José M. Arandes

Pressure drop in conical spouted beds

Abstract The limitations of the few correlations in the literature for the design of conical spouted beds and the non-validity of these conventional correlations proposed for cylindrical spouted beds have been proven. Consequently, original hydrodynamic correlations for spouting and jet spouting, corresponding to conical contactors, have been proposed for the calculation of the maximum pressure drop and of the pressure drop in stable operational conditions. The hydrodynamic study has been carried out with different geometries of the contactor—inlet system (different angles and diameters of inlet) and with solids of different particle sizes, densities and shape factors, so that the correlations obtained are of general applicability.

Expansion of spouted beds in conical contactors

Abstract The expansion of conical spouted beds has been studied on a wide experimental base (using contactors of different geometries and solids of different diameters and sphericities). The correlation obtained for calculating the global voidage from the operation conditions is of a more general application than those previously proposed in the literature, which are generally centred on the study of voidage in the spout. The global incipient voidages are delimited for both stable regimes corresponding to two voidage ranges: spouting and jet spouting. While the correlation for calculation of expansion can be applied for the calculation of global minimum jet spouting voidage, a correlation is proposed for the calculation of the global minimum spouting voidage. This equation is applicable in a wide range of operation conditions.

Correlation for calculation of the gas dispersion coefficient in conical spouted beds

Abstract On the basis of the experimental study of air velocity profiles in a pilot plant scale unit, the validity of the hypotheses of the gas flow model proposed for conical spouted beds, that is to say, flow rate conservation along each streamtube and plug flow in the spout zone, has been proven. A correlation has been obtained for calculation of the local velocity as a function of the contactor geometric factors (angle, inlet diameter) and of the operating conditions (solid density, particle size, relative air velocity). The validity of the gas flow model has been proven in a wide range of operating conditions and a correlation has been obtained for calculation of the dispersion coefficient as a function of the following moduli: bed upper diameter/contactor base diameter, Archimedes number, tangent of the angle, relative air velocity.

Thermal recycling of polystyrene and polystyrene-butadiene dissolved in a light cycle oil

A study has been made of the cracking on a mesoporous silica of polystyrene (PS) and polystyrene-butadiene (PS-BD) dissolved in a light cycle oil (LCO) from a product stream of a commercial fluid catalytic cracking (FCC) unit. This study has been carried out in a reactor of short contact time (3 s) in the 723–823 K range. This strategy for simultaneous valorization of plastics and solvent avoids the technological problems inherent to the treatment of solid postconsumer-plastics and the limitation to heat transfer in the process of pyrolysis. The cracking of plastics has a synergistic effect on the conversion of LCO, as it contributes to increasing the yield of gasoline (C5–C12). The cracking of the PS/LCO blend produces high yields of styrene, whereas the cracking of the PS-BD/LCO blend produces a stream of products with petrochemical interest.

Simulation and multiplicity of steady states in fluidized FCCUs

Abstract Multiple steady states are conditions with important consequences for both operation and control of industrial scale FCCs. In order to predict these conditions and to develop strategies for preventing unsteady states, the present study considers a phenomenological model including both fluidized regenerator and riser cracker.

Hydrodynamics of nearly flat base spouted beds

Abstract The hydrodynamic behaviour of a nearly flat base spouted bed (angle 150▿) was studied in a pilot plant unit,using solids of different densities and particle diameters and with different values of the contactor inlet diameter. It was determined that the equation of Mathur and Gishler with an exponent of 0.10 for the (D0/Dc) modulus is suitable for calculation of the minimum spouting velocity. Original correlations for prediction of the maximum pressure drop, of the pressure drop for stable operation and of bed viodage in the bed expansion are proposed. It is proved that the maximum spoutable bed height can be calculated using the equation proposed by Morgan et al. for conventional spouted beds. For small particle diameters the equation of Malek and Lu is also valid.

Calculation of the kinetics of deactivation by coke in an integral reactor for a triangular scheme reaction

Abstract The kinetics of deactivation by coke deposition has been studied for a SiO2-Al2O3 catalyst in the isomerization of n-butenes in the 150-240°C temperature range. The kinetic model is a separable one, with a kinetic equation of the Langmuir—Hinshelwood—Hougen—Watson type for each one of the steps of the main reaction and of the deactivation reaction. The deactivation corresponds to the blockage of active sites by coke coming from degradation of cis-butene and trans-butene. The experimentation has been carried out in an isothermal integral reactor by working with a linear sequence of temperature—time. The treatment of the deactivation data for kinetic parameter calculation consists in rigorously solving the design equation for plug flow reactor; this method takes into account the effect of the composition of all the components on deactivation. The kinetic model has been verified by comparing the experimental results with those foreseen in the simulation of the isothermal operation and with different sequences of temperature-time. The procedure for both obtaining and analysing the deactivation kinetics data is particularly useful for complex reaction systems. In these systems, simplified methods for experimentation and calculation used to isolate the effect of composition on deactivation are not applicable.

Direct Synthesis of Dimethyl Ether From (H2+CO) and (H2+CO2) Feeds. Effect of Feed Composition

The effects of feed composition on the conversion of CO and CO2, selectivity to DME, yield of DME and product distribution are studied in the synthesis of DME from syngas and from (H2+CO2) in a single reaction step using the bifunctional catalysts CuO-ZnO-Al2O3/gamma-Al2O3 and CuO-ZnO-Al2O3/NaHZSM-5. For feeds made up of H2 and CO, the maximum conversion levels of CO, yield of DME and selectivity to DME obtained with both catalysts are very similar, close to 95 %, 75 % and 80 %, respectively, although the catalyst CuO-ZnO-Al2O3/gamma-Al2O3 requires a higher H2/CO ratio. For the feeds made up of H2 and CO2, the catalyst based on NaHZSM-5 zeolite (moderately acid function) performs better due to the fact that higher water content in the reaction medium leads to its adsorption on the Lewis acid sites of gamma-Al2O3 and limits the transformation capacity of methanol to DME.

Conversion of syngas to liquid hydrocarbons over a two-component (Cr2O3-ZnO and ZSM-5 zeolite) catalyst : Kinetic modelling and catalyst deactivation

Abstract The present study describes the kinetics of syngas transformation into liquid hydrocarbons (boiling point in the gasoline range) using as catalyst a mixture of a metallic component, Cr 2 O 3 –ZnO, and of an acidic component, ZSM-5 zeolite. Experimental results were obtained in an isothermal fixed-bed integral reactor. The validity of several kinetic models, available for methanol synthesis, is analysed and modifications are proposed. These changes involve a rate equation with a CO 2 concentration-dependent term. Catalyst deactivation is also evaluated and the effect of the operating conditions on coke deposition is established. Moreover, the rate of CO conversion and the change of catalytic activity with time-on-stream were described using a kinetic model showing a weak influence of temperature.

Effect of the operating conditions on the conversion of syngas into liquid hydrocarbons over a Cr2O3–ZnO/ZSM5 bifunctional catalyst

The effect of the operating conditions (pressure, temperature, space time, CO/H2 ratio in the feed and time on stream) on the conversion of syngas into liquid hydrocarbons over a Cr2O3–ZnO/ZSM5 bifunctional catalyst has been studied by means of experimentation in an integral fixed bed reactor. On the basis of the results, the global stoichiometry of the process is established and the relative importance of the operating variables in order to reach a good compromise between catalyst activity and gasoline quality is analysed.