ky thuat xuc tac - tiet 3

7/30/2019 ky thuat xuc tac - tiet 3

1/72

Trng i hc Cng nghip

TS. Nguyn Mnh Hun

K THUT XC TCCATALYST TECHNOLOGY


2/72

CHNG 3NGHIN CU TNH CHT XP CA VT LIU MAO QUN

Trong cng nghip: Hu ht l phn ng xc tc d th.

Cht tham gia, sn phm: thng trng thikh (hi) hoc lng. Cht xc tc: trng thi rn, hu ht l vt liu

mao qun.


3/72

1. Khi nim v cu trc ca VLMQ: S phn b kch thc ht Hnh dng v kch thc cc tp hp ht B mt ring:l din tch b mt tnh cho mt n v khi

lng; bao gm din tch b mt bn trong v bn ngoicc ht (m2/g)



4/72

Th tch l xp ring (mao qun ring): l khng gianrng tnh cho mt n v khi lng; bao gm rng giacc ht v bn trong mi ht (m3/g)

Hnh dng mao qun:mao qun hnh tr, hnh cu,hnh khe v hnh chai. Phn b kch thc ca cc mao qun hoc phn b lxpda trn nhng gi thit v hnh dng mao qun . Sphn b c xc nh theo s bin i ca th tch hocb mt ca l xp vi kch thc mao qun



5/72

Theo qui nh ca IUPAC (International Union of Pure andApplied Chemistry):

- VLMQ ln:d > 50 nm (d: ng knh trung bnh ca maoqun )

- VLMQ trung bnh: 2 < d < 50 nm- VLMQ vi mao qun: d < 2 nm

Trong :

n: tha s hnh dng, vi mao qunhnh tr: n = 0,5S: b mt ring ca VLMQV: th tch mao qun



6/72

2. Hin tng b mt v Hp ph

2.1 S Hp ph Kh v Hi trn b mt rn2.1.1 Cc khi nim v nh ngha

S hp ph:l s tng nng ca kh( hi trn b mt phncch pha (rn kh). Cht hp ph:l cht c b mt thc hin s hp ph. Cht b

hp ph l cht b ht ln trn b mt ca cht hp ph.V d: than hot tnh hp ph khi CO, than l cht hp ph, cnkh CO l cht b hp ph

B mt ring: l din tch b mt ca cht hp ph tnh cho 1gram cht hp ph, c n v: [m2/g]



7/72

Vn 7:Hp ph vt l v ha hc



8/72

Cc kiu lc hp ph:

Hp ph vt l Hp ph ho hc



9/72



10/72

Vn 8:ng hp ph ng nhit



11/72

3. ng ng nhit hp phLng x cht b hp phph thuc p sut cn bng P, nhit T, bn cht cacht b hp ph v bn cht ca vt liu rn:

x = f( P, T, cht hp ph, cht b hp ph )x (gam hoc g/mol hoc cm3)

Khi T l mt hng s:x l mt hm ng bin vi p sut cn bng. Khi p sut Ptng n p sut hi bo ho ca cht kh b hp ph Psti mt nhit cho thmi quan h gia x v P c gi l ng nhit hp ph

x = f( P)n p sut bo ha Ps, nh hp ph bng ht chn khng, v o cc gi tr lngkh b hp ph x cc gi tr P/Psgim dn (P/Ps = 1 - 0) v nhn c ngng nhit gii hp (nh hp ph).



