Search Results (48)

The development of sustainable catalysts from renewable resources is a key challenge for reducing the cost of industrial catalytic processes and waste valorization. In this work, low-cost heterogeneous active catalysts were prepared based on pyrolyzed forest residues, forming valuable porous support materials (Biochar) able to efficiently accommodate the highly active heteropolyacid HPW₁₂. Further, magnetic functionality was incorporated in the novel catalytic materials by the impregnation of NiFe₂O₄. The resulting magnetic composites were characterized by FTIR-ATR, SEM-EDS, ICP-OES, BET, XRD, potentiometric titration and magnetometry. The novel HPW₁₂@NiFe₂O₄@Biochar composites were able to valorize the glycerol to produce the fuel additive solketal with high conversion and high selectivity after only 3 h of reaction via acetalization reaction with acetone. The biochar catalytic composite prepared from cork presented higher pore size than the same prepared from forest biomass. This property was crucial to achieve the best conversion (89%) and the highest solketal selectivity (96%). Additionally, reusability capacity was verified, supporting the potential of the cork-pyrolyzed-based composites as potential low-cost catalytic material to produce fuel additives, such as solketal, under sustainable conditions. This may contribute one step further toward a future with greener energy, increasing the viability of biodiesel industry waste. Full article

A series of novel functional polycarbonates, specifically poly(solketal glycidyl ether carbonate-co-propylene carbonate)s with varying compositions, were synthesized through the ring-opening copolymerization of solketal glycidyl ether, propylene oxide, and carbon dioxide. The reaction was catalyzed by rac-(salcy)Co^IIIX complexes with bis(triphenylphosphine)iminium salts as co-catalysts, achieving high selectivity. The resulting terpolymers exhibited number-average molecular weights ranging from 2 × 10⁴ to 1 × 10⁵ and a narrow, bimodal molecular weight distribution, with dispersities of 1.02–1.07 for each mode. Interestingly, the addition of a small amount of water to the reaction mixture yielded a terpolymer with a unimodal molecular weight distribution and a dispersity of 1.11. Subsequent acidic hydrolysis of the solketal protective groups produced poly(glyceryl glycerol carbonate-co-propylene carbonate). All terpolymers were amorphous, with T_g near or below room temperature. The hydroxyl-functional polycarbonates underwent cyclodepolymerization under milder conditions compared to polycarbonates with protected hydroxyl groups. Full article

Solketal is an important chemical product with widespread applications, and the raw materials glycerol and acetone are inexpensive, making it highly economically viable. The glycerol-acetone condensation reaction is a typical acid-catalyzed reaction. Traditional homogeneous acidic catalysts cause significant environmental pollution and are difficult to recover. Herein, PEG-800 was used as an additive, and a one-pot process was employed to prepare a series of aluminum phosphate catalysts (xP-Al-O) with different P/Al molar ratios. The physical and chemical properties of the prepared xP-Al-O catalysts were thoroughly investigated using XRD, FTIR, SEM, Py-FTIR, BET, and NH₃ (CO₂)-TPD methods. The results indicated that different P/Al molar ratios indeed affect the catalyst structure, and all prepared xP-Al-O samples exist in the form of amorphous aluminum phosphate, with weak acidic sites dominating the surface. The prepared catalysts were investigated for their catalytic behavior in the acetalization reaction of glycerol and acetone. The 1.1P-Al-O catalyst exhibited the highest acetone glycerol acetal yield and demonstrated good catalytic stability. Full article

The role of p-benzoquinone (BQ) as a photocatalyst in the synthesis of solketal under UV irradiation has been studied, along with the combined use of BQ/TiO₂ P25 as a photocatalytic system for the process. The presence of the O₂/O₂^−• redox couple is essential for the reaction to take place. However, experiments with p-benzoquinone as a superoxide radical scavenger failed, with the opposite effect of enhancing the reaction being observed. It was found that p-benzoquinone and oxygen compete for photogenerated electrons in the conduction band of titania. A redox equilibrium between p-benzoquinone and hydroquinone (H₂Q), mediated by the O₂/O₂^−• system, was identified as a key factor in enabling the reaction. Furthermore, EPR spin-trapping experiments confirmed the presence of the carbon-centered radical 2-hydroxypropan-2-yl, which was determined to be the main radical species involved in the process. Either acetone or 2-propanol can generate this radical, with the BQ/H₂Q redox system being pivotal in the formation of the hemiacetal intermediate. This intermediate is subsequently converted into the final acetal (solketal), with H₂Q acting as a photoacid through an excited-state proton transfer (ESPT) mechanism. The photoacid behavior of hydroquinone was confirmed using pyridine as a basic probe, as the formation of hydroquinone–pyridine adducts was detected by Raman spectroscopy. Full article

