Adsorption thermodynamics and kinetic investigation of aromatic amphoteric compounds onto different polymeric adsorbents

The adsorption behavior ofp-aminobenzoic acid and o-aminobenzoic acid onto the different polymeric adsorbents was systematically investigated as a function of the solution concentration and temperature. Experimental results indicated that the equilibrium adsorption data of the four polymeric adsorbents fitted well in the Freundlich isotherm. The adsorption capacity of multi-functional polymeric adsorbent NJ-99 was the highest, which might be attributed to the strong hydrogen-bonding interaction between the amino groups on the resin and the carboxyl group of aminobenzoic acid. The adsorption capacity of o-aminobenzoic acid onto any adsorbent was higher than p-aminobenzoic acid. Thermodynamic studies suggested the exothermic, spontaneous physical adsorption process. Adsorption kinetics results showed that the adsorption followed the pseudo-second-order kinetics model and the intraparticle mass transfer process was the rate-controlling step.

DESORPTION OF VOCs FROM POLYMERIC ADSORBENTS UNDER MICROWAVE FIELD

Desorption of volatile organic compounds (VOCs) from polymeric adsorbents by microwave was investigated experimentally. Two kinds of organic compounds, benzene and toluene, were separately used as adsorbates in this work. Results showed that the application of microwave to regenerate the polymeric adsorbents not only can get higher regeneration efficiency in comparison with the use of heat regeneration, but also make the temperatures of the fixed beds much lower than that when using the heat regeneration. The weaker the polarity of a polymeric adsorbent, the easier its regeneration was.

ADSORPTION OF PHENYLACETIC ACID ON MACROPOROUS POLYMERIC ADSORBENTS

Several macroporous polymeric adsorbents (NDA-999, XAD-8, X-5 and XAD-2) were employed in the study to adsorb phenylacetic acid from aqueous solution. Effect of salt and ambient temperature on adsorption was studied using NDA-999 adsorbent and the adsorption process conforms to Freundlich抯 model reasonably. Adsorption dynamics were conducted in batch experiments in order to make clear the mechanism of adsorption process. It is proved that the squared driving force mass transfer model can be adopted to elucidate the process. The treatment process of industrial wastewater containing high strength of phenylacetic acid was proposed for cleaner production of phenylacetic acid.

Thermodynamic study of adsorption of phenolic compounds onto Amberlite XAD-4 polymeric adsorbents and its acetylized derivative MX-4

Adsorption equilibrium isotherms of phenolic compounds, phenol, p cresol, p chlorophenol and p nitrophenol, from aqueous solutions by Amberlite XAD 4 polymeric adsorbent and its acetylized derivative MX 4 within temperature range of 283 323K were obtained and fitted to the Freundlich isotherms. The capacities of equilibrium adsorption for all four phenolic compounds from their aqueous solutions increased around 20% on the acetylized resin, which may be contributed to the specific surface area and the partial polarity on the network. Estimations of the isosteric enthalpy, free energy, and entropy for the adsorption process were reported.

ADSORPTION BEHAVIOR OF PHENOLIC COMPOUNDS ONTO POLYMERIC ADSORBENTS MODIFIED WITH 2-CARBOXYBENZOYL GROUPS

Two hypercrosslinked polymeric adsorbents （ZH-01 and Amberlite XAD-4 resin） were employed to remove three kinds of phenolic compounds including phenol, 4-nitrophenol and 2,4-dinitrophenol from aqueous solutions. The study was focused on the static equilibrium adsorption behavior, the column dynamic adsorption and desorption profiles. The Freundlich model gave a perfect fitting to the isotherm data. The adsorbing capacities for these three compounds on ZH-01 were higher than those on Amberlite XAD-4 within the temperature range 288-318 K, which was attributed to the large micropore area and 2-carboxybenzoyl functional groups on the network of ZH-01 resin. The adsorption for phenol and 4- nitrophenol on ZH-01 was a physical adsorption process, while for 2,4-dinitrophenol it was a coexistence process of physical adsorption and chemisorption＇s transitions. The column test showed the advantages of ZH-01 in the dynamic adsorption processes of phenolic compounds. Being used as the desorption reagent, sodium hydroxide solution showed an excellent performance.

Estimation of the Isotherms of Phenol on Activated Carbons and Polymeric Adsorbents under Supercritical Condition

A method named as 'volume-expanding and pressure-reducing adsorption' is proposed. It can be used to measure the isotherms under supercritical condition. The adsorption isotherms of phenol on activated carbons and polymeric adsorbents are estimated and compared respectively for the systems of 'phenol-activated carbon-supercritical fluid CO2' and 'phenol-polymeric adsorbent-supercritical fluid CO2'. The results show that the amount of phenol adsorbed on the activated carbons and the polymeric adsorbents under the supercritical condition is much less than that under the general condition, which can be utilized to develop a technology regenerating the activated carbon with supercritical fluid. Moreover, the effects of ethyl alcohol, used as the third component, on the isotherms of phenol on the activated carbons and polymeric adsorbents under the supercritical condition are also investigated.

