CoBr2-MnBr2 containing catalysts for catalytic oxidation of p-xylene to terephthalic acid

Catalytic oxidation of p-xylene (PX) to terephthalic acid (TA) was studied with catalysts containing cobalt acetate, manganese acetate, CoBr₂ and MnBr₂. The catalysts contain neither highly corrosive hydrogen bromide nor other metal ions, and have the advantage of easy catalyst recovery. The effects of Br/Co atomic ratio, reaction time and temperature, PX concentration, oxygen pressure, and catalyst concentration on PX conversion and product/intermediate yields were investigated. The catalyst system had a suitable reaction temperature of 100 °C, which was much lower than the commercial process temperature (175–225 °C). The maximum product (TA) yield was 93.5%, obtained at a Br/Co atomic ratio of three. Higher Br concentration resulted in the lower TA yield, which was ascribed to the benzylic bromide formation. The synthesis of TA could be adequately described as four reaction steps in series (PX → p-tolualdehyde → p-toluic acid → 4-carboxybenzaldehyde → TA), with a pseudo-first-order rate equation for each step, and the third step was rate-limiting. The rate constant ratios (k_j/k₃, j = 1 → 4) obtained at 100 °C were similar to the k_j/k₃ values reported earlier for cobalt acetate/manganese acetate/HBr catalysts in a range of 185–191 °C.     

Drop properties and pressure fluctuations in liquid–liquid–solid fluidized-bed reactors

Characteristics of size, rising velocity and distribution of liquid drops were investigated in an immiscible liquid–liquid–solid fluidized-bed reactor whose diameter was 0.102 and 2.5 m in height. In addition, pressure fluctuations were measured and analyzed by adopting the theory of chaos, to discuss the relation between the properties of liquid drops and the resultant flow behavior of three (liquid–liquid–solid) phase in the reactor. Effects of velocities of dispersed (0–0.04 m s⁻¹) and continuous (0.02–0.14 m s⁻¹) liquid phases and fluidized particle size (1, 2.1, 3 or 6 mm) on the liquid drop properties and pressure fluctuations in the reactor were determined. The resultant flow behavior of liquid drops became more irregular and complicated with increasing the velocity of dispersed or continuous liquid phase, but less complicated with increasing fluidized particle size, in the beds of 1.0 or 2.1 mm glass beads. In the beds of 3.0 or 6.0 mm glass beads, the effects of continuous phase velocity was marginal. The resultant flow behavior of liquid drops was dependent strongly upon the drop size and its distribution. The drop size increased with increasing dispersed phase velocity, but decreased with increasing particle size. The drop size tended to increase with approaching to the center or increasing the height from the distributor. The size and rising velocity of liquid drops and correlation dimension of pressure fluctuations have been well correlated in terms of operating variables.     

Crystallization and morphological features of syndiotactic polystyrene induced from glassy state

Spherulitic growth rates and microstructure of syndiotactic polystyrene (sPS) cold-crystallized isothermally at various temperatures, T_c (115–240 °C), have been investigated by small-angle light scattering (SALS), optical microscopy and transmission electron microscopy. The derived activation energy for sPS chain mobility at the crystal growing front is 5.4 kJ/mol, which is relatively lower than that of isotactic polystyrene, 6.5 kJ/mol. In addition, the Hv scattering invariant (Q_Hv) measured by SALS on the crystallized sPS samples displays a pronounced minimum at 150 °C. Despite a wide range of T_c used, however, the sample crystallinity estimated by Fourier transformation infrared spectroscopy remains unchanged. Prior to crystallization, the correlation length derived from the Vv patterns on the basis of Debye–Bueche model is ca. 1.13 μm regardless of T_c used. Interconnected domains with a width of ca. 1.8±0.5 μm are readily observed in all the crystallized samples under phase contrast microscopy and the phase-separated structure is conserved within sPS spherulites whose diameters are increased with increasing T_c.

Based on the above facts, we conclude that the presence of a Q_Hv minimum is ascribed to the resultant events of the two competitive transitions i.e. liquid–solid crystallization, and liquid–liquid demixing resulting from the spinodal decomposition (SD). At lower T_c, the unstable SD transition overwhelms the crystallization. Despite the low chain mobility, the coarsening process driven by the interfacial energies has reached a certain level before crystalline nucleation takes place. At higher T_c, on the other hand, cold crystallization becomes the dominant process due to the enhanced chain mobility, leading to the suppression of ongoing SD coarsening process. At an intermediate T_c range, comparable competition of the phase separation and crystallization prohibits the development of ordered symmetry within spherulites, giving the presence of Q_Hv minimum.     

