Tiêu chuẩn iso 06293 2 1998

A Reference number ISO 6293 2 1 998(E) INTERNATIONAL STANDARD ISO 6293 2 First edition 1 998 05 01 Petroleum products — Determination of saponification number — Part 2 Potentiometric ti tration method[.]

Fir st e itio

19 8-0 -01

Prod its p tr oler s — Déter mination de l n ice de sa onification —

Partie 2: Méthode p r titr age p tentiométriq e

© ISO 19 8

Al r i hts r es r ve Unle s oth r w is s e ifie ,n p r t of this p blc tio ma b r epr od c d or uti ze in a y for m or b a y me n ,ele tr onic

or me h nic l in lu in p oto o yin a d micr ofim,w ith ut p r mis io in wr itin fr omth p bls e

Inter natio al Org nizatio for Sta d r dizatio

Ca e p stale 5 • C -121 Ge è e 2 • Switze a d

Intern t c ntr al@is c

X.4 0 c c ; a 4 0 et p is ; o is c ; s c ntr al

Pr i te in Switze a d

Forew ord

ISO (he Inter national Organization for Stan ardization) is a w orldwide federation of national stan ard b dies (ISO

memb r b dies) The w ork of pre ar i g International Stan ar ds is nor maly car ried out throu h ISO tec nical

commite s Eac memb r b d interested in a s bject for w hic a tec nical commite has b en esta ls ed has

the rig t to b r epresented on that commite International organization , gover nmental an non-governmental, in

laison with ISO, also tak e p rt in the wor k ISO cola orates closely with the International Electrotec nical

Commis ion (IEC) on al mater s of electr otec nical stan ar dization

Dr af International Stan ard ado ted by the tec nical commite s ar e cir culated to the memb r b dies for votin

Publcation as an Inter national Stan ar d r eq ir es a pr ov al by at le st 7 % of the memb r b dies castin a vote

International Stan ar d ISO 6 9 -2 w as pre ar ed by T ec nical Commite ISO/TC 2 , Petroleum prod cts an

lubricants

This fir st edition, together with ISO 6 9 -1, can els an re laces ISO 6 9 :19 3, whic has b en tec nicaly

r evised

ISO 6 9 con ists of the folowin p rts, u der the gener al title Petroleum prod cts — Determination of

sa onification n mb r:

— Part 1: Colour -in icator titr ation method

— Par t 2: Potentiometr i titration method

An ex A for ms an integr al p r t of this p r t of ISO 6 9

Petroleum products — Determination of saponification number —

W ARNING — The u e of this part of ISO 6 9 ma in olv h zardou materials, o eration a d e uipme t

This part of ISO 6 9 doe not purport to a dre s al of th s fety pro lems a sociate with its u e It is the

re p n ibi ty of th u er of this part of ISO 6 9 to e tabls ap ropriate s fety a d h alth pra tic s a d

d termin th ap lc bi ty of re ulatory l mitation prior to u e

This p rt of ISO 6 9 sp cifies a method for the determination, by p tentiometric titration, of the amou t of

con tituents in p troleum prod cts that wi sa onify u der the con ition of the test ISO 6 9 -1 sp cifies a

deter mination by colour in icator titr ation

The method is a plca le to mater ials havin sa onification n mb r s in the r an e 2 mg K OH/g to 2 0 mg K OH/g

Comp u d of s lfur , phosphoru , halogen an some other comp u d re ct w ith the alk al an acid u der the

test con ition

1 Th r esults o use cra k case a d turbin ois, a d o ois co tainin th comp u ds a o e as a ditiv co stitu nts,

sh uld b inter pr ete with care, b arin in min th p s ible hig er v lu s o tain ble d e to th se a ditio al r eactio s

