Reactive Distillation Process Research Articles

Design and multi-objective optimization of reactive pressure-swing distillation process for separating tetrahydrofuran-methanol-water

The low-energy and low-cost process development and design has always been a hot topic and challenge in separating azeotropic systems in the world. In this paper, a novel, energy-saving reactive pressure-swing distillation (RPSD) was, for the first time, designed for separating the ternary mixture of tetrahydrofuran (THF)-methanol–water. In the reactive distillation column, the process of reacting water with ethylene oxide to produce ethylene glycol for the first time was used to separate THF-methanol–water mixture, then the residual mixtures were separated by two pressure-swing distillation columns. Two feasible RPSD separation processes were investigated in terms of thermodynamic modeling and T-xy phase diagram analysis to achieve optimal separation sequence. The two designed separation processes were optimized by a multi-objective genetic algorithm and heat integration to maximize economic benefit. Results demonstrated that, compared to the conventional pressure-swing distillation process, the total annual cost of the designed two heat-integrated processes based on the RPSD-B process were greatly reduced, i.e., 45.9% and 52.2%, respectively. This paper has important guiding significance for the separation and purification of multicomponent azeotropes.

Photocatalytic reactive distillation - A novel process intensification approach for purification of electronic-grade silicon tetrachloride

In order to remove the hydrogen-containing impurities in silicon tetrachloride which are difficult to remove because of the exceptionally low content, a photochlorination reactive distillation process has been proposed to obtain the electronic-grade silicon tetrachloride in this paper. The photochlorination reaction kinetics of C-H compound impurity was studied to verify the photochlorination reactive distillation process. The influence of the key factors in the photochlorination process, such as structure of tubular reactor and the layout of the ultraviolet light, on the content of methylchlorosilane (CH3SiCl3) was investigated in tubular reactor. The industrial production experiments and corresponding simulation of the photochlorination reaction followed by distillation process to conduct deep separation of trace amounts of CH3SiCl3 in silicon tetrachloride raw material were studied to verify the feasibility of process and the accuracy of model. Furthermore, the photochlorination reactive distillation process was proposed to execute further process intensification of purification process of silicon tetrachloride. Finally, after sensitivity analysis and optimization, the photochlorination reactive distillation process achieved 1626.82 $/year TAC savings compared with the photochlorination reaction followed by distillation process.

Process intensification in bio-jet fuel production: Design and control of a catalytic reactive distillation column for oligomerization

Biojet-fuel represents a promising avenue for decreasing CO2 emissions within the aviation industry. Among different biojet-fuel production processes, the Alcohol-to-Jet (ATJ) process stands out as highly promising. Despite its potential, the ATJ process currently faces economic challenges due to low yields and high energy usage. This study introduces a strategy for enhancing the economic feasibility of the ATJ process through process intensification, specifically by incorporating a novel reactive distillation column in the oligomerization stage. This innovative process was evaluated and compared with its conventional counterpart. The total annual cost, eco-indicator 99, and individual risk were chosen as critical parameters for assessing the improvements in cost, environmental impact, and safety brought about by the reactive column. Additionally, control studies were conducted using both Proportional-Integral (PI) and Model Predictive Control (MPC) controllers to determine the feasibility of operating the reactive distillation column. The results suggest that the reactive distillation process offers 20 % cost savings, reduces environmental impact by 50 %, and lowers risk by 22 % when compared to the conventional process. In terms of control strategies, the study found that the catalytic column can be successfully operated using both traditional feedback control and more advanced techniques, such as model predictive control.

An efficient multi-criteria decision making for assessing the optimization of reactive extractive distillation in terms of economy, environment and safety

In order to effectively separate complex azeotropic mixtures, it is crucial to consider economic, environmental, and safety factors during the process design and optimization. This study presents a systematic approach to separate a ternary azeotropic mixture of tetrahydrofuran, methanol, and water by employing multi-objective optimization and multi-criteria decision making. Two energy-efficient configurations, i.e., double-column reactive extractive distillation and reactive-extractive dividing wall column, are proposed by integrating reaction and extractive distillation in a single unit. The developed processes are then optimized using a multi-objective particle swarm optimization algorithm, considering the aforementioned factors. Finally, a multi-criteria decision making technique is applied to rank the Pareto frontier solutions obtained from the optimization process, using a combination of gray relational analysis and entropy weight method. Compared to the base case, the double-column reactive extractive distillation process exhibits a significant reduction in total annual cost (59.39 %) and CO2 emissions (61.75 %). Through comprehensive evaluation, the double-column reactive extractive distillation process is found to be the most effective separation solution among the proposed and existing processes. This systematic approach can be extended to other complex aqueous azeotropic systems for their design, optimization, and decision making.

