EFFECT OF SULPHIDING PARAMETERS ON THE INITIAL ACTIVITY BEHAVIOR OF A SUPPORTED NICKEL MOLYBDATE HYDROSULPHURIZATION CATALYST

The influence of some sulphiding parameters on the activity of a supported nickel-molybdate catalyst was studied for the gas phase hydrodesulphurization of thiophene carried out at atmospheric pressure. The optimum activation procedure involved prereduction with hydrogen at 300^°C followed by presutphidation with pure H₂S at 400^°C. The differences in activity observed were substantially maintained over the testing time when the reaction temperature was 300^°C. At 400^°C they were maintained only for limited periods. Catalyst deactivation was observed under either sulphiding or reducing atmospheres. The results are discussed in terms of possible structural changes involving molybdenum sulphide nucleation and crystal growth, which ted to the proposal of three stages for the initial catalyst transformation: oxide monolayer sulphidation, formation of small defected sulphide crystallites, and sulphide multilayer growth.     

SURFACE AREA FORMATION IN DRY FGD SORBENTS

Dry flue gas desulfurization (DFGD) technologies are being developed which require sorbents with high specific surface areas capable of large sulfur dioxide uptake. Specifically, novel methods of controlling S0₂ in a fiuidized bed absorber are being studied which will have the capability of isothermal operation at optimum temperature for S0₂ uptake with alkaline sorbents. This paper reports on a study of surface area development with respect to time for three sorbent materials (pure calcium carbonate, dolomitic limestone and pressure hydrated dolomitic limestone) undergoing thermal decomposition in the temperature range of 600-850°C (1100-1550°F). Two of these sorbents (calcium carbonate and dolomitic limestone) confirm observations made by others of a lag time between recrystalization of the product from the reactant and the development of the maximum surface area. A model is presented which predicts the surface area development by accounting for the surface area generated by thermal decomposition and the surface area lost due to sintering. The parameters necessary for the model were obtained from the experimental data. The ability of the model to predict the surface area change with respect to time is shown to be good for the conditions tested.     

A KINETIC STUDY OF THE SULPHURIZATION OF RESIDUAL ASPHALTS

The kinetics of the sulphurization reaction of residual asphalts were investigated at temperatures of 220^°-250^°C and reaction time of 1 hr. The apparent reaction order varied from 1.40-3.50 for the range of temperature studied. The maximum reaction order was obtained at 24O^°C which appeared to be the optimum reaction temperature. The apparent kinetic rate parameters estimated for the sulphurization reactions were activation energy of 99.5 kJ/mol and a frequency factor of 15.48 × 10⁸. The rate parameters show some good agreement with other work reported in the literature.     

DESORPTION ISOTHERMS OF APPLES AT SEVERAL TEMPERATURES

The desorption isotherms of apples of the Granny Smith variety, treated with 0.5% citric acid aqueous solution, were determined using the gravimetric static method. Experiments at three temperature levels: 20^°C, 40^°C and 60^°C and ten water activity levels from 0.112 to 0.856 were carried out. Along with five well known models - modified Chung-Pfost, modified Halsey, modified Oswin, modified Henderson and GAB (Guggenheim-Anderson-de Boer), a new fraction-linear model has been applied to fit the data and to calculate the isosteric heat of desorption determination.     

