Low-pressure Column Research Articles

Process Simulation of the Separation of Aqueous Acetonitrile Solution by Pressure Swing Distillation

The separation of aqueous acetonitrile solution by pressure swing distillation (PSD) was simulated and optimized through Aspen Plus software. The distillation sequence of the low pressure column (LPC) and high pressure column (HPC) was determined with a phase diagram. The pressures of the two columns were set to 1 and 4 atm, respectively. Total annual cost (TAC) was considered as the objective function, and design variables, such as the tray number, the reflux ratio, and the feeding position, were optimized. The optimum process parameters were obtained. For the reduction of energy consumption, the PSD with full-heat integration was designed. The TAC of this method is lower by 32.39% of that of the PSD without heat integration. Therefore, it is more economical to separate acetonitrile and water mixture by PSD with full-heat integration, which provides technical support for the separation design of such azeotropes.

Isolation and characterization of Stigmasta-7, 22-dien-3-ol (α-Spinasterol) from Entada africana stem bark crude extract

The phytochemical investigation of the stem bark extracts of Entada africana led to the isolation and characterization of Stigmasta-7,22-dien-3-ol from the dichloromethane soluble portion of acetone/methanol (1:1v/v) crude extract. The powdered stem bark sample of Entada africana was defatted with hexane and extracted with acetone/methanol (1:1v/v) mixture. The dichloromethane soluble fraction was purified on a low pressure column containing silica gel 60 (60-200 mesh). The purification afforded an isolate coded Enac3 (85 mg) with Rf value of 0.404 in hexane/ethyl acetate (4:1). The isolate was characterized using IR, NMR data and in comparison with literature. Analysis of spectroscopic data and literature comparison suggests Enac3 as stigmasta-7, 22-dien-3-ol. The isolation of stigmasta-7, 22-dien-3-ol from the stem bark of Entada africana suggests the presence of useful bioactive principles which could be exploited for medicinal purposes.

Azeotropic pressure swing distillation of hydrochloric-water for hydrogen production in the Cu[sbnd]Cl cycle: Thermodynamic and design methods

A pressure swing distillation (PSD) process is designed and analyzed in this paper for the maximum boiling azeotrope separation of an HCl-water binary mixture to recycle concentrated HCl (aq) within the CuCl cycle of thermochemical hydrogen production. Aspen Plus simulation and EES software are used to evaluate the characteristics of the PSD apparatus in terms of flow streams, thermodynamic properties and compositions in the binary azeotropic mixture. A heat transfer and mass transfer analysis (with the McCabe-Thiele method) are also used to predict the height of the packed bed distillation column. Results indicate that both analyses predict the same values for the low and high pressure packing column height of 1.7 m and 2 m, respectively. Due to the component's volatility changes through the azeotropic transition at the HCl-water separation, the minimum and maximum concentration of the HCl (aq) would be at the distillate ports of low and high pressure columns, respectively. Moreover, to break the azeotropic point of HCl (aq) in the PSD system, the minimum required low pressure feed concentration at the operating line slopes of 0.2, 0.4, 0.6 and 0.8 should be 0.086, 0.092, 0.097 and 0.103, respectively. From the results, the re-boiler and condenser heat duties at the high pressure distillation column are more affected with the change in the slope of the operating line, compared to the low pressure side.

Robust Control of Partially Heat-Integrated Pressure-Swing Distillation for Separating Binary Maximum-Boiling Azeotropes

Previous studies of partially heat-integrated pressure-swing distillation (PHI-PSD) for separating the binary maximum-boiling azeotropes methanol/trimethoxysilane and ethylenediamine/water have demonstrated difficulties in dynamic control due to the complexity of these processes. In this paper, efforts are made to find new robust control structures to improve the dynamic controllability of these processes in three different types of PHI-PSD sequences. First, for the high-pressure column (HPC) → low-pressure column (LPC) sequence of PHI-PSD for separating the methanol/trimethoxysilane azeotrope, five new control structures are established and three of them are robust. Second, the dynamic controllability of the LPC → HPC sequence of PHI-PSD for separating the methanol/trimethoxysilane azeotrope is investigated for the first time and four robust control structures are proposed. Finally, two new robust control structures are proposed for PHI-PSD for separating the ethylenediamine/water azeotrope. The crucial ...

