New Process for 2,6-Dimethylnaphthalene Synthesis by Using C₁₀ Aromatics as Solvent and Transmethylation-Agentia: High-Efficiency and Peculiar Subarea-Catalysis over Shape-Selective ZSM-5/Beta Catalyst

Abstract

A new methylation (2-methylnaphthalene (2-MN) with methanol) process using low-value C 10 aromatics (C 10 A) as solvent and transmethylation-agentia was developed for the lower-cost synthesis of 2,6-dimethylnaphthalene (2,6-DMN), by using a ZSM-5/Beta composite catalyst. Especially, there is a peculiar subarea-catalysis over this catalyst due to both the reactant/product shape selectivity and the ingenious acidity design. Concretely, methylation (2-MN with methanol) and transmethylation (C 10 A with 2-MN) are catalyzed by the weak + medium + strong acid sites inside 12-ring pore and on the external surface of zeolites, while almost no transmethylation (but methylation and second shape-selective isomerization of fatter DMNs to β,β-DMN) occurs inside the smaller 10-ring pore (rejecting larger-molecular C 10 A) with mainly weak−medium acidity. Here, both the high-efficiency synergy of methylation with transmethylation and the meritorious isomerization incubated a 2-MN conversion of 52.98% and a 2,6-DMN yield of 11.01%. Our work may provide a promising model for the rational design of an excellent catalyst for a complicated reaction system.

Methylation of Naphthalene with Methanol over the Al-Modified SiO2 Zeolite Catalysts

“…Generally, the alkylation of NA and methanol follows an acid-catalyzed reaction . According to the XRD results, it is known that 30Al-SiO 2 is an amorphous silica–aluminate.…”

“…The methylation reaction is carried out at weaker acidity, while other side reactions such as isomerization, dealkylation, and disproportionation require strong acidity. 64 Therefore, the Al content is properly adjusted to give the catalyst some reasonable acid sites, which leads to improvement of both the conversion and selectivity of the target product, as shown in Table 4.…”

“…Generally, the alkylation of NA and methanol follows an acid-catalyzed reaction. 64 According to the XRD results, it is known that 30Al-SiO 2 is an amorphous silica−aluminate. Meanwhile, the Si-(OH)-Al group, as a small unit of 30Al-SiO 2 , plays a crucial role in these acid-catalyzed reactions.…”

Insight into the Alkylation‐Efficiency of Methanol with Toluene over HZSM‐5 Zeolite II: Acidic Properties also Significantly Affects Reacting‐Pathways

“…Moreover, the former catalyst showed an alkylation‐selectivity of only 60.6% for forming xylene, but an alkylation‐selectivity of 16.6% to form C 9+ aromatics and a much higher content of benzene in aromatic products. These are because the strength of acidity required for catalyzing the reactions follows an order: alkylation < dealkylation < disproportionation, and here toluene alkylation is just catalyzed by weak‐medium acid sites . On the one hand, the excessively strong acidity resulted in intense dealkylation (the backward reaction of alkylation).…”

“…These are because the strength of acidity required for catalyzing the reactions follows an order: alkylation < dealkylation < disproportionation, and here toluene alkylation is just catalyzed by weak-medium acid sites. [23,52,[55][56][57] On the one hand, the excessively strong acidity resulted in intense dealkylation (the backward reaction of alkylation). And then an accelerated aromatic-based cycle (in MTO side-reaction) also occurs with producing mainly ethylene and some propylene through the demethylation of trimethylbenzenes and 1,2,4,5tetramethylbezene [41][42][43] (proved by the increased selectivity of C 2 aliphatics in the gas product for ZSM-5-C, listed in Table 3).…”