Novel synthesis of -caprolactam from cyclohexanone-oxime via Beckmann rearrangement over mesoporous molecular sieves MCM-48

Vapor-phase synthesis of -caprolactam (-C) from cyclohexanone-oxime (CHO) has been studied at 1 atm and 300–400 °C using SiMCM-48 and AlMCM-48(X) with Si/Al molar ratios X in a fixed-bed, continuous flow reactor. The catalysts were characterized with ICP-AES, XRD, TEM, FT-IR, N₂-adsorption, ²⁷Al and ²⁹Si MAS NMR and TPD of ammonia. An increase of X value in AlMCM-48(X) enhances both the BET surface area and the unit cell parameter but diminishes the acid amount. In the reaction of CHO, benzene, toluene, ethanol and 1-hexanol were utilized as solvents. The CHO conversion increases with the reaction temperature, whereas the -C selectivity exhibits the opposite trend due to side reactions. The catalyst stability is greatly enhanced by using ethanol and 1-hexanol as the solvents due to their production of water vapor via dehydration. Excellent catalytic performance of AlMCM-48(10) is attained at 1 atm, 350 °C and W/Fc 74.6 g h/mol by using 1-hexanol in the feed; the CHO conversion and the -C selectivity exhibit higher than 99% and 90%, respectively, during at least 130 h process time.     

Effect of carbonization time on the structure and electromagnetic parameters of porous-hollow carbon fibres

A series of polyacrylonitrile-based porous-hollow carbon fibres (PAN-PHCFs) were prepared by carbonizing PAN porous-hollow cured fibres at 1073 K for different times in nitrogen. The effects of carbonization time on the structure, electrical volume conductivity and electromagnetic parameters were investigated. Results indicate that the degree of graphitization increases as carbonization time increases. The electrical volume conductivity increases as the degree of graphitization and carbonization time increase. The real and imaginary parts of the complex permittivity (′ and ″) increase with carbonization time increasing. The values of ′ and ″ of composites of PAN-PHCFs and paraffin are 13.76 and 10.09 when the carbonization time is 240 min, and the electrical volume conductivity of PAN-PHCFs is 190.47 Ω⁻¹ m⁻¹.     

The effect of crystallographic orientation and solution aging on the electrical properties of sol–gel derived Pb(Zr0.45Ti0.55)O3 thin films

Lead zirconate titanate—Pb(Zr_0.45Ti_0.55)O₃ thin films are grown on Pt_1 1 1/Ti/SiO₂/Si_1 0 0 substrates by a sol–gel method with 1 0 0/0 0 1 and 1 1 1 preferred orientations. Film orientation was controlled mainly by the annealing process and temperature. Films with 1 0 0/0 0 1 orientation consist of a uniform microstructure with micron size grains, whereas films with 1 1 1 orientation contain sub-micron grains. The electrical properties were influenced markedly by the microstructure and orientation of the films. The 1 1 1 oriented films exhibit a square-like hysteresis loop with remnant polarization (P_r) reaching 46 μC/cm² under 550 kV/cm, whereas 1 0 0/0 0 1 oriented films have a P_r of 20 μC/cm² with more slim hysteresis curves. Aging of the precursor solutions resulted in films growing with 1 0 0/0 0 1 texture and displaying inferior electrical properties.     

Fischer-Tropsch Synthesis: Catalyst activation of low alpha iron catalyst

Activation with three different gases (H₂, CO and synthesis gas) over an Fe100/K1.4/Si4.6/Cu2.0 catalyst was conducted to investigate the effects of pretreatment gas on Fischer-Tropsch Synthesis (FTS) activity and selectivity. Catalyst slurry was withdrawn from the reactor at increasing time intervals of FTS for Mössbauer spectroscopic analysis. Activation with CO produced the highest syngas conversion while H₂ generated the lowest; syngas activation produced a slightly lower conversion than CO activation. CO activation transformed the majority of the iron into χ-Fe₅C₂ and Magnetite with only 12% -Fe_2.2C being detected. Unlike the CO activated catalyst, the syngas activated iron catalyst resulted in a lower amount of χ-Fe₅C₂ than -Fe_2.2C. The initial high (64%) content of -Fe_2.2C decreased gradually to below 30% while CO conversion decreased from 83% to 55%. During this period, χ-Fe₅C₂ increased from initial 10% to 33%. Magnetite changed little during the process while the form of carbides interchanged. Hydrogen activation yielded a low CO conversion of 50% and only 8% χ-Fe₅C₂ and 16% -Fe_2.2C was formed while Magnetite was as high as 75% after the FTS reaction rate became constant. Although activation gas type had a significant effect on syngas conversion, hydrogen, syngas and CO activations produced similar H₂ to CO usage ratio, hydrocarbon product distribution, olefin fraction, alpha value and CO₂ selectivity.     

