High crude oil prices beginning in the mid-2000s spurred worldwide interest in finding and developing additional sources of
transportation fuels. One such consideration is the conversion of carbon-containing solids (coal, petroleum coke, and biomass) and
natural gas into high-quality, clean-burning transportation fuel.
The most common methods for production of liquids from carbonaceous solids and
natural gas start by first converting the feedstock to a mixture of carbon monoxide and hydrogen called synthesis gas (or syngas).
This is accomplished by partial oxidation and/or reforming reactions in gasification and reforming units. Syngas can then be converted
into hydrocarbons and oxygenates.
The most common technologies for converting syngas into liquids incorporate Fischer-Tropsch
synthesis or Methanol synthesis. The FischerTropsch process was discovered in the 1920s. It has been commercially practiced in several
different forms to produce hydrocarbon liquids from coal and natural gas. These liquids can be converted like crude petroleum into refined
fuels and petrochemical feedstocks.
Syngas can also be converted to methanol, which is the primary method of methanol
production, and has been practiced converting both natural gas and coal into chemical-grade methanol. Methanol is typically produced as a
building block to manufacture other chemicals and within limits has been blended with conventional gasoline.
An alternative commercially proven route for
converting syngas to liquid fuels is through conversion of methanol to conventional gasoline. MTG gasoline meets the requirements for conventional gasoline, is fully
compatible with refinery gasoline and meets the ASTM D4814 Specification for Automotive Spark-Ignition Engine Fuel. Mobil developed
a fixed bed methanol-to-gasoline process (MTG) in the 1970s using a proprietary ZSM-5 zeolite catalyst. Mobil commercialized the
first gas-to-gasoline plant in New Zealand in 1985. The New Zealand plant produced 14,500 kB/D of gasoline and was operated by
the New Zealand Synthetic Fuels Corporation, a joint venture between the government of New Zealand and Mobil, until 1995. Operation
of the first coal-to-gasoline plant via MTG technology began in 2009 in China by Jincheng Anthracite Mining Group (JAMG). This 2,500
B/D gasoline plant began operations in June 2009 and successfully demonstrated the coal-to-gasoline concept.
Both the Fischer-Tropsch and MTG routes can convert synthesis gas to liquid transportation
fuels. However, their respective product slates are very different. The Fischer-Tropsch process
typically produces a broad spectrum of straight-chain paraffinic hydrocarbons that can be further
refined to produce commercial-quality gasoline, jet fuel, and diesel. In contrast, MTG selectively
converts methanol to one liquid product: ultra-low-sulfur, low-benzene regular octane gasoline.
The EMRE MTG Process
Methanol-to-gasoline chemistry was discovered by Mobil scientists in the 1970s. Over years
of extensive studies and pilot plant operations, ExxonMobil developed an understanding of the
MTG reactions and process conditions necessary to consistently produce motor gasoline. A
range of process schemes were considered, including a variety of fixed and fluid catalyst
By 1979, a fixed bed design was completed and had been thoroughly demonstrated at 4 bbl/d
capacity. In this design, methanol is first dehydrated over an amorphous alumina catalyst to an
equilibrium mixture of di-methyl ether (DME), methanol, and water releasing about 1/6th of the
methanol dehydration and hydrocarbon synthesis heat of reaction. The DME reactor effluent
is mixed with inert recycle gas and introduced into the MTG reactors. In the MTG reactors, methanol and DME are completely dehydrated by a ZSM-5 zeolite catalyst forming light olefins
and water. At the MTG reactor conditions, light olefins oligomerize into higher olefins, which
combine through various reaction paths into paraffins, naphthenes, and methylated aromatics.
The shape-selective MTG catalyst limits the hydrocarbon synthesis reactions to about C11.
In the MTG process, the conversion of methanol to hydrocarbons and water is virtually complete
with the product being a mixture of synthesis hydrocarbons and water with a limited amount of
- gases. The dehydration and synthesis reactions release about 1.74 MJ of heat per kg
This heat release would result in a temperature rise of about 600ºC in an adiabatic reactor
system. In the MTG design, the temperature rise from methanol feed to MTG reactant is
limited to about 100ºC by controlling the volume of recycle gas. The conversion reactor inlet
temperature is controlled by adjusting the temperature of the recycle gas by heat exchange
with the reactor effluent. Reactor effluent is also used to preheat, vaporize, and superheat the
methanol feed to the DME reactor.
Reactor effluent is then further cooled to 25–35°C and passed to a product separator, where
light gases are disengaged and liquid hydrocarbon and water are separated. The gas phase
(mostly light hydrocarbons) is returned to the recycle gas compressor. The water phase can be
sent to effluent treatment or recycled within the overall complex. The liquid hydrocarbon product
(raw gasoline) contains mainly gasoline boiling range material as well as dissolved hydrogen,
carbon dioxide, and light hydrocarbons.
After separation of raw gasoline from light gases and water, the raw gasoline is processed
through a de-ethanizer to remove remaining C2
- gases, followed by a stabilizer column that
’s and C4
’s as LPG fractions to control the vapor pressure of the gasoline.
At this point, the MTG gasoline is consistent with conventional gasoline with the exception of
a concentration of 1,2,4,5-tetramethylbenzene, or durene, that is higher than typical gasoline.
Durene is a compound that crystallizes at moderate temperatures and affects gasoline
performance and appearance. A maximum durene content of 2% has been set to ensure
drivability and performance consistent with petroleum-based fuel. To achieve this level of durene
content, MTG gasoline is split into a light fraction and heavy fraction, which concentrates the
durene with the other higher aromatics. This heavy fraction is processed in a mild hydrotreater
that reduces the durene content primarily through isomerization and de-methylation reactions
with minimal effect on gasoline yield and octane.
