New Task-Specific and Reusable ZIF-like Grafted H₆P₂W₁₈O₆₂ Catalyst for the Effective Esterification of Free Fatty Acids

Abstract

The catalytic esterification of free fatty acids is an important reaction pathway for chemical synthesis and biodiesel production, wherein efficient heterogeneous catalysts are sought to replace mineral acids. Herein, the esterification of oleic acid together with some familiar fatty acids is demonstrated with methanol over a heterogeneous heteropolyacid-functionalized zeolite imidazolate framework [H 6−n P 2 W 18 O 62 n− /ZIF(H n His.) +n ]. This new heterogeneous catalyst (named as HPA/ ZIF(His.) throughout the text) with an average particle size of 80 nm was prepared via condensation of histamine with zinc chloride and characterized by means of Fourier transform infrared (FT-IR), X-ray diffraction (XRD), UV−vis, energy-dispersive X-ray spectrometry, Brunauer−Emmett−Teller, thermogravimetric analysis (TGA), inductively coupled plasma -optical emission spectrometry (ICP-OES), and scanning electron microscopy. According to the performed characterizations, an HPA loading of 40.5 wt % is obtained for HPA/ZIF(His.) from ICP-OES analysis. Moreover, a typical type-IV isotherm with similar adsorption−desorption properties as seen for ZIF-8 is attained. In addition, TGA measurement confirms less stability of HPA/ZIF(His.) compared to that of pure ZIF(His.). The catalytic performance of the nanomaterial is evaluated with respect to temperature, catalyst loading, and methanol/oleic acid ratio and leads to a high yield of methyl ester (>90%) under reflux for 4 h. The preliminary kinetic studies confirm a pseudo-first-order kinetic model for the esterification of oleic acid. To explore the scope of the HPA/ZIF(His.) catalyst in methyl ester production, other free fatty acids with various chain lengths are also successfully tested. Although the nanocatalyst loses a part of its activity during reuse, however, it is stable over at least four recycles as confirmed by XRD and FT-IR. Eventually, the response surface methodology (RSM) is used as a statistical modeling approach to get the best-optimized reaction conditions compared to the performed single-variable benchmarking experiments. Therefore, the central composite design (CCD) and RSM attained a platform to determine the relationship among the reaction time, acid/methanol molar ratio, and catalyst dosage.

UV-visible light-induced photochemical synthesis of benzimidazoles by coomassie brilliant blue coated on W–ZnO@NH2nanoparticles

“…However, observation of a high adsorption capacity at a relatively high pressure ( P / P 0 > 0.8) suggests the coexistence of meso- and macro-pores. 41 The pore size distribution of W–ZnO was calculated by the BJH method in the range of 1–100 nm ( Fig. 6b ).…”

Methyl Oleate Synthesis by TiO2 Photocatalytic Esterification of Oleic Acid: Optimisation by Response Surface Quadratic Methodology, Reaction Kinetics and Thermodynamics

“…The difference between them is the order of the forward (esterification) and the backward reaction (hydrolysis). Based on literature findings, free fatty acid esterification by heterogeneous catalysis was satisfactorily described by the HSE1HN, [45] HSE1H2, [57] and HSE2H2, [66,72] HSE1H2, [73] and HSE2H2 models, [74,75] respectively. The Langmuir-Hinshelwood (L-H) kinetic model was as the fifth model that considers a heterogeneous system with complete miscibility between reagents and a heterogeneous catalyst with active homogeneous sites.…”

Experimental and molecular dynamics simulation study on the delivery of some common drugs by ZIF‐67, ZIF‐90, and ZIF‐8 zeolitic imidazolate frameworks

“…The principle crystalline phase involved reflections at 7.3 , 10.1 , 12.8 , 17.5 , and 19.1 attributed to the (011), (002), ( 112), (222), and (123) planes, respectively, (JCPDS, 89-3739). [34] Fourier transform infrared (FT-IR) spectrum of ZIF-8 showed distinct bands at 1575-1700 cm À1 , ascribed to the C═N stretching within the imidazole ring (Figure 3b). [38,39] Bands in the spectral regions of 500-1350 and 1350-1500 cm À1 are, respectively, due to bendings and other stretches in the imidazole ring.…”

“…[38,39] Bands in the spectral regions of 500-1350 and 1350-1500 cm À1 are, respectively, due to bendings and other stretches in the imidazole ring. [34] Scanning electron microscopy (SEM) image of the synthesized ZIF-8 showed an inhomogeneous distribution of crystallites ranging from 30 to 300 nm with a platelet-like morphology (Figure 3c). Figure 3d shows the elemental survey by X-ray photoelectron spectroscopy (XPS), which confirms the presence of the ZIF-8 framework elements including Zn, C, N, and O.…”

“…ZIF-8 was prepared and characterized according to the previous publication with minor modifications. [33,34] Nanometer-sized ZIF-8 crystals were synthesized by a simple solvothermal method by mixing a warm methanol solution (20 ml) of 0.12 g of zinc nitrate hexahydrate Zn (NO 3 ) 2 Á6H 2 O with 0.42 g of 2-methylimidazole (Hmim). Noteworthy, the two solutions were filtered by a filter paper before mixing.…”