Low-temperature oxidation of p-xylene in liquid phase using acetaldehyde as accelerator. I. Stirred tank reactor

The oxidation of p-xylene in the presence of acetaldehyde as accelerator and cobalt acetate as catalyst at 60–100° was studied using a semi-batch process in a stirred reactor. Better yields of terephthalic acid (up to 98%) were given than with other methods although the operation was similar. Diffusion was the rate-determining step, and possibilities for improving reaction rate are discussed.     

Quantum Size Effects in Catalysis by TiO2/Platinum: The Switch from Partial Oxidation to Partial Hydrogenation of Styrene

The promotional effects of CO₂ and Ni were studied on Co/Mn/Br catalyst in the liquid-phase oxidation of p-xylene to terephthalic acid using molecular oxygen as an oxidant and acetic acid as a solvent individually as well as in combination. The enhanced activity of Co/Mn/Br catalyst was observed on both CO₂ and Ni promoters independently and also in combination. The activity enhancement in the combination of CO₂ and Ni promoters on this catalyst is found to be remarkable.     

AROMATIZATION OF PROPYLENE OVER HZSM-5: A DESIGN OF EXPERIMENTS (DOE) APPROACH

Aromatization of propylene was performed in a continuous reactor over HZSM-5 catalysts. A full-factorial design of experiments (DOE) methodology identified the effects of temperature (400°–500°C), Si:Al ratio (50–80), propylene feed concentration (8.9–12.5 mol.%), and catalyst amount (0.2–1.0 g) on propylene conversion as well as the yields of benzene, toluene, p-xylene, o-xylene (BTX), and total BTX. The Si:Al ratio and amount of the HZSM-5 catalyst influenced all of the responses, while temperature affected all the responses except the yield of p-xylene. An increase in feed concentration significantly increased the yields of benzene, toluene, and total BTX. An interaction between propylene feed concentration and catalyst amount influenced the yields of benzene, toluene, and total BTX. This interaction indicated that a higher feed concentration promotes aromatization at higher catalyst concentrations. By contrast, the interaction of Si:Al ratio with propylene feed concentration was found significant for p-xylene and o-xylene yields, but not for benzene and toluene, suggesting that xylenes are synthesized on different sites than those for benzene and toluene. These interaction effects demonstrate how the use of DOE can uncover significant information generally missed using traditional experimental strategies.     

A kinetic study of the reaction between terephthalic acid and ethylene oxide in a nonsolvent system

Kinetics of the reaction between terephathalic acid and ethylene oxide, catalysed by triethylamine, was studied in a high-pressure reactor without using solvent. This reaction was carried out at a temperature range of 80–100°C and at a pressure range of 10–15 Kg/cm² beyond the corresponding vapor pressure of ethylene oxide. Effects of temperature, catalyst concentration, mole ratio of ethylene oxide to terephthalic acid, particle size of terephthalic acid, pK value of the tertiary amine and stirrer speed were experimentally investigated on the yield of bis(2-hydroxyethyl) terephthalate and reaction rates. It was found that the bulk reaction of terephthalic acid with ethylene oxide occurred in the liquid phase. Based on experimental results a reaction mechanism to synthesize bis(2-hydroxyethyl) terephthalate from terephthalic acid and ethylene oxide in a nonsolvent system was proposed, and rate constants were obtained with a model based on this proposed reaction mechanism. The activation energy of the reaction was found to be between 3.67–8.28 kcal/mole in the temperature range of 80–95°C.     

Homogeneous and two phase sulphonation of some aromatic hydrocarbons

The two phase sulphonation of benzene, toluene and p-xylene with concentrated sulphuric acid has been studied in a one litre batch reactor. The kinetic rate constants as a function of sulphuric acid concentration and the overall mass transfer coefficient times the interfacial area per unit volume of the acid phase as a function of agitation speed have been determined. The rates of sulphonation of toluene and p-xylene relative to that of benzene in the range 15.5–17 mol/litre sulphuric acid have been found to be 64 and 280 respectively. Finally, it has been shown that in aromatic sulphonation no linear relationship exists between the logarithms of the partial rate factors and the relative cation localisation energies. This is in contrast to the behaviour of some other electrophilic aromatic substitution such as halogenation, but is similar to aromatic nitration.     

A comparison of rates of disproportionation and transalkylation of m-xylene

The relative rates of toluene transalkylation, disproportionation and benzene transalkylation of m-xylene over a catalyst consisting of 72% HY zeolite, 18% β-AlF₃ and 10% (all w/w) Cu have been studied at a temperature of 723K, reciprocal space velocity of 352 g h^?1 mol^?1 and at total pressures varying between 101 and 911.93 kPa. The catalysed disproportionation of m-xylene is fastest and this has been explained in terms of the greater basicity of m-xylene over either benzene or toluene, whereas the catalyst is acidic. Thus m-xylene would be expected to adsorb more strongly on the catalyst.     

