5-7 OCTOBER

ISFR

2011

91

TOLEDO (SPAIN)HYDRORREFORMING OVER Ni/h-BETA OF THE THERMAL CRACKING PRODUCTS
OF LDPE, HDPE AND PP FOR FUEL PRODUCTION
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:jose.aguado@urjc.esAbstract
Chemical treatments for plastic wastes deserve special attention nowadays because of the valuable products obtained,
raw materials for chemical processes or fuels. For fuel production, thermal cracking of the polymers must be followed byhydrogenation or hydroreforming of the pyrolysis products in order to reduce olefin content which may cause rubberformation. In this work a two-staged process (thermal cracking / hydroreforming of the products) has been developed forthe degradation of LDPE, HDPE, PP and their mixture for fuels production. A hierarchical Beta zeolite nickel-supportedcatalyst has been used in the second stage. Characterization of the products shows high selectivities to gasoline (C5-C12)and light diesel (C13-C18) as well as high RON numbers and Cetane indexes.

Keywords: polyolefins, fuels, thermal cracking, hydrorreforming, Ni/hierarchical Beta.

1. Introduction

2. Materials and Methods

A growing plastic wastes generation and an increasingly
restrictive legislation have determined new alternatives tobe investigated for its recovery apart from mechanicalrecycling and energy-recovery incineration. Chemicaltreatments are a very promising alternative since they
produce valuable products, useful as raw material for theChemical Industry or as fuels.
According to new European Waste Framework Directive
chemical processes leading to fuels obtaining are
considered energy recovery [1]. For fuel production,
thermal pyrolysis of the polymers is not the mostadequate process because of the high amount of olefins
obtained which may suffer oligomerization. A
hydrogenation or hydroreforming of the thermal cracking
products is needed in order to prevent this problem [2].
In the present work a two-stage process (thermalcracking followed by hydroreforming of the products) has
been developed for the degradation of different
polyolefins (LDPE, HDPE, PP and their mixture). A
hierarchical Beta zeolite nickel-supported catalyst has
been used in the hydrotreatment stage. Nickel has beenchosen because of its low cost and high capacity forolefinic double bonds hydrogenation. As for the support,
hierarchical Beta zeolite combines medium-high acidity
along with a bimodal micro/mesoporous structureaccessible to large molecules.
The aim is to characterize the so-obtained products andtest their capacity to be used as automotive fuels, bothgasoline and diesel, regarding to the performance ofsome properties, e.g. RON number or cetane index,bromine index and total aromatic content.

Hierarchical Beta zeolite (h-Beta) has been synthesized
by the seed silanization procedure using
phenylaminopropyltrimethoxisilane (Aldrich, +97%) [3].
Nickel has been incorporated on the support byimpregnation using nickel nitrate hexahydrate (Aldrich,>98.5%). Impregnated sample has been calcined at
550ºC in static air and reduced under 30 ml/min
hydrogen flow up to 550ºC. The catalyst (Ni/h-Beta) has
been characterized by X-Ray diffraction, H2-TPR, ICPAES, TEM, NH3-TPD, N2 adsorption-desorption at 77K
and Ar adsorption-desorption at 87K.

interiores libro.indd 91

Raw LDPE (MW a 41600), HDPE (MW a 188000), PP(MW a 450000), all provided by Repsol-YPF, and a
mixture containing 45% LDPE + 27% HDPE + 28% PP
have been chosen as starting raw materials. An initialcharge of 30g for each single polymer or mixture isthermally cracked in a stainless steel autoclave reactor at400ºC for 90 min under nitrogen atmosphere and 700rpm stirring. The gaseous product are vented out throughan ice-cooled tramp and collected into a gases bag for
further analyses. Catalyst is added to the waxy products
remaining in the reactor vessel which is then closed
again. The hydroreforming is carried out under thefollowing conditions: T = 310ºC; t = 45 min; H2 pressure =20 bar; catalyst to feed ratio = 1:30. Characterization of
the products includes gas chromatography (for gases
and liquids), aromatics measurement by HPLC, Bromine
Index determination and RON number and Cetane Index
calculations.

