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.     

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.     

Synthesis of tadpole-shaped copolyesters based on living macrocyclic poly(-caprolactone)

Synthesis of an asymmetric tadpole-shaped aliphatic copolyester consisting of a poly(-caprolactone) ring and two poly(l-lactide) tails was reported for the first time. First, a high molecular weight cyclic PCL macroinitiator (M_n = 31,000) was prepared by intramolecular photocross-linking of “living” chains. Polymerization of l-lactide was resumed by the tin dialkoxide containing macrocycles, thus making the targeted tadpole-shaped copolyester available. A preliminary investigation of the crystallization of these copolyesters was carried out by differential scanning calorimetry and polarized optical microscopy.     

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.     

Structural organization of catalytic functions in Mo-based oxides for propane selective oxidation

Several single phasic MoVO-based mixed oxides, all of which have a layer structure in the direction of c-axis and a high dimensional arrangement of metal octahedra in a–b plane, were synthesized by hydrothermal method and their catalytic performance in the selective oxidation of propane to acrylic acid were compared in order to elucidate structure effects on catalytic property and roles of constituent elements. It was clearly demonstrated that the catalyst with the particular arrangement of MO₆ (M = Mo, V) octahedra forming slabs with pentagonal, hexagonal and heptagonal rings in (0 0 1) plane of orthorhombic structure was exclusively superior both in the propane oxidation activity and in the selectivity to acrylic acid to the other related Mo- and V-based layer oxide catalysts consisting of either pentagonal or hexagonal ring unit. The role of constituent elements was clarified by the comparison of catalytic performance of MoVO, MoVTeO and MoVTeNbO, all of which have the same orthorhombic structure. Mo and V, which were indispensable elements for the structure formation, were found to be responsible for the catalytic activity for propane oxidation. Te located in the central position of the hexagonal ring promoted the conversion of intermediate propene effectively, resulting in a high selectivity to acrylic acid. The introduced Nb occupied the same structural position of V and the resulting catalyst clearly showed the improved selectively to acrylic acid particularly at high conversion region, because the further oxidation of acrylic acid to CO_x was suppressed.     

Effects of sodium promoter on the mechanism of biphenol hydrogenation over Pd/C catalyst

The effect of sodium promoter on the catalytic hydrogenation of biphenol (BP) was investigated. Several reaction products were identified and the change in their distribution with time was analyzed to find the reaction mechanism. Different amount of sodium salt was impregnated on Pd/C to observe its effect on the composing reactions of BP hydrogenation. The existence of sodium metal decreased the CC bond hydrogenation, but accelerated the CO bond hydrogenation resulting in the increase of the yield to bicyclohexyl-4,4′-diol (BHD). The promotional effect of Na on the supported palladium on carbon catalysts were explained by electronic and geometric factors.     

Cs exchanged phosphotungstic acid as an efficient catalyst for liquid-phase Beckmann rearrangement of oximes

Cs exchanged phosphotungstic acid is a highly efficient and environmentally benign solid acid catalyst for the liquid-phase Beckmann rearrangement of ketoximes to the corresponding amides. The catalysts Cs_xH_3−xPW₁₂O₄₀ (x = 1.5, 2, 2.5 and 3) were prepared by a titration method. The characterization results indicated that the primary Keggin structure remained intact after exchanging the protons with Cs ions. Moreover, the Cs exchanged catalysts were insoluble and exhibited larger BET surface area than the parent acid. The catalysts exhibited high reactivity and selectivity for the formation of -caprolactam, the precursor of Nylon 6, from cyclohexanone oxime. The catalyst can be recovered after reaction without any structural transformation.     

Self-assembly through hydrogen-bonding and C–Hπ interactions in metal complexes of N-functionalised glycine

The complex [Ni(L1)₂(py)₂]. toluene (L1 is N-phthaloylglycinato and py is pyridine) was prepared from solid state reaction whereas co-crystals having composition 2[Ni(L1)₂(py)₃(H₂O)] · [Ni(L1)₂(py)₂(H₂O)₂] · 2py · 2H₂O was obtained from solution state reaction.     

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).     

Efficient ring-opening polymerization of -caprolactone using anilido-imine–aluminum complexes in the presence of benzyl alcohol

A number of new anilido-imine–Al complexes ortho-C₆H₄(CHNAr¹)(NAr²)AlMe₂ [Ar¹ = C₆H₅, Ar² = C₆H₅ (2a); Ar¹ = 2,6-Me₂C₆H₃, Ar² = 2,6-Me₂C₆H₃ (2b); Ar¹ = 2,6-Et₂C₆H₃, Ar² = 2,6-Et₂C₆H₃ (2c); Ar¹ = 2,6-ⁱPr₂C₆H₃, Ar² = 2,6-Me₂C₆H₃ (2d); Ar¹ = 2,6-ⁱPr₂C₆H₃, Ar² = 2,6-Et₂C₆H₃ (2e)] were synthesized, characterized and used as initiators for the ring-opening polymerization of -caprolactone in the presence of benzyl alcohol. The effect of initiator structure and reaction conditions, such as benzyl alcohol/Al molar ratio and reaction temperature on the reactivity, and polymer molecular weight were investigated. The polymerization of -caprolactone initiated by these complexes was found to take place in an immortal fashion.     