12/72

Hin tng tr, vng khuytca cc VLMQ c h mao

qun trung bnh



13/72

Hnh dng ca ng ng nhit hp ph v vng tr thhin nhng c im v bn cht v hnh dng mao qun.Theo Brunauer, L.Deming, W.Deming v Teller (BDDT): ccc loi VLMQ khc nhau c quy chun ha bi IUPAC:

Loi I: VLMQ khng c maoqun hoc vi mao qun (d


14/72

i vi kiu IV v V,De Boer ngh cc dng vng trkhc nhau cho cc loi vt liu c cu trc mao qun trungbnh khc nhau:



15/72



16/72

4. Cc phng trnh Hp ph ng nhit+ Co nhieu loai ng ang nhiet.+ Cac loai ng ang nhiet o, bat ke la cxay dng nen bang con ng ly thuyet hay thcnghiem, eu la nhng bieu thc tng oi ngianbieu th s phu thuoc cua nong o be matcac phan t chat b hap phu (trong trng hp

xuc tac la chat phan ng) vao ap suat canbang cua no.


ng ang Th t h h t b h h Th t h h t h


17/72

ng ang

nhiet.

Ten goi ngang nhiet

Phng trnhbieu dien

Ap dung choloai hap phu

ng ang nhietLangmuir

ng ang nhietFreundlich

ng ang nhiet Henry

ng ang nhietFrumkin - ShlyginTemkinPyjev

ng ang nhiet

Brumauer Emmett Teller(BET)

Hap phu hoa hocva hap phu vat ly



Hap phu hoa hoc

Hap phu vat lynhieu lp

v- The tch chat b hap phu, vm The tch chat happhu can e trai mot lp tren be mat ap suatcan bang,P, P3 ap suat hi bao hoa cua chat b hap phu,

o che phu be mat.Cac ky hieu khac bieu dien cac hang so khacnhau


18/72

Vn 9:Phng trnh hp ph Langmuir



19/72

2.1.2.1 Phng trnh hp ph ng nhit LangmuirCac gia thiet:

a) Cac tieu phan cua chat b hap phu lien ket vinhng trung tam nh v xac nh tren be mat,b) Moi mot trung tam ch co the hap phu mot tieu phan

ma thoi,c) Be mat ong nhat ve mat nang lng va khong co stng tac gia cac tieu phan a b hap phu. Co the ara nhieu ly do chong lai cac gia thiet tren. Tuy nhienphng phap Langmuir van la phng trnh thuan tien nhat

va trong nhieu trng hp cho ta nhng ket qua ganung hoac lam c s e xay dng nhng mo hnh vatly phc tap hn.



20/72

o che phu be

matpap sut hi baohoab - h s can bnghp ph

Khi 1, be mat a c lap ay bi mot lp n phan tTrong trng hp hap phu nhieu chat, phng trnh ng angnhiet Langmuir co dang:

Ngc lai, neu khi hap phu phant phan ly thanh nhng tieu phanth phng trnh se co dang:

Phng trnh c Langmuir ngh nhsau



21/72

S hp ph theo phng trnh Langmuir(a): th -P , (b): phn t b hp ph


P0

(b)

(a)


22/72

+ Cac ng ang nhiet hap phu vat ly co nhieu dang khacnhau.+ Nam 1950 Brunauer la ngi au tien chia thanh 5 dang.+ Cac dang khac (I) ai lng hap phu khong dng lai mclp n phan t.

Loi I: ng nhit LangmuirLoi II: ng nhit trn b mt cht rnkhng l xpLoi III v V: ng nhit, ng thi

tng tc gia cc phn t mnh hntng tc gia phn t - b mtLoi IV: ng nhit v c s ngng ttrn b mt



23/72

Vn 10:Thuyt BET



24/72

+ Thuyet do BrunauerEmmettTellera ra nam 1938.

+ La phng phap thuan tien exac nh be mat vat ran va cacchat xuc tac d the.



25/72

Cac tac gia thuyet BET gia thiet rang:+ trang thai can bang toc o hap phu

(ngng tu) tren be mat con t do bang toco giai hap (bay hi) t lp n phan t thnhat.+ Cac lp tiep theo cung nh cac lp th

nhat.



