Comparative Analysis: Trays versus Packed Columns in Pressure-Swing Distillation for the Separation of Tetrahydrofuran, Water and Ethanol Azeotropic Mixture

This paper delves into the comparative study of tray and packed column pressure swing distillation systems, focusing on the separation of a ternary mixture containing ethanol, tetrahydrofuran (THF), and water. The study particularly emphasizes the production of 99.5 w/w% tetrahydrofuran from the downstream product of 1,4-butanediol synthesis via diethyl maleate. Pro/II simulation software is utilized to explore various system configurations, including sieve trays, valve trays, and packed columns. Material and energy balances are performed to ascertain stream compositions and energy demands. The investigation encompasses the effects of column operating pressure on condenser and reboiler temperatures, as well as the implications of utility streams. A rigorous distillation model is employed to compare valve tray, sieve tray, and random packing (utilizing Norton Super Intalox) column designs by varying the number of trays, reflux ratio, and second distillation column pressure. Heat exchangers are integrated into the model, and their areas and utility flow rates are computed and integrated into the economic assessment. Economic analysis, guided by Net Present Value (NPV) calculations over a 20-year span, drives the selection of the most cost-effective design. Results demonstrate that while all designs are energy-efficient, the packed column system emerges as the most economical choice, offering a comprehensive framework for the separation process. Furthermore, optimal design configurations and operating conditions for both tray and packed column systems are outlined, providing valuable insights for industrial applications.

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 pressureswing distillation with the low pressure column performing at 30 kPa and the atmospheric pressure column at 101 kPa. 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%.

Comparison of continuous homogenous azeotropic and pressure-swing distillation for a minimum azeotropic system ethyl acetate/nhexane separation

Continuous homogenous azeotropic distillation(CHAD) and pressure-swing distillation(PSD) are explored to separate a minimum-boiling azeotropic system of ethyl acetate and n-hexane. The CHAD process with acetone as the entrainer and the PSD process with the pressures of 0.1 MPa and 0.6 MPa in two columns are designed and simulated by Aspen Plus. The operating conditions of the two processes are optimized via a sequential modular approach to obtain the minimum total annual cost(TAC). The computational results show that the partially heat integrated pressure-swing distillation(HIPSD) has reduced in the energy cost and TAC by 40.79% and 35.94%, respectively, than the conventional PSD, and has more greatly reduced the energy cost and TAC by 62.61% and 49.26% respectively compared with the CHAD process. The comparison of CHAD process and partially HIPSD process illustrates that the partially HIPSD has more advantages in averting the product pollution, energy saving, and economy.

A Mathematical Model for Designing Optimal Shape for the Cone Used in Z-flow Type Radial Flow Adsorbers

Nonuniform flow distribution along the radial direction usually exists in a Z-flow type radial flow adsorber,which will decrease the utilization of adsorbent and the switching time and may result in operating safety problems in cryogenic air separation.In order to improve the uniformity of the flow distribution along the radial direction in the adsorber,a differential equation is derived through pressure drop analysis in the Z-flow type radial adsorber with a cone in the middle of the central pipe.The differential equation determines the ideal cross-sectional radii of the cone along the axis.The result shows that the cross-sectional radius of the cone should gradually decrease from 0.3 m to zero along the axis to ensure that the process air is distributed uniformly in the Z-flow type radial flow adsorber and the shape of the cone is a little convex.The flow distribution without the cone in the central pipe is compared under different bed porosities.It is demonstrated that the proposed differential equation can provide theoretical support for designing Z-flow type radial flow adsorbers.

Design and control of methyl acetate-methanol separation via heat-integrated pressure-swing distillation

Design and control of pressure-swing distillation(PSD) with different heat integration modes for the separation of methyl acetate/methanol azeotrope are explored using Aspen Plus and Aspen Dynamics. First, an optimum steady-state separation configuration conditions are obtained via taking the total annual cost(TAC) or total reboiler heat duty as the objective functions. The results show that about 27.68% and 25.40% saving in TAC can be achieved by the PSD with full and partial heat integration compared to PSD without heat integration. Second,temperature control tray locations are obtained according to the sensitivity criterion and singular value decomposition(SVD) analysis and the single-end control structure is effective based on the feed composition sensitivity analysis. Finally, the comparison of dynamic controllability is made among various control structures for PSD with partial and full heat integration. It is shown that both control structures of composition/temperature cascade and pressure-compensated temperature have a good dynamic response performance for PSD with heat integration facing feed flowrate and composition disturbances. However, PSD with full heat integration performs the poor controllability despite of a little bit of economy.

