do an cracking xuc tac

7/27/2019 Do an Cracking Xuc Tac

1/85

n Tt Nghip SVTH: Phm Vn Mnh Lp: Lc Ho Du K53

3

Mc lc

Li cm n

M u

Phn i

tng quan

7

Ch-ng i.

mc ch ngha v c s l thuyt ca qu trnhI. Mc ch v ngha ca qu trnh 81. S lc v lch s pht trin ca qu trnh

cracking xc tc. 8

2. Mc ch ca qu trnh cracking xc tc. 93. ngha ca qu trnh cracking xc tc. 9II. c ch phn ng. 91. Phn ng phn hu cc mch, phn ng cracking.

13

2. Phn ng ng phn ho (izome ho).14

3. Phn ng chuyn di hydro di tc dng ca xctc.

144. Phn ng trng hp.

14

5. Phn ng alkyl ho v kh alkyl ho.14


2/85


4

6. Phn ng ngng t to cc.14

III.ng hc cho qu trnh cracking xc tC.15

IV. Cracking xc tc cC hydrocacbon ring l.16

1. S bin i cc hydrocacbon paraffin.16

2. S bin i ca hydrocacbon olefin.18

3. S bin i cc hydrocacbon naphtenic.20

4. S bin i ca hydrocacbon thm.21

V. Cracking phn on du m.24

Ch-ng II

xc tc ca qu trnh Cracking

i. Vai tr ca xc tc trong qu trnh cracking.2

7

ii. Nhng yu cu cn thit i vi xc tc.2

7


3/85


5

1. Hot tnh xc tc phi cao.2

7

2. chn lc xc tc phi cao.2

9

3. n nh phi ln.2

9

4. m bo bn c v nhit.3

0

5. Xc tc phi m bo thun nht cao.3

0

6. Xc tc phi bn vi cht lm ng c xc tc.3

0

7. Xc tc phi c kh nng ti sinh.3

0

8. Xc tc phi d sn xut v r tin.3

1

iii.Zeolite v xc tc cha zeolite.3

1


4/85


6

1.Xc tc zeolite.3

1

1.1.Thnh phn ha hc ca zeolite.3

1

1.2.Cu trc ca Zeolit.3

3

2.Zeolit v xc tc cha Zeolit dng cho qu trnhcracking.

3

4

iv. Nhng thay i tnh cht xc tc khi lm vic.3

7

v. Ti sinh xc tc.3

9

vi. Cc dng hnh hc ca xc tc.4

1

Ch-ng III

NGuyn Liu V Sn PHm Ca qu trnh cracking xc tc


5/85


7

i. Nguyn liu ca qu trnh cracking xc tc.4

3

ii. sn phm ca qu trnh cracking xc tc.4

5

1.Sn phm kh.4

5

2.Xng cracking xc tc.4

7

3.Phn on si cao hn.4

8

PHn iiCng ngh cracking xc tc

Ch-ng i

Cc yu t nh h-ng n qu tnh cracking xc tc

i. Nhit .5

1

ii. p sut.5

3


6/85


8

iii.Mc chuyn ho.5

4

iv. Tc np liu ring.5

5

v. T l lng xc tc, nguyn liu hay bi s tunhon xc tc.

5

6

vi. Hiu ng nhit.5

7

Ch-ng ii

Cng ngh cracking xc tc

i. lch s pht trin cng ngh cracking xc tc.5

8

ii. la chn cng ngh cracking xc tc.6

0

iii.dy chuyn fcc vi thi gian thip xc ngn.6

1

1.S dy chuyn FCC thi gian tip xc ngn.6

1


7/85


9

2.Nguyn l hot ng.6

2

iv. Hng pht trin v cI thin FCC trong lc hodu.

6

4

Kt lun

Ti liu

tham kho

6

6


8/85


10

Phn I

Tng quan

Trong cng ngh ch bin du m cc qu trnh

chuyn ha ha hc di tc dng ca cht xc tc chim

mt t l rt ln v ng vai tr v cng quan trng.

Cht xc tc trong qu trnh chuyn c kh nng lm

gim nng lng hot ha ca phn ng v vy m tng

tc phn ng ln rt nhiu . Mc khc , khi c mt

cht xc tc th phn ng c kh nng tin hnh nhit

thp hn iu ny rt quan trng i vi nhng phn

ng c hiu ng dung nh phn ng hydro ha , alkyl

ha , polime ha v.v...

S c mt cht xc tc va thc y nhanh qu trnh

chuyn ha ha hc, va c kh nng to ra nhng nng

cn bng cao nht, c ngha l tng hiu sut ca

qu trnh. iu quan trng nht l cht xc tc c kh

nng tng nhanh khng ng u gia cc loi phn ng

m v phng din nhit ng l chng xy ra cng lc

trong qu trnh, trong iu kin nh nhau, ngi ta gi

y l tnh cht chn la ca xc tc. Ngi ta

nghin cu rt nhiu loi cht xc tc v ngi ta cng

li dng tnh cht chn la ca n m hng phn ng

ca qu trnh ch bin theo chiu c li nhm thu

c nhng sn phm chnh t hiu sut v cht lng

tt nh mong mun.


9/85


11

Chnh v l do cho nn p ng ngy cng

nhiu nhu cu dng xng du th ngi ta nghin cu

v ci tin dn qu trnh cracking xc tc. Qu trnh

cracking xc tc vi dy chuyn cng ngh FCC l uim hn c.

Ch-ng I

Mc ch ngha v c s l thuyt

I. Mc ch v ngha.1. S l-c v lch s pht trin ca qu trnh

cracking xc tc [1,106]

Qu trnh cracking xc tc c nghin cu t

cui th k XIX nhng mi n nm 1923, mt k s ngi

Php tn l Houdry mi ngh a qu trnh vo p

dng trong cng nghip. n nm 1936, nh my cracking

xc tc u tin c xy dng M ca cng ty Houdry

Process Corporation. Cho n nay, sau hn 60 nm pht

trin, qu trnh ny ngy cng c ci tin v hon

thin, nhm mc ch nhn nhiu xng hn v cht lng

xng ngy cng cao hn v t nguyn liu c cht lng

ngy cng km hn. ng thi ngoi mc ch nhn xng,

ngi ta cn nhn c c nguyn liu c cht ngjcao

cho cng ngh tng hp ho du v ho hc.


10/85


12

Qu trnh cracking c nghin cu t lu nhng

giai on u ch l cc qu trnh bin i di tc

dng n thun ca nhit v p sut (qu trnh

cracking nhit )vi hiu sut v cht lng thp, tinhnh iu kin khc nghit, ti nhit cao v p

sut cao tuy nhin n cng c nhng u im l c th

ch bin cc phn cn nng ca du m m cracking xc

tc khng thc hin c.

nng cao hiu sut, cht lng, cho php tin

hnh qu trnh nhng iu kin mm mi hn (nhit

thp hn, p sut thp hn) ngi ta a vo qu

trnh nhng cht m c kh nng lm gim nng lng

hot ho, tng tc phn ng, tng tnh cht chn lc

(hng phn ng theo hng cn thit) v n khng b

bin i trong trong qu trnh phn ng l ch xc

tc v qu trnh c gi l qua qu trnh cracking xc

tc. Cho n nay, qu trnh ny ngy cng c ci

tin, hon thin v mi mt (cng ngh, xc tc. thit

b) cho ph hp hn.

2.Mc ch ca qu trnh cracking xc tc [1,106]Mc ch ca qu trnh cracking xc tc l nhn cc

cu t c tr s octcao cho xng t hay xng my bayt nguyn liu l phn cn nng hn, ch yu l phn

ct nng hn t cc qu trnh chng ct trc tip AD

(Atmospheric Distillation) v VD (Vacuum Distilantion)

ca du th. ng thi ngoi mc ch nhn xng ngi


11/85


13

ta cn nhn c c cc nguyn liu c cht lng cao

cho cng ngh tng hp ho duv ho hc. Ngoi ra cn

thu thm mt s sn phm ph khc nh gasoil nh,

gasoil nng, kh ch yu l cc phn t c nhnh lcc cu t qu cho tng hp ho du.

3. ngha ca qu trnh cracking xc tc [1.107,3.62]

Qu trnh cracking xc tc l qu trnh khng th

thiu c trong bt k mt nh my ch bin du no

trn th gii, v qu trnh ny l mt trong cc qu

trnh chnh sn xut xng c tr s octan ca. Xng thu

c ca qu trnh ny c dng phi trn vi cc

loi xng khc to ra cc mc xng khc nhau. Khi

lng xng thu t qu trnh chim t l rt ln khong

70-80% so vi tng lng xng sn xut t cc qu

trnh.

Cracking xc tc chim mt v tr c bit quan

trng trong cng nghip ch bin du m. Lng du m

dng ch bin bng cracking xc tc l tng i

ln.V d nh : vo thng mt nm 1965 tng lng du

m nc m ch bin l 1500 tn/ngy trong c 800

tn/ngy (tc khong 53%) c ch bin bng cracking

xc tc.

II. C ch phn ng [1.107, 2.122]C ch ca qu trnh cracking xc tc l c ch ion

cacboni. C s ca l thuyt ny l da vo tm hot

tnh l cc ion cacboni, chng c to ra khi cc phn


12/85


14

t hydrocacbon ca nguyn liu tc dng vi tm axit

ca xc tc loi Bronsted (H+) hay Lewis (L). Mt cch

tm tt, thuyt ny a ra cc giai on c bn sau:

a. To ioncacboni

- T hydrocacbon parafin :CnH2n+2 + L(H

+)

CnH2n+1 + H2

+ CnH2n+1 + H2

CnH2n+2 + H+ +CnH2n+3

+ CmH2m+1 + C n-mH2(n-m)+2

- T olefin: y l thnh phn khng c trong

nguyn liu ban u ca qu trnh m n c to ra do

s phn hy cc hydroccbon thm ,Parafin , naphten

,...Olefin l hp cht rt hot ng ,nh vy m n

tham gia vo phn ng to Ion cacboni do s tc dng

ca olefin vi tm axit Bronsted ca xc tc:

Ion cacboni to thnh do s tc dng ca olefin vi

tm axit Lewis ca xc tc:

+ H+ (xt)+

R1 CH C R2 + (xt)

H

R1 CH C R2

H H

RH + R+

H Al O Si

O

Oolefin

Al O Si

O

O


13/85


15

hoc l:

CnH2n + H+ +CnH2n+1

CnH2n + LH +CnH2n+1 + L-

T hydrocacbon naphten:

Khi hydrocacbon naphten tc dng vi tm axit ca

xc tc hay cc ion cacboni khc, s to ra cc ion

cacboni mi tng t nh qu trnh xy ra vi parafin.

T hydrocacbon thm:

Ngi ta quan st thy s to thnh ion cacboni l

s kt hp trc tip ca H+ vo nhn thm:

Cc hydrocacbon thm c mch bn di th s to

thnh ion cacboni cng ging nh trng hp parafin.

