46061883-nghiencuuxuctac
TRANSCRIPT
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n tt nghip: Nghin cu xc tc Pd-Me /C*cho qu trnh hydrodeclo ha
PHN 1
TNG QUAN L THUYT
1.1. t vn
1.1.1. Hp cht clo hu c: c tnh - ng dng - nh hng ti h sinh thi
Hp cht clo hu c l hp cht m trong phn t c cha mt hoc nhiu
nguyn t clo gn vi gc hu c. C th phn loi cc hp cht clo hu c thnh:
Hp cht clo hu c no, khng no v hp cht clo hu c thm.
Hp cht clo hu c no c cha cc nguyn t clo lin kt vi mt gchydrocacbon no mch h hoc mch vng. V d etyl clorua CH3-CH2-Cl.
Hp cht clo hu c khng no c cha cc nguyn t clo lin kt vi mt gc
hydrocacbon khng no mch v hoc mch vng. V d TTCE Cl2-C=C-Cl2.
Hp cht clo hu c thm c cha cc nguyn t clo lin kt vi mt hay
nhiu vng thm. V d Benzyl clorua .
V ngun gc, mt s t cc hp cht clo hu c hnh thnh t cc hin tng
t nhin nh trong khi ni la, chy rng, cn a s l kt qu ca cc qu trnh
tng hp nhn to.
Cht clo hu c c s dng rng ri trong cng nghip nh c tnh ty ra
tt. Chng thng c dng trong cc quy trnh git l, lm sch b mt kim loi,
ty du m nhn. Ngoi ra, chng cn c ng dng lm dung mi, ph gia,
nguyn liu tng hp nha. V d: Diclometan lm ha cht ty sn, sn xut cht
to bt; vinyl clorua l nguyn liu sn xut nha PVC; tricloetylen l ph gia sn
xut keo, 1,4-diclobenzen dng sn xut thuc tr su, thuc nhum, ha cht
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n tt nghip: Nghin cu xc tc Pd-Me /C*cho qu trnh hydrodeclo ha
kh mi trong nh v sinh, thuc dit mi; pentaclophenol dng sn xut thuc
st trng
Mi nm trn th gii sn xut v tiu th khong 24 triu tn cht clo hu
c. Sau khi thi ra mi trng, chng tch ly li gy nguy hi cho mi trng v
sc khe con ngi. Trong h nc ngm v nc thi cng nghip thng tm
thy mt s hp cht nh DCE, TCE, TTCEvi nng khng nh.
Cc hp cht cha clo a s gy hi cho sc khe con ngi, chng c vi
da v mt, khi ht phi cc hp cht cha clo d bay hi c th gy bun nn, ngt
xu, hn m, thm ch t vong. c bit, cc hp cht clo hu c khi i vo c th
ngi c kh nng tch ly v tn ti rt lu, chng gy ra nhiu loi bnh c tnh
di truyn. V d: DDT (di-(para-clophenyl)-tricloetan) l hp cht cha clo c
s dng rng ri sau chin tranh th gii th hai phng chng st rt, st pht
ban, ng dng trong cng ngh sn xut vi si. Tuy nhin, DDT tch ly trong c
th ngi gy cc bnh v thn kinh v ung th. Dixin l cht c chin tranh,
ngi nhim phi dixin sinh ra con ci d tt, di chng ko di qua nhiu th h.
i vi mi trng, cc hp cht clo hu c gp phn ph hy tng zn, gy
ma axit v c hi vi cc sinh vt sng. V d dixin c th hy dit c h sinh
thi, CFCs (clo flo cacbon), tetraclorua cacbon, metyl cloroform gy suy gim tng
zn trong tng bnh lu. Vic ny lm gia tng cng bc x ca cc tia cc
tm, lm cht cc sinh vt ph du trong nc bin, gy ung th i vi con ngi
v ng vt. Cc hp cht clo hu c c mch vng thng c cu trc n nh,
tn ti rt bn vng v lun chuyn trong mi trng thng qua chui thc n.Thi gian phn hy cc hp cht ny ko di ti hng chc nm, rt kh x l
chng mt cch trit v i khi vic x l li sinh ra nhiu sn phm ph c hi
hn.
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V nhng l do , chng ta cn phi c bin php gim lng pht thi cc
hp cht clo hu c v nghin cu x l trit chng trc khi thi ra mi
trng.
Hnh 1 v 2 m t lng cht clo hu c pht thi ra mi trng khng kh v
nc ti cc nc Ty u trong mt s nm qua.
Hnh 1: Lng cht clo hu c pht thi ra khng kh ti Ty u [2]
Hnh 2: Lng cht clo hu c pht thi ra mi trng nc ti Ty u [2]
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n tt nghip: Nghin cu xc tc Pd-Me /C*cho qu trnh hydrodeclo ha
T hai hnh trn ta c th thy, cc nc Chu u ang t ra mc tiu gim
thiu lng hp cht clo hu c ra mi trng. C th mc tiu l ti nm 2010
gim 50% lng cht thi cha clo vo khng kh v gim 75% lng cht thi
cha clo vo nc, so vi nm 2001.
1.1.2. Hp cht tetracloetylen (TTCE) [1,2]
a. c tnh ca TTCE
Tetracloetylen (TTCE) c cng thc ha hc l C2Cl4, tn quc t l:
tetrachloroethene hay perchloroethylene, perchloroethene, perc, hoc PCE, c cng
thc cu to nh sau:
TTCE l mt cht lng khng mu, khng bt chy v c mi c trng.
TTCE khng c sn trong t nhin m c tng hp vi khi lng ln trong
cng nghip ha cht.
TTCE d bay hi, n d b ph hy khi tip xc vi cc kim loi mnh (Ba,
Li), xt n da, kalicacbonat, cc xit mnh. TTCE tan c trong ru, te,
benzen, chloroform, du, hexan v ha tan c nhiu hp cht hu c.
Bng 1 a ra nhng tnh cht vt l c trng ca TTCE.
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Bng 1: Mt s tnh cht vt l quan trng ca TTCE.
Khi lng phn t M, g.mol-1 165,8
Nhit si (101.3 kPa), oC 120
Nhit nng chy, oC -22,7
T trng , g/cm3 1.622
p sut hi (20oC), kPa 19
nht (20oC), mPa.s 1.62
tan trong nc (20o
C), g.kg-1
0,15b. Sn xut TTCE
TTCE c sn xut bng con ng clo ha hoc xyclo ha nguyn liu
gc nh propylen, dicloetan, clopropan hoc clopropen.
Michael Faraday l ngi u tin tng hp c TTCE bng phng php
phn hy nhit t tetracloetan, phn ng nh sau:
C2Cl6 C2Cl4 + Cl2
Hu ht TTCE hin nay c sn xut bng phng php clo ha cc hp
cht hydrocacbon nh nhit cao. V d: phn ng ca 1,2 dicloetan vi clo
400 oC thu c TTCE, phng trnh nh sau:
ClCH2CH2Cl + 3 Cl2 Cl2C=CCl2 + 4 HCl
Xc tc cho qu trnh l KCl v AlCl3 hoc C*, sn phm chnhTTCE c
thu li bng phng php chng ct.
c. ng dng ca TTCE
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http://en.wikipedia.org/wiki/1,2-Dichloroethanehttp://en.wikipedia.org/wiki/1,2-Dichloroethanehttp://en.wikipedia.org/wiki/1,2-Dichloroethanehttp://en.wikipedia.org/wiki/1,2-Dichloroethanehttp://en.wikipedia.org/wiki/1,2-Dichloroethanehttp://en.wikipedia.org/wiki/Hydrogen_chloridehttp://en.wikipedia.org/wiki/1,2-Dichloroethanehttp://en.wikipedia.org/wiki/Hydrogen_chloride -
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TTCE hin nay l mt ha cht thng mi cng nh l mt hp cht trung
gian quan trng trong cng nghip ha hc. Sn lng sn xut TTCE nm 1995
trn th gii c tnh t 712000 tn, TTCE sn xut ra c s dng trong cc
lnh vc ch yu sau:
55% lm hp cht trung gian trong cng ngh tng hp hu c: l
nguyn liu cho vic sn xut cc dung mi v cht ti lnh nh R113, R114 v
R115. TTCE cn dng sn xut cc cht thay th CFC nh HFCs v HCFCs
25 % TTCE c dng cho cng nghip lm sch v ty du m b mt
kim loi nh c tnh ha tan chn lc nhiu hp cht hu c v v c.
