Conventional Reactive Distillation Research Articles

Partial heat-integrated reactive distillation process for producing n-propyl acetate using a heat exchanger network

ABSTRACT In this work, a partial heat-integrated reactive distillation process was studied to yield n-propyl acetate. To optimize the operating parameters of two distinct processes, the sequential iteration optimization method was employed. The heat exchanger network (HEN) is an effective approach for the heat-integrated design of a distillation process. Compared with the conventional reactive distillation process, the total annual cost, CO2 emissions and total energy consumption of the partial heat-integrated reactive distillation process decreased by 20.7%, 31.1%, and 32.2%, respectively. The thermodynamic efficiencies of reactive distillation process and partial heat-integrated reactive distillation process were 4.33% and 9.86%, respectively. The significance of this paper is crucial in guiding the process of partial heat-integrated reactive distillation for the production of n-propyl acetate.

A novel solar reactive distillation based production of algal biodiesel: Retrofitting, carbon cost and process economics

In this contribution, solar power driven reactive distillation based process is developed for the production of algal biodiesel. For industrial scale operation, the conventional reactive distillation (cRD) is designed to retrofit with a parabolic trough collector (PTC) that yields cRD-PTC based scheme. To serve the same purpose, we have subsequently proposed a solar reactive distillation based configuration. The optimal design and operating conditions of both processes are determined with two conflicting objectives: minimising the total annual cost (TAC) and maximising the purity of biodiesel. For this, the optimisation is performed by the technique for order of preference by similarity to ideal solution embedded non-dominated sorting genetic algorithm-II. Further, we evaluate those process units in terms of the emission trading system based carbon pricing (ETS-CP) and social cost of carbon (SCC) considering the availability of solar energy during day time only. The attractiveness of the proposed solar reactive distillation based process lies in its total annual cost savings of 9.92% (ETS-CP) and 19.06% (SCC), whereas they are 6.67% (ETS-CP) and 16.14% (SCC), respectively for the conventional reactive distillation coupled with parabolic trough collector (cRD-PTC) process. It is further investigated that the total annual cost savings comes down when the proposed configurations are operated with solar (2000 working hours/year) and thermal energy (6000 working hours/year) throughout the year. Finally, the economic feasibility of the biodiesel production processes is studied with the usage of solar heat for the entire operating time.

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.

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.

Green solvent production of ethyl lactate via process intensification

BackgroundEthyl lactate is a green solvent with many applications in the chemical industry. Several studies of ethyl lactate production can be found in the available literature, including conventional reactive distillation designs, but the green solvent design is not clearly defined in the open literature. Also, several thermodynamic models must be verified as it is important for predicting the binary interaction parameter. Moreover, process design arrangements are crucial for the process intensification proposed. MethodsHerein, the proposed green solvent designs are figured out with the various process design arrangements, including conventional design and three designs of reactive distillation column (RDC), named Design-1 to Design-3. The binary interaction parameters from three thermodynamic models (UNIQUAC, UNIFAC, NRTL) are validated. The process simulation and economic evaluation in terms of the total capital cost (TCC), total operating cost (TOC), as well as total annual cost (TAC) are analyzed using Aspen Plus. Significant findingsThe thermodynamic model assessment found that the UNIFAC is applicable for RDC system, but NRTL is preferred for the extractive distillation system. RDC using side stream combined with direct separation (Design-1) is strongly recommended because the TCC and TOC reduce to 57.3% and 17.5%, respectively. The RDC using a side stream combined with extractive distillation separation (Design-2) has the lowest energy consumption (saved 26.3%) and less in TOC (saved 17.5%). Finally, the lowest TAC is Design-1 (saved 40.2%), followed by Design-2 (saved 30.9%) and Design-3 (saved 17.8%), as compared to conventional design.

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.

