Reactive Distillation Research Papers - Academia.edu (original) (raw)

2000, Chemical Engineering Science

The design and operation issues for reactive distillation systems are considerably more complex than those involved for either conventional reactors or conventional distillation columns. The introduction of an in situ separation function within the reaction zone leads to complex interactions between vapor}liquid equilibrium, vapor}liquid mass transfer, intra-catalyst di!usion (for heterogeneously catalysed processes) and chemical kinetics. Such interactions have been shown to lead to the phenomenon of multiple steady-states and complex dynamics, which have been veri"ed in experimental laboratory and pilot plant units. We trace the development of models that have been used for design of reactive distillation columns and suggest future research directions.

2003, Chemical Engineering and Processing: Process Intensification

In the last years chemical process industries have shown permanently increasing interest in the development of reactive separation processes (RSP) combining reaction and separation mechanisms into a single, integrated unit. Such processes bring several important advantages among which are increase of reaction yield and selectivity, overcoming thermodynamic restrictions, e.g. azeotropes, and considerable reduction in energy, water and solvent consumption. Important examples of reactive separations are reactive distillation (RD) and reactive absorption (RA). Due to strong interactions of chemical reaction and heat and mass transfer, the process behaviour of RSP tends to be quite complex. This paper gives an overview of up-to-date reactive separation modelling and design approaches and covers both steady-state and dynamic issues. These approaches have been applied to several different RA and RD processes including the absorption of NO x , coke gas purification, methyl acetate synthesis and methyl tertiary butyl ether (MTBE) synthesis. #

2006, Separation and Purification Technology

The possibility of manufacturing a biodegradable polymer from lactic acid has led to extensive research in recovery of lactic acid produced by fermentation, by different downstream processing routes. This paper assesses the suitability of different downstream processing options such as reactive extraction, adsorption, electrodialysis, esterification and reactive distillation. It compares the costs of different process routes. The assessment indicates that the conventional precipitation of calcium lactate, followed by acidification, esterification and hydrolysis will be the most economical route although it generates large quantity of gypsum sludge.

1988, Chemical Engineering Science

A new set of transformed composition variables is introduced to simplify the design equations for single-feed, multicomponent reactive distillation columns. Based on these equations. a general method of calculating minimum refiux ratios for reactive distillation columns is presented. The new composition variables are also used to derive simple relationships between the dependent design variables which are not evident when the design equations are written in terms of mole fractions.

2007, Industrial & Engineering Chemistry Research

In this paper, a novel rate-based description of nonreactive and reactive dividing wall columns is presented. These highly integrated units promise advantages in the context of process intensification. Until now, published studies have been focused on the nonreactive columns, based on equilibrium stage models, whereas the modeling of both dividing wall columns and reactive dividing wall columns, using the rate-based approach, has not been done yet. In the presented model, special attention is given to phenomena that have not been considered in previous publications (e.g., heat transfer through the dividing wall). The model has been applied to a nonreactive, ternary alcohol mixture and successfully validated. The transesterification of carbonates has been identified as an interesting system for the reactive dividing wall column. This reaction system is equilibrium limited and characterized by high conversion, yet low selectivity. Initial simulation studies demonstrate that the selectivity can be significantly increased by means of the reactive dividing wall column. Besides, this highly integrated unit enables a more efficient separation of products and nonconverted reactants, resulting in a reduction in the separation unit number.

2007

We here report our studies on the upgrading of flash pyrolysis oil using an improved alcohol treatment method. The method consists of treating pyrolysis oil with a high boiling alcohol like n-butanol in the presence of a (solid) acid catalyst at 323 -353 K under reduced pressure (,10 kPa). Using this approach, the water content of the pyrolysis oil is reduced significantly. Variables like the type of alcohol (n-butanol, ethylene glycol, 2-ethyl-hexyl-alcohol) and liquid and solid acids were explored and the product properties of the resulting upgraded pyrolysis oil (kinematics viscosity, water content, pH and heating value) were determined. On the basis of these screenings studies, n-butanol and the solid acid Nafion SAC13 seem to have the highest potential. The product properties of the upgraded pyrolysis oils, and particularly the heating value and the acidity are considerably improved. These improvements are not only due to blending effects but also the result of the occurrence of chemical reactions (a.o. esterification).

2004, Computers & Chemical Engineering

The potential benefits of applying reactive distillation (RD) processes are taxed by significant complexities in process development and design. The design problem is formulated in the wider context of process development and engineering. From that perspective design methods for RD units developed over the last decades are classified and described. A fingerprint of the most representative work in the three categories, graphical, optimisation-and heuristic-based, is presented and deficiencies are identified. In response to a need for a more integrated design methodology, a conceptual model is offered which uses a hierarchy of embedded design spaces of increasing refinement and conjugates the strengths of both the graphical-and optimisation-based methods. analysis methods evaluation methods good enough models DESIGN DESCRIPTION PHYSICAL BEHAVIOUR PREFERED ALTERNATIVE BUILDING BLOCKS Abstract description Refined description definition/ specification

