B CNG THNG TRNG I HC CNG NGHIP TP.HCM KHOA TI CHNH NGN HNG

CHUYN MN HC ti:

GVHD : Th.S Tng Th Thanh Thy Nhm Lp :3 : HTN2

TP. H Ch Minh, ngy 31 thng 12 nm 2010

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MC LCM U............................................................................................................................4 1. Cu to...........................................................................................................................5 2. Tnh cht vt l.............................................................................................................6 2.1. Nhit nng chy v nhit chuyn thy tinh....................................................7 2.2. Khi lng ring......................................................................................................7 2.3. Tnh tan....................................................................................................................9 2.4. To mng...............................................................................................................10 2.5. Kh nng chu du v dung mi.............................................................................14 2.6. Tnh cht dnh keo dn...........................................................................................14 2.7. Kh nng chng thm kh.......................................................................................14 3. Tnh cht ha hc........................................................................................................15 3.1. Phn ng acetal ha...............................................................................................15 3.2. Phn ng ether ha.................................................................................................16 3.3. Phn ng ester ha.................................................................................................17 3.4. Phn ng to phc..................................................................................................17 3.5. Phn ng to mch nhnh......................................................................................18 3.6. Phn ng phn hy.................................................................................................18 4. Tng hp......................................................................................................................18 4.1. Tng hp monomer vinyl acetate...........................................................................19 4.2. Tng hp polyvinyl acetate....................................................................................20 4.3. Tng hp polyvinyl alcohol...................................................................................21 5. ng dng.....................................................................................................................23 5.1. X si tng hp......................................................................................................23 5.2. Keo dn.................................................................................................................24 5.3. Cht kt dnh..........................................................................................................24 5.4. H v ph giy.......................................................................................................25 5.5. H si v hon thin...............................................................................................25 5.6. Tc nhn to nh....................................................................................................26 5.7. Mng PVA.............................................................................................................26 2

5.8. Gm.......................................................................................................................27 5.9. Cc sn phm c..................................................................................................27 5.10. Lp ph bo v.....................................................................................................28 5.11. M phm..............................................................................................................28 5.12. Cc mn giy nn.................................................................................................28 5.13. Ha cht trung gian..............................................................................................28 5.14. Ti thp................................................................................................................29 KT LUN......................................................................................................................30 TI LIU THAM KHO..............................................................................................31

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M U

Polyvinyl l nhm hp cht cao phn t c hnh thnh t phn ng polymer ha cc hp cht vinyl. C th k n y nh: polyvinyl acetate, polyvinyl formate, polyvinyl benzoate, polyvinyl ether Tuy nhin, trong nhm ny c mt loi polymer khng th tng hp trc tip t monomer vinyl c. chnh l polyvinyl alcohol (PVA). Nh vy, nguyn nhn no lm cho PVA khng th tng hp c trc tip t monomer vinyl alcohol? PVA c cu to v tnh cht ra sao? Quy trnh sn xut PVA trong cng nghip nh th no? V n c nhng ng dng g trong i sng cng nh trong sn xut? Bi tiu lun ny s i su vo tm hiu v lm sng t nhng vn trn. cng chnh l mc ch v phm vi nghin cu ca bi tiu lun. Cui cng, em xin chn thnh cm n thy Nguyn Quang Khuyn tn tnh hng dn v cung cp ti liu, nh m em c th hon thnh bi tiu lun ny trong thi hn cho php. Mc d c gng ht sc nhng vi s hiu bit cn hn ch nn bi tiu lun s khng trnh khi nhng thiu st. Em rt mong nhn c s ng gp kin ca thy v cc bn!

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1. Cu ton v cu trc ca polyvinyl alcohol (PVA) l:H2 C H C OH

n

Khi nhn vo cng thc ny, mt s ngi ngh rng monomer ca n phi cH 2C

cng thc:

C H

OH

Thc t khng nh vy, PVA c tng hp t qu trnh thy phn polyvinyl acetate v hp cht vinyl alcohol khng tn ti. Ngay sau khi c to ra, vinyl alcohol chuyn ha v dng ng phn bn hn l acetandehyde. Ph thuc vo mc thy phn (mc th, DS) v khi lng phn t ( trng hp, DP) m c th tng hp c mt lot cc hp cht PVA c thnh phn khc nhau. Da vo mc thy phn, PVA c chia thnh 2 loi: PVA thy phn mt phn v PVA thy phn hon ton. Cu trc ca PVA thy phn mt phn nh sau:H2 C H C OR

n

Vi R = H hoc COCH3 nhit thng, PVA l cht rn v nh hnh. Khi un nng, PVA b mm ha, c th ko di nh cao su v khi n s kt tinh. Gin Rnghen ca PVA khi ko c chu k dc theo si l 2.52 A v mng li tinh th c kch thc: a= 7.81 A , b= 5.51 A , c= 2.52 A v cu trc n t, gc = 91.410, song cng c ti liu cho l cu trc gi hnh thoi vi kch thc: 50 0 0 0

a= 7.60 A , b= 5.60 A , c= 2.52 A bao gm hai mch kt hp vi nhau bng cu hydroxyl vi khong cch l 2.8 2.9 A . Cc mt xch dc theo mch c s kt hp u ui v mch l ziczac. Tnh kt tinh vi chu k cu trc si l 2.52 A , cho thy trong phn t khng c s phn b u ha cc nhm OH m theo s phn b thng k. Da vo s khc nhau v cu trc khng gian m ta c PVA cc dng isotactic, syndiotactic hay atactic. Tng hp PVA bng cch thy phn polyvinyl formate th PVA to ra dng syndiotactic, thy phn polyvinyl benzoate to PVA dng izotactic, thy phn polyvinyl acetate (PVAc) to hn hp 3 loi: isotactic, syndiotactic v atactic, trong atactic chim ch yu.0 0

