CONVERSION OF LDPE TOWARDS TRANSPORTATION FUELS BY A TWO-STAGE
PROCESS USING Ni/Al-SBA-15 AS CATALYST
D. P. Serrano1,3, J. M. Escola2, M. Arroyo2 and A.Alba
1Department of Chemical and EnergyTechnology, Rey Juan Carlos University, Tulipán s/n, Móstoles, Madrid, Spain.
2Department of Chemical and Environemtal 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
The effect of the Si/Al atomic ratio of mesostructured Ni/Al-SBA-15 catalysts has been studied in the hydroreforming of theoil resulting from the thermal cracking of low-density polyethylene. The size of the nickel particles over Al-SBA-15 increased
with the Si/Al atomic ratio of the supports. The enhancement of the Si/Al atomic ratio of the Al-SBA-15 increased the share oflight diesel (C13 – C18) hydrocarbons, reaching a 40% for Si/Al = 100. All the catalysts allowed obtaining a high hydrogenation
degree (87%) and the fuels contained a low share of aromatics (< 5%)

Keywords: LDPE, fuels, hydrogenation/hydroreforming, SBA-15.

1. Introduction
The waste plastics cause serious environmental
problems. The main components of the plastic waste
were polyolefins (LDPE, HDPE and PP). Catalytic
conversion of polyolefin plastic wastes into fuels overacid catalysts catalysts is one of the technologies that isreceiving increased attention due to the interestingproducts obtained (gasoline, diesel, fuel, etc)[1,2]In previous works, a two-stage process comprisingthermal cracking of the polyolefins followed by catalytichydroreforming was devised. This process allows thehigh content of olefins usually obtained in the thermal
cracking of the plastics to be removed. Additionally, itenables to tailor the selectivity towards the desiredproducts. In this regard, high selectivity towards
gasolines (> 55%) was obtained previously over Ni/hBeta catalyst [3,4].
In this work, we have studied another catalyst (Ni/AlSBA-15) varying its Si/Al atomic ratio. Unlike Ni/h-Beta,
this catalyst showed remarkable selectivity toward diesel
fuels due to its mild acidity, that was tuned by adjusting
the Si/Al atomic ratio.

550 ºC for 5h. The catalyst Ni/Al-SBA-15 was preparedby the incipient wetness and sonication method with anickel nitrate solution using a solution volume/ porevolume ratio of 1.
LDPE was thermally cracked at 400ºC for 90 min. The
obtained oils were a mixture of C5 – C40, formed chiefly
by n-paraffins + olefins and used as feed of thesubsequent hydroreforming stage. The hydroreforming
reactions were performed in an autoclave at 310 ºC
under 20 bar of hydrogen for 45 min using an oil/catalyst
mass ratio=30.

3. Results and Discussion
Table 1 summarizes the main textural properties of thecatalysts Ni/Al-SBA-15 obtained varying the Si/Al atomic
ratio within the 15 – 100 range. All the catalysts showed
BET surface areas above 400 m2 g-1, pore volumes
higher than 0.6 cm3 g-1 and average pore sizes within 8 –10 nm. Likewise, the nickel content of the catalysts waswithin 6 – 10% (see table 2). Figure 1 illustrates the TEM
micrographs of Ni/Al-SBA-15-15 and Ni/Al-SBA-15-100,
wherein it is clearly seen that the size of the nickel
particle increased with the Si/Al atomic ratio.

2. Materials and Methods

Table 1. Physicochemical Properties of the catalysts.

Al-SBA-15 was obtained by a post-synthesis alumination
method [5]. Hence, solution A formed by 100 mL of anaqueous solution of AlCl3·6H2O was left under stirring at
60 ºC for 1h. Solution B, formed by 100 mL of anaqueous TMAOH was mixed and added to solution A.
The molar hydrolysis ratio [TMAOH]/[Al] was 2. The
resulting mixture was heated at 60ºC for 1 h. 2 g of pure
SBA-15 was added at room temperature under stirringfor 5 h. The obtained solid products were separated byfiltration, dried overnight at 110 ºC and calcined in air atCatalyst

BET(m2/g)

Ni/Al-SBA-15-15
Ni/Al-SBA-15-30
Ni/Al-SBA-15-50
Ni/Al-SBA-15-70
Ni/Al-SBA-15-100

411
440
548
492
527

Pore
Volume(cm3/g)
0.71
0.62
0.71
0.66
0.68

6th International Symposium on Feedstock Recycling of Polymeric Materials (ISFR2011), Toledo, Spain
5 – 7 October 2011

