Pyrolytic Behavior of Long-Chain Alkyl Quaternary Ammonium Bromide Inside Nanopores

Yanhui Niu,Quan Wan,Shuguang Yang,Wenbin Yu

doi:10.3389/fenrg.2021.799237

Abstract

The pyrolytic behavior of organic matter inside nanopores was studied by simultaneous thermogravimetric/differential scanning calorimetry analyzer coupled with Fourier transform infrared spectroscopy (STA/TG-FTIR). Nanoporous silica was prepared by a hydrothermal method using long-chain alkyl quaternary ammonium bromide (CnTAB, n = 12, 14) as a template. The pyrolytic behavior of CnTAB inside nanopores with different diameters was investigated and compared with that of CnTAB inside and outside nanopores. The results showed that the pyrolytic removal process consisted of the following features: 1) CnTAB underwent carbon chain decomposition and oxidation; 2) the DSC exothermal peak of CnTAB came mainly from its oxidative combustion, and the oxidative combustion temperature decreased with increasing pore size; 3) the CnTAB inside nanopores underwent crystallization–amorphous state phase transition, and CnTAB got trapped inside the calcined nanopores. In addition, the pyrolytic behavior of CnTAB inside the calcined nanopores was found to be similar to that of the uncalcined nanopores. This study aims to understand the storage and transformation processes of organic hydrocarbons under nanopore-confinement effect.

Highlights

Nanoporous materials play an important role in the storage and conversion of unconventional energy (Yu et al, 2021), adsorption and separation of biomolecules (Kumar et al, 2018), and catalytic pyrolysis of hydrocarbons (Yuan et al, 2013)
This study shows that the interaction between the inorganic nanoporous silica and organic CnTAB has a significant effect on the pyrolysis of CnTAB
The pyrolytic behavior of the CnTAB inside nanopores indicates that the weight loss process of pristine CnTAB has no DSC exothermic peak, and only the sharp endothermic peak in an air atmosphere was observed

Summary

Introduction

Nanoporous materials play an important role in the storage and conversion of unconventional energy (Yu et al, 2021), adsorption and separation of biomolecules (Kumar et al, 2018), and catalytic pyrolysis of hydrocarbons (Yuan et al, 2013). Most studies on the mechanism of organic–inorganic interfaces have focused on small organic molecules in single size nanopore, but the physicochemical properties of Pyrolytic Behavior of CnTAB Inside Nanopores organic macromolecules have not been well studied. The pyrolysis behavior of organic macromolecules inside nanopores is related to the pathway of the cracking of natural petroleum organic matter inside nanopores to form petroleum and natural gas small hydrocarbon molecules (Cao et al, 2021; Leushina et al, 2021). The pyrolysis behavior of organic matter can explain the pyrolysis temperature, pyrolysis mechanism, and the storage and conversion of unconventional energy inside the nanopore. In the energy field, most of the research on the pyrolysis behavior of organic macromolecules inside nanopores has focused on natural nanoporous minerals (Bu et al, 2017; Du et al, 2021) with complex compositions, uncontrollable structures, and heterogeneous pore sizes. The long-chain alkyl quaternary ammonium bromide CnTAB was selected for comparison as organic matter, because of alkyl chains and ammonium ions, which are typical groups of natural organic matter in source rocks

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Conclusion