Optimization design for removal of radioactive Kr from Xe using pressure swing adsorption

The goal of this paper is to remove radioactive Kr from Xe based on the development of a viable PSA (pressure swing adsorption) process, because it normally requires a few years for ⁸⁵Kr to achieve a significant decay level of this isotope. A general purpose model is built to remove ⁸⁵Kr in the cyclic PSA process with partial differential equations. Because there are no steady state and constant operating variables in the operation of the PSA process, the design of PSA at each step is critical for satisfactory performance. Thus, an optimization technique based on a genetic algorithm is used. The optimization leads to significant improvement for PSA. Moreover, for the physical model based design, changes in the operation of the process mean the original design condition may no longer be a true reflection of the desired quality. An iterative learning design is also proposed. This work aims to find out the optimal design condition for PSA.     

Production of argon free oxygen by adsorptive air separation on Ag‐ETS‐10

The purification of different components of air, such as oxygen, nitrogen, and argon, is an important industrial process. Pressure swing adsorption (PSA) is surpassing the traditional cryogenic distillation for many air separation applications, because of its lower energy consumption. Unfortunately, the oxygen product purity in an industrial PSA process is typically limited to 95% due to the presence of argon which always shows the same adsorption equilibrium properties as oxygen on most molecular sieves. Recent work investigating the adsorption of nitrogen, oxygen and argon on the surface of silver‐exchanged Engelhard Titanosilicate‐10 (ETS‐10), indicates that this molecular sieve is promising as an adsorbent capable of producing high‐purity oxygen. High‐purity oxygen (99.7+%) was generated using a bed of Ag‐ETS‐10 granules to separate air (78% N₂, 21% O₂, 1% Ar) at 25°C and 100 kPa, with an O₂ recovery rate greater than 30%. © 2012 American Institute of Chemical Engineers AIChE J, 59: 982–987, 2013     

Production of dehydrated fuel ethanol by pressure swing adsorption process in the pilot plant

Fermented ethanol is gaining wide popularity as a car fuel additive. The pressure swing adsorption (PSA) process is attractive for the dehydration of bioethanol on the industrial scale, since its energy consumption is low and it is capable of producing a very pure product. 3 ? zeolite possesses micro-pores which, due to their small size, adsorb water molecules but not ethanol molecules. In this work, up to 2 kL/day of dehydrated ethanol (99.5% by weight) was successfully produced with 3 ? zeolite by the pressure swing adsorption process. The cycles of the PSA process were operated under the following variables: feed flow rate (27–62 Nm³/hr of 93.2% by weight), purge/feed ratio (30–24%), adsorption temperature (130–140 °C) and adsorption pressure (1.2 atm).     

Oxygen Production by Pressure Swing Adsorption

Abstract

The specific oxygen production capacity and the oxygen recovery of a pressure swing adsorption (PSA) process for the production of oxygen from ambient air by selective adsorption of nitrogen can be increased by operating the process at a superambient temperature. The higher temperature operation provides more efficient desorption of nitrogen from the adsorbent which more than off-sets the detrimental effects of the lower selectivity and capacity of adsorption of nitrogen from air at the elevated temperature. The concept is demonstrated by evaluating the performance of an eight-step PSA-oxygen process to produce a 90% oxygen product stream at different temperatures. It is shown that 10% higher oxygen production capacity and 14.5% larger oxygen recovery can be obtained by operating the PSA process at 60°C compared to its performance at 30°C. The PSA process and its performance data from a pilot plant are discussed.     

