Wagner A. Carvalho

Mesoporous redox molecular sieves analogous to MCM-41

The synthesis of MCM-41 analogue mesoporous metallosilicates with high specific surfaces, containing the redox active metals Ti, V, Cr, Mn, Fe, or Co, from an aqueous gel, under reflux is described. Their X-ray diffractograms reveal a highly ordered array of the mesopores. A strong host-guest interaction between the incorporated template molecules and the pore walls, observed by 13 C n.m.r., indicates the incorporation of the metals, which is further evidenced by u.v.-vis and 29 Si n.m.r. spectroscopy. These mesoporous metallosilicates are active as catalysts for the liquid phase oxidation of cyclohexane with aqueous H 2 O 2 or tert -butyl hydroperoxide.

Use of a La(III)-modified bentonite for effective phosphate removal from aqueous media.

A bentonite from the Northeast Brazilian region was modified with lanthanum (NT-25La) using an ion exchange process. Lanthanum incorporation in the natural clay, as well as the properties of the clay materials, were confirmed by X-ray diffraction, X-ray fluorescence, specific surface area and scanning electron microscopy (SEM/EDX). Phosphate adsorption equilibrium and kinetic tests were performed at different temperatures. The adsorption data have shown that NT-25La reaches equilibrium between modified clay and phosphate solution within 60 min of contact. The phosphate retention at room temperature reached 95%, when initial phosphate concentration in solution was 5 mg L(-1). A kinetic-order variable model provided satisfactory fitting of the kinetic data. Adsorption of phosphate was best described by a Langmuir isotherm, with maximum phosphate sorption capacity of 14.0 mg g(-1). Two distinct adsorption mechanisms were observed that may influence the adsorption processes. The investigation pointed out that the phosphate adsorption occurs via physisorption processes and that the use of NT-25La provides a maximum phosphate sorption capacity higher than many commercial adsorbents.

Solvent-free conversion of glycerol to solketal catalysed by activated carbons functionalised with acid groups

Activated carbons prepared from agricultural waste were modified to introduce surface acid sites by treatment with HNO3 or H2SO4. These acid-functionalised materials were studied as heterogeneous catalysts for the solvent-free acetalisation of acetone with glycerol to produce 2,2-dimethyl-1,3-dioxolane-4-methanol (solketal). The best catalyst was prepared by treatment with concentrated sulphuric acid and achieved 97% conversion of glycerol with high selectivity towards solketal by reaction with acetone at room temperature. The catalytic behaviour of the activated carbons was correlated with their physicochemical properties through characterization by N2-physisorption, XPS, elemental analysis, TGA and Boehm titration of the acid sites.

Cyclohexane Oxidation: Can Gif Chemistry Substitute for the Classical Process ?

Cyclohexane oxidation was studied using the GifIV, the GoAggII, the GoAggIII and the GoChAgg systems. The GifIV system gives a conversion of cyclohexane of 40%, with a concentration of one + ol of 0.120 M, but shows low selectivity and needs large quantities of metallic zinc. The GoAggII system produces a 0.143 M solution of one + ol with 100% selectivity but is too slow for any industrial use. The GoAggIII system allows accumulation of the oxidation products. A 0.370 M solution of one + ol can be produced in 180 min of reaction time, but large quantities of catalyst are needed and the selectivity of one + ol is only 80%. Addition of HCl during the accumulations allows obtaining a 0.267 M solution of one + ol with 100% selectivity in 60 min of reaction time, compared to a 0.3 M solution of one + ol with only 80% selectivity in 40 min in the industrial oxidation process. On the other hand, the catalyst forms iron (hydr)oxide particles during the reaction and the pyridine has to be substituted by a cheaper and a less toxic solvent. The GoChAgg system is less active and deactivates rapidly during the accumulations. The best result obtained so far is a 0.120 M solution of one + ol with 100% selectivity in 120 min of reaction time. Substituition of pyridine by tert-butanol reduces the activity of the GoAggIII and the GoChAgg systems. Precipitation of the catalyst and rapid deactivation are observed. Up to now we could only prepare a 0.040 M solution of one + ol. Even so, we hope to find a solvent/buffer system which avoids the deactivation of the catalyst while maintaining the high activity and selectivity of the process.

