The tradeoffs which should make you question whether biofuels really do reduce greenhouse gases

In mid-2022, a Sydney crane company proudly touted its shift into a new type of biofuel, hydrotreated vegetable oil (HVO), which “reduces greenhouse gases by up to 90 per cent”.

For a fuel dubbed “renewable diesel”, the feel-good stats and sustainable-sounding name appears to be the perfect quick-fix for Australia’s high-pollutin’ transport industry, which accounts for slightly more than 18 per cent of the country’s total emissions.

HVO are second generation biofuels, which can be made from vegetable oils like rapeseed, sunflower, soybean, or palm oil as well as animal fats.

Only two companies are known to be using HVO in Australia, — BHP in its Yandi mines and Marr Contracting in Sydney — and although plans are afoot, none is made here yet, but both hope it will put a dent in their transport emissions costs.

Can diesel ever be renewable, and can a fuel that is used as a direct replacement for its fossil counterpart, burns the same way, and gives off similar levels of carbon dioxide, almost touch carbon neutrality?

The answer, as ever with facts washed in eco-green, is nuanced: HVO can be renewable when emissions are measured over its lifecycle — and because it doesn’t have to count tailpipe emissions — and under the right conditions it can hit high double digit carbon dioxide reductions.

The oft-quoted 90 per cent figure, however, comes with an asterisk. Neste, the HVO pioneer and largest supplier in the world, says its 75-95 per cent reduction figures depend on the region which provides the testing methodology — some are more lenient than others — and the raw materials used to make its fuel.

HVO are second generation biofuels, which can be made from vegetable oils like rapeseed, sunflower, soybean, or palm oil as well as animal fats.

“It can be possible if the whole supply chain has really efficient and interesting things happening, but it is uncommon. I don’t think I’ve seen any published work that would suggest something quite that good,” says Dr Marguerite Renouf, agri-food life cycles expert and deputy director of Queensland University of Technology’s Centre for Agriculture and the Bioeconomy.

Furthermore, it’s unclear whether those reductions can stack up as feedstocks run short, and more land must be turned over to fuel production: animal and agriculture byproducts are less emissions intensive than deliberately-grown biofuels crops.

“Biofuel targets could lead to indirect land use change and influence local food security…increasing global GHG emissions rather than decreasing them.”

2018 IPCC report

Competition for biofuel feedstocks is already fierce in the US and the International Energy Agency is forecasting a global supply shock between 2023 and 2027, as demand grows.

“Maladaptive actions could increase the risk of adverse climate-related outcomes. For example, biofuel targets could lead to indirect land use change and influence local food security…increasing global GHG emissions rather than decreasing them,” noted the global response chapter of the IPCC’s 2018 report.

Green-flavoured diesel

Most drivers are familiar with E10, the ethanol-blended petrol that is the cheapest option at every petrol station. Biodiesel is similar, and HVO is the latest edition.

Biodiesel is made by esterification: an oily feedstock — animal fats, restaurant deep fryer leftovers, crops, you name it — is treated with an alcohol, usually methanol, and a catalyst. This produces glycerin and a fuel made of fatty acid methyl esters (FAME).

“Generally biofuels give you an improved emission profile but there are some unresolved emissions, especially if you are looking at air toxics.”

Nicolas Surawski

The problem is this fuel must be blended in order to work in a normal engine. Blends with higher biodiesel content produce more of a whole new range of emissions, including formaldehyde and alkanes which react to produce ozone, says UTS environmental engineer Dr Nicolas Surawski.

“Generally biofuels give you an improved emission profile but there are some unresolved emissions, especially if you are looking at air toxics,” he told Cosmos Weekly.

HVO is the next variation. It’s produced from the same oils but instead uses hydrogen to crack open the biggest molecules which then swaps in one of its own atoms, allowing it to burn more cleanly than fossil fuels.

“The feedstock is hydrogenated. Hydrogen is used in the manufacturing process to polymerize the fuel, and that makes a linear straight chain molecule to get good combustion performance,” Surawski says.

