Conversion Of Propylene Glycol Research Articles

Vapor-phase oxidation of propylene glycol-methanol mixture to methyl lactate on CeO2/Al2O3 catalyst

The vapor-phase oxidation of mixtures of propylene glycol with methanol and ethanol to methyl and ethyl lactate, respectively, on supported CeO2/Al2O3 catalyst at 210-2500С was investigated. Air oxygen and a flow reactor with a fixed catalyst bed were used. A 20% solution of propylene glycol in alcohol was supplied to the reactor inlet. Oxidation of propylene glycol in the presence of methanol occurs according to the overall reaction CH3CHOHCH2OH +O2 + СН3OH = CH3CHOHCOOСН3 +2H2O. First, hydroxyacetone is formed, which is further oxidized to pyruvic aldehyde, which adds alcohol to form a hemiacetal. Next, this hemiacetal is rearranged according to Cannizzaro into methyl lactate. At 2200C and catalyst load < 2 mmol PG/gcat/h, the selectivity for methyl lactate reached 70 wt.% at 100% propylene glycol conversion. In the presence of ethanol, the formation of a significant amount of acetaldehyde and its aldol condensation products, as well as the formation of diethoxyethane, was observed. Therefore, the selectivity for ethyl lactate at 100% propylene glycol conversion did not exceed 45%.

Modifier Effect in Silica-Supported FePO4 and Fe-Mo-O Catalysts for Propylene Glycol Oxidation.

Currently, catalytic processing of biorenewable raw materials into valuable products attracts more and more attention. In the present work, silica-supported FePO4 and Fe-Mo-O catalysts are prepared, their phase composition, and catalytic properties are studied in the process of selective oxidation of propylene glycol into valuable mono- and bicarbonyl compounds, namely, hydroxyacetone and methylglyoxal. A comparative analysis of the main routes of propylene glycol adsorption with its subsequent oxidative conversion into carbonyl products is carried out. The DFT calculations show that in the presence of adsorbed oxygen atom, the introduction of the phosphate moiety to the Fe-containing site strengthens the alcohol adsorption on the catalyst surface with the formation of the 1,2-propanedioxy (–OCH(CH3)CH2O–) intermediate at the active site. The introduction of the molybdenum moiety to the Fe-containing site in the presence of the adsorbed oxygen atom is also energetically favorable, however, the interaction energy is found by 100 kJ/mol higher compared to the case with phosphate moiety that leads to an increase in the propylene glycol conversion while maintaining high selectivity towards C3 products. The catalytic properties of the synthesized iron-containing catalysts are experimentally compared with those of Ag/SiO2 sample. The synthesized FePO4/SiO2 and Fe-Mo-O/SiO2 catalysts are not inferior to the silver-containing catalyst and provide ~70% selectivity towards C3 products, while the main part of propylene glycol is converted into methylglyoxal in contrast to the Ag/SiO2 catalyst featuring the selective transformation of only the secondary C-OH group in the substrate molecule under the studied conditions with the formation of hydroxyacetone. Thus, supported Fe-Mo-O/SiO2 catalysts are promising for the selective oxidation of polyatomic alcohols under low-temperature conditions.

Effect of organic linker substituent on catalytic activity of UiO-66 metal-organic framework in selective oxidation of propylene glycol: homolytic versus heterolytic activation of hydrogen peroxide

A family of isoreticular metal-organic frameworks, based on the UiO-66 structure with NH2-, OH-, HSO3-, and NO2-substituted terephthalic acid, are synthesized and tested as catalysts in liquid-phase oxidation of propylene glycol (PG) with hydrogen peroxide and compared with the catalytic performances of unsubstituted UiO-66. The obtained materials are characterized by X-ray diffraction, FT-IR, thermogravimetric analysis (TGA), nuclear magnetic resonance spectroscopy (1H NMR), and Fourier-transform infrared spectroscopy (FT-IR) of adsorbed CO and scanning electron microscopy (SEM) methods. Hydroxyacetone (HA) is the main product over all X-UiO-66 catalysts under the reaction conditions used. The nature of substituent drastically affects the PG conversion and the oxidant utilization efficiency. The presence of electron-withdrawing groups in the organic linker leads to preferential heterotic activation of H2O2, whereas the increase of electron density around Zr active sites, promoted by electron-donating groups, enhances the unproductive homolytic oxidant decomposition. The insertion of NO2 group results in almost double increase in the HA yield (15.5 vs. 8.8%) and hydrogen peroxide utilization efficiency (98 vs. 36%) in comparison with the reaction catalyzed by H-UiO-66. The NO2-UiO-66 can be recycled without the loss of the catalytic activity and preserves its structure after the catalytic cycle.

