Techno-economic and life cycle assessment of triisobutane production and its suitability as biojet fuel

Abstract

This study assesses the potential of triisobutane as a sustainable biojet fuel blending component to reduce the environmental impacts caused by the continually growing aviation sector. Cellulosic isobutanol, used as feedstock, was sequentially upgraded through dehydration, oligomerization, and hydrogenation processes to produce triisobutane (2,2,4,6,6-Pentamethylheptane). The dehydration process yield is 99.1% of isobutene, and the achieved conversion of isobutene to triisobutene in the oligomerization stage is 90%. The optimal operation conditions to produce the maximum amount of triisobutene during the isobutene oligomerization are 100 °C, 0.20 MPa, and a space–time τ’ of 5.5 g h/L. Triisobutene is converted quantitatively to triisobutane through a final hydrogenation stage. The production model was simulated using Aspen Plus® v.10 software. The production costs were calculated based on a biorefinery that uses 16,264 kg/h of isobutanol to obtain 10,723 kg/h of triisobutane. The predicted minimum triisobutane selling price is 1.34 €/kg or 1.04 €/L. The environmental assessment carried out in Simapro® v.9.0 software, estimated emissions of the isobutanol upgrade to triisobutane of 7 gCO2eq/MJ. A combined footprint of 65 gCO2eq/MJ is obtained considering the 58 gCO2eq/MJ emitted in isobutanol production, which represents a 28% reduction of greenhouse gas emissions compared with the conventional Jet A1 production. Physico-chemical properties of triisobutane were estimated using group contribution methods, and the results comply with the ASTM D7566 standards. The Payload vs. Range analysis confirmed the capabilities of triisobutane as a biojet fuel blend component for a given range flight.