Terephthalic acid synthesis at higher concentrations in high‐temperature liquid water. 1. Effect of oxygen feed method

We conducted terephthalic acid (TPA) synthesis from p‐xylene in high‐temperature liquid water (HTW) at 300°C. The p‐xylene concentration at the reaction condition was 0.2 mol L^?1, which is the highest to date in research that achieved at least 80 mol % yields of TPA in HTW. Pure oxygen gas was the oxidant. Increasing the MnBr₂ catalyst concentration increased the rate of TPA formation only slightly. In contrast, whether oxygen was fed in small, quick, discrete bursts, or fed continuously significantly affected the p‐xylene conversion and the TPA selectivity. Adding oxygen in quick bursts and small increments led to high selectivities (>90 mol %) of TPA. Continuous addition of oxygen failed to do so. In addition to identifying the sensitivity of this synthesis to the oxygen feed method, these results also demonstrate the feasibility of HTW for TPA synthesis at higher concentrations, and hence high TPA production per unit reactor volume. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

The efficient liquid‐phase oxidation of aromatic hydrocarbons by molecular oxygen in the presence of MnCO3

BACKGROUND: The liquid‐phase catalytic oxidation of aromatic hydrocarbons by molecular oxygen is a commercially important process. We consider the MnCO₃‐promoted oxidation of toluene to produce benzaldehyde and benzoic acid. In this investigation, toluene was oxidized with 25.0% conversion and 80.8% selectivity with respect to benzoic acid in the presence of MnCO₃ under 1.0 MPa of oxygen at 190 °C for 2 h. RESULTS: Moreover, the oxidation of other aromatic hydrocarbons, such as ethylbenzene, p‐xylene, m‐xylene, o‐xylene, and p‐chlorotoluene, were also efficiently promoted by MnCO₃. CONCLUSION: It is concluded that an efficient oxidation of aromatic hydrocarbons can be achieved in the presence of MnCO₃ under solvent‐free conditions. The catalytically active species are high‐valence Mn generated via the action of MnCO₃ with oxygen. Copyright © 2007 Society of Chemical Industry     

Synthesis and melt spinning of fully aromatic thermotropic liquid crystalline copolyesters containing m‐hydroxybenzoic acid units

Fibers of fully aromatic thermotropic copolyesters based on p‐acetoxybenzoic acid (p‐ABA), hydroquinone diacetate (HQDA), terephthalic acid (TPA), and m‐acetoxybenzoic acid (m‐ABA) were prepared by a high‐temperature melt‐spinning technique. Two types of the copolyesters were prepared by a high‐temperature melt polycondensation reaction using 33 mol % of kink (m‐ABA) and 67 mol % linear monomer units (p‐ABA, TPA, HQDA), and characterized by differential scanning calorimetry (DSC), polarized optical microscopy, wide‐angle X‐ray diffraction (WAXD), and intrinsic viscosity measurements. The mechanical properties and the morphology of the fibers were also determined by tensile tester, WAXD, and scanning electron microscopy (SEM). The copolyesters exhibited phase‐separated nematic liquid crystalline morphology within a broad temperature range in an isotropic matrix. DSC analysis of the copolyesters revealed broad endotherms associated with the nematic phases. The melting and spinning temperatures were in a processable region. Fibers exhibit well‐developed fibrillar structure parallel to the fiber axis. The highly oriented morphology of the fibrils is slightly dependent on the type of the linear monomer. The strength and modulus values determined for the fibers that contain equal molar composition of the linear p‐ABA, HQDA/TPA units are comparable to other reported rigid systems containing fully aromatic species. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2580–2587, 2002     

Phenoxaphosphino‐Modified Xantphos‐Type Ligands in the Rhodium‐Catalysed Hydroformylation of Internal and Terminal Alkenes

