Sorption mechanism of copper ions on synthetic and natural dentine hydroxyapatites

Removal of copper ions from aqueous solutions on synthetic and dentine waste hydroxyapatites (HAP) was investigated in batch sorption experiments. Kinetics of sorption followed a pseudo-first order model. Steady-state data show agreement with the Sips isotherm compared with Freundlich and Langmuir models. The higher surface area and carbonated nature of synthetic hydroxyapatite were not sufficient to reach higher sorption capacity than natural one. Ion-exchange and precipitation contributed on  removal of Copper despite level ionization of hydroxyapatites. Proton and metal exchanges with copper ions contributed to process of sorption with prevalence of proton-exchange at low copper ion concentrations. High temperatures promoted the removal efficiency of Cu(II) onto the natural and synthesised hydroxyapatites. The thermodynamic parameters showed that sorption process was spontaneous, endothermic and associated entropy at the solid/solution interface increased at high temperatures

Modelling CO2 adsorption in a thin discrete packing

Local dynamics of CO2 adsorption in a discrete packing contained in a thin tube was assessed by 3D modelling. Thin tube packed bed adsorbers are currently used over tube structures in thermochemical energy storage systems and atmospheric revitalization of confined spaces. Driven by interplays between key factors such as the exothermicity and the fluid flow, the advective transport was found less effective than the diffusive one on the breakthrough trends of CO2 which displayed significant concentration gradients at both inter- and intra-particle scales. The lack of angular symmetry inside the particles by the reduction in resistance to mass transfer in area of solid particles exposed to high velocities led to greater convective transports from bulk of the gaseous phase to the pores. The result of the modelling agreed with the experimental data obtained at the exit of the adsorber, helping reduction in reliance on the empirical dispersion models used in the one-dimensional modelling

Modelling the reaction of uranium with carboxylic groups on surfaces through mono- and multi- dentate surface complexes on the basis of pH and redox potential

An analytical expression is proposed to simulate effects of pH and redox potential (E) on the sorption of uranium onto bioorganic model particles in saline or other aquatic environments. The elaborated expression is intended to avoid use of the classical approach of sorption which relies on experimental data and empirical models. The goal is to produce an expression that provides a distribution coefficient (Kd e.g. mL g-1) as function of pH, E and ligand concentration (through complex formation in solution) by applying a surface complexation model on one type of mono-dentate surface sites >(SuOH) as well as utilizing multi-dentate surface sites >(SuOH)c. The formulation of the worked out expression makes use of correlations between the surface complexation and hydrolysis constants for all species and sorption sites. The model was applied to the sorption of uranium onto bioorganic sites with and without carbonates in solution e.g. Log Kd: +2.75 at pH 8 for 2 sites per nm2. The calculated distribution coefficients were found very sensitive to the presence of carbonates, e.g. Log Kd: -7.0 at pH 8 for 2×10-3 M total carbonate. The potential reduction of uranium U(VI) and its complexes (carbonates) which are the primary stable species in surface waters, to U(IV) during sorption was simulated in association with a decrease in the redox potential and was found generally below the redox stability limits of water. The calculated distribution coefficient values were validated by the values reported in literature for the sorption of uranium onto specific adsorbents. The investigated simulations are also applicable to the sorption of other redox sensitive elements

A Comparative Study of Diffusion Coefficients from Convective and IR Drying of Woodchip

Convective and infared (IR) Halogen Drying processes are used in the woodchip biomass industry to test the moisture content of woodchip. Woodchip drying, though energy intensive, is necessary to increase the calorific content of woodchip, in turn increasing combustibility. The bulk process within the production of woodchip uses convective drying with agitation. Analysis of the diffusion in wood can be used to estimate the time to dry lumber to a specified moisture content value. Relationships between the effect of temperature and moisture content allow more accurate predictions and operational evaluations of driers. The aim of this study was to investigate constant heat source convective and IR drying by comparing the drying curves when batch drying a sample of woodchip biomass whilst controlling the heat source temperature at 328K, 338K, 348K and 358K. This was achieved through comparison of pre-exponential diffusion coefficients and activation energy, determining the temperature dependency of these terms in convective and IR drying of wetted wood. Lower temperatures increased drying time for both convective and IR drying, with convective drying taking up to 5 times longer than IR. The pre-exponential diffusion coefficient and activation energy found for IR drying were m2.s-1 and J.mol-1. The convective drying pre-exponential diffusion coefficient and activation energy calculated was m2.s-1 and J.mol-1 respectively

