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The power of testing, Process technology.

El poder la prueba, The state-of-the-art test centers of Sulzer Chemtech's business unit Process Technology offer customers pilot testing services for a wide range of single units of operation and combinations thereof. A comprehensive number of separation and polymer reaction units, highly skilled test center engineers, and analytical equipment are all available for tests of systems on a pilot scale. This testing can validate the assumptions made in process design and supports customers with their development projects.
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  4346 P rocess simulation has progressedimmensely. Comprehensive elec-tronic databases of physical prop-erties have become available for purecomponents and for mixtures. All of these data can be accessed with littleeffort from personal computers. Chemicaland process engineers have been able togreatly improve their efficiency and pro-ductivity thanks to these tools, user-friendly graphical interfaces, efficientcodes, and broad correlation libraries.Today, alternative designs and hybridprocess solutions that combine units of operation and parametric-sensitivityanalyses can be obtained rapidly— 22| Sulzer Technical Review 2/2011 1 Thin-filmevaporator. INNOVATION Pilot testing services for a wide range of unit operations The power of testing The state-of-the-art test centers of Sulzer Chemtech's business unit Process Technology offer cus-tomers pilot testing services for a wide range of single units of operation and combinations thereof.  A comprehensive number of separation and polymer reaction units, highly skilled test center engineers,and analytical equipment are all available for tests of systems on a pilot scale. This testing can validatethe assumptions made in process design and supports customers with their development projects. which enables engineers to offer increas-ingly complex optimization solutions.In 1966, Thomas Sherwood, a distin-guished professor of chemical engineer-ing at MIT, emphasized that any engi-neering design process involved makingassumptions 1) . The options he proposedfor obtaining missing data were: askingthe company’s laboratory, building apilot plant, or purchasing the know-how.Several decades later, the tools haveevolved but this description remainsvery accurate. Diverse needs for pilot testing From an economical point of view, pilottesting becomes necessary when it ismore expensive to cover the uncertaintyof the assumptions with reserve than torun a pilot test. However, there are alsocases where the range of the uncertaintycannot be quantified. Rectification is a separation technologythat has been intensively studied.Nowadays, many chemical separationscan be properly simulated without theneed for any testing. After engineershave identified the frame of the uncer-tainty, some design margins can be builtin—typically, by increasing the refluxratio, adding more trays, or lengtheningthe packed beds. The concentration of aqueous hydrogen peroxide by evapora-tion and rectification is a good exampleof a system that can be quite well pre-  dicted. Purifications might be challengingto simulate when the feed contains manydifferent chemicals. During the sizing of rectificationcolumns for products from coal tar, it isnot unusual to find over 100 peaks onthe chromatogram of the feed. Someexotic chemicals are not even found incommon databases. In such cases, itmight be necessary to run a validationtest for the simulation of the rectification.This is especially true when rectificationis required to lower the concentration of specific components below a thresholdvalue because of their toxicity and wherethere is limited confidence in the simu-lation results.The process of evaporation as a unitoperation is reasonably well understood.The challenges related to the modelingof the vapor-liquid equilibria are similarto those in rectification. Film evaporation is often used for processes undervacuum and for handling feed withhigher viscosity. Piloting might beneeded to optimize and verify the con-centration of residual low-boiling impu-rities in a high-boiling product or thelosses of low-boiling product when evap-orated out of a higher-boiling purge 1 .Additionally, pilot tests allow the vali-dation of the calculated overall heattransfer coefficient.Pilot testing is also necessary for separation by fractional crystallization. This staged separation technique reliesupon solid-liquid phase transition andon the virtue of selectivity found in solid-liquid equilibrium. It allows multicom-ponent mixtures to be split into narrowfractions, ultimately leading to toppurities of selected components.Although the solid-liquid phase equilibriaare known for many binary and eventernary systems, it is still not possible