Syngas

Is referred to as synthesis gas, in the broadest sense, a gas mixture is used for a synthesis, as, for example, the mixture of nitrogen and hydrogen for ammonia synthesis. In the narrower sense, under synthesis gas industrially manufactured gas mixtures containing mainly carbon monoxide and hydrogen in addition to varying amounts of other gases. Depending on the manufacturing process, or intended use are also some other terms for synthesis gas in use: If synthesis gas derived from water, it is called water gas, with methane as the source gas gap. Methanol synthesis gas is synthesis gas for methanol production, oxo gas for the hydroformylation (or oxo ).

Production

The preparation of synthesis gas can be effected from solid (s- solid), the liquid ( liquid L ) and gaseous ( G Gaseous ) starting materials ( starting materials ) in principle.

Synthesis gas from solid reactants

In the production of synthesis gas from the solid reactants, especially the coal gasification is mentioned. Is C (s) here in a mix of partial (partial / incomplete ) oxidation with air or pure oxygen - - Coal O2 ( g) and gasification with steam - H2O ( g ) to a mixture of carbon monoxide - CO ( g) and hydrogen - H2 ( g ) are reacted. By the Boudouard equilibrium CO (g ) is still with C (s ) and carbon dioxide - CO2 ( g) in equilibrium:

Furthermore, the water -gas shift reaction must be taken into account:

The reaction with the oxygen by the exothermic reaction thereby provides the energy required to achieve the high reaction temperature for the endothermic gasification reaction of coal with water vapor.

Careful selection of the starting materials, the composition of the synthesis gas can be controlled ( depending on the desired carbon monoxide and hydrogen content).

Because in addition to carbon, coal other elements are still included (sulfur, nitrogen, vanadium, ... ), the synthesis gas obtained after the reactor must still be consuming cleaned and treated. Here, especially water, CO2, soot and H2S must be removed.

In addition, coal is in principle the use of other solids such as biomass (wood, straw ) is conceivable, however, this is also a pre-treatment of the starting materials and a post-treatment or purification of the synthesis gas is necessary.

Synthesis gas from liquid reactants

As the liquid starting materials for synthesis gas different crude oil distillates can be used, both low-boiling and high-boiling fractions. Low-boiling distillates may be implemented according to the removal of sulfur by reaction with steam in accordance with the steam reforming process. The steam reforming process is an endothermic reaction which is carried out over a heterogeneous catalyst ( reaction example pentane )

The use of high-boiling oil fractions ( flashed visbroken residue, see cracking), partial oxidation is carried out, which makes do without a catalyst ( Example response pentane )

Synthesis gas from gaseous reactants

The most important gaseous reactant for synthesis gas production is natural gas. The natural gas is reacted with water vapor in this case after the steam reforming process:

Natural gas supplies in comparison with the other reactants the highest proportion of hydrogen to carbon monoxide ratio. In addition to the steam reforming process can be reacted to form synthesis gas by partial oxidation of natural gas also:

Synthesis gas for ammonia synthesis, also produces, by partial oxidation, in which case air is used instead of pure oxygen. The resulting carbon monoxide is converted to a second reaction step with water vapor to CO2 and additional hydrogen ( implemented ):

After separation of CO2 then a mixture of N2 and H2 is obtained, which must then be adjusted to the desired N2/H2-Molverhältnis.

Syngas cleaning

To all the above production process, close after the reactor more or less on time-consuming and complex cleaning and treatment processes. Essentially, these are:

• Soot separation
• Dewatering and Drying
• Removal of sulfur compounds
• Setting the desired CO: H2 ratio
• CO2 capture.

Use

The most common synthesis gases are used:

In addition to these chemical- technical applications of synthesis gas can be used biotechnologically via fermentation. Products of this option can bsp. Be alcohols such as ethanol, butanol, and 1,2-propanediol, acetone, as well as organic acids.