26/72

Gia thuyet quan trong nhat: nhiet hap phu lp th hai va tat ca cac lp tiep theo labang nhau va bang nhiet hoa long cua kho. Nhng nhiet hap phu cua lp th nhat thkhac.Phng trnh ang nhiet co dang:



27/72


Vn 11:Vt liu vi mao qun


28/72

III. Nghin cu cu trc xp ca VLMQ1/ Vt liu vi mao qun (microporosity)

+ Cc zeolit, than hot tnh, vt liu khong st v nhiucht mang xc tc ... c l xp bao gm ch yu l cc vi

mao qun.+ Khi nh hp ph khng c ng tr.+ ng knh mao qun trung bnh < 20Ao



29/72

- Phng trnh BET khng cn y gi tr xc nhSring. Nhiu phng php da vo s phn tch ng ng

nhit hp ph tm kim cc thng tin nh lng v l

xp vi mao qun m c trng ca n l ng ng nhithp ph kiu I. Khng ch p dng nhng kt qu tm c t ng hp

ph ng nhit kiu I cho cc vt liu vi mao qun m cncho c nhng vt liu khc cha mt phn l xp l vi maoqun.



30/72

Mt s phng php nghin cu c trngcu trc cc h VL vi mao qun : Phng php Bond v Spencer

Phng phpHalsey v Everett. Phng phpZwietering v Krevelin. Phng phpDubinin v Kaganber.



31/72

1.1 Phng php Bond v Spencer- Nguyn tc: S dng mt cht hp ph chun c cng tnh cht vicht nghin cu c b mt bit.- Cht b hp ph c dng l neon v tin hnh o (xc nh) ngng nhit hp ph nhit phng v nm trong vng Henry.- Phng php ny mi ch s dng vi cht hp ph c ngun gc

cacbon. Cht hp ph tiu chun c dng l b hng (mui cacbon) vd loi ELF8 c gi tr b mt ring l:+ Sr=100 m2/g (theo phng php knh hin vi in t)+ Sr=112 m2/g (theo phng php hp ph nit -1980C)+ Sr=105 m2/g (theo nhit thm t ca metanol)


CHNG 3


32/72

tnh b mt ring ca than , than cc, than hot tnh. Gi thit:

Khi p sut 1atm gi tr x0c v x0rtng ng (bng nhau) nn:

Sc, Sr: b mt ring ca cht hp ph nghin cu v cht chun.x0c, x0r: gi tr hp ph tnh trn mt n v b mt mu nghin cu v bhng tiu chun tng ng p sut 1 atm.

V s hp ph tun theo nh lut Henry

chnh xc ca phng php ny ph thuc rt nhiu vo cht hp

ph chun.


CHNG 3


33/72

1.2 Phng php Halsey v Everett.- Nguyn tc: S dng min tuyn tnh ca ng ng nhit hp phdng I vng Henry.- Nu p sut kh nh, nhit cao th mc lm y s rt nh, cngha l tng tc gia nhng phn t to thnh hp ph c th b qua. Nng ca cc phn t cch b mt mt khong r tun theo phn s Bosman:

C=C0.exp(- U/RT)U : l th nng

Gi dx l lng cht b hp ph trn b mt dS v th tch dS.drdx=(C-C0)dS.dr


CHNG 3


34/72

Nu coi b mt l ng nht th lng hp ph trn din tch S c xcnh nh sau:

Trong :

r0: khong cch nh nht ca phn t hp ph c th ti gn b mtNu chp nhn rng trng thi kh tun theo quy lut ca kh l tng (v ginh l p sut thp v nhit cao)

Nh vy vng Henry ta c hng s:

y I l gi tr tch phn:


CHNG 3


35/72

1.3. Phng php Zwietering v Krevelin.- Phng php ny cng tnh ton b mt ring qua h s Henry K0.- C s l thi gian sng trung bnh 1ca phn t c hp ph trn b mthp ph, hoc thi gian ca mt dao ng o.- Phng trnh gi tr hp ph c dng:

Gi tr S l b mt ring ca cht hp ph, cm2/g. H s Henry c dng:

E1: l nhit vi phn hp ph, coi l bng nhau vi tt c phn b mt (coib mt l ng nht).Nhc im ca phng php ny l chnh xc khng cao, do gi tr okh tnh chnh xc.


