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.
Synthesis of faujasite type zeolites from calcined kaolins
Preparation de zeolites A, X et Y a partir de kaolins, la temperature de calcination etant liee au type de zeolite
On the crystallization mechanism of zeolite ZSM-5: Part 1. Kinetic compensation effect for the synthesis with some diamines
Abstract Zeolite ZSM-5 was synthesized from the initial gel: 33 Na 2 O: 44 R : Al 2 O 3 : 100 SiO 2 : 4000 H 2 O: 25 H 2 SO 4 , where R is tetrapropylammonium bromide (TPA) and C 2 , C 3 , C 4 , and C 6 diamines are in the temperature range 423–453 K. The kinetic analysis of the crystallization of ZSM-5 permits us to follow the role of the used templates during the consecutive steps of the process. The diminishing of the crystallization rate with the increasing of the linear dimension of the molecule is proved. A kinetic compensation effect (KCE) was established between activation energy and the preexponential factor. The obtained KCE is proof for the uniform mechanism of crystallization of zeolite with C 2 , C 3 , C 4 , and C 6 diamines and for a different one for the synthesis with TPA.