The solubility of the modifying ligand is an important parameter for the efficiency of a rhodium‐catalysed hydroformylation system. A facile synthetic procedure for the preparation of well‐defined xanthene‐type ligands was developed in order to study the influence of alkyl substituents at the 2‐, and 7‐positions of the 9,9‐dimethylxanthene backbone and at the 2‐, and 8‐positions of the phenoxaphosphino moiety of ligands 1 – 16 on solubility in toluene and the influence of these substituents on the performance of the ligands in the rhodium‐catalysed hydroformylation. An increase in solubility from 2.3 mmol⋅L⁻¹ to >495 mmol⋅L⁻¹ was observed from the least soluble to the most soluble ligand. A solubility of at least 58 mmol⋅L⁻¹ was estimated to be sufficient for a large‐scale application of these ligands in hydroformylation. Highly active and selective catalysts for the rhodium‐catalysed hydroformylation of 1‐octene and trans‐2‐octene to nonanal, and for the hydroformylation of 2‐pentene to hexanal were obtained by employing these ligands. Average rates of >1600 (mol aldehyde) × (mol Rh)⁻¹×h⁻¹ {conditions: p(CO/H₂) = 20 bar, T = 353 K, [Rh] = 1 mM, [alkene] = 637 mM} and excellent regio‐selectivities of up to 99% toward the linear product were obtained when 1‐octene was used as substrate. For internal olefins average rates of >145 (mol aldehyde)×(mol Rh)⁻¹×h⁻¹ {p(CO/H₂) = 3.6–10 bar, T = 393 K, [Rh] = 1 mM, [alkene] = 640–928 mM} and high regio‐selectivities up to 91% toward the linear product were obtained.     

Synthesis and chemical properties of dielectric polyphenylenes with nitro group

Polyphenylenes consisting of nitrophenylene and didodecyloxy‐p‐phenylene units have been synthesized by Pd‐catalyzed organometallic polycondensation. The polymers showed good solubility and had number–average molecular weights (M_n) of 13,000–37,000. Their spin‐coated films showed fairly high dielectric constants (ε) of 3.75–6.36. The polymers were electrochemically active with electrochemical reduction peaks in the range of ?1.72 to ?1.99 V versus Ag⁺/Ag in an acetonitrile solution of [NEt₄]BF₄ (0.10M). The polymer composed of 2,3′‐dinitrobiphenyl and didodecyloxy‐p‐phenylene units showed thermotropic liquid crystalline phase at about 240°C. Cast films of the polymer had a birefringent phase at room temperature, suggesting self‐assembly of the polymer in the solid. XRD studies revealed that the polymers assumed an ordered structure assisted by aggregation of the long alkoxy side chains in the solid. The polymer main chain in the cast film is considered to be aligned parallel with respect to the surface of substrates. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Separation of fullerenes C60 and C70 using a crystallization‐based process

A crystallization‐based process that separates pure fullerenes C₆₀ and C₇₀ from their mixture using o‐xylene as the solvent has been developed. Isothermal solid–liquid equilibrium phase diagrams of the C₆₀‐C₇₀‐o‐xylene ternary system for a number of temperatures were first determined at 1 atm. Taking advantage of the shift in solvent‐free composition of the C₆₀‐C₇₀ double saturation point with temperature and based on the solid solution‐forming phase behavior between C₆₀ and C₇₀, the flowsheet of a general crystallization process was then synthesized. It involved the fractionation of a C₆₀‐C₇₀ fullerene mixture into C₆₀‐rich and C₇₀‐rich solid solutions using temperature‐swing crystallization, followed by purification of the solid solutions with multistage crystallization into pure C₆₀ and C₇₀ solids. To demonstrate process feasibility, bench‐scale batch experiments were performed using a commercially available fullerene mixture that was pretreated by adsorption to remove higher fullerenes. C₆₀ and C₇₀ solids of purity higher than 99 wt % were obtained. © 2009 American Institute of Chemical Engineers AIChE J, 2010     

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     

Revamping an Existing Aromatics Complex with Simulated Moving‐Bed Reactor for p‐Xylene Production

A simulated moving‐bed reactor (SMBR) for the production of p‐xylene is studied as part of a proposal to modify an existing aromatics complex in order to increase the production of benzene and p‐xylene. The proposed complex includes a single‐stage crystallization unit to further purify high p‐xylene streams from a selective toluene disproportionation and said SMBR units. Mass balances for two cases are estimated, namely, the current flow of reformate fed to the complex and a twofold flow. Results show significant increases of benzene and p‐xylene for both cases compared to the current production of the complex.     