This study investigates the improvement of combustion performance, engine emissions, energy, exergy, and thermodynamic efficiencies by adding oxygenated additives to diesel/biodiesel blends. Five different fuel mixtures (D100, D80B20, D50B50, D30B50S20, and D30B50G20) were tested in a diesel engine. The positive effects of the additives on engine efficiency became evident. In terms of combustion performance, the maximum in-cylinder pressure was observed with D100; however, a decrease of 11.51% was noted with the D50B50 mixture, while an increase of 7.51% was achieved with the addition of butyl diglycol. The addition of butyl diglycol also increased the heat release rate by 34.36%. Regarding exhaust emissions, the D30B50G20 fuel produced the lowest CO emissions (0.02%), while HC emissions decreased by 80% compared to D100. Smoke opacity was also found to be lower with D30B50G20. However, these additives led to a 2.65% decrease in certain performance metrics. On the other hand, the sustainability analysis revealed that the most efficient fuel mixture was D30B50G20. Full article

The current paper reports the asymmetric synthesis of a focused library of enantiostructured triacylglycerols (TAGs) constituting a potent drug of the NSAID type (ibuprofen or naproxen) along with a pure bioactive n-3 polyunsaturated fatty acid (PUFA) intended as a novel type of prodrug. In this second category, a TAG prodrug of the terminal sn-1 or sn-3 position of the glycerol skeleton is acylated with a single saturated medium-chain fatty acid (C6, C8, C10, or C12), and another with the drug entity; the PUFA (EPA or DHA) is located in the sn-2 position. This was accomplished by a six-step chemoenzymatic approach, two of which were promoted by a lipase, starting from enantiopure (R)- and (S)-solketals. The highly regioselective immobilized Candida antarctica lipase (CAL-B) played a crucial role in the regiocontrol of the synthesis. The most challenging key step involved the incorporation of the drugs that were activated as oxime esters by the lipase exclusively in the terminal position of glycerol that is protected as a benzyl ether. All combinations, a total of 32 such prodrug TAGs, were prepared, isolated, and fully characterized, along with 24 acylglycerol intermediates, obtained in very-high-to-excellent yields in the majority of cases. Full article

Glycerol is a biogenic waste that is generated in both the biodiesel and oleo-chemical industries. The value addition of surplus glycerol is of utmost importance for making these industries economically profitable. In line with this, glycerol is converted into glycerol carbonate, a potential candidate for the industrial production of polymers and biobased non-isocyanate polyurethanes. In addition, glycerol can also be converted into solketal, which is the protected form of glycerol with a primary hydroxyl functional group. In this contribution, we developed a microwave-assisted solvent and catalyst-free method for converting solketal into solketal carbonate. Under conventional heating conditions, the reaction of solketal with dimethyl carbonate resulted in 70% solketal carbonate in 48 h. However, under microwave heating, 90% solketal carbonate was obtained in just 30 min. From the perspective of sustainability and green chemistry, biomass-derived heterogeneous catalysts are gaining importance. Therefore, in this project, several green catalysts, such as molecular sieves (MS, 4Å), Hβ-Zeolite, Montmorillonite K-10 clay, activated carbon from groundnut shell (Arachis hypogaea), biochar prepared from the pyrolysis of sawdust, and silica gel, were successfully used for the carbonyl transfer reaction. The obtained solketal carbonate was thoroughly characterized by ¹H NMR, ¹³C NMR, IR, and MS. The method presented here is facile, clean, and environmentally benign, as it eliminates the use of complicated procedures, toxic solvents, and toxic catalysts. Full article

This report describes the asymmetric synthesis of a focused library of enantiopure structured triacylglycerols (TAGs) comprised of a single saturated fatty acid (C6, C8, C10, C12, C14 or C16), a pure bioactive n-3 polyunsaturated fatty acid (EPA or DHA) and a potent drug (ibuprofen or naproxen) intended as a novel type of prodrug. One of the terminal sn-1 or sn-3 positions of the glycerol backbone is occupied with a saturated fatty, the remaining one with a PUFA, and the drug entity is present in the sn-2 position. This was accomplished by a six-step chemoenzymatic approach starting from enantiopure (R)- and (S)-solketals. The highly regioselective immobilized Candida antarctica lipase (CAL-B) played a crucial role in the regiocontrol of the synthesis. All combinations, a total of 48 such prodrug TAGs, were prepared, isolated and fully characterized, along with 60 acylglycerol intermediates, obtained in very high to excellent yields. Full article