ADSORPTION OF DINITROPHENOLS ONTO POLYMERIC ADSORBENTS AND ITS MECHANISM

The adsorption of 2,4-dinitrophenol and 2.6-dinitrophenol on non-polar and polar adsorbents was studied. The results showed that the equilibrium adsorption did not comply with the Langmuir equation and was not mono-layer absorption. It is of interest to notice that the effect of pH on the adsorption of 2.4-or 2,6-dinitrophenol onto ADS-7 and ADS-21 was very small. The result is explained by hydrogen bonding interaction between 2, 4- or 2. 6-dinitrophenol and the adsorbent ADS21. The large adsorption capacity of dinitrophenol onto ADS-21, which was about 500 mg/g at an equilibrium concentration of 400 mg/L. and the small dinitrophenol leakage in the effluent from ADS- 21 column presented a good prospect for treatment of wastewater containing dinitrophenol with absorbent ADS-21.

STUDY ON THE TREATMENT OF INDUSTRIAL WASTEWATER CONTAINING TRIETHYLAMINE WITH POLYMERIC ADSORBENTS

The treatment of the industrial wastewater, in which the concentration of triethylamine (TEN) and CODcr was around 3450 mg/L and 22400 mg/L respectively, was studied by adsorption of macroporous resins. Results demonstrate that the polymeric adsorbent CHA-111 has excellent effect on the adsorption and desorption of TEN. The concentration of TEN in the effluent is less than 30mg/L, and the removal efficiency of TEN and total CODcr exceed 99% and 95% respectively. The accumulation and resource reuse of TEN can be realized in this process.

EFFECT OF WEAK INTERACTIONS ON PHENOL ADSORPTION FROM AQUEOUS SOLUTIONS BY AMINATED POLYMERIC ADSORBENTS

Adsorption behaviors of phenol from aqueous solutions have been investigated in batch systems at 303 K and 318 K respectively, using hypercrosslinked polymeric adsorbent （CHA111）, aminated hypercrosslinked polymeric adsorbents （NDA101, NDA103, NDA105） and weakly basic polymeric adsorbent （D301） with a view to studying the effect of hydrogen bonding and Van der Waals interactions between adsorbate and the adsorbent. All adsorption isotherms can be well fitted by Langmuir and Freundlich equations. Compared with D301 driven by hydrogen bonding interaction only and CHA111 driven by Van der Waals interaction only, phenol adsorption on aminated adsorbents driven by both hydrogen bonding and Van der Waals interactions were apparently different, i.e., negative effect for NDA105, positive effect for NDA101 and synergistic effect for NDA103. In this synergistic action, some weak interactions would contribute more or less to the adsorption than they work individually.

SYNERGISTIC INTERACTIONS ON PHENOL ADSORPTION FROM AQUEOUS SOLUTIONS BY POLYMERIC ADSORBENTS

In this paper,the adsorption behaviors of phenol on polymeric adsorbents(Amberlite XAD4,NDA101,and D301) were investigated in batch system at 293,303,and 313 K,respectively.As the results shown,the adsorption isotherms of phenol on all adsorbents can be well fitted by Langmuir and Freundlich equations,which indicate a favorable and exothermic process.The adsorption capacity on a newly developed aminated adsorbent,NDA101,on which adsorption could be achieved by both hydrogen bonding interaction and π-π interaction,are higher than that on a weak base adsorbent,D301,on which adsorption could be achieved by hydrogen bonding interaction only,and on a nonpolar adsorbent,XAD4,on which adsorption could be achieved by π-π interaction only.The results of this paper indicate that the synergistic effect of some weak interactions,which occur simultaneously would contribute more to the adsorption than that occur individually.

SINGLE AND BINARY ADSORPTION PERFORMANCE OF SALICYLIC ACID AND 5-SULFOSALICYLIC ACID ONTO HYPERCROSSLINKED POLYMERIC ADSORBENTS

Single and binary adsorption behaviors of salicylic acid and 5-sulfosalicylic acid onto hypercrosslinked polymeric adsorbents,i.e.NDA-101 and NDA-99 were investigated.The Freundlich model can successfully describe all the adsorption isotherms tested,which indicates a favorable and exothermic adsorption process.The adsorption of salicylic acid relies on π-π interaction,while the electrostatic interaction further influences the adsorption of 5-sulfosalicylic acid onto NDA-99.The adsorptive capacity of salicylic acid on NDA-99 decreases but increases on NDA-101 with 5-sulfosalicylic acid as the background component in a binary solute system.The amount of 5-sulfosalicylic acid adsorbed was decreased with the increase in initial concentration of salicylic acid on both adsorbents.The competition for the adsorption sites is considered to be predominant in the solid-to-liquid interaction process.The adsorption selectivity of salicylic acid onto NDA-101 is higher than onto NDA-99 by more than an order of magnitude.Thus,combination technique involving NDA-101 followed by NDA-99 can be effectively applied to separate and recover salicylic acid and 5-sulfosalicylic acid from wastewater.

