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STANDARD TEST METHOD HEAT STABLE AMINE SALTS BY CONDUCTIMETRIC TITRATION 1 of 10

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CODE WORDS

Heat Stable Amine Salts, Conductimetric, titration

ORIGINATOR

MANAGEMENT DEPARTMENT UNIT ORIGINATOR DATE

GTP Laboratory Lab. And Quality Nicola Magarelli 04/2016

REVISION OF THE PROCEDURE

MANAGEMENTS DEPARTMENTS POSITION REVIEWED BY: DATE

GTP Laboratory Lab. And Quality Nicola Magarelli 04/2016

APPROVAL OF THE PROCEDURE

MANAGEMENT DEPARTMENT POSITION APPROVED BY: DATE

GTP GTP Site Manager O. Ayoub

Suggested Date for next review:

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STANDARD TEST METHOD HEAT STABLE AMINE SALTS BY CONDUCTIMETRIC TITRATION 2 of 10

This document should be revised every two years or when the situation so warrants

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CONTENT

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STANDARD TEST METHOD HEAT STABLE AMINE SALTS BY CONDUCTIMETRIC TITRATION 3 of 10

1. SCOPE:

1.1 Aqueous solutions of amines, such as methyl diethanolamine (MDEA), are analyzed to
determine the concentrations of "bound amine" (protonated amine; amine which has
neutralized an acid), "free amine" (amine which has not reacted with an acid), anions of weak
acids (e.g., acetate, formate), and excess NaOH.

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STANDARD TEST METHOD HEAT STABLE AMINE SALTS BY CONDUCTIMETRIC TITRATION 4 of 10

1.2 Total amine concentration is calculated as the sum of bound and free amine concentrations.
Amine concentrations from 100 ppm to 95 wt% can be determined.

2. OUTLINE OF METHOD:

2.1 A sample of MDEA (lean or rich) is mixed with water and titrated with NaOH while monitoring
the electrical conductance of the solution. From the consumption of NaOH the bound amine
concentration is calculated.

2.2 A similar titration with HCl leads to the calculation of free amine and weak acid anions
concentrations.

2.3 Addition of a known amount of acetic acid to the titration solution enhances the accuracy of free
amine and weak acid anion determinations.

2.4 Excess NaOH in the amine solution is determined by a third titration, when necessary.

3. APPARATUS & MATERIALS:

3.1 Conductance meter and probe.

3.2 Buret, 20 mL capacity, readable to 0.02 mL.

3.3 Balance, analytical, readable to 0.0001 g.

3.4 Beakers, 100 mL.

3.5 Continuous stirring device (e.g., magnetic stirrer and 1/8 x 1 inch stirring bar).

4. REAGENTS:

4.1 NaOH solution, 0.1 N, aqueous (Standardize with HCl).

4.2 HCl solution, 0.1 N, aqueous (Standardized by Na 2CO3).

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STANDARD TEST METHOD HEAT STABLE AMINE SALTS BY CONDUCTIMETRIC TITRATION 5 of 10

4.3 Acetic acid solution, 1 N, aqueous.

4.4 Water, conductance grade or distilled R.O. water.

4.5 Potassium acid phthalate (potassium biphthalate), primary standard.

5. SAMPLE PREPARATION:

5.1 Portions of amine solutions are taken as received, weighed, and transferred to the titration
beaker.

5.2 A monotonic titration in increments of about 0.1 mL has worked well on MDEA lean amine.

6. QUALITY CONTROL:

6.1 Reagents should be stored to prevent titer changes due to evaporation or contamination.

6.2 HCl reagent and Acetic Acid reagent titers should be verified monthly by one standardization
titration.

6.3 NaOH reagent titer need be verified only when the HCl titer goes beyond control limits.
Statistical process control charts should be maintained on the titer checks.

6.4 Restandardization is required when control limits are exceeded.

7. REAGENT STANDARDIZATION

7.1 Reagents are standardized by titration with colorimetric, potentiometric, or conductometric

7.2 NaOH reagent is standardized against dried primary standard potassium acid phthalate.

7.3 HCl and Acetic Acid reagents are standardized against standardized NaOH reagent.

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STANDARD TEST METHOD HEAT STABLE AMINE SALTS BY CONDUCTIMETRIC TITRATION 6 of 10

7.4 The standardized titer of the reagents must be the average of at least 3 determinations.

8. PROCEDURE:

8.1 Of the three titration procedures given here, the Bound Amine should be performed first.

8.2 Only if no bound amine is detected, should the Excess OH- titration be done.

8.3 The Free Amine procedure is affected by Excess OH- when present.

8.3.1 Bound Amine:

8.3.1.1 1. Weigh 2 grams of amine solution and quantitatively transfer to the titration
beaker.

8.3.1.2 Record weight to the nearest 0.002 g.

8.3.1.3 Add conductance water (ca. 45 mL) to bring solution level to top of vent holes in
conductance probe. In not, add more.

8.3.1.4 Begin continuous stirring without visible vortex.

8.3.1.5 Titrate with 0.1 N NaOH to at least 3 mL beyond the beginning of the increased
slope evidencing excess OH- .

8.3.1.6 Determine the equivalence point from a graph of the titration curve (conductance
vs. mL of titrant in excel), and calculate the bound amine concentration (see
"Calculations")

8.3.2 Free Amine

8.3.2.1 1. Weigh 0.3 grams of amine solution and quantitatively transfer to the titration
beaker. Record weight to the nearest 0.0005 g.

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STANDARD TEST METHOD HEAT STABLE AMINE SALTS BY CONDUCTIMETRIC TITRATION 7 of 10

8.3.2.2 Add 0.4 grams (or 0.4 mL) Acetic Acid reagent to the titration beaker. Record the
amount to the nearest 0.0005 g (or 0.0005 mL).

