Giáo Trình Phân Tích Chuẩn Độ Điện Thế Oilpac_E.pdf

OIL Potentiometric Analysis Collection OIL PAC 6 6040 003 Methods for the titrimetric / potentiometric analysis of petrochemical products Dear User, You have decided to purchase a Metrohm titrator who[.]

OIL Potentiometric Analysis Collection

as is possible in order to facilitate daily analytical work

In this Application binder you will find descriptions of the corresponding analytical methods with comments,

explanations and - particularly important - printouts of the instrument parameters and examples of curves

All these methods are stored on the Method memory card You only need to insert the card, load the required

method into the titrator's working memory and off you go!!!

We hope that your work will be both pleasant and successful,

YourMetrohm

Additional information

– These methods have been drawn up taking into account the latest standards In particular, they make use ofthe newest methods and the newly developed Metrosensors, which have been specially designed for non-aqueous titrations

– All methods have been designed so that you can adopt them in your oil laboratory as so-called SOPs(Standard Operating Procedures)

– Of course, almost all these methods, at least as far as their titration part is concerned, can be further automated

In the Appendix you will find an example of the complete automation of the titrimetric determination of thebase number For details please contact your local Metrohm supplier, whose address can be found on theInternet under:

www.metrohm.com Distributors

– The Method memory card supplied can be used with the 785 and 751 Titrinos (from program version 20).You or your Metrohm supplier can also use the demo version of VESUV 3.0 (VESUV = Verification Supportfor Validation), which is also supplied, to load the parameter sets into the 716, 736 or 751 Titrinos (751:

<program version 20) The demo version can be converted to a full version by purchasing a «VESUV ware Dongle»

Hard-– The supplied CD ROMs contain, among other things:

• The VESUV backup file; this allows you to copy the 25 methods into the 716, 736, 751 and 785 Titrinos.For further information please read the section «Restore methods» in the VESUV Instructions for Use orcontact your Metrohm supplier

If the VESUV software is used instead of the printer for receiving the data then the «curve» report must bedeleted at the Titrino and the latter set to «mplist» (VESUV can only process measuring point lists)

• Acrobat Reader for installation on your PC so that you can read the PDF files

• Application Bulletins Nos 80, 101, 125, 135 and 177

– The method overview can be removed from the binder and stored together with the OIL PAC card at thecorresponding instrument

– We recommend that only those methods that are actually required are loaded into the instrument

Symbols used

c(X) Concentration of substance X in mol/L («amount-of-substance concentration»)

M(X) Molar mass of substance X in g/mol

p Pressure in bar or mbar

pn Standard pressure (1013.25 mbar)

t Temperature in °C

T Temperature in K

V Volume in L, mL

Vn Standard volume (V at 1013.25 mbar and 0 °C) in L (or dm3) or mL

w(X) Mass fraction of substance X, e.g w(HCl) = 35%

F(X) Volume fraction of substance X, e.g F(EtOH) = 40%

?(X) Mass concentration of substance X, e.g ?(Pb2+) = 1 g/L

List of methods

A - Acid and base numbers

Method 1 Titer determination for base number

Method 2 Base number

Method 3 Basic nitrogen

Method 4 Titer determination for acid number

Method 5 Acid number

B - Bromine number and bromine index

Method 6 Titer determination

Method 7 Blank value of solvent

Method 8 Bromine number of cyclohexene

Method 9 Bromine index of heptane

C - H2S / COS / mercaptans / total sulfur

Method 10 Titer determination of AgNO3

Method 11 Sulfur compounds in petroleum products

Method 12 Sulfur compounds in gases / absorption solutions

Method 13 Total sulfur in petroleum products (Lamp method, ASTM D 1266-98)

D - Saponification and hydroxyl numbers

Method 14 Saponification number

Method 15 Hydroxyl number

E - Chloride and organically bound chlorine

Method 16 Titer determination of AgNO3

Method 17 Chloride in water and fouled catalysts

Method 18 Organically bound chlorine in crude oil

F - Absorption solutions for gases

Method 19 Alkalinity of amine-containing gas-absorbing solutions (Jefferson method)Method 20 Analysis of used alkaline absorbing and washing solutions

G - Metals [Me(II)] in lubricating oils

Method 21 Titer determination of EDTA solutions

Method 22 Sum of Ba, Ca, Mg, Pb and Zn in unused lubricants

H - Further methods

Method 23 Ca and Mg in water (water hardness)

Method 24 Pb in leaded gasoline

Remarks concerning the literature references

Metrohm

You can obtain the Application Bulletins and Application Notes free of charge from Metrohm Ltd., CH-9101Herisau (Switzerland) or from your Metrohm supplier The Metrohm Application Notes can also be viewed in anddownloaded from the Internet, «www.metrohm.com»

All the additional methods can be obtained against payment at the corresponding addresses:

ISO Central Secretariat

1, Rue de Varembé, P.O Box 56

Universal Oil Products

Des Plaines, Illinois (USA)

Index / Key Word List (Method Nr.)