ADSORPTION OF 4-METHYLANILINE IN AQUEOUS SOLUTION BY BENZOYLCONTAINING POLYMERIC ADSORBENTS

New polymeric adsorbents(ZH-02,ZH-03)containing benzoyl group for adsorbing and removing 4-methylanilinefrom its aqueous solutions were prepared.Studies on the isotherms and the comparison of desorption conditions evidencedthrough the adsorption of 4-methylaniline in water onto ZH-02 and ZH-03,namely that there are chemisorption's transitionsat a proper higher temperature.Mini-column adsorption studies of 4-methylaniline on XAD-4,ZH-02 and ZH-03 at 288 Kshow that the breakthrough capacities are 2.39,2.99 and 3.19 mmol/g and the total capacities are 3.45,3.92 and4.35 mmol/g,respectively.

Adsorption selectivity of salicylic acid and 5-sulfosalicylic acid onto hypercrosslinked polymeric adsorbents

Both bottle-point and column-feeding experi-ments involving different solutes and sorbents were carried out to investigate the adsorption selectivity and separation performance of salicylic acid and 5-sulfosalicylic acid.Their adsorption isotherms onto such hypercrosslinked polymeric adsorbents as NDA-100 and NDA-99 could be well described by the Freundlich equations whose characteristics describe extrathermic and favorable adsorption processes.The adsorp-tion towards NDA-100 mainly depended on the p-p interac-tion,while that towards NDA-99 was extremely influenced by the static-electric interaction.Additionally,the adsorptive capacity of salicylic acid on NDA-99 decreased while it increased on NDA-100 with the presence of 5-sulfosalicylic acid in the adsorptive environment as the competitive component.Comparatively,the adsorption capacity of 5-sulfosalicylic acid decreased on both resins with salicylic acid as the competitive component.In fact,the difference in the interaction between adsorbent and adsorbate resulted in the straight antagonism on the effective adsorption sites on the adsorbent.In conclusion,the adsorption selectivity of salicylic acid onto NDA-100 was obviously larger than that onto NDA-99 with the existence of 5-sulfosalicylic acid in the adsorptive environment.A satisfactory separation and recovery of tested solutes in aqueous phase could be foresee-ably achieved by the sequencing adsorption technique involving NDA-100 as well as NDA-99.

EFFECT OF pH ON THE ADSORPTION OFp-AMINOBENZOIC ACID ON POLYSTYRENE-BASED ADSORBENTS

In the present study the adsorptive properties of p-aminobenzoic acid with hypercrosslinked and multi-functional polymeric adsorbents at different solution pHs were systematically investigated in accordance with the particular physicochemical characteristics of the aromatic amphoteric compound involving both Lewis acid and Lewis base functional groups. It was found that the equilibrium adsorption data of the three polymeric adsorbents fitted well in the Langmuir and Freundlich isotherm equations. Studies at various pH levels indicate that the capacity of the adsorbents for adsorption of the ionic forms of adsorbate is less than that for the corresponding neutral species. At pH 3.78, the adsorption capacities of the three adsorbents are the highest. Whereas the adsorption property of multi-functional polymeric adsorbent NJ-99 is the largest, which may be attributed to the strong hydrogen-bonding interaction between the amino groups on the resin and the carboxyl group of p-aminobenzoic acid. The trend of the adsorption capacities of the three adsorbents towards p-aminobenzoic acid with the solution pH is in accord with the dissociation curve of the neutral molecular p-aminobenzoic acid. The adsorption forces include π-π interaction, hydrogen-bonding interaction and electrostatic attraction or repulsion when there exist the molecular and ionic adsorbing species at different pHs in aqueous solution.

Binary competitive adsorption of naphthalene compounds onto an aminated hypercrosslinked macroporous polymeric adsorbent

An aminated hypercrosslinked macroporous polymeric adsorbent was synthesized and characterized. Adsorption isotherms for 1 amino 2 naphthol 4 sulfonic acid(1, 2, 4 acid) and 2 naphthol obtained from various binary adsorption environments can be well fitted by Freundlich equation, which indicated a favorable adsorption process in the studied range. Adsorption for 1, 2, 4 acid was an endothermic process in comparison with that for 2 naphthol of an exothermic process. 2 naphthol molecules put a little influence on the adsorption capacity for 1, 2, 4 acid. However, the adsorption to 1, 2, 4 acid depressed that to 2 naphthol in a large extent for the stronger electrostatic interaction between 1, 2, 4 acid and adsorbent. The predominant mechanism can be contributed to the competition for adsorption sites. And the simultaneous environment was confirmed to be helpful to the selective adsorption towards 1,2,4 acid based on the larger selectivity index.

