Reactive Distillation Systems Research Articles

Artificial neural networks strategy to analyze the magnetohydrodynamics Casson-Maxwell nanofluid flow through the cone and disc system space

The Casson-Maxwell model is particularly useful for studying viscoplastic fluids or fluids with yield stress, making it applicable to various engineering applications, including extrusion processes, coating applications, and biomedical fluid dynamics. Casson-Maxwell fluid flow enhances mass transfer rates due to the combined effects of non-Newtonian viscosity and viscoelastic behavior. This is particularly useful in processes where mass transfer limitations play a significant role, such as in multiphase reactions or reactive distillation systems. In the context of the above applications the present model, is the combination of Casson- Maxwell fluids that flow through the varying gap of the spinning cone and disk system (CDS) for the heat transfer enhancement. The magnetic field is also imposed in the upright direction to the flow field. The solution of the transform equations has been obtained through artificial neural networks (ANN). The skin friction, heat transfer rate, and comparative analysis have been done. The Casson-Maxwell parameters that depend on the viscoelastic behavior and high viscosity term, causes the fluid to slow down and tends to store the temperature, for a long time as compared to traditional fluids. The radial component of velocity decreases due to the increase in magnetic field. The relative error of the reference and targeted dates is calculated to demonstrate the best precision efficiency of ANN, with a range of 10−3 to 10−4.

Optimal design and operation of reactive distillation systems and reactive dividing wall systems with pressure swing distillation and hybrid distillation-pervaporation

Process intensification is essential in exploring more energy-efficient processes, and key examples related to fluid separations are reactive distillation and hybrid distillation-pervaporation processes. This work will consider the reaction and separation of a general quaternary reactive system with a minimum boiling binary azeotrope AC, in a reactive distillation column where, given the thermodynamics limitations, further downstream separation is required. Low and high chemical equilibrium is considered for the reaction. For the downstream purification, both pressure swing distillation and a hybrid distillation-pervaporation process are considered. For each of the structures, their intensified equivalent dividing wall structures are also considered, including a hybrid reactive dividing wall system. It is shown that reactive distillation followed by a hybrid distillation-pervaporation system can save up to 24% energy compared to reactive distillation with pressure swing separation, and that the dividing wall column counterpart structures have lower production-based total annualised costs than the corresponding base systems.

Unfavorable process intensification of double column reactive extractive distillation system

This study evaluated the energy saving potential of process intensified double column reactive extractive distillation (DC-RED) through three case studies. The results showed that process intensified technologies, thermally coupled reactive extractive distillation (TC-RED) and dividing wall reactive extractive distillation (DW-RED), did not yield any energy savings compared to conventional DC-RED. Contrary to the expectation, the elimination of the remixing effect in the process intensified DC-RED did not lead to any energy savings. Further analysis revealed that the remixing effect was not significant enough to achieve energy savings through process intensification, and the strong reaction exotherm in DC-RED reduced the potential for energy saving. Additionally, the higher interconnection flowrate in TC-RED and DW-RED resulted in higher energy consumption due to the increased boil-up ratio. Moreover, the lower feed temperature to the solvent recovery column (SRC) led to less energy efficiency and larger reboiler duty. An alternative energy saving scheme was proposed by adding a heat exchanger (HEX). The addition of HEX led to energy savings of 37.23 % in Acetonitrile (ACN)/Isopropanol (IPA)/Water separation, 45.62 % in Ethyl Acetate (EA)/Ethanol (EtOH)/Water separation, and 39.21 % in IPA/EA/Water separation.

Direct production of diethyl carbonate from ethylene carbonate and ethanol by energy-efficient intensification of reaction and separation

This study presents a novel process for producing diethyl carbonate and ethylene glycol directly from ethylene carbonate and ethanol through reactive distillation. Previous studies have mainly focused on investigating two reactive distillation systems with a pressure swing azeotropic separation for producing diethyl carbonate. By integrating the two separated reactive distillation systems into a single flowsheet, an energy-efficient process is enabled. Especially, the need for separating the azeotrope mixture is eliminated, and the primary feed of methanol is not required due to the reaction stoichiometry. Two design alternatives have been proposed based on the reactive distillation configuration and catalyst employed. The first design significantly reduces the amount of equipment needed by utilizing two reactive distillation columns, while the second design offers high energy savings, as all reactions occur in a single reactive distillation column. Compared to the conventional process of producing individual dimethyl and diethyl carbonate, both design alternatives result in total energy consumption reductions of 12% and 24%, respectively, as well as total annual cost reductions of 12% and 14%, respectively. Furthermore, both design alternatives demonstrate a reduction in CO2 emissions by 15% and 11% respectively. Not only do these results demonstrate their economic viability, but they also indicate their effectiveness in CO2 mitigation. From an industry perspective, the two proposed design alternatives can be effectively implemented for the direct production of diethyl carbonate and mono-ethylene glycol by intensifying the existing dimethyl carbonate production process.

