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Structural and Catalytic Characterization of HCl-Modified Molecular Sieves for Enhanced Esterification of Free Fatty Acids

Document Type : Full research article

Authors

1 Chemical Engineering Department, Faculty of Engineering, Behbahan Khatam Alanbia University of Technology, Behbahan, Iran.

2 Department of Chemical Engineering, Faculty of Engineering, Behbahan Khatam Alanbia University of Technology

10.30473/ijac.2026.77445.1344

Abstract

In this study, the catalytic performance of commercial molecular sieves (MS) was enhanced through a systematic acid modification process using hydrochloric acid (HCl) at varying molar concentrations (0.25, 0.5, and 1.0 M). The influence of acid strength on the structural, morphological, and elemental properties of the catalysts was rigorously evaluated using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and energy-dispersive X-ray spectroscopy (EDX). Analytical results revealed that acid treatment facilitated the selective removal of extra-framework cations and induced framework dealumination, effectively modulating the Si/Al ratio and increasing surface acidity. The EDX analysis suggested an optimal Si/Al ratio of 4.5 for the 0.5 M HCl-treated sample, which maintained framework integrity while maximizing active site accessibility. The catalytic efficiency was assessed through the esterification of oleic acid for biodiesel production. The MS-0.5 M catalyst exhibited superior performance, achieving a free fatty acid (FFA) conversion of 87.57% under optimized reaction conditions (methanol-to-oil ratio of 20:1, 3 wt% catalyst, and 95 °C). In contrast, higher acid concentrations (1.0 M) resulted in structural degradation and a subsequent decline in catalytic activity. This study demonstrates that precisely controlled acid modification is a robust analytical approach for developing high-performance, stable, and cost-effective heterogeneous catalysts for sustainable biofuel synthesis.

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References
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Iranian Journal of Analytical Chemistry
Volume 12, Issue 2 - Serial Number 24
September 2025
Pages 83-93
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