Replacement of lead was also necessary for modern engines with three-way catalytic converters. Many brands of gasoline sold today in Europe, and around the world, have some level of oxygenates to enhance octane rating. However, oxygenates are being used in gasoline for far more than just the replacement of toxic compounds (e.g. lead). Responding to requirements for cleaner, more breathable air, oxygenated fuels are used to reduce ozone-forming smog, hazardous carbon monoxide pollution, and other toxic air pollutants.

Oxygenates are oxygen-rich compounds which, when they are added to motor vehicle fuels, make them burn more cleanly, thereby significantly reducing toxic tailpipe pollution. Although great strides have been made in reducing automotive emissions, air quality continues to be a serious concern in many areas, especially in large cities. Among industrialised nations, pollution from motor vehicles is responsible for nearly half of the human-caused nitrous oxides, two-thirds of the carbon monoxide (CO) and about half of the hydrocarbon emissions. Cleaner burning oxygenated fuels are one of the leading tools in fighting automotive air pollution.

Oxygenates are produced from a variety of feedstocks. Methanol, derived primarily from natural gas, is one feedstock used in the production of the most commonly used oxygenate, methyl tertiary butyl ether (MTBE).

Another oxygenate, ethanol, is derived primarily by fermenting corn and other agricultural products and is used directly as an additive or as a feedstock for the production of ethyl tertiary butyl ether (ETBE).

Isobutylene, which is the other feedstock used in both MTBE and ETBE production, is also derived from natural gas or as a by-product of petroleum refining.

1.2.2.2 Characteristics of oxygenates
Oxygenates contain oxygen atoms in addition to carbon and hydrogen atoms, whereas gasoline itself lacks oxygen atoms. The presence of oxygenates in gasoline promotes cleaner fuel combustion within the engine, boosts fuel octane values, and reduces vehicle air emissions. Two types of oxygenates are commonly added to gasoline: alcohols and ethers.

In alcohols, each oxygen atom is linked to a carbon atom and a hydrogen atom, forming a carbon-oxygen-hydrogen sequence. Ethanol is by far the most commonly used alcohol oxygenate. Other alcohols that are used (or that could potentially be used) as fuel oxygenates include methanol and tertiary-butyl alcohol (TBA). TBA is also of interest as a product of MTBE degradation and a potential impurity from MTBE manufacture.

In ethers, each oxygen atom is linked to two carbon atoms, forming a carbon-oxygen-carbon sequence. MTBE is by far the most commonly used ether oxygenate, due to its high octane properties, its fungibility, cost effectiveness and supply flexibility.

However, there is an increasing interest in ethyl tertiary-butyl ether (ETBE) due to its potential as a biofuel component.

Other ethers that are used (or that could potentially be used) as fuel oxygenates include tertiary-amyl methyl ether (TAME), tertiary-amyl ethyl ether (TAEE) and diisopropyl ether (DIPE).

1.2.3 Oxygenates in gasoline
1.2.3.1 Composition
In Europe, the typical content of MTBE in gasoline is 2-4% by volume, although higher concentrations are used in some areas, for example Finland, and for some fuel specifications. The oxygen content of current EU gasolines can be found in the "EU Fuel Quality Monitoring - 2003 Summary Report" (web link http://europa.eu.int/comm/environment/air/pdf/fqm_Summary_2003.pdf).  In the majority of cases this will represent the volume of ethers used.

Another important reason for the widespread use of MTBE is feedstock flexibility. MTBE can either be made inside the refinery, using petroleum-derived raw materials, or it can be produced externally, using natural gas feedstocks, thereby ensuring ready availability and reducing dependence on crude oil for the production of automotive fuels.

Furthermore some quite recent studies have shown that the octane appetite of modern cars seems to differ from that of previous populations. It appears that the conventional measures of anti-knock quality (RON and MON) are no longer appropriate for modern engines. The modern Japanese and European cars equipped with knock sensors prefer fuels of high sensitivity and high RON. Adding MTBE in the gasoline is a way to improve these properties in the fuel.

1.2.4.2 Air quality benefits
MTBE provides considerable air quality benefits, which can be divided into two main categories. There are the direct effects, largely due to more complete fuel combustion, and the indirect effects, arising from the dilution of other, less desirable, gasoline pool components.

Direct effects include the reduction of specific pollutants limited by law, such as carbon monoxide (CO) and unburned hydrocarbons (HCs), as well as other serious pollutants such as particulate matter (PM) and ground-level ozone (O₃).

Indirect effects include the reduction of sulphur, olefins, aromatics and benzene levels, regardless of whether the fuel is used in current or older technology vehicles.

The extent of MTBE’s air quality benefits depends on various parameters, such as the percentage of blended MTBE, the presence of catalyst devices, the type and age of engine and the driving cycle. Nevertheless, there is general agreement in the industrial and scientific communities on broad values.

Carbon monoxide: CO emission is reduced on average by at least the same percentage as MTBE content in gasoline.

Unburned hydrocarbons: For each 1 or 2% of MTBE, there is a 1% reduction in total HC emissions.

Particulate matter: It is estimated that each 1% of MTBE results in a 2 to 3% PM emission reduction.

Ozone: MTBE generates about half the ozone compared with iso/alkylates and one-tenth that of aromatics.

Benzene: It is estimated that, for each 1% of MTBE, there is an equivalent percentage reduction in benzene emissions, both evaporative and exhaust.

Olefins: MTBE displays low vapour pressure and low volatility compared to olefins. Converting olefins to MTBE in the refinery removes some of the most reactive and volatile components from the gasoline pool.

Lead: MTBE is an effective substitute for lead, a toxic compound that has been phased out in most parts of the world.

As an example of the potential air quality benefits of MTBE, the following significant reductions of pollutants have been achieved through the use of reformulated gasoline containing 10-15% MTBE, compared to conventional gasoline:

20-25 % less carbon monoxide

10-15% less unburned hydrocarbons

About 30% less particulate matter                                  

20-30% less benzene

5% less nitrogen oxides                        

15% less evaporative emissions             

Reduction of ground-level ozone

In Finland, the widespread use of oxygenated fuel containing 9-13% MTBE has reduced CO emissions by 10-20% and hydrocarbons by 5-10%.


1.2.5 Extent of oxygenates use
1.2.5.1 World market
The ether oxygenates world market today can be reasonably approximated by using MTBE figures, as the volume of TAME and ETBE combined is far less than MTBE.

The MTBE market grew strongly in the 1990's.  Since then the market has been broadly flat with growth in Asia compensating for reduced demand in the US. For instance, the 1999 world consumption of 20,700 kt/a was about double that of 1992. The driving force for the growth was the US Clean Air Act.

In 2003 world demand was 19,000 kt/a..

1.2.5.2 European market
The annual production volume of MTBE in the year 2003 in the EU was 2 612 000 tonnes. About 609 000 tonnes was imported and about 539 000 tonnes was exported outside the EU in the year 2003 (CMAI).  The annual consumption of MTBE within the EU was hence 2 577 000 tonnes in the year 2003 (see table below)
For the future no substantial increase in MTBE usage is expected.

Production, import, export and consumption in EU in 2003 (tonnes/year) (1)