MDI Suspension Crystallization with the GEA Messo PT Wash Column

Ultra Purificationof 4,4‘ MDISuspension Crystallization withthe GEA Messo PT Wash ColumnFeatures• Flexible product purity - Purity >99.5% down to theeutectic as needed.• Feedstock - Operates on a range of feed stocks with thevariations in feed impurity composition being absorbedby the system.• Economics - Continuous operation and energy efficientsuspension based crystallization ensure the operatingcosts are significantly lower than other separationtechniques.• Maintenance - Low rotating speeds and the robustconstruction of the GEA Messo PT Purifier TM providetrouble free operation.GEA Messo PT can provide assistance in determining theoptimum configuration and cost information for your specificcircumstances.ApplicationMethylene diisocyanate is used in the production ofpolyurethane plastics and foams. It is applied over a widerange of products including rigid plastics, paints andadhesives, automotive parts and foams for insulation, beddingand packaging.The reaction process generates three main isomers; these are2,4’ MDI, 4,4’ MDI and 2,6’ MDI. The 2,4’ MDI and 4,4’ MDIare the most commercially important as their ratio in thestarting product determines the stiffness of the foam producedwhen the isocyanate is reacted with a polyol. The monomersalso react to form dimers that differ in solubility and producea cloudy product.The phase diagram for a solution of 2,4’ MDI’ and 4,4’ MDI’ isshown below. The eutectic limits the separation of the isomers.However for MDI this composition is a desirable product forthe further production of polyurethane foams.TemperaturePure 2,4’+ LiquidT eq, 4,4”T eq, 2,4’T eutecticPure 4,4’+ LiquidX e100% 2,4’ 100% 4,4’engineering for a better worldGEA Process Engineering

Process Description – The melt crystallizationprocess is carried out in an industrially proven scraped surfacecrystallizer where final purification is completed in the GEAMesso PT wash column. The feed product is cooled inside thecrystallizer where part of the product is converted into purecrystal solids leaving the impurities concentrated in theresidual mother liquor.The crystallizer consists of a jacketed vessel with a rotatingscraper assembly. Evaporating refrigerant or a secondarycoolant in the outer jacket cools the inner wall of the vessel.The scraper sweeps the wall surface and prevents buildup ofcrystals to maintain a clean heat transfer surface andcontinuous supply of product crystals.Each individual crystal provides growth surface that canabsorb the supersaturation caused by cooling the product atthe swept surface. With billions of individual crystals present,this will provide near ideal growth conditions and ensure theproduction of ultra-pure crystals.The GEA Messo PT wash column completes the separation ofthis mixture of pure product crystals and residual motherliquor. This separation is based on GEA Messo PT’s patentedwash column technology and is an essential component in thispurification process.The crystal slurry is compressed within the GEA Messo PTwash column to remove most of the mother liquor and form apacked crystal bed. This bed consists of the pure productcrystals surrounded by some residual mother liquor. The newcrystals entering the wash column will force the bed towardthe scraper assembly at the opposite end. The scraperdisintegrates the crystal bed and a circulation pump providesmelted product to reslurry the crystals.The circulation flow carries the crystals to a heat exchangerwhere e.g. steam or any other heat source provides the heatnecessary to melt the crystals. The melted product can then bedischarged to product storage.The melted product in the recirculation stream countercurrentlywashes the residual mother liquor from the packed crystal bedas it moves through the wash column. The length of the crystalbed provides an extremely efficient wash zone for removal ofany remaining impurities in the mother liquor ensuring ultrapureproduct. Unlike other solid/liquid separation devicesoperating with a much shorter bed depth, the wash liquidforms an internal reflux loop and is therefore recovered asrecrystallized product in the melt circuit instead of leavingwith the mother liquor.Experience – GEA Messo PT is a technology orientedengineering company with over 40 years experience in thedesign and execution of crystallization plants worldwide. Westarted by crystallizing water from liquid food products in1973 and since then have built and installed over 120purification units around the world including applications forwater, PX, PDCB, phosphoric acid as well as many otherclassified organic chemicals.New developments in process technologies pose new challengesevery day which require innovative and low-cost solutions.Practical orientation and customer requirement play a vitalrole in this connection. GEA Messo PT consistently orientatesitself towards the needs of the customer.GEA Messo PT has been certified according to DIN ISO 9001standard since 1996 and since June 2003 the ISO 9001:2000standards were implemented following an audit by theinternational bureau Lloyd’s Register Quality Assurance.Crude FeedRejectProductRecrystallization provides heatrequired to warm up crystal massfrom Tcrys to TmeltMother LiquorFilter/pistonSlurry inletSteam inTcrysP2Purified ProductCrystal bedNot washedWashedScraperCondensate outCrystal FlowTmelt∆H mP1CoolantSteamP1 > P2CrystallizerSolid-Liquid SeparationNext Steps – On-site demonstration of this technology is possible in various configurations using GEA Messo PT’s pilot plants.For more information regarding this technology and your specific configuration requirements please contact us at:info.niropt.nl@gea.com or phone +31.73 6390 390.GEA Messo PTDe Beverspijken 7b, 5221 EE ‘s-Hertogenbosch, The NetherlandsTel +31 73 6390 390, Fax +31 73 6312 349info.niropt.nl@gea.com, www.gea-messo-pt.comTS10.052012-H