Mass-separating Agents Research Articles

Separation of the cyclohexane-benzene mixture by the extractive distillation process using ethylene glycol as a solvent

The importance of cyclohexane lies in the fact that it is the main precursor for the production of Nylon 6 and Nylon 6.6, two of the most important synthetic fibers. Cyclohexane (CHX) is produced by catalytic hydrogenation of benzene (BZ), where cyclohexane with benzene is obtained as a product. Since CHX and BZ have close boiling temperatures, and similar molecular structures, their separation by conventional binary distillation is complicated. Thus, ethylene glycol (EG) was selected as a solvent in an extractive distillation (ED) process for the separation of the CHX-BZ mixture in Aspen Plus V9®; where the use of ethylene glycol as a solvent allowed us to obtain cyclohexane and benzene with purities of 99.91 mol%. In addition, compared to the extractive distillation with heat integration (EDHI) process that uses [C5(MIM)2][NTf2]2 + H2O as a mass separation agent; the use of EG as a solvent promotes an energy decrease of 41.14%, a saving of 55.07% in the Total Annual Cost (TAC), and a decrease of 72.38% in CO2 emissions. These outcomes underscore the efficacy of ethylene glycol as a suitable solvent in the purification of the cyclohexane-benzene mixture.

Glutathione Disulfide as a Reducing, Capping, and Mass-Separating Agent for the Synthesis and Enrichment of Gold Nanoclusters

Water-soluble nanoclusters, which are facilely enrichable without changes in the original properties, are highly demanded in many disciplines. In this contribution, a new class of gold nanoclusters (AuNCs) was synthesized using glutathione disulfide (GSSG) as a reducing and capping agent under intermittent heating mode. The as-prepared GSSG–AuNCs had a higher quantum yield (4.1%) compared to the conventional glutathione-protected AuNCs (1.8%). Moreover, by simply introducing the GSSG–AuNC solution to acetonitrile at a volume ratio of 1:7, a new bottom phase was formed, in which GSSG–AuNCs could be 400-fold enriched without changes in properties, with a percentage recovery higher than 99%. The enrichment approach did not need additional instruments and was potentially suitable for large-scale enrichment of nanoclusters. Further, density functional theory calculations indicated that the hydrogen bonding between GSSG and acetonitrile plays a key role for the bottom phase formation. Our work suggests that the highly emissive GSSG–AuNCs possess great potential not only in fluorescent measurements but also in other scenarios in which high-concentration AuNCs may be needed, such as catalysis, drug delivery, and electronic and optical industries.

Prospects for Novel Pinch Analysis Application Domains in the 21st Century

Pinch Analysis was originally developed as a thermodynamically-based methodology for targeting and design of industrial heat recovery systems. Subsequent extensions of pinch analysis have since been developed; for example, mass pinch analysis is derived directly from analogies between heat and mass transfer, and has led to application for the efficient use of mass separating agents (MSAs) in process plants. More recent literature shows Pinch extensions for numerous applications, including energy sector planning using diverse quality measures. Other Pinch techniques have also been developed using time as the quality index, for applications such as production planning, financial analysis, supply chain management, isolated energy system design, batch process scheduling, carbon dioxide sequestration, and human resource allocation. These applications demonstrate how common problem structures allow an elegant solution approach to be developed for seemingly diverse applications. In this paper, past applications of Pinch Analysis are reviewed, and its further prospective extensions that may be developed, based on similar analogies, for non-conventional problem domains are discussed.

A Numerical Tool for Simultaneous Targeting and Design of Mass Exchange Networks

Design of cost-effective Mass Exchange Networks (MENs) that involves mass integration can help to minimize the amount of mass separating agent (MSA) purchased, waste MSA generated by industries, reduce operating costs and mitigate environmental issues associated with MSA disposal. Design of MENs can be done using graphical and numerical methods, as well as using mathematical modelling. This work describes a new approach for simultaneous targeting and design of MENs in which both targeting and network design stage can be solved in a single template, in order to overcome the limitation of graphical tools such as MENs Composite Curves (CCs) and Grid Diagram. CCs cannot completely map individual rich and lean process streams, or process and utility streams. On the other hand, the numerical technique known as Composition Interval Table (CIT) failed to show individual rich and lean stream mass cascades and cannot be used for MENs design. The newly developed numerical approach in this paper employs the Segregated Composition Interval Table (SECIT) to simultaneously locate mass pinch point, determine the minimum utility targets and perform SECIT Mass Allocation (SMA) that can be used to visualize in SECIT Network Diagram (SND).This work can be applied in industries to minimize liquid waste and reduce environmental pollution A case study is presented to demonstrate the validity and advantages of the proposed approach. This paper also shows that SECIT and SND can be a vital combination of numerical and graphical visualization tools for targeting and design of complex MENs.