Thi gian sng ca cc ion cacboni c to ra dao

ng t phn triu giy n hng pht. Cc ion cacboni

ny to ra nm trong lp cc phn t hp ph, chng l

nhng hp cht trung gian rt hot ng i vi nhiu

phn ng xy ra khi cracking.

b. Giai on bin i ion cacboni

Cc ion cacboni l nhng hp cht rt hot ng

,chnh v vy khi c to ra t giai on trn li

nhanh chng tham gia vo cc phn ng bin i khc

nhau nh :

H+CH2 CH3

+

CH2 CH3H+


14/85


16

Phn ng ng phn ho:

RCCCC CCCCR

n nh ca ion cacboni theo bc l gim dn nh

sau :

C3+ (bc 3) > C2

+ (bc 2) > C3+ (bc 1)

Ion cacboni tc dng vi phn t trung ho to thnh

ion cacboni mi v phn t mi (hydrocacbon no hay i)

theo phn ng vn chuyn ion hydrit.

C+nH2n+1 + CmH2m CnH2n

+ C+mH2m+1

C+nH2n+1 + CmH2m+2 CnH2n+2 +

C+mH2m+1

Phn ng cracking: Cc ion cacboni c s nguyn t

cacbon ln xy ra s phn hu v t mch v tr so

vi nguyn t cacbon tch in. Sn phm phn hu l

mt phn t hydrocacbon trung ho v ion cacboni mi c

s nguyn t cacbon nh hn:

.

Nu ba lin kt CC v tr th lin kt CC v

tr [A] l c xc sut t mch ln nht, sau n v

tr [B] v cui cng n v tr [C].

R C C C C C C+

C

C

[A] [B]

[C]

R CH2 CH CH3+

CH3

R C CH2+

CH3

R CH CH2+

++


15/85


17

Vi ion cacboni mch thng:

i vi ion cacboni l ng ng ca benzen, v d

nu p dng quy tc v tr bnh thng th v tr

rt bn vng. Chnh v vy m ngi ta cho rng

proton phi c kt hp vi mt trong nhng lin kt

CC trong nhn thm to thnh nhng hp cht trung

gian, sau mi phn hu theo quy tc nu trn. Khi

phn hu, in tch ion cacboni s dch chuyn theo s

sau:

Nh vy trong hydrocacbon thm hiu ng tch in

nhn thm l nguyn nhn quan trng hn so vi nguyn

nhn l s bin i ion cacboni bc hai thnh bc ba.

Cc ioncacboni l ng ng ca Benzen m c mch

nhnh cng di th tc xy ra cng lnv cng d. V

d nh ioncacboni izobutyl-benzen c tc ln hn 10

ln so vi ioncacboni izopropyl-benzen .

Cc nhm metyl , etyl , rt kh b t ra khi nhnBenzen ( v l nng lng lin kt ln ) v do kh

to c ion CH3+ v C2H5

+. iu ny gii thch c

v sao trong xng cracking xc tc li c hm lng

hydrocacbon c mch nhnh bn ngn l ln v cng gii

+

CH3 CH CH2 R+

RCH3 CH CH2+

C

C C+

C

CH C+

+C

C C

C+

H


16/85


18

thch c l v sao trong sn phm kh ca qu trnh

cracking li nhiu hydrocacbon mch nhnh.

c. Giai on dng phn ng

Giai on ny xy ra khi cc ion cacboni kt hp vi

nhau hoc chng nhng hay nhn nguyn t hydro ca xc

tc to thnh cc phn t trung ho.

Trong iu kin m chng ta tin hnh qu trnh

cracking xc tc, mt s lng ln cc phn ng ha hc

xy ra v chng quyt nh cht lng hiu sut ca qu

trnh. l cc phn ng sau:1. Phn ng phn hu cc mch, phn ng cracking.L phn ng phn hu b gy mch nhng phn t c

kch thc ln (trng lng phn t ln) thnh nhng

phn t c kch thc nh hn (trng lng phn t nh

hn). y l phn ng chnh ca qu trnh.

+ Phn hu parafin to olefin v parafin c trng

lng phn t nh hn

CnH2n+2 CmH2m + CpH2p+2 (n = m + p)

+ B gy mch olefin to olefin nh hn

CnH2n CmH2m + CpH2p (n = m + p)

+ Hydrocacbon thm c nhnh bn b b gy to thnh

parafin v hydrocacbon thm c nhnh nh hn

ArCnH2n+1 ArCmH2m+1 + CpH2p (n = m + p)

+ Naphten b b gy m vng to cc olefin (tr vng

hexan)

CnH2n CmH2m + CpH2p (n = m + p)


17/85


19

naphten olefin olefin

CnH2n C6H12 + CmH2m + CpH2p (n = m +

p+ 6)

naphten xyclohexan olefin olefin

2. Phn ng ng phn ho (izome ho).L phn ng to ra nhng hydrocacbon c cu trc

mch nhnh (cu t lm tr s octan tng ln).

n-olefin izo-olefin

n-parafin izo-parafin

3. Phn ng chuyn di hydro d-i tc dng ca xctc.

Nh c xc tc m c s phn b li hydro cho nn

lm no c mt s hydrocacbon i (sn phm phn hu),

v vy lm tng c tnh n nh ho hc ca sn phm

thu.

Naphten + olefin hydrocacbon

thm + parafin

4. Phn ng trng hp.Ch yu xy ra vi hydrocacbon i.

CnH2n + CmH2m CpH2p (n + m = p)

5. Phn ng alkyl ho v kh alkyl ho.Phn ng alkyl ho xy ra nhit thp, lm gim

hiu sut kh.


18/85


19/85


21

Hp ph nguyn liu trn tm hot hot tnh xctc.

Cc phn ng ha hc. Nh hp ph cc sn phm phn ng ra khi b mt

hot tnh ca xc tc.

Khuch tn hi sn phm ra khi vng phn ng.Tc chung ca qu trnh nh vy s c quyt

nh bi giai on no chm nht.

Phn ng xy ra trong vng ng hc hay vng khuch

tn, hon ton ph thuc vo bn cht ca xc tc c

s dng, ph thuc vo bn cht ca nguyn liu v vo

ch cng ngh ca qu trnh. Cc nghin cu cho

thy, nu qu trnh cracking xc tc nguyn liu l

gazoil nh (nguyn liu mu) trn xc tc dng cu khi

kch thc ht xc tc t 3 5 mm v nhit l 450

5000C th phn ng xy ra vng trung gian gia ng

hc v khuch tn. Cn khi cracking lp si (FCC) ca

xc tc nhit 480 5300C th phn ng xy ra

vng ng hc.

Tc ca phn ng cracking xc tc, trong a s

cc trng hp c miu t bng phng trnh bc mt

c dng:

k = v0.n.ln(1 x) (n 1)x

y:

k: tc ca phn ng (mol/g.h)

v0 : tc truyn nguyn liu (mol/h)


20/85


22

n: s mol sn phm c to thnh t 1 mol

nguyn liu

x: mc chuyn ha (phn mol).

i vi phn on du trn xc tc zeolit, phng

trnh bc 1 li c dng sau:

k=vo/(1-x)

v0 l tc th tch khng gian truyn

nguyn liu (m3/m3.h).

IV. Cracking xc tc cc hydrocacbon ring l.1.

S bin i cc hydrocacbon paraffin. [1.109]

Cc hp cht parafin l cu t quan trng ca phn

on gazoil. Cc nghin cu qu trnh cracking xc tc

parafin s gip cho php tin hnh m hnh ha cc hin

tng ca qu trnh.

Nng lng hot ha ca phn ng cracking parafin

gim dn nu chiu di mch hydrocacbon parafin tng.

V d:

n-C6H14 n-C7H16

n-C8H18

E(kcal/mol) 36

29 24

V vy khi cracking, mch hydrocacbon parafin cng

di, cng d b b gy. V d khi cracking xc tc cc

parafin nhit 5500C nh sau:


21/85


22/85


24

%V 9 12 19 49 8,5

1,6

S phn b ny khng i xng nhau qua C3. S c mt

mt lng ln H2 v metan cho thy rng cng mt lc xy

ra nhiu phn ng, c th c c phn ng cracking nhit

cng vi cc phn ng ca ion cacboni nh nu

trn. Phn ng chnh to sn phm s ph thuc vo

tng quan gia cc phn ng cracking (theo quy tc )

v phn ng vn chuyn hydro ca ion cacboni.

Do cracking xc tc m lm gim kch thc ca ion

cacboni R+ cc ion c kch thc nh nh +CH3 hay+C2H5

s kh to ra (do ct mch v tr so vi cacbon

mang in tch). V th trong sn phm u tin to ra C3

hay C4

nhiu hn C1

v C2

so vi qu trnh cracking

nhit.

2. S bin i ca hydrocacbon olefin [1.110].Hydrocacbon olefin c mt trong hn hp phn ng l

do phn ng cracking parafin, naphten hay alkyl thm.

Hydrocacbon olefin l nhng hp cht hot ng hn,

trong giai on u tin ca qu trnh, chng tham gia

phn ng to ion cacboni bi qu trnh hp th mt

proton vo lin kt i. Ion cacboni va to ra s b

cracking theo quy tc , khi to thnh mt olefin

nh hn v mt ion cacboni bc mt m ion ny c th

RRH R1+

+

+ R1H+

R2 olefin++


23/85


24/85


25/85


27

Cc olefin trong qu trnh cracking xc tc cn tham

gia phn ng ngng t, ng vng to hydrocacbon thm

a vng v vng thm a t l cc:

3. S bin i cc hydrocacbon naphtenic [1.112]Sn phm bc 1 ca qu trnh cracking xc tc

naphten l olefin c cng s nguyn t cacbon. V d

vi xycloparafin C3 v C4 sn phm u tin quan st

c l propen v buten tng ng. Cc naphten c mch

bn di hn thng b ct nhnh to xyclohexan v

olefin. Sau vng naphten c th b kh hydroddeer

to thnh hydrocacbon thm. c trng phn b sn phm

khi craking naphten l to thnh mt lng ln cc hp

cht c nhnh v hydrocacbon thm so vi cracking

paraffin.

V d:

Phn ng phn hy vng naphten to izo-parafin:

CH2 CH2 CH2 CH2 CH2 CH2 H2+ + + 3

CH2 CH CH2 CH2 CH2 CH3H2 H2 H2

H2+ 2CH2 CH2 CH3

C3H8 +

+ H23

CH3 CH3 CH2 CH2 CH2 CH CH3

CH3


26/85


28

Phn ng ng phn ha vng naphten

Phn ng chuyn v cc nhm bn:

Nhn chung, sn phm cracking naphten c c trng

no hn so vi cracking paraffin. Trong sn phm, do

phn ng trn xc tc m hydrocacbon c s nguyn t

ln hn 3 chim phn ch yu. V vy khi cracking xc

tc cc hp cht naphten s cho nhiu sn phm lng

hn, ngha l hiu sut xng s cao hn. Do ngi tacho rng naphten l thnh phn l tng nht ca nguyn

liu cracking xc tc.

4. S bin i ca hydrocacbon thm [1.112, 2.114,3.92]

Cc hydrocacbon thm m c gc alkyl nh bn th

rt kh b cracking ngay c khi c mt ca cht xc tc, v vng benzen c bn cao .V vy m trong qu

trnh cracking xc tc, cc hp cht alkyl thm do vng

thm c bn cao hn nn trc tin s xy ra qu

trnh ct nhnh alkyl.

