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Zeolit - rây phân tử và những khả năng ứng dụng thực tế đa dạng

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- Phản <strong>ứng</strong> đồng <strong>phân</strong> hoá o-xylen<br />

CH 3<br />

CH 3<br />

CH 3<br />

CH 3<br />

CH 3<br />

CH 3<br />

o-xylen m-xylen p-xylen<br />

Tõ o-xylen cã thÓ tr−íc tiªn chuyÓn thµnh m-xylen, nh−ng v× tiÕt diÖn<br />

ngang cña m-xylen lín h¬n kÝch th−íc cöa sæ cña xóc t¸c zeolit, nªn m-xylen<br />

l¹i ®−îc chuyÓn ho¸ tiÕp thµnh p-xylen.<br />

- hay metyl hoá toluen bằng metanol<br />

CH 3<br />

- H O 2<br />

+ CH OH 3<br />

CH 3<br />

CH 3<br />

+ CH 3 OH - H 2<br />

O<br />

CH 3<br />

(1)<br />

CH 3<br />

CH 3<br />

+<br />

+<br />

CH 3<br />

CH 3<br />

CH 3<br />

CH 3<br />

CH 3<br />

CH 3 CH3<br />

CH 3<br />

CH 3<br />

+<br />

+<br />

(2)<br />

CH 3<br />

CH 3<br />

CH 3<br />

VÒ nguyªn t¾c, metyl ho¸ toluen cã thÓ thu ®−îc hµng lo¹t hîp chÊt<br />

kh¸c nhau. §iÒu nµy th−êng xy ra trong xóc t¸c ®ång thÓ, hay trªn c¸c xóc<br />

t¸c r¾n cã kÝch th−íc mao qun lín. Nh−ng ®èi víi zeolit cã tÝnh lùa chän kÝch<br />

th−íc, th× chØ p-xylen lµ cã thÓ tho¸t ra khái cöa sæ cña zeolit lµm xóc t¸c, cßn<br />

c¸c hîp chÊt kh¸c Ýt cã kh n¨ng t¹o thµnh, hay bÞ chuyÓn ho¸ tiÕp thµnh p-<br />

xylen. Xóc t¸c thùc hiÖn ®−îc ®iÒu ®ã lµ zeolit ZSM-5.<br />

36

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