A clean engine has a longer life, performs better and emits fewer pollutants. But it also needs high quality fuels. Since basic fuels from refineries do not satisfy these requirements, they are increasingly blended with multifunctional additive systems.

Composition of multipurpose additives

Under the name Keropur® BASF offers its customers in the petroleum industry a range of additive packages. The main active component in these additive systems is polyisobuteneamine (PIBA), a detergent serving as a surface active substance which is both more effective and more eco-friendly than other products.

Polyisobuteneamine (PIBA) in Keropur® keeps the inlet valves clean

 
When developing fuel additives, researchers have to develop products satisfying a complex profile of requirements:

• They must be extremely effective at the lowest possible concentration.
  
• Like medications, they must be free from undesirable side effects.
  
• They must perform in various fuels in different types of vehicle under all operating conditions.

Long-chain hydrocarbon amines are particularly suitable as detergent additives

During the approximately twenty year history of developing detergent additives, one class of chemical substances has clearly come out on top: long-chain hydrocarbons with amino groups. The hydrocarbon content, however, consists mainly of polyisobutene. Detergent additives act like surfactants and largely satisfy the complex profile of requirements. However, they have one drawback: all the processes so far used to manufacture such surfactants involve the use of chlorine or chlorine-containing compounds. This means that organically bound chlorine automatically enters the target molecule. The aim was thus not only to produce a chlorine-free product, but also to find an ecoefficient synthetic route.

 
Gasoline additives are required which can burn without forming residues. Besides small amounts of nitrogen, the detergent (like gasoline itself), therefore, should consist exclusively of the chemical elements carbon, hydrogen and possibly oxygen. Other elements, such as halogen, should not be present to prevent the formation of by-products and pollutants (e.g. dioxin formation). PIB amines are the most extensively marketed detergent additive.

The polymer chemists of BASF succeeded in developing a chlorine-free polymerization of a completely new, highly reactive polyisobutene. This meant that a polyisobutene was available for the first time which contained large numbers of terminal double-bonds and was thus suitable for consecutive reactions under less drastic experimental conditions.

Scientists used this polyisobutene as a starting material for the production of fuel additives. The necessary nitrogen could be incorporated into this polymer using chlorine-free processes for the first time:
 
Chlorine-free synthetic route for PIBA
 
By means of hydroformylation followed by reductive amination, they produced polyisobuteneamine (PIBA). In combination with carrier oils, such as alkylene oxides, PIBA "washes down" organic residues from the surfaces of the engine intake system or forms a protective film preventing such deposits.

The required amount of gasoline additive has to be tailored to the respective fuel. The usual dosages in Europe are 0.3 - 0.5 g pure Keropur (additive system) per liter of gasoline. This reduces fuel consumption by up to four per cent and even more the output of pollutants .

 
During process development, the fluorine-containing catalysts used to produce the polyisobutene presented special challenges. The use of this substance results in the formation of hydrogen fluoride. The process chemists and engineers thus had to modify the process concept and select the construction materials such that the corrosive potential of hydrogen fluoride could be controlled.

To optimize the process, highly reactive polyisobutene requires proper analytical tools. The methods of choice are 1H-NMR and 13C-NMR spectroscopy, which are used to identify and quantify the content of terminal double bonds and other olefinic structures.

 
Thorough engine tests under real operating conditions were essential to determine and optimize the application characteristics of polyisobuteneamine as a fuel additive. Engine plus fuel constitute a highly complex system involving countless variables. No laboratory test can simulate the conditions prevailing in an internal combustion engine. This is why thirteen engines are running around the clock all year long in the development department. Their gasoline consumption was about 300,000 liters in 2004.

 
The further improvement of gasoline additives is a long-term project for BASFs researchers and developers. By the year 2010, the number of registered automobiles will have increased even further, especially in Asia. This trend is naturally causing concern about increasing environmental pollution. Only by continuously perfecting automobile technology on one hand and fuel quality on the other, will it be possible to significantly reduce specific emissions. New engine technologies such as the direct injection gasoline engine place different demands on fuels than conventional engines. BASFs additives are also being tested in these new engines.

Mitsubishi GDI® Motor

Keropur® keeps the injector in the
direct-injection gasoline engine clean

The highly reactive polyisobutene is also suitable as a starting material for the synthesis of diesel additives. Entering the booming diesel additive business with new, tailored system solutions is a further part of BASFs growth strategy and is facing its researchers with new challenges.