Kinetic studies of liquid phase ethyl tert-butyl ether (ETBE) synthesis using macroporous and gelular ion exchange resin catalysts

Ethyl tert-butyl ether (ETBE) synthesis from ethanol (EtOH) and tert-butyl alcohol (TBA) was studied with different macroporous and gelular ion exchange resin catalysts. Purolite^® (CT-124, CT-145H, CT-151, CT-175 and CT-275) and Amberlyst^® (15 and 35) ion exchange resins were used for the present work. Effect of various parameters such as catalyst type, temperature, reactants feed molar ratio and catalyst loading were studied for the optimisation of reaction condition. Among the catalysts studied, Purolite CT-124 gave the best results for TBA conversion and selectivity towards ETBE. Kinetic modelling was performed with this catalyst and activation energy and water inhibition coefficient were determined. Heterogeneous kinetic models [e.g., Eley-Rideal (ER), Langmuir-Hinshelwood-Hougen-Watson (LHHW)] were unable to predict the behaviour of this etherification reaction, whilst the quasi-homogeneous (QH) model represented the system very well over wide range of reaction conditions.     

Use of bipolar membranes for ion exchange resin regenerant production

The utilisation of electrodialysis bipolar membranes to prepare hydrochloric acid and sodium hydroxide from a sodium chloride solution was tested at West Thurrock Power Station. The product chemicals were then used to regenerate full scale ion exchange units on the site and the results compared to normal operation with commercial regenerants. The large scale pilot plant was found to operate satisfactorily and the quality of produced chemicals was in line with predictions. The adoption of on-site, on-demand production of regenerants could offer immediate advantages for remote installations which would otherwise be dependent on the transport of dangerous chemicals over long distances. In the longer term further advances in the selectivity of commercially available membranes and the prevailing cost of commercial regenerants are considered the key factors governing the future rate of implementation of this novel process.     

An empirical model for kinetics of boron removal from boron-containing wastewaters by ion exchange in a batch reactor

In this study, it was investigated boron removal from boron containing wastewaters prepared synthetically. The experiments in which Amberlite IRA 743, boron specific resin was used was carried out in a batch reactor. The ratio of resin/boron solution, boron concentration, stirring speed and temperature were selected as experimental parameters. The obtained experimental results showed that percent of boron removal increased with increasing ratio of resin/boron solution and with decreasing boron concentration in the solution. Stirring speed and temperature had not significant effects on the percent of total boron removal, but they increased the starting boron removal rate. As a result, it was seen that about 99 % of boron in the wastewater could be removed at optimum conditions. On the other hand, the process kinetics were predicted by using heterogeneous fluid-solid reaction models. It was seen statistically that the kinetics of this process agreed the pseudo- second order model, as follows: X_Bl(1−X_B) = 11,241.5[OH][C]^−1.76[S/L]^2.17exp(−19,57l.2/RT)t^1.24     

Model for the determination of diffusion coefficients of heterovalent ions in macroporous ion exchange resins by the zero-length column method

A generalized theoretical model for the measurement of effective diffusion coefficients of heterovalent ions in macroporous ion-exchange resins by the zero-length column method was developed. The model includes the resistance to mass transfer both in the particle and in the film and described ion fluxes with Nernst-Planck equations. Equilibrium was described using the Langmuir type empirical equation. The values of intraparticle diffusivity of Cu²⁺, Cd²⁺, Zn²⁺, and H⁺ on commercial Lewatit TP-207 were obtained by non-linear regression, these values agree fairly well with data reported previously in literature. The following trend was observed: D_Cu>D_Zn>D_Cd.     

Lactic acid recovery from a model of Thermotoga neapolitana fermentation broth using ion exchange resins in batch and fixed-bed reactors

This study focused on the integration of lactic acid adsorption and desorption onto commercially available resins in batch reactors with consequent scale-up in fixed-bed reactors. Amberlite® IRA-900, IRA-400, IRA-96 and IRA-67 were used as adsorbents for lactic acid recovery from solutions that mimic the fermentation broth of Thermotoga neapolitana. The best resins were further tested in adsorption–desorption batch experiments, over 13 cycles, with IRA-67 showing an average removal efficiency of 97%. IRA-67 was tested in fixed-bed reactor experiments and an average desorption efficiency of 68% was achieved using three bed volumes of 0.5 M NaOH as the desorbing agent.     

