Effective intraparticle diffusion coefficients of CoCl2 in mesoporous functionalized silica adsorbents

The scope of this work is to determine the effective intraparticle diffusion coefficient of CoCl2 over mesoporous functionalized silica. Silica is selected as a carrier of the functionalized groups for its rigid structure which excludes troublesome swelling, often found in polymeric adsorbents. 2-(2-pyridyl)ethyl-functionalized silica is selected as a promising affinity adsorbent for the reversible adsorption of CoCl2. The adsorption kinetics is investigated with the Zero Length Column (ZLC) method. Initially, experiments were performed at different flow rates to eliminate the effect of external mass transfer. The effect of pore size (60 Å and 90 Å), particle size (40⋅10−6 m–1000⋅10−6 m) and initial CoCl2 concentration (1 mol/m3–2.0 mol/m3) on the mass transfer was investigated. A model was developed to determine the pore diffusion coefficient of CoCl2 by fitting the experimental data to the model. The pore diffusion coefficients determined for two different pore sizes of silica are D p (60 Å) =1.95⋅10−10 [m2/s] and D p (90 Å) =5.8⋅10−10 [m2/s]. The particle size and the initial CoCl2 concentration do not have an influence on the value of diffusion coefficient. However, particle size has an influence on the diffusion time constant. In comparison with polymer adsorbents, silica based adsorbents have higher values of diffusion coefficients, as well as a more uniform and stable pore structure

Sorption kinetics for the removal of aldehydes from aqueous streams with extractant impregnated resins

The sorption kinetics for the removal aldehydes from aqueous solutions with Amberlite XAD-16 and MPP particles impregnated with Primene JM-T was investigated. A model, accounting for the simultaneous mass transfer and chemical reaction, is developed to describe the process. It is based on the analogy to the diffusion and reaction in a stagnant liquid sphere, but corrected for the porosity and particle properties influencing the diffusion. The developed model describes the kinetic behavior of the process in the low concentration region rather well. However, in the high concentration region, larger discrepancies are observed. Initially, the influence of the flow rate was investigated to eliminate the effect of the external mass transfer. The influence of the particle morphology was investigated for both physical and reactive sorption. Physical sorption experiments were used to determine the factor τ that takes the particle properties influencing the diffusion into account. It was shown that the diffusion is faster in XAD-16 than in MPP impregnated systems. Reaction rate constant kx was determined by fitting the model to the experimental data. Sorption of benzaldehyde appears to be significantly slower (kx ~ 10−4 l/mol s) than the sorption of pentanal (kx ~ 10−3 l/mol s) due to the slower chemical reaction. The influence of the particle size was investigated for the sorption of pentanal with XAD-16. It was observed that the particle size does influence the diffusion term, but does not have an effect on the reaction rate. On the other hand, the extractant loading influences the reaction rate slightly in the low concentration region, whereas the initial concentration of the solute has more pronounced effect

Design and results of a first generation pilot plant for supercritical water desalination (SCWD)

A pilot plant of 5 kg/h based on the principle of supercritical water desalination (SCWD) has been designed, built and operated. The detailed design, operating procedures and performance of the plant is presented in this paper, along with the first results. Firstly, the plant has been tested for feed streams of 3.5 wt% NaCl to evaluate the stability and repeatability of the system, with the results indicating that mass balance closure is good and that reproducible results can be obtained. Furthermore, the results showed that 93% of the feed is recovered as fresh drinking water, which corresponds with expected results from phase equilibria simulations. The plant was further tested for higher feed concentrations of up to 16 wt% NaCl. For all feed concentrations, the NaCl concentration of the SCW was that of drinking water quality (< 600 ppm). Experimentally, using a single stage separator, a concentrated brine (38 wt% NaCl) was obtained and calculations showed that with a two-stage flash-evaporation scheme, zero liquid discharge (ZLD) can be obtained. Further modifications to the plant and tests with other salt mixtures are recommended in order to advance to industrial application

Optimization of layered double hydroxide stability and adsorption capacity for anionic surfactants

Low cost adsorption technology offers high potential to clean up laundry rinsing water. From an earlier selection of adsorbents (Schouten et al. 2007), layered double hydroxide (LDH) proved to be an interesting material for the removal of anionic surfactant, linear alkyl benzene sulfonate (LAS) which is the main contaminant in rinsing water. The main research question was to identify the effect of process parameters of the LDH synthesis on the stability of the LDH structure and the adsorption capacity of LAS. LDH was synthesized with the co-precipitation method of Reichle (1986); a solution of M2+(NO3)2 and M3+(NO3)3 and a second solution of NaOH and Na2CO3 were pumped in a beaker and mixed. The precipitate that was formed was allowed to age and was subsequently washed, dried and calcined. The process parameters that were investigated are the concentration of the initial solutions, M2+/M3+ ratio and type of cations. The crystallinity can be improved by decreasing the concentration of the initial solutions; this also decreases the leaching of M3+ from the brucite-like structure into the water. The highest adsorption capacity is obtained for Mg2+/Al3+ with a ratio 1 and 2 because of the higher charge density compared to ratio 3. Storing the LDH samples in water resulted in a reduction of adsorption capacity and a decrease in surface area and pore volume. Therefore, LDH is not applicable in a small device for long term use in aqueous surroundings. The adsorption capacity can be maintained during storage in a dry N2 atmosphere

Axial dispersion in gases flowing through a packed bed at elevated pressures

Axial dispersion in upward gas flow is investigated by pulse and displacement experiments in a vertical, packed column with different concentrations of the tracer and at pressures up to 1.5 MPa. The responses to the introduced pulse and step changes are measured at two locations and the extent of axial dispersion, respresented by the Bodenstein number, is determined by curve fitting in the time domain. The performed experiments demonstrate that the residence time distribution is considerably affected by density differences between the tracer and carrier gas, particularly at elevated pressures. Obtained Bodenstein numbers for step changes from nitrogen to a helium/nitrogen mixture and vice versa differ by as much as a factor ten, depending on the helium concentration and column pressure. The difference in axial dispersion may be ascribed to gravitation-driven instabilities as due to vertical density gradients in the case of a heavy gas displaced by a light gas; density gradients in the step changes from a light to heavy gas evidently inhibit axial dispersion. The presented observations are of major importance for the description of flow behaviour of gases in packed bed reactors where density gradients exist due to temperature and concentration gradients, particularly because many processes operate at elevated pressures