materials and chemistry 1 theoretical study of amine degradation university of texas, 10 january...
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1Materials and Chemistry
Theoretical study of amine degradation
University of Texas, 10 January 2008
Eirik F. da Silva, Karl A. Hoff, Kristin Rist Sørheim, Odd Gunnar Brakstad and Hallvard F. Svendsen
SINTEF Materials and Chemistry, NTNU and University of Florida
2Materials and Chemistry
Outline
Application of Computational Chemistry
Toxicity and Biodegradation
Mechanistic Interpretation of Results
Carbamate Degradation
3Materials and Chemistry
Computational Chemistry
Quantum Mechanical calculations (HF, DFT, MP2..) Potentially accurate results without any experimental input. Cost of calculations increase with the quality of results and the
size of the system being studied.
Solvation models (PCM, SM, Cosmo-RS ….) Simplified representation of interactions in a liquid
Classical simulations (Molecular Dynamics, Monte Carlo) Simplified “ball-and-stick” representation of molecules. Can represent a liquid phase explicitly. Quality of results depend
on parameterization.
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Exploring Reactions
Computational Chemistry can be used to explore any reaction.
No general answers concerning the stability of species.
Experimental guidance is important.
Illustration from: helix.nih.gov
5Materials and Chemistry
Snøhvit and REACT
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OSPAR ConventionClassification of chemicals
Commercial chemical solvents like MDEA/piperazine are classified as red Red Category: Chemicals shall be phased out and/or substituted
ClassificationWater GreenChemicals on PLONOR list GreenHormone disturbing chemicals BlackList of prioritised chemicals that are contained in "resultatmål 1 (prioritetslisten) St. meld. nr 25 (2002-2003)"
Black
Biodegradability < 20 % and log Pow >= 5 BlackBiodegradability < 20 % and toxicity EC50 or LC50 <= 10 mg/l BlackTwo out of three categories: Biodegradability < 60% log Pow >= 3, IEC50 or LC50 10 mg/l
Red
Inorganic and EC50 or LC50 <= 1 mg/l RedBiodegradability < 20% RedOther chemicals Yellow
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Absorption Chemistry
Tertiary amines Secondary amines Sterically hindered
amines
Primary amines Some cyclical
amines
8Materials and Chemistry
• Regeneration energy requirement• Rate of reaction/Mass transfer • Cyclic capacity
• Molecular weight (per active site)• Foaming properties• Water solubility
• Molecular transport properties• Corrosion• Chemical stability• Toxicity and Biodegradation• Cost
Solvent selection criteria
9Materials and Chemistry
REACT
Determine experimentally the ecotoxicity and biodegradability of a wide set of process chemicals.
Develop understanding of degradation in both process and environmental conditions.
Chemicals identified as promising shall be characterized by measurement of thermodynamical and kinetic data.
New solvents will be implemented in a process modeling tool and simulations performed to assess the process performance and energy requirements.
10Materials and Chemistry
REACT
Ecotoxicity/biodegradablity
Molecular modeling/
QSAR studies
Process modeling
Solvent characterization
New solvent with thermal and chemical stability at process conditions
Classified as green or yellow
Degradationmechanisms
11Materials and Chemistry
Selection of chemicals for testing
28 Candidates for first test campaign selected from Alkanolamines known to be in commercial operation (MEA, MDEA, AMP,
DEA etc.) New candidates deemed promising based upon earlier experience +
molecular modeling studies Cyclic amines Linear polyamines Sterically hindered amines
A larger set of data is required in order to correlate results with molecular structure
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Ecotoxicity studies
Ecotoxicity tests recognized by OSPAR and by Norwegian Pollution authorities Phytoplankton: Skeletonema costatum (ISO/DIS 10253) – all
chemicals Marine biodegradation test (OECD 306) – all chemicals Bioaccumulation testing – calculations
Other bioassay studies Microtox assay – all chemicals Response studies in Calanus finnmarchicus – method
development on selected chemicals
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Skeletonema – EC-50 resultsSkeletonema - EC50
100
101
102
103
104
EDA1.3-propane-diamine
MEAMPA
4-amino-1-butanolAMP
MMEAEAE
AEEADETAAMPD
DEABHEDGA
DMMEADEEAAEPDMDEAMIPADIPA
PyrrolidinePiperidinePiperazine
MorpholineHydroxyethylpiperazine
EC-50 (mg/L)
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BOD resultsBOD
0 20 40 60 80 100
EDA1.3-propane-diamine
MEAMPA
4-amino-1-butanolAMP
MMEAEAE
AEEADETAAMPD
DEABHEDGA
DMMEADEEAAEPDMDEAMIPADIPA
PyrrolidinePiperidinePiperazine
MorpholineHydroxyethylpiperazine
BOD (% of ThOD)
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Bioaccumulation test
Chemical test to determine the distribution of a chemical between two immiscible phases; octanol and water
The calculations were based on the difference between free energy of solvation in water (dGswater) and in the water-immiscible solvent octanol (dGsoctanol).
LogPOW =
Results: No tested chemicals were bioaccumulating (all water-soluble)
water octanol 1000
2.303 1.987 298
dGs dGs x
x x
-
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Toxicity and log Pow correlation
1
10
100
1000
-2 -1.5 -1 -0.5 0 0.5 1 1.5 2
Calculated log Pow
Sk
ele
ton
em
a E
C5
0
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Observations on degradation Sterically hindered amines degrade slowly. No obvious trends between different classes of amines. Initial search for correlation between calculated bond
breaking energies and degradation rates gave no correlation.
EPI suite of models fail to predict trends in biodegradability.
Most of the amines displaying high degradability are known enzyme substrates1: 8/10 Known enzyme substrates had BOD over 20 2/14 Amines not known be enzyme substrates have BOD over 20
1: BRENDA database (www.brenda.uni-koeln.de)
18Materials and Chemistry
Proposed Mechanism for Copper Amino Oxidase:
Prabhakar and Siegbahn J. Comp. Chem. (2003)
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Proposed Mechanism for Trimethylamine Dehydrogenase:
Basran, Sutcliffe and Scrutton J. Bio. Chem. (2001)
20Materials and Chemistry
Proposed Mechanism for Ethanolamine Oxidase:
Warncke Biochemistry (2005)
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Degradation Products
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23Materials and Chemistry
How to understand and predict biodegradation
Can degradation be accounted for by a single enzyme? Determine similarity with known amine substrates.
Develop QSAR based on likely reaction path(s). Quantum Mechanical calculations on key intermediates.
Experimental work to determine intermediates and final products
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Carbamate Degradation
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Transition State for Carbamate Degradation
Relative barriers: MEA: 55 kcal/mol DEA: 60 kcal/mol MPA: 53 kcal/mol EDA: 1700 kcal/mol
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Conclusions
The amines tested show a relatively large span in both ecotoxicity and biodegradability
Most tertiary and sterically hindered amines are red Of the candidates identified as yellow, several are
promising solvents. For natural gas CO2 removal the gas is not oxidative. It
may therefore be easier to find a candidate solvent fulfilling the requirements of process stability and biodegradability
The relevance of these results for large scale post-combustion CO2 capture needs to be investigated further
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Acknowledgements:
The REACT project is funded by the Research Council of Norway, through the strategic PETROMAKS program
Co-funded by Shell Technology Norway and Statoil ASA
Thank you for your attention!