A Closer Look at Gas-To-Liquids
What are Gas-to-Liquids?
The term gas-to-liquids (GTL) refers to a refinery process of converting natural gas from its gaseous state into a liquid state. This is accomplished by changing the methane-rich, shorter-chain hydrocarbons into longer ones.
How Are Gas-to-Liquids Created?
Natural gas can be converted into gas-to-liquids in multiple different ways either directly by converting the methane into methanol in one step or by using an intermediate such as syngas to make the conversion. Either way the net result is a liquid synthetic fuel. Several GTL conversion techniques include:
- Fishcher-Tropsch Process - The Fishcher-Tropsch Process begins by partially oxidizing the methane in natural gas into carbon dioxide, carbon monoxide, water, and hydrogen. The ratio of hydrogen to carbon monoxide is adjusted using the "water gas shift reaction", which is an important, naturally-occurring reaction that has a number of other useful industrial applications. Meanwhile the excess carbon dioxide in the mixture is removed using an aqueous solution of alkanolamine. Finally, the water is removed which yields synthesis gas (syngas) which can then be chemically reacted over a catalyst such as cobalt or iron to yield the liquid hydrocarbons.
- Methanol to Gasoline process (MTG) - The Methanol to Gasoline process (MTG) was developed by oil company Mobil during the 1970s. It also utilizes the naturally-occurring water shift reaction described above. It involves conversion of the natural gas into syngas and then conversion of the syngas into methanol. The methanol is then dehydrated to yield dimethyl ether. The dimethyl ether is then further dehydrated using a zeolite catalyst to yield gasoline. This variety of gasoline is often referred to as M-gas in reference to Mobil.
- Syngas to Gasoline Plus Process (STG+) - The Syngas to Gasoline Plus Process (STG+) is an expansion of the MTG process. It involves converting the syngas derived from the original natural gas directly into drop-in gasoline or jet fuel. To achieve this a thermochemical single-loop process is used. The process utilizes a series of four fixed bed reactors.
- 1.) Methanol Synthesis - The first part of the process involves methanol synthesis. In this first reactor the syngas is converted into methanol and passes through a catalyst bed.
- 2.) Dimethyl Ether Synthesis - The second part of the process involves the synthesis of dimethyl ether. The methanol gas from reactor one is fed into reactor two and exposed to a catalyst which dehydrates it to form dimethyl ether.
- 3.) Gasoline Synthesis - In the third part of the process gasoline is synthesized. The gas dimethyl gas from reactor two is fed into reactor three to convert it into hydrocarbons that include alkanes, cycloalkanes, and aromatics. This converts the the carbon from C6 into C10.
- 4.) Gasoline Treatment - The fourth phase of the process involves treating the gasoline. The product from the third reactor is fed into the fourth reactor which provides transalkylation and hydrogenation treatment. This reduces the presence of durene, isodurene, and trimethylbenzene and produces a higher octane.
What Are the Uses and Benefits of Gas-to-Liquids?
- Separation - The final phase involves taking the product from reactor four and condensing it into gasoline. This gasoline along with the remaining non-condensed gas is then separated using a condenser/separator. The non-condensed gas is then sent back to reactor one to begin the loop all over again and yield more condensed gas.
Gas-to-Liquids can be used for fuel and energy in many of the same ways that gasoline, diesel, and other petroleum products can be used. The major advantages of turning natural gas into gas-to-liquids is that it increases the value of the product. It makes it much easier and more economically feasible to transport. This allows so called “stranded wells” which do not have ready access to a transportation network of pipelines to still be valuable assets. Unlike liquefied natural gas (LNG) which must be kept very cold and thus transported in special containers, GTL can be transported using the existing infrastructure because it has similar physical properties. GTL also has a higher energy concentration than LNG.
A Closer Look at Liquefied Natural Gas
What is Liquefied Natural Gas?
Liquefied Natural Gas (LNG) is natural gas which has had its temperature lowered to the point of liquefaction. LNG is odorless and colorless as well as non-corrosive and non-toxic. Because it is a liquid instead of a gas LNG is much more dense than traditional natural gas and takes up only about 1/600th the space that a comparable quantity of natural gas would take up. In terms of scale this is comparable to compressing a beach ball into the size of a ping pong ball.
LNG celebrates the 100th anniversary of its patent this year. In 1914 the patent was filed and three year later the first LNG facility was built in West Virginia. Since then it has gained a steady foothold in the oil and gas sector and it has gained momentum even more quickly in recent years as more liquefaction plants in have come online and new companies have entered the market in response to increasing energy demands.
How is Liquefied Natural Gas Created?
LNG is created by cooling the natural gas, which is composed primarily of methane to its liquefaction point of -260° Fahrenheit. This is done in specially designed liquefaction plants and generally the LNG will need to be reconditioned into its gas form at LNG terminals after it has been transported. During the liquefaction process oxygen, sulfur, nitrogen, carbon dioxide, and water are separated and filtered out. This leave the LNG in a very pure state. Most LNG is transported in very large ocean tankers with thick, double hulls to keep it cold.
What Are the Uses and Benefits of Liquefied Natural Gas?
One of the major advantages that LNG offers is a reduction in CO2 emissions and other greenhouse gases. This makes it very popular within the context of the larger trend toward more eco-friendly power solutions. It also allows to meet emission standards that many other fossil fuels cannot. Another big benefit of LNG is that it is non-flammable and very safe to transport.
Once the LNG has been reconditioned into its gaseous state it can be used in the same ways as traditional natural gas, such as for heating homes, offices, hospitals, schools, and other residential, commercial, and industrial buildings. It can also be used as fuel for cooking, water heating, and in many household appliances and industrial equipment. LNG terminals have even been built in Texas and Louisiana.
In many ways GTL and LNG can be seen as competing technologies. Each offer their own sets of advantages which make them useful and applicable in different ways. Because the energy market is so large and because production of natural gas is increasing, it is likely that both GTL and LNG will only see their production ramp up in the coming years. Natural gas, NGLs, GTL, and LNG play a crucial role in the energy sector and that role will continue to increase in the foreseeable future.