Dynamics of oxygen storage and release on commercial aged Pd-Rh three-way catalysts and their characterization by transient experiments

The present work has provided new fundamental information on the effects of aging (mileage, km) of a commercial Pd-Rh (9:1, w/w) three-way catalyst (TWC) on (a) the H₂ chemisorption, (b) the redox properties of washcoat material, and (c) the dynamic oxygen storage and release properties of TWC. Hydrogen chemisorption in the 25–400 °C range was found to decrease with increasing aging of TWC. On the other hand, H₂ chemisorption performed at 200 and 400 °C resulted in a significantly larger amount of chemisorbed hydrogen (exceeding the monolayer value based on the noble metals) compared to that obtained after chemisorption at 25 °C. This is due to the onset of a hydrogen spill over process in the 200–400 °C range. The features of H₂-TPD spectra were found to strongly depend on the aging of TWC. Hydrogen chemisorption at 25 °C followed by TPD after a given pre-treatment of the catalyst surface might be considered as a procedure for a good estimate of the metal dispersion of a commercial Pd-Rh TWC. The redox properties of the oxygen storage components of the washcoat of a commercial Pd-Rh TWC were found to drastically change with increasing aging of TWC. It was found that the oxygen storage capacity (OSC) of the TWC investigated decreases significantly with catalyst aging in the 0–56,000 km range and in the temperature range of 500–750 °C. In the case of fresh TWC, the presence of 20 ppm SO₂ or 10% CO₂ in a 1.5% O₂/He gas mixture used for oxygen storage (oxidizing gas) was found to result in a large decrease in the amount of dynamic OSC measured by alternating switches between oxidizing and reducing feed gas compositions. The shift in time of the peak maximum of the transient response of CO₂ obtained during the switch O₂/He → He → CO/He (t) can be ascribed to the alteration of the kinetics of the oxygen back-spillover process and not to the kinetics of CO oxidation on the metal surface.     

Kinetics for benzoylation of sodium 4-acetylphenoxide via third-liquid phase in the phase-transfer catalysis

In this research, the kinetics for synthesizing 4-acetylphenyl benzoate (R^*COOR) from benzoylation of sodium 4-acetylphenoxide via third-liquid phase-transfer catalysis was investigated. The reaction rate was observed to be strongly dependent on agitation speeds in the third-phase catalytic reaction. By forming the third-liquid phase, the observed reaction can be greatly enhanced to give a product yield of 100% in a duration of 3 min at 20 °C and 200 rpm. If a third-liquid phase was not formed in the liquid–liquid system, the reaction rate is very slow and the product yield is only 2% in 3 min at 20 °C. The reaction conducted in third-liquid phase-transfer catalytic system is faster than that in LLPTC system by 25–28 times. The amount of catalytic intermediate (QOR) in the third-liquid phase was about 50% of the catalyst initially added and kept about 30% of it remained after 1 min, and only small amounts of a catalytic intermediate residing in the organic phase were observed during the reaction using methyl t-butyl ether as the solvent. The concentration of catalytic intermediate slightly decreased with increasing reaction time, while the molar ratio of QOR to benzyl tri-n-butylammonium cation in the third-liquid phase remained almost constant after 1 min and increased with increasing agitation speeds. The experimental results were well described by the pseudo-first-order kinetics. The present work shows an effective method to synthesize 4-acetylphenyl benzoate.     

Kinetics and phase equilibria of competing aldolization and elimination in a three-phase reactor

Butyraldehyde was aldolized with formaldehyde over a weakly basic anion-exchange resin catalyst in aqueous solvent in a batch reactor operating at atmospheric pressure and at temperatures 50–70°C. The reaction mixture was a liquid–liquid–solid system, an emulsion, the phase equilibria of which were studied through chemical analysis of the organic and aqueous phase as well as of the mixed emulsion. Simplified rate equations were derived starting from molecular reaction mechanisms on the catalyst surface. A liquid–liquid reactor model for the fitting of the experimental results was developed on the basis of the rate equations and the phase equilibria. The model described very well the experimental data.     

