Hierarchical Zeolites from Production Sand Waste as Catalysts for CO2 to Carbon Nanotubes CNTs: Exploration and Production Sustainability
Authors: Watcharasing Sunisa , Wattanakit Chularat , Thivasasith Anawat , Kiattikomol Prapoj 
Published: August 2022

This project targets to convert sand waste from oil & gas production, which is typically disposed as landfill, to be the higher-value products, called "Hierarchical Zeolites". This project also explores opportunities to lower amount of sand waste to landfill and try to convert CO2 to CNTs, as part of Sustainable Development Goals. Hierarchical Zeolites is developed with nanosheets morphology to overcome limitation of conventional zeolites in terms of, 1) microporous structure improvement to enhance the mass transport through active sites, 2) longer catalyst lifetime, and 3) higher surface area. With these superior characteristics, it is popularly used in wide range of applications ranging from adsorption, separation, and ion-exchange to catalysis. In this work, the Hierarchical Zeolites are utilized as catalysts for CO2 conversion to CNTs, which is the futuristic materials. Methods,

The procedure to produce hierarchical zeolites with nanosheet morphology for ZSM-5, and Faujasite (FAU) topologies have been developed. Production sand waste is used as a silica source; after it is passed sand pretreatment and silica extraction steps, for hierarchical zeolites synthesis, to reduce their production cost. Physicochemical properties of the synthesized hierarchical zeolites are analyzed, such as surface area, porosity, topology, and textural properties. These physicochemical properties will be compared with the one obtained using the commercial silica sources. Then, the developed Hierarchical zeolites are applied as catalyst for CNTs production from CO2. The fixed bed Chemical Vapor Deposition (CVD) technique is introduced for CNTs synthesis, as its low energy cost consumption, high quality of CNTs synthesis. The physical properties of CNTs, including tube diameter, graphitic structure (ID/IG).

To prove of concept for extracting silica source as a substance for hierarchical zeolite synthesis and use as catalyst for CNTs production from CO2. Two types of hierarchical zeolites nanosheet (ZSM-5, and FAU) have been successfully synthesized from nano silica obtained froms and waste, with high yield more than 75%. The hierarchical-FAU, and hierarchical -FAU-5's performance on CNTs production from CO2 are compared together. It was found that the hierarchical-FAU provide the best catalyst for CNT production with the CNTs yield of 28.9%, the average diameter of 22.8 nm and ID/IGof 0.68. The optimal condition for hierarchical zeolites synthesis will be further applied in the prototype phase, in the 50X up-scaling. This technology is expected to lower an amount of production sand waste disposal to landfill. Moreover, the synthesized hierarchical zeolites will be further explored in other advanced reactions apart from CNTs synthesis, such as catalytic cracking.

Hierarchical zeolites from production sand waste are firstly initiated and successfully achieved in PTTEP. From these findings, information will be applied to the process design of Hierarchical zeolites synthesis in prototype, and scale-up phase.