5-7 OCTOBERISFR2011

81

TOLEDO (SPAIN)PRODUCTION OF HYDROGEN AND CARBON MATERIALS FROMPOLYPROPYLENE BY COMBINED CATALYSTS
Z.W. Jiang1, J. Gong1, H.O. Yu1, J. Liu1 and T. Tang1
1 State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy ofSciences, Changchun 130022, PR China
E-mail: ttang@ciac.jl.cn

Abstract
Feedstock recycling is of great interest environmentally for providing a suitable method treating waste plastics. Syntheticpolymers, especially polyolefin, consist of carbon element and hydrogen element, in which the content of hydrogen
element is 14.3 wt %. Thus the used polyolefin is an affluent resource for the production of carbon materials andhydrogen energy. In previous studies, we have found that the combination of solid acid and nickel catalyst could
efficiently promote the conversion of virgin or waste polypropylene into carbon nanotubes and hydrogen. In this report, we
systematically explored the effects of halogenated compounds combined with nickel catalyst on the yield and morphologyof the produced carbon nanotubes. The results showed a synergistic catalysis of these materials with nickel catalyst inpromoting the formation of carbon materials and the production of hydrogen. The work offers a new potential way totransform waste plastics containing halogenated additives into carbon materials and hydrogen.

Keywords: Polypropylene, combined catalysts, carbon nanotube, nickel catalysts, hydrogen.

1. Introduction
Polyolefin, which consist of carbon element andhydrogen element, is widely applied in the modern
society. Thus the used polyolefin is an affluent resource
for the production of carbon materials and hydrogenenergy. It is a hard and necessary task to find a suitable
method treating waste plastics for feedstock recycling. In
previous studies, we have found that the combination ofsolid acid and nickel catalyst could efficiently promote theconversion of virgin or waste polypropylene (PP) into
carbon nanotubes and hydrogen [1-3]. However, thecomposition of a real polymer material is very complex.
For instance, a lots of polymer materials contain halogencontained flame retardants for safe consideration. In thisreport, we focus on the effects of halogenatedcompounds (combined with nickel catalyst) on the yieldand morphology of the carbon materials via thecarbonization of PP.

halogenated compounds. Fig. 1 shows the dependenceof the yield and microstructure of char on the content ofchlorinated paraffin. When the content of chlorinatedparaffin is lower than 0.5 wt%, the char yield increased
sharply, and the morphology of the produced carbon
varied with increasing chlorine content.

2. Materials and Methods
Polypropylene (PP) with melt flow index of 0.8 g/min was
mixed with Ni2O3 (from Lingfeng Chemical Company ofShanghai) and inorganic solids in a Brabender mixer at
100 rpm and 190 oC for 10 min. The concentration of
Ni2O3 was 5 wt % [4-5]. The above PP mixture was put
into a crucible or a fixed bed reactor and pyrolyzed at
designated temperature.

3. Results and Discussion
As we know, chlorinated paraffin is one of flame
retardants used in the recipe of polymer materials. Thus
some used polymers, such as PP, contained this kind ofinteriores libro.indd 81

Fig. 1. Dependence of the yield and microstructure ofchar on the content of chlorinated paraffin (Cl-70) in
crucible at 820 °C.
We further found that many halogenated compoundsshowed a synergistic effect with nickel catalysts on thecarbonization of PP, such as decabromodiphenyl ether,
NH4Br, FeCl3, CuCl and so on. In the cases of PP andPP mixtures with halogenated compounds, the yields ofresidual char were zero, meaning that halogenatedcompounds or their derivatives could not catalyze the26/9/11 13:12:59

82

6th International Symposium on Feedstock Recycling of Polymeric Materials

carbonization of the degradation products under theexperimental conditions. When a small amount of
halogenated compounds was added into mixture of
PP/Ni2O3, the char yield was greatly promoted comparing
with that from PP/Ni2O3 composite, indicating thesynergistic effect between halogenated compounds andNi2O3 on the formation of residual char. A similar
phenomenon was also observed in the combination
between chlorinated carbon nanotubes and nickel
catalyst.
Fig 2 presents the effect of Cl/Ni molar ratio on the charyield of PP during combustion experiments at 820 °C.
After adding just 0.060 wt% CuCl (Cl/Ni=0.0100) to
PP/5.0Ni2O3, the char yield increases rapidly from 4.5 to
29.9 wt%. Then the char yield goes up rapidly withincreasing CuCl. However, after CuCl increases to 0.751
wt% (Cl/Ni= 0.125), the char yield begins to decrease.
Therefore, we could conclude that, when CuCl is lessthan ~0.751 wt% (Cl/Ni> ~0.125), the promoting effect of
Ni2O3 and CuCl on the char yield of PP increases withincreasing CuCl; subsequently, the char yield goes up toa maximum value (Cl/Ni= 0.125), after which thepromoting effect of Ni2O3 and CuCl on the char yielddecreases with increasing CuCl. That is to say,
Cl/Ni=0.125 is the optimal ratio for catalytic carbonizationof PP.

production of hydrogen via the carbonization of PP.
Furthermore, the content of halogenated compounds
played a key role in the yield and morphology of the
produced carbon nanotubes. Our latest results haveshowed that the above combined catalysts can also
promote the carbonization of polyethylene, polystyrene
and ethylene-propylene copolymers. Thus we believethat the combined catalysis is a general-purpose method
for feedstock recycling of waste polymers.

References[1] T. Tang. Synthesis of Multiwalled carbon nanotubes
by catalytic combustion of polypropylene. Angew ChemInt Ed. 44 (2005) 1517-1520.
[2] Z.W. Jiang and T. Tang. Polypropylene as a carbon
source for the synthesis of multi-walled carbon
nanotubes via catalytic combustion. Carbon 45 (2007)
449-458.
[3] R.J. Song and T. Tang. The combined catalytic actionof solid acids with nickel for the transformation ofpolypropylene into carbon nanotubes by pyrolysis. Chem.
Eur. J. 13 (2007) 3234-3240.
[4] H.O. Yu and T. Tang. Promoting carbonization ofpolypropylene during combustion through synergistic
catalysis of a trace of halogenated compounds and Ni 2O3
for improving flame retardancy. Polymer 50 (2009) 62526258[5] H.O. Yu and T. Tang. Promoting carbonization ofpolypropylene during combustion through synergistic
catalysis of a trace of halogenated compounds and Ni 2O3
for improving flame retardancy. J. Phys. Chem. C 114(2010) 13226–13233

Fig. 2. Effect of Cl/Ni molar ratio on the char yield (C %)in CuCl-Ni2O3/PP mixture in crucible at 820°C.
A similar result was obtained in a pyrolyzer experiment.
We investigated the mass balance of pyrolysis of Ni2O3CuCl/PP in fixed bed reactor at different Cl/Ni molar ratio.
The results showed that the char yield reached amaximum at a Cl/Ni molar ratio of 0.125. With increasing
Cl/Ni molar ratio, the liquid fraction increased and the gas
fraction decreased. The produced H2 reached amaximum at a Cl/Ni molar ratio of 0.0125.

4. Conclusions
Although the presence of halogenated compounds is atrouble for preparing oil products using waste polymers, it
becomes an advantage for producing carbon materials
and hydrogen. The results showed a synergistic catalysisof halogenated compounds with nickel catalyst inpromoting the formation of carbon materials and theinteriores libro.indd 82

26/9/11 13:13:00