Oxidation Of P-xylene Research Articles

Highly efficient Cu(II) coordination polymer catalyst for the conversion of hazardous volatile organic compounds

Three novel coordination polymers (CPs), namely [Cu(μ-1κO,2κN-L)2]n (1), [Zn (μ-1κO,2κN-L)2(H2O)2]n (2) and [Cd (μ-1κOO’,2κN-L)2]n (3) [where HL = 4-(pyrimidin-5-ylcarbamoyl)benzoic acid], were synthesized and characterized by elemental analysis, ATR-IR, TGA, XPS and single-crystal X-ray diffraction. Despite having the same organic ligand, the various metal cations had an impact in the subsequent frameworks. Hirshfeld surface analysis was performed to investigate the intermolecular interactions and to examine the stability of the crystal structures of the three polymers. Their catalytic performances were screened for the peroxidative oxidation of Volatile Organic Compounds (VOCs), with toluene and p-xylene selected as model substrates. Tert-butyl hydroperoxide (t-BuOOH or TBHP) (aq. 70 %) was employed as the oxidant. The catalytic oxidation of toluene yielded benzyl alcohol, benzaldehyde and benzoic acid. The copper CP 1 exhibited the highest total yield for toluene oxidation, reaching approximately 36% in an aqueous medium. For p-xylene oxidation, tolualdehyde, methylbenzyl alcohol, and toluic acid were produced as the primary products, accompanied by minor ones. The experiments were conducted under diverse conditions, manipulating key parameters such as the choice of solvent (water or acetonitrile), type of oxidant (t-BuOOH or H2O2), the concentration of the oxidant and reaction temperature. In the presence of catalyst 1, a maximum total yield of ca. 80% was achieved for p-xylene oxidation.

A Benign Synthesis Route to Terephthalic Acid via Two-Step Electrochemical Oxidation of P-xylene

Terephthalic acid is conventionally synthesized through the AMOCO process under harsh conditions, making milder electrosynthesis routes desirable. Electrooxidation of p-xylene has been demonstrated but the degree of oxidation is limited, resulting in low terephthalic acid yields. Here, we demonstrate a process with two electrochemical steps enabling the complete oxidation of p-xylene into terephthalic acid. The first electrochemical step achieves C-H activation of p-xylene using electrochemically generated bromine as a mediator, while the second electrochemical step does alcohol oxidation of 1,4-benzenedimethanol into terephthalate on NiOOH. The divided cell in the first step simultaneously generates acid and base that are utilized subsequently, negating the need of external acid and base addition and thus offering a cost competitive synthesis route. The competing bromide oxidation in the second step is suppressed by using constant voltage electrolysis at 0.50 V, where an optimal yield of terephthalic acid of 81% is achieved.

Preparation of cobalt catalyst supported on perovskite-type oxide and application in liquid-phase selective oxidation reaction

Abstract Cobalt catalyst supported on the perovskite-type oxide sodium tantalate, NaTaO3 (NTO) was prepared by using the hydrothermal method and used in liquid-phase p-xylene oxidation, which led to p-methyl benzyl alcohol, p-tolualdehyde, and p-toluic acid. Investigation showed that the formation of alcohol and aldehyde was a competitive reaction. Further oxidation of the alcohol did not occur. On the other hand, the oxidation of p-tolualdehyde led to the formation of acid. Co-NTO catalyst showed higher selectivity toward the route of p-tolualdehyde than the p-methylbenzyl alcohol compared with the bulk Co3O4.

Covalent bonding of N-hydroxyphthalimide on mesoporous silica for catalytic aerobic oxidation of p-xylene at atmospheric pressure.

The surface of SBA-15 mesoporous silica was modified by N-hydroxyphthalimide (NHPI) moieties acting as immobilized active species for aerobic oxidation of alkylaromatic hydrocarbons. The incorporation was carried out by four original approaches: the grafting-from and grafting-onto techniques, using the presence of surface silanols enabling the formation of particularly stable O-Si-C bonds between the silica support and the organic modifier. The strategies involving the Heck coupling led to the formation of NHPI groups separated from the SiO2 surface by a vinyl linker, while one of the developed modification paths based on the grafting of an appropriate organosilane coupling agent resulted in the active phase devoid of this structural element. The successful course of the synthesis was verified by FTIR and 1H NMR measurements. Furthermore, the formed materials were examined in terms of their chemical composition (elemental analysis, thermal analysis), structure of surface groups (13C NMR, XPS), porosity (low-temperature N2 adsorption), and tested as catalysts in the aerobic oxidation of p-xylene at atmospheric pressure. The highest conversion and selectivity to p-toluic acid were achieved using the catalyst with enhanced availability of non-hydrolyzed NHPI groups in the pore system. The catalytic stability of the material was additionally confirmed in several subsequent reaction cycles.

