ABC Titration For Spent Caustic

Question 1

2. Procedure

Answer 1

1. Sample must be mixed well
2. Verify no bubbles in burette or jn line of automatic dispenser and if using automatic dispenser it has been zeroed
3. Add 25mL Barium Chloride to Erlenmeyer flask
4. Add 5mL spent sulfide caustic sample to Erlenmeyer flask
5. Add small amount of phenolphthalein indicator to Erlenmeyer flask (should turn bright pink in color)
6. Place stir bar in flask and place flask on stir plate
7. Titrate sample with 1N Hydrochloric acid from bright pink to a pinkish white color (where white color from Hydrochloric acid no longer dissipates). A white or clear color indicates over titration. Record volume of 1N Hydrochloric acid . Do not zero out burette or automatic dispenser
8. Add 5mL Formaldehyde to Erlenmeyer flask (color should return to bright pink
9. Continue to Titrate sampler to same pinkish-white as before. Record this volume of HCl used as point B. Do not zero out automatic dispenser
10. Add small amount of methyl orange indicator to Erlenmeyer flask and sample should be bright orange
11. Continue to Titrate with HCl till sample turns faint reddish color (blood red = over titration. Record amount of 1N HCl used as point C.

Question 2

3. Calculations

Answer 2

Multiply number from A,B,&C points by 6.2 if you used 1N HCl, if you used 0.5N HCl, multiply by 3.1.

Question 3

4. Troubleshooting and maintenance

Answer 3

• using automatic dispenser, make sure no air in line
• if sample becomes over-titrated start over
• verify correct reagents used and correct multiplication values used to calculate answer
• if sample does not return to original bright pink after adding formaldehyde, it means B endpoint equal to A endpoint and no Na2S in sample
• if endpoint C less than 70, the complex 2 board man should be notified by phone immediately and chemist over lab and unit foreman should know

Question 4

1. Purpose

Answer 4

Caustic used in Sat Gas Plants to remove H2S and Mercaptans. Typically caustic is sent to spent tank when it is >15-20% spent or when the NaOH falls below 8.0, but this could differ from caustic to caustic. ABC titration analyst measures combinations of three alkali components (NaOH, Na2S, and Na2CO3) in Spent Caustic. Filled spent caustic tanks checked to verify no hydrocarbons are present and it does not contain suspended solids. Visible hydrocarbon and material clarity testing ensures no volatiles in caustic which would interfere with end users process.