Catalytic Fast Pyrolysis of Kraft Lignin over Hierarchical HZSM-5 and Hβ Zeolites

Yadong Bi,Jianli Hu,Guihua Xu,Hui Chen,Xiaojuan Lei

doi:10.3390/catal8020082

Yadong Bi, Jianli Hu + Show 3 more

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https://doi.org/10.3390/catal8020082

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Abstract

The hierarchical HZSM-5 and Hβ zeolites were prepared by alkaline post-treatment methods adopting Na2CO3, TMAOH/NaOH mixture, and NaOH as desilication sources, respectively. More mesopores are produced over two kinds of zeolites, while the micropores portion is well preserved. The mesopores formed in hierarchical Hβ zeolites were directly related to the basicity of the alkaline solution, indicating that Hβ zeolite is more sensitive to the alkaline post-treatment. The hierarchical HZSM-5 and Hβ zeolites are more active than the parent one for catalytic fast pyrolysis (CFP) of Kraft lignin. Hierarchical zeolites retained the function of acid catalysis, while additionally creating larger mesopores to ensure the entry of bulkier reactant molecules. The increase of the condensable volatiles yield can be attributed to the improvement of the mass transfer performance, which correlates well with the change of mesoporous surface area. In particular, the condensable volatiles yield for the optimized hierarchical Hβ reached approximately two times that of the parent Hβ zeolites. In contrast to the parent HZSM-5, the optimized hierarchical HZSM-5 zeolite significantly reduced the selectivity of oxygenates from 27.2% to 3.3%.

Highlights

Lignocellulose is the most abundantly available raw material on the earth for the production of biofuels
Compared with the other two components, lignin itself is composed of aromatic polymer structure, it has the lowest aromatics yield and highest coking under the same catalytic fast pyrolysis (CFP) conditions [7]
The mesoporous surface area is only 18 m2 /g, which is negligible compared to the microporous surface area of 395 m2 /g

Summary

Introduction

Lignocellulose is the most abundantly available raw material on the earth for the production of biofuels. It is mainly composed of carbohydrate polymers (cellulose, hemicellulose), and a cross-linked aromatic polymer (lignin). Removing oxygen from raw materials efficiently is usually a challenge for the catalytic fast pyrolysis (CFP) of lignocellulose to produce a high-energy density fuel with good combustion performance [2]. Pyrolysis vapors can be upgraded by catalytic conversion over solid acid catalysts such as zeolites to generate products of lower oxygen content [3]. In CFP process, coke formation leads to rapid deactivation caused by blocking zeolite pores, and declines the carbon conversion efficiency. Compared with the other two components, lignin itself is composed of aromatic polymer structure, it has the lowest aromatics yield and highest coking under the same CFP conditions [7]

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