Conventional Distillation Column Research Articles

Design and optimization of reaction-separation-recycle systems using a pseudo-transient continuation model

The reaction-separation-recycle (RSR) systems are an important part of chemical processes. Due to the interaction between reaction and separation sections, the behavior of RSR processes becomes highly complex and non-linear, posing different challenges for their design and optimization. The purpose of this study is to design and optimize RSR processes for irreversible liquid phase reaction systems using the pseudo-transient continuation (PTC) approach within an equation-oriented programing environment. This approach was applied to investigate one binary system and four ternary systems. The differential-algebraic models of the proposed process flowsheets were solved until the steady-state conditions were reached. The tray bypass efficiency method was incorporated into the PTC to circumvent the need for discrete optimization. The results demonstrated that in those cases where the product was heavier than the reactants, employing a stripping column was more economical than using a conventional distillation column for both the binary and ternary systems. In the ternary systems with two recycle streams, when the product was the intermediate component in terms of boiling point, the utilization of a divided-wall distillation column (DWC) resulted in a total annual cost saving of 35 % and 41 % compared to direct and indirect separation methods, respectively.

An alternative to methanol recovery from ternary mixture: Replacing extractive with reactive distillation for maximizing economical potential and resource recovery

This paper investigates the recovery of methanol from the propylene oxide (PO)/methanol/water mixture using reactive distillation (RD). The mixture presents a challenge due to the azeotrope formation between PO and methanol. To overcome this challenge, three RD scenarios, designated as Case 1, Case 2, and Case 3, are proposed. The primary principle underlying these cases is leveraging a reaction between PO and water, resulting in the production of propylene glycol (PG). This reaction consumes PO and thus eliminates the PO-methanol azeotrope, and reduces reboiler duty via the release of reaction heat. Case 1 utilizes one reactive distillation column (RDC) and one conventional distillation column (CDC) to recover methanol while reducing a quarter of the water content via the PO-water reaction. High purity methanol is obtained in the RDC distillate, while high purity PG is collected at the bottom of the CDC. Likewise, Case 2 follows the same approach as Case 1, with an additional PO stream to halve the water content. On the other hand, Case 3 employs a single RDC with a greater additional PO stream to react with all water content in the mixture, yielding high purity methanol at the distillate and PG at the bottom. These cases are simulated using Aspen Plus software, and their designs are optimized to minimize the total annual cost (TAC). The results are compared to a base case, represented by the side-stream extractive distillation (SSED) method. Cases 1, 2, and 3 demonstrate TAC reductions of 7.8 %, 27.7 %, and 60 %, respectively, compared to the base case. Additionally, the PG produced by the PO-water reaction presents opportunities for generating extra profit of 6.356 × 107 $ a−1, 7.248 × 107 $ a−1, and 8.98 × 107 $ a−1 in Cases 1, 2, and 3, respectively. Given the financial benefits observed in each case, these configurations may serve as attractive alternative methods for methanol recovery from the PO/methanol/water mixture.

Global Modeling of Heat-Integrated Distillation Column Based on Limited Local Measurements

The heat-integrated distillation column (HIDiC) has more energy-saving potential than conventional distillation columns. However, its nonlinearity and coupling effects pose significant challenges for the online operation of the HIDiC. To overcome these challenges, it becomes necessary to utilize accurate nonlinear models for design optimization or control schemes. Traditional modeling methods require extensive tray information, implying the impractical use of numerous sensors in real-world applications. This paper proposes a modeling approach for the HIDiC based on a limited number of measurements. It only requires the measurement of a finite amount of tray information to construct a global model of the HIDiC. This method serves as an online observer, providing real-time information about the entire column, and also enables the prediction of tray concentration changes. The proposed model forms the basis for developing model-based online monitoring and control schemes. Experimental simulation results demonstrate that the proposed method achieves high accuracy in global observation and prediction for the HIDiC.

