Thermal Modification Effect on Supported Cu-Based Activated Carbon Catalyst in Hydrogenolysis of Glycerol

Heterogeneous Catalysts for Conversion of Biodiesel-Waste Glycerol into High-Added-Value Chemicals

The valuable products produced from glycerol transformation have become a research route that attracted considerable benefits owing to their huge volumes in recent decades (as a result of biodiesel production as a byproduct) as well as a myriad of chemical and biological techniques for transforming glycerol into high-value compounds, such as fuel additives, biofuels, precursors and other useful chemicals, etc. Biodiesel has presented another challenge in the considerable increase in its byproduct (glycerol). This review provides a recent update on the transformation of glycerol with an exclusive focus on the various catalysts’ performance in designing reaction operation conditions. The different products observed and cataloged in this review involved hydrogen, acetol, acrolein, ethylene glycol, and propylene glycol (1,3-propanediol and 1,2-propanediol) from reforming and dehydration and hydrogenolysis reactions of glycerol conversions. The future prospects and critical challenges are finally presented.

Potential heterogeneous nano-catalyst via integrating hydrothermal carbonization for biodiesel production using waste cooking oil

Hydrothermal carbonization (HTC) provides alternatives technique to produce a nanosize activated carbon from biomass with a high surface area. Herein, this study we prepared empty fruit bunch-based activated carbon (EFBHAC) using HTC technique. The activated carbon was then functionalized with K₂CO₃ and Cu(NO₃)₂ to produce bifunctional nano-catalyst for simultaneous esterification-transesterification of waste cooking oil (WCO). The physicochemical properties were performed i.e. N₂ sorptions analysis, TPD-CO₂/NH₃, FESEM, EDX, FTIR and XRD analysis. The results revealed that produced EFBHAC possessed a BET surface area of 4056.17 m² g^-1, with pore volume of 0.827 cm³ g^-1 and 5.42 nm of pore diameter resulting from hydrolysis, dehydration decarboxylation, aromatization and re-condensation during HTC process. Impregnation of EFBHAC with K₂CO₃ and Cu(NO₃)₂ granted a high amount of basicity and acidity of 9.21 mmol g^-1 and 31.41 mmol g^-1, respectively, accountable to high biodiesel yield of 97.1%, produced at the optimum condition of 5 wt% of catalyst loading, 12:1 of methanol to oil molar ratio at 70 °C for 2 h. More than 80% of biodiesel was produced after the 5th cycle depicted the good reusability. The transformations from WCO to biodiesel was confirmed via ¹H NMR, FTIR and TGA analysis. Fuel properties revealed kinematic viscosity of 3.3 mm² s^-1, cetane number of 51, flash point of 160.5 °C, cloud and pour point of 11 °C and -3 °C, respectively. These results show the excellent potential of waste materials to prepare bifunctional nano-catalysts to produce higher biodiesel yield which has potential to be commercialized.

Glycerol Valorization over ZrO2-Supported Copper Nanoparticles Catalysts Prepared by Chemical Reduction Method

Copper nanoparticles (NPs) and ZrO2-supported copper NPs (Cu NPs/ZrO2) were synthesized via a chemical reduction method applying different pH (4, 7 and 9) and evaluated in a glycerol dehydration reaction. Copper NPs were characterized with transmission electron microscopy (TEM) and UV–vis spectroscopy. Transmission electron microcopy (TEM) results revealed a homogeneous distribution of copper NPs. A hypsochromic shift was identified with UV–vis spectroscopy as the pH of the synthesis increased from pH = 4 to pH = 9. Zirconia-supported copper NPs catalysts were characterized using N2 physisorption, X-ray diffraction (XRD), TEM, X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR), temperature-programmed desorption of ammonia (NH3-TPD) and N2O chemisorption. The presence of ZrO2 in the chemical reduction method confirmed the dispersion of the copper nanoparticles. X-ray diffraction indicated only the presence of tetragonal zirconia patterns in the catalysts. XPS identified the Cu/Zr surface atomic ratio of the catalysts. TPR patterns showed two main peaks for the Cu NPS/ZrO2 pH = 9 catalyst; the first peak between 125 and 180 °C (region I) was ascribed to more dispersed copper species, and the second one between 180 and 250 °C (region II) was assigned to bulk CuO. The catalysts prepared at pH = 4 and pH = 7 only revealed reduction at lower temperatures (region I). Copper dispersion was determined by N2O chemisorption. With NH3-TPD it was found that Cu NPs/ZrO2 pH = 9 exhibited the highest total quantity of acidic sites and the highest apparent kinetic constant, with a value of 0.004 min−1. The different pH applied to the synthesis media of the copper nanoparticles determined the resultant copper dispersion on the ZrO2 support, providing active domains for glycerol conversion.

Recent Advances in Glycerol Catalytic Valorization: A Review

Once a biorefinery is ready to operate, the main processed materials need to be completely evaluated in terms of many different factors, including disposal regulations, technological limitations of installation, the market, and other societal considerations. In biorefinery, glycerol is the main by-product, representing around 10% of biodiesel production. In the last few decades, the large-scale production of biodiesel and glycerol has promoted research on a wide range of strategies in an attempt to valorize this by-product, with its transformation into added value chemicals being the strategy that exhibits the most promising route. Among them, C3 compounds obtained from routes such as hydrogenation, oxidation, esterification, etc. represent an alternative to petroleum-based routes for chemicals such as acrolein, propanediols, or carboxylic acids of interest for the polymer industry. Another widely studied and developed strategy includes processes such as reforming or pyrolysis for energy, clean fuels, and materials such as activated carbon. This review covers recent advances in catalysts used in the most promising strategies considering both chemicals and energy or fuel obtention. Due to the large variety in biorefinery industries, several potential emergent valorization routes are briefly summarized.