The magic of syngas
- the link from feedstock to synthetic product
In the biofuels media you frequently read about “syngas”. What is syngas, where does it come from and how is it used? A wide range of synthetic products can be produced from syngas: clothes, solvents and fuels to mention a few. Through gasification and chemical reactions the molecules are split and joined into the wanted formulas.
The origin of syngas
The word syngas is derived from “synthesis gas”, that is gas used to produce something through chemical synthesis. Syngas is a mixture of hydrogen and carbon monoxide.
Syngas is normally derived from feedstocks containing carbon, such as
- heavy oil
- natural gas or
The heating phase
Syngas is usually produced through the process of gasification of the feedstock at very high temperatures, normally between 800 and 1500°C, depending on feedstock and process. These high temperatures can be obtained from an external heat source or by a process of partial oxidation where a part of the feedstock is reacted with oxygen to release heat.
The reaction phase
During the gasification the feedstock reacts with oxygen, water vapor and carbon dioxide or for oxygen-rich materials the reaction is simply triggered by thermal decomposition.
The purification phase
The result of gasification is a raw syngas that is not yet clean enough to use. A purification process takes care of impurities such as carbon dioxide, water vapor, methane, sulfur compounds, tar and ash. After purification the proportion between hydrogen and carbon monoxide is also adjusted depending on what the syngas will be used for. Now we have a syngas ready to be used in a variety of synthesis processes.
The catalytic phase
When the syngas is in contact with different catalysts, often containg compounds of metals such as copper, cobalt, manganese or iron, new complex molecules are formed. By experimenting with different catalysts scientists are constantly coming up with new ways of creating already existing molecular combinations. This is how it has nowadays become possible to create environmentally friendly fuels from syngas.
What can be made from syngas?
A wide range of synthetic materials, solvent, fuels and fertilizers have their origin in syngas. A few examples follow below:
Methanol becomes plastics, adhesives and fuels
Methanol is the simplest of the alcohols with the molecular formula CH3OH. It is one of the most important base chemicals
with a world production at over 40 million tons per year.
Methanol is used as the feedstock for production of formaldehyde, acetic acid, propylene and various esters. These in turn are the chemical building block in the production of plastics, resins, pharma¬ceuticals, adhesives, paints and much more.
Methanol is also used as a component of fuels. Biodiesel is normally made using methanol, DME (Dimethyl Ether) made from methanol is a bottled household gas component and direct blending of methanol into gasoline is gaining momentum.
A relatively new use of methanol is the production of propylene with DME as an intermediate. Propylene can then be reacted to either higher alcohols and aldehydes in the so-called OXO process or to propylene oxide - the starting point of a new branch on the methanol product tree which creates polyether polyols used in the production of plastics.
Ammonia becomes fertilizers and nylon clothes
Ammonia is a colourless gas with molecular formula NH3. We all know the pungent odour of ammonia, but you may not be aware of the fact that much of the food on your table is also produced with the help of ammonia as a fertilizer.
Ammonia is made from syngas by first converting it to pure hydrogen. This is done with the help of a the water gas shift reaction. The purified hydrogen is then reacted with nitrogen from the air in the so-called Haber-Bosch synthesis to form ammonia.
Ammonia is the base for nitrogen fertilizers, including ammonium, nitrate and urea fertilizers. These fertilizers play an important role in attaining high agricultural yields and are key to our ability to provide sufficient food for growing populations.
Ammonia is also the feedstock for most synthetic nitrogen-containing compounds including amine and nitro compounds. Ammonia plays an important role in the production of plastics like nylon and polyurethane.
Hydrogen - a fuel of the future
Hydrogen (molecular formula H2) is the lightest and most abundant chemical element in the universe. Most of the stars in the main sequence consist of hydrogen, but on earth hydrogen is scarce in its elemental form.
Hydrogen made from syngas does not only play an important role in the production of ammonia. It is also used in the refinery industry to extract more diesel and gasoline from crude oil. This is done by decreasing the chain-lengths of hydrocarbons in two processes called hydrodesulfurization and hydrocracking.
It is also extensively used in a large variety of hydrogenation reactions where hydrogen is added to unsaturated hydrocarbons.
Hydrogen has also been promoted as the energy carrier and fuel of the future. The advantage of a fuel based on hydrogen is that when combusted only water forms and it is a preferred fuel for fuel cells. Among the disadvantages is the difficulty to store hydrogen which as a gas has a low volumetric heat value and requires extremely low temperatures to be possible to liquefy. Comparing with alternative energy carrier solutions it is not unlikely that hydrogen will always remain the fuel of the future. Maybe it will remain an exotic fuel used in liquid form for spacecraft launch rockets where the high energy content per weight unit is valuable and fuel cost a minor concern.
|Hydrogen is a colourless gas with a purple glow in its plasma state. Here you can see the spectral lines of hydrogen.|