Control structure design of an industrial crude terephthalic acid hydropurification process with catalyst deactivation

Purified terephthalic acid (PTA) is a fundamental raw material for polyester and textile industry. The p-xylene oxidation process and crude terephthalic acid (CTA) hydropurification process are the two main sections of industrial PTA production. 4-Carboxybenzaldehyde is a byproduct of the first section that can lower the polymerization rate and the average molecular weight of the polymer. In this work, an improved complete plant dynamic model of the second section, CTA hydropurification with catalyst deactivation, was developed based on Aspen Dynamics. The present contribution considered the performance of the proposed catalyst deactivation model (Azarpour and Zahedi, 2012). Moreover, we designed a control structure for this process with catalyst deactivation, and the performance of the resulting control structure was analyzed using several criteria. Results showed that the proposed system provides a better control system and higher profit for the process.     

Poly(ethylene terephthalate) Recycling and Recovery of Pure Terephthalic Acid. Kinetics of a Phase Transfer Catalyzed Alkaline Hydrolysis

Poly(ethylene terephthalate) (PET) taken from post‐consumer soft‐drink bottles was subjected to alkaline hydrolysis with aqueous sodium hydroxide after cutting it into small pieces (flakes). A phase transfer catalyst (trioctylmethylammonium bromide) was used in order the reaction to take place in atmospheric pressure and mild experimental conditions. Several different reaction kinetics parameters were studied, including temperature (70–95°C), NaOH concentration (5–15 wt.‐%), PET average particle size, catalyst to PET ratio and PET concentration. The disodium terephthalate received was treated with sulfuric acid and terephthalic acid (TPA) of high purity was separated. The ¹H NMR spectrum of the TPA revealed an about 2% admixture of isophthalic acid together with the pure 98% terephthalic acid. The purity of the TPA obtained was tested by determining its acidity and by polymerizing it with ethylene glycol using tetrabutyl titanate as catalyst. A simple theoretical model was developed to describe the hydrolysis rate. The apparent rate constant was inversely proportional to particle size and proportional to NaOH concentration and to the square root of the catalyst amount. The activation energy calculated was 83 kJ/mol. The method is very useful in recycling of PET bottles and other containers because nowadays, terephthalic acid is replacing dimethyl terephthalate (the traditional monomer) as the main monomer in the industrial production of PET.     

Improved selectivity in the toluene alkylation reaction through understanding and optimising the process variables

It has been demonstrated that it is possible to produce p-xylene with near-perfect selectivity by optimising the process variables of the toluene alkylation reaction over a B/ZSM-5 catalyst. This has been achieved specifically by minimising the undesirable isomerisation of p-xylene on the external acid sites of the catalyst by controlling the contact time. This offers a superior route to high selectivity compared to multiple pre-treatments of the catalyst to eliminate external acid sites (for example, by silanisation). Additionally, a high toluene:methanol feed ratio is beneficial because it minimises the methanol dehydration reaction. A further benefit is that the maximum theoretical conversion of toluene is limited, which diminishes p-xylene product inhibition. These findings confirm that toluene alkylation is best operated in a multistage reactor, but also highlight the need for removal of p-xylene as well as addition of methanol between stages. The method of catalyst preparation is not critical, provided that there is sufficient boron present (≥6.5 wt%) and any boron lost through sublimation during the reaction is replenished. It has been found that an active catalyst can be produced in situ by either loading a physical mixture of hydroboric acid and HZSM-5 into the reactor prior to reaction or even placing a bed of hydroboric acid upstream from a bed of HZSM-5. The in situ-formed catalyst readily achieves >99.9% selectivity to the desired p-xylene isomer, under optimised conditions.     

Grafting acrylonitrile on kenaf fibers using ceric ion–p-xylene redox pair

Polyacrylonitrile was grafted onto kenaf fibers in aqueous media by ceric ion–p-xylene redox system. The graft yield dependence on p-xylene concentration in the range 1.8–45.0 × 10⁻⁴M showed a minimum accompanied by an enhanced yield. This suggested the existence of two kinetically distinct grafting reactions associated with two precursor-initiating species, a p-xylyl radical and a diradical. The frequency of graft F_g and the average molecular weight of grafted polymer M_v were inversely related at varying concentrations of p-xylene with values for M_v of up to 5.18 × 10⁴. The effect of ceric ion concentration on M_v showed that the ion is nonterminating at low concentrations in the range 8.3–33.3 × 10⁻³M. The graft yield showed positive temperature dependence in the region of 30–40°C and a negative one at higher temperatures, resulting in a decrease in the initial rate of graft at 70°C by a factor of 8 compared to its value at 40°C. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1751–1755, 1999     

Kinetics of the reaction between terephthalic acid and ethylene oxide under high pressure

Kinetics of the reaction between terephthalic acid and ethylene oxide in n-butanol solvent, catalyzed by triethyl amine, was investigated under high pressure. Effect of temperature, catalyst concentration, ethylene oxide to terephthalic acid ratio and stirrer speed was studied on the rate of formation of bis(2-hydroxy-ethyl)terephthalate. It was found that the reaction of terephthalic acid with ethylene oxide occurred in the liquid phase. The experimental data were correlated with a model based on S_N2 reaction mechanism and the activation energy of the reaction was found to be between 19.3–21.6 kcal/mole in the temperature range of 60–100°C.     

