Assessment the Effective Factors on the Size and Shape of Synthesized γ-Al2O3 Granules via Oil Granulation Method

Nowadays, the heterogeneous catalysts play an undeniable role in chemical processes. Catalysts are generally synthesized in powder form which need to be shaped for industrial uses, which requires a separate cost. In this research, the single-step synthesis of ϒ-Al2O3 as catalyst support with spherical shape was performed by dripping the precursor solution in an oil column and the effect of synthesis conditions such as the temperature and length of oil column (paraffin), the concentration of granule hardening solution (ammonia) and heating rate of calcination temperature was evaluated. The results showed that increasing the temperature of the paraffin column decreases the surface tension and improves the movement of the injected gels, and they easily enter the ammonia layer by crossing the paraffin layer boundary. Decreasing the concentration of ammonia solution in the ion exchange step within the structure of the granules is very suitable and prevents the disintegration of the granules. The results showed that the heating rate of the calcination temperature should be set at the lowest value so that cracks and fractures do not occur on the granule surface due to the slow release of water and other solvents in the gel. Gamma aluminum oxide (alumina) granules synthesized in the conditions of paraffin column temperature of 60 °C and length of 30 cm, concentration of ammonia solution of 10% and calcination temperature of 700 °C with the heating rate of 1 °C/min had dimensions around 3 mm. Moreover, the sphericity factor of the produced granules was less than 0.05, which indicates the appropriate quality of this method for the synthsis of granular support catalyst. In addition, the characterization of the granules showed that their surface area is 78.9 m2.g-1 and they have suitable pores size and volume for use as a catalyst support.