Some aspects of homogeneous and two-phase aromatic sulphonation

The two-phase sulphonation of benzene and toluene with concentrated sulphuric acid solutions at 30°C has been studied in a continuous stirred tank reactor (1.06 dm³ capacity). The rates of reaction, as a function of sulphuric acid concentration and the overall mass transfer coefficient times, and the interfacial area per unit volume of the acid phase as a function of agitation speed, have been determined. In homogeneous systems, the kinetic rate constants and the relative rates of sulphonation of a series of aromatic hydrocarbons have been measured in the range of 13–16 mol dm^?3 sulphuric acid. It has been shown that the rates of sulphonation of compounds, with levels of reactivity beyond that of m-xylene, are likely to be affected by diffusional phenomena.     

Two phase nitration of toluene—III

Initial nitration rates of toluene have been measured at sulphuric acid strengths between 76 and 79 per cent in a stirred cell with pure toluene, and also in a stirred batch reactor with a dilute solution of toluene in an inert solvent.The results are consistent with the rates in both cases occurring within the transition from the slow to the fast reaction diffusional regime. With the stirred reactor and diluted toluene reasonable values of 44·cm^?1 and 1·03×10^?3 cm sec^?1 are obtained for the interfacial area per unit volume of the acid phase and the overall mass transfer coefficient, respectively.However, when the organic phase is pure toluene, both stirred cell and stirred reactor rates are lower than expected. The conclusion is drawn that the formation of nitronium ions, rather than their attack on the toluene, is the rate limiting kinetic step under these conditions. The rate constants for the formation of nitronium ions from nitric acid in 78·45 per cent sulphuric acid is estimated to have the value 0·40 sec^?1 at 25°C.     

DIRECT OXIDATION OF ETHYLENE TO ACETALDEHYDE IN A HOLLOW FIBER MEMBRANE REACTOR†

A hollow fiber membrane reactor, which resembles a tube-and-shell heat exchanger, was developed for homogeneous catalytic reactions with gas reactants and products. The gas stream flows through the tube side while the reaction takes place in the catalyst solution which fills the shell side. The separation load of product from the catalyst solution can be reduced by using a hollow fiber membrane reactor instead of a conventional bubble column reactor. The reactor operates in a plug-flow pattern with a large mass transfer area per unit volume of catalyst solution

This concept was investigated experimentally using the direct oxidation of ethylene to acetaldehyde reaction in an aqueous solution of palladium (H) chloride-cupric chloride with a silicone rubber membrane reactor and a polypropylene membrane reactor. It was experimentally demonstrated that membrane reactors could achieve higher production rates per unit volume of catalyst than the conventional sparged reactor. The experimental data were in good agreement with the predictions by the mathematical model. The conditions under which the membrane reactor will be more advantageous than the conventional sparged reactors can be readily ascertained with the analytical solution of the simplified membrane reactor model.     

Experimental technique for kinetic study of hydrogenation of fatty acid methyl esters in vapor phase

A new approach to kinetic studies of fat hydrogenation is discussed. An experimental setup is described in detail. An example of reactor performance in hydrogenation of fatty acid methyl esters is given. aPresent address: AB Karlshamns Oljefabriker, S-292 00 Karlshamn, Sweden. Notation: c, outlet concentration, mol/m³ ; c_o, inlet concentration, mol/m³: c_b, concentration in bulk fluid, mol/m³ ; c_s concentration at catalyst surface, mol/m³ ; d,pore diameter, m; D_e, effective diffusivity, m²/s; E, activation energy of reaction, J/mol; h, heat transfer coefficient, J/m² s K; ΔH, heat of reaction, J/mol; k_c, mass transfer coefficient, m/s; p, partial pressure, Pa; p_o, saturated vapor pressure, Pa; qf, total flow to reactor, m³/s; q_rec, recycle flow, m³/s; R, observed reaction rate per unit particle volume, mol/s m³ ; R_g, gas constant, J/mol K; r, observed reaction rate per unit mass of catalyst, mol/kg s; r_p particle radius, m; T_b, temperature of gas in bulk flow, K; T_s, temperature of gas at catalyst surface, K;-v, molar volume, m³/mol; V, volume of catalyst bed, m³ ; W, catalyst mass, kg. Greek symbols: σ, surface tension, N/m; λ_e, effective thermal conductivity of catalyst particle, J/m s K.     

