ly thuyet qua trinh luyen kim

8/6/2019 Ly Thuyet Qua Trinh Luyen Kim

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GS.TSKH Bi Vn M-u (Ch bin)

PGS.TS Nguyn Vn Hin. PGS.TS Nguyn K Bnh. PGS.TS Tr-ng Ngc Thn

L thuyt cc qu trnh

luyn kim

H Ni, 9 - 2006

Nh xut bn khoa hc k thut


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i hc, cho k s-, cn b nghin cu khoa hc v cn b qun l ngnh luyn

kim v cc ngnh khc c lin quan.

Quyn sch ca tp th cn b ging dy u ngnh Tr-ng i hc

Bch Khoa H Ni bin son, do GS. TSKH Bi Vn M-u ch bin v phn cng

bin son nh- sau:GS.TSKH Bi Vn M-u : ch-ng 4,6,7 v 8.

PGS.TS Nguyn Vn Hin: ch-ng 1 v 3.

PGS.TS Tr-ng Ngc Thn: ch-ng 2.

PGS.TS Nguyn K Bnh : ch-ng 5.

Mc d cc tc gi c nhiu c gng, song cun sch kh trnh khi

-c thiu st. Rt mong -c c gi gp ph bnh. Th- gp xin gi v

Nh xut bn Khoa hc k thut - 70 Trn H-ng o - H Ni. Chng ti xin

chn thnh cm n.

Cc tc gi.


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CHNG 1

QU TRNH CHY NHIN LIU

1. 1. M u

Cc qu trnh luyn kim phn ln u tin hnh nhit cao trong cc thit b luyn kim

bng cch t nhin liu, tc l gy ra s chy. Ty theo loi nhin liu (rn, lng hay kh) v

phng php t chy m ta c sn phm chy c tnh oxy ha hay tnh hon nguyn thch hp

vi yu cu cng ngh ca qu trnh luyn kim.

Do s chy chng nhng m bo cho l luyn kim c nhit cao m cn to ra sn

phm chy c tnh cht cn thit tham gia tch cc vo cc phn ng luyn kim trong l.V d: Qu trnh hon nguyn oxt kim loi yu cu sn phm chy phi c tnh kh thc

hin phn ng :

MeO + CO = Me + CO2

hay MeO + H2 = Me + H2O

Nu qu trnh l oxy ha cc tp cht trong kim loi lng th yu cu sn phm chy phi

c tnh oxy ha thc hin phn ng :

[X] + CO2 = (XO) + CO

hay [X] + H2O = (XO) + H2Nh vy trong ha luyn, s chy ca nhin liu chng nhng l ngun cung cp nhit m

cn to ra mt trng cn thit tin hnh qu trnh luyn kim. V vy cng ha qu trnh chy

l mt bin php ch yu cng ha qu trnh luyn kim. Mt trong nhng bin php l dng

kh giu oxy trong qu trnh ha luyn.

Nhng phn ng chy kh c ngha quan trng i vi qu trnh ha luyn l phn ng

chy CO, H2. Nhng phn ng chy nhin liu rn c ngha quan trng i vi qu trnh ha

luyn l phn ng chy cacbon.

Nhin liu dng trong luyn kim cn t nhng yu cu sau y:- C hiu ng nhit ln.

- Gi thnh r.

- Sn phm khi to thnh do qu trnh chy khng c hi n sn phm phn ng m tch

cc tham gia vo qu trnh luyn kim.


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1.2. Nhit ng hc ca phn ng chy kh

1.2.1. Chy oxit cacbon (CO)

Kh oxit cacbon l thnh phn ch yu ca nhin liu kh. Trong luyn kim CO

c hai cng dng: t chy cung cp nhit v dng lm cht hon nguyn oxt kim

loi. V chy CO ta nhiu nhit, ng thi kh CO c i lc mnh vi oxy nn c th ly

oxy ca nhiu oxit kim loi. Phn ng chy CO:

2CO + O2 = 2CO2 (1 - 1)

(H0298(1-1) = -566108J

Theo quy lut pha:

C = k p + 2 = 2 1 + 2 = 3

Bc t do bng 3, nh- vy c ngha l thnh phn pha kh -c xc nh bi ba

yu t.

%CO, %CO2, %O2 = f(T, P, C)

Theo nguyn l Lsactli nh h-ng ca nhit v p sut s l m thay i thnh

phn cn bng: khi p sut tng th CO chy mnh v cho nhiu CO 2 khi nhit tng

th CO2 phn ha mnh, cho nhiu CO.

lm c s phn tch cc quy lut nhit ng hc ca phn ng, chng ta s

thit lp ph-ng trnh quan h gia (G v hng s cn bng KP ca phn ng vi nhit

.

KP(1) =22

2

.2

2

OCO

CO

PP

P(1 - 2)

(G0T = (HT0 - T(S0T (1 - 3)

Trong (H0T v (G0

T l hm s ca nhit

(H0T = (H0298 - (

T

PdTC298

(1 4)

(S0T = (S0

298 - (

TP

T

dTC

298

(1 5)

y(

CP l bin thin nhit dung ng p ca cht tham gia phn ng v tothnh phn ng. (CP cng l hm nhit . Cch tnh nh- sau:

(CP = 2CPCO2 - 2CP

CO CP 2o

(CP = 2.36,53 2.29,08 29,08 = -14,18J/mol0.k

(S0298 (1-1) = 2.213,72 2.148.00 205,15 = 174,71 J/mol0.k

(H0298(1-1) = -566108J


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Thay gi tr (H0298(1-1) v (S0

298 (1-1) vo cng thc ca Vanhp.

(G0T = -RTlnkp. Ta c:

lgkP(1-1) =

1

298

298lg74,008,9

29574

T

T

T(1-6)

Trong cng thc (1-6) t lg )(1

298

248 TT

T

N!

ta c:

lgkP(1-1) = )(74,008,929574

TT

N (1-7)

Nu tnh n gin

lgkP(1-1) =575,4575,4

0)11(298

0)11(298

S

T

H

lgkP(1-1) = 08,929574

.

lg2

2

2

2

!

TPP

P

OCO

CO(1-8)

Bng 1 1 : Gi tr hng s cn bng kP(1-1)

Nhit , oK Theo (1-7) Theo (1-8)

1000

1600

2000

2600

20,118

8,760

4,912

1,342

20,42

9,37

5,68

2,28

T bng 1-1 v th hnh 1-1 ta thy nhit cng tng th hng s cn bng ca phn ng

chy CO cng gim, ngha l s chy CO cng khng hon ton. Trong pha kh cn bng, ngoiCO2 v O2 cn c phn CO cha chy. Hay ni cch khc l nhit cao, kh CO2 bi phn ly mt

phn, mc phn ly cng tng khi nhit cng cao. T i n kt lun rng, nhit cao i

lc ha hc ca CO v O2 gim, nn kh nng hon nguyn ca n cng gim i .

G , KJ)

CO+HO=H +

CO (I-15)

22

2

2CO+O

=H +2C

O (I-1

)

2 2

2

2H +O =

2HO(I-1

1)

22

2


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S phn ly ca CO2 (hay s chy khng hon ton ca CO) nhit cao lm cho nhit

chy tnh theo l thuyt (l nhit ca sn phm chy khi gi thit CO chy hon ton v khng

c s mt mt nhit ra mi trng xung quanh) v nhit chy thc t c s sai khc.

Nhit chy l thuyt theo phng trnh:

! cyQ

T .

y :

y - trng lng ca tng cht kh trong sn phm chy (gam)

c - t nhit trung bnh ca sn phm chy (J/g.oK)

Q - nhit lng ca phn ng chy CO (J)

Nu CO chy hon ton th Q nCO(H (J)

nCO - s phn t gam kh CO b chy

(H - hiu ng nhit ca phn ng 2CO +O2 = 2CO2(tc l nhit pht ra khi c 1 phn t gam CO chy hon ton).

Trong trng hp CO chy khng hon ton (hay CO2 b phn ly mt phn v mc phn

ly ca CO2 l Evi gi thit phn ng vit cho mt phn t CO tham gia th Q tnh nh sau:

Q = nCO (1 - E) (H = (1 - E)Q

Khi nhit chy l:

T = Tcy

)1(.

)1(E

E!

V bao giE cng nh hn 1 nn T < T. Vy s phn ly ca CO2 c th tnh theo hng s

cn bng ca phn ng ( 1 - 1 ).

Gi s lc u trong h thng c mt phn t gam CO2 nguyn cht. Nu gi phn ly ca

CO2 l E th khi phn ng cn bng trong pha kh ta s c:

E - phn t gam CO

(1 - E) - phn t gam CO2

0,5E - phn t gam O2

Vy tng s phn t gam ca cc cht kh trong sn phm chy l(l - E) + E + 0,5E = 1 + 0,5E


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Nu gi p sut tng ca h l P thi p sut ring phn cn bng ca tng cht kh trong

l:

E

E

E

E

E

E

5,015,0

5,01 .

5,01

)1(

2

2

!

!

!

PP

PP

PP

O

CO

CO

Thay vo phng trnh (1-2) ta c:

Kp(1-1) =P3

2)1)(2(

E

EE (1-9)

Khi phn ly E rt nh th c th coi (1 - E) } 1 v (2 + E) } 2. Vy:

3

)11( .

2

PKp !E (1-10)

Vy phn ly E ca CO2 t l nghch cn bc ba vi p sut. Nhit tng th Kp(1-1) gim

(xem bng l-l), do E tng ln. Nh vy c th thay i p sut hoc nhit lm cho E tin

ti 0, tc l lm cho s chy CO c hon ton.

1.2.2. S chy Hydro (H2)

Hydro l kh c i lc vi oxy kh mnh. N c th chy vi oxy theo phn ng sau :

2H2 + O2 = 2H2O (l- ll)(H0298(1-11) = -503933J

V nhiu mt, phn ng chy H2 ging vi phn ng chy CO. V vy nhng quy lut chng

ta va xt i vi phn ng chy CO cng thch hp i vi phn ng chy H2.

(G0(1-11) = -503933 + 117,36T (1-12)

lgKP(1-11) = 13,626320

T

(1-13)

Vy cng nh CO, tr s cn bng ca phn ng chy H2 gim khi nhit tng, ngha l

nhit cao H2 chy khng hon ton hay H2O phn ly mt phn. Nhit cng cao mc phnly cng tng.

Ta c th xc nh c phn ly ca H2O bng phng php hon ton ging nh i vi

CO2.


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Bng1 2: Gi tr hngs cn bng(1-11)

Nhit , T0K KP(1-11)

600

1000

1500

2000

2500

3000

37,740

20,190

11,417

7,050

4,398

2,643

Nu cng gi thit lc u trong pha kh c 1 phn t gam hi nc H2O v gi mc

phn ly ca n l E. Cng l lun ging nh trn, ta c:

KP(1-11) = POH

OHOH

.

)1)(2(

3

2

2

22

E

EE

OH2E nh, c th tnh gn ng:

Khi OH2E = 3)111( .

2

PKP (1-14)

Vy cng nh trn, c th thay i nhit v p sut cho EH2Op 0, tc l s chy H2 c

hon ton.

T gin (GT = f(T) ta c th so snh v kh nng chy ca CO v H2 nhit 1083oK i lc

ha hc ca H2 v CO bng nhau (v (Go(1-11) = ( G

o(1-11)) hay Kp(l 1) = K p(1 - 11) Thp hn nhit

1083oK i lc ha hc ca -H2 vi O2 yu hn (v (Go(1-1) > (G

o(1-11) hay KP(1-11) > KP(1-1)) Cn nhit

cao hn 1083oK th ngc li.

1 2.3. Phn ngkhnc

Phn ng kh nc l phn ng tc dng gia CO v hi ncH2O + CO - H2 + CO2 (1-15)

KP(1-15) =COOH

COH

PP

PP

.

.

2

22

(1-16)


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C th tnh theo phng php gin tip bng cch tr phn ng (1-1) cho phn ng ( 1 - 11 )

ta c :

2CO + O2 = 2CO2 (l - 1)

2H2 + O2 = 2H2O (l 11)

2(CO + H2O) = 2(CO2 + H2)

(G0(1-15) = ][2

1 0)111(

0)11( GG

lgK0P(1-15) = ]lg[lg21

)111()11( PP KK

KP(1-15) =)111(

)11(

P

P

K

K(1-17)

T phng trnh ny chng ta tnh c:

lgKP(1-15) = 469,11591

T

(1-18)

V phn ng tin hnh trong iu kin khng c s thay i th tch cc cht kh nn hng s

cn bng d tnh bng p sut ring phn hay bng nng phn trm th tch cng bng nhau.

KP(1-15) = ))(%(%))(%(%

.

.

2

22

2

22

COOHCOH

PP

PP

COOH

COH! (1-19)

Bc t do ca phn ng C = 3 - 1 + 1 = 3 c ngha l thnh phn cn bng ca phn ng ( 1 -

1 5) ph thuc vo ba thng s.

-


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V d :

PCO = f ),,( 22 HPT CO

tOH

H

CO

CO

P

Pb

P

Pa

2

2

2

; !!

a, b - c trng cho i lc ha hc ca CO v H2 vi O2

T = 1083oK th a = b, c ngha l i lc ha hc ca CO v H2 vi O2 bng nhau.

T < l0830k th a < b, c ngha l i lc ha hc ca CO vi O2 ln hn i lc ha hc ca H2

vi O2

T > 1083o

K th a > b, c ngha l i lc ha hc ca CO vi O2 km hn i lc ha hc caH2 vi O2

Kt lun ny ph hp vi kt lun khi xt qu trnh chy CO v H2

T hng s cn bng KP(1-15) ta c th vit :

Kp(1 - 15) =a

b(1-20)

Do ta c :

b = a. KP(1-15) (1-21)

mt nhit khng i th KP(1- 15) = const v quan h gia b v a l mt ng thng, cngha l nhit khng i c v s im cn bng v chng lin h vi nhau bi phng trnh (

1 - 21).

1.2.4. S chy kh Mtan


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Mtan l thnh phn c bn ca kh t thin nhin, c s dng rng ri trong luyn kim.

Kh thin nhin c s dng trong cc loi l nung , l luyn thp, l cao trong cc l lun st

trc tip t qung.

Phn ng chy kh Mtan:

(1) CH4 + O2 = 2CO + 4H2 (H0

298(1) = -71300J

(2) OHCOOCH 2224 21

2

1! (H0298(2) = -400700J

Phn ng (1) v (2) u pht nhit cc hng s cn bng ca chng c biu din nh sau:

,10)..()(

.).()(

.

.32

4

342

2

2

42

)1(

24

2

OCH

PHCO

PP

PPK

OCH

HCOP !! P = PCO + 242 OCHH PPP

).(%)(%

).(%)(%

.

.

22/1

4

22/1

2/1

2/1

)1(

24

22

OCH

OHCO

PP

PPK

OCH

OHCOP !!

