Biorefinery platforms – Biobased syngas
Concept
- Syngas is an abbreviation for synthesis gas, which is a mixture comprising, mainly, carbon monoxide (CO) and hydrogen (H2). Raw syngas can contain significant amounts of carbon dioxide (CO2), methane (CH4), water (H2O) and nitrogen (N2), as well as other hydrocarbons and condensable compounds.
- The name comes from its use as intermediate in producing Synthetic Natural Gas (SNG) and for producing ammonia or methanol.
- Syngas can be produced from natural gas, coal, biomass or any hydrocarbon feedstock, by reaction with steam (steam reforming), carbon dioxide (dry reforming) or oxygen (gasification and high temperature pyrolysis).
- Biobased syngas is produced from biomass.
Figure 1. Biorefinery platforms – Biobased syngas
Applications
- Direct heat and power generation. After cleaning, syngas can be used as a fuel for heat and power generation. This can be realised either in stand-alone combined heat and power plants or through co-firing in large-scale power plants.
- Production of natural gas through the methanation of H2 and CO. The cleaned gas, consisting primarily of CO and H2, reacts in a methanation reactor in the presence of a catalyst to produce CH4 and H2O. The resulting gas, after H2O condensation, is Renewable Natural Gas (RNG).
- Fischer-Tropsch (F-T) synthesis. F-T synthesis is a set of high-performance catalytic processes (mainly with ruthenium, cobalt and iron catalysts) that can be used to produce a mixture of hydrocarbons (syncrude) with different chain lengths from synthesis gas. Possible products from F-T synthesis are gasoline, diesel, jet fuel, paraffinic waxes and lubricants.
- Production of methanol. Syngas is conditioned to remove impurities such as tars and methane, and to adjust the H2:CO ratio to 2:l. The syngas is then reacted over a catalyst at elevated temperatures and pressures to form methanol. The process is conventionally performed in a fixed-bed tubular reactor operating at 60-100 bar and 250-280ºC over a Cu/ZnO-based catalyst. Dimethyl ether (DME) can also be synthesized by adding a step of methanol dehydration.
- Production of hydrogen. In order to increase the H2 yield and to lower the CO content of the syngas, the water-gas-shift (WGS) reaction or chemical looping can be used. H2:CO ratio can have a great impact on end-application performance and potential uses. - Syngas fermentation. Syngas components are converted to alcohols (ethanol, butanol) and other chemicals (acetic acid, butyric acid, methane) by acetogenic bacteria through the Wood-Ljungdahl pathway or its derivatives.