Sulfur (M 11 / 12 / 13)

T Tap water (M 17 / 23)Tetraalkyl lead (M 24)Titer determination (M 1 / 4 / 6 / 10 / 16 / 21)Total acid number – TAN (M 5)

Total base number – TBN (M 2)Total sulfur (M 13)

U Used refinery caustic solution (M 20)

W Washing solution (M 20)Water hardness (M 23)

Method 1 – Titer determination for the base number

• 6.3014.223 Exchange Unit, 20 mL

• 6.0229.100 Solvotrode; 6.2312.000 electrolyte diluted 1:1 with ethanol (approx

2 mol/L LiCl in ethanol)

• 6.2104.020 electrode cableRecommended accessories

General Most standard solutions/titrants are commercially available as ready-to-use

solu-tions and have a relatively stable titer However, their titer is valid for 20 °C Pleasenote that non-aqueous solvents have a coefficient of expansion which is four timeslarger 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 µL higher,i.e a titer of 1.000 at 20 °C will be 0.995 at 25 °C Titer determinations and sampleanalysis should therefore be carried out at the same temperature whenever pos-sible The following titrants are available from Merck:

– No 109065 c(HClO4) = 0.1 mol/L in anhydrous acetic acid (glacial acetic acid)– No 100326 c(HCl) = 0.1 mol/L in isopropanol (IPA)

If the titer is to be determined then this is done by comparing it with a so-calledprimary titrimetric standard The content of these hardly changes, they are avail-able with a defined degree of purity, can be dried and are directly traceable tostandard reference materials (e.g from NIST = National Institute of Standardsand Technology, USA) Such recommended primary titrimetric standards or sec-ondary standards are:

– Merck No 104874 Potassium hydrogen phthalate, M = 204.23 g/mol– Merck No 108382 Tris(hydroxymethyl)aminomethane, M = 121.14 g/mol

1.1 Titer determination of c(HClO4) = 0.1 mol/L with KH phthalate

Weigh out approx 200 mg KH phthalate into a beaker to 0.1 mg Add 40 mLglacial acetic acid and stir the mixture at room temperature until everything hasdissolved (5 10 min) After the addition of 40 mL toluene the electrodes are im-mersed and the solution is titrated with HClO4 until after the first endpoint (instru-ment parameters and an example of a curve are given in the appendix)

0.1 mol HClO4 reacts with 0.1 mol KH phthalate

1 mL c(HClO4) = 0.1 mol/L corresponds to 20.423 mg KH phthalateTiter = (C00 / C01) / EP1

EP1 = titrant consumption up to the endpoint, in mLC00 = weight KH phthalate in mg

C01 = 20.423 mg (1mL c(HClO4) = 0.1 mol/L corresponds to 20.423 mg

KH phthalate)Calculation

Reaction

1.2 Titer determination of c(HCl) = 0.1 mol/L with TRIS

Approx 100 mg TRIS is weighed out into a beaker to 0.1 mg exactly and dissolved

in approx 5 mL dist H2O 50 mL Isopropanol and 40 mL toluene are added, the

electrodes are immersed and the solution is titrated with HCl until after the first

endpoint (instrument parameters as for HClO4; an example of a curve is given in

0.1 mol HCl reacts with 0.1 mol TRIS

1 mL c(HCl) = 0.1 mol/L corresponds to 12.114 mg TRIS

– The mean value of the titer is stored as common variable C30 in the Titrino.

– If you want to prepare the titrant yourself then proceed as follows:

For c(HClO 4 ) = 0.1 mol/L in glacial acetic acid: Approx 800 mL glacial acetic

acid is placed in a 1 liter volumetric flask It is treated with 8.6 mL (14.45 g)

w(HClO4) = 70%, reagent grade (1.68 g/cm3), made up to the mark with glacial

acetic acid and mixed

For c(HCl) = 0.1 mol/L in isopropanol: Approx 800 mL IPA is placed in a 1 liter

volumetric flask It is treated with 9.8 mL (11.4 g) w(HCl) = 32% reagent grade

(1.16 g/cm3), made up to the mark with IPA and mixed

Method parameters & calculation Titration curves

dos.rate max ml/min

signal drift 30 mV/min

req.smpl size: all

limit smpl size: OFF

activate pulse: OFF

-Method 2 – Determination of the base number

maintenance and checks

Components in oil products that exhibit a basic reaction are determined as a mulative total under the base number These are chiefly primary organic and inor-ganic amino compounds, but the salts of weak acids and basic salts ofpolycarboxylic acids, as well as some heavy metal salts and detergents, are alsodetermined The determination is used to assess relative alterations during theworking life of the product

cu-The base number is the amount of basic components, expressed as mg KOH, that

is contained in 1 g sample

– Titrant: c(HClO4) = 0.1 mol/L in glacial acetic acid– Solvent mixture I: glacial acetic acid/toluene 1:1– Solvent mixture II: glacial acetic acid/chlorobenzene 1:2**