Dynamic controllability strategy of reactive-extractive dividing wall column for the separation of water-containing ternary azeotropic mixture

The reactive-extractive dividing wall column (REDWC), which combines conventional reactive distillation, extractive distillation, and dividing wall column, is a highly integrated process with a compact physical space and strong interrelations between variables. It is challenging to design robust control strategies for the REDWC process. However, there are no investigations reported on the control of REDWC. In this study, through analyzing open-loop controllability indicators of the steady-state process, the basic control structure (CS1) is constructed. Subsequently, four proportional-integral control schemes are further established on the CS1: the proportional control structure (CS2), the internal composition control structure (CS3), the feedforward control structure (CS4), and the three-point temperature control structure (CS5) with feedforward loops. The dynamic performance tests are conducted with ± 10 % feed flow rate and ± 10 % feed composition disturbances. The qualitative research demonstrates that the CS5 offers the best dynamic performance in terms of settling time, steady-state deviations, and overshoots without the use of expensive composition controllers. With the integral absolute error (IAE) as an evaluation criterion, it is quantitatively demonstrated that the CS5 has the best robustness and should be the preferred control scheme. Another key finding shows that the vapor split ratio and the stoichiometric ratio of the reactants are two crucial degrees of freedom to guarantee product quality in the REDWC. The major contributions of this work are to provide a meaningful reference for the control of the REDWC and even more complicated distillation.

Optimization and model-based control of sustainable ethyl-methyl carbonate and diethyl carbonate synthesis through reactive distillation

As excellent solvents of lithum-ion electrolyte, ethyl-methyl carbonate (EMC) and diethyl carbonate (DEC) are synthesized through transesterification of dimethly carbonate (DMC) and ethanol. Process intensification, optimization and the corresponding control scheme of the synthesized process are essential when sustainability is becoming a necessity. In the present work, the intensified flowsheet for EMC and DEC production process was firstly proposed and optimized with conventional reactive distillation (RD) and reactive dividing wall column (RDWC), respectively. Compared with RD process, RDWC could achieve 25.3% and 8.2% total annualized cost reduction for EMC and DEC production process, respectively. And carbon dioxide emission could be decreased by 29.4% and 11.7% by further integrating RD and separation column into RDWC arrangement for DEC and EMC production. Then multi-loop PI control schemes were developed as benchmark and linear model predictive controller was designed to handle the persistent feed disturbance. The superiorities of model-based controllers for the strongly interactive and coupled system are demonstrated by the dynamic response comparisons in terms of settling time, overshoot and integral of squared error (ISE), especially for the controlled variables with poor control performance under conventional multi-loop PI control structure. To summarize, the comprehensive control performance index-ISE with MPC is reduced by 55.9%–99.1%, as compared to those under PI control strategy.

Life cycle and techno-economic assessment of ethyl lactate production via reactive distillation with structured catalytic packing

A novel ZSM-5@SiC structured catalytic packing (ZSM-5@SiC SCP) was recently proposed to combine catalysis and separation functionality in one unit for reactive distillation (RD) towards the synthesis of green solvent ethyl lactate (EL). This work conducts life cycle assessment (LCA) and economic analysis for the RD process to identify relevant hot spots and suggest further development. Based on the cradle-to-gate LCA, the major environmental hot spots of the proposed RD process based on SCP are identified as in the section of raw materials extraction and RD. Compared to the petrochemical counterparts, bio-derived lactic acid and ethanol show the advantage to reduce carbon emission and resource depletion, but having significant impacts on aggravate stratospheric ozone depletion and land use especially. LCA results also show that preparation ZSM-5@SiC SCP creates environmental impacts due to the usage of electricity and relevant raw materials. Comparative LCA and economic analysis were conducted for the RD processes using ZSM-5@SiC SCP and seepage catalytic packing internal (SCPI), respectively, and a conventional process with separated reaction and separation unit operations. The findings suggest that compared to the conventional process RD processes can reduce greenhouse gas emissions and total annual cost (TAC) due to process intensification. The process employing ZSM-5@SiC SCP incurs a higher TAC than that based on SCPI (with resin catalysts), which is due to its comparatively low catalytic activity, requiring more ZSM-5@SiC SCP and higher column to achieve the production target.