Vapor-phase oxidation of propylene glycol-methanol mixture to methyl lactate on CeO2/Al2O3 catalyst

The vapor-phase oxidation of mixtures of propylene glycol with methanol and ethanol to methyl and ethyl lactate, respectively, on supported CeO2/Al2O3 catalyst with 10 wt.% CeO2 content was studied. The steel flow reactor with a fixed catalyst bed (4 cm3) was used. 20 wt.% solution of propylene glycol in alcohol was fed to the reactor inlet by Waters 950 pump at LHSV= 0.5-0.8 h-1. Reaction temperature and pressure were varied in the interval of 190-250 0C and 1.3-1.8 bars respectively. Compressed air was given to the reactor inlet at the molar ratio of propylene glycol/O2 = 1. The reaction products were analyzed using gas chromatography (Agilent 7820A) and 3C NMR (Bruker Avance 400) methods. Studied oxidation of propylene glycol in the presence of methanol describes by total reaction CH3CHOHCH2OH +O2 + СН3OH = CH3CHOHCOOСН3 +2H2O At first, hydroxyacetone is formed that is further oxidized to pyruvic aldehyde, which attaches alcohol to form hemiacetal. Then, hemiacetal of methyl glyoxal rearranges into methyl lactate by Cannizzaro. At 220 0C and load on a catalyst of < 2 mmol PG/gcat/h, the selectivity towards methyl lactate reaches 70 wt.% at 100 % propylene glycol conversion. The main by-products are formed as the result of acetaldehyde transformation. Acetaldehyde could be formed at hydroxyacetone aldol decondensation. In the presence of ethanol, the formation of a significant amount of acetaldehyde and its aldol condensation products as well as the formation of diethoxyethane are observed. Therefore, ethyl lactate selectivity at 100 % propylene glycol conversion does not exceed 45 %. Supported CeO2/SiO2 contact was tested in this oxidation reaction also. However, CeO2/SiO2 provides the low, up to 25%, selectivity towards methyl lactate at full propylene glycol conversion. It was shown that at the same conditions methyl lactate is formed with higher selectivity then ethyl lactate. The high methyl lactate yield up to 70 wt.% could be obtained via vapor-phase oxidation of 20% mixture of propylene glycol with methanol by air oxygen on supported CeO2/Al2O3 catalyst at 210 - 220°С and at time contact of 3-4 seconds.

Ag-Pd nanoparticles prepared by laser ablation for selective oxidation of propylene glycol to lactic acid

Silver/palladium composite nanoparticles (NPs) obtained by pulsed laser ablation in liquid (PLAL) technique catalyze oxidation of propylene glycol (PG) to lactic acid (LA) in alkaline media. The PLAL technique allows obtaining silver/palladium NPs with different silver/palladium molar ratio. Addition of palladium increases PG conversion (up to 52%) and LA selectivity (up to 88%). The reaction temperature and silver/palladium molar ratio strongly affects the catalytic activity of the silver/palladium composite NPs.

Propylene glycol oxidation with hydrogen peroxide over Zr-containing metal-organic framework UiO-66

Zirconium-based metal–organic framework UiO-66 catalyzes oxidation of propylene glycol (PG) using hydrogen peroxide as green oxidant. Hydroxyacetone (HA) is the main oxidation product, while the main side product is acetic acid (AcA). The nature of the solvent drastically affects PG adsorption, oxidant utilization efficiency and product yields. The best catalytic performance (85% selectivity towards HA at ca. 10% PG conversion) was achieved with water–acetonitrile (3/7 (v/v)) mixture as a solvent. Additives of radical chain scavengers produce a rate-inhibiting effect, suggesting radical chain mechanism of the oxidation process. The PG oxidation over UiO-66 proceeds without leaching of the active metal into solution, and the catalysis has a truly heterogeneous nature. The catalyst can be recycled without significant loss of activity and selectivity and retains its structure during at least five reuses.

