Application of low-cost adsorbents for dye removal – A review

Industrial, agricultural, and domestic activities of humans have affected the environmental system, resulting in drastic problems such as global warming and the generation of wastewater containing high levels of pollutants. As water of good quality is a precious commodity and available in limited amounts, it has become highly imperative to treat wastewater for removal of pollutants. In addition, the rapid modernization of society has also led to the generation of huge amount of materials of little value that have no fruitful use. Such materials are generally considered as waste, and their disposal is a problem. Also, there are some materials that are available in nature that have little or no use. The utilization of all such materials as low-cost adsorbents for the treatment of wastewater may make them of some value. An effort has been made to give a brief idea of an approach to wastewater treatment, particularly discussing and highlighting in brief the low-cost alternative adsorbents with a view to utilizing these waste/low-cost materials.

Low-Cost Adsorbents: Growing Approach to Wastewater Treatment—a Review

Adsorption of phenol by bentonite.

Microbial production of 1,3-propanediol: recent developments and emerging opportunities.

Recovery, concentration and purification of phenolic compounds by adsorption: A review

An investigation was made of the effects of surface properties on the uptake of phenol by carbonaceous adsorbents and on subsequent regeneration by acetone leaching. As-received carbons derived from different source materials were evaluated at pH values 2 and 9, and the surface properties of selected adsorbents were varied by surface oxidation with concentrated HNO3 and/or heat treatment under nitrogen. Carbons derived from different source materials exhibited similar total uptake and reversible (acetone extractable) uptake at pH 2 but exhibited a wide range of reversibility at pH 9, conditions that promote oxidative coupling reactions. Surface acidity was investigated as a factor contributing to the reversibility of as-received carbons, and surface oxidation was evaluated as a means of improving regenerability. Oxidation of coal- and wood-based adsorbents with concentrated HNO3 increased surface acidity as measured by Boehm titration techniques and reduced the uptake of phenol but increased the reversibl...

/pdf/effect-of-carbon-adsorbent-surface-properties-on-the-uptake-1cn2a30g5u.pdf

Effect of Carbon Adsorbent Surface Properties on the Uptake and Solvent Regeneration of Phenol

A means is proposed for separating propylene glycol and other compounds bearing multiple hydroxyl groups by reversible chemical reaction. Glycols react with aldehydes in cyclic acetalization reactions to form substituted dioxolanes. Propylene glycol reacts with formaldehyde and acetaldehyde to form 4-methyl-1,3-dioxolane and 2,4-dimethyl-1,3-dioxolane. The reaction is catalyzed homogeneously by strong mineral acids or heterogeneously by cation exchange resins in the acid form. Separation processes utilizing this reaction would include an acetalization step, several distillative separation steps and finally a hydrolysis step in which the reaction is reversed. Both reaction steps must be forced to completion by removing the reaction product simultaneously. The equilibrium and kinetics of the reaction with formaldehyde were studied experimentally in systems catalyzed by Amberlite IR-120 ion exchange resin. A number of solvents were screened for their ability to extract 2,4-dimethyl-1,3-dioxolane from aqueous solution. Aromatic hydrocarbons exhibited the highest distribution into the organic phase. To achieve an effective separation of propylene glycol from aqueous solution by combined reaction with formaldehyde and distillation, formaldehyde would have to be present in excess and would be difficult and costly to separate from the aqueous solution. In reactive distillation using acetaldehyde as a reactant this is not a problem. A largemore » flow of acetaldehyde would be necessary to recover the propylene glycol sufficiently in a distillative process. In a process combining reaction and extraction into an organic solvent this problem is avoided. Process simulation indicates the energy input of such a process is less than half of the energy required in a triple-effect evaporation process. This benefit is offset by higher capital costs and increased complexity in the reaction/extraction process.« less

/pdf/recovery-of-propylene-glycol-from-dilute-aqueous-solutions-2ndpsk6tsv.pdf

Recovery of propylene glycol from dilute aqueous solutions via reversible reaction with aldehydes

During recovery of product carboxylic acids from fermentation broths, it is important to maximize the selectivity for the desired acid, as opposed to substrate sugars. In this work uptakes of glucose and competitive uptakes of lactic acid and glucose have been measured for the extractant Alamine 336 in various diluents and three commercially available basic solid polymeric sorbents. The results show that swelling is the main factor governing the selectivity between lactic acid and glucose for the polymeric sorbents. Because of a high uptake capacity and relatively low swelling, Dowex MWA-1 gives a higher selectivity in the pH 5−6 range than do Amberlite IRA-35 and Reillex 425. Extraction with Alamine 336 provides a much higher selectivity, but a lower capacity, than the polymeric sorbents. The extent of water coextraction depends strongly on the diluent used, and larger amounts of water coextracted correspond to larger uptakes of glucose.