– Buffer solution pH = 4.0 (6.2307.100) and pH = 7.0 (6.2307.110)– Ethanol, dist H2O, hexane

** For environmental reasons the use of this solvent mixture should be avoided.

– When not in use the Solvotrode is stored in electrolyte solution(approx 2 mol/L LiCl in ethanol)

– Before use the electrode is placed in dist H2O overnight

– After each titration the electrode is rinsed with solvent mixture, then with nol and finally with dist H2O It is then immersed for 1 min in dist H2O, rinsedwith ethanol and the next sample is titrated The ground joint of the diaphragm

etha-is loosened from time to time so that electrolyte can flow out The joint etha-is thenlightly pressed together again If precipitates are formed on the electrode dur-ing the titration (occurs with used oils and with some additives) then these areremoved by placing the electrode in a stirred solution of hexane

– In order to check the electrode functions (slope, response behavior, etc) pleaseproceed as follows:

Rinse the electrode with dist H2O and dab it dry with a soft tissue (e.g Kleenex).Immerse in buffer solution pH = 7.0, stir for 1 min and then read off the potential

in mV After rinsing with dist H2O and dabbing it dry the same procedure isrepeated in buffer solution pH = 4.0 With good electrodes a potential differ-ence of >150 mV is obtained at 20 25 °C If the difference is <150 mV then theelectrode is cleaned with hexane and ethanol, immersed for 1 min in dist H2O,the ground joint of the diaphragm is loosened slightly and then pressed to-gether again The measurements are then repeated The test provides infor-mation about whether the electrode is correctly filled with electrolyte and con-nected correctly to the Titrino Loose cable connections can also be recog-nized immediately

Method 2 – Determination of the base number

Depending on the expected base number, 0.1 5 g well-mixed sample is weighed

into the titration vessel After the addition of 50 125 mL solvent mixture the

solu-tion is titrated with c(HClO4) = 0.1 mol/L (instrument parameters and an example

of a curve are given in the appendix)

Analysis

CalculationBase number in mg KOH / g sample = (EP1 – C31) x C01 x C02 x C30 / C00

EP1 = titrant consumption up to the last EP**, in mL

C00 = sample weight in g

C01 = 0.1 (concentration HClO4 in mol/L)

C02 = 56.106 (molar mass KOH in g/mol)

C30 = titer of titrant (see Method 1)

C31 = possible blank value of solvent (in mL HClO4)++

** In the presence of basic components of differing strengths, several endpoints could occur EP1

always represents the strongest base The last endpoint is always used for calculating the total

base content.

++ This value is obtained by titrating, under the same conditions, the same volume of solvent as will

be used subsequently for the analysis of the sample The result (in mL HClO 4 ) is stored in the

Titrino as common variable C31.

– ASTM D 2896-88

Standard Test Method for Base Number of Petroleum Products by

Potentio-metric Perchloric Acid Titration

– ASTM D 4739-87

Standard Test Method for Base Number Determination by Potentiometric

Titra-tion

– ISO 3771:1994

Petroleum Products – Determination of Base Number – Perchloric Acid

Poten-tiometric Titration Method

– Metrohm Application Bulletin No 80

Literature

Method parameters & calculation Titration curve

dos.rate max ml/min

signal drift 10 mV/min

req.smpl size: all

limit smpl size: OFF

activate pulse: OFF

Method 3 – Basic Nitrogen

kero-The basic nitrogen in the sample is given as mg N / kg (ppm N)

– Titrant: c(HClO4) = 0.02 mol/L in glacial acetic acid (200 mL c(HClO4) =0.1 mol/L diluted with glacial acetic acid to 1 liter)

– Toluene, reagent grade– Anhydrous acetic acid (glacial acetic acid), reagent grade– Ethanol, dist H2O

Depending on the expected N content, 1 25 g sample is weighed out into thetitration vessel and dissolved in 50 mL toluene 50 mL glacial acetic acid is added,the electrodes and titrating tip are immersed and the solution is titrated with c(HClO4)

