Determination of the Total Acid Number (TAN) with Potentiometric Method

Determination of the Total Acid Number (TAN) with Potentiometric Method

Equipment
Potentiometer = 751 GPD Titrino / Titroprocessor
Electrodes = 6.0133.100 pH glass electrode; input 1
6.0729.100 Ag/AgCl reference electrode ( LiCl sat in ethanol); input 2
6.0331.000 Pt auxiliary electrode; input Ref.
Differential potentiometry

Reagents
c(TBAOH) = 0.1 mol/L in isopropanol/methanol; D0
TBAOH = Tetrabutyl ammonium hydroxide

Sample
app. 1.5 g of used motor oil
50 mL solvent: chlorobenzene : isopropanol (2 : 1)

Remarks
· Calculations:

TAN=(EP1-C01)*C02*C03/C00;2;mg/g

TAN = acid of sample, calculated as mg KOH per g of sample
C01 = blank value, consumption of titrating agent by solvent mixture (0 mL)
C02 = concentration of titrating agent (0.1 mol/L)
C03 = molecular mass of KOH (56.106 g/mol)

. Answer

TAN = (0.680) x 0.1 x 56.106 / 1.6646 = 2.29 mg/g

EP1 = 0.680 mL
C00 = 1.6646 g

· Store glass electrode in dist. water over night. Before titrating,
precondition it in solvent during 10 - 30 min.
· The 6.0430.100 Ag Titrode may be used instead of the 6.0133.100
and 6.0331.000 electrodes. In this case, you make differential
potentiometry with only two electrodes, the Ag Titrode and the
6.0729.100 reference electrode.

Literature

· Metrohm Application Bulletin No. 80: Determination of the acid / base
number in petroleum products (TAN/TBN)
· ASTM D 2896 - 80
· DIN 51596

Method documentation

'pa
751 GPD Titrino 15215 751.0010
MET U TAN
parameters
>titration parameters
V step… 0.10 ml
dos.rate max…. ml/min
signal drift …OFF mV/min
equilibr.time …50 s
start V:… OFF
pause …100 s
dos.element:… internal D0
meas.input: …diff.
temperature… 25.0 °C
>stop conditions
stop V: …abs.
stop V …10 ml
stop U… OFF mV
stop EP …9
filling rate max…. ml/min
>statistics
status: …OFF
>evaluation
EPC …20 mV
EP recognition:… last
fix EP1 at U …OFF mV
pK/HNP: …OFF
>preselections
req.ident: …OFF
req.smpl size:… value
activate pulse: …OFF
------------
'fm
751 GPD Titrino 15215 751.0010
MET U TAN
>calculations

TAN=(EP1-C01)*C02*C03/C00;2;mg/g

C00= 1.6646
C01= 0
C02= 0.1
C03= 56.106
------------
'fr
751 GPD Titrino 15215 751.0010
U(init) 27 mV MET U TAN
smpl size 1.6646 g
EP1 0.680 ml -236 mV
TAN 2.29 mg/g
stop V reached
============
'cu
751 GPD Titrino 15215 751.0010
start V 0.000 ml MET U TAN
1.0 ml/div dU=200.0 mV/div
============