Bc t do ca 2 phn ng (1) v (2):C= 3 1 + 2 = 4

Tc l bn bin c lp ca h thng ny s l nhit v 3 nng ca 3 cu t.

Trong khong rng nhit , cc hng s cn bng ca phn ng (1) v (2) u rt ln:

T, oK 500 1000 1500 2000

lgKp(1) 12,80 11,46 11,08 10,80

lgKp(2) 83,60 41,81 27,84 20,83

Khi bng nhit cn bng chuyn dch t phi sang tri, sn phm phn ng s gim (v

phn ng ta nhit).Khi ri vo vng nhit cao, Mtan b phn hy:

(3) CH4 = C + 2H2 (H0

298(3) = 74800J

KP(3) = 100).(%

)(%

4

22

2

4

2

CH

PH

P

P

CH

H!

y P l p sut tng: P =42 CHH

PP

Hng s cn bng phn ng (3) ph thuc nhit theo phng trnh sau:

lgKP(3) = 79,1100186,0lg957,53348 TTT

Gi tr lgKP(3) cc nhit khc nhau s l:

T, oK 773 1273 1773 2273

LgKP(3)-0,40 1,71 2,37 2,50


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Nh vy khi nhit tng hng s cn bng KP(3) tng, c ngha l s phn ly ca Mtan

tng.

Bc t do phn ng (3) C = 2 2 + 2 = 2

Cn bng ca phn ng (3) c xc nh bi 2 thng s: Nhit d v nng ca mt cu

t. S phn hy Mtan xy ra ng k khi T > 5730K (3000C).

nhit 12730K, Mtan b phn ly hon ton trong thnh phn hn hp kh c: 98,11%H2

v 1,89%CH4 (vi P = 101325Pa)

Khi tng p sut cn bng phn ng chuyn dch sang tri:

Thnh phn hn hp kh cn bng (P = 101325Pa)

T0, K CH4 H2

723 53,8 46,2

1273 1,89 98

nhn c st khi hon nguyn trc tip qung st ngi ta khng dng trc tip kh

thin nhin m dng sn phm ca s chuyn ha Mtan (chnh l CO, H2).

(4) CH4 + CO2 = 2CO + H2O (H0

298(4) = 247000J

(5) CH4 + H2O = CO + 3H2 (H0

298(5) = 206000J

(6) CH4 + 2H2O = CO2 + 4H2 (H0

298(6) = 165000J

nhit cao hng s cn bng ca cc phn ng (4), (5), (6) u ln hn 1 tc l t 10

n 108. nhit thp T = 5730K th KP(4) , KP(5) , KP(6) tng ng bng 10-12, 10-10, 10-8

Di y l nh hng ca nhit ti hng s cn bng ca phn ng chuyn ha kh thin

nhin.T0, K 723 1273 1773 2273

lgKp(4) -12,2 1,25 5,76 7,98

lgKp(5) -10,0 1,40 5,36 7,32

lgKp(6) 7,44 1,55 4,94 6,40

tng tc qu trnh chuyn ha kh thin nhin ngi ta x dng cht xc tc NiO v

nhit 11730K n 13730K. chuyn ha ngi ta dng kh thot ra t c l ng thc hin qu

trnh hon nguyn. Trong kh c l ng c cha CO2 chuyn ha Mtan theo phn ng (4). Sau

chuyn ha, ngi ta thu c kh hon nguyn cha 30%CO v 70% H2.

1 3. C ch v ng hc ca phn ng chy kh

1 3. 1 . S bc chy ca hn hp kh

Nhit bc chy ca hn hp kh c xc nh bi quan h gia tc ta nhit (do phn

ng chy) v tc thot nhit ra mi trng xung quanh. Phng trnh ta nhit :

qta = Q.v = Q.K.Cn (l-22)


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y :

Q - Hiu ng nhit ca phn ng chy

v - Tc phn ng chy

K - Hng s tc phn ng chy

C - Nng cht tham gia phn ng

n - Bc phn ng

qthot = Edn. )( XTV

F(1-23)

F, V - din tch b mt v th tch ca bnh ng

Edn h s dn nhit

T - nhit do phn ng ta ra

X- nhit mi trng

Biu din quan h gia qta v qthot vi nhit theo phng trnh (1-22) v (1 -23) chng

ta c mt s nhn xt sau (hnh 1-3):

qt

,qt

t

qt

,qt

t

nhit thp (X1) u tiu khi T = X ta c qta > qthot ng cong a nm trn ng cong

b1. Vy nhit ta ra ln hn nhit thot ra ngoi, nn bnh ng c t nung nng ln, tng ng

vi s tng ln ca tc ta nhit (theo ng cong a) ng thi tc thot nhit cng tng ln

theo ng cong b1

Ti im M nhit T1 qta v qthot bng nhau, lc s t nung nng ca mt h b

ngng li, h thng gi nhit khng i T 1

Nu nhit trong bnh t nhin cao hn T1 th qthot tr nn ln hn qta hn hp li ngui

tr li n T1 V vy nhit T1 s cn bng nhit c t ng thit lp v phn ng c c

tnh n nh. Ngha l tin hnh vi nhit khng i.

Trong vng nhit thp, tc qu trnh rt nh, hu nh khng quan st c nn trn

thc t qu trnh khng tin hnh c.

X1 X2Xth


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- nhit cao (X2) lc ny ng b2 di ng a hay bt k nhit no trong bnh

u c qta > qthot. Qu trnh tin hnh lm cho hiu s (qta - qthot) tng ln dn n s tch nhit

trong h thng. S chnh lch ny cng tng khi nhit v tc phn ng cng tng. Lc u

qu trnh tin hnh rt chm sau tng ln v tc ca n t c gi tr rt ln, do hn hp

bc chy.

- nhit ti hn (Xth) ng cong bth gp ng cong a v bt u t Xth h thng t nung

nng l do phn ng chy pht nhit. T th nhit do h thng thu vo (nh phn ng pht nhit) v

lng nhit ca h truyn ra mi trng bng nhau. Nhng khc vi trng hp nhit thp l

y s cn bng nhit khng bn vng, ch cn tng nhit ln hn Tth mt t cng lm cho cn

bng b ph v. Khi qta > qthot cng ging nh trng hp X2 qu trnh chy rt mnh.

Bi vy, nhit Xth gi l nhit ti hn. Thp hn nhit. Xth phn ng tin hnh n

nh, cao hn Xth phn ng tin hnh vi s gia tc. Nhit nh vy gi l nhit bc chy, n

c xc nh trn gin khi b tip tuyn vi a.Nhit bc chy ph thuc :

- Hnh dng kch thc v vt liu lm bnh (qua tr s Edn F, V) trong cng thc (1 -23).

- Tr s ca hiu ng nhit v c trng ng hc ca phn ng (Q, E, Ko) trong phng

trnh (1 -22).

- Nu thay i iu kin gim dc ca ng cong b v chuyn dch ng cong a ln

pha trn th dn ti s h thp nhit bc chy v ngc li.

V d, gim din tch b mt ring ca hnh )(

V

Fs lm tng nhit ta ra trong mt n v th tch

ca hn hp phn ng, tng p sut tng cng nh p sut ring phn ca cc cu t tham gia phn ng...

u gim nhit bc chy.

1 3.2. C ch dy chuyn ca phn ngchy kh.

a) c im: nhit cao hn nhit bc chy, cc phn ng chy kh (H 2 ,CO) u

tin hnh theo c cu dy chuyn. Cc phn ng dy chuyn pht trin c l nh cc gc t do c

hot tnh cao (gc t do c th l nguyn t, hay ion...).

L thuyt phn ng dy chuyn da trn hai nguyn tc sau y:

- Cc gc t do c hot tnh rt ln trong cc phn ng vi phn t bo ha ha tr.- Khi tc dng vi cc phn t bo ha ha tr, ha tr ca cc gc t do khng mt i, v

pht sinh ra nhng gc t do mi.

Dy chuyn b gin on khi gc t do ca hai dy chuyn va chm nhau to thnh phn t

bo ha ha tr.

V d: Gc t do H, OH


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H + O2 = OH + O

phn ng ct t dy chuyn : OH + H = H2O

Nghin cu quan h gia nhit bc chy ca hn hp kh vi p sut c biu din

hnh (1 - 4).

T hnh 1 - 4 chng ta thy rng nhit T > TN th hn hp kh ch c mt gii hn p

sut bc chy l P1 (on RS). Trong gii hn ny khi P > P1 hn hp bc chy. Khi P < P1 oxy ha

chm (khng bc chy).

Khong nhit TM - TN c hai gii hn bc chy: P > P1 V P < P2 to nn mt bn o

bc chy mi M.

Gii hn th ba : P > P3 xy ra s bc chy, qu trnh tin hnh vi tc rt ln. y lng

kh thot ra rt ln v lng nhit thot ra cng rt ln.

Qu trnh bc chy ph thuc vo p sut c xc nh bi ba trng hp sau y:


17/236

X X

Va chm bc mt: l gc t do va chm vo thnh bnh gy nn s ct t dy chuyn.

H + thnh bnh = 2

1

H2

Tc va chm bc mt c biu th bi cng thc

V1 = K1 .P (1-24)

Va chm bc hai: Va chm bc hai lm phn ng dy chuyn pht trin.

V d : H + O2 = HO + O

O + H0 = OH + H

Hai gc t do tham gia vo qu trnh chy. Do phn ng dy chuyn pht trin. Tc

va chm bc hai c biu th bi phng trnh:

V2 = K2 P2 (1 - 25)

- Va chm bc ba: Khi gc t do va chm phi nhng phn t kh tr c mt trong hn hp

kh (v d : Ar, N2 v.v...). Gc t do khi va chm vo nhng phn t kh tr s chuyn nng lng

cho n v bin thnh phn t bo ha ha tr. Va chm bc ba xy ra p sut cao. Phn ng dy

chuyn b ct t do va chm bc ba nh sau:

v d : H + H + M = H2 + M*

O2 + H + M = HO2 + M*

Phng trnh tc va chm bc ba

V3 = K3P3

Biu din phng trnh (1-24), (1-25), (1-26) trn hnh 1-5 ta c nhn xt:


18/236

p sut

T O n P1 tc va chm ph thuc vo s va chm bc mt (ng V1 nm trn ng

V2 v V3). C ngha l gii hn di bc chy quan h vi s va chm vo thnh bnh gy nn s

gin on dy chuyn phn ng. Vy p sut thp s ct t dy chuyn l do gc t do va chm

vo thnh.

- T Pl n P2 quyt nh do va chm bc hai. Phn ng dy chuyn pht trin (ng V2

nm trn ng Vl v V3)

- P > P2 quyt nh do va chm bc ba (ng V3 nm trn ng Vl v V3) phn ng dy

chuyn t on. Vy p sut cao s ct t dy. chuyn do va chm bc ba.

b) S chy Hydr H2

Bng thc nghim ngi ta chng minh rng: phn ng chy hydr vi oxy theo c cu

dy chuyn trong phn ng chy ca n, ngoi cc phn t hot tnh l H v nhm OH cn c oxynguyn t tham gia vi tc dng mnh hn c Hydr nguyn t. Ch vi nng oxy rt nh c

th lm gim nhit bc chy ca hn hp kh ti nhit bnh thng. Theo Xmnp th c ch

chy dy chuyn ca phn ng chy Hydr rt phc tp, c th phn chia thnh cc loi phn ng

sau y:

-Phn ngphtsinhdychuyn :

(1) H2 + O2 p HO2 + H

hay H2 + O2 p 2OH

Nhit to thnh gc OH l 83682J/mol hat nng ca phn ng vo khong E =188284,5J

Hng s tc phn ng

K(1) = 10-10.e-7500/T cm3/sec

Tc phn ng ( 1) l:

v(1) = n(1) K(1) (H2) (O2)


19/236

Trong n(1) l s phn t hot tnh to ra trong mt n v thi gian

(2) OH + H2p H2O + H

Phn ng (2) tiu hy nhng phn t hot tnh gc OH to thnh phn t H2O nhng

ngc li to ra phn t hot tnh mi l H, m bo cho dy chuyn pht trin. Phn ng ny pht

nhit (58512J/phn t gam).

Tc ca n ph thuc vo nng nhm OH trong cng ngn la.

v(2) = K(2) (H2) (OH)

Trong K(2) l hng s tc ca phn ng (2)

K(2) = 7.10-12 sec/. 3

7000

cme T

X

Phn ng chia nhnh dy chuyn

(3) H + O2p OH + O

(4) O + H2p OH + H

Nhng phn ng ny l nhng phn ng quan trng trong qu trnh chy dy chuyn. y

mt phn t hot tnh mt i th to thnh hai cht im hot tnh. Cng c ngha l to ra mt y

chuyn phn ng mi, lm cho tc qu trnh c gia tc.

V(3) = K(3) (O2) (H)

K(3) = 0,94.10-10. sec/3

7550

cme T

Tc phn ng (4)

V(4) = K(4)p (H2) (O)

K(4) = 2.10-10. sec/3

3000

cme T

Bng 1-3 di y so snh kh nng ng hc ca phn ng. Nu ln gi tr ca hng s tc

ca phn ng nhit 8000K.

Bng1-3:Hngstc phn ngnhit 8000K

S th t phn ng Phn ng K, cm3/sec

(1)

(2)(3)

(4)

H2 + O2p 2OH

H2 + OH p H2O + HO2 + H p OH + O

H2 + O p OH + H

10-22

4.10-13

10-14

5.10-12

Phn ngct t dy chuyn trn thnh bnh thnh bnh

thnh


20/236

(5) 2H H 2

(6) 2OH H 2O2

Gm c cc thnh phn

p sut thp, cc cht im hot tnh H, O v OH khuch tn n thnh bnh, b hp ph

trn v tc ng vi cc cht im hot tnh khc t th tch ca bnh i vo to thnh nhng

phn t H2x O2 v H2O ng thi truyn nng lng cho thnh bnh hay ta ra xung quanh, cc

phn t H2 , O2 v H2O c to thnh b gi li mt cch yu t trn thnh bnh nn sau c

nh ra i vo pha kh.

- Phn ngct t dy chuyn trongth tch .

- Khi nng cao p sut th phn ng ct t dy chuyn trn thnh bnh (5) c thay th

bng phn ng ct t y chuyn trong th tch (7)

(7) H + O2 + M p HO2 + M*

2HO2 p H2O2 + O2

Tc ca phn ng ny tng ln rt nhanh khi tng p sut (t l vi P

3

). Phn ng phttrin c l do nhng phn t th ba M (c th l H2 , O2 ,H2O hay kh tr) khi va chm bc ba,

phn t th ba s hp ph nng lng ca cc phn t hot ha, gii phng nng lng tha v to

thnh hp cht trung gian.

v(7) = K(7) (O2) (M) (H)

K(7) = 2,4.10-33cm3/sec

Khi nng lng hot ha nh (E p O) th thc t K(7) khng ph thuc vo nhit .

