Formation Of Methacrylic Acid Research Articles

The kinetic model of the combined heterogeneously catalyzed condensation and esterification of propionic acid and methyl propionate with formaldehyde and methanol

In this work we aim for developing a kinetic model for the methyl methacrylate and methacrylic acid synthesis by the combined condensation and esterification of methyl propionate and propionic acid with formaldehyde and methanol in the presence of the silica-supported boron-phosphorus-oxide catalyst promoted by oxides of tungsten and zirconium. The dependencies of the formation rates of methyl methacrylate, methacrylic acid and diethyl ketone from the concentrations of methyl propionate, propionic acid, formaldehyde and methanol were studied, and reaction orders of every product formation with respect to each reagent were determined. Methacrylic acid is formed predominantly by condensation of methyl propionate with formaldehyde, and methyl methacrylate hydrolysis is insignificantly. The methyl methacrylate formation reaction rate is limited by the methyl propionate adsorption rate on the catalyst surface, and both reactions of methyl methacrylate and methacrylic acid formation are inhibited due to adsorption of formaldehyde, propionic acid and methanol. Based on obtained data, the reaction scheme was offered, which includes formation of intermediates such as 3-hydroxy-2-methylpropanoic acid, its methyl ester and 3,3-dihydroxy-2-methylpentanoic acid. From this reaction scheme the kinetic model was derived using steady state approximation. The reaction rate constants and their activation energies for this model were calculated from experimental data. Validity of the model was experimentally confirmed by the correlation between experimental and theoretically calculated data. Therefore, the developed kinetic model satisfactorily describes the process of the combined condensation and esterification of methyl propionate and propionic acid with formaldehyde and methanol as well as partial cases of condensation of methyl propionate with formaldehyde and propionic acid with formaldehyde, and is suitable for process optimization and technological calculations.

Elucidating the role of H2O in promoting the formation of methacrylic acid during the oxidation of methacrolein over heteropolyacid compounds.

The involvement of water in the selective oxidation of MAL to MAA over a pure Keggin-type H3PMoO12O40 catalyst was investigated using an in situ DRIFTS reactor coupled with a mass spectrometer for the first time to elucidate the reaction pathway associated with water. Comparing the spectra and activity data using D2O instead of H2O during transient switching experiments has allowed us to evaluate the possible active sites where D2O is activated. It has been found that, during the cycling switches of D2O in and out of the MAL + O2 gas feed at 320 °C, the formation of MAA-OD product is increased and decreased when D2O is added and removed, respectively. This suggests that the deuterium from D2O is involved in the production of gas phase MAA-OD. In addition, the in situ DRIFTS-MS results obtained from the isotopic switches between D2O and H2O reveal changes in the characteristic infrared bands of the Keggin unit between 1200 and 600 cm-1. It is found that the isotopic exchange possibly occurs on the bridging oxygen of Mo-O-Mo unit, where water is activated for the formation of MAA. Based on the in situ DRIFTS-MS analysis from the transient switching experiments, the reaction mechanism associated with the effect of water on the selective oxidation of MAL to MAA over Keggin-type H3PMoO12O40 catalyst is proposed.

Strong Brønsted acid-modified chromium oxide as an efficient catalyst for the selective oxidation of methacrolein to methacrylic acid

Gas–phase oxidation of methacrolein to methacrylic acid was carried out over an acid-modified Cr2O3/SiO2 catalyst. While only total oxidation occurred over bare Cr2O3/SiO2, the acid-modified Cr2O3/SiO2 showed catalytic activity for the formation of methacrylic acid. In particular, H3PW12O40 strong Brønsted acid was the most effective modifier for improving both activity and selectivity. The interface between Cr2O3 and H3PW12O40 particles on SiO2 appears to be responsible for the formation of active sites for the selective formation of methacrylic acid. The strong Brønsted acid would help the activation of methacrolein through rendering it more electrophilic, which is a key step for the formation of methacrylic acid over the present catalyst.

The role of steam in selective oxidation of methacrolein over H3PMo12O40

Role of steam in selective oxidation of methacrolein with molecular oxygen over H3PMo12O40 catalyst was investigated. Addition of steam to feed gas significantly enhanced both catalytic activity and selectivity to methacrylic acid, which were fivefold and twice increases, respectively, under the optimal steam pressure (PH2O = 0.13 atm). Kinetic analysis demonstrated that the addition of steam caused 200-fold increase in the pre-exponential factor for the formation of methacrylic acid, leading to the significant increase in the activity. The steam in the feed gas varied hydrous state of H3PMo12O40 under the reaction conditions, while did not alter redox property, molecular and crystalline structures, and surface area of the catalyst. In the presence of steam at 573 K, three H2O per one H3PMo12O40 were absorbed and hydrated protons like [H3O]+ were formed in the bulk of H3PMo12O40. Methacrolein was adsorbed on the surface of the hydrous catalyst, but not on anhydrous one at all. Based on the results, it was concluded that activation of methacrolein readily occurred on the catalyst in the presence of steam, leading to the significant increase in the pre–exponential factor. Quantum chemical calculation supported the smooth activation of methacrolein by the reaction with [H3O]+ without any transition state.