15 % TTCEc s dng trong cng nghip git kh lm sch vi si.
TTCE c s dng nh mt dung mi c kh nng loi b du dnh vi si sau
khi an, dt cng nh cc qu trnh s dng my mc khc. l nh kh nng
lm sch du, m, hydrocacbon m khng lm nh hng ti bn cht ca vi si
ca TTCE.
5%cn lic s dng vo cc mc ch khc nh lm cht tuyn kh,mc in, thuc nhum, cht bi trn
d. nh hng ca TTCE ti mi trng v con ngi
Hng ngy, hn 90% TTCE s dng c thi trc tip ra mi trng
trong 99,86 % thi trc tip vo khng kh, 0,13 % vo nc v 0,1% vo t,
lng TTCE ny v ang gy ra nhng hu qu nghim trng ti mi trng v
sc khe con ngi.
Khi TTCE c thi vo khng kh, n thng b phn hy sau mt vi tun,
to ra nhng hp cht gy nh hng xu ti tng zn. Khi con ngi tip xc
vi TTCE c trong nc thi, kh thi cng nghip trong mt thi gian lu, vi
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mt nng nht nh s c triu chng bun nn, au u, chng mt, nu nng
hn c th dn n hn m v t vong. TTCE thng gy ra cc bnh v thn kinh,
gan, cc bnh ng h hp cp tnh v mn tnh, ngoi ra TTCE l nguyn nhn
dn n nhiu loi bnh ung th.
Theo thng k ca c quan dch v sc khe v con ngi (DHHS), TTCE
nm trong s 31 cht c xut hin nhiu nht, nguy him nht i vi sc khe
con ngi.
Theo tiu chun nc thi cng nghip TCVN 5945:1995, hm lng TTCE
cho php trong nc thi cng nghip loi A, B, C l 0,02; 0,1; 0,1 mg/L.
Chnh nhng tc ng nguy him ca TTCE i vi con ngi v mi trng
sng nh vy, cc nh khoa hc trn th gii ang khn trng nghin cu tm ra
phng php gim nhng nh hng bt li ny.
1.2. Cc phng php x l hp cht clo hu c
Hin nay cc phng php chnh ang c s dng x l cc hp cht clo
hu c l: phng php xy ha, phng php kh, phng php sinh hc,
phng php kt hp xy ha kh.
1.2.1. Phng php xy ha
Bn cht ca phng php xy ha l t cc hp cht cha clo nhit
cao, c hoc khng c mt ca cht xc tc. Cc sn phm to ra gm c CO2 , H2 ,
Cl2 v mt s sn phm ph khc. Hin nay, phng php ny l con ng nhanhnht, d nht x l TTCE trong nc v kh thi.
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a. Phng php xy ha khng s dng xc tc [3]
Phng php xy ha khng s dng xc tc l qu trnh ph v lin kt clo
trong phn t bng cch thiu t hp cht clo hu c trong dng xy khng kh
nhit cao (hn 900 oC). Phng php ny t ra km hiu qu v chi ph rt cao.
Mt khc n nguy him v sau khi t to ra cc sn phm ph nh ixin v
ibenzfuran, l nhng hp cht cn c hi hn gp nhiu ln.
b. Phng php xy ha c s dng xc tc [7, 11]
u im ca phng php ny l chuyn ha ca qu trnh cao, hn 90%.
Cc hp cht cha clo c bin i thnh cc hp cht an ton hn nh CO2,H2O v Cl2 nhit 550oC, thp hn so vi phng php khng s dng xc tc.
Xc tc thng s dng trong qu trnh ny l Pd hoc Pt trn cht mang -
Al2O3, tuy nhin xc tc Pt thng b ng c bi chnh hp cht cha clo. Hng
nghin cu hin nay ca cc nh khoa hc trn th gii l nng cao n nh ca
hot tnh xc tc, c th thay i t l kim loi qu Pd, Pt, thay i nhit phn
ng, ch hot ha xc tc, lu lng dng H2.
nh gi chung v phng php xy ha, u im ca n l phn hy hon
ton mt s hp cht clo hu c, cng ngh khng phc tp. Tuy nhin phng
php ny c mt s nhc im ln nh: Km an ton, khng tn dng c sn
phm, gy nhim mi trng. Trong phng php xy ha, vic thu gom, vn
chuyn hp cht clo hu c n ni x l tng i phc tp, nguy him v tn
km. Vic sinh ra cc sn phm ph c hi hin cha c cch khc phc.Vic t
chy cng lm tng ng k lng pht thi CO2 ra mi trng, gy mt cn bng
sinh thi, c th dn n thay i kh hu. L do l a s cc hp clo hu c l do
con ngi tng hp nn ch khng phi sn c trong t nhin. Hn th na,
phng php ny c nh gi l khng xanh, trong khi xu hng sn xut
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hin nay ang l: hn ch pht thi ra mi trng, tn dng ngun thi trong cng
nghip ti ch.
1.2.2. Phng php sinh hc [2]
y l phng php s dng cc loi vi khun c kh nng phn hu c
cc hp cht clo hu c thnh cc sn phm t c hi. S dng k thut ny m
bo cc sn phm ca qu trnh khng gy nhim mi trng v khng c hi i
vi sc khe con ngi. Tuy nhin phng php ch c th x l cc hp cht clo
hu c vi s lng khng nhiu m li cn thi gian x l kh di. Cc sn phm
ca qu trnh to ra khng c ti s dng vo sn xut. Do vy, k thut ny
cha gii quyt c tt c cc vn nhim, c th kt hp vi cc phng
php khc t hiu qu cao hn.
1.2.3. Phng php kh
Thng thng dng H2 kh clo ca cc hp cht clo hu c s dng cc kim
loi qu v kim loi ph tr mang trn mt s loi cht mang, c tc dng ct t
lin kt C-Cl sau thay nguyn t Cl bng nguyn t H, phng php ny gi l
hydrodeclo ha (HDC).
u im ca phng php ny l tc phn ng nhanh, hiu sut cao,
khng to ra cc sn phm c hi cho mi trng, c li v mt kinh t.
im gii hn cho qu trnh kh trong cng nghip l chn lc v n
nh hot tnh ca xc tc. Cc hng nghin cu hin nay ang tp trung vo vic
nng cao thi gian sng ca xc tc, chn lc ra cc sn phm c gi tr cao trongcng nghip.