Hi nc c tc dng lm tr ngi cho s bc chy hydr v oxy:

V d : 5700

C khng c H2O P2 = 9,1.103

Pa2% H2O P2 = 8,0.10

3Pa

2% H2O P2 = 7,0.103 Pa

C th biu din phn ng chy dy chuyn ca hyro bng s sau:

thnh

(H)kh (H) thnh bnh

(H)thnh bnh (H) hp th

(H) hp th + (H) kh (H2) hpth

Khuch

22 OH

2HO

2OH

2HOH

2HO

OH2

...2OH

...2HOH


21/236

c) S chy o xt ca chon (CO)

S chy oxit cacbon cng c c trng bng cc quy tc chung nh s chy hydro. N

cng c bn o bc chy, nhng gii hn bc chy di v trn u cao hn s chy hydro. Mt

c im khc vi s chy ca hydro l oxit cacbon kh chy rt km. Mun lm cho n bc chy

c th phi bt tia la in mnh, ngoi ra ngn la khng n nh, lan truyn chm, d tt,

nhng ch cn cho vo mt t hi nc th hn hp chy mnh hn ln. Ngi ta xc minh rng,

hi nc c nh hng quyt nh n tc chy hydro.

VCO = f( OHP 2 )

Nu OHP 2 p O th vCOp O

Thc nghim xc nh rng, tc chy ca hn hp oxit cacbon-oxy khi tha oxit

cacbon t l bc nht vi hm lng hi nc.

Vi hn hp tha oxy th nh hng ca hi nc t hn. C th thay i hm lng oxy

trong mt khong kh ln cng khng lm nh hng r rt ti tc chy ca oxit cacbon.

Qua phn tch trn ta thy rng, c ch ca qu trnh chy CO c lin quan vi nguyn t

hot tnh hydro.

Theo nghin cu ca Xmnp th c ch dy chuyn ca s chy CO c lin quan vi

nguyn t hot tnh hydro.

Theo nghin cu ca Xmnp th c cu dy chuyn ca s chy CO c th biu din bng

phng trnh sau:

Phn ng pht sinh dy chuyn:

H2O + CO = H2 + CO2

H2 + O2 = 2OH

- Phn ng ni tip dy chuyn

OH + CO = CO2 + H

O + H2 = OH + H

- Phn ng ct t dy chuyn trn thnh bnh

H + thnh p 22

1H + thnh


22/236

- Phn ng ct t dy chuyn trong th tch (trong khng gian ca bnh)

CO + O + M p CO2 + M+

S tng hp ca phn ng chy dy chuyn CO nh sau :

c

c

1.3.3. C ch v nghc ca phn ngkhnc

Phng trnh phn ng : CO2 + H2p CO + H2O

Phn ng tin trin c l nh cht xc tc tri qua cc giai on hp ph v gii ph cc

cht tham gia phn ng. Cc phn t kh H2 v CO tham gia phn ng u b hp ph trn b mt

cht xc tc. Khi chng b bin dng rt nhiu. v d dng cht xc tc l Pt th c cu nh sau :

(1) H2(K) + Pt = Pt . (H2)h.ph

Sau cc phn t CO2 trong pha kh va p vo b mt cht xc tc hp ph H2(2) Pt .(H2)h.ph + CO2(K) = Pt(CO)h.ph + H2O

Cui cng l phn t CO c tch ra khi b mt cht xc tc

Pt (CO)h.ph = Pt + CO(K)

v = f(v1sl - v2s2)


23/236

v1- tc hp ph CO trn b mt cht xc tc ng vi S 1

v2 - Tc gii ph CO2 trn b mt cht xc tc ng vi S2

Phng trnh tc :

COH

H

PPK

PKv

!

2

2

2

1

K1 - hng s tc ca phn ng ( 1 ).

K2 - hng s tc ca phn ng (2).

T phng trnh tc ta nhn xt rng : tc phn ng khng ph thuc vo s c mt

ca CO2 trong hn hp kh. iu c gii thch bng s hp ph tng i yu ca CO 2 trn b

mt xc tc Pt

Nhn t ch yu tng tc phn ng l tng p sut ring phn ca hydro trong hn hp

kh, hay ni cch khc l tng cc phn t hot tnh lm cho phn ng pht trin.

Mt s nh nghin cu khc trnh by c cu phn ng kh nc vi cht xc tc l oxit st.CO + H2O = CO2 + H2

Qu trnh rt phc tp, c th trnh by qu cc khu sau y:

Phn t hi H2O c hp ph trn b mt cht xc tc bin dng mnh n ni lin kt

phn t ca n b ph v. Nguyn t oxy c gi li trn b mt cht xc tc cn hyro c tch

ra i vo pha kh.

(l) H2O = (O)h.ph + H2(K)

Nhng phn t kh CO chuyn ng trong pha kh gy nn nhng .va chm c hiu qu vi

b mt cht xc tc (m trn c nhng nguyn t oxy hp ph). CO s tc dng v nguyn toxy b hp ph bin thnh phn t CO2 v gii phng b mt xc tc:

(2) (O)h.ph + CO(K) = CO2(K)

Giai on th hai l khu chuyn bin chm nht hn ch ton b qu trnh.

n

OH

HCO

H

OHCO P

PPK

P

PPKv

!

1

21

2

2

2

2

2

n - bc phn ng.

Phng trnh cho ta thy tc ca phn ng s gim i khi cho thm kh H 2 vo v bc caphn ng theo s tiu hao ca CO tin ti 1. nh hng ca nhit c th nh gi bng phng

trnh hng s tc ca phn ng hn ch nh sau


24/236

TAeK

8250)2(

!

1.4. nhit ng hc ca phn ng chy cacbon

1 4. 1 . c im chung

Gia cacbon v oxy c th xy ra nhng phn ng sau y:

Phn ng chy hon ton

( 1) C + O2 = CO2 (Ho248(1) = -394142J

Phn ng chy khng hon ton

(2) C +2

1O2 = CO (H

o248(2) = -223431J

Phn ng chy tip

(3) CO +2

1O2 = CO2 (H

o248(3) = -283054J

Phn ng kh ha cacbon

(4) C + CO2 = 2CO (Ho248(4) = 170711J

Nhn xt chung:

- Chy hon ton cho ta hiu ng ln nht, chy khng hon ton cho ta hiu ng nhit thp

nht. Bi v sn phm kh cn tip tc chy na.

Q1 = Q2 + Q3

- Phn ng chy khng hon ton xy ra trong iu kin thiu oxy, cn phn ng chy hon

ton xy ra trong iu kin tha oxy.

- Phn ng kh ha cacbon l phn ng thu nhit. Vy khi nng cao nhit , phn ng cho

ta nhiu CO.

1 4.2. Nhit nghc ca phn ngchy cacbon .

Phng trnh nhit ng hc.


25/236

113,98916

lg

48,174170711

069,929502

lg

71,173566108

156,911670

lg

31,175223431

044,020586

lg

84,0394142

)4(

0)4(

)3(

0)3(

)2(

0

)2(

)1(

)1(

!

!(

!

!(

!

!(

!

!(

TK

TG

TK

TG

TK

TG

TK

TG

p

p

p

p

o

T th (l-6) chng ta c th nhn xt rng.

ng (2) chng t rng, nhit cng tng th gi tr (G0T cng nh. c ngha l nhit

cao CO tn ti cng nhiu.

- ng (2) v (3) ct nhau nhit 978oK.

iu chng t rng nhit bn ca CO v CO2 bng nhau. V (G0(2) = (Go(3)

T> 978oK(Go(2) < (Go(3). nhit cao hn 978

oK kh CO bn hn CO2.

T < 978oK(Go(2) > (Go(3) c ngha l nhit thp, kh CO2 bn hn khi CO.

ng (3) khi nhit tng th (G0 tng. Vy khi nhit tng i lc CO vi oxy gim.

Suy ra trong l cao phn ng hon nguyn gin tip bng kh CO ch xy ra nhit thp ( thn

l).

Trong iu kin tha oxy (ng cong (2)) khi nhit tng (G0T gim qu trnh chy tin

hnh hon ton.Nh vy qu trnh chy cacbon c th tin hnh trong iu kin tha oxy hay tha cacbon

(thiu cacbon, hay thiu oxy). Nhng d cho qu trnh chy c tin hnh theo cch no v c nhng

phn ng trung gian no i chng na th thnh phn cui cng ca sn phm chy cng s do s

cn bng ca hai phn ng sau y quyt nh:

Tha oxy (thiu cacbon) 2CO + O2 = 2CO2


26/236

Thiu oxy (tha cacbon) C + CO2 = 2CO

Kt qu nghin cu nhit ng hc h thng C-O cho php ta i n kt lun chung nh sau:

Trong iu kin tha cacbon (thiu O2) nhit cao hn 1300oK (trn 1000oC) th sn

phm chy duy nht l CO. Nhit cng gim th lng CO2 cng nhiu v t ti 40% 970 -

980oK.

Trong trng hp tha oxy nhit n 1700 - 1800 oK th cacbon v CO chy hon ton

thnh CO2 nhit cao hn bn cnh CO2 cn c CO (hoc khng chy m nm trong sn phm

cui cng). nhit cao pha kh cha rt nhiu CO mc d tha oxy.


27/236

1. 4.3. Nhit nghc ca phn ngkh ha cacbon (phn ngBen -la Bu.oa)

Phn ng ny c ngha thc t rt quan trng i vi nhiu qu trnh luyn kim. Phn ng

kh ha cacbon l phn ng thun nghch. Theo nguyn l chuyn dch cn bng ca Lsactli ta

cng thy s b rng: Nhit tng cho ta nhiu CO, p sut tng pha kh cho nhiu CO2

nh hng ca nhit n cn bng ca phn ng kh ha cacbon

C + CO2 = 2CO (l-27)

Bc t do C = K P + 2 = 2 2 + 2 = 2

V vy %CO (%CO) = f(T, P)

KP =2

2

CO

CO

P

P(1-28)

Bng 1-4 . Hng s cn bng ca phn ng khi P = 101325Pa

KP(1-27)

T0, K Cgrapht Cv nh hnh

800

900

1000

1200

1400

-2,03

-0,78

+0,20

+1,68

+2,74

-1,85

-0,68

+0,27

-

0

28,99001lg !T

KpCgraphit

P = 101325Pa T = 978oK, bn ca CO v CO2 bng nhau.

T > 978oK bn ca CO ln hn CO2

T < 978oK bn ca CO2 ln hn CO.


28/236

ng cong biu din thnh phn pha kh cn bng CO, CO2 ca phn ng ph thuc vo

nhit to thnh hai vng:

Vng I : tha CO so vi CO cn bng

Vng II : tha CO2 so vi CO2 cn bng

Ly im a trong khu vc I. Nu nh T = const ta c im a:

%CO = m v a c % CO = m. T ta thy %CO(a) > % CO(a)

V vy vng I s xy ra qu trnh:

2CO p CO2 + C

vng ny cacbon l pha bn vng. V vy trong iu kin khng th tin hnh c

phn ng kh ha cacbon (thnh CO) di bt k hnh thc no (v d phn ng hon nguyn trc

tip oxit kim loi bng cacbon rn MeO + C = Me + CO khng th tin hnh c)

Trong vng II ta ly im b. Nu T = const ti b ta c % CO2 = n v b ta c % CO2 = n

v:

% CO2(b) > % CO2(b')

V vy qu trnh s xy ra:

CO2 + C = 2CO.

- Nu qu trnh xy ra trong iu kin ng nhit (T = const) v ng p (P = const) th a s

chuyn dch theo chiu a p a' gp ng cong ng p P = const. im b s dch chuyn theo

b p b n P = const.

- Nu trong iu kin on nhit, ng p th h s t nung nng theo ng a p a" do s

phn ly 2CO p CO2 + C.- Nu thc hin trong iu kin ng nhit, ng tch th v phn ng phn ly CO l phn

ng lm gim s phn t kh trong h, nn p sut ca h thng gim i. V th mt mt im a di

chuyn theo chiu a p a' gim CO i, nhng mt khc ng cong cn bng ng p cng

khng cn nm v tr ng vi p sut ban u cho ca h na m phi dch chuyn xung n

v tr mi tng ng vi p sut ca pha kh khi cn bng thp hn so vi p sut ban u. im

gp nhau ca a p a' v ng cong chnh l trng thi cn bng ca h iu kin .

Trong trng hp nh vy ta c th tnh c thnh phn ca pha kh cn bng theo tr s

Kp nu nh bit c thnh phn ban u (CO v CO2) ca h. V d nh khi chuyn t trng thi

ban u (c thnh phn l pCO2 V pCO) sang trng thi cn bng c PCO2 v PCO th p sut ring

phn ca CO s gim i mt lng l x v nh vy p sut ring phn ca CO2 s tng ln mt

lng l O,5x. Do khi cn bng ta c:

PCO = pCO - x ;

PCO = pCO2 + O,5x


29/236

)5,0(

)(

22

22

xp

xp

P

PK

CO

CO

Co

COP

!!

Gii phng trnh ta c:

x = pCO + 0,25KP - pCOCOpCO KppKp222

2)25,0(

- Nu trng thi ban u ca h

P = pCO + pCO2 = 101325Pa

Vi PCO = 101325Pa, pCO2 = 0 v Kp = 1 ( 9730K) ta tnh c x = 0,5. Vy thnh phn pha

kh cn bng 9270K l

PCO = 50662Pa

PCO2 = 25331Pa

P = PCO + PCO2 = 50662+ 25331 = 75993Pa


30/236

b. nh hngca p sut n cn bngca phn ngkh ha cacbon

Phn ng tin hnh trong iu kin c hai pha (pha kh CO, CO2 v pha rn C), phn ng li

thay i th tch. Vy khi p sut thay i s lm cho thnh phn cn bng kh thay i.

Xy dng gin quan h % CO, %CO2 vi nhit khi p sut thay i ta thy rng: khi

p sut gim th nhng ng cong phi nm di ng p sut cao, c nh vy mi tha mn

iu kin T = const nu P1 > P2 > P3 th %CO(1) < %CO(2) < %CO(3)S ph thuc gia hng s cn bng v nhit c biu din bng phng trnh.

)(2

2

TfP

PK

CO

COP !!

T phng trnh ny c th tm thy s ph thuc thnh phn cn bng vo p sut chung

ca h.

P = PCO + PCO2

PCO = P PCO2 (1-29)

Gii h phng trnh (1-28), (1-290 ta c:

PKKK

P ppp

CO .42

2

!

PKKK

PP ppp

CO .42

2

2!

5 2

7

C

Nh vy r rng rng mt nhit nht nh (ng vi mt gi tr KP nht nh) v mt psut P th ta hon ton c th tnh c thnh phn pha kh cn bng. Da vo phng trnh ny ta

cng thy c thnh phn cn bng' ca pha kh ph thuc vo nhit v p sut (hnh 1-8, l-9).

c) nh hngca trngthi cacbon n cn bngca phn ng

Kt qu thc nghim xc nh rng, phn ng ha cacbon ph thuc vo trng thi cacbon

(GoT= 2Go

CO GoCO2 - G

oC


31/236

T

GGG

T

G

P

PK

o

COo

COo

Co

T

CO

COp 576,4

2

576,4lglg 2

2

2 !