CH3

CH2 CH3

CH3

CH3

CH3

CH3


27/85


29

Nhng toluen c bn rt ln, v th khng th

tch nhm metyl hay etyl trong iu kin cracking. Mch

alkyl cng di th cng d b b gy v nu mch alkyl

li c nhnh th tc ct nhnh cn ln hn nhiu.iu ny d dng gii thch khi xem xt nng lng hot

ha ca hydrocacbon thm:

Loi hydrocacbon thm Nng lng hot ho

(kcal/mol)

C6H5C2H5 50

C6H5C4H9 34

C6H5CHCH2CH3 19

CH3

C6H5CHCH3 17,5

CH3

V d:

Khi cracking xc tc propyl benzen, phn ng xy ra

nh sau:

C6H5CH2CH2CH3 C6H6 + CH3CH=CH2

Cn khi cracking nhit li xy ra theo hng khc:

C6H5CH2CH2CH3 C6H5CH3 + CH2=CH2

Cc phn ng khc li xy ra trong qu trnh

cracking xc tc hydrocacbon thm l:

Phn ng ng phn ho: Cc hydrocacbon thm cha

nhiu gc metyl d tham gia phn ng ng phn ho do

s chuyn v cc nhm metyl theo vng benzen.


28/85


30

V d:

Hydrocacbon thm cn tham gia phn ng chuyn v

nhm metyl ngoi phn t: (1,2,3)

Hydrocacbon thm c nhnh alkyl di c th khp

vng to hydrocacbon thm d vng:

Cc hydrocacbon thm a vng xy ra phn ng

ngng t v to cc:

hay

CH3

CH3

t C, xc tco

CH3

CH3

CH3CH3t C, xc tco

para-xylen meta-xylen octo-xylen

2

t C, xc tco

CH3

CH3

CH3

+

CH3

CH3CH3

t C, xc tco

CH2 CH2 CH2 CH3

CH2 CH2 CH2 CH3

H25+

2 + CH2 CH2

2

H2 H22


29/85


31

Cc hydrocacbon thm a vng ngng t cao to cc d

hp ph trn b mt xc tc. V vy chng km hm qu

trnh lm nh hng n qu trnh cracking cc loi

hydrocacbon khc.

Trong iu kin ca cracking xc tc, cc bin i

ca hydrocacbon ring l c th tm tt nh sau:

Olefin v parafin

Parafin Olefin v hydro

izo-parafinCc hp cht olefin c trng

lng thp

Parafin v

dien

Olefin Parafin hay

naphten v hydrocacbon thm

Polyme, cc

Olefin

v parafin

Naphten Xyclohexan v olefin

Hydrocacbon thm

Olefin

Parafin v

alkyl thm c mch bn ngn


30/85


32

Hydrocacbon thm ng phn ho,

chuyn v nhm alkyl

(alkyl thm) Sn phm ngng

t, cc

Ngoi ra cn xy ra cc phn ng bc 2 nh:

Naphten + Olefin Hydrocacbon

thm v parafin

Hydrocacbon thm + Olefin Sn phm ngng

t, cc

V.

Cracking phn on du m [1.114] cracking xc tc phn on du m, do qu trnh

rt phc tp, nn thc t khng th miu t tt c cc

phn ng ho hc xy ra trong qu trnh. Do ngi ta

thng a ra s kho st cc hng phn ng chnh

trong qu trnh cracking xc tc. V d khi nguyn liu

l phn gazoil chng ct chn khng, ta c th dng s

sau:

Gasoil chn khng

HCO

LCO

Xng

C4 v kh

Cc

Hnh 1. s chng ct gasoid chn khng


31/85


33

LCO - phn on du nh ca cracking xc tc

HCO - phn on du nng ca cracking xc

Nhn s phn ng chng ta thy rng, cc sn phm

ph l LCO v HCO cn phi to iu kin thun li

chng chuyn ho tip thnh xng, ng thi c gng hn

ch qu trnh to kh v cc. S hnh thnh cc l

khng mong mun, v cc bm trn tm hot tnh ca xc

tc, dn n lm gim hot tnh ca xc tc. Sn phm

cc c to ra l mt h vng thm c ngng t cao,

nn khc vi cacbon t do. S hnh thnh cc c th docc nguyn nhn sau:

Do bn cht ca nguyn liu cracking

Do cht xc tc ca qu trnh c chn lc khng

cao

Do ch cng ngh cha ti u.

Cc c to thnh trong qu trnh c th phnchia thnh 3 phn chnh l:

Lng cc do phn ng ho hc

Lng cc ng phn hp ph ho hc trn b mt

xc tc

Lng cc do nguyn nhn nh hp ph chm v t l

% tng ng gia chng l 55-75/10-20/5-10


32/85


34

ch-ng IIxc tc ca qu trnh Cracking

S pht trin v ci tin qu trnh cracking xctc trong cng nghip ch bin du m, ngoi vic ci

thin v nguyn liu, h thng thit b, ch cng

ngh v.v..., th ta thy rng ci chnh l do s ci

tin trong vic s dng cc cht xc tc. Phn ng

cracking xc tc ch yu xy ra trn b mt xc tc,

chiu hng ca phn ng ph thuc rt nhiu vo bn

cht ca xc tc. Xc tc c dng trong qu trnh

cracking thng l xc tc rn, xp, c ngun gc thin

nhin hay tng hp, vi b mt ring ln. Xc tc

cracking u tin c dng l t st thin nhin c

tnh axit (v d loi montmorillonit).

V d: Lin X vo nhng nm 1919 - 1920 dng

xc tc AlCl3 trong h thng cracking sn xut xng.

Xc tc AlCl3 tin hnh nhit thp 200 3000C.

Nhng trong qu trnh s dng ngi ta thy c nhiu

nhc im sau: Xc tc b mt mt nhiu do to phc

vi cc hydrocacbon ca nguyn liu, iu kin tip xc

gia xc tc v nguyn liu khng tt, cho hiu sut v

cht lng xng thp.V sau ngi ta nghin cu s dng aluminosilicat v

nh hnh m u tin l t st bentonit. Vo nm 1936

Lin X s dng xc tc aluminosilicat quy m

cng nghip. Ngi ta tin hnh tng hp


33/85


35

aluminosilicat trong cc nh my ch to xc tc. Sau

trong cng nghip ch bin du m ngi ta dng

ph bin xc tc aluminosilicat tng hp v n c hot

tnh v chn lc tng i cao. Xc tc ny tngc s dng trong cng nghip cracking sut 30 nm.

Tuy vy, hin nay vic ci thin xc tc vn khng

ngng pht trin v n cui thp nin 60 ca th k

20, ngi ta chuyn sang ch yu dng xc tc cha

zeolit.

M vo nm 1972 s dng khong 80% cht xc

tc cha zeolit cho qu trnh cracking xc tc. Hng

nm M tiu th 130 nghn tn xc tc, trong ch

c 14 nghn tn l khng cha zeolit.

I. Vai tr ca xc tc trong qu trnh cracking

[2.119].

Xc tc trong qu trnh cracking c tm quan trng

rt ln. N c kh nng lm gim nng lng hot ha

ca phn ng, do vy m tng mc phn ng ln rt

nhiu. V d khi c mt ca xc tc 400o 5000C cc

olefin chuyn ha nhanh hn 1 000 10 000 ln so vi

craking nhit Dng xc tc cho php qu trnh tin hnh

iu kin mm hn, khi c mt xc tc lm tng tc

phn ng lm tng nng sut. Ngoi ra xc tc c tnhchn lc nn hng qu trnh ch bin theo nhng phn

ng c li thu c nhiu sn phm chnh mong mun, t

sn phm ph.


34/85


36

II. Nhng yu cu cn thit i vi xc tc

Xc tc cho qu trnh cracking i hi nhng yu cu

sau:

1. Hot tnh xc tc phi cao: [1.120]

Hot tnh xc tc l yu cu quan trng nht i vi

xc tc dng trong qu trnh cracking.

V mc ch ca cracking l nhn xng, nn phng

php dng hiu sut xng thu c nh gi hot

ng ca xc tc s n gin hn, hot tnh ca xc tc

cng cao s cho hiu sut xng cng ln. Do vy, hot tnh ca xc tc thng c biu din thng qua

ch s hot tnh. l gi tr ca hiu sut xng

(%KL) khi cracking nguyn liu mu trong iu kin

phng th nghim. Hot tnh xc tc ph thuc vo tnh

cht vt l - ha hc ca xc tc, m trc ht l ph

thuc vo thnh phn ha hc ca xc tc cng nh ph

thuc vo iu kin cng ngh ca qu trnh. Trong thc

t sn xut, da vo hot tnh ca xc tc, ngi ta

phn xc tc thnh cc loi nh sau:

+ Xc tc c hot tnh cao, hiu sut xng > 45%

+ Xc tc c hot tnh trung bnh, hiu sut xng t

30 n 40%

+ Xc tc c hot tnh thp, hiu sut xng < 30%.

Thnh phn ho hc, %

Oxyt nhm 13


35/85


37

Oxyt silic 87

Oxyt cc nguyn t t

him

2 4

Oxyt natri 0,02 0,2

Trng lng rt, g/cm3 0,8 0,9

hot tnh n nh 55 60

hot tnh theo ASTM 75 80

bn do mi mn, % 94 96

Thnh phn c ht, %

n 20 m

n 40 m

n 100 m

< 2 3

15 25

96 98

B mt ring, m2/g 400 450

Bng 1. Tnh cht ca xc tc FCC

Mt khi nim quan trng l hot tnh n nh ca xc

tc. Xc tc mi, trong iu kin cracking thng c

hot tnh cao, theo thi gian lm vic, hot tnh

gim dn ti mt gi tr n nh. Lc ny ngi ta coi

l hot tnh n nh ca xc tc hay hot tnh

bn, hot tnh cn bng. Sau mt thi gian lm vic ko

di na, hot tnh ca xc tc b gim xung do cc

to ra che ph nhanh cc tm hot tnh ca xc tc.


36/85


38

2. chn lc xc tc phi cao

Trc tin cht xc tc lm tng tc ca cc phn

ng c li trong nhng iu kin nhit v p sut

nht nh, sau c tc dng lm gim tc cc phn

ng ph ,nht l nhng phn ng gy ng c xc tc nh

phn ng to cc [6. 104]

chn lc ca xc tc l kh nng ca xc tc lm

tng tc cc phn ng c li, ng thi lm gim tc

cc phn ng khng mong mun. Trong qu trnh

cracking, chn lc ca xc tc quyt nh kh nng

to cc sn phm c gi tr ca n, l cc cu t

xng c tr s octan cao. Ngi ta c th nh gi

chn lc bng cch xc nh t l gia hiu sut xng

v cc (hay kh) cng mt su bin i. Xc tc

thng c nh gi ng thi hot tnh v chn

lc ca n so vi xc tc mu khi tin hnh trong cng

mt iu kin cracking. T s gia hiu sut xng v

cc (hay kh) cng ln th chn lc xc tc cng

cao. Sau mt thi gian lm vic c hot tnh v

chn lc ca xc tc u b gim do c nhng thay i

v tnh cht ca xc tc trong iu kin lm

vic.[1.121]

3. n nh phi ln [3.73].Xc tc ch to ra cn phi gi c nhng c tnh

ch yu (hot tnh, chn lc) sau mt thi gian lm

vic lu di. Cht xc tc c thi gian lm vic lu

di th gi thnh chi cho cht xc tc cng thp ( cho


37/85


39

d tin mua xc tc c t ) hn so vi khi mua xc

tc r m thi gian lm vic ngn.

n nh xc tc c trng cho kh nng khng thay

i cc tnh cht trong qu trnh lm vic. Xc tc c

n nh cng cao cng tt trong qu trnh s dng.