Design of a multiproduct reactive distillation system for DEC and EMC production

Multiproduct processes are gaining interest as part of the development of intensified structures. In this work, an optimal design of a flexible diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) multiproduct process is developed. DEC is a main product that is commonly produced through multi-reaction dimethyl carbonate (DMC) transesterification. However, EMC, an intermediate product, also has a significant market interest. This work explores the use of a multiproduct process that integrates a reactive and a separation column to produce either DEC or EMC. The design was obtained aided by a process optimization task with genetic algorithms tied to Aspen Plus rigorous simulations. The results show that a common design for the production of both products can be obtained, with total annual cost savings of 22% with respect to a base design taken from the literature. Additionally, an initial dynamic analysis shows that the multiproduct process can be controlled in the face of feed flow and composition disturbances.

Co-process intensification in the synthesis and design of reactive double dividing-wall distillation columns

In most cases, the reactive single dividing-wall distillation column (R-SDWDC) and its corresponding conventional reactive distillation system (CRDS) fail to yield the best performance in the separations of reacting mixtures with unfavorable reaction kinetics and/or unfavorable thermodynamics properties. In this work, a novel methodology of co-process intensification is proposed for the synthesis and design of reactive dividing-wall distillation columns. The methodology leads to the establishment of a reactive double dividing-wall distillation column (R-DDWDC), and the included intermediate separating section plays a vital role in coordinating these two kinds of process intensification and consequently guarantees its optimum performance. In terms of two example systems involving the separations of the ideal quaternary reversible reaction with a somewhat unfavorable ranking of relative volatilities (A + B ↔ C + D with αA > αC > αB > αD) and the transesterification of methyl acetate with n-propanol, the proposed methodology is evaluated. The R-DDWDC is found to yield much better performance than the CRDS and R-SDWDC in the separations of the reacting mixtures with somewhat unfavorable ranking of relative volatilities, and such outcomes definitely corroborate the effectiveness and advantages of the proposed methodology for process development. Although the proposed methodology is developed solely based on the separations of the reacting mixtures with somewhat unfavorable ranking of relative volatilities, it is of great implication to the separations of the other reacting mixtures with unfavorable reaction kinetics and/or unfavorable thermodynamics properties.

Investigation on catalytic distillation for ethyl acetate production with different catalytic packing structures

Here, the performances of tea-bag catalytic packing (TBP) and supported catalytic packing (SCP) in the reaction distillation of ethyl acetate were designed and compared. There are significant differences in the distribution of efficiency factor and reaction rate between them. The results can provide a theoretical reference for the design of reactive distillation. The catalytic packing is the core component of the catalytic distillation, and how the catalyst exists in the packing has significant influence on the process. To investigate the effect of catalyst packings on the catalytic distillation process, the classical ethyl acetate reactive distillation system was utilized, and a supported catalytic packing (SCP) was prepared in comparison with the conventional tea-bag catalytic packing (TBP). Laboratory scale experiments showed that the ethyl acetate conversion of the SCP was superior to the TBP at a low catalyst loading. The effects of reaction kinetics, mass transfer performance and actual catalytic efficiency of the packings on this process were regarded as reasons and studied by combining the experiments and numerical simulation. Results suggested that the relatively immediate “ in-situ separation” caused by the rapid reaction kinetics and better mass transfer performance of SCP may be a main reason for the difference of the conversion.