= 0.02 mol/L (instrument parameters and an example of a curve are given in theappendix) After each titration the electrodes are placed in toluene under stirring inorder to remove any (interfering) precipitates They are then rinsed with ethanoland placed in dist H2O for 1 min After briefly rinsing again with ethanol the nexttitration is carried out

Method 3 – Basic Nitrogen

Basic nitrogen in mg/kg (ppm N) = (EP1 – C31) × C01 × C02 × C03 × C30 / C00

C00 = Sample weight in g

C01 = 14.01 (molar mass of N in g/mol)

C02 = 0.02 (concentration of HClO4 in mol/L)

C03 = 1000 (conversion factor for kg)

C30 = titer of titrant

C31 = possible blank value of solvent (in mL HClO4)

– The titer of the 0.02 mol/L HClO4 is determined against

tris(hydroxymethyl)-aminomethane (primary titrimetric standard)

– The method produces high-bias results if the sample, besides the organic

ni-trogen compounds, contains other bases (e.g sodium soaps in alkaline-washed

distillates or inorganic bases in crude oils)

Method parameters & calculation Titration curve

dos.rate max ml/min

signal drift 20.0 mV/min

req.smpl size: all

limit smpl size: OFF

activate pulse: OFF

-Method 4 – Titer determination for the acid number

• 6.3014.223 Exchange Unit, 20 mL

• 6.0229.100 Solvotrode; 6.2320.000 electrolyte c(tetraethylammonium bromide)

= 0.4 mol/L in ethylene glycol

• 6.2104.020 electrode cable

Most standard solutions/titrants are commercially available as ready-to-use tions Their titer is normally not stable (CO2 uptake; for TBAOH additionally deami-nation – breakdown to form e.g tertiary amines) The manufacturer also sets thetiter for 20 °C Please note that non-aqueous solvents have a coefficient of expan-sion that is four times larger than that of water! This means that, for a temperaturedifference of 5 °C and a theoretical consumption of 10.00 mL, the actual consump-tion will be 50 µL higher, i.e a titer of 1.000 at 20 °C will be 0.995 at 25 °C Titerdeterminations and sample analysis should therefore always be carried out at thesame temperature whenever possible The following titrants are available fromMerck:

solu-– No 105544 c(KOH) = 0.1 mol/L in isopropanol– No 109162 c(TBAOH) = 0.1 mol/L in isopropanol/methanolThe titer is determined by comparing it with a so-called primary titrimetric stan-dard The content of these hardly changes, they are available with a defined de-gree of purity, can be dried and are directly traceable to standard reference mate-rials (e.g National Institute of Standards and Technology, USA) Such primarytitrimetric standards / secondary standards are:

– Merck No 104874 Potassium hydrogen phthalate, M = 204.23 g/mol– Merck No 102401 Benzoic acid, M = 122.12 g/mol

4.1 Titer determination of c(KOH) = 0.1 mol/L with KH phthalate

Recommended accessories

General

Approx 200 mg KH phthalate is weighed out into a beaker to 0.1 mg and solved in approx 40 mL dist H2O After addition of 20 mL isopropanol the elec-trode and buret tip are immersed and the solution titrated with KOH until after thefirst endpoint (instrument parameters and an example of a curve are given in theappendix)

dis-Method 4 – Titer determination for the acid

number

Calculation

0.1 mol KOH reacts with 0.1 mol KH phthalate

1 mL c(KOH) = 0.1 mol/L corresponds to 20.423 mg KH phthalate

Titer = C00 / C01 / EP1

EP1 = titrant consumption up to the endpoint, in mL

C00 = weight of KH phthalate, in mg

C01 = 20.423 (1 mL c(KOH) = 0.1 mol/L corresponds to 20.423 mg KH phthalate)

4.2 Titer determination of c(TBAOH) = 0.1 mol/L with benzoic acid

Remarks

Calculation

Approx 100 mg benzoic acid is weighed out into a beaker to 0.1 mg and dissolved

in 50 mL isopropanol The electrode and buret tip are immersed and the solution

titrated with TBAOH until after the first endpoint (instrument parameters as for

KOH; an example of a curve is given in the appendix)

0.1 mol TBAOH reacts with 0.1 mol benzoic acid

1 mL c(TBAOH) = 0.1 mol/L corresponds to 12.212 mg benzoic acid

Titer = (C00/C01) / EP1

EP1 = titrant consumption up to the endpoint, in mL

C00 = weight of benzoic acid, in mg

C01 = 12.212 (1 mL c(TBAOH) = 0.1 mol/L corresponds to 12.212 mg benzoic

Method parameters & calculation Titration curve

Methods 4.1 & 4.2 (example)

dos.rate max ml/min

signal drift 10.0 mV/min

req.smpl size: all

limit smpl size: OFF

activate pulse: OFF

Method 5 – Determination of the acid number

• 6.3014.223 Exchange Unit, 20 mL

• 6.0229.100 Solvotrode; 6.2320.000 electrolyte c(tetraethylammonium bromide)

