DEACTIVATION OF A MULTIMETAL SUPPORTED CATALYST FOR ANILINE N-ALKYLATION WITH ALCOHOL

A multicomponent catalyst, containing platinum, tin and calcium on a s ilica gel support was tested for N-alkylation of MeEt-aniline (MEA) wi th 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 h as an average crystallite diameter of 55-165 Angstrom and a crystallin ity degree of 30-90%, depending upon the activation-working conditions , and after reduction it contains Pt3Sn alloy. Catalyst deactivation i s caused by the formation of a strongly bonded coke layer containing n itrogen, which interacts with the Pt-component leading to the formatio n 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 c atalyst activity/selectivity. The amount of N-containing coke depends upon MEA purity and operational conditions controlling the reaction se lectivity. 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-isopropylidene methoxy-MeEt-aniline (IM) in the reactor. The IM concentration depends upon operational conditions and catalyst composition. Cleaning of cru de MEA by distillation and adsorption of heavy impurities on silica an d operating at proper conditions yielded low IM concentration with a s table yield of N-isopropylmethoxy-MeEt-aniline 63-65% and selectivity about 95% within a 200 h period of operation. The N-containing coke ca nnot be removed by treatment of the catalyst with nitrogen or hydrogen , but oxidative regeneration allows to reestablish the active phase wi th the same initial activity/selectivity patterns.