– Titrant: bromide/bromate solution ô0.02 Nằ (see Method 6)
– Solvent mixture I (for aliphatic hydrocarbons): consisting of 714 mL glacial acetic acid, 134 mL carbon tetrachloride, 134 mL methanol and 18 mL w(H2SO4)
= 20%
– Solvent mixture II (for aromatic hydrocarbons): consisting of 714 mL glacial acetic acid, 134 mL 1 methyl-2-pyrrolidone*, 134 mL methanol, 18 mL w(H2SO4)
= 20%.
* Fluka No. 15780, Merck No. 105215
100 mL solvent mixture is placed in the titration vessel. The titration is started when the solution has cooled down to 0...5 °C (instrument parameters and an example of a curve are given in the appendix).
Blank value = EP1 (mL titrant) = C31
Temperature measured by the Pt 1000 sensor (°C) = C44 Recommended accessories
General
Reagents
Titration instructions
(apply to both bromine number and bromine index)
Calculation
Method 7 – Blank value of the solvent for the determination of the bromine number and the bromine index
– ASTM D 1159-84
Standard Test Method for Bromine Number of Petroleum Distillates and Com- mercial Aliphatic Olefins by Electrometric Titration
– ISO 3839:1996
Petroleum products – Determination of Bromine Number of Distillates and Ali- phatic Olefins – Electrometric Method
– ASTM D 5776-99
Standard Test Method for Bromine Index of Aromatic Hydrocarbons by Poten- tiometric Titration
– ASTM D 2710-92
Standard Test Method for Bromine Index of Petroleum Hydrocarbons by Electrometric Titration
Literature
Method parameters & calculation Titration curves Method 7.1
Method 7.2
'pa785 DMP Titrino 02287 785.0010 date 2000-11-16 time 16:43 0 MET Ipol M7.1
parameters
>titration parameters
V step 0.020 ml dos.rate max. ml/min signal drift OFF mV/min equilibr.time 30 s start V: OFF pause 60 s I(pol) 1 àA electrode test: OFF temperature 25.0 °C
>stop conditions
stop V: abs.
stop V 2 ml stop U OFF mV stop EP 9 filling rate max. ml/min
>statistics
status: ON mean n= 3 res.tab: original
>evaluation
EPC 200 mV EP recognition: all fix EP1 at U OFF mV
>preselections
req.ident: id1 req.smpl size: all limit smpl size: OFF activate pulse: OFF ---
'de785 DMP Titrino 02287 785.0010 date 2000-11-16 time 16:43
MET Ipol M7.1 def>formula
Blank=EP1
RS1 text Blank RS1 decimal places 3 RS1 unit: mL RS1 limit control: OFF Temp=C44
RS2 text Temp RS2 decimal places 1 RS2 unit: °C RS2 limit control: OFF
>silo calculations
match id: OFF
>common variables C31=MN1
>report
report COM1:full;curve;
>mean MN1=RS1
>temporary variables ---
'cf785 DMP Titrino 02287 785.0010 date 2000-11-16 time 16:43
MET Ipol M7.1 C-fmla
---
Method 7 –
Blank value of the solvent
for the determination of the bromine number and the bromine index
Method 8 – Bromine number of cyclohexene
• 6.3014.223 Exchange Unit, 20 mL
• 6.0308.100 double Pt electrode with 6.2104.020 electrode cable
• 6.1110.100 Pt 1000 temperature sensor with 6.2104.080 electrode cable
• 6.1414.010 titration vessel lid and 6.1418.250 titration vessel with thermostatic jacket
• Thermostat/cryostat or ice bath
The bromine number gives the fraction of unsaturated compounds (mostly C=C double bonds) in petroleum products. The double bonds are split with the attach- ment of bromine:
R - C = C - R + Br2 → R - CBr - CBr - R This method has been tested for the following products:
– Generally for distillates with a boiling point below 327 °C (620 °F) and a volume fraction of 90% lighter than 2-methylpropane.
– This includes gasoline (petrol) with and without lead additives, kerosenes and gas oils.
– Commercial olefins (mixtures of aliphatic monoolefins) with a bromine number 95...165.
– Propenes (trimers and tetramers), butene trimers, mixtures of nonenes, octenes and heptenes.
– The method is not suitable for normal α-olefins.
The bromine number (BN) is the number of mg bromine (Br2) that are bound or added by 100 g sample.