2009, Computers & Chemical Engineering

Catalytic reactive distillation offers new opportunities for manufacturing fatty acid esters, involved both in biodiesel and specialty chemicals. A key problem is the effective water removal in view of protecting the solid catalyst and avoiding costly recovery of the alcohol excess. This work proposes a novel approach based on dual esterification of fatty acid with light and heavy alcohols, namely methanol and 2-ethylhexanol. These two complementary reactants have an equivalent reactive function but synergistic thermodynamic features. The setup behaves rather as reactive absorption combined with reactive azeotropic distillation with heavy alcohol as co-reactant and water-separation agent. Another element of originality is the control of the inventory of alcohols by fixing the reflux of heavy alcohol and the light alcohol column inflow. This strategy allows achieving both stoichiometric reactant feed rate and large flexibility in ester production. The distillation column for recovering light alcohol from water is not longer necessary. The result is a compact, efficient and easy-to-control multi-product reactive setup.

2004

The synthesis of complex distillation columns has remained a major challenge since the pioneering work by Sargent and Gaminibanadara that was reported in 1976. In this paper we first provide a review of recent work for the optimal design of distillation of individual columns using tray-by-tray models. We examine the impact of different representations and models, NLP, MINLP and GDP, as well as the importance of appropriate initialization schemes. We next provide a review of the synthesis of complex column configurations for zeotropic mixtures and discuss different superstructure representations as well as decomposition schemes for tackling these problems. Finally, we briefly discuss extensions for handling azeotropic mixtures, reactive distillation columns and integration in process flowsheets. Numerical examples are presented to demonstrate that effective computational strategies are emerging that are based on disjunctive programming models that are coupled with thermodynamic initialization models and integrated through hierarchical decomposition techniques.

2011, Chemical Engineering Journal

A kinetic investigation for the esterification of butyric acid with n-butanol over Dowex 50Wx8-400 was conducted. The catalytic experiments were performed in a reactive distillation mode, in which the byproduct (water) is eliminated to prevent the reverse reaction from taking place. The experimental parameters are reaction temperatures (100-110 • C), molar ratios of reactants (butyric acid/n-butanol = 0.25-4) and catalyst loading (10-40 g/L), and their effect on the reaction rate was found that the conversion increased with temperature and catalyst loading whereas it decreased as the molar ratio of reactants increased. The rate equations were derived on the basis of the pseudo-homogeneous (PH) model, Langmuir-Hinshelwood (LH) model and Eley-Rideal (ER) model. From the best fit models showing good correlation between experimental and simulation results, the surface reaction was determined to be the rate determining step, while competitive adsorption on a catalyst surface and weak interaction between resin and water by-product were confirmed in the esterification reaction of butyric acid with n-butanol.

1999, Chemical Engineering Science

Structured packed columns, in which the catalyst particles are enclosed within wire gauze envelopes ("sandwiches") are promising reactor configurations for reactive distillation and hydroconversions. By allowing preferential channels for the gas and liquid phases, counter-current operation is achieved even for millimeter sized catalyst particles without the problem of flooding. This paper reports the results of a comprehensive experimental study of the hydrodynamics of structured packed columns of 0.1 and 0.24 m diameter. The pressure drop is found to increase sharply when the superficial liquid velocity exceeds a certain threshold value. This threshold corresponds to the situation in which a maximum flow of liquid in the packed channels is realized and the excess liquid flows through the "open" channels. The liquid flow in the open channel causes a sharp rise in the pressure drop. A model is developed to describe the holdup of liquid in the open channels. With increasing liquid flow rate, the pressure drop is found to increase exponentially with the liquid holdup within the open channels. Liquid phase residence time distribution studies lead to the conclusion that there is a good exchange of the liquid phase inside and outside the packed channels. The residence time distribution can be described by an axial dispersion model. Compared with a trickle bed reactor, the results of this study show that a structured packed column has a much larger operating window at a much lower pressure drop.

1993, Industrial & Engineering Chemistry Research

This paper presents results of computer simulations of the synthesis of methyl tert-butyl ether (MTBE) in a fixed-bed reactor and in a reactive distillation column. These calculations clearly showed the advantages of MTBE synthesis in a catalytic distillation tower. Furthermore, the computer simulations showed that multiple steady states may occur in the reactive distillation column during MTBE synthesis in a broad range of operating conditions. An analysis of some sensitivity studies is presented.

2011, Fuel

Deoxygenation of methyl esters and triglycerides was studied for production of either a-olefins or diesel components. The reactions were carried out in a reactive distillation fashion in which products are quickly removed from the reaction mixture in flowing He. The effects of He flow rate, reaction temperature, active component and support were studied. PtSnK supported on silica was found to be the best catalyst for selective production of a-olefins. Palm kernel oil and coconut oil were also deoxygenated to produce aolefins or diesel components, depending on reaction conditions.