Dynamic control analysis of interconnected pressure-swing distillation process with and without heat integration for separating azeotrope

Dynamic controls of pressure-swing distillation with an intermediate connection(PSDIC) process of ethyl acetate and ethanol separation were investigated.The double temperature/composition cascade control structure can perfectly implement effective control when ±20% feed disturbances were introduced.This control structure did not require the control of the flowrate of the side stream.The dynamic controllability of PSDIC with partial heat integration(PHIPSDIC) was also explored.The improved control structure can effectively control ±20% feed disturbances.However,in industrial production,simple controller,sensitive and easy to operate,is the optimal target.To avoid the use of component controllers or complex control structure,the original product purities could be maintained using the basic control structure for the PSDIC process if the product purities in steady state were properly increased,albeit by incurring a slight rise in the total annual cost(TAC).This alternative method without a composition controller combined with the energy-saving PSDIC process provides a simple and effective control scheme in industrial production.

Investigation on a vertical radial flow adsorber designed by a novel parallel connection method

Due to the increasing global demand for industrial gas, the development of large-scale cryogenic air separation systems has attracted considerable attention in recent years. Increasing the height of the adsorption bed in a vertical radial flow adsorber used in cryogenic air separation systems may efficiently increase the treatment capacity of the air in the adsorber. However, uniformity of the flow distribution of the air inside the adsorber would be deteriorated using the height-increasing method. In order to reduce the non-uniformity of the flow distribution caused by the excessive height of adsorption bed in a vertical radial flow adsorber, a novel parallel connection method is proposed in the present work. The experimental apparatus is designed and constructed; the Computational Fluid Dynamics(CFD) technique is used to develop a CFD-based model, which is used to analyze the flow distribution, the static pressure drop and the radial velocity in the newly designed adsorber. In addition, the geometric parameters of annular flow channels and the adsorption bed thickness of the upper unit in the parallelconnected vertical radial flow adsorber are optimized, so that the upper and lower adsorption units could be penetrated by air simultaneously. Comparisons are made between the height-increasing method and the parallel connection method with the same adsorber height. It is shown that using the parallel connection method could reduce the difference between the maximum and minimum radial static pressure drop by 86.2% and improve the uniformity by 80% compared with those of using the height-increasing method. The optimal thickness ratio of the upper and lower adsorption units is obtained as 0.966, in which case the upper and lower adsorption units could be penetrated by air simultaneously, so that the adsorbents in adsorption space could be used more efficiently.

NUMERICAL SIMULATION OF THE EFFECT OF MALDISTRIBUTION IN A FIXED BED ADSORBER

The paper deals with the modeling of the effect of maldistribution in pollutant abatementtrichloroethylene（TCE）concerning low concentration(10-5-10-8kg·m-3)adsorption in an adsorber.Such a concentration range is rather typical in many an environmental application.Isotherms andbreakthrough curves for TCE adsorption are obtained both for a commercial activated carbonSorbonorit 4 and a laboratory adsorber of dB/dP=11.Two two-dimensional nonequilibrium isothermalmodels are developed to describe the mass transfer in the fixed bed taking into account the effect ofmaldistribution.It is found the simulation results with maldistribution are in very good agreementwith the experimental findings.Low concentration TCE adsorption in a fixed bed of activated carbonis found to be strongly influenced by maldistribution.The non-uniform distributions of concentrationand loading of the pollutant in the adsorber are predicted by the model.Maldistribution and its ef-fect on the initial breakthrough of TCE in

DIFFUSION MODES IN A DIFFUSION-CELL ADSORBER

Theoretical considerations on diffusion modes of adsorbates in diffusion-cell adsorbers are being investigated. By studying the effects of the operating and model parameters on the response curves calculated by surface diffusion model and pore diffusion model, and noting the differences in the results, the following conditions are recommended for the prediction of the prevailing diffusion mode in diffusion-cell experimentsλ≤0.1,BiB≥100,and N≥1The theoretical prediction thus obtained checks well with experimental data taken from literature. New solutions are also presented for the surface diffusion model and the pore diffusion model with rectangular adsorption isotherm.

