Pengembangan Katalis Bentonit Termodifikasi Asam Silikotungsten dan Sn(II) Secara Ultrasonikasi Untuk Sintesis Butil Levulinat

Bayu Wiyantoko, Prof. Dr. rer. nat. Karna Wijaya, M.Eng; Dr. Aulia Sukma Hutama, S.Si., M.Si; Prof. Dr. Is Fatimah, M.Si.

2026 | Disertasi | S3 Ilmu Kimia

Penelitian ini bertujuan untuk menghasilkan butil levulinat (BL) menggunakan katalis Keggin asam silikotungsten (AST) tersubstitusi Sn(II) yang diimpregnasi pada bentonit. Metode ultrasonikasi berperan penting pada tahapan aktivasi asam bentonit, impregnasi AST dan SnCl2, serta esterifikasi asam levulinat (AL) dan butanol. Penelitian ini berfokus pada aktivasi asam dan aktivasi termal pada bentonit, impregnasi AST secara konvensional dan ultrasonik, serta metode esterifikasi AL secara pencampuran mekanik dan gelombang ultrasonik. Penelitian ini menerapkan prinsip kimia hijau untuk mempelajari perubahan karakter fisikokimia dan kinerja katalitik, yang meliputi konversi AL, rendemen dan selektivitas BL, serta stabilitas katalis. 

Hasil penelitian menunjukkan aktivasi asam pada bentonit yang dilanjutkan dengan impregnasi Keggin AST secara ultrasonik memberikan perbedaan karakter fisikokimia di antaranya perbedaan rasio d001/d110 yang lebih besar dibandingkan metode konvensional, dispersi Keggin AST yang lebih merata, total keasaman katalis yang meningkat, konversi 100% substrat AL, selektivitas BL 98%, pelindian AST yang minimum selama 6 jam reaksi esterifikasi pada temperatur 120 °C, serta stabilitas katalis hingga siklus kelima pada uji reusabilitas. Hasil ini memberikan bukti interaksi yang kuat antara bentonit teraktivasi asam dengan Keggin AST. 

Penggantian proton secara parsial pada katalis AST/bentonit teraktivasi dengan Sn(II) memberikan pengaruh pada tingkat keasaman yang bertambah meskipun stabilitas katalis menurun. Katalis Sn2AST/bentonit teraktivasi berhasil mengonversi AL 100?n menghasilkan rendemen BL 97% pada temperatur 80 °C selama 100 menit dengan bantuan gelombang ultrasonik. Eksperimen reusabilitas menunjukkan tingkat stabilitas katalis Sn2AST/bentonit teraktivasi hingga siklus ketujuh dengan tetap mempertahankan struktur katalis serta persentase konversi yang tinggi. Gelombang ultrasonik yang digunakan pada sintesis katalis maupun produksi BL adalah pendekatan prinsip kimia hijau yang memberikan hasil nyata dan signifikan terkait aktivitas katalitik, efisiensi proses, dan keberlanjutan. 

This study aims to develop an efficient and sustainable catalytic system for the production of butyl levulinate (BL) via the esterification of levulinic acid (LA) with butanol, employing a Sn(II)-substituted silicotungstic acid (STA) catalyst supported on bentonite. Ultrasonication was utilized throughout the catalyst preparation and reaction stages, including bentonite acid activation, STA and SnCl? impregnation, and the esterification process. The effects of acid activation, thermal activation, conventional and ultrasound-assisted STA impregnation, as well as mechanical and ultrasonic-assisted esterification methods, were systematically evaluated. These strategies were designed based on green chemistry principles to elucidate their impact on catalyst physicochemical properties and catalytic performance, including LA conversion, BL yield, BL selectivity, and catalyst stability and heterogeneity through reusability and hot-filtration tests.

The findings reveal that the combination of bentonite activation and ultrasound-assisted impregnation of STA produces a catalyst with markedly improved physicochemical and catalytic properties. Relative to the conventionally prepared catalyst, the ultrasound-assisted catalyst displayed a higher d001/d110 ratio, superior STA dispersion, and greater total acidity. Consequently, the catalyst achieved complete LA conversion with 98% BL selectivity. In addition, the catalyst exhibited negligible active-species leaching during the 6 h reaction and retained its catalytic performance over five reuse cycles. These results highlight the strong interaction between bentonite and STA, which effectively stabilizes the active species and enhances both catalytic efficiency and durability.

Moreover, the partial substitution of protons in STA by Sn(II) on acid-activated bentonite enhanced the acidity of the catalyst by generating additional active sites, albeit with a modest decrease in catalyst stability. Nevertheless, the Sn?STA/activated bentonite catalyst displayed remarkable catalytic efficiency, delivering complete LA conversion and a 97% BL yield at a relatively low reaction temperature of 80 °C within only 100 min under ultrasound-assisted conditions. Stability assessments confirmed that the catalyst preserved its structure and catalytic performance throughout seven consecutive reuse cycles, highlighting its potential as a robust and sustainable catalyst for BL production. The integration of ultrasonic-assisted catalyst synthesis and esterification not only aligns with the principles of green chemistry but also provides significant enhancements in catalytic activity, process efficiency, and sustainability. 

Kata Kunci : lempung bentonit, Keggin asam silikotungsten, timah, asam levulinat, butil levulinat, ultrasonikasi