0

0

0

2. Tnh cht vt lTt c cc PVA c alcol phn mt phn v hon ton u c nhiu tnh cht thng dng, lm cho polymer c gi tr cho nhiu ngnh cng nghip. Cc tnh cht quan trng nht l kh nng tan trong nc, d to mng, chu du m v dung mi, bn ko cao, cht lng kt dnh tuyt vi v kh nng hot ng nh mt tc nhn phn tn - n nh. Tm tt cc tnh cht ca PVA (c trng bi loi Elvanol) c trnh by trong bng 2.1. Bng 2.1. Tnh cht ca PVA Dng Mu sc T trng ring Th tch ring, in3/lb Ch s khc x, nD25 dn di, mng do ha, % bn ko, kh, cha do ha, psi cng, do ha, Shore Nhit hn gn nhit, kh, cha do ha, 0C Nhit c p, do ha, 0C Bt Trng ti kem 1.27 1.31 22.9 21.1 1.49 1.53 Di 600 Di 22000 10 100 165 210 100 150 6

bn nhit, trn 1000C trn 1500C trn 2000C bn bo qun (mt vi nm) H s dn n nhit, 0 - 450C Nhit dung ring, cal/g/0C Tnh bt chy nh hng ca nh sng nh hng ca axit mnh nh hng ca kim mnh nh hng ca axit yu nh hng ca kim yu nh hng ca dung mi hu c

Lm thm mu chm Lm thm mu nhanh Phn hy Khng gy hng 7*10-5 12*10-5 0.4 Chy vi tc ca giy Khng nh hng Ha tan hoc phn hy Chy mm hoc ha tan Chy mm hoc ha tan Chy mm hoc ha tan Khng nh hng

2.1. Nhit nng chy v nhit chuyn thy tinh Vic xc nh trc tip nhit nng chy ca PVA rt kh v PVA b phn hy nhit nng chy. Thng thng nhit nng chy ca PVA c xc nh gin tip, gi tr ny khng c tnh tuyt i v nhit nng chy ca polymer khng l mt im. Bn cnh , nhit nng chy ca PVA cn ph thuc vo lng nc b hp ph trong phn t polymer. Tng t nhit nng chy, nhit chuyn thy tinh ca PVA cng thay i theo lng nc b gi trong polymer. Do vy, cng mt khi lng phn t, nhit chuyn thy tinh Tg c th khng ging nhau. Nhiu nghin cu cho thy nhit chuyn thy tinh ca PVA chia lm 2 nhm: nhm c nhit chuyn thy tinh trn 800C dng trong sn xut s xi, nhm cn li c nhit chuyn thy tinh khong 80 0C c dng cho cc ng dng khc. 2.2. Khi lng ring Khi lng ring ca PVA c xc nh theo phng php tuyn ni. N thay i ty theo trng hp v nhit ca qu trnh x l nhit. Chng hn, khi nghin cu trn cc mng PVA (loi thy phn hon ton) c trng hp thay i t 309 (mc thp nht) n 4570 (mc cao nht), sau khi x l nhit cc nhit khc nhau ta thu c kt qu sau: 7

Bng 2.2. Khi lng ring ca PVA (thy phn hon ton) theo nhit x l v trng hp Nhit x l 0C trng hp 309 708 1288 2317 4570

40 1.2824 1.2854 1.2879 1.2896

80 1.2893 1.2920 1.2949 1.2954

120 1.2961 1.2965 1.2987 1.3006 1.3020

180 1.3044 1.3036 1.3039 1.3050 1.3045

200 1.3094 1.3062 1.3065 1.3088 1.3088

T bng s liu ta thy, khi lng ring ca PVA ph thuc ch yu vo nhit x l nhit. S thay i khi lng ring theo nhit x l nhit c gii thch da trn c s nhit ng hc ca qu trnh bin i pha trong PVA. Nh ta bit, tt c cc hp cht cao phn t trng thi rn u tn ti mt trong 2 pha v phng din tinh th hc l pha kt tinh v pha v nh hnh. Trong pha kt tinh, vt cht c cu trc cht ch, ngc li trong pha v nh hnh, cu trc ca vt cht khng c cht ch bng. Bi vy trong pha v nh hnh, c nhiu l xp. Pha kt tinh c cu trc cht ch nn khi lng ring ln. Pha v nh hnh c nhiu l xp nn khi lng ring nh. Vt liu PVA ni ring, cc hp cht cao phn t khc dng rn ni chung u cha c pha tinh th ln pha v nh hinh. Do vy, khi lng ring ca n c tnh theo cng thc:

Trong : x t l pha kt tinh;

khi lng ring ca pha kt tinh.

khi lng ring ca pha v nh hnh. Gia pha kt tinh v pha v nh hnh c cn bng nhit ng v cn bng ng lc hc. Qu trnh x l nhit cng iu kin c hc, nhit x l cng cao, phn tinh th trong PVA tng theo lm tng khi lng ring ca vt liu.