Selectivity between Lactic Acid and Glucose during Recovery of Lactic Acid with Basic Extractants and Polymeric Sorbents

Recovery of propylene glycol (1,2-PD) from aqueous solution was studied in batch experiments using extractants consisting of ion pairs of Aliquat 336 and phenylboronate in 2-ethylhexanol, toluene, o-xylene, or diisobutyl ketone. The heterogeneous complexation constant {beta}{sub 11} calculated from the results of 25 C was highest in 2-ethylhexanol (49--100 (mol/L){sup {minus}1}). The equilibrium water concentration in the extractants was 8--12 wt% and decreased with increasing uptake of 1,2-PD. Nearly all extractant/diluent systems exhibited stoichiometric overloading. Evidence for aggregation of the ion-pair extractant in the organic phase was found from water solubilization studies and {sup 1}H NMR spectroscopy studies. The complexation constant decreased with increasing temperature. Up to 80% of the extracted 1,2-PD was back extracted into water after acidification with CO{sub 2}. The extractant could then be regenerated by stripping CO{sub 2} from solution at temperatures exceeding 110 C. However, at these temperatures the color of the extractant changes, and the extraction capacity is reduced to about 60% of its original value. Regeneration by contacting with aqueous solutions of Na{sub 2}CO{sub 3} did not cause extractant degradation; regeneration effectiveness increased with increasing pH.

Recovery of propylene glycol from dilute aqueous solutions by complexation with organoboronates in ion-pair extractants

Extractants consisting of an ion-pair of Aliquat 336 with phenylboronate or 3-nitrophenylboronate were prepared in various diluents (2-ethylhexanol, toluene, o-xylene or diisobutylketone). In batch experiments propyleneglycol (1,2-PD) was effectively extracted even at low concentrations. Heterogeneous complexation constants {beta}{sub 11} calculated at 25 C were 45-120 (mol/1){sup {minus}1} in 2-ethylhexanol, 34.8 (mol/l){sup {minus}1} in toluene, 37.6 (mol/l){sup {minus}1} in o-xylene and 14.4 (mol/l){sup {minus}1} in diisobutylketone. In 2-ethythexanol, there was no significant effect of extractant concentration on the complexation constant. Equilibrium water concentration in the extractants was 8-12 wt %, decreasing with 1,2-PD uptake. Nearly all extractant/diluent systems exhibited overloading (more than stoichiometric uptake of 1,2-PD). Evidence for aggregation of the ion-pair extractant in organic phase was found from water solubilization studies (molar solubilization ratios up to 10) and {sup 1}H NMR spectroscopy studies. Solubilization of 1,2-PD within hydrophilic aggregate interiors may explain the observed overloading. The complexation constant decreased with increasing temperature, but not enough to make back extraction after a temperature change attractive. Back extraction may be achieved after acidification with carbon dioxide to convert the organoboronate anion to the corresponding organoboronic acid. Up to 80% of the extracted 1,2-PD was backextracted in a batch extraction using C0{sub 2}. The extractant could then be regenerated by stripping carbon dioxide from solution at temperatures exceeding 110 C. However, at these temperatures the extractant appears to undergo a transformation in which color changes and extraction capacity is reduced to about 60% of original value.

/pdf/recovery-of-propylene-glycol-from-dilute-aqueous-solutions-k6l2jfz7y1.pdf

C.J. King

Papers

Effect of Carbon Adsorbent Surface Properties on the Uptake and Solvent Regeneration of Phenol

Recovery of propylene glycol from dilute aqueous solutions via reversible reaction with aldehydes

Selectivity between Lactic Acid and Glucose during Recovery of Lactic Acid with Basic Extractants and Polymeric Sorbents

Recovery of propylene glycol from dilute aqueous solutions by complexation with organoboronates in ion-pair extractants

Recovery of propylene glycol from dilute aqueous solutions by reversible chemical complexation with organoboronates