10.12. Xc nh hm lng ethanol

 

S dng phng php 1 hoc phng php 2 tr khi c nhng ch dn khc trong chuyn lun ring.

Phng php 1

Tin hnh phng php sc k kh (Ph lc 5.2) s dng cc dung dch sau:

Dung dch 1: Cha ethanol chun (ethanol tuyt i) 5% (tt/tt) v propan 1-ol(chun ni) 5% (tt/tt).

Dung dch 2: Ha long mt th tch ch phm th bng nc c mt dung dch cha ethanol 4,0 - 6,0% (tt/tt).

Dung dch 3: Chun b nh dung dch 2 nhng thm va cht chun ni to ra nng cui cng ca chun ni cha trong dung dch ny l 5,0% (tt/tt).

Qu trnh sc k c th thc hin bng cch dng ct (1,5 m x 4 mm) nhi ht xp polymer (100 - 120 mesh) (Porapak Q hoc Chromosorb 101 u thch hp) vi nhit l ct t 1500C, nhit bung tim v detector 1700C.

Tnh hm lng phn trm ethanol cn c vo cc din tch pic ethanol trong sc k thu c t dung dch 1 v dung dch 3.

Phng php 2

Vi nhng ch phm th m trong theo quy nh ca chuyn lun ring s dng cn cng nghip, xc nh hm lng ethanol ging nh phng php 1 nhng chun b dung dch 2 bng cch ho long mt th tch ch phm th vi nc to mt dung dch c nng tng cng ca methanol v ethanol t 4,0 n 6,0% (tt/tt).

Xc nh hm lng methanol bng cch thc hin qu trnh sc k nh m t phng php 1 nhng chun b cc dung dch nh sau:

Dung dch 1: Cha methanol chun 0,25% (tt/tt) v propan 1-ol (chun ni) 0,25% (tt/tt).

Dung dch 2: Ho long mt th tch ch phm th bng nc c mt dung dch cha methanol t 0,2 n 0,3% (tt/tt).

Dung dch 3: Chun b nh dung dch 2 nhng thm va cht chun ni c nng cui cng ca chun ni trong dung dch ny l 0,25%.

Tng lng ethanol v methanol phi trong gii hn quy nh ca chuyn lun ring v t s gia lng methanol v lng ethanol tm c phi tng ng t l ny ca cn cng nghip s dng.

Phng php 3

Phng php ny ch dng kho st nhng ch phm dc dng lng, chc chn cha ethanol ng thi vi cc cht tan khc, nhng cc cht ny phi c tch khi ethanol khi ct.

Khi ct nu trong mu th, ngoi ethanol v nc, cn c ln cc cht bay hi khc th cc hng dn thch hp s c quy nh trong chuyn lun ring.

Hm lng ethanol cha trong mt cht lng c biu th bng s th tch ethanol trong 100 th tch cht lng y 20 oC 0,1oC v c hiu l phn trm ethanol tnh theo th tch / th tch.

Hm lng cng c th c biu th bng gam ethanol cho 100 g cht lng v c hiu l phn trm ethanol tnh theo khi lng/khi lng.

Lin quan gia t trng 20 oC 0,1oC, t trng tng i ( hiu chnh chn khng) v hm lng ethanol ca hn hp nc v ethanol c ghi trong Bng ca t chc Quc t v o lng hp php (1972) * Khuyn co Quc t s 22**

(* (International Organisation for Legal Metrology) (1972)

** (International Recommendation) No 22)

Thit b

Thit b (hnh 10.12) bao gm mt bnh cu thu tinh y trn (A) gn vi mt u ct c b phn by hi (B), b phn ny c ni vi mt ng sinh hn (C) t thng ng. Tip theo l mt ng dn gn vo phn thp ca ng sinh hn dn dch ct vo bnh hng (D). Bnh hng c vch nh mc dung tch 100 ml hoc 250 ml. Trong sut qu trnh ct, bnh hng ny c nhng trong cc (E) cha hn hp v nc . Ngoi ra cn c thm mt a c khot thng mt l trn ng knh khong 6 cm t di bnh ct bo him.