Design of intensified chemical processes for the production of ethyl tert-butyl ether

Process intensification contributes to the design of processes with better sustainability performance by allowing several tasks to be performed within the same equipment unit, for instance, reaction and separation. This work aims at the design of intensified processes using a phenomena-based methodology. A gradual intensification approach is used, and each structure is evaluated from economic and environmental considerations. A production process of ethyl tert-butyl ether (ETBE) was selected as a base flowsheet to be intensified. The process consists of one reactor and three conventional distillation columns. Three intensified process alternatives are developed, which employ technologies such as reactive distillation column (RDC), dividing wall column (DWC), and reactive dividing wall column (RDWC). The fully intensified structure, based on a RDWC, showed the best economic indicator with a total annual cost reduction of 26.7% with respect to the base case process; the partially intensified structures showed similar improvements of 18%. The energy savings offered by the intensified flowsheets provide direct benefits from environmental considerations.

Enhancing Techno Economic Efficiency of FTC Distillation Using Cloud-Based Stochastic Algorithm

A liquefied petroleum gas plant facility (LPGPF) is a series of binary distillation columns used to separate natural gas into four alkanes: ethane, propane, butane, and pentane. The conventional distillation column design consists of three binary distillation columns and six heat exchangers to perform the process. Each heat exchanger consumes immense energy to heat up the reboiler and condense the distillate. There are several process technologies that can minimize distillation column energy consumption. In this research, a fully thermally coupled distillation column (FTCDC) was proposed to minimize energy consumption by reducing the number of heat exchangers and tray columns. An FTCDC has the capability to reduce capital expenditure, operational expenditure, and total annual cost (TAC). The complexity of the FTCDC arises from its process integration. In each column, the intersection composition depends on complex mass and energy balances at the column inlet and outlet and each tray. Process integration, including material recycling and heat recovery, increases the complexity significantly. Moreover, the decision variables are multi-intersection composition for each column to achieve optimum objective function, increasing the number and complexity of the computational load such that effective stochastic optimization algorithms are required. The proposed method was designed using a rigorous vapor liquid equilibrium (VLE) FTCDC model and incorporated with recent stochastic optimization algorithms, such as a genetic algorithm, particle swarm optimization (PSO), an imperialist competitive algorithm, and a duelist algorithm, to determine hydrocarbon composition in the FTCDC intersection. To increase the efficiency and effectiveness of the FTCDC optimization design, cloud computing was utilized. The result was compared with conventional methods such as Fenske-Underwood-Gilliland, a Fenske-Underwood-Gilliland modification, and VLE. The optimization objective function is to minimize TAC with hydrocarbon composition in the FTCDC intersection as decision variables. The optimization using the VLE-PSO method reduces TAC up to 26.28%. All designs were validated using a rigorous model with Aspen HYSYS commercial software. This study's primary goal is to improve the performance of FTCDCs using stochastic algorithms and cloud-based computing capacity. The large amount of computation is handled by cloud-based computing resources, enabling reliability and durability.

Modeling of Nitrogen Removal from Natural Gas in Rotating Packed Bed Using Artificial Neural Networks.

Novel or unconventional technologies are critical to providing cost-competitive natural gas supplies to meet rising demands and provide more opportunities to develop low-quality gas fields with high contaminants, including high carbon dioxide (CO2) fields. High nitrogen concentrations that reduce the heating value of gaseous products are typically associated with high CO2 fields. Consequently, removing nitrogen is essential for meeting customers' requirements. The intensification approach with a rotating packed bed (RPB) demonstrated considerable potential to remove nitrogen from natural gas under cryogenic conditions. Moreover, the process significantly reduces the equipment size compared to the conventional distillation column, thus making it more economical. The prediction model developed in this study employed artificial neural networks (ANN) based on data from in-house experiments due to a lack of available data. The ANN model is preferred as it offers easy processing of large amounts of data, even for more complex processes, compared to developing the first principal mathematical model, which requires numerous assumptions and might be associated with lumped components in the kinetic model. Backpropagation algorithms for ANN Lavenberg-Marquardt (LM), scaled conjugate gradient (SCG), and Bayesian regularisation (BR) were also utilised. Resultantly, the LM produced the best model for predicting nitrogen removal from natural gas compared to other ANN models with a layer size of nine, with a 99.56% regression (R2) and 0.0128 mean standard error (MSE).

