An Overview of Biodiesel Production via Calcium Oxide Based Catalysts: Current State and Perspective

Abstract

Biodiesel is a clean, renewable, liquid fuel that can be used in existing diesel engines without modification as pure or blend. Transesterification (the primary process for biodiesel generation) via heterogeneous catalysis using low-cost waste feedstocks for catalyst synthesis improves the economics of biodiesel production. Heterogeneous catalysts are preferred for the industrial generation of biodiesel due to their robustness and low costs due to the easy separation and relatively higher reusability. Calcium oxides found in abundance in nature, e.g., in seashells and eggshells, are promising candidates for the synthesis of heterogeneous catalysts. However, process improvements are required to design productive calcium oxide-based catalysts at an industrial scale. The current work presents an overview of the biodiesel production advancements using calcium oxide-based catalysts (e.g., pure, supported, and mixed with metal oxides). The review discusses different factors involved in the synthesis of calcium oxide-based catalysts, and the effect of reaction parameters on the biodiesel yield of calcium oxide-based catalysis are studied. Further, the common reactor designs used for the heterogeneous catalysis using calcium oxide-based catalysts are explained. Moreover, the catalytic activity mechanism, challenges and prospects of the application of calcium oxide-based catalysts in biodiesel generation are discussed. The study of calcium oxide-based catalyst should continue to be evaluated for the potential of their application in the commercial sector as they remain the pivotal goal of these studies.

New Catalysts for Biodiesel Production under Supercritical Conditions of Alcohols: A Comprehensive Review

“…Although most heterogeneous alkaline catalysts have been successful in increasing biodiesel production from various feedstocks, there are some obstacles to its adoption for commercial purposes. For instance, the reaction is slower compared to homogeneous alkaline catalysts and requires a high temperature (can reach 900 °C) to calcine the catalyst as a final preparation step [25] . Regardless of these issues, Tan et al [26] .…”

“…For instance, the reaction is slower compared to homogeneous alkaline catalysts and requires a high temperature (can reach 900 °C) to calcine the catalyst as a final preparation step. [25] Regardless of these issues, Tan et al [26] considered the environmental impact along with the low cost of the catalyst among the most important factors classifying heterogeneous catalysts as an alternative to biodiesel production. In their work, they mainly focused on the recent percentage content of waste cooking oil methyl esters (WCOMEs) as a comparison between homogeneous (NaOH, KOH) and heterogeneous (CaO derived from ostrich and chicken eggshells) catalysts in the transesterification reaction.…”

A Short Review on Catalyst, Feedstock, Modernised Process, Current State and Challenges on Biodiesel Production

“…However, leaching of metal ions from the surface of the CaO into the biodiesel was observed [153,154] The second class of base catalysts, e.g., mixed metal oxide catalysts, have also received some attention for this application as they offer improved basicity and mechanical strength compared to single metal oxides [155]. Biodiesel yields greater than 80% were achieved at temperatures of 60-64.5 • C when mixed metal oxides or bimetallic oxide catalysts such as Al 2 O 3 -SnO, Al 2 O 3 -ZnO [156], CaO-CeO 2 , CaZrO 3 [157], and CaO-MgO [158] were used. However, it was observed that the activity of the CaO-MgO catalyst on biodiesel production using vegetableoil-based feedstock reduced significantly after four successive trials [25].…”

Use of NaNO3/SiAl as Heterogeneous Catalyst for Fatty Acid Methyl Ester Production from Rapeseed Oil

“…Among simple metal oxides, transesterification using CaO [11][12][13][14][15][16][17][18][19][20] and MgO [7,17,21,22] has been widely researched, as both oxides are relatively cheap and present an acceptable activity. Other metal oxides have been studied, such as SrO [17,19,23], BaO [17], ZnO [19], TiO 2 [19], ZrO 2 [19], CeO 2 [24], or La 2 O 3 [24].…”