A review on catalytic conversion of biodiesel derivative glycerol to bio-olefins

Bioglycerol-to-Propylene Routes: From Fundamental Catalysis to Process Design and Marketing

“…For high-temperatures (>400 °C), Corma et al , have been the first ones to build a complex mechanism for converting glycerol to olefins and aromatics over acid surfaces without an external H 2 supply (Scheme ). The integral pathways toward gas products (i.e., olefins, CO x and paraffins) involve the catalytic dehydration of glycerol, cracking, and hydrogen producing-consuming reactions on acid sites at temperatures mainly higher than 450 °C. ,, H 2 is formed mainly through C–C and C–H cleavages, water–gas shift (WGS), decarbonylation, and dehydrogenation reactions, and is then transferred to dehydrated intermediate molecules by hydrogenation and hydrogen-transfer events, thereby producing light olefins; mainly ethylene and to a lesser extent propylene. ,,, The latter are involved mainly in further aldol-condensation and Diels–Alder rearrangements to form heavier paraffins or even aromatics, which negatively affects the formation of propylene as target product. An optimal balance between all these reactions is therefore required to improve propylene yield.…”

“…High-temperature GTP ,,,,,,, exploits simultaneous glycerol dehydration and cracking under inert atmosphere to form propylene and ethylene at temperatures higher than 400 °C, whereas H 2 is generated in situ and directly activated on the catalytic sites. ,,, Nevertheless, the viability of this strategy is questionable because it involves the following drawbacks: Intensive energy spending on sensible and latent heats for vaporizing glycerol and water mixture. Huge volume expansion induced by the vaporization of glycerol and water, which greatly increases the investment cost. Low experimental yield of propylene, which in the best of cases cannot exceed the theoretical values between ∼33.3% and ∼77.7% because part of the glycerol is converted at high temperatures through H 2 transfer reactions and cracked in C, CO x emission and H 2 O, according to the following reactions (eqs –): 3 C 3 O 3 H 8 → C 3 H 6 + 6 C + 9 H 2 O 3 C 3 O 3 H 8 → 2 C 3 H 6 + 3 CO + 6 H 2 O ...…”

“…41,66,67 H 2 is formed mainly through C−C and C−H cleavages, water−gas shift (WGS), decarbonylation, and dehydrogenation reactions, and is then transferred to dehydrated intermediate molecules by hydrogenation and hydrogentransfer events, thereby producing light olefins; mainly ethylene and to a lesser extent propylene. 35,41,66,67 The latter are involved mainly in further aldol-condensation and Diels−Alder rearrangements to form heavier paraffins or even aromatics, which negatively affects the formation of propylene as target product. An optimal balance between all these reactions is therefore required to improve propylene yield.…”

“…Indeed, GTP routes is undergoing advances in research in terms of both fundamental catalysis and process design ,,− by exploring different transformation strategies from both heterogeneous and homogeneous catalysis. GTP routes are being investigated through high-temperature processes, ,,,,,, multisteps reactions, including triple-stage reactors, , separate double reactors, ,, tandem or dual-bed catalysts, ,,, and single-step conversion strategies. ,,,− ,,,,− These studies conclude that in the future GTP catalysis may become a sustainable bridging route between the biorefinery and polyolefin industries.…”

“…Indeed, GTP routes is undergoing advances in research in terms of both fundamental catalysis and process design ,,− by exploring different transformation strategies from both heterogeneous and homogeneous catalysis. GTP routes are being investigated through high-temperature processes, ,,,,,, multisteps reactions, including triple-stage reactors, , separate double reactors, ,, tandem or dual-bed catalysts, ,,, and single-step conversion strategies. ,,,− ,,,,− These studies conclude that in the future GTP catalysis may become a sustainable bridging route between the biorefinery and polyolefin industries. Nonetheless, integrating GTP routes in a unified network, from biomass to sustainable propylene, raises intrinsic challenges, such as the nature of the most efficient GTP configurations, control of the interoperability of multisteps and/or combined bed reactors, influenced by contact states between catalyst beds, operating conditions, reaction mechanisms, and so forth.…”