On the Production of Hydrogen from Bio-Oil: A Representative Study Using Propylene Glycol

In a bio-refinery focused on fast pyrolysis, hydrogen (H2) producible from reforming of the aqueous fraction of bio-oil with steam can be utilized for upgrading pyrolytic lignin into fuels by hydrotreatment. In this work, propylene glycol (PG) was chosen as a typical compound symbolizing higher polyols in the bio-oil aqueous fraction. Catalytic processing of PG into H2 at low temperature (T = 500°C) was investigated using several commercial catalysts such as Ni/Al2O3, Ru/Al2O3, Ru/C, Pt/C, and Pd/C in a laboratory-scale fixed-bed reactor. The efficiencies of the catalysts were presented as selectivity to CO, CO2, CH4 and H2, and PG conversion into gaseous phase. Wide ranges of temperature (300–500°C), W/FO (18.6–92.9 g h/mol), and S/C ratio (5.6–12.7 mol/mol) were examined using Ni/Al2O3. At T = 500°C, H2 selectivity (73.7%) and PG conversion (66.2%) were maximized using ratios of catalyst mass to molar flow rate of PG (W/FO) = 18.6 g h/mol and steam to carbon (S/C) = 12.7 (10 wt% PG solution). It was found that Ni/Al2O3 demonstrates stable operation for at least 6 h of time-on-stream. Finally, a plausible reaction pathway for PG reforming was proposed.

Propylene glycol oxidation with tert-butyl hydroperoxide over Cr-containing metal-organic frameworks MIL-101 and MIL-100

Chromium-based metal-organic frameworks MIL-101 and MIL-100 catalyzed oxidation of propylene glycol (PG) using tert-butyl hydroperoxide (TBHP) as oxidant. The main oxidation product was hydroxyacetone (HA) while minor oxidation products were acetaldehyde and acetic acid. The best results (88% selectivity toward HA at ca. 10% PG conversion) were achieved over MIL-101 using acetonitrile as solvent. In water, CC bond cleavage products predominated. MIL-101 and MIL-100 revealed different behavior toward adsorption of PG from MeCN solution, which affected their catalytic performances. Additives of radical chain scavengers produced a strong rate-inhibiting effect whereas the presence of molecular oxygen accelerated the reaction, suggesting radical chain mechanism of the oxidation process. The oxidation of PG over MIL-101 at 50°C proceeded without leaching of the active metal into solution and the catalysis had the truly heterogeneous nature. The MIL-101 catalyst could be recycled without significant loss of activity and selectivity and preserved its structure during, at least three, catalytic cycles.

New catalysts for carboxylation of propylene glycol to propylene carbonate via high-throughput screening.

High throughput methodologies screened 81 different metal salts and metal salt combinations as catalysts for the carboxylation of propylene glycol to propylene carbonate, as compared to a 5 mol% Zn(OAc)2/p-chlorobenzene sulfonic acid benchmark catalyst. The reactions were run with added acetonitrile (MeCN) as a chemical water trap. Two new catalysts were thereby discovered, zinc trifluoromethanesulfonate (Zn(OTf)2) and zinc p-toluenesulfonate. The optimal reaction parameters for the former catalyst were screened. Zn(OTf)2 gave an overall propylene carbonate yield of greater than 50% in 24 h, twice as large as the previous best literature yield with MeCN as a water trap, with 69% selectivity and 75% conversion of propylene glycol at 145 °C and 50 bar CO2 pressure.

Optimization of in situ hydrogenolysis of glycerol to propylene glycol and ethanol

Alternative ways of converting crude glycerol from biodiesel production to value-added products are in high demand to solve the issue of increasing glycerol surplus. Propylene glycol (PG) and ethanol are examples of valuable chemicals that had been successfully produced from glycerol through in situ hydrogenolysis in our previous studies. This study aimed to determine the optimum conditions for maximizing the yields of PG and ethanol through in situ hydrogenolysis of glycerol. Depending on the targeted products, the optimum process conditions, obtained through statistical analysis and experimentally confirmed with a high PG yield of 47.2%mol, were 220°C, 51 min and 1.0:1.0 water to glycerol mass ratios (WGMR). However, the complex reactions involved in the production of ethanol lead to inconclusive results for the optimization. The key to maximizing the PG yield from in situ hydrogenolysis of glycerol is to operate the system at mild reaction temperatures (e.g., 220°C) at which the further conversion of PG to ethanol is slowed. Meanwhile, a 1:1 mixture of water and glycerol minimizes the side reactions and improves the PG formation. The ethanol production alone from glycerol does not seem economically justified for large scale production due to its low yield. However, co-production of PG and ethanol might be a viable solution.