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 preparation of carbon-supported PdCo alloy electrocatalysts for methanol-tolerant oxygen reduction reaction

Carbon-supported PdCo alloy electrocatalysts of different Pd/Co atomic ratios were simply prepared in an aqueous solution at room temperature with NH₄F as a complexing agent and H₃BO₃ as a buffer, followed by NaBH₄ reduction. As-prepared PdCo bimetallic nanoparticles show a single-phase face-centered-cubic (fcc) disordered structure, and the mean particle size is found to decrease with increase in Co content. TEM images demonstrated that the as-prepared PdCo alloy nanoparticles are well dispersed on the surface of the carbon support with a small particle size and a relatively narrow particle size distribution. For example, the average particle size of a Pd₂Co₁/C catalyst is ca. 3.0 nm, which is much smaller than that of the PdCo/C bimetallic nanoparticles reported by others. An activity evaluation of the oxygen reduction reaction (ORR) on as-prepared PdCo/C catalysts with a rotating disk electrode (RDE) technique indicated that the maximum ORR mass activity was observed for a Pd:Co atomic ratio of 4:1, but the highest specific activity was found on a Pd:Co atomic ratio of 2:1. Kinetic analysis reveals that the ORR on PdCo/C catalysts follows a four-electron process leading to water. Moreover, the PdCo/C catalyst exhibited much higher methanol tolerance during the ORR than the Pt/C catalyst, assessing that it may function as a methanol-tolerant cathode catalyst in a direct methanol fuel cell (DMFC).     

Modelling and simulation of a gas–solids dispersion flow in a high-flux circulating fluidized bed (HFCFB) riser

Radial solids velocity profiles were computed on seven axial levels in the riser of a high-flux circulating fluidized bed (HFCFB) using a two-phase 3-D computational fluid dynamics model. The computed solids velocities were compared with experimental data on a riser with an internal diameter of 76 mm and a height of 10 m, at a high solids flux of 300 kg m⁻² s⁻¹ and a superficial velocity of 8 m s⁻¹. Several hundreds of experimental and numerical studies on CFBs have been carried out at low fluxes of less than 200 kg m⁻² s⁻¹, whereas only a few limited useful studies have dealt with high solids flux. The k– two-phase turbulence model was used to describe the gas–solids flow in an HFCFB. The model predicts a core–annulus flow in the dilute and developed flow regions similar to that found experimentally, but in the region of highest solids concentration it is somewhat overpredicted at the level close to the inlet.     

Catalytic ozonation for the degradation of nitrobenzene in aqueous solution by ceramic honeycomb-supported manganese

Catalytic ozonation of nitrobenzene in aqueous solution has been carried out in a semi-continuous laboratory reactor where ceramic honeycomb and Mn–ceramic honeycomb have been used as the catalysts. The presences of the two catalysts significantly improve the degradation efficiency of nitrobenzene, the utilization efficiency of ozone and the production of oxidative intermediate species compared to the results from non-catalytic ozonation, and the improvement of them is even more pronounced in the presence of Mn–ceramic honeycomb. Adsorptions of nitrobenzene on the two catalytic surfaces have no remarkable influence on the degradation efficiency. Addition of tert-butanol causes the obvious decrease of degradation efficiency, suggesting that degradation of nitrobenzene follows the mechanism of hydroxyl radical (OH) oxidation. Some of the main operating variables like amount of catalyst and reaction temperature exert a positive influence on the degradation efficiency of nitrobenzene. Initial pH also presents a positive effect in the ozonation alone system while the optimum working initial pH is found to be around 8.83 and 10.67 to the processes of ozonation/ceramic honeycomb and ozonation/Mn–ceramic honeycomb, respectively. The surface characteristics measurement of the two catalysts indicates that the loading of Mn increases the specific surface area, the pH at the point of zero charge (pH_PZC) and the density of surface hydroxyl groups, and results in the appearance of new crystalline phase of MnO₂. The results of mechanism research confirm that the loading of Mn promotes the initiation of OH.     

Mechanism of heterogeneous catalytic ozonation of nitrobenzene in aqueous solution with modified ceramic honeycomb

The degradation efficiencies of nitrobenzene in aqueous solution were investigated by semi-continuous experiments in the processes of ozone alone, ozone/ceramic honeycomb (CH) and ozone/modified ceramic honeycomb (MCH). MCH with 1.0% Mn and 0.5% Cu had more pronounced catalytic ability than CH to accelerate the degradation of nitrobenzene, to increase the utilization efficiency of ozone, to improve the concentrations of hydrogen peroxide (H₂O₂) formation and hydroxyl radical (OH) initiation, and to enhance the removal efficiency of TOC. The modification process of CH with the metals enhanced the density of surface hydroxyl groups, which determines the initiation of OH from ozone decomposition and the generation of intermediate species on heterogeneous catalytic surface, yielding the acceleration of the degradation of nitrobenzene in aqueous solution. Possible reaction mechanism of ozone with heterogeneous catalytic surface in aqueous solution was proposed, and the formation mechanism of H₂O₂ and OH was also discussed according to the combined reactions in heterogeneous and homogeneous catalytic systems.     