Features of the determination of amlodipine in a biological material

The purpose of the work is to determine the optimal conditions for isolating amlodipine, to purify it by the method of column chromatography and to develop a method for detecting it in biological material. TLC, GC-MS, low pressure column chromatography, and HPLC were used for analysis. We studied the comparative isolation of amlodipine from biological material using 13 isolating agents of organic nature, water, and aqueous solutions. The use of acetone as an insulating agent for the extraction of amlodipine from tissues of cadaver organs has been substantiated. The possibility of purification of the analyzed compound from the endogenous substances of the biomaterial is shown by the method of reversed phase chromatography in a column of the Silasorp S-18 sorbent of 30 μm. A technique has been developed for detecting amlodipine in the tissues of cadaveric organs (liver), which corresponds to the necessary parameters of linearity, selectivity, accuracy, precision and stability. The limits of detection and quantification of amlodipine by the proposed method are 0.25·10-6 and 4.0·10-6 g, respectively, in 1 g of the biomaterial.

Analysis of the high-energy electron population in surface-wave plasma columns in presence of collisionless resonant absorption

In surface-wave plasmas, the energy can be transferred to the plasma electrons through both ohmic (collisional) and collisionless heating mechanisms. At very low pressure, when the electron–neutral collision frequency is much lower than the wave frequency (collisionless regime), a resonance is excited close to the tube walls where the electron plasma frequency in the radially-inhomogeneous plasma column reaches the wave frequency. In such conditions, the sharp rise of the component of the surface-wave electric field perpendicular to the tube axis can induce transit-time heating. At the resonant point, the long-wavelength electromagnetic surface wave can also be converted into short-wavelength electrostatic Langmuir waves that propagate down the density gradient. In this work, spatially-resolved trace-rare-gases optical emission spectroscopy combined with collisional-radiative modeling is used to analyze the electron energy distribution function (EEDF) and wave–particle interactions in low-pressure argon plasma columns sustained by an electromagnetic surface wave at 600 MHz (over-dense plasma). The EEDF is found to depart from a Maxwellian with the presence of a high-energy tail. The relative population of high-energy electrons increases with the axial distance towards the end of the plasma column where the electron density decreases and the resonance point becomes closer to the discharge axis. Over the range of experimental conditions examined, the high-energy tail increases with the characteristic length of the plasma density gradient at the resonance point; a feature that can be linked to collisionless electron heating by Landau damping of Langmuir waves.

Comparison of flowsheets for THF/water separation using pressure-swing distillation

An eloquent optimization method was recently proposed and tested on the separation of tetrahydrofuran and water using pressure-swing distillation. The purpose of this paper is to compare the results of this rigorous optimum design with the design presented in a 1985 paper, which used heuristic engineering optimization. The new design uses more feed preheating in the low-pressure column and a higher pressure with more trays in the high-pressure column. Simulation results show that the old design has a 14% lower energy cost.

Economic optimization of in situ extraction of inhibitors in acetone-ethanol-butanol (ABE) fermentation from lignocellulose

Abstract The inhibitors produced in the pretreatment (phenolics, furans, and organic acids) as well as in the fermentation (butanol and organic acids) limit acetone, butanol, and ethanol (ABE) production from lignocellulose. To reduce their negative impact on the fermentation, a process involving simultaneous saccharification, ABE fermentation, and detoxification by liquid–liquid extraction was proposed and economically optimized. Although several extractants may be used to reduce butanol toxicity increasing the reactor performance, simultaneous detoxification of inhibitors from pretreatment (IFP) is difficult due to their high boiling point. Hence, the simultaneous detoxification system was evaluated using the biocompatible extractant: oleyl alcohol (boiling point of ∼350 °C). Given that oleyl alcohol and IFP have a high boiling point, a heat-integrated distillation system with low-pressure columns was proposed to reduce the energy requirements of the purification of IFP and products from the fermentation. The simulations were performed rigorously in Aspen Plus® and Matlab® at different concentrations of IFP. Although IFP and butyric acid production become feasible ABE production by SSF-E at concentrations of IFP between 13.5 and 30 g/l, the energy requirements were between 1.2- and 2.4-fold higher than that for IFP concentrations of 9 g/l, respectively.