Optimizing algal biodiesel production from a novel reactive distillation based unit: Reducing CO2 emission and cost

The algal biodiesel as a potential alternative to conventional petroleum fuel and first-generation biofuel has been explored extensively but the efficacy of its production in a reactive distillation (RD) unit is yet to be analyzed thoroughly. In this contribution, the performance of the RD column is enhanced by process intensification and optimization. A multi-objective optimization (MOO) strategy is framed for optimizing the RD column for three conflicting objectives. For this MOO, the elitist non-dominated sorting genetic algorithm (NSGA-II) is employed. From the obtained Pareto-optimal front, one optimal solution for RD design is selected using the technique for order of preference by similarity to ideal solution (TOPSIS) with entropy information for weighting of objectives. To further reduce the environmental impact and optimal usage of internal energy, a novel thermally coupled reactive distillation (TCRD) column is suggested. Finally, a biodiesel production unit is developed by integrating a decanter with the TCRD column, to produce biodiesel product of 99.45 wt.% purity. Performance of the TCRD column is better than the conventional RD column, in terms of CO2 emission reduction (14.49%) and total annual cost savings (3.72%). Energetic sustainability of the proposed biodiesel process is determined by net energy ratio (NER) of 1.79, net energy value (NEV) of 18.2 and net renewable energy value (NREV) of 41.4 MJ/kg.

Simulation, optimization and control of the process of synthesis of ethyl propionate by reactive distillation

This paper proposes the continuous production process of ethyl propionate by reactive distillation and the energy-saving heat pump reactive distillation process. The process is optimized with the goal of minimizing the total annual cost (TAC). In response to energy saving and emission reduction, the cost of CO2 emissions is considered in TAC. The results show that, compared with the conventional reactive distillation process, the CO2 emission cost of the heat pump reactive distillation process is reduced by 59.39%, and TAC is reduced by 17.09%, which shows that the heat pump reactive distillation process is more economical and more environmentally friendly. The dynamic control research of conventional reactive distillation and heat pump reactive distillation is carried out. The temperature control schemes CS1 and CS2 are respectively proposed, and the dynamic response of CS1 and CS2 under external disturbances is analyzed. The test results show that both CS1 and CS2 can simply and effectively control product quality, indicating that the heat pump reactive distillation process also has practical advantages in terms of automatic control. The above conclusions provide the basis for the design and implementation of the continuous production of ethyl propionate, as well as a reference for solving similar problems.

Novel heat pump reactive distillation and dividing-wall column reactive distillation processes for synthesizing isopropyl acetate to save TAC and reduce CO2 emissions

Focusing primarily on the issue of high energy consumption in isopropyl acetate (IPAC) production, a heat pump reactive distillation (RD-HP) process and a dividing-wall column reactive distillation (RD-DWC) process were proposed. Chemical software Aspen Plus (version 10) was used to investigate the steady state simulations. In this work, RD-HP and RD-DWC processes were compared with conventional reactive distillation (CRD) in energy saving, economic, and environmental performance. In addition, TAC was used as the objective function, and the sequential iterative procedure was proposed for the design of three processes, and the optimal parameters were obtained. The results manifested that the IPAC product of three processes all reached the purity index (mole fraction 98.20%). Compared with CRD, the TAC of RD-HP and RD-DWC were reduced by 13.46% and 21.31%, CO2 emissions were reduced by 13.25% and 20.17%, respectively. The thermodynamic efficiency of three processes are 7.69%, 9.02%, and 10.57%, respectively.

A Heat-Integrated Reactive Distillation Process for Methyl Lactate Hydrolysis

Lactic acid is predominantly produced through microbial fermentation of renewable feedstocks. However, direct separation and purification of lactic acid from the fermentation broth is difficult. A two-step process involving (1) esterification of raw lactic acid with methanol to produce methyl lactate, and (2) hydrolysis of the methyl lactate to produce high-purity lactic acid, is commonly used. The hydrolysis step is typically carried out in a reactive distillation (RD) column to overcome equilibrium limitations by continuous removal of the product(s). However, the conventional RD process is highly energy intensive and has relatively low thermodynamic efficiency. We show that the energy requirement of the RD column can be significantly reduced by implementing external heat integration via a heat pump. Specifically, we show that a vapor-recompression-based reactive distillation (VRC-RD) column offers up to 63.4% energy savings relative to the conventional RD column. The energy savings are further increased to 64.9% in a pre-compressor split (PCS-VRC-RD) configuration. This reduction in the total utilities requirement results in an increase in thermodynamic efficiency from 21.4% for the conventional RD column to 38.7% for the VRC-RD column and to 40.3% for the PCS-VRC-RD column. For a payback period of 5 years, these energy savings respectively correspond to 32.0% and 33.8% reduction in the total annual cost (TAC) relative to the conventional RD column.

