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PROCESS & TECHNOLOGY FOR METHANOL AND DME

2.1 MANUFACTURE OF SYNGAS

There are two distinctly different types of feedstock for syngas: from hydrogen deficient
feedstocks such as coal, coke or residual hydrocarbons, biomass and hydrogen rich fuels such
as methane (natural gas) or naphtha. The easiest way to produce syngas is from hydrogen rich
fuels via steam reforming.

2.1.1
CHEMICAL REACTIONS INVOLVING SYNGAS FORMATION

2.1.1.1

STEAM REFORMING OF NATURAL GAS OR NAPHTHA
Natural gas is one of the most important sources of syngas production, due to its low cost and
lower GHG emission compared to coal, and the ease of conversion either to hydrogen or to
syngas. Natural gas and lower hydrocarbons such as ethane, naphtha or biogas are easily
converted to syngas following the pathway as shown below:

CH + H O ↔ CO +3 H ΔH = +206kJ/mol
4 2 2
This reaction is known as steam reforming. However, this reaction is highly endothermic;
therefore external energy is required to be supplied to the process.
With steam reforming of natural gas or lower hydrocarbons, the hydrogen to carbon monoxide
ratio is of the order of 3 to 4. This ratio is not favourable for production of methanol since
for methanol production; stoichiometric ratio of hydrogen to carbon monoxide is about 2.
However, steam reforming is suitable when hydrogen production is the objective. For hydrogen
production, the carbon monoxide in the steam reformate is used to generate hydrogen by shift
reaction:
CO + H O ↔ CO + H ΔH = -41kJ/mol
2 2 2
This carbon dioxide is separated by pressure swing absorption to recover pure hydrogen.
Steam reforming is carried out using Nickel catalyst at about 700°C to 1000°C. For higher
hydrocarbons, a pre-reformer is installed in the upstream methane reformer to convert the
higher liquid hydrocarbons to lighter hydrocarbons in presence of hydrogen before entering
into the methane reformer. The main advantage here is the flexibility to process higher
hydrocarbons for production of hydrogen. The reaction temperature of the pre-reformer is
about 400 to 500°C. The catalyst used in pre-reforming is also based on Nickel, but to prevent
coke formation, some noble metal such as Rhodium is deposited on the supported Nickel
catalyst.
While steam reforming is a simple process to produce hydrogen, it is energy intensive.
Moreover, the higher ratio of hydrogen to carbon monoxide makes this process unviable for
direct use in methanol production. However, the presence of excess hydrogen may be very
conveniently used to reform some carbon dioxide produced during the reaction to convert this
into carbon monoxide. Thereby the desired ratio of 2:1 for hydrogen and carbon monoxide
could be achieved for production of methanol.

2.1.1.2
PARTIAL OXIDATION OF NATURAL GAS, OTHER HYDROCARBONS (POX)

Another major route for production of syngas from lower hydrocarbons or natural gas/biogas

Methanol and DME Production: Survey and Roadmap | 2017 27