Catalytic Intramolecular Dehydration Of Monoethanolamine To Ethylenimine

The catalytic intramolecular dehydration of monoethanolamine was carrier out over mixed oxide catalysts or zeolite catalysts in the presence of nitrogen at atmospheric pressure. The effects of the factors involved in the catalysts compose, catalysts preparation methods and conditions, and dehydration reaction conditions on the catalytic properties have been investigated. The deactivation and regeneration of catalysts have been preliminarily discussed. At the same time the catalysts have been characterized by XRD, N₂ physical adsorption, TG-DTG, FT-IR, NH3-TPD, SEM, HRTEM and XRF. The results show that:1.Si-Ba-Cs-P mixed oxide catalyst is the advisable catalyst for the catalyticintramolecular dehydration of monoethanolamine.2.The advisable preparation conditions of Si-Ba-Cs-P mixed oxide catalyst are identicalvolume two-stage impregnation: phosphorus oxide is impregnated into the Si/Ba mixed oxidecarrier firstly and then cesium oxide is impregnated into above catalysts, there are the samecalcination conditions of 800℃/4 h. The advisable elements compose of mixed oxidecatalysts is Si/Ba/Cs/P=50/0.3/0.9/1.0. The advisable reaction conditions are 420℃,Ni/monoethanolamine (gas volume ratio) =9, and gas total space velocity=2500 h^-1.3.The ethylenimine selectivity and the catalyst property of resist carbon deposition canbeen improved if Si/Ba mixed oxide carrier is modified by steam and then the modifiedcarrier is impregnated by phosphorus and cesium oxide. The ethylenimine selectivity and thecatalyst property of resist carbon deposition can been improved if the boron oxide isimpregnated into the Si-Ba-Cs-P mixed oxide catalyst.4.The polymers formed by monoethanolamine and ethylenimine polymerization thatcover with the active center on the catalyst surface are the main cause of the Si-Ba-Cs-Pmixed oxide catalyst deactivation. The catalytic properties of the spent catalysts can berecovered to the original value, when the catalysts were calcinated at 800℃in air.5.HZSM-5 is the advisable zeolite catalyst for catalytic intramolecular dehydration ofmonoethanolamine.6.The ethylenimine selectivity can been obviously improved when HZSM-5 zeolites aredisposed by some surface modified methods, such as: carbon deposit pretreatment, chemicalliquid deposition (CLD) of SiO₂, and phosphorous and cesium oxide modified method or theabove methods cooperated each other. Because these modified methods make the strong acid site poisoned and decrease the diameter of zeolites pore, the appropriate acidity and pore diameter are formed to produce ethylenimine. There is the maximal ethylenimine yield on the phosphorous and cesium oxide modified HZSM-5 zeolite catalyst. The advisable preparation conditions are identical volume one-stage impregnation, the phosphorous oxide content is 2.9% (weight percent) and the cesium oxide content is 5.2% (weight percent). The advisable reaction conditions are 420℃, N₂/monoethanolamine (gas volume ratio) =9, and gas total space velocity=2500 h^-1.7. The MFI structure stability of phosphorous and cesium oxide modified HZSM-5 zeolite catalysts are decreased with the increase of cesium oxide content. The modified method by phosphorous and cesium oxide make the strong acid site and moderate strong acid site poisoned in and out zeolite pores and decrease the diameter of zeolites pore, so the ethylenimine selectivity is increased.8. The polymers formed by monoethanolamine and ethylenimine polymerization that cover with the active center on the catalyst surface is the main cause of the phosphorus and cesium oxide modified zeolite catalyst deactivation. The catalytic properties of the spent catalysts can be recovered to 93% the original value, when the catalysts were calcinated at 800℃in air.