Presently there are only six full-scale Fischer-Tropsch (F-T) Gas-to-Liquids (GTL) plants operating in the world and all of these are based on the process discovered by two German chemists, Dr. Franz Fischer and Dr. Hans Tropsch almost a hundred years ago. These two chemists showed that passing a mixture of hydrogen and carbon monoxide, known as synthesis gas, over a catalyst could produce long chain hydrocarbons. Their technology was used by the Germans during World War II to produce gasoline and diesel fuels. The South African company, Sasol, started using F-T technology in the early 1950s to produce gasoline and chemicals, derived from South Africa’s abundant coal resources via gasification to synthesis gas. However there are alternatives to producing liquid hydrocarbons from natural gas, some already commercialized and some in the early development stage. This blog describes several of these alternatives.
Methanol-to-Gasoline (MTG) Technology
For the production of liquid fuels, a major alternative to Fischer-Tropsch technology is Methanol-to-Gasoline technology.
Both technologies require synthesis gas (hydrogen and carbon monoxide) which can be generated from any carbonaceous feedstock; coal, natural gas, or biomass. With F-T technology the primary product of interest is diesel fuel. Secondary products are hydrocarbons in the naphtha boiling range (C5 – C12.) Because of its highly paraffinic nature, F-T derived naphtha is more useful as feedstock for olefins production than for gasoline. The primary product of MTG technology, on the other hand, is gasoline.
ExxonMobil MTG (www.exxonmobil.com)
MTG technology was first commercialized by Mobil in the early 1980s in a plant in New Zealand. Prior to its merger with Exxon, Mobil had developed a zeolite catalyst (ZSM-5) which could effectively convert methanol to a mixture of hydrocarbons comparable to crude oil-derived gasoline with the following composition:
A 14,500 bpd plant was constructed at Montunui, New Zealand. The plant included two methanol trains each of 2,200 metric tons/day capacity. The plant was successfully operated for several years (from 1985 to 1997) until it was eventually sold to Methanex Corp. who shut down the MTG portion of the complex, but continued to operate the methanol plants by adding distillation columns to purify the crude methanol which was used for the MTG process.
A second MTG plant with a capacity of 2,500 BPD of gasoline was licensed by ExxonMobil to Jincheng Anthracite Mining Group (JAMG) in 2009. This is not actually a GTL project as the synthesis gas is derived via coal gasification. A much larger MTG plant of 25,000 bpd was subsequently licensed to JAMG. Regarding other ExxonMobil GTL MTG projects, G2X Energy is planning a 12,500 BPD plant in Lake Charles, Louisiana. Two other ExxonMobil licensed MTG projects include a 16,000 bpd Gulf Coast project being developed by ZeoGas LLC and a 3,500 bpd project by Sundrop Fuels in Louisiana. None of these have yet reached commercial production.
Primus Green Energy (www.primusge.com)
Primus Green Energy Inc. based in Hillsborough, New Jersey has also developed a methanol to gasoline process designated as Primus STG+TM. While they have yet to commercialize their technology, Primus claims it has the highest documented conversion efficiency (70%) in the industry. The following figure shows a schematic diagram of their STG+ ™ Gas-to-Gasoline system:
Interestingly, Primus has announced a 160 metric ton/day methanol plant based on Marcellus shale gas. No specific location has been announced but there is an agreement with Tauber Oil Company to offtake all of the methanol. A second 160 metric ton/day methanol plant was announced for a site in Alberta, Canada based on natural gas from the Montney and Duvernay fields. Primus has also announced plans to add three additional North American methanol plants with capacities ranging from 160 to 640 metric tons/day. When and if any of these methanol projects add gasoline production is yet to be determined.
Siluria Technologies (www.siluria.com)
In my Aug. 11, 2016 blog, I described Siluria’s Oxidative Coupling of Methane (OCM) process to produce ethylene and their demonstration plant at Braskem America’s Laporte Texas, plant site. Siluria has also developed ethylene to liquids (ETL) technology for converting the ethylene from its OCM process to distillate fuels such as gasoline and diesel. This involves oligomerization of ethylene to higher molecular weight hydrocarbons that can be specifically targeted for the desired liquid fuel product. In contrast to F-T and MTG processes, this technology does not require the natural gas to first be converted into synthesis gas.
GTC Technology US LLC (www.gtctech.com)
An alternate methane coupling process, designated GT-G2A is offered by GTC Technology. Instead of oxygen to activate the methane feedstock, their process uses bromine. The technology involves four steps: first is reaction of methane and bromine (Br2) to form methyl bromide; second is a synthesis conversion to hydrocarbon fuels and hydrogen bromide (HBr); the last two steps involve HBr conversion to Br2 for recycle and finally product separation into aromatics and diesel fuel. Laboratory work began in 2003 with a demonstration unit operated in 2008 and 2009. In my own personal experience, this will be a most challenging technology to successfully commercialize. Hydrogen bromide is a very corrosive chemical and I’m aware of at least two prior chemical processes based on bromine technology that had major corrosion problems and were eventually abandoned.
In contrast to the above technologies, Intrexon’s approach to conversion of methane to liquid fuels is unique. They have developed a bioconversion platform utilizing methanotrophic bacteria, (methanotrophs) to consume the carbon content of natural gas thereby upgrading it to more valuable hydrocarbon products. Their technology has demonstrated production of isobutanol, a C4 alcohol, via the following pathways:
Farnesene, a 15 carbon long-chain branched, unsaturated hydrocarbon, is another product that has been produced utilizing their methanotrophic technology.
Intrexon formed Intrexon Energy Partners to further develop their methane to isobutanol process. A pilot plant, located in South San Francisco, became operational last year. They hope to generate sufficient data to eventually commercialize the technology. As reported in my Dec. 13, 2016 blog, isobutanol can be converted into jet fuel known as ATJ (Alcohol to Jet Fuel.)
While Intrexon is currently focusing on commercializing its isobutanol technology, their farnesene route is also a potential Gas-to Liquid technology as farnesene can be upgraded into a synthetic diesel fuel.
Other than ExxonMobil’s MTG technology, which has already been successfully commercialized, the other technology alternatives to F-T described above are still in various stages of development. If and when these alternates achieve commercial status is still an open question.