Comprehensive Study of Isobutane Selective Oxidation Over Group I and II Phosphomolybdates: Structural and Kinetic Factors

Various phosphomolybdates were synthesized using cations from Groups 1 and 2 of the periodic table. These compounds were of the form M x H3−xn [PMo12O40], with n being the cationic charge (+1 or +2). XRD analysis shows pure phosphomolybdic acid has a triclinic structure. A body centered cubic (BCC) structure gradually develops with addition of Group 1 cations, and the triclinic phase is completely replaced by the BCC phase once metal cations occupy a volume greater than 9–11 A3 per phosphomolybdate anion. The Group 2 compounds do not form a cubic phase, however the triclinic phase distorts once cationic volume is greater about 5 or 6 A3 and appears to become somewhat amorphous. Isobutane selective oxidation over the compounds yielded methacrolein (primary product), 3-methyl-2-oxetanone (lactone), acetic acid, propene, methacrylic acid, carbon dioxide and water as products. Propene was formed over the Group 1 compounds exclusively and methacrylic acid formation was observed with BaH[PMo12O40] only. Products form via two distinct processes: Category 1 product has an exponential profile and coverage is consistent with a Langmuir model, Category 2 formations are consistent with desorptions from within the bulk of the substrates. Methacrolein forms via both Category 1 and 2 processes, whilst all other products are formed by Category 2 exclusively. A rigorous kinetic analysis yielded accurate activation parameters. Category 1 methacrolein formation apparent activation energies ranged from 34.7 ± 1.3 to 119 ± 4 kJ mol−1. Category 2 formations ranged from 34.3 ± 0.4 to 726 ± 172 kJ mol−1. No relationship between activity and composition or structure could be ascertained, despite investigation into correlations using several different models.

11-Molybdo-1-vanadophosphoricacid H4PMo11VO40 supported on ammonia-modified silica as highly active and selective catalyst for oxidation of methacrolein

Gas-phase oxidation of methacrolein to methacrylic acid has been carried out over various unsupported and supported H4PMo11VO40 catalysts. While SiO2-supported H4PMo11VO40showed low selectivity to methacrylic acid, H4PMo11VO40 supported on NH3-modified SiO2, which was prepared by using an impregnation method with acetone as the solvent, exhibited high selectivity (~ 90%) and high activity for the formation of methacrylic acid. The activity of H4PMo11VO40/NH3-modified SiO2was more than five times higher than that of the corresponding unsupported catalysts.

ChemInform Abstract: The Oxidative Dehydrogenation of Isobutyric Acid to Methacrylic Acid on Ion Exchange Modified 12-Heteropoly Oxometalates.

The oxidative dehydrogenation of isobutyric acid (IBA) to methacrylic acid (MAA) has been studied over a series of 12-heteropoly oxometalate catalysts. H3PMo12O40, Cs3PMo12O40. (NH4)3PMo12O40, and a series of catalysts prepared using an ion exchange modification that resulted in the formation of mixed cation composition salts (NH4+/Cs+) were studied to investigate the contribution of the cation in the IBA to MAA process. Whereas the product selectivities obtained with the parent acid and ammonium salt were similar, those obtained with the cesium salt were markedly different. Studies of the self exchanged salts provided insight into the role of protons in the process, while investigations of the Cs+/NH4+ ion exchanged materials indicated that the cation can participate directly in the IBA to MAA reaction. The formation of MAA and acetone appears to involve a common intermediate, whereas propene forms through a different route.