4. m bo bn c v bn nhit: [3.73]

Trong qu trnh lm vic, xc tc c xt vi nhau v

c xt vi thnh thit b lm cho xc tc d b v, do

lm tn tht p sut qua lp xc tc tng ln, lm

mt mt xc tc ln. V vy m xc tc phi m bo bn c.

Khi lm vic nhit c th thay i, khi nhit

cao qu m nu xc tc khng c bn nhit th c th

b bin i cu trc dn n lm gim cc tnh cht ca

xc tc.

5. Xc tc phi m bo thun nht cao [3.73]

Xc tc cn ng nht v thnh phn, v cu trc, v

hnh dng, v kch thc. Khi kch thc khng ng u

s to ra nhng vng phn lp v c tr lc khc nhau

v do s phn lp theo kch thc nn s ph v ch

lm vic bnh thng ca thit b. Mt khc khi kch

thc khng ng u lm tng kh nng v vn dn n

mt mt xc tc. Cu trc l xp khng ng u s lm

gim b mt tip xc dn n lm gim hot tnh xc

tc.


38/85


40

6. Xc tc phi bn vi cc cht lm ng c xc tc

[3.73]

Xc tc phi chng li c hiu qu tc dng gy ng

c ca nhng hp cht ca nit, lu hunh ( NH3, H2S ),

cc kim loi nng ko di thi gian lm vic ca xc

tc.

7. Xc tc phi c kh nng ti sinh [3.73]

y l yu cu quan trng trong qu trnh s dng

xc tc. Xc tc c kh nng ti sinh tt s nng cao

c hiu qu v nng sut ca qu trnh, lng tiuhao xc tc cng gim xung.

Xc tc b mt hot tnh trong qu trnh phn ng do

nguyn nhn chnh l cc to thnh sau phn ng bm

trn b mt hot ng ca xc tc. V th ti sinh

xc tc cn phi t cc trong l ti sinh.

Cng vi vic ci tin v hon thin dy truyn cng

ngh cracking xc tc, ngi ta cn khng ngng nng

cao cht lng xc tc tng hiu sut ch bin ca

qu trnh cng nh nng cao hiu qu ca qu trnh ti

sinh xc tc. T ch ch ding xc tc axit Al-Si dng

v nh hnh, ngi ta nghin cu thnh cng v a

vo ng dng loi xc tc dng kt tinh zeolie. Thnh

tu ny c th coi l cuc cch mng trong cng ngh

cracking xc tc. Loi xc tc ny cho hiu sut xng

v diezel cao, lm gim c t l cc v kh. Trong

nm 1969 c gn 90% cc phn xng cracking xc tc

M v Canada s dng xc tc zeolite X,Y, chng rt


39/85


40/85


42

(Me+)x[(Al2O3)x.(SiO2)y]z.2H2O

Trong : Me - l cation bi tr in tch

x,y - l cc h s tng ng

z - s phn t nc kt tinh trong Z

n v cu trc c bn ca Zeolit l t din TO4,

l mt cation T c bao quanh bi 4 ion O-2. Nu T l

Si th SiO4 l t din trung ha in tch , nu l nhm

Al3+ th t din AlO-4 mang mt in tch m:

O2-

O2- O2-

Si4+

O2-

Hnh 2. T din SiO4

O2-

O2- O2-

Al3+

O2-

Hnh 3. T din AlO-4

S thay th Si+4 bng nhm Al+3 lm xut hin mt

in tch m trong mng tinh th v n c b tr bi

cation b tr in tch hay cation i.

Tnh cht ca Zeolit c thay th bi cc cu trc

v hnh thi ca chng ,tc l s sp xp trt t ca


41/85


43

t din , phn th tch rng , s tn ti cc mao qun

v cc l ,kch thc ca cc mao qun v cc l. Ngoi

ra tnh cht ca Zeolit cn ph thuc vo t l Si/Al

v cation b tr in tch (K+

, Na+

...)

Quy tc Lowenstion xc nh rng : 2 nguyn t nhm

khng th tn ti ln cn nhau , ngha l trong cu

trc Zeolit khng th tn ti cc lin kt Si-O-Si v

Si-O-Al . V vy m t l Si/Al lun lun ln hn hoc

bng 1.

1.2 cu trc ca Zeolit [1.117]

V cu to, zeolit c to thnh t cc n v cu

trc c bn gi l n v cu trc Sodalit (hnh 4).

Nu cc n v ny ni vi nhau theo cc mt 4 cnh,

ta c zeolit loi A. Nu ni vi nhau theo mt 6 cnh,

ta c zeolit loi X hay Y c cu trc tng t nh

faurazit (hnh 5).

Hnh 4. n v c bn ca

zeolit

Hnh 4. Cu trc soladit.

Si+

O

O

Al+


42/85


44

Zeolit A Zeolit X

Hnh 5. Cu trc ca zeolit A v X, Y.

Ngy nay ngi ta ch to c hng trm loi

zeolit, chng -c c tr-ng bi kch th-c cc ca

s khc nhau. V d c tr-ng ca mt s loi zeolit

c dng ph bin trong cracking xc tc c dn

ra bng sau:

Zeolit Thnh phn ho hc ng knh l trung

bnh,

A Na2O.Al2O3.2SiO2.4,5

H2O

3,6 3,9

X Na2O.Al2O3.2,5SiO2.6

H2O

7,4

Y Na2O.Al2O3.4,8SiO2.8

,9H2O

7,4

Mordenit Na8O(Al2O3)8(SiO2)40.

24H2O

6,7 7,0 (2,9

5,7)


43/85


45

ZSM-5 v

11

5,4 5,6

Bng 2. c trng c bn ca mt vi loi zeolit

2. Zeolit v xc tc cha Zeolit dng cho qu trnh

cracking [1.117,118,119]

Khi ch to xc tc cracking, hm lng natri (Na)

cn phi gim ti cc tiu bi v s c mt ca Na

nhit cao v c mt hi nc, n lm gim i ng k

hot tnh cng nh chn lc ca xc tc cracking.Khi thay th Na bng cc cation kim loi ha tr ln

hn 2 hay bng 2, th d nh canxi (Ca), reni (Re) hay

cc nguyn t t him, s lm thay i c trng cu

trc ca zeolit. Kch thc l tng ln, ng thi khi

li to ra cc tm axit lm hoi tnh ca xc tng

ln.

Ngi ta cho thy rng, zeolit cha oxyt silic cng

nhiu, lng oxyt nhm cng t th axit ca n cng

tng. ng nhin khi tng t s oxyt silic/oxyt nhm,

khng c dn n ph hy cu trc ca zeolit. Hay ni

cch khc l t s ny cng ch tng n mt gii hn

nht nh.

Tnh cht hp ph ca zeolit xut hin khi chng

c tch m, bi v trong qu trnh tng hp, cc l

rng ca tinh th b cht y cc phn t nc. Nc c

th tch khi tinh th khi ta sy kh zeolite n nhit

t 300 3500C. Lc ny mng tinh th ca zeolite vn


44/85


46

c bo ton. Sau khi dehydrat ha, zeolite c dung

lng hp ph rt ln.

bn nhit cao cng l c trng rt quan trng

ca zeolite. Th d zeolite NaA bn n 6500C, NaY bn

n 700 750 0C , CaY n 8000C, LaY n 8500C. bn

nhit ca zeolit tng khi tng hm lng SiO2 hay tng

kch thc ca cc cation kim loi.

Qu trnh cracking xc tc thng dng zeolit loi

X, Y c cha cc nguyn t t him hay dng trao

i ion v c x l bng cc phng php c bit,

ng thi kt hp vi cc hp phn lm tng bn c,

bn nhit hay iu chnh kch thc l xp. Zeolit c

hot tnh cracking ln, v th ngi ta thng dng n

dng hn hp vi xc tc v nh hnh hay

aluminosilicat tinh th v c gi l xc tc cha

zeolit. Trong sn xut xc tc, ngi ta trn 10 n

20% (KL) zeolit v vi hp phn nh vy, xc tc cng

rt hot ng, hn hn xc tc aluminosilicat thng

thng. Hn na cc ch tiu kinh t cng t tt hn.

Trong cng nghip, ngi ta ch to xc tc cha

zeolit hai dng chnh. Xc tc dng cu v xc tc

dng bt. Xc tc dng bt v sau ci tin thnh xc

tc vi cu thng c p dng cho qu trnh crackinglp si (FCC), cn xc tc dng cu vi kch thc ht

t 3 n 5 mm thng c dng cho qu trnh cracking

xc tc chuyn ng (TCC).


45/85


47

Zeolit c hai loi kch thc l xp: kch thc

ca s v kch th-c l ln, khi -a chng vo trn

ln vi aluminosilicat, chng ta s iu chnh c cu

trc l ca chng nhn c kch thc l trong giihn thch hp nht, nhm tng chn lc ca xc tc.

V d, trong xc tc cha zeolit loi A, kch thc l

ca n khng vt qu 4 n 5. Trong cc l nh vy

propylen c th chuyn qua t do, nhng iu li

khng xy ra i vi izo-butylen. Do trn xc tc

nh vy c th tin hnh qu trnh polyme ho chn lc

propylen c trong hn hp vi izo-butylen m khng phi

phn tch chng. Hay t zeolit vi kch thc 5 c th

dng lm xc tc cracking chn lc n-parafin c

trong hn hp vi izo-parafin, v trong iu kin ,

izo-parafin b cracking khng ng k.

Xc tc cha zeolit X v Y c kch thc l khong 8

n 10 c dng cracking nguyn liu c thnh phn

phn on rng (v d gazoil). Khi cc phn t ln

ca nguyn liu vn c th d dng ti b mt ca xc

tc, cn cc phn t nh hn c th tip xc vi cc

tm hot tnh b mt trong ca xc tc. V cc l hp

cht cao phn t nn chng thng tp trung b mt

ngoi ca xc tc v do vy to iu kin thun li choqu trnh t chy cc khi ti sinh xc tc.

Zeolit loi X, Y, ZSM-5 (11) l loi c cc tnh

cht thch hp nht cho qu trnh cracking xc tc.

Kch thc l ln ca chng xp x 10 s cho php


46/85


48

khuch tn d dng cc phn t ca nguyn liu vo b

mt l xp ca chng cng nh khuch tn sn phm ra

ngoi. V vy chng c s dng ch to xc tc

cracking cng nghip. Thng thng cc zeolit ny lloi trao i cation (H+, NH4

+ hay cation a ha tr)

kt hp vi cc phng php x l thch hp v phi

trn vi aluminosilicat v nh hnh. Loi xc tc ny

c hot tnh cao hn hng trm ln v c chn lc

cao hn so vi xc tc aluminosilicat thun khit. Hiu

sut xng tng ln t nht l 20%, trong khi hiu

sut cc v kh li gim khi tin hnh cng mt iu

kin.

trn th gii cc cht xc tc cracking c nhiu

hng sn xut, l: Grace, Engel Grard, Mobil,

Fihtrol, AK20, Crosfiel, Catalystics

Cc c trng c bn ca xc tc cracking l: thnh

phn, trng lng tt, cu trc xp, hot tnh,

thnh phn c ht v bn.