2009, Chemical Engineering and Processing: Process Intensification

We performed steady state and dynamic simulations of a reactive Petlyuk column through an equivalent reactive dividing wall column (RDWDC). In the case of the reaction between ethanol and acetic acid catalyzed by sulfuric acid to produce ethyl acetate and water, we have found that the reactive Petlyuk column can achieve set point changes in two control loops of temperature. Also, for load rejection, the control loops can eliminate the effect of the disturbances in the feed composition. These results and previous knowledge reported about thermally coupled distillation columns and reactive distillation were considered to design and implement a RDWDC.

We describe a hierarchy of methods, models, and calculation techniques that support the design of reactive distillation columns. The models require increasingly sophisticated data needs as the hierarchy is implemented. The approach is illustrated for the production of methyl acetate because of its commercial importance, and because of the availability of adequate published data for comparison. In the limit of reaction and phase equilibrium, we show (1) the existence of both a minimum and a maximum reflux, there is a narrow range of reflux ratios that will produce high conversions and high purity methyl acetate, and (3) the existence of multiple steady states throughout the entire range of feasible reflux ratios. For finite rates of reaction, we find (4) that the desired product compositions are feasible over a wide range of reaction rates, up to and including reaction equilibrium, and (5) that multiple steady states do not occur over the range of realistic reflux ratios, but they are found at high reflux ratios outside the range of normal operation. Our calculations are in good agreement with experimental results reported by Bessling et al., [Chemical Engineering Technology 21 (1998) 393].

2006, Chemical Engineering Science

Kinetics of side reactions of the formation of n-butyl acetate in the heterogeneously catalyzed esterification of n-butanol with acetic acid were studied in an isothermal fixed-bed flow reactor at temperatures between 100 and 120 • C. The observed side reaction products are isomers of butene, di-n-butyl ether, sec.-butyl-n-butyl ether as well as sec.-butanol and sec.-butyl acetate. Three ion-exchange resin catalysts with a similar matrix but different sulfonation are compared: Puroliteீ CT 269 is mono-sulfonated whereas Amberlystீ 46 is surface-sulfonated and Amberlystீ 48 is bi-sulfonated. Puroliteீ CT 269 and Amberlystீ 48 are fully sulfonated in the gel phase, whereas Amberlystீ 46 is only surface-sulfonated. The ion-exchange capacities of Puroliteீ CT 269 and Amberlystீ 48 are similar, that of Amberlystீ 46 is lower by a factor of 5. Despite this, all three catalysts show only minor differences in their activity regarding the esterification. Regarding the formation of side products, Puroliteீ CT 269 and Amberlystீ 48 give similar results: side reactions proceed to significant extent. For Amberlystீ 46, however, side reactions were found to be almost negligible. It is concluded that the esterification occurs mainly on or near the external surface of catalysts particles whereas side reactions occur mainly in the pores. This work shows that surface-sulfonated catalysts like Amberlystீ 46 are very attractive for the production of esters by reactive distillation.

1999, Chemical Engineering Science

A pilot-plant research of butylacetate synthesis via catalytic distillation has been performed. Katapak in combination with CY packing were used as the experimental column packings. Computer simulation has been performed to study the process and to evaluate the experimental data. A new technology of high-purity butylacetate production has been designed, based on the pilot plant data.

2004, Chemical Engineering and Processing: Process Intensification

The ethyl acetate synthesis via reactive distillation is studied theoretically and experimentally using different catalytic packings. Experiments are carried out in laboratory scale in a 50 mm diameter column, packing height of 3 m, and in semiindustrial scale in a 162 mm diameter column, packing height of 12 m. The experimental set-up is similar for both cases. The commercially available packings studied are Sulzer KATAPAK  -S and Montz MULTIPAK  -1.

2004, AIChE Journal

A rigorous rate-based modeling approach to reactive distillation equipment is presented in detail. This approach has succeeded from the three-year project "Reactive Distillation" initiated by SUSTECH and supported by the EU in the frame of the BRITE-EURAM program. As a result, a steady-state rate-based simulator DESIGNER has been created and tested with industrially important reactive distillations. First, a thorough description of the model development, including process hydrodynamics and kinetics, is given. The general structure of DESIGNER is highlighted. Furthermore, numerical problems, simulation issues, and validation of the developed simulator are discussed, whereas several industrially important applications are demonstrated. The main advantages of DESIGNER are the direct account of mass and heat transport (rate-based approach), multicomponent mass-transport description via the Maxwell-Stefan equations, consideration of a large spectrum of reactions (homogeneous and heterogeneous; slow, moderate, and fast; equilibrium and kinetically controlled), reaction account in both bulk and film phases, availability of different hydrodynamic models, and a large choice of hydrodynamic and mass-transfer correlations for various types of column internals (trays, random and structured packings, catalytic packings). Particular attention is devoted to the mass-transfer model, including the reaction in the film region, to the catalyst efficiency determination based on the mass transfer inside the catalyst and to the hydrodynamic models for reactive trays.

