Engineering the Surface Chemistry and Morphology of Polymeric Carbon Nitrides Towards Greener Heterogeneous Catalysts for Biodiesel Synthesis

Abstract

Biodiesel remains one of the most promising alternatives to replace fossil fuel‐derived petrodiesel. Nonetheless, conventional biodiesel synthesis relies on homogeneous alkali‐based catalysts that involve long and tedious purification steps , increasing biodiesel production costs. Heterogeneous catalysts have emerged as promising alternatives to circumvent these drawbacks, as they can easily be recovered and reused. Herein, polymeric carbon nitride dots and nanosheets are synthesized through a solid‐phase reaction between urea and sodium citrate. Their morphology and surface chemistry are tuned by varying the precursor's ratio, and the materials are investigated as catalysts in the transesterification reaction of canola oil to biodiesel. A conversion of > 98% is achieved using a 5 wt% catalyst loading, oil to methanol ratio of 1:36 at 90 °C for 4 h, with the performance maintained over at least five reuse cycles. In addition, the effect of the transesterification reaction parameters on the reaction kinetics is evaluated, which follows a pseudo‐first‐order (PFO) regime. Combined with a deep understanding of the catalyst's surface, these results have allowed us to propose a reaction mechanism similar to the one observed for homogenous alkali catalysts. These carbon nitride‐based nanoparticles offer a metal‐free and cost‐effective alternative to conventional homogeneous and metal‐based heterogeneous catalysts.

Exploiting the potential of calcined sodium citrate as a novel and efficient heterogeneous catalyst for biodiesel synthesis

“…Heterogeneously basic catalyzed transesterifications reported in the literature present molar ratios ranging from 1 : 6 to 1 : 36 oil to methanol. 54,55,67,68 Zhang et al 42 reported the transesterification of castor oil using a carbon-based calcium composite. A conversion of 95% was achieved with a molar ratio of 1 : 18.…”

“…It is believed that the catalytic mechanism proceeds similarly to homogeneous base-catalyzed transesterification reactions. 54,55,68 Thus, it begins with the nucleophilic attack of methanol on the electrophilic carbonyl of the ester, forming a tetrahedral intermediate zwitterion. Subsequently, a proton transfer from the intermediate to the basic sites on the catalyst surface occurs, enabling the rearrangement to eliminate the alkoxide ion and form the fatty acid methyl ester (FAME).…”

Carbon Nitride-Based Nanomaterials as a Sustainable Catalyst for Biodiesel Production

“…It is interesting to note that even at low LiK-PHI loading values, such as 0.5%, a significant conversion of 81% is obtained, followed by 1.6 and 2.7 wt % of the catalyst with 94 and 97% of conversion, respectively. de Medeiros et al also studied the catalyst loading ranging from 1 to 7 wt % for the transesterification of canola oil with methanol to produce biodiesel using CNs synthesized from different molar ratios of urea and sodium citrate . The authors showed that the catalyst loads of 1, 3, 5, and 7% have 0.41, 2.86, 97.5, and 98.0% of reaction yield, respectively.…”

“…In addition, for mpg-C 3 N 4 , symmetrical pores were recognized in its flake structure. A variety of CN-based nanomaterials have been previously studied in the literature, and all of them presented layer/flake morphology with unique characteristics. − …”

“…de Medeiros et al also studied the catalyst loading ranging from 1 to 7 wt % for the transesterification of canola oil with methanol to produce biodiesel using CNs synthesized from different molar ratios of urea and sodium citrate. 44 The authors showed that the catalyst loads of 1, 3, 5, and 7% have 0.41, 2.86, 97.5, and 98.0% of reaction yield, respectively. Here, the conversion of canola oil to biodiesel with 1.6 wt % of LiK-PHI already showed a high conversion of 94% and, therefore, this amount of the catalyst was selected and maintained for subsequent optimization steps.…”