Synthesis of Template-Free ZSM-5 from Rice Husk Ash at Low Temperatures and Its CO₂ Adsorption Performance

Abstract

In this paper, a green synthesis method for ZSM-5 zeolite is explored to reduce the synthesis cost, environmental hazard, and reaction temperatures. For the ZSM-5 samples prepared at low temperatures, the influence of factors such as the hydrothermal temperature, crystallization time, and the number of seeds is systematically investigated. The adsorption isotherm of CO 2 is used for fitting analysis of adsorption models and determination of the adsorption selectivity. The results show that the best one among the three samples presents the highest CO 2 adsorption capacity of 2.39 mmol/g at 273 K and 15 bar. It is prepared with a hydrothermal temperature of 393 K, crystallization time of 7 days, and a seed crystal of 1 wt %. The dual-site Langmuir model can well describe the experimental data, indicating that double adsorption sites rather than the simple single-layer adsorption are dominant in samples. As the pressure increases, the adsorption capacity calculated by the model is much lower than the actual value with a deviation index of 12.5%. At a pressure of 1 bar, the optimal selectivity is attained with sample L-20, viz., CO 2 /N 2 of 34.3 and CO 2 /O 2 of 70.2. The green synthesis method reported in this research can be used to successfully prepare ZSM-5 zeolite, and it shows excellent CO 2 adsorption performance. In addition, the use of low-cost raw materials and template-free synthesis methods will facilitate the large-scale application of green synthesis processes in the future.

CO2adsorption performance of template free zeolite A and X synthesized from rice husk ash as silicon source

“…37 The major disadvantages of using organic template agent are it is not environment friendly and is noneconomical and it also requires additional heat treatment to remove the template agent. 26,38 To our knowledge, this study is one among the few reports on the preparation of zeolite NaA and NaX with a large surface area from rice husk ash and also having a better CO 2 adsorption performance. The main results of the present study are (i) conversion of the waste rice husk into an environmentally friendly silicon source and used it for the synthesis of zeolites.…”

“…37 The major disadvantages of using organic template agent are it is not environment friendly and is non-economical and it also requires additional heat treatment to remove the template agent. 26,38…”

“…The silica sources used such as fumed silica, colloidal silica, silicic acid, and silicon alkoxides are environmentally hazardous and expensive. 26,27 In the literature, it is reported that synthesis of zeolite used in industry using the above mentioned silica source may cost up to 40% of the total production cost. 28 Hence, alternative low cost and environmentfriendly silica sources such as clay minerals (smectite, sepiolite, kaolin, palygorskite, attapulgite, vermiculite, etc.…”

Zeolite ZSM‐5 synthesized from natural silica sources and its applications: a critical review

“…Because the major components of fly ash are silica and alumina that are chemically comparable to the components of zeolite, several studies have focused on converting fly ash to ZSM‐5 zeolite 80‐82 . Rice husk ash is an agricultural by‐product with a high content of amorphous SiO 2 that can be collected when the husks are treated with alkali solutions 84,87 . Natural clays or minerals (such as kaolin, diatomite, rectorite, among others) are often employed to efficiently produce ZSM‐5 zeolite.…”

“…To overcome these issues, various mesoporous agents have been used to form the ZSM‐5 structure, including monosaccharides and disaccharides (such as glucose and sucrose), which are low‐cost mesoporous agents that can be adapted into a green approach to introduce secondary mesopores into the zeolite structure 68,78,110 . Some studies have utilized alcohol, 111,112 mesoporous carbon, 113,114 inorganic ions, 115 and anionic surfactants 116 to synthesize ZSM‐5 zeolite, while other investigations have claimed a template‐free synthesis of ZSM‐5 69,87,117‐119 . In particular, a recent study employed sugarcane residues, an inexpensive biomass‐based source, as crystal growth modifiers to considerably reduce the quantity of organic template tetrapropylammonium hydroxide (TPA‐OH) required to synthesize ZSM‐5 zeolite 120 .…”