Tungstophosphoric Acid Catalyst Research Articles

Modeling and simulation of biodiesel synthesis in fixed bed and packed bed membrane reactors using heterogeneous catalyst: a comparative study

In this study, modeling and simulation of biodiesel synthesis through transesterification of triglyceride (TG) over a heterogeneous catalyst in a packed bed membrane reactor (PBMR) was performed using a solid catalyst and compared with a fixed bed reactor (FBR). The kinetic data for the transesterification reaction of canola oil and methanol in the presence of solid tungstophosphoric acid catalyst was extracted from the published open literature. The effect of reaction temperature, feed flow rate, disproportionation of the reactants, and reactor length on the product performance was investigated. Two-dimensional and heterogeneous modeling was applied to PBMR and the resultant equations were solved by the Matlab software. Moreover, the velocity profile in the membrane reactor was obtained. The results showed the best conditions for this reaction are 180 °C, the molar ratio of methanol to oil equal 15:1, and the input flow rate of 0.5 mL/min. In this condition, a conversion of 99.94% for the TG can be achieved in the PBMR with a length of 86 cm while a length of 2.75 m is required to achieve this conversion of the FBR. Finally, the energy consumption for the production of 8000 ton/y biodiesel in a production plant using the PBMR and the FBR was obtained as is 1313.24 and 1352.44 kW, respectively.

MCM-41-supported tungstophosphoric acid as an acid function for dimethyl ether synthesis from CO2 hydrogenation

We mixed an MCM-41-supported tungstophosphoric acid (TPA) catalyst with a commercial CuO–ZnO–Al2O3 methanol synthesis catalyst (MSC) and optimized the mixing ratios/reaction conditions towards high performance in dimethyl ether (DME) synthesis by CO2 hydrogenation. First, a series of TPA/MCM-41 catalysts were synthesized at a TPA loading of 30, 40, 60, and 80 wt% and characterized by combining various techniques. The results of X-ray fluorescence spectroscopy confirmed the loading of stoichiometric TPA amounts in each TPA/MCM-41 catalyst, while the N2 adsorption-desorption measurements and the scanning transmission electron microscopy images were showing the decoration of MCM-41 pores with TPA clusters. X-ray diffraction and infrared spectroscopy results identified some structural distortions in TPA clusters especially at relatively low loadings and the results of temperature programmed desorption of ammonia measurements quantified the consequences of these changes in TPA structure on the acid properties. The optimized TPA loading in TPA/MCM-41 was 60 wt% with CuO–ZnO–Al2O3:TPA/MCM-41 = 4:1 at 40 000 mL CO2 gcat−1 h−1 and H2:CO2 = 3:1 at 250 °C and 45 bar. At these conditions, the rate was 1551.5 gDME kgcat−1 h−1, to the best of our knowledge, the highest rate for the direct DME synthesis from CO2 hydrogenation in a single-pass reactor. This performance was originated from the high density of acid sites in TPA/MCM-41 owing to exceptionally high surface area of MCM-41 offering a monolayer dispersion of TPA even at a TPA loading of 60 wt%. These results present a broad potential of TPA/MCM-41 as an acid function in the catalyst mixture for the single-pass DME synthesis from CO2 hydrogenation, especially if used together with an MSC specifically designed for CO2 hydrogenation.

Vanadium Substitution as an Effective Way to Enhance the Redox Ability of Tungstophosphoric Acid and for Application of NH3-SCR

A novel TiO2-supported vanadium-substituted tungstophosphoric acid (PW11V/TiO2) catalyst was designed and applied for selective catalytic reduction of NOx by NH3. Compared with the commercial tungstophosphoric acid (PW12/TiO2), PW11V/TiO2 displayed a nearly 90% activity improvement at 300 °C. In addition, the favorable resistance and stability to SO2 were also obtained over PW11V/TiO2 catalyst. Phase analysis and spectroscopy results indicated the vanadium was successfully incorporated into the molecular structure of PW12, and the Keggin framework still keep stable over the TiO2 support. H2-TPR test proved the incorporation of vanadium promoted the redox ability of PW11V. The present study provides us an effective way to improve the performance of catalytic removal of NOx through tungstophosphoric acid catalyst. After introduction of V species, the obtained PW11V/TiO2 catalyst show better NH3-SCR performance and N2 selectivity than PW12/TiO2 catalyst.

