Applications for Syngas

As mentioned, syngas is an important source of valuable chemicals. These include

• Hydrogen, produced in refineries

• Diesel gasoline, using Fischer-Tropsch synthesis

• Fertilizer, through ammonia

• Methanol, for the chemical industry

• Electricity, generated through combustion

It should be noted that a major fraction of the ammonia used for fertilizer production comes from syngas and nitrogen (see Section 9.4.3).

9.2.1 Production of Syngas

Gasification is the preferred route for the production of syngas from coal or biomass. The low price of natural gas is currently encouraging syngas produc­tion from it, but the situation may change when the price rises. A steam refor­mation reaction is used to produce syngas from natural gas that is mainly CH4. This reaction is also the most widely used commercial method for bulk produc­tion of hydrogen, which is one of the two components of syngas.

9.2 Syngas

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Подпись: CH4 + H2O Подпись: Catalyst Подпись: *CO + 3H2 + 206 kJ/mol Подпись: (9.1)

In the steam reforming method, natural gas (CH4) reacts with steam at high temperatures (700-1100 °C) in the presence of a metal-based catalyst (nickel).

If hydrogen production is the main goal, the carbon monoxide produced is further subjected to a shift reaction (see Eq. 9.2), as described in the next section, to produce additional hydrogen and carbon dioxide.

The ratio of hydrogen and carbon monoxide in the gasification product gas is a critical parameter in the synthesis of the reactant gases into desired products such as gasoline, methanol, and methane. The product desired determines that ratio. For example, gasoline may need the H2/CO ratio to be 0.5 to 1.0, while methanol may need it to be ~2.0 (Probstein and Hicks, 2006, p. 124). In a com­mercial gasifier the H2/CO ratio of the product gas is typically less than 1.0, so the shift reaction is necessary to increase this ratio by increasing the hydrogen content at the expense of CO. The shift reaction often takes place in a separate reactor, as the temperature and other conditions in the main gasifier may not be conducive to it.

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