= 0.4 mol/L in ethylene glycol

• 6.2104.020 electrode cable

Components in petrochemical products that exhibit an acidic reaction are mined as a cumulative total under the acid number These are compounds (acids,salts) with pKa values <9 The determination is used to assess relative alterationsduring the working life of the product A global relationship between the acid num-ber and signs of corrosion has not yet been demonstrated

deter-The acid number is the number of mg KOH that are required to neutralize 1 gsample

– Titrant: c(KOH) = 0.1 mol/L in isopropanol/methanol (e.g Merck No 105544)– Solvent: 500 mL toluene + 495 mL isopropanol + 5 mL H2O

– Buffer solutions pH = 4.0 (6.2307.100) and pH = 7.0 (6.2307.110)– Ethanol, dist H2O, hexane

– When not in use the Solvotrode is stored in electrolyte solution (TEA-Br inethylene glycol)

– Before use the electrode is placed in dist H2O overnight

– After each titration the electrode is rinsed with solvent mixture, then with nol and finally with dist H2O It is then immersed for 1 min in dist H2O, rinsedwith ethanol and the next sample is titrated The ground joint of the diaphragm

etha-is loosened from time to time so that some electrolyte can flow out The joint etha-isthen lightly pressed together again If precipitates are formed on the electrodeduring the titration (occurs with used oils and with some additives) then theseare removed by placing the electrode in a stirred solution of hexane

– In order to check the electrode functions (slope, response behavior, etc) ceed as follows:

pro-Rinse the electrode with dist H2O and dab it dry with a soft tissue (e.g Kleenex).Immerse in buffer solution pH = 7.0, stir for 1 min and then read off the potential

in mV After rinsing with dist H2O and dabbing it dry the same procedure isrepeated in buffer solution pH = 4.0 With good electrodes a potential differ-ence of >150 mV is obtained at 20 25 °C If the difference is <150 mV then theelectrode is cleaned with hexane and ethanol, immersed for 1 min in dist H2O,the ground joint of the diaphragm is loosened slightly and then pressed to-gether again The measurements are then repeated The test provides infor-mation about whether the electrode is correctly filled with electrolyte and con-nected correctly to the Titrino Loose cable connections can also be recog-nized immediately

Recommended accessories

General

Definition

Reagents

Storage, maintenance and

checks of the electrode

Method 5 – Determination of the acid number

Depending on the expected acid number (AN), 0.1 10 g (AN 100 250 → 0.1 g,

AN 5 20 → 1 g, AN 0.05 1 → 10 g) well-mixed sample is weighed out into the

titration vessel After the addition of 50 125 mL solvent mixture the solution is

titrated with c(KOH) = 0.1 mol/L (instrument parameters and an example of a curve

are given in the appendix)

Acid number in mg KOH / g sample = (EP1 – C31) x C01 x C02 x C32 / C00

EP1 = titrant consumption up to the last EP**, in mL

C00 = sample weight in g

C01 = 0.1 (concentration KOH in mol/L)

C02 = 56.106 (molar mass KOH in g/mol)

C30 = titer of titrant (see Method 4)

C31 = possible blank value for solvent (in mL KOH)++

** If several strong acids are present then several endpoints may be obtained EP1 corresponds to

the strongest acid and could be used to calculate the «Strong Acid Number» The last endpoint is

always used for the total acid content If no endpoint is obtained and the titration curve increases

diagonally then a so-called Fix-EP (EPA or EPB) can be defined experimentally and used for the

calculation.

++ The blank value is obtained by titrating, under the same conditions, the same volume of solvent as

will be used subsequently for the analysis of the sample The result (in mL KOH) is stored in the

Tirino as common variable C31.