A hybrid reactive distillation system with high selectivity pervaporation was examined to produce butyl acetate and methanol via transesterification of methyl acetate with butanol. High selectivity pervaporation was combined with reactive distillation to eliminate a hitherto required column for the separation of a methanol and methyl acetate azeotrope. The polyamide-6 membrane was used for this purpose because of its high selectivity for methanol while also allowing sufficient permeate flux. The high purity methyl acetate recovered in the retentate stream leads to high conversion in the reactive distillation column, which enhances the energy savings (up to 71%) of this process. The feasibility of the proposed hybrid processes and several alternative designs were evaluated by rigorous simulation and optimization using the Aspen Plus software package. The effects of several designs and operating variables were also investigated for the proposed design. The high potential of the hybrid reactive distillation and pervaporation system for butyl acetate production is very promising; it may not only reduce the total annual costs relative to conventional systems but may also provide an attractive strategy to address problems associated with methanol and methyl acetate azeotropes in the effluent generated in the polyvinyl alcohol industry.

2004, Chemical Engineering and Processing: Process Intensification

The scale-up of reactive distillation columns with catalytic packings requires the knowledge of reaction kinetics, phase equilibrium and packing characteristics. Therefore, pressure drop, liquid holdup and separation efficiency have been determined for the catalytic packing MULTIPAK ® . A new hydrodynamic model that describes the counter-current gas-liquid flow for the whole loading range and considers the influence of the column diameter has been implemented into a ratebased column model. Simulation results for the methyl acetate synthesis are compared with pilot plant experiments that cover a wide range of different process conditions. The experiments are in good agreement with the simulation results and confirm the applicability of the modelling approach for reactive distillation processes with catalytic packings.

The challenges in the chemical processing industry today are environmental concerns, energy and capital costs. Catalytic distillation (CD) is a green reactor technology which combines a catalytic reaction and separation via distillation in the same distillation column. Utilization of CD in chemical process development could result in capital and energy savings, and the reduction of greenhouse gases. The efficacy of CD and the economic merits, in terms of energy and equipment savings, brought by CD for the production of biodiesel from waste oil such as yellow grease is quantified. Process flow sheets for industrial routes for an annual production of 10 million gallon ASTM purity biodiesel in a conventional process (reactor followed by distillation) and CD configurations are modeled in Aspen Plus. Material and energy flows, as well as sized unit operation blocks, are used to conduct an economic assessment of each process. Total capital investment, total operating and utility costs are calculated for each process. The waste oil feedstock is yellow grease containing both triglyceride and free fatty acid. Both transesterification and esterification reactions are considered in the process simulations. Results show a significant advantage of CD compared to a conventional biodiesel processes due to the reduction of distillation columns, waste streams and greenhouse gas emissions. The significant savings in capital and energy costs together with the reduction of greenhouse gases demonstrate that process intensification via CD is a feasible and new green process for the biodiesel production from waste oils.

2002, Chemical Engineering and Processing: Process Intensification

We have carried out a step-by-step design study of a reactive distillation (RD) column for synthesis of tertiary-amyl ether (TAME) in order to investigate the influence of the choice of hardware on column design. Two different types of internals are compared: active Raschig rings and catalytic bales. Firstly, an equilibrium (EQ) stage model is used to obtain conceptual column design parameters. Detailed mass transfer and pressure drop calculations are then carried out to determine the column diameter and heights of the reactive and non-reactive sections of the RD column. Active Raschig rings have superior mass transfer characteristics but poorer pressure drop characteristics as compared to catalytic bales and therefore yield shorter and fatter column configurations. The detailed hardware configuration is finally checked with a rigorous nonequilibrium (NEQ) stage model to ensure that the designs are adequate and to investigate scope for further improvement. Our study underlines the importance of using NEQ models for column design and optimization. EQ stage models provide only initial estimates of column designs. The chosen column configurations must be carefully checked with rigorous NEQ models. Furthermore, our study reveals that the amount of catalyst used in the reactive section needs to be carefully chosen; excess of catalyst could lead to promotion of the reverse reaction of TAME to the reactants.

2007, Control Engineering Practice

2007, Chemical Engineering Science

This paper reports on the development of a new industrial process for the production of trioxane (C 3 H 6 O 3 ), the cyclic trimer of formaldehyde (CH 2 O). Trioxane is synthesized from concentrated aqueous formaldehyde solutions, which are inherently reactive complex multicomponent mixtures. Based on the knowledge on the physical chemistry of these complex solutions, reliable modeling of processes containing formaldehyde solutions has recently become possible. This was the key to the process development of the present work. The new trioxane process uses solely distillations for the purification. This is a great advantage compared to the existing process in which an extraction step with tedious solvent recovery is necessary. Conceptual process design was carried out with ∞/∞-analysis using reactive distillation line diagrams. They show the possibility of a pressure swing distillation. Distillation experiments were carried out to validate the results. They prove the feasibility of all distillation cuts and, hence, of the entire process. The resulting new process, including all recycles, was successfully simulated based on a rigorous physico-chemical equilibrium stage model using Chemasim. Moreover, quantitative 1 H NMR experiments were carried out, in which the trioxane formation as well as the formation of important side products in highly concentrated formaldehyde solutions containing up to 0.10 g g −1 sulfuric acid was studied at temperatures up to 338 K to gain reliable information on reaction kinetics, needed for process design. ᭧

