Chemical Modeling of the TMA- CO 2 -H 2 O System in Forward Osmosis - - PowerPoint PPT Presentation

Chemical Modeling of the TMA- CO2-H2O System in Forward Osmosis

• G. Kolliopoulos, T.J. Clark1, A.M. Holland1 and

V.G. Papangelakis

Department of Chemical Engineering and Applied Chemistry, University of Toronto, Ontario, Canada, M5S 3E5

1Forward Water Technologies, 945 Princess Street, Kingston, ON, K7L 5L9

Forward Osmosis (FO)

Difference in H2O activity: the driving force of the process No application

• f

hydraulic pressure

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Advantages of FO:

• High H2O recovery (>90%)[1]
• Energy savings based on equivalent work:

72-85% comparing with Reverse Osmosis (RO), Evaporation-Condensation[2]

• Lower membrane fouling (vs. RO)

[1]T.Y. Cath et al., J. Membr. Sci. 281 (2006), pp. 70–87 [2]R.L. McGinnis, M. Elimelech, Desalination 207 (2007), pp. 370-382

Challenges of FO:

• FO-specific membranes
• Ideal draw solute:

– Highly soluble – Easily separated from the DDS – Recoverable products upon separation

Conceptual FO Process Flow Diagram

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FO Process Treatment Window

Draw Solution

Thermolytic salts exhibit phase change upon heating:

• NH3-CO2 (well studied)

– formation of carbamates (stable in solution-difficult to separate)

• Trimethylamine (TMA)-CO2 (newly proposed)

– no formation of carbamates (easier separation) – higher water flux N Concentration (molal) CO2 Concentration (molal) Osmotic Pressure (atm) Carbonated NH3 3.53 3.53 88.5 Carbonated TMA 3.53 3.53 104.8 Carbonated NH3 13.84 7.5 366.1 Carbonated TMA 13.84 13.5 371.7

Objective

Develop an accurate mathematical model describing the various equilibria in the ternary system TMA-CO2-H2O in

• rder to design an integrated FO process:

a) Develop analytical techniques for the determination

• f total dissolved TMA and CO2 at high concentrations

b) Verify the properties binary TMA-H2O system (well studied since the 1930s) - ionization constant and its vapour-liquid equilibria (VLE) c) Generate thermodynamic data for the ternary system TMA-CO2-H2O that can be incorporated in chemical chemical modeling software, such as OLI (www.olisystems.com)

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a) Analytical Techniques for total dissolved TMA and CO2

b) Binary TMA-H2O System

Binary TMA-H2O System - Ionization Constant

Known mass (20 g) of 2 M HCl was titrated with aqueous TMA at 25 °C:

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2.14% Error

OLI-MSE

Binary TMA-H2O System - VLE

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[6] S.D. White, B.K. O'Neill, Journal of Chemical & Engineering Data, 38 (1993) 234-237.

VLE (20 °C)

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Liquid Samples

• Water content measured by

Karl-Fischer titration Vapor Samples

• Mole fraction of H2O in the

vapor phase determined on the basis of i) molecular weight of TMA and H2O, ii) measured mass

• f vapor phase, and iii) ideal-gas

law

Binary TMA-H2O System - VLE (20 °C)

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c) Ternary TMA-CO2-H2O System

pH-Composition Experiments (4 and 25 °C)

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CTMA=42 wt.% in H2O Inject CO2(g) (P=5 bar) for 60 min Sample every 10 min

TMA(aq)+CO2(g)+H2O = TMAH++HCO3-

VLE (50 and 60 °C)

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Liquid Samples

• Water content measured by Karl-

Fischer titration and GC (Agilent Technologies 7890A with thermal conductivity detector - Capillary column: CPVolamine 30x0.32, Agilent Technologies CP7447) Vapor Samples

• GC:

i. Injection of He into the vapor flask (room T); contents at 100 kPa absolute pressure ii. Sealed flask placed in controlled hot-air chamber; contents to at least 10 °C higher than T at which sample was collected à contents vaporized completely prior to withdrawing sample

Experimental Results vs. OLI-MSE

4 °C 25 °C

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TMA Evaporation

Regressed OLI-MSE Model

4 °C 25 °C

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Evaluation of Developed Model

pH and composition experimental measurements (25 °C) in solutions that were not used to fit the model:

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Conclusions

• Speciated VLE for TMA-H2O are consistent with literature data

(embedded in OLI-MSE model)

• Significantly low accuracy of the default OLI-MSE model for

TMA-CO2-H2O, as a result of missing binary interaction parameters

• Existing

databank for TMA-CO2-H2O was improved by incorporating these parameters between the dominant species, i.e., TMAH+ and HCO3-,as well as TMA and HCO3-

• Developed OLI-MSE model is able to predict the properties of

TMA-CO2-H2O with Absolute Average Relative Deviation (AARD) of 8, 15, 10 and 1% for total pressure, partial pressures

• f TMA and CO2as well as pH, respectively

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Acknowledgements

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