An Efficient and Recyclable Sn-Based Phosphotungstic Acid with Tunable Brønsted/Lewis Acidity for Selective Oxidation of Benzyl Alcohol

A series of metal ion (M = Sn2+, Fe3+, Ni2+, Co2+, Ag+, Cu2+) exchanged tungstophosphoric acid (H3PW12O40; TPA) catalysts with tunable Bronsted/Lewis acidity were synthesized and exploited for the oxidation of benzyl alcohol (BzOH) to benzaldehyde (BzH) using hydrogen peroxide (H2O2) as oxidant. The structure of these M-TPA composite salts was also characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analyses (TGA) and solid-state 31P nuclear magnetic resonance (NMR) probe molecule method. Among these M-TPAs, the Sn1/2H2PW12O40 catalyst, which presented strong Bronsted acidity, the synergistic effect of Bronsted/Lewis and pseudo-liquid characteristic property, exhibited excellent catalytic activity and durability with 98.2% of BzH selectivity and 95.1% of BzH yield. The optimal conditions for the oxidation of BzOH optimized by response surface methodology (RSM) were as follows: n(BzOH)/n(H2O2) = 1:1.25, catalyst amount of 5.5 wt.% to BzOH, water amount of 17 mL, 3.3 h of reaction time, and temperature 393 K. Moreover, further kinetic study confirmed that the reaction order was 2.64 and the activation energy was 21.75 kJ mol-1.

One-pot conversion of levulinic acid into gamma-valerolactone over a stable Ru tungstosphosphoric acid catalyst

In this paper ruthenium exchanged tungstophosphoric acid (TPA) catalysts with different ruthenium loading (RuxTPA (x = 1,2,3)) were studied for conversion of levulinic acid (LA) into gamma-valerolactone (GVL) (a potential fuel/fuel additive). Studies were also conducted on a Ru/C catalyst as Ru/C catalysts have recently been reported to have significant promise for this reaction. Under the conditions used (130 °C, 1.0 MPa H2, 2 h in 1,4 dioxane solvent) one of the prepared catalysts achieved excellent conversion and selectivity to GVL. This catalyst also compared favorably to Ru/C catalysts that have been previously studied in terms of rate of production of GVL per gram Ru. Characterization studies showed that Ru metal surface area and extent of Lewis and Brønsted acidity were characteristics that had a significant influence on the conversion and selectivity of the RuxTPA catalysts studied. The best performing Ru3TPA catalyst was found to be highly recyclable with only a slight decrease in selectivity of GVL (from 100% to 98.3%) being observed after five cycles of testing.

Preparation, Characterization and Application of Silica-Supported Tungstophosphoric (HPW/SiO2) Acid Catalyst to the Synthesis of 1, 8-Dioxoacridine Carboxylic Acid Derivatives in Semi Aqueous Condition

An efficient, recyclable silica supported tungstophosphoric acid (HPW/SiO2) catalyst was prepared by simple stirring method. The catalyst was characterized using FT-IR, X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), and scanning electron microscopy (SEM) techniques. The catalyst was explored in semi aqueous condition toward synthesis of 1,8-dioxoacridine carboxylic acid derivatives. It was recycled up to four runs and a very marginal loss was detected. The targeted compounds were synthesized in a very short time period and simple work procedure with excellent yield.

Facile preparation of cesium salt of tungstophosphoric acid for catalytic synthesis of one-pot two-component 1,3,4-oxadiazole derivatives in water: A doubly green approach

Solid acid catalysts facilitate many organic reactions, Cesium salt of tungstophosphoric acid (CsPW) exhibits excellent catalytic activity due to its safety, efficiency, strong acidity, cost-effectiveness and being water tolerant. CsPW has provided promising results under aqueous conditions with the high catalytic efficiency for the synthesis of target 1,3,4-oxadiazoles. The prepared catalyst was fully characterized by FT-IR, X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), scanning electron microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDAX) and X-ray photoelectron spectroscopy (XPS). 1,3,4-oxadiazoles synthesis is an environmentally friendly, clean and safe synthetic process in short reaction time, simple workup, excellent yield and catalytic recovery. The best yield results (94%) were obtained using cesium tungstophosphoric acid catalyst by model compound in just 40 min. In addition, thermodynamic and kinetic model reaction analysis was also conducted at a temperature range of 298–323 K under the influence of the catalyst. The reaction under kinetic analysis was found to be more regulated than thermodynamic, which may be attributed to the influence of the optimum amount of catalyst being used.

