Mechanism of transmethylation in anisole decomposition over HZSM-5: Experimental study

Abstract

This work investigated the decomposition of anisole (methoxyl-based lignin model compound) in a fluidized bed reactor over no catalysts and a series of HZSM-5 zeolite catalysts with different Si/Al atomic ratios. Transmethylation reaction was identified as the initial step of the thermal decomposition of anisole, leading to the prominent production of phenolic compounds. Methyl phenols were identified as the main products, with the yield of o-cresol being higher than that of p-cresol at the temperatures below 600˚C. The transmethylation reaction over HZSM-5 zeolite catalyst was found to occur at temperatures 150˚C lower than those for non-catalytic reaction, with the yield of the phenolic compounds being promoted by 2.5 times. Production of the main phenolic compounds during the catalytic decomposition of anisole was enhanced to different extents depending on the Si/Al ratio. The highest selectivity of 79 wt. % was achieved over the zeolite catalyst with a Si/Al ratio of 80. The Brønsted acid sites of the catalyst played a significant role in both the preferential formation of phenolic compounds and preservation of the methyl group.

Deoxygenation in anisole decomposition over bimetallic catalysts supported on HZSM-5

“…However, it showed a BTX selectivity of 78.9 wt.%, lower than that obtained over Ni-Mo. Our research group has recently reported the conversion of anisole over non-metal HZSM-5 zeolite [10]. Compared to the results previously reported, both the yield and selectivity of BTX have been enhanced by the addition of the bimetallic sites (on average by 20% and 36% respectively) [10,32].…”

“…Experiments were carried out in the bench scale fluidised bed reactor (Diameter*Height mm = 32mm×600mm); further details of the rig can be found in literature [10,32].…”

“…Anisole (or methoxybenzene) is typically used as model compound of the methoxyl-based lignin-derived compounds, since the methoxy functionality is the only one present in the molecule [8]. The decomposition of anisole is a two-step process which consists of transmethylation and deoxygenation reactions [9][10][11]. The first step, transmethylation, primarily yields methyl-containing phenolics (Phs) and subsequently aids the formation of AHs [12][13][14][15][16].…”

“…The first step, transmethylation, primarily yields methyl-containing phenolics (Phs) and subsequently aids the formation of AHs [12][13][14][15][16]. During the deoxygenation step, the Phs further react to produce AHs, naphthenic hydrocarbons and even cycloalkanes [9][10][11]. Catalysts consisting of active metals dispersed on a solid support have showed favourable catalytic activity on the fast pyrolysis of lignin and the upgrading of the derived bio-oil for the production of AHs [11,17,18].…”

Development of Bifunctional Hydrodeoxygenation Catalyst Rh‐HY for the Generation of Biomass‐Derived High‐Energy‐Density Fuels

“…In contrast with a higher deactivation and lower cyclohexane selectivity observed for guaiacol HDO, the HDO of phenol/anisole mixture catalyzed with 0.8Rh‐HY‐R, even at low temperatures and high time space, exhibited high activity, stability, and selectivity toward deoxygenated products. These differences in deactivation rate and selectivity can be rationalized in two ways: 1) both the aromatic alcohol and the aromatic ether adsorb weakly to the catalyst surface and act as inefficient coke precursors; and 2) intermediate products derived from guaiacol transalkylation, such as catechol, methylcatechols, veratrole, and methylguaiacols, can also act as poisoning motifs for both the metallic and acid sites in the catalyst …”