Fuels such as propane, ethane and butane are known as natural gas liquids (NGLs). As contradictory as the name seems to be (how can a gas be a liquid?), they are hydrocarbon liquids that are components of raw natural gas when the gas is pumped out of the ground. NGLs are measured in gallons and barrels, like any other liquid.
They are cleaner burning than most fuels, in use all over the world and their abundance and affordability provide the potential to help lift large segments of the world’s population out of energy poverty. This is especially the case in countries in which access to energy sources is not always reliable due to transportation or political issues.
NGLs are commonly used in various sectors of the economy for consumer and industrial purposes. Some common uses include fuel for cooking, feedstocks for petrochemical plants and as part of the fuel mix for transportation, according to the U.S. Energy Information Administration (EIA), the independent statistical arm of the Department of Energy.
Many people are familiar with propane, which is used to heat homes and as an option for people to cook with smaller stoves and barbecues. It can also be used as a backup energy source when the primary one fails due to severe weather events such as wind storms, hurricanes or flooding.
Ethane is another widely used NGL as an ingredient in plastic items such as shopping bags and household products such as detergent and antifreeze.
Other NGLs include butane, which is used in lighter fuel, while isobutane and pentane and pentane-plus are used to formulate gasoline.
Manufacturing of plastics
NGLs are a much cleaner resource than crude oil to manufacture plastics for the same reason that natural gas is cleaner than coal to generate electricity: burning gas produces significantly fewer emissions of carbon dioxide (CO2), in this case, 27% less than oil.
Plastics manufacturing accounts for only 4-8% of total oil consumption, according to Yale Climate Connections. However, if the current pace of plastics manufacturing continues, the share of oil consumption used for plastics will rise to 20% by 2050, the Yale report said.
The growth in plastics production has occurred in the U.S. in regions that are rich in shale oil and gas formations. This has happened in parallel with increased unconventional production of oil and gas, according to the U.S. Department of Energy. Significant resources include the Marcellus and Utica shales in the Northeast, the Permian Basin in Texas and New Mexico, and the Haynesville Shale in Louisiana, among others.
Older plastics were manufactured with petroleum byproducts, but now that unconventional production techniques such as horizontal drilling and hydraulic fracturing techniques are widely available and costs have declined, plastic is typically made from NGLs because they are abundant and more affordable. Some companies are able to generate additional revenue from exporting NGLs.
Growth of natural gas production in the Appalachian region has been “near-exponential” and the volume generated from that area has been predicted to increase for several decades, the DOE said. Appalachian natural gas production is anticipated to quadruple from 2013 to 2050. The natural gas produced in Appalachia contains valuable resources in the form of NGLs such as ethane and propane. Both of these commodities are utilized as key feedstocks to manufacture the compounds for creating plastics. Propane is used as a feedstock to manufacture ethylene and propylene for chemicals and plastics.
After propane and ethane are extracted, they are delivered to cracking facilities known as crackers. Ethane is manufactured into ethylene, which is the foundation of polyethylene and remains one of the most widely used plastics for bottles, packaging and synthetic materials such as clothing. At dehydrogenation plants, propane is converted into propylene, which is the foundation of polypropylene, the plastic that is used in manufacturing vehicles and food packaging.
Through the end of 2019, over $200 billion was invested by the industry for 333 new chemical and plastics projects because of the large volume of ethane produced, according to Columbia University’s Climate School.
Before ethane and propane can be shipped via pipelines or trucks, they are separated from natural gas in a process called fractionation. After ethane reaches a certain boiling point in a facility called a fractionator, it is removed from the natural gas stream. Ethane is made into plastic after its liquid form undergoes the intense heat that cracks or takes apart the molecules in a plant called an ethane cracker. By 2025, ethane production in the Appalachian region by 2025 will grow by 20 times its 2013 level, according to the Department of Energy.
Propane is a heavier gas and requires a longer boiling process. There are three propane dehydrogenation (PDH) plants in the U.S. that only manufacture propylene from propane feedstock. One plant is owned by Flint Hills Resources and has an estimated propane feedstock capacity of 30,000 barrels per day; the Dow Chemical plant has a propane feedstock requirement of 35,000 barrels per day and the Enterprise Product Partners’ PDH plant is estimated to be about 35,000 barrels per day. Propylene and the other olefins are able to be converted into plastics, resins, glues, solvents and coatings.