Method parameters & calculation Titration curve

dos.rate max ml/min

signal drift 20.0 mV/min

req.smpl size: all

limit smpl size: OFF

activate pulse: OFF

Method 6 – Titer determination for the bromine number and the bromine index

• 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 thermostaticjacket

• Thermostat/cryostat or ice bath

The two titrants (for bromine number and bromine index) are not available mercially and must be prepared by the operator We recommend c(Na2S2O3) =0.1000 mol/L as the secondary standard You should not make up this solutionyourself as a further secondary standard would still have to be used to determineits titer A solution whose titer is known can be ordered, e.g., from Merck under thenumber 109147

com-In an acidic solution bromide is oxidized quantitatively by bromate to form mine Bromine then oxidizes iodide quantitatively to form iodine The releasediodine is reduced to form iodide again by thiosulfate:

bro-KBrO3 + 6 H+ + 5 Br– → 3 H2O + 3 Br2

3 Br2 + 6 KI → 6 KBr + 3 I2

2 Na2S2O3 + I2 → Na2S4O6 + 2 NaIKBrO3 is available in a very pure form (e.g Merck No 104912) It is dried at 180 °Cand allowed to cool down in a desiccator

6.1 Titer determination for the bromine number

Preparation of the titrant c(KBrO3) = 1/6 x 0.5 mol/L = 0.08333 mol/L («0.5 N»);bromide-bromate solution:

51 g KBr and 13.92 g KBrO3 are dissolved separately in dist H2O The two tions are rinsed into a single 1000 mL volumetric flask and made up to the markwith dist H2O

solu-Reagents

– Anhydrous acetic acid (glacial acetic acid), analytical grade– Fuming hydrochloric acid, w(HCl) = approx 37%, analytical grade– Potassium iodide solution, w(KI) = 15%

– c(Na2S2O3) = 0.1000 mol/L

Titration

50 mL glacial acetic acid and 1 mL HCl are placed in an Erlenmeyer flask Theflask is sealed and cooled in an ice bath for 10 min 1.00 mL bromide-bromatesolution (0.08333 mol/L, «0.5 N») and 5 mL potassium iodide solution are thenadded slowly as the contents are swirled about; the flask is then resealed andallowed to stand in the ice bath for a further 5 min After the addition of 100 mLdist H2O the released iodine is titrated with c(Na2S2O3) = 0.1000 mol/L (instru-ment parameters and an example of a curve are given in the appendix)

Recommended accessories

General

Preparation of the titrant

Titer determination

Titer = (EP1 x C02) / C01 / C00

EP1 = titrant consumption up to the endpoint, in mL

C00 = 1 = volume of bromide-bromate solution, in mL

C01 = 0.5 = «normality» of bromide-bromate solution

C02 = 0.1 = concentration of titrant, in mol/L

6.2 Titer determination for the bromine index

Preparation of the titrant c(KBrO3) = 1/6 x 0.02 mol/L = 0.00333 mol/L («0.02 N»),

bromide-bromate solution):

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

Reagents

– Anhydrous acetic acid (glacial acetic acid), analytical grade

– Fuming hydrochloric acid, w(HCl) = approx 37%, analytical grade

– Potassium iodide solution, w(KI) = 15%

– c(Na2S2O3) = 0.1000 mol/L

Titration

50 mL glacial acetic acid and 1 mL HCl are placed in an Erlenmeyer flask The

flask is sealed and cooled in an ice bath for 10 min 25.0 mL bromide-bromate

solution («0.02 N») and 5 mL potassium iodide solution are then added slowly as

the contents are swirled about; the flask is then resealed and allowed to stand in

the ice bath for a further 5 min After the addition of 100 mL dist H2O the released

iodine is titrated with c(Na2S2O3) = 0.1000 mol/L (instrument parameters and an

example of a curve are given in the appendix)

Calculation

Titer = (EP1 x C02) / C01 / C00

EP1 = titrant consumption up to the endpoint, in mL

C00 = 25 = volume of bromide-bromate solution, in mL

C01 = 0.02 = «normality» of bromide-bromate solution

C02 = 0.1 = concentration of thiosulfate solution, in mol/L

– The mean value of the titer is stored as common variable C33 in the Titrino.

Preparation of the titrant

Titer determination

Remarks

Method 6 – Titer determination for the

bromine number and the bromine index

Literature – ASTM D 1159-84

Standard Test Method for Bromine Number of Petroleum Distillates and mercial Aliphatic Olefins by Electrometric Titration

Com-– ISO 3839:1996Petroleum products – Determination of Bromine Number of Distillates and Ali-phatic Olefins – Electrometric Method

– ASTM D 1491-71Standard Test Method for Bromine Index of Aromatic Hydrocarbons by Poten-tiometric Titration

– ASTM D 2710-92Standard Test Method for Bromine Index of Petroleum Hydrocarbons byElectrometric Titration

Method 6 – Titer determination for the bromine number and the bromine index

Method parameters & calculation Titration curve

Methods 6.1 & 6.2 (example)

dos.rate max ml/min

signal drift 50.0 mV/min

req.smpl size: all

limit smpl size: OFF

activate pulse: OFF

-Method 6 – Titer determination for the

bromine number and the bromine index

Method 7 – Blank value of the solvent for the determination of the bromine number and the bromine index

