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PROCESS & TECHNOLOGY FOR METHANOL AND DME

The new process developed by Air product is in slurry phase. An inert mineral oil and powdered
catalyst slurry is used as a reaction medium and heat sink. As the feed gas bubbles through
the catalyst slurry forming MeOH, the mineral oil transfers the reaction heat to an internal
tubular boiler where the heat is removed by generating steam. The ability to remove heat and
the large oil slurry inventory allows the LPMEOH™ reactor to operate at isothermal conditions.
This process can handle carbon monoxide rich syngas with wide compositional variations. Due
to the ability to process CO-rich syngas, an upstream water-gas-shift (WGS) unit to increase
the syngas H /CO ratio is not needed. Also carbon dioxide removal step could be avoided. It is
2
possible to make full utilization of feed H , if carbon dioxide is available [34].
2
2.2.2

PRODUCTION OF DME
Technically, the process of producing DME from methanol consists of simple dehydration of
methanol to DME as per the reaction shown below:
2 CH OH ← CH CO CH + H O ∆ H – 50.6 kJ/Mol
3 → 3 3 2
This is an exothermic and equilibrium reaction. Therefore, the reaction can be reversed
depending upon the concentration of the different reactants and the equilibrium constant.
DME is produced via fixed-bed catalytic dehydration of methanol obtained from syngas. Until
1975, DME was produced as a by-product (3-5 wt%) during high-pressure methanol synthesis.
The new low pressure methanol synthesis route does not give any DME as a by-product.
Therefore, as an alternative for DME production, dehydration of methanol over solid acids is
the preferred technology.
In conventional DME production by dehydration of methanol, the feed is pumped at about 10 to
12 atm. pressure and mixed with recycled methanol before it is evaporated in the reactor. The
dehydration reaction is conducted in an adiabatic reactor loaded with a dehydration catalyst.
The operating temperature range is of the order of 290- 400 C with about 80% conversion of
0
methanol.
The reactor effluent is cooled and the DME is separated from methanol and water. The recovered
methanol is sent back to the dehydration reactor. The catalyst used is acid catalysts based on
γ alumina or silica alumina. However, it is the convenient route for small-scale manufacture of
DME for chemicals and fuel applications, at least till the market is fully developed. [90].
Compared to the two step synthesis of DME, the single step process is economically and
technically more attractive. In this case both methanol synthesis and dehydration is carried
out in single reactor. At present, the single step process of DME production is carried out with
bi-functional catalyst. This route is preferred for dedicated plants for DME, but the technology
is yet to get matured. Moreover, synthesis of a bi-functional catalyst is a challenging task,
since the presence of two kinds of active sites on the surface may affect its overall catalytic
properties.

Liquid or slurry phase process for DME is also available from Air products. These slurry phase
technologies can handle higher concentration of carbon dioxide in syngas. Technology for
Dehydration of DME is also available from Fuel DME Production Co.Ltd, DME Institute through
Licenser (Mitsubishi Gas Chemical/JGC), Japan. [128]
The selection of the particular route is normally based on the overall economics, desired product
flexibility and type of feedstock with its consistent availability. For large scale plants however it
is preferred to go via methanol production since it offers product flexibility depending upon the
market demand. Once methanol is available it is easily converted either to target chemicals or
to DME, hydrogen or synthetic gasoline.

42 Methanol and DME Production: Survey and Roadmap | 2017