Optimal sequencing of conventional distillation column train for multicomponent separation system by evolutionary algorithm

Abstract The best structure of multicomponent separation techniques can be obtained using optimal distillation sequencing. Because distillation sequences contribute significantly to the fixed and operational cost of the entire chemical process, developing a systematic approach for choosing the most appropriate and economic distillation sequences becomes an important field of study. Due to its high dimensional space and combinatorial nature, synthesis of the optimal conventional distillation column sequence is a tough problem in the field of process plant development and optimization. A novel method for the synthesis of an optimal conventional distillation column sequence is suggested in this study. Genetic algorithm, an evolutionary algorithm is at the heart of the proposed method. The Total Annual Cost (TAC) is the main basis used to evaluate alternative configurations. To estimate the total cost of each sequence, rigorous methods are used to design all columns in the sequence. The proposed method’s performance and that of the conventional quantitative approach are compared using the results of a five component benchmark test problem used by researchers in this field. According to the comparison results, the suggested algorithm outclasses the other methods and is more adaptable than other existing approaches.

A Comparison of the Exergy Efficiencies of Various Heat-Integrated Distillation Columns

Distillation has relatively low thermodynamic efficiency, so it is a prime target for process intensification studies. The current research aims to study exergy losses in various heat-integrated distillation columns. A conventional industrial-scale i-butane/n-butane fractionator has been selected as a case study for the comparison of the performances of various heat-integrated designs. The Aspen Plus® process simulator is used to perform steady-state simulations and exergy analyses of the conventional distillation column (CDC), internally heat-integrated distillation column (iHIDiC), externally heat-integrated double distillation columns (EHIDDiC), and vapor recompression (VRC) systems. The results of these exergy analyses show that a modified VRC system (ηE = 10.69%) is the most efficient design for this separation. The exergy efficiency of the conventional VRC system is the same as that of the CDC (ηE = 9.27%). The EHIDDiC system (ηE = 9.77%) is somewhat better than the CDC, whereas iHIDiC shows poor exergy efficiency (ηE = 8.09%), even lower than the CDC.

Simultaneous optimization of economic, environmental and safety criteria for algal biodiesel process retrofitted using dividing wall column and multistage vapor recompression

The present study deals with the multiobjective optimization (MOO) of retrofitted in situ algal biodiesel process. Transesterification of the algal lipids is intensified using ultrasonication and catalyzed using the ionic liquid catalyst. Process includes the retrofitting of two conventional distillation columns into a dividing wall column (DWC), which is further intensified using multistage vapor recompression (DWC-MVR) in order to decrease the energy consumption and CO2 emission from the process. Excel based hybridised multiobjective differential evolutionary dynamic local search (HMODE-DLS) algorithm is used for the constrained MOO, whereas Aspen Plus is used for the process development. Break even cost (BEC), eco indicator (EI99) and individual risk (IR) are considered as objectives to evaluate economic, environmental impact, and safety of process, respectively. Initially, bi-objective case studies were analyzed and finally, all three objectives are studied in one case. Pareto optimal solutions obtained from HMODE-DLS algorithm are then ranked by the simple additive weighted method to find out the best solution. MOO resulted in the significant decrease in BEC (~20%), EI99 (~48%) and IR (~10%).

Energy, exergy, economic and environmental analysis of a novel steam-driven vapor recompression and organic Rankine cycle intensified dividing wall column

The dividing wall column (DWC) is a typical thermal coupled distillation column to separate the ternary mixture instead of the conventional two-column sequence. However, the energy utilization of DWC is the same as the conventional distillation column with large energy consumption. The current energy intensification measures for DWC is to use the vapor recompression (VRC) technology for retrofitting the stream cycle and use organic Rankine cycle (ORC) for waste heat recovery. The large top and bottom temperature difference of DWC limits the energy and economic benefit of VRC and also the production of ORC is not high. In this paper, unlike the general electric-driven VRC and waste heat recovery to save the energy consumption of the DWC (VRC-WHRS-DWC), a novel steam-driven VRC and waste heat recovery assisted DWC (SD-VRC-WHRS-DWC) is proposed to form a new energy utilization mode of DWC. As comparison, DWC and VRC-DWC are also developed. The single- and multi-objective genetic algorithms are used to optimize the different processes. All the processes are evaluated by energy, exergy, economic and environmental (4E) analysis. The result shows the cascade utilization of the steam in steam-driven system can effectively increase the economic benefit and decrease the energy consumption of DWC with the large temperature difference between top and bottom.

