Preparation of discrete colloidal ZSM-5 crystals with high Al-content

A new method for synthesis of discrete colloidal ZSM-5 particles with SiO2/Al2O3 M ratios as low as 30 and sizes .4–1 micrometer has been developed. The relation between the synthesis parameters and synthesis yield, crystal structure, crystallinity, particle size and morphology was investigated. The synthesis yield increases and the deviation of the SiO2/Al2O3 ratio in the product from that in synthesis mixture decreases with increasing autoclave temperature suggesting that the introduction of aluminium into the zeolite structure is favoured by high autoclave temperature during the synthesis and that temperature determines the lower limit of the SiO2/Al2O3 ratio. The SiO2/Al2O3 ratio in the synthesis mixture decreases with autoclave temperature suggesting that the introduction of aluminium into the zeolite structure is favoured by high autoclave temperature during the synthesis and that the temperature determines the lower limit of SiO2/Al2O3 ratio. Synthesis mixture, aimed to yield a high SiO2/Al2O3 ratio, gives smaller zeolite crystals, higher specific surface areas, higher geometric areas (external surface area of the crystals) and a more oval crystal shape compared with lower ratios, synthesised at the same temperature. Higher autoclave temperature during the synthesis gives larger zeolite crystals and a more hexagonal crystal shape compared with zeolites synthesised at lower temperatures, for the same SiO2/Al2O3 ratios.