An Investigation into the Conversion of Propylene Glycol to 2,4-dimethyl-1,3-dioxolane over an Acid Catalyst Using Gas Chromatography

In the presence of an acid catalyst, PG react reversibly with acetaldehyde to form 2,4-dim-ethyl-1,3-dioxolane (24DMD). The effects of different operational parameters on PG conversion had been analyzed in paper, parameters included temperature, reaction time, amount of catalyst and aqueous acetaldehyde/PG molar ratio. Under optimal condition, 85% conversion of PG in aqueous solution was achieved within 180 min of reaction. The analysis of PG was conducted by gas chromatograph. Furthermore, reaction followed the second-order reaction kinetics, and the reaction rate constant was found to be 29.68min-1.

Degradation of propylene glycol wastewater by Fenton's reagent in a semi-continuous reactor

Propylene glycol (PG) wastewater seriously threatens aquatic lives and causes health damage to human beings. Several early studies for PG degradation focused on biological process, which usually proceeds at a slow rate and is often inhibited by substances which are toxic to the microorganisms. In this paper, Fenton method was exploited for treating PG wastewater in a semi-continuous reactor with adding ferrous sulfate (FeSO 4) and hydrogen peroxide (H 2O 2) to the reactor, respectively. Semi-continuous applications of H 2O 2 and Fe 2+ could result in low steady state of HO , which would minimize HO scavenging and further increase PG oxidation efficiency. Under the optimal conditions, 99.1% of PG conversion and 88.4% of COD removal were achieved. In addition, pseudo-first-order model, in which the concentration of HO was assumed to remain constant, was established. The intrinsic activation energy of HO with PG, calculated by Arrhenius-equation was 35.18 kJ/mol. The intrinsic reaction rate constant of HO with PG around optimal conditions was 1.56–1.72 × 10 8 M −1 s −1. After Fenton's reaction, PG molecules could not be thoroughly oxidized to H 2O and CO 2. Intermediates, such as aldehyde, acetone, methanol, formic acid, and acetic acid, were checked by GC–MS, which all had a very low content and toxicity. As a homogeneous catalytic oxidation, Fenton oxidation is a feasible treatment for PG wastewater for its low toxicity, low price, and high efficiency.

Synthesis, characterization and catalytic behavior of AlTf/UVM-7 as new green catalysts for the glycols etherification reactions

Bimodal porous Al–UVM-7 system materials with different Si-to-Al ratios were prepared using the Atrane route. These were converted in strong acid heterogeneous AlTf-based catalysts after the treatment with methanolic solutions of triflic acid. The materials so obtained were used as catalysts for the conversion of ethylene glycol (EG) and propylene glycol (PG) with octanol under solvent-free conditions. The process is selective to short ethoxylated structures resulting in the corresponding monoethers. While the conversion of EG and PG was very high (>94%) irrespective of the support characteristics, 1-octanol was transformed only in low degree (3–35%), and its conversion depends on both the Si/Al molar ratio and the catalyst texture (Al–UVM-7 or AlTf–UVM-7). Recyclable experiments showed the catalysts are stable and the reuse occurred without changes in the chemical composition.

Vapor-Phase Catalytic Synthesis of 2-Methylpyrazine over a Nanocrystalline Ferrite Catalyst

Vapor-phase synthesis of 2-methylpyrazine (2-MP), from propylene glycol (PG) and ethylenediamine (ED), has been studied over ferrite catalysts in a temperature range of 523−773 K. The performance of MnFe2O4 was observed to be better than that of Zn1-xMnxFe2O4 (x = 0, 0.25, 0.5, 0.75). The reaction was determined to be almost stoichiometric, with an ∼98% conversion of PG. A maximum yield of 80% of 2-MP could be obtained at a temperature of 723 K, using a feed of ED, PG, and water (ED:PG:H2O molar ratio of 1:1:2) over MnFe2O4. The influence of reactant molar ratio, reaction temperature, weight hourly space velocity (WHSV), and time on stream (TOS) on the product yield has been studied. Catalyst characterization was made using X-ray diffraction (XRD), surface area measurement and ammonia desorption methods, scanning electron microscopy that has been coupled with energy-dispersive X-ray analysis (SEM−EDX), and Mossbauer spectroscopy. Increasing the manganese content in Zn1-xMnxFe2O4 (x = 0, 0.25, 0.5, 0.75, a...