Dynamic adsorption of Xe on a fixed-bed adsorber at 77 K

In designing a fixed-bed adsorber, it is vital to understand dynamic adsorption properties of the unit. Temperature is an important effect on adsorbent performance, as the dynamic adsorption coefficients tend to increase with decreasing temperature. To minimize the volume of the fixed-bed adsorber, the dynamic adsorption characteristics of Xe were studied at 77 K by employing a variety of adsorbents under different operational conditions. The carbon molecular sieve performed better than that of activated carbon. Both operational conditions and the presence of gaseous impurities were found to affect the adsorption properties.

Economic and entropy production evaluation of extractive distillation and solvent-assisted pressure-swing distillation by multi-objective optimization

Extractive distillation(ED)and solvent-assisted pressure-swing distillation(SA-PSD)are both special distillation processes that perform good at separating pressure-insensitive azeotropes.However,few reported studies have compared the performance of the two processes.In this paper,ED processes with N-methylpyrrolidone(NMP)and dimethlac-etamide(DMCA)as entrainer,SA-PSD process with isopropyl-alcohol(IPA)as solvent and SA-PSD process with partial heat integration(PHI-PSD)are proposed to achieve high purity separation of a mixture of cyclohexane/2-butanol system.The optimal operating conditions of the processes are obtained after optimizing with NSGA-Ⅱ algorithm when total annual cost(TAC)and the entropy production of process are set as objectives.The optimal results show that the optimal PHI-PSD process has lower TAC by 28.7% and the lower entropy production by 39.5% than the optimal SA-PSD process while the ED process with NMP as entrainer has lower TAC by 50.9% and the lower entropy production by 56.1% than the optimal SA-PSD process.The optimal results show that the ED process with NMP as entrainer has the best economic and thermodynamic efficiency among the four proposed processes in this paper.

Characterization of P-nitrophenol Adsorption Kinetic Properties in Batch and Fixed Bed Adsorbers

P-nitrophenol（PNP） adsorption in batch and fixed bed adsorbers was studied. The homogeneous surface diffusion model（HSDM） based on external mass transfer and intraparticle surface diffusion was used to describe the adsorption kinetics for PNP in stirred batch adsorber at various initial concentrations and activated carbon dosages. The fixed bed model considering both external and internal mass transfer resistances as well as axial dispersion with non-linear isotherm was utilized to predict the fixed bed breakthrough curves for PNP adsorption under the conditions of different flow rates and inlet concentrations. The equilibrium parameters and surface diffusivity（Ds） were obtained from separate experiments in batch adsorber. The obtained value of Ds is 4.187×1012 m2/s. The external film mass transfer coefficient（kf） and axial dispersion coefficient（DL） were estimated by the correlations of Goeuret and Wike-Chang. The Biot number determined by HSDM indicated that the adsorption rate of PNP onto activated carbon in stirred batch was controlled by intraparticle diffusion and film mass transfer. A sensitivity analysis was carried out and showed that the fixed bed model calculations were sensitive to Ds and kf, but insensitive to DL. The sensitivity analysis and Biot number both confirm that intraparticle diffusion and film mass transfer are the controlling mass transfer mechanism in fixed bed adsorption system.

Pd-M-TiO_(2)(M=Mn,Cu,Ce and Fe)as passive NO_(x) adsorber(PNA)at low temperature

A series of transition metal Mn,Cu,Ce and Fe were loaded on TiO_(2) by sol-gel method with noble metal Pd as promotor for the application of passive NO_(x) absorber.Experiments on adsorption and desorption of NO_(x) were conducted and characterization methods such as X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS),transmission electron microscopy(TEM)and in situ Fourier transform infrared spectroscopy(in situ DRIFTS)were involved.The experimental results show that Mn-contained catalysts,Mn-Ti and Pd-Mn-Ti,performed excellent NO_(x) adsorbing ability and appropriate desorption temperature window.On the other hand,Ce-and Cu-contained samples were not suitable for the purpose of PNA.In addition to the low adsorption capacity,these two series of catalysts released massive amount of NO below 150℃.Characterization results indicated that Pd was highly dispersed on all catalysts.The loading of Pd lowered not only the valence states of transition metals but surface oxygen percentage as well.From in situ DRIFTS tests,the Pd had little influence on the types of adsorbed substances for Mn,Ce and Cu series.However,the storage forms of NO_(x) were obviously different on Pd-Fe-Ti and Fe-Ti.

