Presentation on theme: "Amrit Kalra, Ray French, Sheila Dubey, Ashok Dewan"— Presentation transcript:
1 Amrit Kalra, Ray French, Sheila Dubey, Ashok Dewan Thermodynamic (non)co-operation between Phase Equilibria and Ionic Dissociation of Organic acids in Water/Condensate/Gas systemsAmrit Kalra, Ray French, Sheila Dubey, Ashok DewanShell Global Solutions (US) Inc.3333 Highway 6 South, Houston TX 77082Presentation at OLI User Conference, October 23 – , Morristown NJ
2 Volatile Fatty Acids (VFAs) Source: 1) Can be naturally found in oil field waters 2) Acid stimulation of wellsVolatile Fatty acids: Low molecular weight carboxylic acidsFormic acid Acetic acid Propionic Acid Butyric acidHCOOHCH3COOHCH3CH2COOHCH3CH2CH2COOHHighlight:HAcaqH++Ac-KdissHAcaqvKHenryUse:Thermodynamics / Chemistry frameworkExperimental Physical Properties DataOLI Stream AnalyzerDissociationVLE partitioning
3 VFAs can increase CO2 corrosion rates X-65 Steel3 % NaClpCO2 = 0.96 barpH = 4T = 25 oC1000 rpmSource: Effect of organic acids in CO2 corrosion, Paper No , NACE 2007Questions?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?
4 VFA’s influence on TOL and BOL Corrosion (for TOL and BOL Corrosion)HYDROCARBONTop-of-Line (TOL) & Bottom-of-Line (BOL) Corrosion
5 Phase distribution of Acetic acid in Water/Gas/Condensate VAPORWATERHAcaqH++Ac-v21KdissKHenryKaq, dimerHYDROCARBONKo/wHCKv, dimerKv, dimer1HAcHAcVAPOR2v2KHenry1HAcHAcHAc2HCaq2Kaq, dimerKdissKo/wHYDROCARBONWATERH++Ac-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.
6 Effect of pH and temperature on Ionic Chemistry of H2S, CO2 and NH3 Effect of pH on CO2, H2S and NH3 speciationEffect of temperature on CO2 speciation
7 Dissociation of Organic acids (C1-C4) in water Stream AnalyzerHAcaqH++Ac-KdissExperimental DataDissociation constants of organic acids in aqueous solutions, G. Kortum, W. Vogel, and K. Andrussow, London Butterworths 1961pKd of Formic acid is one pH unit less than (C2-C4) acids.Not recommended to lump them all together for Corrosion and Phase Equilibria calculationsTemperature effect on Kd: factor of 5 [0 to 200oC]Pressure effects are relatively small: factor of 1.04 [1 to 100 atm]
8 Mi is molality and Pi is partial pressure Henry’s Law constants of Organic acids (C1-C4)HAcaqvKHenryT = 25 oCT = 25 oCKHenry = Mi / PiMi is molality and Pi is partial pressureExperimental DataLack of good literature data on temperature dependent KHAssuming 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)
9 Thermodynamic (non) co-operation KH TrueKH ApparentHAcHAcvvStream AnalyzerKHKHKH, Molar atm-1HAcHAcAc-+H+aqaqKdissKdissH++Ac-From Stream Analyzer:Acetic acid at pH = 5, 1 atm, 25 oC, HAc + Ac- = 1mM[HAc]aq = mM [Ac-] = mM[PHAc]vap = x 10-9 atmKH True = 5500M/atm KH Apparent = M/atmUsually, total concentration (dissociated + undissociated) is measured in water analysisKHenry should be coupled with degree of dissociation
10 Partitioning of Organic acids between Oil and Water 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)C1 extrapolation: Ko/w =Linear plot for Ko/w as a function of carbon number, for organic acids.All four acids (C1-C4) should not be lumped together.Simulations done in Stream Analyzer for model HC’s.Ko/w is weak function of temperature.
11 Phase distribution of Acetic acid in Water/Gas/Condensate VAPORWATERHAcaqH++Ac-v21KdissKHenryKaq, dimerHYDROCARBONKo/wHCKv, dimerDimerization can be ignored forOA in Water phase < 10 %OA in gas phase < 1 %Engineering data and Thermodynamic Framework for four organic acids (C1-C4) is obtained for different operating conditions
12 Acetic Acid: Comparison of MSE and H+ models Dissociation of Acetic acidNot significant difference in the value of pKdHenry’s Law Constant MSE : M atm-1(25 oC and 1 atm) H+ : M atm-1
13 ConclusionsDetermination of “Free” organic acids is the key in Corrosion studies; correct thermodynamic model is essentialOrganic acids show competing behavior for dissociation and partitioning into the vapor phaseKH is very temperature sensitiveGood confirmation of experimental data with Stream Analyzer for the H+ modelNeed additional data modeling efforts on organic acids for MSE model to represent influence of methanol & glycols