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2.3. Tnh tan Kh nng tan ca PVA trong nc ph thuc vo thy phn, trng hp, nhit v nhit x l nhit. Tin trnh ha tan PVA bt u t s trng cng nh tt c cc polymer khc. Ph thuc vo thy phn v nhit : PVA thy phn trn 95% khng tan trong nc lnh m ch tan trong nc nng (65 700C) dung dch t nng ti a 10 12 %. PVA thy phn 88% tan trong nc nhit phng. PVA thy phn 80% ch tan trong nc c nhit khong 10 40 0C, trn 400C dung dch tr nn m v sau PVA kt ta. PVA thy phn 50% khng tan trong nc lnh v nng m ch trng nhng tan trong hn hp ru v nc (thng dng CH3OH). Ph thuc vo trng hp (khi lng phn t): kh nng ha tan trong nc cng l mt hm ca khi lng phn t, khi lng phn t cng thp th PVA cng d tan. Ph thuc vo nhit x l nhit: khi x l nhit PVA, nhit x l nhit tng s lm tng tinh th ha v gim ha tan trong nc. Dung dch nc ca PVA chu c lng ng k cc ru n chc nh metanol, etanol v isopropanol, t l tng khi phn trm thy phn ca PVA gim. V d: lng isopropanol ti a c th a vo nhit phng m khng lm kt ta phn PVA, thay i t khong 40% i vi Elvanol 72 60 ti khong 60% i vi Elvanol 50 42. Ch mt vi loi hp cht hu c c th l dung mi i vi cc loi PVA thy phn hon ton. V d: cc hp cht ny l cc hp cht cha nhiu nhm hydroxyl nh glyxerin, etylen glycol v mt s loi glycol polyetylen thp hn; cc amin nh etanolamin, mui etanolamin v cc amit nh formamit, etanol formamit v etanol axetamit. Hot ng dung mi ln PVA dng nh c h tr bi cc nhm hydroxyl, amino v amit. Hu ht cc dung mi k trn u cn nhit ha tan thm ch mt lng nh PVA thy phn hon ton. V d: PVA thy phn hon ton c th c ha tan 9

trong glyxerin nu gia nhit ti 120 1500C, nhng hn hp to gel khi lm ngui ti nhit phng. Dietylentriamin v trietylentetramin thuc s t dung mi hu c ha tan PVA nhit phng. nht ca dung dch PVA tng theo thi gian lu tr. Nng dung dch cng ln, s gia tng nht theo thi gian cng mnh. Mt khc, dung dch PVA vi thy phn cao v khi lng phn t ln cng lm tng nht. S tng nht ny ph thuc vo nhit , nhit thp c th lm tng nhanh hn. PVA thy phn hon ton c nht bn. Cc mui hu c, ure hoc cc alcol bo c thm vo dung dch PVA thy phn hon ton ng vai tr nh cht n nh nht. 2.4. To mng V PVA thng c ha tan trong nc trc khi s dng nn kh nng to mng ca chng rt quan trng trong hu ht cc ng dng. Mng v lp ph PVA khng cn chu k ng rn, s to mng d dng xy ra bng cch cho nc bay hi khi dung dch. So vi cc loi nha, bn ko ca PVA cao v so vi cc vt liu tan trong nc khc th n kh ni bt. bn ko ca PVA thay i theo mt s yu t nh phn trm thy phn (xem hnh 2.1), trng hp, hm lng cht do ha v m.

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Hnh 2.1. Mi quan h gia bn ko v % thy phn i vi mng PVA khng do ha Khi cc yu t khc khng i, bn ko tng theo trng hp. V d: mng cn t PVA khng do ha c nht cao, trung bnh v thp v trong iu kin m tng i 35% c bn ko trung bnh tng ng l 18000, 17000 v 9000 psi.

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Hnh 2.2. Mi lin quan gia bn ko v phn do ha ca mng PVA

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Hnh 2.3. Mi lin quan gia dn di v phn do ha ca mng PVA ( nht cao, dng thy phn hon ton, iu kin 50 phn RH) Gi tr bn ko gim khi mc alcol phn gim. V d: vi m tng i 50%, mng cn t PVA c alcol phn hon ton, nht cao th c bn ko cao hn khong 20% so vi mng cn t PVA nht cao ch c alcol phn 88%. B sung cht do ha nh glyxerin vo PVA lm gim bn ko ca mng (xem hnh 2.2), mc d vic b sung cht do ha lm tng cc c tnh dn di ca mng. dn di thay i t di 10% ti hn 600% l kt qu trc tip ca vic b sung cht do ha (xem hnh 2.3).

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2.5. Kh nng chu du v dung mi PVA khng b nh hng bi du thc vt v ng vt, m v hydrocacbon du m. Kh nng chu dung mi tng theo mc thy phn. Khng c s khc nhau ng k trong kh nng chu dung mi gia cc loi c nht thp, trung bnh v cao trong khong thy phn c th. Cc loi thy phn mt phn hu ht khng b nh hng bi cc este, ete, xeton, hydrocacbon bo, thm v cc loi ru cao hn. Ru n chc thp hn c th ha tan hoc lm trng cc loi thy phn mt phn nhng nh hng ca cc dung mi ny ln cc loi thy phn hon ton th khng ng k. 2.6. Tnh cht dnh keo dn Mt trong cc thuc tnh quan trng hn ca PVA l keo dn ca n hay bn kt dnh. iu ny c th l do kh nng d to mng ca n v thu c bn ko cao hn. Nh vy, PVA l mt trong nhng loi nha gi tr nht sn xut keo dn v cng vi nh tng polyvinyl acetate to nn ngnh cng nghip keo dn nha tng hp. Tng t vi cc thuc tnh keo dn ca PVA l cc tnh cht kt dnh ca n. Trong cc ng dng keo dn, PVA c s dng lin kt hoc cn mng 2 b mt, trong cc ng dng lm cht kt dnh, n c dng lin kt mt s loi ht, si hay cc vt liu khc. 2.7. Kh nng chng thm kh Mt trong nhng thuc tnh c bit nht ca PVA l kh nng chng thm kh ca n. Nh trnh by trong bng 2.3 v 2.4, mng PVA hu nh khng thm tt c cc loi kh, tr hi m v NH3. Cc nghin cu i vi mng PVA thy phn hon ton, loi nht thp 250C, m tng i 0% khng th hin s truyn kh oxi v nit. Di cc iu kin tng t, tc truyn kh cacbonic ch l 0.02g/m2 trong 1 gi. chng thm kh cao c gi tr i vi vt liu thm c bao gi nh x phng v cc lp ph bo v. Bng 2.3. Tc thm kh ca PVA Kh thm (g/m2/gi) Mng A Mng B Mng C 14

