Th. El-Nabarawy

Activated Carbons Tailored to Remove Different Pollutants from Gas Streams and from Solution

Non-activated carbon ‘A’, physically-activated carbons P1–P4, zinc chloride-activated carbons Z1–Z4 and potassium sulphide-activated carbons K1–K4 were prepared from Maghara coal (Sinai, Egypt). The surface areas of these carbons were determined by investigating the adsorption of carbon dioxide at 298 K and of nitrogen at 77 K. The decolourization powers of the carbons were determined from methylene blue adsorption at 308 K. The adsorption of methanol, benzene, n-hexane, n-octane and α-pinene at 308 K was also determined using equilibrium and flow techniques. The removal of ammonia and phenol from water was investigated on some selected samples. The activated carbons showed high capacities towards the removal of organic pollutants from water and from gas streams via adsorption. Their capacity towards a particular pollutant depends on the method of activation and is related to the textural and/or the chemistry of the carbon surface.

Removal of Pollutants from Water Using Untreated and Treated Sawdust and Water Hyacinth

Sawdust and water hyacinth are waste products which have no economical application in Egypt. They even constitute a solid waste as far as the environment is concerned. As-received sawdust and water hyacinth were treated with phosphoric acid, phosphoric acid + urea or phosphoric acid + urea + dimethylformamide. The as-received and treated samples were used for the removal of Methylene Blue, iodine, phenol and ammonia from their aqueous solutions. The optimum conditions for the maximum adsorption of each pollutant were determined. The isotherms obtained obeyed the Freundlich and Langmuir equations in a satisfactory manner. The initial stages of adsorption follow first-order kinetics as predicted from the Lagergren equation. Sawdust and water hyacinth show promising potentialities for the removal of pollutants from water and can, at least, be used as precursors for the preparation of efficient adsorbents for the removal of pollutants from water.

Surface and Catalytic Properties of Al2O3, CuO/Al2O3 and ZnO/Al2O3 Systems:

Pure alumina, CuO/Al2O3 and ZnO/Al2O3 have been calcined in the temperature range 500–1000°C and the phase changes involved followed using DTA and XRD techniques. The surface properties of all the calcination products were determined from the adsorption of nitrogen at 77 K and the chemisorption of pyridine at 423 K. The catalytic conversion of isopropanol on all the thermal products was also investigated. The surface areas of CuO/Al2O3 and ZnO/Al2O3 decreased while the pore radii increased with increasing calcination temperature from 500°C to 1000°C. CuAl2O4 forms above 800°C while ZnAl2O4 crystallizes at 600°C The acidity of the surface decreased when the calcination temperature was increased above 500°C. The conversion of isopropanol proceeds via dehydration of the alumina catalysts. CuO/Al2O3 and ZnO/Al2O3 surfaces catalyze both the dehydration and dehydrogenation of this alcohol.

Effect of cation exchange on the sorption properties of zeolites

The sodium ions in Na-Y zeolites were partially exchanged with Li, K, Ba, Mg and Ca ions. The adsorption of benzene, carbon tetrachloride, chloroform, methanol and water vapour at 30°C has been measured on Ba-Y zeolite, while the adsorption of carbon tetrachloride and water vapour was followed on Na-Y and all its cation-exchanged forms. The observed adsorption characteristics have been related to the dielectric constant of the adsorbate molecule and to the electrostatic field strength of the zeolite sample. The amount of adsorbate irreversibly adsorbed may also be related to these parameters.

Removal of Ammonia from Aqueous Solution Using Activated Carbons

The surface areas of non-activated, activated and modified activated carbons were determined from the adsorption of nitrogen at −196°C and of carbon dioxide at 25°C. The base neutralization capacities were determined from the adsorption of NaOH, Na2CO3, NaHCO3 and NH4OH. The amount of oxygen combined to the carbon surface was estimated by measuring the pressure of CO and CO2 obtained on outgassing the carbon sample in the temperature range 300–1000°C. The surface area of activated carbon is not a determining factor in its ammonia adsorption. The surface acidity of the active carbon is a good measure of its capacity for ammonia removal. Ammonia adsorption increases appreciably upon surface oxidation of carbons with oxidizing gases and solutions. The acidic groups on the surface of carbons differ in their strength. Only a fraction of the surface covered by the carbon–oxygen groups is responsible for the capacity of the carbon towards ammonia. Most of the adsorbed ammonia is recovered upon treatment with dilute hydrochloric acid leaving the surface free for successive ammonia adsorption cycles.