Mixed-ligand aminoalcohol-dicarboxylate copper(II) coordination polymers as catalysts for the oxidative functionalization of cyclic alkanes and alkenes

Abstract New copper(II) catalytic systems for the mild oxidative C–H functionalization of cycloalkanes and cycloalkenes were developed, which are based on a series of mixed-ligand aminoalcohol-dicarboxylate coordination polymers, namely [Cu2(μ-dmea)2(μ-nda)(H2O)2]n·2nH2O (1), [Cu2(μ-Hmdea)2(μ-nda)]n·2nH2O (2), and [Cu2(μ-Hbdea)2(μ-nda)]n·2nH2O (3) that bear slightly different dicopper(II) aminoalcoholate cores, as well as on a structurally distinct dicopper(II) [Cu2(H4etda)2(μ-nda)]·nda·4H2O (4) derivative [abbreviations: H2nda, 2,6-naphthalenedicarboxylic acid; Hdmea, N,N′-dimethylethanolamine; H2mdea, N-methyldiethanolamine; H2bdea, N-butyldiethanolamine; H4etda, N,N,N′,N′-tetrakis(2-hydroxyethyl)ethylenediamine]. Compounds 1–4 act as homogeneous catalysts in the three types of model catalytic reactions that proceed in aqueous acetonitrile medium under mild conditions (50–60°C): (i) the oxidation of cyclohexane by hydrogen peroxide to cyclohexyl hydroperoxide, cyclohexanol, and cyclohexanone, (ii) the oxidation of cycloalkenes (cyclohexene, cyclooctene) by hydrogen peroxide to a mixture of different oxidation products, and (iii) the single-pot hydrocarboxylation of cycloalkanes (cyclopentane, cyclohexane, cycloheptane, cyclooctane) by carbon monoxide, water, and a peroxodisulfate oxidant into the corresponding cycloalkanecarboxylic acids. The catalyst and substrate scope as well as some mechanistic features were investigated; the highest catalytic activity of 1–4 was observed in the hydrocarboxylation of cycloalkanes, allowing to achieve up to 50% total product yields (based on substrate).

Uses of brazilian natural zeolite in the removal of toxic metal cations from wastewater

The cation exchange capacity of Brazilian natural zeolite, identified as scolecite, was evaluated to application in wastewater control. We investigated the sorption process of Cr(III), Ni(II), Cd(II) and Mn(II) in synthetic aqueous effluents, including ion exchange isotherms of single-metal solutions at 25, 40 and 60°C by batch experiments, and the studies of ion selectivity in a binary combination solution. Ion exchange of metals from the singlemetal solutions follows the order: Cr>Mn>Cd>Ni. Chromium ion exchange is suppressed by the presence of Cd, probably due to the lower Cd hydrated radius and a hydration enthalpy lower than Cr. All the ion exchange were endothermic. The cations removal increases with pH, probably because when the concentration of H3O+ is higher, the competition by negative sites on the zeolite surface enhances and the metal exchange is reduced accordingly.

APROVEITAMENTO DE RESÍDUO DE BIODIESEL PARA PREPARAÇÃO DE CARVÕES ÁCIDOS COM ELEVADA ATIVIDADE CATALÍTICA NA REAÇÃO DE ETERIFICAÇÃO DO GLICEROL

UTILIZATION OF BIODIESEL WASTE FOR ACID CARBON PREPARATION WITH HIGH CATALYST ACTIVITY IN THE GLYCEROL ETHERIFICATION REACTION. Environmentally friendly acid carbon (CG) catalysts, containing a high amount of sulfonated and oxygenated groups, were prepared from glycerin, a biodiesel waste. CGs were produced by glycerin carbonization in the presence of H2SO4 at 1:3 m:m ratio in a closed autoclave at 180°C for different times: 0.25; 1; 3 and 6 hours (CG-0.25h; CG-1h; CG-3h and CG-6h, respectively). The catalyst properties for all carbons were evaluated in the glycerol etherification reaction with tert-butyl alcohol (TBA). The yield for mono-tert-butyl glycerol (MTBG), di-tert-butyl glycerol (DTBG) and tri-tert-butyl-glycerol (TTBG) was high and very similar for all CGs, of about 43% and 20% for the MTBG and DTBG + TTBG, respectively. Furthermore, the activity of these catalysts were close to those obtained using a commercial resin, Amberlyst-15, of about 50% and 27% for MTBG and DTBG + TTBG, respectively.Environmentally friendly acid carbon (CG) catalysts, containing a high amount of sulfonated and oxygenated groups, were prepared from glycerin, a biodiesel waste. CGs were produced by glycerin carbonization in the presence of H2SO4 at 1:3 m:m ratio in a closed autoclave at 180oC for different times: 0.25; 1; 3 and 6 hours (CG-0.25h; CG-1h; CG-3h and CG-6h, respectively). The catalyst properties for all carbons were evaluated in the glycerol etherification reaction with tert-butyl alcohol (TBA). The yield for mono-tert-butyl glycerol (MTBG), di-tert-butyl glycerol (DTBG) and tri-tert-butyl-glycerol (TTBG) was high and very similar for all CGs, of about 43% and 20% for the MTBG and DTBG + TTBG, respectively. Furthermore, the activity of these catalysts were close to those obtained using a commercial resin, Amberlyst-15, of about 50% and 27% for MTBG and DTBG + TTBG, respectively.