Oxi Cacbondioxit Nit Hydro Heli

0 0.02 0 0 0.02

0 0 0 0 0.02

0 0 0 0 0

Bng 2.4. Kh nng thm hi m ca mng PVA (loi thy phn hon ton, nht trung bnh) dy (mm) Mu 1 3 Mu 2 3 g/m2/24 gi 7.0 147 g/100in2/24 gi 0.45 9.5 g/100in2/24 gi/mm chiu dy 1.4 29

3. Tnh cht ha hcPVA l mt polymer cha nhiu nhm OH, do vy n c tnh cht ca mt ru a chc. PVA c th tham gia cc phn ng ester ha, ether ha, acetal ha, to phc vi mui ca kim loi 3.1. Phn ng acetal ha Phn ng acetal ha thc cht l phn ng cng hp i nhn gia mt aldehyde v mt ru a chc.C H2 H C OH H2 C H C OH O H C O H2 C H C CH 3 H C O

+ H 3C

C H

C H2

+ nH2O

C hai nhm hydroxyl gn nhau s tham gia phn ng acetal ha vi mt phn t aldehyde, kt qu l lng nhm hydroxyl t do trong PVA gim ng k sau khi thc hin phn ng. Ta c th acetal ha PVA bng nhiu aldehyde khc nhau. Vi mi mt aldehyde, mc acetal ha ti a cng khc nhau. Bng 3.1. Mc acetal ha ti a ca mt s aldehyde 15

Aldehyde Acid B-buthylaldehyde sulfonic Acid Ortho-benzadehyde sulfonic Acid 2,4-benzadehyde sulfonic Palmitinaldehyde Chloracetaldehyde Ortho-chlorobenzadehyde Benzadehyde

Phn trm acetal ha (%) 57.6 44.0 36.0 85.0 85.8 84.6 83.0

Khi dng cc dialdehyde lm tc nhn acetal ha ta s thu c PVA c cu trc khng gian do d hnh thnh cu ni acetal gia cc phn t PVA ln hn. Phn ng ca ceton vi PVA chm hn nhiu so vi aldehyde. Tuy nhin, vn tc phn ng ca ciclohexanon cng bng vi vn tc phn ng ca aldehyde. Phn ng acetal ha ng vai tr quan trng trong sn xut x PVA. 3.2. Phn ng ether ha PVA c th hnh thnh ether rt d dng. N hnh thnh ether ni phn t bng cch loi nc. Thng trong phn ng ny xc tc l acid hoc kim mnh, dn ti sn phm khng ha tan. Ether quan trng nht trong thng mi c hnh thnh t phn ng ca alkylen ocid vi PVA. V d nh PVA c th tham gia phn ng ether ha vi cc ethylene oxide OHH to nn nhng sn 2phm cn d tan trong nc hnC PVA. H2 c H C H H H C CH C C H2 C C C

+

2

2

OH

OH

O

H2

O

H2 C

C H H2 C

OH

Hydro trong nhm hydroxyl ca PVA kh linh ng n c th tham gia phn ng vi cc acid chlocarboxylic hnh thnh cc hp cht c nhm chc acid trong mch nhnh. V d nh phn ng ca PVA vi natri monocloaxetat to thnh ether glyconic:

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OH C H2 H C OH H2 C H C OH

+ ClCH2COONa

C H2

H C O

H2 C H2 C

C H COOH

+ NaCl

OH H2 3.3. Phn ng ester ha H H C H2 C C C

PVA d dng tham gia cc phn ng ester ha vi cc acid v c ln hu c.OH OH O C O CH3

+ CH3COOH

C H2

H C

H2 C

C H

+ H2O

Phn ng ca ester clofocmat vi PVA dn n polyvinyl cacbonat:C H2 H C

+ ClCOOR

C H2

H C

+ HCl

OH

OCOOR

Ure v PVA phn ng to thnh cao phn t cacbamat este:C H2 H C

+ H2NCNH2O

C H2

H C

+ NH3

OH

O C NH 2 O

3.4. Phn ng to phcH H2

HO H2

H H H2 H H Cng nh2 cc ru a chc khc, PVA d dng to phc vi cc hp cht v c C C C C + B OH C C C C + 2H2O

nh acid boric: OH

OH

HO

O B OH

O

17

H PVA hnh thnh phc vi ng trong mi trng trung tnh hoc base yu. Phc H 2C CH2 CH O O HC ny khng ha tan pH nhng c th ha tan trong amoniac. H 2C CH H 2C O H Cu O H O H HC CH2 CH2 O

H

H

Mt khc, iod cng phn ng vi PVA thy phn hon ton cho phc c mu xanh c trng ging nh mu ca phc gia iod v amylose. Iod cho phc mu vi PVA thy phn mt phn. 3.5. Phn ng to mch nhnh PVA d tham gia phn ng to thnh mch nhnh khi c mt cc cht sinh gc t do nh peroxide, persulfate. Phn ng to thnh mch nhnh ca PVA c th c thc hin khi PVA dng lng hay dng rn. Cc nh sn xut li dng tnh cht ny sn xut x PVA bin tnh. 3.6. Phn ng phn hy PVA l mt polymer km bn nhit. Khi b un nng ti 2000C trong chn khng, PVA b phn hy sinh ra nc v bt c g mu nu hnh thnh. Tip tc un nng ti 4000C PVA li b phn hy ln th hai cho ra cc sn phm l cc hydrocarbon thp phn t v mt t sn phm nha ha. Cc cht oxy ha mnh nh KMnO4, K2Cr2O7, O3 c kh nng gy ra phn ng oxy ha ct mch cng nh oxy ha u mch PVA.