(!!

i Vi GoC ta c th tnh c:

GoC = GoCth tch + G

oCb mt

Hay

GoC = NCQC th tch + CCL

FW

Nc - s nguyn t cacbon trong mt phn t gam

W C - sc cng b mt cacbon

QCth tch - l th nhin ng th tch ca mt tinh th cacbon.

Lc - l kch thc ca tinh th cacbon c dng mt hnh lp phng vi cnh l Lc.

CLF

l din tch b mt th tch ca mt phn t gam cacbon. Vy:

T

GGL

FN

P

Po

COo

COCC

CthtichC

CO

CO

576,4

2.

lg2

2

2

!

WQ

i vi cacbon trng thi grapht tinh th th i th LC ln nn tr s 0pCL

Fta c th

b qua gi tr ny. Lc G0

C = NCQC th tch .Tc l th nhit ng ca cacbon c gi tr cc tiu,

cn i vi cacbon dng v nh hnh c ht nh (LC nh) nn tr s CCL

FW ln. Ta khng th

b qua c.. Do kt qu trong hai trng hp khc nhau, ta c gi tr Kp khc nhau.

Vy s chuyn bin ca cacbon t dng v nh hnh sang dng grapht c nh hng r rt

n thnh phn cn bng kh.

lgKp v nh hnh = 133,310.423,010.260,0lg576,48138 262 TTT

T

lgKpgraphit = 28,99001 T

Bng 1-5: Gi tr hng s cn bng (KP) ca phn ng C + CO2 = 2CO

Nhit , 0K Cgrapht Cv nh hnh

800

900

-1,971

-0,721

-1,85

-0,68


32/236

1000

1200

1500

2000

-0,279

1,779

3,279

4,780

-0,27

-

-

-

Trong trng hp k n hot tnh ca cacbon

CCO

COP

aP

PK

.2

2

!

Nu aC > aC (gi s c hai loi than)

Th

"

22

22

CO

CO

CO

CO

P

P

P

P

Nh vy tng hot tnh ca cacbon s lm tng hm lng CO trong pha kh, ngha l tng

phn ng kh ha cacbon.

Phn ng kh ha cacbon c tc dng rt quan trng i vi qu trnh luyn kim. V d trong

l cao kh l i t di ln trn n na trn ca thn l cha nhiu CO hn so vi pha kh cn bng

iu kin , nn CO s phn ly thnh CO2 v C mui (v c Fe mi c hon nguyn lm xc

tc): Cmui to thnh ng li trong cc khe h ca cc qung hoc trong gch chu la lt tng l

ngy cng nhiu, lm cho qung b v vn, tng l mau b ph hng.

phn di ca l, khong t thn l tr xung phn ng tin hnh v pha to thnh CO

(tc l theo chiu kh ha cacbon). C ngha l vng ny rt thun li cho phn ng hon nguyntrc tip oxit kim loi bng cacbon pht trin .

vng nhit cao nh ni l th phn ng C + CO 2 = 2CO thc t ch tin hnh v pha

to thnh CO v phn ng ny l phn ng quyt nh thnh phn sn phm chy than cc trong l.

1 4.4. Phn nggia cacbon v hinc

Trong qu trnh luyn kim, phn ng gia cacbon v hi nc cng thng gp. Phn ng

kh ha cacbon bng hi nc c th tin hnh bng hai phn ng sau:

C + H2Oh = CO + H2 (1-30) (Ho298(1-30) = 140251J

C + 2H2Oh = CO2 + 2H2 (1-31) (Ho298(1-31) = 109791JC hai phn ng u thu nhit nn khi tng nhit u pht trin theo hng kh ha

cacbon bng hi nc. Nhng (Ho298(1-30) > (Ho298(1-31) Vy nhit cng tng th phn ng ( 1-30)

pht trin mnh hn (hnh 131)

Bc t do : C = K - P + 2 = 3 - 2 + 2 = 3

Vy (%H2) = f(T, P, %H2O)


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Phng trnh nhit ng c th tnh ton qua hai phn ng sau y:

(l) C + CO2 = 2CO

(2) H2O + CO = H2 + CO2

Cng phn ng (1) v (2) ta c phn ng (1-30), (l-31)

Vy:

(Go(1-30) = (Go(1) + (Go(2)

lgKP(1-30) = lgKP(1) + lgKP(2) , do KP(1-30) = KP(1) . Kp(2)

(Go(1-31) = (Go(1) + 2(G

o(2)

lgKP(1-31) = lgKp(1) + 2lgKP(2), do Kp(1-31) = KP(1) . K2P(2)

(Go(1-30) = 140251 146,36T

lgKP(1-30) = 644,77325

T

(Go(1-31) = 109791 118,24T

lgKP(1-31) = 176,65734

T

Nhn xt :

- Phn ng (1-30) sn phm u l kh c th chy c v u c th lm cht hon nguyn.

Cn phn ng (1-31) ch c H2 l kh chy v lm cht hon nguyn. C hai u tin hnh ng thi,

sn phm kh l CO, CO2, H2.

S pht trin ca mi phn ng ph thuc vo nhit . N tun theo nh lut chung ca s chy

cachon (CO bn nhit cao, CO2 bn nhit thp).

T : l083oK th kh nng ca phn ng (1-30) bng (l-31)

T > 1083oK th kh nng ca phn ng (1-30) tin hnh mnh hn phn ng (1-31)

T < 1 083oK th ngc li.

- T hai phn ng trn ta cng c phn ng kh nc:

o

Hnh 1 6: (GTT0 ca phn ng trong h C O - H


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H2 + CO2 = H2O + CO

Nhng iu nhn xt trn ph hp vi phn ng kh nc

Khi c mt C v CO2 ta cng c phn ng kh ho cacbon

C + CO2 = 2CO

Vy khi c mt C v H2O hi s xy ra bn phn ng nu trn, nhng phn ng kh

nc v phn ng kh ha cacbon s quyt nh thnh phn cn bng ca phn ng gia C v H2O

hi.

T gin ca phn ng kh nc, khi c mt cacbon s c phn ng kh ha cacbon (hnh

l-11). Nh vy thnh phn cn bng ca sn phm kh cui cng phi tha mn hai phn ng trn

chnh l im gp nhau ca hai trng biu din ca phn ng kh nc v phn ng ng kh ha

cacbon (ty theo nhit v p sut). Vy :

Khi P = PCO + PCO2 = const th tng nhit s c ngha l di chuyn trng thi cn bng

ca h theo ng cong cn bng ng p dn ln pha trn, ct cc ng ng nhit nhng nhit

ngy cng cao. Do tr s a, b ngy cng ln.

iu chng t rng khi tng nhit th phn ng (1 -30) chim u th. nhit rt

cao tc dng ca phn ng (1-31) thc t khng cn. Nu gi nhit khng i, gim p sut th

tc dng cng tng t nh khi tng nhit v gi nguyn p sut.

1.5. C ch v ng hc ca s chy cacbon

1.5. 1. c trngnghc ca phn nggia cacbon v oxy

Phn ng gia cacbon v oxy (hay CO2 , H2O) u l phn ng d th tin hnh theo phng

thc :

Cht kh I + rn = cht kh II

V vy qu trnh tin hnh phn ng theo nhng quy lut ca phn ng d th bao gm cc

bc sau y:


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Bc 1 - Phn t kh I khuch tn n b mt vt rn. C ngha l s khuch tn oxy n b

mt cacbon.

Bc 2 - Phn t kh I b b mt vt rn hp ph: oxy b b mt cacbon hp ph.

Bc 3 - Cht kh I b hp ph phn ng vi vt rn: phn ng gia kh oxy vi cacbon.

Bc 4 - Sn phm trung gian tch ra to thnh cht kh II l sn phm phn ng. l CO 2

sn phm ny bi hp ph trn b mt cacbon rn.

Bc 5 - Cht kh II - CO2 c gii ph (nh ra) v khuch tn vo pha kh. Cc bc hp

ph phn ng ha hc, gii ph c lin quan mt thit vi nhau, nn thng thng ngi ta gi

chung ba bc l bc hp ph - phn ng ha hc.

Qu trnh thuc phm vi ng hc hay khuch tn l ty thuc vo quan h gia kh nng

tc phn ng ha hc hay tc khuch tn. Tc l ty thuc vo quan h gia hng s ng

hc v h s khuch tn (K/D).

1 5.2. C ch ca s chy cacbon rn

Khi cacbon v oxy tc dng vi nhau th ngoi phn ng

C + O2 = CO2 hoc C + O2 = 2CO thng cn c phn ng

CO2 + C = 2CO.

Trn thc t kh ngn nga c phn ng ny xy ra. V vy kh xc nh c ch phn

ng chy cacbon vi oxy. Thc t chy cacbon vi oxy thng qua s hp ph phn t oxy trn b

mt cacbon rn lm suy yu s lin kt trong phn t ca n, ng thi cng lm cho mng tinh th

cacbon b bin dng t nhiu, to thnh s lin kt khng bn vng, ln khi c mt phn t oxy khc

va p vo mng s b ph v, cc nguyn t cacbon v oxy mi c gii phng s cng vi phn

t oxy to thnh CO v CO2. nhit thp, trn b mt cacbon hp ph oxy s thot ra CO2 :

Cmng . O2(hph)p CO2(K)

nhit cao, s hp ph ha hc xy tin hnh trn b mt cacbon vo to thnh phc

cht.

2Cmng + O2(k) = 2Cmng . O(hph)

Phc cht s b phn hy khi phn t xy va p vo ch nguyn t cacbon lin kt yu nht

(t cacbon nht)

Cmng . O2(hph) + C (mng) + O2(k)p CO(k) + CO2(k)Biu din theo s cu to mng

O2

+ CO(k) + CO2(k)


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Hay c th vit

2[Cmng. O2(hph)] + C(mng) + O2(k)p 2CO(k) + CO2(k)

Hoc c th tin hnh phn ly nhit nhm phc cht khi ta tip tc nung n cao hn

na v cho ta hon ton CO.

Cmng .O2(hph)p CO2(K)

Biu din theo mng.

Trong qu trnh Cgraphit hp ph xy, nhng nguyn t cacbon bin gii c ha tr t do s

ng vai tr quyt nh trong vic hnh thnh cc phc cht b mt. Nhng nguyn t cacbon bn

trong mng tinh th ch c mt in t ha tr t do, cn ccbon bin gii ty theo s lin kt ca

chng trong mng tinh th m c hai hoc ba ha tr cha bo ha. V th cacbon graphit c tnh

hp ph kh mnh. Ngoi ra nhng sai lch trong cu trc tinh th ca graphit cng lm tng kh

nng hp ph ca n ln rt nhiu.

1 5.3. nghc v c ch ca phn nggia caebon vi CO2

- ng hc: phn ng gia cacbon vi CO2 c mt ngha ht sc quan trng trong qu

trnh luyn kim. N c tc dng quyt nh thnh phn pha kh khi t chy nhin liu rn trong

iu kin tha cacbon, c bit l i vi qu trnh l cao v l sinh kh. Kt qu nghin cu xc

nhn rng : tc phn ng ph thuc vo nhit , p sut, tc dng kh CO 2 trng thi caebon,

xc tc.v.v..

Bc phn ng iu kin p sut bnh thng (P = 101325Pa) l bc 1. Vy.

2,COVV = K .

2COP

Thc nghim xc nhn rng nhit cao hn 1073oK th tc ca qu trnh kh ha

cacbon mi ng k. Nhit ln hn 12730K tc qu trnh kh ha cacbon rt ln.

Nu nh trong cacbon c mt nhng kim loi Na, K, Ca, Ba, Ni, Mn, chng s c tc dng

lm xc tc cho phn ng kh ha cacbon v tc qu trnh tng ln. Gii thch iu ny l do

Biu din theo mng

+ 2CO(k) + CO2(k)

O2

+ CO(k)


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nhng kim loi xm nhp vo mng cacbon, lm cho mng d b ph hy, to iu kin cho

kh CO2 hp ph trn b mt cacbon cng nhiu.

Tc dng kh CO2 cng ln th tc kh ha cng tng, v khc phc c tr lc ca

khuch tn ngoi. Nhng tc dng kh cng ch tng ln n mt gii hn no , nu khng s

tng tr lc khuch tn trong.

C ch : C th biu th c ch phn ng kh theo s sau :

+ Trc tin CO2 b hp ph trn b mt cacbon to thnh 2 nhm k ten v k tn :

2C(mng) + CO2(k)p C(mng) + O(hph) + C(mng).CO(hph)

Biu din theo mng:

+ nhit 500-600oC nhm K ten khng bn vng, b phn ly (nhng cacbon khng b

ph v mng).

Cmng . CO(hph) p C(mng) + CO(k)

Tng nhit ln, nhm Ktn kt hp cht ch vi b mt cacbon nn khi b phn ly ng

thi mng tinh th cacbon b ph v.

Cmng .O(hph)p C(mng) + CO(k)

+ Kh CO2 trong pha kh va p vo b mt cacbon, ph v nhm ktn v mng cacbon: C

th chia ra lm hai loi c ch va p

k tn k ten

(K)

+ CO(K)


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Trng hp th nht cc phn t kh CO2 ch ph v nhm Ktn phn b trn b mt tinh

th, gii phng chng vo pha kh, cn CO2 hon ton khng b ph v.

Cmng .O(hph) + CO2(k)p C(mng) + CO(K) + CO2(K)

Trng hp th hai, khi va p vo b mt, cacbon cng b ph v bin thnh CO tr v pha

kh, cn nguyn t oxy th b gi li trn b mt cacbon rn, to thnh nhm Ktn vi nguyn t

cacbon nm l ra ngoi.

Cmng . O(hph) + CO2(K)p C(mng) O(hph) + 2CO(K)

Ni chung phn ng C + CO2 = 2CO chu nh hng ca nhiu nhn t, nhng ch yu l

nhit , p sut, trng thi vt l ca cacbon v cc tp cht trong cacbon. Hot nng ca phn ng

ph thuc vo bn ca mng tinh th cacbon. Mng cacbon cng khng hon chnh, cc tp cht

trong mng cng nhiu lm mng cng bin dng. Do lm suy yu s lin kt trong mng tinh

th, nguyn t cacbon d dng tch ra khi mng.

nhit cao, qu trnh cn ph thuc vo s khuch tn CO2 n b mt cacbon v phthuc vo xp ca cacbon.

1 5.4. nghc v c ch phn ngphn ly CO

Phn ng : 2CO p CO2 + C

Thc t phn ng c th xy ra trong khong nhit 573-1173 oK, mnh nht l 773-

873oC. Nhng do s lin kt trong CO rt cht ch (nhit to thnh CO l 10.000J/phn t gam) cho

nn s phn ly CO i hi phi c cht xc tc. Cht xc tc mnh nht l Fe sau n Co, Ni.