Pressure-Swing Distillation for Separating Pressure-Insensitive Minimum Boiling Azeotrope Methanol/Toluene via Introducing a Light Entrainer: Design and Control

In this paper, pressure-swing distillation (PSD) is applied to separate pressure-insensitive minimum boiling azeotrope methanol/toluene via introducing chloroform as a light pressure-swing entrainer. The feasibility of this process is verified by analyzing the residue curve maps. Both partially and fully heat-integrated PSD processes are implemented. The steady-state designs of these processes are optimized based on total annual cost (TAC). In this extended PSD process, the high-pressure column (HPC) serves as the homogeneous azeotropic distillation column, while the low-pressure column (LPC) serves as the entrainer recovery column. It is found that the HPC has large temperature slope in the stripper section while with relatively flat trend above. This unique phenomenon makes it beneficial to reduce the energy consumption by preheating the feed and recycling stream using low-grade heat. Both conventional and partially heat-integrated extractive distillation processes with aniline as the entrainer are also...

Mitigating an increase of specific power consumption in a cryogenic air separation unit at reduced oxygen production

Specific power consumed in a Linde double column air separation unit (ASU) increases as the quantity of oxygen produced at a given purity is decreased due to the changes of system requirement or market demand. As the plant operates in part load condition, the specific power consumption (SPC) increases as the total power consumption remains the same. In order to mitigate the increase of SPC at lower oxygen production, the operating pressure of high pressure column (HPC) can be lowered by extending the low pressure column (LPC) by a few trays and adding a second reboiler. As the duty of second reboiler in LPC is increased, the recovery of oxygen decreases with a lowering of the HPC pressure. This results in mitigation of the increase of SPC of the plant. A Medium pressure ASU with dual reboiler that produces pressurised gaseous and liquid products of oxygen and nitrogen is simulated in Aspen Hysys 8.6®, a commercial process simulator to determine SPC at varying oxygen production. The effects of reduced pressure of air feed into the cold box on the size of heat exchangers (HX) are analysed. Operation strategy to obtain various oxygen production rates at varying demand is also proposed.

Design and Control of Reactive Distillation Sequences with Heat-Integrated Stages To Produce Diphenyl Carbonate

Reactive distillation (RD) in quaternary systems has gained importance when one of the reagents is in excess. In this work, higher energy savings in a reactive distillation sequence is addressed to produce diphenyl carbonate, which is a crucial precursor of polycarbonate. Energy savings were attained through heat integration between the high-pressure RD column and the low-pressure separation column. The design of sequences with heat-integrated stages was done by combining simulation and optimization. The sequence with one heat-integrated stage realized the minimum energy consumption with energy savings around 22% and cost savings around 12% in comparison with the conventional reactive distillation sequence. Also, two control schemes for the best design configuration have also been studied in this work. The results showed that the control scheme that manipulates the reboiler duty and reflux ratio to control two stage temperatures can provide excellent responses under throughput and feed composition disturb...

Determination of pesticides in fatty matrices using gel permeation clean-up followed by GC-MS/MS and LC-MS/MS analysis: A comparison of low- and high-pressure gel permeation columns

Two low-pressure columns (Bio-Beads SX-3) and three high-pressure GPC columns were compared for clean-up of a wide range of pesticides in fatty matrices of vegetable or animal origin. The GPC fractions were analyzed by GC-MS/MS and LC-MS/MS without additional clean-up. The performance of the GPC clean-up on the five column types was compared in terms of solvent consumption, lipid removal, pesticide recovery and repeatability.It was found that for fatty matrices, mainly consisting of high molecular weight triglycerides i.e. most vegetable oils and animal fats, good fractionation is obtained for the majority of the pesticides. On the other hand, for fats and oils containing relatively high amounts of low molecular weight triglycerides, i.e. butter fat and palm kernel oil, none of the columns provided sufficient clean-up and cause interferences and system contamination, especially in the case of GC-MS/MS analysis. For the latter case, best results in terms of lipid removal and pesticide recovery were obtained on a set (2×300mmlength) of narrow bore (7.5mm ID) columns packed with 5µm PL Gel material. Column loadability is, however, much lower on that set of columns compared the other evaluated GPC columns, impairing overall method sensitivity.

