H.M.A. Asghar

Removal of mercaptans from a gas stream using continuous adsorption-regeneration

The removal of the mercaptan, 1-methyl-1-propanethiol, from aqueous solutions using a non-porous, electrically conducting carbon-based adsorbent (Nyex 1000) was investigated. The adsorption process was found to be rapid (equilibrium capacity achieved within 5 minutes) with low adsorptive capacity (of the order of 0.4 mg g(-1)) when compared with activated carbon. Electrochemical regeneration of the Nyex 1000 in a simple divided electrochemical cell within a sequential batch treatment unit restored 100% of the adsorbents adsorptive capacity using treatment times as low as 20 minutes by passing a current of 0.5 A. The sorptive characteristics of a Nyex-water slurry were also modelled and investigated both in a bubble column and in a continuous adsorption-regeneration treatment system. It was demonstrated that the continuous removal-destruction system could achieve a step reduction in challenge gas concentration of approximately 75% for a period of 35 minutes with a current of 5 Amps. This was attributed to mass transfer enhanced by a combination of adsorption and chemical reaction with free chlorine species generated in the electrochemical process.

Removal of humic acid from water using adsorption coupled with electrochemical regeneration

A novel and economic waste water treatment technology comprised of adsorption coupled with electrochemical regeneration was introduced at the University of Manchester in 2006. An electrically conducting adsorbent material called Nyex™ 1000 (Graphite intercalation based material) was developed for the said purpose. This adsorbent material delivered significantly lower adsorption capacity for the removal of a number of organic pollutants. With the aim to expand the scope of newly developed adsorbent material called Nyex™ 2000, we studied the adsorption of humic acid followed by electrochemical regeneration. Nyex™ 2000 is a highly electrically conducting material with an adsorption capacity almost twice that of Nyex™ 1000 (intercalation based graphite compound) for humic acid. The adsorption of humic acid onto both Nyex™ adsorbents was found to be fast enough keeping almost the same kinetics with approximately 50% of the adsorption capacity being achieved within the first twenty minutes. The parameters affecting the regeneration efficiency, including the treatment time, charge passed and current density, were investigated. The regeneration efficiency at around 100% for Nyex™ 1000 & 2000 adsorbents saturated with humic acid was obtained using the charge passed of 8 and 22 Cg−1 at a current density of 7mA cm−2 during a treatment time of 30minutes, respectively.

Improved phenol adsorption from aqueous solution using electrically conducting adsorbents

The electrically conducting and partially porous graphite based adsorbent (called NyexTM 2000) was tested for its adsorption capacity and electrochemical regeneration ability for the removal of phenol from aqueous solution. Nyex™ 2000 was tested in comparison with Nyex™ 1000, which is currently being used for a number of industrial waste water treatment applications. Nyex™ 1000 exhibited small adsorption capacity of 0.1 mg g−1 for phenol because of having small specific surface area of 1 m2 g−1. In contrast, Nyex™ 2000 with specific surface area of 17 m2 g−1 delivered an adsorption capacity of 0.8 mg g−1, which was eight-fold higher than that of Nyex™ 1000. Nyex™ 2000 was successfully electrochemically regenerated by passing a current of 0.5 A, charge passed of 31 C g−1 for a treatment time of 45 minutes. These electrochemical parameters were comparable to Nyex™ 1000 for which a current of 0.5 A, charge passed of 5 C g−1 for a treatment time of 20 minutes were applied for complete oxidation of adsorbed phenol. The comparatively high charge density was found to be required for Nyex™ 2000, which is justified with its higher adsorption capacity. The FTIR results validated the mineralization of adsorbed phenol into CO2 and H2O except the formation of few by-products, which were in traces when compared with the concentration of phenol removed from aqueous solution. The electrical energy as required for electrochemical oxidation of phenol adsorbed onto Nyex™ 1000 & 2000 was found to be 214 and 196 J mg−1, respectively. The comparatively low energy requirement for electrochemical oxidation using Nyex™ 2000 is consistent with its higher bed electrical conductivity, which is twice that of Nyex™ 1000.

Free chlorine formation during electrochemical regeneration of a graphite intercalation compound adsorbent used for wastewater treatment

Abstract An innovative process aiming at the removal and oxidation of refractory and toxic organic contaminants from wastewater has been developed at the University of Manchester. The process is based on the adsorption of organics onto a graphite intercalation compound (GIC) adsorbent followed by its electrochemical regeneration. This paper investigates the formation of free chlorine species during the electrochemical regeneration of GIC adsorbent in a sequential batch reactor under a range of experimental conditions including the initial concentration of chloride ions, current density and pH. The effect of chloride ions concentration showed that the generation of free chlorine was occurring under the influence of mass transfer. It has been shown that the effect of increasing the current density on the rate of formation of free chlorine was larger than that achieved by increasing the chloride contents of catholyte. However, the current efficiency was not found to be improved with an increase of current density. The concentration of free chlorine formed during electrochemical oxidation of water with sodium sulphate as catholyte was significantly lower than that obtained during electrochemical regeneration in the presence of the GIC adsorbent that highlighted the significance of GIC particles in enhancing the rate of formation of free chlorine. These findings regarding the formation of free chlorine during electrochemical regeneration of GIC adsorbent has important implications for optimising the conditions to minimise the formation of chlorinated breakdown products and for electrochemical disinfection.

Potential Graphite Materials for the Synthesis of GICs

The potential of various graphite materials including Chinese flake graphite, Madagascan flake graphite, natural vein graphite, recycled vein graphite, and synthetic graphite for the preparation of -bisulfate was investigated through electrochemical intercalation method. All the graphite materials were characterized using laser particle size analyzer, SEM analysis, XRD analysis, and X-ray EDS elemental analysis. Chinese flake and Madagascan flake graphite materials were found to be capable of synthesizing GIC-bisulfate through electrochemical intercalation. Natural vein, recycled vein, and synthetic graphite materials did not show any evidence of forming GIC-bisulfate. The formation of GIC-bisulfate was verified through XRD results. Thermal exfoliation volume was observed as an indicator of GIC-bisulfate when the electrochemically treated material was exposed to a sudden thermal shock at a temperature of 850 °C.

Removal of Tartrazine From Water by Adsorption with Electrochemical Regeneration

An innovative process has been developed at University of the Manchester in order to remove organic contaminants from wastewater using graphite intercalation compounds (GICs) as adsorbents with electrochemical regeneration. The present study has demonstrated the removal of tartrazine, from water by adsorption and electrochemical regeneration. The adsorption of tartrazine onto GIC adsorbent was shown to be a quick process, however, with extremely low adsorption capacity compared to porous adsorbents. Low adsorption capacity of the adsorbent is being compensated by rapid electrochemical regeneration associated with low energy consumption that makes the process cost-effective. Regeneration efficiency of around 100% could be obtained in an electrochemical cell by passing a charge of 18 C g−1 for 18 min through a 10-mm thick adsorbent bed. A series of adsorption and regeneration cycles showed that there was little loss in adsorbent capacity, demonstrating that tartrazine loaded GIC adsorbent could be effectively regenerated electrochemically.