Displacement Band Chromatography of Hydrogen Sulfites for Enrichment of Sulfur Isotopes

Abstract

Experimental studies were conducted on the enrichment of sulfur isotopes by displacement band chromatography. In these studies, a band of hydrogen sulfite (bisulfite) ions from a sulfurous acid or bisulfite-salt solution was continuously displaced by bisulfate ions from a sulfuric acid or bisulfate-salt solution in a column packed with aminated polystyrene-divinyl benzene resin under varied process conditions. The sulfur isotopes were enriched through isotopic exchange between the bisulfite ions on the resin and the sulfurous acid and/or bisulfite-salt solution in contact with the resin within the moving band. During the isotopic exchange, S-34 isotope was favored in the resin phase and S-32 isotope in the liquid phase. As a result, the S-34 isotope was gradually enriched at the rear of the band, and S-32 isotope at the front. The effects of the various process conditions were evaluated on separative power, height equivalent to a theoretical plate, and operational simplicity. The highest separative power, 3.05 g S-34/cm³/yr, was achieved with an ammonium bisulfite feed displaced by a sulfuric acid displacer at 65°c operating temperature.     

Note: Two-Enthalpy Feed for Distillation with Vapor Feed and Refrigerated Condenser

Abstract

The use of two-enthalpy feed, which involves splitting the feed, condensing part of it, and sending both the liquid and vapor streams to the distillation column, is explored for columns that have a vapor feed and require refrigeration in the column condenser. The use of two-enthalpy feed can reduce both capital and operating costs compared to condensing all the feed. Compared to use of partial cooling and use of a two-phase feed, two-enthalpy feed reduces the condenser heat duty, but the feed cooling occurs at a lower temperature.     

Superheavy Isotope Enrichment Using a Carbon Isotope Enrichment Plant

Abstract

A¹³C isotope distillation separation plant was used to search for naturally-occurring superheavy isotopes. Superheavy (X^?) isotopes of carbon in CO would be only slightly less volatile than the normal ¹²C¹⁶O. Over 100,000 mol CO were passed through the distillation columns without product withdrawal during the experiment. Following cessation of flows, 201 gas samples were collected from the bottom of the high enrichment column. An argon impurity in the CO provided a “wedge” to enrich X^? isotopes at the CO/Ar interface in the column. Carbon isotopic compositions were used to calculate which samples might contain the superheavy isotopes. Enrichments of X^? isotope concentration of ～10⁵ were obtained in several 0.1 mol samples, which were analyzed for the existence of X^? isotopes at another laboratory. A limited amount of extremely pure ¹³CO was produced as a side benefit.     

Hybrid Simulated Moving Bed Processes for the Purification of p‐Xylene

Abstract

A parallel two‐zone and four‐zone SMB hybrid process was developed for p‐xylene purification. By placing a high‐productivity parallel two‐zone SMB in front of an existing four‐zone SMB, feed was enriched in the parallel two‐zone SMB before it was fed to the four‐zone SMB, which allows a higher feed rate to the four‐zone SMB. A general design procedure for hybrid SMB‐SMB process was developed. Simulations were done with Aspen Chromatography and Aspen Plus. Overall adsorbent productivity was increased by more than 100%, but with 3–5% lower overall p‐xylene recovery. With overall recovery of the hybrid process matching the base case, the feed rate was doubled and the overall adsorbent productivity was 50% higher than the base case. The heat duties of distillation columns per unit product were similar for these hybrid processes compared to the base case. If a two‐feed raffinate distillation column was used, the heat duty of distillation columns per unit product in the hybrid process was 2–4% lower than the base case. Both parallel two‐zone and four‐zone SMBs were also developed for use in a hybrid SMB‐crystallization process for p‐xylene purification. SMB productivity can be increased from 31% to 75% by adding additional pumps between columns to operate columns at their pressure limits. Although additional pumps are useful for both systems, the productivities of the parallel two‐zone SMBs were 9% and 16% higher than the corresponding four‐zone SMBs with the same number of recycle pumps. For a four‐zone SMB with two columns per zone and eight recycle pumps, a 114% increase of productivity was achieved, which is 22% higher than a parallel two‐zone with one column per zone and four recycle pumps.     