Dynamic modeling and optimal control of reactive batch distillation: An experimental case study

In the present study, dynamic modeling, optimal operation and control of a reactive batch distillation process is illustrated based on experimental and simulation studies using methyl acetate production case study. An equilibrium stage model, incorporating non-ideal VLE and start-up region of heating, is developed based on data generated on an experimental unit by identifying five input parameters representing uncertainties. The optimal control problem is solved using genetic algorithm, considering the objective function identified on the basis of trend analysis using the developed dynamic model, to find the optimal reflux ratio, heat input to the reboiler, and mole ratio of methanol to acetic acid in the initial reaction mixture. Open-loop and closed-loop implementations clearly illustrate the improved performance with respect to the quantity of methyl acetate in the distillate product with a reasonably high conversion and product purity within reasonably short batch duration, illustrating the successful optimal control implementation experimentally.

Research progress in reactive distillation

As a special distillation process, reactive distillation technology has been widely used in the petrochemical field due to its outstanding advantages such as high efficiency and energy saving. It has been paid more and more attention from researchers in the field of chemical process enhancement since the 1920s. With the progress of social development level, resource conservation and environmental friendliness have become the general trend. In order to pursue the maximization of energy utilization and higher economic benefits, scientific researchers have developed a variety of new reactive distillation processes suitable for various occasions considering the advantages and limitations of traditional reactive distillation technology. The biggest difference from traditional reactive distillation is that the new processes have the characteristics of saving equipment investment, low reaction energy consumption, improving mass transfer, heat transfer efficiency and energy utilization rate. In order to fully understand and apply the technology, this paper describes the process flow of traditional and new reactive distillation technologies in detail, and focuses on analyzing and summarizing the latest developments in the industrial application of reactive distillation technologies in various fields. Finally, it points out that reactive distillation technologies issues that need attention and future development directions.

Understanding the Quantitative Matching Principle of Reaction and Distillation for the Reactive Distillation Process of Cyclohexyl Acetate Synthesis

The matching problem of reaction and separation in reactive distillation (RD) is an urgent problem, and the main reason for little relevant research is that there is no suitable RD for experiments. To understand the matching principle, this work designed KRD001#SCPI and HY@SiC catalytic packings, which tend to different coupling ratios of reaction and separation. The pilot-scale RD experiments and corresponding simulation of cyclohexyl acetate production were studied to verify matching coupling of different reaction RD requirements. Upon verification of this, conventional RD processes were considered from economic, environmental, and energy perspectives, and a new matching form of RD was further proposed based on uneven product distribution. For a ternary reaction system where product was heavy, product concentration moved downward, catalytic packings with high reaction rates were needed at lower reaction sections to avoid a reverse reaction, and those with high separation efficiency are needed at the upper section to separate product and reactants better.

Effect of ethanol on selective oligomerization of isobutene and the simulation of reactive distillation process

AbstractThis paper investigates the selective oligomerization of isobutene in mixed C4 using ethanol as an inhibitor. The effects of ethanol/isobutene, reaction temperature, and reaction space velocity on isobutene oligomerization were examined using two β molecular sieve catalysts. The results indicate that the optimal reaction conditions, at the same calcination temperature, are as follows: The mass ratio of ethanol to isobutylene is 20%, the reaction pressure is 1 MPa, the reaction temperature is 65°C, the reaction space velocity is 2 h−1, the dimerization product C8 has fewer types, and the selectivity can reach over 15%. After adding ethanol, there is a significant inhibitory effect on n‐butene. Furthermore, we used reactive distillation technology to simulate isobutene oligomerization. By optimizing the sensitivity of the tower's operating conditions, we obtained the optimal operational parameters of the tower. Under optimal operating conditions, the conversion rate of isobutene can reach over 80%. The mass fraction of C8 in the oligomerization product accounted for 57.44%, C12 accounted for 8.29%, and ETBE accounted for 34.23%. The reactive distillation technology can improve product selectivity.