A functionalized activated carbon adsorbent prepared from waste amidoxime resin by modifying with H_(3)PO_(4) and ZnCl_(2) and its excellent Cr(Ⅵ)adsorption

With the application of resins in various fields, numerous waste resins that are difficult to treat have been produced. The industrial wastewater containing Cr(Ⅵ) has severely polluted soil and groundwater environments, thereby endangering human health. Therefore, in this paper, a novel functionalized mesoporous adsorbent PPR-Z was synthesized from waste amidoxime resin for adsorbing Cr(Ⅵ). The waste amidoxime resin was first modified with H3PO4 and ZnCl_(2), and subsequently, it was carbonized through slow thermal decomposition. The static adsorption of PPR-Z conforms to the pseudo-second-order kinetic model and Langmuir isotherm, indicating that the Cr(Ⅵ) adsorption by PPR-Z is mostly chemical adsorption and exhibits single-layer adsorption. The saturated adsorption capacity of the adsorbent for Cr(Ⅵ) could reach 255.86 mg/g. The adsorbent could effectively reduce Cr(Ⅵ) to Cr(Ⅲ) and decrease the toxicity of Cr(Ⅵ) during adsorption. PPR-Z exhibited Cr(Ⅵ) selectivity in electroplating wastewater. The main mechanisms involved in the Cr(Ⅵ) adsorption are the chemical reduction of Cr(Ⅵ) into Cr(Ⅲ) and electrostatic and coordination interactions. Preparation of PPR-Z not only solves the problem of waste resin treatment but also effectively controls Cr(Ⅵ) pollution and realizes the concept of “treating waste with waste”.

Deciphering the linear relationship in the activity of the oxygen reduction reaction on Pt electrodes:A decisive role of adsorbates

Despite substantial efforts in developing high-performance catalysts for the oxygen reduction reaction(ORR),the persistent challenge lies in the high onset overpotential of the ORR,and the effect of the elec-trolyte solution cannot be ignored.Consequently,we have systematically investigated the impact of adsorbate species and concentration,as well as solution pH,on the ORR activity on Pt(111)and Pt(poly)electrodes.The results all tend to establish a linear quantitative relationship between the onset potential for ORR and the adsorption equilibrium potential of the adsorbate.This finding indicates the decisive role of adsorbates in the onset potential for ORR,suggesting that the adsorption potential of adsorbates can serve as an intuitive criterion for ORR activity.Additional support for this conclusion is derived from experimental results obtained from the oxygen evolution reaction on Pt(poly)with different adsorbate species and from the hydrogen evolution reaction on Pt(111)with iodine adsorption.We further propose both an empirical equation for the onset potential for ORR and the concept of a potential-regulated adsor-bate shielding effect to elucidate the influence of adsorbates on ORR activity.This study provides new insights into the high onset overpotential of the ORR and offers potential strategies for predicting and enhancingORRactivity inthefuture.

Modeling of the Adsorption Allowing for the Changing Adsorbent Activity at Various Stages of the Process

The goal of this work is,first of all,to construct a mathematical model of the mass transfer process in porous adsorption layers,taking into account the fact that in most cases the adsorption process is carried out in nonstationary technological modes,which requires a clear description of its various stages.The scientific contribution of the novel model is based on a probability approach allowing for deriving a differential equation that takes into account the diffusion migration of adsorbed particles.Solving this equation allows us to calculate the reduced degree of the adsorption surface coverage along the flow and,thereby,calculate the efficiency of the mass transfer process.The model also makes it possible to determine the slip coefficient,the internal diffusion coefficient and the degree of filling of the internal surface of the pores of the adsorbent layer,which corresponds to the completion of the initial stage of adsorption and the transition of the process to a stable mode.In this case,the problem is to calculate a non-isothermal turbulent boundary layer when flowing around the surface of an adsorbent.Next,the problem of identifying the main control parameters of the model has been solved.Based on such analysis and experimental studies to assess the influence of process control parameters,the patterns of adsorption purification and solution separation have been established and the design of a highly efficient adsorption apparatus with a fixed layer of porous adsorbent have been developed.

