Aldol Condensation of Cyclohexanone and Furfural in Fixed-Bed Reactor

Abstract

Aldol condensation reaction is usually catalysed using homogeneous catalysts. However, the heterogeneous catalysis offers interesting advantages and the possibility of cleaner biofuels production. Nowadays, one of the most used kinds of heterogeneous catalysts are hydrotalcites, which belong to a group of layered double hydroxides. This paper describes the aldol condensation of cyclohexanone (CH) and furfural (F) using Mg/Al mixed oxides and rehydrated mixed oxides in order to compare the catalyst activity after calcination and rehydration, as well as the possibility of its regeneration. The catalysts were synthesized by calcination and subsequent rehydration of the laboratory-prepared and commercial hydrotalcites, with Mg:Al molar ratio of 3:1. Their structural and chemical properties were determined by several analytical methods (inductively coupled plasma analysis (ICP), X-ray diffraction (XRD), diffuse reflectance infrared Fourier transform spectroscopy (DRIFT), specific surface area (BET), thermogravimetric analysis (TGA), temperature programmed desorption (TPD)). F-CH aldol condensation was performed in a continuous fixed-bed reactor at 80 °C, CH:F = 5:1, WHSV 2 h−1. The rehydrated laboratory-prepared catalysts showed a 100% furfural conversion for more than 55 h, in contrast to the calcined ones (only 24 h). The yield of condensation products FCH and F2CH was up to 68% and 10%, respectively. Obtained results suggest that Mg/Al mixed oxides-based heterogeneous catalyst is suitable for use in the aldol condensation reaction of furfural and cyclohexanone in a fixed-bed reactor, which is an interesting alternative way to obtain biofuels from renewable sources.

Recent Advances in the Catalytic Upgrading of Biomass Platform Chemicals Via Hydrotalcite-Derived Metal Catalysts

“…Svobodová et al [27] performed similar work and used furfural and cyclohexanone in the aldol condensation reaction to produce high energy-density aviation fuel. The reaction between them can be used to produce long chain ketones containing 11 or 16 carbon atoms.…”

Green Synthesis of 3-Hydroxybutyraldehyde from Acetaldehyde Catalyzed by La-Ca-Modified MgO/Al2O3

“…They found that the formation of carbon deposits led to the catalytic deactivation. The used catalyst contained a significant amount of carbon (14.9 wt%), while the precursor only contained 2 wt% [39,40]. In addition, the presence of impurities in the reactants or the formation of inactive metal hydroxides by by-product H 2 O may probably reduce the activity of the catalyst.…”

Preparation of β‐hydroxy Ketones via High Efficient Aldol Reaction over Nickel Oxide Nanoparticles as a Powerful and Reusable Heterogeneous Catalyst: Central Composite Design

“…These catalysts have several limitations, including possible corrosion, production of large amounts of contaminated wastewater, and high‐cost related to the catalyst recovery [14] . In contrast, heterogeneous catalysts brings some advantages such as simple catalyst recovery, reduction of effluent streams and by‐products, and high selectivity [15,16] . Various heterogeneous catalysts such as modified zeolite, [17] magnetically retrievable catalyst, [18] metal oxide, [19,20] mixed metal oxides, [21–23] and so on have been used in aldol condensations.…”

“…[14] In contrast, heterogeneous catalysts brings some advantages such as simple catalyst recovery, reduction of effluent streams and by-products, and high selectivity. [15,16] Various heterogeneous catalysts such as modified zeolite, [17] magnetically retrievable catalyst, [18] metal oxide, [19,20] mixed metal oxides, [21][22][23] and so on have been used in aldol condensations. Among them, metal oxides can cover the most proceedings and catalyst families used in variant industries.…”