Will The Real Carbon Footprint Please Stand Up?


Slippery things, these carbon footprints can be. In principle, they are simple: the sum of all global warming emissions from cradle to grave of a given product. However, the wrinkle comes with multi-product processes – how is that footprint allocated between the various products coming out? And along the same lines, what exactly is a product, anyway?

I highlighted the relevance of these two questions in a recent paper (Johnson, E. (2017), A carbon footprint of HVO biopropane. Biofuels, Bioprod. Bioref., 11: 887–896. doi:10.1002/bbb.1796). It presents an estimate of the carbon footprint of HVO biopropane, sometimes called BioLPG, which is the newest biofuel to go commercial. Finnish oil company Neste will soon be the largest producer: its Rotterdam refinery is expected to start delivering in December 2017 output that will total to some 40,000 tonnes per year. Total is reportedly producing at some of its refineries in France, ENI at the Porto Marghera ‘biorefinery’ in Italy – these might sum to 10,000-15,000 tonnes a year – and minor quantities are being produced elsewhere.

HVO biopropane is created alongside HVO diesel (often called ‘renewable diesel’), in a process similar to the making of margarine or the hydrotreating of fossil fuels. Natural fats and oils are reacted at temperature and pressure with hydrogen (and a catalyst) that splits the esoteric bond linking each oil/fat molecule’s three long-chain hydrocarbons (typically around C16 or so) to its propyl backbone. The long-chain hydrocarbons, accounting for nearly 95% of the mass, go off to become renewable diesel. Most of the rest of the reaction output is that propyl backbone, which has been hydrogenated to propane – make that biopropane.

Biopropane’s Place Among Energy Products

But is that HVO biopropane a product? According to rules established by the European Union’s Renewable Energy Directive (RED), I think not. It is a ‘residue’, an unavoidable output of a process aimed at making something else (in this case, renewable diesel). Examples of residues, says RED, are: glycerine made alongside conventional biodiesel (the fatty-methyl-ester FAME type); or tall oil made in pulp mills. Because they are residues, not products, according to RED’s rules, both glycerine and tall oil are allocated a production footprint of zero. All the footprint is allocated to the intended product, i.e. FAME biodiesel or pulp. They incur footprint only in their further processing and transport.

If HVO biopropane is classified as a residue, then its footprint is really low, about 5-12 g CO2e per MJ at a lower heating value of biopropane. This is far below the footprints of fossil gasoline or diesel, which RED pegs at around 83 g CO2e per MJ, and it is also well below the footprints of most biofuels. But, if HVO biopropane is deemed a product, according to RED’s rules, its footprint falls somewhere between 20-40 g CO2e. This variation depends on the precise feedstocks used: rape, soy or palm oil come out highest, while used-cooking-oil (also considered a residue) comes out lowest.

In this previous case, RED’s rules are that footprint be allocated among all products according to their ‘energy content’, their heating values. But what if, instead, allocation were done according to their ‘revenue content’, their market values? This shuffles the deck once again. HVO biopropane’s footprint tumbles to 9-20 g CO2e. Many analysts think that market value is a better allocation key than heating value, but then many analysts also agree with RED that heating value is the ‘right’ way to go.

Finally, what about indirect land use change (iLUC). This phenomenon is caused by increased demand for biofuels that indirectly causes forests (usually in places like Brazil or Indonesia) to be knocked down and planted with crops. Most analysts would concede that iLUC is real, but there is great debate as to how to measure it and what its values should be. For this study, I did not joint that debate, I just used iLUC values proposed by the European Commission. If they were implemented – which currently they are not – they would bump the footprint massively. HVO biopropane would come in mostly around the 80-100 g CO2e range, equal or worse to the fossil fuels it’s meant to displace.

So the conclusion is that footprints can go all over the place, depending on the method of calculation. To me, there is a strong similarity to financial statements. Earnings per share, for instance, can look very different, depending on which accounting conventions have been applied. I don’t think this is necessarily good or bad, but it does mean that footprints should be handled with care – there is a great possibility of comparing apples to oranges.

This study, A carbon footprint of HVO biopropane was recently published in the journal Biofuels, Bioproducts and Biorefining.

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