 

 

 

 

 

 

 

 

Hnh 10.12. Dng c xc nh hm lng ethanol (Kch thc tnh bng mm)

 

Xc nh bng l o t trng

ong chnh xc 25 ml ch phm 20oC 0,1oC chuyn vo bnh ct. Pha long vi 100 ml - 150 ml nc ct v thm vi ht bt. Lp h thng chng ct. Chng ct v hng khng di 90 ml dch ct vo bnh nh mc 100 ml. iu chnh nhit dch ct ti 20oC 0,1oC; pha long n 100 ml bng nc ct 20oC 0,1oC. Xc nh t trng tng i 20oC 0,1oC bng l o t trng.

Hm lng ethanol tnh bng phn trm theo th tch bng 4 ln tr s ch ra trong ct 3 Bng 10.12. (Lin quan gia t trng, t trng tng i v hm lng ethanol trong dung dch). Biu th kt qu vi mt s thp phn.

 

Xc nh bng cn thy tnh

ong chnh xc 50 ml ch phm 20 oC 0,1 oC chuyn vo bnh ct. Pha long vi 200 ml - 250 ml nc ct v thm vi ht bt. Lp h thng chng ct. Chng ct v hng khng di 180 ml dch ct vo bnh nh mc 250 ml. iu chnh nhit dch ct ti 20oC 0,1oC; pha long n 250 ml bng nc ct 20 oC 0,1oC.

Chuyn dch ct vo mt ng ong hnh tr c ng knh ln hn ng knh bu ca cn thy tnh t nht 6 mm. Nu th tch dch ct khng , tng lng mu gp i v pha long dch ct n 500 ml bng nc ct 20oC 0,1oC.

Hm lng ethanol tnh bng phn trm theo th tch bng 5 ln tr s ch ra trong ct 3 Bng 10.12 (Lin quan gia t trng, t trng tng i v hm lng ethanol trong dung dch). Biu th kt qu dng c mt s l thp phn.

 

Bng 10.12. Lin quan gia t trng, t trng tng i v hm lng ethanol

.

 

r 20

(kg/m-3)

T trng tng i

ca dch

ct o trong khng kh 20oC (d)

Hm lng ethanol tnh theo % (tt/tt) 20oC

 

r 20

(kg/m-3)

T trng tng i ca dch ct o trong khng kh 20oC (d)

Hm lng ethanol tnh theo % (tt/tt) 20oC

1

2

3

1

2

3

968,0

0,9697

25,09

983,5

0,9853

11,02

968,5

0,9702

24,64

984,0

0,9858

10,60

969,0

0,9707

24,19

984,5

0,9863

10,18

969,5

0,9712

23,74

985,0

0,9868

9,76

970,0

0,9717

23,29

985,5

0,9873

9,35

970,5

0,9722

22,83

986,0

0,9878

8,94

971,0

0,9727

22,37

986,5

0,9883

8,53

971,5

0,9733

21,91

987,0

0,9888

8,13

972,0

0,9738

21,45

987,5

0,9893

7,73

972,5

0,9743

20,98

988,0

0,9898

7,34

973,0

0,9748

20,52

988,5

0,9903

6,95

973,5

0,9753

20,05

989,0

0,9908

6,56

974,0

0,9758

19,59

989,5

0,9913

6,17

974,5

0,9763

19,12

990,0

0,9918

5,79

975,0

0,9768

18,66

990,5

0,9923

5,42

975,5

0,9773

18,19

991,0

0,9928

5,04

976,0

0,9778

17,73

991,5

0,9933

4,67

976,5

0,9783

17,25

992,0

0,9938

4,30

977,0

0,9788

16,80

992,5

0,9943

3,94

977,5

0,9793

16,34

993,0

0,9948

3,58

978,0

0,9798

15,88

993,5

0,9953

3,22

978,5

0,9803

15,43

994,0

0,9958

2,86

979,0

0,9808

14,97

994,5

0,9963

2,51

979,5

0,9813

14,52

995,0

0,9968

2,16

980,0

0,9818

14,07

995,5

0,9973

1,82

980,5

0,9823

13,63

996,0

0,9978

1,47

981,0

0,9828

13,18

996,5

0,9983

1,13

981,5

0,9833

12,74

997,0

0,9988

0,80

982,0

0,9838

12,31

997,5

0,9993

0,46

982,5

0,9843

11,87

998,0

0,9998

0,13

983,0

0,9848

11,44