Enhanced fluorine-doped tin oxide immobilized on polyurethane foam for crude glycerol photoconversion to value-added product

Abstract

The abundant production of crude glycerol from biodiesel transesterification has raised significant environmental concerns, underscoring the need to convert crude glycerol into value-added products. Such conversions offer economic benefits and contribute significantly to environmental preservation. However, impurities in crude glycerol impede its direct application and necessitate costly purification processes. In response to this challenge, our study explores the feasibility of directly converting crude glycerol into value-added derivatives through photocatalysis using a fluorine-doped tin oxide (FTO) catalyst immobilized on polyurethane foam (PU) as a supporting material. This investigation aims to assess the potential of FTO-PU photocatalyst foam for achieving high crude glycerol conversion and product selectivity. FTO-PU synthesis involved a simple mixture method, combining pre-weighed FTO powder during the PU preparation process. Characterization techniques, including X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscope – Energy Dispersive X-ray (SEM-EDX), Thermogravimetric analysis (TGA), and Brunauer-Emmett-Teller (BET) analysis, were employed to evaluate the FTO-PU foam. FTO is evenly distributed on PU foam, obstructing intrinsic PU pores, leading to a smaller surface area for FTO-PU than FTO catalysts. Despite the decreased surface area and pore size, the FTO-PU catalyst demonstrated remarkable performance, achieving a high conversion of crude glycerol (94%) and high selectivity to ethyl acetate (86%) with a corresponding yield of 81%. Several critical parameters were evaluated: light power (30 W, 50 W, 70 W, 90 W, 120 W), reaction time (30 min, 60 min, 90 min, 120 min, 150 min), glycerol concentration (10 wt%, 15 wt%, 20 wt%) and FTO loading into PU (1%, 2%, 3%). Optimal conditions were determined as 2% FTO loading, 70W light intensity, 60 minutes reaction time, and 10 wt% crude glycerol concentration. Even after six cycles, the FTO-PU catalyst foam exhibited significant conversion efficiency value (%) and selectivity value (%), indicating its stability and reusability. A comparative evaluation of FTO-PU catalysts in the photoconversion of crude glycerol has elucidated the substantial role of FTO and PU components in achieving high conversion rates and selectivity. When evaluating FTO-PU catalysts with pure glycerol, it becomes evident that the conversion and selectivity are higher than crude glycerol, underscoring the influence of impurities on the product conversion process. Nonetheless, it is remarkable to highlight that crude glycerol exhibits significant conversion rates and selectivity, particularly when employing FTO-PU catalysts. This is attributed to FTO's capability to facilitate C-O and C-C bond cleavage without leaching active sites when integrated with PU foam. Ultimately, the immobilized FTO-PU foam proves promising for efficient crude glycerol conversion and is a foundation for developing advanced materials in photocatalytic systems.