Bng 2 m t cc nghin cu v xc tc qu trnh HDC trn th gii
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Bng 2: Cc xc tc thng dng cho qu trnh HDC [7]
XC TC I TNG CN X L
NiMo/Al2O3 Chlorinated benzenesNi/Mo - Al2O3 Dichloromethane, 1,1,1-TCA, TCE, PCE
Pd/C 1,2,4,5-Tetrachlorobenzene
Ni/SiO2 v zeolite Y Chlorophenols, dichlorophenols,
trichlorophenols, pentachlorophenol
Pd/Al2O3, Rh/Al2O3 Chlorobenzene
Pt/C, Pd/ - Al2O3 4-Chloro-2-nitrophenol
Rh/SiO2 Dichloroethane (DCA), TCE
Pt/Al2O3 Dichloroethylene (DCE)
Pd/C* Chlorofluorocarbons
Pt/cc cht mang Carbon tetrachloride (CCl4)
Pt/ - Al2O3 Carbon tetrachloride
Pt/MgO Carbon tetrachloride
PdO/ - Al2O3 1,1,2-TrichlorotrifluoroethaneNi/zeolite Y Carbon tetrachloride
PdCuSn/C* PCE
PtCuAgAu/C* 1,2-Dichloropropane
Ni/ ZSM-5 v Al2O3 TCE and TCA
Pd/C TCE, TCA, and chlorobenzene
Pd/ Al2O3, AlF3 1,1-Dichlorotetrafluoroethane,
dichlorodifluoromethaneCc kim loi nhm VIII Dichlorodifluoromethane
Pd, Rh, Pt/ Al2O3 PCE
Pd/SiO2 1,1,1-Trichloroethane (TCA)
NiMo/ Al2O3 PCE, TCE, 1,1-dichloroethylene, cis-
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dichloroethylene and trans-dichloroethylene
Pd/ - Al2O3 CF2-Cl2 (CFC-12)
Ni-Raney, Ni/ SiO2, Pd/Al2O3,
Pt/ Al2O3,Pt/Rh/Al2O3,
Ru/ Al2O3 v sulfided NiMo/Al2O3
Dichloromethane, chloroform, carbon
tetrachloride, 1,1,1-TCA, TCE and PCE
Pt/ Al2O3 TCA
Pt, Pd/ Vycor, Al2O3, C, AlF3 Chloromethanes, chlorobenzene
1.2.4. Phng php xy ha kh kt hp [7]
y l phng php mi s dng xc tc l kim loi qu trn cht mang (v
d Pt/Rh/ -Al2O3 ), cng vi dng kh l O2 v H2 mt t l nht nh, a vo
thit b phn ng nhit > 400 oC. Phng php ny cho php ph hy cu trc
cha clo ca nhiu phn t. S kt hp c qu trnh xy ha v qu trnh kh mang
li kt qu c bit cao: hiu sut > 90% v xc tc duy tr c hot tnh trong 2
nm. Qu trnh ti sinh xc tc c th c thc hin d dng v thun tin.
C ch phn ng vi tetracloetylen c xut nh sau:
Tng qut:
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Tuy nhin nhc im ca phng php ny l sn phm khng c kh nng
ti s dng, nhit cung cp cho phn ng cn kh ln (>400 oC), nguy c chy n
vn c th xy ra. V vy phng php ny hin mi c th nghim trn m
hnh nh.
1.2.5. Phng php khc
Mt s phng php khc thng dng nh:
Hp ph TCE, PCE, DCE bng C* (vi nc hoc kh nhim bn). Phng
php ny c th tch loi nhng hp cht Clo hu c nhng khng phn hy
chng, cho nn chng ta cn x l su hn.
Kh bng kim loi: dng Fe kh clo ca cc dung dch hu c.
Dng dung mi metanol phn hy mt s hp cht nh PCE.
Cc phng php ny b gii hn bi hiu qu khng cao, quy m nh, tuy
nhin c th l gii php tm thi trong trng hp hn ch v cng ngh.
Trong s cc phng php nu trn, phng php HDC t ra u vit hn hn
v ha hn mt tng lai pht trin bn vng trong nn cng nghip, n ny
nghin cu xc tc Pd-Me/C* cho qu trnh HDC TTCE.
1.3. Phn ng HDC
1.3.1. nh ngha
Phn ng HDC l phn ng ct b lin kt C-Cl ca hp cht clo hu c trong
dng kh H2 v thay th nguyn t Cl bng nguyn t H.
R Cl + H2 R H + HCl
V d:
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CCl2=CCl2 + H2 CHCl=CCl2 + HCl
CHCl=CCl2 + H2 CHCl=CHCl + HCl
CHCl=CHCl + H2 CHCl=CH2 + HCl
CHCl=CH2 + H2 CH2=CH2 + HCl
CH2=CH2 + H2 CH3-CH3
Ngi ta s dng xc tc thc y phn ng xy ra iu kin mm, nhit
v p sut thp.
1.3.2. Xc tc
Xc tc cho phn ng HDC thng c dng kim loi mang trn cht mang.
Cc kt qu nghin cu cho thy Pt, Pd, Ni v Rh c hiu qu tt, n nh cao
hn cc kim loi khc trong phn ng HDC pha kh. Ngi ta c th s dng xc
tc n kim loi, a kim loi, hoc oxit ca cc kim loi chuyn tip nh: xit
ng, xit cban, xit mangan, xit st, xit crm, xit niken.
V cht mang, - Al2O3 v SiO2 l nhng cht mang c kh nng s dngcho xc tc HDC, tuy nhin chng d b tn cng bi sn phm HCl nn b mt
hot tnh nhanh chng. Trong khi C* c gi thnh r, tr v mt ha hc, din
tch b mt ln, tr thnh mt cht mang tim nng cho phn ng HDC pha kh.
a. Kim loi Pd [1]
Pd (palladium) l kim loi qu thuc nhm VIII B, chu k 5, s hiu nguyn
t 46. Pd kim loi c mu trng bc, c pht hin ra t nm 1803 bi William
Hyda Wollsaton. Mui nitrat, clorua ca Pd tan chm trong axit.
Pd c nhiu ng dng trong nhiu ngnh khc nhau:
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Trong ngnh in t: Pd c dng lm in dung gm a lp, u cm bin
in t, hoc lm lp bo v cho cm bin in t v cc mi hn c bit.
Trong cng ngh: Pd dng trong thit b lm sch kh, thit b ch to hydro
tinh khit, l nh Pd c kh nng hp ph hydro tt.
Trong vic lm xc tc: Pd tn mn trn C l xc tc cho qu trnh hydro ha
v dehydro ha, ng dng cho phn ng cracking cc sn phm du m. u im
ca vic s dng Pd lm xc tc l chuyn ha cao, tc dng nhanh. Tuy nhin,
n c nhc im l gi thnh cao, nhanh mt hot tnh.
Ngoi ra, Pd cn c ng dng khc trong cc ngnh nhip nh, nghthut
b. Cht mang C* [1]
C* l mt trong nhng vt liu hp ph tt, din tch b mt ln, t 500 n
1500 m2/g. Ngoi thnh phn chnh l cacbon, than hot tnh cn cha 5-10% khi
lng cc nguyn t khc dng xit kim loi, hydrxit. Trong thnh phn cc
xit kim loi thng cha cc nguyn t: Al, Si, Fe, Mg, Ca, Na, K, S, P.
Mt s c trng ca C* l din tch b mt ring, cu trc l xp, cc c
trng ny lin quan mt thit n tnh cht hp ph ca C*.
Din tch b mt ring l din tch b mt tnh cho mt n v khi lng, n
bao gm tng din tch b mt trong mao qun v bn ngoi cc ht.
Hnh dng mao qun trn b mt C* c th chia ra lm bn loi c bn: hnh
tr, hnh khe, hnh chai, hnh nm. Phn b kch thc ca cc mao qun hoc l
xp c xc nh theo s bin i ca th tch hoc din tch b mt mao qun
vi kch thc mao qun.
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n tt nghip: Nghin cu xc tc Pd-Me /C*cho qu trnh hydrodeclo ha
Theo tiu chun ca IUPAC, c th chia kch thc mao qun thnh ba loi:
Mao qun ln c ng knh mao qun trung bnh ln hn 50 nm, mao qun trung
bnh c ng knh t 2 n 50 nm, mao qun b c ng knh nh hn 2 nm.
Trong qu trnh hp ph, ngi ta thng nh gi kh nng hp ph ca C*
thng qua din tch b mt ring v phn b l xp. Din tch b mt ring cng
ln th kh nng hp ph cng cao. Kch thc mao qun ln th dung lng hp
ph thp nhng tc hp ph cao. Cc mao qun ln thng l ni cha cc ht
xc tc kim loi sau qu trnh ngm tm. Vi h mao qun trung bnh, ngoi hin
tng hp ph c th xy ra hin tng ngng t mao qun, khi kch thc mao
qun b thu hp li. i vi h mao qun nh, dung lng hp ph thng cao
nhng tc hp ph chm.
u im ca C* khi s dng lm cht mang cho xc tc l tnh tr, r, din
tch b mt ln. B mt ln ca C* c c l nh cu trc x rng tha hng t
ngun gc hu c v iu kin hnh thnh. Ngoi ra, vic x l C* sau khi dng rt
n gin.
