Product Purity Specifications Research Articles

A systematic matrix-based method for synthesis and optimization of Reaction/Distillation processes including Reactive Distillation

In order to reach product purity specifications, reactor outlet streams are often purified using distillation columns, and the unreacted feed is recycled to the reactor. This makes Reaction-Separation processes very important in chemical industries. In the current study, a new version of the Reaction/Distillation Matrix algorithm previously presented by the authors is presented. The current version of the algorithm is capable of generating Reactive Distillation configurations as attractive process alternatives and also recycle streams to prevent the loss of unreacted feed components. Besides, major modifications have been carried out to the algorithm to make it more efficient and user-friendly. Production of cumene and dimethyl ether were studied as case studies to evaluate the performance of the developed algorithm. The conventional sequences generated using the Reaction/Distillation Matrix algorithm were simulated by Aspen Plus and then optimized using the Genetic Algorithm. It is observed that cost of reactive distillation configuration was approximately 62 % and 10 % lower than for the conventional process in the cumene production and dimethyl ether production case studies, respectively.

Energy-Saving Designs for Separation of a Close-Boiling 1,2-Propanediol and Ethylene Glycol Mixture

Separation of 1,2-propanediol and ethylene glycol is an important task for coproduction of these two compounds via hydrogenolysis of glycerol for the purpose of utilizing this biodiesel byproduct. These two compounds exhibit close-boiling behavior which requires many stages of a regular column and also large energy consumption to meet stringent product purity specifications. In this paper, several alternative designs are investigated in order to save steam cost and also total annual cost of this separation task. Alternative designs considered include multieffect distillation, heterogeneous azeotropic distillation, and extractive distillation. Significant reductions of 38.3% in steam cost and 30.6% in total annual cost as compared to the regular column can be obtained by a design flowsheet via an extractive distillation system using triethylene glycol as entrainer. Methods for further improving the economics of this extractive distillation system have also been investigated. A simple worthwhile improved de...

Batch distillation employing cyclic rectification and stripping operations

Several strategies have been proposed to increase the operating efficiency of batch distillation. In this study, conventional batch rectification and inverted batch stripping are used cyclically to promote high product flow rates for a binary fractionation. Process controls are implemented to maintain constant product purity specifications by varying the slope of the operating line. While rectifying, the light component is removed as distillate, concentrating the heavy component in the reboiler. As a result, the distillate rate decreases with time. The column is then changed from rectification to stripping modes, and the heavy component is removed as bottoms product, concentrating the light component in the distillate drum. This causes the bottoms rate to diminish with time, and the column is once again converted back to rectifying mode. Cyclic operation, transitioning from batch rectifying to stripping back to rectifying, continues until all of the initial charge is fractionated or is combined with a new charge. The fractionation of ethanol and 1-propanol using the proposed operating strategy is shown to provide several advantages including energy and time savings when compared to conventional batch or inverted batch distillation alone.

Design and Control of a Methyl Methacrylate Separation Process with a Middle Decanter

In an industrial process to produce methyl methacrylate, a mixture including methyl methacrylate, methanol, and water needs to be separated. The methyl methacrylate and water are designed to be drawn out of this separation process as two product streams while methanol as an excess reactant should be recycled back to the esterification reactor. An industrial feasible design flowsheet includes three columns, a decanter and two internal recycle streams. In this work, a simple design flowsheet is devised with a distillation column, a bottom decanter, and a stripper. This column/decanter/stripper design can further be simplified into an even simpler design flowsheet with only one distillation column with sidedraw and a middle decanter. Optimal design and dynamic control of this simplified separation process are investigated in this paper. It is shown that the product purity specifications can be maintained despite feed disturbances by holding a tray temperature above the sidedraw location and another one below the sidedraw location.

Design and Control of Heterogeneous Azeotropic Column System for the Separation of Pyridine and Water

The design and control of two types of separation systems using heterogeneous azeotropic distillation have been studied in the literature. One type (e.g., isopropyl alcohol dehydration) is to add a light entrainer (cyclohexane) into the system so that a minimum-boiling ternary azeotrope is formed which can split into two liquid phases in a decanter. This type of system also introduces two additional azeotropes (isopropyl alcohol−cyclohexane and water−cyclohexane), thus dividing the ternary system into three distillation regions. Another type (e.g., acetic acid dehydration) does not contain azeotrope in the original system. However, due to a tangent pinch near the pure water end an entrainer (isobutyl acetate) is added into the system to aid the separation. This type of system has only one binary heterogeneous azeotrope (water−isobutyl acetate); thus there is only one distillation region. In this paper, design and control of a different residue curve map (RCM) type of separation system utilizing heterogeneous azeotropic distillation will be studied. An example of this RCM type is pyridine and water separation using toluene as entrainer. Adding toluene into this system introduces two additional azeotropes, one is minimum-boiling binary heterogeneous azeotrope (water−toluene) and the other one is a binary homogeneous azeotrope (pyridine−toluene). There is no ternary azeotrope for this system. Two alternative design flow sheets are compared in this paper to find the one which is most economical and also meet stringent product purity specifications. A simple overall control strategy of this process has also been developed which requires only one temperature control loop in each column.