Adsorption and Desorption of Carbon Dioxide and Nitrogen on Zeolite 5A

The adsorption equilibrium data of CO₂ and N₂ at (303, 333, 363, 393, 423) K ranging 0-1 bar on zeolite 5A is reported. The pressure and temperature range covers the operating pressure in adsorption units for CO₂ capture from power plants. Experimental data were fitted by the multi-site Langmuir model. The adsorbent is much more selective to CO₂: loading at 303 K and 100 kPa is 3.38 mol/kg while loading of N₂ at the same pressure is 0.22 mol/kg. The Clausius-Clapeyron equation was employed to calculate the isosteric enthalpy of adsorption. The fixed-bed adsorption and desorption of carbon dioxide and nitrogen on zeolite 5A pellets has been studied. A model based on the bi-LDF approximation for the mass transfer, taking into account the energy and momentum balances, had been used to describe the adsorption kinetics of carbon dioxide and nitrogen. The model predicted satisfactorily the breakthrough curves obtained with carbon dioxide–nitrogen mixtures. Desorption process (consisting of depressurization, blowdown, and purge) was also performed. Following the feasibility of concentration and capture of carbon dioxide from flue gases by Pressure Swing Adsorption (PSA) process was simulated. A CO₂ recovery of 91.0% with 53.9% purity was obtained using a five-step Skarstrom-type PSA cycle.     

Carbon-based oxygen selective desiccants for use in nitrogen PSA

Techniques for the production of composite oxygen selective adsorbents are disclosed. These adsorbents are comprised of a carbon molecular sieve (CMS) which is kinetically selective for the adsorption of oxygen over nitrogen and an agent for the sorption of water such as LiCl or SiO₂. The adsorption properties of the composite adsorbents and results obtained from pressure swing adsorption (PSA) process testing are presented. The composite adsorbents improve the nitrogen PSA process performance (recovery and productivity) over the use of conventional desiccants which do not exhibit oxygen selectivity. Using a standard nitrogen PSA process cycle, replacement of conventional inorganic desiccants like alumina with the current CMS-based desiccants improved air recovery 2 to 4 percentage points and increased nitrogen productivity 15 to 20% at 70°F and a nitrogen purity of 99.5%.     

变压吸附技术在气体分离提纯中的应用

介绍了变压吸附技术的基本原理、发展概况及基本工作过程,并阐述了该技术在氢气的分离与提纯、二氧化碳的分离与提纯、一氧化碳的分离、空气分离制氧、空气分离制氮、碳的脱除等工业过程中的应用,对变压吸附技术今后的发展提出了展望。     

Predictive Dynamic Model of Air Separation by Pressure Swing Adsorption

A general dynamic model is developed for separation of air over a carbon molecular sieve and a zeolite adsorbent for production of nitrogen and oxygen. The proposed model is validated using experimental data from working laboratory scale N₂–PSA and laboratory scale O₂–PSA systems. Simulations studies are performed to investigate the effect of changing various process variables, such as the duration of PSA steps, bed length and feed inlet velocity.     

The Ozone Treatment for Nitrogen Removal from Liquid Wastes at High Salinity: Full-Scale Optimization and Economical Aspect

The study involved the optimization of the flow scheme of a full-scale platform for industrial liquid wastes. Non-hazardous liquid wastes from natural gas extraction (spent brine) represent 26% of the total influent wastes. For elevated salinity this waste is strongly inhibitory for traditional biological processes. The implementation of the treatment solution is represented by advanced oxidation with ozone in a separate line to remove the ammonia nitrogen with the direct transformation in nitrogen gas. The ratio of bromides/nitrogen greater than 0.4 was evaluated as being the determining factor to activate the process. Ammonia, without the formation of secondary nitrogen compounds, decreases up to 21 mgL^?1 dosing 300 mgO₃ L^?1 and equal to 0 mgL^?1 at maximum ozone. In addition, the catalytic effect of bromides determines a reduction of nitrate to final concentrations of 5 mgL^?1. Any carcinogenic compounds, such as bromates, or residual stripped ammonia were not noted. The economical evaluation was reported.     

Improvement of a fed‐batch process for high level xylanase production by a Bacillus strain

In this paper, the improvement of a fed‐batch fermentation from the point of view of an industrial xylanase production process is described. The Bacillus strain chosen for this study is able to produce high quantities of a xylanase that is suitable to be used as bleach boost agent in chlorine‐free bleaching sequences of paper pulp. It was found that xylo‐oligosaccharides (hydrolysis products from xylan by xylanase action) were indispensable for induction of the enzyme synthesis, but that their presence in quantities of only 0.1 g dm^?3 xylose equivalents led to catabolite repression. A substrate‐limited fed‐batch process, that is the most adapted, was furthermore improved with regard to nutrient requirement of the microorganism, especially the nitrogen source. A process with constant supply of a culture medium containing xylan, peptone and mineral nitrogen was able to produce 20 240 nkat cm^?3 with a productivity of 910 nkat cm^?3 h^?1, which places the process among the best ever reported. © 2001 Society of Chemical Industry     

