Impact of Coprocessing Biocrude with Petroleum Stream on Hydrotreating Catalyst Stability

Coprocessing of biocrudes from hydrothermal liquefaction (HTL) of biomass and wastes with petroleum streams in refinery hydroprocessing has significant potential to accelerate the production of renewable transportation fuels in the near term. However, HTL biocrudes with some problematic characteristics can potentially cause faster deactivation of the catalysts, which is one of the biggest barriers to the adoption of biocrude in the current refinery process. In this work, we investigated the deactivation modes of a sulfide NiMo/Al2O3 hydrotreating catalyst used for coprocessing HTL biocrude (from wastewater sludge) with straight-run diesel. Spent catalysts were collected after coprocessing diesel with different biocrudes after >300 h time on stream and characterized by various techniques. Their catalytic activities were evaluated by model compound testing. Loss of catalyst activity was observed after coprocessing biocrudes. No structural change of the catalyst after coprocessing biocrudes was observed, and catalyst deactivation was largely due to catalyst fouling by carbonaceous species and metal contaminants (such as Fe and K) from biocrudes. Inorganic contaminant deposition leads to the external coating of the catalyst pellets on the top of the reactor, whereas the carbonaceous species potentially bind near the sulfide active phase, thereby blocking access to the active edge sites. Pretreatment of the HTL biocrude can reduce problematic species and alleviate catalyst deactivation during coprocessing.

Automated summary

The coprocessing of biocrudes with petroleum streams has potential for renewable fuel production, but can cause catalyst deactivation. This study investigated the deactivation modes of a hydrotreating catalyst used for coprocessing biocrude with diesel. It was found that catalyst deactivation was mainly attributed to fouling by carbonaceous species and metal contaminants from biocrudes.