Synthesis of Renewable Energy Integrated Combined Heat and Mass Exchange Networks

In this paper, a methodology for systematically integrating the synthesis of combined heat, mass, and regeneration exchange networks with solar thermal is presented. The process considered involves the removal of ammonia from ammonia-rich gaseous streams using water-based solvents as the mass separating agent (MSA) and subsequent regeneration of the ammonia-rich MSA stream using steam stripping. A composite superstructure, which comprises the stage-wise superstructure for the synthesis of the heat exchanger network subsystem, primary mass exchanger network subsystem, regeneration subsystem and integrated solar thermal with periodic heat storage, is developed. In order to simplify the modelling of the unpredictable availability of solar thermal energy within the composite superstructure, a multi-periodic synthesis approach is adopted. Sensitivity analysis was performed to establish the price at which solar thermal is favoured over fossil-derived energy as the hot utility source. The economics of the resulting solution is evaluated using net present value, and it was found that, to obtain a positive NPV, the stripping cost in the retrofitted network will have to be as low as possible, or annual operating cost of the non-retrofitted primary mass exchange network will have to be high.

Molecular design of mass-separating agents for separation of cyclic ethers and acetonitrile from water

The conductor-like screening model for realistic solvation (COSMO-RS) and molecular dynamics simulation were used to evaluate the salting-out capacity of piperazine-containing Good's buffers (GBs) on the removal of 1,4-dioxane, 1,3-dioxolane, and acetonitrile from water. The general formula of piperazine-based GBs is 2-[4-(2-hydroxyethyl)piperazin-1-yl]alkanesulfonic acid, HO − (CH2)2 − N<CH2CH2CH2CH2 > NH+ − (CH2)n − SO3−, (n = 1–10). The buffers with n = 1 to 4 are commercially available, while the buffers with n = 5 to 10 are molecular designed in order to predict their salting-out effects on the organic solvent + water systems. The isobaric vapor-liquid equilibria of the ternary piperazine-based GB + organic solvent + water systems were predicted. The studied organic solvents are miscible with water at any composition under ambient condition and form a minimum boiling azeotropes. It was observed that the piperazine-based GBs are able to shift the azeotropic composition. The activity coefficients of water and organic solvents in presence of piperazine-based GBs were predicted using the COSMO-RS model. The influence of alkyl chain length between the zwitterion end groups on the phase behavior of the ternary systems was evaluated. Piperazine-based GBs have displayed potent mass-separating agents in the recovery of 1,4-dioxane, 1,3-dioxolane, or acetonitrile from water. The hydrogen bonds formation in MSA + organic solvent + water mixture was analyzed using molecular dynamics simulation.

Natural Gas Liquids from the Associated Flare Gas Stream: Monetized in Real-Time via Various Qualitative Products

Typically, the raw natural gas, released from underground porous reservoir rocks and passed through well bore system, that brings it to the surface wellhead is much different from the sweetened natural gas used by consumers. Conventionally, starting at the wellhead, down to the gas processing plants, the natural gas is purified to yield pure methane –rich stream and sweetened natural gas liquids (NGLs) comprising mostly, molecules that are heavier than methane like ethane, propane, butanes, pentanes and hexane plus hydrocarbon components. Consumers use natural gas in either of the two streams in various forms, such as, residential fuel for domestic heating, cooking, refrigeration and air conditioning; energy source which competes with petroleum products like fuel oil, diesel and liquefied petroleum gas (LPG); and feedstock to both petrochemical and chemical industries for manufacturing various intermediate chemicals and finished products such as ammonia (synthetic nitrogen fertilizer), methanol, chloromethanes, oxalcohols polythene, textiles, paints, synthetic drugs, toys, solvents, car tyres, explosives, soles of shoes et cetera. This investigation on the real-time monetization of natural gas liquids (NGLs) from the flared associated stranded natural gas in Nigeria, theoretically, reviewed the purification, recovery and separation of NGLs from a bulk natural gas stream, starting at the well head, to the gas processing plants, which normally entail, change of phase using either an Energy-Separating Agent(ESA) such as refrigeration for partial and total liquefaction/ fractionation or a Mass-Separating Agent (MSA) such as, the adsorption and absorption processes. It showed that the NGL volume extractable depends on the amount of gas available (flow rate), the NGL contained in the gas (composition), the processing technique employed by the processing plant et cetera. Usually, NGLs can comprise from 5% to over 50% of the natural gas stream. With a flow rate of 20million scfd (20MMscfd) on a sweetened composition of the flared associated stranded natural gas stream in Nigeria (table 3), the real-time daily NGLs component by component was obtained table 4, which indicates that about 160 bpd of ethane, 122 bpd propane, et cetera, would be available for monetization in various qualitative products that are in very high demand.

