(253h) Hydrodeoxygenation of Bio-Oil Via in-Situ Alkene Dehydrogenation

The abundance of waste biomass and its extracted lignin and its intrinsic aromatic network could provide the chemical industry with a rich, sustainable, and renewable hydrocarbon supply. This potential source of green added-value chemicals, like benzene, toluene and xylenes (BTX) boosts the interest on biorefinery and its integration with the existing petrochemical state-of-the-art processes. With the relatively high oxygen content in bio-oil, which hinders its heating value and processability, hydrodeoxygenation (HDO) becomes a crucial step in biorefineries [1], [2]. Conventionally, HDO is processed using high-pressure (up to 200 bar) expensive hydrogen [1]. Consequently, the use of a hydrogen donor is investigated as an alternate strategy by using solvent and/or co-feeding at different operating conditions [3]–[5]. Optimally, the reaction used to produce hydrogen should in itself also lead to added-value byproducts. Hence, dehydrogenation of alkanes can be an interesting choice as valuable alkenes would be generated as shown in Figure 1.

This research aims to demonstrate HDO of bio-oil via in-situ alkane dehydrogenation. Alkanes such as ethane and propane are the primary feeds of the petrochemical value chain to produce the building block chemicals ethylene, propylene, and aromatics. Therefore, the incorporation of alkenes production with upgraded bio-oil would improve the overall outlook of HDO. This research seeks to increase bio-oil conversion due to the catalytic formation of reactive hydrogen at the catalyst surface derived from the dehydrogenation of alkenes. In addition, this research seeks to increase alkane conversion derived from the continuous consumption of hydrogen for bio-oil upgrading. To investigate alkane and bio-oil conversions, experiments are conducted on a single catalytic system comprised of HDO and alkane dehydrogenation catalysts in a continuous up-flow reactor. To achieve higher hydrogen formation from thermodynamic equilibrium perspective, these experiments are conducted at atmospheric pressure and high temperature environment using guaiacol as model compound. Catalytically, these studies were conducted on Ni-Mo and MoO₃ based catalyst for HDO, and Cr-based catalyst for alkane dehydrogenation [1], [6]–[9].

A bio-oil conversion similar to that achieved through the use of hydrogen was observed, with products having a higher C/O ratio, as well as ethylene production, when using alkane dehydrogenation catalysts and a superior conversion with HDO catalysts. In addition, increases in reaction temperature and catalyst loading have a significant positive effect on HDO performance. On the other hand, catalytic dehydrogenation of ethane suffers a decline in conversion after 30 minutes of time-on-stream until it reaches a plateau; the introduction of bio-oil model compounds accelerates this decline through catalyst deactivation, necessitating frequent of catalyst re-activation. In summary, the results demonstrated the feasibility of replacing hydrogen with alkanes and there is scope by further developing the process through more effective catalyst formulations.

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