• 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 thermostaticjacket

• Thermostat/cryostat or ice bath

The blank value is the amount of titrant consumed by the solvents used Thisvalue is stored in the Titrino, e.g as common variable C31, and is later subtractedduring the calculation (bromine number, bromine index) Whereas it can often beneglected in the determination of the bromine number, it plays a particularly impor-tant part in the determination of the bromine index Special instrument parametersare used as only a small titrant consumption is to be expected

7.1 For the bromine number (large bromine consumption)

– Titrant: bromide-bromate solution «0.5 N» (see Method 6)– Solvent mixture: consisting of 714 mL glacial acetic acid, 134 mL 1,1,1-trichloroethane, 134 mL methanol and 18 mL w(H2SO4) = 20%

7.2 For the bromine index (small bromine consumption)

– Titrant: bromide/bromate solution «0.02 N» (see Method 6)– Solvent mixture I (for aliphatic hydrocarbons): consisting of 714 mL glacialacetic acid, 134 mL carbon tetrachloride, 134 mL methanol and 18 mL w(H2SO4)

= 20%

– Solvent mixture II (for aromatic hydrocarbons): consisting of 714 mL glacialacetic 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 startedwhen the solution has cooled down to 0 5 °C (instrument parameters and anexample 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

Method parameters & calculation Titration curves

dos.rate max ml/min

signal drift OFF mV/min

req.smpl size: all

limit smpl size: OFF

activate pulse: OFF

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 thermostaticjacket

• Thermostat/cryostat or ice bath

The bromine number gives the fraction of unsaturated compounds (mostly C=Cdouble bonds) in petroleum products The double bonds are split with the attach-ment of bromine:

R - C = C - R + Br2 → R - CBr - CBr - RThis method has been tested for the following products:

– Generally for distillates with a boiling point below 327 °C (620 °F) and a volumefraction of 90% lighter than 2-methylpropane

– This includes gasoline (petrol) with and without lead additives, kerosenes andgas oils

– Commercial olefins (mixtures of aliphatic monoolefins) with a bromine number95 165

– Propenes (trimers and tetramers), butene trimers, mixtures of nonenes, octenesand heptenes

– The method is not suitable for normal α-olefins

The bromine number (BN) is the number of mg bromine (Br2) that are bound oradded by 100 g sample

The use of chlorinated solvents should be avoided because of environmental sons Tests have shown that 1,1,1-trichloroethane can be replaced by diethyl car-bonate (Fluka No 32080, Merck No 802898)

rea-– Titrant: 0.08333 mol/L bromide-bromate solution («0.5 N») 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 theexpected bromine number (see following table) 0.5 20 g is added, made up tothe mark with trichloroethane and mixed 100 mL solvent mixture and a 5.0 mLaliquot 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)

Method 8 – Bromine number of cyclohexene

Expected bromine number Sample weight in g

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 = «normality» 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 «sample» (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

dos.rate max ml/min

signal drift OFF mV/min

req.smpl size: all

limit smpl size: OFF

activate pulse: OFF

-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 thermostaticjacket

• Thermostat/Cryostat or ice bath

The bromine index is the fraction of reactive unsaturated compounds (mostly C=Cdouble bonds) in hydrocarbons encountered in the petrochemical industry Thedouble bonds are split with the attachment of bromine:

C - R = C - R + Br2 → R - CBr - CBr - RThis 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 brominenumber (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 («0.02 N») 2.04 g KBr and0.556 g KBrO3 are dissolved separately in dist H2O The two solutions arerinsed into a single 1000 mL volumetric flask and made up to the mark withdist H2O

– Solvent mixture: consisting of 714 mL glacial acetic acid, 134 mL pyrrolidone*, 134 mL methanol and 18 mL w(H2SO4) = 20%

1-methyl-2-* 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 ofsample (1 30 g) corresponding to the expected bromine index (see followingtable) The mixture is cooled down to 0 5 °C and the titration is started when thistemperature has been reached (instrument parameters and an example of a curveare given in the appendix)

Expected bromine index Sample weight in g

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

Method parameters & calculation Titration curve

dos.rate max ml/min

signal drift OFF mV/min

req.smpl size: all

limit smpl size: OFF

activate pulse: OFF

-Method 10 – Titer determination of AgNO3

• 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 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 µL higher, i.e a titer of 1.000 at 20 °C will be0.995 at 25 °C Titer determinations and sample analysis should therefore always

coef-be carried out at the same temperature whenever possible

Neither sulfides nor mercaptans are suitable as standard substances They areeither 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 NaClsolution 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