The use of chlorinated solvents should be avoided because of environmental rea- sons. Tests have shown that 1,1,1-trichloroethane can be replaced by diethyl car- bonate (Fluka No. 32080, Merck No. 802898).
– Titrant: 0.08333 mol/L bromide-bromate solution (ô0.5 Nằ). 51 g KBr and 13.92 g KBrO3 are dissolved separately in dist. H2O. The two solutions are rinsed into a single 1000 mL volumetric flask and made up to the mark with dist. H2O.
– Solvent mixture: consisting of 714 mL glacial acetic acid, 134 mL 1,1,1- trichloroethane, 134 mL methanol and 18 mL w(H2SO4) = 20%.
The titer of the titrant has already been determined according to Method 6 (com- mon variable C33). Before the analysis itself the blank value of the solvent mixture is determined and stored in the Titrino as common variable C31 (Method 7). 10 mL 1,1,1-trichloroethane is placed in a 50 mL volumetric flask. Depending on the expected bromine number (see following table) 0.5...20 g is added, made up to the mark with trichloroethane and mixed. 100 mL solvent mixture and a 5.0 mL aliquot of the sample are placed in the titration vessel. The mixture is cooled down to 0...5 °C and the titration is started when this temperature has been reached (instrument parameters and an example of a curve are given in the appendix).
Recommended accessories
General
Definition
Reagents
Analysis
Method 8 – Bromine number of cyclohexene
Expected bromine number Sample weight in g
0 ... 10 20 ... 16
10 ... 20 10 ... 8
20 ... 50 5 ... 4
50 ... 100 2 ... 1.5
> 100 1 ... 0.5
Table of sample weights
Calculation
Remarks
Literature Bromine number (BN) in g Br2 / 100 g sample = (EP1 - C31) x C01 x C33 x C02 / C00
Temperature measured by the Pt 1000 sensor ( in °C) = C44 EP1 = titrant consumption up to endpoint, in mL
C00 = sample weight in g in a 5 mL sample aliquot C01 = 0.5 = ônormalityằ of titrant
C02 = 7.99 = conversion factor for bromine C30 = titrant titer
C31 = blank value of solvent mixture, in mL titrant
Cyclohexene is used as the ôsampleằ (theoretical bromine number = 194.54).
Approx. 0.5 g cyclohexene is weighed out into the 50 mL volumetric flask and made up to the mark with 1,1,1-trichloroethane.
– ASTM D 1159-84
Standard Test Method for Bromine Number of Petroleum Distillates and Com- mercial Aliphatic Olefins by Electrometric Titration
– ISO 3839:1996
Petroleum products – Determination of Bromine Number of Distillates and Ali- phatic Olefins – Electrometric Method
– Metrohm
Application Bulletin No. 177
Method parameters & calculation Titration curve Method 8
Method 8 – Bromine number of cyclohexene
'pa785 DMP Titrino 02287 785.0010 date 2000-11-16 time 17:05 0 MET Ipol M8
parameters
>titration parameters
V step 0.050 ml dos.rate max. ml/min signal drift OFF mV/min equilibr.time 30 s start V: OFF pause 60 s I(pol) 1 àA electrode test: OFF 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 200 mV EP recognition: all fix EP1 at U OFF mV
>preselections
req.ident: id1 req.smpl size: all limit smpl size: OFF activate pulse: OFF ---
'de785 DMP Titrino 02287 785.0010 date 2000-11-16 time 17:05
MET Ipol M8 def>formula
BrNo=(EP1-C31)*C01*C33*C02/C00 RS1 text BrNo RS1 decimal places 2 RS1 unit: g/100g RS1 limit control: OFF Temp=C44
RS2 text Temp RS2 decimal places 1 RS2 unit: °C RS2 limit control: OFF
>silo calculations
match id: OFF
>common variables
>report
report COM1:full;curve;
>mean MN1=RS1
>temporary variables ---
'cf785 DMP Titrino 02287 785.0010 date 2000-11-16 time 17:05
MET Ipol M8 C-fmla
C01 0.5 C02 7.99
Method 9 – Bromine index of heptane
• 6.3014.213 Exchange Unit, 10 mL, and/or 6.3014.223, 20 mL
• 6.0308.100 double Pt electrode with 6.2104.020 electrode cable
• 6.1110.100 Pt 1000 temperature sensor with 6.2104.080 electrode cable
• 6.1414.010 titration vessel lid and 6.1418.250 titration vessel with thermostatic jacket
• Thermostat/Cryostat or ice bath
The bromine index is the fraction of reactive unsaturated compounds (mostly C=C double bonds) in hydrocarbons encountered in the petrochemical industry. The double bonds are split with the attachment of bromine:
C - R = C - R + Br2 → R - CBr - CBr - R This method has been tested for the following products:
– Globally for olefin-free hydrocarbons with a boiling point below 288 °C (550 °F) and a bromine index of 100...1000.