toprecisely predict the separation withoutrunning pilot tests. One of the challenges is the effect of the crystal habitus (shape), which canstrongly influence the ability of the crys-tallized mass to hold back part of themother liquor with the impurities 2) . Thepilot test results allow for a reliabledesign of an industrial unit. The purifi-cation of acrylic acid to the “glacial”grade is a typical example, as shown infigure 2 .A different situation with a similarconsequence is found in the scale-up of  liquid-liquid extraction columns. Thistechnology provides many advantages,such as low energy consumption andthe possibility of concentrating and purifying chemicals that are diluted ina bulk liquid. Agitated columns are pre-ferred for many applications becausethey allow for controlled energy inputin the agitated sections. In most of thecases, however, pilot tests should be performed to verify that the system is behaving as the liquid-liquid equilibriumdata have predicted. Some mixtures contain salts or impu-rities that may affect the interfacialtension and thereby strongly influencethe specific interfacial surface and phaseseparation. Through pilot tests, agitatedcolumns 3 have been successfully scaledup to 3.1 meters in diameter. For largervolume flows, packed columns are oftenpreferred because of their higher through-put. The diameter of a liquid-liquidextraction column can be scaled up withgood reliability as long as the axial back-mixing is properly considered. A test ina pilot column is often necessary in orderto verify this phenomenon 3) . 23Sulzer Technical Review 2/2011 | 2 a and 2  b  Acrylic acid crystallization unit and pilot plant for crystallization. INNOVATION 3  Agitated liquid-liquid extraction column inpilot scale. a)b)  Membrane separation processes, suchas pervaporation andmembrane filtra-tion (reverse osmosis, nanofiltration inaqueous and solvent mixtures), arereceiving increased attention in theindustry because of their ability to crossazeotropes and because of their energyefficiency 4) . Membranes have complex structures,and innovation is very dynamic in thispromising field. The fundamentals of membrane design have been addressed 4) , but the specific throughput and selectivityof a membrane for a given mixture isseldom precisely predictable. Since thenecessary surface area of a membrane hasa strong impact on the investment of theplant, pilot testing is generally advisable.The testing with membranes allows themeasurement of selectivity and through-put. It is also possible to test the effectof impurities on the membrane’s perform-ance through long-term stability tests.The challenges in processing might go beyond concentration and purificationissues. Often, products prone to col-oration—like triethanolamine or unsat-urated fatty acids—are processed. Dif-ferent solutions can be applied to avoidor minimize color formation dependingon the mechanisms affecting this. Examples are: oxidization due to air(leakage) or other oxidants present inthe feed, thermal cracking at the hotwalls of an evaporator, or thermalcracking in the bulk if products areexposed to longer residence time. Whenexperience is lacking, a pilot test can berun in a falling-film evaporator, a thin-film evaporator, or a rectification columnto verify the color of the end products.Sometimes, for instance in the cosmeticindustry, it is necessary to removeunpleasant odors. Odors might, on thecontrary, need to be concentrated, as inthe beverage industry. The moleculesresponsible for the odor usually cannot be simulated as chemicals. Unless expe-rience already exists for the application,it is necessary to run pilot tests to reliablypredict the outcome.Pilot testing is commonly needed in polymer technology for the design of specific production processes and for thescale-up of equipment 4 . In these poly-merization processes, the viscositychanges by several orders of magnitude.It can increase by factors beyond 10 6 .The prediction of flow behavior andphase equilibria becomes very challeng-ing. It is necessary to test on pilot scale,in particular, for new polymers and elas-tomers, prior to designing an industrialunit. The requirements for pilot test facilities Large companies are usually wellequipped with their own testing facilities.Standard equipment generally includesstirred tank reactors, rectificationcolumns, evaporators, and liquid-liquidextraction columns. Depending on themarket segment, specialized technologies,such as membrane separation rigs, areimplemented. The challenges of havingin-house facilities are mainly in thecontrol of costs and the maintenance of the expertise. It is expensive to own all possibletesting rigs. Rental units are sometimesa good alternative in these cases. Nev-ertheless, safety measures, personal pro-tection, and environmental regulationsadd to the costs required to finance