The 5th ISFR (October 11-14, 2009, Chengdu, China)

CATALYTIC CRACKING AND DEHYDROCHLORINATION
OF POLYPROPYLENE / POLYVINYL CHLORIDE USING
MgO COMPOSITESQian Zhou*, Yu-Zhong Wang
Center for Degradable and Flame-Retardant Polymeric Materials (ERCEPM-MoE), Collegeof Chemistry, State Key Laboratory of Polymer Materials Engineering, Sichuan University,Chengdu 610064, China;
Tel: +86-28-85410755;Fax: +86-28-85410755;
E-mail:qzhou@scu.edu.cn
1. Introduction
Recycling of waste plastics is of great interest due to the serious environmental problemscaused by waste plastics. Among the various methods of resource recovery, polymer pyrolysis,
aiming to degrade waste plastics to fuel oil or valuable chemicals for a variety of downstream
processes, is the most promising technology for resource recovery from waste polymer
materials. However, polyvinylchloride (PVC) in waste plastics will cause corrosion problems
and a contamination of all product streams with chlorinated organics during pyrolysis.
Therefore the dehydrochlorination of waste plastics is a must for this reaction. Different
sorbents for dehydrochlorination were investigated, and among these sorbents, alkaline earthoxides such as MgO attracted significant attention as effective dehydrochlorination catalysts
and chemsorbents. However, they are far from the requirement of realizing commercial use ofthis process due to the limited dehydrochlorination degree and fast deactivation of the catalysts
caused by large amounts of HCl produced during the reaction. On the other hand, loweringpyrolysis temperature and increasing pyrolysis rate, which will decrease energy consumption ofthis process, are also very necessary for this reaction. In this paper a lanthanum modified MgO
catalyst, La-MgO, and carbon-coated nano-MgO have been developed with bothdehydrochlorination and catalytic cracking ability, which will be very useful in the recycling ofchloride-containing waste plastics.
2. Experimental
2.1 Preparation of MgO composites
MgO/Carbon: sucrose and magnesium nitrate were dissolved in deionized water andprecipitated by ammonium hydroxide until the pH value reached 9.5, then the precipitation
was dried under air at 90 ºC for 12 hours to obtain Mg(OH)2 / Sucrose precursors. The- 26 -PARTⅠ PYROLYSISprecursors were heated from room temperature to 500 ºC at a rate of 2 ºC /min and kept at thistemperature for 2 hours.
La-MgO composite: magnesium nitrate and lanthanum nitrate were dissolved indeionized water and precipitated by ammonium hydroxide until the pH value reached 9.5,
after the resulting suspension stayed for 1 h at this pH; the precipitate was thoroughly washedwith absolute ethanol. The obtained samples were treated under air at 120 ℃ for 12 h andcalcined at 500 ℃ for 5 h.
2.2 Degradation procedure and product analysis
The pyrolysis of PP/PVC was carried out in a glass reactor by batch operation. In atypical catalytic run, sorbents (2 g) were mixed with PP/PVC (10 g, in a weight ratio ofPP/PVC/sorbents = 4/1/1), and reacted at 400 °C until no liquid was produced. The chlorine
contents in products were analyzed by oxygen bomb combustion and the chlorine ion
selective electrode method (ISE). The components of pyrolysis oils were analyzed using anGC-MS.
3. Results and discussion
The MgO/Carbon composite oxide and th La-MgO composite were adopted for pyrolysis
of a typical PVC-containing plastics (polypropylene/polyvinyl chloride). For chlorine
distribution (Fig.1), the carbon-coated MgO from sucrose-assisted synthesis shows
prominently superior dechlorination ability than MgO: the evolved chlorine is sharply
decreased to 2.1 wt % (MgO: 15.7 wt %). The increased interactions between sorbents and theproduced HCl due to the higher surface area of the MgO/C composite oxides may account forthe superior dechlorination ability. On the other hand, the carbon deposited on MgO
nanocrystals is able to promote the decomposition of organochlorine. On the otherhand,
La-MgO also shows excellent dehydrochlorination ability than MgO: the evolved chlorine issharply decreased to 0.65 wt %. Moreover, it shows prominent catalytic cracking ability for
PP/PVC.

Fig. 1 Chlorine distribution from pyrolysis of PP/PVC at 400 ºC.

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The 5th ISFR (October 11-14, 2009, Chengdu, China)
Acknowledgement
The authors thank the financial support of the 863 program (Contract No:
2007AA06Z325) and the National Science Fund for Distinguished Young Scholars(50525309)
References[1] W. Kaminsky, F. Hartmann, Angew. Chem. Int. Edit., 2000, 39, 331.

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