Drop properties and pressure fluctuations in liquid–liquid–solid fluidized-bed reactors

Characteristics of size, rising velocity and distribution of liquid drops were investigated in an immiscible liquid–liquid–solid fluidized-bed reactor whose diameter was 0.102 and 2.5 m in height. In addition, pressure fluctuations were measured and analyzed by adopting the theory of chaos, to discuss the relation between the properties of liquid drops and the resultant flow behavior of three (liquid–liquid–solid) phase in the reactor. Effects of velocities of dispersed (0–0.04 m s⁻¹) and continuous (0.02–0.14 m s⁻¹) liquid phases and fluidized particle size (1, 2.1, 3 or 6 mm) on the liquid drop properties and pressure fluctuations in the reactor were determined. The resultant flow behavior of liquid drops became more irregular and complicated with increasing the velocity of dispersed or continuous liquid phase, but less complicated with increasing fluidized particle size, in the beds of 1.0 or 2.1 mm glass beads. In the beds of 3.0 or 6.0 mm glass beads, the effects of continuous phase velocity was marginal. The resultant flow behavior of liquid drops was dependent strongly upon the drop size and its distribution. The drop size increased with increasing dispersed phase velocity, but decreased with increasing particle size. The drop size tended to increase with approaching to the center or increasing the height from the distributor. The size and rising velocity of liquid drops and correlation dimension of pressure fluctuations have been well correlated in terms of operating variables.     

Mass transfer effects in the H2SO4 catalyzed pivalic acid synthesis

The synthesis of carboxylic acids from alkenes, carbon monoxide and water according to the Koch process is usually carried out in a stirred gas–liquid–liquid multiphase reactor. Due to the complex reaction system with fast, equilibrium reactions and fast, irreversible reactions the yield and product distribution depend on a number of process parameters. The effect of some of these parameters was studied for the production of pivalic acid, using sulfuric acid as a catalyst. For the 96 wt.% sulfuric acid catalyst solution used the main reactions are relatively fast with respect to mass transfer and mixing. Therefore, aspects like the position of the injection point, inlet concentration, agitation intensity and injection rate all influence the yield obtained. The presence of an inert organic liquid phase was found to be beneficial, due to a combined effect of enhanced gas–liquid mass transfer and a ‘local supply’ effect for carbon monoxide near the hydrocarbon reactant inlet.     

The mechanism model of gas–liquid mass transfer enhancement by fine catalyst particles

In order to present the enhancement of gas–liquid mass transfer by heterogeneous chemical reaction near interface, the mechanism model has been proposed to describe the mass transfer rate for a gas–liquid–solid system containing fine catalyst particles. The composite grid technique has been used to solve the model equations. With this model the effect of particle size, first-order reaction rate constant, distance of particle to gas–liquid interface and residence time of particle near gas–liquid interface on the mass transfer enhancement have been discussed. The particle–particle interaction and slurry apparent viscosity can be considered in the model. The experimental data have been used to verify the model, and the agreement has been found to be satisfied.     

Dispersion of liquid–liquid systems in a mixer with a reciprocating agitator

In this paper, the experimental results of dispersion of two immiscible liquids in a vibromixer are presented. The investigations covered three of the most important problems for vibro-mixing of liquid–liquid systems: the critical conditions, power consumption, and phase dispersion. The data obtained were presented in dimensionless correlations describing the influence of both: the operating conditions and physical properties of dispersed liquids on the process. Also new forms of dimensionless numbers for vibro-mixing are proposed.     

Novelties of liquid–liquid–liquid phase transfer catalysis Alkoxylation of p-chloronitrobenzene

Liquid–liquid–liquid phase transfer catalysis (L–L–L PTC) offers orders of magnitude intensification of rates of reaction and better selectivities than the biphasic PTC. The catalyst-rich middle phase is the main reaction phase. The etherification or alkoxylation of p-chloronitrobenzene (PCNB) was conducted by using alkanol and alkali instead of the metal alkoxide. A kinetic model is presented and validated.     

Kinetics and phase equilibria of competing aldolization and elimination in a three-phase reactor

Butyraldehyde was aldolized with formaldehyde over a weakly basic anion-exchange resin catalyst in aqueous solvent in a batch reactor operating at atmospheric pressure and at temperatures 50–70°C. The reaction mixture was a liquid–liquid–solid system, an emulsion, the phase equilibria of which were studied through chemical analysis of the organic and aqueous phase as well as of the mixed emulsion. Simplified rate equations were derived starting from molecular reaction mechanisms on the catalyst surface. A liquid–liquid reactor model for the fitting of the experimental results was developed on the basis of the rate equations and the phase equilibria. The model described very well the experimental data.     