4. Tng hpPolyvinyl alcohol c th nhn c t qu trnh thu phn cc polyvinyl ester khc nhau nh polyvinyl acetate, polyvinyl formate, polyvinyl benzoate hoc t qu trnh thu phn polyvinyl ether. Tuy nhin, tt c cc PVA thng mi u c sn xut t qu 18

trnh thu phn polyvinyl acetate. Vic tng hp PVA c tin hnh qua nhiu bc, c th c minh ha nh sau: Vinyl acetate Trng hp Polyvinyl acetate Thy phn Polyvinyl alcohol

4.1. Tng hp monomer vinyl acetate T acetylene v acid acetic Phn ng tng hp vinyl acetate t acetylene v acid acetic khng ph bin do c chi ph nguyn liu cao nn ch cn mang tnh lch s cng ngh ha hc. Acetylene phn ng vi acid acetic khong nhit t 160 200 0C pha kh trong thit b phn ng tng si c mt acetate km tm trn than hot tnh lm xc tc. Hn hp sau phn ng c lm ngui tr v trng thi lng. Kh khng ngng t ch yu l acetylene c lm sch hon lu li thit b phn ng. Dng lng c em chng ct thu cc sn phm c nhit si thp l acid acetic v mt phn acetylene cn trong hn hp, t y thu c vinyl acetate trong sn phm y.HC CH

+

H 3C

COOH

xt

H 2C

C H

O

C O

CH3

T ethylene v acid acetic Vi s pht trin ca cng ngh ha hc, acetylene dn dn b ethylene thay th. Phn ng tng hp vinyl acetate t ethylene v acid acetic cng xy ra pha kh. u tin dng kh ethylene c sc vo trong b cha acid acetic nhit 1200C. Sau khi ra khi pha lng ethylene mang theo hi acid acetic c trn vi oxy ri np vo thit b phn ng. Xc tc cho phn ng ester oxy ha ethylene l paladi phn b cht mangxt Al2O3. Nhit ca phnHng vo khong t 1752 2000C di p sut t 5 9 bar. H C C O C CH 3 H 2C CH2 + COOH 3CH O

Sau khi ra khi thit b phn ng dng sn phm c lm ngui ri i xuyn qua glycol tch vinyl acetate sau tip tc i qua dung dch Na2CO3 tch acid acetic. 19

Phn cn li c a qua thit b tch CO2 ln trong ethylene cha phn ng ri quay v vi nhp liu. Phn lng c chng ct thu cc hp cht c nhit si thp c cha vinyl acetate. Sn phm chng ct c em i chng phn on s thu c vinyl acetate sn phm nh. 4.2. Tng hp polyvinyl acetate Phn ng trng hp vinyl acetate xy ra theo c ch gc chui. Tng t cc phn ng trng hp theo c ch gc chui khc, phn ng trng hp vinyl acetate c th tin hnh theo 4 dng l: trng hp khi, trng hp dung dch, trng hp huyn ph v trng hp nh tng. Phn ng trng hp vinyl acetate l phn ng ta nhit rt ln. Trng hp khi c nhit ta ra rt ln nn rt kh kim sot, trng hp khi t c s dng v to ra khi polyvinyl acetate gy kh khn cho cc cng on x l tip theo. Trng hp huyn ph gp kh khn khi tch v lm sch cc ht polymer ra khi hn hp sau phn ng cn trng hp nh tng th cc cht to nh v cht lm bn nh ln bn trong polymer. Do vy, ch c trng hp dung dch l ph hp cho qu trnh sn xut polyvinyl alcohol. Bng 4.1 Nhit trng hp ca mt s monomer Monomer Ethylene Vinyl acetate -Vinyl pyridin Methyl acrylate H (kcal/mol) 22.7 21.3 18.7 18.6 Monomer Acrylonitrile Styrene Methyl metacrylate -Methyl styrene H (kcal/mol) 17.3 16.7 13.6 8.4

Dung mi thch hp trng hp dung dch vinyl acetate l methanol hay acetone. Nhng ch c methanol l ph hp vi qu trnh chuyn ha t polyvinyl acetate thnh polyvinyl alcohol. Khi lng phn t c kim sot trong qu trnh ch to v rt quan trng trong vic xc nh cc thuc tnh ca sn phm cng nh li ch ng dng. Qu trnh ny thng c iu chnh bng cc cht ct mch trong qu trnh trng hp polyvinyl acetate. Qu trnh trng hp dung dch thng c dng li khi t chuyn ha thch hp. Phn vinyl acetate cha phn ng c thu hi, cn dung dch polyvinyl acetate trong methanol c chuyn qua thit b thy phn.

