Muhammad Arif Malik

Water purification by electrical discharges

There is a continuing need for the development of effective, cheap and environmentally friendly processes for the disinfection and degradation of organic pollutants from water. Ozonation processes are now replacing conventional chlorination processes because ozone is a stronger oxidizing agent and a more effective disinfectant without any side effects. However, the fact that the cost of ozonation processes is higher than chlorination processes is their main disadvantage. In this paper recent developments targeted to make ozonation processes cheaper by improving the efficiency of ozone generation, for example, by incorporation of catalytic packing in the ozone generator, better dispersion of ozone in water and faster conversion of dissolved ozone to free radicals are described. The synthesis of ozone in electrical discharges is discussed. Furthermore, the generation and plasma chemical reactions of several chemically active species, such as H2O2, O•, OH•, HO2•, O3*, N2*, e-, O2-, O-, O2+, etc, which are produced in the electrical discharges are described. Most of these species are stronger oxidizers than ozone. Therefore, water treatment by direct electrical discharges may provide a means to utilize these species in addition to ozone. Much research and development activity has been devoted to achieve these targets in the recent past. An overview of these techniques and important developments that have taken place in this area are discussed. In particular, pulsed corona discharge, dielectric barrier discharge and contact glow discharge electrolysis techniques are being studied for the purpose of cleaning water. The units based on electrical discharges in water or close to the water level are being tested at industrial-scale water treatment plants.}

Synergistic effect of plasmacatalyst and ozone in a pulsed corona discharge reactor on the decomposition of organic pollutants in water

Plasmacatalytic effects of ?-alumina, ?-alumina, and silica gel in a pulsed corona discharge (PCD) reactor on the decomposition of aqueous methylene blue are described. Methylene blue concentration in the effluent was reduced to 23% of the inlet concentration by PCDs in water. Under the same experimental conditions, addition of ?-alumina further reduced it to 8%, ?-alumina to 4%, and silica gel to below the detection limits. PCDs with silica gel were run for >100?h in a continuous flow reactor and methylene blue in the effluent remained below the detection limit. A hybrid system of plasmacatalysis and ozonation is also described. Phenol concentration in the effluent was reduced to 84% of the inlet concentration by PCDs in water. Under the same experimental conditions, addition of either silica gel or ozone further reduced it to around 35%, and simultaneous addition of silica gel and ozone to 14% of inlet concentration. Decolourization of pre-adsorbed methylene blue on silica gel has been demonstrated. Adsorption and stabilization of the chemically active species on silica gel was indicated by experimental evidence. A significant improvement in the rate of decomposition of organic pollutants in water has been realized by hybridizing plasmacatalysis and ozonation in a PCD reactor.

Synergistic effect of pulsed corona discharges and ozonation on decolourization of methylene blue in water

The effect of O2 and O3 bubbling on decolourization of methylene blue by pulsed corona discharges in water was studied. The pulsed corona discharges were produced by charging an 80 pF capacitor with a 40 kV DC source, through a 100 MΩ resistor, and discharging it into a needle-plate type reactor at 60 Hz through a rotating spark gap switch. A 20 ml sample of 13.25 mg l-1 methylene blue in distilled water was decolourized in 120 min. Bubbling O2 at 10 ml min-1 through the discharge region reduced the decolourization time to 25 min. Bubbling O2 containing 1500 µmol O3 l-1 at 10 ml min-1 reduced the decolourization time to 8 min. The O3 was produced by fractionating input energy between a water treatment reactor and a O3 generator, i.e. no additional energy was consumed for O3 production. Under the same experimental conditions methylene blue solution in tap water was decolourized in >210 min by corona discharge in solution, in 30 min by corona discharge with O2 bubbling, and in 11 min by corona discharge with bubbling of O2 containing 1500 µmol O3 l-1.

Ion-exchange properties of 4-vinylpyridine–divinylbenzene-based anion exchangers for ferric chloride complex anions

Abstract 4-Vinylpyridine–divinylbenzene-based anion exchangers were synthesized by suspension polymerization. Diluent mixtures containing a range of cyclohexane to cyclohexanone ratio were employed to dilute monomers at the time of polymerization. The ion exchangers were characterized for porosity, ion exchange capacity and t 1/2 for exchange of (FeCl 4 ) − ions adsorbed on resins and those in the surrounding solution. A gradual increase of cyclohexane fraction in the diluents from 0% to 100% resulted in: a gradual increase in pore volume from 0.1 to 1.6 ml/g; shift of pore diameter of major fraction of pores from 0.5 μm; and a decrease in breakthrough volume capacity for (FeCl 4 ) − from 0.7 to 0.2 meq/ml. The t 1/2 value decreased from 63 to 8 s followed by an increase to 70 s at 0%, 50% and 100% cyclohexane in the diluents, respectively.

Synthesis of superabsorbent copolymers by pulsed corona discharges in water

Pulsed corona discharges have been utilized for plasma polymerization in aqueous solution for the first time. Superabsorbent copolymers, i.e., poly(acrylamide-co-acrylic acid) hydrogels, were synthesized by aqueous solution polymerization using free radicals produced by pulsed corona discharges as initiator and N,N-methylene-bis-acrylamide as cross-linking agent. Acrylic acid contents in the monomers varied from 0% to 50%. The copolymers thus formed adsorbed 30–1100 g H2O/g of copolymer. The FTIR spectra of the copolymers are comparable with the published FTIR spectra of the corresponding copolymers synthesized by a conventional chemical method and by γ-ray technique.

Pore volume determination by density of porous copolymer beads in dry state

Abstract A quick, easy and novel method to determine pore volume of porous copolymer beads on the basis of their density (d) in dry state is developed. The only apparatus required is a 10-ml measuring cylinder. The equations to calculate pore volumes are: 11.993d2−14.03d+4.2 for styrene–divinylbenzene; 13.221d2−15.654d+4.7223 for 4-vinylpyridine–divinylbenzene, 5.2348d2−8.0647d+3.1612 for glycidylmethacrylate–ethyleneglycoldimethacrylate, 11.365d2−12.925d+3.7972 for 4-vinylpyridine–ethyleneglycoldimethacrylate and 5.7388d2−7.6575d+2.6864 for N-vinylcarbazole–divinylbenzene. An ideally close match of pore volume calculated by these equations and the pore volume measured by mercury porosimetry is achieved.

Porous 4-Vinylpyridine-Divinylbenzene Copolymers– Varying Porosity in Different Bead Sizes of a Single Batch

Abstract Ion-exchangers, adsorbents, supported catalysts, etc, derived from porous copolymer beads are employed as medium in fine chemical separation processes. In these processes the exchange of reagents completes earlier in the smaller beads than in the larger beads in the same lot, which reduces the separation efficiency. So, it is potentially advantageous to preferentially introduce the macropores in the larger beads, as the macropores provide fast access to the reagents into the inner portions of the beads. In this study, camphor-a sublimable organic compound was employed as a diluent to create porosity in 4-vinylpyridinedivinylbenzene copolymer beads produced by o/w suspension polymerization technique. Camphor preferentially introduced macropores in the larger beads in the reaction. The results are explained on the basis of removal of diluent by sublimation phenomenon from the polymerizing droplets at a faster rate from the smaller beads as compared to the larger beads in the same batch.