Fernando V. Díez

Catalytic hydrodechlorination of tetrachloroethylene over red mud.

Hydrodechlorination of tetrachloroethylene was investigated using red mud (RM, a by-product in the production of alumina by the Bayer process) as the catalyst. Use of RM as a hydrodechlorination catalyst is of interest from an industrial point of view because its cost is much lower than that of commercial catalysts. Hydrodechlorination reactions were carried out in a continuous fixed bed reactor. The influence of catalyst sulfiding, temperature (50-350 degrees C), pressure (2-10MPa), hydrogen flow rate and the presence of solvents (hexane, heptane, benzene and toluene) on the reaction was studied. Sulfided red mud is active as a hydrodechlorination catalyst, conversion of tetrachloroethylene increases as the pressure and temperature increase. The solvents did not influence the conversion, nor were side reactions involving the solvent observed. The kinetics of the reaction was studied at 350 degrees C and 10MPa, conditions for which mass transfer limitations were negligible. A good fit of a Langmuir-Hinselwood model to the experimental data was obtained.

Solvent extraction of molybdenum and tungsten by Alamine 336 and DEHPA

Equilibrium data at 25°C have been obtained for the extraction of molybdenum and tungsten with Alamine 336 and DEHPA (di-2-ethylhexylphosphoric acid), and molybdenum-tungsten solutions with DEHPA from sulfuric acid solutions. The extractant (10% by volume) was dissolved in kerosene, and 2-ethylhexanol (2% by volume) was used as modifier. Extraction data are reported for initial concentration of molybdenum between 1 and 10 g 1−1 and tungsten between 5 and 10 g 1−1 as a function of initial pH, organic/aqueous phase volume ratio and tungsten/molybdenum ratio. Alamine 336 extracts both molybdenum (pH° 1–2) and tungsten (pH° 3) with a high yield, while DEHPA selectively extracts molybdenum at pH° 3. Optimal selectivity for the extraction of molybdenum in the presence of tungsten is achieved at pH° 3 and organic phase/aqueous phase volume ratio 12.

Combustion of methane over palladium catalyst in the presence of inorganic compounds: inhibition and deactivation phenomena

Abstract The influence of the presence of different inorganic gases, often found in methane-containing industrial off-gases (NH3, NO2, H2, H2O, SO2, H2S, CO and CO2) on the catalytic combustion of methane over a Pd/Al2O3 catalyst is studied in the present work, in a range of concentrations corresponding to typical industrial emissions, such as those of coke oven facilities. Results show that the effect of SO2 and H2S on the catalyst is similar, both compounds causing partially irreversible poisoning, whereas water (present in the feed or formed by combustion of H2 or CH4) causes reversible inhibition in the absence of sulphur compounds. Nitrogen-containing compounds increase methane conversion in the absence of sulphur-containing compounds, but ammonia has the opposite effect when sulphur compounds are present. The other compounds studied do not affect appreciably the catalytic combustion of methane.

A new method for enhancing the performance of red mud as a hydrogenation catalyst

Abstract A new method is presented for improving the performance of red mud as a hydrogenation catalyst (a residue from the production of alumina by the Bayer process that contains iron oxides), based on the method developed by K.C. Pratt and V. Christoverson, Fuel 61 (1982) 460. The activation method consists essentially in dissolving red mud in a mixture of aqueous hydrochloric and phosphoric acids, boiling the resulting solution, adding aqueous ammonia until pH=8, and filtering, washing, drying and calcining the resulting precipitate. The catalyst thus obtained is characterised, and after sulphidation, tested (activity and life) for the hydrogenation of a light fraction of an anthracene oil. The catalytic performance is compared with that of sulphided untreated red mud and sulphided red mud activated by the method of Pratt and Christoverson. This activation method has proved to be more effective in improving the performance of red mud as a hydrogenation catalyst than the method of Pratt and Christoverson, since the activated catalyst presents a slightly higher level of activity and a markedly extended active life.

