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7/28/2019 Cc loi cht xc tc
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Cc loi cht xc tc(ng ngy 06.09.2007 14:00 & 12026 lt xem)
Cc cht xc tc c th to c ra t rt nhiu vt liu bao gm cc kim loi,
oxt kim loi, sulfuakim loi v cc oxit cch nhit. Tu thuc vo s dng, cc
vt liu xc tc c th dng khngcht nn hoc cht nn trn mt cht mang. Dng
thc ca cht xc tc c quyt nh bi thitb nh v phn ng dng xc tc.
1. Cc cht xc tc kim loi khng cht nn.Mt vi cht xc tc cng nghip c
s dng dng cc kim loi khng cht nn. Thng thng,
mt qu trnh xc tc yu cu mt din tch b mt kim loi ln gim ti thiu cc
yu cu cho chtxc tc. Tuy nhin, c mt vi qu trnh m tc phn ng trn mi n
v din tch b mt xy ra rtnhanh m ch cn c mt din tch b mt kim loi hot
ng nh l . Cc cht xc tc kim loi khngcht nn c rt nhiu dng: dng dy,
dng l, dng li, dng ht th, dng bt v dng mnh khung(Raney).
Cc cht xc tc kim loi khng cht nn dng dy, l v li thng c gi l cc
cht xc tckim loi khng cht nn dng khi khi cc ht kim loi dng khi.
Thng thng cc cht xc tc nyc s dng cho cc phn ng iu chnh s truyn khi
nhit cao.
"Black" l bt kim loi m ta thu c khi kh mui kim loi hoc ngng t hi
kim loi. Cc chtxc tc kim loi khng cht nn dng bt thng c to ra t cc
ht kim loi tng i ln c dintch b mt thp. Nhng vt liu ny t khi c s dng
vi mt t l ln nhng c th c dng trongcc thit b trn cht nho gin on
trong ngnh cng nghip dc phm.
Cc cht xc tc kim loi khng cht nn dng khung c to ra nh ngm chit
ra mt thnhphn t mt hp kim, cn li cc ht hot ng dng vt liu xp c din
tch b mt ln. V d inhnh cho loi ny l cht xc tc niken Raney. Cht xc
tc ny c iu ch t hp kim niken-nhm,nh ngm chit ra c hu ht nhm bng
dung dch kim gi li mt cht xc tc niken xp. NikenRaney l mt cht xc tc
hidro ho rt tt s dng trong cc thit b trn bt nho nhng chng dnc thay
th bi cc cht nn.
Ba v d ca phn ng dng cht xc tc kim loi khng cht nn c a ra trong
bng 3Bng 3: Cc phn ng dng cht xc tc kim loi khng cht nn
Phn ng Cht xc tc v dng xc tc
Oxi ho amoniac4NH3 + 5O2 4NO + 6H2O
Li platin hoc rodi
Oxi ho metyl ancol thnh formaldehitCH3OH + O2 CH2O + H2O
Li hoc cc ht bc
Hidrat ho acrinitrin thnh acriamitCH2CH2CN + H2O CH2CHCONH2
ng Raney
2. Cc cht xc tc nng chyVic sn xut cc cht xc tc nh lm nng chy cc
oxit khng cn c s dng rng ri. Sn
phm nng chy c din tch b mt khng ng k v phi t c iu ny trong vic
hot ho chtxc tc (v d bng cch kh). Trong phn ny, cht xc tc quan trng
nht c to ra l cht xc tc
Xc tc ha hc
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tng hp amoniac. Cht xc tc ny c sn xut nh lm nng chy qung Manhtit
cng vi cccht h tr thch hp. R rng cc k thut c khng cn ph hp vi cht
xc tc nng chy v nguynliu phi c c, nghin phn on c kch c ph hp.3. Cc
cht xc tc oxit
Cc cht xc tc oxit c th d dng chia ra lm 2 loi chnh : cht cch in
v cht bn dn. Chtcch in l nhng vt liu m nhng ht cation trng thi ho
tr 1. Cc v d cho loi oxt cch inbao gm Al2O3, SiO2 v 3Al2O3 v
3Al2O3.2SiO2. Cc vt liu ny s dng ch yu nh l axt rn hoc lbaz rn v nh
l cht nn cho cc ht hot tnh xc tc khc.
Cc oxt bn dn l vt liu m trong cc ht kim loi c chuyn i qua li tng
i d dnggia hai trng thi ho tr. iu ny c th l gia hai trng thi xi ho
khc nhau nh trong:
Fe2O3 Fe3O4hoc s chuyn i gia ion dng v kim loi trung tnh, ging
cc xt d b kh nh l ZnO v CdO.Cc xt bn dn c s dng ph bin hu ht trong
cc phn ng oxi ho chn lc. Cc v d v ccphn ng xc tc bi cc oxt c cho
trong bng 4.