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6th International Symposium on Feedstock Recycling of Polymeric Materials

Table 1. Textural and chemical properties of the catalyst.
BET / external surface area (m2·g-1)
Micro / mesopores volume (cm3·g-1)
Micro / mesopores diameter (nm)Si/Al molar ratio
Acidity (meq·g-1)
Nickel content (wt %)578 / 35
0.216 / 0.162
0.6 / 3.1
250.301
6.2

The hierarchical zeolite is made of aggregates 200-400nm size. The voids between them, caused by thecalcination of the silanization agent, form a secondary
mesoporosity which means more than 40% of thecatalyst total pore volume. This secondary porosity
permits large molecules to access to acid sites and so
improves the activity of the catalyst. As for the metallic
phase, nickel presence diminishes BET and externalsurface areas and total pore volume as well as acidity
regarding to the original support up to the shown values.
Regarding to the catalytic results, it is easy to see thathigh selectivities to products useful as automotive fuels
can be achieved. Table 2 shows selectivities to gasoline(C5-C12) and light diesel (C13-C18) obtained in all thereactions. PP provides the higher selectivity to gasoline(67.9%) among the pure polymers, while LDPE leads tothe higher amount of light diesel (26.6%). Results for themixture are very similar to those for PP. No matter what
the starting feed is, the total amount of usable fuelsremains very similar, upon 83%, varying only the ratio
between gasoline and light diesel in a narrow range.
Taking into account the carbon atom number
distributions large differences appear, as PP is moreeasily cracked than the polyethylenes [4] and leads tohigher amounts of nonanes. For the mixture, thedistribution is very similar to that of PP and muchdifferent to that expected as a mere lineal combination of
the components, pointing out some synergetic effect. A
reasonable explanation is that tertiary radicals formed in
the PP structure could favour the cracking of the otherpolymers.
Table 2. Selectivities to usable fuels of thehydroreforming products (wt %).
Polymer

Gasoline

LDPE
HDPE
PPMixture

54.5
63.2
67.9
68.3

Lightdiesel
26.6
21.6
14.8
15.7

Total amountof usable fuels
81.1
84.8
82.7
84.0

Further to the properties of these fuels, figure 1 gatherssome parameters related to their adaptation toautomotive use. As it was expected, metallic function ofthe catalyst reduces olefin content in a large extent up toa minimum of 2,44 gBr2/100g sample (95% reduction) forinteriores libro.indd 92

25
Total aromatic content

100Gasoline RON number

2080wt %Table 1 shows the main properties of the activatedcatalyst.

LDPE . On the contrary, total aromatic content increases
due to the acid function of the zeolite [5] that, besides
cracking, performs secondary reactions as cyclization
and aromatization, especially in a batch system. Finally,
RON numbers and Cetane indexes indicate that theseproducts could be used as automotive fuels. All Cetaneindexes exceed European specifications [6] (minimum of51) up to 87 for HDPE hydroreforming diesel. RON
numbers are very close to the lower limit (95).

1560

1040

5200LDPE

HDPE

PP

MixtureBromine Index

0100

LDPE

HDPE

PP

MixtureDiesel cetane index

80g Br2/100g sample

3. Results and Discussion

8060604040202000LDPE

HDPE

PP

Mixture

LDPE

HDPE

PP

MixturePolymer

Polymer

Thermal cracking products
Hydroreforming products

Fig. 1. Properties of the thermal cracking andhydroreforming products.

4. Conclusions
A two-stage process combining thermal cracking andfurther hydroreforming over Ni/h-Beta can be used forfuel production from different polyolefins. The soobtained products are mainly gasoline and light diesel
with low olefin and high aromatic contents. All gasolines
present high RON number without any additive and all
diesels have cetane indexes above specifications.

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] J. Aguado, D. P. Serrano and J. M. Rodríguez. Zeolite
Beta with hierarchical porosity prepared fromorganofunctionalized
seeds.
MicroporousandMesoporous Materials 115 (2008) 504-513.
[4] A. Marcilla, J. C. Quesada, S. Sánchez and R. Ruiz.
Study of the catalytic pyrolysis behaviour of polyethylenepolypropylene mixtures. Journal of Analytical and Applied
Pyrolysis 74 (2005) 387-392.
[5] Y. Fan, X. Bao, G. Shi, W. Wei and J. Xu. Olefin
reduction of FCC gasoline via hydroisomerization
aromatization over modified HMOR/HZSM-5/HE
composite carriers. Applied Catalysis A: General 275(2004) 61-71.
[6] Directive 2009/30/CE of 23 April 2009.

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