2007, Chemical Engineering Research & Design

The combination of reactive distillation and a divided wall column leads to a reactive divided wall column. The first use of such a reactive divided wall column for the hydrolysis of methyl acetate is presented here. For the development of this system, kinetic data for the involved reactions was determined at the University of Stuttgart, mini plant experiments were performed

2006, Chemical Engineering Science

A methodology to improve the efficiency of stochastic methods applied to the optimization of chemical processes with a large number of equality constraints is presented. The methodology is based on two steps: (a) the optimization of the simulation step, which involves the optimum choice of design variables and subsystems to be simultaneously solved; (b) the optimization of the nonlinear programming (NLP) problem using stochastic methods. For the first step a flexible tool (SIMOP) is used, whereby different numerical procedures can be easily obtained, taking into account the problem formulation and specific characteristics, the need for specific initialization schemes and the efficient solution of systems of nonlinear equations. This methodology was applied to the optimization of a reactive distillation process for the production of ethylene glycol. Due to the complexity of the mathematical model, several different numerical procedures were generated, and their influence on the computational burden and on the reliability and accuracy of the optimization to reach the global optimum were studied. The results obtained suggest that in addition to the choice of design variables, the structure of subsystems associated to numerical procedures has a considerable impact on the performance of the optimizers. ᭧

1998, Computers & Chemical Engineering

A nonequilibrium model for simulation of homogeneous reactive distillation has been developed. Mass transfer accompanied by simultaneous chemical reaction is described by the Maxwell !&fan equations. Calculations were done for the process to produce ethyl acetate that has been treated extensively in literature. It was found that reactions could, under certain conditions, have a significant impact on component efficiencies, thus emphasizing the need for rate-based models for reactive distillation. By means of parametric sensitivity studies it is shown that the effects of operational and design parameters on column behavior can be very complicated. 0

2000, AIChE Journal

Visual methods of determining how to distribute reaction zones within a binary reac-ti®e distillation column were studied using both the Ponchon ᎐ Sa®arit and McCabe ᎐ Thiele methods modified to account for the reaction. Two types of reactions are compatible with a totally binary system: isomerization and dimerization. For isomerization with a hea®y reactant and a light product, both diagrams indicate the potential for a pinch point if the reaction zone is in the stripping section and no such potential if the zone is in the rectifying section. These same diagrams show that the column will ha®e fewer stages and less usage of utility to yield the same final top and bottom products with the reaction in the rectifying section. The situation re®erses if the reactant is the light species for isomerization, suggesting reaction should then take place in the stripping section. The heat effect from the isomerization reaction is considered for four cases depending on whether the reaction is endothermic or exothermic. E®en if the heat of the isomerization is dominant, the results do not change: with a hea®y reactant and a light product, the separation performance is better when the reaction takes place in the rectifying section. In the dimerization reaction, where two light reactants form a hea®y product, the light reactant enriches as we go down the column and the composition profile is re®ersed in a Ponchon᎐ Sa®arit diagram with the reaction in the rectifying section e®en if there is no pinch point. Results on the location of reaction zones are confirmed by rigorous simulations.

1998, Computers & Chemical Engineering

Reactive distillation offers a number of potential advantages, so that many traditional operations are currently being investigated in order to discover further applications of this technology. Increasingly, it is perfonued in columns with catalytic packings that combine the advantages of normal structured packings and heterogeneous catalysts. Analysis of reactive distillation is difficult due to strong physico-chemical interactions, and it is even more complicated for catalytic distillation (reactive distillation in catalytic packings), where the knowledge of column hydraulics, as e.g. hold-ups, pressure drop, and liquid distribution, is more important than in the case of traditional unit operations. In this paper, a detailed rate-based approach for modeling and simulation of catalytic distillation is presented, including all major aspects of the description of column hydraulics, mass and energy transfer, chemical reactions and thermodynamic non-idealities. The model equations have been implemented into the ABACUSS large scale modeling environment. Even in the frame of such sophisticated modeling, a variety of experimental parameters have to be determined. It is shown how these parameters appear in the model equations and how experiments and computer simulation interact. For a completely new class of catalytic packings all experimental parameters have been derived in accordance with the model assumptions in the form of correlations. All models have been formulated for dynamic operation and numerical implications of the dynamic modeling are addressed. For the semi-continuous catalytic distillation of the quatemary reactive mixture of acetic acid, methanol, methyl acetate, and water, simulated and experimental results are presented and compared. Based on the integration of detailed modeling, experimental parameter determination and a modem simulation platform it is possible to predict the dynamic, non-linear and non-ideal process behavior successfully. 0

1996, Computers & Chemical Engineering

While both the dynamic modelling, and to a lesser extent, the optimisation of reactive batch distillation have been studied in the past, issues related to control and on-line operation of such a process have not been properly addressed. In this study, a priori optimal profiles of the operating variables are established for an industrial reactive distillation process. The optimal profiles are found either by maximising the profitability or by minimising the operating time subject to constraints on the reactor temperature and the loss of volatile reactant in the distillate. The control properties at optimal and non-optimal conditions are assessed. A one-point column control scheme with a PI-controller is designed to implement the optimal profiles. The controller performance is tested using a simulation model including disturbances in the reaction model and in the reboiler heat duty. The fully automatic operation of the process according to the optimal policies is demonstrated in conjunction with both a continuous controller and a real time control system. Good performance is achieved in both cases.