Photocrosslinking of solvent-based acrylic pressure-sensitive adhesives (PSA) by the use of selected photoinitiators type I

This study investigated the photocrosslinking of solvent-based acrylic pressure-sensitive adhesives (PSA) containing selected photoinitiators type I, known as α-cleavage photoinitiators. Photocrosslinking of PSA, especially of acrylic PSA, is well established crosslinking process using the UV radiation technology. UV-initiated crosslinking of acrylic PSA allows the synthesis of the wide range of UV-crosslinkable PSA with the interesting features. Especially, the important balances of properties such as adhesive and cohesive strength which are typically critical for the application performance can be achieved by this technology. The selection of suitable photoinitiator plays an important role to obtain the optimum properties of acrylic PSA including tack, peel adhesion, and shear strength. In this study, the investigations on different saturated conventional photoinitiators of type I for solvent-based PSA were carried out. The effects of photoinitiator concentration, UV crosslinking time and UV dose on the tack, peel strength, and shear strength were explored in detail for guiding the choice of photoinitiators to fabricate advanced PSA for industrial usage.     

Recovery of vinyl chloride from by-streams of polyvinyl chloride production by TPSA in a multitubular adsorber

This work aims at developing an efficient and feasible adsorption-based separation process for the separation of vinyl chloride and nitrogen, on activated carbon, by employing a multitubular packed bed geometry, with adsorbent material inside the tubes. Using this geometry, a 2-dimensional mathematical model of a temperature pressure swing adsorption process was used to developed a 6-step three multitubular adsorbers system capable of separating and purifying an industrial scale gas stream of a 40:60% (v/v) vinyl chloride/nitrogen mixture into a 95% (v/v) vinyl chloride stream and a nitrogen stream with a vinyl chloride limit concentration of 8 ppm (w/w). The process reported energy consumption of 4.88 × 10⁶ J/kg_VCM and recovery capacity of 24.35 kg_VCM/(m³_unit h). The multitubular geometry enabled the use of lower adsorbent loads, shorter cycle times, and lower regeneration temperatures. An equivalent 1-dimensional model has also shown to satisfactorily estimate the performance of the current equipment.     

Carbon molecular sieves for gas separation processes

The development and commercialization of carbon molecular sieves (CMS) are closely connected with the development of pressure swing adsorption (PSA) processes for the separation of gases. It was already known in the 1960s that certain carbonaceous materials have a molecular sieving effect similar to that of the well known zeolitic molecular sieves. The effect was observed during basic research on anthracite and bituminous coal which are both known to be porous. However, the separation effect, e.g. for oxygen/nitrogen, was very small. It was not until the 1970s that large-scale production of uniform quality CMS suitable for commercial application in PSA processes was established. Nowadays, different types of CMS are successfully used in PSA plants, e.g. for the generation of nitrogen from air, for the production of methane from biogases, and for the recovery of hydrogen from coke oven and steam reforming gases^1–4.     

Fabrication and application of Diachem® electrodes

Conductive diamond coated electrodes have undergone intensive investigation over the past number of years. The unique electrochemical properties of diamond electrodes such as their extreme chemical resistance, even at high doping concentrations, and high overvoltage for water electrolysis opens the door to numerous applications. For the industrial use of extremely promising electrode material sufficient availability, also for large area electrodes is necessary. The development of large area DIACHEM^® electrodes therefore has been performed on a range of base materials of numerous material geometries. For the production of these electrodes a large area HFCVD process is used which allows for reproducible coatings of substrates up to 50×100 cm. A doping with boron allows the reproducible setting of the resistivity of the diamond coating in the range of 5 to 100 m Ω cm. The extent to which DIACHEM^® electrodes have been developed by now means that they can presently be applied in various industrial applications. The most important applications include: industrial waste water treatment, in particular the mineralization of toxic organic compounds; the disinfection of water; circulation systems with water which are only possible through use of an electrochemical recycling process; electrochemical synthesis, in particular from strong oxidising solutions and galvanic processes such as the recycling of chrome baths. Previous investigations have shown that the use of DIACHEM^® electrodes results in either a significant improvement in the effectiveness or that the process was only possible through use of this particular electrode material. The user gains a combination of the typical advantages of the electrochemical process with the high efficiency of the DIACHEM^® electrode which, in turn, has generated enormous interest in this particular material. In order to satisfy this interest, CONDIAS GmbH offers the DIACHEM^® electrode commercially.     