Exploration on the combustion chemistry of p-xylene: A comprehensive study over wide conditions and comparison among C8H10 isomers

Pyrolysis and oxidation of p-xylene over wide conditions were studied in this work in order to provide a comprehensive insight into the combustion chemistry of p-xylene. Concerning this goal, the pyrolysis of p-xylene was investigated in a flow reactor at pressures from 0.04 to 1 atm over the temperature range of 1000–1600 K. Key radicals, isomers and PAH products including three xylyl isomers, benzyl, xylylene isomers, styrene, benzene, fulvene, indene, naphthalene and phenanthrene, were identified and quantified using synchrotron vacuum ultraviolet photoionization mass spectrometry. The oxidation of p-xylene was studied in a jet-stirred reactor at 10 atm, 800–1300 K and equivalence ratios of 0.5–2.0 with a residence time of 0.5 s. Oxidation products were quantified by using gas chromatography combined with mass spectrometry and Fourier transform infrared spectrometry. A kinetic model for p-xylene combustion over wide conditions was developed based on our previously proposed p-xylene oxidation model and validated against the new experimental measurements in this work and literature reported experimental data, including flow reactor oxidation, laminar premixed flame, ignition delay time and laminar burning velocity. In the flow reactor pyrolysis, p-xylene mainly undergoes unimolecular decomposition to yield p-xylyl, which mainly suffers the H-loss reaction to form p-xylylene and isomerization reaction to form o-xylyl. The resonantly stabilized fulvenallenyl and benzyl radicals play an important role in the formation of bicyclic and tricyclic PAHs including indene, naphthalene, and phenanthrene. In the JSR oxidation, p-xylene is predominantly consumed via H-abstraction by oxygenated radicals such as OH, O, and HO2 forming p-xylyl, which can be oxidized by HO2 and eventually converted to p-methylbenzaldehyde. As the most abundantly produced oxygenated aromatics, further consumption of p-methylbenzaldehyde results in the formation of other observed oxygenated aromatics such as cresol, benzofuran, and benzaldehyde. The combustion chemistry of three C8H10 isomers, i.e., p-xylene, o-xylene, and ethylbenzene, were also compared in terms of pyrolysis and oxidation fuel reactivity, and PAHs formation and growth, showing remarkable fuel isomeric effects.

First principles investigation of manganese catalyst structure and coordination in the p-xylene oxidation process

The oxidation of p-xylene to terephtalic acid is important for the production of polyethylene terephthalate (PET). This work investigates the coordination of the Mn catalyst species under operating conditions.

Surface reconstruction enabling MoO2/MoP hybrid for efficient electrocatalytic oxidation of p-xylene to terephthalic acid

Selective oxidation of p-xylene (PX) to terephthalic acid (TA) remains exceptionally challenging since it easily undergoes deep oxidation. Herein, a nickel foam-supported molybdenum dioxide/molybdenum phosphide hybrid electrocatalyst (MoO2/MoP/NF) is reported for highly selective generation of TA via electrocatalytic oxidation (ECO) of PX in alkaline medium. The efficient MoO2/MoP/NF anode material displays a unique cluster-like nanocone architecture, showing abundant active sites and rapid charge transfer kinetics. Benefit from the synergy between MoO2 and MoP, the MoO2/MoP/NF provides a high TA selectivity of 94.8% and an outstanding faradaic efficiency of 76.9% at the conversion of 71.6%. Additionally, the anodic oxidation of PX over MoO2/MoP/NF promotes the cathodic hydrogen production. The potential-induced surface reconstruction of the as-synthesized MoO2/MoP/NF yields new phases of phosphomolybdate and potassium molybdate. The top P site on the phosphomolybdate surface facilitates the adsorption of reaction intermediates but weakens the adsorption of TA, thereby yielding high selectivity toward TA.