Mathematical Model Analysis for Mass and Rates of Woodchip IR Drying

The production of woodchip biomass, by meansofdrying, is of importancewith respect to environmental concerns. This has been highlighted by reports of carbon production through utility usage of commercial sites, where drying is often among the most energy intensive operations within industrial processes. It is therefore crucial to dry wood in efficient way in order to derive high quality products and increase end use process efficiency. Akey component for dry fuel suppliers is the moisture content of the woodchip product. Halogen (infrared) drying is the foremost method used on site to measure moisture content ofwood fuel for supply,as this takes less time,asmaller sample size and less human interaction, in comparison with convective drying. This study investigated the drying behaviour of static woodchip fuel using an infrared source at temperatures rangingfrom 50 to 80°C and atmospheric pressure. With the longest drying time (time until a rate of 0.001g per 99 seconds is reached) of just over three hours and the shortest under an hour and a half. Mathematical models of the drying rates were determined through statistical analysis and the significance of the initial drying periods relevant to rates of falling and constant profiles were analysed for the different temperatures. Statistically the model with the best fit at the temperatures measured was a diffusion model with 6 exponential terms and coefficients with the SSE value 0.2424, R2of 0.9989 and RMSE of less than0.009. Models with 4 coefficients were also able to fit the data well with SSE values of below 0.03. Differentiating the resulting equations of fit at constant temperature resulted in models for the rate of mass lost over time

Tuning the wettability of wire mesh column:pore-scale flow analysis

The pore-scale behaviour of liquid flow over wire mesh stainless-steel packing of variable contact angle is relevant for mass and heat exchanges in multiphase chemical systems. This behaviour was investigated by imaging experiments and 3D volume-of-fluid modelling. The surface of the wire mesh ring was modified by alumina coating to reach both hydrophilic and hydrophobic characteristics. The cycle of capillary droplet flow over the uncoated ring exhibited penetration of the hydrophilic mesh openings, adherence to the surface of the ring and accumulation as drips at the bottom region of the rings. However, over the hydrophobic ring, the droplet exhibited low adherence to the ring surface, accumulation at the top surface of the ring, no penetration of the openings, slip by the gravitational forces over the vertical curvature and accumulation as drips at the bottom region. In agreement with the classical observations at the macroscale, the observations at the pore-scale confirmed the increase of the wetting efficiency, liquid holdup and effective surface area at increased liquid flowrate and reduced contact angle. The 3D model was in reasonable agreement with Stichlmair's model for the liquid holdup, particularly in the hydrophilic zone of the contact angle and low flow as well as in a reasonable agreement with Linek's model for effective area, particularly in the hydrophobic range of the contact angle

Deactivation of the preferential oxidation of CO in packed bed reactor by 3D modelling and near-infrared tomography

Scaling up the results on catalyst deactivation to industrial operations, where transport phenomena are of significance, is often not straightforward. The operations of industrial reactors are judiciously focused on the dynamics of the deactivation along the axial length of the reactors, which are generally known approximately. Processes of strong energy release or fast chemical kinetics, such as oxidation reactions, cracking, etc., are associated with a deactivation where the time characteristics of the flow and transports are of magnitudes of the deactivation time-on-stream. Local deactivation of the preferential oxidation of CO was investigated by three-dimensional modelling of flow, mass and heat transfers inside a packed-bed reactor and validated by near-infrared tomography. The profiles of deactivation were sensitive to the rates of deactivation, heat transfer by dispersion and intra-particle mass transfer. At pore scale of the packing, pronounced deactivation was revealed near the wall due to a preferential flow circulation. The deactivation progressed at the exteriors of the catalytic particles, particularly over the regions in contact with the convective flow. Unlike the mass dispersion, the heat dispersion promoted the deactivation by shifting the moving waves of deactivation upstream, leading to asymmetrical maps inside the catalytic particles