An environmentally friendly production of ester‐biolubricant from oleic acid

AbstractThe production of oleic‐based trimethylolpropane (TMP) esters via the esterification reaction between oleic acid (OA) and TMP in a reactive distillation system, employing the environmentally friendly catalyst methanesulfonic acid, was explored. The homogeneous acid catalyst, the OA/TMP molar ratio within 1.0–3.0, the esterification reaction enhancement and a new purification technique, using choline hydroxide (ChOH), for obtaining choline carboxylate as a subproduct, were studied. It was found that using an OA/TMP molar ratio of 3.0, only unreacted OA remained as an impurity. The deleterious or beneficial effect of intermediate products, unreacted OA and temperature on the kinematic viscosity were unraveled. The kinematic viscosity behavior for the products was practically independent of temperature but an abrupt enlargement of the kinematic viscosity was observed in the presence of functional groups in the intermediate esters, even greater than the Mark–Houwink counterpart effect. On contrary, the presence of OA in the final product decreased the kinematic viscosity attending to its lower molecular weight with respect to the trimethylolpropane trioleate one. It was found that trimethylolpropane monooleate is undesirable for the viscosity index, whereas the presence of trimethylolpropane dioleate could also increase the viscosity index to a small extent, requiring a complex purification process. Finally, it is possible to affirm that the optimal TMP‐based lubricant obtained using an OA/TMP molar ratio of 3.0, after OA neutralization presented good marginal benefit and a viscosity index of 208.7, which is applicable for gear lubricants. © 2022 The Authors. Biofuels, Bioproducts and Biorefining published by Society of Industrial Chemistry and John Wiley & Sons Ltd.

Biodiesel Production from Used Cooking Oil Using Integrated Double Column Reactive Distillation: Simulation Study

Dependency on fossil – based energy has become a global problem. Indonesia has started a movement in changing energy sources from fossil to new and renewable energy. Biodiesel is one of the renewable energy sources. Used cooking oil is one of the prospective feed-stock in biodiesel production. Used cooking oil contains 21.84% free fatty acid and 78.16% triglycerides. This study simulated the production of biodiesel from used cooking oil using the Aspen Plus v10 software. The production system used an Integrated Double Column Reactive Distillation (IDC-RD) system. The thermodynamic method employed in the simulation system was UNIQUAC. This study used the sensitivity analysis function in the Aspen Plus v10 application to analyze the effect of reflux ratio, the bottom to feed ratio, and the methanol to oil ratio on the reaction conversion. The reflux ratio applied in the simulation was 0.5 – 200, the bottom to feed ratio was 0.25 - 0.9, and the methanol to oil ratio was 1: 3 - 9:8. It was found that the esterification column with a reflux ratio of 0.5, a bottom to feed ratio of 0.5, and a methanol-oil ratio of 4: 1 resulted in a conversion of 96.59%. It was also demonstrated that the transesterification column with a reflux ratio of 0.5, a bottom to feed ratio of 0.5, and a methanol-oil ratio of 3: 1 resulted in a conversion of 99.98%.

A framework to evaluate the impact of uncertainty on design and operation of reactive distillation systems

This work is motivated by the current obstacles hindering the implementation of reactive distillation in industry, mainly related to the complexities of its design and control, as well as the impact of uncertainties thereupon. A framework to systematically investigate the impact of uncertainty on reactive distillation processes is presented, considering the relevant control system and potential redesign of the column, possibly including additional ancillary equipment, with the aim to make the process more robust and to mitigate risk. The framework also considers the impact of operational uncertainties, showing that a system which can tolerate design uncertainty may nevertheless still be sensitive to operational uncertainties, in which case the mitigation strategies presented in this work should be applied to enhance system robustness. This framework can be used in an early design stage to quantify the impact of specific input parameters on process performance and costs, and it can therefore be used to steer the experimental work to focus on determining the most critical parameters for a reactive distillation process. Three case studies are considered showing that, for reactive distillation, uncertainty in the rate constant has a more significant impact on the system performance than a similar uncertainty in chemical equilibrium.

An investigation of the interactions between system characteristics and controllability for reactive distillation systems

Reactive distillation is an emerging process intensification technology, although its operation and control are complex due to the interactions between reaction and separation within the column. In this work, the impact of reaction and separation, as well as design parameters, on the controllability of reactive distillation processes is investigated, using a systematic methodology developed. Case studies of industrial interest are considered, varying in the key (reaction, separation and design) parameters, in order to investigate the relative impact of the latter on the controllability of the reactive distillation systems. It is shown that the system with slower kinetics demonstrates an increased difficulty in rejecting feed disturbances for both one point (V-only) and two-point (LV) control configurations. Even when linear model predictive control (MPC) is considered based on a state-space representation of the model, the system with slower reaction kinetics is still more difficult to control, for both set point change and load disturbance. It is also shown that revision of the optimal steady state design variables, such as the total number of stages, may be beneficial for the controllability of the process. The importance of maintaining feed ratio in stoichiometric processes is identified and discussed, as failure to do so may result in failure to maintain both product purities when two point control is considered.