Ngoi ra Cr, Mn, Al, Ti cng c tc dng xc tc cho phn ng ny. Cc cht xc tc hp th trnb mt lm suy yu s lin kt trong phn t CO. Do khi mt phn t CO khc n va p vo

th n rt d tc dng vi nguyn t xy v li nguyn t cacbon trn b mt cht xc tc (hnh l-

12). Lng cacbon do phn ng phn ly CO tit ra trn b mt xc tc rt ln. C khi gp hng

chc ln trng lng xc tc. Qua nghin cu ca Chupharp v Antnp

2 CO(K)2


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thy rng tc phn ly t l thun vi p sut ca n. Ngha l phn ng c bc mt vi

CO

Khi ly Fe lm cht xc tc th nng lng hot ha

E = 142259J/phn t gam

Do tc phn ly c biu din theo phng trnh:

COT PeKV .

142259

0

!

Tc l CO ch tham gia phn ng ha hc bng mt phn t CO. Cn mt phn t CO th

hai th tham gia vo qu trnh hp ph phn ly. Chnh v th nn phi c cht xc tc mi tin hnh

c.


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V cht xc tc ng vai tr quyt nh trong phn ng phn ly CO nn c ch gm hai

bc:

Bc 1: CO hp ph trn b mt cht xc tc Fe.

Fe(kt tinh) + CO(K) = Fe(kt tinh) . CO(ph)

Bc 2: To thnh CO2 khi mt phn t CO trong pha kh n va chm vo b mt cht xc

tc ca st nh sau:

Fe(kt tinh) . CO(hph) + CO(K) = Fe(kt tinh) .C + CO2

Khong cch gia cc ht nhn nguyn t trong phn t CO l 1,14 A, cn khong cch

gia cc nguyn t trong mng tinh th st (hng s mng) 773 873 oK l 2,89Q

% . Khi CO b

hp ph trn b mt st th khong cch gia cc ht nhn phn t CO b dn ra lm cho mi lin

kt trong phn t ca n suy yu i. Lc cc phn t CO khc c th ly xy i mt cch ddng khi n va p vo CO hp ph v li cacbon trn b mt st (hnh 1- 12).

Phn ng phn ly CO khi c mt ca cht xc tc l Fe c tc hi rt ln v l mt hin

tng tt nhin s xy ra trong mt s qu trnh luyn kim. V vy ng thi vi vic nghin cu v

c ch ng hc ca phn ng, ngi ta cn tm cch hn ch phn ng, tc l tm cch gim tc

dng xc tc ca cht xc tc.

Ngi ta thy rng, nu cho thm mt t sulphat ng th tc dng xc tc ca st gim i

v nu cho vo 5% th st hon ton mt tc dng xc tc cho s phn ly CO Tc dng ca cc cht

sulfua cng th.

Kt qu nghin cu cho thy rng, nguyn nhn lm mt tc dng ca cht xc tc l do

sulfua v sufat ng b hon nguyn to thnh lu hunh ny tc dng vi st to thnh sulfua st,

tiu dit cc trung tm hot tnh.


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Ch-ng 2

Qu trnh phn ly oxit, cacbonatv sunfua kim loi

2.1. i lc ho hc v bn nhit ng hc ca oxit, cacbonat vsunfua.

D-i tc dng ca nhit cao, nhiu hp cht ho hc b phn hu (hay phn li) to ra cc cht hoc hp cht n gin hn. Nung vi l mt trong nhng th din hnh ca qu trnh phn li. Nguyn nhn dn n s phn li hp cht l do ngunnhit cung cp t bn ngoi lm tng nng l-ng dao ng nhit ca cc thnh phn(phn t, nguyn t hoc ion) cu thnh hp cht n mc v-t qu nng l-ng lin kt banu gia chng.

Cc hp cht khc nhau c bn nhit ng hc khc nhau. Bc (Ag), thu ngn(Hg) oxit b phn li nhit 300 - 400 0C v tit ra kh oxi, trong khi nhm (Al) v

canxi (Ca) oxit hu nh- khng b phn hu ngay c nhit gn 2000 oC. Trong s ccsunfua th CaS l hp cht bn vng nht, ng-c li CuS km bn nht.

S d c s khc bit nh- vy l v bn ca cc hp cht ny -c quyt nhbi i lc ho hc ca kim loi vi oxi v l-u hunh. Theo Van't Hoff th-c o i lc ho hc lcng hu ch ti a -c gii phng t phn ng ho hc tin hnh theo chiu nghch.Cng ny ng bng s gim nng l-ng t do hay en talpi t do hoc cn gi l nng l-ngGibbs (k hiu ca Lin X c l Z, M l F, cc n-c chu u l G) trong iu kin nhit v p sut khng i.

(i lc)p,T = - (G (2-1)

Nu biu th:(G = (H - T.(S (2-2)

,trong (H v (S l s thay i nhit hm v entropi trong phn ng, T l nhit [K], th

(i lc)p.T = -(H + T.(S (2-3)

T ph-ng trnh (2-3) cho thy, nhit t-ng i thp, nhit hm (H c nhh-ng r rt ti i lc, cn nhit cao l thnh phn entropi T. (S. i vi cc phn ngto nhit mnh do (H >> T. (S, nn c th coi nhit hm l th-c o ca i lc. Du ca(S c ngha quyt nh ti s ph thuc ca i lc vo nhit . Nu (S < 0, i lc sgim khi nhit tng v ng-c li.

Trn cc hnh (2-1), (2-2) v (2-3) m t ph thuc nhit ca th nhit ng sinhthnh oxit, cacbonat v sunfua, trong :

- A, B, C, D ch dung sai nhit: A s 1 kcal, B s 3 kcal, C s 10 kcal, D > 10 kcal- K hiu nguyn t v oxit t-ng ng cc nhit khc nhau:


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Nguyn t Oxit

- Nhit nng chy M [M]- Nhit si B [B]- Nhit thng hoa S [S]- Nhit bin i pha trng thi rn T [T]

Nhit [0C]

(G0

st[kcal]


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Hnh 2-1:Ph thuc (G0st ca cc oxit vo nhit

1. CaCO3 = CaO + CO2

2. MgCO3 = MgO + CO2

3. FeCO3 = FeO +CO24. CaMg(CO3)2 = CaO + MgO + 2CO2

5. CaCO3 +Fe2O3 = CaO. Fe2O3 + CO2

6. 2CaCO3 + Fe2O3 = 2CaO. Fe2O3 +

2CO2

7. 2CaCO3 + SiO2 = 2CaO. SiO2 +

2CO2

Hnh 2-2:Ph thuc (G0st cu cacbonat vo nhit

p

(G

0st[103kJ/kmol]

p Nhit [0C]

p Nhit Hnh 2-3:Ph thuc (G0st ca sunfua vo nhit


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Ph-ng trnh t-ng ng dng cho tnh ton nhit ng sinh thnh oxit v sunfuatrong cc khong nhit cho tr-c -c trnh by trong cc bng (2 -1),(2-2). K hiu x - l dung sai ca (G0st trong phm vi s 10 kcal/mol oxi hoc l-u hunh.

T cc hnh (2-1), (2-2) v (2-3) thy rng, cc -ng biu din (G0st = f (T)chuyn mt cch c quy lut v pha cc tr s m hn theo chiu tng i lc ho hcca kim loi vi O2, CO2 v S2. Nh- vy phn trn gin tp trung cc hp cht kmbn, cn phn d-i l cc hp cht rt bn. Quy lut nhit ng hc ny l c s quan

trng cho vic gii quyt nhiu v luyn kim. Chng hn, i vi oxit, nu kim loino c i lc i vi oxi ln hn th c th ly oxi t oxit km bn hn (MeO), hay ni cchkhc kim loi ny (Me') c kh nng hon nguyn oxit km bn theo phn ng.

MeO + Me' = Me'O + Me

y chnh l c s ca ph-ng php hon nguyn nhit kim v qu trnh kh oxitrong thp.

Nu mt nguyn t no c kh nng to ra nhiu oxit, th oxit ho tr thp nhtca nguyn t ny c bn ln nht. S gim bn ca cc oxit st theo th t FeOp Fe3O4p Fe2O3 l mt th d minh ho. Kinh nghim thc t ch r, cc oxit kim loiho tr cao hon nguyn d dng hn so vi oxit ho tr thp.

T-ng t nh- oxit, nhng sunfua bn hn c th phn hu cc sunfua km bn.

Kh nng ca Ca v Mg to thnh cc sunfua rt bn -c s dng cho qu trnh kh l-uhunh trong gang v thp.

2.2. Cn bng ho hc trong cc phn ng phn li

Cng nh- nhiu qu trnh ho hc khc, nhng iu kin x c nh, trng thi cnbng ca phn ng phn li s -c thit lp, tc l tc phn ng theo chiu thun vtheo chiu nghch bng nhau. Trng thi ny -c c tr-ng bi mt i l-ng khng iv gi l hng s cn bng K p. Tr s Kp gip ta bit r cn bng chuyn v pha no,mc thc hin phn ng, bn vng v l-ng cc sn phm cui cng ti a c ththu -c.

Bng 2-1: Ph-ng trnh nng l-ng t do tiu chun ca cc oxit

(G0T = A + BTcal/mol O2

Phn ng A BKhong nhit

K(1) (2) (3) (4)

4/3 Al(s) + O2(g) = 2/3 Al2O3(s) - 266330 49,81 298 - 931,74/3 Al(l) + O2(g) = 2/3 Al2O3(s) - 268200 51,89 931,7 - 2000

4/3 Sb(s,l) + O2(g) = 2/3 Sb2O3(s) - 111810 42,03 293 - 9284/3 Sb(l) + O2(g) = 2/3 Sb2O3(l) - 104800 34,70 928 - 1698

4/3 Sb(l,g) + O2(g) = 1/3 Sb4O6(g) - 154420 65,64 1698 - 2000

4/5 Sb(s) + O2(g) = 2/5 Sb2O5(s) - 91100 44,04 298 - 903

4/5 Sb(l) + O2(g) = 2/5 Sb2O5(s) - 88410 41,18 903 - 1500

4/3 As(s) + O2(s) = 2/3 As2O3 (s) - 104400 42,38 298 - 542

4/3 As(s) + O2(s) = 2/3 As2O3 (l) - 97570 29,77 542 -730,3

(1) (2) (3) (4)4/3 As(s) + O2(g) = 1/3 As4O6(g) - 92030 22,13 730,3 - 8831/3 As4(g) + O2(g) = 1/3 As4O6(g) - 102820 34,33 883 - 2000


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4/5 As(s) + O2(g) = 2/5 As2O5(s) - 87470 45,78 298 - 8831/5 As4(g) + O2 (g) = 2/5 As2O5(s) - 82310 51,33 883 - 2000

2 Ba(s) + O2 (g) = 2 BaO(s) - 265840 44,72 298 - 977

2 Ba(l) + O2 (g) = 2 BaO(s) - 266800 45,74 977 - 1911

2 Be(s) + O2 (g) = 2 BeO(s) - 285800 46,26 298 - 15562 Be(l) + O2(g) = 2 BeO(s) - 284720 46,72 1556 - 2000

4/3 Bi(s) + O2(g) = 2/3 Bi2O3(s) - 98330 42,17 298 - 5444/3 Bi(l) + O2(g) = 2/3 Bi2O3(s) - 94030 46,63 544 - 1090

4/3 Bi(l) + O2(g) = 2/3 Bi2O3(l) - 85370 38,86 1090 - 1600

4/3 B(s) + O2 (g) = 2/3 B2O3(s) - 203410 42,01 298 - 723

4/3 B(s) + O2(g) = 2/3 B2O3(l) - 197090 33,61 723 - 2000

2 Cd(s) + O2(g) = 2 CdO(s) - 124280 47,12 298 - 594

2 Cd(l) + O2(g) = 2 CdO(s) - 126980 51,66 594 - 10382 Cd (g) + O2 (g) = 2 CdO(s) - 171780 95,08 1038 - 2000

2 Ca(s) + O2(g) = 2 CaO(s) - 300940 48,94 298 - 1124

2 Ca(l) + O2(g) = 2 CaO(s) - 304040 51,60 1124 - 17602 Ca(g) + O2(g) = 2 CaO(s) - 375960 92,42 1760 - 2000C(s) + O2(g) = CO2(g) - 94260 -0,27 298 - 2000

4/3 Cr(s) + O2(g) = 2/3 Cr2O3(F) - 180870 41,21 298 -1823

4/3 Cr(s) + O2(g) = 2/3 Cr2O3(F) - 186130 44,00 1832 - 2000

2 Co(E, K, F, l) + O2(g) = 2 CoO(s) - 1 37,30 298 - 2000

4 Cu(s) + O2(g) = 2 Cu2O(s) - 79260 32,30 298 - 1357

4 Cu(l) + O2(g) = 2 Cu2O(s) - 86400 37,32 1357 - 15024 Cu(l) + O2(g) = 2 Cu2O(l) - 57020 17,82 1502 - 2000

2 Cu(s) + O2(g) = 2 CuO(s) - 73700 40,96 298 - 1357

2 Cu(l) + O2(g) = 2 CuO(s) - 74600 41,32 1357 - 17202 Cu(l) + O2 (g) = 2 CuO(l) - 66220 36,42 1720 - 2000

2 Ge(s) + O2(g) = 2 GeO(s) - 121200 38,32 2 98 - 1200

4/3 Au(s) + O2(g) = 2/3 Au2O3(s) - 290 42,53 298 - 5002 H2(g) + O2(g) = 2 H2O(g) - 117700 26,24 298 - 2000

4/3 In(s) + O2(g) = 2/3 In2O3(s) - 147700 50,40 298 - 429,6

4/3 In(l) + O2(g) = 2/3 In2O3 (s) - 148790 53,44 429,6 - 2000

2 Mn(l) + O2(g) = 2 MnO (s) - 194720 42,24 1517 - 2000

2 Hg(g) + O2 (g) = 2 HgO (s) - 12940 50,36 298 - 630

2 Hg(g) + O2 (g) = 2 HgO (s) - 66280 88,24 630 - 1500Mn(s) + O2 (g) = MnO2 (s) - 131530 33,95 298 - 2000

(1) (2) (3) (4)

2 Ni(s, l) + O2 (g) = 2 NiO (s) - 114740 44,18 298 - 20004/5 P(s,l) + O2(g) = 1/5 P4O10(s) - 144510 45,42 298 - 553

1/5 P4(g) + O2(g) = 1/5 P4O10(g) - 141500 41,00 631 - 1800

4 K(s,l) + O2(g) = 2 K2O(s) - 175060 74,88 298 - 10494 K(s) + O2(g) = 2 K2O(s) - 248580 145,24 1049 - 1500


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Se(s) + O2(g) = SeO2(s) - 54940 44,83 298 - 490Se(l) + O2 (g) = SeO (s) - 55940 46,86 490 - 595