Optimized interesterification of virgin olive oil with a fully hydrogenated fat in a batch reactor: Effect of mass transfer limitations

The lipase‐catalyzed interesterification of virgin olive oil and fully hydrogenated palm oil (FHPO) was studied in a batch reactor operating at 75 °C. The reactions between olive oil {rich in OOO (32.36%), OPO (21.7%) and OLO (11.6%) [L = linoleic; O = oleic; P = palmitic acid]} and the fully hydrogenated fat {(36.5% PSP, 28.8% PPP, 23.2% SPS) [S = stearic acid]} produced semi‐solid fats. For an initial weight ratio of olive oil to FHPO of 60 : 40, the reaction product is a complex mixture of triacylglycerol (TAG) species. The TAG profile of the fat product is time dependent. Because of the high viscosity of the liquid reagent phase, it was important to determine if mass transfer effects were significant. Hence, the reaction was optimized with respect to the type and speed of agitation employed, temperature, use of solvent, and the type of biocatalyst. Three immobilized lipases [from Thermomyces lanuginosus (TL IM), Rhizomucor miehei (RM IM) and Candida antarctica B (Novozym 435)] were compared as catalysts for the interesterification reaction. Equilibrium is reached four times faster (in 1–4 h) with a magnetic stirrer to provide agitation than when agitation is not sufficient, i.e. when orbital agitation is employed. Equilibrium was reached faster with Lipozyme TL IM than with the other two lipases. The effects of all the factors investigated on the composition of the products have also been determined. Semi‐solid fats obtained with the non‐specific Novozym 435 contain levels of unsaturated fatty acid residues on sn‐2 sites that are similar to the products obtained with the 1(3)‐regiospecific enzymes Lipozyme TL IM and RM IM. The chemical properties of the product semi‐solid fat were characterized. The fat prepared using optimal reaction conditions contained 17.20% OPO, 13.61% OOO, 11.09% POP, and 10.35% OSP isomers as the primary products. The induction time obtained in the assay of the oxidative stability of the fat product was 21 h at 98 °C. The lipases Lipozyme TL IM and Novozym 435 were very stable with residual activities of 90 and 100%, respectively, after 15 batch reaction cycles.     

Application of the Maxwell-Stefan approach to ion exchange in microporous materials. Batch process modelling

A model comprising external and intraparticle mass transfer resistances has been developed to describe ion exchange in microporous materials. The Maxwell-Stefan approach has been adopted due to their well documented advantages over Nernst-Planck relationships, particularly the facts of taking into account non-idealities, ion-ion and ion-solid interactions, and being easily applied to multicomponent systems.The model was tested with data available on literature, namely batch experiments on mercury (II) removal from aqueous solution using ETS-4 microporous titanosilicate (pore diameters between 3-4 Å). Calculated results point out it provides excellent fittings (AAD=4.93%; 44 data points) and exhibits fine predictive capability. Actually, the model is able to simulate ion exchange process with average deviations well inside the experimental accuracy (5-8%), using model parameters correlated from data measured under different operating conditions. This feature was analysed with three independent sets of data, and the average absolute deviations found increased only to 4.94%, 5.32%, and 7.72%. Such behaviour may be attributed to the sound physical principles of Maxwell-Stefan theory.The Nernst-Planck and the pseudo second-order kinetic models have been adopted for comparison. The Nernst-Planck based model provides higher deviation (AAD=5.57%) but offers good representations also; the last one is totally unable to describe solution concentration along time (AAD=60.93%), though it is one of the most applied equation in the field.     

Synthesis of mass exchange network for batch processes—Part I: Utility targeting

Synthesis of optimal mass exchange network (MEN) for continuous processes based on Pinch Analysis has been rather well established. In contrast, very little work has been done on mass exchange network synthesis (MENS) for batch process systems. The batch process systems referred to in this work can be defined as processes which operate discontinuously and deliver the products in discrete amounts, with frequent starts and stops. There is a clear need to develop a MENS procedure for batch process systems which are industrially very common as well as important. Techniques developed in this paper for the batch MENS involved the first key steps in the synthesis task, i.e. setting the utility targets ahead of batch MEN design. The utility-targeting approach employs the vertical and horizontal cascading approaches in a newly developed tool, i.e. time-dependent composition interval table that has been adapted from heat exchange network synthesis for batch processes. Prior to MEN design, the targeting procedure establishes the minimum utility (solvent) and mass storage targets for a maximum mass recovery network. These targets are essential for network design and batch process rescheduling.     

Synthesis of mass exchange network for batch processes—Part II: Minimum units target and batch network design

The first part of this series of papers (Chem. Eng. Sci. 59(5) (2004) 1009) presented a methodology for identifying the minimum utility targets for a mass exchange network (MEN) for a batch process. This paper describes the methodology for setting the minimum number of mass exchange units target and a procedure for designing a maximum mass recovery network that features the minimum utility targets. The time-grid diagram and the overall time-grid diagram that include the time dimension in network design have been introduced to provide a better representation of the mass exchange network for a batch process. The systematic network design procedure also includes a technique to simplify and evolve the preliminary batch MEN to reduce the number of mass exchangers to the minimum.     