Enzymatic degradation of poly(propylene carbonate) and poly(propylene carbonate-co--caprolactone) synthesized via CO2 fixation

Poly(propylene carbonate) (PPC) and poly(propylene carbonate-co--caprolactone) (PPCCL) were synthesized via the zinc glutarate catalyzed copolymerization of carbon dioxide (CO₂) and propylene oxide (PO) without and with -caprolactone (CL), respectively. In addition, poly(-caprolactone) (PCL) was prepared via the homopolymerization of CL with the aid of methyl triflate catalyst. The polymer products were characterized in terms of their chemical compositions, molecular weights, and thermal properties. Films of these polymers were tested with a series of enzymes (four different families and a total of 18 enzymes) in a phosphate buffer in order to characterize their enzymatic degradabilities. This is the first report demonstrating that PPC films exhibit positive enzymatic degradability with Rhizopus arrhizus lipase, esterase/lipase ColoneZyme A, and Proteinase K. Moreover, PPCCL films exhibited positive enzymatic degradability with most of the enzymes utilized in our study, and thus PPCCL has an enzymatic degradability comparable to that of PCL. In particular, the PPCCL films exhibit excellent enzymatic degradability with Pseudomonas lipase, Rhizopus arrhizus lipase, and esterase/lipase ColoneZyme A. Considering its excellent enzymatic degradability, the PPCCL terpolymer has potential biomedical applications. In conclusion, ZnGA-catalyzed copolymerizations of CO₂ and PO with or without CL are chemical fixation processes of CO₂ that can be used to produce enzyme-degradable aliphatic polymers.     

An empirical model for kinetics of boron removal from boroncontaining wastewaters by the electrocoagulation method in a batch reactor

Boron removal from boron containing wastewaters prepared synthetically via the electrocoagulation method was studied. The experiments in which aluminum plate electrode was used were carried out in a batch reactor. The solution pH, initial boron concentration, current density, type of supporting electrolyte, temperature of solution and stirring speed were selected as experimental parameters. The obtained experimental results showed that efficiency of boron removal increased with increasing current density and decreased with increasing boron concentration in the solution. Supporting electrolyte had not significant effects on the percent of total boron removal. pH was very important parameter effecting boron removal and optimum pH was determined to be 8.0. This pH value reached an agreement with activity-pH diagrams for Al⁺³ species in equilibrium with Al(OH)₃ and boron species in aqueous media. As a result of increasing interaction between boron ions and dissolved aluminum ions in solution, the increasing solution temperature increased boron removal efficiency. Increasing stirring speed decreased boron removal efficiency where the increasing stirring speed decreased the capability of floc formation of aluminum ions. As a result, it was seen that about 99% of boron in the wastewater could be removed at optimum conditions. In addition, the process kinetics was predicted by using heterogeneous fluid–solid reaction models. It was seen statistically that the kinetics of this process agreed with the pseudo-second-order model as follows: X_B/(l−X_B) = 18,241[OH][C]^−3.45[CD]^7.79[t]^1.41[S]^−3.65exp[−30,668/RT].     

MoV-based catalysts in ethane oxidation to acetic acid: Influence of additives on redox chemistry

The formation of acetic acid and/or ethylene by oxidation of ethane is strongly dependent on X additives or Y promotor added to MoVO-based catalysts. MoV_0.4X_0.12YO_z (X = Nb; Y = Pd;  = 10⁻⁴) catalysts were prepared by the slurry method and their structural properties were studied by in situ (redox conditions) XRD, Raman and XPS techniques. The reactivity during reduction and reoxidation was analysed by thermal analysis (TGA/DSC). The oxidation of ethane was carried out in a conventional fixed bed microreactor with on line analysis by gas chromatography. Results show that Nb exerts mainly a structural effect as it is responsible for the stabilisation of molybdenum (VI) by formation of solid solutions with V, and that Pd modifies the rate of reduction of the solid catalysts. The increase of selectivity to acetic acid observed by Pd promotion is likely due to the transformation of ethylene to acetic acid occurring on neighboring Pd–V active sites.     

