanol process, introduced commercially in 1966 by Imperial Chemical Industries (ICI).

Table 11.1 Properties of methanol.

Synonyms

Methyl alcohol, wood alcohol

Chemical formula

CH3OH

Molecular weight

32.04

Chemical composition (%)

Carbon

37.5

Hydrogen

12.5

Oxygen

50

Melting point

-97.6 °C

Boiling point

64.6 °C

Density at 20 °C

791 kg m-3

Energy content

5420 kcal kg-1

173.6 kcal mol-1

Energy of vaporization

9.2 kcal mol-1

Flash point

11 °C

Autoignition temperature

455 °C

Explosive limits in air

7-36%

This new process using a more active Cu/ZnO catalyst, and operating at 250 to 300 °C and 100 atm [113], put an end to the high-pressure methanol synthesis technology which operated under much more severe conditions. The use of these highly active catalysts was made possible by the lower content of catalyst poisons such as sulfur or metal carbonyls in the syn-gas feed. Not much later, Lurgi launched its own process with even lower operating temperature and pressure (230-250 °C, 40-50 atm). During the past 40 years, considerable further improvements have been made in methanol synthesis from carbon oxides (CO containing some CO2) and hydrogen, making this technology a rather mature one. Using the low-pressure process, selectivity for methanol is now in excess of 99.8% with an energy efficiency of nearly 75%. Current research is aimed at developing new ways to synthesize methanol at even lower temperature and pressure from diverse origin carbon oxides/hydrogen feeds, as well as by direct oxidation of methane which is a superior method from an energetic viewpoint.

Today, almost all methanol worldwide is produced from syn-gas. However, as discussed in Chapter 12, new ways for its production directly from methane (natural gas) without going through syn-gas, as well as by hydrogenative chemical recycling of carbon dioxide are being developed.

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Responses

  • diana
    How wood alcohol was made, methanol, 1920s?
    7 years ago

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