Synthesis of Zeolite EMT with Aid of Sodium Phosphate

Abstract

Since the successful synthesis of pure hexagonal faujasite EMT was reported in 1989 by Delprato and co-workers, 1 there has much interest in this potentially useful large-pore zeolite with 12-ring aperture and twodimensional direct channel systems. [2][3][4][5][6][7][8][9][10][11][12] In the alkylation of isobutane with 2-butene, EMT has been found to perform much better than its cubic analogues FAU. 13,14 However, a major disadvantage of the EMT zeolite was the high cost of the templates1,4,7,10,13,-16-hexaoxacycleoctadecane. Approaches to reduction of the amount of 18-crown-6 ether include the use of surfactants 15 and auxiliary organic additives 16,17 and the SINTEF method reported by Wendelbo et al. 21,22 The amount of 18-crown-6 ether has been reduced to 0.4-0.5 per Al 2 O 3 in recent reports. 15-20 However, it would result in a mixture of EMT and FAU and eventually in pure FAU if the amount of 18-crown-6 ether was reduced further. [15][16][17][18]21 Besides that, with the decrease of the amount of 18-crown-6 ether, the crystallization time also increased greatly. 21 Recently, the EMT was synthesized with an 18-crown-6 ether/Al 2 O 3 ratio of 0.14 via the SINTEF method. 21,22 Unfortunately, the crystallinity of the product was low, even though it had undergone crystallization for a long period of time and other phases would form while prolonging the crystallization time further. Long crystallization time was also a drawback in acquiring a more cost-effective procedure for synthesis of EMT. Approaches toward resolving this problem such as increasing temperature, raising the pH, and adding fluoride 18 have not been particularly successful because those methods would in some case lead to more defects of structure and mixed phases of crystals.On the other hand, as was well-known, the evolution of the hydrogel toward the crystalline was a rather complex physico-chemical process. For the crystallization occurred in an aqueous medium upon heating, the water and cation-water complexes were considered to play an important role during crystallization. 23 In the case of EMT, it was synthesized in a dense gel that was highly thixotropicsthe viscosity of gel without agitation was 10 times that with agitation. 19,21 It would bring about the slow crystallization rate of EMT and increase the probability of nucleating other phases. 21 So improving the transportation of the water-crowded inorganic species and structural-directing agents was of great help in shortening the crystallization time. Here, we provide an approach to successfully synthesize pure zeolite EMT with high efficiency, that is, the synthetic period is shortened from 30 days to 6 days and the ratio of 18-crown-6 ether/Al 2 O 3 decreases to 0.33 by the aid of the auxiliary agent of Na 3 PO 4 ‚12H 2 O.The procedure for synthesizing EMT was based on the Delprato method. The NaOH, auxiliary, and 18-crown-6 ether were dissolved in distilled water first and then colloidal silica (26 wt % SiO 2 , 0.5 wt % Na 2 O) was added to the mixture dropwise with stirring...

Nucleation and Crystal Growth Features of EMT-Type Zeolite Synthesized from an Organic-Template-Free System

“…However, the use of other structure-directing agents and various initial systems have resulted in intergrown EMT-FAU (CSZ-1, ECR-30, ZSM-20, ZSM-3) materials. − Thus, until recently, the synthesis of pure EMT-type zeolite was possible solely by employing an exotic template (18-crown-6 ether) . Many attempts have been carried out to reduce the consumption of crown ether, for instance, by recycling organic structure-directing agents (OSDAs) after the synthesis or using the “SINTEF” tumbling approach, surfactants, and less-expensive organic and inorganic auxiliary additives. − Although the synthesis of the EMT-type zeolite was optimized, still the use of 18-crown-6 ether remained indispensable for the production of this promising material.…”

Seed-directed synthesis of EMT-type zeolite from an organic-template-free system

“…Many approaches have been used in the past decades to reduce its content in the reacting mixture, for instance, adding surfactant or auxiliary agent of Na 3 PO 4 $12H 2 O [8,9], adopting continuous tumbling method during the entire aging and crystallization period [10], using a steam-assisted crystallization (SAC) method [2], etc. Even though the molar ratio of 18-crown-6 ether/Al 2 O 3 has been greatly decreased to 0.14 [10], it still exists.…”