Remoção de chumbo(II) em sistemas contínuos por carvão ativado com vapor

Fixed-bed column studies were undertaken to evaluate the performance of a commercial Brazilian activated carbon in removing Pb(II) from aqueous environment. Breakthrough points were found out for the metal adsorption by varying different operating parameters like feed concentrations (10 and 20 mg L-1) and bed heights (0.5, 1.5 and 2.8 cm). A good agreement was observed between the experimental data and the values predicted by the bed depth service time (BDST) model. Regeneration of the exhausted columns was possible with HCl, and the adsorption capacity was maintained after three adsorption-desorption cycles.

UTILIZATION OF BIODIESEL WASTE FOR ACID CARBON PREPARATION WITH HIGH CATALYST ACTIVITY IN THE GLYCEROL ETHERIFICATION REACTION

UTILIZATION OF BIODIESEL WASTE FOR ACID CARBON PREPARATION WITH HIGH CATALYST ACTIVITY IN THE GLYCEROL ETHERIFICATION REACTION. Environmentally friendly acid carbon (CG) catalysts, containing a high amount of sulfonated and oxygenated groups, were prepared from glycerin, a biodiesel waste. CGs were produced by glycerin carbonization in the presence of H2SO4 at 1:3 m:m ratio in a closed autoclave at 180°C for different times: 0.25; 1; 3 and 6 hours (CG-0.25h; CG-1h; CG-3h and CG-6h, respectively). The catalyst properties for all carbons were evaluated in the glycerol etherification reaction with tert-butyl alcohol (TBA). The yield for mono-tert-butyl glycerol (MTBG), di-tert-butyl glycerol (DTBG) and tri-tert-butyl-glycerol (TTBG) was high and very similar for all CGs, of about 43% and 20% for the MTBG and DTBG + TTBG, respectively. Furthermore, the activity of these catalysts were close to those obtained using a commercial resin, Amberlyst-15, of about 50% and 27% for MTBG and DTBG + TTBG, respectively.Environmentally friendly acid carbon (CG) catalysts, containing a high amount of sulfonated and oxygenated groups, were prepared from glycerin, a biodiesel waste. CGs were produced by glycerin carbonization in the presence of H2SO4 at 1:3 m:m ratio in a closed autoclave at 180oC for different times: 0.25; 1; 3 and 6 hours (CG-0.25h; CG-1h; CG-3h and CG-6h, respectively). The catalyst properties for all carbons were evaluated in the glycerol etherification reaction with tert-butyl alcohol (TBA). The yield for mono-tert-butyl glycerol (MTBG), di-tert-butyl glycerol (DTBG) and tri-tert-butyl-glycerol (TTBG) was high and very similar for all CGs, of about 43% and 20% for the MTBG and DTBG + TTBG, respectively. Furthermore, the activity of these catalysts were close to those obtained using a commercial resin, Amberlyst-15, of about 50% and 27% for MTBG and DTBG + TTBG, respectively.

SELECTIVE HYDROGENOLYSIS OF GLYCEROL TO PROPYLENE GLYCOL IN A CONTINUOUS FLOW TRICKLE BED REACTOR USING COPPER CHROMITE AND Cu/Al2O3 CATALYSTS

Fil: Sepulveda, Jorge. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Santa Fe. Instituto de Investigaciones en Catalisis y Petroquimica ; Argentina