Determining catalyst loading in reactive distillation column

The widespread industrial application of reactive distillation technology is inseparable from the development of catalytic packing. However, systematic research on the heterogeneous catalyst loading in the reactive distillation column is vacant, and existing studies about catalyst loading on each stage and their distribution ignore the physical structure of the reactive distillation column. In this work, Modular Catalytic Structured Packing combining catalyst bags and structured packing sheets is applied in the modeling and optimization of reactive distillation processes. The catalyst loading on each stage is obtained from three parameters: the catalyst volume fraction of catalytic packing, the catalytic distillation column diameter, and the height of the theoretical stage. Using the effective diffusivity method, a simplified non-equilibrium stage model is chosen to simulate the reactive distillation process, and the bubble-point method for solving the non-equilibrium stage model’s equation system is introduced. The genetic algorithm optimizes both catalyst volume fraction and the number of theoretical stages in the reactive section. Case studies of methyl acetate esterification and ethyl tert-butyl ether (ETBE) synthesis show that greater theoretical stages of the reactive section and enough reflux ratio will reduce the demand of catalysts. Redistribution of catalyst is implemented by dividing the reactive section into several. The non-uniform distribution of catalyst will reduce both energy consumption and catalyst amount for the methyl acetate system, but insignificant for ETBE synthesis, due to different interactions of reaction and separation.

Pilot-scale validation and novel design of reactive distillation with HY@SiC foam catalytic packing for cyclohexyl acetate production

For reactive distillation (RD) process limited by the separation efficiency of gas–liquid mass transfer, if the physical size of the alternating operation in reaction and separation can be further reduced, it would greatly promote the efficiency of the RD process. For this purpose, a structured HY@SiC catalytic packing was developed in which the gas–liquid mass transfer separation process and the catalytic reaction occurred simultaneously on its surface. The HY@SiC catalytic packing was used in a pilot-scale column for experimental study on production of cyclohexyl acetate (CA) by RD to verify the performance of the catalytic packing for the first time. Furthermore, a RD model based on the HY@SiC catalytic packing was established based on the reaction kinetics of HY zeolite catalyst obtained in this work. Finally, a novel RD process with double recycle stream for CA production was proposed, which will be optimized design with TAC minimize as the optimization objective based on sequential iterative algorithm.

Unraveling the matching of reaction and separation for reactive distillation process based on reaction equilibrium degree (RED)

The multiplicity of matching between reaction and separation for reactive distillation (RD) process leads to a more complex design of RD column, however, the exploration of coupling problem between reaction and separation for the design of reaction section in the RD column is still a blank of RD research. In this article, a design framework for the reaction section in the RD column based on the reaction equilibrium degree (RED) is demonstrated. The interaction relationship between residence degree and separation efficiency of reaction section is established by means of spline interpolation method. Herein, the synthesis of malonic acid (MA) from dimethyl malonate (DM) hydrolysis, as a case study, was investigated to obtain coupling regularities of reaction and separation for specified design targets and further design the reaction section of RD column from principle. The results validated the effectiveness of the proposed framework and provided theoretical guidance for challenging RD process.

Investigation of sustainable reactive distillation process to produce malonic acid from dimethyl malonate

The new energy battery is currently a hot research topic, leading to an increase in the demand for malonic acid (MA) as a raw material. The objective of the present work is to find a potential reactive distillation (RD) process to solve the problem of low conversion and high energy consumption in hydrolytic system. In the meantime, the RD technology still faces the problem of how to distribute water in the RD column. Aiming at the problem, four different RD processes are proposed: RD combined water separation process (RDWS), RD combined with MA concentration process (RDMC), RD combined methanol separation process (RDMS), and single RD process (SRD). Beforehand, reaction kinetic of dimethyl malonate (DM) hydrolysis was investigated using the ion exchange resin catalysts, and the developed RD model was verified via pilot-scale RD experiments. Finally, the proposed RD process is analyzed from the aspects of economic and environmental and compared with the traditional reaction + distillation (R + D) process. Consequently, the proposed SRD process is a better economy-saving and environment-friendly technology, and has certain directive significance for the industrial production of MA.