CHNG 3


36/72

1.4. Phng php Dubinin v Kaganber.- C s: thuyt th nng ca Polani. Khong cch hp ph gn vi bmt vt th rn c c trng bng b mt ng th. C ngha lnhng b mt c th hp ph nh nhau.- Theo Polani cht b hp ph trn b mt dng lng.

y:x: lng cht hp ph (tnh bng gam) p sut P: t trng ca cht lngV: th tch c in y cht hp ph V=f()


CHNG 3


37/72

Dubinin v cc ng s cho rng: Th hp ph xut hin l do lcphn cc v lc phn tn, khng ph thuc vo nhit , nhng thayi theo bn cht ca cht hp ph v cht b hp ph. Thc t, lcphn cc v phn tn l hm ca phn cc ca cc phn t cht bhp ph. Do vy:

S ph thuc ca lgx vo [lg(PS/P)]2 cdng ng thng vi dc l D v cttung ti lg(Wo).T gi tr lg(W0) c th tnh c thtch ca cc l nh (vi mao qun)


CHNG 3


38/72

Thuyt Dubinin c Kaganber s dng tnh b mt ring.Vng hp ph n lp th c th biu hin phn b Gause ca cht hp ph cctm b mt:

- Gi tr lgxm(ct trc tung) l logarit ca th tch n lp, ch khng phi l thtch l. Kt qu ca phng php ny cho php ta tnh c gi tr ca b mtring. Ngi ta coi rng c th s dng n vng p sut thp P/PS=10-4.- Phng php ny p dng rt thnh cng cho cht b hp ph l CO2nhit thng. Hn ch ca phng php ny l ch p dng cho vt liu

c c trng hon ton mao qun nh.


CHNG 3


39/72


Vn 12:Vt liu mao qun trung bnh

CHNG 3


40/72

2/ Vt liu mao qun trung bnh (mesoporosity)2.1/ S ngng t mao qun v nh lut Kelvin ng kh hp ph khng trng vi ng hp ph .

S sai khc l do p sut mao qun cn tr skh hp ph ca hi ngng ng nh p sut hpph.

ng knh mao qun trung bnh: 20 Ao < d < 500 Ao


CHNG 3


41/72

Phng trnh Kelvin xc nh mi quan h gia t s P/Ps

v rk

l bnknh ca git lng hnh thnh bn trong mao qun.

Trong :g: sc cng b mt ca cht lng ngng tVL:th tch mol ca cht lng ngng t:gc thm trk:bn knh Kelvin c nh ngha nh sau:r1, r2:cc bn knh cong ca mng lng

f:tha s ph thuc hnh dng ca mng lng, nh vy gin tip phthuc vo hnh dng ca mao qunf = 1 : mng hnh tr hoc bn trf = 2 : mng bn cu

f = 3: mng hnh cu


CHNG 3


42/72

Hnh dng ca mt s mng lng khi hp ph v nh hp ph.

(1): hnh tr : hp ph trong mao qun hnh tr h(2): hnh bn cu : kh hp ph trong mao qun hnh tr

(3): hnh bn tr : kh hp ph trong mao qun hnh khe


CHNG 3


43/72

- Khi hp ph trong mao qun hnh tr h hai u, thnhmao qun c che ph bi mt mng cht b hp phcho n khi xy ra ngng t mao qun. Trong qu trnhhp ph mng lng c dng kiu hnh tr. Ngc li sau

khi xy ra ngng t, mao qun mng lng c dng bncu.- T phng trnh Kelvin: P/Psca qu trnh thot hit mao qun ngng t lun lun nh hn P/Ps ca

qu trnh hp ph.