Development of alternative methanol/dimethyl carbonate separation systems by extractive distillation — A holistic approach

Separation of dimethyl carbonate (DMC) with methanol (MeOH) is fundamentally difficult as DMC forms an azeotrope with MeOH. In this context, a holistic, three-tiered approach was undertaken to develop alternative MeOH/DMC separation systems by extractive distillation. To that end, a preliminary entrainer screening was conducted in the first tier using predictive UNIFAC-DMD and COSMO-SAC models. Based on calculated selectivities at infinite dilution (Sij∞), twelve potentially promising candidates were chosen out of 35 solvents. These mass separating agent (MSA) candidates were allowed to be advanced to the next level of screening in which the limiting activity coefficients of methanol as well as dimethyl carbonate in those selected solvents were experimentally measured by the technique of headspace gas chromatography. At this level of screening, a composite Z-score taking both selectivity and solvency factors into account was employed. Two solvents — methyl salicylate and ethyl benzoate with relatively high values of the composite Z-score were identified for further vapor ​– liquid equilibrium (VLE) experiment in the second tier where four sets of data were measured using a dynamic recirculation cell. The effectiveness of the two solvents acting as entrainers was further quantitatively assessed by simulation in the last tier, and compared with that of others being used industrially or proposed in the literature. Through a sequential iterative optimization scheme, extractive distillation system for each entrainer was optimized based on both conventional and heat-integrated schemes. The simulation results reveal that the effectiveness of methyl salicylate as an MSA outperforms all other entrainers.

Designing new mass-separating agents based on piperazine-containing good’s buffers for separation of propanols and water azeotropic mixtures using COSMO-RS method

The isobaric vapor-liquid equilibria of the binary 1-propanol + water, 2-propanol + water, and 2-methyl-2-propanol (tert-butanol) + water systems were predicted using the conductor-like screening model for realistic solvation (COSMO-RS) method. The phase behavior of the 1-propanol/2-propanol/tert-butanol + water + piperazine-based Good’s buffer systems were predicted. The effect of piperazine-containing Good’s buffers, 2-[4-(2-hydroxyethyl)piperazin-1-yl]alkanesulfonic acid, as mass-separating agents on the separation of proponals from water were discussed. The influence of alkyl chain length between the zwitterion end groups, R = methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, and decyl was evaluated. Further, the effect of 4-(2-hydroxyethyl)piperazine-1-(2-hydroxypropane sulfonic acid) was also evaluated. Piperazine-based Good’s buffers are expected to be effective mass-separating agents to have practical application in the separation of propanol from water.

Synthesis of mass exchange networks for single and multiple periods of operations considering detailed cost functions and column performance

Mass exchange network synthesis (MENS) can be used to reduce pollutant emissions into the environment as well as reduce the need for mass separating agents (MSAs). Designing an efficient network using mathematical programming is not a trivial task, due to the fact that the design equations involved are highly non-linear. Chemical plant process parameters also change from time to time due to issues such as changes in environmental conditions, plant start-up/shut-downs, changes in process feed quality, change in product quality demand, and some other disturbance in the system. Such changes in process parameters result in what is known as multi-period operations; hence the synthesised network has to be flexible to handle these changes. In order to circumvent the issues associated with solving non-linear equations in mathematical programming environment, most methods have simplified the cost functions for MENS. Solutions obtained from these methods may not be realistic because the simplified cost functions are based on the assumption that the diameter of a column is 1m or 2m and that the capital cost of packed columns are dependent only on the height of the column. The simplified models do not make provision to check whether the resulting designs are prone to flooding, operate at optimal pressure drops or even whether the ratio of column diameter to size of packing materials would enhance efficient operations. Furthermore the models assumed single period operations for mass exchange network systems. This paper presents a new synthesis method for single and multi-period MENS using detailed cost functions and correlations which check whether selected columns are prone to flooding or not and whether they have optimal pressure drops that ensure efficient separations as well as optimal use of MSAs. The solutions obtained are compared with an existing method that used pinch technology.