The second law optimal state of a diabatic binary tray distillation column

A new numerical procedure to minimize the entropy production in diabatic tray distillation columns has been developed. The method was based on a least square regression of the entropy production at each tray. A diabatic column is a column with heat exchangers on all trays. The method was demonstrated on a distillation column separating propylene from propane. The entropy production included contributions from the heat transfer in the heat exchangers and the mass and heat transfer between liquid and vapor inside the distillation column. It was minimized for a number of binary tray distillation columns with fixed heat transfer area, number of trays, and feed stream temperature and composition. For the first time, the areas of heat exchange were used as variables in the optimization. An analytical result is that the entropy production due to heat transfer is proportional to the area of each heat exchanger in the optimal state. For many distillation columns, this is equivalent to a constant driving force for heat transfer. The entropy production was reduced with up to 30% in the cases with large heat transfer area and many trays. In large process facilities, this reduction would ideally lead to 1-2 GWh of saved exergy per year. The most important variable in obtaining these reductions is the total heat transfer area. The investigation was done with a perspective to later include the column as a part in an optimization of a larger process. We found that the entropy production of the column behaved almost as a quadratic function when the composition of the feed stream changed. This means that the feed composition is a natural, easy variable for a second law optimization when the distillation column is a part of a process. The entropy production was insensitive to variations in the feed temperature.     

A Novel Procedure of Hydrogen Isotope Separation Based on Chemical Exchange and a Selective Permeable Membrane

Abstract

It is shown theoretically that a novel process of hydrogen isotope separation can be obtained by combining bithermal isotopic exchange with transport through a selective permeable membrane. The theory of the process predicts that a small column with high separation and very small inventory can be realized. The method is attractive especially for small and medium scale processes, such as tritium enrichment, heavy water upgrading, and final deuterium concentration.     

FIBONACCI SEARCH FOR OPTIMAL FEED LOCATION

Abstract

A Fibonacci search technique is used in conjunction with a rigorous mullicomponenl distillaiion computer module to find the optimal feed location within a section of a distillation column. The function lo be minimized can be one of the following:

?key component ratio difference

?reflux ratio or reboiler ratio

?condenser duty or reboiler duty

This technique has been used successfully in the relocation of feed stages of many existing distillation columns and thus saved energy consumption. We shall describe this technique with a sample problem.     

重氧水分离级联中氘和氧18浓度分布及其影响

在水精馏法分离同位素的系统中,氘和氧18同时得到富集,情况比较复杂。为使该系统的模拟更加贴近实际情况,提出了一种可同时计算氘和氧18浓度分布及氧16/氧18分离系数的新方法。此方法将不同的水分子划分为四个集总,简化了复杂的同位素交换反应网络。然后利用ASPEN PLUS的反应精馏模块进行计算。对一个五塔级联的水精馏制氧18水系统的模拟计算表明,产品中氘浓度达到了70.7%,氧18浓度达到了98.0%。在最后一个精馏塔内,随着氘含量的增加,氧16/氧18分离系数α_cal从接近α_H216O/H218O变得更接近α_D216O/D218O。     

SEPARATION OF STABLE NITROGEN ISOTOPES BY ION EXCHANGE CHROMATOGRAPHY

ABSTRACT

The ion exchange chromatography technique was used for the enrichment of nitrogen 15 (¹⁵N). A set of columns filled with the ion exchange resin Wofatit KPS (medium porosity type) with 5.4?cm I.D. and 1.5?m height was set up. Ammonia NH₄ ⁺/NH₃ aq. was chosen as the isotopic exchange system. The ammonium bands formed in the columns were eluted by a solution of sodium hydroxide. The isotope separation factor, ?, was found to decrease with increasing temperature or ammonia concentration. Operational conditions of temperature and ammonium concentration were proposed as the optimum for the production of the enriched isotope by using the present process. Results showed that: (1) the rear part of the band is enriched in ¹⁵N, while the frontal part is depleted; (2) it is possible to obtain 7.6?at. % of ¹⁵N after a 60?m displacement of the ammonium band. The analytical determination of the samples was made by emission spectrometry (NOI-6E).     

Systematic Modeling of the (13C) Isotope Cryogenic Distillation Process

Isotopic enrichment by low-temperature distillation of carbon monoxide is difficult to handle, the experiments providing with the necessary data are time-consuming and difficult to perform, so the mathematical modeling of the process is an appropriate approach to study and to further control the column. This paper develops a mathematical model for the (¹³C) isotope cryogenic distillation process using two subsystems of the plant: the hydrodynamic part and the isotope-separation part. The model is validated using experimental data from the pilot column from the National Institute for Research and Development of Isotopic and Molecular Technologies Cluj-Napoca. The proposed model is suitable for various cryogenic distillation columns, using the proper parameters.     

