The field of the petrochemical separations is rich of onerous examples that can be favourably realized using membrane operations such as gas separation and membrane reactor. However, polymeric membranes have low resistance to a high temperature and heavy hydrocarbons. Therefore, significant improvements are expected by a full development of inorganic membranes, like zeolitic ones. However, their application at industrial level is strongly limited by reproducibility problems in the preparation steps ?1?, presence of intercrystalline defects in the zeolite layer and high manufacturing costs ?2?. FAU zeolite crystals have cavities of 1.3 nm in diameter interconnected by pores of 0.74 nm [3]; FAU zeolite membranes were applied to the separation of CO2/N2 [4], benzene/cyclohexane [4, 5], propylene/propane, ethylene/methane [4] and p-xylene/o-xylene mixtures [6] with interesting separation factors. Thin FAU (Na-Y, Si/Al=1.5-3) zeolite membranes were synthesised, with a two steps method, on porous ?-Al2O3 tubular supports: the seeding is followed by a secondary growth. The secondary growth method, decoupling the zeolite nucleation from the crystal growth, allows to optimise the conditions of each step independently [7]. Seeding is a critical step that can influence the membrane quality. In particular, a new procedure for the seeding crystals was designed and used to realize the selective zeolitic layer on the inner tubular support surface. The effect of the support pore size (200, 100 and 60 nm), seeding time (6-18 hrs) and hydrothermal treatment (24 and 30 hrs) were considered. The membranes (FAU/Na-Y) prepared were characterized by scanning electron microscopy, energy dispersive X-ray and powder X-ray diffractometry. Pure gas permeation experiments at room temperature showed higher permeances (5-45 ?mol/m2 s Pa) and selectivity (2.97-3.48 for H2/N2 and 2.49-3.95 for H2/CO) close to those similar membranes reported in literature. The best results in terms of the reproducibility and selectivity were found using supports with dpore=60 nm.
FAU zeolite membrane by a new preparation method
C Algieri;P Bernardo;G Barbieri;E Drioli
2004
Abstract
The field of the petrochemical separations is rich of onerous examples that can be favourably realized using membrane operations such as gas separation and membrane reactor. However, polymeric membranes have low resistance to a high temperature and heavy hydrocarbons. Therefore, significant improvements are expected by a full development of inorganic membranes, like zeolitic ones. However, their application at industrial level is strongly limited by reproducibility problems in the preparation steps ?1?, presence of intercrystalline defects in the zeolite layer and high manufacturing costs ?2?. FAU zeolite crystals have cavities of 1.3 nm in diameter interconnected by pores of 0.74 nm [3]; FAU zeolite membranes were applied to the separation of CO2/N2 [4], benzene/cyclohexane [4, 5], propylene/propane, ethylene/methane [4] and p-xylene/o-xylene mixtures [6] with interesting separation factors. Thin FAU (Na-Y, Si/Al=1.5-3) zeolite membranes were synthesised, with a two steps method, on porous ?-Al2O3 tubular supports: the seeding is followed by a secondary growth. The secondary growth method, decoupling the zeolite nucleation from the crystal growth, allows to optimise the conditions of each step independently [7]. Seeding is a critical step that can influence the membrane quality. In particular, a new procedure for the seeding crystals was designed and used to realize the selective zeolitic layer on the inner tubular support surface. The effect of the support pore size (200, 100 and 60 nm), seeding time (6-18 hrs) and hydrothermal treatment (24 and 30 hrs) were considered. The membranes (FAU/Na-Y) prepared were characterized by scanning electron microscopy, energy dispersive X-ray and powder X-ray diffractometry. Pure gas permeation experiments at room temperature showed higher permeances (5-45 ?mol/m2 s Pa) and selectivity (2.97-3.48 for H2/N2 and 2.49-3.95 for H2/CO) close to those similar membranes reported in literature. The best results in terms of the reproducibility and selectivity were found using supports with dpore=60 nm.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