Surface, Acidic and Catalytic Properties of Silica—Alumina Catalysts in Relation to Their Chemical Composition

Silica–alumina catalysts of varying chemical compositions were prepared under controlled conditions, employing the coprecipitation technique. The surface properties were determined from the adsorption of nitrogen at 77 K. The acidity was investigated by determining the adsorption of pyridine at 423 K and by following its thermal desorption up to 773 K. The conversion of 2-propanol at 523 K and the cracking of cumene at 693 K were investigated using the pulse microcatalytic technique. The surface area decreased and the mean pore volume increased with increasing alumina content. The amount of acid present and its surface density increased while the relative acid strength decreased with an increase in the alumina content. The extent of dehydration of 2-propanol increased with increasing surface acid density and proved to be insensitive to the acid strength. The cracking of cumene appears to depend on the surface area, the amount of acid present and the acid strength of the catalyst, although its dependence on these parameters is of a relative complex nature.

Dehydrogenation of cyclohexane in relation to some textural and catalytic properties of Ni/Al2O3 and Co/Al2O3 catalysts

Ni/Al2O3 and Co/Al2O3 catalysts of different compositions have been prepared. Their structural properties were determined using X-ray diffraction and differential thermal analysis. The textural properties of these catalysts were determined from nitrogen adsorption at 77 K. The catalysts were reduced with hydrogen at 673 K and the adsorption of hydrogen on the reduced catalysts was measured at 320 K. Dehydrogenation of cyclohexane at flow rates of 10–30 ml/min and at 633–723 K was investigated. The loading of alumina with metal oxides leads to changes in the textural properties depending on the degree of loading and on the loaded metal oxide. The adsorption of hydrogen allowed the determination of important catalytic parameters. Dehydrogenation of cyclohexane on the investigated catalysts followed fraction order kinetics. The dehydrogenation activity has been related to the H2 uptake and to the extent of metal dispersion on the support.

Effect of γ-Irradiation on the Chemisorption and Catalytic Activity of Ni/Al2O3 and Co/Al2O3 Systems

The textural properties of non-irradiated and γ-irradiated Ni/Al2O3 and Co/Al2O3 systems with different chemical compositions were determined from the adsorption of nitrogen at 77 K. Chemisorption of hydrogen at 320 K and hydrogenation of benzene at 400 K were studied on the reduced catalysts. The surface areas of γ-irradiated catalysts are higher than those of their non-irradiated equivalents. γ-Irradiation also increases the hydrogen uptake, the metallic surface area and the percentage dispersion of the metal on the support. The hydrogenation activity also increases upon irradiation with γ-rays. All these changes are more pronounced in catalysts with a high metal loading.

Benzene hydrogenation activities of supported nickel catalysts in relation to their chemisorption properties

Samples of nickel on alumina (1.1–10.4 wt.% Ni) were prepared by impregnating alumina in hydrated nickel nitrate. The textural properties of the calcined catalysts have been determined from nitrogen adsorption at 77 K. Calcined catalysts were reduced prior to determination of the chemisorbed benzene at 308 K or chemisorbed hydrogen at 383 K. Hydrogenation of benzene was also determined at 473 K using the flow technique. The surface area of NiO/Al2O3 catalysts decrease and their mean pore radii increase with an increase in NiO content. These changes are more pronounced for catalysts containing more than 5% metal. Chemisorption of benzene proceeds via the formation of π-bonds with nickel. The chemisorption of hydrogen indicated that the percentage dispersion decreases and the crystallite size increases with an increase in metal loading. Dispersion, crystallite size and metal surface are important factors in determining the activity of supported nickel catalysts for benzene hydrogenation.

Texture Properties of Undoped and Na2O-doped V2O5/Al2O3, Catalysts

Pure alumina, V2O5–Al2O3 and Na2O-doped V2O5/Al2O3 samples have been obtained and roasted in air over the temperature range 400–750°C. The textural properties of all the calcination products have been determined from nitrogen adsorption studies at 77 K. The inclusion of V2O5 in alumina modifies the textural characteristics leading to an enhancement of activation at temperatures ≤450°C and to an enhancement of sintering at higher temperatures. Furthermore, AlV2O4 which formed at temperatures below 750°C resulted in a tremendous change in the textural properties. Three types of sintering were detected, i.e. particle-particle adhesion, pore widening and phase change. Doping with Na2O retards sintering and at low calcination temperatures gave solids with higher surface areas compared to undoped samples. This has been attributed to activation brought about by the decomposition of NaNO3 and the evolution of nitrogen oxides.