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TOLEDO (SPAIN)HYDROREFORMING OF LDPE THERMAL CRACKING WAXES OVER Ni/h-BETA
CATALYSTS WITH DIFFERENT Ni PARTICLE SIZE OBTAINED FROM DIFFERENTNi PRECURSORS
J. Aguado1, D. P. Serrano2,3, J. M. Escola1 and L. Briones1
1Department of Chemical and Environmental Technology, Rey Juan Carlos University, Tulipán s/n, Móstoles, Madrid, Spain.
2Department of Chemical and Energy Technology, Rey Juan Carlos University, Tulipán s/n, Móstoles, Madrid, Spain.
3IMDEA Energía, Tulipán s/n, Móstoles, Madrid, Spain.

e-mail:josemaria.escola.saez@urjc.esAbstract
Fuel production from polymer wastes by different chemical processes is a novel route for their energy recovery which
deserves special attention because of the valuable products obtained. In order to prevent rubber formation, thermal
pyrolysis of the polymers must be followed by hydrogenation or hydrorreforming of the products, where bifunctional
catalysts are neccesary. It is expected that hydrogenation activity is inversely correlated to the metal particle size. In thiswork, three different Ni precursors have been used to obtain Ni particles of different sizes on a hierarchical Beta zeolite.
The three catalyts have been tested in the hydroreforming of LDPE thermal cracking waxes indicating that hydrogenation
is improved with lower nickel particle sizes.

Keywords: LDPE, fuels, hydrogenation/hydroreforming, Ni particle size, Ni precursors.

1. Introduction
Among all available options for polymer wastes recovery
and treatment, chemical processes are the newest andpossibly the most interesting ones because of thevaluable products obtained. In this sense, fuel production
from waste polymers by means of chemical treatments isa novel route for their energy-recovery [1] which reduces
disposal rates while obtaining valuable products. Since
thermal pyrolysis of the polymers leads to a high amountof olefins wich may cause rubber formation in theinjection systems of automobiles, further hydrogenationor hydroreforming of the thermal cracking products isrequired [2].
Hydroreforming is performed over bifunctional catalysts
which often consist in small metal particles supported onan acid porous solid. A decrease in metal particle size ismeant to increase metal phase dispersion, improving thehydrogenation function. In this work three different nickel
precursors(nitrate,acetylacetonateandtris(ethylenediamine)nickel chloride) have been used toimpregnate a hierarchical Beta zeolite which is expected
to vary the final size of the obtained Ni particles [3].
Smaller metal particles are also expected to improve thehydrogenation of the LDPE thermal cracking product.

2. Materials and Methods
Hierarchical Beta zeolite has been synthesized by a seedsilanization procedure using phenylaminopropyltrimethoxisilane (Aldrich, +97%) [4]. Nickel has been
incorporated on the support by impregnation using nickel

interiores libro.indd 77

nitrate hexahydrate (Aldrich, >98.5%), nickel(II)acetylacetonate(Aldrich,95%)
ortris(ethylenediamine)nickel(II) chloride hydrate (TEDAN,Aldrich, 99.999%). Impregnated samples have beencalcined at 550ºC in static air and reduced under 30
ml/min hydrogen flow up to 550ºC. The catalysts havebeen characterized by X-Ray diffraction, H2-TPR, ICPAES, TEM, NH3-TPD, N2 adsorption-desorption at 77K
and Ar adsorption-desorption at 87K.
Raw LDPE (Repsol-YPF, MW 416000), was chosen asstarting material. An initial charge of 30 g LDPE isthermally cracked in a stainless steel autoclave reactor at400ºC for 90 min under nitrogen atmosphere and 700rpm stirring. The waxy products are hydroreformed overthe chosen catalyst in the same reactor. The
hydroreforming is carried out under the following
conditions: T = 310ºC; t = 45 min; H2 pressure = 20 bar;catalyst / feed ratio = 1:30. Characterization of theproducts includes gas chromatography, aromatics
measurement by HPLC, Bromine Index, RON numberand Cetane Index.

3. Results and DiscussionHierarchical Beta zeolite is made of aggregates 200-400nm size. The voids between them, caused by thecalcination of the silanization agent, form a secondary
mesoporosity which enlarges total pore volume (0.447
cm3g-1). This secondary porosity allows a better
dispersion of the Ni particles along the surface than in
traditional zeolites.