There are some drawbacks to NGLs—storing and transporting them can be costly since they require specialized trucks, equipment and storage containers. They need low temperatures and must remain in a liquid state to be shipped.
Since 2000, the demand each year for plastic and its products has nearly doubled, according to the 2020 report by the Columbia University’s Climate School. The increasing global population, better economic conditions and other technological innovations will spur more demand for plastic and its byproducts in the coming decades, according to a report by the International Energy Agency (IEA).
A Center for International Environmental Law (CIEL) report, Plastic & Climate, explains that one major drawback of manufacturing plastic is that it is “among the most energy-intensive materials to produce.” Christof Ruehl, a senior research scholar at Columbia University’s Center on Global Energy Policy, said that other options besides using plastics also produce carbon emissions. Replacing plastic with paper or glass are also energy-intensive processes.
Use with renewable energy
When natural gas is utilized in conjunction with renewable energy, it can be advantageous in the energy transition, according to a 2019 report conducted by the United Nations Economic Commission on Europe. That’s because carbon-free products such as hydrogen can be created when natural gas is partnered with renewable energy sources. The use of gas can also embrace carbon capture, use and storage.
Since natural gas has a multitude of uses, it can be transported easily and be “adapted to carry hydrogen, either mixed in with natural gas or as self-contained systems,” the UN report said.
Natural gas can play a large role in carbon capture and storage (CCS) because the depleted gas fields can become potential CO2 storage locations, such as those in fields offshore Norway and the Netherlands. Carbon capture and use (CCU) can “offer electricity storage options and thus ‘assist sector coupling, by enabling the integration of renewable energy into the gas grid,’” according to the UN report, citing the International Association of Oil and Gas Producers (IOGP) May 2019 report. This goal can be achieved by processing CO2 with renewable hydrogen or utilizing electricity whose source is from renewables to co-process water and CO2.
“When renewable hydrogen is reacted with CO2 to produce synthetic methane, this allows additional options for supply of renewable gas into the network with minimal infrastructure upgrades,” according to the UN report, citing the IOGP report.
Energy companies such as Equinor and Exxon Mobil have started the development of carbon capture and storage (CCS) projects. There are 21 CCS projects in operation or under development as of 2018, according to the UN report. These CCS projects are used in the U.S. for enhanced oil recovery.
A project formed by Penn State EMS Energy Institute researchers and H Quest Vanguard, a Pittsburgh-based start-up company, seeks to lower global greenhouse gas emissions while also finding other solutions for the chemical and material industries.
Randy Vander Wal, a professor of energy and mineral engineering and materials science and engineering, and affiliate at the EMS Energy Institute, has been working with H Quest Vanguard on various projects to use the startup’s plasma technology to utilize non-emissive uses of coal and natural gas, according to an article by Penn State University.
Disrupting the current process of cracking hydrogen molecules could lower costs, use less energy and create fewer greenhouse emissions.
“H Quest’s microwave plasma technology catalyzes reactions in a novel way and allows very rapid—1,000 degrees Fahrenheit per second—heating of gas, which is not possible with conventional heating technologies such as boilers, furnaces, heat exchangers, or inductive heaters,” the article said.
Other companies are turning to combining the use of natural gas with renewable energy.
Dominion Energy, a massive utility company with more than 7 million customers, constructed wind turbines along the Virginia coast in 2021 and also plans to construct new power plants that use natural gas, according to the New York Times.
The Environmental Defense Fund has been working with the oil and gas industry to find ways to reduce methane emissions. In 2012, the group started an extensive series of 16 independent, rigorously executed projects that combined more than 140 research and industry experts [PDF] from 40 institutions and 50 companies.
The result is that the groups found “practical, cost-effective solutions that are possible now, and we’re driving innovation to develop new ones,” while these cost-effective methane reduction projects would result in at least $164 million in net savings for operators, the EDF said.
- Natural gas liquids (NGLs) are used all over the world to cook food and heat homes, and as a component in the transportation fuel mix.
- The dramatic growth in NGL production from the shale revolution has resulted in a cleaner, cheaper feedstock for the manufacture of plastics.
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