Products with a bromine index of >1000 should be determined as the bromine number (Method 8).
The bromine index (BI) is the number of mg bromine (Br2) that are bound or added by 100 g sample.
– Titrant: 0.00333 mol/L bromide-bromate solution (ô0.02 Nằ). 2.04 g KBr and 0.556 g KBrO3 are dissolved separately in dist. H2O. The two solutions are rinsed into a single 1000 mL volumetric flask and made up to the mark with dist. H2O.
– Solvent mixture: consisting of 714 mL glacial acetic acid, 134 mL 1-methyl-2- pyrrolidone*, 134 mL methanol and 18 mL w(H2SO4) = 20%.
* Fluka No. 15780, Merck No. 105215
The titer of the titrant has already been determined according to Method 6 (com- mon variable C33). Before the analysis itself the blank value of the solvent mixture is determined and stored in the Titrino as common variable C31 (Method 7).
100 mL solvent mixture is placed in the titration vessel together with the amount of sample (1...30 g) corresponding to the expected bromine index (see following table). The mixture is cooled down to 0...5 °C and the titration is started when this temperature has been reached (instrument parameters and an example of a curve are given in the appendix).
Expected bromine index Sample weight in g
0 ... 10 30 ... 25
10 ... 50 25 ... 15
50 ... 100 15 ... 10
100 ... 1000 10 ... 1
Recommended accessories
General
Definition
Analysis
Table of sample weights Reagents
Method 9 – Bromine index of heptane
Bromine index (BI) in mg Br2 / 100 g sample = (EP1 – C31) x C01 x C33 x C02 / C00 Temperature measured by the Pt 1000 sensor (in °C) = C44
EP1 = titrant consumption up to endpoint, in mL C00 = sample weight, in g
C01 = 0.02 = ônormalityằ of titrant
C02 = 7990 = conversion factor for mg bromine C33 = titrant titer
C31 = blank value of solvent mixture, in mL titrant – ASTM D 2710-92
Standard Test Method for Bromine Index of Petroleum Hydrocarbons by Electrometric Titration
– ASTM D 5776-99
Standard Test Method for Bromine Index of Aromatic Hydrocarbons by Electrometric Titration
– Metrohm
Application Bulletin No. 177
Calculation
Literature
Method parameters & calculation Titration curve Method 9
Method 9 – Bromine index of heptane
'pa785 DMP Titrino 02287 785.0010 date 2000-11-17 time 08:45 0 MET Ipol M9
parameters
>titration parameters
V step 0.050 ml dos.rate max. ml/min signal drift OFF mV/min equilibr.time 30 s start V: OFF pause 60 s I(pol) 1 àA electrode test: OFF temperature 25.0 °C
>stop conditions
stop V: abs.
stop V 5 ml stop U OFF mV stop EP 9 filling rate max. ml/min
>statistics
status: OFF
>evaluation
EPC 200 mV EP recognition: all fix EP1 at U OFF mV
>preselections
req.ident: id1 req.smpl size: all limit smpl size: OFF activate pulse: OFF ---
'de785 DMP Titrino 02287 785.0010 date 2000-11-17 time 08:45
MET Ipol M9 def>formula
BrIndex=(EP1-C31)*C01*C02*C33/C00 RS1 text BrIndex RS1 decimal places 2 RS1 unit: BrInd RS1 limit control: OFF Temp=C44
RS2 text Temp RS2 decimal places 1 RS2 unit: °C RS2 limit control: OFF
>silo calculations
match id: OFF
>common variables
>report
report COM1:full;curve;
>mean MN1=RS1
>temporary variables ---
'cf785 DMP Titrino 02287 785.0010 date 2000-11-17 time 08:45
MET Ipol M9 C-fmla
C01 0.02 C02 7990 ---
Method 10 – Titer determination of AgNO3
Recommended accessories
General
Preparation
Titer determination
Remarks
• 6.3014.223 Exchange Unit, 20 mL
• 6.0430.100 Ag Titrode with Ag2S coating and 6.2104.020 electrode cable
• 6.1414.010 titration vessel lid and 6.1415.310 titration vessel
• 6.1440.010 gas inlet and overflow tube
The titrant c(AgNO3) = 0.01 mol/L in IPA is not available commercially and must be prepared by the operator. Please note that non-aqueous solvents have a coef- ficient of expansion which is four times larger than that of water! This means that, for a temperature difference of 5 °C and a theoretical consumption of 10.00 mL, the actual consumption will be 50 àL higher, i.e. a titer of 1.000 at 20 °C will be 0.995 at 25 °C. Titer determinations and sample analysis should therefore always be carried out at the same temperature whenever possible.