Ngoi nhng u im trn xc tc cha zeolit vn cn

mt s nhc im nh sau:

+ Gi thnh sn xut chng cao

+ Nu s dng xc tc zeolit nguyn cht th tc

trao i cht ca qu trnh phc hi v trao i nhit

b hn tc chnh bn thn phn ng xc tc. V vy


47/85


49

m ta dng xc tc cha zeolit (zeolit tm trn cht

mang, 2 20% trn aluminosilicat tng hp).

Ni tm li, xc tc cha zeolit cho qu trnh

cracking c nhiu u im hn hn cc xc tc khc, nn

hin gi y cc nc cng nghip ch bin du m v

kh tin tin, ngi ta ln lt thay th xc tc cha

zeolit cho aluminosilicat tng hp. Hin nay ngi ta

ang s dng xc tc zeolit siu bn, n p ng c

mi yu cu ca xc tc trong qu trnh cracking.

IV. Nhng thay i tnh cht xc tc khi lm vic[1.122]

Xc tc cracking trong qu trnh lm vic b gim

hot tnh v chn lc. Hin tng ny ngi ta gi

l qu trnh tr ho xc tc. Qu trnh tr ho xc tc

cng nhanh nu ta tin hnh qu trnh iu kin cng

ngh kh khn, kht khe tng (v d nhit qu

cao, thi gian tip xc qu di, nguyn liu xu).

Ngoi ra cn xy ra cc qu trnh khc lm tng tc

tr ho. Chng ta c th phn qu trnh tr ho xc tc

lm hai qu trnh chnh, l s tr ho do tc dng

ca cc cht lm ng c xc tc v s tr ho do tc

dng lm thay i cc tnh cht l - ho ca xc tc.

Nguyn nhn ca s tr ho xc tc c th l do:

Tc dng ca cc c t nh NH3, CO2 ca cchp cht lu hunh m c bit l H2S nhit

cao.


48/85


50

S tch t cc kim loi nng di dng ccoxyt lm thay i chc nng ca xc tc.

S tc ng ca nhit cao v hi ncCc hp cht kh tc dng vi xc tc c th chia

lm 3 nhm:

Nhm khng tc dng vi xc tc nhit thp hn 6200C nh CO, CO2 v NH3.

Nhm lm gim hot tnh ca xc tc nhngkhng lm gim chn lc nh hi nc.

Nhm lm gim chn lc ca xc tc (H2S nhit trn 4250C v NH3 , SO2, SO3 nhit

trn 6200C).

T kinh nghim thao tc cng ngh cracking cho thy,

hot tnh ca xc tc c th c duy tr nu ta thm

hi nc vo nguyn liu, hay vic x l trc v sau

khi ti sinh xc tc. Thm hi nc khi ch bin nguyn

liu c lu hunh s c tc dng m v khi li lm

tng qu trnh n mn thit b v sn phm ca qu

trnh n mn li lm nhim bn xc tc, dn ti lm

gim hot tnh, chn lc ca xc tc.

Tc dng ng thi ca nhit cao v ca hi nc

lm gim hot tnh tng cng ca xc tc. Khi p dng

lp si (FCC), do cn phi duy tr iu kin cc t

lng ng trn xc tc v xc tc khng b qu nhit

khi ti sinh, ngi ta phi a vo mt lng nh hi

nc. Hn na, cng cn phi trnh s to cc qu t,

v iu dn ti ph v cn bng nhit ca h l phn


49/85


51

ng v ti sinh, do nhit to ra trong qu trnh ti

sinh khng b nhit thu vo ca cc phn ng

cracking trong l phn ng.

Hm lng cc trn xc tc khi ra khi l phn ng

ph thuc vo lng xc tc tun hon trong h thng.

i vi a s cc qu trnh FCC, khi dng xc tc

zeolit, lng cc to ra thng chim vo khong 1,3

n 1,8% KL xc tc, cn sau khi ti sinh l 0,1 n

0,05% KL.

Cc hp cht c kim v cc hp cht cha nit trong

nguyn liu u l cc phn t lm gi ho nhanh xc

tc. Nhiu nghin cu ch ra rng, s c mt ca cc

hp cht nit trong nguyn liu lm gim hiu sut xng

v cc sn phm trng. V d, hm l-ng nit tng t

0,1 n 0,4% KL, hiu sut xng b gim i ti 2 ln,

cn hiu sut gazoil nh cng b gim, ng thi lm

tng hiu sut cn nng v gazoil nng. Khi tng nhit

, tc dng c hi ca cc hp cht nit s gim.

S u c xc tc bi cc kim loi cng c

nhiu nghin cu cp ti v ch r c ch tc dng

ca chng n hot tnh ca xc tc. Khi lng ng cc

oxyt kim loi nng trn xc tc s dn ti lm gim

su cracking v gim hiu sut xng do tng qu trnhto cc.

Khi hm lng cc hp cht lu hunh trong nguyn

liu tng th hm lng cc kim loi nng nh niken v

vanadi cng tng theo, v a phn chng u tp trung


50/85


52

phn cn nng v phn on nha - asphan. V d, trong

du m c lu hunh th c ti 90% phc cht porphirin

cha vanadi, cn trong du cha t lu hunh th l

phc vi niken.V. Ti sinh xc tc [1,2,3]

Xc tc cracking sau mt thi gian lm vic b mt

hot tnh do cc to thnh bm trn b mt, hot mt s

phn ng ph to polymer che ph cc tm hot tnh ca

xc tc. xc tc c th lm vic c bnh thng,

phi ti sinh xc tc khi phc li hot tnh ca

n.

Bn cht ca qu trnh ti sinh l t chy cc bm

trn b mt xc tc. [2.121]. Ngi ta tin hnh t

cc bng khng kh nng trong l ti sinh xc tc. Kt

qu ca qu trnh t chy cc l sinh ra CO v CO2. Cc

phn ng chy ny ta nhiu nhit. Ngoi ra cn cc

phn ng kh cc hp cht lu hunh. Cc phn ng xy

ra khi ti sinh xc tc c miu t nh sau:

C + O2 CO2 Q = 33,927 34,069

MJ/kg

C + O2 CO Q = 10,629 10,314

MJ/kg

CO + O2 CO2 Q = 23,650 23,755

MJ/kg

H2 + O2 H2O Q = 1210,043

1210,252 MJ/kg

2

1

2

1

2


51/85


53

S + O2 SO2 Q = 9,132 9,222

MJ/kg

SO2 + O2 SO3

MeO + SO3 MeSO4

MeSO4 + 4H2 MeO + H2S + 3H2

Nhit lng to ra c dng cp nhit cho xc

tc mang vo l phn ng, ngoi ra cn tn dng sn

xut hi nc dng trong nh my.

Nhit ti sinh ph thuc nhiu vo cht xc tc

c dng v loi l ti sinh. Mc ti sinh cn phi

khng ch cht ch khng ch bo m hot tnh ca

xc tc m cn m bo vn v sinh mi trng, v

th khng nn c mt CO trong kh khi thi. Hn na,

qu trnh chy cng khng xy ra nhit qu cao

hay tch nhit cc b dn ti ph hu xc tc. Cn nu

nhit qu thp th tc ti sinh s chm, cc bm

trn xc tc chy khng trit . Sau khi ti sinh, hm

lng cc cn li trn xc tc phi l cc tiu (lng

cc cn cn li t 0,1 n 0,3% KL xc tc) khi

phc ti a hot tnh ca xc tc.[1.123,124]

Kh nng ti sinh c th nh gi bng cng chy

cc, cng chy cc cng cao, qu trnh ti sinh

cng nhanh, th tch thit b ti sinh yu cu cng

nh. Cng chy cc ph thuc vo nhiu yu t:

nhit , p sut ring phn ca oxy, hm lng cc bm

trn xc tc, cht xc tc v.v...


52/85


54

Yu t nhit nh hng ln cng chy cc: Qua

nghin cu ta thy nhit khong 540 6300C tin hnh

ti sinh xc tc l tt nht.

Tc ti sinh c th biu din theo phng trnh:

RT

En

OHOCPKPV

)1(K

22 21

Trong :

V - tc ti sinh.

PO2, PH2O - p sut ring phn ca oxy v

hi nc.

C - hm lng cc bm trn xc tc.

n - bc phn ng theo cacbon

K1, K2 - hng s.

Vy tng tc ti sinh th ta phi tng nhit

ti sinh (hiu qu nht vng ng hc), tng p

sut ring phn ca oxy trong khng kh, gim ng

knh cc ht xc tc.

Xc tc c ng knh l xp cng ln v ng u

th qu trnh ti sinh cng nhanh v oxy d khuch tn.

Tuy vy iu ny b gii hn bi bn ca xc tc v

mt s tnh cht khc ca n.

Qu trnh ti sinh xc tc bng phng php t cc

cha gii quyt c vic kh cc kim loi nng hp ph

trn xc tc. V vy hon thin qu trnh ti sinh

ngi ta tin hnh thm qu trnh trao i ion kh

cc kim loi nng, iu ny gii quyt c s nng cao

c hiu qu ca qu trnh ti sinh xc tc.


53/85


54/85


56

CH-ng IIINGuyn Liu V Sn PHm

Ca QuTRnh Cracking Xc Tc

I. Nguyn liu ca qu trnh cracking xc tc

[1.124,125].

So vi cc qu trnh xc tc khc cracking xc tc

c cng sut ln nht: cng sut cm cracking xc tc

t ti 3,2 4,8 triu tn/nm, ngha l cng sut cu

n ch thp hn cm chng ct kh quyn chn khng.

Vi cng sut cao nh vy nn dung lng tng ca qu

trnh cracking xc tc cao. V d Hoa K nm 1967

cracking xc tc chim 55% lng du th. Con s ny

phn nh thnh phn phn on ca nguyn liu cracking

xc tc thay i rng [8.95]. Nguyn liu c bn cho

qu trnh cracking xc tc l phn ct chn khng ca

cn du th khi chng ct kh quyn. Chng thng cha

5 10% phn on si n 3500C v c nhit si cui

ti 520 5400C (chim khong 25 30% du th). Trong

nhiu trng hp, ngi ta cng c th dng c phn

on nh ca chng ct kh quyn, phn on kerosen-

gazoil ca cracking nhit hay cc ho v c th c phn

rafinat ca qu trnh kh asphan mazut v gudron trong

sn xut du nhn hoc l phn on mazut ca du t

kim loi. Cc c trng quan trng nht ca nguyn liu

c nh hng quyt nh n cc ch tiu ca qu trnh

cracking l thnh phn phn on, hng s c trng K,


55/85


57

thnh phn nhm hydrocacbon, hm lng nha - asphan,

hm lng cc tp cht nit, lu hunh, kim loi v cc

ho.