The use of activated carbon-based catalysts for the production of solketal and γ-valerolactone (GVL), two products of interest for biorefinery processes, was investigated. Activated carbons (ACs) were prepared by chemical activation of olive stones, an agricultural byproduct, using H₃PO₄ to olive stone mass impregnation ratios (IRs) of 1:1 and 3:1, and under nitrogen or air atmosphere. The ACs showed S_BET values of 1130–1515 m²/g, owing to the presence of micropores (0.45–0.60 cm³/g). The use of an IR of 3:1 delivered a wider pore size distribution, with mesopore volume increasing up to 1.36 cm³/g. XPS confirmed the presence of phosphorus groups with surface concentrations of 2.2–3.2 wt% strongly bonded the AC surface through C-O-P bonds. The ACs were tested as acid catalysts for the acetalization of glycerol in a stirred batch reactor at temperatures of 30–50 °C, glycerol concentrations of 1.5 to 3.4 mol/L, and 1–3 wt% catalytic loading. The catalytic activity was clearly correlated with the quantity of C-O-P acid groups determined by TPD, which increased when ACs were prepared under air atmosphere. The AC prepared with IR 3:1 under air achieved full selectivity to solketal, with activation energy of 49 kJ/mol and conversion of up to 70%, matching the equilibrium conversion value under the optimum reaction conditions. A bifunctional catalyst was prepared over this AC by deposition of 5 wt% zirconium and tested in stirred batch reactor for the hydrogenation of levulinic acid (LA) using isopropyl alcohol (IPA) as solvent and H₂ donor, with LA:IPA ratios from 1:1 to 1:7 and temperatures between 160–200 °C. The catalyst reached full LA conversion and a GVL yield higher than 80% after only 12 h at 200 °C. A test conducted in the presence of water revealed that it was an inhibitor of the reaction. The identification of isopropyl levulinate as an intermediate suggests that the most likely reaction pathway was dehydration, followed by hydrogenation and cyclization, to obtain GVL. Kinetic modelling of the results showed a value of 42 kJ/mol for the hydrogenation step. The reusability of the catalyst was tested for five consecutive reaction cycles, maintaining most of the activity and selectivity towards GVL. Full article

This study explored the preparation of pure silica KIT-6, as well as KIT-6 materials with an enhanced concentration of surface OH groups through aluminum incorporation or NH₄F treatment. These materials with various contents of surface OH groups were subsequently modified via the post-synthesis grafting of sulfonic groups using 3-mercaptopropyltrimethoxysilane as a precursor, followed by oxidation to introduce acidic sites. The catalysts were thoroughly characterized using XRD, nitrogen adsorption/desorption, SEM-EDS, TEM, and FT-IR techniques to confirm their structural and chemical properties. The catalytic activity of acid-functionalized mesoporous silicas of the KIT-6 structure was further evaluated in the acetalization of glycerol to produce solketal. The results demonstrated a significant influence of the surface OH group concentration and acidic site density on catalytic performance, with KIT-6_F_SO₃H showing the highest efficiency in glycerol-to-solketal conversion. This study provides valuable insights into the design of efficient catalytic systems for the valorization of biodiesel-derived glycerol into high-value chemicals, offering a sustainable approach to waste glycerol utilization. Full article

This study describes the production of solketal esters from used soybean cooking oil (USCO) via enzymatic hydroesterification. This process consists of the complete hydrolysis of USCO into free fatty acids (FFAs) catalyzed by crude lipase extract from Candida rugosa (CRL). The resulting FFAs were recovered and utilized as the raw material for an esterification reaction with solketal, which was achieved via an open reaction. For this purpose, lipase Eversa^® Transform 2.0 (ET2.0) was immobilized via physical adsorption on treated epicarp particles from Acrocomia aculeata (macauba), a lignocellulosic residue. A protein loading of 25.2 ± 1.3 mg g⁻¹ with a support and immobilization yield of 64.8 ± 2.5% was achieved using an initial protein loading of 40 mg g⁻¹ of support. The influence of certain parameters on the esterification reaction was evaluated using a central composite rotatable design (CCRD). Under optimal conditions, a FFAs conversion of 72.5 ± 0.8% was obtained after 150 min of reaction at 46 °C using a biocatalyst concentration of 20% wt. and a FFAs–solketal molar ratio of 1:1.6. The biocatalyst retained 70% of its original activity after ten esterification batches. This paper shows the conversion of two agro-industrial waste into valuable materials (enzyme immobilization support and solketal esters). Full article