Novel Reactive Distillation Process for Cyclohexyl Acetate Production: Design, Optimization, and Control.

A side-reactor column (SRC) configuration, comprising a vacuum column coupled with atmospheric side reactors, is proposed to overcome the thermodynamic restriction in the esterification of cyclohexene with acetic acid to produce cyclohexyl acetate. Meantime, this configuration can avoid the utilization of the high-pressure steam and provide enough zone for catalyst loading. In order to obtain the minimum total annual cost (TAC), the process is optimized by a mixed-integer nonlinear programming optimization method based on the improved bat algorithm. The results indicate that the optimized SRC configuration saves about 44.81% of the TAC compared to the reactive distillation process. Based on the optimized SRC process, dynamic control is carried out. The dual-point temperature and temperature-composition control structures are proposed to reject throughput and feed composition disturbances. The dynamic performances demonstrate that the temperature-composition control structure is better in maintaining product purity.

Process synthesis and 4E evaluation of hybrid reactive distillation processes for the ethanol and tert-butanol recovery from wastewater

Aiming at achieving the high-purity recovery of ethanol (EtOH) and tert-butanol (TBA) from industrial waste with low carbon emission, the processes intensified by hybrid reactive distillation combined with pressure-swing distillation (PSD) and extractive distillation (ED) are proposed in this work. The optimum procedure of the sequential iterative method is applied to select an optimal pressure for these hybrid reactive distillation processes. From the economic and environmental impact perspective, the results indicated that the reactive-extractive-/pressure-swing hybrid distillation has significant economic and environmental advantages. The REPDC-REPC (reactive-extractive-/pressure-swing hybrid distillation) process is the most potential and competitive, saving 56.47% TAC and reducing 69.23% CO2 emissions, and has 67.51% thermodynamic efficiency, minor exergy destruction, and most enormous total exergy efficiency. Meanwhile, the work also demonstrates that the operating pressure of the column plays an important role, which positively affects the energy saving of the recovery process.

Simulation, optimization and intensification of the process for co-production of ethyl acetate and amyl acetate by reactive distillation

A new energy-saving process is proposed here for the co-production of ethyl acetate (EtAC) and amyl acetate (AmAC) by reactive distillation(RD). The thermodynamic feasibility of the ethyl acetate/amyl acetate system was determined based on its physical properties. As amyl acetate has a higher water-carrying capacity than ethyl acetate, water can be removed from the reaction system in the form of azeotrope to improve the conversion rate, and amyl acetate can be easily separated from the water. The reactive distillation process of ethyl acetate-amal acetate co-production with different alcohol feed ratios was studied in this paper. When the amyl alcohol to ethanol feed mole ratio was set at 2, the process performed better in terms of economy and energy consumption; it also had a less environmental impact at the same time. The reactive distillation process with intermediate condenser and intermediate reboiler (RD-IC-IR) process and the reactive dividing-wall column (RDWC) process are established based on process optimization. Compared with the RD process, the TAC and CO2 emissions for the RD-IC-IR process reduced by 21.92 % and 28.27 %, respectively, and the thermodynamic efficiency improved 38.86 %; the TAC and CO2 emissions for the RDWC process reduced by 36.11 % and 42.49 %, respectively, and the thermodynamic efficiency improved 74.45 %.

Ternary liquid–liquid equilibria for 2-phenylethyl acetate + 2-phenylethanol + water and 2-phenylethyl acetate + acetic acid + water at atmospheric pressure

2-Phenylethyl acetate can normally be produced by the esterification of 2-phenylethanol with acetic acid via a reactive distillation process. The multiphase coexistence behavior is a component of esterification and is important for the design of the reactive distillation process. In this report, the ternary liquid–liquid equilibrium (LLE) results of 2-phenylethyl acetate + 2-phenylethanol + water and 2-phenylethyl acetate + acetic acid + water at 303.15, 323.15, and 343.15 K under atmospheric pressure are presented. The ternary LLE data regression results were obtained using NRTL and UNIQUAC models with an absolute average deviation (AAD%) value of less than 2 %. The determined binary interaction parameters were verified by the GUI-MATLAB tool. Furthermore, the results predicted by the UNIFAC model for the investigated ternary LLE systems are acceptable.

