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Chromium(III)
Based Ziegler-Natta Catalysts for Olefin Polymerization
(Mangkin Ziegler-Natta
Berasaskan Kromium(III) untuk Pempolimeran Olefin)
J.X.
Wong* & S.N. Gan
Department
of Chemistry, Faculty of Science, University Malaya
Kuala
Lumpur, Malaysia
M.J.
Aishah
Chemistry
Division, Centre for Foundation Studies in Science, University Malaya,
Kuala
Lumpur, Malaysia
Diserahkan:
23 Oktober 2009 / Diterima: 21 October 2010
ABSTRACT
Four
chromium based oxo-trinuclear carboxylate complexes were prepared by reacting
chromium(III) nitrate nonahydrate with acetic acid and substituted carboxylic
acids. They were characterized using infrared spectroscopy (FT-IR).
Chromium content of the complexes was determined by titrimetry method. The
chromium(III) monochloroacetate complex, [Cr3O(ClCH2COO)6.3H2O]NO3.3H2O
in combination with diethylaluminium chloride formed heterogeneous catalyst
system for ethylene polymerization. Both Al/Cr ratio and temperature influenced
the catalytic activity. The maximum activity was 1768 gPE/gCr/hr/atm, achieved
by polymerizing at 29°C and monomer pressure around 1 atm, with Al/Cr ratio
30.8. Effect of chloro-substituent groups on carboxylic ligand was studied by
comparing the catalytic acitivities of chromium(III) monochloroacetate,
chromium(III) dichloroacetate, chromium(III) trichloroacetate and chromium(III)
acetate.The polymerization reaction was found to be first order with respect to
the monomer during the initial stage. The activity decreases very rapidly
presumably due to fast decay of the active sites. The polyethylene was characterized
using FT-IR and DSC,
and the results showed that it was of high density and crystallinity.
Keywords:
Chromium based complexes; ethylene polymerization; Ziegler-Natta catalyst
ABSTRAK
Empat
kompleks kromium berasaskan okso-trinuklear karboksilat telah dihasilkan
melalui tindak balas antara Cr(NO3).9H2O
dengan asid asetik dan asid karboksilik tertukarganti. Kompleks kromium yang
disediakan telah dikaji dengan spektroskopi inframerah dan kaedah penitratan.
Kompleks kromium(III) mono-kloro asetat [Cr3O(ClCH2COO)6.3H2O]NO3.3H2O
bergabung dengan di-etilaluminium klorida untuk membentuk sistem mangkin
heterogenous bagi pempolimeran etilena. Aktiviti pemangkinan dipengaruhi oleh
nisbah Al/Cr dan suhu. Aktiviti maksimum bagi pempolimeran etena tercapai
apabila suhu pempolimeran adalah 29°C dan nisbah Al/Cr 30.8, iaitu 1768
gPE/gCr/j/atm. Faktor pengaruh kumpulan kloro tertukarganti pada ligan
karboksilat telah dikaji dengan menggunakan kompleks kromium(III) di-kloro
asetat, kromium(III) tri-kloro asetat dan kromium(III) asetat sebagai mangkin.
Pempolimeran etilena dalam kajian ini adalah linear terhadap etilena pada
permulaan tindak balas. Plot aktiviti lawan masa tindak-balas menunjukkan graf
jenis lengkung menurun. Polietilena yang dihasilkan dikaji dengan FT-IR dan DSC dan keputusan menunjukkan bahawa polietilena yang terhasil
mempunyai darjah ketumpatan yang tinggi.
Kata kunci: Kompleks
berasaskan kromium; mangkin Ziegler-Natta; pempolimeran etilena
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*Pengarang untuk surat-menyurat; email:
junxuan@perdana.um.edu.my
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