Solketal, a widely used glycerol-derived solvent, can be efficiently synthesized through heterogeneous catalysis, thus avoiding the significant product losses typically encountered with aqueous work-up in homogeneous catalysis. This study explores the catalytic synthesis of solketal using solid acid catalysts derived from recovered carbon blacks (rCBs), which are obtained through the pyrolysis of end-of-life tires. This was further converted into solid acid catalysts through the introduction of acidic functional groups using concentrated H₂SO₄ or 4-benzenediazonium sulfonate (BDS) as sulfonating agents. Additionally, post-pyrolytic rCB treated with glucose and subsequently sulfonated with sulfuric acid was also prepared. Comprehensive characterization of the initial and modified rCBs was performed using techniques such as elemental analysis, powder X-ray diffraction, thermogravimetric analysis, a back titration method, and both scanning and transmission electron microscopy, along with X-ray photoelectron spectroscopy. The catalytic performance of these samples was evaluated through the batch mode glycerol acetalization to produce solketal. The modified rCBs exhibited substantial catalytic activity, achieving high glycerol conversions (approximately 90%) and high solketal selectivity (around 95%) within 30 min at 40 °C. This notable activity was attributed to the presence of -SO₃H groups on the surface of the functionalized rCBs. Reusability tests indicated that only rCBs modified with glucose demonstrated acceptable catalytic stability in subsequent acetalization cycles. The findings underscore the potential of utilizing end-of-life tires to produce effective acid catalysts for glycerol valorization processes. Full article

The valorization of the large amount of crude glycerol formed from the biodiesel industry is of primordial necessity. One possible direction with high interest to the biorefinery sector is the production of fuel additives such as solketal, through the acetalization of glycerol with acetone. This is a chemical process that conciliates high sustainability and economic interest, since solketal contributes to the fulfillment of a Circular Economy Model through its use in biodiesel blends. The key to guarantee high efficiency and high sustainability for solketal production is the use of recovery and recyclable heterogeneous catalysts. Reported works indicate that high yields are attributed to catalyst acidity, mainly the ones containing Brönsted acidic sites. On the other hand, the catalyst stability and its recycling capacity are completely dependent of the support material and the acidic sites incorporation methodology. This review intends to conciliate the information spread on this topic and indicate the most assertive strategies to achieve high solketal production in short reaction time during various reaction cycles. Full article

In this work, a series of vanadium-substituted phosphomolybdic acids were synthesized and tested as the catalysts for the synthesis of solketal, a green fuel bioadditive, from the condensation reaction of glycerol with acetone. The objective was to demonstrate that an easily synthesizable solid catalyst can efficiently promote glycerol condensation with acetone at room temperature. The activity of pristine heteropolyacid (i.e., H₃PMo₁₂O₄₀) and its vanadium-substituted cesium salts (Cs_3+nPMo_12-nV_nO₄₀; n = 0–3) was evaluated in condensation reactions carried out at room temperature. Among the catalysts tested, Cs₄PMo₁₁VO₄₀ was the most active and selective towards a five-member ring solketal isomer (dioxolane). A high yield of solketal (i.e., 95% conversion and 95% selectivity to solketal) was achieved in glycerol condensation with acetone at room temperature within a short reaction time (2 h). The influence of the main reaction parameters, such as the acetone–glycerol molar ratio, catalyst load, and reaction temperatures, was investigated. The greatest activity of the Cs₄PMo₁₁VO₄₀ catalyst was correlated to its greatest acidity. Full article

The composites of heteropolyacids (H₃PW₁₂, H₃PMo₁₂) incorporated into amine-functionalized silica materials were used for the first time as heterogeneous catalysts in the valorization of glycerol (a major waste from the biodiesel industry) through acetalization reaction with acetone. The polyoxotungstate catalyst H₃PW₁₂@AptesSBA-15 exhibited higher catalytic efficiency than the phosphomolybdate, achieving 97% conversion and 97% of solketal selectivity, after 60 min at 25 °C, or 91% glycerol conversion and the same selectivity, after 5 min, performing the reaction at 60 °C. A correlation between catalytic performance and catalyst acidity is presented here. Furthermore, the stability of the solid catalyst was investigated and discussed. Full article