Sulfuric acid modified clinoptilolite as a solid green catalyst for solvent-free α-pinene isomerization process

• Published in: Microporous and mesoporous materials 2021-09, Vol.324, p.111266, Article 111266
• Main Authors: Miądlicki, Piotr, Wróblewska, Agnieszka, Kiełbasa, Karolina, Koren, Zvi C., Michalkiewicz, Beata
• Format: Article
• Language: English
• Subjects: Camphene; Clinoptilolite; Green chemistry; High value-added chemicals; Isomerization; Limonene; Natural compounds; Zeolites; α-Pinene
• ISSN: 1387-1811; 1873-3093
• DOI: 10.1016/j.micromeso.2021.111266

The isomerization of α-pinene – a renewable bioresource – was investigated as a relatively simple method for the syntheses of camphene and limonene, industrially important products. The catalytic activity of H2SO4-modified clinoptilolite was evaluated without any solvent and the results show its applicability as a novel, green, reusable and promising catalyst in organic syntheses. The method is cost-effective and energy efficient because of the use of relatively low temperatures: at 30 °C and after 1 h, conversion was equal to 18%. In addition, this process has a short-time performance: 100% conversion after only 4 min at 70 °C. Camphene and limonene were the products that were formed with the highest selectivities of 50% and 30%, respectively. Clinoptilolite modified by H2SO4 solutions (0.01–2 M) as a catalyst for α-pinene isomerization has not been described up to now. The catalyst samples were characterized using various instrumental methods (XRD, FT-IR, UV–Vis, SEM, and XRF). The nitrogen sorption method was used to determine the textural parameters, and the acid-sites concentration was established with the help of the titration method. The mixtures of compounds were analyzed via gas chromatography (GC). The comprehensive kinetic modeling of α-pinene isomerization over the most active catalyst (clinoptilolite modified by 0.1 M H2SO4 solution) was performed. The first order kinetics of α-pinene conversion was found, and the value of the reaction rate constant at 70 °C was equal to 8.19 h−1. It was concluded that the high activity of the prepared modified clinoptilolite in α-pinene isomerization is a multifaceted function of textural properties, crystallinity, chemical composition, and acid-sites concentration. [Display omitted] •New concept of sustainable and ecological technology of organic syntheses•H2SO4-modified clinoptilolite is an efficient catalyst for α-pinene isomerization•Cost-effective and energy-efficient process even at low temperatures•Very fast α-pinene isomerization: 100% conversion after 4 min at 70 °C•Camphene and limonene are main products with 50% and 30% respective selectivities