Adsorptive Separation of o‐/p‐Aminoacetophenones using Acidic Ion Exchange Resins

Abstract

Separation of o‐/p‐aminoacetophenones (o‐/p‐AAPs) is investigated by a two‐step process: selective solubilization in an organic solvent followed by reactive adsorption on functionalized polymers. Since, p‐AAP and o‐AAP show inter‐ and intra‐molecular hydrogen bonding, respectively, the former is solubilized to a much lesser extent than the latter in an organic solvent. For example, o‐AAP dissolves completely while p‐AAP shows only 1.8% saturation solubility in toluene. Selective solubilization of o‐AAP in toluene, therefore, gives pure p‐AAP as residual solid in high yields. In the subsequent adsorption step, a strongly acidic ion exchange resin removes selectively the trace amounts of p‐AAP from the toluene phase giving pure o‐AAP.     

Xylene Isomerization in the Liquid Phase Using Large‐Pore Zeolites

Three large‐pore zeolites, Beta with Si/Al ratios of 25 and 35 and Mordenite with an Si/Al ratio of 30, were studied in the conversion of o‐xylene at 493 K. Maximum conversion was achieved by the catalyst with the highest Si/Al ratio due to faster diffusion of the isomer inside the zeolite channels because of the lower acidity of the solid even with larger crystal size. A kinetic study was then carried out over this catalyst between 473 and 513 K in a batch reactor in the liquid phase. The activation energies obtained do not indicate the presence of diffusional constraints towards any isomer. Finally, the kinetic model obtained was simulated in a fixed‐bed reactor and compared to ZSM‐5 in the temperature range from 493 to 533 K. An increment in p‐xylene production of 20 % on average was obtained.     

Manganese Dioxide and N‐Hydroxyphthalimide. An Effective Catalytic System for Oxidation of Nitrotoluenes with Molecular Oxygen

The inexpensive manganese dioxide has been proven to be an efficient auxiliary for oxidizing N‐hydroxyphthalimide (NHPI) to form the phthalimide N‐oxyl radical via reduction and reoxidation. The combination of manganese dioxide and NHPI could catalyze effectively the oxidation of nitrotulenes by molecular oxygen. Thus, the oxidation of p‐nitrotoluene with molecular oxygen (0.4 M Pa) in the presence of manganese dioxide (10 mol %) and NHPI (10 mol %) in acetic acid at 110 °C for 4 h proceeded with 97 % conversion, and gave p‐nitrotoluene in 89 % isolated yield.     

Homogeneous Tubular‐Flow Process for Monoolein Preparation

Esterification of fatty acids with glycerol is characterized by negligible solubility of the two liquid phases. The reactions to mono‐, di‐ and triglycerides taking place in the fatty acid phase, are limited by chemical equilibrium. The scope of this study is to investigate in a tubular reactor the conversion of a homogeneous mixture of oleic acid and glycerol in tert‐butanol. The liquid composition in this study was 1 mol of oleic acid, 6 mol of glycerol and 14 mol of tert‐butanol. Experiments were conducted in a tubular reactor at 35 atm over a temperature range of 200–240 °C and residence times of 0.7–17.6 h to determine the kinetics and the chemical equilibrium. The selectivity to monoolein was >95 mol %. A reversible second order reaction fits the data well.     

Synthesis of high performance polyamides utilizing copper‐catalyzed amidation of a dibromoarene with different diamides

A series of diphenylquinoxaline‐containing polyamides were prepared from the condensation polymerization of 2,3‐bis (4‐bromophenyl) quinoxaline (DBQ) with various primary and secondary diamides via copper‐catalyzed amidation reaction. The polyamides were characterized with FTIR, NMR, GPC, differential scanning calorimeter, and thermo gravimetric analysis, and their solubility and viscosity were measured. The polyamides synthesized here are amorphous and showed relatively good solubility in polar aprotic solvents and demonstrate the ability to form brownish hard films by solvent casting; their inherent viscosities ranged from 49 to 55 mL/g. The average molecular weights of polyamides were in the range of M_w = 11,950–5592 g/mol (MWD = 1.21–1.87). These polyamides had relatively high thermal stability with T_g values up to 276°C, 10% weight loss temperatures (T_10%) in the range of 364–476°C, and char yields at 600°C in N₂ up to 72%. They also exhibit emission in the solid state and in dilute (0.2 g/dL) DMAc solution at 425–484 nm with photoluminescence quantum (?_f) yields in the range of 14–23%. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Optimization of solvent crystallization process in obtaining high purity anthracene and carbazole from crude anthracene