Dynamic methods and new reactors for liquid phase molecular catalysis

Kinetic data acquisition and screening of transition metal complexes for homogeneous liquid phase catalysis calls for numerous testing in multiphase G/L, L/L and G/L/L systems. It is shown first, with an example in asymmetric hydrogenation, why detailed kinetics must be performed. Then, new reactors leading to fast experimental techniques are proposed. A liquid–liquid centrifugal partition chromatography is evaluated for determining rate constants and partition isotherms by combining frontal analysis and elution chromatography, the catalyst being maintained in a stationary aqueous phase. Two microreactors offering short residence time have also been tested and compared with a fast test reaction (t_R ca. 5–20 s). The combination of reacting pulses, carrier liquids and micromixer is proposed as a general high throughput tool for the investigation of G/L, L/L and G/L/L catalytic systems in a fast sequential way.     

The influences of the gas rate dissolution and mass-transfer limitation at the interfaces on selectivity of gas–liquid processes in stirred reactors with a suspended catalyst

A complex mathematical model accounting for the hydrogen dissolution process in suspensions and mass-transfer steps at the liquid–solid interface for the gas and liquid components is given. The calculated data according to the model for the reaction A→B→C shows, that the yield of an intermediate product B is very much affected by the relation of the gas component mass-transfer coefficient on the gas–liquid interface to that on the liquid–solid one. The hydrogenation of chlornitroaromatic compounds was analysed. The kinetics of the catalytic reduction of p-chlornitrobenzene to p-chloraniline via corresponding arylhydroxilamine on the Ir/C catalyst experimentally in a batch reactor has been studied. In this process the first reactions depend on the hydrogen concentration but the second ones are not dependent — this is a disproportion of the intermediate product to the final product — amine.     

Liquid back-mixing in packed-bubble column reactors: a state-of-the-art correlation

The extent of liquid back-mixing in gas–liquid concurrent upflow packed-bubble column reactors is quantified in terms of an axial dispersion coefficient or its corresponding dimensionless Péclet number. Effects of reactor operating conditions on the axial dispersion coefficient are not properly accounted for by the available literature correlations, wherein most often the Péclet number is expressed solely in terms of the gas and liquid Reynolds numbers or superficial velocities. Based on the broadest experimental databank (1322 measurements, 11 liquids, four gases, 28 packing materials, 14 columns diameters, Newtonian, non-Newtonian, aqueous, organic, coalescing and non-coalescing liquids, high pressure, bubble and pulsing flow regime conditions), a state-of-the-art liquid axial dispersion coefficient correlation is obtained by combining neural network modeling and dimensional analysis. Thorough qualitative and quantitative analyses of the constructed databank demonstrate the robustness of the proposed correlation to restore the variety of trend variations of liquid Péclet numbers reported in the literature.     

Kinetics of phase transfer catalyzed reduction of nitrochlorobenzenes by aqueous ammonium sulfide: Utilization of hydrotreater off-gas for the production of value-added chemicals

The reduction of nitrochlorobenzenes (NCBs) was carried out in an organic solvent, toluene, under liquid–liquid mode with phase transfer catalyst, tetrabutylammonium bromide (TBAB). The selectivity of chloroanilines (CANs) was found to be 100%. The reaction rate of m-nitrochlorobenzene (MNCB) was found to be highest among the three NCBs followed by o- and p-nitrochlorobenzene (ONCB and PNCB). The reactions were found to be kinetically controlled with apparent activation energies of 22.8, 19.6 and 9.4 kcal/mol for ONCB, PNCB and MNCB, respectively. The effects of different parameters such as TBAB concentration, NCB concentration, sulfide concentration, ammonia concentration, and elemental sulfur loading on the conversion and reaction rate of NCBs were studied to establish the mechanism of the reaction. The rate of reaction of NCBs was found to be proportional to the concentrations of the catalyst and NCBs and to the cube of the concentration of sulfide. A generalized empirical kinetic model was developed to correlate the experimentally obtained conversion versus time data for the three NCBs.     

