Calcium-modified hierarchically porous aluminosilicate geopolymer as a highly efficient regenerable catalyst for biodiesel production

Abstract

A new class of highly active solid base catalysts for biodiesel production was developed by creating hierarchically porous aluminosilicate geopolymer with affordable precursors and modifying the material with varying amounts of calcium. For the catalysts containing $8 wt% Ca, almost 100% conversion has been achieved in one hour under refluxing conditions with methanol solvent, and the high catalytic activity was preserved for multiple regeneration cycles. Temperature-programed desorption studies of CO 2 indicate that the new base catalyst has three different types of base sites on its surface whose strengths are intermediate between MgO and CaO. The detailed powder X-ray diffraction (PXRD) and Xray photoelectron spectroscopic (XPS) studies show that the calcium ions were incorporated into the aluminosilicate network of the geopolymer structure, resulting in a very strong ionicity of the calcium and thus the strong basicity of the catalysts. Little presence of CaCO 3 in the catalysts was indicated from the thermogravimetric analysis (TGA), XPS and Fourier transform infrared spectroscopy (FT-IR) studies, which may contribute to the observed high catalytic activity and regenerability. The results indicate that new geopolymer-based catalysts can be developed for cost-effective biodiesel production.

Biodiesel Processing Using Sodium and Potassium Geopolymer Powders as Heterogeneous Catalysts

“…Only a few mixed or doped oxide systems presented similar or better performances when tested in such mild conditions. Sharma et al [13] achieved high yields (> 95%) by using shorter times (1 h) and with lower amounts of calcium geopolymer catalysts. Nevertheless, those authors used a methanol to oil ratio of 165:1, equivalent to 5418% of methanol, which is completely impractical for proper industrial use.…”

“…The microstructure of geopolymers is temperature dependent: an amorphous structure is present at low temperatures, while heat treatments above~500-700 • C lead to (partially) crystalline structures [11]. Geopolymers have been recently investigated as potential heterogeneous catalysts for biodiesel production [12][13][14][15]. The catalyst's specific surface area is relevant for the reactions using heterogeneous catalysts because it represents the catalytic site's accessibility, and for mesoporous materials, the surface area can be large.…”

Synthesized Geopolymers Adsorb Bacterial Proteins, Toxins, and Cells

“…GPs have a xerogel-like network structure made up of 20-40 nm-sized nanoparticles (Kriven et al, 2004;Dinesh et al, 2014) that have chemical compositions, local chemical structures, and surface characteristics similar to those of zeolites (Kriven et al, 2004;Nel et al, 2009). In addition, GPs can be specifically tailored to control porosity in meso/macroscale, physicochemical properties, and functionality (Dinesh et al, 2014;Sharma et al, 2015). Porous GPs with exposed nanostructures have been developed for emerging applications such as drug delivery (Jamstorp et al, 2011) catalysis (Sharma et al, 2015), and antibacterial activity (O'Connor et al, 2010).…”

Fly Ash-Based Geopolymers as Sustainable Bifunctional Heterogeneous Catalysts and Their Reactivity in Friedel-Crafts Acylation Reactions

“…In the field of heterogenous catalysis, in particular, various catalytically active sites, acidic, basic and redox active centres, can be generated within the geopolymer framework by ion-exchange, allowing their use in a wide range of catalytic applications. Clay-based geopolymers as supports for various catalytically active transition metals and nanoparticles have recently been reported for different applications [7][8][9][10][11]. More recently, clay-based geopolymers acting as true solid acid catalysts, exploiting inherent acid sites in their structure, have been developed for fine chemical applications [12,13].…”