Bng 4. Cc phn ng c xc tc bng oxtPhn ng Cht xc tc v dng xc tc
Oxi ho n-butan thnh andehit maleic Cc vin hoc dng trn V2O5Oxi ho
metyl ancol thnh formaldehitCH3OH +1O2 CH2O + H2O
Cc vin oxt Fe-Mo hoc vin Fe-Mo
Cracking xc tc naptha Cc ht vi cu zeolit/SiO2 - Al2O34. Cc cht
xc tc c cht nn
Cc ht xc tc thng c phn tn trn cht nn. Mc ch chnh ca vic s dng
thnh phnhot tnh xc tc cho cht nn l lm tng ng k s khuych tn v sinh
ra cc cht hot tnh cao.Khi nim trc y v cht nn l mt cht tr, dng lm
phng tin phn b hp phn cu t xctc t tin, nh l kim loi qu, tn dng c
hiu qu ln hn na ca cc kim loi so vi kim loidng khi, v d nh l bt
platin. Tuy nhin, vi cc cht xc tc kim loi thng th vic s dng chtnn
thng nhm mc ch ch yu l nng cao n nh ca cht xc tc. iu ny c th t cnh
s tng tc ph hp ca cc thnh phn hot tnh vi cht nn. Do , vic la chn
cht nn lcc k quan trng trong vic thit k mt cht xc tc. Cc c tnh vt l
v ho hc cn c trong vicla chn cht nn c a ra trong bng 5
Bng 5. Cc tnh cht vt l v ho hc ca cht nnTnh cht vt l Tnh cht ho
hc
Bn c hc Khi lng th tch (dung trng) ph
hp Cp ngun (hoc b) thot nhit Lm long pha qu hot tnh Tng din tch
b mt hot tnh Ti u ho xp cht xc tc Ti u ho kch c cu t v tinh th
kim loi
Tr vi cc phn ng ph n nh di cc iu kin phn ng v
iu kin ti sinh Phn ng vi cht xc tc lm tng
hot tnh c trng hoc tnh chn lc Lm n nh cht xc tc chng li s
dnh kt Lm gim ti thiu s nhim c cht xc
tcMc d mt bng tm tt chi tit cc c im c lit k trong bng 5 nhng cng
nn bit rng
khng mt cht nn no c th p ng tt c cc yu cu trn. Cc vt liu cht nn
thng cs dng nht l Al2O3, SiO2, 3Al2O3.2SiO2 v ccbon hot tnh. Bng 6
tm tt ton b vt liu cht nns dng cho Ty u trong nm 1990. Mt vi vt liu
khc c s dng gii hn lm cht nn nh lTiO2, MgO, Cr2O3 v Zn2O3 (ZnO2).
Vic dng Cr2O3 lm cht nn cho cht xc tc l rt hn ch bi ctnh t nhin ca
n.
Bng 6. Lng tiu th cht nn xc tc Ty u vo nm 1990Cht nn Tn/nm
Al2O3 47315
SiO2 45224
3Al2O3.2SiO2 24473
Corierit Mg2Al4SiO5O18 nguyn khi 3600
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Cacbon hot tnh 825Nh ch ra trong phn trc ( hnh 1 v 2), vt liu
cht nn c th di nhiu dng khc nhau
nh l dng khi cu, dng ht, dng p tri, dng hnh tr v dng bt. Nhng vt
liu cht nn ny cth c tm bng mui kim loi ca pha hot ho cn dng. Mt cht
nn dng bt c th c hpnhp vo hn hp kt ta hoc cht nn c th c kt ta t
dung dch trong qu trnh sn xut.Cht nn c cu trc nh dng nguyn khi (hnh
2) thng khng ph bin m trong cc ht hot
tnh thng c phn tn trn din tch b mt ln trng ra ton b b mt. Dng
khi thng lvt liu s dng khi n sp xp song song u nhau, c cc rnh thng
khng ni lin nhau. Dngcht nn ny c bit hu ch v gim p rt thp ca n v iu
thun li ny c tn dng trongcht xc tc cho khi xe t lm gim ti thiu nng
lng tn tht ca ng c. Bng 7 cho bit mtvi cht xc tc c cht nn.
Bng 7 Cc phn ng dng cht xc tc c cht nn.Phn ng Cht xc tc v dng xc
tc
Hyro ho tinC2H2 C2H4
Dng cu v dng vin Pd/ Al2O3
Tng hp metyl ancolCO + 2H2 CH3OH
Dng vin Cu/ZnO/Al2O3
Gim bt s oxi ho ca nit trong NOx 2H2 +
2NO 2H2O + N2Dng nguyn khi c lp trng tm Pt