Turning the carbon cycle to one’s advantage

Sellers of HVO have dubbed it ‘renewable’ and even ‘green’ because the emissions are recycled through the carbon cycle.

Biofuels made by companies that operate in Europe, like Neste and Eni which are the biggest players there, must meet strict rules such as shaving a minimum 60 per cent off greenhouse gas emissions compared to fossil fuels. They achieve this because biofuel emissions are not counted at all in the lifecycle emissions profile.

Gas and coal, when taken out of the ground and burned, release stored carbon dioxide gas into the atmosphere that does not become new coal or gas reserves; but biofuels are derived from crops which absorb carbon dioxide from the atmosphere, and when it’s burned that carbon dioxide is reabsorbed again.

As a result, HVO has a carbon footprint as low as 5 g CO2e/MJ to as high as 102 g CO2e/MJ.

Biofuels are derived from crops which absorb carbon dioxide from the atmosphere, and when it’s burned that carbon dioxide is reabsorbed again.

Putting this in context, in 2021 average emissions in Australia for passenger cars and light SUVs was 146.5 g/km, while heavy SUVs and light commercial vehicles was 212.5 g/km. These figures are high, globally, because Australia is one of two countries in the world without fuel efficiency standards (Russia is the other one).

A study testing cars using HVO in Europe using real world conditions and under the new Worldwide Light Vehicle Harmonised Testing Procedure (WLTP) at ambient temperatures, found carbon dioxide emissions were around 137 g/km compared to fossil diesel and emissions reductions for pure HVO were around 4 per cent.

Studies show HVO particulate emissions are lower than fossil diesel.

Palm oil is still bad

The biggest contributor to HVO’s emissions profile is not transportation of finished fuel, or those tailpipe emissions even if they aren’t radically different to fossil diesel, but where the feedstock comes from and how it’s grown. 

“The way you make a fuel has a big impact on the emissions it produces,” says Richard Brown, director of Queensland University of Technology’s Biofuel Engine Research Centre.

“If you put lots of fertiliser on the crop, which itself uses lots of greenhouse gases, if you use lots of diesel machinery while you grow it, or transport it a long way to be processed, you gradually increase the emissions. In the worst possible case you could create more emissions than the carbon dioxide that was absorbed by the plant in the first place.”

Even within a country there will be variations, for example Australia’s vastly different rainfall rates and soils mean a crop grown for biofuel in fecund NSW fruit bowls will have a different emissions starting point than one grown around Darwin.

“In the worst possible case you could create more emissions than the carbon dioxide that was absorbed by the plant in the first place.”

Richard Brown

In the case of HVO, palm oil use is one of the most contentious issues. Oil majors Eni and Total have sworn off palm oil for HVO as of this year, while other manufacturers like Preem deny using the stuff at all.

Neste says its 32 Indonesian palm oil suppliers are certified, but that also comes with difficulties: in 2020 a study showed many of the certified palm oil plantations including those where Neste sources its raw materials were elephant or orangutan habitats as recently as 1999.

The European Union (EU) requires that any land deforested since 2008 can’t be used for biofuels raw materials production. Any land that was converted from rainforest or another virgin state before 2008, can be certified as sustainable, however.

Renouf says every biofuel will come with a tradeoff.

“Our emphasis here in Australia is on prioritising the use of residual biomass, so something that doesn’t require new agricultural production.”

Marguerite Renouf

“There’s no such thing as a free lunch. You’re never going to find a product that ticks all of the boxes all of the time,” she says.

“The bottom line with biofuels generally, and they all teeter to varying degrees around this conclusion, is you can get really good greenhouse gas savings but they usually have some tradeoffs which you have to carefully manage.

“Our emphasis here in Australia is on prioritising the use of residual biomass, so something that doesn’t require new agricultural production.”

Her work on Queensland sugar cane residue for biofuels is an example. Sugar cane tops the tables for biofuel crops and the state is set to be a massive contributor in the coming years to biofuel feedstock, but at the same time the run-off is highly damaging for the Great Barrier Reef, a side effect Renouf says is an unacceptable tradeoff.

More in Cosmos Weekly