Bottled gas is an internationally popular energy source for cooking and heating and for barbeques. The fuel stored in the pressurised cylinder is liquefied petroleum gas (LPG).
LPG is a mixture of propane and butane which can be recovered as a condensate (referred to as natural gas liquids, or NGL) during liquefied natural gas processing. It is also produced on crude oil refineries as a light product for regional distribution in bulk, or as bottled gas.
The popularity of LPG has grown because it is perceived as a relatively clean fuel. It burns with a clean flame with minimal particulate pollution. It is also transportable to remote regions where natural gas pipelines do not run and never will. However, as a fossil fuel LPG produces carbon dioxide greenhouse gas emissions and therefore contributes to climate change.
Future-proofing your LPG business
Fossil-free alternatives to LPG exist. Bio-LPG is a sustainable biofuel. E-propane and e-DME (e-dimethyl ether) are also technically viable options which can be produced from biogenic CO2 and renewable electricity. To grow the opportunity, technical advances, increased scale and investment in the best projects in ideal geographies are required to make these renewable e-fuels affordable to the masses.
How good is the match with DME? The physical properties of LPG allow it to be stored as a liquid in a low-cost, carbon-steel cylinder at around 8 bar at room temperature. Under these conditions, it has a volumetric energy density of 25 MJ/litre. And DME is a close comparison. It exerts a vapour pressure of around 4 bar at room temperature and has a volumetric energy density of 18.7 MJ/litre.
A low-cost, fossil-free alternative to LPG, such as low-carbon intensity DME, could benefit a quarter of the world’s population directly by delivering ‘clean cooking’. It would also enrich planetary health for the benefit all.
It’s quite a prize. How do we get there?
Enabling the world to enjoy clean cooking
LPG has led a transition from burning solid fuels such as cow dung, wood and coal, so it is an advance in itself. But now we could go further. Cleaner cooking is essential to reduce household air pollution, which accounts for many premature deaths due to smoke inhalation. LPG is already the primary source of heat for cooking in India and there are initiatives underway to increase its uptake.
Beyond India, where it is rapidly taking off, about one third of the world’s population does not have access to clean cooking. These three billion people predominantly live in Asia, South Asia and sub-Saharan Africa. Cleaner burning stoves, electrification and biogas will enable clean cooking for many. However, increased use of LPG is expected to be the main new fuel and technology option for clean cooking, so a renewable alternative would have a big impact.
Price sensitivity is high in these emerging economies and the transition to fossil-derived LPG is an expense that many cannot afford. Subsidies are being considered to overcome that cost hurdle in some locations, but it raises questions.
Low-carbon fuels, especially e-fuels, are of course generally more expensive today than the fossil fuel incumbents they displace. Price-sensitivity in these emerging markets places a huge emphasis, therefore, on the need for low-cost production of low-carbon DME to enable fair access to clean, defossilised fuels for all. To get there, innovation and smart projects will be required.
Methanol to DME
Methanol would be difficult to use as an LPG replacement. That’s because at room temperature liquid methanol does not exert sufficient vapour pressure to drive it out of a cylinder as a gas. On the other hand, conversion of methanol to DME is technically possible.
In 1985, ExxonMobil started up the Motunui Synthetic Fuels Plant in New Zealand. The idea was to produce gasoline from natural gas. The process used steam methane reformers to convert methane into syngas, which was reacted to produce methanol. A fixed-bed reactor system converted the methanol to DME. In this reaction, two methanol molecules are joined and dehydrated, resulting in DME.
Storage two of gas LPG in the horizontal tanks and pipeline.
The future of low-carbon DME could be based on a similar pathway where biomethane is reformed to syngas. As an alternative route to low-carbon intensity DME, the syngas could be generated by gasification of waste biomass or municipal solid waste. In this gasification pathway, oxygen is often used in the gasifier for process intensification and to simplify capture of the resulting CO2.
Green e-methanol can be produced from the direct hydrogenation of CO2 using electrolytic green hydrogen. This reaction between CO2 and hydrogen avoids the intermediate step of converting the CO2 to syngas using the reverse water gas shift reaction. Once the e-methanol is formed, it can be converted to e-DME using the reaction described above.
Direct e-DME production
The established pathways for DME production are through methanol as an intermediate. This pathway requires separate plants for methanol synthesis followed by DME production.
RealCarbonTech (RCT) is a clean fuels company based in the US. Its technology can produce e-DME in a single plant fed with CO2 and electrolytic green hydrogen. This plant has the same design as a methanol plant, but when tailored for the production of DME the process uses a different catalyst in the reactor. The benefit of the RCT approach is simplification of the process since it omits one reaction stage, resulting in reduced capital expense.
Tomasz Zmysłowski, CEO of RCT, says that “one of the advantages is our modular plant construction approach. This means we do not need a high concentration of renewable power or biogenic CO2 in one location. It also enables off-grid systems which can produce e-methanol or e-DME as a convenient way to move green electrons to consumers of energy or processors of sustainable chemicals.”
RCT has plans to construct a commercial unit which will have the capability to convert circa 170,000 tonnes per year of biogenic CO2 and electrolytic green hydrogen to produce more than 100,000 tonnes per year of e-DME.
Commercial operations are scheduled to start in late 2026 and early 2027. “There is still some capacity available for partners willing to consider off-take agreements from this project”, adds Zmysłowski. Product from the plant can be delivered to New York or any other US port.
Not the only horse in the race
If e-DME is a strong contender to substitute fossil LPG as a low-carbon bottled gas, it is not the only horse in the race. Additionally, bio-LPG is in use today and other solutions have been proposed.
Bio-LPG can be produced from hydroprocessing of esters and fatty acids (HEFA). This process reacts plant-based oils and animal fats with hydrogen. In the US, facilities in California, Louisiana, and other states have the capacity to produce more than 4.5 million gallons per year of bio-LPG. As with sustainable aviation fuel, this HEFA biofuel is the dominant form of sustainable LPG today.
E-propane can be produced from electrolysis of CO2 and water. The electrochemical system is catalysed by an imidazolium-functionalised Mo3P and is being researched at the Illinois Institute of Technology. It may have potential for the long term, especially in locations with abundant solar, wind or hydro power. However, as with all e-fuels, e-propane comes at a significant cost premium versus fossil LPG and bio-LPG.
Ammonia: a limited alternative
Another option to mention is ammonia. Liquid ammonia is distributed in transportable cylinders for industrial refrigeration and metals heat treatment applications today. It is also used on rubber plantations to convert liquid latex to solid rubber. Packaged ammonia supply is often incorporated into specialty gases and chemical gases businesses in the industrial gases sector.
Ammonia is combustible and burns with a carbon-free flame. Its volumetric energy density is 12.7 MJ/litre, close to half that of LPG. If the ammonia is produced as blue, or green ammonia this could be a pathway to provide low-carbon heat. However, the toxicity of ammonia would prevent its use in domestic applications and limit its field of application to industrial settings.
In other words, it is not the best broad option as an alternative here, though it could have its place.