Efficient Catalytic Performance of Calcined Tungstophosphoric Acid for the Claisen-Schmidt Condensation under Solvent-Free Reaction

Effect of calcination of tungstophosphoric acid catalyst was evaluated in terms of the synthesis of chalcone derivatives via Claisen-Schmidt condensation using the reaction of acetophenone and several substituted aldehydes. The catalyst was characterized before and after calcination by FT-IR to assess the effectiveness of the synthesis of the desired products. The calcined tungstophosphoric acid catalyst (HPW-CL) showed a better performance and high yield of Claisen-Schmidt products in a short period of time. It was also found out that the calcined tungstophosphoric acid provides a chemo selective, efficient and environmentally benign synthesis of chalcone in an excellent yield in a solvent-free system.

Synthesis and catalytic properties of macroporous SiO2-coated CNT-sieve-composite-supported 12-tungstophosphoric acid catalysts with dual pore structure for the Baeyer–Villiger oxidation of cyclic ketones under microwave irradiation

Carbon nanotube sieves (CNTs-S) with a flutelike shape were synthesized by cutting and perforating using a chemical oxidation etching method. Using the obtained CNTs-S as a hard template, SiO2-coated CNTs-S dual pore structures (CNTs-S@SiO2) were formed. Finally, tungstophosphoric acid was supported on CNTs, CNTs-S, and CNTs-S@SiO2 matrices by the incipient wetness method to obtain the corresponding supported catalysts PW12/CNTs, PW12/CNTs-S, and PW12/CNTs-S@SiO2. The results showed that obtained 30%PW12/CNTs-S and 30%PW12/CNTs-S@SiO2 catalysts in 30 wt% dipping solution had the best catalytic performance for Baeyer–Villiger oxidation of cyclic ketones by H2O2. The conversion of cyclohexanone was 94% and 91%, respectively, in 5 min under microwave irradiation. Cyclopentanone and adamantanone approached quantitative conversion and the selectivity of corresponding lactones reached 100%. The dual pore structure catalyst showed very excellent cyclic stability.

A comparative study on the synthesis of ethyl propionate in a pervaporation membrane reactor

In this study, esterification of propionic acid with ethanol over a tungstophosphoric acid catalyst was conducted in a batch reactor and in a pervaporation membrane reactor (MR). The performance of the esterification was determined in terms of the propionic acid conversion. Effects of the reaction temperature within the range of 50 °C–70 °C, the initial molar ratio of reactants (1:1, 2:1, 3:1), and the catalyst concentration (10–20 g cat/kg reactant) on the propionic acid conversion were investigated. A poly(vinyl alcohol) membrane was prepared and used to remove the water from the reaction media simultaneously. Conversion results of the batch reactor (BR) and the MR were compared. Results showed that the conversion of the reaction was improved by using MR. As the highest conversion of 80.7% was obtained in the BR, 92.9% of acid conversion was achieved in the MR at 70 °C when the alcohol:acid molar ratio was 3:1. The conversion of the propionic acid-ethanol esterification was enhanced between the values from 15% to 27% by using MR. Activation energy of the reaction carried out in the MR was found as 39.6 kJ/mol.

Alcoholysis of Furfuryl Alcohol into n-Butyl Levulinate Over SBA-16 Supported Heteropoly Acid Catalyst

In this work, n-butyl levulinate a potential renewable chemical in the energy sector and in the field of fine chemical synthesis has been synthesized via alcoholysis of furfuryl alcohol in batch process at atmospheric pressure over SBA-16 supported tungstophosphoric acid (TPA) catalyst. In order to characterize and correlate the catalytic activity, the wet impregnated TPA/SBA-16 catalysts were subjected to the physico chemical characterization techniques such as X-ray diffraction, N2-physisorption, SEM, TEM, FT-IR, NH3-TPD and pyridine adsorbed FT-IR analysis. The retention of 3D mesoporous structure and TPA structure even after impregnation was confirmed by XRD and N2-physisorption. The impregnation of TPA over SBA-16 creates the more number of available active acidic sites for the reactants. 25 wt% TPA/SBA-16 offers 97% selectivity to n-butyl levulinate with complete conversion of furfuryl alcohol in 3 h. Various reaction parameters were optimized to achieve the best catalytic activity. These results imply that the conversion of furfuryl alcohol to n-butyl levulinate go on with the formation of the intermediate 2-butoxymethylfuran. The recyclability of the catalyst and characterization of the spent catalyst was also studied. SBA-16 supported TPA catalyst is effective in the conversion of furfuryl alcohol to n-butyl levulinate at atmospheric pressure.

