Deactivation of a multimetal supported catalyst for aniline N-alkylation with alcohol

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Abstract

A multicomponent catalyst, containing platinum, tin and calcium on a silica gel support was tested for N-alkylation of MeEt-aniline (MEA) with methoxyisopropanol in a continuous fixed bed reactor at atmospheric pressure in the presence of hydrogen. It was found that the active Pt-Sn-Ca phase is located in the macro pores of the silica carrier; it has an average crystallite diameter of 55-165 Å and a crystallinity degree of 30-90%, depending upon the activation-working conditions, and after reduction it contains Pt3Sn alloy. Catalyst deactivation is caused by the formation of a strongly bonded coke layer containing nitrogen, which interacts with the Pt-component leading to the formation of a surface complex Pt...N with electron transfer from nitrogen to Pt. ' Pure ' coke (without nitrogen) up to 4 wt.-% does not affect the catalyst activity/selectivity. The amount of N-containing coke depends upon MEA purity and operational conditions controlling the reaction selectivity. The strongly poisoning N-containing coke is produced by the red-colored oxidation-condensation products present in crude MEA and/or by a relatively high concentration of intermediate N-isopropylidenemethoxy-MeEt-aniline (IM) in the reactor. The IM concentration depends upon operational conditions and catalyst composition. Cleaning of crude MEA by distillation and adsorption of heavy impurities on silica and operating at proper conditions yielded low IM concentration with a stable yield of N-isopropylmethoxy -MeEt-aniline 63-65% and selectivity about 95% within a 200 h period of operation. The N-containing coke cannot be removed by treatment of the catalyst with nitrogen or hydrogen, but oxidative regeneration allows to reestablish the active phase with the same initial activity / selectivity patterns.

Original languageEnglish
Pages (from-to)139-152
Number of pages14
JournalApplied Catalysis A: General
Volume118
Issue number2
DOIs
StatePublished - 27 Oct 1994

Keywords

  • 1-Methoxy-2-propanol
  • 2-Methyl-6-ethyl-aniline
  • Calcium
  • Deactivation
  • N-alkylation
  • Platinum
  • Selectivity (N-isopropylmethoxy-2-methyl-6- ethylaniline, N-isopropylidenemethoxy-2-methyl-6-ethylaniline, coke)
  • Silica
  • Tin

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