C* c tnh cht kh clo, ngi ta a ra mt thng s dy bn hp ph
kh Clo, o lng hiu qu loi b clo ca C*. chnh l dy cn thit ca
lp C* c th gim mc clo trong dng t 5 ppm xung 3.5 ppm. di ny cng
b chng t hot tnh ca C* cng mnh.
c. Kim loi th hai [1]
St l kim loi chuyn tip thuc nhm VIII, chu k 4, s hiu nguyn t 26.Fe ng dng nhiu nht trong xy dng, ngoi ra, Fe c chn lm xc tc cho
mt s qu trnh nh tnh cht xy ha kh.
Niken l kim loi chuyn tip thuc nhm VIII B, chu k 4, s hiu nguyn t
28. Ni cng c kh nng kh clo nhng hot tnh km hn Pd. Tuy vy, u im
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rt ln ca Ni l r v d kim hn nhiu so vi Pd nn c th ng dng lm xc
tc trn quy m ln.
d. C ch phn ng HDC [6, 7]
Phn ng HDC c gi thit xy ra theo hai c ch: ni tip v song song.
Cc phn ng c th xy ra trong qu trnh HDC bao gm:
Trong * l biu th mt phn hot ng trn b mt xc tc, RClx l hp
cht hu c cha clo.
Phn ng (4) v (6) xy ra trn b mt xc tc, gia phn t RClx v nguyn
t H hp ph trn b mt xc tc. Phn ng (5),(7) l phn ng nh hp ph.
Phn ng tng qut c th vit nh sau:
C th d dng nhn thy: sn phm ca phn ng hydrodeclo ha khng ch
l mt cht khng cha clo m l mt hn hp nhiu cht c th cn cha clo, nn
c ch ni tip khng cn chnh xc. C ch song song m t phn ng HDC tt
hn [7].
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C ch phn ng HDC TTCE vi xc tc n kim loi nh sau:
Hnh 3: c ch phn ng HDC TTCE vi xc tc n kim loi Pd [6].
M t c ch phn ng: u tin, cc tm hot tnh Pd hp ph H2 v chuyn
hydro phn t v dng hydro nguyn t. TTCE cng b hp ph ln cc tm hot
tnh, lin kt C-Cl trong phn t TTCE b nguyn t H v Pd tn cng, hnh thnhlin kt mi C-H v H-Cl. Sn phm phn ng tch ra khi tm hot tnh xc tc
v i ra ngoi.
C th thy vai tr ca kim loi Pd va l ct lin kt C Cl, va l to ra cc
hydro nguyn t (H*) t H2. Hydro nguyn t mi sinh ra s thay th cc nguyn
t Cl b ct i, to lin kt vi Cl cn li to thnh HCl, ng thi cc nguyn t
H cng c dng ti sinh Pd mt hot tnh. Do Pd phi lm c hai nhim vnn kh nng xc tin qu trnh hydro ha TTCE khng cao v kh nng b ng
c bi HCl sinh ra l rt ln. Chnh v vy xc tc cha n kim loi Pd thng
nhanh b mt hot tnh.
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Khi thm kim loi th hai vo hp phn xc tc, Fe v Ni s tham gia vo c
ch phn ng, sau che chn cho Pd khi b ng c bi Cl. Pd vn gi vai tr
hp ph H nguyn t v ct t lin kt C-Cl trong phn t TTCE nh bnh
thng, to ra sn phm C2H6. Kim loi th hai cng tham gia ct lin kt C-Cl
nhng li to ra cc hp cht trung gian. Sau , cc hp cht trung gian ny nh
hp ph kim loi, hnh thnh lng ln sn phm C2H4. Ngoi ra, Fe v Ni c
ng knh nguyn t b hn Pd, che chn cho Pd khi b mt hot tnh bi tc
ng ca sn phm HCl. S khc nhau gia c ch n kim loi v a kim loi l
ch sn phm cui c cha mt lng ln olefin v ch cha mt lng nh
parafin.
1.4. Cc phng php iu ch xc tc [22]
Hin nay trn th gii ang s dng cc phng php iu ch xc tc HDC
nh sol-gel, trao i ion, ngm tm. Mi phng php u c nhng u nhc
im ring:
Phng php sol-gel ng dng vi kim loi mang trn cht mang SiO2,
phng php ny cho ng knh ht kim loi phn tn trn cht mang nh,
phn tn tt. ng knh ca cc ht kim loi sau khi to gel l khong vi nm.
Trong iu kin tt nht, phng php sol-gel to ra tinh th kim loi vi ng
knh 2 -3 nm c nh v trong mao qun ca SiO2. Khi ht kim loi c bo
v v khng b thiu kt trong sut qu trnh hot ng nhit cao. Nhc im
ca phng php ny l quy trnh phc tp, thi gian iu ch xc tc di, cn s
dng nhiu loi ha cht to phc v cu ni trung gian cho qu trnh tng hp.
Phng php trao i ion s dng nha trao i ion. Ngi ta nh t t dung
dch mui kim loi vo cc ng cc ht nha trao i ion v khuy u. Sau
lc, sy cc ht nha, ly cc ht nha kh i kh nhit cacbon. Phng php ny
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n tt nghip: Nghin cu xc tc Pd-Me /C*cho qu trnh hydrodeclo ha
cho phn tn kim loi trn xc tc rt cao nhng kh kim sot s mt mt kim
loi trong qu trnh tng hp.
Cui cng, phng php c s dng rng ri nht l phng php ngm
tm.
V d khi iu ch xc tc cho phn ng HDC TTCE, dung dch mui kim
loi (Pd(NO3)2, Fe(NO3)2, Ni(NO3)2) c tm ln b mt C*, sau ta cho bay hi
nc d s thu c kim loi mang trn cht mang. u im ca phng php ny
l tin hnh nhanh, n gin. Tuy nhin, mun thu c phn tn kim loi cao
ta cn khuy u trong v sau khi tm. Xc tc kim loi c chun b bng
phng php ngm tm thng c tm kim loi ln, ng knh ht khong 5-30
nm, phn b hu ht trn b mt cht mang.
1.5. Hng nghin cu ca ti
Trong n ny, em s dng phng php ngm tm tng hp xc tc
lng kim loi Pd-Fe/C* v Pd-Ni/C* v thay i th t tm nhm tm ra xc tc
tt nht cho phn ng HDC TTCE. Nhng nghin cu bc u cho thy, so vi
xc tc n kim loi qu, xc tc lng kim loi th hin nhiu u im r rt v
hot tnh v thi gian lm vic. Ngoi vic tit kim c kim loi qu, s c mt
ca kim loi th hai gip ci thin hot tnh v chn lc xc tc, lm mm ha
iu kin tin hnh phn ng. iu ny m ra trin vng p dng thc t cho phn
ng HDC trong qu trnh x l hp cht clo hu c.
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Tn ha cht Cng thc phn t Hng sn xut tinh khit (%)
Paladi nitrat Pd(NO3)2.2H2O Merck 99,9
Niken nitrat Cu(NO3)2.3H2O Merck 99,9St (III) Nitrat Fe(NO3)3.9H2O
Nitric acid HNO3 Merck 67
Than hot tnh C*
Dng c cn dng gm c: My khuy t, sng, t sy, l nung, cn, micro-
pipet, cc c m 100ml
2.1.2. Quy trnh tng hp xc tc
Quy trnh tng hp xc tc c m t trn hnh 4.