Process simulation of sodium methoxide production from methanol and sodium hydroxide using reactive distillation coupled with pervaporation

This research investigates the process simulation of sodium methoxide (NaOCH3) synthesis from methanol (CH3OH) and sodium hydroxide (NaOH) under three synthesis schemes: schemes A, B, and C. Scheme A consisted of one equilibrium reactor and two distillation columns, scheme B one reactive distillation column and one distillation column, and scheme C one reactive distillation column and pervaporation membrane. The simulation parameters included CH3OH/NaOH feed flow ratio (1.2-1.6), number of stages (5-30), bottom flow rate (1400-1600 kg/h), and feed stage location (5, 10, 15, 20, 21, 22, 23, and 24). The simulation parameters were varied to determine the optimal NaOCH3 synthetic conditions under different schemes with 0.01 wt% water content, maximum 45 wt% NaOCH3, and lowest total energy consumption. The results showed that scheme C had the lowest total energy consumption (34.25 GJ/h) under the optimal synthetic condition of 1.4 for CH3OH/NaOH feed flow ratio, 25 for the number of stages, 1550 kg/h for the bottom flow rate, and the 24th feed stage location, with the NaOCH3 flow rate of 675 kg/h. Scheme C thus holds promising potential as an energy efficient alternative for synthesis of NaOCH3. The novelty of this research lies in the use of pervaporation membrane in place of distillation column to separate CH3OH from water and to lower energy consumption and capital cost

Gas flow visualisation in low aspect ratio packed beds by three-dimensional modelling and near-infrared tomography

Nonuniform local flow inside randomly porous media of gas-solid packed beds of low aspect ratios ranging from 1.5 to 5 was investigated by three-dimensional modelling and near-infrared tomography. These beds are known to demonstrate heterogeneous mixing and uneven distributions of mass and heat. The effects of the confining wall on flow dynamics were found nonlinear, particularly for aspect ratios lower than 3. High velocities were mainly observed in regions near the wall of aspect ratio value of 1.5 and those of values higher than 3, owing to high local porosities in these zones. Mass dispersion characterised by both experimental near-infrared imaging and by particle tracking showed discrepancies with literature models, particularly for aspect ratios lower than 3. Uncertainties were more significant with the radial dispersion due bed size limits. Beyond this value, the wall affected more the axial dispersion, confirming the nonlinear impact of the wall on global hydrodynamic

Alkaline wood ash, turbulence, and traps with excess of sulfuric acid do not strip completely the ammonia off an agro-waste digestate

The present study combined two nutrient management strategies to improve the marketability of a waste-derived fertilizer: (a) isolation of ammoniacal nitrogen and (b) preparation of a bulk soil amendment. The wood fly ash with low content of pollutants was added to an agrowaste anaerobic digestate as alkaline stabilizer, which promoted the volatilization of ammonia and adsorption processes, and as nutrient supplement. The 39.71 ± 1.44 g blend was incubated for 60 hours at 20°C and 100 rpm in a closed chamber (250-mL Schott Duran® bottle) with a 5.21 ± 0.10 mL sulfuric acid trap of 10 different concentrations (0.11, 0.21, 0.32, 0.43, 0.54, 0.64, 0.75, 0.86, 0.96, and 1.07 mol/L). For analytical purposes, the sulfuric acid, water-soluble, and water-insoluble fractions of the blend were isolated after the incubation. The 1.07 mol/L sulfuric acid solution contained 23.69 ± 5.72 % more of ammonical nitrogen than the 0.11 mol/L solutions. However, in all cases the amount of nitrogen in the H2SO4 compartment was lower than the one in the water-soluble and water-insoluble fractions. Only the 15.52 ± 2.13 % of the nitrogen accounted after the incubation was found in the H2SO4 trap. The bottleneck of the NH3 stripping process was the rate of mass transfer at the interface between the blended fertilizer and the headspace of the closed chamber. The organic phosphorus was more susceptible to be adsorbed during the alkaline treatment with non-intrusive acidification than the nitrogen and carbon. Activation of the ash as adsorbent before mixing with the digestate should improve the properties of the blend as slow release fertilizer, since more nutrients would end in the water-insoluble fraction