Modelling of the concentration-time relationship based on global diffusion-charge transfer parameters in a flow-by reactor with a 3D electrode

A concentration versus time relationship model based on the isothermal diffusion-charge transfer mechanism was developed for a flow-by reactor with a three-dimensional (3D) reticulated vitreous carbon (RVC) electrode. The relationship was based on the effectiveness factor (η) which lead to the simulation of the concentration decay at different electrode polarisation conditions, i.e. −0.1, −0.3 and −0.59 V versus SCE; the charge transfer process was used for the former and mix and a mass transport control was used for the latter. Charge transfer and mass transport parameters were estimated from experimental data using Electrochemical Impedance Spectroscopy (EIS) and Linear Voltammetry (LV) techniques, respectively.     

Applying rotary jet heads for mixing and mass transfer in a forced recirculation tank reactor system

An approximation to an ideally mixed tank reactor can be obtained by vigorous stirring with mechanical mixers. For an aerated reactor the gas dispersion contributes to the mixing process. Mixing can also be achieved by recirculation of a portion of the liquid through either an internal or an external loop.In this study, we determine mixing times in water and CMC solutions and oxygen mass transfer coefficients in water for a tank reactor system where a small fraction of the total liquid volume is rapidly circulated through an external loop and injected through the nozzles of rotary jet heads at 1-9 bar gauge pressure into the bulk liquid. Liquid feed can be added to the bulk volume or it may be injected into the pressurized recirculation loop. Gas is always fed to the recirculation loop, and the heat of reaction is removed in a plate-type heat exchanger inserted in the recirculation loop. The system has a very simple design with no internal baffles or heat exchange area, and between batches the rotary jet heads are used for cleaning in place.Mixing time decreases and mass transfer increases with increasing circulation flow rate. For nozzle diameters between 5.5 and and with one or two rotary jet heads, it is shown that a remarkable saving in power input for a fixed mixing time or mass transfer coefficient can be obtained by using a large nozzle diameter and two rather than one rotary jet heads.At the experimental conditions of the study the system is scaleable by simple formulas, and the power input to achieve a certain mixing time is proportional to the bulk liquid volume.     

A generalized model for the measurement of effective diffusion coefficients of heterovalent ions in ion exchangers by the zero-length column method

A generalized theoretical model for the measurement of effective diffusion coefficients of heterovalent ions in ion exchange resins by the zero-length column method was developed. The model included the resistance to mass transfer both in the particle and in the film and described ion fluxes with Nernst-Planck equations. Equilibria were described using a model based on the mass action law. The values of intraparticle diffusivity of Cu²⁺, Cd²⁺, Zn²⁺, and H⁺ on commercial Amberlite IR-120 were obtained by non-linear regression, these values agree fairly well with data reported previously in literature. The following trend was observed: D_Cu>D_Zn>D_Cd.     

Numerical simulation of mass transport in a filter press type electrochemical reactor FM01-LC: Comparison of predicted and experimental mass transfer coefficient

This paper studies flow characteristics and their effect on local mass transfer rate to a flat plate electrode in a FM01-LC electrochemical reactor. 3D reactor simulations under limiting current and turbulent flow conditions were performed using potassium ferro-ferricyanide electrochemical system with sodium sulfate as supporting electrolyte. The model consists of mass-transport equations coupled to hydrodynamic solution obtained from Reynolds-averaged Navier–Stokes equations using standard k–? turbulence model, where the average velocity field, the turbulence level given by the eddy kinetic energy and the turbulent viscosity of the hydrodynamic calculation were used to evaluate the convection, turbulent diffusion and the concentration wall function. The turbulent mass diffusivity was evaluated by Kays–Crawford equation using heat and mass transfer analogies, while wall functions, for mass transport, were adapted from Launder–Spalding equations. Simulation results describe main flow properties, concentration profiles throughout the entire volume of the reactor and local diffusion flux over the electrode. Overall mass transfer coefficients estimated by simulation, without fitting parameters, agree closely with experimental coefficients determined from limiting current measurements (1.85% average error) for Re between 187 and 1407.     

The mass production of carbon nanotubes using a nano-agglomerate fluidized bed reactor: A multiscale space-time analysis

The scaled-up mass production of carbon nanotubes (CNTs) was reviewed by a multiscale analysis from the delicate catalyst control needed at the atomic level, CNT agglomerate formation at the mesoscopic scale, to the continuous mass production process on the macroscopic scale. A four level analysis that considered CNT assembly, agglomerate structure, reactor hydrodynamics and coupled processing was used. Atomic scale catalyst design concepts were used to modulate the CNT structure. On the reactor scale, the design consideration was on getting suitable CNT and catalyst agglomerates with good fluidization behavior and transport properties. A pilot plant with high yield (15 kg/h) and purity (> 99.9%) was demonstrated, which made a great stride for extensive applications of CNTs. Other nano-agglomerate structures can also be considered using the multiscale time and space analysis, which will benefit mass production and applications of nanomaterials in future.     