Compact process for cumene manufacture: Synthesis, design and control

A compact single-unit process is developed for continuous cumene manufacture via the alkylation of benzene with propylene. The design combines reactive distillation (RD) and dividing-wall separation in a single column. In terms of the TAC, it is significantly cheaper (42%) than the conventional “reaction followed by separation process” and only slightly more expensive than the RD process. The controllability of the developed compact design is confirmed via rigorous dynamic simulations that demonstrate effective process operation for large production rate and feed composition changes using a simple decentralized temperature inferential control system. The developed compact design is especially suitable for capacity expansion in space-constrained cumene manufacturing facilities.

Simulation and design of a heat-integrated double-effect reactive distillation process for propylene glycol methyl ether production

A double-effect reactive distillation (DERD) process was proposed for the production of propylene glycol methyl ether from propylene oxide and methanol to overcome the shortcoming of low selectivity and high-energy consumption in the tubular plug-flow reactor. A single-column reactive distillation (RD) process was conducted under optimized operating conditions based on sensitivity analysis as a reference. The results demonstrated that the proposed DERD process is able to achieve more than 95% selectivity of the desired product. After that, a design approach of the DERD process with an objective of the minimum operating cost was proposed to achieve further energy savings in the RD process. The proposed DERD configuration can provide a large energy-savings by totally utilization of the overhead vapor steam in the high-pressure RD column. A comparison of the single-column RD process revealed that the proposed DERD process can reduce the operating cost and the total annual cost of 25.3% and 30.7%, respectively, even though the total capital cost of DERD process is larger than that of the RD process.

Catalyst screening and reaction kinetics of liquid phase DME synthesis under reactive distillation conditions

While conventional DME synthesis is exclusively operated in a gas phase heterogenous reaction system, reactive distillation unveils the potential for a process intensified, compact and efficient DME production. In a catalyst screening, various solid acid catalysts were examined in the liquid phase dehydration of methanol to DME. Ion exchange resins proofed to be more active than zeolites and more stable than perfluorsulfonic acids. Reaction kinetics on the two most promising commercial ion exchange resins, the oversulfonated resin Amberlyst® 36 and the chlorinated resin TreverlystCAT400 were studied in a profile reactor setup over the full range of water fractions relevant for DME reactive distillation processes. CAT 400 was found to show a lower activity than Amberlyst® 36 at identical temperatures, however, due to the higher thermal stability, significantly higher conversions could be achieved. In the kinetic fitting, it was found that the conventional Eley-Rideal and Langmuir-Hinshelwood mechanisms are not capable to describe the experimental data over the wide range of water fractions due to the highly non-linear inhibition by water resulting from the distinct swelling properties of ion exchange resins. To account for this behavior, a new kind of kinetic model with dedicated water inhibition term is introduced and discussed. This model allows the precise description of reaction kinetics over the whole studied operating range for both investigated catalysts and reflects the temperature-dependent inhibition by water. The new kinetic model is an essential building block for the design of industrial scale DME reactive distillation processes.

A novel economical reactive distillation with two reaction sections for separating isobutene in C4 to save energy and reduce CO2 emissions

In this study, the conventional reactive distillation (RD) process and the reactive distillation with two reaction sections (RD-TRS) are proposed to separate isobutene from C4. The arrangement of RD-TRS strengthens reaction and distillation processes, and reduces the operation cost and capital investment. Because the temperature between the top and bottom of the RD-TRS column is less than 15 ℃, the vapor recompression heat pump technology can be applied. Hence, the heat pump reactive distillation with two reaction sections (HRD-TRS) is proposed. Finally, the three processes are optimized with the minimum total annual cost (TAC) as the evaluation indicator. The results show that, compared with RD, CO2 emissions of RD-TRS and HRD-TRS processes decreases by 16% and 21%, respectively; TAC of RD-TRS and HRD-TRS decreases by 19.7% and 52.7%, respectively; TEC of RD-TRS and HRD-TRS decreases by 21.6% and 75.5%, respectively. The thermodynamic efficiency increases from 18% for RD, to 19% for RD-TRS, and 22% for HRD-TRS.