Process intensification in duplex pressure swing adsorption

As an alternative to the Pressure Swing Adsorption (PSA) based on the Skarstrom cycle or its variants, a novel two-bed PSA - called duplex PSA - has been proposed by Hirose and independently by Leavitt to get both products of high purities. A modified duplex PSA has been presented to achieve process intensification, that is, to enhance the product purities and productivities. Simulation studies were carried out to explore the attainable product purities and possible process intensification for CO₂ capture with the original and modified duplex PSA. The volume reduction of beds that can be realized with modified duplex PSA is about 100-50 times the original duplex PSA depending upon the product purities.     

An improved phase‐inversion process for the preparation of silica/poly[styrene‐co‐(acrylic acid)] core–shell microspheres: synthesis and application in the field of polyolefin catalysis

Spherical and well‐dispersed silica/poly[styrene‐co‐(acrylic acid)] (SiO₂/PSA) core–shell particles have been synthesized using an improved phase‐inversion process. The resulting particles were successfully used as supports for polyolefin catalysts in the production of polyethylene with broad molecular weight distribution. Through the vapor phase, instead of the liquid phase in the traditional process, a non‐solvent was introduced into a mixture of micrometer‐sized SiO₂ and PSA solution. The core–shell structure of the resulting SiO₂/PSA microspheres was confirmed using optical microscopy, scanning electron microscopy, Fourier transfer infrared spectrometry, thermogravimetric analysis and measurement of nitrogen adsorption/desorption isotherms. In order to avoid agglomeration of particles and to obtain a good dispersion of the SiO₂/PSA core–shell microspheres, the non‐solvent was added slowly. As the concentration of PSA solution increased, the surface morphology of the core–shell particles became looser and more irregular. However, the surface area and the pore volume remained the same under varying PSA concentrations. The SiO₂/PSA core‐shell microspheres obtained were used as a catalyst carrier system in which the core supported (n‐BuCp)₂ZrCl₂ and the shell supported TiCl₄. Ethylene/1‐hexene copolymerization results indicated that the zirconocene and titanium‐based Ziegler–Natta catalysts were compatible in the hybrid catalyst, showing high activities. The resulting polyethylene had high molecular weight and broad molecular weight distribution. Copyright © 2010 Society of Chemical Industry     

Phosphate Esters Functionalized Dihydroxyl Soybean Oil Tackifier of Pressure-Sensitive Adhesives

Dihydroxyl soybean oil (DSO) has shown potential as a tackifier for pressure-sensitive adhesive (PSA) applications, and perchloric acid was used previously as a catalyst to open the oxirane rings of epoxidized soybean oils (ESO) when we prepared DSO and PSA. Phosphoric acid is a more eco-friendly catalyst than perchloric acid; therefore, the objective of this work was to prepare DSO using phosphoric acid as a catalyst and thereby create DSO-contained phosphate esters, or PDSO. The chemical scaffolds of PDSO were elucidated with ¹H, ¹H–¹H COSY, ³¹P NMR, FTIR, MALDI-TOF MS, and GPC. ESO PSAs were prepared from a mixture of ESO/PDSO. The ESO PSA prepared with PDSO had peel strength on a plastic carrier comparable to commercial PSA, and while on an aluminum carrier, the ESO PSA had a stronger peel strength. ESO PSA prepared with phosphoric acid was also stronger than the peel strength of the ESO PSA prepared with DSO using perchloric acid.     