Novel Heat-Pump-Assisted Extractive Distillation for Bioethanol Purification

The purification of bioethanol fuel involves an energy-intensive separation process to concentrate the diluted streams obtained in the fermentation stage and to overcome the azeotropic behavior of the ethanol–water mixture. The conventional separation sequence employs three distillation columns that carry out several tasks, penalized by high-energy requirements: preconcentration of ethanol, extractive distillation, and solvent recovery. To solve this problem, we propose here a novel heat-pump-assisted extractive distillation process taking place in a dividing-wall column (DWC). In this configuration, the ethanol top vapor stream of the extractive DWC is recompressed from atmospheric pressure to over 3.1 bar (thus to a higher temperature) and used to drive the side reboiler of the DWC, which is responsible for the water vaporization. For a fair comparison with the previously reported studies, we consider here a mixture of 10 wt % ethanol (100 ktpy plant capacity) that is concentrated and dehydrated using ethylene glycol as mass-separating agent. Rigorous process simulations of the proposed vapor recompression (VRC) heat-pump-assisted extractive DWC were carried out in AspenTech Aspen Plus. The results show that the specific energy requirements drop from 2.07 kWh/kg (classic sequence) to only 1.24 kWh/kg ethanol (VRC-assisted extractive DWC); thus, energy savings of over 40% are possible. Considering the requirements for a compressor and use of electricity in the case of the heat-pump-assisted alternative, it is possible to reduce the total annual cost by approximately 24%, despite the 29% increase of the capital expenditures, for the novel process as compared to the optimized conventional separation process.

Entrainer-Enhanced Reactive Distillation for the Production of Butyl Acetate

A new reactive distillation (RD) process using a mass separation agent (extraneous entrainer) for the efficient production of butyl acetate from butanol and acetic acid via an esterification reaction was proposed. Until now, butyl acetate, a product of the esterification reaction, has been used as an internal entrainer in the production of butyl acetate. It has also been accepted that a configuration consisting of a prereactor followed by a reactive distillation column is most suitable for the production of butyl acetate. The use of an internal entrainer may shift the reaction equilibrium to be favorable to the reverse reaction in the reactive section, limiting the reaction yield. However, an extraneous entrainer, such as cyclohexane, can resolve the problem. It can be used to break the water–alcohol azeotrope and remove water more efficiently from the reactive section. In this study, we proposed a single reactive distillation configuration without a prereactor and the use of an extraneous entrainer (cycl...

Systematic Synthesis of Mass Exchange Networks for Multicomponent Systems

The synthesis of mass exchange networks (MENs) is an important systematic tool for screening mass-separating agents (MSAs) and satisfying the mass transfer demands while considering process, enviro...

Synthesis of mass integration networks: Integrated approach to optimization of stream matching for a metal pickling process

The purpose of this techno-economic feasibility study is to develop a procedure for the cost-effective synthesis and optimization of schemes to recover in-plant a valuable ingredient from waste streams and at the same time reduce the COD property. MILP and MINLP algorithms are used. The model minimizes the total annualized cost of the mass exchange network (MEN). The procedure involves a two-stage process: first, using the MILP, the pinch point location is identified along with the selection of an optimal set of mass separating agents (MSAs). At this stage the effect of each selected MSA on COD is scrutinized. In the second stage, the MINLP is applied to realize the optimal matching of waste and lean streams through the direct minimization of equipment capital cost. An example is presented to show the applicability and advantages of the proposed novel procedure. The project was found to be highly profitable.

Design and simulation of an entrainer-enhanced ethyl acetate reactive distillation process

This paper presents an approach to intensify a reactive distillation (RD) process for ethyl acetate (EtAc) production using a mass separation agent (entrainer), and a new process flowsheet with a sidedraw to the RD column. The heterogeneous azeotrope formed by water and EtAc contains less water than that is produced by the esterification reaction. N-butyl acetate is selected as an appropriate entrainer to withdraw the accumulated H 2O from the RD column rectifying section. The equilibrium stage model based on the RADFRAC module of Aspen Plus is employed for the steady-state simulation of the improved process flowsheet. The stage number of the rectifying section and reactive section, sidedraw location and flowrate, sidedraw aqueous phase reflux flowrate, and overhead organic reflux flowrate are investigated to determine an optimal flowsheet design. The entrainer-enhanced EtAc RD process efficiently uses the raw materials and significantly increases the process efficiency, allowing significant energy savings. Remarkably, compared to previously reported RD processes, the energy consumption of this novel process is about 32% lower while the capital investment almost remains the same.