Optimizing the Load Distribution of the p-Xylene Oxidation Process in a Continuous Reactor

The liquid-phase oxidation of p-xylene (PX) is the key step in the purified terephthalic acid (PTA) production technology. With the improved oxidation technology and intensified competition in the PTA industry, it is crucial to develop a more efficient and energy-saving PX oxidation technology. In this work, the oxidation load distribution for two reactors was optimized through the experiment and simulation. The results showed that the temperature of the first reactor has a substantial influence on the overall PTA production. An increase in temperature in the first reactor reduced the impurity content. However, increasing the reactor or crystallizer temperature has little impact on the morphology of solid particles. Furthermore, with a fixed total residence time of the two reactors, extending the residence time of the first reactor has no impact on reducing impurities, while the reduction of impurities is observed in the second reactor.

P-Xylene Oxidation to Terephthalic Acid: New Trends

Large-scale terephthalic acid production from the oxidation of p-xylene is an especially important process in the polyester industry, as it is mainly used in polyethylene terephthalate (PET) manufacturing, a polymer that is widely used in fibers, films, and plastic products. This review presents and discusses catalytic advances and new trends in terephthalic acid production (since 2014), innovations in terephthalic acid purification processes, and simulations of reactors and reaction mechanisms.

Spherical TiO2 /Cr2O3 Composites Synthesized Using Ion-Exchange Resins as a Template

Two samples of TiO2 /Cr2O3 composites were synthesized as spherical grains by stepwise thermal treatment of ion-exchange resins, which were preliminarily saturated with chromium cations Cr3+ and dichromate anions Cr2O7 2– and covered with a film-forming solution of titania. The modes of calcination were based on thermal analysis and determined by the type of ion-exchange resin chosen as a template. The obtained composites consist mostly of the α-Cr2O3 phase, while the content of the TiO2 phase does not exceed 4 %. The composites retain the spherical grain shape of the initial ion-exchange resins with the size from 370 to 660 μm. Grains of the sample based on cationite, which adsorbs Cr3+ ions, have a pore structure with swells and voids. Grains of the sample based on anionite have fractures and cracks over the entire surface due to nonuniform distribution of adsorbed Cr2O72– anions in the initial anionite. The composites exhibit the catalytic activity in the complete oxidation of p-xylene. The sample based on cationite is more active. This may be related to a smaller accessible specific surface area of titania in the anionite-based sample due to formation of the Ti3+ solid solution in α-Cr2O3.

Inhibiting COx formation on WOx-loaded Au/TiO2 photocatalyst for selective oxidation of p-xylene to p-methyl benzaldehyde

Photocatalytic selective oxidation of p-xylene with O2 offers a mild pathway to synthesize p-methyl benzaldehyde (p-MBA), which is one of the primary precursors in the manufacture of fine chemicals. Here, we report that Au/WOx/TiO2 photocatalyst selectively catalyzes the oxidation of p-xylene to p-MBA with 88.6% selectivity at 1.0% conversion, the formation of COx is suppressed to 0.8%. Kinetic experiments indicate that p-methylbenzyl alcohol and p-MBA are initial products. p-Methylbenzyl alcohol is further oxidized to form p-MBA, p-methylbenzyl acid and COx; p-MBA is further oxidized to p-methylbenzyl acid and COx. On TiO2 surface, p-methylbenzyl alcohol is more prone to directly combust to COx by O2–. Loading of WOx can weaken the adsorption ability of p-methylbenzyl alcohol on the catalyst surface to avoid the combustion. Meanwhile, WOx and Au can facilitate the separation of photo-generated carriers to attain high activity and suppress the O2– formation to obtain high selectivity.