Neither sulfides nor mercaptans are suitable as standard substances. They are either not available in a sufficiently pure form or are difficult to handle. We there- fore recommend the following substances for use as the primary titrimetric stan- dard or secondary standard: extra-pure NaCl (e.g. Merck No. 106406) or an NaCl solution of known content, e.g. c(NaCl) = 0.1000 mol/L (5.8443 g/L NaCl), Metrohm No. 6.2301.010.
Preparation of c(AgNO3) = 0.1 mol/L in isopropanol (IPA)
16.99 g AgNO3 (e.g. Merck No. 101512) is dissolved in 80 mL dist. H2O and made up to 1 liter with IPA.
Preparation of the titrant c(AgNO3) = 0.01 mol/L in IPA
100 mL c(AgNO3) = 0.1 mol/L (see above) is placed in a 1000 mL volumetric flask.
Add 80 mL dist. H2O and make up to the mark with IPA.
Reagents
Acidic solvent: 2.7 g CH3COONa x 3 H2O is dissolved in 25 mL dist. H2O, treated with 4.6 mL glacial acetic acid and made up to 1 liter with IPA.
Titration
100 mL acidic solvent and 1.000 mL c(NaCl) = 0.1000 mol/L are placed in the titration vessel and titrated with c(AgNO3) = 0.01 mol/L (instrument parameters and an example of a curve are given in the appendix).
Calculation
10 mL c(AgNO3) = 0.01 mol/L correspond to 1 mL c(NaCl) = 0.1 mol/L Titer = C01 / EP1
EP1 = titrant consumption up to the endpoint, in mL C01 = 10
– The titer should be determined every week or every time a new titrant solution is prepared.
– The mean value of the titer is stored as common variable C34 in the Titrino.
Method parameters & calculation Titration curve Method 10
'pa785 DMP Titrino 02287 785.0010 date 2000-11-17 time 09:15 0 DET U M10
parameters
>titration parameters
meas.pt.density 4 min.incr. 10.0 àl dos.rate max. ml/min signal drift 30.0 mV/min equilibr.time 32 s start V: OFF pause 0 s meas.input: 1 temperature 25.0 °C
>stop conditions
stop V: abs.
stop V 20.000 ml stop U OFF mV stop EP 9 filling rate max. ml/min
>statistics
status: ON mean n= 3 res.tab: original
>evaluation
EPC 5 EP recognition: all fix EP1 at U OFF mV pK/HNP: OFF
>preselections
req.ident: id1 req.smpl size: all limit smpl size: OFF activate pulse: OFF ---
'de785 DMP Titrino 02287 785.0010 date 2000-11-17 time 09:15
DET U M10 def>formula
Titer=C01/EP1
RS1 text Titer RS1 decimal places 4 RS1 unit:
RS1 limit control: OFF
>silo calculations
match id: OFF
>common variables C34=MN1
>report
report COM1:curve;full;
>mean MN1=RS1
>temporary variables ---
'cf785 DMP Titrino 02287 785.0010 date 2000-11-17 time 09:15
DET U M10 C-fmla
C01 10 ---
Method 10 – Titer determination of AgNO3
Method 11 – Sulfur compounds in petrochemical products
• 6.3014.223 Exchange Unit, 20 mL
• 6.0430.100 Ag Titrode with Ag2S coating and 6.2104.020 electrode cable
• 6.1414.010 titration vessel lid and 6.1415.310 titration vessel
• 6.1440.010 gas inlet and overflow tube
Sulfur compounds contained in petrochemicals do not just have an unpleasant odor, they are also environmentally undesirable and have a corrosive effect. This method describes the determination of hydrogen sulfide and mercaptans in liquid hydrocarbons (gasoline (petrol), kerosene, naphtha and similar distillates). The sulfur compounds are titrated with silver nitrate solution, whereby silver sulfide and silver mercaptides are formed. Two well-defined potential jumps are obtained.
