Liquid-phase degradation of HDPE over alkali-treated natural zeolite catalysts
- PDF / 1,350,729 Bytes
- 6 Pages / 597.28 x 842.28 pts Page_size
- 59 Downloads / 178 Views
Liquid-Phase Degradation of HDPE over Alkali-Treated Natural Zeolite Catalysts Seung Won Jeong, Jong-Ho Kim and Gon Seo' Department of Chemical Technology and The Research institute for Catalysis, Chonnam National University, GwanNu 500-757, Korea (Receh'ed 4 .hme 2001 , accepted 9 .hdy 200t)
Abstraet-('atabtic pertbrmance of alkali-treated natural zeolites was studied in the liquid-phase catab.tic degradation of HDPE. Alkali treatlnent of natural zeolite with a moderate NaOH ~lution brought about the tbrmation of mea~po~vs mad a decrease in acid site density', resulting in a c(msiderable improvelnent of its catalytic activity, l-Iowc~er, atkali treatment with highly concentrated NaOfI solutions induced zeolite structure destruction, resulting in lower activity,. ,IDPE comersion and product selectivity of alkali-treated natural zeofites were discussed in tel~s of their pore structures, acidities and the diffusion properties of large molecules. Key words: H DPE, Natural Zeolite, Degradation, Alkali Treatment
INTRODUCTION
breakage of pore ~trances by the dissolution ofaluminttm, enhances the diffusion rate of the large polymer molecules. In addition, a decrease in the number of aluminum atoms in zeolite skeletons reduces their acid site densities, suppressing carbon deposits. As a result, acid treatment considerably improves the catalytic activity of natural zeolites, but it is limited in the modification of zeolite phase because of the low solubility of the silica-a major component of zeolite. Alkali treatment, as opposed to acid treatment, has not yet been widely considered as a modification method for natural zcolites, chiefly because alkali can dissolve zeolite itsels With a proper concentratiom however, it may be helpful to improve their catalytic activities, if the alkali removes only the impurities and dissolves the surface, in particular, the formation of mesopores on the zeolite surface, via partial dissolution by alkali, may improve considerably their activities by enhancing the diffusion rates of the large polymer molecules. Lowering acid site d~lsity by alkali treatment can also contribute to the suppression of carbon d~T~ositson their external surface. in this study, the liquid-phase catalytic degradation oft tDPE was carried out over alkali-treated natural zeolite catalysts. The variation of their catalytic activities by varying the extent of the alkali treatment was discussed relating to the changes in the pore structures and acidic properties of the natural zeolites.
Polymer production has steadily increased due to its cmvenience, excellent processibility, and low price. With the rapid increase of waste polymers, however; efficient and ecologically safe ways of disposing the waste have not as yet been established. Although burying and incineration are convenient, they cause severe soil contamination and air pollution. The conversion of waste polymers to fuels or chemical feedstocks is an effective way of recycling and reducing pollution, but it is prohibitively expensive. The liquid-phase degradat
Data Loading...