Novel synthetic strategy toward shape memory polyurethanes with a well-defined switching temperature

Shape memory polyurethanes (SMPUs) have been synthesised via a novel synthetic methodology, resulting in an improvement of the phase separation in the multi-block structure of the polyurethane and in its shape memory properties. ABA block copolymers based on semi-crystalline poly(-caprolactone) and amorphous poly(propylene oxide) (PPO) were used as precursor for the SMPUs. For their synthesis, poly(-caprolactone) diols have been converted into isocyanate end-capped prepolymers by using a mixture of 3(4) isocyanato-1-methyl-cyclohexylisocyanate isomers, after which a coupling with low-T_g poly(propylene oxide) oligomers is done. The shape memory polymers are obtained by reaction of the ABA block copolymers with hexamethylenediisocyanate and 1,4-butanediol as chain extender. Using this new strategy, a flexible segment (PPO) was introduced between the hard and the switching segments of the SMPU. For comparison, SMPUs without flexible segment have also been prepared with the conventional synthetic route. DSC, isostrain experiments and cyclic shape memory tests revealed narrower switching temperatures for the SMPUs including a flexible segment.     

Low temperature sintering of barium titanate ceramics assisted by addition of lithium fluoride-containing sintering additives

By addition of LiF-containing sintering additives to commercial BaTiO₃ powder, more than 98% of the theoretical density was reached at a sintering temperature of 900 °C both on powder compacts and laminates. Dielectric measurements were performed on ceramic samples in the temperature and frequency ranges from −20 °C to 125 °C and from 10³ to 10⁶ Hz, respectively. High relative permittivity (_r  3160) and low dielectric loss (tan δ  0.014) were measured for tapes of the favoured material. The breakdown strength for tapes with a thickness of about 80 μm is 30 kV/mm. The microprobe analysis showed, that no interfacial reaction between the dielectric layer and the Ag-electrode had occurred.The newly developed barium titanate ceramics completely densifying at 900 °C turned out to be promising for integration of buried capacitors in LTCC multilayers.     

Preparation of poly(-caprolactone) grafted titanate nanotubes

This work reported for the first time the surface functionalization of titanate nanotubes (TNTs) with biodegradable poly(-caprolactone) (PCL). A “grafting from” approach based on in situ ring-opening polymerization of -caprolactone from TNTs with a special surface modification was adopted to prepare the PCL-g-TNTs. The thickness of the grafted PCL shell can be controlled by increasing reaction time. After grafted with PCL, both the dissolubility and flexibility of the tubes were greatly improved. The obtained PCL-g-TNTs can easily disperse in several organic solvents, and the dispersal stability depends on solvent polarity and PCL shell thickness. Furthermore, the PCL immobilized on the surface of TNTs still possessed a good biodegradable capacity and could be completely decomposed in the presence of Pseudomonas (PS) lipase. The PCL-g-TNTs reported here are promising in biotechnology applications due to good dissolubility, flexibility, biocompatibility and the tubular nano-structure.     

Effects of zinc oxide on thermal shock behavior of zinc sulfide– silicon dioxide ceramics

Thermal shock resistances of ZnO and non-ZnO containing ZnS–SiO₂ composite ceramics are observed using water quenching method. The residual strengths are measured as function of quenching temperature differences. The thermal shock damage parameters R and R are evaluated to compare with experimental results. Specimens with low thermal shock damage parameters show acute strength degradation up to 76% at a lower quenching temperature difference of 250 °C. The 1% ZnO containing specimen with medium density and higher thermal shock damage parameter values demonstrates a minimal strength drop of 36% at a higher quenching temperature difference of 300 °C. The evaluated R and R values correspond well with the residual strength at elevated temperature difference. It implies that the good thermal shock resistance of ZnS–SiO₂ system can be achieved by improving fracture toughness with moderate ZnO addition and pores.     

Development of kinetic model for the reaction between SO2/NO and coal fly ash/CaO/CaSO4 sorbent

Sorbents for semidry-type flue gas desulfurization (FGD) process can be synthesized by mixing coal fly ash, calcium oxide, and calcium sulfate in a hydration process. As sorbent reactivity is directly correlated with the specific surface area of the sorbent, reacting temperature, concentration of the reacting gas species and relative humidity, two major aim in the development of a kinetic model for the FGD process are to obtain an accurate model and at the same time, incorporating all the parameters above. Thus, the objective of this work is to achieve these two aims. The kinetic model proposed is based on the material balance for the gaseous and solid phase using partial differential equations incorporating a modified surface coverage model which assumes that the reaction is controlled by chemical reaction on sorbent grain surface. The kinetic parameters of the mathematical model were obtained from a series of experimental desulfurization reactions carried out under isothermal conditions at various operating parameters; inlet concentration of SO₂ (500 ppm  C_0,SO2  2000 ppm), inlet concentration of NO (250 ppm  C_O,NO  750 ppm), reaction temperature (60 °C  T  80 °C) and relative humidity (50%  RH  70%). For a variety of initial operating conditions, the mathematical model is shown to give comparable predictive capability when used for interpolation and extrapolation with error less than 7%. The model was found useful to predict the daily operation of flue gas desulfurization processes by using CaO/CaSO₄/coal fly ash sorbent to remove SO₂ from flue gas.     