Kinetic study of the gas-phase hydrogenation of aromatic and aliphatic organochlorinated compounds using a Pd/Al2O3 catalyst

The hydrodechlorination of dichloromethane (DCM), tetrachloroethylene (TTCE), chlorobenzene (CBZ) and 1,2-dichlorobenzene (DCBZ), all of them alone and in mixtures, over a commercial Pd/Al(2)O(3) catalyst in a continuous packed-bed reactor was studied in the present work. Results indicate that the reaction kinetics for the single compounds are pseudo-first order kinetics. The reactivity of the compounds studied is very different. So, whereas aromatic compounds and tetrachloroethylene can be fully converted at the operation conditions reported in this work, dichloromethane conversions are lower than 30% in all the cases. The hydrodechlorination of mixtures of organochlorinated compounds shows important inhibition effects, these effects increase as the number of chlorine atoms in the molecule increase. Reaction kinetics for the hydrogenation of mixtures can be represented by a Langmuir-Hinshelwood model.

Catalytic hydrogenation of anthracene oil with red mud

Abstract Red mud, and red mud activated by dissolution in hydrochloric acid and reprecipitation with ammonia, were tested as catalysts for the hydrogenation of an anthracene oil in a trickle-bed reactor. Conversion data were determined for the different polyaromatic compounds in the anthracene oil. Red mud shows appreciable catalytic activity, which is enhanced by the activation. Although both red mud and activated red mud are less active than a commercial Ni-Mo/γ-alumina hydrotreating catalyst, the difference in activity is smaller when conversion to hydroaromatics instead of total conversion of reactants is considered.

Hydrodynamics of a rotating disc contactor

Abstract The hydrodvnamic behavior of a rotating disc contactor (72 mm in diameter, operating height of 1.1 m, 22 mixing compartments) was studied using the two-phase system water—kerosene. Parameters such as the axial dispersion coefficient, the total hold-up, the hold-up profile and the characteristic velocity were measured at various flow rates and rotor speeds. A comparison of the experimental results and values predicted from several correlations is reported. Some modifications for the calculation of the total hold-up and the hold-up profiles are suggested.

Characterization and deactivation studies of an activated sulfided red mud used as hydrogenation catalyst

Abstract Red mud is a residue in the production of alumina by the Bayer process that contains oxides of Fe and Ti, active as hydrogenation catalyst in sulfided form, and whose catalytic activity can be improved by the activation method proposed by Pratt and Christoverson. The development of its activity and selectivity with reaction time was studied for the hydrogenation of a light fraction of an anthracene oil, and compared with untreated sulfided red mud. Catalyst samples were collected at different reaction times, and their texture, morphology and composition characterized by nitrogen adsorption, SEM and SEM–EDX. The loss of catalytic activity of activated sulfided red mud is slower than for untreated sulfided red mud. The main cause of this decrease in catalytic activity is the loss of surface area and superficial Fe.

Characterization of polyarylamide fibers by inverse gas chromatography

Two types of commercial polyaramide fibers have been characterized by inverse gas chromatography. Using the fibers as stationary phases, adsorption isotherms for nonane, decane and undecane were obtained. Specific surface areas and isosteric heats of adsorption were also obtained by this method. Experimental results have been discussed as a function of hydrocarbon--fiber interaction and fiber crystallinity.

Hydrodechlorination of tetrachloroethylene over modified red mud: deactivation studies and kinetics

Abstract In previous works, sulphided red mud (a by-product in the production of alumina by the Bayer process) was shown to be active as catalyst for the hydrodechlorination of tetrachloroethylene, although it presented low stability at reaction conditions. In this work, the performance of red mud modified according to different methods proposed in the literature has been studied. The activation methods tested consist essentially in dissolving the red mud in an acid solution (HCl or a mixture HCl/H3PO4), followed by precipitation with ammonia and calcining at 500°C. Catalysts prepared by these methods have been found to present better activity and resistance to deactivation than unmodified red mud. Fresh and used samples of the catalysts tested were characterised by nitrogen adsorption, X-ray diffraction, scanning electron microscopy, X-ray dispersion spectroscopy, temperature programmed oxidation, NH3 temperature programmed desorption and thermogravimetric analysis. Results lead to think than in the case of modified red mud, deactivation is related with fouling phenomena, whereas in the case of unmodified red mud, the poisoning by HCl is the main deactivation cause. Finally, the kinetic of the hydrodechlorination of tetrachlorethylene over the two modified red mud was studied, both with and without addition of CS2 in the reaction feed. In all the cases a kinetic model based on the Langmuir–Hinselwood postulates, considering chemisorption of both TTCE and H2 (associatively adsorption) in analogous active sites, provided a good fit to the experimental data.