Introducing a novel air separation process based on cold energy recovery of LNG integrated with coal gasification, transcritical carbon dioxide power cycle and cryogenic CO2 capture

An integrated coal gasification process with a novel double-column cryogenic air separation unit (ASU) based on the LNG (liquefied natural gas) cold energy recovery is proposed and analyzed. The process consists of a trans-critical carbon dioxide power generation cycle, a shift converter unit and cryogenic CO2 capturing system. ASU is used to produce high purity oxygen (99.99%) and nitrogen (99.99%). The specific power demand per flow rate of pure oxygen is 0.11 kWh/kg. Due to effective integration between two distillation columns in the ASU, the latent heat of the condenser in high pressure column is exchanged with reboiler of the low pressure column. The outlet LNG stream from ASU is utilized as cold source of the condenser in the trans-critical CO2 power cycle. The results show energy saving in the ASU and trans-critical power generation are 2301.6 kW and 14,217.6 kW respectively. The produced high purity gaseous oxygen is sent to the coal gasification unit to participate in the gasifier reactions. In this process, 99.83% of carbon dioxide with 99.80% purity, is captured and the required power is about 0.10 kWh/kg CO2.

Separation of an azeotropic mixture of dimethyl carbonate and methanol via partial heat integration pressure swing distillation

AbstractA method for dimethyl carbonate and methanol separation using pressure swing distillation is presented, and the optimum design is proposed by minimizing the total annual cost as the objective function. It is revealed that compared with no heat integration pressure swing distillation (HIPSD), partial HIPSD reduces the total annual cost by 20.01%. This paper presents a criterion for selection of the temperature control stage in the low‐pressure column (LPC), the temperature profile of which is quite close to linear. Additionally, the influences of the temperature stage in the LPC on the dynamic responses in the partial HIPSD are investigated. The results show that the composition/temperature cascade control structure with stage 10 or 31 selected as the control stage in the LPC can achieve efficient controllability of the process, even for large feed flow rates and composition disturbances. © 2016 Curtin University of Technology and John Wiley & Sons, Ltd.

Control of a triple-column pressure-swing distillation process

Abstract The separation of the ternary mixture of acetonitrile, methanol and benzene into three high-purity products is complicated by the presence of three binary azeotropes that divide the ternary diagram into three distinct regions. Fortunately the compositions of two of these azeotropes change significantly with pressure. The economic optimum flowsheet has been developed in a recent paper in the literature that uses a process with three columns operating at different pressures. Three high-purity products are produced as bottoms streams from the three columns with the distillate of the third column recycled back to the first column. The plantwide dynamic controllability of this complex, non-ideal interacting process is studied in this paper. An effective control structure is developed that controls one temperature in each column. Pressure compensation in the low-pressure column improves load rejection of both throughput and feed composition disturbances. No on-line composition measurement is required.

Separation process of butanol-butyl acetate-methyl isobutyl ketone system by the analysis to residual curve and the double effect pressure-swing distillation

The separation of ternary mixture of butanol, butyl acetate, and methyl isobutyl ketone (MIBK) was initially analyzed by the residual curve. In this process, MIBK was chosen as the azeotropic agent during the first step of separation. The optimum mass ratio of extra MIBK was 1.6 in the modified feed stream according to the residual curve. Thus on this condition the top product was butanol-MIBK azeotrope while the bottom product was butyl acetate in the preliminary separation of the mixture. Then the butanol and MIBK azeotrope was separated by the double effect pressure-swing distillation with the low pressure column performing at 30kPa and the atmospheric pressure column at 101kPa. The optimal operating conditions were then obtained by using Aspen Plus to simulate and optimize the process. The results showed that the mass purities of butanol, butyl acetate, and MIBK were all more than 99% and reached the design requirements. Additionally, compared with the traditional distillation with outside heating, the double effect pressure swing distillation saved the reboiler duty by 48.6% and the condenser duty by 44.6%.

