Macroporous Exchange Research Articles

Adsorption properties of macroporous exchangers functionalized with various weak-base groups for aromatic acids: Coupling DFT simulation with batch experiments

Anion exchange resin has an excellent effect on the removal of aromatic acids in wastewater, while the adsorption affinities of the resins with different functional groups are various. In this work, six macroporous weak-base anion exchange resins were synthesized, and the adsorption characteristics of the resins for three typical aromatic acids including benzenesulfonic acid (BSA), benzoic acid (BA), phenol (PH) were investigated. The results showed that the adsorption performance for BSA and BA on these resins were more sensitive to pH than that for PH. The adsorption capacities of the secondary amine resins to aromatic acid in salt-rich environment were higher than that of the tertiary amine resins. In the binary system, when the adsorption mechanisms of the two adsorbates are overlapped to some extent, the competition between them on the resins was more significant. Density functional theory (DFT) simulations confirmed that the adsorption of BSA by the resins was mainly due to electrostatic interaction, and the adsorption of PH was attributed to hydrogen bond, while BA adsorption was the synergism of these two interactions. The functional resins with high binding energies and high natural bond orbital (NBO) charge transfer had good salt resistances. Furthermore, NaCl aqueous solution was suitable for desorption of BSA on the resins, while the proper desorbent for BA and PH was ethanol. These results indicated that DFT could guide the selection of the functional groups and provided an effective method for the design of selective separation materials for aromatic acids in wastewater.

Laccase Immobilization on D380 Macroporous Exchange Resin by Cross-Linking with Glutaraldehyde

Macroporous exchange resins have been applied as supports for enzyme immobilization. The supporters were activated by cross-linking with glutaraldehyde, then Laccase was immobilized. Parameters of the immobilization process were optimized. The results of repeated batch showed the optimal immobilization conditions (10% of glutaraldehyde, pH=3, temperature=45 °C). In addition, the biocatalyst also showed good operational stability, maintaining 45% of its initial activity after 10 cycles of oxidation of ABTS. The immobilized laccase had potential for application in the continuous decolorization of textile effluents.

Adsorption of Aromatic Sulphonic Acids onto Macroporous Exchangers: Effect of the Chemical Structure of the Adsorbent on the Adsorption Capacity

The adsorption of 2-naphthalene sulphonic acid from aqueous solution was studied using macroporous weak base exchangers with different matrices. This study reports the results of the favourable adsorption behaviour of 2-naphthalene sulphonic acid onto polymeric anion exchangers. The difference in adsorption affinity, together with the enthalpic and entropic changes associated with the adsorption process, was interpreted in terms of the chemical structure of the exchangers and appropriate interaction between the non-polar moiety of the aromatic anion and the exchanger matrices. The exchanger matrix had a distinct influence on the adsorption capacity of the aromatic sulphonic acid.

Selective Removal of Chromates by Macroporous Exchanger Amberlyst A-21

Sorption studies of chromate on weakly basic macroporous anion exchanger Amberlyst A-21 were performed as a function of pH (2 - 9), temperature (20 - 40 °C) and concentration (0.4 - 80 mmol.l−1). Chromate sorption was observed to decrease with the increase in initial pH of the solution, with a sorption maxima at pH 2 and increased with the increase in temperature. The changes in pH and in the ratio of chloride ions released to chromate ions sorbed suggested that the anion exchange process was accompanied by hydrolysis and Donnan invasion. The FTIR spectra and isosteric heat of sorption besides showing the hydrolysis / Donnan invasion of resin under different experimental conditions of concentration, pH and temperature also showed the dimerization of the chromate species inside the resin phase.

Intraparticle Diffusion during Selective Sorption of Trace Contaminants: The Effect of Gel versus Macroporous Morphology