Mass transfer area in different gas-liquid reactors as a function of liquid properties

Using pilot-scale test plant, the interfacial area per unit volume was investigated in different gasliquid reactors, i.e. packed column, bubble column and free jet reactor. The interfacial area was studied as a function of liquid viscosity and of operating parameters. As a rule, identical test conditions were maintained in all the measurements, in order to obtain comparable results. The interfacial area was determined by chemical means using the sulphite system (a solution of sodium sulphite in water as model liquid and air as gaseous medium). The viscosity of the solution can be increased by adding carboxymethyl cellulose without significantly affecting the reaction kinetics. The addition of a surfactant to the sulphite system allowed comparative measurements at reduced surface tension. Based on a large number of measurements, the correlations of the interfacial area are expressed as power laws. The inclusion of experiments with a jet tube reactor and a stirring vessel allows an extensive comparison of all reactors. All tests were carried out with the same material system and the same method was used to determine the interfacial area per unit volume. Therefore, a comparison with respect to mass transfer is possible.     

Toward Understanding of Two‐Phase Eccentric Helical Reactor Performance

Mass transfer investigations in a two‐phase gas‐liquid Couette‐Taylor flow (CTF) reactor and a numerical flow simulation are reported. The CTF reactor is characterized by high values of the mass transfer parameters. Previous mass transfer investigations have yielded high values of the volumetric mass transfer coefficients (of the order of 10^–1 s^–1) and the specific interfacial area, compared to those obtained in a stirred tank (10³ m² m^–3). In order to intensify mass transfer in the CTF reactor, an eccentric rotor (rotating inner cylinder) was used. In the eccentric annulus with rotating inner cylinder, due to frequent variation of the hydrodynamic flow field parameters, nonlinear hydrodynamic conditions occurred. These conditions can influence the rate of mass transfer. The experimental results of benzaldehyde oxidation in an eccentric CTF reactor confirmed an increase in mass transfer, as against a concentric CTF reactor. Numerical simulation of the Couette‐Taylor (helical) flow was performed in a concentric and in an eccentric annulus. Calculation of parameters such as velocity, static pressure, kinetic energy and energy dissipation rate revealed a significant effect of gap eccentricity on the flow behavior.     

GAS ABSORPTION IN A HOLLOW FIBER DEVICE

The absorption of S0² and NH³ from air and air/CO ² streams was studied for the first time in a certain novel hollow fiber mass transfer device, for various inlet gas compositions, liquid compositions, gas flow rates, and liquid flow rates. The gas and liquid flows were countercurrent. Analyses of the amounts of S0²and NH³ absorbed demonstrate that the hollow fiber unit has a relatively small membrane resistance and is an effective gas scrubbing device. Additionally, it offers a large interfacial area per unit volume, and avoids flooding problems entirely     