REACTION KINETICS PARAMETERS DESCRIBING DISPLACEMENT BY ACIDS OF STRUCTURAL METALLIC IONS FROM CLAY MINERALS

Chemical kinetics parameters describing reactions of naturally-occurring clay minerals with acids were determined using batch reaction and analytical techniques. Clay minerals included sodium montmo-rillonite, kaolinite, and illite, reacting with hydrochloric acid, nitric acid, and sulfuric acid. Two acid concentrations were examined at 50 and 70^°C. Displacement by acids of aluminum and magnesium from clays was found to follow pseudo-first order kinetics. Data analysis verified the batch reaction technique for determining kinetics parameters of acid-clay reactions and demonstrated acid neutralization by naturally-occurring clays. For reactions of sodium montmorillonite with hydrochloric acid, nitric acid, and sulfuric acid, reaction rate coefficients for displacement of aluminum ranged from 1·73 × 10^-4 kg/mol-hr at 50^°C to 3·02 × 10^-3 kg/mol-hr at 70^°C. Displacement of magnesium from sodium montmorillonite by these acids occurred at rates ranging from 3·68 × 10^-4 kg/mol-hr at 50^°C to 1·12 × 10^-2 kg/mol-hr at 70^°C. Activation energies for displacement by acids of aluminum from sodium montmorillonite were calculated to range from 31,000J/mol to 112,000J/mol, while activalion energies for displacement of magnesium from sodium montmorillonite ranged from 36.000 J/mol to 103,000 J/mol. For reactions of illite with acids, reaction rate coefficients for displacement of aluminum were determined to be 1·45×10^-4Kg/mol-hr at 50^°C to 1·7×10^-3kg/mol-hr at 70^°C. Displacement of magneisum by acids from illite occurred at rates from 6·06 × 10^-4 kg/mol-hr at 50^°C to 5·97 × 10^-3 kg/mol-hr. Activation energies for reactions of acids with illite ranged from 33,000 J/mol to 62,000 J/mol for displacement of aluminum and from 9,400 J/mol to 29,000 J/mol for displacement of magnesium.     

THE EFFECT OF TEMPERATURE TREATMENT ON PENETRANT TRANSPORT IN COAL

The macromolecular structure of coals thermally treated at 35^°C, 100^°C and 150^°C was investigated by dynamic penetrant transport in thin coal sections. The effects of temperature, carbon content in coal, and penetrant type on the transport mechanism were investigated. Dynamic swelling studies showed that penetrant transport into coal is a function of the average molecular weight between crosslinks, M_c. The penetrant transport mechanism at low activity is Fickian diffusion. The transport mechanism deviates from Fickian diffusion to anomalous transport, when the carbon content in coal and penetrant activity increase. Variations of the diffusion coefficients and relaxation constants were determined using a diffusion/relaxation coupled model.     

VAPOR-LIQUID EQUILIBRIA OF H2S AND C02 AND ETHYLENE GLYCOL AT ELEVATED PRESSURES

The solubility of H₂S and C0₂ in ethylene glycol has been measured at temperatures in the range 25^° to 125^°C at pressures up to 6.7 and 20 MPa respectively. The data have been correlated using the Peng-Robinson equation of state. Henry' coefficients have also been obtained from the experimental data. Values of the vapor phase composition predicted by the equation of state have been compared with some experimental data and with published data.     

DYNAMIC CHARACTERIZATION OF THE INTERMEDIATES FORMED IN THE OXIDATION OF PROPENE OVER Pt/SiO2

Stable intermediates are formed during the total oxidation of propene on Pt/SiO₂ by nitrous oxide at 290-320^°C. The surface coverage of the intermediates is 0.75(±0.08) without depending on the particle sizes of Pt. The intermediates consist of at least four species, each of which is consecutively and irreversibly converted at similar rate constant, forming the final product of propane by reaction with H₂.     

REDUCTION OF SULPHUR DIOXIDE BY METHANE OVER TRANSITION METAL OXIDE CATALYSTS

The reduction of sulfur dioxide by methane for the production of elemental sulfur using two hydrodesulfuriz-ation catalysts was studied. Oxides of cobalt-molybdenum and molybdenum alone supported on γ-alumina were employed. The reactions were carried out in a quartz reactor at 650^°C and 750^°C and at molar feed ratios (SO₂/CH₄ varying between 0.50 to 2.50. The physicochemical stale of the catalysts was examined by SEM, BET and X-ray diffraction. Molybdenum oxide was converted to sulphide after the chemical reaction. The cobalt molybdenum catalyst was found to be the more active of the two; however, the molybdenum catalyst exhibited higher elemental sulphur yield (99%). Side reactions resulted in the formation of H₂S, COS, CO, and elemental carbon. The production of these is minimized by operating at molar feed ratios greater than 1 and low temperature. The production of H2S is favoured over COS below 700^°C.     

PRODUCTION OF ACTIVATED CARBON FROM COAL CHARS USING MICROWAVE ENERGY

The microwave induced reaction of carbon with carbon dioxide has been investigated as a method of production of activated carbon using coal char. Factors which control the carbon-carbon dioxide reaction in a microwave environment were also studied.