CHNG 3


44/72


Khi hp ph mng lng c:

CHNG 3


45/72

So snh (1) v (2): v f, g, VL, cos, r1u dng nn:ln (P/Ps)khp < ln (P/Ps)hp hay (P/Ps)khp < (P/Ps)hp

Chnh s sai khc ny gy nn vng trtrn ng ng nhit hpph v kh hp ph ca cc VLMQ trung bnh.

NGHIN CU TNH CHT XP CA VT LIU MAO QUN

CHNG 3


46/72

ng ng nhit hp ph, nh hp ph i vi VLMQ trung bnh


CHNG 3


47/72

VLMQ mao qun ln: khng to thnhmng lng khi :

Biu din qu trnh hp ph trongmao qun ln

th ln(P/Ps)HP = ln(P/Ps)khp(P/Ps)HP = (P/Ps)khpCho nn ng ng nhit hp phv nh hp ph trng nhau


CHNG 3


48/72

2.2/ S phn b kch thc trong VLMQ trung bnh- Phng php c ng dng nhiu nht l phng php ca Barrett,Joyner v Halenda ( BJH). p dng cho nhnh kh hp ph trn ngng nhit.- C s ca phng php: phng trnh Kelvin vi iu kin: sau khi bayhi cht lng ngng t, cht lng cn lu li trn thnh mao qun mt mng

hp ph a lp c chiu dy t. Chiu dy t c xc nh theo cng thcsau:

x: lng cht b hp ph P/Pstng ng (mol/g)VL: th tch ca mt mol cht b hp ph (m3/mol)Sr: b mt ring ca cht hp ph xc nh theo phng trnh BET (m2/g)Bn knh ca mao qun rpc tnh theo biu thc:


CHNG 3


49/72


Vn 13:Xc nh din tch b mt

ring ca vt liu

CHNG 3


50/72

IV. Xc nh b mt ring ca xc tcCng thc tnh b mt ring ca xc tc :

Vi :

Sm:din tch b mt ca mt phn t cht b hp ph (m2)Gn ng c th xem: Sm =tit din ngang ca cht b hp phN:s Avogadro = 6,022. 1023 mol-1nm:s mol cht b hp ph to ra mt lp n phn t trn b mt 1 gamxc tc


CHNG 3


51/72

- Cht b hp ph thng dng di dng lng -kh.- Gi tr Smca cht b hp ph khng phi l ilng tuyt i.- Hin nay thng dng nht l kh tr nh N2, Ar,He, Kr... Dng cc cht hu c cn phi thn trngbi v n ph thuc tnh cht ca cht hp ph vnhit .


CHNG 3NGHIN CU TNH CHT XP CA VT IU MAO QUN


52/72




53/72




54/72

- Thn trng i vi nhng trng hp m cht b hp ph ctng tc ha hc vi b mt cht hp ph.Do thngla chn cc kh tr v nhit thp xc nh b mtring.- N2l cht kh c s dng nhiu nht.

Mt s trng hp cn c s khuch tn tt trong cc vimao qun, phi chn cc nguyn t hay phn t b hn N2.Thng s dng:Ar, He, H2.

Hn ch: H2c th hp ph ha hc, cn He th kh thaotc thc nghim, do vic ng dng chng b hn ch.




55/72

ng dng phng trnh BET tnh b mt ring trthnh mt phng php tiu chun trong nghin cuVLMQ.

T phng trnh BET ta xc nh s mol nm t gi tr Vm

nh sau:

Phng trnh ny c ng dng trong khong P/Ps= 0,05 0,35 v C>1




56/72

- Xydng biu m P/V(Ps-P) ph thuc voP/Ps- Phng trnh BET c ngdng trong khong P/Ps= 0,05

0,35v C>1




57/72

Ngoi ra c th tnh C theo cng thc:

Nghin cu vi cht b hp ph l N2, gi tr thc nghim ca (1 - 2) trncc VLMQ khc nhau l:- Hp kim Cu: 1 - 2 = 776 cal / mol- Gel Cr2O3: 1 - 2 = 738- Cr2O3nung : 1 - 2 = 835- SiO2: 1 - 2 = 794

Tm li phng trnh BET ni chung u c th p dng xc nh Sr catt c mi cht rn trong phm vi gi tr P/Psca cht b hp ph = 0,05 0,35 v hng s C >1.