Separation network design with mass and energy separating agents

The mathematical model developed in this paper deals with simultaneous synthesis of the integrated separation network, where both mass separating agents (MSAs) and energy separating agents (ESAs) are taken into account. The proposed model formulation is believed to be superior to the available ones. Traditionally, the tasks of optimizing ESA-based and MSA-based processes were either performed individually or studied on a heuristic basis. In this work, both kinds of processes are incorporated into a single comprehensive flowsheet and a novel state-space superstructure with multi-stream mixings is adopted to capture all possible network configurations. By properly addressing the issue of interactions between the MSA and ESA subsystems, lower total annualized cost (TAC) can be obtained by solving the corresponding mixed-integer nonlinear programming (MINLP) model. A benchmark problem already published in the literature has been investigated to demonstrate how better conceptual designs can be generated by our proposed approach.

Optimization of combined heat and mass exchanger networks using pinch technology

AbstractThis article examines the benefits that may be obtained by combining the optimisation of heat and mass exchanger networks. This study uses a Pinch Technology approach to the targeting of Combined Heat and Mass Exchanger Networks (CHAMENs), and illustrates it with application to three examples. The first example has just one external mass separating agent (MSA), the second has both process and external MSAs, and the third is an extension of the second with a heat exchanger network integrated. The major benefits arise when it is possible to cool the process MSA with an excess capacity to remove mass. This reduces the flowrate of the external MSA (since this exists below the pinch) and can even do away entirely with the need for it. This also leads to a reduction in the capital cost requirements of both the process and the external MSAs, as well as a reduction in regeneration costs. The implication of this is that a limitation to the use of the available capacity of process MSAs is their mass exchange temperature. It was also found (in the example in which hot/cold utilities are used to enhance mass exchange) that the mass exchanger network synthesis (MENS) costs generally dominate over the heat exchanger network synthesis (HENS) costs. Other examples presented in this article support these conclusions. Copyright © 2007 Curtin University of Technology and John Wiley &amp; Sons, Ltd.

A Simultaneous Optimization Method for the Structure and Composition Differences of a Mass Exchange Network

This article presents a new method to calculate the composition differences (ɛ) for targeting the minimum total annualized cost (TAC) of a mass exchange network (MEN), which is based on the combination of composition interval diagram (CID) with mathematical programming. The total cost target consists of the capital cost of the process units and the operating cost for mass separating agents (MSAs). The value of total cost varies considerably with the composition differences, so the values of ɛ should be optimized in order to obtain minimum TAC of a MEN. This article considers ɛ as a set of unequal variables for each equilibrium equation of a rich-lean stream pair, employing them to build the CID and mathematical model, which optimizes the structure and composition differences simultaneously. Two examples are applied to illustrate the proposed method and the results demonstrate that the approach introduced by this article is simpler and more convenient than the methods in previous literatures.

Determination of Mass Separating Agent Flows Using the Mass Exchange Grand Composite Curve

In this paper we set out the principles for using the grand composite curve (GCC) of mass exchange network synthesis (MENS) for selection of external mass separating agents (MSAs). These principles enable us to systematically choose between alternative external MSAs as well as the minimum flowrate for each MSA selected. This paper emphasizes that the cheapest MSA is not necessarily the one with the lowest cost per unit mass of MSA, but rather the one with the lowest overall cost of removal of the mass load, which depends on both the MSA cost and its permissible concentration change. It also demonstrates the importance of consideration of the composition levels of the MSAs in relation to the target compositions of the rich streams and to the capital cost implications of the resulting mass transfer driving forces. In this respect the use of the GCC is superior to procedures developed so far. We illustrate the principles presented by application to two example problems.

Entrainer-enhanced reactive distillation

This paper presents a novel approach in reactive distillation (RD) processes, the use of a Mass Separation Agent (entrainer). This technique enables to overcome limitations due to distillation boundaries, and increase the degrees of freedom in design. As application the catalytic esterification of fatty acids with light alcohols C2–C4 is studied. In a standard RD device a supplementary separation step is needed for recovery and recycle of the alcohol that distillates in top with the water product. The problem can be solved elegantly by making use of an internally recycled entrainer. This should fulfil the following conditions: form minimum-boiler ternary heterogeneous azeotrope, allow quantitative water removal by L–L separation or steam stripping, and give acceptable impurity in the final product. Moreover, the entrainer enhances the reaction rate, by higher reactant concentration in the reaction space, and offers better protection of catalyst against deactivation. The paper discusses in more detail the conceptual design of a process for the esterification of lauric acid with 1-propanol and sulphated zirconia as catalyst. The following aspects are investigated: chemical and phase equilibrium, entrainer selection, kinetic design and optimisation. Minimum and maximum entrainer ratios have been identified. The use of entrainer leads to 50% reduction in the amount of catalyst.