Inter‐integration reactive distillation with vapor permeation for ethyl levulinate production: Equipment development and experimental validating

AbstractEthyl levulinate, one of the main derivatives of levulinic acid (LA), is of significant potential as platform chemicals for bio‐based materials. The esterification of LA was generally carried out in a conventional batch reactor or in a conventional reactive distillation column. However, traditional methods are hard to deal with equilibrium limited reactions and azeotropic issues. Therefore, the inter‐integration reactive distillation with vapor permeation (R‐VP‐D) process, which integrated reaction, vapor permeation, and distillation into one single unit, is proposed in this paper and validated in the pilot‐scale experiments. A comparative study is made between a pilot‐scale RD column with and without VP module. Owing to the water‐selective VP membrane and the ingenious design of related apparatuses, the R‐VP‐D process reveal a superiority in LA conversion of 21.9% maximum higher than RD without VP process and removing of product water about 53.6% from VP module, which indicates its promising industrial application in process intensification field.

Heat-pump-assisted reactive distillation for direct hydration of cyclohexene to cyclohexanol: a sustainable alternative

As an important raw material to produce many useful chemicals, cyclohexanol production attracts much attention to obtain high purity product, leading to high energy consumption. Traditional technologies include three routes: oxidation of cyclohexane, hydrogenation of phenol and direct hydration of cyclohexene. Without the risk of explosion and having a low price of raw material, the direct hydration of the cyclohexene route is selected in this paper. Four processes with different phase-refluxed or with/without a stripper configuration for the direct hydration of cyclohexene are investigated, including aqueous-phase-refluxed conventional reactive distillation (ACRD), an organic-phase-refluxed conventional reactive distillation (OCRD), an aqueous-phase-refluxed reactive distillation with a stripper (ARDS), and an Organic-phase-refluxed reactive distillation with a stripper (ORDS). The results show that the conventional reactive distillation (ACRD and OCRD) has a relatively low capital cost but has high operating costs due to high energy consumption, while the ARDS and ORDS show better performance than the OCRD and ACRD, but still have considerably high energy consumption. The ORDS shows better performance due to a slightly higher conversion of cyclohexene to cyclohexanol and the potential to achieve the better performance in terms of energy and economic considerations. Integration of a novel confirmation with heat pump assisted reactive distillation (HPRD) is investigated to further improve the energy efficiency and thereby reduce CO2 emission. The results show that the HPRD process realizes a significant energy saving of 58% and achieves 62% and 24% reductions in specific CO2 emission and total annualized cost, respectively, compared to ORDS, demonstrating high feasibility and environmental sustainability.

Techno-Economic Analysis of Alternative Designs for Low-pH Lactic Acid Production

Lactic acid production is highly affected by the fermentation pH. The need for neutralizing agents and the salts produced during fermentation have a significant impact on the overall process performance. Changing the neutralizing agent and allowing lower pH fermentation can improve the process profitability. This work investigates the impact of fermentation parameters and evaluates the process economics of alternative downstream processing designs to produce lactic acid. The results show that low-pH fermentation (pH = 3.86) was profitable (internal rate of return, IRR > 10%) at a fermentation yield of 0.97 g/g sucrose. Decomposing the salt subproduct to reduce the environmental burden associated with gypsum disposal has a significant impact on the economic performance, resulting in a lower IRR than the other designs. Although the salt decomposition process has a high energy demand, it is compensated by the savings obtained in the downstream processing, thus resulting in a similar overall energy demand when compared to conventional reactive distillation. A novel process configuration with ammonium sulfate subproduct shows potential for 3 p.p. higher IRR and up to 30% lower fuel demand in comparison with the conventional process. Therefore, alternative downstream processes could drive low-pH fermentation to outperform the conventional process without any neutralizing agent.