2 Th se extr an o s materials inclu e certain or ga ic acids a d most n n-alk al so ps Th o o r of hydro e sulfid n ar

th e d of th b ck -titratio ste is a in icatio of th pr ese ce of certain re ctiv sulfur comp u ds, b t oth r re ctiv sulfur

comp u ds, as w el as th se of chlorin , p osp or us a d oth r interferin materials, giv n simple in icatio d r i g th test

A gra imetr ic d termin tio of faty acid co te t is a alter nativ pr oce ure for th estimatio of such comp u ds

The folowin stan ar ds contain provision whic , thr ou h r efer en e in this text, con titute pr ovision of this p rt of

ISO 6 9 A t the time of publcation, the edition in icated w ere vald A ll stan ard are s bject to r evision, an

p r ties to agre ments b sed on this p rt of ISO 6 9 are en ouraged to in estigate the p s ibi ty of a plyin the

most recent edition of the stan ard in icated b low Memb r s of IEC an ISO maintain register s of c rr ently vald

Inter national Stan ar ds

ISO 3 9 :19 7, W ater for analytical la or atory u e — Sp cification an test method

ISO 6 9 -1:19 6, Petroleum prod cts — Determination of sa onification n mb r — Part 1: Colour-in icator titration

method

ISO 6 5 -2:19 3, Re gents for c emical analy is — Par t 2: Sp cification — Fir st ser ies.

ISO 6 5 -3:19 7, Re gents for c emical analy is — Par t 3: Sp cification — Secon ser ies

For the pur poses of this p r t of ISO 6 9 , the folowin definition a ply

3.1 s p nify

to h dr oly e a fat with alkal to for m an alcohol an the salt of a faty acid

3.2 s p nific tion n mber

the n mb r of mi igrams of p tas ium h dr oxide that is con umed by 1 g of a sample u der the sp cified con ition

of this test

4 Principle

A test p r tion of k nown mas , dis olved in butan-2-one, is he ted w ith a k now n amou t of alcoholc p tas ium

h dr oxide solution The ex es alk al is p tentiometricaly titrated with stan ar d volumetric h dr oc loric acid solution

an the sa onification n mb r is calc lated

Du n the analy is, u e only re gents sp cified in ISO 6 5 -2 an ISO 6 5 -3, if lsted there, or if not, of

r ecog ized analytical gr ade Use only disti ed water or w ater ac or din to gr ade 3 of ISO 3 9

5.1 Eth nol 9 % (V/V) ethanol, or 9 p r ts of 9 % (V/V) ethanol to whic has b en ad ed 1 p r t of methanol or

a solute alcohol

1 For th p rp ses of this p r t of ISO 6 9 , th expr es io s “% (m/m)” a d “% (V/V)” ar e use to re r ese t th mas a d

v lume fr actio s of a material r esp ctiv ly

2 For ro tin a aly is, 9 % (V/V) pro a -2-ol ca b su stitute for eth n l w ith ut compromisin th se sitivity or precisio

of th meth d Eth n l sh uld alway b use for r efere tests

5.2 Pota sium h droxid , c(KOH) = 0,5 mol/l, stan ar d volumetr i alcoholc solution

Pr ep r e in ac or dan e with 5.2.1 or u e a commer cialy avaia le solution Stan ar dize in ac or dan e w ith 5.2.2

5.2.1 Preparation

Ad a proximately 2 g of sold K OH to 1 ltr e of ethanol (5.1) in a 2 ltr e conical flask Boi gently whie stir rin for

10 min to 15 min Ad at le st 2 g of b r i m h dr oxide [Ba(OH)

2 ] an b i gently for a fur ther 5 min to 10 min

CAUTION — Barium h droxid is stron ly alk alne a d toxic if in e te Us prote tiv clothin to a oid

s v re ir itation c u e by conta t w ith th sk in

Alow to co l an stan at r oom temp r atur e for at le st 2 h in the dark T ran fer to the storage container by

fitr ation or pr es ur e displacement u der iner t gas con ition (car bon dioxide-r ee)