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6th International Symposium on Feedstock Recycling of Polymeric Materials

Figure 1 shows the XRD patterns of the three calcined
catalysts. Asterisks point out the NiO main reflections.
800Acetylacetonate

600

Scherrer mean NiO particle size = 35 nm

lower particle size. Likewise, the catalyst prepared withacetylacetonate shows higher hydrogenation activity thanthe hierarchical Beta prepared with TEDAN, despite its
lower nickel content. This is ascribed to the presence oflower size nickel particles.

*400

*

*

200
0Intensity (a.u.)

10203040506070

800

Nitrate

600

15 nm

400
200
010203040506070800

TEDAN

600

240 nm400
2000102030405060702Fig. 1. XRD patterns of the three impregnated andcalcined catalysts.
The larger the precursor molecule, the larger the average
NiO crystallites obtained, as it is inferred from Scherrer
equation applied to the peak at 43º. The big molecules ofTEDAN can enter neither the zeolitic micropores nor thesmall secondary mesopores, so they remain on the large
mesopores or the external surface favouring the sinteringof the nickel cations during the calcination and activation
stages, leading to NiO particles up to 500 nm. Thisbehaviour is also supported by TEM images, which are
shown as figure 2. Using TEDAN, extremely large metal
particles are formed, being wide areas deprived of nickel.
Differences between the other two precursors are muchless significant according to XRD data. Regarding themicrographs, nitrate, the smallest precursor, provides
more uniform metal particles, most of them between 1045 nm, while acetylacetonate, the medium sized allows
obtaining very small particles, with a minimum size of 3.4nm, although the mean size (35 nm) determined by XRD
is larger than that with nitrate (15 nm). The presence oflarge particles may be due to the very high amount ofacetylacetonate solution needed to impregnate thezeolite (ten times the pore volume) caused by its low
solubility in most solvents, leading to a certain amount ofsolute in the outer surface. Low solubility is also thereason of the lower final Ni content reached.
The hydroreforming of the LDPE thermal cracking
product indicates that the three catalysts show somedifferences regarding to the hydrogenating function.
Using the bromine index of the samples as an indicative
parameter, the results are as follows (table 1). All thecatalysts are able to hydrogenate the feed in a large
extent (> 90%). However, some differences can beobserved among catalysts. Comparing the samples
prepared with nitrate and TEDAN which contain similar
content of nickel (5.5 – 5.95%), it is appreciated thatnitrate shows a higher hydrogenation activity, due to its

interiores libro.indd 78

Fig. 2. TEM micrographs of the three catalysts.
Table 1. Nickel content and bromine index of thecatalysts in the hydroreforming of LDPE thermal cracking
waxes.

Ni content(wt%)
Bromine index(g Br2/100 gsample)

Thermalcracking
waxesAcetylacetonate

NitrateTEDAN-3.97

5.95

5.57

54.1

4.5

1.4

5.6

4. Conclusions
Different size Ni particles can be achieved using different
precursors. The size of the nickel particles is related tothe size and chemical nature of the starting precursor.
The lowest bromine index fuel was attained with thehierarchical Beta prepared with nickel nitrate.
Consequently, the hydrogenation activity was improved
on decreasing the nickel particle size.

References[1] Directive 2008/98/CE of 19 November 2008.
[2] J. Walendziewski and M. Steininger. Thermal andCatalytic conversion of waste poliolefines. Catalysis
Today 65 (2001) 323-330.
[3] D. J. Lensvelda, J. G. Mesua, A. J. van Dillena and K.
P. de Jong. The application of well-dispersed nickel
nanoparticles inside the mesopores of MCM-41 by use ofa nickel citrate chelate as precursor. Studies in Surface
Science and Catalysis 143 (2000) 647-657.
[4] J. Aguado, D. P. Serrano and J. M. Rodríguez. Zeolite
Beta with hierarchical porosity prepared fromorganofunctionalizedseeds.
MicroporousandMesoporous Materials 115 (2008) 504-513.

Acknowledgments
Financial support by project URJC- CM-2010-CET-5450
is acknowledged.

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