Cristiane A. Henriques

Kinetic modeling and equilibrium studies during cadmium biosorption by dead Sargassum sp. biomass

A basic investigation on the removal of cadmium(II) ions from aqueous solutions by dead Sargassum sp. was conducted in batch conditions. The influence of different experimental parameters; initial pH, shaking rate, sorption time, temperature and initial concentrations of cadmium ions on cadmium uptake was evaluated. Results indicated that cadmium uptake could be described by the Langmuir adsorption model, being the monolayer capacity negatively affected with an increase in temperature. Analogously, the adsorption equilibrium constant decreased with increasing temperature. The kinetics of the adsorption process followed a second-order adsorption, with characteristic constants increasing with increasing temperature. Activation energy of biosorption could be calculated as equal to 10 kcal/mol. The biomass used proved to be suitable for removal of cadmium from dilute solutions. Its maximum uptake capacity was 120 mg/g. It can be considered an optimal result when compared to conventional adsorbing materials. Thus Sargassum sp. has great potential for removing cadmium ions especially when concentration of this metal is low in samples such as wastewater streams.

An evaluation of copper biosorption by a brown seaweed under optimized conditions

A basic investigation into the removal of copper ions from aqueous solutions by Sargassum sp. was conducted in batch conditions. The influence of different experimental parameters such as initial pH, shaking rate, sorption time, temperature, equilibrium conditions and initial concentrations of copper ions on copper uptake was evaluated. Results indicated that for shaking rates higher than 100 rpm no significant changes in copper accumulation were observed, as well as for pH values between 3.0 and 5.0. No marked effect on the biosorption of copper was detected for temperatures between 298 and 328K. The Langmuir model better represented the sorption process, in comparison to the model of Freundlich. The process followed a second-order kinetics and its calculated activation energy was 5.2 kcal/mol. Due to its outstanding copper uptake capacity (1.48 mmol/g biomass) Sargassum sp. proved to be an excellent biomaterial for accumulating and recovering copper from industrial solutions.

Competitive biosorption of cadmium(II) and zinc(II) ions from binary systems by Sargassum filipendula

The present work describes our study on the competitive biosorption of Cd(II) and Zn(II) ions onto Sargassum filipendula from single component and binary systems. Results showed that S. filipendula was an efficient biosorbent for the removal of Cd(II) and Zn(II) ions from an aqueous solution. The equilibrium experimental data for the single component system for the two metallic species fitted well to Langmuir and Langmuir-Freundlich isotherm models. Seven isotherm models were tested with the equilibrium data for modeling of the binary system. Based on the sum of squares error, the Langmuir-Freundlich isotherm model showed the best fit to the binary adsorption data. The influence of the additional cation on the behavior of the biosorption of Cd(2+) and Zn(2+) was analyzed comparing single component and binary isotherms. It was observed that Zn(2+) had a relevant effect on the Cd(2+) biosorption, but the interference of Cd(2+) on the sorption of Zn(2+) was considerably less intense.

On the stability of MCM-41 after ion-exchange and impregnation with cesium species in basic media

Abstract The stability of MCM-41 after ion exchange and impregnation with cesium species and calcination was investigated. A pure silica and two Al-containing samples (Si/ Al ≅ 25 ), the latter synthesized either in the sodium or in the cesium form, were used as test samples. The conditions chosen for the various treatments were those usually employed to introduce basic species in zeolites or in mesoporous materials aiming at their use in catalysis. The results show that even mild basic media (pH≅8.5) can be detrimental to the stability of the structure and that impregnation with cesium acetate followed by calcination caused a severe damage to the structure. Al-containing samples were less resistant than the purely siliceous one to basic media.

Influence of Ni content on physico-chemical characteristics of Ni, Mg, Al-Hydrotalcite like compounds

The physico-chemical properties of a series of Ni,Mg,Al-HTLC with Al/(Al+Mg+Ni) = 0.25 and low Ni/Mg ratios were studied by means of X-ray diffraction (XRD), thermogravimetric (TGA) and thermodifferential (DTA) analysis, N2 physissorption and temperature programmed reduction (TPR). The as-synthesized materials were well-crystallized, with XRD patterns typical of the HTLCs in carbonate form. Upon calcination and dehydration the dehydroxilation of the layers with concurrent decomposition of carbonate anions produced mixed oxides with high surface area. XRD analysis indicated that the different nickel and aluminum oxides species are well-dispersed in a poor-crystallized MgO periclase-type phase. As observed by TPR, the different Ni species showed distinct interactions with Mg(Al)O phase, which were influenced by both nickel content and calcination temperature. Regardless of the the nickel content, the reduction of nickel species was not complete as indicated by the presence of metallic dispersions.