8.3.2.3 Add conductance water (ca. 45 g) to bring solution level to top of vent holes in
conductance probe. Begin continuous stirring without visible vortex.

8.3.2.4 Titrate with 0.1 N HCl to at least 3 mL beyond the beginning of the increased slope
evidencing excess H+.

8.3.2.5 Determine the equivalence points from a graph of the titration curve (conductance
vs. mL of titrant), and calculate the free amine and weak acid anions concentrations.

8.3.2.6 If no bound amine was found in procedure A, perform an "Excess NaOH" titration
(next procedure) before calculating free amine results.

8.3.3 Excess NaOH 1. (Same as Step A-1) 2. (Same as Step A-2)

8.3.3.1 Titrate with 0.1 N HCl to at least 3 mL beyond the beginning of the positive slope in
the titration curve (see Figure A-3).

8.3.3.2 Determine the equivalence point from a graph of the titration curve (conductance
vs. mL of titrant), and calculate the "excess NaOH" .

8.3.4 CALCULATIONS

8.3.4.1 A. Bound Amine Figure XXXX shows a typical titration curve for bound amine. The
equivalence point is found, as illustrated, at the intersection of extrapolations of the
linear portions of the titration curve.

8.3.4.2 The concentration of bound amine is calculated as follows: 15 15 V * N [B] = ---------

8.3.4.3 Insert equation.

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STANDARD TEST METHOD HEAT STABLE AMINE SALTS BY CONDUCTIMETRIC TITRATION 8 of 10

8.3.4.4 Where [B ] = Bound Amine concentration, meq/g

8.3.4.5 V = volume of NaOH titrant to the equivalence point, mL

8.3.4.6 N = Normality of NaOH titrant, meq/mL

8.3.4.7 W = weight of amine sample, g

8.3.4.8 Conversion of Bound Amine concentration from meq/g to wt% is accomplished by:
wt% = ( meq/g)*M/10 (2) Where M = equivalent weight of the amine, mg/meq =
119 for MDEA, 61 for MEA, 105 for DEA B.

8.3.4.9 Free Amine and Weak Acid Anions Figure A-2 shows a typical titration curve for free
amine and anions of weak acids. Two equivalence points are evident here.

8.3.4.10 The first equivalence point is found, as illustrated, at the intersection of the
extrapolations of the first two portions of the titration curve.

8.3.4.11 The second equivalence point is found, as illustrated, at the intersection of the
extrapolations of the second and third linear portions of the titration curve.

8.3.4.12 The concentration of free amine is calculated as follows: (V1 * Nh) + (Wac * Nac)
[F] = ------------------------------------ - [Cex]

8.3.4.13 Where [F] = Free Amine concentration, meq/g

8.3.4.14 V1 = volume of HCl titrant to the first equivalence point, mL

8.3.4.15 Nh = Normality of HCl titrant, meq/mL

8.3.4.16 Wac = weight of acetic acid added, g

8.3.4.17 Nac = Normality of acetic acid, meq/g

8.3.4.18 W = weight of amine sample, g

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STANDARD TEST METHOD HEAT STABLE AMINE SALTS BY CONDUCTIMETRIC TITRATION 9 of 10

8.3.4.19 [Cex] = excess NaOH concentration, meq/g

8.3.4.20 The concentration of titrable anions of weak acids is: Nh *(V2 - V1) - (Wac * Nac)
[A] = ---------------------------------------- (4) W

8.3.4.21 Where

8.3.4.22 [A] = titrable anion concentration, meq/g

8.3.4.23 V2 = volume of HCl titrant to the second equivalence point, mL

8.3.4.24 Conversion of meq/g concentration to wt% is accomplished by Equation 2,

8.3.4.25 For weak acid anions, one must assume an equivalent weight, such as 60 (acetic
acid) or 46 (formic acid).

8.3.4.26 Excess NaOH Figure A-3 shows a typical titration curve for excess NaOH.

8.3.4.27 Only one equivalence point is shown here, although if the tiration were
continued, the remaining curve would look much like the free amine titration.

8.3.4.28 The equivalence point is found, as illustrated, at the intersection of the

8.3.4.29 The concentration of excess NaOH is calculated as follows:

8.3.4.30 V3 * Nh [Cex] = ----------------- (5)

8.3.4.31 Where Cex = excess NaOH concentration, meq/g

8.3.4.32 V3 = volume of HCl titrant to the equivalence point, mL

8.3.4.33 Notes 1. For greater sensitivity, more amine solution may be taken. To reduce
titrant consumption, take less amine solution. Amounts specified in the procedure

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STANDARD TEST METHOD HEAT STABLE AMINE SALTS BY CONDUCTIMETRIC TITRATION 10 of 10

are optimized for amine solutions containing on the order of 0.5 meq/g bound
amine and 3 meq/g free amine. If less than 1 mL of titrant is required to the first
endpoint, titrate a larger sample. Ambiguity of bound amine and excess OH- results
can be resolved by titrating excess OH- 3 mL beyond the endpoint, then back-
titrating with NaOH.

8.3.4.34 2. Acetic acid is added to enhance the segregation of free amine from the weak
acid anions in the titration. If the amount of amine in the titration is less than 0.45
meq, the amine titration (from zero to V1 in Figure A-2) will not be observed, and
concentration calculation may be meaningless. Increase the amount of amine
solution. For extremely weak free amine solutions (less than 0.45 meq in at least 50
g) the acetic acid addition may be eliminated, with potential loss of distinction
between free amine and low concentrations of weak acid anions.

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