58/72

th ng nhit hp ph vi gi tr P/PS khc nhau -ph thuc vo hng s c


Bi tp 3


59/72

1. V2. Tm c S = (c -1)/Vmcv I = 1/Vmc Vm

3. Tnh NA: s Avogrado, A: din tch chim gi bi 1 phn t Nito, MV: thtch phn t gram ca Nito (22.4 l)4. Tnh din tch b mt ring: As= Vmk/khi lng xc tc (m2/g)

Tnh din tch b mt ring ca 1 xc tc bit d liu cho hp ph ngnhit N

2(

ads= cm3 N

2ti 25oC v 1 atm) 0.1g xc tc bit din tch chim

gi bi 1 phn t Nito l 0.162 nm2

p



60/72


Vn 14:Xc nh xp v min phn

b mao qunca vt liu



61/72

V. Xc nh xp ca vt liu mao qun- nh gi xp ca vt liu, c bit l vt liu c xp km, ngi ta dng phng php gn ng. Dngphng php ny c th nh gi c xp m

bng s hp ph nc.- xp m l i lng phn xp so vi b mtchung.




62/72

Phng php c tin hnh nh sau:Cn xc tc ri em sy kh n khi no

trng lng khng i. Cn phi chnh xc n 0,01 gam. Sau cho vo chn nungv y bng vi hay li kim loi. Chn c nhng vo trong cc nc, un sitrong 2h. Sau mu c lm lnh n nhit phng, gn kh trong phu lc 20pht.- Lng hp ph nc W tnh theo cng thc:

g1: trng lng mu sau khi hp phgo: trng lng mu trc khi hp ph

- xp m c xc nh theo cng thc:

g2: trng lng vt th trong nc ccn bng thu lc tnh




63/72

VI. Xc nh min phn b mao qunS phn b mao qun theo kch

thc ng vai tr quan trng trong qu trnh khuch tn bn trong ca phnng ha hc xc tc. xc nh phn b mao qun xc tc theo kchthc th trc ht cn phi xc nh kch thc mao qun ca xc tc.Theo phng php BJH p dng cho nhnh kh hp ph trn ngng nhit, ta c cng thc:

r = rk + ttrong : r: bn knh mao qun ca xc tc rnrk: bn knh Kelvin c xc nh theo cng thc




64/72

t:chiu dy mng hp ph a lp trn thnh mao qun

x:lng cht b hp ph P/Pstng ngVL:th tch ca mt mol cht b hp phSr:b mt ring ca cht hp ph xc nh theo phng trnh BETXc nh rk:

Trong :f:tha s ph thuc hnh dng ca mng, n gin, phng php BJH githit rng mng bn cu nn f = 2g:sc cng b mt ca cht lng ngng t:gc thm t. n gin thng chn = 0 cos = 1




65/72

Khi g = const, ta c s ph thuc:

V = Vi - Vi+1:chnh lch thtch cht b hp ph (P/Ps)i v(P/Ps)i+1V:biu din s tng th tchca mao qunr = ri - ri+1:chnh lch ngknh mao qun cht b hp ph (P/Ps)i v (P/Ps)i+1Phng trnh (3) biu din s

phn b th tch mao qun cacht hp ph.Trng hp i vi Al2O3c 2 cc i tngng vi ng knh mao qun l 22 Ao v 41

Ao. i vi SiO2c 1 cc i tng ng ving knh mao qun l 50 Ao.

Q

Bi tp 4:


66/72

Bi tp 4:


67/72

Bi tp 4:


68/72

Bi tp 4:


69/72

Bi tp 4:


70/72

Bi tp 4:


71/72

Bi tp 4:


72/72

ky thuat xuc tac - tiet 3

Documents