Khi cracking trn xc tc cha zeolit, do c hot

tnh cao m nh hng ca thnh phn phn on ca

nguyn liu khng phi l yu t quan trng. Quy lut

thng thng l khi tng phn nh (hay cn gi l

nh) ca nguyn liu, hiu sut hydrocacbon loi C3, C4

v xng u tng ln, cn hiu sut H2 v cc gim

xung. Nu nguyn liu l phn ct chn khng c t

phn on nng (


56/85


58

hu s to nhiu kh lm gim hiu sut xng v gim c

tr s octan ca xng. Nguyn liu khng cho php cha

hm lng ln hydrocacbon thm a vng (v trong qu

trnh d ngng t to cc bm trn b mt xc tc),asphan v cc tp cht cha N v S.

Nguyn liu cng nng cng cha nhiu asphan v kim

loi, khi cracking cn phi qua x l bng hydro ho

lm sch nhn c nguyn liu c cht lng cao cho

qu trnh cracking xc tc.

Ni tm li, trc khi a nguyn liu vo qu trnh

cracking xc tc, chng ta phi nghin cu k cht

lng ca nguyn liu, loi xc tc dng v tu theo

iu kin k thut, hiu qu ca cc phng php lm

sch nguyn liu yu cu nguyn liu dng m ngi ta

quyt nh phng php lm sch nguyn liu cho thch

hp.

Trong cng nghip cracking xc tc, ngi ta c th

s dng mt trong cc nhm nguyn liu sau:

Nhm 1: l nhm nguyn liu nh c tn l phn

on kerosen - sola nhn c t qu trnh chng ct

trc tip v c gii hn si t 210 n 3600C. Chng c

t trng trung bnh t 0,860 n 0,830. Trong lng

phn t trung bnh vo khong 190 200. y l nhm

nguyn liu tt nht dng sn xut xng t v xng

my bay.


57/85


59

Nhm 2: l nhm nguyn liu ly t phn on

gazoil chng ct chn khng c nhit si t 300 n

5000C (hay 5500C). Nhm ny c cc c trng l t trng

trung bnh t 0,880 n 0,920, trng lng phn t

trung bnh t 280 n 330.

Nhm 3: l nhm nguyn liu c thnh phn rt

rng, c gii hn si t 210 5000C.

Nhm 4: l nhm nguyn liu c nhit si t 300

4500C.

Trong s cc nhm nguyn liu k trn th nhm

gazoil chn khng l ph bin nht trong qu trnh

cracking xc tc. Trong nhng nm gn y, khi nguyn

liu tt ngy mt cn dn v nht l khi ch to c

xc tc cracking mi v cng ngh mi c hiu qu hn,

ngi ta tin ti s dng nguyn liu ngy cng nng

hn, cht lng xu hn m vn cho php nhn c xngvi nng sut cao v cht lng tt. l xu hng ci

tin qu trnh cracking xc tc trong hin i v trong

tng lai.

II. Cc sn phm ca qu trnh cracking xc tc

[1,2,3]

Cht lng ca sn phm cracking xc tc thay i

trong mt khong rt rng v ph thuc vo nhiu yu t

nguyn liu, loi xc tc v cc thng s cng ngh ca

qu trnh. Trong thc t qu trnh cracking xc tc

thng nhn c cc sn phm sau:


58/85


60

1. Sn phm kh

Hiu sut kh cracking chim khong 10 25% lng

nguyn liu em cracking. Hiu sut ny ph thuc vo

iu kin cracking. Thnh phn ca kh cracking ph

thuc vo bn cht ca nguyn liu v bn cht ca xc

tc.

Ch tiu Nhm 1 Nhm 2 Nhm 3 Nhm 4

T trng 0,8300,87

0

0,8300,92

0

0,8700,8

85

0,8700,8

75

Thnh

phn phn

on

t0 si

u (0

C)

200 215 300 315 225 235 n 250

t0 si 10%

(V)

225 240 335 355 290 305 275 300

t0 si

50%

260 270 420 445 390 400 335 375

t0 si

80%

490 500 385 450

t0 si

90%

290 320 520 540

t0 si 315 360 540 550 515 520 420 490


59/85


61

cui (95%) (95%) (95%)

Hm lng

S (%) TL 0,2 0,6 0,6 1,8 0,35

0,75

0,5 1,4

cc %

TL

0,2 0,9 0,2 0,3 0,05

0,2

Bng 3. c tnh 4 nhm nguyn liu ca qu trnhcracking xc tc.

Kh hydrocacbon % khi lng

C1 C2

C3

C4

C5

10 25

25 30

30 50

10 20

Bng 4: Sn phm kh ca qu trnh

cracking.

Sn phm kh c a n b phn tch kh. Sau khi

phn on, kh kh c s dng lm nhin liu kh.

Cn phn on propan propylen v butan butylen

c dng lm nguyn liu cho qu trnh alkyl ho hay

nguyn liu tng hp ho du v ho hc. Phn on C5

c pha vo xng. Trong phn on C3, hm lng propylen

c th t ti 70 80%. Trong phn on C4, hm lng

buten l 45 55%, hm lng izo-butan l 40 60% v hm

lng n-butan nh, ch vo khong 10 20%.


60/85


62

2. Xng cracking xc tc

Xng l sn phm chnh ca qu trnh, hiu sut xng

cracking xc tc thng thu c t 30 55% lng nguyn

liu em cracking. Hiu sut xng v cht lng xng ph

thuc vo cht lng nguyn liu, xc tc v ch cng

ngh.

Nu nguyn liu c hm lng hydrocacbon naphten th

cho hiu sut v cht lng xng cao. Nu nguyn liu

c hm lng ln parafin th nhn c xng c tr s

octan thp. Trong nguyn liu c hm lng lu hunhcao th xng nhn c c hm lng lu hunh ln,

thng chim khong 15% trng lng lu hunh cha

trong nguyn liu.

Xng nhn c t qu trnh c t trng khong 0,72

0,77. Tr s octan theo phng php nghin cu (RON)

khong 8791.

Thnh phn ho hc ca xng cracking xc tc khc

hn vi xng cracking nhit v xng chng ct trc

tip. Xng cracking xc tc c tr s octan cao hn, c

cha 9 10% trng lng hydrocacbon thm. Ni chung

xng cracking xc tc l cu t c bn ch to xng

thng phm.

Phn on xng cc dy chuyn cng ngh Lin bang

Nga thng c nhit si cui l 1950C, cn cc nc

khc thay i c th l 204 hay 2200C. Chng c tnh

cht c trng c trnh by bng sau:


61/85


63

204d

Hm lng S (% KL)

Tr s octan (sch)RON

MON

Thnh phn

hydrocacbon (%)

Hydrocacbon thm

OlefHin

Naphten

Parafin

0,72 0,77

0,01 0,20

87 95

78 85

25 40

15 30

2 10

35 60

(izo-parafin chim phn

chnh)

Bng 5. c trng ca xng Cracking xc tc

3. Phn on si cao hn.

Phn on ny c chia thnh:

Phn on 195 3500C v phn cn c nhit caohn 3500C

Phn on 195 2700C dng ch to nhin liukerosen

Phn on 195 3500C dng ch to nhin liudiezen

Phn on 270 4200C lm nguyn liu sn xutcacbon k thut.

Phn on ln hn 3500C hay ln hn 4200C c dnglm FO hay nguyn liu cho qu trnh cc ho.


62/85


64

Thnh phn v tnh cht c trng ca phn on

kerosen gazoil c trnh by bng sau:

Ch tiuPhn on c nhit si, 0C

195

270

270

350

350

420

> 420

204d

Nhit ng c,

0C

Tr s xetan

Tr s it, g/100 g

Hydrocacbon thm, %

V

cc ho

conradson, % KL

0,860,

95

40

60

20 35

10 20

0,86

0,97

20

50

5 10

60 80

0,05

1,0

0,960,

99

0 5

3 5

50 75

5 10

1

11

1025

Bng 6. c trng ca cc phn

on.

Sn phm c trng cho cc phn on ny l:

* Gazoil nh:


63/85


65

Gazoil nh ca qu trnh c nhit si 175

3500C. So snh vi nhin liu diezen th n c tr s

xetan thp v hm lng lu hunh kh cao.

Vi nguyn liu l phn on xola t du h

parafinic th gazoil nh nhn c tr s xetan cao (45

56). Vi nguyn liu hydrocacbon naphten thm th

gazoil c tr s xetan thp (25 35).

Cht lng gazoil nh khng ch ph thuc vo thnh

phn nguyn liu m cn ph thuc vo cht lng xc

tc v ch cng ngh. Gazoil nh dng lm cu t pha

cho nhin liu diezen, c th lm nguyn liu sn xut

b hng hay lm cu t pha long mazut.

Gazoil nh c c tnh sau:

T trng 204d = 0,83 0,940

Thnh phn ho hc gm:

Lu hunh 1,7 2,4% trng lng

Hydrocacbon olefin 6%

Hydrocacbon thm 30 50%

Cn li l hydrocacbon parafin v naphten.

* Gazoil nng:

L sn phm cn ca qu trnh. Cht lng ca n ph

thuc ch cng ngh, ngun nguyn liu v cht lng

gazoil nh.

Gazoil nng c nhit si > 3500C, c t trng 204d

= 0,89 0,99, n cha mt lng ln tp cht c hc.


64/85


66

Hm lng lu hunh trong cao hn khong 1,5 ln so

vi nguyn liu ban u.

Dng lm nguyn liu cho cracking nhit v cc ho

hoc lm nhin liu t l. Ngy nay ngi ta cn dng

n lm nguyn liu sn xut b hng.


65/85


67

Phn IICng Ngh CrackingXc Tc

Ch-ng I.

Cc yu t nh h-ng n qu trnhcracking xc tc

nh hng n cc ch tiu lm vic ca qu trnh

cracking xc tc khng ch l nguyn liu v cht xc

tc m cn c cc thng s cng ngh ca qu trnh. Cc

thng s cng ngh bao gm: nhit , p sut, tc

np liu khng gian th tch hay trng lng (cn gi

l tc np liu ring), bi s tun hon xc tc v

mc bin i hay su chuyn ho.[1.127]

i. Nhit [1.130].Qu trnh cracking xc tc thng tin hnh nhit

480 5500C. Khi tin hnh tng nhit , lc u

hiu sut xng tng v sau t n cc i ri gim

xung. iu ny l do qu trnh phn hu tng, lm phn

hu c cc cu t xng va c to thnh.

390 420 450 480 510 540 425 450 475 500 525 C

30

20

10

0

4

6

8

10

Hiu

sut

x

ng

v

Hiu

sut

cc,

NC(sch),

%95

100

90

85

80 40

50

60

70

80

%V

Nhit

Ch s octan

chuyn ha


66/85


68

Hnh 6. S ph thuc ca hiu sut sn phm cracking

vo cc thng s cng ngh.

Khi tng nhit , phn ng phn hu tng nhng ng

thi cc phn ng bc 2 nh dehydro cng tng, lm tng

hiu sut hydrocacbon thm v olefin. Khi trong sn

phm kh hm lng C1 C3 tng, cn C4 gim, t trng

v tr s octan tng ln.

