Fischer-Tropsch Synthesis: Diesel From Carbon Monoxide

By

Home / Fischer-Tropsch Synthesis: Diesel From Carbon Monoxide
Fast cars powered by synthetic fuel.

Will cars of the future use synthetic octane-an efficient alternative to fossil fuels? Image by Josh Rogan

Diesel and gasoline are fuels that power modern society.

The two mainstays find use in most aspects of everyday life, from the transport of people to the manufacture of the clothes on their backs.

To some, these fossil fuels are akin to the horses drawing carriages of the late 19th century. Moreover, the consensus among scientists and most engineers is: Climate change, resulting from fossil fuel usage, endangers life as we know it.

Although there is significant support in mainstream society for replacing fossil fuels, the energy and auto industry are slow to do so. Perhaps the present pace of change signifies something more significant-replacement of fossil fuels with synthetic fuel may be the alternative that mainstream industry seeks.

Alternatives to Fossil Fuels: Synthetic Gasoline and Diesel

Ironically, science derives synthetic fuel from the products of automotive combustion: carbon monoxide and water.

The momentous discovery took place in the laboratories of Hans Tropsch and Franz Fischer in 1923. The two German chemists derived wood alcohol (methanol) from carbon monoxide and water (waste products from the internal combustion engine) using Zinc as a catalyst.

A subsequent transformation to octane occurred in far less quantity than methanol. Since that discovery, researchers have spent years of research trying to force methanol into further reaction towards diesel and octane. However, the labyrinthine nature of the transformation amounts to a ‘kind of molecular genesis’—taking atoms and rearranging their geometries into hydrocarbons.

Breakthroughs in the synthesis of octane or diesel from carbon monoxide and water have, for the most part, been drowned out by plentiful, cheap fossil fuel. Moreover, the technological breakthroughs have been hard fought. The original synthesis of diesel from carbon monoxide was a paltry 2 percent efficiency. Presently, however, the improved reactions have yielded higher efficiencies.

Chemistry Behind the Fischer-Tropsch Synthesis

Initially, the Fischer-Tropsch Synthesis process involved two distinct reactions: methanol from carbon monoxide and a subsequent reaction of methanol to form a hydrocarbon mixture of diesel and octane.

Researchers found that iron and other metals of the autoclave accelerated the reaction of methanol to diesel and octane.

On the Periodic Table of Elements, iron falls in an area known as the Transition Metals. These elements are known to be electron-dense, and because of this, give the metals the properties of good electrical conductivity, and magnetism.

The properties allow one to conceptualize how the electrons influence carbon monoxide to rearrange its carbon-oxygen bonds to react with the hydrogens to form methanol (and ultimately to octane or diesel). The reaction has a kind of polarizing effect upon the carbon monoxide.

Fischer_Tropsch_Schematic

The Fischer-Tropsch reaction entails Carbon Monoxide reacting to form octane or diesel. Schematic Drawn with Chem Draw 14. Copyright Image by John A Jaksich. All Rights Reserved

In terms of a reaction geometry: Carbon monoxide is known to be a ‘flat-or-planar molecule,’ and the polarizing properties of the transition metal’s electrons allow the reaction to proceed.

This type of polarization, once deposited upon a non-reactive matrix, allows the carbon monoxide more surface area in which to react- the lab then extracts the hydrogens from the water solvent.

Moreover, later studies point to how other transition metals participate in the Fischer-Tropsch synthesis.

Transition Metals: The Role of Catalyst

The discovery of the synthesis was a serendipitous one-the original discovery detailed how the methanol reacted in a steel autoclave to generate hydrocarbon. Because steel is not strictly iron-but an alloy of composed a mixture of transition metals-the discovery gave chemists the impetus to experiment with the reaction conditions.

Since that time, scientists have found Ruthenium, Rhodium, Copper, and alloys containing these elements with Iron and Cobalt accelerated the Fischer-Tropsch reaction. Had the initial discovery been performed on strictly an iron autoclave, then its elaboration may have taken longer.

Why is the Fischer-Tropsch Reaction Complex?

The explosive nature of combustion is not only difficult to reverse but frighteningly so. However, as a reaction, it is achievable and pursued by chemists and engineers daily. 

Most chemical reactions take place as a result from either an input of heat or by releasing heat to the surroundings. The process of reversing combustion requires the energy from burning fuel be recouped plus extra energy be utilized in the new process-strictly not identical to combustion. The metals (catalysts) accelerate the transformation by arranging the carbons, hydrogens and oxygens in a ‘most favored geometric state’ to form methanol from carbon monoxide. Thus, the metal catalysts simplify the process.

Fire and Thermodynamics

Fire (combustion) is chaotic but follows a predictable path when investigated by Thermodynamics (the study of heat). In Thermodynamics, the states of matter are important to the scientist-while the intermediate states (the process of the burn) elude scientific description.

Chemical engineers measure combustion by the amount of initial and final substances and the change in temperature from the process. Thus, the rhetorical question does not apply: How much does fire weigh? Combustion (fire) is the desired ‘chemical reaction.’

Fischer-Tropsch Reaction Fuels Chemistry

The research involved with the Fischer-Tropsch reaction is a milestone in fuels chemistry. The chemical processes involved offer a glimpse into future energy solutions.

Leave a Comment