Catalytic oxidation of methacrolein to methacrylic acid over silica-supported 11-molybdo-1-vanadophosphoric acid with different heteropolyacid loadings

Catalytic oxidation of methacrolein (MAL) to methacrylic acid (MAA) over SiO 2-supported H 4PMo 11VO 40 with different H 4PMo 11VO 40 loadings was investigated. H 4PMo 11VO 40/SiO 2 showed high activity in comparison with unsupported H 4PMo 11VO 40, and 3.3 mol% H 4PMo 11VO 40/SiO 2 (50 wt.% H 4PMo 11VO 40) had the highest activity, which was five-times larger than that of unsupported H 4PMo 11VO 40 due to high dispersion of H 4PMo 11VO 40 on SiO 2, as determined by temperature-programmed desorption of benzonitrile. On the other hand, the supported catalysts were less selective toward the formation of MAA. From X-ray diffraction and Raman spectroscopy, it was determined that H 4PMo 11VO 40 decomposed to form MoO 3 on SiO 2 during the catalytic reaction. Since SiO 2-supported MoO 3 and unsupported MoO 3 had only very low selectivity toward the formation of MAA in the oxidation of MAL, it was concluded that the formation of MoO 3 caused the decrease in the catalytic performance of the supported catalysts.

Photopolymerization and structure formation of methacrylic acid based hydrogels: The effect of light intensity

Poly(methacrylic acid) (PMAA)-based pH-sensitive hydrogels are widely used for biomedical and pharmaceutical fields because of their unique swelling properties and highly hydrated structure. To better serve various applications, it is necessary to have a thorough understanding of the reaction mechanism and the structure formation of synthesized hydrogels. In this study, the PMAA hydrogels crosslinked with tri(ethylene glycol) dimethacrylate (TEGDMA) were synthesized using free radical photopolymerization in a water/ethanol mixture. The effect of light intensity on the reaction kinetics and structure formation was addressed through a series of analytical methods, including photo-differential scanning calorimetry (PhotoDSC), photo-rheometry, and dynamic light scattering (DLS) goniometry. The copolymerization of the photocurable MAA/TEGDMA system was enhanced as the light intensity increased at low resin conversion. However, the light intensity decreased the reaction rate at high resin conversion. The use of a high light intensity significantly shortened the reaction time to reach macrogelation and increased the swelling ratio of formed hydrogels, which can be explained by the relative rates of intra- and intermolecular reactions during the microstructure formation.

Synthesis and characterization of MoVTeCeO catalysts and their catalytic performance for selective oxidation of isobutane and isobutylene

A series of Mo-based catalysts (MoVCeO, MoTeCeO, MoVTeO, and MoVTeCeO mixed metal oxides) were prepared and tested for the oxidation of isobutane and isobutylene. Characterization results (XRD, FTIR, TPR, XPS, and BET) showed that their structure and properties depend on the composition of the calcined samples. Catalytic tests showed that molybdenum may be the key element for the activation of isobutane, whereas the selective oxidation of isobutylene to methacrolein (MAL) might proceed mainly on the surface of the TeMo-containing crystalline phase. In addition, Te4+ may favor the formation of methacrylic acid (MAA). The incorporation of Ce ions may modify the redox process of the catalysts and thus influence the catalytic behaviors for the selective oxidation of isobutane. Thus, the selectivities and yields of MAL and MAA can be increased over these specially designed catalysts.

Characterization of Compositional Heterogeneity in Chemically Amplified Photoresist Polymer Thin Films with Infrared Spectroscopy

We demonstrate a general approach to characterize compositional heterogeneity in polymer thin films using Fourier transform infrared (FTIR) spectroscopy. Polymer films with varying degrees of heterogeneity were prepared using a model chemically amplified photoresist where a photoacid catalyzed reaction-diffusion process results in the formation of methacrylic acid (MAA) rich domains. Within these domains, the carboxylic acid groups dimerize through hydrogen bonding. FTIR measurements of the relative fraction of hydrogen-bonded vs free carboxylic groups are used to quantify the degree of compositional heterogeneity. The FTIR data from compositionally homogeneous systems, statistical copolymers, and polymer blends follow the expected linear dependence of the relative hydrogen-bonded fraction with composition. For the chemically amplified photoresist system, the FTIR data deviate substantially from that of the homogeneous distribution. Furthermore, parameters describing the size of the heterogeneity can be determined from a solid sphere model of the deprotected regions catalyzed by the diffusing photoacid. The degree of the spatial heterogeneity varies with changes in the photoacid concentration, reaction conditions, and initial copolymer composition. Increased nonreactive comonomer content decreases the degree of heterogeneity by reducing the hydrogen-bonding efficiency, which is consistent with the dilution of MAA groups.