Recovery of Tritium from Wastewater Generated by Decommissioning of Gas Cooled Reactors (GCR)

The recovery of tritium from wastewater generated by the decommissioning of a 166‐MWe GCR, Tokai‐1, nuclear reactor was evaluated. The dimensions of two tritium separation columns, water distillation process and hydrogen‐isotope exchange with hydrophobic Pt‐catalyst, were evaluated numerically under the assumptions that the recovery of tritium from the wastewater would be completed in five years and the wastewater after the recovery of tritium would be suitable for release into the environment. It was found that, in addition to lower steam, the column was smaller than that for the water distillation process. The hydrogen‐isotope exchange process was suitable for the treatment of wastewater, not only for a process design point of view but also for a reduction of energy consumption.     

NO-HN03 Exchange System for Production of 14N Highly Depleted of 15N

Abstract

The isotopic exchange reaction between NO and HNO₃ was used to prepare ¹⁴N highly depleted ¹⁵N. This required an efficient reflux system of low holdup to convert oxides of nitrogen to nitric acid by reaction with oxygen and water. A study of the characteristics of the one constructed showed that less than 1 part in 32,000 of the nitric acid was lost from the refluxer as oxides of nitrogen. ¹⁴N with an atom fraction of less than 0.00004 of ¹⁵N was prepared at the rate of 46.0 g/day. The application of the refluxer to a system for producing ¹⁵N is discussed.     

Analysis of Ternary Distillation Column Sequences

Abstract

Eight complex distillation column configurations for a ternary feed mixture are modeled and studied. A modified complex method is used to minimize the cost of the configurations. Optimum regions for each configuration depending on the feed composition are derived. The result provides guidelines for the synthesis of distillation column configurations.     

Continuous Ion-Exclusion Chromatography System for Acid/Sugar Separation

ABSTRACT

A simulated moving bed ion exclusion chromatography system was constructed for the continuous separation of the components in an aqueous feed solution of sucrose and sulfuric acid. A system of 18 columns was arrayed about a central manifold system. Each column was packed with approximately 820 mL of porous cationic exchange resin. The system was designed for the flexibility to use fluid recycle loops and unrestricted placement of all inlet and outlet streams. Monitoring and control functions were performed using a Camile 2000 process controller integrated with a custom-built control computer. The aqueous feed solution, usually containing 10 wt.% sucrose and 10 wt.% sulfuric acid, was generally introduced into the system at a rate of roughly 2 L/hr. Approximately 4 L/hr of water was used to elute materials through the separation system. After optimization, the separation system allowed greater than 95% recovery of the feed sucrose in an exit stream containing 8.8 wt.% sucrose and 98% recovery of the feed acid in a second exit stream containing 5 wt.% acid.     

REILLEX™-HPQ ANION EXCHANGE COLUMN CHROMATOGRAPHY: REMOVAL OF PERTECHNETATE FROM DSSF-5 SIMULANT AT VARIOUS FLOW RATES

ABSTRACT

The 1% breakthrough volumes (BTV) for TcO₄^on Reillex^?-HPQ anion exchange resin columns have been measured as a function of flow rate. The 1% BTV is defined as that point in the column loading when an aliquot of eluent contains 1% of the activity of an equivalent aliquot of column feed solution. The 2.54 × 50 cm     

Separation of Water and Nitric Acid with Porous Hydrophobic Membrane by Air Gap Membrane Distillation (AGMD)

Abstract

This study investigates the effect of operation parameters on the separation of nitric acid‐water mixture using air gap membrane distillation (AGMD). Porous hydrophobic PTFE membrane was used. The performance was evaluated based on the permeate flux and the nitric acid selectivity. Operating parameters such as feed solution temperature, feed concentration, flow rate, and air gap width were varied. Nitric acid selectivity was found to increase with the increase in feed solution temperature, feed concentration, flow rate, and air gap width. Permeate flux increased, when the feed temperature and the flow rate were increased. The effect of recirculation of the feed solution was also studied. With the recirculation mode, at different initial solution volumes, it was observed that the nitric acid concentration in the feed and the permeate, increased. The rate of flux decline was greater, when the initial feed solution volume was lower.     

