Distillation Sequences Research Articles

Compared novel thermally coupled extractive distillation sequences for separating multi-azeotropic mixture of acetonitrile/benzene/methanol

In this paper, extractive distillation applies to separate acetonitrile/benzene/methanol, the medicine is a compounding of multi-azeotropes via introducing chlorobenzene as a solvent. In order to achieve the purpose of energy saving and CO2 emission reduction, ten novel thermally coupled separation sequences including direct sequences, indirect sequences, hybrid sequences and solvent splitting sequences are established and explored based on extractive dividing wall column (EDWC) and side-stream extractive distillation column (SSED). The corresponding optimal parameters are determined by effective and convenient sequential iterative optimization procedures on the basis of minimized total annual cost (TAC) and meanwhile CO2 emissions are calculated to evaluate environmental impact. The comparison results illustrate that the solvent splitting SSED sequence has more advantages in energy consumption, environment impact and economic cost than others, reducing at most 38.44%, 32.84% and 38.41% in terms of total reboiler duty, TAC and CO2 emissions.

Comparison of extractive distillation separation sequences for acetonitrile/methanol/benzene multi‐azeotropic mixtures

AbstractBackgroundThe extractive distillation‐based separation of a multi‐azeotropic mixture has several optional solvents and schemes. The screen of a suitable solvent was performed and diverse extractive distillation sequences were compared for separating the specified mixture of acetonitrile/methanol/benzene.ResultAs a solvent breaking all binary azeotropes, chlorobenzene was selected over aniline on the basis vapor–liquid equilibrium diagrams and infinite dilution factors. Four separation sequences were optimized by the sequential iterative procedure on the basis of minimal total annual cost (TAC), and CO2 emissions were calculated. Among four sequences, sequence III, composed of two extractive distillation columns and one solvent recovery column, is the best scheme from environmental and economic viewpoints. Simple partial heat integration was further implemented and can save 20.08% and 8.86% in terms of energy cost and TAC.ConclusionThe results demonstrate that the separation of acetonitrile/methanol/benzene is fully achievable using common extractive distillation with chlorobenzene as solvent. Moreover, there is a trade‐off between heat transfer in the reboiler‐condenser and corresponding energy consumption variations due to pressure changes when considering heat integration. © 2018 Society of Chemical Industry

Modeling, simulation and intensification of hydroprocessing of micro-algae oil to produce renewable aviation fuel

Micro-algae are photosynthetic organisms, which represent a promissory renewable raw material for biofuels production, since they can be cultivated in non-fertile lands, avoiding the competition with food crops for land use. From micro-algae, oil can be obtained oil that can be converted to biodiesel, green diesel and biojet fuel. In particular, the renewable aviation fuel is one of the less explored biofuels; nevertheless, for the aviation sector, this is the best alternative to reduce CO2 emissions, allowing its sustainable development. In order to produce hydrocarbons in the boiling point range of jet fuel, we need to transform the micro-algae oil. A number of research projects report the use of micro-algae oil for the production of biojet fuel through the hydrotreating process. However, the application of process intensification strategies for the hydroprocessing of micro-algae oil has not been reported. Therefore, in this work we propose the modeling, simulation and intensification of the hydrotreating process to produce biojet fuel, considering micro-algae oil as raw material. The hydroprocessing of micro-algae oil is modeled in Aspen Plus processes simulator, based on data from an experimental study recently reported. The produced renewable hydrocarbons are purified through conventional and intensified distillation sequences; thereby, conventional and intensified hydrotreating processes are defined and evaluated in terms of total annual costs, CO2 emissions and biojet fuel price. Simulation results show that the implementation of intensification strategies leads to the production of biojet fuel with reduced carbon dioxide emissions, 34% less, and a competitive price per liter, 78% cheaper than fossil jet fuel price.