Triethylene glycol recovery by an energetically intensified thermosyphon-assisted falling film distillation unit: Experimental assessment on a pilot-scale unit and in-silico comparison with a conventional column from natural gas processing

Facing the emerging needs for energy-enhanced separation units, this work evaluated the triethylene glycol (TEG) regeneration, used as a dehydrating agent of natural gas from wells, by a novel thermosyphon-assisted falling film distillation technology, called Destubcal. The pilot-scale device has an innovative heat supply through a two-phase closed thermosyphon, which ensures a uniform energy distribution along the entire distillation tube. Based on current operating data from industrial water-rich TEG streams, different operating conditions were performed in the pilot-scale unit. The best recovery ratio (99.0%) was obtained with an evaporator temperature of 180 °C and a feed flow rate of 15 L/h. However, in order to maximize the bottom TEG composition, the best experimental condition achieved was 17 L/h and bottom temperature of 152.07 °C, due to an evaporator temperature of 170 °C. As a result, the Destubcal unit saved around 38.4% in energy requirement and reduced 49% the column height when compared to a conventional distillation column for the same recovery degree. Therefore, the proposed Destubcal technology can be considered a feasible alternative as recovery column for TEG regeneration in natural gas beneficiation units, with advantages of reduced dimensions and energy-saving operation.

Reclamation of Halon 1301 using industrial-scale heat-pump-assisted batch distillation: Design, simulation, and experiment

In this study, the reclamation of Halon 1301 from an industrial waste gas mixture using an existing heat-pump-assisted batch distillation system was investigated. A cold water circuit and a hot water circuit are added to the conventional vapor compression heat pump for easy operation. To design and optimize the separation, where several design variables and constraints must be verified and satisfied, a modification of the design methodology proposed by Long et al. (2020) was used. Following design using Aspen Hysys software in the simulation of the shortcut column and heat pump system and Aspen Batch Modeler in the simulation of batch distillation, experimental operation of the existing heat-pump-assisted batch distillation system was performed to purify Halon 1301. The experimental performance matched well with that in the simulation. The purification of Halon 1301 with purity of 99.9% was accomplished after 22 h under the designed and optimized operating conditions. The results show that the reboiler duty and operating costs of the existing industrial system can be saved by as much as 100.0% and 36.5%, respectively, compared with a conventional batch distillation column. In addition, the total CO2 emission was reduced by as much as 43.7% compared with that of the conventional process. Moreover, the proposed design is convenient and gives reliable performance. This study demonstrated that the use of an advanced distillation configuration in industrial applications is practically viable and economical.

Simultaneous separation of ternary mixture using modified dual compression middle vessel batch distillation column: Control and dynamic optimization

BackgroundMultivessel batch distillation has been found to be an effective method for the separation of multi-component mixtures. In this article, an effort has been made to devise a fast middle vessel batch distillation column (MVBDC) for the ternary separation of an Ethanol/Propanol/Butanol mixture by the means of inducing vapor compression in the system. MethodsASPEN PLUS V12 has been used to generate the initial steady-state flowsheet of the process for equipment sizing. In contrast, ASPEN Dynamics was used to evaluate the performance of the batch distillation with various control structures and to perform a dynamic optimization on the proposed batch distillation column. MATLAB was used to identify single-input single-output transfer functions for more effective PID controller tuning. Significant FindingsThe proposed Middle vessel batch distillation was found to separate each component of the mixture to a purity of 99 mol% in 22 h (for the cascade control structures) and 21.73 h (for the temperature control structure). This was found to be significantly lesser than the batch time of a conventional batch distillation column (28.12 h), while the energy consumed by the proposed column was 3.4 MMkcal lesser than the energy consumed by the conventional column. Dynamic optimization further reduced the batch time by 14.4% while simultaneously reducing the energy consumed by 20.3%.

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.

Evaluation of mechanical vapor recompression in the reactive distillation of the N-butanol esterification process

The process of producing esters is usually performed through esterification in a reactor followed by a distillation column to separate the products. However, this design limits the reagent conversion. Reactive distillation is an alternative to get around this issue as it allows greater reagent conversions in reactions limited by chemical equilibrium. It is one of the most famous process intensification techniques. On the other hand, mechanical vapor recompression has been used to recycle waste heat to improve efficiency of conventional distillation columns. In this context, this work evaluated the inclusion of a mechanical vapor recompression system in a reactive distillation process to obtain n-butyl acetate via n-butanol esterification with acetic acid. Systems with and without recompression were simulated in an Aspen Plus™ environment. The addition of recompression resulted in a reduction of 33.65% in the annual cost of the process, while not significantly affecting the purity of the desired product and the reagents’ conversion. From an environmental point of view, the mechanical vapor recompression system adoption resulted in a 12.69% reduction in CO2 emissions, contributing positively to meeting the requirements of the environmental regulations.