Results indicate that the reaction rate is primarily controlled by the electric field strength. The reaction rate or conversion follows an Arrhenius type relationship with substitution of the electric field strength for temperature. In other instances, temperature is easily determined and therefore used in these calculations. In this case, the particle temperature is nearly impossible to measure. This means that we need an easily calculated variable to use in our calculations. The input microwave power will serve as this variable. It is easily determined, and is also useful in calculations because, as stated earlier, when input power (in the form of electric field strength) is substituted for temperature in equations of the Arrhenius type, the reaction rate is related in a similar manner, Because of difficulties associated with the direct measurement of particle temperature in the microwave energy field, only reactor skin temperatures were measured.

The char surface area, as calculated using the B.E.T. equation, was increased dramatically by the microwave process. The prod uct had a high degree of microporosity and was a good adsorbent of NO_x gas in air. The solids residence time for the coal char in direct microwave contact was on the order of minutes. Reactor skin temperature measurements at the reaction zone suggest that reaction occurred at approximately 600^°F(316^°C).     

Dehydration of Low-Grade Asparagus

Dehydration by a forced convection process is one potential method to add value to low-grade asparagus for marketing purposes. The objectives of this study were to determine the optimum drying temperature, air velocity, and predrying blanching treatment and study the effects of those parameters on the drying curves for low-grade asparagus and the efficiency of the drying process. The ranges of investigation were 60 to 93^°C and 0.14 to 0.44 m/s for drying temperature and air velocity, respectively. Drying at 51 ^°C and 0.30 m/s yielded product with an optimum quality, and drying at 79^° C and 0.18 m/s yielded the optimum process efficiency of 17.9%. Drying temperature, air velocity, and predrying blanching treatment all affected the rate of drying in the constant-rate drying period and the length of the constant-rate drying period. In the falling-rate period, all of the process parameters studied had some effect on the shape of the drying curve.     

THERMODYNAMIC BEHAVIOR OF GREEN WHOLE AND DECAFFEINATED COFFEE BEANS DURING ADSORPTION

Differential and integral thermodynamic parameters were estimated for whole green coffee beans decaffeinated with either ethyl acetate (EADB) and methylene chloride (MCDB). Adsorption isotherms were prepared at 25, 35, and 45^°C. Changes in thermodynamic properties were estimated by the method of Othmer. Variations in the integral enthalpy with respect to moisture indicated that MCDB have a heterogeneous distribution of binding forces at the active sites. EADB showed smaller enthalpy values at lower moisture contents as compared to MCDB, and maintained a distribution of binding energy at the active sites similar to that of whole beans. We suggest storing MCDB at 25^°C with a moisture content of 0.9 g H₂O/100 g d.m., and of 2.3-4.0 g H₂O/100 g d.m. for EADB and whole beans, to obtain maximum stability.     

CONVECTIVE DRYING OF BANANA, GUAVA AND POTATO PIECES : EFFECT OF CYCLICAL VARIATIONS OF AIR TEMPERATURE ON DRYING KINETICS AND COLOR CHANGE

Pieces of banana, guava and potato were dried in a two-stage heat pump dryer capable of precise control of air humidity with predetermined cyclic variations of air temperature entering the drying chamber. The air temperature variations tested were : a cosine, a reversed cosine and three different square wave profiles with peak-to-valley variations from 20^°C to 40^°C. The cycle time was about 60 minutes with drying time of approximately 300 minutes. The drying samples were placed on trays in a thin layer. With appropriate choice of temperature-time variation, it is possible to reduce the overall color change while maintaining high drying rates.     

DYNAMIC KINETICS OF THE COMMON INTERMEDIATES FORMED IN CO AND CO2 HYDROGENATIONS ON Rh/MgO

Stable intermediates are formed during both CO and CO₂ hydrogenations on Rh/MgO at 190-220^°C. The intermediates consist of at least four species, each of which is consecutively and irreversibly converted at a similar rate, forming the final product of CH₄ by reaction with H₂     

KINETICS AND MODELING OF BENZENE OXIDATION

The gas phase oxidation of benzene over a V₂O₅ + P₂O₅ + MoO₃ + Sb₂O₃ catalyst supported on kieselguhr carrier is studied at the temperature range 344-393^°C. 14 different kinetic models are tried to determine the mechanism of benzene oxidation. It is shown that benzene oxidation takes place via a two step redox mechanism which is first order with respect to benzene and 1/2 or 1st order with respect to oxygen. Rate constants for both models are presented.     

