Syngas is produced via gasification which turns organic fuels (such as biomass resources) into low to medium energy gaseous compounds by supplying less oxygen than is needed for complete combustion of the fuel. In its simplest form, syngas is composed of carbon monoxide (CO) and hydrogen (H2), which provide the building blocks to produce a number of organic compounds (figure 1). Several commercial chemicals are currently produced from syngas. At present, most of these products use natural gas or coal as the feedstock, but biomass resources could also be used.
Hydrogen is the principal product made from syngas and is produced as both a main product and as a by-product. World consumption of hydrogen in 1999 was 15,864 billion ft3 (60% to produce ammonia, 23% for use in oil refineries, 9% for methanol production, 8% for merchant hydrogen).
Ammonia (NH3) is the second largest chemical produced from syngas (world production of 143 million tonnes in 1996). It is used primarily to make fertilizers with a small fraction used in plastics and explosives.
Methanol (CH3OH) can be used as a transportation fuel, either pure (M100) or as an 85% blend (M85), or transformed to diesel, ethanol, or gasoline. Currently, its major use is as a key building block (intermediate) chemical that is used to produce other industrial organic chemicals such as formaldehyde (used by the construction industry), methyl tertiary-butyl ether (MTBE; used as an oxygenated in gasoline and in industrial solvents), and acetic acid (used to produce resins for paints, adhesives, paper coatings, and textile finishing agents; used to produce cellulose acetate fibers and cellulosic plastics; and used to make polyester). Nearly one-half of the global production of acetic acid comes from methanol. Methanol can also be used to produce synthetic fuels and dimethyl ether (DME; an aerosol propellant).
The oxysynthesis process uses syngas to produce C3-C15 aldehydes which are subsequently converted into alcohols, acids, or other derivative chemicals used in solvents, synthetic detergents, flavorings, perfumes and other cosmetic products, healthcare products (such as Vitamin A), and other high value commodity chemicals. Longer chain aldehydes (C11-C14) are typically used to produce surfactants used in the detergent industry. The oxosynthesis process is the fourth largest commercial use of syngas.
Higher alcohols (such as ethanol, butanol, etc.) can also be produced from syngas.
The Fischer-Tropsch synthesis (FTS) process collectively refers to the process of converting CO and H2 mixtures (syngas) to liquid hydrocarbons (chemicals composed of hydrogen and carbon) over a transition metal catalyst (such as alkalized Fe). The FTS has attracted an enormous amount of research and development effort over time and is can be used to produce synthetic gasolines and diesel fuels. The isosynthesis reaction converts syngas to isobutane and isobutene.