2011, Computers & Chemical Engineering

The design optimization of reactive distillation columns (RDC) is characterized by complex nonlinear constraints, nonlinear cost functions, and the presence of many local optima. The standard approach is to use MINLP solvers that work on a superstructure formulation where structural decisions are represented by discrete variables and lead to an exponential increase in the computational effort. The mathematical programming (MP)

2010, Applied Biochemistry and Biotechnology

Biodiesel is a clean burning fuel derived from a renewable feedstock such as vegetable oil or animal fat. It is biodegradable, non-inflammable, non-toxic, and produces lesser carbon monoxide, sulfur dioxide, and unburned hydrocarbons than petroleum-based fuel. The purpose of the present work is to present an efficient process using reactive distillation columns applied to biodiesel production. Reactive distillation is the simultaneous implementation of reaction and separation within a single unit of column. Nowadays, it is appropriately called “Intensified Process”. This combined operation is especially suited for the chemical reaction limited by equilibrium constraints, since one or more of the products of the reaction are continuously separated from the reactants. This work presents the biodiesel production from soybean oil and bioethanol by reactive distillation. Different variables affect the conventional biodiesel production process such as: catalyst concentration, reaction temperature, level of agitation, ethanol/soybean oil molar ratio, reaction time, and raw material type. In this study, the experimental design was used to optimize the following process variables: the catalyst concentration (from 0.5 wt.% to 1.5 wt.%), the ethanol/soybean oil molar ratio (from 3:1 to 9:1). The reactive column reflux rate was 83 ml/min, and the reaction time was 6 min.

This paper presents a novel hybrid process combining thermally coupled reactive distillation with membrane-based pervaporation for enhanced production of n-butyl acetate. A conventional reactive distillation process was used as the base case and first optimized for the transesterification of methyl acetate with n-butanol to produce n-butyl acetate. It was observed that methyl acetate recovered in the recycle stream significantly affects the con-version in the reactive distillation column and overall energy efficiency of the whole process. The existing and proposed configurations were evaluated and optimized by simulation in Aspen Plus. The integration of thermally coupled reactive distillation and pervaporation improved the energy efficiency of the reactive distillation process by preventing remixing effect in the reactive distillation column and eliminating the azeotropic nature of the methanol and methyl acetate in the recycle stream, respectively. Finally, integration of the thermally coupled reactive distillation with a commercial pervaporation membrane was explored to take synergistic advantage of the thermally coupled reactive distillation and pervaporation hybrid configuration. As a result, the proposed hybrid design showed remark-ably improved energy efficiency and economics. The total reboiler duty and total annual cost reduced to 63 and 43%, respectively, compared to those of the base case.

2000, Catalysis Today

New synthesis routes have been investigated for the production of dinitrotoluenes (DNTs) from toluene or an equimolar mixture of 2-nitrotoluene (2-NT) and 4-nitrotoluene (4-NT) and nitric acid using solid acids as heterogeneous catalysts. The main objective was the replacement of liquid sulphuric acid. A secondary goal was the increase of 4-NT and 2,4-DNT in the product mixture, which are more valuable products. Particular consideration was given to the feasibility of future large-scale process implementation. Continuous flow vapour phase reaction, and liquid phase reaction with simultaneous distillation were investigated. DNT formation in the vapour phase reaction was negligible with all solid acids tested. Preshaped silica impregnated with sulphuric acid was the most active catalyst but a continuous loss of sulphuric acid with time-on-stream was observed. Zeolite beta provided a higher 4-NT to 2-NT ratio than ZSM-5, ZSM-12 and mordenite, but deactivated after 5-10 h on-stream. Regeneration of beta was possible by thermal treatment. The para-selectivity of mordenite could be improved by the creation of a mesoporous system. In the reaction with simultaneous distillation, supported liquid acids exhibited true catalytic behaviour for the conversion of NT to DNT, but a loss of the impregnated acid was observed. Zeolite beta was about half as active as supported liquid acids and gave an exceptionally high 2,4-DNT selectivity of up to 94%, compared to 74-79% obtained with all other solid acids.

2005, Chemical Engineering Research and Design

A procedure that combines feasibility analysis, synthesis and design of reactive distillation columns is introduced. The main interest of this methodology lies on a progressive introduction of the process complexity. From minimal information concerning the physicochemical properties of the system, three steps lead to the design of the unit and the specification of its operating conditions. Most of the methodology exploits and enriches approaches found in the literature. Each step is described and our contribution is underlined. Its application is currently limited to equilibrium reactive systems where degree of freedom is equal to 2 or less than 2. This methodology which provides a reliable initialization point for the optimization of the process has been applied with success to different synthesis. The production of methyl-tert-butyl-ether (MTBE) and methyl acetate are presented as examples.