Stor e the solution in a c emicaly resistant disp n in b tle out of contact with cork , r ub er, or sa onifia le

sto cock lubricant, an protected by a g ard tub containin soda lme or non-ibr ou soda si cate a sorb nt

Glas b tles ar e not r ecommen ed for stor age

5.2.2 Sta d rdization

Stan ardize freq ently enou h to detect c an es of 0,0 0 5 mol/l, prefera ly again t 2,0 g to 2,1 g of pure

p tas ium acid phthalate (5.7), w hic has b en dried for 1 h at 1 0 °C, weig ed w ith an ac urac of ± 0,0 0 2 g an

dis olved in 10 ml ± 0,01 ml of car bon dioxide-r ee wate u in phenolphthalein (5.6) to detect the en -p int

5.3 Hy roc loric a id, c(HCl) = 0,5 mol/l, stan ar d volumetr i aq e u solution

Pr ep r e in ac or dan e with 5.3.1 or u e a commer cialy avaia le solution Stan ar dize in ac or dan e with 5.3.2

5.3.1 Preparation

Mix 4 ml of con entr ated h dr oc lor i acid [3 ,4 % (m/m)] with 1 ltr e of w ate

5.3.2 Sta d rdization

Stan ar dize freq ently enou h to detect c an es of 0,0 0 5 mol/l, prefera ly by electrometric titration of

a pr oximately 8 ml (ac urately me s r ed) of the 0,5 mol/l alcoholc p tas ium h dr oxide solution (5.2) diuted w ith

12 ml of car bon dioxide-r ee wate

1 Beca se of th relativ ly larg co ficie t of cu ic exp nsio of org nic lq ids such as eth n l or pro a -2-ol, th sta d r d

alco olc solutio s sh uld b sta d rdize at temp ratures close to th se employe in th titratio s of sample, a d close to

2 °C

2 Wh r e sa o ificatio n mb r s b low 2 ar e exp cte , b ter pr ecisio may b o tain d by su stitutin 0,1 mol/l p tas ium

hydr oxid a d hydr ochloric acid solutio s for th 0,5 mol/l re g nts in 5.2 a d 5.3, a d th se in cla ses 7 a d 8 No exact

precisio v lu s ar e yet a aia le for this tech iq e

5.4 Buta -2-on (meth leth lk eton ), r eagent gr ade

NOT — Store th b ta -2-o e in a d r k or brown glas b tle

5.5 Petrole m spirit, 6 °C to 8 °C b i n r an e

5.6 Ph nolphthalein, neutr alzed in icator solution

Dis olve 1,0 g of phenolphthalein in 10 ml of ethanol (5.1) an neutralze to a faint pink colour with 0,1 mol/l

ethanolc p tas ium h droxide solution

5.7 Pota sium a id phth late

5.8 Pota sium c lorid , 3,0 mol/l aq e u solution

Dis olve 2 5 g of sold p tas ium c lor i e (K Cl) in 1,0 ltr e of w ate

5.9 Xy le e

5.10 Chloro e ze e

CAUTION — Chloro e ze e is h rmful to the e vironme t Altern tiv solv nts are u d r inv stig tion

6 Apparatus

Or dinar y la or ator y a p r atu an glas war e, in lu in :

6.1 Conic l fla k a d c ndens r

A conical flask , 2 0 ml or 3 0 ml ca acity, alk al-resistant (se the folow in note), to w hic is atac ed a straig t or

mu hro m-yp r eflu con en er The str aig t yp con en er s al b fited to the flask by me n of a grou d