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4.3. Tng hp polyvinyl alcohol Phn ng thy phn polyvinyl acetate c th c xc tc bng cc acid v c hay kim, thng thng s dng xc tc kim trong dung mi l methanol. Dung dch NaOH polyvinyl acetate di tc dng ca xc tc kim s tham gia phn ng thy phn:OCOCH 3 OH H2 C CH

+ CH3OH

H2 C

CH

+ CH3COOCH3

Thng thng lng nc c trong methanol dng lm dung mi rt nh, nu methanol b ln nc, lc nc s tham gia phn ng thy phn cnh tranh vi NaOH methanol:H2 C CH

+ HOH

H2 C

CH

+ CH3COOH

OCOCH 3

OH

CH3COOH +

NaOH

CH3COONa

+

H 2O

Acid acetic mi sinh ra phn ng vi NaOH:

Khi ton b NaOH phn ng ht tc dng xc tc khng cn, qu trnh thy phn b ngng. Cng nh bt c polymer no thu c t qu trnh trng hp gc, polyvinyl acetate c mch nhnh do s chuyn mch ca gc t do. Khi thc hin phn ng thy phn, cc mch nhnh xut pht t cc nhm acetyl s b phn hy lm gim trng hp ca polymer. Phn trm alcol phn c iu chnh bng cch cho php phn ng alcol phn din ra hon ton hoc dng li mc mong mun. Do phn ng thy phn lm tch cc nhm acetyl nn n thng c gi tn l qu trnh deacetyl ha. Ngay khi kim c cho vo dung dch polymer, s thy phn xy ra to nhng bng polyvinyl alcohol kt ta. Cc bng ny bao bc cc nhm acetyl cha phn ng nn hiu sut chuyn ha khng cao. V vy, trc khi cho kim, dung dch polymer c lm lnh hn ch tc phn ng. Khi t n nhit cn thit, kim c cho vo dung dch, hn hp c khuy u v c a ln bng ti dng gel. Phn ng deacetyl ha bt u xy ra. Gel c thu gm ri em i mt thi gian qu trnh xy ra trit hn. Dng lng tch ra khi bng ti bao gm methanol v methyl acetate c thu hi tch methanol. Polyvinyl alcohol c p tch hon 21

ton cc cht lng, sau c ra bng nc ha tan NaOH v mt phn methanol cn li trong hn hp. Sau khi p, polyvinyl alcohol c em i sy nhit t 60 800C v cc tinh th PVA xut hin trong lc sy. Qu trnh sy kh s ngng li khi cc tinh th PVA cha mt lng nc va phi.

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Hn hp polyvinyl acetate v methanol

Thy phn

My trn

NaOH Khuy

My p Polyvinyl alcohol kh

Bng ti gel ha My nghin gel Khu gel

My sy

My ry Bn cha Dung mi thu hi Lng thu hi ng bao Polyvinyl alcohol thnh phm

Hnh 4.1 S dy chuyn tng hp PVA.

5. ng dng5.1. X si tng hp PVA l loi x c i lc vi nc rt ln trong s cc x tng hp. c tnh ny em li cho n nhng ng dng c bit, m khng mt loi x no c th thay th, cng nh l mt trong nhng im bt li ln nht ca x. Loi PVA tan c trong nc c dng dt nhng loi vi dng lm vi nn cho cc sn phm thu, ng ten hay 23

vi d cho cc thy li th t my bay. Loi PVA c x l khng tan trong nc c dng lm ch thu, loi c cng lc ln c th dng lm lp lt trong v bnh xe cao su do kh nng lin kt vi cao su kh ln. Nhc im khc ca PVA l kh nng khi phc bin dng n hi ca n vo hng nh nht trong s cc x tng hp. 5.2. Keo dn bn ko cao v c tnh keo dn ca PVA khin chng c ng dng rng ri trong sn xut keo dn vi cc th loi a dng t keo dn t cho giy ti keo dn hot ha m. PVA dng ring hoc kt hp vi cht n, cht mu v cht chng tan c s dng rng ri lm keo dn t cho giy. Kt hp PVA vi tinh bt hay st em li hiu qu c bit v tit kim. Mt t l nh PVA lm tng bn v kh nng chu nc ca keo dn tinh bt v dextrin. Khi cn kh nng chu nc ti a th nn s dng PVA loi alcol phn hon ton. Loi keo dn nh m t trong U.S Patent 2.413.570 v 2.487.488 ca cng ty Du Pont c kh nng chu nc vt tri. Cc loi keo dn ny, c bit l hn hp ca PVA v tinh bt n vi st loi acid c u th v kh nng gia cng trn my tt hn nha ureformaldehyde. ng dng ca keo dn chu nc trn c s PVA l trong ba giy, giy dn tng v ti giy. Cc loi PVA thy phn mt phn thng c la chn dng cho keo dn hot ha m do chng nhy nc lnh hn loi thy phn hon ton. Khi PVA c s dng lm keo dn hot ha m, xu hng qun li s gim bt v t b vn cc nhit cao. 5.3. Cht kt dnh PVA l cht kt dnh hiu qu cao i vi nhiu loi vt liu khc nhau trong c si vi. N cng c s dng kt dnh cc ht xc tc, nt chai, va v sn phm ph thi. Vi vai tr l cht kt dnh trong gm, PVA to ra cc tnh cht p n v bn mu cao v vy gim nt v. PVA c s dng lm cht kt dnh cho vi v ruy bng khng dt, th hin kh nng bm dnh tuyt vi vi c si bng v si t tm. Trong hu ht cc ng dng 24