Large‐scale computational screening of metal‐organic frameworks for CH4/H2 separation

Molecular simulations were performed to study a diverse collection of 105 metal‐organic frameworks (MOFs) for their ability to remove CH₄ from CH₄/H₂ mixture. To investigate the practical industrial application in a pressure swing adsorption (PSA) process, working capacity was also considered in addition to selectivity. The results show that MOFs are promising candidate for this separation, which give higher adsorption selectivity with similar working capacity and higher working capacity with similar selectivity than the traditional nanoporous materials such as carbonaceous materials and zeolites. To quantitatively describe the structure–property relationship for CH₄/H₂ mixture separation in MOFs, a new concept named “adsorbility” was defined, which shows strong correlation with limiting selectivity, with a correlation coefficient (r²) of 0.86. This work shows that although MOFs are promising materials for CH₄/H₂ mixture separation, more investigations that consider both selectivity and working capacity are necessary to screen MOFs in practical PSA application. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

Solvent Vapor Recovery by Pressure Swing Adsorption. III. Comparison of Simulation with Experiment for the Butane—Activated Carbon System

Abstract

A fully predictive (no adjustable parameters), nonisothermal, multicomponent mathematical model was developed and used to simulate a pressure swing adsorption (PSA) process designed for the separation and recovery of concentrated butane vapor from nitrogen using BAX activated carbon. Nearly quantitative agreement with experiment was realized with this model over a wide range of process conditions, and for both the transient and periodic state process dynamics and the periodic state process performance. The model also verified some unique characteristics of this PSA process, and it revealed some of the subtleties associated with accurately simulating a PSA-solvent vapor recovery (SVR) process. These subtleties included the need to account for the adsorbate heat capacity and the temperature dependence of the gas-phase physical properties. No PSA models in the literature have included both of these features, which were critical to the accurate prediction of the heat effects in this PSA-SVR process.     

Simultaneous removal of carbon,nitrogen and phosphorus from wastewater by coupling two-step anaerobic digestion with a sequencing batch reactor

The objective of this study was to develop an integrated process for simultaneous removal of carbon, nitrogen and phosphorus from industrial wastewaters. The process consisted of a-two step anaerobic digestion reactor, for carbon removal, coupled with a sequencing batch reactor (SBR) for nutrient removal. In the proposed process, carbon is eliminated into biogas by anaerobic digestion: acidogenesis and methanogenesis. The volatile fatty acids (VFA) produced during the first step of anaerobic digestion can be used as electron donors for both dephosphatation and denitrification. In the third reactor (SBR) dephosphatation and nitrification are induced through the application of an anaerobic–aerobic cycle. This paper describes the first trials and experiments on the SBR and a period of 210 days during which the SBR was connected to the acidogenic and methanogenic reactors. It was shown that nitrification of ammonia took place in the SBR reactor, during the aerobic phase. Furthermore, denitrification and VFA production were achieved together in the acidogenic reactor, when the efflux of nitrates from the SBR reactor was added to the first reactor influx. The proposed process was fed with a synthetic industrial wastewater, the composition of which was: total organic carbon (TOC)=2200 mg dm⁻³, total Kjeldahl nitrogen (TKN)=86 mg dm⁻³, phosphorus under phosphate form (P-PO₄)=20 mg dm⁻³. In these conditions, removals of carbon, nitrogen and phosphorus were 98%, 78% and 95% respectively. The results show that the combination of the two-step anaerobic digestion reactor and an SBR reactor is effective for simultaneous carbon, nitrogen and phosphorus removal. Reactor arrangements enabled zones of bacterial populations to exist. Complete denitrification occurred in the acidogenic reactor and hence the anaerobic activity was not reduced or inhibited by the presence of nitrate, thus allowing high TOC removal. Stable phosphorus release and phosphorus uptake took place in the SBR after coupling of the three reactors. A fast-settling compact sludge was generated in the SBR with the operational conditions applied, thus giving good separation of supernatant fluid. The benefits from this process are the saving of (i) an external carbon source for denitrification and phosphorus removal, (ii) a reactor for the denitrification step. © 1998 Society of Chemical Industry