SOLUTION MONITORING GUIDELINES FOR AMINE SYSTEMS Amine Best Practices Group (ABPG) Represented by Nate Hatcher 2011 Brimstone-STS Sulphur Recovery Symposium Vail, CO DISCLAIMER The information and data furnished in this presentation are provided in good faith for general informational purposes. This material is not intended to replace good engineering judgment based upon site-specific data and circumstances. While the views expressed are generally held under consensus, they do not necessarily represent the specific views of ABPG member individuals or companies. Outline Objectives of Amine Solvent Analysis (i.e. What-You-Need-To-Know) Solvent Analysis Tests (i.e. What-You-Get) Definitions & Terminology Validation & Normalizing Tools Sampling Techniques and Pitfalls Conclusions
Solvent Analysis Objectives Qualitate and Measure the chemical species and properties of amine solutions that are important to making the correct operational decisions and adjustments to: 1) Meet, maintain, model and optimize treating performance, and 2) Maintain the safety, reliability, environmental performance, and mechanical integrity of the plant What You Need to Know Total and reactive concentration of all amines in solution Acid gas concentrations in lean+rich amine Levels of contaminants that impact treating effectiveness, capacity, inventory, or corrosiveness of the amine solution Water content of the solution (if you don t know everything else in solution) Visual appearance and characteristics of the sample What You Get Amine Strength Free amine, regenerable free base (RFB) Total amine Reacted (Bound) amine = Total Free Bound with what?? Expressed as %wt of the dominant amine thought to be in solution Amine strength amine concentration
What You Get Acid Gas Concentrations %wth 2 S or CO 2 in solution or loadings in moles per mole amine Which amine strength definition was used to convert to loadings (Free or Total)? Typically titrated with potential interferences Periodic validation versus other methods (GC gas, material + energy balances) What You Get Heat Stable Salts and Metals Report that varies considerably by vendor Maximum permissible concentrations that vary considerably by vendor Reported as ppmw or %wt of total solution or as equivalent amine (HSAS) Sometimes cations are reported Sometimes insoluble metals are reported Degradation products Varies by system and by vendor method Important if viscosity, surface tension, boiling temperature, or solution corrosiveness are impacted by the particular critter What You Get Water Content Typically calculated by difference from everything else that was measured Fine if you are confident that everything was measured Hydrocarbon Content Typically not measured Sometimes can be inferred by clarity of the sample Appearance Color & clarity Out of the sample tubing vs. sitting on the benchtop after a month
Definitions Parameter Analyte Description Amine Strength Free amine (FA) Regenerable Free Base (RFB) Amine (molecular) available for acid gas absorption Reacted Amine Bound amine (BA) Amine that is reacted with an acid gas or other acid anion and is either in the protonated or carbamate form Total Amine FA + BA All amine in solution Acid Gas CO 2 Loading Moles of CO 2 (as HCO 3, CO 3=, carbamate) per mole total amine H 2 S Loading Moles of H 2 S (as HS, S = ) per mole total amine Total acid gas loading Moles of CO 2 + H 2 S per mole of total amine Acids, Bases, Individual cations, Acidic and basic charged ions that accumulate in the Heat stable salts (HSS) anions or total HSS solution via absorption and/or reaction of absorbed components or by deliberate or unintentional addition. Heat Stable Amine Salt (HSAS) Protonated amine, AmH + Protonated amine that is thermally non-regenerable because it is associated with heat stable salt(s) Common Analysis Methods Parameter Free amine (FA) Bound amine (BA) Total amine (FA+BA) CO 2 Loading H 2 S Loading Total acid gas loading Individual cations (e.g. Na+), anions or total HSS Protonated amine, AmH + Methods Colorimetric, ph and conductometric titration ph and conductometric titration ph and conductometric titration, GC, Ion chromatography (I/C) Total Inorganic Carbon (TIC), GC, colorimetric titration Silver nitrate precipitation potentiometric titration Starch-Iodine (Tutweiler analysis) Acidify, cook and back titrate Weak acid ion conductometric titration Ion chromatography (I/C) or ICP Backcalc figure from above or by bound amine titration Titration - 101 Industry method of choice for amine strength Simple & inexpensive to perform Add a standardized amount of reactant of known concentration into a known weight/volume of unknown material Use a tracking property or indicator (ph, color, conductivity) of the solution to relate the unknown material to the standard
Colorimetric vs. ph Endpoint Color indication methods involve human interpretation and subjectivity Not all end points are sharp The color indicator must change in the ph range of the break Auto-titrators are more precise Conductivity vs. ph Conductivity breaks are sharper (esp. for HSS contaminated solvents) Bound amine by ph must be done by difference Errors amplify when subtracting two numbers of similar sizes Both are preferable over colorimetric Source: An Analytical Method for Determining Bound and Free Alkanolamines in Heat Stable Salt Contaminated Solutions, Cummings, A.L. Veatch, F.C., Keller, A.E., Mecum, S.M., and Kammiller, R.M., AIChE Summer Nat l. Mtg, Symposium on Gas Processing, Aug. 21, 1990. As accessed via http://www.mprservices.com/library/pages/publications.aspx on 9/5/11.
Analysis Validation Round Robin Duplicate Testing Benchmarking vs. Standards Charge Balance Calculated vs. Measured ph Analysis Normalization Refinery MDEA Case Parameter Average Range Deviation % MDEA (total) %wt 43.4 42.8 44 2.0 DEA %wt 0.6 0.6 0.6 0.0 HSAS as MDEA %wt 2.2 2.0 2.6 19.3 Sodium ppmw 129 110 147 20.3 Acetate ppmw 514 251 844 81.6 Formate ppmw 6834 5887 8440 26.4 Sulfate ppmw 36 22 61 76.6 Thiocyanate ppmw 1532 1129 2119 45.7 Total anions ppmw 9288 7994 11453 26.3 H 2 S loading mol/mol 0.0012 0.0008 0.0017 53.0 CO 2 loading mol/mol 0.0002 0.0002 0.0002 0.0 Solution ph 9.9 9.7 10.1 2.9 Charge Balance Results: Refinery MDEA Case
Analysis Normalization Different labs use different definitions, terminology, and methods Apples must be compared with Apples Example Normalization Tool Sampling and Lab Analysis H 2 S Oxidation Chemistry N 2 O 2 AIR GAP 2HS - + 2O 2 H 2 O + S 2 O 3 = AMINE Good Sampling Practices Minimizing Air Contamination Prepurge sample containers w/ N 2 Fill slowly with sample tube near bottom of bottle Leave minimal air gap at top of sample if not prepurged Obtaining a Representative Sample Flush the sample line thoroughly Good design is helpful 2008 Optimized Gas Treating, Inc.
Sampling Systems Minimizing Air Contamination in the Lab Sparge and pickle lab reagents with N 2 Do not leave sample bottles opened to atmosphere Minimize agitation and time spent in contact with air Titrate in a baggie Flashing Loss in Rich Samples Generally a concern for total acid gas loadings > 0.5 mol/mol Becomes increasing worse at higher loadings Entrained light ends from HP Contactors exacerbate losses
Flashing Expectations in 45%wt MDEA Sampling Temperature (Deg. F) Max H 2 S Loading (mole/mole Amine) 90 0.86 120 0.70 150 0.48 Minimizing Flashing Losses Sample coolers help Sample cylinder (constant pressure type) instead of bottle to maintain sample under pressure Vented vapors and sample can be stabilized in strong base (5% KOH or NaOH) Summary Most Critical Monitoring Variables Furnished Amine Concentrations (Total + Reactive) Acid Gas Concentrations Water Concentration Contaminants Visual Terminology and definitions remain obstacles to comparing analyses from different labs Further Guidelines on amine strength furnished Amine analyses should be viewed with deep suspicion until validated