Benzoic acid and substituted benzoic acids as interfacial corrosion inhibitors for copper in HClO4

Corrosion of copper in HClO₄ solution containing various concentrations (10^–7–10^–4 M) of benzoic acid,p-toluic acid,p-nitrobenzoic acid, phthalic acid and terephthalic acid has been studied at 30° C. These compounds inhibit corrosion effectively even in trace concentration. The corrosion rate is a function of temperature, concentration and nature of the inhibitor. The inhibitor efficiency calculated from weight loss and polarization methods are in good agreement. Thermodynamic parameters for adsorption of inhibitors have been evaluated by using the Bockris-Swinkels adsorption isotherm withn=5 as the configurational function. The corrosion inhibition is discussed from a view point of adsorption of inhibitor molecules at the metal-solution interface.     

Product distribution in the aromatization of dilute ethene over H-GaAlMFI zeolite: effect of space velocity

Influence of space velocity on the aromatization of dilute ethene (5 mol% in N₂) over H-GaAlMFI zeolite catalyst, having high acidity (0.46 mmol g⁻¹, measured in terms of the pyridine chemisorbed at 400 °C) and high concentration of non-framework Ga-oxide species (0.32 mmol g⁻¹), at atmospheric pressure covering a wide temperature range (300–500 °C) has been thoroughly investigated. The selectivity of aromatics, propene, propane and C₄ hydrocarbons and alkane/aromatics and H₂/aromatics mole ratios are strongly influenced by the space velocity. The results indicate that the aromatization involves H₂ transfer reactions predominantly at the lower temperatures and/or higher space velocities whereas dehydrogenation reactions become predominant at higher temperatures and/or lower space velocities. The distribution of aromatics and C₈-aromatic isomers depends strongly upon the amount (i.e. yield) of aromatics and C₈-aromatics, respectively, formed in the process. The primary aromatics produced in the process are found to be mainly p- and o-xylenes. The aromatics distribution is, however, controlled by the aromatics inter-transformation (viz. isomerization, alkylation/dealkylation and disproportionation) reactions. The p-xylene/m-xylene ratio is decreased as expected, but the p-xylene/o-xylene ratio is increased with increasing both the space velocity and temperature. The increase of p-xylene/o-xylene ratio is found to be unusual, much above the equilibrium value.     

精对苯二甲酸生产工艺新进展

介绍了近年以对二甲苯（PX）和对苯二甲酸（PTA）为原料生产聚酯的基本情况,以及以PX为原料的液相空气氧化法与加氢精制法生产PTA的工艺.着重论述扩大PTA生产规模、开辟生产PX新技术路线的最新动态,以及新型催化剂和超临界技术的应用等.     

Environmentally friendly liquid phase oxidation: enhanced selectivity in the aerial oxidation of alkyl aromatics,epoxidations and the Baeyer–Villiger oxidation using novel silica supported transition metal ions

Active transition metal species (Co, Cu, Cr, Ni or Mn) supported on a chemically modified silica gel are used as heterogeneous catalysts in a range of liquid phase oxidation reactions: alkyl aromatic side chain oxidations, epoxidations of alkenes and Baeyer–Villiger oxidations of linear ketones to esters and cyclic ketones to lactones. The catalyst employs metal centres bound to the silica surface via a hydrophobic spacer chain and is thus chemically robust and has a relatively high loading for a supported reagent (c 0.4 mmol g⁻¹). The Cr version of the catalyst promotes the oxidation of ethylbenzene to acetophenone in a solvent‐free system at a rate of 5.5% h⁻¹ (>370 turnover h⁻¹). It is also active for the oxidation of p‐chlorotoluene and p‐xylene to p‐chlorobenzoic acid and p‐toluic acid respectively. Cyclohexene is converted to its oxide at room temperature at a rate of c 28% h⁻¹ (c 12 turnover h⁻¹) using either the Ni or Cu versions of the catalyst. The room temperature Baeyer–Villiger oxidation of cyclohexanone is achieved at a rate of 44% h⁻¹ (49 turnover h⁻¹) using the Ni‐containing catalyst. The same material also promotes the Baeyer–Villiger oxidation of linear aliphatic ketones and aromatic side chains. All the above systems use either air or molecular oxygen as the oxidant rather than peroxides or peracids. © 1999 Society of Chemical Industry     