Cc thng sNhit trung bnh trong

TBP

415 452 480 513

Hiu sut cc sn phm

(%TL)

Kh kh 2,31

Kh bo 5,00 5,13 8,34 18,8

0

Xng 30,29 7,49 9,41 9,45

Gasoil nh 59,20 30,72 32,45 37,4

2

Gasoil nng 53,30 46,30 28,1

0

Cc 3,20 3,30 3,50 6,60Tng cng 100,0

0

100,0

0

100,0

0

100,

00

su chuyn ho (%TL) 40,80 46,70 53,70 71,9


67/85


69

0

Tr s octan ca xng

(RON)

khng c pha ch

84,10 91,70 93,70 94,4

0

c pha 0,8 ml TEP/ 1lt

xng

93,00 98,20 98,20 98,5

0

T trng ca xng 1515d 0,748 0,748 0,75

7

Bng 7. nh hng ca hydrocacbon n hiu sut vcht lng ca sn phm vi nguyn liu l phn on

xola (du m Lin X).

ii. p sut.nh hng ca p sut n hiu sut v cht lng

xng ca qu trnh cracking c trnh by trn hnh 7.

Khi tng p sut, hiu sut xng tng ln, hiu sut

kh C1 C3 gim, hm lng olefin v hydrocacbon thm

gim, hm lng hydro-cacbon no tng v do vy cht

lng xng gim (tr s octan NO gim).

Nhit

,

C,

%KIL

N

SP

tng,

Xng,

Kh,

%KL

Cc,

%KL

Cn,

%KL

Mt

mt,

RHno,%

V

RHO,

%V

RHa,

%V

40 64, 81, 49, 11, 3,7 32, 3,2 66, 7,7 25


68/85


69/85


71

Hnh 7. nh hng p sut n hiu sut

v cht lng xng

Vy khi tng p sut s tng hiu sut xng, cn

hiu sut kh gim, nhng qu trnh to cc tng. Vic

tng p sut ca qu trnh cracking xc tc khng c

hiu qu kinh t cao. V vy ch tin hnh p sut

thng.

iii.Mc chuyn ha [1.127,128].i vi hydrocacbon tinh khit, khi tham gia phn

ng, mc chuyn ho c o bng lng sn phm to

thnh theo thi gian. Nhng i vi phn on phc tp

nh phn on du m, trong cracking xc tc ngi ta

li o lng xng l sn phm chnh v sn phm nh kh

v cc. Nu gi y l % th tch ca sn phm vi im

si cui cao hn im si cui ca xng, th chuyn

ho C c tnh theo biu thc:

C = 100 y

ng nhin cch xc nh nh vy cha st vi thc

t. hiu chnh theo s bin i ho l trong qu

trnh to xng v kh, ngi ta xc nh mc bin

i theo cng thc sau:


70/85


72

C = 100 y(100 z)

y z l % xng c trong

nguyn liu.

Trong qu trnh cracking xc tc, ngoi mc bin

i, cn c cc thng s khc quan trng khc.

iv. Tc np liu ring [1.128].Tc np liu ring (hay tc khng gian np

liu) l t l gia lng nguyn liu c np trong

mt n v thi gian trn lng xc tc trong reactor

(hay t l v th tch ca chng) v c k hiu bngM/H/M hay V/H/V (V/V/H).

Nu P l p sut trong reactor v c tnh bng

(at) th chuyn ho C c lin quan vi M/H/M theo

biu thc:

M/H/M

P.K

C100

C

Phng trnh biu din p dng rt ng vi trng

hp xc tc c nh, y khng xy ra s chuyn ng

ri hay s xo trn ca hi nguyn liu v sn phm.

Trong trng hp cracking xc tc vi lp si ca xc

tc (FCC), chuyn ho C l ph hp vi cng thc

sau:

M/H/M

P.K

100

C1100

C2

K l hng s tc tng cng ca qu trnh.


71/85


73

Ta thy rng khi tng tc np liu ring, s lm

gim chuyn ho. Cn khi gim tc np liu ring

th chuyn ho tng, v rng tc np liu l i

lng ngc vi thi gian phn ng. Khi s dng xc tcc hot tnh cao, ta c th tng tc np liu v

nh vy s tng c nng sut ca thit b.

Trong thc t, nu dng xc tc aluminosilicat v

nh hnh, tc np liu th tch ch t t 4 5

h1. Nhng nu dng xc tc cha zeolit, tc np liu

th tch l 80 120 h1

khi tnh trong ng ng ca

reactor v t 20 30 h1 khi tnh trong lp si ca

reactor.

Khi tng tc np liu, nu ta tng nhit phn

ng, s tng tr s octan ca xng v tng hiu sut

olefin trong kh. l phng php chnh iu khin

ch sn phm propylen v buten trong qu trnhcracking xc tc.

M/H/M

0,2 1,0 2,0 3,0

70

50

30

10

6

10

%KL%V

2

%%

Cc

2 4 6 8 10

chuyn chuyn

C

80

60

40

20

6

10

2

%KL%V

X/RHHnh 8. nh hng ca tc np

liu rin

Hnh 9. nh hng ca


72/85


74

v. T l l-ng xc tc, nguyn liu hay bi s tunhon xc tc [1.129]

Khi dng xc tc cha zeolit, cho php gim t l

X/RH xung cn 10/1 so vi xc tc v nh hnh l

20/1. Nu khi dng cng ngh xc tc chuyn ng vi

kch thc ht xc tc t 3 5 mm, t l X/RH cn thp

hn na, ch khong 2 5/1.

Khi thay i t l X/RH s lm thay i nhit ca

reactor, thay i thi gian lu ca xc tc trong

reactor v l ti sinh, ng thi cng lm thay i c

lng cc bm trn xc tc trong mt chu trnh.

Nu ch n nh, tng t l X/RH s lm tng

chuyn ho, tng hiu sut cc/nguyn liu, nhng hm

lng cc bm trn xc tc li gim xung. iu ny

c gii thch l do lng cc c dn ra mt

lng xc tc ln hn. Khi gi tc np liu M/H/M l

khng i, nu tng t l X/RH th thi gian tip xc

gia xc tc v nguyn liu gim, v nh vy hot

tnh trung bnh ca xc tc tng ln. l l do t

hiu qu cao ca qu trnh vi xc tc lp si (FCC).

Nh t hiu qu cao m cho php gim kch thc ca

thit b. Nhng d dng nhn thy rng, nu tng cao

qu mc tun hon xc tc s lm nh hng n qu

trnh tch hi bm trn xc tc v lm nh hng n


73/85


75

qu trnh ti sinh l ti sinh v cc trang thit b

km theo.

Ni chung thng s bi s tun hon xc tc rt quan

trng trong qu trnh cracking xc tc, n nh hng

khng nhng ln hiu sut v cht lng sn phm n

cc thng s khc m cn nh hng n vic xc nh

kch thc cc thit b chnh ca qu trnh. V vy ta

phi chn c thng s ny mt cch ti u.

vi. Hiu ng nhitHiu ng nhit ca qu trnh bng tng hiu ng

nhit ca cc phn ng ring bit ca qu trnh, hiu

ng nhit ph thuc vo su chuyn ho.

Ch-ng IICng ngh cracking xc tc


74/85


76

I. Lch s pht trin cng ngh cracking xc tc

[1,2,3]

Qu trnh cracking xc tc c nghin cu t

cui th k 19, nhng mi n nm 1923, mt k s ngiPhp tn l Houdry mi ngh a qu trnh p dng

vo cng nghip. V n nm 1936 nh my cracking xc

tc u tin ca Cng ty Houdry Praess Corporahon c

xy dng M. Dy chuyn cracking xc tc u tin ny

c a vo cng ngh ch bin du, l h thng

cracking xc tc trong lp xc tc tnh, h thng lm

vic gin on. V sau ny, h thng loi trn i

vo lch s v n c nhng nhc im sau:

+ Qu trnh lm vic gin on nn nng sut thit

b thp

+ Ch lm vic ca h thng khng n nh v vic

iu chnh cc thng s k thut ca h thng kh khn,

phc tp trong vn hnh

+ Trong qu trnh lm vic hot tnh ca xc tc

thay i lin tc lm nh hng n cht lng sn phm

v cn bng vt cht ca h thng.

Nm 1941, xut hin qu trnh cracking vi lp xc

tc chuyn ng thay th cho qu trnh Houdry. Vic

tin hnh cracking v ti sinh xc tc c thchin cc thit b ring bit.

+ Thit b phn ng (reactor)

+ Thit b ti sinh (regenerator)


75/85


77

Xc tc t thit b phn ng vo thit b ti sinh

v ngc li hoc bng t chy, hoc bng cng bc.

Xc tc lm vic c cha cc chuyn ng vo l ti

sinh, cn xc tc ti sinh vo l phn ng to thnhmt chu trnh lin tc. Dy chuyn loi ny Nga c

tn gi l loi 43-1 v 43-102, cn nc khc c tn

l Thermofor (TCC) hay Houdry Flow. Tuy nhin cc dy

chuyn ny cng v sau cng lin tc c ci tin so

vi dy chuyn ban u khu vn chuyn xc tc (

dng vn chuyn bng hi thay cho vn chuyn bng c

hc).

Nm 1942, dy chuyn cracking xc tc lp si (FCC)

u tin c a vo hot ng vi cng sut 12.000

thng nguyn liu/ngy. Loi dy chuyn ny c tn l

Up Flow (model I). Trong dy chuyn ny, xc tc c

a ra t nh l phn ng v l ti sinh.

Sau , vo nm 1944 ngi ta tng ng knh ca

cc thit b phn ng v ti sinh, qu trnh tch hi

sn phm c thc hin ngay trong thit b phn ng,

ti sinh xc tc dng tng si v qu trnh thi cng

ngy cng c ci tin cho xc tc chuyn ng t

pha di v ly ra ngoi y thit b. Dy chuyn c

thit b hot ng nh vy mang tn l Dow Flow modelII, v l dng nguyn thu ca thit b phn ng v

ti sinh lp si hin i ngy nay. Tip theo, ngi ta

cng ci tin c hnh dng ca xc tc. Xc tc ph

bin l loi c dng hnh vi cu, nn gim c s mt


76/85


78

mt xc tc hay s mi mn thit b, nng cao hiu qu

tch ca cc xyclon.

Trong dy chuyn model I, t l xc tc/nguyn liu

u (X/RH) ch t gii hn cc i l 3, nhng model

II t l X/RH c th tng ln t 3 10. n nm

1946, model III l loi cn bng p sut c thit

k bi hng M. W. Kellogg.

Nm 1947, hng UOP thit k loi FCC trong

thit b phn ng v thit b ti sinh chng ln nhau

trn cng mt trc. n nm 1951, loi Orthor Flow utin ca M. W. Kellogg xut hin. Sau hng Standard

Oil thit k mt loi FCC mi gi l model IV, l

ci tin ca model III v dy chuyn cng ngh model IV

u tin p dng trong cng nghip vo nm 1952.

Cng vi thi gian, FCC ngy cng c ci tin

c c hiu sut, cht lng xng cao hn v c th

dng nguyn liu ngy cng nng hn, vi cht lng

nguyn liu ngy cng xu hn.

II. La chn cng ngh cracking xc tc [1,3]

Qua lch s pht trin ca qu trnh cracking xc

tc, ng thi qua phn tch nh gi cc yu cu khc

nh ch lm vic, nguyn liu xc tc... ta thy qu

trnh FCC c rt nhiu u im v thun li, h thng

ny c s dng ngy cng ph bin trong cng nghip

du m, n c cc hng cng nghip hng u trong

lnh vc ny nh UOP, Kellogg, Shell, IFP, Exxon...