Chiral analysis of derivatized amino acids from kefir by gas chromatography

The amino acids present in the kefir samples were derivatized using different alkyl chloroformates combined with alcohols and chromatographed on a (3-O-butanoyl-2,6-di-O-pentyl)-γ-cyclodextrin (Lipodex E) chiral gas–liquid chromatographic column. The combination of derivatization reagents that led to better chromatographic performance for standard amino acid solutions was critically compared. All the chloroformate/alchohol mixtures lead to fast and quantitative reactions. However, the ethyl chloroformate/ethanol mixture was selected since the number of enantioseparated amino acid derivatives was higher. The derivatization was applied to samples of kefir grains grown in raw and in skimmed UHT milk. The samples were previously pretreated by elution from a low-pressure ion-exchange columns. Standard addition calibration curves have been used for the quantitative determinations of amino acid derivatives in both samples, and the figs. of merit of the proposed method have been assessed. The l- and d- configuration of d- and l-alanine, d- and l-valine, d-proline, l-threonine, aspartic and glutamic acids, methionine, and cysteine were detected and quantitatively determined.

Design and control of pressure-swing distillation for azeotropes with different types of boiling behavior at different pressures

The mixture of n-heptane and isobutanol presents minimum- and maximum-boiling azeotropes as the pressure changes. Two different pressure-swing distillation (PSD) processes are available for this mixture if the pressure of the low-pressure column is set as atmospheric. The steady states of the two available PSDs are optimized by minimizing the total annual cost (TAC) following a sequential iterative optimization procedure. On the basis of the steady-state results, the dynamic control of the two available PSDs and a comparison between them are presented. The conventional PSD (CPSD) is more economical but less controllable than the unusual PSD (UPSD), which has seldom been studied in the published literature. These two different PSD processes should be considered for the separation of this type of mixture according to their advantages.

Non-isothermal numerical simulations of dual reflux pressure swing adsorption cycles for separating N2 + CH4

A non-isothermal model of dual reflux pressure swing adsorption (DR-PSA) was developed using a commercially available software package to numerically solve the dynamics of the unit operation. Importantly the model includes a full energy balance, which is a feature not reported previously in the literature for simulations of DR-PSA cycles even though bed temperature swings of 10–20K have been observed in experimental studies. The simulation allowed solution of the pressure-flow network for cycles in the PL-A configuration, where feed gas enters the middle of the low pressure column and where pressure inversion is conducted by transferring gas rich in the more adsorbed component between beds. At cyclic steady state the simulations contained material balance errors comparable in magnitude to those reported previously for isothermal DR-PSA simulations; however, these were accounted for using a robust correction scheme. Predictions of the pressure, flow and temperature profiles within the beds for a range N2+CH4 mixtures being separated using activated carbon were in good agreement with the corresponding results of 24 DR-PSA experiments recently reported by Saleman et al. (2015). The root mean square deviation of the predicted methane mole fractions from the experimental values were 0.003 and 0.024 for the light (N2-rich) and heavy (CH4-rich) product streams, respectively. Parametric studies conducted with the model show how the cycle design can be optimised with respect to reflux flow and the feed-purge step duration, and also illustrate the need for reliable values of the sorption mass transfer coefficient.

Pressure swing distillation of azeotropic mixture – A simulation study

Summary The aim of this work is to simulate a pressure-swing distillation column for the separation and purification of ethanol from the ethanol–water binary system. The choice for this system is due to the importance of the ethanol–water separation. A steady-state equilibrium-stage model based on normalised MESH equations is used to simulate pressure-swing distillation column applied for the production of ethanol. All the work has been carried out using Aspen Plus simulator, version 13.2. Among the activity coefficient models available, the WILSON-RK model with binary parameters predicted by the Aspen Plus simulator is shown to be the most accurate to correlate the experimental vapor-/liquid equilibrium (VLE) data available for the ethanol–water system. The simulation has been satisfactorily carried out for a mixture of 20 mol% ethanol in water at 1 atm pressure and 90 °C with a molar flow rate of 100 kmol/h. The adjusting parameters include D/F ratio and reflux ratio of the two columns to get water purity of 99.5 mol% from the bottom of the Low Pressure Column (LPC) and the ethanol purity of 99.7 mol% from the bottom of High Pressure Column (HPC).