Selective Oxidation of Methacrolein towards Methacrylic Acid on Mixed Oxide (Mo, V, W) Catalysts. Part 1. Studies on Kinetics

Comprehensive kinetic studies of the oxidation of methacrolein on mixed oxide (Mo, V, W) catalysts have been undertaken in order to find ways of catalyst improvement to achieve a high selectivity toward methacrylic acid. Steady-state kinetic experiments were carried out in a differential recycle reactor that behaves like an ideal continuous stirred tank reactor (CSTR). A kinetic model based on the scheme of Mars−van Krevelen was developed for a fair representation of the reaction rates of methacrolein conversion, methacrylic acid formation, byproduct formation, and selectivity toward methacrylic acid. For a better understanding of the kinetics, transient experiments were carried out in an apparatus to render possible sorption studies as well as transient kinetic experiments, which are powerful tools to study independently both the oxidation of the aldehydes on the catalyst in the absence of oxygen and the reoxidation of the catalyst. Steady-state kinetic data and transient experiments agree well. It could be clearly shown that the conversion of methacrolein is mainly determined by the reoxidation of the catalyst and that the selective oxidation of the aldehydes and the consecutive oxidation of the acids occur on different domains of the catalyst.

Photopolymerization and structure formation of methacrylic acid based hydrogels in water/ethanol mixture

Hydrogels are a desired material for biomedical and pharmaceutical applications. To better control the synthesized hydrogels for various applications, it is necessary to have a thorough understanding of hydrogel structure and reaction mechanism. In this study, pH-sensitive hydrogel networks consisting of methacrylic acid (MAA) crosslinked with tri(ethylene glycol) dimethacrylate (TEGDMA) were synthesized by free-radical photopolymerization in the water/ethanol mixture. Reaction rate was measured using Photo-differential scanning calorimetry (PhotoDSC) with a modified sample pan designed for handling volatile reagents. A photo-rheometer and a dynamic light scattering (DLS) goniometer were used to follow the changes in viscosity and molecule size of the resin system during photopolymerization. It was found that the rate of polymerization increased and more compact and less swelling gels would form with a higher water fraction in 50 wt% solvent/reactant mixture. This is because the weaker interactions between the MAA and the solvent give a higher opportunity for propagation and a higher reaction rate. And the hydrophobic TEGDMA and initiator tend to form aggregates in the higher water solution, contributing to the inhomogeneous microgel formation. This mechanism is conformed by viscosity measurement, DLS analysis, scanning electron microscopy (SEM) observation, and kinetics analysis.

Catalyst Design for Methacrolein Oxidation to Methacrylic Acid

Heteropoly compounds (HPCs) with the general formula CsMHPVMo11O40are prepared and tested as catalysts. The influence of elements entering the formula on the catalyst properties is studied: Cs defines the acidity and specific area, V controls the selectivity, and the transition metal M defines the mobility of oxygen in the bulk and the catalyst activity. The mechanism of methacrolein oxidation over HPCs is investigated. Using the response method and mass spectrometry of the reaction mixture, it is shown that only the catalyst oxygen atoms take part in the formation of methacrylic acid and that the transport of active oxygen to adsorbed methacrolein plays a key role in the oxidation process. A correlation between the HPC activity and the redox ability of the metal cation M n+ ↔ M n+ i (i= 1 or 2) is found. New catalysts for methacrolein oxidation to methacrylic acid are developed on the basis of this correlation. These are the salts of PVMo-poly acid with Cs, Cu, and the transition metal M as cations. These catalysts are more active (a conversion of up to 91%) and selective (up to 98%) compared to conventional catalysts for methacrolein oxidation to methacrylic acid.

Kinetics of Oxidative Dehydrogenation of Isobutyric Acid Over K2HPMo12O40 Catalyst

The kinetics of oxidative dehydrogenation of isobutyric acid has been studied in gas phase over the K2HPMo12O40 catalyst. The rate of consumption of isobutyric acid and of formation of methacrylic acid and acetone depending on the degree of conversion of isobutyric acid indicated an autocatalytic reaction mechanism. A model of MoVI-O-MoV site has been suggested and the autocatalytic process to be due to formation of this site.

Effects of NH4+, Cs+, and H+ Counterions of the Molybdophosphate Anion in the Oxidative Dehydrogenation of Isobutyric Acid

Mixed ammonium–cesium salts of the molybdophosphoric acid (Csx(NH4)3−x[PMo12O40]) have been prepared by solid-state cationic exchange using the ammonium salt impregnated with the suitable quantity of cesium nitrate at incipient wetness. Structural characterization of the solids showed that the exchange is quantitative and that ammonium and cesium cations are randomly distributed in the lattice. Catalytic activity of these salts in the oxidative dehydrogenation of isobutyric acid increases as the amount of cesium increases up to 3 Cs per heteropolyanion. Between 3 and 3.1 Cs, the catalytic activity abruptly falls and, simultaneously, the major product switches from methacrylic acid to acetone. This abrupt change in the activities for x≈3 corresponds to the strong decrease of the rates of formation of methacrylic acid and propene, whereas the rate of formation of acetone remains almost unmodified. Under the conditions of reaction, departure of ammonia was total for x≥2 and partial for x<2. Therefore, catalysts formed at steady state have to be considered as acid ammonium–cesium salts when x<2 and acid cesium salts when 2<x<3. So, very few protons are needed in order to obtain an active and selective catalyst in MAA.

