A Review on the Catalytic Acetalization of Bio-renewable Glycerol to Fuel Additives

Abstract

The last 20 years have seen an unprecedented breakthrough in the biodiesel industry worldwide leads to abundance of glycerol. Therefore, the economic utilization of glycerol to various value-added chemicals is vital for the sustainability of the biodiesel industry. One of the promising processes is acetalization of glycerol to acetals and ketals for applications as fuel additives. These products could be obtained by acid-catalyzed reaction of glycerol with aldehydes and ketones. Application of different supported heterogeneous catalysts such as zeolites, heteropoly acids, metal-based and acid-exchange resins have been evaluated comprehensively in this field. In this review, the glycerol acetalization has been reported, focusing on innovative and potential technologies for sustainable production of solketal. In addition, the impacts of various parameters such as application of different reactants, reaction temperature, water removal, utilization of crude-glycerol on catalytic activity in both batch and continuous processes are discussed. The outcomes of this research will therefore significantly improve the technology required in tomorrow's bio-refineries. This review provides spectacular opportunities for us to use such renewables and will consequently benefit the industry, environment and economy.

Oxidative Dehydration of Glycerol over Molybdenum- and Vanadium-Based Catalysts

“…From the intersection of the natural logarithm of the reaction rate with 1 / T (K), the apparent activation energy was calculated (Figure 7). The value obtained (57.1 kJ mol -1 ) agrees with the value obtained by Talebian-Kiakalaieh and Amin, 33 who performed the glycerol dehydration using HSiW-γ-Al 2 O 3 supported ); TOF glycerol (TAS) and TOF glycerol (BAS): TOF glycerol calculated considering TAS and BAS, respectively; Al: alumina; 10MoAl, 10VAl, 10Mo10VAl: catalysts containing molybdenum, vanadium, and molybdenumvanadium, respectively. in ZrO 2 and measured a global activation energy of 46.9 kJ mol -1 .…”

“…With exception of bimetallic material, it was observed that the TOF increases as surface area increases, according to the greater activity expected for materials with greater area available to convert glycerol. 33 When analyzing only the effect of Brønsted acid sites in the TOF, the cooperative effect between the Brønsted and Lewis sites in the acrolein formation is confirmed, since 10MoAl, even with the smallest quantity of Brønsted acid sites between supported materials, has the highest selectivity to acrolein, indicating that not only the Brønsted sites act in the acrolein formation.…”

Green Production of Glycerol Ketals with a Clay-Based Heterogeneous Acid Catalyst

“…Glycerol ketals are interesting as fuel additives (oxygenates) [20][21][22], fuel antioxidants [23] and as reactive oxygen species (ROS) scavengers able to act in-vitro and in-vivo [24]. Solketal, in particular, is known to reduce gum formation and particulate emissions, enhance fuel flow in cold conditions, improve stability towards oxidation, and boost octane number when it is added to gasoline, which contributes to reducing the environmental impact (the LD50 for fish is higher than 3100 ppm for solketal, while for MTBE it is 1000 ppm) [25]. [19]).…”

An Efficient Acetalization Method for Biomass‐Derived Furfural with Ethanol Using γ‐Al2O3‐Supported Catalysts

“…Based on DRIFTS results, we propose a possible reaction mechanism of Ni 1.5 Rh 1.5 /γ‐Al 2 O 3 ‐catalyzed acetalization for FFR and two ethanol molecules containing active α‐hydrogen atoms, as shown in Figure . First, the nickel center of Ni 1.5 Rh 1.5 /γ‐Al 2 O 3 polarizes the C=O bond of FFR; thus, the coordination of the oxygen atom of carbonyl to Ni(0) center forming Ni δ+ ‐(η 1 ‐O,C‐FFR) species can enhance the carbonyl's electrophilicity step in this case . Simultaneously, rhodium center of Ni 1.5 Rh 1.5 /γ‐Al 2 O 3 reacts with the alcohol (Step 1, Figure ), promoting a hydride transfer to the oxygen atom of the furfural carbonyl and forming a rhodium‐ethoxide intermediate (Step 2, Figure ).…”

“…First, the nickel center of Ni 1.5 Rh 1.5 / γ-Al 2 O 3 polarizes the C=O bond of FFR; thus, the coordination of the oxygen atom of carbonyl to Ni(0) center forming Ni δ + -(η 1 -O,C-FFR) species can enhance the carbonyl's electrophilicity step in this case. [51] Simultaneously, rhodium center of Ni 1.5 Rh 1.5 / γ-Al 2 O 3 reacts with the alcohol (Step 1, Figure 6), promoting a hydride transfer to the oxygen atom of the furfural carbonyl and forming a rhodium-ethoxide intermediate (Step 2, Figure 6). The protonated carbonyl group undergoes the nucleophilic attack of O atom of the ethanol [52] and subsequently, a second molecule of ethanol is added to the rhodium center (Step 3, Figure 6).…”