玛湖凹陷二叠系风城组页岩油储层特征及高产主控因素

通过岩石薄片、扫描电镜、低温氮气吸附、高压压汞、岩心荧光、激光共聚焦显微镜和产液剖面等实验分析测试资料,对玛湖凹陷二叠系风城组储层特征及页岩油高产主控因素进行了详细研究。研究结果表明:①玛湖凹陷二叠系风城组页岩油储层类型可划分为砂岩类、白云岩类和泥岩类等,粉砂岩类储层以陆源碎屑沉积物为主,泥岩类储层以陆源-内源混积物为主,白云(灰)岩类储层以内源化学沉积为主;玛湖凹陷风城组粉砂岩类、白云岩类和泥岩类储层孔隙喉道尺寸依次减小,孔隙连通性依次变差。②玛湖凹陷风城组粉砂岩类储层含油性最好,其次是泥岩类储层,白云岩类储层含油性最差,孔径较大的孔隙和微裂缝中的游离油含量较高,孔径较小的孔隙中的吸附油含量较高。③玛湖凹陷风城组优质烃源岩和优质储层分别控制着页岩油的高产区域和高产层段,长英质矿物含量、有效孔隙度值、游离油孔隙度值、裂缝密度和脆性指数等均较高的储层是页岩油高产的有利层段。

In situ investigation of atmospheric corrosion behavior of PCB-ENIG under adsorbed thin electrolyte layer

The effects of relative humidity (RH) on a printed circuit board finished with electroless nickel immersion gold (PCB-ENIG) under an adsorbed thin electrolyte layer (ATEL) were investigated in situ via the measurement of cathodic polarization curves, electrochemical impedance spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy to clearly elaborate the corrosion behavior of PCB-ENIG in the atmospheric environment. Results indicated that the cathodic process of PCB-ENIG under ATEL was dominated by the reduction of dissolved oxygen, corrosion products, and H2O. The cathodic current density of PCB-ENIG increased progressively with increasing RH. Moreover, its cathodic current density in the solution was greater than that under ATEL. This result demonstrated that the diffusion process was not the controlling step during the limiting reduction of cathodic oxygen. When the polarization potentials were located in a more negative region, the cathodic polarization current density gradually decreased under 75% and 85% RH. Notably, the anodic process became the controlling step in the extremely thin liquid film during the remainder of the experiment.

Dielectric Relaxation of Adsorbed Water in Wood Cell Wall under Equilibrium and Non-Equilibrium State

This article summarized systematically the previous investigations on t he dielectric relaxation of wood, the main substances and extractives in wood at oven-dry state, and the dielectric relaxation based on the adsorbed water in w o od cell wall under equilibrium and non-equilibrium state. Moreover, some expect a tions for future research were proposed on this basis. The purpose of this artic le is to provide other researchers an overall understanding about the research i n this region, and further to promote the research onto a new and higher level.

Synthesis of Li^+ adsorbent(H_2TiO_3) and its adsorption properties

H2TiO3 was obtained from the acid-modified adsorbent precursor Li2TiO3,which was synthesized by a solid-phase reaction between TiO2 and Li2CO3.The extraction ratio of Li＋ from Li2TiO3 was 98.86%,almost with no Ti4＋ extracted.The effects of lithium titanium ratio,calcining temperature and time were investigated on the synthesis of Li2TiO3.Li2TiO3,H2TiO3 and the adsorbed Li＋ adsorbent were characterized by XRD and SEM.The lithium adsorption properties were investigated by the adsorption kinetics and adsorption isotherm.The results indicate that H2TiO3 has an excellent adsorptive capacity for Li＋.Two simplified kinetic models including the pseudo-first-order and pseudo-second-order equations were selected to follow the adsorption processes.The rate constants of adsorption for these kinetic models were calculated.The results show that the adsorption process can be described by the pseudo-second-order equation,and the process is proved to be a chemical adsorption.The adsorption process that H2TiO3 adsorbs Li＋ in LiCl solution well fits the Langmuir equation with monolayer adsorption.