Efficient One-Step Conversion of a Low-Grade Vegetable Oil to Biodiesel over a Zinc Carboxylate Metal–Organic Framework

Abstract

In this study, a metal–organic framework, namely, Zn3(BTC)2 (BTC = 1,3,5-benzenetricaboxylic acid), was solvothermally synthesized and employed as a catalyst for biodiesel production from degummed vegetable oil via a one-step transesterification and esterification reaction. The resulting Zn3(BTC)2 particles exhibit a well-defined triclinic structure with an average size of about 1.2 μm, high specific surface area of 1176 m2/g, and thermal stability up to 300 °C. The response surface methodology–Box–Behnken design (RSM–BBD) was employed to identify the optimal reaction conditions and to model the biodiesel yield in relation to three important parameters, namely, the methanol/oil molar ratio (4:1–8:1), temperature (45–65 °C), and time (1.5–4.5 h). Under the optimized reaction conditions (i.e., 6:1 methanol/oil molar ratio, 65 °C, 4.5 h), the maximum biodiesel yield reached 89.89% in a 1 wt % catalyst, which agreed very well with the quadratic polynomial model’s prediction (89.96%). The intrinsic catalytic activity of Zn3(BTC)2, expressed as the turnover frequency, was found to be superior to that of other MOF catalysts applied in the transesterification and esterification reactions. The reusability study showed that the as-synthesized Zn3(BTC)2 catalyst exhibited good stability upon three consecutive reuses without a noticeable decrease in the methyl ester yield (∼4%) and any appreciable metal leaching (<5%). Furthermore, a preliminary technoeconomic analysis showed that the total direct operating cost for the kilogram-scale production of Zn3(BTC)2 is estimated to be US$50, which may sound economically attractive.

Functionalized organic–inorganic hybrid porous coordination polymer-based catalysts for biodiesel production via trans/esterification

“…76 Alternatively, unlike T. M. M. Marso's two-step reaction, another MOF, Zn 3 (BTC) 2 (BTC = 1,3,5-benzenetricaboxylic acid), was fabricated by Lunardi et al to prepare biodiesel from degummed palm oil (DPO) via one-step trans/esterification, and the highest FAME yield was 89.89% under the optimized reaction conditions. 77 It was reported that Zn 3 (BTC) 2 emerged as a triclinic structure, possessing a large specific surface (1176 m 2 g −1 ) and reasonable thermal stability (up to 300 °C), as well as a mass of macropores and mesopores, which made it available for macromolecular substrate contacting with the Lewis acid catalytic site (Zn 2+ ) and promoted mass transport. The proposed mechanism for one-step trans/esterification is shown in Fig.…”

Engineering of Active Sites in Metal–Organic Frameworks for Biodiesel Production

“…Recently, Zn 3 (BTC) 2 MOF (BTC: 1,3,5-benzenetricarboxylate) was solvothermally synthesized and its catalytic performance was studied in the simultaneous transesterification and esterification of degummed palm oil (DPO) to FAME (biodiesel). [53] Zn 3 (BTC) 2 was first reported by Yaghi et al, consisting of zinc(II) ions coordinated to BTC ligand and water with an open-framework having voids that are decorated by coordinately unsaturated metal centers upon removal of water by heating. [54] The characterization of Zn 3 (BTC) 2 by Lunardi et al revealed the existence of a hierarchical macro/ microporous structure and abundant open metal sites which can behave as Lewis acids.…”

“…b) Comparison of the TOF value and conversion yield of Zn 3 (BTC) 2with the above commented catalysts for the transesterification and esterification reactions. Reproduced with permission [53]. Copyright 2021, American Chemical Society.…”

Efficient biodiesel production from oleic and palmitic acid using a novel molybdenum metal–organic framework as efficient and reusable catalyst

“…Heterogeneous solid base catalysts usually provide higher rates compared with the acid counterparts under milder reaction conditions. However, they cannot be directly employed for oil having more than 2 wt% FFA due to side reactions, such as saponification and hydrolysis, and decrease both the catalyst activity and the ester yield 15 . Hence, solid acid catalysts are applied when dealing with low-quality or non-edible vegetable oils containing significant quantities of FFAs and water 15 .…”

“…However, they cannot be directly employed for oil having more than 2 wt% FFA due to side reactions, such as saponification and hydrolysis, and decrease both the catalyst activity and the ester yield 15 . Hence, solid acid catalysts are applied when dealing with low-quality or non-edible vegetable oils containing significant quantities of FFAs and water 15 . Molybdenum compounds have been recognized as versatile catalysts, because of the ability of this metal to be on the solid surface in different oxidation states, ranging from Mo 6+ to metallic Mo (Mo 0 ) 16 .…”