Willibrordus Petrus Maria van Swaaij

Principles of a novel multistage circulating fluidized bed reactor for biomass gasification

In this paper a novel multistage circulating fluidized bed reactor has been introduced. The riser of this multistage circulating fluidized bed consists of several segments (seven in the base-case design) in series each built-up out of two opposite cones. Due to the specific shape, a fluidized bed arises in the bottom cone of each riser segment. Back-mixing of gas and solids between the segments is prevented effectively. The absence of back-mixing combined with the enlarged solids residence time in each segment (each segment is a fluidized bed) creates the opportunity to operate, spatially divided, separate process steps in a single reactor. The benefit of a concept in which different processes are carried out in separate segments of the same reactor has been demonstrated for the specific case of biomass gasification. In the novel reactor it is possible to create oxidation segments in which O2 reacts exclusively with char (carbon). This results in an increased carbon conversion and consequently improved gasification efficiency. Creating an exclusive char combustion zone, aimed at improving both the carbon conversion and the thermal efficiency, has also been applied successfully in a conventional CFB biomass gasifier (ECNs CFB 100 kg wood/h) by building a flow restriction in the riser between the primary air nozzles and the biomass feed point.

The oxidation of sulphide in aqueous solutions

The purpose of this work was to study the catalytic effect of activated carbon particles 7.5 μm in diameter on the initial oxidation rate of bisulphide, with oxygen as oxidant, in an aqueous solution buffered at a pH of 9.7 and at temperatures of 48.5, 35 and 25 °C. Two reactors were used: a stirred gas—liquid contactor to determine the kinetics and a continuous flow reactor to demonstrate that a continuous process is possible. The liquid phase oxidation of sulphide was found to be much faster in the presence of activated carbon. Kinetic equations for the initial rate of reaction are given separately for homogeneous and heterogeneous oxidation. As activated carbon shows a strong catalytic activity, it can be of interest in the oxidation of sulphide in industrial and other waste waters at low temperatures.

Polymerization of liquid propylene with a 4th generation Ziegler-Natta catalyst-influence of temperature, hydrogen and monomer concentration and prepolymerization method on polymerization kinetics

In a batch-wise operated autoclave reactor, liquid propylene was polymerized using a 4th generation, TiCl4/MgCl2/phthalate ester-AlEt3-R2Si(OMe)2, Ziegler-Natta catalyst system. By using a calorimetric principle it was possible to measure full reaction rate versus time curves for obtaining data on polymerization kinetics, under industrially relevant conditions. The influence of polymerization temperature, the hydrogen and monomer concentration, and the prepolymerization method on reaction kinetics were investigated. A new method for prepolymerization, the so-called non-isothermal prepolymerization, is described. In this short prepolymerization procedure featuring an increasing polymerization temperature the thermal runaway on particle scale was avoided. It was shown that this prepolymerization method can relatively easily be applied to an industrial process, with the introduction of a continuous plug flow reactor, giving a narrow residence time distribution, acceptable yield-in-prepolymerization and a method for monitoring catalyst activity. Using different methods for calculating the monomer concentration at the active site of the catalyst, the influence of polymerization temperature was determined. It was shown that at high polymerization temperatures, the reaction rate is barely influenced by polymerization temperature, when no prepolymerization is used. This is ascribed to thermal runaway on particle scale of a fraction of the catalyst particles. When a prepolymerization is used, this effect disappears and thermal runaway is avoided. When systematically reducing the monomer concentration (Cm,bulk) in the bulk by replacing part of the liquid propylene by hexane, the reaction rate proved to be remarkably independent of the monomer concentration. With reducing Cm,bulk, reaction rate decreased very slowly until Cm,bulk=150 g/l. When further decreasing Cm,bulk, reaction rate dropped rapidly. The hydrogen concentration was varied over a wide range at 60°C and 70°C. For both temperatures it was shown that reaction rates increased rapidly with increasing hydrogen concentration at low hydrogen concentrations. At higher hydrogen amounts, this effect disappeared and a maximum reaction rate was found.

Selective removal of H2S from sour gases with microporous membranes. Part II. A liquid membrane of water-free tertiary amines

In the present study the application of a liquid membrane for selective removal of H2S from gases also containing CO2 was investigated. The liquid membrane was filled with pure methyl-di-ethanol-amine (MDEA). A theoretical model was developed to describe: (a) the chemical equilibrium between the dissolved gas and MDEA in the membrane and (b) the physical equilibrium between the solute (CO2 and H2S) in the gas and the liquid phase. Experimentally H2S and CO2 fluxes were determined in a setup consisting of two well mixed gas phase compartments separated by a flat liquid membrane. The fluxes were interpreted with the theoretical model and separately measured physical constants (solubility, diffusivity and the porosity/tortuosity factor of the membrane material). No reaction of CO2 with MDEA was observed which is attributed to the absence of water. A weak acid/base interaction of H2S and MDEA was found to increase the H2S transport through the membrane which includes higher selectivity. This effect is more pronounced at lower partial pressures of H2S.