A novel route to α,ω-telechelic poly(-caprolactone) diols, precursors of biodegradable polyurethanes, using catalysis by decamolybdate anion

A new convenient route for the synthesis of poly(-caprolactone) (PCL) with α,ω-telechelic diols' end-groups is presented. Synthesis of α,ω-telechelic PCL diols (HOPCLOH) was achieved by ring-opening polymerization (ROP) of -caprolactone (CL) catalyzed with ammonium decamolybdate (NH₄)₈[Mo₁₀O₃₄] and using diethylene glycol (DEG) as initiator. Obtained HOPCLOH was characterized by ¹H and ¹³C NMR, FT-IR, GPC and MALDI-TOF. Comparative studies demonstrate that ammonium decamolybdate (NH₄)₈[Mo₁₀O₃₄] is better catalyst than Sn-octanoate (SnOct₂) toward CL polymerization in presence of DEG, under the conditions tested. A biodegradable poly(ester-urethane-urea) derivative was efficiently prepared from synthesized HOPCLOH. Obtained polymer shows minor differences with respect to the properties recorded for a poly(ester-urethane-urea) obtained from commercial HOPCLOH.     

Cyclometalated platinum(II) complex with C^N^N tridentate ligand as sensitizer for lanthanide luminescence

The preparation, characterization and photophysical properties of heterobinuclear complexes {Pt(C^N^N)(CCbpy)}Ln(hfac)₃ (C^N^N = 2-(6-(naphthalen-3-yl)-4-phenylpyridin-2-yl)pyridine; HCCbpy = 5-ethynyl-2,2′-bipyridine; Ln = Nd, Eu, Yb; hfac = hexafluoroacetylacetonate) are described. With excitation at 390  λ_ex  500 nm which is the MLCT/LLCT absorption region of the Pt(C^N^N)(CCbpy) chromophore, lanthanide luminescence is successfully attained by Pt → Ln energy transfer from the platinum(II) antenna chromophore to the lanthanide center across the bridging CCbpy ligand.     

Self-assembly hydrothermal assisted synthesis of mesoporous anatase in the presence of ethylene glycol

Mesoporous nanocrystalline anatase was prepared hydrothermally employing P123 as structure-directing agent. Ethylene glycol was used as a key synthesis parameter to fine tune the morphology, crystal size and pore size of the resultant mesophases. The incorporation of EG in the synthesis gel resulted in the formation of 1–2 μm sphere-like shapes and led to an increase in the specific surface area from 95 to 170 m²/g, decrease in the average pore size from 11 to 4.8 nm, and decrease in the average crystallite size from 17 to 12 nm. These mesophases were used as photocatalysts for the UV degradation of methylene blue and methyl orange. The mesoporous anatase phases photodegraded MB 1.5–3× faster than commercially available P25 and showed limited photocatalytic behavior for methyl orange.     

Thermodynamics of densification of powder compact

This paper established a necessary condition for the sintering of powder compacts by examining the total free energy balance in terms of the particle size, neck size and contact number. The thermodynamic analysis of the proposed model clarifies the relation of shrinkage (q) of powder compact-contact angle ()-relative density at a given dihedral angle (_e) of a grain boundary. Faster densification proceeds in the region with a larger coordination number (n) of particles at a small q value. A large shrinkage is needed to eliminate the large pores formed in the structure of small n value. Full density can be achieved in the range of 117° < _e < _c, where _c is the critical dihedral angle allowing the shrinkage required for full densification. The derived concepts are effective to interpret the densification of hierarchical particle clusters. The relative density of ceria powder compact approached nonlinearly unity with decreasing ratio of pore size (r(P)) to grain size (r) and this tendency was well expressed by the present densification model. The influence of grain growth on the densification of powder compact and size of large pore isolated in a dense matrix are also quantitatively discussed.     