-glas joint; the mu hro m-yp con en er s al fit lo sely to p r mit ventin of the flask Al glas war e s al b

c emicaly cle n

NOT — Th flasks sh uld b cle n d by n n-alk aln cle nin a e ts to match th cle nln s o tain d by th use of

chr omosulfu c acid (se war nin ) For th comp r iso of cle nin eficie c , th visu l a p ara ce a d los in mas o

h atin may b use Deterg nt cle nin , or th use of oth r str on oxidizin a e ts, a oids th sp cific h zar ds r elate to

chr omosulfu c acid, a d is preferr ed for ro tin a aly is Flasks of b rosi cate glas are preferr ed New flasks may giv hig

v lu s, a d old flasks th t h v b come etch d by lo g use sh uld n t b use Bla k tests sh uld b ru co curr ently o

b th use a d n w flask s

W ARNING — Chromos lfuric a id is a h alth h zard It is toxic, a re og ize c rcinog n a it contain

Cr(VI) comp u d , highly corosiv a d p te tialy h zardou in conta t w ith org nic materials W he

u in c romos lfuric a id cle nin solution, e e prote tion a d prote tiv clothin are e s ntial Ne er

pipete th cle nin solution by mouth Afer u e, do not p ur cle nin solution dow n th drain, but

n utralze it with gre t c re, owin to th con e trate s lfuric a id pre e t, a d disp s of it in

a cord nc with sta d rd proc d re for toxic lab ratory w aste (c romium is hig ly d n erou to th

e vironme t)

Non-c romium containin , stron ly oxidizin a id cle nin solution are also hig ly cor osiv a d

p te tial y h zardous in conta t with org nic materials, but do not contain c romium w hic h s spe ial

disp s l pro lems

6.2 Hotplate, he ted by either electr i ity or ste m

6.3 Pote tiometric titrator, of hig precision, ca a le of distin uis in the carb nate ion from the h droxide ion

in the titr ation of re gent grade p tas ium h dr oxide (K OH) by h dr oc loric acid Automatic, r ecordin or man al

a p ratu ar e s ita le

6.4 Ele trod s, of hig q alty T he cle nin an maintenan e of the electr odes ar e des r ib d in an ex A

6.4.1 Combin tion gla s ele trod , or a s ita le glas electr ode an a s ita le r efer en e electr ode

NOT — Eith r siv r chlo d (AgCl) satur ate lthium chlorid (LiCl) or satur ate p tas ium chlorid (K Cl)/calomel

electro es are suita le refere ce electr od s

6.5 Stir er, either mag etic stir r in b r s or a pr op ler stir r er , ca a le of pr ovidin ver y vigor ou agitation

NOT — Th o timum ma n tic stirr i g b r h s b e fo n to b a 2 mm ¥ 5 mm plain p lytetraflu r oethyle e (P F )

co te c ln er

6.6 Be k ers, of ca acity 2 0 ml or 3 0 ml, tal for m, with or without sp ut

6.7 Titration a s mbly, typicaly as i u tr ated in fig r e 1

6.7.1 Stirer, of varia le sp ed, either mec anical or electrical, with pro eler or p d le of inert mater ial, or a

mag etic stirer w ith stir rin b rs (6.5) Al electrical devices s al b grou ded (e rthed) so that no p rmanent

c an e to the meter r eadin oc ur s d r i g the cour se of the titr ation

K ey

1 L a for r efer en e ele tr od

2 Elo g te b r ete tip (in fr ont of stir r er)

3 Refer en e ele tr od , B

4 Sle v with gro n -gla s c nta t joint

5 Shield d le d for gla s ele tr od

6 Bakelte s p or t

7 Gla s ele tro e,C (inter naly s ield d)

8 Be ker , A

9 Pr op ler stir r er , D (b hin b rete tip)

Fig re 1 — T ypic l titration c l a s mbly

6.7.2 Burete, man al or automatic, of ca acity 10 ml or 2 ml, grad ated in 0,0 ml division , an calbr ated w ith

an ac ur ac of ± 0,0 ml

6.7.3 Titration sta d, ca a le of s p or tin the b aker , electr odes, stir r er an bur ete

1 An arr an eme t th t alows for th remo al of th b ak er with ut distur bin th electr od s, b r ete a d stirr er is d sira le