Effect of Process Conditions on Catalytic Hydrothermal Oxidation of p-Xylene to Terephthalic Acid

This study investigates the influence of hydrothermal process conditions on the yield of terephthalic acid (TPA). Deionised water was employed as a green reaction medium substitute for acetic acid solvent widely used in the Amoco oxidation process for TPA production. Utilising the unique properties of water at elevated temperature and pressure, TPA was synthesised from p-xylene under subcritical (250 °C, 300 °C and 350 °C) and supercritical (400 °C) water conditions in a 10 mL micro-bomb batch reactor. Process conditions, including hydrogen peroxide (H2O2) oxidant concentrations, manganese bromide (MnBr2) catalyst and water loadings, were varied at a fixed reaction time of 60 minutes. The p-xylene conversion and TPA yield were determined using high-performance liquid chromatography (HPLC). In addition, the presence of chemical functional groups and chemical compositions of the reaction products were examined using Fourier transform infrared spectroscopy (FTIR) and gas chromatography-mass spectrometer (GC-MS), respectively. It was found that an optimum TPA yield of 94.56% was observed at 350°C with hydrogen peroxide, deionised water and manganese bromide catalyst set at 1.5 mL, 2.5 mL, and 2 mL, respectively. Other major reaction products identified were p-tolualdehyde and 1,4-hydroxymethyl benzaldehyde.

Photocatalytic oxidation of p-xylene coupled with hydrogen evolution over MOFs-based bifunctional catalyst

Photocatalytic oxidation of organic small molecules accompanied by the release of hydrogen is considered to be a dual optimal route to obtain green energy and high value-added oxidation products through a green way. A TiO2-CdS/Ni bi-functional catalyst combining the advantages of MOFs, semiconductor materials and metal nanoparticles was prepared by using MIL-125 as a precursor. The prepared composite catalyst has strong photoresponsiveness, abundant catalytic sites and the ability to oxidize aromatic compounds. The hydrogen evolution capacity can reach 6.6 mmol·g−1·h−1 over TiO2-CdS/Ni in the presence of hole sacrificial agent. The hydrogen production was 81.9 μmol·g−1 h−1 in the system with PX instead of hole sacrificial agent, and 521.2 μmol·g−1 of TALD oxidation products can be obtained with high selectivity. The high activity of the catalytic system can also be extended to the oxidation of toluene and benzyl alcohol, which can generate hydrogen of 33.3 μmol·g−1·h−1 and 1.6 mmol·g−1·h−1, and 620.3 μmol·g−1 and 4.2 mmol·g−1 of benzaldehyde were produced at the same time, respectively. This study successfully extends the strategy of photocatalytic oxidation of organic small molecule coupled with hydrogen evolution to PX and other compounds.

Inhibiting Cox Formation on Wox-Loaded Au/Tio2 Photocatalyst for Selective Oxidation of P-Xylene to P-Methyl Benzaldehyde

Inhibiting Cox Formation on Wox-Loaded Au/Tio2 Photocatalyst for Selective Oxidation of P-Xylene to P-Methyl Benzaldehyde

Aerobic oxidation of C-H bonds to carboxylic acids enabled by decatungstate photocatalysis

Direct aerobic oxidation of p-xylene using cobalt, manganese and bromide ion catalyst system, named the Amoco method, is a fundamentally important process to produce terephthalic acid in industry. However, it still suffers from harsh conditions and potential environmental pollution. Herein, we disclose an aerobic oxidation of alkyl aromatics to carboxylic acids through decatungstate photocatalysis featuring mild and green conditions (i.e., ambient temperature, visible light irradiation and atmospheric O2 as the green oxidant). It is scalable for the synthesis of terephthalic acid, which shows a significant potential for industrial production. Various substituted toluene derivatives were well applicable, thus furnishing acid and ester products in good yields.

Regulating effects of anthraquinone substituents and additives in photo-catalytic oxygenation of p-xylene by molecular oxygen under visible light irradiation

This paper reports that the optical properties of anthraquinone (AQ) and its photo-catalytic performance in the visible light-driven p-xylene (PX) oxidation can be fine-tuned and improved through varying its skeleton substituents at the molecular level, and the electron-withdrawing substituent exhibits a better improvement effect than the electron-donating one. The best catalyst 2-carboxyanthraquinone (AQ-COOH) can achieve 70.9% PX conversion and 88.2% p-toluic acid selectivity under visible light illumination and 1 atm O2 pressure. The addition of benzenesulfonic acid in the above photocatalytic system can further increase PX conversion to 86.7%, along with a significant improvement in the selectivity of p-carboxybenzaldehyde and terephthalic acid, which likely originates from the unique recombination behavior of the photo-generated charge carriers of the catalyst and the additive driven by the strong interactions between their aromatic skeletons and acidic substituents. Furthermore, AQ-COOH can achieve almost quantitative yield of acetylacetone in ethylbenzene photooxidation and the regulating effect of toluene's para-position substituents on its reactivity is also reported in the AQ-COOH photocatalysis system. Based on quenching tests and EPR spectral characterizations, the oxygen vacancies (h+), superoxide free radicals (O2•-) and singlet oxygen (1O2) as the photo-generated active species are involved in the proposed photo-catalysis mechanism.