Modelling and simulation of zero-gravity distillation units with metal foams

The zero-gravity distillation (ZGD) is a promising concept to realize a small-scale distillation process. In contrast to gravity in conventional distillation columns, capillary forces, e.g. created using metal foams, are employed to guide the liquid phase in countercurrent flow to the vapour phase. In this work, a predictive model for simulation of ZGD units is presented. It includes the momentum, heat and species transfer in the liquid and vapour phase. The feed stream as well as the distillate and bottom product streams are included into consideration. Furthermore, the thermal conduction in the unit walls is taken into account. The fluid dynamics of the vapour and liquid is captured in a simplified manner using the concept of hydrodynamic analogy. The developed model was implemented in the MATLAB® software. Simulations of ZGD units in two-dimensional approximation could be validated using experimental data from the literature for ZGD with total reflux. With the validated model, the influence of the wall material and the initial composition on the ZGD process was explored. The focus of a further parametric study was laid on the impact of varying reflux ratio and boil-up ratio.

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.

Concept of a Flexible Wetted‐Wall Column for the Distillation of Specialty Chemicals

AbstractThe trend of increasing product diversity and decreasing production amounts led to the requirement of higher flexibility of production processes of specialty chemicals. Conventional distillation columns, mostly equipped with structured packings, lack the flexibility to handle product changeovers and throughput. Thus, a newly designed distillation column for specialty chemicals is presented. A numerical model was implemented to analyze the potential of the wetted‐wall column. The simulation of the distillation of a binary methanol/water mixture demonstrated that the wetted‐wall column can generate the desired concentration and temperature profiles. Furthermore, analyses of the pressure drop and separation efficiency with the test system chlorobenzene/ethylbenzene were conducted.

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.

Optimization and eco-efficiency analysis of extractive distillation processes with different solvents for separating the ternary mixture embedding two azeotropes

The selection of feasible solvent is of great significance for separating azeotropes via extractive distillation since various solvents can cause different product orders, flowsheet structures, and eco-efficiencies of extractive distillation processes. Limited efforts are focused on the effect of various solvents on the separation of ternary mixtures embedding two azeotropes, especially for the design of the extractive dividing-wall column separation configurations. To fill the research gap, the separation of azeotropic mixtures embedding two azeotropes is investigated using extractive distillation method with various solvents through taking the methyl acetate/ethyl acetate/methanol mixture as an example. First, the theoretical thermodynamic feasibility of four solvents including ethylene glycol, dimethyl sulfoxide, chlorobenzene, and aniline is explored. The individual light-heavy component orders are determined through the thermodynamic insights including the construction of the pseudo binary vapor–liquid phase equilibrium diagrams and overall phase diagrams with residue curves and iso-volatility curves after adding solvents, while are further verified using σ-profiles from microscopic mechanism. Second, the conceptual design of the extractive distillation flowsheets including conventional extractive distillation and extractive dividing-wall column separation configurations with individual solvents is performed. The effects of various solvents on the flowsheet structures and product orders are analyzed. Afterwards, the extractive distillation flowsheets are simulated and optimized economically to minimize the total annual costs through the genetic algorithm, except for the solvent ethylene glycol due to the unfeasibility of realistic simulation. The eco-efficiency analysis is performed via quantifying the Eco-Indicator 99 and thermodynamic performances as well as economic costs. The results indicate that the extractive distillation processes with dimethyl sulfoxide or chlorobenzene as solvent can show a certain degree of advantage compared with that using aniline as solvent in terms of eco-efficiency. The optimal separation configuration is the extractive dividing-wall column containing two dividing-walls with CB as solvent, and its Eco-efficiency Comparison Index increased to 80.54% compared to the worst scheme that is the extractive dividing-wall column containing one dividing-wall with AN as solvent.