Hnh 4: Quy trnh tng hp xc tc
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Pha dung dchPd(NO
3)
2, Fe(NO
3)
3,
Ni(NO3)
2
Ngm tmxc tc Khuy 3h
Sy 80oC 4h,120oC 3h,
180 oC 1hNung 300oC 3h
Hot ho xc tc300 oC 3h
Cht mang(nghin, sng)
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n tt nghip: Nghin cu xc tc Pd-Me /C*cho qu trnh hydrodeclo ha
Cht mang C* c nghin, sng vi mt sng 0,3 mm. Sau dung dch
Pd(NO3)2 , Fe(NO3)3 , Ni(NO3)2 c pha theo nng tnh ton. S dng cc cc
c m 100 ml, mi cc cha 1g C*, thm 3 ml nc deion lm t b mt, khuy
u trong 1h. Dng micro-pipet ly v tm t t cc dung dch Pd(NO3)2 , Fe(NO3)3
, v Ni(NO3)2 vo, th t tm v th tch mi ln tm theo tnh ton. Sau khi tm,
cc cc c khuy u trong 3h, cho bay hi nc d bng cch sy 80 oC
trong 4h, sy 120 oC trong 3 h v 180 oC trong 1h. Nung xc tc nhit 300 oC
trong 3h, tc gia nhit 3 oC / pht. Cui cng, xc tc c hot ha 300 oC
trong 3h, c dng H2/ Ar 10% (80 ml/pht) chy qua.
Xc tc tng hp c dng ht mu en, mn, t l thnh phn ca cc mu xc
tc tng hp c m t trong bng 4
.
Bng 4: Cc mu xc tc tng hp
K hiu mu Hp phn (%) K hiu mu Hp phn (%)
BM 1 100Pd/C* BM 6 75Pd 25Ni/C*
BM 2 75Pd 25Fe/C* BM 7 50Pd 50Ni/C*
BM 3 50Pd 50Fe/C* BM 8 25Pd 75Ni/C*
BM 4 25Pd 75Fe/C* BM 9 100Ni/C*
BM 5 100Fe/C*
2.2. nh gi c trng ha l ca xc tc
2.2.1. Phng php hp ph v nh hp ph vt l N2
Hp ph v nh hp ph vt l N2 hot ng theo nguyn tc:
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Vt liu c hp ph kh N2 ti nhit N2 lng l 77oK. T phng trnh
BET:
( ) 0.
1
.
1
. P
P
CV
C
CVPPV
P
mmaa
+=
Trong :
Va: s mol kh b hp ph p sut Pa,(mol/g).
C: hng s BET.
Vm: th tch cn thit hnh thnh n lp hp ph trn b mt, mol/g.
P: p sut kh (mmHg).
P0: p sut hi bo ho ca cht b hp ph ti nhit cho (mmHg).
C th xy dng c th biu din mi quan h ( )PPVP
0
.v
0P
P
,
l mt ng thng trong khong P/P0 = 0,05 0,3. Da vo h s gc v im
ct trc tung ca ng thng biu th mi quan h gia P/Va(Pa-P) v P/Po, xc
nh c Vm v t tnh c din tch b mt ring S(m2/g) theo cng thc:
S=Vm. an.Na.10-20
Trong :
an: tit din ngang ca phn t Ni, oA.
Na: =6,023.1023 mol-1, s Avogadro
Trn c s xc nh lng N2 m vt liu c th hp ph vo cng nh nh rakhi thay i p sut m ngi ta xc nh c cu trc xp v din tch b mt
ring ca vt liu.
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n tt nghip: Nghin cu xc tc Pd-Me /C*cho qu trnh hydrodeclo ha
Trong nghin cu ny, cc mu xc tc c xc nh din tch b mt ring
v cu trc xp iu kin: nhit 77oK trn thit b ca hng Micromeritic
ASAP 2010.
2.2.2. Phng php ICP AES v AAS
ICP-AES (Inductively-Coupled Plasma Atomic Emission Spectrometry) v
AAS (Atomic Absorption Spectrophotometric) l cc phng php phn tch c
ng dng xc nh hm lng kim loi thc t trong cc mu xc tc. Nguyn l
ca cc phng php ny l axit ha, a mu v dng lng, ph v lin kt ca
cc nguyn t kim loi vi nhau v vi cht mang. Ngi ta lm bay hi mu
nhit nguyn t ha, sau o nng nguyn t kim loi t do thng qua mc
hp th hay pht x nh sng ca nguyn t kim loi ti mt tn s quang ph
c trng. T kt qu phn tch ny, ta nh gi c hiu qu ca qu trnh iu
ch xc tc, so snh gia hm lng kim loi l thuyt v thc t, c c s liu
thc t thc hin cc phng php phn tch khc nh hp ph xung CO.
Trong n ny, cc mu xc tc c phn tch hm lng kim loi a ln
cht mang bng ICP AES v AAS ti Phng th nghim Cng ngh Lc Ha du
v Vt liu Xc tc trng i hc Bch khoa H Ni.
2.2.3. Phng php hp ph xung CO
y l phng php xc nh phn tn ca mt s kim loi trn b mt xc
tc v kch thc cc phn t hot ng trn c s: o lng kh CO hp ph ln
kim loi trn b mt ca mu phn tch (trong trng hp ny l Pd) v t tnh
c s phn b kim loi trn b mt cht mang.
Trong nghin cu ny, phn tn ca cc tm kim loi trn cht mang c
xc nh bng phng php hp ph xung CO iu kin nhit 350oC, lu
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n tt nghip: Nghin cu xc tc Pd-Me /C*cho qu trnh hydrodeclo ha
lng dng CO/Ar 10% l 10ml/pht trn thit b Autochem II ca hng
Micromeritic.
2.2.4. Phng phpTEM [1]
nghin cu c trng phn b v kch thc cc tm kim loi ca xc tc,
em s dng k thut hin vi in t truyn qua (transmission electron
microscopy - TEM).
Knh hin vi in t truyn qua l mt thit b nghin cu vi cu trc vt rn,
s dng chm in t c nng lng cao chiu xuyn qua mu vt rn mng v s
dng cc thu knh t to nh vi phng i ln (c th ti hng triu ln),nh c th to ra trn mn hunh quang, phim quang hc, hay ghi nhn bng cc
my chp k thut s.
Ta bit rng knh hin vi quang hc s dng nh sng kh kin quan st
cc vt nh, do phn gii ca knh hin vi quang hc b gii hn bibc
sngnh sng kh kin, v khng th cho php nhn thy cc vt c kch thc rt
nh.
Mt in t chuyn ng vi vn tc v, s c xung lngp = m0.v, v n
tng ng vi mt sng cbc sng cho bi h thc de Broglie:
Ta thy rng bc sng ca in t nh hn rt nhiu so vi bc sng nh
sng kh kin nn vic s dng sng in t thay cho sng nh sng s to ra thitb c phn gii tt hn nhiu knh hin vi quang hc.
Cu to v nguyn l lm vic ca knh hin vi in t truyn qua:
* Sng phng in t.
