Production of Light Olefins from Methanol Using Aluminoborosilicates Containing Calcium -Effects of Crystal Si z e of Silicate and Alkaline Earth Metal Salts on Catalyst Life

Abstract

Recently we have found that ZSM-5 type zeolites containing calcium show the excellent catalyst performance for methanol conversion to light olefins at high temperatures above 500°C and that the crystal size is controlled by adding boric acid. s The catalyst life of the microcrystalline aluminoborosilicate containing calcium synthesized in the presence of boric acid increased with a decrease in the crystal size. In this paper, in order to extend further the catalyst life, the zeolites were mechanically mixed with various alkaline earth metal carbonates. The methanol conversion was carried out over the CaCO₃-mixed aluminoborosilicates containing calcium with various crystal sizes (Fig.1). The catalyst life increased with a decrease in the crytal size of the zeolite used. In the case of the microcrystalline zeolite with crystal size of 0.3 μm, the catalyst lifetime with higher yield than 50% for C₂H₄ and C₈H₆, was extended extreamly to about 130 h. Effects of the amount of alkaline earth metal carbonates on the catalyst life and the initial product distribution were also studied (Table 2, Fig.2). It was found that among the alkaline earth metal carbonates, the mechanical mixing of the microcrystalline zeolite with SrCO₃ in a weight ratio of 2: 1 was effective for elongation of the catalyst life. The yields of C₂H₄ and BTX decreased with an increase in a weight ratio of SrCO₈/zeolite. On the other hand, the yield of C₈H₁₀ increased with the weight ratio. These results seem to be attributed to the change of acidity of the zeolites. The steam stability of CaCO₈- or SrCO₈-mixed microcrystalline zeolite was also investigated by means of ²⁷A1-MASNMR. It was found that the mixing of SrCO8 has a little effect on the resistance to steaming of microcrystalline zeolite. The long-term catalyst life test of the SrCO₈-mixed microcrystalline zeolite was carried out by using dimethyl ether instead of methanol (Fig.4). The time with higher yield than 60% for C₂H₄ and C₈H₆ was about 2600 h.