77/85


79

nghin cu hon thin hn nhm mc ich t nng

sut hiu qu cao nht, s dng nguyn liu nng hn,

tit kim c xc tc... v phi l kinh t nht.

Qua thc t dng h thng cracking xc tc lp si

s dng xc tc dng bi hay vi cu, ngi ta thy n

c nhiu u im hn h thng cracking xc tc trong

lp xc tc chuyn ng. Nhng u im l:

+ Cc thit b chnh ca qu trnh l thit b phn

ng v thit b ti sinh u c cu to rt n gin,

so vi cc dng thit b khc ca qu trnh cracking

thc t chng l hnh rng.

+ S tun hon xc tc t thit b phn ng n

thit b ti sinh v ngc li l nh s vn chuyn

lin tc ca hi v kh trong mt gii hn rng.

+ Do s khuy trn mnh m ca xc tc v hi nguyn

liu dn n s ng nht v nhit trong ton b th

tch lp xc tc thit b phn ng cng nh thit b

ti sinh, khc phc c hin tng qu nhit cc b.

+ H thng ny c kh nng ch bin cc dng nguyn

liu khc nhau, nh t nguyn liu l phn on kerosen

n nguyn liu nng l mazut, lm tng tnh vn nng

ca h thng.

+ H thng ny c cng sut lm vic ln v c thi

gian tip xc ngn (thi gian tip xc gia nguyn liu

v xc tc l cc tiu) dn n vic t c hiu sut

xng cc i v olefin nh khng xy ra phn ng ngng

t bc hai m to xng. ng dng phng php ti


78/85


80

sinh (chy hon ton CO trong thit b ti sinh) dn

n t hm lng ct cn rt thp trong xc tc.

Qua cc u im ta chn s cng ngh xc tc

lp si FCC vi thi gian tip xc ngn cho qu trnh

cracking xc tc.

III. Dy chuyn FCC vi thi gian tip xc ngn

Trc ht nguyn l ca qu trnh cracking xc tc

c th miu t bng s sau:

Qu trnh cracking xc tc thng c tin hnh

iu kin cng ngh sau:

Nhit 470 5500C

p sut trong vng lng ca l phn ng 0,27 MPa

Tc khng gian th tch truyn nguyn liu tu

theo dy chuyn cng ngh c th t 1 120m3/m3.h

Xc tc l zeolit mang tnh axit.

1. S dy chuyn FCC thi gian tip xc ngn:

Dy chuyn cng ngh FCC gm ba b phn chnh:

Nguyn

Chunb

Lphn

Sn phmqua chng

Xc tc

Xc tc

L ti sinhxc tc1


79/85


81

Reactor

Ti sinh v vn dng nhit ca kh khi

Phn on phn chia sn phm.

a)Thuyt minh dy chuyn cng ngh1. B cha nguyn liu u 15.

Thit b gia nhit

2. Bm16. ng dn hi sn

phm

3. Van tit lu17. Thit b phn ng FCC

4. L t18. Thp ti bay hi

5. Thit b phn ly tch cn bn 19. Bphn ng ng

6. B cha sn phm 20.Xyclon 2 cp

7. Thit b trao i nhit 21.Thit b ti sinh xc tc

8. Thit b lm mt bng khng kh 22.Van l

9. Thit b lm lnh bng nc 23.Bung lng tch


80/85


82

10. Thp chng tch sn phm 24.Ni hi tn dng nhit

11. B lng tch 25.Thit b tn dng nhit

12. Thp tch kh 26.Thit b lc in

13. Thp n nh 27.My nn kh

14. Thit b phn dng2. Nguyn l hot ng:+ B phn Reactor - ng ng:

Nguyn liu mi t b cha nguyn liu (1) c cho

qua thit b trao i nhit ng chm, nguyn liu mi

c th c trn vi phn tun hon (HCO) (6),(l phn

on du nng ca qu trnh cracking xc tc ) v cn

y thit b (5), sau cho qua l t nng nguyn

liu cracking Nguyn liu cracking c tip xc vi

xc tc nng ti sinh i vo y ca ng ng(19),

khi nguyn liu bay hi cng vi hn hp ca hi

nng v xc tc c i ln pha trn ti nh ca ng

ng, ng thi xy ra cc phn ng cracking xc tc.

Hu ht nguyn liu u tham gia phn ng v chuyn ho

trong ng ng, cn reactor c dng nh mt thit b

tch xc tc v hi hydrocacbon.

Mt b phn c thit k c bit, b tr gn

van chn, dng hi nc thi xc tc v du, lm nh


81/85


83

vy s hn ch n mc ti a hin tng trn quay tr

li ca xc tc v hi kh lm vic. Vng ng ng

v b phn tch hi ca reactor c thit k cho qu

trnh FCC vi thi gian tip xc ngn gia xc tc vdu. Sau khi tch khi xc tc, hi sn phm nng (16)

c chuyn ti ct phn on. Xc tc lm vic (10)

c cho qua vng tch hi (cn gi l b phn ra xc

tc) bng cch thi hi nc vo. B phn ra khng ch

lm nhim v ui ht hydrocacbon hp ph trn xc tc

m cn lm ti cc ht xc tc chng khng dnh vo

nhau trc khi sang l ti sinh. Cn iu chnh mt tc

hi thch hp cho nhim v ny. Cn thit phi kim

tra cht ch thi gian lu ca xc tc trong b phn

ra trnh phi dng qu nhiu khng kh trong l ti

sinh. p sut trong reactor c khng ch bng b phn

iu chnh p sut ca ct phn on.

+ L ti sinh v khi tn dng nhit ca khi l:

Xc tc c cha cc (cc bm trn xc tc) c

chuyn qua van iu khin (23) v khng ch bi b kim

tra mc xc tc trong l phn ng, sau i vo l ti

sinh. Xc tc vo l ti sinh theo hng tip tuyn vi

thnh l. Mc ch chnh ca ti sinh l t chy cc

bm trn xc tc lm vic bng oxy ca khng kh,khi to thnh CO, CO2, hi nc, nh vy m tr

li b mt hot tnh cho xc tc. Sau khi nn, khng

kh t c cho vo y l ti sinh, qua li phn

phi trn c hiu qu khng kh v xc tc. S chy


82/85


84

cng xy ra trong lp si v t c iu , tc

ca khng kh phi t ln hn 1 m/s. Xc tc ti

sinh c chuyn vo ng ng sau khi ui c sch

kh qua mt van l m s hot ng van ny c khngch, iu khin t ng nh b phn iu chnh nhit

ca reactor, ri sau xc tc c trn vi nguyn

liu cracking v hon thnh mt chu trnh. ng thi

ngi ta tho xc tc bn gi ho ra, b sung xc

tc mi m bo hot tnh n nh ca xc tc

theo thi gian lm vic.

Kh ca qu trnh chy cc v cc ht xc tc chuyn

ng t pha c vo pha long nh l ti sinh, qua

hai cp xyclon gi li cc ht xc tc v tch kh.

Sau , kh khi c qua bung lng (23) tch tip

bi xc tc, ri qua b phn tn dng nhit( 24), tip

theo kh khi c lm sch bi xc tc bng lc

in(26) ri i ra ngoi theo ng khi.

+ B phn phn chia sn phm:

Hi sn phm (16) c np vo ct phn on chnh

chia thnh cc sn phm khc nhau, xng v phn nh

hn c cho qua b phn ngng t ri vo thit b tch

kh. Sau khi tch kh, ta nhn c phn on C1,C2( I

), cc sn phm ny c th c dng lm kh nguynliu cho dy chuyn. Phn on C3,C4(II) cha nhiu

propylen v buten c dng lm nguyn liu cho dy

chuyn alkyl ho v sn phm tip theo l xng kh

butan


83/85


85

T ct phn on chnh, ta cn nhn c cc phn

on sn phm nh naphta nng, LCO v HCO. Phn HCO c

th cho tun hon li mt phn , v cui cng l phn

du cn c lm sch khi bn xc tc (5). Mt phnsn phm nh ca thit b tch bn xc tc cng c

cho tun hon cng vi HCO.

IV. H-ng pht trin v

ci tin ca FcC trong

lc du [1.150,151]

T thp nin 90 tr li

y, qu trnh FCC vn khng

ngng c ci tin c v

cng ngh v xc tc to

cho FCC trong tng lai ph

hp vi yu cu ca cng ngh lc - ho du, ng thi

cho php s dng c nguyn liu nng hn, nhim bn

hn, ngha l vi cht lng nguyn liu ngy cng xu

hn. T mc tiu , cc nh thit k v cng ngh

t ra cc nhim v chnh sau:

1- Ci tin v cng ngh thch ng vi nguyn

liu c cht lng xu m hiu sut xng hay phn ct

vn t cc i, gim lng cc, nng cao cht lngca xng.

2- Ch to v ci tin cht xc tc c bn nhit,

bn c cao, bn vi cc c t, c hot tnh cao v n

nh, d ti sinh v c thi gian lm vic lu di hn.


84/85


86

3- Chn la cc thng s lm vic ti u bng cc

cng ngh iu khin v kim tra tin tin, hin i.

4- Ci tin cc trang thit b cng vi cng ngh

khng nhng nng cao cht lng sn phm m cn cho

php kt hp sn xut cc nguyn liu cho tng hp ho

du v ho hc. V d nh nhn etylen, propylen,

buten...

Ch trong vng vi chc nm tr li y, ngoi vic

nng cao, ci tin v p dng xc tc mi c hiu qu,

ngi ta thit k cc dy chuyn FCC hin i sn

xut c khng nhng nhiu xng vi cht lng cao hn

m cn cho php nhn cc nguyn liu cho tng hp ho

du. Thnh cng , trc ht phi k n qu trnh FCC

vi thi gian cracking ngn v siu ngn (MSCC), hay

qu trnh cracking su (DCC).

Ti liu tham kho


85/85


1. L Vn Hiu. Cng ngh ch bin du m; Nh xut

bn KH v KT- H Ni 2009.

2. PGS. TS. inh Th Ng. Ho hc du m; Nh xut bn

KH v KT- H Ni 2010.3. B mn Nhin liu. Cng ngh ch bin du m v

kh; Trng i hc Bch khoa H Ni; 1983.

4. V Th Lin, L Vn Hiu. Cng ngh ch bin du

kh. Trng i hc Bch khoa H Ni; 1982.

5. Trn Mnh Tr. Ho hc v cng ngh ch bin du

m. Trng i hc Bch khoa H Ni; 1974.

6. Trn Mnh Tr. Du kh v du kh Vit Nam. Nh

xut bn Khoa hc v K thut H Ni; 1996.

7.Trn Quc Sn .Mt s phn ng ca hp cht hu c.

nh xut bn Gio Dc , nm 2001

8.on thin tch. Du kh Vit Nam ; nh xut bn i

Hc Quc Gia TPHCM 2001

9..H-Minamil , Curent FCC Technologies , nm 1993.

10.Ch.Marcilly , Catalytic Cracking , nm 1991.

11. W. L. Nelsson. Petroleum rafinery engineering.

New York; 1998.

12. D. Michael. Winfield the UOP processing guide;

1994.

do an cracking xuc tac

Documents