Ion exchanger beads are commercially available in two different physical morphologies, namely, gel and macroporous. While gel-type (or microporous) exchanger particles are essentially homogeneous solid phases with closely spaced functional groups, a single macroporous ion exchanger bead may be viewed as an ensemble of tiny microgels with an interconnected network of pores. Macroporous exchangers are gaining acceptance in environmental applications due to their durability, resistance to oxidation, and less susceptibility to fouling by natural organic matters. Many environmentally significant synthetic aromatic compounds, namely, chlorophenols, naphthalene and benzene sulfonic acids, nitrophenols, and quaternary benzylammonium compounds exist as ions in the aqueous phase over a wide range of pH and are very selectively removed by polymeric exchangers with hydrophobic matrixes. Anionic pentachlorophenol (PCP-), a widely used pesticide and wood preservative, was used in the study as a representative aromatic anion. This paper presents significant differences in intraparticle diffusion behaviors during sorption of trace PCP- onto gel and macroporous anion exchangers. While an increase in competing chloride ion concentration had no appreciable effect on the effective intraparticle diffusivity for gel exchangers, the same resulted in a significant enhancement of intraparticle diffusivity of macroporous exchangers. For exchangers with gel morphology, solid-phase diffusion is the primary intraparticle solute transport mechanism. For macroporous exchangers, on the contrary, the slower pore diffusion between the microgels of a single spherical bead is the rate-limiting step. The experimental observations were substantiated using an intraparticle parallel solute transport model. From a generic viewpoint, the macroscopic observation of the effect of competing solute (chloride) concentration on the effective intraparticle diffusivity during selective sorption may be used to gather microscopic knowledge about the morphology of the sorbent material. Geosorbents, although not spherical and quite complex in composition, are characteristically similar to macroporous exchangers where clusters of sorption sites are separated by pores filled with liquid. It is postulated that an enhanced understanding of the sorption behaviors of geosorbents can be obtained through the use of surrogate macroporous polymeric materials.

Intraparticle diffusion during selective ion exchange with a macroporous exchanger

Chlorophenols, quaternary ammonium compounds, benzene and naphthalene sulfonates and benzene carboxylates are examples of environmentally significant synthetic organic compounds which exist as ions in water over a wide range of pH values. This study discusses the sorption kinetics, and more specifically, intraparticle diffusion behaviors of trace concentrations of pentachlorophenate (PCP −) and other chlorophenates onto a commercially available macroporous polymeric anion exchanger (IRA-900). The anion exchanger is essentially biphasic, i.e. every single exchanger particle contains an enormous number of tiny microgels and an interconnected network of pores. Ion exchange functional groups reside solely within the microgels. For comparison, a gel or microporous anion exchanger is also included in the study. Experimental results reveal a distinctly different type of effect of competing chloride ion concentration on gel and macroporous ion exchangers pertaining to sorption of pentachlorophenate (PCP −). While the effective intraparticle diffusivity of PCP − for gel-type resin remained unaltered with a change in competing chloride concentration, the same increased significantly for the macroporous exchanger with an increase in chloride concentration. Pore diffusion is considered to be the predominant intraparticle transport mechanism for highly preferred PCP − inside the macroporous exchanger. Under the normal hydrodynamic conditions of a fixed bed column run, intraparticle diffusion was found to be the rate-limiting step. For various chlorophenates, the effective intraparticle diffusivities were inversely correlated to the octanol–water partition coefficients of their parent chlorophenols.

Investigations on the usefulness of tiron in separation of metal ions on the macroporous anion-exchanger amberlyst A-26

The possibility of application of a sulpho-derivative of an aromatic organic complexing agent—tiron—for separation of cations on the macroporous anion-exchanger Amberlyst A-26 has been investigated. Comparative results obtained with Amberlite IRA 400 have proved the macroporous exchanger to be the more useful. The dependence of retention on pH obtained has been established by the batch method for: Ag, Ni, Co(II), Mn(II), Zn, Cd, Pb, Cr(III), Fe(III), Ga, Al, In, Bi, Ti(IV), V(V) By taking advantage of selectivity differences, the following mixtures have been separated: AlGa, AlTi(IV), Ti(IV)Ni, NiFe(III), NiFe(III)Ti(IV).

Uber den einflub der chemischen struktur von phosphorsauren kationenaustauschern auf deren thermischen stabilitat in wasser

AbstractThermal stability of different phosphorus‐containing cation exchangers in water has been studied. It has been shown that at heating to temperatures of 80–180°C the phosphorus content decreases on account of (1) thermal hydrolysis leading to phosphoric acid formation and (2) matrix splitting leading to phosphorus‐containing soluble organic compounds. Therefore for precise percentage loss determination [so‐called dephosphorilation degree (DD)] it is necessary to mineralize the organic compounds. A comparative study of the following cation exchangers has been carried out: KF‐I—nonporous styrene‐divinyl‐benzene phosphorylated copolymer (A); KF‐II—the same, but macroporous (B); KFP—macroporous exchanger with styrene‐divinylbenzene matrix containing methylene‐phosphoric acid groups (C); KF‐7—nonporous exchanger prepared by copolymerization of β‐β‐dichlorethyl‐phosphoric acid ester, vinylacetate, and divinylbenzene (D). The most stable are the macroporous exchangers with styrene‐divinylbenzene matrix B and C. The nonporous exchanger A having the same chemical structure as B is less stable. With increasing temperature the phosphorus splitting increases, though the Arrhenius equation is not fulfilled. The DD values at 80°C and a heating duration of 1 to 20 days are not more than 5%. At 180°C DD is as high as 6 to 50%, depending on resin structure and heating duration.