Hydrothermal synthesis of free-template zeolite T from kaolin

Abstract

Free-template zeolite T crystals were synthesized via hydrothermal synthesis by utilizing the activated kaolin as silica and alumina source, with the molar composition of 1 SiO2: 0.04 Al2O3: 0.26 Na2O: 0.09 K2O: 14 H2O. Observation of the formation of free-template zeolite crystals were done at temperature 90°C, 100 °C and 110 °C respectively. It was therefore determined that during the 120 h of the synthesis at 90 °C, zeolite T nucleated and formed a first competitive phase with zeolite L. As temperature increases to 100 °C, zeolite T presented itself as a major phase in the system at time 168 h. Subsequently, development of Zeolite T with second competitive phase of zeolite W was observed at temperature 110 °C. In this study, XRD and SEM instruments were used to monitor the behavior of zeolite T crystals with respect of temperature and time. By using natural resource of kaolin clay as a starting material, this paper hence aims to provide new findings in synthesis of zeolite T using low energy consumption and low production cost.

Important Synthesis Parameters Affecting Crystallization of Zeolite T: A Review

“…Meanwhile, crystal formation of zeolite T (either by hydrothermal synthesis or aided with microwave-, or sonochemical-irradiation) is affected by several primary factors. From the past and recent literature, several cases involve crystals' behavior upon several factors, namely SiO 2 /Al 2 O 3 ratio, alkalinity (n (OH)-)/n (SiO 2 )), water ratio, synthesis temperature and crystallization time, and the addition of structure-directing agents (SDA) [1,3,4,8,16,[19][20][21][22], while pressure is not directly involved in zeolite T synthesis [23]. This review summarizes the factors that affect the growth of zeolite T. However, the ratio of SiO 2 /Al 2 O 3 depends on the alkalinity of the composition.…”

“…Since zeolite T favors high alkalinity crystallization, controlling the ratio of SiO 2 /Al 2 O 3 is crucial to prevent it from exceeding the optimal range (3 to 4). Otherwise, the composition mixture can promote the crystallization of competitive phases, such as zeolite L and/or W [2,20]. The SiO 2 /Al 2 O 3 ratio was found to affect the crystallization behavior, such as nucleation rate, crystal purity and intensity, and application performance [1,2,4,5].…”

“…Moreover, SDA can accelerate the nucleation and crystallization phase. As an example, for TMAOH, the hydroxide anion within it will provide the necessary alkalinity to facilitate the formation of anionic silicates, thus expediting the rate of dissolution of silicate and aluminate [3,7,20,21,28,30]. Additionally, the authors in [7] reported that providing an abundant amount of SDA will create high supersaturation conditions and steric stabilization of proto-nuclei, which are the critical factors in forming zeolite nanoparticles without aggregation [30].…”

“…Additionally, the authors in [7] reported that providing an abundant amount of SDA will create high supersaturation conditions and steric stabilization of proto-nuclei, which are the critical factors in forming zeolite nanoparticles without aggregation [30]. Determination of the exact amount of SDA needed in synthesizing zeolite, especially ERI-type zeolite, is crucial because erionite (ERI) intergrowth crystals will not form effectively if the system contains a large amount of cation [7,13,20,21].…”

“…Materials 2021, 14, x FOR PEER REVIEW 12 of 14 amount of SDA needed in synthesizing zeolite, especially ERI-type zeolite, is crucial because erionite (ERI) intergrowth crystals will not form effectively if the system contains a large amount of cation [7,13,20,21].…”