Plutonium oxide polishing for MOX fuel fabrication

Los Alamos National Laboratory (LANL) successfully polished 120 kg of plutonium from surplus nuclear weapons for the European Mixed Oxide (MOX) Lead Test Assembly (LTA), managed by Duke, COGEMA, and Stone & Webster (DCS). The purified oxide was fabricated into fuel pellets, which comprised the LTAs. The LTAs have been inserted into the Catawba (SC, USA) nuclear reactor, where they are presently being used to generate electricity. The material used in the MOX LTA represents the first plutonium oxide from LANL to be polished under the quality requirements set forth by the Nuclear Regulatory Commission (NRC). In addition, the MOX project has been hailed as the “largest single nonproliferation project in history” by US Ambassador Linton Brooks (23/9/04). The process flow for PuO 2 purification was based on aqueous recovery that included various unit operations (dissolution, ion exchange, oxalate precipitation, and calcination). Data from a variety of chemical and physical analyses demonstrate product quality and process consistency. Further process optimization experiments will be performed prior to polishing an additional 330 kg of PuO 2 for the Mixed Oxide Fuel Fabrication Facility (MFFF) at Savannah River Site. During LTA production in 2004, approximately 500 L of 7 M nitric acid was used for washing impurities from the plutonium in order to meet product purity specifications. The majority of this acid was sent to the LANL Radioactive Liquid Waste Treatment Facility (TA-50) as effluent. Optimization experiments during 2006 and 2007 will investigate the use of recycled HNO 3 for PuO 2 washing and ion exchange. If successful, aqueous polishing processes will re-use almost all of the nitric acid that would otherwise have been sent to TA-50. In addition, an overall reduction in the volume of nitric acid used during ion exchange will be tested. The use of new Inconel calcination boats will also be verified. Additional process optimization activities will be conducted to validate the use of 100% quaternized Reillex ion exchange resin. Qualification exercises will include a series of process runs, followed by chemical analyses to assess product oxide impurity levels. Once the optimized processes have been qualified, the production phase of the project will begin.

Design and Control of a Complete Heterogeneous Azeotropic Distillation Column System

In this work, design and control of an industrial-scale complete heterogeneous azeotropic distillation column system of isopropyl alcohol (IPA) + water (H2O) with cyclohexane (CyH) as an entrainer is investigated. There are two feasible approaches to design the complete flowsheet for the separation of IPA and H2O. One approach is to use a total of three columns and another simpler design is to use only two columns. From total annual cost (TAC) analysis, optimum design of the two-column approach has been established and it is much more economical than the three-column approach. The suitable control strategy of this complete heterogeneous azeotropic distillation column system has also been studied extensively in this paper. From process analysis and dynamic simulation, the developed overall control strategy is rather unconventional which seems to contradict several common control heuristics. The proposed control strategy requires two temperature-control loops in the first column and one temperature-control loop in the second column. This overall control strategy is tested with both feed composition and flow rate disturbances. The product purity specifications of the IPA and wastewater streams can all be met despite various disturbance changes.

Ambulatory Pneumothorax in Pulmonary Tuberculosis

Los Alamos National Laboratory (LANL) successfully polished 120 kg of plutonium from surplus nuclear weapons for the European Mixed Oxide (MOX) Lead Test Assembly (LTA), managed by Duke, COGEMA, and Stone & Webster (DCS). The purified oxide was fabricated into fuel pellets, which comprised the LTAs. The LTAs have been inserted into the Catawba (SC, USA) nuclear reactor, where they are presently being used to generate electricity. The material used in the MOX LTA represents the first plutonium oxide from LANL to be polished under the quality requirements set forth by the Nuclear Regulatory Commission (NRC). In addition, the MOX project has been hailed as the “largest single nonproliferation project in history” by US Ambassador Linton Brooks (23/9/04). The process flow for PuO2 purification was based on aqueous recovery that included various unit operations (dissolution, ion exchange, oxalate precipitation, and calcination). Data from a variety of chemical and physical analyses demonstrate product quality and process consistency. Further process optimization experiments will be performed prior to polishing an additional 330 kg of PuO2 for the Mixed Oxide Fuel Fabrication Facility (MFFF) at Savannah River Site. During LTA production in 2004, approximately 500 L of 7 M nitric acid was used for washing impurities from the plutonium in order to meet product purity specifications. The majority of this acid was sent to the LANL Radioactive Liquid Waste Treatment Facility (TA-50) as effluent. Optimization experiments during 2006 and 2007 will investigate the use of recycled HNO3 for PuO2 washing and ion exchange. If successful, aqueous polishing processes will re-use almost all of the nitric acid that would otherwise have been sent to TA-50. In addition, an overall reduction in the volume of nitric acid used during ion exchange will be tested. The use of new Inconel calcination boats will also be verified. Additional process optimization activities will be conducted to validate the use of 100% quaternized Reillex ion exchange resin. Qualification exercises will include a series of process runs, followed by chemical analyses to assess product oxide impurity levels. Once the optimized processes have been qualified, the production phase of the project will begin.