Se(l) + O2 (g) = SeO(g) - 35170 11,88 595 - 1027

1/2 Se2(g) + O2(g) = SeO2 (g) - 48530 24,94 1027 - 2000

2 Si(s) + O2 (g) = 2 SiO(g)

*

- 45200 -39,42 298 - 1683

2 Si(l) + O2 (g) = 2 SiO(g) - 72300 -23,02 1683 - 2000Si(s,l) + O2 (g) = SiO (s) - 208390 41,42 298 - 1683

2 Fe(E, F, K) + O2(g) = 2 FeO(s) - 114140 38,41 298 - 900

2 Fe(K,H,l) + O2(g) = 2 FeO(l) - 132830 35,68 900 - 1803

3/2 Fe(E) + O2(g) = 1/2 Fe3O4(E) - 130600 32,21 1803 - 2000

3/2 Fe(E) + O2(g) = 1/2 Fe3O4(F) - 124120 40,92 298 - 950

3/2 Fe(l) + O2(g) = 1/2 Fe3O4(F, l) - 130300 38,87 950 - 1179

4/3 Fe(E) + O2 = 2.4 Fe2O3(E) - 128530 38,75 1179 - 1800

4/3 Fe(E, F) + O2(g) = 2/3 Fe2O3(F, - 128360 46,18 298 - 1159

4/3 Fe(K, H) + O2(g) = 2/3 Fe2O3(K) - 103800 37,14 1159 - 1745

2 Pb(s, l) + O2(g) = 2PbO(s) - 93260 -24,50 600,5 - 20002 Pb(l) + O2(g) = 2 PbO(l) - 14180 69,74 298 - 1600

2 Pb(l) + O2(g) = 2 PbO(g) - 289420 51,82 298 - 923

4 Li(s,l) + O2(g) = 2 Li2O(s) - 286000 56,20 923 - 1393

2 Mg(s) + O2(g) = 2 MgO(s) - 290830 99,68 1393 - 2000

2 Mg(l) + O2(g) = 2 MgO(s) - 352060 35,74 298 - 1517

2 Mg(g) + O2(g) = 2 MgO(s) - 184980 46,91 1683 - 1983

2 Mn(s) + O2(g) = 2 MnO(s) - 217780 28,98 298 - 1000Si(l) + O2(g) = SiO2(s) - 13440 69,22 298 - 1187

4 Ag(s) + O2(g) = 2 Ag2O(s) - 200480 127,70 1187 - 20004 Na(s,l) + O2(g) = 2 Na2O(s) - 269260 -2,50 298 - 2000

4 Na(g) + O2(g) = 2 Na2O(s) x - 7740 17,48 298 - 2000

S2(g) + O2(g) = 2 SO(g) x - 86520 26,06 298 - 15001/2 S2(g) + O2(g) = SO2(g) - 73030 42,37 298 - 723

1/3 S2(g) + O2(g) = 2/3 SO3(g) - 77180 46,15 723 - 1006

Te(s) + O2(g) = TeO2(s) - 79960 38,04 1006 - 1300

Te(l) + O2(g) = TeO2(s) - 71770 48,54 298 - 505

Te(l) + O2(g) = TeO2(l) x - 138730 48,92 505 - 1898

(1) (2) (3) (4)

Sn(s) + O2(g) = SnO2(l) - 138500 40,29 1898 - 2000Sn(l) + O2(g) = SnO2(s) - 122550 42,72 298 - 1150Sn(l) + O2(g) = SnO2(l) - 224900 41,93 1150 - 2000

Ti(E) + O2(g) = TiO2(s) - 224080 40,93 298 - 1500

Ti(F) + O2(g) = TiO2(s) - 136750 40,64 298 - 1500

W(s) + O2(g) = WO2(s) - 258650 40,15 298 - 1500U(s,l) + O2(g) = UO2 (s) - 212940 40,01 298 - 1400


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3/4 U(s,l) + O2(g) = 1/4 U3O8(s) - 193570 37,66 600 - 20002/3 U(s) + O2(g) = 2/3 UO3(s) - 194230 47,14 298 - 692,7

4/3 V(s) + O2(g) = 2/3 V2O(s) - 166200 51,10 692,7 - 1180

2 Zn(s) + O2(g) = 2 ZnO(s) - 168960 94,70 1180 - 2000

2 Zn(l) + O2(g) = 2 ZnO(s) - 220280 45,01 298 - 11352 Zn(g) + O2(g) = 2 ZnO(s) - 261030 44,40 1135 - 1478

Zr(E) + O2(g) = ZrO2(E) - 260430 42,87 1478 - 2000

Bng 2-2: Ph-ng trnh nng l-ng t do tiu chun ca cc sunfua

Go

T = A + BTcal/mol S2

Phn ng A B Khong nhit oK

(1) (2) (3) (4)4/3 Al(s) + S2 = 2/3 Al2S3 -131500 - 298

4/3 Sb(s) + S2 = 2/3 -57160 46,49 298 - 8212 Ba(s) + S2 = 2 BaS (s) -235570 46,11 298 - 977

4/3 Bi(s) + S2 = 2/3 Bi2S3(s) -58690 46,36 298 - 544

4/3 Bi(l) + S2 = 2/3 Bi2S3(s) -61020 50,58 544,5 - 1023

2 Cd(s) + S2 = 2 CdS(s) -99320 43,92 298 - 594

2 Cd(l) + S2 = 2 CdS(s) -100790 46,36 594 - 1038

2 Cd(g) + S2 = 2 CdS(s) -146800 90,66 1038 - 1273

2 Ca(E) + S2 = 2 CaS(s) -258870 45,62 298 - 673

2 Ca(F) + S2 = 2 CaS(s) -259100 45,92 673 - 1124

2 Ca(l) + S2 = 2 CaS(s) -263560 49,88 1124 - 1760

2 Ca(g) + S2 = 2 CaS(s) -336710 91,44 1760 - 20002 C(s) + S2 = 2 CS 81000 -42,00 298 - 2200C(s) + S2 = CS2 -3100 -1,73 298 - 1600

2 CO + S2 = 2 COS -45720 37,40 298 - 1500

2 Ce(s, l) + S2 = 2 CeS(s) -267000 40,00 298 - 2200

9/4 Co(s) + S2 = 1/4 -79240 39,81 298 - 1048

8/3 Co(s) + S2 = 2/3 Co4S3 -61900 23,21 1048 - 1153

(1) (2) (3) (4)

2 Cu2(E) + S2 = 4 CuS(s) -42960 48,46 298 - 376

2 Cu2(F) + S2 = 4 CuS(s) -45000 53,68 376 - 9004 Cu(s) + S2 = 2 Cu2S(E) -64960 20,17 298 - 376

4 Cu(s) + S2 = 2 Cu2S(F) -63420 14,95 376 - 1356

4 Cu(l) + S2 = 2 Cu2S(F,l) -50920 6,0 1356 - 1800

H2 + S2 = 2 HS 6000 0,0 298 - 22002 H2 + S2 = 2 H2S -43160 23,61 298 - 1800

4/3 Ir(s) + S2 = 2/3 Ir2S3 (s) -64500 44,66 1000 - 1600


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2' Fe'(s) + S2 = 2' FeS2' (s) -86700 90,0 600 - 11002 FeS(s) + S2 = 2 FeS2 -73600 68,00 600 - 1200

2 Fe(E) + S2 = 2 FeS (E) -74320 31,18 298 - 412

2 Fe(E) + S2 = 2 FeS (F) - 71820 25,12 412 - 1179

2 Fe(K) + S2 = 2 FeS (s) - 72140 25,48 1179 - 1463

2 Fe(K) + S2 = 2 FeS (l) - 60520 16,6 1463 - 1674

2 Pb(s) + S2 = 2 PbS (s) - 72710 34,17 298 - 6002 Pb(l) + S2 = 2 PbS (s) - 75160 38,25 600 - 1387

2 Pb(l) + S2 = 2 PbS (l) - 66840 32,25 1387 - 1500

2 Mg(s) + S2 = 2 MgS(s) - 199300 45,6 298 - 923

2 Mg(l) + S2 = 2 MgS(s) - 203600 50,3 923 - 1380

2 Mg(g) + S2 = 2 MgS(s) - 268700 97,5 1380 - 2000

2 Mn(E) + S2 = 2 MnS (s) - 18000 30,64 293 - 1000

2 Mn(F) + S2 = 2 MnS (s) - 129070 31,71 1000 - 1374

2 Mn(K) + S2 = 2 MnS (s) - 130160 32,50 1374 - 1410

2 Mn(H) + S2 = 2 MnS (s) - 138020 33,11 1410 - 15172 Mn(l) + S2 = 2 MnS (s) - 138020 37,72 1517 - 18032 Mn(l) + S2 = 2 MnS (l) - 125540 30,80 1803 - 2000

2 Hg(l) + S2 = 2 HgS (s) - 58570 51,16 298 - 630

2 Hg(g) + S2 = 2 HgS (s) - 86690 95,73 630 - 800

Mo(s) + S2 = MoS2 (s) - 52560 10,2 1073 - 1373

2 Ni(s) + S2 = Ni3S2 (s) - 75650 35,81 298 - 1000

2' Pt'(s) + S2 = 2 PtS2 - 43750 43,8 700 - 11002' Pt'(s) + S2 = 2' PtS' - 66100 43,6 1000 - 1700

Si(s) + S2 = SiS2 (s) - 50000 - 298

4 Ag(s) + S2 = 2 Ag2S (E) - 44800 22,10 298 - 4524 Ag(s) + S2 = 2 Ag2S (F) - 41980 16,52 452 - 1115

4 Ag(s) + S2 = 2 Ag2S (l) - 40380 15,09 1115 - 1234

4 Ag(l) + S2 = 2 Ag2S (l) - 51800 24,33 1234 - 15004 Na(s) + S2 = 2 Na2S (s) - 208000 56,1 298 - 371

(1) (2) (3) (4)

4 Na(l) + S2 = 2 Na2S (s) - 210500 62,9 371 - 11874 Na(g) + S2 = 2 Na2S (s) - 303000 140,8 1187 - 1192

4 Na(g) + S2 = 2 Na2S (l) - 300600 138,8 1192 - 1600

2 Sr(s) + S2 = 2 SrS (s) - 237000 - 298S2 = 2 S (rh) - 30590 37,75 298 - 573

S2 = 1/4 S8 - 24800 28,29 298 - 1300

S2 = 1/3 S6 22150 24,58 298 - 1300

S2 = 2 S (g) 77250 - 29,70 298 - 2200

W + S2 = WS2 - 62360 23,0 298 - 1400

2 Zn(s) + S2 = 2 ZnS (s) - 121130 45,40 298 - 6932 Zn(l) + S2 = 2 ZnS (s) - 123480 48,54 693 - 1180


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2 Zn(g) + S2 = 2 ZnS (s) - 178330 95,00 1180 - 1500

Phn ly oxit, cacbonat v sunfua l nhng phn ng ho hc d th. Khc vi cnbng ho hc trong cc h ng th, cn bng ho hc d th t n ti trong h bao gmnhiu pha v nhiu cu t. h thng ho cc trng thi cn bng trong nhng h phctp ny, c th s dng quy tc pha Gibbs -c biu th bng quan h sau y:

C = K - f + n,trong :C - l s bc t do, tc l thng s (nhit , p sut, nng ...) c th thay i

trong gii hn nht nh m khng dn ti s thay i s pha.K- tng s cc cu t khng ph thuc, thc cht l tng s cc nguyn t ring

bit cu thnh h tr i s ph-ng trnh lin kt cc nguyn t ny v i nhau.f - s pha.n - s cc yu t bn ngoi tc dng ln cn bng ca h. i vi cc qu trnh

luyn kim, trong s cc yu t bn ngoi th nhit v p sut ng vai tr c bitquan trng. Do vy n trong ph-ng trnh (2 -4) c th thay bng s 2.

C = K - f + 2 (2 - 5)Sau y chng ta hy s dng quy tc pha phn tch cn bng ho hc ca

mt s phn ng phn li.

a. Cn bng ca phn ng phn li canxi cacbonat.

Nu CaCO3 v CaO khng ho tan vo nhau trong phn ng:CaCO3 (s) CaO (s) + CO2 (g)

th f = 3 gm 2 pha ng-ng t l CaCO 3 v CaO cng pha kh CO2; s cu t K = 2 vCaCO3 -c to thnh t CaO v CO2. Nh- vy, h c mt bc t do (C = 2 - 3 + 2 = 1)ngha l trong gii hn nht nh, c th thay i hoc l p sut, hoc l nh it m khng lm s pha trong h thay i. ng vi mi gi tr ca p sut p CO2 th nhit hon ton -c xc nh v ng-c li. iu ny cng c th suy ra t ph-ng trnh ngp Van't Hoff (s cp sau) trong k P (i vi tr-ng hp ny hng s cn bng K P =pCO2) ch l hm s ca nhit .

b. Cn bng cuphn ng phn li ng oxit.

Phn li ng oxit tin hnh theo cc phn ng.

Cu2O = 2Cu +2

1O2 (a)

2CuO = Cu2O +2

1O2 (b)

xc nh -c s bc t do ca phn ng phn li ng ho tr mt, ta hy tms cu t v s pha tn ti trong h cc trng thi khc nhau (khi hay ng-ng t: rn, lng)

nh vic s dng gin pha Cu - CuO trn hnh 2 - 4.


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Trong cc h phn ng (a) v (b), s cu t n = 2. Nu oxit v ng phn li u

pha ng-ng t, c ngha l phn ng phn li tin hnh d-i nhit nng chy ca Cu 2Ov Cu, th s pha - f s bng 3 (2 pha rn l Cu v Cu2O v pha kh), s bc t do caphn ng s l.

C = 2 - 3 + 2 = 1iu ny c ngha l, i vi phn ng phn li xt khi trng thi cn bng th ng

vi nhit xc nh l mt p sut ring phn xc nh ca kh O2 (PO2). Ph thucdng ny -c m t bng -ng VIII i vi phn ng (a) v -ng I i vi phn ng (b)trn hnh 2 - 4b.

Cng vi cc phn ng phn li ny, nh-ng nu tin hnh trng thi nng chy, th sbc t do ca h s thay i trong nhng tr-ng hp xc nh. Ti cc vng dung dchc lp L1 v L2 trn hnh 2.4a, s bc t do s l:

C = 2 - 2 + 2 = 2Trn hnh 2-4b c s thay i s bc t do t 1 n 2. Ph thuc nhit - p sut

ca cc vng L1 v L2 khng cn biu th bng nhng -ng cong m l nhng mt

phng xc nh trn gin pha. T y c th suy ra, ti nhng vng xt nh c ththay ddooix cng lc khng ph thuc ln nhau c nhit T v p sut p m trng thi cnbng ca h vn -c duy tr.

vng cng tn ti 2 dung dch L 1 v L2 th f = 2 v C = 1. y li l tr-ng hp phthuc ca p sut oxi vo nhit v -c c tr-ng bng -ng VI trn hnh 2-4b v-ng B trn hnh 2-4c.