Optimal design and operation of reactive distillation systems based on a superstructure methodology

A novel methodology for the simultaneous optimisation of design and operation of a complex reactive distillation process, considering a number of process alternatives (e.g. pre-/side-reactor, side-stripper, additional columns etc.), is presented. The methodology is based on a superstructure approach, and a detailed cost-based objective function, solved by MINLP optimisation. The methodology is illustrated using different case studies of industrial interest with varying separation and reaction characteristics. For easy separations, in terms of relative volatilities and boiling points order, a single reactive distillation column is found to be optimal for both fast and slower kinetics. However, when the separation is more challenging (i.e. product is a middle-boiler), the design is more complex, even for fast kinetics, and additional processing units, such as a pre-reactor and/or additional distillation columns, are required to meet the product quality specifications. It is found that the design, i.e. the capital cost, mainly depends on the relative boiling point rankings. For operation, chemical reaction equilibrium is the dominant factor. It is demonstrated, however, that the combined effects of separation and reaction must be considered carefully when designing a reactive distillation process. The liquid holdup has an impact on the reaction performance, and proper choice of holdup can lead to a more flexible design, able to mitigate production failure issues even for slower reactions.

Unraveling the influence of residence time distribution on the performance of reactive distillation – Process optimization and experimental validation

This work is the first to explore the influence and illustrate the impact of the stage average residence time distribution (SARTD) in the reaction section on the performance of reactive distillation (RD) systems, providing guidance for the design of the internals and industrial applications of RD processes. The experimental validation and process optimization were performed using the ethyl levulinate production as case study. Kinetics of the esterification reaction between levulinic acid (LA) and ethanol was explored using an ion exchange resin as catalyst, and then fitted by a pseudo-homogeneous model, providing basic data for subsequent RD pilot-scale experiment and process simulations. The RD experiment was successfully carried out for two catalyst-loading conditions (uniform or non-uniform per stage) to illustrate the impact of SARDT on the RD performance. The experimental results show that the conversion of LA increases by 10.85% (percentage points) after catalyst loading redistribution. A genetic algorithm (GA) with global convergence and fast convergence speed was used to realize the optimization of SARTD instead of using arbitrary settings. The objective function to be minimized was the reboiler duty per unit product (RDP). The optimization results show that the conversion of LA increases by 3.06% (percentage points) and RDP decreases by 10.09% if the SARTD is optimally redistributed. Based on this, it can be predicted that the total catalyst-loading can be reduced by reasonable catalyst redistribution in the industrial applications of RD. In addition, a new method for optimal design of SARTD is proposed, paving the way for optimizing other RD processes.

Integrated design and control of reactive distillation processes using the driving force approach

AbstractSuperior controllability of reactive distillation (RD) systems, designed at the maximum driving force (design‐control solution) is demonstrated in this article. Binary or multielement single or double feed RD systems are considered. Reactive phase equilibrium data, needed for driving force analysis and design of the RD system, is generated through an in‐house property prediction tool. Rigorous steady‐state simulation is carried out in ASPEN plus in order to verify that the predefined design targets and dynamics are met. A multiobjective performance function is employed to evaluate the performance of the RD system in terms of energy consumption, sustainability metrics (total CO2 footprint), and control performance. Controllability of the designed system is evaluated using indices like the relative gain array (RGA) and Niederlinski index (NI), to evaluate the degree of loop interaction, as well as through dynamic simulations using proportional‐integral (PI) controllers and model predictive controllers (MPC). The design‐control of the RD systems corresponding to other alternative designs that do not take advantage of the maximum driving force is also investigated. The analysis shows that the RD designs at the maximum driving force exhibit enhanced controllability and lower carbon footprint than the alternative RD designs.

Simultaneous design & control of a reactive distillation system – A parametric optimization & control approach

We present a detailed dynamic model for a reactive distillation system, based on which we develop design-dependent explicit optimal control strategies. A mixed-integer dynamic optimization formulation is then proposed integrating design, control and operational components, the solution of which allows us to derive explicit closed-loop strategies that maintain stable and operable conditions in the presence of process disturbances. The simultaneous approach is illustrated with the design of a methyl tert-butyl ether reactive distillation system example as a part of the developed model library in the RAPID SYNOPSIS project.

Process intensification of reactive distillation using improved RCMs: Acetic acid production

Residue curve maps (RCMs) are useful for the synthesis and analysis of both conventional multicomponent separation and reactive distillation (RD). However, the RCMs do not provide any quantitative performance measure to compare the process alternatives for process intensification. We develop a new velocity vector concept that consists of the speed and direction of the composition change in RCMs for process intensification of reactive distillation. Process intensification in reactive distillation can be thought of as locating multiple process operations in a single continuous column. Optimizing the process intensification in a continuous column can be transformed into finding an optimal path from the initial composition to the target one in RCMs. The optimal path can be determined by minimizing the total processing time required for travelling the path in RCMs. We propose a two-step design method for the RD process consisting of conceptual or structural design based on the new residue curve map and parameter optimization of the process based on rigorous simulation. This new process design method is illustrated by application to a reactive distillation system using an auxiliary reaction for the production of methyl acetate.