Modeling of the Co-Mn-Br catalyzed liquid phase oxidation of p-xylene to terephthalic acid and m-xylene to isophthalic acid

The current kinetics of PX or MX oxidation in liquid phase failed to incorporate the effect of the proposition and concentration of Co-Mn-Br ternary catalyst, although they play a significant role in the oxidation rate and selectivity. In this work, based on the catalytic mechanism of hydrocarbon oxidation and collision theory, a three-parameter model containing the catalyst proposition and concentration was developed. The reliability of this model was confirmed by comparing experimental data at different catalyst concentrations and ratios. The parameters α and β are related to the reactivity of Co and Mn ions respectively, and they are transferrable between PX and MX oxidation. However, the parameter γ is only related to the methyl reactivity of PX or MX with Br. The predicted relative reactivity of PX to MX is close to the famous Hammett structure-reactivity relationship.

High-performance differential evolution algorithm guided by information from individuals with potential

In the differential evolution (DE) algorithm, many adaptive methods have been studied in terms of fitness values. However, few studies exist on the information from individuals with potential, which presents a large difference in fitness values from that of previous individuals and contains much evolution information. This study proposes a high-performance DE (PDE) algorithm guided by information from individuals with potential. In PDE, all individuals are divided into individuals with potential and individuals without potential according to their improvement in fitness values. The experience learned from the generation of individuals with potential is used to guide future individuals. At each generation, the selection probability of each strategy in the strategy pool is determined by the strategy’s contribution to the improvement in fitness values when generating individuals with potential. The parameters are randomly generated with two distributions, and the location parameters of the two distributions are adjusted on the basis of the improvement in fitness values of individuals with potential. Different individuals (with or without potential) may have different characteristics and evolution methods. Therefore, the generation process of individuals with potential is separated into two cases according to whether they are from previous individuals with or without potential. The study results of the two cases are applied to guide the evolution of current individuals with and without potential. The proposed algorithm is evaluated by comparing it with five advanced DE variants on CEC2005 and seven up-to-date evolutionary algorithms on CEC2014. Comparison results demonstrate the competitive performance of the proposed algorithm. The PDE is also applied to estimate the parameters of a kinetic model of p-xylene oxidation process.

Efficient oxidation of p-xylene to terephthalic acid by using N,N-dihydroxypyromellitimide in conjunction with Co-benzenetricarboxylate

The MOF Co-BTC (BTC = benzenetricarboxylate) has been synthesized by a hydrothermal method, and characterized by means of N2 physical adsorption, X-ray diffraction, scanning electron microscope, thermogravimetric analysis, and X-ray photoelectron spectroscopy. The material has multiple crevices, as opposed to a pore structure, and shows high thermal stability, with Co in the divalent state. It has been used in conjunction with N,N-dihydroxypyromellitimide to catalyze the oxidation of p-xylene to terephthalic acid, the reaction conditions for which have been investigated and optimized. At 150 °C, with acetonitrile as solvent instead of acetic acid and in the absence of corrosive bromine, the conversion of p-xylene reached 100 % and the selectivity for terephthalic acid exceeded 97 %. Under the optimized conditions, Co-BTC exhibits stronger catalytic activity than cobalt(II) acetate, and maintains excellent stability during the reaction. The reaction mechanism has been deduced, and the roles of N,N-dihydroxypyromellitimide and Co-BTC as synergistic catalysts in the reaction have been clarified.

Concurrent Quality-Relevant Canonical Correlation Analysis for Nonlinear Continuous Process Decomposition and Monitoring

The main focus of this work is to propose a data-driven residual generation based performance monitoring method for a industrial nonlinear p-xylene (PX) oxidation reaction process. In the proposed ...