PVA hot ng nh cht kt dnh, c th thu c cc kt qu tuyt vi nh s dng ch 3 5% PVA rn. 5.4. H v ph giy PVA cung cp cho cc nh sn xut giy mt loi nha tan trong nc lm tng bn, trong, chu du m, khng thm kh v nh nng cao cht lng in ca cc sn phm giy. Thit b ph v h truyn thng c th c s dng p dng dung dch nc vo giy. Giy chu du m c th c to ra bng cch h b mt bng PVA. Nu cn kh nng bn du m tuyt i th mt lp ph lin tc c th c p dng. Din tch in trn giy c h bng PVA cho bng cao hn l do gim kh nng thm ca mc in cng nh phng mn hn do mc phn tn u hn. i khi n c ng dng trong hp giy thng thng. ng ngc nhin l ch cn mt lng nh PVA l c th tng bn v mm do ca lin kt, k ngang, ch s, bn in phi v nhiu loi giy cht lng cao khc. Giy Glassine c h bng PVA ci thin bn, trong, bng, kh nng chu du v bn kch thc. N t b nh hng bi m v lo ha v PVA ht m t hn mt s tc nhn lm trong v khng bay hi. 5.5. H si v hon thin bn ko cao, mm do, bn mi mn tt v bm dnh cng vi tan trong nc chng t tnh c ch ca PVA nh mt tc nhn h si. Qu trnh h c th c p dng bng cc phng php h si thng thng, cun ch vi si dc v si an. Cc kt qu tt cng thu c vi tt c cc loi si nh v si xe bao gm c si tng hp t cng n h. D tan trong nc, PVA c th d dng loi b khi cc vt mu xm. Trong mt s trng hp n c th c loi b trong b nhum m khng kh h. Mt trong nhng u im quan trng nht ca vic s dng PVA nh mt h ph l nh cu oxy sinh ha thp (BOD). Cc kt qu kim tra cho thy rng PVA c BOD5 ch l 200ppm so vi BOD5 ca tinh bt l 5000. 25

PVA cng c s dng rng ri nh mt cht hon thin vi, c bit khi kt hp vi nha nhit rn. 5.6. Tc nhn to nh Mt tnh cht quang trng ca PVA l kh nng hot ng nh mt tc nhn to nh khng ion. Nh th, n c mt s u im so vi nhiu cht to nh khc. N hot ng ch yu nh mt keo bo v v dung ha dn nng cc cht in ly, c bit l acid. Hn na, n to thnh hn hp cht nh ha h tr vi mt s tc nhn hot ng b mt. Hot ng to nh tng cng v s kt hp cng thng t lm c hn. PVA c th s dng to nh hay phn tn mt s lng ln cc vt liu nh du thc vt, du khong, dung mi, cht do ha, sp v nha. Cho d n hot ng va nh tc nhn hot ng b mt va nh keo bo v v l tc nhn to nh tt khi s dng ring th cc kt qu i khi cng c ci thin nh thm mt lng nh sn phm nh tc nhn hot ng b mt kh dng bt Duponol. ME c bit hiu qu trong vic lm gim sc cng b mt. Nh tng bn c th c to ra t PVA trong c mi trng acid v kim. Trong mt s ng dng n c dng nh mt cht kt dnh v cht lm c cng nh tc nhn to nh. Ni chung, loi PVA thy phn mt phn l tc nhn to nh hiu qu hn so vi loi thy phn hon ton, loi nht cao hiu qu hn loi nht thp. Thng th 2 5% PVA trn tng khi lng nh tng c th c s dng cho nh tng kiu du trong nc cha 30 50% pha phn tn. Vi nhng th nghim ban u, ch 3% PVA hay 2.5% PVA v 0.5% tc nhn hot ng b mt l . 5.7. Mng PVA Nhiu ng dng trong sn xut bao gi gm ti v ng giy cha du, m, sn v ha cht nn s dng mng PVA. Bao gi mt lng n v cc vt liu x phng, cht ty trng kh, h l, thuc tr su v cht kh trng trong cc ti cha nha tan trong nc to thun li cho vic ng dng chng. Lng cn trc c th thm vo nc m khng lm v bao gi hay loi b giy gi, nh tit kim thi gian v gim vt liu mt mt. Cc ti hn gn lm t mn ny 26

c th c s dng bao gi chn khng hay kh cc vt liu cn trnh oxy bo qun cc tnh cht ca n. Mng PVA c s dng lm cc liu oxy, trong c chn khng hay c ti, nh mt lp ph cho kim loi nh bng cn bo v trnh kh nh oxy v hydrosulfur. Khi c nh hng bng cch ko cng, mng phn cc nh sng. Tnh cht u vit ny l u im khi sn xut knh mt, n bn v mt s k thut chp nh. Do mc bm dnh thp vi mt s vt liu nha khc, mng PVA ngn chn s bm nm mc. Khi cn bn mng v kh nng chu dung mi ti a, loi thy phn hon ton c nht cao hay trung bnh c s dng. Vi mng tan trong nc lnh nn s dng loi thy phn mt phn. 5.8. Gm Mt s ng dng trong gm s dng PVA. Mt trong nhng ng dng l sn xut b n. Ch 0.1% PVA, trn c s khi lng kh ca t st, khi thm vo nc o khun c th ci thin cc c tnh lm vic. Mt ng dng khc ca gm l cht kt dnh tm thi. V d: 2 3% PVA trn c s khi lng kh ca gm cho kt qu tt trong sn xut cc ng Steatite. tan trong nc m bo s phn b ng nht ca cht kt dnh. S dng PVA lm cht kt dnh cn t p lc hn n Steatite v to thnh ng c thnh nhn hn. bn siu cao t cht kt dnh lm gim s mt mt do gia cng v vn hnh my mc. Cc cng b ch ra rng mt lng nh PVA c thm vo Steatite to ra cc ht mm d gia cng trong cc my t ng c kh v thng cho cc c tnh c tt. PVA cng cho cc kt qu tt khi lm cht kt dnh cho thnh phn men bng. Trong ng dng ny, 1% PVA (trn c s khi lng kh ca thnh phn men bng) l . 5.9. Cc sn phm c PVA c do ha c th c c thnh cc chi tit dng cao su c cng t 10 100. bn cao, mm do v chu du m, dung mi hu c, khng thm kh, bn lo ha tt c trng cho cc chi tit ny. Chng khng thch hp cho nhng ng dng i hi mc chu nc cao. PVA sn c dng ng, que, tm v cc chi tit c khc nhau. 27

