Carbon Nanotube Production From Ethylene in CO2/N2 Environments

Abstract

Carbon nanotubes (CNTs) have high surface areas and excellent mechanical, electrical, and chemical properties, thus they can be useful in applications related to extraction and conversion of energy. They can be readily produced from hydrocarbon feedstocks. In this work, ethylene, the most voluminously produced hydrocarbon, was used as a CNT feedstock. It was pyrolytically decomposed at elevated temperatures (984–1130 K) to generate CNTs, by catalytic chemical vapor deposition (CVD) on stainless steel substrates. To explore possible utilization of carbon dioxide, a typical combustion byproduct, the ethylene gas was introduced to a preheated CVD reactor at the presence of various amounts of CO2, in a balance of inert nitrogen gas. The ethylene pyrolyzates were assessed at the presence/absence of catalysts and CO2 to identify the gaseous carbon growth agents. Experimental findings were also contrasted to predictions of a detailed chemical kinetic model. It was found that whereas decomposition of ethylene was somewhat inhibited by CO2 at the presence of the catalyst support, its conversion to CNTs was promoted. CNTs consistently formed at 5% CO2. Maximum yields of CNTs occurred at 1130 K, whereas highest CNT quality was achieved at 1080 K. Hydrogen and 1,3-butadiene (C4H6) were experimentally found to be the most abundant species of ethylene thermal decomposition. This was in agreement with the model, which also highlighted the importance of unimolecular hydrogen elimination.