Biosorption of lead by the brown seaweed Sargassum filipendula -batch and continuous pilot studies

The biosorption of lead by the brown alga Sargassum filipendula was studied. pH 4.0 was the optimum value for the biosorption of lead. Isotherms indicated that for solutions containing 0.03 ± 0.001 up to 3.27 ± 0.04 mmol/L of lead, 2.0g/L was the optimum biomass concentration. The Langmuir model was fitted to represent the experimental data, and the kinetics of biosorption presented equilibrium in 30 min. The continuous system operated for 56 hrs presenting a 100% binding of ionic lead, which corresponds to an accumulation of 168 g lead, equivalent to a load of 1.7 mmol ionic lead/g Sargassum filipendula. The results that were obtained in a continuous system showed a gradual saturation of the biomass in the reactors.

Aldol Condensation of Citral with Acetone on Basic Solid Catalysts

The catalytic performance of solids with basic properties, such as CaO, MgO and hydrotalcites, was evaluated in the aldol condensation of citral and acetone, the first step in the synthesis of ionones from citral. The best results were obtained with CaO and hydrotalcite with high conversions (98%) and selectivities (close to 70% for the main product) observed for both of the catalyst. Such pseudoionone yields were greater than those reported in the literature for the homogeneous reaction.

Characterization of the coke formed from o-xylene over mordenites at different pressures under N2 and H2

Abstract The influence of the carrier gas (H 2 or N 2 ), at different pressures, on coking over two mordenite samples during o -xylene transformation was evaluated at 623 K. The results showed that the carrier gas has a significant effect on the amount and on the composition of the coke formed. For the two samples used, coke formed in the presence of H 2 consisted mainly of CH 2 Cl 2 soluble molecules, while under N 2 the formation of insoluble coke was favoured. Whatever the carrier gas or the total pressure, the same families of compounds were identified in the soluble fraction, the main ones being C n H 2 n −28 , C n H 2 n −22 and C n H 2 n −16 . For the sample strongly dealuminated, increasing the pressure decreased the coke build up under H 2 , confirming the inhibition effect of H 2 on coke formation, but an opposite effect was observed under N 2 . Due to its mesoporous system, this sample has a rather stable activity whatever the carrier gas. For the sample with a high density of acid sites, the limiting quantity of coke was rapidly attained, deactivation was relatively fast and poisoning by coke was greater under N 2 . A relatively small amount of coke render it inactive indicating that deactivation is due to pore mouth blockage.

Influence of basic properties of Mg,Al-mixed oxides on their catalytic activity in knoevenagel condensation between benzaldehyde and phenylsulfonylacetonitrile

The catalytic performance of Mg,Al-mixed oxides (MO20, MO25 and MO33) derived from hydrotalcites was evaluated in the Knoevenagel reaction between benzaldehyde and phenylsulfonylacetonitrile at 373 and 383 K. The best results were obtained for the sample MO20 that presented the highest basic sites density and external area and the smallest crystallite sizes. The relative amount of basic sites with weak to intermediate strength also played an important role on catalytic performance. By increasing the catalyst content from 1 to 5 wt.% at 383 K, a complete conversion of the reactants is attained, producing α-phenylsulfonylcinnamonitrile with a selectivity of 100%.

Conversion of natural gas to higher valued products : light olefins production from methanol over ZSM-5 zeolites

Abstract The conversion of methanol to light olefins catalyzed by ZSM-5 zeolites with different SAR or impregnated with phosphorus was investigated. The increase in SAR reduced the density and the strength of the acid sites, favoring both the catalytic stability and the production of light olefins, particularly propene. The incorporation of phosphorous also reduced the density and the strength of the acid sites of HZSM-5 zeolite; besides, BET specific area and microporous volume linearly decreased. The increase of P content decreased the activity and improved the stability. The highest propene/ethene molar ratio was observed for the sample with 4 wt. of P.