Pervaporation Separation of p-/o-Xylene Mixtures Using HTPB-Based Polyurethaneurea Membranes

Hydroxy terminated polybutadiene (HTPB)-based polyurethaneurea membranes with and without cross-linkage were synthesized and first used as membrane material to separate p-/o-xylene mixtures by pervaporation. Compared with HTPB-PU (without cross-linkage) membranes, HTPB-DVB-PU (cross-linked HTPB-PU with divinyl benzene) membranes demonstrated a lower degree of swelling in xylene isomer solutions and noticeable improved separation factor of p-/o-xylene. On the other hand, the amount of p-xylene adsorbed in HTPB-DVB-PU membranes increased significantly rather than that of o-xylene. While the separation factor of p-/o-xylene increased but the total flux decreased with increasing DVB content, which can be ascribed to the improved chemical structure and more homogeneous chain structures of the HTPB-DVB-PU membranes. The p-xylene normalized permeation rate and separation factor of p-/o-xylene of HTPB-DVB-PU membrane reached 2.70 kgµm/m²h and 2.23, respectively, at a feed concentration of 10 wt% p-xylene at 30°C.     

Preparation of silicalite-1@Pt/alumina core–shell catalyst for shape-selective hydrogenation of xylene isomers

A silicalite-1@Pt/alumina core–shell catalyst that combined molecular sieving and hydrogenation was synthesized by coating silicalite-1 onto the surface of Pt/alumina pellet. While a Pt/alumina catalyst had no selectivity in the hydrogenation of xylene isomers, the silicalite-1@Pt/alumina core–shell catalyst showed much higher efficiency for the hydrogenation of p-xylene than for that of m- and o-xylene. The shape-selective hydrogenation catalyst has great potential for application in xylene separation.     

Destruction of chlorinated organics by hydrotreatment using Ru/TiO2 catalyst

Catalytic hydrodechlorination reactions of p‐chloro‐m‐cresol (PCMC) and p‐chloroaniline (PCA) were investigated in a slurry reactor using a Ru/TiO₂ catalyst. The organic reaction intermediates, m‐cresol and aniline, were further converted into methylcyclohexanol and cyclohexylamine respectively. Kinetics of PCMC hydrogenation was studied over the ranges in temperature, 323–373 K, H₂ partial pressure, 0.34–1.38 MPa, PCMC concentration, 3.5–14 mM and catalyst loading, 0.1–2 kg/m³. The reaction orders with respect to PCMC and H₂ were evaluated as 0.5 and 0.8 respectively. It was found that aniline hydrogenation is the rate‐determining step in the hydrotreatment of PCA. Kinetics of aniline hydrogenation was studied at 343 and 363 K over the ranges in H₂ partial pressure, 0.34–1.38 MPa, aniline concentration, 5.4–21.5 mM and catalyst loading, 0.1–0.6 kg/m³. The reaction orders with respect to aniline and H₂ were found to be 1.3 and 1.0 respectively. © 2012 Canadian Society for Chemical Engineering     

Esterification of stearic acid with p-cresol over modified Indian bentonite clay catalysts

The esterification of stearic acid with p-cresol using modified Indian bentonite clay catalysts has been reported. The reaction was studied over exchanged clays, acid activated clays, exchanged acid activated clays, aluminium pillared clay, aluminium pillared acid activated clay, molecular sieve Al-MCM-41, zeolite Hβ, ZrO₂, S-ZrO₂, p-TSA, montmorillonite K10, and montmorillonite KSF in o-xylene for 6 h. The catalysts were characterized by X-ray diffraction and surface area measurements. The acidity was determined by n-butylamine back-titration method and DRIFTS after pyridine adsorption. Acid activated Indian bentonite (AAIB) was found to be a better catalyst compared to other catalysts in the esterification of stearic acid with p-cresol.     

Comparative kinetic study of ethylbenzene isomerisation on acidic and non-acidic Pt/Al2O3 catalysts

Ethylbenzene (EB) isomerisation to o-, m- and p-xylene was investigated in a microcatalytic reactor on acidic and non-acidic Pt/Al₂O₃ catalysts. Total conversion and product yield distribution data were determined on both catalysts for EB and the xylenes in the temperature range 513–673 K and 1.8 atm. Total conversion of each of the C₈ isomers went through a maximum as the temperature was increased. The onset of reaction occurred at a lower temperature, and the initial rates were higher on the acidic catalyst. Furthermore, the acidic catalyst was found to be very selective in the production of p-xylene at temperatures less than 563 K, and of p- and o-xylene at temperatures less between 563 and 593 K. The Wei-Prater method was used for the calculation of absolute rate constants for EB isomerisation on both catalysts. Generally, the rate constants were higher on acidic Pt/Al₂O₃.