pilotplants. In addition to the pilot rigs them-selves, analytical devices, a chemicalstorage system, and a ventilation systemare necessary. Often, the pilot plantinstallations have to be explosion-proofed, which requires the use of evenmore expensive equipment. Special attention has to be paid toproper installation regarding leak-tight-ness and insulation. Because pilot andmini-plant units exhibit low liquid hold-up volumes and relatively large surfaceareas, leakage and heat losses have amuch stronger impact on the test resultsthan in industrial-size units. In order tominimize these effects, advanced heattracing and expensive sealing systemshave to be employed.The companies running polymeriza-tion processes face similar issues. Theownership of a pilot plant is oftenlimited to a stirred tank. The implemen-tation and operation of a loop reactorand a finishing section represent expen-sive investments for occasional process development.Another prohibitive aspect of in-house testing is the level of competenceof the operating personal. Pilot testingshould verify the assumptions andincrease the confidence in the process 24| Sulzer Technical Review 2/2011 INNOVATION 4 Polymerization pilot plant.  design. Ultimately, the pilot test will setthe basis for the design of a large-scaleunit. An unrecognized mistake in thetest can lead to disastrous design errorsand financial losses. The staff runningthe test must, therefore, be well trained.Long years of experience and practicehave great value. The correct operation of the controlloops illustrates this issue. In a largeplant, it usually takes a week or moreto properly tune the control loops. In apilot test, the time and the amount of feed available are limited. Therefore, thetuning must be completed within a fewhours.Innovation leads to new solutions,hybrid processes, and, more generally,process intensification. The combinationof technologies, such as distillation andpervaporation, liquid-liquid extractionand stripping, or evaporation and crys-tallization is quite complex to perform. The knowledge and experience neces-sary to operate such combinations at thepilot scale are seldom available inchemical plants. A further issue is thenecessity of owning and maintaining allthe pilot plants for the diverse technolo-gies. Finally, it is often advantageous tohave different pilot plant scales for asingle technology. Customer testing facilities at Sulzer Chemtech Sulzer Chemtech acquired the companyKühni in 2009. The existing processsolution competencies were combinedinto a single business unit namedProcess Technology. The unit offersprocess design, engineering services,process equipment, modular plants, andskids for a wide range of process solu-tions. It also covers pilot testing for allavailable unit operations, and it providesthe opportunity to combine them.The following pilot units and analyticalequipment are available at various loca-tions 5 : ã Distillation –7 columns Ø 30mm up to 500mm –batch or continuous–bubble cap trays, slit trays,structured packing, and spinning band ã Evaporators–3 falling-film evaporators–3 thin-film evaporators 1 –2 short-path evaporators ã Liquid-liquid extraction–4 columns Ø 32mm–150mm 3 –3 mixer-settlers Ø 40 mm, 3 mixer-settlers Ø 100 mm ã Membrane technology–benchtop systems–pilot units–pressure-driven membrane pilot-scale unit ã Crystallization–3 falling-film crystallizers 2 –2 static crystallizers–1 suspension crystallizer ã Polymerization technology–static-mixer reactors for thepolymerization of variousmonomers, e.g., styrene andlactides (lactic acid diester) 4 –degassing rig for devolatilization–expandable polystyrene (EPS)pilot line–various extruders and staticmixers for additive mixing tests ã Analytical capabilities–GC-FID, GC-HWD, headspace GC–HPLC–UV-VIS spectrometry–titration (acid-base, Karl-Fischervolumetric and coulometric)–solid or moisture content bythermobalance ã Measurement of physical properties–density–viscosity–surface or interfacial tension–rheology 25Sulzer Technical Review 2/2011 | INNOVATION References 1) Sherwood, T.K.,  A Course in Process Design . Cambridge, MA:MIT Press, 1963. 2) Chianese, A. and M. Parisi, Kinetics: Fundamentals of Nucle- ation andCrystal Growth in Melt Crystallization. Eds. J. Ulrichand H. Glade. Aachen: Shake Verlag, 2003, pp. 41-69. 3) Mögli, A. and U. Bühlmann, The Kühni Extraction Column in Handbook of Solvent Extraction. Eds. T. C. Baird, M. H. I. Lo,and C. Hanson. New York: Wiley Interscience, 1983. 4) Jonquières, A. et al., “ Industrial state-of-the-art of pervapora-tion and vapor permeation in the western countries. ” Journal of Membrane Science 206, 2002, pp. 87–117. 5 Sulzer test center in Allschwil, Switzerland. Laurent Zuber Sulzer Chemtech Ltd.Gewerbestrasse 28P.O. Box4123 AllschwilSwitzerlandPhone +41 61 486
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