The Optimal Design of a Distillation System for the Flexible Polygeneration of Dimethyl Ether and Methanol Under Uncertainty

Two process designs for the separation section of a flexible dimethyl ether and methanol polygeneration plant are presented, as well as an optimization method which can determine the optimal design under market uncertainty quickly and to global optimality without loss of model fidelity. The polygeneration plant produces a product mixture that is either mostly dimethyl ether or mostly methanol depending on market conditions by using a classic two-stage dimethyl ether production catalytic reaction route in which the second stage is bypassed when the market demand is such that methanol production is more favourable than dimethyl ether. The downstream distillation sequence is designed to purify the products to desired specifications despite the wide variability in feed condition that corresponds to the upstream reaction system operating either in DME-rich or methanol-rich mode. Because the optimal design depends on uncertain market conditions (realized as the percentage of the time in which the plant operates in either DME-rich or methanol-rich mode), this uncertainty is considered in the formulation of the optimal design problem. The results show that using one set of flexible distillation columns for two different objectives is superior to the “traditional” approach of using two different sets of distillation columns which are each optimized for one specific operating condition. Different approaches to design under uncertainty were considered, with a scenario-based two-stage stochastic formulation with a uniform distribution of the uncertain parameter recommended as the preferred formulation.

Multiobjective Early Design of Complex Distillation Sequences Considering Economic and Inherent Safety Criteria

Inherent safety aspects are not usually considered as a driving force during the conceptual design stage of chemical plants. Instead, after the selection of the optimal economic flowsheet, safety is added to the design. However, this sequential design approach could be applied to inferior designs due to protection devices’ cost overrun. The objective of this work is to implement a strategy to simultaneously design a profitable and inherently safer distillation train. Two safety indexes, a disaggregated version of the Safety Weighted Hazard Index and Dow’s Fire and Explosion Index, have been adapted to quantify the inherent safety performance. A large-scale multiobjective MILP problem is formulated. Thus, two strategies of objective reduction are utilized: principal component analysis coupled with Deb’s algorithm and a method based on the dominance structure. The results prove the suitability of these safety index as inherently safer metrics, and showcase the ability of the objective reduction methods to d...

Novel Process to Reduce Benzene, Thiophene, and Pyrrole in Gasoline Based on [4bmpy][TCM] Ionic Liquid

Regulations on benzene-, nitro-, and sulfur-containing aromatic hydrocarbon content in commercial gasolines are becoming more restrictive due to environmental and health issues. The benzene content in reformulated commercial gasoline is currently around 1%. The reduction of benzene levels to comply with future regulations will imply significant changes in refinery configurations. This paper reports a novel extraction process to simultaneously separate benzene, thiophene, and pyrrole from a gasoline using the 1-butyl-4-metylpyridinium tricyanomethanide ([4bmpy][TCM]) ionic liquid (IL). A distillation sequence is also proposed for the isolation of the three aromatic hydrocarbons. The conceptual design of the whole process has been based on experimental data from the liquid–liquid extraction and vapor–liquid separation of benzene, thiophene, and pyrrole from isooctane using the IL [4bmpy][TCM]. A COSMO-based/Aspen Plus methodology has been used to simulate the conceptual design. The a priori COSMO-based/Aspe...

Energy-saving thermally coupled ternary extractive distillation process by combining with mixed entrainer for separating ternary mixture containing bioethanol

The major intrinsic obstacle of extractive distillation is the high energy consumption. It is an actual problem for reducing energy consumption of extractive distillation processes. Two thermally coupled ternary extractive distillation processes were studied to separate the ternary azeotropic mixture tetrahydrofuran/ethanol/water using a single component solvent (dimethyl sulfoxide) and a mixed solvent (dimethyl sulfoxide and ethylene glycol) as entrainer. The optimal conditions of all ternary extractive distillation processes were obtained based on the minimal total annual cost. Thermodynamic efficiency and CO2 emissions index were also considered to evaluate the energy efficiency and environmental impact of alternative ternary extractive distillation processes. The results show that the use of mixed entrainer can result in reduction in both energy consumption and total annual cost for the same ternary extractive distillation configuration. Comparisons of the conventional ternary extractive distillation process and thermally coupled ternary extractive distillation process 1 (combining extractive distillation column with entrainer-recovery column) with mixed entrainer show that a thermally coupled extractive distillation sequence with a side rectifier present the best results. However, thermally coupled ternary extractive distillation process 2 (combining extractive distillation column with entrainer-recovery column) does not show good result due to existence of remixing effect.