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http://vi.wikipedia.org/wiki/%C4%90i%E1%BB%87n_t%E1%BB%ADhttp://vi.wikipedia.org/wiki/Th%E1%BA%A5u_k%C3%ADnhhttp://vi.wikipedia.org/wiki/Quang_h%E1%BB%8Dchttp://vi.wikipedia.org/wiki/K%C3%ADnh_hi%E1%BB%83n_vi_quang_h%E1%BB%8Dchttp://vi.wikipedia.org/w/index.php?title=%C3%81nh_s%C3%A1ng_kh%E1%BA%A3_ki%E1%BA%BFn&action=edit&redlink=1http://vi.wikipedia.org/w/index.php?title=%C4%90%E1%BB%99_ph%C3%A2n_gi%E1%BA%A3i&action=edit&redlink=1http://vi.wikipedia.org/wiki/K%C3%ADnh_hi%E1%BB%83n_vi_quang_h%E1%BB%8Dchttp://vi.wikipedia.org/wiki/B%C6%B0%E1%BB%9Bc_s%C3%B3nghttp://vi.wikipedia.org/wiki/B%C6%B0%E1%BB%9Bc_s%C3%B3nghttp://vi.wikipedia.org/w/index.php?title=%C3%81nh_s%C3%A1ng_kh%E1%BA%A3_ki%E1%BA%BFn&action=edit&redlink=1http://vi.wikipedia.org/wiki/%C4%90i%E1%BB%87n_t%E1%BB%ADhttp://vi.wikipedia.org/wiki/V%E1%BA%ADn_t%E1%BB%91chttp://vi.wikipedia.org/wiki/Xung_l%C6%B0%E1%BB%A3nghttp://vi.wikipedia.org/wiki/S%C3%B3nghttp://vi.wikipedia.org/wiki/B%C6%B0%E1%BB%9Bc_s%C3%B3nghttp://vi.wikipedia.org/w/index.php?title=H%E1%BB%87_th%E1%BB%A9c_de_Broglie&action=edit&redlink=1http://vi.wikipedia.org/wiki/K%C3%ADnh_hi%E1%BB%83n_vi_quang_h%E1%BB%8Dchttp://vi.wikipedia.org/wiki/%C4%90i%E1%BB%87n_t%E1%BB%ADhttp://vi.wikipedia.org/wiki/Th%E1%BA%A5u_k%C3%ADnhhttp://vi.wikipedia.org/wiki/Quang_h%E1%BB%8Dchttp://vi.wikipedia.org/wiki/K%C3%ADnh_hi%E1%BB%83n_vi_quang_h%E1%BB%8Dchttp://vi.wikipedia.org/w/index.php?title=%C3%81nh_s%C3%A1ng_kh%E1%BA%A3_ki%E1%BA%BFn&action=edit&redlink=1http://vi.wikipedia.org/w/index.php?title=%C4%90%E1%BB%99_ph%C3%A2n_gi%E1%BA%A3i&action=edit&redlink=1http://vi.wikipedia.org/wiki/K%C3%ADnh_hi%E1%BB%83n_vi_quang_h%E1%BB%8Dchttp://vi.wikipedia.org/wiki/B%C6%B0%E1%BB%9Bc_s%C3%B3nghttp://vi.wikipedia.org/wiki/B%C6%B0%E1%BB%9Bc_s%C3%B3nghttp://vi.wikipedia.org/w/index.php?title=%C3%81nh_s%C3%A1ng_kh%E1%BA%A3_ki%E1%BA%BFn&action=edit&redlink=1http://vi.wikipedia.org/wiki/%C4%90i%E1%BB%87n_t%E1%BB%ADhttp://vi.wikipedia.org/wiki/V%E1%BA%ADn_t%E1%BB%91chttp://vi.wikipedia.org/wiki/Xung_l%C6%B0%E1%BB%A3nghttp://vi.wikipedia.org/wiki/S%C3%B3nghttp://vi.wikipedia.org/wiki/B%C6%B0%E1%BB%9Bc_s%C3%B3nghttp://vi.wikipedia.org/w/index.php?title=H%E1%BB%87_th%E1%BB%A9c_de_Broglie&action=edit&redlink=1http://vi.wikipedia.org/wiki/K%C3%ADnh_hi%E1%BB%83n_vi_quang_h%E1%BB%8Dc -
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Trong TEM, in t c s dng thay cho nh sng (trong knh hin vi
quang hc). in t c pht ra t sng phng in t. C hai cch to ra
chm in t:
Th nht l s dng ngun pht x nhit in t: in t c pht ra t mt
catt c t nng (nng lng nhit do t nng s cung cp cho in t ng
nng thot ra khi lin kt vi kim loi. Do b t nng nn sng pht x nhit
thng c tui th khng cao v n sc ca chm in t thng km. Nhng
u im ca n l rt r tin v khng i hi chn khng siu cao. Cc cht ph
bin dng lm catt l W, Pt, LaB6...
Th hai l s dng sng pht x trng (Field Emission Gun). Cc TEM s
dng nguyn l ny thng c vit l FEG TEM: in t pht ra t catt nh
mt in th ln t vo v th ngun pht in t c tui th rt cao, cng
chm in t ln v n sc rt cao, nhng c nhc im l rt t tin v i
hi mi trng chn khng siu cao.
* Cc h thu knh v lng knh.
V trong TEM s dng chm tia in t thay cho nh sng kh kin nn vic
iu khin s to nh khng cn l thu knhthy tinh na m thay vo l cc
thu knh t. Thu knh t thc cht l mt nam chm in c cu trc l mt cun
dy cun trn li lm bng vt liu t mm. T trng sinh ra khe t s c
tnh ton c s phn b sao cho chm tia in t truyn qua s c lch thch
hp vi tng loi thu knh. Tiu c ca thu knh c iu chnh thng qua t
trng khe t, c ngha l iu khin cng dng in chy qua cun dy. V
c dng in chy qua, cun dy s b nng ln do cn c lm lnh bng
nc hoc nitlng.
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Nguyn l ghi nh trng sng v trng ti trong TEM: L thu knh ghi
nhn chm in t u tin t mu vt v lun c iu khin sao cho vt s v
tr c kh nng ly nt khi phng i ca h c thay i.
* B phn ghi nhn v quan st nh.
Khc vi knh hin vi quang hc, TEM s dng chm in t thay cho ngun
sng kh kin nn cch quan st ghi nhn cng khc. quan st nh, cc dng c
ghi nhn phi l cc thit b chuyn i tn hiu, hot ng da trn nguyn l ghi
nhn s tng tc ca in t vi cht rn.
Mn hunh quang v phim quang hc: l dng c ghi nhn in t da trnnguyn l pht quang ca cht ph trn b mt. Trn b mt ca mn hnh, ngi
ta ph mt lp vt liu hunh quang. Khi in t va p vo mn hnh, vt liu s
pht quang v nh c ghi nhn thng qua nh sng pht quang ny. Cng tng
t nguyn l ny, ngi ta c th s dngphim nh ghi li nh v nh ban u
c lu di dngphim m bn v s c trng ra sau khi s dng.
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Hnh 5: Cu to my chp TEM.
S to nh trong TEM:
Xt trn nguyn l, nh ca TEM vn c to theo cc c ch quang hc,
nhng tnh cht nh ty thuc vo tng ch ghi nh. im khc c bn ca nh
TEM so vi nh quang hc l tng phn khc so vi nh trong knh hin vi
quang hc v cc loi knh hin vi khc. Nu nh nh trong knh hin vi quang hcc tng phn ch yu em li do hiu ng hp th nh sng th tng phn
ca nh TEM li ch yu xut pht t kh nng tn x in t.
2.2.5. Phng php FE SEM
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1, 2. Thit b o & iu khin lu lng kh
3. Thit b bay hi nguyn liu TTCE
4. B trn
5. L gia nhit
6. ng phn ng
Hnh 6: S h phn ng vi dng hydro clo ha TTCE
Phn ng HDC TTCE c tin hnh p sut thng, trn h thng s
phn ng lm bng thp khng g. Xc tc th nghim t trung tm ng phn
ng (lm bng thch anh, di 500 mm, ng knh 5mm). Nhit vng phn ng
c iu khin bng l in, vi sai s 1OC, s dng thit b iu khin nhit
RKC C100 (Taiwan). Cc kh s dng cho phn ng v kh mang c kim sot
bng b iu khin lu lng Omega FMA 5400/5500.
Nguyn liu TTCEc gi 25 OC v a ti phn ng di dng hi bo
ha bi kh mang argon. Sn phm ca phn ng c phn tch trc tip bng sc
k kh (Trace GC Ultra - Italy), ct TR5 260E143P (Thermo Electron
Corporation) v detector FID c kh nng nhn bit cc hp cht hydrocacbon
cha clo vi nng > 1 ppm.
Cc thng s nghin cu qu trnh phn ng:
Lng xc tc: 50 mg.
Lu lng dng H2: 80 ml/pht (10%H2/Ar).
Lu lng dng Ar: 120 ml/ pht (99,99% Ar).
Nhit vng phn ng: 3000C.
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Trc khi phn ng, xc tc c hot ha 300 0C trong 3h bng dng kh
10%H2/Ar lu lng 80 ml/pht.