Production of a biodiesel additive in a stirred basket reactor using immobilized lipase: Kinetic and mass transfer analysis

?A laboratory-scale stirred basket reactor (SBR) was constructed to study the synthesis of an n-butyl oleate ester using Novozym 435. An ester yield of approximately 98% was obtained after 6 h using an equimolar substrate ratio, 3.5 g of enzyme, a reaction temperature of 40 °C, and an impeller speed of 200 rpm. The kinetic data were modeled as a ping-pong bi-bi mechanism using a non-linear regression technique. Statistical analysis of the results showed that a model that incorporated the inhibitory effect of n-butanol yielded the best fit with the following parameters: V _max =24.8mmol L^?1 min^?1, K _{m, oleic acid} =190.8mM, K _{m, n-butanol} =544.7 mM, and K _{i, n-butanol} =158.3mM. Mass transfer effects on the enzyme kinetics were also studied, and the absence of internal and external diffusion limitations on the reaction in the SBR was confirmed by considering calculated values of the Thiele modulus and the Damkohler number. Novozym 435 exhibited satisfactory performance in repeated-batch experiments using SBR.     

Prediction of mass transfer coefficients in an asymmetric rotating disk contactor using effective diffusivity

Mass transfer characteristics have been investigated in a 113 mm diameter asymmetric rotating disk contactor of the pilot plant scale for two different liquid–liquid systems. The effects of operating parameters including rotor speed and continuous and dispersed phase velocities on the volumetric overall mass transfer coefficients are investigated. The results show that the mass transfer performance is strongly dependent on agitation rate and interfacial tension, but only slightly dependent on phase flow rates. In this study, effective diffusivity is used instead of molecular diffusivity in the Gr?ber equation for estimation of dispersed phase overall mass transfer coefficient.The enhancement factor is determined experimentally and there from an empirical expression is derived for prediction of the enhancement factor as a function of Reynolds number. The predicted results compared to the experimental data show that the proposed correlation can efficiently predict the overall mass transfer coefficients in asymmetric rotating disk contactors.     

Experimental investigation of dynamic mass transfer during droplet formation using micro-LIF in a coaxial microchannel

The mass transfer of Rhodamine 6G from the droplet to the continuous phase in a coaxial micro-channel is studied using micro-LIF (Laser-Induced Fluorescence). The mass distribution inside droplet is measured and visualized. The experimental results affirm that there exists the internal circulation inside the droplet and it could enhance the convective mass transfer. The stagnant center of vortices is also observed. The extraction fraction could reach 40%-80%. In order to establish the mass transfer model, different flow rates of the dispersed and continuous phase are adopted. The high continuous phase flow rate and low dispersed phase flow rate are both beneficial to enhance mass transfer by expediting the internal circulation. A modified mass transfer model is found to calculate the extraction fraction. A good agreement between the model and experiment in various conditions demonstrates that the mass transfer model in this work is reliable and feasible.     

Modeling and simulation of mass transfer in near-critical extraction using a hollow fiber membrane contactor

In this study is presented a general methodology to predict the performance of a continuous near-critical fluid extraction process to remove compounds from aqueous solutions using a hollow fiber membrane contactor. The stabilization of the gas-liquid interface in the membrane porosity and a high surface area to contact both phases represent some of the advantages that hollow fiber contactors offer over conventional contactor devices for the extraction of compounds from liquid feeds.A mathematical model has been developed integrating a resistances-in-series mass transfer system that takes into account boundary layers, membrane porosity and thermodynamic considerations with mass balances of the membrane contactor. Simulation algorithms were easily implemented with low calculation requirements.The system studied in this work is a membrane based extractor of ethanol and acetone from aqueous solutions using near-critical CO₂. Predictions of extraction percentages obtained by simulations have been compared to the experimental values reported by Bothun et al. [2003a. Compressed solvents for the extraction of fermentation products within a hollow fiber membrane contactor. Journal of Supercritical Fluids 25, 119-134]. Simulations of extraction percentage of ethanol and acetone show an average difference of 36.3% and 6.75% with the experimental data, respectively. More accurate predictions of the extraction of acetone could be explained by a better estimation of the transport properties in the aqueous phase that controls the extraction of this solute.When the model was validated, the effect of the configuration and the operating parameters was studied and local mass transfer resistances were evaluated. The proposed approach allows the evaluation of the relevance of membrane hydrophobicity for extraction in solutions under different thermodynamic conditions. This original methodology based on well-known phenomenological equations represents a general approach which could be applied in other processes using membrane contactors with different configurations.