Method parameters & calculation Titration curve

dos.rate max ml/min

signal drift 30.0 mV/min

req.smpl size: all

limit smpl size: OFF

activate pulse: OFF

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 unpleasantodor, they are also environmentally undesirable and have a corrosive effect Thismethod describes the determination of hydrogen sulfide and mercaptans in liquidhydrocarbons (gasoline (petrol), kerosene, naphtha and similar distillates) Thesulfur compounds are titrated with silver nitrate solution, whereby silver sulfideand 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 thesample is usually measured in by volume, this volume must be multiplied by thesample 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% andmade 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 isthen passed over the solution, the sample is added according to the table givenbelow 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

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 H 2 S)

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 H 2 S)

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

Method parameters & calculation Titration curves

dos.rate max ml/min

signal drift 10.0 mV/min

req.smpl size: all

limit smpl size: OFF

activate pulse: OFF

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 pleasant odor, they are also environmentally undesirable and have a corrosiveeffect

un-The sulfur compounds are absorbed in alkaline solutions (for apparatus see low, «Literature») 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-chainmercaptans (<C4) two well-marked potential jumps are obtained The first poten-tial jump corresponds to H2S, the second to the short-chain mercaptans The AgTitrode with Ag2S coating is used as the indicator electrode

be-The results are given as mg S / m3 dry gas (H2S sulfur, mercaptan sulfur, COSsulfur)

– Titrant: c(AgNO3) = 0.01 mol/L in IPA (see Method 10)

– Absorption solution I for H 2 S and mercaptans: w(KOH) or w(NaOH) = 30% in

dist H2O with the addition of 5 g/L Na2EDTA (for complexing the heavy als)

met-– Absorption solution II for carbonyl sulfide: w(monoethanolamine) = 5% in

etha-nol (50 g monoethaetha-nolamine + 950 g ethaetha-nol)

– 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).

H 2 S and mercaptans

The contents of the first two absorption vessels are rinsed into the titration vesselwith O2-free dist H2O A stream of nitrogen is passed over the solution and themixture is titrated with c(AgNO3) = 0.01 mol/L «Refinery Caustic Solutions» nor-mally contain many mercaptans as well as H2S In this case the titration is brokenoff after EP1 (H2S) and a smaller amount of sample is used to carry out a secondtitration for the mercaptans In the presence of H2S and short-chain mercaptans(<C4) two endpoints are obtained, EP1 = H2S, EP2 = short-chain mercaptans Ifonly H2S or only short-chain mercaptans are present or if there is a mixture of H2Sand longer-chain mercaptans (>C4) then only one endpoint will be obtained Itmay be possible to identify the particular compound from the initial potential (in-strument parameters and examples of curves in the appendix)

Method 12 – Sulfur compounds in gases and

absorption solutions

Carbonyl sulfide

The absorption solution (third vessel) is rinsed into the titration vessel with O2-free

ethanol A stream of nitrogen is passed over the solution and the mixture is titrated

with c(AgNO3) = 0.01 mol/L More than one endpoint can be obtained (COS

de-composes in the presence of water: COS + H2O → H2S + CO2) The last endpoint

is used for the calculation (same instrument parameters as for H2S and

Gas is streamed though the apparatus at a flow rate of 0.1 L/min for 30 min at 27 °C

Liters of gas sampled (V) = 30 x 0.1 x (273/300) = 2.73 liter

mg / m3 H2S-S = EP1 x C01 x C34 x C02 / C00

mg / m3 mercaptan-S = (EP2 - EP1) x C01 x C34 x C03 / C00

mg / m3 COS-S = EP1* x C01 x C34 x C03 / C00

* EP recognition last

C00 = gas sample volume in liters, converted to 273 Kelvin

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

C34 = titrant titer

– Both H2S as well as mercaptans and carbonyl sulfide are oxidized by

atmo-spheric oxygen and can then no longer be determined in the titration This is

the reason why work is carried out under nitrogen

– Mercaptans only react slowly with AgNO3 This means that the titration should

not be carried out too quickly

– Metrohm

Application Bulletin No 135

– DIN 51 855 Part 6

Prüfung von gasförmigen Brennstoffen und sonstigen technischen Gasen

Bestimmung des Gehaltes an Schwefelverbindungen Gehalt an

Schwefel-wasserstoff, Mercaptanschwefel und Kohlenoxidschwefel Potentiometrisches

Verfahren

– ISO 6326-3:1989

Natural gas – Determination of sulfur compounds – Part 3: Determination of

hydrogen sulfide, mercaptan sulfur and carbonyl sulfide sulfur by potentiometry

– UOP Method 212-77

Calculations

Remarks

Literature