2010, Chemical Engineering and Processing

Biodiesel fuel represents an interesting alternative as a clean and renewable substitute of fossil fuels. A typical biodiesel production process involves the use of a catalyst, which implies high energy consumptions for the separation of the catalyst and the by-products of the reaction, including those of undesirable side reactions (such as the saponification reaction). A recently proposed process involves the use of short-chain alcohols at supercritical conditions, avoiding the use of a catalyst and the occurrence of the saponification reaction. This process requires fewer pieces of equipment than the conventional one, but its high energy requirements and the need of special materials that support the reaction conditions makes the main product, biodiesel fuel, more expensive than petroleum diesel. In this work, a modification of the supercritical process for the production of biodiesel fuel is proposed. Two alternatives are proposed. The process involves the use of either reactive distillation or thermally coupled reactive distillation. Simulations have been carried out by using the Aspen One™ process simulator to demonstrate the feasibility of such alternatives to produce biodiesel with methanol at high pressure conditions. A design method for the thermally coupled system is also proposed. Both systems have been tested and the results indicate favorable energy performance when compared to the original scheme. Furthermore, the thermally coupled system shows lower energy consumptions than the reactive distillation column.

2009, Control Engineering Practice

Subspace monitoring has recently been proposed as a condition monitoring tool that requires considerably fewer variables to be analysed compared to dynamic principal component analysis (PCA). This paper analyses subspace monitoring in identifying and isolating fault conditions, which reveals that existing work suffers from inherent limitations if complex fault scenarios arise. Based on the assumption that the fault signature is deterministic while the monitored variables are stochastic, the paper introduces a regression-based reconstruction technique to overcome these limitations. The utility of the proposed fault identification and isolation method is shown using a simulation example and the analysis of experimental data from an industrial reactive distillation unit.

2002, Chemical Engineering and Processing: Process …

A comparison of computer simulation results of reactive distillation obtained by ASPEN PLUS and HYSYS software was done. Esterification of acetic acid and 1-butanol was chosen as the model reaction proceeding in a reactor and reactive distillation column (RD) system. A nearly equimolar reaction mixture was fed into the equilibrium fixed bed reactor and the liquid product was continuously fed into reaction zone of the reactive distillation column. The same mass balance in the reactor and reactive distillation column was used to compare the adequacy of chosen simulation systems. The results of computer simulation have been consequently compared with pilot plant experimental data. A good agreement was reached.

2009, Chemical Engineering Science

The steady state economic optimization to obtain the most economical controllable design of a double feed ideal reactive distillation (RD) column is demonstrated using real coded genetic algorithm. The novelty of the work is in the development of a simple procedure based on steady state criteria for controllability. The optimization is performed for four scenarios corresponding to a sequential increase in the number of design variables. Results show that limiting the optimization search space to only those designs that satisfy the controllability criteria leads to optimized designs that are only slightly ( < 2%) more expensive than the most economical design without controllability considerations. The former designs however exhibit much better controllability in terms of effectively handling a large through-put change using two-point temperature inferential control and avoiding a steady state transition under open loop operation. Results also show that the location of the fresh feeds is a dominant design variable with designs that do not constrain the feed tray location to be immediately above and below the reactive zone being substantially more economical.

2008, Chemical Engineering and Processing

In this contribution, a sequential and hierarchical approach for the feasibility analysis and the preliminary design of reactive distillation columns is extended to systems involving vapour phase chemical reaction and is successfully... more

1997, Reactive & Functional Polymers

1,3-Dioxolane was prepared from ethylene glycol and formaldehyde in the presence of a cation-exchange resin. The reaction was studied in batch mode, semi-batch reactive distillation mode and in a continuous reactive distillation column. A pseudohomogeneous model explains the batch kinetics. Higher than 98% conversion of formaldehyde was achieved in semi-batch reactive distillation. Recovery of ethylene glycol from aqueous solutions via reaction kith solid paraformaldehyde in a semi-batch reactive distillation mode was also studied.

2021

The separation of 2-Methoxyethanol-toluene azeotropic mixture has high practical significance in both industry and the laboratory because of their multipurpose solvating properties. However, both 2ME and toluene have adverse effects on human and animal health; therefore, researchers have become interested in their separation. A significant amount of 2-methoxyethanol-toluene forming a minimum-boiling azeotrope is discharged by the electrochemical industry. The presence of this azeotrope renders separation a challenging task. Separation techniques, namely pressure swing distillation (PSD) and azeotropic distillation (AD), have not yet been explored. In this study, these separation techniques are evaluated economically and dynamically using a wellknown commercial simulator Aspen Plus®. This study includes the development of process schematics for these alternative separation processes and economic analysis involving total annual cost (TAC) calculations. It is concluded that the heat-integrated PSD technique leads to 21.35% savings in TAC compared to previously reported techniques. Furthermore, a decentralized plant-wide control structure for a suitable separation technique is also developed and tested for ±10% throughput manipulations in fresh feed flow rate and ±5% disturbances in feed composition. This study will significantly help the process engineers overcome the challenges of handling the electrochemical industry's hazardous effluent in environmentally and economically ways.