The first endpoint corresponds to the hydrogen sulfide; the second to the mercap- tans. The Ag Titrode with Ag2S coating is used as the indicator electrode.
The results are given in mg/kg (ppm) H2S sulfur and/or mercaptan sulfur. As the sample is usually measured in by volume, this volume must be multiplied by the sample density to obtain the sample weight.
– Titrant: c(AgNO3) = 0.01 mol/L in IPA (see Method 10)
– Acid solvent for high-molecular mercaptans: 2.7 g CH3COONa x 3 H2O is dis- solved in 25 mL dist. H2O, treated with 4.6 mL glacial acetic acid and made up to 1 liter with IPA.
– Alkaline solvent for low-molecular mercaptans and H2S: 2.7 g CH3COONa x 3 H2O is dissolved in 25 mL dist. H2O, treated with 10 mL w(NH3) = 25% and made up to 1 liter with IPA.
– Nitrogen, O2-free, from a gas cylinder
The titer of the titrant has already been determined according to Method 10 (com- mon variable C34). 100 mL solvent** is placed in the titration vessel and freed from oxygen by passing a stream of nitrogen through it (5 min). The nitrogen is then passed over the solution, the sample is added according to the table given below and the mixture is titrated with c(AgNO3) = 0.01 mol/L (instrument param- eters and an example of a curve are given in the appendix).
ppm mercaptan S expected mL sample
1 ... 50 50
50 ... 100 25
100 ... 300 10
300 ... 500 5
** Acidic solvent for aviation gasoline, kerosene and ôdistillate fuelsằ which normally contain high- molecular mercaptans.
Alkaline solvent in the presence of H2S and for low-boiling hydrocarbon fractions which contain low-molecular mercaptans. entstehen:
Recommended accessories
General
Definition
Reagents
Analysis
Table of sample volumes
Method 11 – Sulfur compounds in petrochemical products
Various types of titration curves may be obtained:
– Normal case; both H2S and mercaptans are present. EP1 = H2S, EP2 = mer- captans
– If only H2S or only mercaptans are present then only one endpoint will be ob- tained. The particular compound type is indicated by the position of the poten- tial jump.
– If elementary sulfur is present then a third, flatter potential jump is obtained after the H2S. Free sulfur reacts with mercaptan to form disulfide:
S0 + R - SH → R - S - S - H
(The elementary sulfur is ignored for the calculation of the mercaptan sulfur.) Hydrogen sulfide
mg/kg H2S-S = EP1 x C01 x C34 x C02 / C00 Mercaptans (together with H2S)
mg/kg mercaptan S = (EP2 - EP1) x C01 x C34 x C03 / C00 (If no H2S is present then the following equation applies:
EP1 x C01 x C34 x C03 / C00)
Mercaptans in the presence of elementary sulfur (together with H2S) mg/kg mercaptan S = (EP3 - EP1) x C01 x C34 x C03 / C00
C00 = sample weight in g = sample volume in mL x density in g/cm3 C01 = 0.01 = titrant concentration in mol/L
C02 = 16030 = molar mass S in g/mol x 1000 /2 C03 = 32060 = molar mass S in g/mol x 1000 C30 = titrant titer
– Both H2S and mercaptans are oxidized by atmospheric oxygen and can then no longer be determined in the titration. This is the reason why work is carried out under nitrogen.
– Mercaptans (particularly high-molecular ones) only react slowly with AgNO3. This means that the titration should not be carried out too quickly.
– Metrohm
Application Bulletin No. 135 – ASTM D 3227-83
Standard Test Method for Mercaptan Sulfur in Gasoline, Kerosene, Aviation Turbine and Distillate Fuels (Potentiometric Method)
– ISO 3012:1991
Gasoline, Kerosene and Distillate Fuels - Determination of Mercaptan Sulfur – Potentiometric Method
– IP 272/71 (1985)
Determination of Mercaptan Sulfur and Hydrogen Sulfide Content of LPG – Electrometric Titration Method
– UOP Method 163-67
Hydrogen Sulfide and Mercaptan Sulfur in Liquid Hydrocarbons by Potentio-
Titration curves
Calculations
Remarks
Literature
Method parameters & calculation Titration curves Method 11 – H2S alone
Mercaptans alone
Method 11 – Sulfur compounds in petrochemical products
'pa785 DMP Titrino 02287 785.0010 date 2000-11-17 time 11:34 0 DET U M11
parameters
>titration parameters
meas.pt.density 2 min.incr. 50.0 àl dos.rate max. ml/min signal drift 10.0 mV/min equilibr.time 20 s start V: OFF pause 20 s meas.input: 1 temperature 25.0 °C
>stop conditions
stop V: abs.
