(253i) Complete Hydrodeoxygenation of Enzymatic Hydrolysis Lignin to Cycloalkane Fuels

Lignocellulose, mainly composed of cellulose, hemicellulose and lignin, is a sustainable feedstock for producing commodity chemicals and fuels. For hundreds of years, cellulose has been utilized in paper production. Recently, cellulose and hemicellulose are converted into bio-ethanol in 2G biorefineries, but enzymatic hydrolysis lignin (EHL) from 2G bioethanol production are poorly utilized, and are regarded as a large volume solid waste [1]. Our previous works focused on EHL depolymerization in ethanol, and produced phenolic products with unsupported Ni [2], Ni-Mo alloy [3] and WO₃ supported on Al₂O₃ [4] as catalysts. Recently, a one-pot method for simultaneous lignin depolymerization and hydrodeoxygenation (HDO) of products is developed. Although noble metals are excellent catalysts for HDO reactions, their high cost hinders their application. In our recent works, we developed non-noble metal catalysts from hydrotalcite precursors, which achieved complete hydrodeoxygenation of EHL into cycloalkane fuel without formation of char.

Ni catalyst derived from the reduction of Ni-Al hydrotalcite (NiAl-LDH) was employed for HDO of EHL. The effects of Ni/Al ratio and reduction condition on the catalyst activity have been examined. The catalyst obtained from the reduction of NiAl-LDH at 460 ^oC (Re-NiAl-LDH-460) showed the highest activity among the catalyst samples examined. With this catalyst, EHL was completely converted and depolymerized at 320 °C under 3 MPa H₂ for 6 h, yielding 133.24 mg/g EHL of cycloalkanes. Meanwhile, the heating value of the product is 42.5 MJ/kg and much higher than that obtained without a catalyst (25 MJ/kg) under the same reaction condition. After that, Fe was introduced into the Ni-Al hydrotalcite, followed by reduction to prepare a NiFe alloy catalyst. The total yield of cycloalkanes was improved to 161.1 mg/g EHL under the same reaction conditions (320 °C, 3 MPa H₂, 6 h). The results of the lignin dimer model compound conversion demonstrate that the NiFe alloy catalyst exhibits high activity in breaking C-O linkages and achieves partial cleavage of C-C linkages.

Reference

[1] L. Dessbesell, M. Paleologou, M. Leitch, R. Pulkki, C. Xu, Global lignin supply overview and kraft lignin potential as an alternative for petroleum-based polymers, Renewable & Sustainable Energy Reviews, 123 (2020).

[2] Y. Sang, M. Chen, F. Yan, K. Wu, Y. Bai, Q. Liu, H. Chen, Y. Li, Catalytic Depolymerization of Enzymatic Hydrolysis Lignin into Monomers over an Unsupported Nickel Catalyst in Supercritical Ethanol, Industrial & Engineering Chemistry Research, 59 (2020) 7466-7474.

[3] Y. Bai, K. Cui, Y. Sang, K. Wu, F. Yan, F. Mai, Z. Ma, Z. Wen, H. Chen, M. Chen, Y. Li, Catalytic Depolymerization of a Lignin-Rich Corncob Residue into Aromatics in Supercritical Ethanol over an Alumina-Supported NiMo Alloy Catalyst, Energy & Fuels, 33 (2019) 8657-8665.

[4] F. Mai, Z. Wen, Y. Bai, Z. Ma, K. Cui, K. Wu, F. Yan, H. Chen, Y. Li, Selective Conversion of Enzymatic Hydrolysis Lignin into Alkylphenols in Supercritical Ethanol over a WO3/γ-Al2O3 Catalyst, Industrial & Engineering Chemistry Research, 58 (2019) 10255-10263.