Mass transfer with chemical reaction in liquid foam reactors

Mass transfer studies were conducted in a stable liquid foam reactor under various operating conditions to evaluate gas holdup, effective interfacial area, liquid-phase mass transfer coefficient and a modified interfacial mass transfer coefficient to include the surface-active agents employed. Gas holdup and effective interfacial area were evaluated experimentally. The interfacial mass transfer coefficient was evaluated semitheoretically, by considering the interfacial region as a separate phase and using the experimental data developed for mass transfer accompanied by a fast first-order chemical reaction. The liquid-phase mass transfer coefficient was also evaluated semitheoretically, using Danckwert's theory for the liquid phase and the experimental data on mass transfer accompanied by a slow pseudofirst-order chemical reaction. An experimental unit was set up to provide a stable flowing foam column, simulating the foam reactor. Mass transfer rates were studied for superfacial gas velocities in the range from 1.5 × 10⁻² m/s to 5 × 10⁻² m/s, giving gas residence times in the range from 20 to 55 seconds. A cationic and nonionic surface-active agent and three different wire mesh sizes, giving bubble size distributions in the range from 2.2 to 5.4 mm Sauter mean diameters, were employed. It is observed that gas holdup is insensitive to the type of surface-active agent; it is however, dependent on wire mesh size and gas velocity. The bubble diameter and, hence, the interfacial area are found to be insensitive to gas velocity in the range studied; they are, however, strong functions of wire mesh size. The liquid-phase mass transfer coefficient increases with increase in gas velocity. The surface-active agent introduces additional resistance to mass transfer in both reaction cases, this being the controlling one in the case of the fast reaction. A comparison with conventional packed bed contactors indicates the mass transfer rates to be about 8 times lower for the foam reactor, for the fast reaction case; for slow reactions, the foam reactor has mass transfer rates approximately 2-4 times higher than those for conventional packed bed contactors.     

Experimental studies of nitrobenzene hydrogenation in a microstructured falling film reactor

Nitrobenzene hydrogenation over palladium catalyst was performed in a microstructured falling film reactor at a range of flowrates (0.5-3 ml/min) and pressure (1-6 bar). Confocal microscopy was used to measure liquid film thickness. Comparison with film thickness prediction equations showed an overprediction of 10-30%. The k_La of this system was estimated to be 3-8 s⁻¹ with interfacial surface area per reaction volume 9000-15000 m²/m³. Conversion was found to be affected by both liquid flowrate and hydrogen pressure, and the reactor operated between the kinetic and mass transfer controlled regimes.     

INTERFACIAL TEMPERATURE RISE AND MULTIPLICITY IN NONISOTHERMAL GAS-LIQUID CSTRs

For exothermic gas-liquid reactions.the interfacial temperature affects the gas-solubility, interfacial reaction rate, mass transfer rate and the bulk temperature of the reactor. An overall heat balance on the reaction-diffusion 'film' relates the interfacial temperature to the bulk variables (temperature, concentration), and the interfacial variables (enhancement factor, etc.). While the interfacial balance shows (apparent) multiplicity of interfacial temperature for a given bulk temperature, uniqueness results when the interfacial balances are solved together with the mass and energy balances for the reactor bulk. It is shown that the state of interface and bulk are intimately related, and thus, consideration of interfacial temperature does not increase the multiplicty of a gas-liquid CSTR. Simple a priori estimates are derived for the interfacial temperature. All of the results are found to be rather independent of kinetic details. The interfacial temperature rise is encouraged by low interfacial heat and mass transfer coefficients, by small liquid residence time in the bulk and by increased heat losses from the reactor bulk.     

Comparison of different reactor types for low temperature Fischer-Tropsch synthesis: A simulation study

The commercially established slurry bubble column and fixed-bed reactors for low temperature Fischer-Tropsch synthesis were compared with novel micro- and monolith-reactors by mathematical modeling. Special attention was paid to the influence of catalytic activity on the reactor efficiency and the losses by mass and heat transfer resistances. The simulation results show that a micro-structured reactor exhibits the highest productivity per unit of catalyst volume followed by slurry bubble column reactor and monolith reactor. The fixed-bed reactor that was assumed to operate in the trickle-flow regime has a particularly low catalyst specific productivity due to severe mass transfer resistances. However, caused by a very low ratio of catalyst and reactor volume the micro-reactor has only a similarly low productivity per unit of reactor volume as the fixed-bed reactor. In contrast, the reactor specific productivity of slurry bubble column reactor and monolith reactor is up to one order of magnitude higher.     