2 Some a p ratus is se sitiv to interfer ence by static electricity, sh wn by er atic mo eme ts of th recor der p n or meter

in icator, wh n th titratio as embly is a pro ch d by th o er ato I this oc urs, suro n th b ak er closely with a c ln er

of co p r g uze th t is electricaly gro n e (e r th d)

6.8 Bala c , ca a le of weig in to the ne r est 0,2 mg

7 Blank test

7.1 Carr y out one or more blank deter mination con urr ently with e c set of samples in the man er des rib d in

7.2 an 7.3

NOT — Bla k d ter min tio s sh uld b ru in d plcate o samples r eq irin th hig est ac urac Th precisio d ta are

b se o d plcate bla k d termin tio s A sin le bla k is suficie t for r outin w ork Du lcate bla k d termin tio s sh uld

a r ee within 0,5 ml Tak e th a era e for calculatio s (se cla se 9)

7.2 Me s r e, from a burete or pip te (se note 1 in this s bclau e) into the conical flask (6.1), 2 ml ± 0,0 ml of

the alcoholc p tas ium h dr oxide solution (5.2) an 2 ml ± 1 ml of the butan-2-one (5.4) Con ect the con en er

to the flask an he t for 3 min afer reflu in b gin (se note 2 in this s bclau e) Turn of the he t source an

immediately ad 5 ml of the p tr oleum spirit (5.5) (se notes 3 an 4 in this s bclau e) by cautiou ly p u n it

down the con en er (dis on ect the con en er if a mu hr oom-yp is u ed)

1 I a v lumetr ic pip te is use , wait 3 s afer d lv r y for complete dr ain g

2 Sta d rd pr oce ure re uir es th t th mixtur e is r efluxe for 10 min How ev r, it is k now n th t some fats ar e r ea iy

dificulty a d are k nown to r eq ire more th n 2 h in some cases Neith r th sh r te e p rio n r th lo g r p r i d sh uld b

use ex e t by mutu l co se t of th intereste p rties Th r eflux time of th bla k sh uld b th same as th t of th sample

in al cases

3 Po r i g 5 ml of p trole m spir it d wn th co d nser at th e d of th sa o ificatio n t o ly rinses th co d nse b t

also co ls th r eactio mixtur e

4 In th case of insulatin ois, th a ditio of p trole m spir it is n t n ces ary

7.3 T itr ate the blank p tentiometr i aly whie hot, w ithout r ehe tin , with the h dr oc lor i acid solution (5.3)

7.4 T ran fer the solution to a b ak er (6.6) W as the flask with two 10 ml p rtion of p tr oleum spir it, an ad

these was in s to the b aker

7.5 Place the b ak er, with a mag etic stir rin b r if u ed, on the titration stan (ited with a mag etic stir plate if

stirin b r s are in lu ed) Immer se the electrodes as far as p s ible, without interfer i g with the stir rer or stir rin

b r s Stir to the maximum agitation without cau in ex es ive a r ation or splater i g of the solution

7.6 T itr ate the blank solution with aq e u h droc lor i acid (5.3), ad ed at the rate of 2 ml/min, u in the

p tentiometr i titr ato

NOT — Tw o inflectio s with corr esp n in e uiv le ce p ints are exp cte Th fir st o e coresp n s to th fre p tas ium

hydroxid (K OH) a d th seco d to th smal amo nt of p tas ium car bo ate (K

2 CO

3 )g n r aly prese t in commer cial KOH

7.7 Recor d the fir st inflection p int

NOT — A pre-a ditio of hydrochlo c acid titr ant ca b use in th bla k to exp dite th titr atio