Sustainable production of renewable aviation fuel through intensification strategies

In the transportation industry, aviation is one of the most dynamic sectors. The forecast indicates that aviation will grow at 4.8% until 2036, which implies that fuel requirements will double along with CO2 emissions. Therefore, the sustainable development of aviation sector faces great challenges and relies on a four-pillar strategy, which includes increasing engine efficiency, optimization of flight trajectories, and alternative fuels. Renewable jet fuel, also known as biojet fuel, consists of hydrocarbons in the range of boiling point of fossil jet fuel, C8-C16, obtained from the biomass processing. There are different pathways to produce biojet fuel, being the hydroprocessing of triglyceride feedstock one of the most reliable and advanced. The hydrotreating process consists of three main steps: hydrodeoxygenation, cracking and isomerizing, and finally purification; also, it allows obtaining biojet fuel with the required properties from different renewable oils. Nevertheless, it has several opportunity areas to decrease energy consumption and environmental impact.Therefore, in this work an analysis of hydrotreating processes to produce biojet fuel is presented in terms of energy consumption, total annual costs, and CO2 emissions. Different renewable raw materials of high productive potential in Mexico are considered; along with the implementation of process intensification strategies for the separation train. Results show that the use of thermally coupled distillation sequences allows designing sustainable processes for the production of biojet fuel economically competitive with fossil jet fuel.

A cost-effective retrofit of conventional distillation sequence to dividing-wall prefractionator configuration

A dividing-wall prefractionator configuration was investigated for a safe and economic retrofit of the conventional sequence using simple distillation columns. In the proposed retrofit configuration, the first column was modified to a dividing wall column as a prefractionator to supply prefractionated multi-feeds to the subsequent column. To investigate the effectiveness of the proposed configuration, nine near-ideal feed mixtures were considered for analysis. The proposed configuration was then compared with several other alternative configurations. The proposed dividing-wall prefractionator efficiently generates prefractionated multi-feed streams avoiding feed mismatch and remixing effect with low modification cost. Moreover, because the proposed retrofit configuration allows for flexible switching between the dividing-wall prefractionator and the conventional operating mode, a safe retrofit is also ensured by reducing the operational risks. Several industrial retrofit cases were studied to validate the proposed dividing-wall prefractionator configuration.

Evaluation of a novel configuration of bottom flashing on dual distillation columns for saving energy

Vapor recompression and bottom flashing are among the developed technologies for enhancing energy efficiency of distillation processes. In this paper, a novel configuration of bottom flashing system is proposed for enhancing energy efficiency of dual columns such as direct distillation sequences. The system is designed to operate between two distillation columns. The proposed system engages two separate distillation columns, both of which can be wide boiling systems. The system incorporates two interacting bottom flashing systems that engage the two distillation columns through heat transfer from the top product of the second column to the bottom product of the first column which in turn results in elimination/reduction of utility requirements of condenser of the second column along with reboiler of the first column. Based on the results of this study, compared to conventional direct sequence distillation, 40.3% reduction in energy requirements and 20.7% reduction total annual costs of the process can be obtained through application of the proposed system.

Energy Integrated Distillation Column Sequence by Driving Force Method and Pinch Analysis

Distillation is a common separation process since its emergence in the early 20th century due to its capability for mass production without compromising the product(s) quality. However, the energy efficiency is still become the challenge for the industry players. Since then, they put so much effort in ensuring the energy efficiency of the process. It is not only for economic purpose but also to address the environmental issue whereby the legislation become stringent over the years. Therefore, this paper aims to investigate the energy efficiency of distillation column sequence by using the pinch analysis method. Rigorous simulation of the distillation for component n-butane, n-hexane, n-heptane and n-nonane has been carried-out for 5 different sequences namely direct, indirect, driving force sequence (indirect-direct), direct-indirect and split for energy analysis. Aspen HYSYS V9 has been used for the simulation while the data was extracted for pinch analysis including the construction of problem table algorithm to obtain the minimum cooling and heating load for each sequence. The results that were analyzed and compared including total heat load, heating load and cooling load. Then the grid diagrams for the best sequence was constructed. From the results of energy analysis, all distillation sequences except for direct-indirect sequence recorded further energy saving compared to the base case whereby the highest saving is driving force sequence at 6.31% total energy saving. It also recorded the highest percentage of heating and cooling load at 4.85% and 9.05% respectively. This paper also strengthens the advantage of driving force method in determining the best sequence since it was proved to produce lower energy consumption compared to others. Then, the energy can be further reduced by using the pinch analysis. Therefore, for this case study, it can be concluded that the heat integration via pinch analysis is a promising method for further saving for any distillation column sequence.