MATHEMATICAL SIMULATION OF STRESSES WITHIN A CORN KERNEL DURING DRYING

Thermal stress and hydro stress within a single com kernel during drying are analysed with the mechanics of elasticity and material. The mathematical model of the stress within a single com kernel during drying is given. A finite element method is developed in details to simulate the maximum principal stress and shear stress within a single com at 75^°C and 50^°C drying air temperatures. The locations of the predicted maximum stresses are described and stress fields at different drying time are obtained. The result shows that the predicted locations of the maximum stresses agree with published materials on stress-crack or burst of com kernels.     

THIN-LAYER DRYING BEHAVIOUR OF VEGETABLE WASTES FROM WHOLESALE MARKET

The thin-layer drying behaviour of vegetable wastes (as a mix of lettuce and cauliflower leaves) from wholesale market for a temperature range of 50-150^°C was determined. Drying of this material was found to take part only in the falling-rate period. The experimental data were fitted to the simple exponential model and the Page model. Both models have good prediction capability, Effective diffusion coefficient varied from 6.03*10^-9to 3.15*10^-8m3/s with an activation energy of diffusion of 19.82 kJ/mol. The temperature dependence of the effective diffusion coefficient was expressed by an Arrhenius-type relationship.     

MODELING OF HYDROPROCESSING REACTIONS

Langmuir-Hinshelwood-Hougen-Watson rate expressions are developed for the hydroprocessing of quinoline, naphthalene and dibenzothiophene based on batch reactor data at 350^°C and at 500 psig. Based on competitive adsorption, the kinetics are extended to binary mixtures of quinoline/naphtha-lene and quinoline/dibenzothiophene. In doing so, the differences in hydrogenation and hydro-genolysis sites are taken into consideration. In all cases, the agreement between the predicted and experimental results are good     

ACETIC ACID AS AN OXYGEN CARRIER BETWEEN TWO PHASES FOR EPOXIDATION OF OLEIC ACID

Acetic acid was found to be an effective oxygen carrier for epoxidation of oleic acid. The reaction model of oleic acid epoxidation in the two-phase reaction system was systematically analyzed and the rate determining step was experimentally identified.

The results indicated that the rate of oxidation of the unsaturated acid was independent of the concentration of oleic acid and depended on the mixing rate and the rate of formation peracetic acid which in turn depended on the concentration of acetic acid, strength of acid catalyst and the oxygen source, hydrogen peroxide. In the region of reaction control, the rate equation of epoxidation was found to be

$

where k = 2.98 × 10^-2 M^-2 min^-1 at temperature of 35^°C.     

THERMAL AND MASS DIFFUSIVITY FROM DYNAMIC SINGLE PELLET EXPERIMENTS

The single-pellet moment techniques previously developed for the evaluation of effective diffusion coefficient and effective thermal conductivity of a porous solid are combined and a procedure is proposed for the simultaneous evaluation of these constants from a single set of pulse response experiments. It is shown that both temperature and concentration response curves can be measured from a single pulse of oxygen injected into hydrogen carrier gas flowing past a catalyst pellet. It is shown that the zeroth moment of the concentration response peaks are sufficient for finding the effective diffusivity while both zeroth and first order moments are required for thermal conductivity. Experiments conducted at 110^°C with a boehmite pellet of porosity 0.57 gave a thermal conductivity value of 3.6 x 10^-4 cal/cm ^°K s and an effective diffusivity (for H₂O) of 0.054 cm2/s. The adsorption equilibrium constant of H₂O was determined as ρ_pK = 24.5 from the first moment data. If sorption resistance to diffusion through the pellet is included in the diffusion coefficient, an apparent value of 0.0011 cm2/s would be obtained for D_eff. This result indicates the importance of separation of diffusion and sorption parameters in the analysis.