(IEA Bioenergy Task 39) Many petroleum refiners in Europe, North America, Latin America and Asia are thinking about upgrading bio-feedstocks using existing infrastructure. Approximately 40 refineries around the world have so far implemented or tested some type of hydroprocessing of mixed petroleum and bio-intermediate feedstocks, co-processing these feeds at biointermediate levels ranging from 2 vol% to 40 vol%. In Scandinavia, 2 units are processing crude tall oil (CTO). In the US, 1 unit had been studying pyrolysis oil upgrading (100% pyrolysis oil) however this has stopped.
In addition to the challenge of bio-crudes typically containing higher level of oxygen than are found in petroleum feedstocks, problematic contaminating elements for fossil fuel refiners include sulphur, nitrogen, phosphorous and
sodium. The two primary approaches so far investigated are co-processing in fluid catalytic cracking (FCC) units or in
hydrotreatment units, and they differ with respect to both product yield and product quality.
Tracing of bio-components/biogenic (vs. fossil) content is a key aspect for coprocessing albeit the way recycled carbon
fuels are evaluated is of high importance as well.
Potential difficulties with co-processing include: 1) increasing pressure drop across the system due to exacerbated coking; 2) catalyst deactivation; 3) equipment corrosion due to high bio-oil acidity; 4) hydrogen consumption; and 5)
exotherms. The changing composition of recycled gases can also create challenges. The typical catalysts are Cobalt–
Molybdenum (CoMo) or nickel–molybdenum (NiMo), and CoMo catalyst are affected by presence of CO. Coprocessing
at more than 10% of bio-content can increase the cloud point of the fuel. For some feedstocks, the upper limit for
coprocessing may be between 5-10%.
The many possible pathways for producing lower carbon fuels using mixed petroleum/biogenic feeds, e.g., by
coprocessing bio-oils with fossil feedstocks in existing petroleum refineries, require validated analytical methods to
qualify the biogenic content of the final fuels. Methods for tracking bio-carbon must be accurate and thus have to be
‘real’ and verifiable (as opposed to calculated) or everyone in the industry will suffer from poor perception from the
outside. For this reason, the biofuel industry recommends directly measuring the renewable content of any coprocessed fuels.
Concerning measurement of bio-carbon content, a recent study evaluating an ASTM D6866 standard
method showed radiocarbon analysis by accelerator mass spectrometry (AMS) to be accurate and reliable for
quantifying the biobased carbon content of hydrocarbon fuels. This method was able to measure absolute biogenic
carbon content to an accuracy of ±0.26% at the 95% confidence level. READ MORE