Hydrodynamics of churn turbulent bubble columns: gas–liquid recirculation and mechanistic modeling

A phenomenological (mechanistic) model has been developed for describing the gas and liquid/slurry phase mixing in churn turbulent bubble columns. The gas and liquid phase recirculation rates in the reactor, which are needed as inputs to the mechanistic reactor model are estimated via a sub-model which uses the two-fluid approach in solving the Navier–Stokes equations. This sub-model estimates the effective bubble diameter in the reactor cross-section and provides a consistent basis for the estimation of the volumetric mass transfer coefficients. The strategy for the numerical solution of the sub-model equations is presented along with the simulation results for a few cases. The overall reactor model has been tested against experimental data from radioactive gas tracer experiments conducted at the Alternate Fuels Development Unit (AFDU), La Porte, TX under conditions of methanol synthesis.     

Simultaneous liquid–liquid demixing and crystallization and its effect on the spherulite growth in poly(ethylene terephthalate)/poly(ether imide) blends

Poly(ethylene terephthalate) (PET)/poly(ether imide) (PEI) blends were miscible in the melt, but exhibited simultaneous liquid–liquid phase separation and crystallization over a wide range of temperature and composition. The interplay between these two processes is expected to dominate the morphological formation in the blends. In this study, the phase diagram of PET/PEI blend was determined to evaluate the envelop within which liquid–liquid phase separation was operative with crystallization. A UCST phase diagram below 240°C was identified for this system. The effect of liquid–liquid phase separation on the growth of PET spherulites was studied by small-angle light scattering (SALS). Nonlinear spherulite growths were observed for the blends at higher crystallization temperatures of 210°C and 220°C, while the growths were basically linear below 210°C. The nonlinear growth behaviour was discussed based on the competition between spherulite growth and spinodal decomposition.     

Liquid phase residence time distribution for a two-phase countercurrent flow in a packed column with a novel internal

The liquid phase residence time distribution (RTD) for gas–liquid countercurrent flow in a packed column with a novel internal was measured by conductivity measurements and an air–water system. The RTD of a liquid tracer is well represented by the ADM and PDE models. At lower gas flow rates, the Peclet number of the liquid in the packed column with the internal is lower than that without the internal; at higher gas flow rates, it is vice versa, especially with an internal with a higher volume fraction. The distribution of the liquid RTD can be improved by using suitable geometric parameters of the internal to give a larger volume fraction and a lower stage height.     

The nitric acid oxidation of 2-octanol. A model reaction for multiple heterogeneous liquid–liquid reactions

The oxidation of 2-octanol with nitric acid has been selected as a model reaction for a heterogeneous liquid–liquid reaction with an undesired side reaction. 2-Octanol is first oxidized to 2-octanone, which can be further oxidized to carboxylic acids. An extensive experimental program has been followed using heat flow calorimetry supported by chemical analysis. A series of oxidation experiments has been carried out to study the influence of different initial and operating conditions such as temperature, stirring speed and feed rate. In parallel a semi-empirical model has been developed to describe the conversion rates.     

Axial mixing in a novel pilot scale gas–liquid reciprocating plate column

Axial mixing in a novel pilot scale landau reciprocating plate column (LRPC) has been investigated for counter-current gas–liquid contacting over a wide range of operating conditions. The experimental results obtained using the dynamic response method were analysed using both the dispersion and compartment models under different boundary conditions and using both the method of moments and the direct time domain parameter estimation techniques. Based on the results, it was identified that axial mixing in this column can be best described using the back flow and the dispersion models solved with “closed–closed” boundary conditions. A general correlation describing the effect of operating parameters on the extent of axial mixing was developed with a mean absolute relative residuals of 6.8%. Similar to other RPC designs, axial mixing in LRPC increases with increasing both phase flows and plates oscillatory velocity. Values of axial dispersion coefficient in this work ranged from 10⁻⁴ to over 3 × 10⁻³ m²/s, which are comparable or less than those in other RPC designs under similar phase velocities and oscillatory conditions, but an almost order of magnitude lower than those measured in bubble columns under similar operating flow rates.     