2011, Chemical Engineering Journal

Hydrolysis of methyl lactate to lactic acid in a reactive distillation column is widely used in the purification of lactic acid. In this work, optimal operations of conventional and inverted batch reactive distillation columns undergoing the hydrolysis reaction are presented. Minimum time optimisation problem is formulated incorporating a process model within gPROMS software and is solved for different range of lactic acid purity and the amount of product using both columns. For a given column type and configuration the minimum operation time is obtained by optimising the reflux ratio profile. For conventional column, the lactic acid being the heaviest in the reaction mixture, reflux ratio policy plays an important role in removing the light product methanol from the top of the column while ensuring the presence of both reactants in the reaction zone to maximise the conversion to lactic acid. For inverted column, reboil ratio policy plays an important role in removing the lactic acid from the bottom of the column while ensuring the presence of both reactants in the reaction zone to maximise the conversion to lactic acid. For some cases (although limited) it is observed that for low lactic acid product purity the conventional column outperforms the inverted column while for high product purity the inverted column outperforms the conventional column in terms of batch time.

2007, Reactive and Functional Polymers

As a prelude to commissioning a reactive distillation column (RDC) for the continuous epoxidation of cyclohexene using tbutylhydroperoxide and a heterogeneous polymer-supported Mo(VI) catalyst, the long-term stability of three candidate polymer-supported Mo catalysts has been evaluated. The polymer catalysts are a polybenzimidazole-supported species, PBI.Mo, and two poly(styrene-divinylbenzene) resin-based species, Ps.AMP.Mo1 and 2, prepared in-house by amination of vinyl benzyl chloride-containing resins using 2-aminomethyl pyridine, followed by loading with Mo. The stability of each polymer catalyst was assessed by recycling a sample 10 times in small batch reactions using conditions that will form the basis of the continuous process. At the same time the loss of Mo from each support has been investigated by isolating any residue from reaction supernatant solutions, following removal of the heterogeneous polymer catalyst, and then using the residues as potential catalysts in epoxidation reactions. This is a powerful technique for identifying unambiguously loss of catalytically active Mo from the support and is not dependent on Mo analytical procedures. All three polymer catalysts are highly active and selective in 10 consecutive reactions but the supernatant solutions also contain catalytically active Mo residues. In the case of PBI.Mo and Ps.AMP.Mo2 the contribution to catalysis from homogeneous Mo species lost from the supports is all but eliminated after aging through 10 cycles, but in the case of Ps.AMP.Mo1 the contribution from leached Mo species remains significant even after similar aging. The major factor determining this differential behaviour seems to be the mole ratio of polymer-bound ligand to Mo which must be significantly above unity to provide long-term retention of Mo.

2003, Catalysis Today

Reactive separations combining mass transfer with simultaneous chemical reactions impose additional requirements on the applied column internals. Traditionally, reactive separation processes have been optimised via operational parameter adjustment. By this way, a direct influence of the internals geometry and structure cannot be taken into consideration. Therefore, the application of process-specific column internals, rather than of the internals currently available on the market, is desirable. Development of new internals is a major focus of interest in an European project entitled Intelligent Column Internals for Reactive Separations. In particular, such development is achieved by the application of modern CFD facilities combined with the rigorous, rate-based process simulation. An important challenge is to provide an opportunity of obtaining hydrodynamic and mass-transfer correlations, necessary for the process description, not only from the experimental measurements, but also directly from the CFD simulations. In this paper, a way to generate virtual correlations is demonstrated for a single-phase flow through structured packings. The rate-based simulation is illustrated with the heterogeneously catalysed synthesis of n-hexyl acetate via reactive distillation.

2011, Chemical Engineering Research and Design

In this work, we obtain and compare the control properties of thermally coupled reactive distillation sequences and thermally coupled extractive distillation sequences with those of conventional reactive and extractive distillation configurations. All sequences have been designed using a multiobjective genetic algorithm with restrictions. The theoretical control properties of those schemes were obtained using the singular value decomposition technique in all frequency domain. In order to complete the control study, the distillation options were subjected to closed-loop dynamic simulations. The effects of total stages, reactive stages, and extractant/feed ratio on the energy consumption and control properties are obtained for the intensified distillation options. The results show that there are cases in which integrated reactive and extractive sequences do not only provide significant energy savings with respect to the conventional reactive and extractive arrangements, but also may offer dynamic advantages in high energy consumption conditions.

2004, Chemical Engineering and Processing: Process Intensification

In this contribution, the benefits of using dynamic models of different complexity and size for process design, optimal operation and control of catalytic distillation processes are discussed for the case study of the heterogeneously catalysed reactive distillation of methyl acetate. Dynamic reactive distillation experiments at pilot plant scale were performed using the catalytic structured packing MULTIPAK. A dynamic rate-based model were developed which contains hydrodynamic effects as liquid holdup, liquid backmixing and pressure drop as well as reaction kinetics and which describes the process behaviour accurately. For offline and online optimisation and control, reduced order and simplified models were applied. A systematic control structure selection and controller design studies for the experimental column were conducted. The linear controller shows good performance over a wide range of operating conditions.