Energy Integrated Distillation Column Sequence by Driving Force Method and Pinch Analysis for Five Components Distillation

Distillation is an energy-driven process that is recognised as the most widely used in chemical and petrochemical industries. Energy efficiencies have always been the key issue for this technology to survive. Therefore, this paper aims to investigate the use of driving force method to determine the best distillation sequence for energy efficiency. The method is supported using pinch analysis for the opportunity to extend the energy saving in the process. The distillation process involved five alkanes components which are n-hexane, n-heptane, n-octane, n-nonane and n-decane. The rigorous simulations for 14 possible distillation column sequences including driving force sequence have been carried-out by using ASPEN HYSIS V9 software. Then, the data were extracted for pinch analysis and the best sequence was determined based on total load, heating load and cooling load. The grid diagram for heat exchanger network was then proposed for the best sequence. From the results, it can be claimed that the use of pinch technology enhanced the energy saving most of the sequences. The best sequence is sequence no. 9 that recorded percentage saving of 34.83 % for total load, 33.87 % for heating load and 35.84 % for cooling load. On the other hand, driving force sequence (sequence no. 5) also accounted as one of the highest efficiency and still become an attractive method for best sequence determination. As a conclusion, further energy saving can be achieved via the use of pinch analysis in any distillation sequence.

Intensification and performance assessment of the formic acid production process through a dividing wall reactive distillation column with vapor recompression

Distillation operation in the production of formic acid (FA) involves a large amount of investment and has high-energy requirements. Thus, process intensification is crucial in minimizing the energy consumption and investment. Dividing wall column (DWC) is one such way of achieving it. Aim of this study is to design a dividing wall reactive distillation column (DWRDC) with vapor recompression in the production of FA instead of normal reactive distillation – distillation sequence and investigate the performance in terms of energy, cost, and carbon emission. A patented FA production process is chosen as a base case. The intensification of the base case FA production process is then carried out through the application of (i) DWRDC, (ii) vapor recompression in a distillation column, and (iii) vapor recompression in DWRDC. The performance of the new intensified processes is subsequently investigated for multiple performance indexes. It is observed that an impressive saving of 18.33% in utility cost, 8.4% in total annual cost (TAC), 2.55% in cost of manufacturing (COM), and 17.68% in carbon emission can be secured with the proposed new intensification as compared to its conventional counterpart for a payback period of 4 years.

Multiplicities in dividing wall distillation columns in the purification of bioethanol: energy considerations

In this paper, we present results about the energy requirements in the reboilers of an extractive dividing wall distillation column and a thermally coupled distillation sequence with a side rectifier for bioethanol dehydration using glycerol as entrainer, and the study generates the appearance of multiple steady states. During the energy optimization of the dividing wall distillation column, using glycerol as entrainer, the recycle streams were varied until the energy consumption in the reboiler was obtained and the multiple steady states can present a difference of up to 400%. This finding is important since we are interested in detecting the optimal energy consumption in order to reduce the environmental impact caused by the usage and production of energy from petroleum. This information is being used in a current pilot plant in order to detect the optimal operation conditions to dehydrate bioethanol.

Simultaneous design of separation sequences and whole process energy integration

This paper presents a novel methodology for the optimisation of the preliminary design of heat-integrated multicomponent distillation sequences. This is achieved through use of a reduced process superstructure where the role of splitting each adjacent key component pair is assigned to an individual separation column, greatly reducing the size and complexity of the problem. This methodology uses information about other process streams on site with which heat can be exchanged within the initial design in order to find a plant-wide optimal separation configuration with the aim of reducing the cost of heating provided by utilities including those used for heating and cooling process streams. In order that this model can be formulated as a mixed-integer linear program, this model utilises a discretised temperature grid where stream temperatures are allowed to vary. This methodology was tested on an example of a mixed alkane feed stream, with the sequence changing dependent on the degree of process integration. The method was found to have the potential for significant cost reductions compared to a heuristic design, with the example exhibiting a cost saving of over 50% and a reduction in CO2 associated with process heating of almost 60%, though the magnitude of these savings is highly dependent on the specific example to which it is applied.

