Modelling of ethanol pyrolysis in a commercial CVD reactor for growing carbon layers on alumina substrates

Abstract

Chemical vapour deposition (CVD) is widely used for preparation of pyrolytic carbons from various precursors. The prediction of deposition kinetics requires deep understanding of all transport phenomena involved. In this work, we perform the computational modelling of ethanol pyrolysis in a commercial CVD reactor (a tube furnace). The reactor is employed for growing carbon layers on alumina substrates. The inlet gas flow is produced by evaporating azeotrope ethanol/water mixture and mixing it with inert gas (argon). The modelling is performed in 3D and 2D statements using Marinov mechanism with 57 species participating in 383 reactions. The heat and species transport is taken into account with temperature dependent physical properties. It is shown that the inlet gas velocity in the 2D statement should be corrected for a meaningful comparison with the 3D case. A good agreement is found between species mole fractions at the substrate position for 3D and 2D statements at low volume flow rates, while at high flow rates some deviations are observed. The temperature at the substrate position is found to be lower than at the reactor wall due to inflow of a colder gas. The main pyrolysis products at moderate temperatures (around 900°C) are water, ethylene, hydrogen, carbon monoxide, and methane. With increasing temperature, the mole fractions of hydrogen, acetylene, and carbon monoxide increase, while those of water and methane become smaller. With increasing ethanol/water volume flow rate, the mole fractions of ethanol and pyrolysis products saturate at some constant values due to incomplete thermal decomposition of ethanol in the reactor volume. The rise of argon flow rate leads to the decrease of pyrolysis products mole fractions due to decrease of residence time. The obtained results can be employed for simulating and analyzing pyrolysis processes in realistic CVD reactors with complex geometry as well as for the development of coupled gas phase and surface reaction model of carbon layer deposition on nanoporous substrates.

Defect-Induced Adsorption Switching (p- to n- Type) in Conducting Bare Carbon Nanotube Film for the Development of Highly Sensitive and Flexible Chemiresistive-Based Methanol and NO2 Sensor

“…It has been reported in the literature that during the decomposition of ethanol at 1200 °C, the following three major steps are involved: (i) initial formation of lower-molecular-weight hydrocarbons (i.e., CH 4 , C 2 H 4 , C 2 H 6 , C 6 H 6 , etc.) and (ii) later on their recombination to produce larger hydrocarbons and polycyclic aromatic hydrocarbon (PAH) and (iii) further pyrolysis of PAH forms carbon soot. , The weight losses of the bare CNT aerogel sample in different temperature zones (Figure ) are analyzed as follows: (i) there is a 3% weight loss at low temperature ∼265/335 °C may be due to the release of adsorbed moisture and volatile organic components and (ii) the major weight loss observed between 400 and 680 °C might be due to carbonization of amorphous carbon (hydrocarbon and PAH) and curing of CNT defects present in the bare CNT aerogel sample. Therefore, bare CNT aerogel film consists of amorphous carbon (hydrocarbon/PAH/soot) along with a network of CNTs.…”

Experimental and Simulation Research on the Preparation of Carbon Nano-Materials by Chemical Vapor Deposition

“…CFD simulation is thus an auxiliary means for reactor design and process optimization, as well as a tool for rational interpretation of experimental data. Therefore, CFD simulation can be successfully used for design and optimization, providing a favorable method for computer-aided advanced CVD deposition [196][197][198]. Zhao et al [194] also performed modeling to predict the effects of process parameters on carbon nanotube growth by CVD at ambient pressure using a simplified 2D geometry model.…”

“…CFD simulation is thus an auxiliary means for reactor design and process optimization, as well as a tool for rational interpretation of experimental data. Therefore, CFD simulation can be successfully used for design and optimization, providing a favorable method for computer-aided advanced CVD deposition [ 196 , 197 , 198 ].…”

Universal map of gas-dependent kinetic selectivity in carbon nanotube growth

“…Despite the claim that the growth rate difference is the key for selective growth methods [16,26], one-by-one measurements show that metallic (m-) and semiconducting (s-)SWCNTs exhibit a similar growth rate without a clear chirality dependence, and the growth rate significantly differs within the same chirality [22,24]. This confusion may arise from complicated decomposition of precursors [27,28]. Since the decomposed products include several carbon sources, as well as etching agents that remove carbon from the catalyst [26,29], the growth kinetics cannot be accurately captured without considering these opposing effects.…”