Comparison between leached metakaolin and leached diatomaceous earth as raw materials for the synthesis of ZSM-5
Inexpensive raw materials have been used to prepare ZSM-5 zeolites with SiO2/Al2O3 molar ratios in the range 20 – 40. Kaolin or Bolivian diatomaceous earth was used as aluminosilicate raw materials and sodium hydroxide and n- butylamine were used as mineralizing agents and template. Dealumination of the raw materials by acid leaching made it possible to reach appropriate SiO2/Al2O3 ratios and to reduce the amount of iron and other impurities. After mixing the components and aging, hydrothermal treatment was carried out and the products were recovered The results clearly show for the first time that well-crystallized ZSM-5 can be directly prepared from leached metakaolin or leached diatomaceous earth using sodium hydroxide and n-butylamine as mineralizing agents and template under appropriate synthesis conditions. A longer induction time prior to crystallization was observed for reaction mixtures prepared from leached diatomaceous earth, probably due to slower digestion of the fossilized diatom skeletons as compared with that for microporous leached metakaolin. The use of leached diatomaceous earth allowed higher yield of ZSM-5 crystals within comparable synthesis times. However, low amounts of Mordenite formed, which was related to the high calcium content of diatomaceous earth. Another considerable advantage of diatomaceous earth over kaolin is that diatomaceous earth does not require heat treatment at high temperature for metakaolinization.
Direct Synthesis of Highly Crystalline ZSM-5 from Indonesian Kaolin
Direct synthesis of ZSM-5 from Indonesian kaolin without calcination for the formation of metakaolin was done through the addition of an alkaline solution (sodium fluoride and sodium hydroxide) and the fusion using sodium hydroxide. Crystallization was conducted through hydrothermal method at 80 °C for four days. XRD diffractogram and FTIR spectra showed that the addition of sodium fluoride solution in the ratio Si/Al = 100 could produce highly crystalline ZSM-5, whereas the use of a sodium hydroxide solution and fusion process did not produce the crystalline ZSM-5. Copyright © 2017 BCREC Group. All rights reserved. Received: 21 st November 2016; Revised: 30 th December 2016; Accepted: 18 th February 2017 How to Cite : Hartati, H., Widati, A.A., Dewi, T.K., Prasetyoko, D. (2017). Direct Synthesis of Highly Crystalline ZSM-5 from Indonesian Kaolin. Bulletin of Chemical Reaction Engineering & Catalysis , 12 (2): 251-255 (doi:10.9767/bcrec.12.2.809.251-255) Permalink/DOI: http://dx.doi.org/10.9767/bcrec.12.2.809.251-255
Synthesis of ZSM-5 from Ethanol-Containing Systems. Influence of the Gel Composition
ZSM-5 zeolite has been synthesized using ethanol as a templating agent. The effects of composition on the physicochemical properties of the zeolite (Al content, crystal and particle sizes) and on the kinetics of the crystallization have been studied. The dilution of the starting gel with water leads to a decrease of both the nucleation and crystal growth rates, whereas the increase of the ethanol/SiO[sub 2] molar ratio favors both processes in agreement with the templating role of the alcohol. The variation of the SiO[sub 2]Al[sub 2]O[sub 3] ratio causes drastic changes in the crystallization: the presence of a high proportion of Al in the gel delays the nucleation period but accelerates the crystal growth step. A certain contribution of the autocatalytic mechanism to the nucleation is present at the lowest SiO[sub 2]/Al[sub 2]O[sub 3] ratio investigated, the autocatalytic nuclei being probably formed around Al species in the gel phase. Thus, pure ZSM-5 cannot be obtained at high SiO[sub 2]/Al[sub 2]O[sub 3] ratios. The enhancement of the basicity leads to a decrease of the nucleation period, whereas a maximum of the crystal growth rate is observed for the intermediate OH[sup [minus]]/SiO[sub 2] ratio of 0.12 due to the competition between crystallizationmore » and crystal redissolution processes at high OH[sup [minus]] concentrations. The Al content of the zeolite is only changed by variation of the SiO[sub 2]/Al[sub 2]O[sub 3] ratio in the gel, its proportion being higher in the zeolite phase.« less