Proposal of Isobutyl Alcohol as Entrainer To Separate Mixtures Formed by Ethanol and Water and 1-Propanol and Water

Isobutyl alcohol (IBA) has been proposed as a solvent to carry out the dehydration of ethanol and 1-propanol by means of a nonconventional distillation process. In this way, isobaric vapor–liquid equilibrium (VLE) and vapor–liquid–liquid equilibrium (VLLE) data at atmospheric pressure have been obtained for the ternary systems ethanol (1a) + water (2) + IBA (3) and 1-propanol (1b) + water (2) + IBA (3). Then, these data have been correlated to obtain a set of parameters capable of estimating VLE and VLLE. According to the results achieved, distillation sequences to separate water and ethanol or 1-propanol have been proposed. Finally, a study about the minimum amount of entrainer required to break the azeotrope of the mixture ethanol/1-propanol + water is carried out.

Open-loop based controllability criterion applied to stochastic global optimization for intensified distillation sequences

The simultaneous design and control optimization of intensified distillation sequences is a challenging topic that has partially been addressed by doing several simplifications in the process dynamics. This work aims to embed a controllability criterion in a global stochastic optimization algorithm that can solve single objective or multi-objective optimization problems. The proposed optimization algorithm takes the steady state results after solving rigorous tray-by-tray calculations in Aspen Plus®, and sends it to an algorithm written in Matlab® through an interface written in Excel® VBA. It has already been tested to minimize the energy consumption in intensified distillation sequences, but this work is an extension that includes the assessment of the process controllability. By simplifying the process dynamic to only first-order responses, it is possible to assess the controllability of distillation sequences by using only steady state information. The proposed optimization algorithm was applied to three cases of intensified distillation sequences. A comparison between the proposed and the rigorous process dynamics at open-loop was done by using the singular value decomposition (SVD) technique. The results showed that the simplified process dynamics can deal with the optimal design and control of intensified distillation sequences.

Reducing energy requirements for ETBE synthesis using reactive dividing wall distillation column

Production of ETBE is one of most important industrial processes. It is used both as biofuel and bio additive in gasoline. The motivation behind its use is that, its blend with gasoline reduces greenhouse gas emissions. Present work focuses on the synthesis of ethyl tertiary butyl ether (ETBE) by using Reactive dividing wall column (RDWC) and a comparative assessment with three other process alternatives as-reactor followed by distillation sequence, reactor plus reactive distillation (RD), and RD. The comparison was done in terms of energy requirements, CO2 emissions, total annual costs (TAC), total investment costs (TIC) and total operating costs (TOC). RDWC proved its forte in saving energy therefore cutting CO2 emissions and handling the reactions limited by chemical equilibrium. RDWC was found to be the most promising alternative out of the four process alternatives. It gave highest purity of the product ETBE 99.999% (mol.), the CO2 emissions were reduced by 74% and 43% as compared to conventional sequence and RD respectively, and also the energy requirements were very less as compared to the conventional sequence and RD. TIC reduction as high as 68% was observed, this also established RDWC as a lucrative option for the synthesis of ETBE.

Dividing-wall columns: Design and control of a kaibel and a satellite distillation column for BTX separation

Dividing wall distillation technologies have been amongst the most important contributions to process intensification efforts over the last few decades. This work focuses on design, dynamics and control of an extended dividing wall distillation column, referred to as a satellite column, and its comparison to the performance of a Kaibel column and to a direct distillation sequence for the separation of BTX mixtures. The results from optimized designs for these distillation structures show that the satellite column is the most energy-efficient configuration, with savings of 24.5% compared to the conventional direct sequence, and 11.8% to the performance of a Kaibel column. As far as the dynamics are concerned, the satellite column shows a similar performance when compared to the Kaibel column and to the conventional direct separation sequence, indicating that the additional energy savings provided by the satellite configuration can be achieved without a deterioration of its control behavior.

Development of an Integrated Reaction–Distillation Process for the Production of Methylal

An integrated reaction–distillation process for the production of methylal from aqueous, methanolic formaldehyde solutions is developed. The process consists of a serial connection of a reactor in which the feed is converted to chemical equilibrium by a heterogeneously catalyzed reaction followed by a pressure-swing distillation sequence, in which a heterogeneously catalyzed reactive section as well as a vapor side draw are used. The catalyst is an acidic ion-exchange resin. The process yields methylal in purities over 0.999 g/g; methanol can be recovered in purities over 0.94 g/g, and water is withdrawn in a purity of 0.99 g/g. The conversion of formaldehyde is above 99.9%. The process development is carried out based on steady-state simulations with a model which explicitly accounts for the oligomerization reactions of formaldehyde in aqueous, methanolic formaldehyde solutions. The model is validated by a comparison to experiments that are carried out in a laboratory glass distillation column.