Improved design and optimization of synthetic n-Butyl acetate process to save energy

ABSTRACT Focusing primarily on the issues of low purity and high energy consumption in n-Butyl acetate production, pressure swing reactive distillation (RD-PS) and a new process combining conventional reactive distillation and pressure swing thermal coupling (RD-PSTC) were proposed. Chemical software Aspen Plus (version 10) was used to investigate the steady state simulations of both processes. Furthermore, the energy consumption and purity of the product were utilized as the objective functions in order to achieve optimal total annual cost (TAC). Compared with RD-PS process, the obtained results showed that RD-PSTC process could save 19.86% TAC, 73.97% CO2 emissions, and 28.84% total energy consumption.

Multi-Objective Assessment of Heat Pump-Assisted Ethyl Acetate Production

Multi-objective (energy–economic–safety) assessment of ethyl acetate production involving a heat pump is presented in this paper. The heat pump is designed to intensify ethyl acetate separation and to reduce the total operating cost. Two ethyl acetate production pathways are upgraded using a heat pump, conventional process and reactive distillation column with a separation unit. Detailed process models including the heat pump environment have been compiled and optimized in the Aspen Plus software. Both benefits and drawbacks of including the heat pump in the processes are evaluated using three different points of view: process energy, economics, and safety. As a result, using a heat pump is highly recommended in both conventional process and reactive distillation column with a separation unit. As a higher level of process integration is achieved using a heat pump, economic aspects are improved; however, safety aspects deteriorate. The final decision on the suitability of using a heat pump depends on whether it is proposed for an existing plant, or a completely new plant is designed. In a new plant, the concept of a thermally coupled process (reactive distillation column with a stripper column) has been proven to be the most promising.

Nano-catalytic heterogeneous reactive distillation for algal biodiesel production: Multi-objective optimization and heat integration

This work proposes a novel reactive distillation (RD) column for the production of algal biodiesel by the use of a heterogeneous nano-catalyst, Ca(OCH3)2. The elitist non-dominated sorting genetic algorithm (NSGA-II) is employed to optimize the design of this RD column to maximize biodiesel purity while minimizing total annual cost and CO2 emissions. The optimal point is recommended by a Pareto ranking method, namely, technique for order of preference by similarity to ideal solution (TOPSIS) with entropy information for the weighting of objectives. To improve biodiesel purity, a decanter is proposed to couple with the RD column at the bottom. Subsequently, performance of the optimal RD column is further improved by retrofitting it with the vapor recompression arrangement. In this proposed intensified configuration, a reactive stage is thermally integrated with the reboiler to constitute a side vapor recompressed RD (SVRRD) column. Finally, a comparative study is performed to quantify the performance improvement of the proposed SVRRD column over the conventional RD column. It is found that there is a 34.6% reduction in CO2 emissions with a payback period of 4.54 years for the vapor recompressor. Hence, the proposed SVRRD is attractive with better performance in terms of energetic, environmental and economic perspectives.

Optimisation of semi-batch reactive distillation column for the synthesis of methyl palmitate

Synthesis of methyl palmitate (MP) has not been considered in the past using a reactive distillation process (continuous or batch) due to the challenge of keeping the reactants palmitic acid (PA) and methanol (MeOH) together in the reactive zone. MeOH, being the lightest in the reaction mixture, travels up the distillation column as distillation proceeds and will be removed from the system via the distillate in a conventional batch reactive distillation (CBRD) column and thus will limit the conversion of PA. Therefore, in this work semi-batch reactive distillation (SBRD) column is proposed where additional methanol will be fed at the bottom of the column in a continuous mode allowing the chemical reaction to continue. However, as water (H2O) is one of the reaction products and is the second lightest component in the mixture, it will travel up the column next and will be removed in the distillate tank. Also due to wide difference in the boiling points of the reaction products and due to diminishing amount of water in the reboiler, the backward reaction will not be a dominating factor and therefore ignored in this work. With this backdrop, optimal performance of the SBRD column is evaluated in terms of conversion of PA to MP and energy consumption via minimization of the operating batch time for a wide range on MP purity.