2.3. p sut v nhit phn li ca oxit, cacbonat v sunfua kim loi.

Nh- trnh by trong phn 2-1, khi nung oxit, cacbonat v sunfua kim loi, cc hp

cht ny b phn hu theo cc phn ng sau y:2 MeO (s) = 2Me (s) + O2 (g)MeCO3 (s) = MeO (s) + CO2 (g)2MeS (s) = 2Me (s) + S2 (g)

trong Me l kim loi ho tr hai.V cc qu trnh phn li ca cc hp cht trn rt t-ng ng [1], nn c th khi

qut chung bng phn ng

AB (s) A (s) + B (g) (2- 6)

PO [mmHg]2

PO

[mmHg]

2

N

hit[C]

Hnh 2- 4: Gin cn bng ca h CuOa) Gin thnh phn-nhit b) Gin p sut-nhit c) Gin thnh phn-p sut

0

% [khi l-ng]

% [khi l-ng]

a) b)c)


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Hng s cn bng ca phn ng (2-6) l

Kp =AB

BA

a

pa .(2-7)

,trong :aA ,aAB l hot ca cc cht tham gia phn ng A, ABpB - p sut cn bng ca cht kh B gii phng t ph n ng phn li.Nu p sut cn bng pB ca kh gii phng t phn ng phn li m cn bng vi

hp cht phn li th p sut ny -c gi l p sut phn li ca hp cht AB.

2.3.1. Phn li oxit, cacbonat v sunfua kim loi nguyn cht trong h thngkhng to thnh dung dch.

Nu cc hp cht phn li dng nguyn cht v trong qu trnh phn li li khngxy ra phn ng to thnh dung dch gia A v AB, th hot ca cc cht tham giaphn ng trong trng thi rn -c coi bng 1 v v vy ph-ng tr nh (2-7) c dng:

KP = pB (2-8)T ph-ng trnh ny ta thy, p sut phn li ca hp cht cho tr-c -c biu th

trc tip bng hng s cn bng ca phn ng phn li.

Thay ph-ng trnh (2-8) vo ph-ng trnh ng nhit Van't = Hoff iu kin ti uchun ((G0 = -RTlnKp), ta nhn -c.

(G0T = - RTlnKp = - RTlnpB (2-9)

T ph-ng trnh (2-9) suy ra, p sut phn li p B l th-c o bn nhit ng hcca hp cht AB nhit xc nh.

Mt khi nim khc cng rt c ngha l nhit phn li. Ti nhit ny,qu trnh phn li hp cht xy ra mnh lit v p sut ca sn phm kh phn li bng psut mi tr-ng chung quanh.

S ph thuc ca p sut phn li vo nhit c th biu th vi chnh xccho php bng ph-ng trnh ng p Van't - Hoff.

RTH

dTpd

dTK

dBp (!! )(ln)(ln (2-10)

hoc. lnpB =R

S

RT

H

RT

G (

(!

((2-11)

Biu ph thuc ca pB vo nhit ca hp chtbt k -c th hin bng -ng cong trn hnh2-5. -ng cong chia h trc to ca gin thnh2 phn:

- I trn -ng cong.- II d-i -ng congNu k hiu p*B l p sut ring phn ca thnh

phn kh B trong mi tr-ng chung quanh, th tuthuc vo quan h gia pB v p*B phn ng thunnghch (2-6) c th tin hnh theo chiu phn lihay oxi ho. S xy ra 3 tr-ng hp sau y:

a. p*B > pB (vng I)H thng trng thi khng cn bng v nu p sut chung quanh khc 1 th

(G = RTln(p*B- pB) > 0 (2-12)

C ngha l phn ng xy ra theo chiu nghch, tc l qu trnh oxi ho. Qu trnh n ytin hnh cho n khi p *B v pB cn bng. Nh- vy, vng I l vng tn ti ca hp cht AB.

Hnh 2-5: Ph thuc ca psut

a

b

1

2 3

3

2

1 I

P

T

II


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b. p*B < pB (vng II) nhit T2, (G < 0, phn ng (2-6) xy ra theo chiu t tri sang phi, hp cht AB bphn li.

c. p*B = pBy l tr-ng hp phn ng t trng thi cn bng v -c th hin bng -ng cong trnhnh 2-5.

T hnh 2-5, c th suy ra ph-ng thc tc ng phn ng t trng thi cn

bng. Nu cc im a, b cc vng I, II -c coi l trng thi ban u ca h cho tr-c, thi vi trng thi a cn bng s xy ra nu p sut ca thnh phn kh B gim (theo mitn 1), tng nhit (theo mi tn 2) hoc bin hnh ng thi c 2 cch (theo mi tn 3).Cn i vi trng thi b th ng-c li, tng p sut (theo 1'), gim nhit (theo 2') hocng thi c 2 cch (theo 3).

2.3.2. Phn li oxit v cacbonat trong h thng to thnh dung dch.

Nhng ph-ng trnh nhit ng hc - m chng ta c dp cp cc phntrn, -c bit lp trn c s nhng gii thuyt:

Cc thnh phn trong h thng phn li trng thi nguyn cht v khng tc dngvi nhau to ra nhng dung dch. Hot ng ca hp cht phn li v sn phm rn

phn li bng 1.Trong thc t luyn kim, oxit, cacbonat v cc sunfua th-ng cha cc tp cht v

trong qu trnh phn li rt c th xy ra phn ng to dung dch gia cc thnh phntrong h thng, do vy hot ng ca cc thnh phn b gim.

D-i y ta hy xt phn ng phn li (2-6) iu kin hp cht phn li AB v snphm phn li A tc dng vi nhau to thnh dung dch khng bo ho. Nu k hiu psut phn li trong tr-ng hp ny l pB, th.

pB = KA

AB

a

a(2-13)

Hng s cn bng K biu th bng hot , do vy ti nhit cho tr-c, hng sny khng ph thuc vo vic cc cht tham gia phn ng dng nguyn cht hay dung

dch. V vy, biu thc (2-8) vn -c p dng cho tr-ng hp ang xt. Thay ph-ngtrnh (2-8) vo (2-13), ta c

pB = pB.A

AB

a

a(2-14)

Nu dung dch to thnh l dung dch l t -ng, th hot ca cc thnh phn sbng nng v -c biu th bng cc phn mol (a i = Ni). Trong tr-ng hp ny, ph-ngtrnh (2-14) c dng

pB = PB .A

AB

N

N(2-15)

D-i y l nhng tr-ng hp xy ra ph bin trong phn li oxit, cacbonat v sunfuakm theo s to thnh dung dch:

a. Hp cht phn li AB v sn phm phn li A ho tan vi nhau to thnh dung dchkhng bo ho.

b. AB dng nguyn cht, cn A th ho tan trong mt cht khc (cng c th lmt tp cht) v cng vi cht to nn dung dch khng bo ho.

c. AB dng nguyn cht, cn A lin kt ho hc vi cht khcd. AB to vi cht khc thnh dung dch khng bo ho, cn A dng nguyn cht.

T ph-ng trnh (2-14) ta thy, p sut phn li pB ln hay nh hn pB l tu thucvo quan h hot gia aAB v aA. Nu aAB > aA th pB > pB. Trong iu kin ny phnng phn li AB xy ra d dng v s cng thun li nu a AB cng ln v aA cng nh.


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Cng t-ng t nh- tr-ng hp trn, nu AB dng nguyn cht (aAB = 1), sn phmphn li A ho tan trong mt cht khc to ra dung dch khng bo ho, thaA


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Ph-ng trnh (2-22) l ph-ng trnh biu th chnh xc nht s ph thuc canng l-ng t do vo nhit , nh-ng v qu phc tp nn t -c s dng trong tnh tonthc t. n gin ho, thay cho ph-ng trnh (2 -22), dng ph-ng trnh gn ng biuth s ph thuc tuyn tnh ca (G0 vo nhit

(G0 = A + B.T (2-23)

Cc h s A v B trong khong nhit (T1 - T2) -c xc nh t cc bng

(2-1) v (2-2).Gi tr ca (G0 -c tnh theo 2 ph-ng trnh (2-22) v (2-23) khng c s chnhlch ln. i vi cc phn ng to thnh oxit th sai s ca (G0 theo 2 cch tnh khong s2510 J. Cc gi tr (G0 ca cc phn ng phn li nhit cao c th tra t cc s taytp hp kt qu cng b ca K. Kelley, Richardson v Jeffes, ca Kellog vKubaschewski.

2.3.4. Mt s yu t nh h-ng ti qu trnh phn li.nh h-ng ca kch th-c htp sut phn li ca phn ng (2-6) ph thuc vo kch th-c ht ca cht phn li

(AB) v cc cht to thnh (A, B), tc l ph thuc vo ln b mt ca chng. Ccphn t (nguyn t, ion...) trn b mt so vi cc phn t bn trong bao gi cng c nng

l-ng b mt d-. Do vy, nng l-ng t do ca cc phn t b mt (G bm) s ln hn ccphn t bn trong (Gtr). Gi tr trung bnh ca nng l-ng t do ca cht to thnh t qutrnh phn li c s l-ng phn t bn trong l n tr v phn t bn ngoi l n bn -c xc nhbng biu thc d-i y:

(G0 = G0bm + G0tr = nbm bmG + ntr trG

Biu thc trn ch c ngha trong tr-ng hp sn phm phn li c c ht mn rtnhiu ln so vi cht -a vo phn li, tc l phn tn ca th rn rt ln.

Nh- vy i vi phn ng (2-6) v ph-ng din nng l-ng nh h-ng ca c ht c thbiu th qua biu thc sau:

(G0 = G0Abm + G0Atr + G

0Bg - G

0ABbm - G

0ABtr (2-24)

Thay (2-24) vo (2-16) ta c:

G-G-G-GG575,4

log Bg0Atr0Abm0ABtr0ABbm00

!(!T

GpB

(2-25)

Ph-ng trnh ny cho thy, nu ht ca hp cht AB cng mn th p sut phnli pB ca n cng ln v nh- vy hp cht s d dng phn li hn. Ng-c li, nu ht casn phm phn li A cng th th p sut phn li cng gim, s phn li s xy ra kh hn.

nh h-ng ca s chuyn bin trng thi.Khi nung oxit, cacbonat v sunfua kim loi, ngoi phn ng phn li cn xy ra cc

qu trnh chuyn bin trng thi ca bn thn hp cht AB v sn phm phn li A, chnghn t pha rn sang pha lng hoc pha hi. qu trnh nng chy hoc bay hi xyra, cn thit phi cung cp cho h mt l-ng nhit nng, mt mt ph v lin kt giacc phn t hay nguyn t ca hp cht AB hoc sn phm A, mt khc dng thchin cng lm tng th tch trong qu trnh chuyn trng thi.

nh h-ng ca s chuyn bin trng thi n th nhit ng tiu chun th hinbng cc im gy trn -ng biu din ph thuc (G0 = f(T) trn cc hnh (2-1), (2-3) vcc -ng cong nung cacbonat trnh by phn sau. Gi tr (G0 ca phn ng phn li cc thi im chuyn pha c th xc nh trn c s ph-ng trnh (2-23), nu thm (Hv (S chuyn pha v dng nhit rung ring ca pha mi.

nh h-ng ca chn khng


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S thay i p sut trong h thng c nh h-ng r rt n bn ca hp cht.T ph-ng trnh (2-14).

(G = RTlnp*B - RTlnpBTa thy, nu p sut ban u trong h thng lch khi iu kin tiu chun (1

at) th tr s (G ca phn ng phn li s thay i. Ni chung, s chnh lch gia p sutphn li hp cht v chn khng cng ln th hp cht cng d b phn li, c ngha lchn khng lm gim bn ca hp cht cho tr-c.

nh h-ng ca tp cht

Trong thc t, oxit, cacbonat v sunfua lun lun cha 1 l-ng tp cht nht nh.Cc tp cht ny c th cng vi sn phm phn li th rn to thnh nhng dung dchrn v do vy lm gim hot ca sn phm phn li aA. Nu gi thit hot ca hpcht AB l aAB khng i trong qu trnh phn li, th nh h-ng ca tp cht n (G caphn ng -c biu th bng ph-ng trnh.

(GT = (G0T + RTlnaA (2-26)

Nh- vy, hot ca sn phm phn li lm gim gi tr d-ng ca (G (tc lchuyn v pha gi tr m) v lm tng tr s ca p sut phn li hp cht. iu nyhon ton ph hp vi ph-ng trnh d-i y:

lnpB =RT

G0( + lnaA

2.3.5. Nhng p dng c th c s l thuyt nhit ng hc i vi phn lia. Oxit

p sut ring phn ca oxi trong khng kh iu kin tiu chun (nhit =25oC, p sut = 9,8 104 Pa) l 2,058 104 Pa (0,21at).

Nu p sut phn li ca oxit nh hn p sut ring phn ca oxi th oxit s bnvng, kim loi b oxi ho.

Tr-ng hp p sut phn li ca oxit ln hn p sut ring phn ca oxi th oxit s bphn hu.

Trong t nhin, phn ln oxit kim loi c psut phn li nh hn p sut ring phn ca oxitrong khng kh cho nn phn ln kim loi tn ti d-idng oxit. Nhng kim loi m oxit ca chng c psut phn li rt ln th hu nh- khng b oxi hotrong khng kh. Hnh 2-6 biu th s ph thucp sut phn li ca mt s oxit kim loi vo nhit. T hnh 2-6 c th suy ra rng, -ng congphn li v tr cng cao (Ag 2O, CuO) th oxitcng d phn li, v ng-c li cng thp (MgO, CaO)th oxit cng kh phn li.

i vi nhng oxit ca cng mt kim loi nh-ngc ho tr khc nhau, qu trnh phn li xy ra theotun t t oxit c ho tr cao ti oxit c ho tr thpv cho n tn nguyn t.

Hnh 2-6: Ph thuc ca p sutphn li oxit kim loi vo nhit

VII II III


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MeO2 Me2O3 Me3O4 MeO Me (2-27)

ng vi mi phn ng c th biu th bng cc ph-ng trnh tng qut d -i y:I. 4MeO2 = 2Me2O3 + O2 Kp1 =

22MeOOP

II. 6M32O3 = 4Me3O4 + O2 KPII =322 OMeO

P

III. 3Me3O4 = 6MeO + O2 KPIII =432 OMeO

P

IV. 2MeO = 2Me + O2 KPIV = MeOOP 2 Ph hp vi tun t phn li, oxit kim loi ho tr cao c p sut phn li ln hn v nh-

vy km bn hn oxit kim loi ho tr thp. iu ny ng vi thc t l oxit kim loi hotr cao d hon nguyn hn so vi oxit ho tr thp ca cng kim loi.

