Downstream, catalyst companies ally with gas-to-liquids process developer

Anne K. Rhodes
Refining/Petrochemical Editor

Texaco Natural Gas, Houston, and Syntroleum Corp., Tulsa, have struck two agreements regarding Syntroleum's modified Fischer-Tropsch (F-T) process for producing fuels from natural gas.

The first, a nonexclusive "master" license agreement, grants Texaco broad rights to use the process, according to Syntroleum. The companies also have agreed to work jointly to accelerate development of cost-savings improvements to Syntroleum's synthetic fuels process.

Texaco is a leading licenser of gasification technology, which produces synthesis gas from bottom-of-the-barrel waste products. The logical link between syngas produced by gasification and synthetic fuels production from syngas is presumed to be the reason for Texaco's deal with Syntroleum.

Criterion Catalyst Co. LP, Houston, also has formed an alliance with Syntroleum. Criterion will manufacture and supply the proprietary catalyst used in Syntroleum's F-T process.

Product yields and qualities have been confirmed in large-scale pilot plant studies using the Criterion catalyst, according to a Criterion press release. Syntroleum's 2 b/d pilot plant has been operating since 1990.

Gas-to-liquids processes

Fischer-Tropsch chemistry has been around since 1923. Salomon Bros., New York, outlined related technological developments in a recent report titled, "Gas-to-Liquids Technology-Dawning of a New Era for Global Natural Gas."

Historically, justification of most F-T-based plants has been politically driven. These plants tended to be built in situations where economical production is of secondary concern. Such was the case in Germany during World War II, and in South Africa during apartheid sanctions.

South Africa's Sasol Corp. developed a process that converts coal to gas to liquids in the 1950s. Sasol refined its process further in the 1980s.

More recent developments include:

Mobil Oil Corp.'s process for converting natural gas to methanol then gasoline, the prototype unit for which has been purchased by Fletcher Challenge Ltd., Auckland, New Zealand.
Exxon Corp.'s Advanced Gas Conversion process, which is operating in a 200 b/d prototype unit in Baton Rouge, La.
Shell Oil Co.'s Synthetic Middle Distillate System (SMDS), which is operating in Bintulu, Malaysia, but, according to Salomon Bros., has yet to be deemed commercial.

The Salomon report stated that, "Smaller niche firms, such as Syntroleum, have made impressive strides in the GTL process."

The implications

The economics of processes like Syntroleum's and Exxon's suggest, according to Salomon, "the dawning of a new era for global natural gas."

"While LNG is developed at $30,000-40,000/b/d, the GTL technology is competitive and may even command an advantage over LNG," says the Salomon report. Salomon estimates that GTL technology can be economic at oil prices at or below $20/bbl.

"The implications are mind-boggling," said Salomon. "The world has an abundance of remote gas currently not planned for development.

"The world contains about 1 trillion bbl of oil and almost an equal amount of natural gas (0.8 trillion bbl of oil equivalent)," said Salomon. "A significant portion is not commercialized or deemed accessible."

Salomon believes GTL technology can allow development of much of the world's remote, inaccessible gas reserves. In addition, says Salomon, competitive GTL technologies have capital costs as low as $13,000/b/d, which is about equivalent to the cost of a grassroots refinery.

According to the Salomon report, Exxon has decided to commercialize Qatar's giant North field using its GTL technology.

"The design concept is revolutionary," said Salomon. "Natural gas from this giant gas field will be converted directly into middle distillates such as heating oil and diesel. This is akin to a natural gas refinery."

Process economics

Mark Agee, Syntroleum president and chief operating officer, concurs with Salomon's estimate of GTL economics, at least when it comes to his company's process.

Agee, a chemical engineer, says Syntroleum has removed the economic barrier to F-T processing. He claims his company's process can convert natural gas to liquid fuels at much lower cost than conventional F-T processes.

"Potential capital costs for 5,000-10,000 b/d plants are low enough to make conversion of gas from small, remote fields economically feasible at current oil prices," says Agee.

According to Syntroleum, the simplified design of the new process allows plants to be operated profitably at oil prices less than $20/bbl, and at smaller sizes that fit more gas fields. Fig. 1 [100997 bytes] shows a typical range of capital costs for Syntroleum plants, and the components that contribute to the cost of finished goods.

The process

Syntroleum Corp. was founded in 1984 by chemical engineer Ken Agee. It was Ken Agee's ideas for an improved process for producing synthetic fuels led to development of the Syntroleum process. Ken Agee, chairman and chief executive officer for the company, continues to spearhead process development.

Conventional F-T processes use steam reforming or a combination of steam reforming and partial oxidation with pure oxygen. By contrast, Syntroleum's process uses autothermal reforming with air to produce synthesis gas with a high nitrogen content.

Syngas from the autothermal reformer has a near-ideal H2-to-CO ratio, according to Syntroleum literature. The ratio can be adjusted further by introducing a small amount of steam or CO2 into the reformer.

The reforming reactor is made of carbon steel and lined with refractory. This approach eliminates the need for air separation and, thus, reduces capital costs.

Fig. 2 [102871 bytes] shows a flow diagram of the process. The unique design of the Syntroleum process allows efficient conversion of gas containing as much as 30% inert materials, such as N2 and CO2.

Conventional F-T processes employ a recycle loop. The Syntroleum F-T process does not.

This one-pass design avoids nitrogen buildup in the system, according to Syntroleum, thus allowing the use of nitrogen-diluted syngas with no performance degradation. Elimination of the recycle compressor loop also reduces capital costs.

The nitrogen in the syngas feed has the added benefit of removing some of the heat generated by the F-T reaction.

A key feature of the new process is its energy efficiency. The system's major energy consumer is air compression (Fig. 2).

Because both the reforming and F-T reactions are highly exothermic, the process heat, combined with the energy produced by combusting the tail gas stream, generates enough power to meet the plant's needs. Surplus power can be exported as either high-pressure steam or electricity.

Syntroleum says a 10,000 b/d synthetic fuels plant can generate more than 50 mw electricity. In addition, the process produces water as a by-product. A 5,000 b/d plant, for example, synthesizes almost 7,500 b/d of water that is easily treated to potable quality.

In addition to its fixed tubular and fluidized-bed F-T reactors, Syntroleum is developing a high-capacity, fixed-bed horizontal reactor. The new reactor will be particularly useful for barge, ship, and platform-mounted installations.

Syntroleum also is developing several chain-limiting catalysts that will restrain the growth of hydrocarbon chains and thereby produce synthetic hydrocarbons primarily in the transportation fuel range. These catalysts also will minimize production of C1-C4 hydrocarbons.

The chain-limiting catalysts will allow for:

Reduction of operating pressures throughout the process
Use of high-capacity, fluidized-bed reactors
Elimination of hydro cracking to produce fuels.

Synthetic lubes

Syntroleum has obtained from Lyondell Petrochemical Co. exclusive rights to license and sublicense a new synthetic wax isomerization process.

The technology was developed by Lyondell, Criterion, Zeolyst, and Syntroleum. It produces synthetic lube base stocks from waxy synthetic crude produced by Syntroleum's F-T process, when a special catalyst system is used.

"This development is a key component in our plans to enter the synthetic lubricants business," said Mark Agee. Syntroleum plans to build a series of natural gas refineries to manufacture synthetic lubricants, solvents, and chemical feedstocks.