Ch phn tch sn phm bng sc k kh c a ra trong bng 5:
Bng 5: Ch o ca my sc k kh
Detector
FIDNhit 2500CKhng kh 130 ml/phtH2 40 ml/pht
N2 30 ml/pht
Ct Ct mao qun, ct Thermo TR-5 30x0.32mm ID x 0.25m film
L Nhit 400C
Thi gian 15 pht
Dng vo
C chia dngTc dng 54 ml/pht
Nhit 1500CT l chia dng 67
Kh mang 0,8ml/pht
Hot tnh xc tc c nh gi qua chuyn ha ca nguyn liu TTCE.
chuyn ha nguyn liu (C) c tnh theo cng thc:
chuyn ha C, % = 100 x
hay C % =100 x
Nguyn Th Thanh Bnh Cng ngh Hu c Ha du 1 K50 Trang 32
S mol TTCE cp vo - S mol TTCE cha phn ng
S mol TTCE cp vo
S mol TTCE cp vo
S mol TTCE phn ng
S mol TTCE cp vo
S mol TTCE cp vo
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n tt nghip: Nghin cu xc tc Pd-Me /C*cho qu trnh hydrodeclo ha
Do s mol TTCE trc v sau phn ng u t l vi din tch pic TTCE khi
phn tch trn sc k nn cng thc trn c thay bng:
C % = 100x
PHN 3
Nguyn Th Thanh Bnh Cng ngh Hu c Ha du 1 K50 Trang 33
Din tch pic TTCE trc phn ng Din tch pic TTCE sauphn ng
Din tch pic TTCE trc phn ng
S mol TTCE cp vo
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KT QU V THO LUN
3.1. c trng cu trc ha l ca xc tc
3.1.1. c trng din tch b mt ring ca xc tc
Din tch b mt ring ca xc tc BM1 (100Pd/C*) xc nh theo phng
php Langmuir l 1181,29 m2/g, ng knh mao qun trung bnh tp trung 9,14
. ng ng nhit hp ph v nh hp ph ca vt liu c a ra trn hnh 7.
Hnh 7: ng ng nhit hp ph ca xc tc BM1
Nh vy, BM1 th hin ng ng nhit hp ph loi 1, khng xut hin
vng tr. iu ny chng t xc tc ny l vt liu vi mao qun.
3.1.2. Hm lng kim loi thc t
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Hm lng kim loi thc t a ln cht mang sau ngm tm c phn tch
bng phng php ICP AES. Kt qu a ra trn hnh 8.
Hnh 8:
So snh tng
hm lng kim
loi theo l
thuyt v thct
Hnh 8
cho thy hm lng kim loi theo l thuyt v theo thc t c s khc bit: Theo l
thuyt, tng hm lng hai kim loi bng 1% khi lng xc tc nhng thc t cc
mu xc tc tng hp c tng hm lng hai kim loi thp hn d kin. Nh
vy, qu trnh ngm tm kim loi ln cht mang mi ch t hiu qu khong 90%.
S sai khc ny c th do qu trnh tng hp xc tc cha chnh xc, hoc do
cc kim loi phn b khng ng u trn b mt cht mang C*.
3.1.3. phn tn kim loi
phn tn ca cc tm kim loi trn cht mang c xc nh bng phng
php o hp ph xung CO. Kt qu phn tn v ng knh hot ng trong xc
tc c a ra trn hnh 9 v 10:
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3.1.4. S phn b kim loi trn b mt xc tc theo phng php TEM
a) C* b) BM1 (100Pd/C*)
Hnh 11: S phn b kim loi trn b mt xc tc
So snh kt qu TEM ca hai mu: cht mang C* n thun v BM1
(100Pd/C*) ta nhn thy: khi tm Pd ln cht mang C*, trn b mt than xut hin
cc ht kim loi, phn b tng i ng u. Chnh cc ht ny l tm hot tnh
ca xc tc, c vai tr hp ph H nguyn t, hp ph TTCE xy ra phn ngHDC.
3.1.5. S phn b kim loi trn b mt xc tc theo phng php FE SEM
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n tt nghip: Nghin cu xc tc Pd-Me /C*cho qu trnh hydrodeclo ha
a) BM1 (100Pd/C*)
b) BM5 (100Fe/C*) c) BM9 (100Ni/C*)
Hnh 12: S phn b n kim loi trn cht mang C*Cng trn mt b mt cht mang, cng phng i 150000 ln, mu cha
kim loi khc nhau, ta quan st thy: Tm kim loi Pd ln C* cho xc tc c bmt mn v ng u; tm kim loi Fe ln C* ta c xc tc c b mt mp m,nhiu gc cnh, v tng i ng u; tm kim loi Ni ln C* ta c xc tc c
b mt khng ng u, c s phn bit cc cm kim loi to nh khc nhau.
Mt khc, khi so snh s phn b kim loi trn b mt xc tc n kim loi
Pd (BM1) v lng kim loi Pd-Fe (BM3), Pd-Ni (BM6) ta c kt qu nh trnhnh 13:
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n tt nghip: Nghin cu xc tc Pd-Me /C*cho qu trnh hydrodeclo ha
a) BM1 (100Pd/C*)
b) BM 3 (50Pd 50Fe/C*) c) BM6 (75Pd 25Ni/C*)
Hnh 13: S phn b kim loi trong mu xc tc lng kim loi
Khi c mt kim loi th hai (Fe, Ni) vo hp phn xc tc Pd/C*, ta thy b
mt xc tc thay i. Fe lm cho b mt xc tc khng cn trng mn, to ra cc
ht ti xp bm trn b mt cht mang C*. Cc m Pd b phn tn thnh cc ht
ri nhng vn tn ti dng m ln. Mt khc, khi c mt kim loi Ni vo hpphn xc tc Pd/C*, xc tc c s kt ht to nh khc nhau v c s phn bin ht
r rng. Ni lm cho b mt xc tc khng cn trng mn, cc m trng Pd tch
ri hn, l ra nn en ca cht mang C*.
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3.2. Hot tnh xc tc Pd-Me/C*
3.2.1. Hot tnh xc tc ca cc mu n kim loi Me/C*
Kt qu th nghim trn cc mu ch cha Pd, Fe hoc Ni 1% khi lngc a ra trn hnh 14.
Hnh 14: chuyn ha TTCE theo thi gian phn ng trn cc mu xc tc Me/ C*
Quan st hnh 14 ta thy: Mu BM1 (100 Pd/C*) cho chuyn ha cao nht trong 3
mu, gi tr cao nht t khong 65%, hai mu cn li t chuyn ha thp hn, cao nht
ch t 51% v 41%. Tuy nhin, c 3 mu ny u th hin s mt hot tnh nhanh chng,
sau 90 pht th hot tnh cn li khong 30% v sau 180 pht hot tnh ca BM5 v BM 9
cn li khong 15%, thm ch hot tnh ca BM 1 ch cn li 2% . iu ny th hin rng
xc tc n kim loi c kh nng kh clo ca TTCE nhng cha n nh, c bit xc tc
n kim loi qu b mt hot tnh nhanh hn nhiu so vi cc kim loi khc. c im nys ngn cn vic trin khai xc tc trn quy m ln v thi gian lm vic ca xc tc qu
ngn.
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3.2.2. Hot tnh xc tc lng kim loi Pd-Fe/C*
nghin cu nh hng ca hp phn Fe n xc tc Pd/C*, h xc tc Pd-
Fe/C* c th nghim phn ng, kt qu a ra trn hnh 15.
Hnh 15: chuyn ha TTCE theo thi gian phn ng trn cc mu xc tc Pd-Fe/ C*
T hnh 15 ta thy: Khi thm Fe vo hp phn xc tc th chuyn ha cc i
tng khng ng k nhng n nh ca xc tc c th duy tr mc 30% (BM3),y l mt u th ln nu so snh vi mu BM1 ch cha n thun Pd/C*,
chuyn ha gim xung cn 2% sau thi gian phn ng 3h. Trong s cc t l Fe b
sung, 50% Fe (BM3) th hin kh nng duy tr hot tnh xc tc tt nht.
3.2.3. Hot tnh xc tc lng kim loi Pd-Ni/C*
nghin cu nh hng ca hp phn Ni n xc tc Pd/C*, h xc tc Pd-
Ni/C* c th nghim phn ng, kt qu a ra trn hnh 16.