THERMODYNAMIC STUDY OF ADSORPTION OF PHENOLIC COMPOUNDS FROM AQUEOUS SOLUTION BY A WATER-COMPATIBLE HYPERCROSSLINKED POLYMERIC ADSORBENT

Equilibrium data for the adsorption of phenolic compounds, i.e., phenol, p-cresol, p-chlorophenol and p- nitrophenol from aqueous solutions by a water-compatible hypercrosslinked polymeric adsorbent (NJ-8) within temperature range of 283-323 K were obtained and correlated with a Freundlich-type of isotherm equation, so that equilibrium constants KF and n were obtained. The capacities of equilibrium adsorption for all the four phenolic compounds on the NJ-8 from aqueous solutions are around 2 times as high as those of Amberlite XAD-4, which may be attributed to the unusual micropore structure and the partial polarity on the network. The values of the enthalpy (always negative) are indicative of an exothermic process, which manifests the adsorption of all the four phenolic compounds on the two polymeric adsorbents to be a process of physical adsorption. The negative values of free energy change show that the solute is more concentrated on the adsorbent than in the bulk solution. The absolute free energy values of adsorption for NJ-8 are always higher than those for Amberlite XAD-4, which indicates that phenolic compounds are preferentially adsorbed on NJ-8. The negative values of the adsorption entropy are consistent with the restricted mobilities of adsorbed molecules of phenolic compounds as compared with the molecules in solution. The adsorption entropy values of phenolic compounds for NJ-8 are lower than those for Amberlite XAD-4, which means the micropores of NJ-8 require more orderly arranged adsorbate.

Microwave-assisted regeneration of hypercrosslinked polymeric adsorbent saturated with nitrophenols

Thermal regeneration ofhypercrosslinked polymeric adsorbent （HPA） was performed at 67℃. Experiments were carried out using a multimode microwave oven operating at 2450 MHz and a thermostatic water bath so as to compare the effect of the different heating mechanisms on the regeneration efficiency of the HPA saturated with nitrophenols. The temperature rise action of the heterogeneous regeneration system under microwave irradiation was described. Additionally, a complete structure and chemical characterization of the regenerated HPA was also carried out in order to study the influence of the subsequent regeneration cycles on the structure and the adsorption capacities of the adsorbents. Structure characterization of the regenerated HPA was accomplished by means of the analysis of FTIR spectra.

STUDY ON THE TREATMENT OF 3—PHENOXY—BENZALDEHYDE INDUSTRIAL WASTEWATER WITH POLYMERIC ADSORBENT

In this paper the two effluents from PBA (3- phenoxy -benzaldehyde) productionprocess were treated by polymeric adsorbent CHA-lll. PBA or PBC(3-phenoxybenzoic acid) was recovered from the wastewater in the process of neutralization. As asecondary treatment method, adsorption with CHA-lll showed better efficency thanPhotocatalytic decomposition and solvent extraction. The optimal technologicalparameters were: adsorption: current velocity: 2.0 BV/hr(bed volume per hour), roomtemperature, desorption: current velocity:10 BV/hr 80℃8% sodium hydroxideaqueous solutions. In conclusion, 90.9% COD in the neutralizing wastewater and98. 4% COD in the hydrolysis wastewater are removed successfully.

ADSORPTION OF PHENOL AND NITROPHENOLS ON A HYPERCROSSLINKED POLYMERIC ADSORBENT

The adsorption of phenol and nitrophenols on hypercrosslinked polymeric adsorbent was studied as a function of the solution concentration and temperature. Adsorption isotherms of phenol and nitrophenols on hypercrosslinked resin were determined. These isotherms were modeled according to the Freundlich adsorption isotherm. The isotherms for phenol and nitrophenols on hypercrosslinked resin were assigned as L curves. Thermodynamic parameters were calculated for all phenol and nitrophenols. The kinetics experiment results showed that the adsorption rates were of the first-order kinetics. The rate constants at 303K were calculated.

TREATMENT OF SORBIC ACID MANUFACTURING WASTEWATER BY HYPERCROSSLINKED POLYMERIC ADSORBENT (NDA-150)

The treatment of sorbic acid manufacturing wastewater by NDA-150 resin was investigated. The experiments show that this process is suitable for the treatment of sorbic acid manufacturing wastewater. About 98% sorbic acid and 50% CODcr were removed under optimal operating conditions, and 70% of sorbic acid in sorbic acid manufacturing wastewater was reclaimed. This process makes it possible to recover valuable materials from the wastewater and to improve the quality of effluent water.