A carbon–carbon coupling reaction catalyzed by a water soluble rhodium catalyst entrapped in mesoporous silica

A Heck-type reaction, comprising a carbon–carbon coupling between an arylboronic acid and styrene, has been performed using a water soluble rhodium catalyst entrapped in the water-filled pores of mesoporous silica particles. The catalyst-loaded inorganic particles were dispersed in a non-polar medium, either a solution of the reactants in an aromatic solvent (toluene or p-xylene) or a solvent-free mixture of the reactants using a large excess of styrene. The reaction occurred at the oil–water interface, i.e., at the silica pore openings. The yield obtained was higher than that obtained in the conventional liquid–liquid two-phase system. The major advantage with having the catalyst “heterogenized” by entrapment into the siliceous material is the simplicity of the work-up process. The porous particles, containing the catalyst, are simply removed by filtration after completed reaction.     

The mechanism model of gas–liquid mass transfer enhancement by fine catalyst particles

In order to present the enhancement of gas–liquid mass transfer by heterogeneous chemical reaction near interface, the mechanism model has been proposed to describe the mass transfer rate for a gas–liquid–solid system containing fine catalyst particles. The composite grid technique has been used to solve the model equations. With this model the effect of particle size, first-order reaction rate constant, distance of particle to gas–liquid interface and residence time of particle near gas–liquid interface on the mass transfer enhancement have been discussed. The particle–particle interaction and slurry apparent viscosity can be considered in the model. The experimental data have been used to verify the model, and the agreement has been found to be satisfied.     

Catalytic hydrotreatment of water contaminated by chlorinated aromatics

The catalytic hydrotreatment at low temperature of water contaminated by chlorobenzene and o-chlorobiphenyl has been studied experimentally using a Pd/C catalyst. Reaction runs have been carried out in a stirred reactor at constant temperature (T=30 °C) and pressure (P1 bar). Liquid phase concentration of chlororganic reactant and hydrogenated products, chloride ions concentration and pH have been measured during reaction time. Experimental results have been modelled assuming gas–liquid and liquid–solid equilibrium and the kinetic constants of the HDCl surface reactions have been evaluated.     

Single bubble formation in high pressure liquid—solid suspensions

Bubble formation from a single nozzle is investigated analytically and experimentally in nonaqueous liquid and liquid—solid suspensions at pressures up to 17.3 MPa. A mechanistic model is proposed to predict the initial bubble size in liquid—solid suspensions, by taking into account the various forces affecting the bubble growth including those induced by the presence of the particles, such as the suspension inertial force and the particle-bubble collision force. It is found that the initial bubble size in the suspensions is generally larger than that in the liquid mainly due to the inertia effect of the suspension. The initial bubble size increases with the solids holdup. The pressure has an insignificant effect on the initial bubble size in both the liquid and liquid—solid suspensions under the conditions of this study. The model can reasonably predict the initial bubble sizes obtained in this study and those reported in the literature.     

Novelties of liquid–liquid–liquid phase transfer catalysis Alkoxylation of p-chloronitrobenzene

Liquid–liquid–liquid phase transfer catalysis (L–L–L PTC) offers orders of magnitude intensification of rates of reaction and better selectivities than the biphasic PTC. The catalyst-rich middle phase is the main reaction phase. The etherification or alkoxylation of p-chloronitrobenzene (PCNB) was conducted by using alkanol and alkali instead of the metal alkoxide. A kinetic model is presented and validated.     

Mass transfer effects in the H2SO4 catalyzed pivalic acid synthesis

The synthesis of carboxylic acids from alkenes, carbon monoxide and water according to the Koch process is usually carried out in a stirred gas–liquid–liquid multiphase reactor. Due to the complex reaction system with fast, equilibrium reactions and fast, irreversible reactions the yield and product distribution depend on a number of process parameters. The effect of some of these parameters was studied for the production of pivalic acid, using sulfuric acid as a catalyst. For the 96 wt.% sulfuric acid catalyst solution used the main reactions are relatively fast with respect to mass transfer and mixing. Therefore, aspects like the position of the injection point, inlet concentration, agitation intensity and injection rate all influence the yield obtained. The presence of an inert organic liquid phase was found to be beneficial, due to a combined effect of enhanced gas–liquid mass transfer and a ‘local supply’ effect for carbon monoxide near the hydrocarbon reactant inlet.     

Local hydrodynamics of gas–liquid-nanoparticles three-phase fluidization

The laser Doppler anemometer (LDA) and conductivity probes were used for measuring the local hydrodynamic performances such as gas holdup and liquid velocity in a lab-scale gas–liquid–TiO₂ nanoparticles three-phase bubble column. Effects of operating parameters on the local gas holdup and liquid velocity were investigated systematically. Experimental results showed that local averaged axial liquid velocity and local averaged gas holdup increased with increasing superficial gas velocity but decreased with increasing TiO₂ nanoparticles loading and the axial distance from the bottom of the bubble column. A three-dimensional computational fluid dynamic (CFD) model was developed in this paper to simulate the structure of gas–liquid–TiO₂ nanoparticles three-phase flow in the bubble column. The time-averaged and time-dependent predictions were compared with experimental data for model validation. A successful prediction of instantaneous local gas holdup, gas velocity, and liquid velocity were also presented.     