8.1 Te t portion

Estimate the sa onification n mb r an select a test p r tion mas fr om ta le 1

NOT — Th mas is b se o a a ticip te b ck -titratio of b tw ee 4 % a d 8 % of th bla k , with a maximum test

p r tio of 2 g

Table 1 — Ma s of te t p rtion

Estimate s p nific tion n mber

mg K OH/g

Ma s of te t p rtion

g

181 to

1 1 to

71 to

31 to

16 to

0 to

4 0

18

1 0

7

3

15

1

2

3

5

10

2

8.2 Determination

8.2.1 Weig the test p rtion, to the ne rest 0,01 g, into the conical flask (6.1) Ad 2 ml ± 1 ml of the butan-2-one

(5.4), folowed by 2 ml ± 0,0 ml of the alcoholc p tas ium h dr oxide solution (5.2) me s r ed from a burete or

pip te (se note 1 in 7.2) Dis olve the dific lt to dis olve samples fir st in 15 ml to 2 ml of x lene (5.9), b for e

ad in the butan-2-one

8.2.2 Con ect the con en er to the flask an he t for 3 min afer reflu in b gin (se note 2 in 7.2) Tur n of the

he t sour ce an immediately ad 5 ml of the p troleum spirit (5.5) (se notes 3 an 4 in 7.2) by cautiou ly p u n

it down the con en er (dis on ect the con en er if a mu hr oom-yp is u ed)

8.2.3 Titrate whie hot, with no pre-ad ition of titrant, with the h dr oc loric acid solution (5.3) as sp cified in 7.6 an

7.7 A complete titr ation c r ve is i u tr ated in fig r e 2

NOT — Th p te tial re din s are fair ly co sta t Th re din b fore a ditio of titra t is – 5 0 mV Th fir st inflectio point

is mo er ately sh r p a d tak es place aro n – 3 0 mV Th seco d inflectio is extremely sh r p a d tak es place aro n

B Bla k

a) Using c rb n te-containin alcoholc K OH

D Bla k

b) Usin c rb n te-fre alcoholc K OH

Fig re 2 — Typic l titration c rv s

Calc late the sa onification n mb r , SN, in mi igr ams of K OH p r gr am, fr om the folowin eq ation:

SN=

H l

m

5 1

(1)

wher e

V

1

is the volume, in mi i tr es, of h dr oc lor i acid solution r eq ir ed for titr ation of the test p r tion;

V

0

is the volume, in mi i tr es, of h dr oc lor i acid solution r eq ir ed for titr ation of the blank solution;

c

H l

is the con entr ation, in moles p r ltr e, of the stan ar d volumetr i h dr oc lor i acid solution;

10 Expression of results

Re or t t he r es lt s, ca lc la t ed in cla use 9, a s sa ponif ica t ion n mb r (mi gra ms KOH p r gr a m of sa mple), a s f olows:

a) for electr i al in ulatin ois: to the ne r est 0,1;

b)

for sa onification n mb r s b low 5 : to the ne r est 0,5;

c) for sa onification n mb r s of 5 an a ov e: to the ne r est 1

The precision of the method, as o tained by statistical examination of interla orator y test res lts, is given in 1 1

an 1 2

1 1 Repe ta i ity l mit

The diferen e b twe n s c es ive test res lts o tained by the same o erator w ith the same a p ratu u der

con tant o er atin con ition on identical test mater ial would, in the nor mal an corect o er ation of the test

method, ex e d 2,7 mg K OH/g in only one case in 2

1 2 Re roducibi ity l mit

The diferen e b twe n two sin le an in e en ent res lts, o tained by diferent o erator s w ork in in difer ent

la orator ies on nominaly identical test mater ial would, in the nor mal an corect o eration of the test method,

ex e d 10,4 mg K OH/g in only one case in 2

12 T est report

The test r ep r t s al contain at le st the folowin infor mation:

a) a r efer en e to this p r t of ISO 6 9 ;

b) the typ an complete identification of the pr od ct tested;

c) the r es lts of the test (se clau e 10);

d) an deviation, by agr eement or other wise, fr om the stan ar d pr oced r es sp cified;

e) the date of the test