Modeling and simulation of a nitric acid recovery process

A nitric acid recovery process using composite distillation columns was modeled and simulated. The composite distillation columns consist of a multistage vacuum tower and an atmospheric pressure tower half of which consists of packed bed. The vacuum tower and the atmospheric pressure tower were modeled by using equilibrium stage method and non-equilibrium stage method respectively. The required thermodynamic properties for nitric acid solution were obtained from correlations based on experimental data. Results of simulations showed good agreement with actual plant data. From the results of simulations it was found that the upper half of the atmospheric pressure column and the vacuum column, consisting of plate column, can be modeled using equilibrium model, but the lower half of the atmospheric pressure column, which are packed parts, can be modeled effectively using non-equilibrium model. The non-equilibrium model developed in the present study showed good agreement with actual operaton data.     

Retrofit of Distillation Columns Using Thermodynamic Analysis

Abstract

Thermodynamic analysis provides the column grand composite curves and exergy loss profiles, which are becoming readily available for a converged distillation column simulation. For example, the Aspen Plus simulator performs the thermodynamic analysis through its Column–Targeting tool for rigorous column calculations. This study uses the column grand composite curves and the exergy loss profiles obtained from Aspen Plus to assess the performance of the existing distillation columns, and reduce the costs of operation by appropriate retrofits in a methanol plant. Effectiveness of the retrofits is also assessed by means of thermodynamics and economics. The methanol plant utilizes two distillation columns to purify the methanol in its separation Section. The first column operates with 51 stages, has a side heat stream to the last stage, a partial condenser at the top and a side condenser at stage 2, and no reboiler. The second column operates with 95 stages, has a side heat stream to stage 95, a total condenser, and high reflux ratio. Despite the heat integration of the columns with the other Sections and a side condenser in column 1, the assessment of converged base case simulations have indicated the need for more profitable operations, and the required retrofits are suggested. For the first column, the retrofits consisting of a feed preheating and a second side condenser at stage 4 have reduced the total exergy loss by 21.5%. For the second column, the retrofits of two side reboilers at stages 87 and 92 have reduced the total exergy loss by 41.3%. After the retrofits, the thermodynamic efficiency has increased to 55.4% from 50.6% for the first column, while it has increased to 6.7% from 4.0% for the second. The suggested retrofits have reduced the exergy losses and hence the cost of energy considerably, and proved to be more profitable despite the fixed capital costs of retrofits for the distillation columns of the methanol plant.     

Evaluation of a two-temperature control structure for a two-reactant/two-product type of reactive distillation column

Several different control structures have been proposed for reactive distillation columns. The appropriate control structure depends on the flowsheet and on the type of reactions occurring in the column. If two reactants are involved and if it is desirable to operate the process without any excess of reactant, it is necessary to manage the fresh feed streams so that the stoichiometry is exactly balanced. A composition analyzer that measures an internal composition in the column is often required. However, if two products are produced, it is possible to avoid the use of an analyzer by using two temperatures in the column to adjust the two feed streams. This type of structure was proposed by Roat et al. [Roat, S., Downs. J., Vogel, E., Doss, J., 1986. Integration of rigorous dynamic modeling and control system synthesis for distillation columns. In: Chemical Process Control—CPC III. Elsevier, Amsterdam.] for the ideal reaction A+B↔C+D in one of the earliest papers dealing with reactive distillation control.The purpose of this paper is to explore the effectiveness of this two-temperature control structure for various column designs (number of reactive stages) to quantify the impact of design on controllability. We also discuss the issues of the selection of the trays whose temperatures are to be controlled and the tuning of the two interacting temperature controllers. Disturbances in production rate and fresh feed compositions are made to examine the rangeability of this control structure. Both an ideal reaction system and the methyl acetate system are studied. One of the main conclusions is that the locations of the temperature control trays should be made such that the two temperature controllers both have direct action (an increase in temperature increases feed), which requires negative openloop process gains for both loops.     

基于传热/传质的乙烯裂解过程脱甲烷塔进料瓶颈识别及流程重构策略

精馏塔进料的组成与温度会影响塔内质量交换和能量利用,不恰当的进料会导致全塔的分离及用能效果变差。针对多进料精馏塔的组合进料问题提出一种识别不合适进料位置的方法,基于塔板的传热温差和传热量、传质浓度差和传质量计算方法提出应用传热/传质复合曲线识别精馏塔进料瓶颈的方法,并将其应用于裂解装置脱甲烷塔进料瓶颈的识别,采用调整进料位置的流程重构策略实现去瓶颈的操作。流程模拟及瓶颈分析结果表明所提出的方法能识别出脱甲烷塔的进料瓶颈,重构流程的方法能实现去瓶颈的操作,并使全塔的传质传热特性、分离效果变好,能耗降低。