New Zealand synfuels commercial MTG plant
In the late 1970s the government of New
Zealand was evaluating ways to utilize
available natural gas resources to address
its growing demand for liquid transportation
fuels in an environment of limited oil supplies.
After examining its alternatives, New Zealand
determined that the gas-to-methanol-to-gasoline route utilizing ExxonMobil’s MTG
technology was the most attractive alternative
and began developing a full-scale commercial
project. The New Zealand Synfuels company was established as a joint venture between
the government of New Zealand and Mobil Oil
Corporation (one of the predecessors of the
Exxon Mobil Corporation). This new company
was charged with constructing and operating
the first commercial gas-to-liquid fuel plant
in the world utilizing established gas-to-methanol
technology and the Mobil fixed bed
MTG technology. On October 12, 1985, New
Zealand Synfuel started up the 14,500 B/D
gas-to-gasoline plant near New Plymouth,
New Zealand. By all accounts, the start-up
of the operation was a complete success
for a world- scale, first-of-its-kind plant and achieved design rate within two days. The first
gasoline was produced on October 17, 1985.
The second methanol unit was commissioned
on December 12th of that year. Subsequently,
additional MTG reactors were streamed
and the complex was operated at 100% of
design capacity by December 27, 1985. The
MTG plant was an excellent example of the
ability to successfully scale up a plant from
a small pilot plant (4 bbl/d). Production
yields (Table 1), product qualities, and
catalyst performance were consistent with
all estimates developed from the pilot plant
data. A comparison of the average gasoline
properties and the range during the first year
of MTG operation is provided (Table 2). It is
clear that the operation is very predictable and stable with little variation in the product. It
is also interesting to compare the MTG gasoline
properties with today’s refinery gasoline.
Table 3 compares the MTG gasoline properties
with the average properties of conventional
gasoline sold in the U.S. markets in 2005. The
two are virtually identical with the only noticeable
difference being MTG gasoline’s lower benzene
content and essentially zero sulphur.
Second-generation MTG technology
The current MTG technology is based on the
original MTG process developed for the New
Zealand plant, with improvements made by
Mobil in the late 1990s leading to a second-generation
technology. The second-generation
technology incorporates improvements derived
from the operation of the New Zealand plant.
These reduce the heat-input requirements and
reduce compressor duty and heat exchange
surface area. These modifications reduce capital
by an estimated 10% to 15% versus the original design.
In addition to the design modifications,
ExxonMobil Research and Engineering Company
(EMRE) has continued to develop zeolite catalyst
technology for the MTG process, and MTG
catalyst research continues at EMRE’s Clinton
Technical Center in New Jersey, with a dedicated
MTG pilot plant facility.
The first second-generation MTG plant began
operating in June 2009 in Shanxi Province,
China, by the Jincheng Anthracite Mining
Group (JAMG). The 2,500 B/D MTG unit is
part of a demonstration complex that includes
coal gasification, gas cleanup, and a methanol
synthesis. After two years of operation, JAMG
and EMRE agreed to a License and Engineering
agreement for two additional MTG units at
12,500 B/D each and initiated engineering in
October 2011. In addition to the coal-to-liquids
plants in China, EMRE has entered into license
agreements for MTG technology for coal,
biomass, and natural gas projects.
Advantages of the EMRE methanol-to-gasoline option
Project development for various carbon-conversion
concepts is a highly complex
process that requires companies to consider
many diverse factors when making the technology decision. EMRE MTG, as a
commercially proven technology, offers an
option that improves the attractiveness for
Both the MTG and Fischer-Tropsch
processes convert coal into synthesis gas as
an intermediary before producing the final
products. However, their respective product
slates are very different. The Fischer-Tropsch
process produces a range of hydrocarbon,
which requires refining and conversion to
produce finished transportation fuels and/or
chemicals. A minimum of two liquid products
are produced. Due to the complexity of the
product distribution, the economic justification
for upgrading/processing multiple fuels or
chemical feedstocks or petroleum specialties
improves for large-scale projects located near
Table 4 is a comparison of MTG product yields versus reported product distribution from both the low-temperature
and high-temperature Fischer-Tropsch process reported by Sasol. In both cases, the liquid
products require hydrocracking/hydrotreating and other reforming processes before the liquid products can be used as transportation fuels.
MTG, in contrast, selectively converts methanol to a single fungible liquid fuel and a small LPG stream. The liquid
product is conventional gasoline with virtually no sulphur and low benzene, which can be sold as is or blended
with ethanol or methanol or with petroleum refinery stocks. This minimizes offsites and logistics complexity
and investment for synthetic fuel distribution. Table 5 provides the typical properties and key composition
characteristics of typical EMRE MTG gasoline.
Low technical and project risk
All of the processes required to produce methanol from coal, coke, or natural gas are well
proven and have been installed worldwide and continually improved by some of the world’s
leading process technology providers, and engineered and constructed by many competent and
competitive EPC contractors. Combining the thoroughly demonstrated EMRE MTG technology
with a proven methanol-production scheme provides a route to synthetic fuel from a variety of
feed sources with minimal technical and project execution risk.
Process simplicity and scalability
The MTG process uses a conventional gas phase fixed bed reactor that is simple to operate and
can be readily scaled to the desired size from 2,500 B/D to more than 20,000 B/D. In the first
commercial application in New Zealand, the process was successfully scaled up from 4 BBL/D to
Interests in alternative clean transportation fuel technology will continue as an alternative to
petroleum refining. EMRE’s commercially proven Methanol-to-gasoline (MTG) technology coupled
with established commercial methanol synthesis technologies provides a competitive, low-risk
option for the production of synthetic transportation fuels from coal, biomass, or natural gas.