Preparation of porous polysulfone beads for selective removal of endocrine disruptors

Porous polysulfone (PSf) beads are prepared using a liquid–liquid phase separation technique. The porous PSf beads are then used for the removal of endocrine disruptors, such as Biphenyl (BP), dibenzofuran (DBF), dibenzo-p-dioxin (DBD), biphenol A (BPA), and diethylstylbestrol (DES) from their aqueous solutions. The endocrine disruptors could be removed efficiently by a simple sorption method with hydrophobic porous PSf beads. The removal ratio was high for endocrine disruptors having high octanol–water distribution coefficients. The effect of sorption time, weight of PSf beads, ethanol amount in the solution, and the porosity of the beads on the removal of endocrine disruptors was investigated. The adsorbed endocrine disruptors in the PSf beads could be effectively removed by 2-propanol or ethanol, which indicated that the beads could be reused. The study suggested that the porous PSf beads have a potential ability to be used for the removal of endocrine disruptors in environmental application.     

Numerical simulations of ultrafine powder coating systems

Numerical simulations for gas–solid two-phase flows were conducted for an experimental coating booth and an industrial coating booth to study the effect of the coating powder size on the performance of the coating process. To optimize coating parameters, simulations were conducted for different coating parameters, such as the size of the coating part, the distance between the coating part and the spray gun, the air flow rate and particle flow rate from the spray gun, the position of the pattern adjust sleeve of the spray gun, and the electrostatic field, in order to increase the coating process efficiency and coating quality.

In numerical simulations, the air flow field is obtained by solving three-dimensional Navier–Stokes equations with standard κ– turbulence model and non-equilibrium wall function. The second phase, the coating powder, consists of spherical particles and is dispersed in the continuous phase, the air. In addition to solving transport equations for the air, the trajectories of the particles are calculated by solving the particle motion equations using Lagrangian method. It is assumed that the particle–particle interaction can be neglected due to low particle volume fraction in coating systems. The electrostatic field is predicted by solving the Laplace equation.     

A carbon–carbon coupling reaction catalyzed by a water soluble rhodium catalyst entrapped in mesoporous silica

A Heck-type reaction, comprising a carbon–carbon coupling between an arylboronic acid and styrene, has been performed using a water soluble rhodium catalyst entrapped in the water-filled pores of mesoporous silica particles. The catalyst-loaded inorganic particles were dispersed in a non-polar medium, either a solution of the reactants in an aromatic solvent (toluene or p-xylene) or a solvent-free mixture of the reactants using a large excess of styrene. The reaction occurred at the oil–water interface, i.e., at the silica pore openings. The yield obtained was higher than that obtained in the conventional liquid–liquid two-phase system. The major advantage with having the catalyst “heterogenized” by entrapment into the siliceous material is the simplicity of the work-up process. The porous particles, containing the catalyst, are simply removed by filtration after completed reaction.     

Modelling of a dynamic multiphase flash: the positive flash: Application to the calculation of ternary diagrams

A general and polyvalent model for the dynamic simulation of a vapor, liquid, liquid–liquid, vapor–liquid or vapor–liquid–liquid stage is proposed. This model is based on the τ-method introduced as a minimization problem by [Comput. Chem. Eng. 22 (7/8) (1998) 897] for steady-state simulation. They suggested modifying the mole fraction summation such that the same set of governing equations becomes valid for all phase regions. Thanks to judicious additional switch equations, the τ-formulation is extended to dynamic simulation and the minimization problem is transformed into a set of differential algebraic equations (DAE). Validation of the model consists in testing its capacity to overcome phase number changes and to be able to solve several problems with the same set of equations: calculation of heterogeneous residue curves, azeotropic points and distillation boundaries in ternary diagrams.     

Mass transfer into/from nanofluid drops in a spray liquid‐liquid extraction column

The performance of a spray liquid‐liquid extraction column at two mass‐transfer directions was experimentally studied in the presence of silica nanoparticles. Toluene‐based nanofluid drops containing 0.0005–0.01 vol % silica nanoparticles were dispersed in aqueous phase and acetic acid (AA) transfer between phases was investigated. The experiments were performed at fixed volumetric flow rates of dispersed and continuous phases. Maximum enhancement of 47.4% and 107.5% in overall mass‐transfer coefficient, respectively, for mass‐transfer direction of dispersed to continuous phase and vice versa were achieved for drops with 0.001 vol % silica nanoparticles. These enhancements can be referred to Brownian motion of nanoparticles and induced microconvection. The results showed that nanoparticles are more effective in augmenting AA transfer from continuous to dispersed phase. Probable reason is that smaller diameter and lower internal turbulence of drops in this transfer direction increase dispersed phase resistance potential to be manipulated by Brownian motion of nanoparticles. © 2015 American Institute of Chemical Engineers AIChE J, 62: 852–860, 2016