Investigating the properties and performance of 3A molecular sieves as an adsorbent to prevent coke formation in olefin dehydration process

Abstract

To study the affinity of 3A aluminosilicate adsorbents to prevent oligomerization of olefin molecules and forming green oil, physical and chemical properties of 3A molecular sieves are measured by using characterization techniques such as temperature-programmed desorption (TPD), nitrogen (N2) and water adsorptions, X-ray diffraction (XRD), X-ray fluorescence (XRF), crushing strength, and carbon dioxide (CO2) adsorption. Moreover, coke formation affinities of the understudy adsorbents are evaluated in a bench-scale system using 1-butene and 1,3-butadiene at temperatures of 220 and 260 °C, and outcomes are validated against the actual data gathered from an industrial scale olefin dehydration plant. Results confirm that the type of binder and the amount of ion exchange affect the performance of a 3A molecular sieve nominated for dehydrating olefinic streams. The binder with the least amount of acidity is preferred, and at least 35% of Na ions of the 4A zeolite should be exchanged with K ions to make it applicable for synthesizing an appropriate 3A molecular sieve. Furthermore, to control the oligomerization and inhibit green oil formation, the CO2 adsorption and acidity of Trisiv shape molecular sieves with the sizes of 1/4 inch should be less than 0.5 wt % and 1.7 mmol NH3/g, respectively. For extrudate shape with the sizes of 1/16 inch CO2 adsorption and acidity should be less than 0.2 wt % and 2.2 mmol NH3/g, respectively.