Efficient continuous-flow synthesis of long-chain alkylated naphthalene catalyzed by ionic liquids in a microreaction system

Abstract

Alkylated naphthalene (AN) is one of the significant naphthalene derivatives that can be used as base oil or additive to meet newly-emerged requirements for lubricants in many fields. In the presence of acidic catalysts and olefins as alkylating agents, AN can be easily synthesized through the Friedel–Crafts reaction, which is commonly used in the production of fine chemicals. In this work, we introduced a novel efficient continuous-flow microreaction system to intensify long-chain alkylated naphthalene production catalyzed by Me₃NHCl–AlCl₃ ionic liquid. Both 1-dodecene as a modeling system and a mixture of C9–C13 α-olefins synthesized from the Fischer–Tropsch reaction obtained from industry were used to study the optimum conditions for long-chain alkylated naphthalene production. Benefiting from rapid micro-mixing and accurate control of the reaction parameters in such a system, our results indicated that a high yield of alkylated naphthalene (>99%) could be obtained within 60 s at a mild temperature (30 °C) and over a wide range of naphthalene/olefin mole ratios (1–10). The contents of multi-substituted alkylated naphthalene and ratio of α-substituted to β-substituted alkylated naphthalene in products could be regulated by changing the reaction temperature and naphthalene/olefin molar ratio. Furthermore, by comparing the catalytic performance of ionic liquid in the two systems, it was found that the loss of AlCl₃ from the ionic liquid to the organic phase is the main reason for catalyst deactivation. Such an issue could be resolved by supplementing fresh AlCl₃, and then the ionic liquid catalyst remained active up to 5 cycles. Combined with high throughput parallel micromixers, this continuous-flow system could be easily scaled up, showing great potential in industrial production.