Analysis of Airborne Carboxylic Acids and Phenols as Their Pentafluorobenzyl Derivatives: Gas Chromatography/Ion Trap Mass Spectrometry with a Novel Chemical Ionization Reagent, PFBOH

The complex photochemical transformations of biogenic hydrocarbons such as isoprene and of anthropogenic hydrocarbons such as aromatics are an important source of carboxylic acids in the troposphere. The identification of unknown carboxylic acids can be difficult, however, due to the lack of standards as well as poor sensitivity and lack of selectivity of existing techniques. In this study, we describe the development of a method to analyze airborne carboxylic acids using derivatization with pentafluorobenzyl bromide (PFBBr) followed by capillary gas chromatography/ion trap mass spectrometry (GC/ITMS) analysis. In addition to the typical electron impact ionization (EI) and methane chemical ionization (CI) mass spectra of pentafluorobenzyl derivatives, we describe the use of pentafluorobenzyl alcohol (PFBOH) as a novel reagent gas for CIMS. Pentafluorobenzyl ions (m/z = 181) were produced at reduced pressure (1 × 10-5−2 × 10-5 Torr) from PFBOH gas, and the resulting CIMS were characterized by the predominance of the [M + 181]+ ions. The carboxylic acid products in the oxidation of isoprene from indoor and outdoor smog chamber experiments were analyzed using the described PFBBr GC/ITMS method. The formation of methacrylic acid in an isoprene/O3 reaction was demonstrated experimentally for the first time, and acrylic acid, one of the U.S. EPA 189 Hazardous Air Pollutants, is first reported here as an isoprene oxidation product. In other outdoor toluene/NOx chamber experiments, we detected a series of carboxylic acids and various phenolic compounds using this method.

Catalytic oxidation of isobutane to methacrylic acid with molecular oxygen over activated pyridinium 12-molybdophosphate

Isobutane was catalytically oxidized to methacrylic acid with molecular oxygen above 300°C over 0 crystalline particles of pyridinium 12-molybdophosphates which were activated by heat-treatment under a nitrogen stream up to 420°C. During the treatment two third of pyridine were released from the sample and one third remained accompanied by the formation of orthorhombic structure. It was proved by IR studies that the catalyst became a reduced state by this treatment. The reduced state was highly stable even under catalytic oxidation conditions with molecular oxygen. 50% selectivity to methacrylic acid and 22% to acetic acid were achieved at 22% conversion of isobutane. The highly stable reduced state and structure of the activated heteropolymolybdophosphate catalyst seem to be responsible for the high activity for isobutane oxidation and high selectivity to methacrylic acid formation.

Formation of methacrylic acid by oxidative dehydrogenation of isobutyric acid: Promoters of iron phosphate catalysts

Various foreign ions were added as promoters into iron phosphate catalysts and their effects on performance in oxidative dehydrogenation of isobutyric acid to methacrylic acid were studied. The best performance was obtained with Pb 2+ promoters and the optimum P/Pb/Fe atomic ratio was found to be in the range of 1.2-1.3/0.15/1 to 1.3-1.4/0.3/1. Properties and catalytic performance of an iron-lead binary phosphate with a P/Pb/Fe atomic ratio of 1.4/0.3/1 were compared with those of an iron phosphate with a P/Fe atomic ratio of 1.2. It was concluded that the Pb 2+ promoter which exists in the catalyst in the form of Pb 2P 2O 7, plays a role in suppressing the consecutive oxidation of the produced methacrylic acid to CO x. The effects of the Pb 2+ promoter were also discussed on the basis of the data of X-ray diffraction spectra, surface area, acidic properties, and reducibility.

Thermal decomposition of crosslinked polymers of some dimethacrylate esters

The thermal decomposition behaviour of a series of dimethacrylate monomers and their crosslinked polymers were investigated by pyrolysis-gas chromatography. The formation of the corresponding monomers and methacrylic acid was monitored to evaluate the relative importance of the two processes, depolymerization and ester group decomposition. As expected, the predominance of either of these processes depends very much upon the structure of the ester, but for most of the polymers investigated there was no clear correlation between it and the amount of monomer liberated. In the case of a sulphur-containing polymer the predominant process of pyrolysis is ester group decomposition and methacrylic acid formation due to the presence of a weak CS bond and easily abstractable H atoms.