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Niro Suspension Crystallization with

Wash Column Separation

Purification of Organic Chemicals

Application

The steady growth in the development of newproducts from a range of organic chemicalintermediates has fueled the demand for high-puritystarting materials. Existing processes also benefitfrom a critical study on the separation techniquesused. Impurities can significantly affect the quality andeconomics of the final product making ultra-purefeedstock essential. Crystallization provides thehighest degree of separation and generally guaranteesproduction of ultra-pure products.

A wide range of organic compounds including the

difficult separations presented by close boilingisomers, azeotropic solutions and even enantiomersare highly suited for purification by crystallization.Over 80% of organic solutions are considered eutecticsystems that provide the possibility for completeseparation by crystallization in a single step. Many(>60%) of the known organic compounds have meltingpoints below 100 C with boiling points being muchhigher. Compounds that easily decompose or react atelevated temperatures are also highly suited forpurification by crystallization.

The feed concentration and the eutectic point will

determine the maximum recovery for anycrystallization process. In general, crystallization isideally suited to provide an efficient end-purificationstep, but the near ideal crystal growth conditions foundin Suspension Crystallization provide pure crystals andacceptable recovery with a single stage. Efficientseparation of these ultra-pure product crystals ensuresthe purity of the final product. In many cases only twostages are required for ultra-pure product and themaximum recovery possible (by operating on or nearthe eutectic point) based on any feed concentration.

The phase diagram for a typical organic solution

illustrates this relationship.

Features

High product purity The ultra-pure crystal from thesuspension crystallization process and the efficientseparation of the Niro wash column provides themaximum purity possible.

High product recovery The maximum product

recovery is determined by the feed and eutecticcompositions for any crystallization system.Suspension crystallization provides the highestrecoveries in a single step.

Continuous operation The suspensioncrystallization process operates as a continuousprocess.

Feedstock Normal variations in feed impuritycomposition are absorbed by the system.

Expansion and debottlenecking The suspension

crystallization process is ideally suited to end-purification and can be easily added to existing units toimprove capacity and final product purity.

Economics The cost of operation is stronglydependent on the specific requirements of the system.Due to the single crystallization step required bysuspension-based systems the operating costs aresignificantly lower than other separation techniques.Niro can provide assistance in determining theoptimum configuration and cost information for yourspecific circumstances.

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Purification of Organic Chemicals Niro Process Technology B.V.

Process Description

The process is based on crystallization in an industry

proven scraped surface vessel crystallizer and finalpurification completed in the Niro Purifier using thisunique wash column separation technology. Thecrystallizer converts the feed into a slurry of pureproduct crystals and the residual mother liquor. TheNiro Purifier separates this slurry into a pure productmelt and the concentrated impurities as mother liquor.

The crystallizer consists of a jacketed vessel with arotating scraper assembly. Refrigerant circulates inthe outer jacket and cools the inner wall of the vessel.

The scraper sweeps the wall surface and preventsbuildup of crystals to maintain a clean heat transfersurface and continuous supply of product crystals.

Each individual crystal provides growth surface thatcan absorb the supersaturation caused by cooling theproduct at the swept surface. With billions of individualcrystals present, this will provide near ideal growthconditions and insure the production of ultra-purecrystals. The resulting low growth rates possible insuspension based crystallization systems allows purecrystal production from even relatively impure mother

liquor.

The Niro Purifier completes the separation of thismixture of pure product crystals and residual motherliquor. The Purifier is based on Niros own washcolumn technology and is an essential component inthis purification process.

A pump delivers the feed to the wash columnassembly and controls the product output from thesystem. A rotating transporter mechanicallycompresses the slurry to remove the mother liquor andform a packed crystal bed. This bed consists of the

pure product crystals surrounded by some residualmother liquor. The new crystals entering the columnforce the bed through the column toward the scraper

assembly at the opposite end. The scraperdisintegrates the crystal bed and a circulation pumpprovides melted product to reslurry the crystals. The

circulation flow carries the crystals to a heatexchanger where steam provides the heat necessaryto melt the crystals. The melted product leavesthrough a pressure control valve that provides thepressure needed to force the wash liquid through thepacked crystal bed. The required pressure is adjusteddepending on the level of the washfront. Thewashfront can be detected by the change intemperature between the washed and unwashedportions of the crystal bed (see diagram).

The melted product in the recirculation streamcountercurrently washes the residual mother liquorfrom the packed crystal bed as it moves through thecolumn. The wash liquid forms an internal reflux loopand therefore does not need to be recovered as withcentrifuge wash liquid. The crystal bed depth providesan extremely efficient wash zone for removal of themother liquor insuring complete removal of allimpurities.

Next Steps

On-site demonstration of this technology is possible invarious configurations from 3 kg/h up to 300 kg/husing one of Niros pilot plants. For more informationregarding this technology and your specificconfiguration requirements please contact:

Niro Process Technology B.V.De Beverspijken 7B5221 EE s-HertogenboschThe Netherlands

Tel: 31 736 390 390Fax: 31 736 312 349info@niro-pt.nlwww.niro-pt.nl