Solvent crystallization is the main method used for preparing anthracene and carbazole from the crude anthracene. The key to the optimization of this method is improving the solubility selectivity of the solvent by means of solvent modulating and process optimization. In this study, the solubility of anthracene, phenanthrene, and carbazole in xylene, dimethylformamide (DMF), DMF with amine/amide, isopropanolamine, and chlorobenzene is examined and the solid‐liquid ternary anthracene–carbazole–DMF/(DMF+19.96% isopropanolamine) system phase diagram is determined and applied in the solvent crystallization process. The results showed that the solubility selectivity of xylene increases with increased temperature. Also, selectivity increases with an increase of the amount of isopropanolamine in the mixture of DMF and isopropanolamine, while decreases with increased temperature. Through multiple washings of crude anthracene with xylene, DMF+19.96% isopropanolamine, and chlorobenzene, it was possible to obtain anthracene and carbazole of purity higher than 98 wt %. © 2013 American Institute of Chemical Engineers AIChE J, 60: 275–281, 2014     

Synthesis and Properties of Random Copolymers of Functionalised Polybenzimidazoles for High Temperature Fuel Cells

A series of polybenzimidazoles (PBIs) incorporating main chain sulphonic acid groups were synthesised as random copolymers with p‐PBI in varying ratios using polyphosphoric acid (PPA) as both the polymerisation solvent and polycondensation reagent. The PPA process was used to produce high molecular weight phosphoric acid (PA) doped PBI gel membranes in a one‐step procedure. These membranes exhibit excellent mechanical properties (0.528–2.51 MPa tensile stress and 130–300% tensile strain) even at high acid doping levels [20–40 mol PA/PRU (polymer repeat unit)] and high conductivities (0.148–0.291 S cm^–1) at elevated temperatures (>100 °C) with no external humidification, depending on copolymer composition. Fuel cell testing was conducted with hydrogen fuel and air or oxygen oxidants for all membrane compositions at temperatures greater than 100 °C without external feed gas humidification. Initial studies showed a maximum fuel performance of 0.675 V for the 25 mol% s‐PBI/75 mol% p‐PBI random copolymer at 180 °C and 0.2 A cm^–2 with hydrogen and air, and 0.747 V for the same copolymer at 180 °C and 0.2 A cm^–2 with hydrogen and oxygen.     

Benzene,Toluene and p‐xylene Interactions and the Role of Microbial Communities in Remediation Using Bioventing

Aromatic hydrocarbons, particularly benzene, toluene and xylene (BTX), are major contaminants at many hazardous waste sites. We studied volatilization and biodegradation of BTX from unsaturated soil through bioventing. Following inoculation with indigenous soil microorganisms obtained from the Dagang Oil Field in Tianjin, China, varying amounts of BTX were added to soil in a stainless steel column provided with a constant flow of CO₂‐ free air and pure N₂. Volatilization‐to‐biodegradation ratios of benzene, toluene and p‐xylene were 6:1, 2:1 and 2:1 respectively. Final concentrations recorded in soil gas after three weeks were 0.128 mg/L benzene, 0.377 mg/L toluene and 0.143 mg/L p‐xylene. Interactions between the contaminants occurred: benzene and p‐xylene degradation were accelerated while toluene was being degraded, and the presence of p‐xylene increased the lag period for benzene degradation.     