Interfacial area and mass transfer in carbon dioxide absorption in TEA aqueous solutions in a bubble column reactor

The hydrodynamic behaviour and mass transfer of carbon dioxide removal process by aqueous solutions of triethanolamine (TEA) are analysed. The experiments were made in a bubble column reactor (BCR) as gas–liquid contactor. The interfacial area and mass transfer coefficient were calculated by using a photographic method based on the bubble diameter determination. The influence of operation conditions, liquid phase nature and chemical reaction on the mass transfer coefficient and gas–liquid interfacial area has been also analysed.     

Iminodiacetic acid synthesis in a microchannel reactor

The synthesis of iminodiacetic acid (IDA) by diethanolamine (DA) dehydrogenation over a Cu/ZrO₂ catalyst in a microchannel rector has been investigated and has been compared to the same synthesis in an autoclave. The output capacity of the microchannel reactor per unit volume of the reaction zone and per unit weight of the catalyst is 4.38 (g IDA)/(cm³ h) and 0.49 (g IDA)/(g Cat h), respectively, while the corresponding output capacities of the autoclave are 0.018 (g IDA)/(cm³ h) and 0.46 (g IDA)/(g Cat h). A kinetic analysis has demonstrated that IDA synthesis proceeds in two steps, yielding N-(2-hydroxyethyl)glycine as an intermediate product. A formal two-step kinetic scheme has been proposed, and the apparent rate constants of the reaction steps have been calculated. These rate constants for the synthesis in the microchannel reactor are several orders of magnitude higher than the corresponding constants for the synthesis in the autoclave. The output capacity per unit volume of the reaction zone for the microchannel reactor is two orders of magnitude higher than for the autoclave. This is evidence that the process in the submillimeter-sized channels is markedly intensified owing to the high heat and mass transfer efficiency.     

Modeling of a continuous rotating disk polycondensation reactor for the synthesis of thermoplastic polyesters

A dynamic multicompartment model is proposed for a continuous flow rotating disk reactor for the finishing stage melt polycondensation of poly(ethylene terephthalate). In the multicompartment reactor model, ethylene glycol is removed from both the bulk melt phase and the film phase formed on the rotating disks. The specific interfacial area for the film phase is estimated using the empirical correlation for polymer film thickness, and the mass transfer coefficient is calculated using the penetration theory. The mass transfer enhancement factor is introduced to account for the increased interfacial area due to ethylene glycol bubbles. The effects of reactor design and operating parameters on molecular weight and ethylene glycol removal have been investigated through model simulations. In particular, a detailed analysis is presented on the ethylene glycol removal rate from the two phases. © 1996 John Wiley & Sons, Inc.     

Nanofiltration thin-film composite membrane on either the internal or the external surface of a polysulfone hollow fiber

The inner and outer surfaces of a porous hollow fiber polysulfone support are compared as substrates for the synthesis of polyamide thin-film composite (TFC) membranes by interfacial polymerization. While both surfaces have pores common of microfiltration membranes, the inner surface has a larger pore diameter than the outer surface (2,700 nm compared to 950 nm). The inner TFC membrane showed higher water nanofiltration permeance than the outer (2.20 ± 0.17 compared to 0.13 ± 0.03 L m⁻² hr⁻¹ bar⁻¹). This was due to the influence of the porosity and roughness, which were different on both support surfaces. These membranes are interesting because they were synthesized in a hollow fiber support with a high membrane area per volume unit (~6,900 m²/m³) and the substrate used was commercial, which means that the TFC membrane obtained is suitable for industrial application. A mathematical simulation of the nanofiltration run with COMSOL Multiphysics 5.3 software confirmed the experimental trends observed.     

