Dehydroisomerisation of α-Pinene and Limonene to p-Cymene over Silica-Supported ZnO in the Gas Phase

Abstract

Silica-supported zinc oxide possessing acid and dehydrogenation functions is an efficient, noble-metal-free bifunctional catalyst for the environment-friendly synthesis of p-Cymene from renewable monoterpene feedstock by gas-phase dehydroisomerisation of α-pinene and limonene in a fixed-bed reactor. The reaction involves acid-catalysed terpene isomerisation to p-menthadienes followed by dehydrogenation to form p-Cymene. Dehydroisomerisation of α-pinene produces p-Cymene with 90% yield at 100% conversion at 370 °C and WHSV = 0.01–0.020 h−1. The reaction with limonene gives a 100% p-Cymene yield at 325 °C and WHSV = 0.080 h−1. ZnO/SiO2 catalyst shows stable performance for over 70 h without co-feeding hydrogen.

Synthesis of p-cymene by the electrocatalytic oxidation of α-terpinene and γ-terpinene

“…The synthesis of p -cymene from plant essential oils and their by-products is a very attractive strategy due to the resources being renewable, abundant, and readily available. Similar studies on chemicals including natural α-pinene, 5 limonene, 6 α-terpinene (α-TP), 7 γ-terpinene (γ-TP), 8 and industrial dipentene (a by-product of turpentine processing) 9,10 have been reported. Unfortunately, many problems exist in these conversions, such as the need to use precious metals or metal oxides as catalysts, long reaction times, high temperatures, and the difficult separation and purification of products.…”

Process Intensification for Sustainable Microwave-Assisted Bio p-Cymene Production from Limonene

“…Some examples have been reported in the literature for this transformation under CH . Despite the engaging results achieved, environment-impacting and harmful conditions were required; for instance, temperatures between 260 and 370 °C, residence times from a few hours to 70 h, and the employment of organic solvents and acidic-modified solids were necessary for conversion. ,,, Therefore, considering the further application of the developed protocol to biorefineries, a compromise should be established between sustainable conditions and p -cymene yields, thus ruling out these above-mentioned works in our considerations.…”

“…Finally, titanium-and silica-supported zinc oxides have also been tested. 25,26 However, the applied reaction conditions were extremely harsh and included temperatures above 300 °C, with 70 h being necessary to achieve the desired product yield. Enabling technologies were also exploited for the intensification of the p-cymene production.…”

“…Catrinescu et al have employed ion-exchanged clays as catalysts, at 150 °C for 15 min, and reported the formation of isomerization, disproportionation, and polymerization products at the same time. Finally, titanium- and silica-supported zinc oxides have also been tested. , However, the applied reaction conditions were extremely harsh and included temperatures above 300 °C, with 70 h being necessary to achieve the desired product yield. Enabling technologies were also exploited for the intensification of the p -cymene production.…”

Operationally simple electrochemical method for the conversion of acetone into high-specification jet fuel

“…This same chemistry can also be performed on p -cymene, which yields p -cresol and acetone, 30 where the cymene can be sustainably derived from α-pinene, limonene, and other terpenes. 31…”