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Sulfamic Acid PurificationProcess Developmentusing OLI Flowsheet: ESP

(One reason we model)

Steven GriseThe Chemours Company

OLI Simulation Conference25-26 October, 2016

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We are Chemours and we unleash the power of chemistry, working hand-in-hand with our customers

• Created from DuPont’s Performance Chemicals businesses

• More than two centuries of experience in the chemical industry making us a 200-year-old start-up

• A rich history of innovation and industry firsts

• A market leader in safety and responsible handling of chemicals

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Market LeaderIn safe production & manufacture of performance chemicals. Combining leading products, applications expertise, and market-shaping chemistryFluoroproducts

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$6.4 Billion

in combined Revenues in

2014 By Region

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Chemical Solutions

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What is Sulfamic Acid ?

• Crystalline, aqueous inorganic strong acid– NH3SO3 or HSO3NH2

• Produced exclusively in Japan and Taiwan– US and Europe plants shut down due to decrease in demand,

production difficulties and problems with disposal of byproducts.

• Primary use as cleaning agent– Excellent for boiler scale.

– Relatively low corrosivity.

• Not specifically toxic– Physiological properties typical of a strong mineral acid.

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How is Sulfamic Acid produced ?

• Strongly exothermic reaction

• Urea + SO3 + H2SO4

• Two step process– Step 1

• NH2CONH2 + SO3 NH2CONHSO3H

• Solvent is Oleum

• Keep temperature low to manage heat and keep conversion low.

– Step 2

• NH2CONHSO3H + H2SO4 2 HSO3NH2 + CO2

• Keep temperature below about 80oC in excess SO3 to minimize impurity formation

• Remove unreacted SO3

• Typical product is ~95% pure (impurities are H2SO4 & NH4HSO4)

– Higher purity obtained via recrystallization

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Why is Chemours Interested ?

• We (as DuPont) were producers in the past

• Chemours was a major manufacturer of H2SO4 and Oleum prior to September 2016.– Business sold to Veolia.

• Is there an opportunity for manufacture of Sulfamic Acid to supply US fracking industry?– Fracking uses Sulfamic as de-scaler and well regenerator.

• Crude 95% product purity is not adequate for application– Some purification would be necessary.

– Look at recrystallization.

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Process Development

• This seemed like a great fit for OLI Flowsheet: ESP

• Fortunate to have been chosen as a Beta tester

• MSE Chemistry model

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OLI Flowsheet: ESP screenshot

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Comparison versus 1958 Patent Example

• US Patent 2,862,790

• Crude feed impurities not quantified in patent. Composition varied to roughly equal NH3/SO4 ratio below.

• Water feed not explicitly defined.

• Crystallizer feed and purge rate fixed.

• Impurity composition agrees well.

• Ratios and production rate agree well– Assumes no product loss through purge (oops)

• All told, agreement is very good !!

Expt'l Model

Crude feed lb/hr 388

NH3SO3 wt% 90 90

H2SO4 wt%10

3.5

NH4HSO4 wt% 6.5

Water feed lb/hr ? 62.9

Crystallizer feed lb/hr 20,800

Crystallizer feed T oC 50

Crystallizer T oC 40

Purge lb/hr 112

Purge H2SO4 conc wt% 12 12.1

Purge NH4HSO4 conc wt% 21.6 22.4

Purge NH4SO3NH2 conc wt% 0 0

Purge NH3SO3 conc wt% 0 (?) 9.2

NH3SO3 Product (Pure) lb/hr 350 339.1

NH3/SO4 ratio mol 0.60 0.61

NH3SO3 Productionlb pure NH3SO3 / 100 Crys Feed

1.68 1.63

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Sulfamic SLE

• Patent is for improved recovery by addition of a base.

• Sulfamic solubility decreases with the addition of NH3.

• Patent claims this addition helps production.

• Note that sulfamic acid solubility changes from about 19 wt% to about 15 wt% with a significant addition of NH3.

• Graph shows results of OLI regression fit.

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OLI Flowsheet: ESP with NH3

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Comparison

• Water feed stated as “unchanged”.

• Crystallizer feed increased slightly with larger crude feed and more recycle.

• Purge rate fixed, but recycle flow did not converge. Fixed recycle ML instead.

• Impurity composition not given in patent; significantly different than previous case.

• Ratios and production rate agree less well

– Assumes no product loss through purge (oops)

• Note patent claim of 60% improvement.– Cannot be explained by solubility graph.

Expt'l Model

Crude feed lb/hr 620

NH3SO3 wt% 90 90

H2SO4 wt%10

3.5

NH4HSO4 wt% 6.5

Water feed lb/hr Same 51.4

Crystallizer feed lb/hr 21039

Crystallizer feed T oC 50

Crystallizer T oC 40

Purge lb/hr 112 210.1

Purge H2SO4 conc wt% ? 0

Purge NH4HSO4 conc wt% ? 31.2

Purge NH4SO3NH2 conc wt% ? 12.2

Purge NH3SO3 conc wt% ? 26.5

NH3SO3 Product (Pure) lb/hr 560 480.3

NH3 feed lb/hr 7.6

NH3/SO4 ratio mol 1.5 1.39

NH3SO3 Productionlb pure NH3SO3 / 100 Crys Feed

2.66 2.28

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What is actually happening ?

• The claim in the patent is that the crystallization is improved with the base.– Presumably through a salting-out effect.

• What actually is happening is that the ammonia complexes with the sulfamate (NH4SO3NH2(aq)) and builds to a new saturation point.

There is very limited dissolution of sulfamic acid in the dissolving tank (~14% dissolves; roughly 79 lb/hr)

• Approximately 2 lb/hr additional sulfamic acid is precipitated in the crystallizer.

• This is a glorified wash step !

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Conclusions and Comments

1. OLI Flowsheet: ESP is a winner ! • Easy to use.

• Very stable.

• Kudos to the development team !

2. We model to gain insight. Sometimes we are surprised.

3. Understanding the chemistry is critical.• Model the process focusing on the electrolytes (using OLI)

• OLI Flowsheet: ESP will be a strong tool in the future

4. By using this modeling approach we have identified a significant opportunity for process simplification and reduced capital investment.

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Chemistry changes life.