Entrainer effect of n-hexanol reactant on coproducing n-butyl and n-hexyl acetate in energy-efficient reactive distillation

This study demonstrates the entrainer effect of a co-reactant alcohol on the feasibility of complete conversion and product recovery in reactive distillation (RD) for concurrently producing n-butyl acetate (BuAc) and n-hexyl acetate (HexAc). Introducing n-hexanol widens heterogeneous liquid regions and more purified common byproduct of water can be removed by liquid-liquid decantation. Thus, the participation of n-hexanol is essential for offering higher purity to water and esters with higher reaction extents achieved. To verify the feasibility of the binary-esterification system, the liquid-liquid equilibrium (LLE) region and liquid composition trajectory are visualized in the quaternary space and it is found that the water purity in the direct sequence of RD is 99.41 mol%, which is higher than that of RD with the BuOH single esterification (99.16 mol%). In terms of energy savings for the binary ester production, the upper reactive dividing wall column is the most effective among the design alternatives and reduces the reboiler duty by 13.35 % compared with the total reboiler duty of two conventional single esterification RD systems.

Nonlinear Optimization Strategies for Process Separations and Process Intensification

AbstractAdvanced nonlinear programming (NLP) strategies based on equation‐oriented (EO) process models are leading to significant improvements in computer‐aided process engineering. The EO paradigm allows the development of large, integrated optimization platforms that expand the scope of continuous optimization tasks in process engineering. In particular, these platforms deploy significantly faster NLP strategies than in commercial simulation tools. Moreover, they exploit exact derivatives and system structure in order to consider much larger and more challenging systems. Finally, they allow the incorporation of much more general models, such as multi‐level optimization and complementarity constraints. For process optimization this allows the treatment of extended models for complex phase equilibrium and process separations. These advances facilitate the optimization of novel integrated systems that arise in process intensification. Several separation case studies are presented that illustrate these optimization concepts and demonstrate their effectiveness for hybrid membrane/distillation separations and reactive distillation systems that typify novel systems in process intensification.

A multi-objective reactive distillation optimization model for Fischer–Tropsch synthesis

In the design of a reactive distillation column, aspects such as column configuration, catalyst loading, tray temperature, and side extraction rates should be well considered. Though preferences in Fischer–Tropsch (FT) synthesis may vary, it is acknowledged that the final product contains a wide range of hydrocarbons including fuel gas, gasoline, diesel, and linear wax. Zhang et al. (2018) previously developed an equation-oriented framework for optimal synthesis of integrated reactive distillation systems for FT processes.Here, we extend the mass, equilibrium, summation, and heat equations to a mathematical program with complementarity constraints to deal with possible dry trays in the non-reactive sections. The purpose of describing disappearing phases is to avoid infeasibilities due to multiple bilinear terms in the model for complicated model structures. The model is implemented by solving initialization steps and a sequence of nonlinear programming problems to determine an optimal structure and operating conditions.Design specifications for multiple products could be set as individual objectives to determine design limits. Moreover, a balance of multiple objectives could be reached by formulating the reactive distillation model as a multi-objective optimization problem. In this work, we employ the augmented ϵ-constraint method. The results show that significant design insights can be gained from the Pareto-optimal front regarding acceptable trade-offs among various objectives.

Simulation and Optimization of Isopropyl Lactate Manufacturing Process

The new chemical processes are investigated in laboratory, usually in batch, with pure reactants, and specific laboratory methods applied for the purification of the products. Scaling-up processes means passing from batch to continuous process, using feed with impurificators, industrial equipment for separation and recirculation or purge for an economic operation with special care for safety and environment. This is why, following a study in laboratory for isopropyl lactate obtaining by transesterification in reactive distillation system, a flowsheet of the industrial process was proposed in this paper. Simulations of the transesterification process were performed. The purpose of these simulations has been to find the optimum solution from energy consumption point of view. Optimum parameters of the reactive distillation were found: the molar ratio isopropanol/methyl lactate R= 1.06, the number of theoretical stages in the distillation zone NTS=2.4 and the reflux ratio RR=2, in a process that produces 1.3 t/h IPL of 96% wt purity.