Presentation is loading. Please wait.

Presentation is loading. Please wait.

Thermodynamic (non)co-operation between Phase Equilibria and Ionic Dissociation of Organic acids in Water/Condensate/Gas systems Amrit Kalra, Ray French,

Similar presentations


Presentation on theme: "Thermodynamic (non)co-operation between Phase Equilibria and Ionic Dissociation of Organic acids in Water/Condensate/Gas systems Amrit Kalra, Ray French,"— Presentation transcript:

1 Thermodynamic (non)co-operation between Phase Equilibria and Ionic Dissociation of Organic acids in Water/Condensate/Gas systems Amrit Kalra, Ray French, Sheila Dubey, Ashok Dewan Shell Global Solutions (US) Inc. 3333 Highway 6 South, Houston TX 77082 Presentation at OLI User Conference, October 23 – 24 2007, Morristown NJ

2 2 Volatile Fatty Acids (VFAs) Source: 1) Can be naturally found in oil field waters 2) Acid stimulation of wells Volatile Fatty acids: Low molecular weight carboxylic acids Formic acid Acetic acid Propionic Acid Butyric acid HCOOHCH 3 COOH CH 3 CH 2 COOHCH 3 CH 2 CH 2 COOH HAc aq H+H+ +Ac - K diss HAc aq HAc v K Henry Dissociatio n VLE partitioning Use: Thermodynamics / Chemistry framework Experimental Physical Properties Data OLI Stream Analyzer Highlight:

3 3 VFAs can increase CO 2 corrosion rates Source: Effect of organic acids in CO 2 corrosion, Paper No. 07319, NACE 2007 Thermodynamics/Phase Behavior of organic acids? Electrochemical properties of organic acids? Mechanism of CO2 corrosion in presence of VFAs? Effect of VFAs on formation and protectiveness of Iron Carbonate scale? Questions? X-65 Steel 3 % NaCl pCO 2 = 0.96 bar pH = 4 T = 25 o C 1000 rpm

4 4 Top-of-Line (TOL) & Bottom-of-Line (BOL) Corrosion VFA’s influence on TOL and BOL Corrosion VFAs (for TOL and BOL Corrosion) HYDROCARBON

5 5 VAPOR WATER HAc aq H+H+ +Ac - HAc v 2 2 1 K diss K Henry K aq, dimer HYDROCARBON K o/w HAc HC K v, dimer HAc 1 2 2 Phase distribution of Acetic acid in Water/Gas/Condensate Main Issue: Phase distribution is more complicated than simple Henry’s Law when the species can ionize and dimerize. Underlying principle: Chemical potential of species is equal in all phases. VAPOR WATER HAc aq H+H+ +Ac - HAc v 2 2 1 K diss K Henry K aq, dimer HYDROCARBON K o/w HAc HC K v, dimer HAc 1 2 2

6 6 Effect of pH and temperature on Ionic Chemistry of H 2 S, CO 2 and NH 3 Effect of pH on CO 2, H 2 S and NH 3 speciation Effect of temperature on CO 2 speciation

7 7 HAc aq H+H+ +Ac - K diss Dissociation of Organic acids (C1-C4) in water pK d of Formic acid is one pH unit less than (C2-C4) acids. Not recommended to lump them all together for Corrosion and Phase Equilibria calculations Temperature effect on K d : factor of 5 [0 to 200 o C] Pressure effects are relatively small: factor of 1.04 [1 to 100 atm] Stream Analyzer Experimental Data Dissociation constants of organic acids in aqueous solutions, G. Kortum, W. Vogel, and K. Andrussow, London Butterworths 1961

8 8 Henry’s Law constants of Organic acids (C1-C4) HAc aq HAc v K Henry K Henry = M i / P i Experiment al Data Lack of good literature data on temperature dependent K H Assuming Infinite Dilution Activity Coefficient (IDAC) independent of temperature, vapor pressures of pure components are instead used to provide T dependence (Refer: Sep 2007 Chemical Engineering Progress, Avoid Common Pitfalls When Using Henry's Law, F.L. Smith and A.H. Harvey) M i is molality and P i is partial pressure T = 25 o C

9 9 Thermodynamic (non) co-operation HAc aq H+H+ +Ac - HAc v K diss KHKH K H True HAc aq + Ac - HAc v K diss KHKH K H Apparent H+H+ K H, Molar atm -1 Usually, total concentration (dissociated + undissociated) is measured in water analysis K Henry should be coupled with degree of dissociation Acetic acid at pH = 5, 1 atm, 25 o C, HAc + Ac - = 1mM [HAc] aq = 0.054 mM [Ac-] = 0.946 mM [P HAc ] vap = 9.79 x 10 -9 atm K H True = 5500M/atm K H Apparent = 100000 M/atm Stream Analyzer From Stream Analyzer:

10 10 Partitioning of Organic acids between Oil and Water Linear plot for K o/w as a function of carbon number, for organic acids. All four acids (C1-C4) should not be lumped together. C1 extrapolation: K o/w = 0.0035 Simulations done in Stream Analyzer for model HC’s. K o/w is weak function of temperature. M.A. Reinsel, J.J. Borkowski and J.T. Sears, Partition Coefficients for Acetic, Propionic, and Butyric Acids in a Crude Oil/Water System J. Chem. Eng. Data 39 (1994)

11 11 Phase distribution of Acetic acid in Water/Gas/Condensate VAPOR WATER HAc aq H+H+ +Ac - HAc v 2 2 1 K diss K Henry K aq, dimer HYDROCARBON K o/w HAc HC K v, dimer HAc 1 2 2 Engineering data and Thermodynamic Framework for four organic acids (C1-C4) is obtained for different operating conditions Dimerization can be ignored for OA in Water phase < 10 % OA in gas phase < 1 %

12 12 Acetic Acid: Comparison of MSE and H + models Dissociation of Acetic acid Not significant difference in the value of pKd Henry’s Law Constant MSE : 63.21 M atm -1 (25 o C and 1 atm) H+ : 92.57 M atm -1

13 13 Conclusions Determination of “Free” organic acids is the key in Corrosion studies; correct thermodynamic model is essential Organic acids show competing behavior for dissociation and partitioning into the vapor phase K H is very temperature sensitive Good confirmation of experimental data with Stream Analyzer for the H+ model Need additional data modeling efforts on organic acids for MSE model to represent influence of methanol & glycols

14 14 Questions??


Download ppt "Thermodynamic (non)co-operation between Phase Equilibria and Ionic Dissociation of Organic acids in Water/Condensate/Gas systems Amrit Kalra, Ray French,"

Similar presentations


Ads by Google