Influence of liquid properties on flow regime and backmixing in a special bubble column

An experiment aimed to link the extent of axial mixing in a special configuration bubble column reactor with different liquid properties (water, 10% K₂CO₃ solution, 20% K₂CO₃ solution, paraffine). The experimental results proved that, increase of liquid viscosity will delay the mean residence time and weaken gas axial backmixing. Increased surface tension leads to lower flow regime transition point and higher overall gas holdup. Surface tension is the dominant factor to influence of gas axial backmixing degree. A simple RTD model for homogeneous–heterogeneous regime is developed in the column of 0.1 m diameter and the corresponding correlation of gas axial dispersion coefficients is . The model is verified by experiments with air/water/paraffine system. Good agreement is found. As a byproduct, a non-empirical formula for gas holdup results, _g/(1−_g)⁴ = 0.579 (u_gμ/σ)^0.918 (μ⁴g/ρ_Lσ³)^−0.252. But both correlations cannot be available for K₂CO₃ solution with addition of small quantities of surface tension in pure liquid.     

Near-ambient X-ray photoemission spectroscopy and kinetic approach to the mechanism of carbon monoxide oxidation over lanthanum substituted cobaltites

We have studied the oxidation of carbon monoxide over a lanthanum substituted perovskite (La_0.5Sr_0.5CoO_3−d) catalyst prepared by spray pyrolysis. Under the assumption of a first-order kinetics mechanism for CO, it has been found that the activation energy barrier of the reaction changes from 80 to 40 kJ mol⁻¹ at a threshold temperature of ca. 320 °C. In situ XPS near-ambient pressure (0.2 torr) shows that the gas phase oxygen concentration over the sample decreases sharply at ca. 300 °C. These two observations suggest that the oxidation of CO undergoes a change of mechanism at temperatures higher than 300 °C.     

Use of different mesostructured materials based on silica as cobalt supports for the Fischer–Tropsch synthesis

To obtain a novel, active and selective to diesel catalytic material for syngas processing via Fischer–Tropsch synthesis (FTS), a series of 20 wt.% cobalt catalysts has been prepared by impregnation of a mesoporous molecular sieve based on silica (SBA-15, Al-MCM-41, INT-MM1), and a commercial amorphous silica for comparison purposes. All materials were characterized by several physico-chemical techniques: AAS, BET surface area, XRD, TPR, and H₂ chemisorption with pulse reoxidation and finally their reactivity on the FTS reaction was evaluated at 523 K, 10 bar, and H₂/CO = 2. Catalytic and characterization results show a great influence of mesoporous support porosity on the structure, reducibility, and FTS catalytic behavior of cobalt oxide species supported over these ordered materials. It was found that the size of supported cobalt oxide species formed during the calcination step increased with the average pore size (D_p) of the mesoporous support. Thus, the catalyst with larger Co oxide species located in wide pore silica showed to be easily reducible, more active and very selective toward the diesel fraction. It seems to be the case of the Co/SBA-15 solid, which showed to be the most active solid (XCO 63%) when the same mass of catalyst was used. Under CO iso-conversion conditions (XCO 40%), Co/SBA-15 was more selective toward the formation of C₅₊ hydrocarbons (80%, α = 0.76) and less selective to CH₄ (15%). On the contrary, when Al-MCM-41 and INT-MM1 were used as supports, a lower selectivity to C₅₊ and CO conversion and higher CH₄ selectivity (20%) were observed due to the decrease of D_p, of the cobalt oxide species size and the reducibility degree of such species.     

Development of mesoporous Al,B-MCM-41 materials: Effect of reaction temperature on the catalytic performance of Al,B-MCM-41 materials for the cyclohexanone oxime rearrangement

A series of aluminum–boron–silicate MCM-41 mesoporous materials and their counterparts treated with NH₄F aqueous solution were synthesized and characterized by using XRD, MAS NMR, nitrogen physisorption, DRIFT, TG-DTA, TP/MS and pyridine adsorption. All of the samples showed typical MCM-41 structural and textural properties. ²⁷Al MAS NMR showed that the aluminum environment was mainly four-coordinated and six-coordinated aluminum for non-fluorinated samples and fluorinated ones, respectively. Boron was in the trigonal framework environment at ca. catalytic reaction temperatures and the NH₄F treatment did not affect the boron environment in our Al,B-MCM-41 materials. All of the Al,B-MCM-41 materials studied contained both Brønsted and Lewis acid sites. However, the strong acid Brønsted/Lewis ratios decreased in the fluorinated catalysts. Moreover, the influence of temperature was studied on the cyclohexanone oxime conversion and the product selectivity in the 623–798 K range. Results indicated that temperatures lower than 748 K favored Beckmann rearrangement to -caprolactam, whereas, at higher temperatures the main reaction was cyclohexanone oxime hydrolysis to cyclohexanone. The aluminum–boron–silicate MCM-41 mesoporous materials treated with NH₄F improved both the selectivity to -caprolactam (related mainly to boron content) and their life span (related to their lower ratios of strong Brønsted/Lewis acid sites).