A new gas to liquids (GTL) or gas to ethylene (GTE) technology

Natural gas is a clean-burning and abundant energy resource, but much of it resides in locations remote from an economic means of transporting it to market. A logical solution for the problem would be to liquefy the natural gas, but this option requires very low temperatures and involves considerable costs. Another solution is to convert the natural gas into hydrocarbon liquids using chemical processing. Fischer-Tropsch technology converts the natural gas into “syngas” (a mixture of carbon monoxide and hydrogen) followed by reaction to liquid fuels. Unfortunately, Fischer-Tropsch technology is expensive.

At Texas A&M University, a research team has conceived a radically new process for converting natural gas into hydrocarbon liquids. It is a “direct” conversion method that does not require producing syngas. The process is essentially three reaction steps and two separation steps to produce hydrocarbon liquids. The process consists of two reaction steps and one separation step to produce ethylene. The process can operate economically with natural gas flows of as low as 300 kSCMD up to any desired capacity.

It is possible to use the GTL technology essentially anywhere natural gas exists from offshore platforms to relatively uninhabited onshore sites. This technology offers an alternative to flaring natural gas when pipelines do not exist. The liquids can be transported in liquid pipelines or in trucks or in tankers. Thus, it offers the opportunity to monetize a resource as well as to reduce undesirable emissions into the atmosphere. The GTE technology is more nearly suited to a location near an existing chemical industry that requires ethylene and/or hydrogen.

SynFuels International Inc. has licensed the technology to commercialize it, and the company has constructed a pilot plant capable of processing 3 kMCMD. The cost of a commercial 300 kSCMD plant should be in the US$ 50–75 million range. The cost of the liquids should be about US$ 25–28 per barrel. Of course, larger capacity plants would require a larger investment but produce a less expensive product.     

Reaction pathway of the catalytic wet air oxidation of phenol with a Fe/activated carbon catalyst

Catalytic wet air oxidation (CWAO) of phenol with molecular oxygen using a home-made Fe/activated carbon catalyst at mild operating conditions (100–127 °C; 8 atm) has been studied in a trickle-bed reactor. Ring compounds (hydroquinone, p-benzoquinone and p-hydroxybenzoic acid) and short-chain organic acids (maleic, malonic, oxalic, acetic and formic) have been identified as intermediate oxidation products. CWAO experiments using each one of these intermediates as starting compound have been carried out (at 127 °C and 8 atm) in order to elucidate the reaction pathway. It was found that phenol is oxidized through two different ways. It can be either para-hydroxylated to hydroquinone, which is instantaneously oxidized to p-benzoquinone or para-carboxylated to p-hydroxybenzoic acid. p-Benzoquinone is majorly mineralized to CO₂ and H₂O through oxalic acid formation whereas p-hydroxybenzoic acid gives rise to short-chain acids. Only acetic acid showed to be refractory to CWAO under the operating conditions used in this work. The catalyst avoids the presence of ring-condensation products in the reactor effluent which were formed in absence of it. This is an additional important feature because of the ecotoxicity of such compounds.     

Halogen-free acylation of toluene over FeSBA-1 molecular sieves

Three-dimensional cage type iron substituted mesoporous silica with different iron contents (FeSBA-1) was synthesized in a highly acidic media using cetyltriethylammonium bromide and tetraethylorthosilicate as a template and a silica source, respectively. Acylation of toluene with acetic anhydride (AA) was carried out over FeSBA-1 mesoporous catalysts with different n_Si/n_Fe ratios in the temperature range 80–180 °C for a time-on-stream of 1–6 h under liquid phase conditions. The important factors affecting the conversion and the selectivity of the reaction, such as the reaction temperature, feed ratio, catalyst weight and time-on-stream were studied and the results are discussed in detail. The reaction conditions were optimized and the n_AA/n_Toluene ratio of 2 and catalyst weight of 0.1 g (3.3 wt% of total reaction mixture) were maintained for all catalytic runs. It was found that the catalytic activity is strongly influenced by the amount of tetrahedral iron in the catalysts. Among the catalysts used in the present study, FeSBA-1(36) showed a high toluene conversion and selectivity to p-methylacetophenone (p-MAP) under the optimized reaction conditions. It was also found that the selectivity for p-MAP was always higher than m-MAP and o-MAP for all the catalysts and the activity of the catalysts changes in the following order: FeSBA-1(36) > FeSBA-1(90) > FeSBA-1(120).     