stop V 20.000 ml stop U OFF mV stop EP 9 filling rate max. ml/min
>statistics
status: OFF
>evaluation
EPC 5 EP recognition: all fix EP1 at U OFF mV pK/HNP: OFF
>preselections
req.ident: id1 req.smpl size: all limit smpl size: OFF activate pulse: OFF ---
'de785 DMP Titrino 02287 785.0010 date 2000-11-17 time 11:34
DET U M11 def>formula
H2S-S=EP1*C01*C34*C02/C00 RS1 text H2S-S RS1 decimal places 2 RS1 unit: mg/kg RS1 limit control: OFF Merc-S=(EP2-EP1)*C01*C34*C03/C00 RS2 text Merc-S RS2 decimal places 2 RS2 unit: mg/kg RS2 limit control: OFF Merc+H2S=(EP3-EP1)*C01*C34*C03/C00 RS3 text Merc+H2S RS3 decimal places 2 RS3 unit: mg/kg RS3 limit control: OFF
>silo calculations
match id: OFF
>common variables
>report
report COM1:full;curve;
>mean MN1=RS1
>temporary variables ---
'cf785 DMP Titrino 02287 785.0010 date 2000-11-17 time 11:34
DET U M11 C-fmla
C01 0.01
Mercaptans & H2S
Method 12 – Sulfur compounds in gases and absorption solutions
• 6.3014.223 Exchange Unit, 20 mL
• 6.0430.100 Ag Titrode with Ag2S coating and 6.2104.020 electrode cable
• 6.1414.010 titration vessel lid and 6.1415.310 titration vessel
• 6.1440.010 gas inlet and overflow tube
Sulfur compounds contained in gaseous hydrocarbons do not just have an un- pleasant odor, they are also environmentally undesirable and have a corrosive effect.
The sulfur compounds are absorbed in alkaline solutions (for apparatus see be- low, ôLiteratureằ). The first two absorption vessels are filled with KOH or NaOH (for H2S and mercaptans); the third with ethanolic monoethanolamine (for carbo- nyl sulfide). The absorbed substances are titrated with silver nitrate with the for- mation of practically insoluble sulfur-Ag compounds. With H2S and short-chain mercaptans (<C4) two well-marked potential jumps are obtained. The first poten- tial jump corresponds to H2S, the second to the short-chain mercaptans. The Ag Titrode with Ag2S coating is used as the indicator electrode.
The results are given as mg S / m3 dry gas (H2S sulfur, mercaptan sulfur, COS sulfur)
– Titrant: c(AgNO3) = 0.01 mol/L in IPA (see Method 10)
– Absorption solution I for H2S and mercaptans: w(KOH) or w(NaOH) = 30% in dist. H2O with the addition of 5 g/L Na2EDTA (for complexing the heavy met- als).
– Absorption solution II for carbonyl sulfide: w(monoethanolamine) = 5% in etha- nol (50 g monoethanolamine + 950 g ethanol).
– Ethanol, dist. H2O (both O2-free) – Nitrogen, O2-free, from gas cylinder
The titer of the titrant has already been determined according to Method 10 (com- mon variable C34).
H2S and mercaptans
The contents of the first two absorption vessels are rinsed into the titration vessel with O2-free dist. H2O. A stream of nitrogen is passed over the solution and the mixture is titrated with c(AgNO3) = 0.01 mol/L. ôRefinery Caustic Solutionsằ nor- mally contain many mercaptans as well as H2S. In this case the titration is broken off after EP1 (H2S) and a smaller amount of sample is used to carry out a second titration for the mercaptans. In the presence of H2S and short-chain mercaptans (<C4) two endpoints are obtained, EP1 = H2S, EP2 = short-chain mercaptans. If only H2S or only short-chain mercaptans are present or if there is a mixture of H2S and longer-chain mercaptans (>C4) then only one endpoint will be obtained. It may be possible to identify the particular compound from the initial potential (in- strument parameters and examples of curves in the appendix).
Recommended accessories
General
Definition
Reagents
Analysis