(22

)MeOOP > ( 322 ) OMeOP > ( 432 ) OMeOP > ( MeOOP )2

Trong luyn kim en cng nh- luyn kim mu, s phn li ca oxit st c nghart quan trng trng. Oxit st ho tr 2 bn vng nhit trn 570 0C, nh-ng nhit thp hn li b phn li. Qu trnh phn li oxit st xy ra tun t theo 2 s sau:

a. > 570oCFe2O3p Fe3O4p FeO p Fe

b. < 570oC

Fe2O3p Fe3O4p FePhn ng ho hc v cc ph-ng trnh nhit ng hc t-ng ng:a. > 570oC

6Fe2O3 = 4Fe3O4 + O2 ( Ho298 = 440156 J

2Fe3O4 = 6FeO + O2 ( Ho298 = 610864 J

3FeO = 2Fe + O2 ( Ho298 = 539736 J

b. < 570oC6Fe2O3 = 4Fe3O4 + O2 ( H

o298 = 440156 J

2

1Fe3O4 =

2

3Fe+ O2 ( H

o298 = 557518 J

Nh- nu nhit d-i 570oC, oxit st ho tr 2 (FeO) khng bn v b phn li

theo phn ng4FeO (r) = Fe3O4 (r) + Fe (r) ( H

o298 = - 48116 J

S ph thuc ca nng l-ng t do v p sut phn li vo nhit trong phn ngphn li oxit st -c th hin trn hnh (2-7).

T hnh2-7 chng ta c th xc nh -c cc vng tn ti bn vng ca cc pha ng-ng t (th rnhoc lng) trong h Fe - O

Cn l-u l, nhit 570oC (843K) c s cng tn ti trong trng thi cn bngca cc cu t Fe, FeO v Fe3O4.

b) Nhit

Hnh 2-7: a) S ph thuc ca nng l-ng t do vo nhit trong phn ngphn li oxit st b) S ph thuc ca p sut phn li oxit st vo

a) Nhit


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hiu r nh h-ng ca vic to thnh dung dch i vi p sut phn li, ta hyxt tr-ng hp phn li niken oxit nhit 1573 K vi gi thit Ni t qu trnh phn li tothnh dung dch 1% vi st.

Qu trnh phn li ny xy ra theo phn ng.2 NiO = 2 Ni + O2 (a)

Trn c s ph-ng trnh (2-7) ta c

K = 22 2

. NiO

O

Ni a

P

a (b)Nu aNiO v aNi = 1, th p sut phn li ca NiO =

2Op = K. T hnh (2-2) ta xc

nh -c gi tr ca (Go ca phn ng (a) ng vi nhit 1573 K l khong 17780 J.p sut phn li ca NiO -c xc nh nh ph-ng trnh (2 -9), tc l.

oG1573( = - 2ln OpRT } 17780 J (c)

2log

Op = -

573,1573,442500

v= - 5,91 (d)

2Op = 1,23.10-6

V Ni to thnh dung dch 1% vi st, nn p sut phn li ca NiO s thay i Nudung dch to thnh l dung dch l t-ng, theo nh lut Raoult ta c:

aNi = NNi, tc l hot ca Ni trong tr-ng hp ny bng nng ca n biu thbng nng phn mol.

Nng NNi tnh theo cng thc p dng cho dung dch hai nguyn.

Ni =? A

? A ? A ji

i

MiMi

Mi

/%100/%

/%

(e)

trong : Ni - nng ca cht ho tan i.Mi - nguyn t l-ng ca cht ho tan i.Mj - nguyn t l-ng ca dung mi ho tan j.

V hm l-ng ca Fe qu nh (1%) so vi nng Ni, nn c th dng cng thc (e) dng rt gn, tc l:

? A

? A

i

j

j

ii

M

Mi

M

M

i

N.100100

!!

Thay cc gi tr bit vo cng thc rt gn, ta xc nh -c N Ni ~ 0,01. tnh p sut phn li trong tr-ng hp to thnh dung dch, ta s dng cng thc

(2-14).

2

Op =2O

p .2

2

Ni

NiO

N

a

Do NiO dng tinh khit v li khng tham gia vo qu trnh to thnh dung dch,nn aNiO = 1. Bi vy:

2

'Op =

2Op .

21NiN

log 2'Op = log

2Op - 2logNNi = -5,91 - 2 log 0,01 = -1,91

2

'Op = 1,23.10-2

ng vi gi tr p sut phn li ny, ta c :oG1573( = -RTln 2

'Op = - 4,575 x 1573 x (-1,91) = 57509 J


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T v d nu trn, c th rt ra nhn xt: Nu cc sn phm ca qu trnh phn lito thnh dung dch vi cht khch th p sut phn li ca hp cht phn li s tng ln, nh m qu trnh phn li s xy ra thun li hn so vi tr-ng hp khng to thnh dungdch.

b. CacbonatCacbonat xut hin trong cc qu trnh luyn kim c ngun gc, hoc l thnhphn khong vt ca qung, hoc d-i dng ca cht tr dung. Trong thc t, th-nggp nhng cacbonat d-i y phn li theo cc phn ng:

MnCO3 = MnO + CO2 oH298( = 116524 kJ

MgCO3 = MgO + CO2 oH298( = 101462 kJ

FeCO3 = FeO + CO2Phn ng phn li st cacbonat tin hnh khng thun li do nh h-ng ca phn nggia cc sn phm to thnh.

3FeO + CO2 = Fe3O4 + COV vy qu trnh phn li FeCO3 -c biu th bng phn ng tng qut sau:

nFeCO3 = mFeO + qFe3O4 + pCO3 + rCO.CaCO3 = CaO + CO2 oH298( = 179284 kJ

Nu c mt Fe2O3 v SiO2, vi iu kin gia cc oxit ny v CaCO3 c s tipxc cht ch th xy ra cc phn ng ph d-i y.

CaCO3 + Fe2O3 = CaO.Fe2O3 + CO22CaCO3 + Fe2O3 = 2CaO.Fe2O3 + 2CO22CaCO3 + SiO2 = Ca2SiO4 + 2CO2

Dolomit phn li qua 2 giai on. Trong giai on u, dolomit phn hu tng phn to thnh CaCO3 v MgO.

CaMg(CO3)2 = CaCO3 + MgO + CO2 oH298( = 124892 kJ

giai on hai, CaCO3 phn li theo phn ng nh- nu.

Trong tr-ng hp phn li cacbonat nguyn cht v khng xy ra phn ng to dungdch gia cht phn li v sn phm phn li, th gi tr oTG( - th-c o bn nhit

ng hc ca cacbonat t l thun vi p sut phn li cc cacbonat )( 32 MeCOCOp . Cc kt

qu tnh ton v thc nghim ch ra rng, p sut phn li cc cacbonat ln hn nhiu sovi phn ln oxit. Hnh 2-8 biu th s ph thuc ca p sut phn li cacbonat vo nhit

Thi gian

Nhit

Hnh 2-9: Cc -ng cong

nung cacbonat trong dng

Nhit

psu

t[toor]

psu

t[kN.m

-2]

Hnh 2-8: Ph thuc ca p sut phn licacbonat )( 32 MeCOCOP , p sut ring phn CO 2

trong kh l )(2 kCOP , v p sut tng p cakh trong l cao vo nhit


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.T hnh 2-8 ta thy, CaCO3 bt u phn li nhit khong 680

oC (im A).Tuy nhin phn ng xy ra chm v c s hn ch ca qu trnh khuch tn CO 2 phn lira khi b mt phn ng qua lp sn phm rn CaO[2]. Khi nhit tng, vn tc phnli cng tng v t gi tr cc i ti im B ng vi p sut tng ca kh. Trong thiim ny, qu trnh phn li xy ra mnh m, nn tiu hao mt l-ng nhit rt ln. V vynhit ti im B khng tng mc du qu trnh nung vn tip tc. im B chnh l

im si ho hc ca cacbonat v trn hnh 2-9 l nhng im gy trn cc -ng cong.

D-i y l im si ho hc ca mt s cacbonat p sut tiu chun (1atm).FeCO3 360 - 510

oCMnCO3 470 - 590

oCMgCO3 595 - 650

oCCaCO3 890 - 920

oC- giai on 1: 710 - 770 oC

CaMg(CO3)2- giai on 2: 890 - 920oC

im si ho hc ca cacbonat c s ba ng v gi tr -c gii thch bi s khcnhau v sch v thnh phn c ht ca cacbonat phn li (iu ny th hin r trn

-ng nung hnh 2.9). hiu r nh h-ng ca tp cht i vi nhit phn li, ta hy xt th d xc

nh nhit phn li ca CaCO3 sch v CaCO3 cha tp cht SiO2 iu kin p sutth-ng.

Qu trnh phn li CaCO3 sch v CaCO3 cha tp cht xy ra theo cc phn ngCaCO3 = CaO + C + O2 (G

o = 136700 - 37,5 T(a)

C + O2 = CO2 (Go = -94200 - 0,2 T

(b)CaO + 1/2 SiO2 = 1/2 Ca2SiO4 (G

o = -1490 (c)(i vi phn ng c, gi tr entropi nh khng ng k, v ch c nhng pha rn

tham gia phn ng) Kt hp phn ng v ph-ng trnh (a), (b) ta cCaCO3 = CaO + CO2

(d)(Go = 425000 - 37,7 T

Hng s cn bng ca phn ng phn li l(Kp)d =

2COp

Thay gi tr ca (Kp)p.1 vo ph-ng trnh 2-9, ta nhn -cRTln

2COp = - 42500 + 37,7T

(e)hay l

2log COp = - T9280 + 8,24 (f)

Nu gi tr p sut phn li bng p sut kh quyn (1atm), th2CO

p = 1 do vy

log2CO

p = 0, ph-ng trnh (f) trong iu kin ny s c dng

T

9280= 8,24

Suy ra nhit phn li CaCO3 sch l: T = 1128 K hay 855oC


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Trong tr-ng hp c tp cht SiO2, ta kt hp cc phn ng v ph-ng trnh (c) v (d)CaCO3 + 1/2 SiO2 = 1/2 Ca2SiO4 + CO2

(G0 = 27600 -37,7 THng s cn bng ca phn ng l ph-ng trnh

Kp(i) =2CO

p

Bng php bin i t-ng t nh- tr-ng hp a, ta nhn -c

log 2COp = - T

6030+ 8,24

Nu2CO

p bng p sut kh quyn (1atm), th log2CO

p = 0, nh- vy

T

6030= 8,24

Suy ra nhit phn li ca CaCO3 cha tp cht SiO2 l T = 733 K hay 460oC.

T th d ny ta suy ra, s c mt ca tp cht ni chung s lm gim nhit phn li ca hp cht.

c. SunfuaT hnh 2-3 biu th ph thuc (G0s.t vo nhit , ta thy hp cht bn vng nht

l CaS, cn km bn nht l CuS. T-ng t nh- i vi oxit v cacbonat, mc phn lica sunfua nhit nht nh -c c tr-ng bi:- hoc l p sut ring phn ca phn t kh l-u hunh- hoc l s thay i entalpi t do (G0Phn t l-u hunh S2 ch c th tn ti trong khong nhit t 700 n 1200

oC,cn gn im si ca l-u hunh (444,5 oC) th nguyn t ny tn ti d-i dng cc phn tS4, S6 v S8. L-u hunh nguyn t xut hin nhit cao.

Nu cc thnh phn tham gia phn ng sinh thnh sunfua dng nguyn cht vkhng kt hp vi nhau to thnh dung dch, th entalpi t do -c tnh theo ph-ngtrnh.

(G0T = -RTlnKp = -2S

TRTlp

Trong tr-ng hp to thnh dung dch v ng thi xy ra s bin i pha, th tt

nht s dng quan h biu th th ho hc ca l-u hunh

QS = (G0

MeS = RTln 2

2

MeS

Me

a

a+ (G

,trong : (G - l tng cc s bin i entalpi t do d-i tc dng ca b in i pha. QS- th ho hc ca l-u hunh.

D-i y ta xt tr-ng hp phn li pyrit - dng sunfua st ph bin trong luyn kimen v luyn kim mu.

Trong h Fe - S, c th tn ti 3 hp cht, l FeS, Fe 2S3 v FeS2. Trong s cchp cht ny th-ng t gp pyrhotin Fe xS (x < 1) v troilit FeS trong qung. Cn Fe 2S3th khng bn v d b phn hu trong qu trnh nung nhit t 200 - 3000C theophn ng.

Fe2S3p FeS + FeS2Pyrit khi phn li to thnh FeS v l-u hunh.Cc phn ng c th xy ra trong qu trnh phn li pyrit:

2FeS2(r) = 2FeS + 2S(s) Ho298 = 164013 kJ

2S(s) = 2S(g) Ho298 = 20920 kJ

2S(g) = 2S(g) Ho298 = -129704 kJ

2FeS2 = 2FeS(g) + S2(s) Ho298 = 55229 kJ


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Entalpi t do ca phn ng tng ph thuc vo nhit trong khong t 600 -11000C -c biu th bng ph-ng trnh:

(G0 = 362753 - 376,56 T [kJ]

logkp =2

log Sp = -T

18955+ 19,68

Khi p = 1 tc l p sut 1atm th T = 690 0C, nh- vy nhit thiu qung stv qung kim loi mu pyrit c th phn li hon ton.

D-i y l p sut phn li ca pyrit cc nhit khc nhau.

Nhit [0C] 575 610 645 655 672 680

p sut phn li [Pa] 100 1800 14200 33466 45600 69066

2.4. C ch v ng hc ca qu trnh phn li

Phn li oxit, sunfua v cacbonat thuc loi cc phn ng ho hc khu vc[4]. cim ca phn ng phn li l: Khu ho hc ca qu trnh gn lin vi cc chuyn bin trng thi rn m kt qu l mng tinh th ca hp cht ban u (AB) b ph hu v-c thay th bng mng tinh th ca sn phm phn li (A).

c th hnh dung mt cch khi qut v c ch v ng hc qu trnh phn licc hp cht nu trn, ta hy xt tr-ng hp phn li cacbonat trn c s l thuyt t xc tc -hp th va G.I. Supharp.

Trong mng tinh th ion ca cacbonat, cc kation kim loi Me 2+ v anion (CO3)2- sp

xp mt cch c quy lut. S sp xp ny phn nh trng thi cn bng cc lc lin ktgia cc ion cu thnh hp cht v c tr-ng cho bn vng c a mng tinh th.

D-i tc dng ca nhit cao, cacbonat b phn li qua 4 b-c sau y:1. Phn hu anion (CO3)

2- bng vic tch ion O2- khi anion (CO3)2- to thnh

CO2 hp ph trn b mt MeCO3(CO3)

2-p O2- (CO2)hp

2. Gii hp ph cc phn t CO2 t b mt cacbonat

O2-

(CO2)h.pp O2-

+ CO2(k)3. Do CO2(k) -c gii phng trong mng li cc cp ion O

2- v Me2+. Chnh cc ionny to nn dung dch rn MeO trong MeCO3. Khi dung dch t ti bo ho th

ly thuyet qua trinh luyen kim

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