Hydrodynamic modelling of circulating fluidised beds

A one-dimensional model for the riser section of a circulating fluidised bed has been developed which describes the steady-state hydrodynamic key variables in the radial direction for fully developed axisymmetric flow. Both the gas and the solid phase are considered as two continuous media, fully penetrating each other. As a first approximation gas phase turbulence has been incorporated in our hydrodynamic model by applying a slightly modified version of the well-known Prandtl mixing length model. To solve the resulting set or transport equations, the solids distribution along the tube radius is required. Several strategies are given to obtain this information. In addition the effect of clusters on the momentum transfer between both phases has been modelled using an empirical correlation. Theoretically calculated results agree well with reported experimental data of different authors

Selectivity of benzene sulphonation in three gas—liquid reactors with different mass transfer characteristics I: Mass transfer and selectivity in a stirred-cell reactor

Liquid benzene was sulphonated with gaseous sulphur trioxide in a stirred-cell reactor, a tube reactor and a new gas—liquid cyclone reactor. The man transfer coefficient kL Varied from low values in the cell reactor to very high values in the cyclone reactor. The products were benzene Sulphonic acid and diphenyl sulphone (byproduct). The selectivity obtained increases with increasing kL. The results of the stirred-cell reactor experiments are reported in Part I. With reaction, large temperature and Viscosity gradients occurred at the gas—liquid interface and kL was found to be independent of stirrer speed. The observed selectivity is interpreted using a simple model of mass transfer followed by a mixed parallel consecutive reaction system, the first reaction being instantaneous with respect to mass transfer.

Selectivity of benzene sulphonation in three gas—liquid reactors with different mass transfer characteristics: II: Mass transfer and selectivity in a cyclone reactor and in a tube reactor

Liquid benzene was sulphonated with gaseous sulphur trioxide in a tube reactor and in a new gas—liquid cyclone reactor. The products are benzenesulphonic acid and diphenyl sulphone (byproduct). The observed selectivity depends on the conversion, the initial benzene concentration and the mass transfer characteristics of the reactor. Minimum diphenyl sulphone formation was obtained for a low initial benzene concentration, a low benzene conversion and with a high liquid-side mass transfer coefficient, as in the cyclone reactor. As the actual mass transfer rate during sulphonation could not be measured, the observed selectivity was related to the mass transfer coefficient determined by the simultaneous absorption of CO2and O2 in aqueous sodium hydroxide solution.

Catalytic combustion of propane in a membrane reactor with separate feed of reactants - III. Role of catalyst load on reactor performance

Abstract This paper deals with a pilot plant study on the catalytic combustion of propane in a membrane reactor with separate feed of reactants. The importance of the amount of catalyst (1% b.w. Pt on γ-Al2O3), deposited on the pore walls of the membrane, is investigated. Two membranes were prepared by the so called urea method, intruding different amounts of the above catalyst (2% and 4% b.w., respectively) in anα-Al2O3 basic porous tubular structure (pore diameter: 0.7 μm; length: 100 mm; internal radius 7 mm; thickness: 3 mm). The performance of the two membranes was tested in a pilot plant, feeding air at one membrane side and a propane/N2 mixture at the other side. Either the kinetics- or the transport-controlled operating regimes were investigated, and, in this last case, operation was considered both in presence and in absence of trans-membrane pressure gradients. From this study the catalyst load of the membrane seems to affect seriously the reactor performance. The more the catalyst deposited in ...

KINETICS AND INFLUENCE OF MASS TRANSFER ON SELECTIVITY IN THE SULFONATION OF BENZENE WITH SULFUR TRIOXIDE

Abstract Available kinetic data on aromatic sulfonation with SO3 are critically reviewed. It is concluded that the kinetic reaction rate of the sulfonation of benzene with sulphur trioxide at 25°C is fast compared to the rate of the mass transfer process, moreover it is concluded that the value of the mass transfer coefficient realized in a particular reactor may influence the selectivity of the sulfonation reaction. Experimental results on sulfonation of 30 vol% benzene in 1,2 dichloroethane using three types of gas-liquid reactors which greatly differ in mass transfer characteristics have been summarized. The results show a decrease of the formation of the by-product diphenyl sulfone with increasing liquid side mass transfer coefficient. Especially in a cyclone reactor, by-product formation could be considerably suppressed. Based on the kinetic picture derived, the relationship between sulfone formation and mass transfer coefficient is qualitatively understood.