Kinetic and mechanistic study of the synthesis of ionone isomers from pseudoionone on Brønsted acid solids

The kinetics of the liquid-phase synthesis of α-, β- and γ-ionones from pseudoionone was studied on Brønsted acid solids. Four silica-supported tungstophosphoric acid catalysts containing different heteropolyacid loadings, as well as a silica-supported triflic acid sample and a commercial resin (Amberlyst 35W) were tested in a batch reactor at 343–383K under autogenous pressure.The final composition of the ionone isomer mixture depended on the catalyst acidic properties and operational conditions. The reaction pathways leading to the three ionone isomers were elucidated by postulating a heterogeneous Langmuir-Hinshelwood-Hougen-Watson (LHHW) kinetic model. First order rate expressions, participation of a single Brønsted acid site in each reaction step and a cationic cyclic intermediate shared by the three ionone isomers were the main model assumptions. It was found that α-, β- and γ-ionones form directly from pseudoionone by cyclization. However, the final concentration of α- and β-ionones is enhanced in consecutive pathways involving the isomerization of γ-ionone. The relative importance of the isomerization steps and the selective formation of α- or β-ionone depend on the Brønsted acid site strength and reaction temperature.

Cellulose with a High Fractal Dimension Is Easily Hydrolysable under Acid Catalysis

The adsorption of three diverse amino acids couples onto the surface of microcrystalline cellulose was studied. Characterisation of modified celluloses included changes in the polarity and in roughness. The amino acids partially break down the hydrogen bonding network of the cellulose structure, leading to more reactive cellulose residues that were easily hydrolysed to glucose in the presence of hydrochloric acid or tungstophosphoric acid catalysts. The conversion of cellulose and selectivity for glucose was highly dependent on the self-assembled amino acids adsorbed onto the cellulose and the catalyst.

One pot selective transformation of biomass derived chemicals towards alkyl levulinates over titanium exchanged heteropoly tungstate catalysts

Alkyl levulinates were produced from biomass derived carbohydrates (glucose, fructose) and platform chemicals (5-hydroxy methyl furfural, furfuryl alcohol and levulinic acid) under feasible reaction condition using titanium modified heteropoly tungstate catalysts. Titanium exchanged heteropoly tungstophosphoric acid (TPA) with variation in titanium content were prepared and various spectroscopic methods were used to characterize these catalysts. The exchange of Ti in TPA essentially created new Lewis acidic sites. The existence of both Lewis and Bronsted acid sites of titanium containing TPA Keggin were directing the selective synthesis of alkyl levulinates from different starting materials. The partially exchanged Ti0.75TPA catalyst yielded about 92–98% of alkyl levulinates from 5-hydroxy methylfurfural, furfuryl alcohol and levulinic acid, whereas 63 and 21% yield was achieved by the alcoholysis of fructose and glucose respectively. Different types of alkyl levulinates were also synthesized from alcoholysis of furfuryl alcohol. The reaction conditions were optimized to achieve maximum yield of alkyl levulinates. The catalyst was easily separated and reused without any loss in activity.

Heteropoly Tungstate Supported on Metal Oxide Catalysts for Liquid Phase Oxidation of Benzyl Alcohol with Hydrogen Peroxide

A series of metal oxide supported tungstophosphoric acid catalysts were prepared by impregnation. The physicochemical and acidic properties of these materials were characterized by a variety of different analytical and spectroscopic techniques, namely Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) method, and nuclear magnetic resonance (NMR), and exploited as heterogeneous catalysts for selective oxidation of benzyl alcohol (BzOH) with hydrogen peroxide (H2O2). Among them, 20 wt.% H3PW12O40/CeO2 catalyst exhibited the best oxidative activity. Further process optimization by response surface methodology (RSM) based on the Box-Behnken design model resulted in a benzyl alcohol conversion of 95.2% and a benzaldehyde yield of 94.2% with 98.9% selectivity, in good agreement with the experimental results. Kinetic studies based on an irreversible parallel reaction model led to an activation energy (Ea) of 44.73 kJ mol-1.