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n tt nghip: Nghin cu xc tc Pd-Me /C*cho qu trnh hydrodeclo ha
Hnh 16: chuyn ha TTCE theo thi gian phn ng trn cc mu xc tc Pd - Ni/ C*
T hnh 16 ta thy: Khi thm kim loi Ni vo, chuyn ha khng tng
nhng hot tnh c phn n nh hn nhiu. ng biu din chuyn ha ph
thuc vo thi gian phn ng c xu hng i ngang v duy tr mc 30-40% (mu
BM6). Nh vy vic b sung Ni ch yu c tc dng duy tr n nh hot tnh xc
tc v t l 25% Ni th hin kh nng h tr tt nht.
Nhn xt:
Trong 2 b xc tc Pd-Fe/C* v Pd-Ni/C*, ta nhn thy hai mu BM3 v
BM6 l xc tc tt nht. C hai kim loi Ni v Fe u gp phn tng tnh n nh
hot tnh ca xc tc, ngoi ra, kim loi Fe cn c tc dng lm tng hot tnh xc
tc.
T y ta tip tc nghin cu nh hng ca th t tm kim loi n hot tnh
xc tc. Vi BM3 v BM6, th t tm kim loi khi tng hp xc tc l tm ng
thi Pd v kim loi th hai (Fe, Ni). Em tng hp thm cc mu xc tc mi c th
t tm nh trong bng 6 nhm kho st c trng phn tn kim loi v
chuyn ha ca cc mu xc tc ny.
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Bng 6: Cc mu xc tc mi tng hp
K hiu Thnh phn Th t tm K hiu Thnh phn Th t tm
BM3 50Pd 50Fe/C* Tm ngthi
BM6 75Pd 25Ni/C* Tm ngthi
BM3 Pd 50Pd 50Fe/C* Tm Pd
trc
BM6 Pd 75Pd 25Ni/C* Tm Pd
trc
BM3 Fe 50Pd 50Fe/C* Tm Fe
trc
BM6 Ni 75Pd 25Ni/C* Tm Ni
trc
3.2.4 c trng phn tn kim loi khi thay i th t tm
Hnh 17: phn tn kim loi khi thay i th t tm
Hnh 17 cho thy khi thay i th t tm kim loi th b mt xc tc c thay i
theo. phn tn cao nht th hin trn mu 50Pd-50Fe/C* tm ng thi v mu
75Pd-25Ni/C* tm ng thi. Mu 75Pd-25Ni/C* tm Ni trc cng cho phn
tn tng i tt.
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Hnh 18: ng knh hot ng ca xc tc khi thay i th t tm
Hnh18 cho thy ng knh ht hot ng ca xc tc khc nhau khi thay i
th t tm. Ta nhn thy mu no c phn tn tm kim loi cao th tng ng
vi ng knh ht hot ng cng b (mu 50Pd 50Fe/C* tm ng thi c ng
knh ht hot ng l 11,04 nm). Ngc li, mu no c phn tn kim loi thp
th ng knh ht hot ng s cao, v d mu 75Pd 25Fe/C* tm Pd trc c
ng knh ht hot ng l 483,35nm.iu ny chng t rng c cc tm hot
ng b, ta nn tm hai kim loi ng thi vi nhau.
3.2.5. c trng phn b kim loi trn b mt xc tc khi thay i th t tm
(phng php FE SEM)
Hnh nh th hin c trng phn b kim loi trn b mt xc tc ca cc mu Pd-
Fe/C* v Pd-Ni/C* khi thay i th t tm, xc nh theo phng php FE SEM
nh sau:
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n tt nghip: Nghin cu xc tc Pd-Me /C*cho qu trnh hydrodeclo ha
a) 50Pd 50Fe/C* tm ng thi b)50Pd 50Fe/C* tm Fe trc c) 50Pd 50Fe/C* tm Pd trc
Hnh 19: S phn b kim loi trn b mt cht mang ca xc tc 50Pd 50Fe/C* khithay i th t tm
Quan st hnh 19 ta nhn thy: khi thay i th t tm th b mt xc tc c
thay i theo. Vic tm ng thi Pd v Fe to ra nhiu tm kim loi nh hn v
ng u hn so vi tm ring bit.
a) 75Pd 25Ni tm ng thi b) 75Pd 25Ni tm Ni trc c) 75Pd 25Ni tm Pd trc
Hnh 20: So snh s phn b kim loi trn b mt cht mang ca xc tc 75Pd25 Ni/C* khi thay i th t tm.
Hnh 20 cho thy vic tm Ni trc s to ra nhiu tm hot tnh nh trn b
mt xc tc. Xc tc 75Pd 25Ni tm Pd trc hoc tm ng thi lm cho cc tm
kim loi phn b khng u v rng bng mu tm Ni trc.
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3.2.6. chuyn ha xc tc khi thay i th t tm
a. Hot tnh xc tc 50Pd-50Fe/C* khi thay i th t tm
Hnh 21: chuyn ha TTCE theo thi gian phn ng trn cc mu xc tc
50Pd-50Fe/ C* thay i th t tm
T hnh 21 ta thy: Khi thay i th t tm kim loi ln cht mang, hot tnh xc
tc cng thay i. BM3 v BM3 Pd cho chuyn ha cao, gi tr cc i t 67%.Tuy nhin, hot tnh ca BM3 Pd km n nh, sau 135 pht phn ng th chuyn
ha ch cn trn 10%. Mu BM3 Fe c chuyn ha thp hn mt cht, gi tr cao
nht t 59%, nhng n nh hn. Sau 180 pht phn ng, chuyn ha ca BM3
v BM3 Fe vn gi mc xp x 30% .
Nh vy, i vi cc mu xc tc Pd-Fe/C*, tm Fe trc hoc tm ng thi th
th chuyn ha cao v n nh hn, tm Pd trc th chuyn ha cao nhng kmn nh.
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n tt nghip: Nghin cu xc tc Pd-Me /C*cho qu trnh hydrodeclo ha
b. Hot tnh xc tc 75Pd-25Ni/C* khi thay i th t tm
Hnh 22:
chuyn ha
TTCE theo thi
gian phn ng
trn cc mu xc
tc 75Pd-
25Ni/ C* thay
i th t tm
T hnh 22 ta thy: Khi thay i th t tm kim loi ln cht mang, hot tnh xc
tc cng thay i r rt. BM6 Ni cho chuyn ha cao hn hn BM6 v BM6 Pd.
chuyn ha cao nht ca BM6 Ni t trn 75%, sau n nh khong 50%.
chuyn ha cao nht ca BM6 t 60% sau n nh khong 30-40%. Mu BM6
Pd cho chuyn ha thp, cao nht ch t 47% v sau 45 pht cn di 30%.
Nh vy i vi Pd-Ni/C*, tm Ni trc th chuyn ha cao v n nh hn
so vi tm Pd trc hoc tm ng thi.
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n tt nghip: Nghin cu xc tc Pd-Me /C*cho qu trnh hydrodeclo ha
KT LUN
T cc kt qu nghin cu xc tc Pd-Me/C* cho phn ng HDC TTCE, em
rt ra kt lun:
1. Vic a kim loi th hai vo hp phn xc tc Pd/C* c tc dng lm tng
phn tn kim loi ny trn b mt cht mang.
2. Cc kim loi th hai Fe, Ni ch yu lm tng n nh ca hot tnh xc
tc. Ngoi ra, Fe gp phn lm tng hot tnh ca xc tc.
3. Vic thay i th t tm c nh hng n hot tnh xc tc: Vi Pd-Fe/C*
tm ng thi hai kim loi, v vi Pd-Ni/C* tm Ni trc s t hiu qu hot tnh
xc tc cao v duy tr n nh nht.
Nhng kt qu trn cho thy, hng nghin cu tip theo nn tp trung vo
vic iu chnh t l cc kim loi ph tr nh Fe, Ni to ra xc tc a kim loi
Pd, Fe, Ni c hot tnh xc tc v n nh lm vic tt nht cho qu trnh HDC
x l cc hp cht clo hu c.
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