Cathodic deposition of molybdenum and vanadium mixed oxyhydroxide films from V-substituted polymolybdophosphate

We report a new electrochemical route for fabricating molybdenum and vanadium mixed oxyhydroxide films on Au electrode from Keggin-type vanadium-substituted polymolybdophosphate. The process involves a potentiodynamic reduction of aqueous 9-molybdo(VI)-3-vanadophosphosphate(V) ([PMo₉V₃O₄₀]⁶⁻) in the potential region between 0 and −0.7 V versus Ag/AgCl. The resulting MoV oxyhydroxide film electrode gave a stable redox behavior in Na₂SO₄ electrolyte of pH 3. X-ray photoelectron spectroscopy revealed that this results from oxidation/reduction of Mo⁵⁺/Mo⁶⁺ in the film which accompanies extraction/insertion of protons for charge compensation. The deposited V ions remained in the film upon repetitive potential cycling without affecting their oxidation state. Voltammetric data in the presence of sodium nitrite showed electrocatalytic activity of the MoV oxyhydroxide toward the electroreduction of nitrite.     

Numerical studies of a tube-in-tube helically coiled heat exchanger

In the present study a tube-in-tube helically coiled (TTHC) heat exchanger has been numerically modeled for fluid flow and heat transfer characteristics for different fluid flow rates in the inner as well as outer tube. The three-dimensional governing equations for mass, momentum and heat transfer have been solved using a control volume finite difference method (CVFDM). The renormalization group (RNG) k– model is used to model the turbulent flow and heat transfer in the TTHC heat exchanger. The fluid considered in the inner tube is compressed air at higher pressure and cooling water in the outer tube at ambient conditions. The inner tube pressure is varied from 10 to 30 bars. The Reynolds numbers for the inner tube ranged from 20,000 to 70,000. The mass flow rate in the outer tube is varied from 200 to 600 kg/h. The outer tube is fitted with semicircular plates to support the inner tube and also to provide high turbulence in the annulus region. The overall heat transfer coefficients are calculated for both parallel and counter flow configurations. The Nusselt number and friction factor values in the inner and outer tubes are compared with the experimental data reported in the literature. New empirical correlations are developed for hydrodynamic and heat-transfer predictions in the outer tube of the TTHC.     

Carbon dioxide as carbon source: Activation via electrogenerated O2 in ionic liquids

The activation of carbon dioxide has been obtained in O₂/CO₂ saturated ionic liquids, via electrochemically generated O₂⁻, at a less negative potential than the one of the direct cathodic reduction of CO₂. This electrochemical activation has been applied to the C–N bond formation from amines and carbon dioxide in the synthesis of organic carbamates. A competitive reaction between electrogenerated superoxide ion and imidazolium cations yielding 2-imidazolones has been pointed out. This procedure allows to avoid the utilization of volatile and toxic organic solvents, supporting electrolytes and catalysts.     

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.     

Synthesis and characterization of a new compound bearing ketone and hydroxyl groups for preparation of ambient temperature self-crosslinking waterborne polyurethanes

A new crosslinker for polyurethane, N-[(1,1-dimethyl-2-acetyl)ethyl]-β-dihydroxy ethylamino propanamide (DDP), was synthesized by Michael reaction using diethanolamine (DEA) and diacetone acrylamide (DAAM). DDP is a dihydroxyl-containing compound with ketone moiety, which crosslinks during film formation through a reaction between ketone of DDP and hydrazide in water-soluble dihydrazide compound, added upon preparation of waterborne polyurethane. The optimal ratio of DEA/DAAM for Michael reaction, determined by gas chromatography (GC), was of 1.05 mol; highest yields (80%) were obtained with this ratio when the reaction was carried out at 90 °C with 12 h of reaction time using acetonitrile as solvent. Experimental conditions of DDP separation from the reaction mixture were predetermined first through thin-layer chromatography, and DDP separation was conducted by column chromatography. DDP with 97% of purity or higher was obtained. The structure of DDP was fully characterized by IR and NMR. The elemental composition and molecular weight of DDP were confirmed by high resolution GC–MS and HPLC–MS, respectively. Polyurethane latexes with DDP and post-added dihydrazide were prepared, and polymer film properties compared with DDP-free latex film. Tensile strength increased with a decrease in elongation in crosslinked polymers. Higher performance in water and solvent adsorptions was also detected.