Studies on the δ‐form complex in the syndiotactic polystyrene–organic molecule system. II. Structural investigation of the δ‐form with p‐ and m‐xylene isomers

Syndiotactic polystyrene (sPS) membranes containing different mole fractions of p‐xylene were prepared by a solution‐casting procedure. Complex formation between sPS and xylene was studied by thermogravimetric analysis and Fourier transform infrared spectroscopy. The stability and desorption behavior of the sPS–guest solvent and phase transitions were studied by differential scanning calorimetry. The formation of the δ‐form complex in the presence of different mole fractions of xylene isomers was analyzed and confirmed. The mole fraction of p‐xylene in the dried membrane was found to be higher than that of the corresponding mole fraction in the isomer solvent solution used for casting. This was attributed to the preferential complexing ability of p‐xylene with sPS. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2882–2887, 2003     

Synthesis of carvacrol by Friedel–Crafts alkylation of o‐cresol with isopropanol using superacidic catalyst UDCaT‐5

BACKGROUND: Alkylation of o‐cresol with propylene or isopropyl alcohol (IPA) over solid acid catalysts results in the formation of carvacrol, which finds potential applications in the synthesis of fine chemicals, intermediates, specialty chemicals, flavours and fragrances. RESULTS: The present work covers evaluation of novel mesoporous superacidic catalysts namely UDCaT‐4, UDCaT‐5 and UDCaT‐6 in the greener synthesis of carvacrol. The catalysts are modified versions of zirconia showing high catalytic activity, stability and reusability. The catalytic activity increases in the following order: UDCaT‐5 > UDCaT‐4 > UDCaT‐6 > sulfated zirconia. The process was optimized and a mathematical model developed to describe the reaction pathway in liquid phase. Carvacrol could be efficiently obtained with a selectivity up to 82% at an isopropanol conversion of 98% after 2 h over UDCaT‐5 at 180 °C. CONCLUSION: The reaction is free from any external mass transfer as well as intraparticle diffusion limitations and is intrinsically kinetically controlled. An overall second‐order kinetic equation was used to fit the experimental data. The activation energy was found to be 19.2 kcal/mol. The reaction was carried out without any solvent in order to make the process cleaner and greener. Copyright © 2009 Society of Chemical Industry     

A new catalytic process for high‐efficiency synthesis of p‐xylene by methylation of toluene with CH3Br

A new catalytic process for p‐xylene synthesis from the methylation of toluene with CH₃Br was proposed. CH₃Br was prepared from the catalytic bromination of natural gas (CH₄), by using H₂O + HBr + O₂ as mediator over supported Rh catalyst. The methylation conditions were investigated using HZSM‐5 or modified HZSM‐5 catalyst. Under optimal reaction conditions, p‐xylene selectivity is up to 93%, and p‐xylene yield is more than 21% at 673 k over the Si—P modified HZSM‐5 catalyst. Compared to the processes using MeOH or dimethyl carbonate (DMC) as methylation agent, this new process is very attractive in an economic standpoint since CH₄ is much cheaper than MeOH and DMC. In addition, the process has other advantages, such as mild reaction conditions, simple operation, high‐product yield, and so on. It is predicted that the process has good industrial potential for para‐xylene production. © 2012 American Institute of Chemical Engineers AIChE J, 59: 532–540, 2013     

Graft copolymerization of acrylic acid onto methylcellulose by potassium permanganate‐p‐xylene redox pair

Poly(acrylic acid) was grafted onto methylcellulose in aqueous media by a potassium permanganate‐p‐xylene redox pair. Within the concentration range from 0.93 × 10^?3 to 9.33 × 10^?3M, p‐xylene, the graft copolymerization reaction exhibited minimum and maximum graft yields and was associated with two precursor‐initiating species, a p‐xylyl radical and its diradical derivative. The efficiency of the graft was low, not higher than 12.9% at a p‐xylene concentration of 0.93 × 10^?3M and suggested the dominance of a competitive homopolymerization reaction under homogeneous conditions. The effect of permanganate on the graft yield was normal and optimal at 135% graft yield, corresponding to a concentration of the latter of 33.3 × 10^?3M over the range from 8.3 × 10^?3 to 66.7 × 10^?3M. The conversion in graft yield showed a negative dependence on temperature in the range 30–60°C and suggested a preponderance of high activation energy transfer reaction processes. The calculated composite activation energy for the graft copolymerization was 7.6 kcal/mol. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 278–281, 2004