METHANOL PLANT DME CONVERSION
DME is an acronym for Di-Methyl Ether Chemical formula: (CH3OCH3)
Chemistry 101
Other Names: Wood ether
Prozone
Dimethyloxide
Methyl ether
Chemistry 101
* Chlorinated Fluorocarbons
DME is a colorless, gaseous,
simple ether that was originally
developed as a replacement
for CFC’s* in an effort to
decrease greenhouse gasses.
DME is Non-toxic and
Biodegradable.
Chemistry 101
•DME can be
made from
Methanol, Coal,
LPG, Natural
Gas, or Biomass.
Chemistry 101
Aerosol Spray Propellants
Excellent CFC Free Solvent
and Raw Material for
Chemical Products
FUTURE USES OF DME
DME is a
Next-Generation
Clean Fuel that
can be used as a
substitute for
Gasoline and Diesel Fuels
DME is adaptable
for use in
Thermal Electrical
Power Generation
Plants,
Cogeneration
Plants and
Stationary Fuel Cell Technology.
DME and The Environment
DME and The Environment
Extremely Low toxicity
Zero Soot Emissions
Zero SO2 Emissions
DME is Non Ozone Depleting and is
not a Greenhouse Gas
Lower NOx
than Diesel
DMEProduction
DME ProductionDME production begins by using natural gas, coal or other raw materials to produce a synthesis gas made up of carbon monoxide and hydrogen. DME is produced from this synthesis gas in one of two ways: “methanol dehydration" (indirect synthesis) or "direct synthesis."
• Methanol dehydration is a process of producing DME from a dehydration reaction, with methanol produced from the synthesis gas.
• Direct synthesis produces DME directly from synthesis gas. The two main varieties are the "fixed bed reactor process" (Haldor Topsoe A/S of Denmark) and the "slurry bed reactor process" (JFE, Air Products and Chemicals, Inc. of the U.S.).
DME Production• Conventional DME production involves a methanol
dehydration reaction but over the last several years there
have been attempts to develop the technology to
synthesize DME directly from synthesis gas (hydrogen,
carbon monoxide) in order to produce it at low cost and in
sufficient quantities to be used as fuel.
• DME synthesis is very similar to methanol synthesis, but
simpler than methanol synthesis considering lower
reaction heat and lower synthesis pressure.
• Direct synthesis of DME requires a temperature of 210-
290°C and pressure of 3-10 MPa; a mixed function
catalyst can be used to achieve methanol synthesis and
dehydration.
DME Production
INDIRECT SYNTHESIS
•Methanol dehydration: a process of
producing DME from a dehydration
reaction of methanol produced from
synthesis gas.
•Methanol dehydration heats and
evaporates liquid methanol so that it is
converted to DME in a dehydration
reactor. The energy consumed in DME
refining is high at about 20% of the
calorific value of the DME product.
DIRECT SYNTHESIS
•Direct synthesis produces DME directly
from synthesis gas. The two main
varieties are the "fixed bed reactor
process" and the "slurry bed reactor
process“.
•DME synthesis generates large
quantities of reaction heat (exothermic),
and how to remove this heat is one of
the major engineering hurdles faced.
Because the methanol synthesis
equilibrium limitation can be avoided in
the direct DME synthesis reaction a
higher conversion rate can be achieved
Conversion of
Methanol Plant to
DME Production
Methanol Plant Conversion to DME
Conversion of the Methanol Plant for DME production would be accomplished most effectively based on the methanol dehydration or “indirect synthesis” process, utilizing the existing desulfurization, reforming, synthesis and distillation processing train.
• High reaction conversion ratio; DME appx. 99%, overall appx. 95%
• The process for methanol and indirect DME production consists of established, mature commercial technology resulting in proven reliability.
• The production duality of fischer-Tropsch type reactors may be utilized in reducing the capitol expense of additional equipment.
• Current commercial availability of catalyst.
Approach Advantages...
Indirect DME Synthesis from Methanol
Sulfur Removal
ReformingMethanol Synthesis
DME Synthesis
DME Distillation
FeedstockDME
Product
DME Production
Existing Plant
Additional Equipment
Legend:
Methanol to DME Indirect Synthesis
Process Flow Diagram
Feed methanol is fed to a DME reactor after vaporization. The synthesis pressure is 1.0 - 2.0 MPaG. The inlet temperature is 220 - 250 °C and the outlet is 300 - 350 °C. Methanol one pass conversion to DME is 70 – 85 % in the reactor. Produced DME with by-product water and unconverted methanol is fed to a DME column after heat recovery and cooling. In the DME column 99.9 DME is separated from the top as a product. Water and methanol are discharged from the bottom and fed to a methanol column for methanol recovery and reprocessing.
Conclusions
Dimethyl ether (DME) is considered a clean energy source and
since it generates no sulfur oxide, less NOx and zero soot during
combustion, its environmental impact is very low.
Owing to its non-toxicity and easy liquefaction properties, DME is
easy to handle and therefore can be used as a domestic-sector fuel
(substitute for LPG), transportation fuel (diesel vehicles, fuel cell
vehicles), power plant fuel (thermal plants, cogeneration plants,
stationary fuel cells), and as a raw material for chemical products.
Currently DME is produced by dehydrating methanol and direct
synthesis plants are now beginning production. Approximately ten
thousand tons per year are produced in Japan, and 150 thousand
tons per year worldwide. Currently, it is primarily used as a spray
propellant. However, given the above-described superior properties,
once DME becomes widely available in large volumes at a
reasonable price, DME could be used as a fuel in a wide variety of
fields.
Conclusions, continued
Methanol production has slowed in North America where the natural
gas required for methanol production is very expensive.
Because of the lower demand for methanol, most, if not all, marginal
methanol production has moved to areas where large supplies of
natural gas are available at a relatively low cost, such as the Persian
Gulf, Trinidad, India or South America.
New plants will likely be built in those areas where natural gas is
abundant and relatively inexpensive as compared to the price in
North America. Accordingly, Methanol Plants are being relocated
and/or converted to DME or GTL production.
Conclusions, continued
The Cheyenne Methanol Plant produces high grade methanol utilizing the
following process steps:
Feedstock Desulfurization and Saturation
Synthesis Gas Production and Heat Recovery
Synthesis Gas Compression
Crude Methanol Synthesis Loop (Fisher -Tropsche)
Distillation
The methanol conversion process used in this plant is comprised of essentially the
same distinct steps as those found in the DME and GTL processes, i.e. (a) syngas
synthesis and compression, (b) product (methanol) synthesis, and (c) product
upgrading. The plant also utilizes a Multi-Tubular Reactor (i.e. a vessel having a
plurality of catalyst-filled tubes affixed therein), and accordingly, is ideal for utilization
as a subsystem for methanol production utilized in the indirect synthesis of DME.
Additionally, since the plant is equipped with a Multi-Tubular FT reactor, other DME
and GTL direct synthesis processes are possible with minor catalyst and subsystem
revisions.
References
Journal of Chemical and Engineering Data, Kenneth N. Marsh, Editor,1992
Large Scale DME Production, Ishinada, Akiera, Mitsubishi Gas Chemical,1997
Modifications of a Methanol Plant for Converting Natural Gas to Liquid Hydrocarbons (U.S. Patent), Peter, Tim; Loring, David; Noda, Leigh,1996
Japan DME Forum, Ohno, Yatoro, 2005
Koenig, Mark D., Environmental Scientist
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