Gas to methanol

Natural gas is the feedstock used in most of the world’s production of methanol. Methanol is a primary liquid petrochemical made from renewable and nonrenewable fossil fuels containing carbon and hydrogen. Containing one carbon atom, methanol is the simplest alcohol. It is a colorless, tasteless liquid and is commonly known as “wood alcohol.”

Stranded gas can be monetized by producing chemical (or fuel grade) methanol and transporting it to the market. Since the 1980s, there has been a significant change in the way the methanol market has worked. Remote producers of methanol have begun to gain market share over long-established production sites close to the customers. Gas economics has been the driving force behind these changes. As gas demand has risen, the methanol producers in North America and Europe have been squeezed out. Because methanol can be transported easily, methanol production has moved to remote locations where gas is cheaper.

Use of methanol

Methanol is a chemical building block used to produce formaldehyde, acetic acid, and a variety of other chemical intermediates. Fig. 1 shows the range of products derived from methanol. A significant amount of methanol is used to make methyl tertiary butyl ether, an additive used in cleaner-burning gasoline. Methanol is one of a number of fuels that could substitute for gasoline or diesel fuel in passenger cars, light trucks, and heavy-duty trucks and buses. Because of its outstanding performance and fire safety characteristics, methanol is the only fuel used in Indianapolis-type race cars. Methanol is also widely considered a leading candidate as the fuel of choice for vehicular fuel-cell applications.

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  Fig. 1—Indirect GTL routes to gas monetization.

History

Methanol was first produced by destructive distillation of wood. As demand grew, synthetic processes were developed to produce methanol economically. Baden Aniline and Soda Factory/Badische Anilin- und Soda-Fabrik (BASF), which did most of the pioneering work on syngas chemistry, was awarded the first patent on the production of methanol in 1913. The first commercial-scale synthetic methanol plant was started in 1923 at BASF’s Leuna works. The methanol manufacture process was based on a zinc/chromia catalyst that converted carbon oxides and hydrogen into methanol at pressures of 300 bar and temperatures exceeding 300°C. The high pressure not only imposed limitations on maximum size of equipment but also resulted in high energy consumption per tonne of product. The early 1970s saw the commercialization of the low-pressure methanol synthesis developed by Imperial Chemical Industries (ICI), which was based on a copper catalyst operating at lower pressures (< 100 bar) and temperatures (200 to 300°C). The process was called ICI’s low-pressure methanol process.

Methanol process

Methanol production typically requires three steps:

• Syngas preparation
• Methanol synthesis
• Methanol purification/distillation

Syngas preparation

Syngas preparation is very similar to the Fisher-Tropsch (FT) gas to liquids (GTL) process, but a major difference is the scale at which syngas is produced. Syngas for methanol synthesis can be prepared either with partial oxidation (POX) or steam reforming of the natural gas feedstock. For a natural gas feedstock with little heavy-hydrocarbon and sulfur impurity in it, a steam-reforming-based plant is considered most cost effective, with better reliability and higher energy efficiency. POX-based units are generally more suited for syngas generation from heavy-hydrocarbon feedstocks (e.g., fuel oil). A POX-based unit for natural gas feed requires a larger air separation plant and typically produces substoichiometric syngas, which requires additional processing for methanol synthesis.

Natural gas can be steam reformed with any of the following schemes:

• Tubular reforming with a fired reformer furnace
• Combined reforming with a fired reformer furnace followed by an oxygen-blown autothermal reforming (ATR)
• Heat-exchange reforming without a tubular reformer furnace, but with ATR

Methanol synthesis

All the commercial methanol plants currently use gas-phase synthesis technology. The synthesis loop pressure, reactor type used, and method of waste-heat recovery broadly differentiate gas-phase methanol-synthesis schemes. All the modern large-capacity methanol processes use low-pressure synthesis loops with copper-based catalysts. Quench-type, multibed intercooled, or isothermal reactors are used to minimize reactor size and maximize recovery of process waste heat.

Methanol purification/distillation

Crude methanol, received from a gas-phase synthesis reactor that uses syngas with a stoichiometric number [stiochiometric number is molar ratio of (H₂ – CO₂)/(CO + CO₂)] of 2 or higher, will have excessive water (25 to 35%). Besides removing the lighter components in a topping column, this water and other heavies are removed in a refining column. Reboiler heat duty is typically obtained by cooling the syngas in the front end of the plant. A two- or three-column distillation scheme is typically used.

Methanol distillation schemes used by different licensors are similar. The two-column distillation scheme offers low capital expenditures, and the three-column distillation scheme offers low-energy-consumption features. The scheme that integrates better with the syngas preparation and synthesis section is normally selected. Several technology providers license the process technology for methanol:

• Synetix
• Lurgi
• Haldor Topsoe
• Mitsubishi Chemicals
• KBR

Screening criteria

Until a few years ago, the size of a large-scale single-train methanol plant was considered to be 2000 to 2500 metric tons per day. However, economies of scale and market conditions are driving the trend toward building larger-sized plants with capacities in excess of 3,000 thousand tons per day. Two plants with capacities of 5000 metric tons per day are currently under construction, and several large methanol plants are under discussion. The typical gas consumption for a world-scale methanol plant ranges from 28 to 31 million Btu per metric ton of product based on LHV of the feed; therefore, a 5000 metric tons per day methanol plant will use approximately 157 MMscf/D of gas. For a project lifetime of 20 years, a gas-field size of at least 1.15 Tcf is required to support a plant of this size.

The economics of methanol are very dependent on the cost of production and the selling price of methanol. The market for methanol is volatile and competitive with large swings in the price. The main components of the production cost of methanol are gas price and the investment cost of the plant. A number of literature sources present the investment costs for steam-reforming-based methanol plants. The investment costs for large-scale methanol plants based on advanced syngas generation technologies are expected to be lower. A producer in a remote location must also consider shipping costs for transporting the methanol product to the market.

Methanol demand

Methyl tertiary butyl ether (MTBE) phaseout in the United States will have an effect on the worldwide methanol demand; however, the phaseout is expected to be slow and prolonged. The methanol market is currently saturated with adequate available capacity. New large-capacity plants are expected to be on stream by 2004–2005.

The methanol market is saturated; however, it is expected that new plants will be built. In the future, new low-cost production will displace existing high-cost producers unless new applications for methanol are established. Besides the traditional markets, methanol has the potential to be used in a variety of applications: power generation by fuel cells, as a transportation fuel directly or by fuel cells, and as a feedstock for the production of olefins. These new applications, if established, could lead to a surge in demand for methanol plants.

Noteworthy papers in OnePetro

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External links

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See also

Gas utilization options

Gas to liquids (GTL)

Gas to power

Gas pipelines

Gas as fertilizer feedstock

Monetizing stranded gas

Stranded gas

Transporting stranded gas as hydrates

PEH:Monetizing_Stranded_Gas