Published November 2015
Gasoline octane improvers/oxygenates include three major compounds—ethanol, methyl tertiary-butyl ether (MTBE), and ethyl tertiary-butyl ether (ETBE). The major exception is in China where methanol is the leading compound consumed, largely because of China’s vast coal-to-methanol capability. tertiary-Amyl methyl ether (TAME) and tertiary-amyl ethyl ether (TAEE) are also consumed in several regions.
Reformulated gasoline (RFG) is gasoline blended to burn more cleanly than conventional gasoline and to reduce some smog-forming and toxic pollutants in the air we breathe. The RFG program was mandated by the US Congress in the 1990 Clean Air Act amendment. The first phase began in 1995 and the second (current) phase began in 2000. RFG is required in cities with high smog levels and is optional elsewhere. RFG is currently used in 17 states and the District of Columbia. About 31.7% of the gasoline sold in the United States is reformulated, and contains octane improvers/oxygenates.
The following pie chart shows world consumption of gasoline octane improvers/oxygenates:
The largest-volume gasoline octane improver/oxygenate used in the world is ethanol. In recent years, ethanol use has grown significantly in the United States and Brazil, and to a lesser extent in other countries. Ethanol is the only octane improver/oxygenate consumed in all countries/regions of the world. The reason for this is that ethanol
- Boosts octane levels.
- Increases combustion efficiency, helps reduce air pollutants.
- Is a renewable resource when made by fermentation.
- Is biodegradable in surface water, groundwater and soil.
- Extends gasoline supplies.
- Decreases emissions of greenhouse gases (GHGs), although the extent of reduction depends on the feedstock and other factors.
- Supports local agriculture. In the industrialized world, agriculture often has a strong political influence on national policies, so increased ethanol production in the United States is supported strongly by Midwestern corn growers. In the less industrialized world, stimulation of local agriculture is very attractive to governmental officials.
- Decreases dependency on imports of crude oil or gasoline if the country is not a producer of crude oil but is a producer of ethanol.
The next leading gasoline octane improver/oxygenate is MTBE. Starting in the late 1970s, MTBE was the predominant choice of gasoline oxygenate used worldwide because of its low cost, high octane value, and easy incorporation into gasoline stock. However, in the late 1990s, MTBE was alleged to cause detrimental environmental impacts by contaminating water supplies. As a result, use in Japan ceased in 2001, and in the United States and Canada in 2006.
MTBE is used primarily as an octane booster in motor gasoline. It is widely used in Europe, the Middle East, and increasingly in Africa where demand for road fuels is expanding rapidly. Mexico is the only country in North America where MTBE is consumed. Reduced lead-content gasoline specifications and the passage of the US Clean Air Act Amendments in 1990 have mandated the use of oxygenated and reformulated gasoline, but ethanol has become the oxygenate of choice.
The United States still produces MTBE but nearly all is exported. There are several large Latin American consumers of MTBE; the largest are Mexico and Venezuela, which import considerable quantities of MTBE from the United States. Both have made some plans to use more ethanol or ETBE to reduce GHGs, but general inertia and fear of higher corn prices have limited the switch. In Brazil, there is no consumption of MTBE, and all production is exported. Historically, around one-third of all world MTBE production is exported.
MTBE will continue to grow strongly in the lesser-developed regions of the world—Central and Eastern Europe, Africa, the Middle East, and Asia (except Japan and certain other countries). In most of these regions, gasoline production and consumption continue to grow at high rates.
The third-largest-volume gasoline octane improver/oxygenate used in the world is methanol. Consumption is primarily in China, with smaller quantities being consumed in Western Europe, the Middle East, and Africa. In addition, methanol is consumed in the production of MTBE/TAME and DMT, with growth forecast for production of dimethyl ether (DME). New Chinese plants are being built to produce methanol from coal, which is in ample supply in the country. Chinese fuel blenders have been motivated to use more methanol, as its price remains attractive relative to gasoline and diesel prices. The Chinese government is currently planning to publish national fuel-blending standards for methanol in gasoline, which should provide further momentum for growth of methanol fuel blending. Growth in world consumption of methanol during 2015–20 is forecast at an average annual rate of 8%, accounted for primarily by China.