Hydrogen production from catalytic gasification of cellulose in supercritical water

Interests in large-scale use of biomass for energy and in hydrogen are motivated largely by global environmental issues. Cellulose and sawdust were gasified in supercritical water to produce hydrogen-rich gas in this paper, and Ru/C, Pd/C, CeO₂ paticles, nano-CeO₂ and nano-(CeZr)_xO₂ were selected as catalysts. The experimental results showed that the catalytic activities were Ru/C > Pd/C > nano-(CeZr)_xO₂ > nano-CeO₂ > CeO₂ particle in turn. Low-concentration sodium carboxymethylcellulose (CMC) (2–3 wt.%) was mixed with particulate biomass and water to form a uniform and stable viscous paste which can be efficiently gasified. The 10 wt.% cellulose or sawdust with CMC can be gasified near completely with Ru/C catalyst to produce 2–4 g hydrogen yield and 11–15 g potential hydrogen yield per 100 g feedstock at the condition of 500 °C, 27 MPa, 20 min residence time in supercritical water.     

Hydrogenation/hydrogenolysis of disulfides using sulfided Ni/Mo catalysts

The mechanism of the hydrogenation/hydrogenolysis of dinitrodiphenyldisulfides using sulfided NiMo/γAl₂O₃ catalysts has been examined in detail. Although two routes are possible, the major pathway involves an initial SS bond cleavage followed by reduction of the nitro group. Importantly, the disulfide hydrogenolysis occurs in the absence of the catalyst with the role of the catalyst thought to be to activate the hydrogen and trap the cleaved intermediate as well as facilitate the reduction of the nitro group. Monitoring the mass balance throughout the reaction demonstrates the difficulty in measuring intrinsic kinetics for gas–liquid–solid reactions. Although the mass balance is restored at the end of the reaction, up to 45% of the substrate/products is found to be adsorbed on the catalyst during the reaction.     

The red–ox treatments influence on the structure and properties of M2O3–CeO2–ZrO2 (M=Y, La) solid solutions

The introduction of trivalent cation — Y³⁺ or La³⁺ — into the lattice of CeO₂–ZrO₂ solid solutions allows to stabilise a cubic structure at low ceria content (30 mol%). The reducibility of the samples has been compared in the experiments of temperature-programmed reduction (TPR). The introduction of lanthanum cations decreases the amount of hydrogen consumed during TPR, while the introduction of yttrium ones increases this value. At the same time, the value of temperature of the maximum speed of reduction (T_max) is independent on the trivalent dopant. The reducibility of these solid solutions did not change during repeated red–ox treatments at temperature below 1220 K. It is connected with the high thermostability of all systems in this temperature interval. TPR up to 1470 K causes a significant shift of T_max value to higher temperature and a slight decrease of hydrogen consumption in two to three cycles. It is suggested that this alterations are connected with the sharp decrease of the specific surface area of all samples and partially phase decomposition of CeO₂–ZrO₂ and Y₂O₃–CeO₂–ZrO₂ solid solutions. Raman characterisation of the oxygen sublattice of the fresh samples and of the samples after TPR has been carried out.     

Surface-nitrogen removal in NO and N2O reduction on Pd(1 1 0): Angular distribution studies of desorbing products

This paper is a report of angle-resolved product desorption measurements in the course of catalyzed NO and N₂O reduction on Pd(1 1 0). Surface-nitrogen removal processes show different angular distributions, i.e. normally directed N₂ desorption takes place in process (i) 2N(a) → N₂(g). Highly inclined N₂ desorption towards the [0 0 1] direction is induced in process (ii) N₂O(a) → N₂(g) + O(a). N₂O or NH₃ desorption follows the cosine distribution characterizing the desorption after the thermalization in process (iii) N₂O(a) → N₂O(g) or (iv) N(a) + 3H(a) → NH₃(a) → NH₃(g). Thus, a combination of the angular and velocity distributions provides the analysis of most of surface-nitrogen removal processes in the course of catalyzed NO reduction.

At temperatures below 600 K, processes (ii) and (iii) dominate and process (iv) is enhanced at H₂ pressures higher than NO. Process (i) contributes significantly above 600 K. Only three processes except for NH₃ formation are operative when CO is used. Only process (ii) was observed in a steady-state N₂O + CO (or H₂) reaction.