Effect of particle shape on fluid flow and heat transfer for methane steam reforming reactions in a packed bed

Numerical simulations of a cylindrical packed bed with tube to particle diameter ratio of 1.4, containing 10 particles, were performed to understand the effect of particle shape on pressure drop, heat transfer and reaction performance. Six particle shapes namely, cylinder as the reference, trilobe and daisy having external shaping, hollow cylinder, cylcut, and 7‐hole cylinder including internal voids were chosen. Methane steam reforming reactions were considered for the heat transfer and reaction performance evaluation. The present study showed that the external shaping of particles offered lower pressure drop, but lower values of effectiveness factor indicating strong diffusion limitations. The internally shaped particles offered increased surface area, led to higher effectiveness factor and allowed to overcome the diffusion limitations. The effective heat transfer and effectiveness factor of the trilobe‐shaped particle per unit pressure drop was found to be the best among the particle shapes considered in the present work. © 2016 American Institute of Chemical Engineers AIChE J, 63: 366–377, 2017     

Direct-Contact Heat Transfer during n-Pentane Vaporization in a Two-Dimensional Water Column

Direct-contact vaporization heat transfer is investigated by analyzing the heat transfer coefficient with the area of liquid-liquid direct-contact interface. The interface areas of liquid-liquid heat transfer are determined by stroboscopic images. At higher temperature, the heat transfer area per unit volume decreases. The water temperature has no significant influence on the heat transfer coefficient. The effects on droplet size distributions of operating variables including inlet water temperature, n-pentane flow rate, and test position with packing and without packing are compared.     

Carbon Dioxide Absorption in Triethanolamine Aqueous Solutions: Hydrodynamics and Mass Transfer

The carbon dioxide absorption process by triethanolamine aqueous solutions was analyzed in a bubble‐column reactor taking into account the chemical reaction mechanism, gas‐liquid interfacial area, and mass transfer rate. A speciation study of this gas‐liquid system was developed by ¹H and ¹³C NMR spectroscopy in order to obtain the reaction mechanism and stoichiometry. The gas‐liquid interfacial area was evaluated considering the variations of bubble size distribution and gas holdup during the operation time. The liquid‐phase mass transfer coefficient was calculated from the carbon dioxide absorption rate data by interfacial area evolution and reaction stoichiometry.     

Melt polycondensation of poly(ethylene terephthalate) in a rotating disk reactor

A multicompartment model is proposed for a semibatch melt polycondensation of poly(ethylene terephthalate) in a rotating disk polymerization reactor and compared with laboratory experimental data. The reactor is a horizontal cylindrical vessel with a horizontal shaft on which multiple disks are mounted. The reactor is assumed to comprise N equal sized compartments and each compartment consists of a film phase on the rotating disk and a bulk phase in which disks are partially immersed. The effects of disk rotating speed, number of disks, reaction temperature, and pressure were investigated. It was observed that ethylene glycol is predominantly removed from thin polymer layers on the rotating disks and the enhanced interfacial area exerted by ethylene glycol bubbles accounts for about 30–50% of the total available interfacial mass transfer area. Although the rate of polymerization increases as more disks are used, the maximum number of disks in a reactor must be determined properly in order to prevent the formation of thick polymer films that result in a reduced specific interfacial area and reduced polymerization efficiency. At a fixed reaction pressure, the equilibrium conversion is reached but the rate of reaction can be further increased by increasing the reaction temperature. The results of the proposed multicompartment model are also compared with those predicted by a simple one-parameter model. © 1995 John Wiley & Sons, Inc.     

The Effect of Adding Straw on Natural Solar Sludge Drying

The effect of straw on natural solar sludge drying was investigated. As the thickness of the stack increased, the rate of water removal per unit area slightly increased and the rate of water removal per unit volume rapidly decreased. The rate of water removal increased as the accumulation of solar energy increased but decreased as the relative humidity increased. On the 23rd day, the moisture content of the dewatered sludge and the chopped straw mixture decreased from 75.2 to 45.1% at a thickness of stack of 30 cm, with an average water evaporation rate of 7.2 kg/m²d.