Life cycle greenhouse gas emissions analysis of catalysts for hydrotreating of fast pyrolysis bio-oil

Abstract

Bio-oil from fast pyrolysis of biomass requires multi-stage catalytic hydroprocessing to produce hydrocarbon drop-in fuels. One process design currently in development involves fixed beds of ruthenium-based catalyst and conventional petroleum hydrotreating catalyst. As the catalyst is spent over time as a result of coking and other deactivation mechanisms, it must be changed out and replaced with fresh catalyst. A main focus of bio-oil upgrading research is increasing catalyst lifetimes to 1 year. Biofuel life cycle greenhouse gas (GHG) assessments typically ignore the impact of catalyst consumed during fuel conversion as a result of limited lifetime, representing a data gap in the analyses. To help fill this data gap, life cycle GHGs were estimated for two representative examples of fast pyrolysis bio-oil hydrotreating catalyst, NiMo/Al 2 O 3 and Ru/C, and integrated into the conversion-stage GHG analysis. Life cycle GHGs are estimated at 5.5 kg CO 2-e/kg catalyst for NiMo/Al 2 O 3. Results vary significantly for Ru/C, depending on whether economic or mass allocation methods are used. Life cycle GHGs for Ru/C are estimated at 80.4 kg CO 2-e/kg catalyst using economic allocation and 13.7 kg CO 2-e/kg catalyst using mass allocation. Contribution of catalyst consumption to total conversion-stage GHGs at 1-year catalyst lifetimes is 0.5% for NiMo/Al 2 O 3 and 5% for Ru/C when economic allocation is used (1% for mass allocation). This analysis does not consider the use of recovered metals from catalysts and other wastes for catalyst manufacture and therefore these are likely to be conservative estimates compared to applications where a spent catalyst recycler can be used.

The influence of catalysts on biofuel life cycle analysis (LCA)

“…From cradle-to-gate, platinum production GHG emissions are 113 kgCO2e/kg [17]. This result agrees with the outcome presented by Snowden-Swan et al [10], who, using different data from that which we used in our analysis, reported a nearly identical GHG intensities for platinum production in South Africa of 112 kgCO2e/kg. Platinum production GHG emissions are high because the 72% of the energy input to the energy-intensive process is electricity, which is produced largely from coal.…”

“…Although several studies have presented advances in catalytic technologies for the transformation of biomass into biofuels [7, 8, and 9], to our knowledge, very few studies have discussed the environmental impact of catalyst use in biofuel production. For instance, Snowden-Swan et al [10], presented a life-cycle analysis (cradle-to-gate) of two catalysts' (NiMo/Al2O3 and Ru/C) production and the environmental impact of using these catalysts in the hydrotreating of fast pyrolysis bio-oil. They estimated that the contribution of catalyst consumption to conversion stage GHG emissions can vary between 0.5% and 5% depending on the co-product treatment method applied.…”

“…They estimated that the contribution of catalyst consumption to conversion stage GHG emissions can vary between 0.5% and 5% depending on the co-product treatment method applied. Snowden-Swan et al [10] did not, however, carry out a full LCA of the renewable hydrocarbon fuel product and therefore did not estimate the catalysts' influence on total life-cycle GHG emissions of the fuel. Jones et al [1] estimated the contribution of catalyst consumption to biorefinery GHG emissions to be less than 1%.…”

The multi-scale challenges of biomass fast pyrolysis and bio-oil upgrading: Review of the state of art and future research directions

“…Ni and zeolite instead of manufactured catalysts). Very limited research has compared the environmental profiles of catalysts for hydrotreating fast pyrolysis oils [748]. Snowden-Swan et al…”

Effects of Coproduct Uses on Environmental and Economic Sustainability of Hydrocarbon Biofuel from One- and Two-Step Pyrolysis of Poplar

“…The remaining CO 2 produced from off-gas combustion is biogenic. The life cycle inventory of the catalyst utilized for the catalytic upgrade was not accounted for in this study because previous studies have shown that the life cycle inventory of the catalyst has little effect on the overall life cycle emission of the pathway. − …”