5.10. Lp ph bo v PVA c s dng nh mt lp ph bo v tm thi chng xc cho cc kim loi c bng cao v cc vt liu nha trong qu trnh sn xut v vn chuyn. C bm dnh rt thp i vi cc vt liu ny v tan trong nc, lp ph c th bc hay ra d dng bng nc m khng mt nhiu thi gian. PVA cng c ch bo v kim loi khi nhng nh hng lm m ca kh. Cc lp ph trn c s PVA c s dng bo v cc di vch tng mu trng khi b bn v to mng x khi vn chuyn. Lp ph c loi b nh bc hay ra. 5.11. M phm Cc tnh cht to nh, kt dnh, to mng v lm c ca PVA u c ng dng trong sn xut m phm. Nh tng c bn cao ca cht bo v du t nhin c th c tng hp t PVA loi thy phn mt phn. Kem lnh, kem lm sch, mt n dng da trn c s PVA c ch to. Cc thuc v Thc phm M khuyn co rng i vi m phm bi ngoi, khng nn s dng PVA vi nng trn 7.5%. 5.12. Cc mn giy nn PVA c p dng t dung dch nc cha mui dicromat nh amoni dicromat s khng tan trong nc khi tip xc vi nh sng t ngoi. Tnh cht ny c s dng trong vic tng hp cc mn giy nn v bn in quang hc. Mn giy nn c tng hp t PVA c s dng rng ri trang tr cc sn phm gm. Nh mt lp ph nhy sng cho mn giy nn, PVA c mt s u im nh tnh ng nht, d p dng, bn kch thc tt v thi gian s dng lu. 5.13. Ha cht trung gian Mt trong nhng ng dng tiu th nhiu PVA nht l ha cht trung gian. Polyvinyl butyrate thng l mt acetal thu c khi cho PVA phn ng vi aldehyde.Phn ng ca PVA vi acrylonitrile thu c mt sn phm dng gm c ng dng lm keo dn nhy p. Vic s dng PVA nh mt polyol sn xut cc ester ca acid bo c tnh cht kh nhanh, tnh cht mi mn bt thng c thc hin t nm 1952. 28

5.14. Ti thp Dung dch long ca PVA loi thy phn mt phn c nht cao cho tc lm mt trung bnh gia du v nc. Khi c trn ti nng 0.05 0.3% khi lng, dung dch ti PVA loi b s nt gy din ra do nc v lm cng hiu qu (yu t cn thiu khi s dng du). C qu trnh ti phun v ti trong b u c tha mn.

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KT LUNPVA khng th tng hp trc tip t monomer vinyl alcohol v hp cht vinyl alcohol khng bn, ngay khi c to ra, vinyl alcohol chuyn v dng ng phn bn hn l acetandehyde. V vy, trong thc t, PVA c tng hp t qu trnh thy phn polyvinyl acetate. Phn ng thy phn polyvinyl acetate c th c xc tc bng acid v c hay kim, thng thng s dng kim trong dung mi methanol. PVA c c trng bi mc thy phn v mc trng hp (hay khi lng phn t) ca polyvinyl acetate ban u. Nh s kt hp 2 yu t ny m mt lot cc hp cht PVA c thnh phn khc nhau c th c tng hp nn. Tnh cht ca cc polymer ny cng thay i ty thuc vo khi lng phn t v phn trm alcol phn. Chng hn nh khi khi lng PVA gim, nhy nc hay kh nng d tan trong nc tng. Khi tng khi lng phn t th thu c bn ko, bn x, dn di v mm do cao hn. Khi phn trm alcol phn tng, bn ko, bn x v dn di cng tng PVA l mt polymer cha nhiu nhm OH. Do , n c tnh cht ca mt ru a chc. N c th tham gia vo cc phn ng nh: ester ha, ether ha, acetal ha PVA c rt nhiu ng dng trong cng nghip cng nh trong i sng. PVA c th c dng lm keo dn, lm cht kt dnh hay cht to nh, c s dng trong sn xut bao gi, trong m phm hay c dng lm x si trong dt may Vi mc ch i tm hiu v polyvinyl alcohol, bi tiu lun ny c bn gii quyt c nhng vn nu ra phn m u v gip chng ta c mt ci nhn tng qut v PVA.

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TI LIU THAM KHO[1] Nguyn Vn Khi, Polymer a nc Ha hc v ng dng, NXB Khoa hc t nhin v cng ngh, H Ni, 2007. [2] Thi Don Tnh, Ha hc cc hp cht cao phn t, NXB Khoa hc v k thut, H Ni, 2000. [3] Hunh Vn Tr, Cng ngh gia cng si ha hc, NXB i hc Bch Khoa TP.HCM, 2006. [4] F. L .Marten, Encyclopedia of polymer science and technology, vol 8 Polyvinyl alcohol, Air Products and Chemicals, Inc.

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