3D graphene aerogel anchored tungstophosphoric acid catalysts: Characterization and catalytic performance for levulinic acid esterification with ethanol

3D graphene aerogel (GA) was synthesized from graphene oxide (GO) using a hydrothermal procedure combined with freeze-drying. Then, they were used to assemble the supported H3PW12O40 (HPW) catalysts. The optimization of the reaction parameters for levulinic acid esterification with ethanol was performed and the catalytic performance of the HPW/GA catalysts was comparatively investigated. The results showed that these catalysts had abundant porous structure. In particular, they were found to be efficient in the synthesis of ethyl levulinate, which is promising in reducing the consumption of petroleum-derived fossil fuels.

Direct catalytic conversion of brown seaweed-derived alginic acid to furfural using 12-tungstophosphoric acid catalyst in tetrahydrofuran/water co-solvent

Furfural, a biomass-derived platform chemical, was produced by acid-catalyzed reaction of alginic acid extracted from brown seaweed. Three acid catalysts, H2SO4, Amberlyst15 and 12-tungstophosphoric acid (H3PW12O40), were compared to evaluate their catalytic performance for the alginic acid conversion. The H3PW12O40 catalyst showed the highest catalytic activity, yielding the maximum furfural yield (33.8%) at 180°C for 30min in tetrahydrofuran/water co-solvent. Higher reaction temperature promoted the conversion of alginic acid to furfural, but the transformation of furfural to humin was also accelerated. To our knowledge, this is the highest furfural yield among studies about the direct catalytic conversion of alginic acid. Furthermore, products distribution with time-on-stream was investigated in detail, which led us to propose a reaction pathway.

Design of a Highly Efficient Indium-Exchanged Heteropolytungstic Acid for Glycerol Esterification with Acetic Acid

A series of highly active, selective, and stable solid indium-exchanged tungstophosphoric acid catalysts had been prepared, characterized and evaluated for bio-derived glycerol esterification with acetic acid to produce valuable biofuel additives. It was found that the Inx/3H3−xPW with nanotube structure owns Lewis acidity and Bronsted acidity in one, which favors for the efficient esterification of glycerol into monoglycerides with higher selectivity. Among all, In0.8H0.6PW presented exceptionally high activity with 88 % conversion and 96 % selectivity to MAG within 30 min of reaction time at 120 °C using 4:1 molar ratio. The better performance came from its remarkable stability, due to the unique Keggin structure, high acidity as well as nanotube structure. In addition, this In0.8H0.6PW catalyst did not suffer from deactivation of water in the six consecutive reaction tests.

Using response surface methodology to optimize ultrasound-assisted oxidative desulfurization

Latest strict environmental regulations have restricted the sulfur content of diesel fuels; therefore, deep desulfurization of fuels is required. Ultrasound-assisted oxidative desulfurization (UAOD) is an alternative for conventional desulfurization methods which can remove sulfur compounds from fuels under mild process conditions. In this study, UAOD of gasoil using tungstophosphoric acid catalyst and tetraoctylammonium bromide as a phase transfer agent in the presence of hydrogen peroxide as an oxidant was optimized. The optimal design of experiments was generated based on central composite face-centered design of Response surface methodology (RSM) to study effects of four process variables such as oxidant volume, mass of catalyst, mass of phase transfer agent and the ultrasonic wave amplitude on the sulfur conversion of gasoil. In addition, a predictive model of sulfur conversion was obtained based on RSM. The optimal values of process variables were evaluated to be 21.96 mL of oxidant, 1 gr of catalyst and 0.1 gr of phase transfer agent to achieve the maximum sulfur conversion of 95.92%.

Synergic effect of tungstophosphoric acid and sonication for rapid synthesis of crystalline nanocellulose

The utilization of sonication in combination with tungstophosphoric acid (PWA) catalyst reduces dramatically the time of operations from 30h to 10min by using an optimum sonication power of 225W. The basic cellulosic structure is maintained, allowing preparing high-quality nanocellulose. The size of the nanocellulose obtained was in the range from 15 to 35nm in diameter and several hundred nanometers in length, with a high crystallinity of about 88%. The nanocellulose shows a surface charge of −38.2mV which allows to obtaina stable colloidal suspension. The surface tension of the stable, swollen aqueous nanocellulose was close to that of water. These characteristics, together with the fast procedure allowed from the synergic combination of PWA and sonication, evidence the high potential of the proposed method for the industrial production of nanocellulose having the properties required in many applications.