Average
Pore Size(nm)
8.3
10.6
8.2
8.2
10.7

Table 2. Nickel content, aromatics and bromine index ofthe catalysts in the hydroreforming of the oil form LDPE
thermal cracking.
Catalyst

Fig. 1. TEM micrographs of the catalysts Ni/Al-SBA-1515 and Ni/Al-SBA-15-100.
Figure 2 shows the yields by groups obtained in thehydroreforming of the product from LDPE thermalcracking over the different Ni/Al-SBA-15 catalysts. The
total yield of liquid hydrocarbons was roughly 95%, whichconstitutes a rather remarkable amount.

80
Thermal
Ni/Al-SBA-15-15
Ni/Al-SBA-15-30
Ni/Al-SBA-15-70
Ni/Al-SBA-15-100

Ni/Al-SBA-15-50

7060%

50

Ni/Al-SBA-15-15
Ni/Al-SBA-15-30
Ni/Al-SBA-15-50
Ni/Al-SBA-15-70
Ni/Al-SBA-15-100

Bromineindex(g Br2/100
g ofsample)
7.4
6.8
6.8
6.6
7.5

Aromatics(%)

Ni content
(%w)

4.1
4.9
4.2
3.7
3.7

10.9
6.1
10.8
9.5
9.8

4. Conclusions
The size of nickel particle over Ni/Al-SBA-15 catalysts isheterogeneus and it increased with the ratio Si/Al. The
increase of the Si/Al atomic ratio of the catalyst
decreased the gasoline selectivity and increased theC13-C18 diesel hydrocarbons selectivity, reaching a 40%.
The olefins were largely hydrogenated (around 87%) andthe aromatic content of the fuels was rather low (< 5%).

405. References30[1] K. H. Lee, N. S. Noh, D. H. Shin, Y. Seo, Comparisonof plastic types for catalytic degradation of waste plastics
into liquid product with spent FCC catalyst, Polym.
Degrad. Stab. 78 (2002) 539 – 544.

20100C1-C4

C5-C12C13-C18

C19-C40Fig. 2. Effect of the ratio Si/Al of the Ni/Al-SBA-15
catalysts in the hydroreforming of the oil from LDPE
thermal cracking
The increase of the Si/Al atomic ratio of the catalyst
decreased the gasoline selectivity and increased theselectivity to C13-C18 light diesel hydrocarbons, reaching
40% for a Si/Al atomic ratio of 100. Additionaly, the total
yield of light and heavy diesel hydrocarbons (C13 – C40)
amounts to 65% for Si/Al atomic ratios above 50. The
main products obtained in the gasoline fraction arenormal paraffins (60 - 80%%) while isoparaffins accountfor 15%. In order to check the degree of hydrogenation of
the olefins present in the reaction medium, the bromine
index of the liquid products was calculated. The thermal
cracking of LDPE contained a great deal of olefins (54gBr2/100 g of sample). All the catalysts exhibited bromine
indexes around 6, which implies a reduction of 87% of
the olefinic double bonds of the feed (see table 2). The
aromatic content in the fuels was low in all the cases,always below 5%. .

[2] K. Gobin, G. Manos, Polymer degradation to fuels
over microporous catalysts as a novel tertiary plastic
recycling method, Polym. Degrad. Stab. 83 (2004) 267 –279.
[3] J. M. Escola, J. Aguado, D. P. Serrano, A. García, A.
Peral, L. Briones, R. Calvo, E. Fernández. Catalytichydroreforming of the polyethylene thermal cracking oil
over Ni supported hierarchical zeolites andmesostructured aluminosilicates. Appl. Cat. B, 106(2011) 405.
[4] J. M. Escola, J. Aguado, D. P. Serrano, L. Briones, J.
L. Diaz de Tuesta, R. Calvo, E. Fernández. Conversionof polyethylene into transportation fuels by thecombination of thermal cracking and catalytichydroreforming over Ni-supported hierarchical Betazeolite. Energy Fuels 26 (2012) 3187.
[5] Zeng, S.,J. Blanchard, M.Breysse, Y.Shi and X.Shu etal., 2005. Post-synthesis alumination of SBA-15 inaqueous solution: A versatile tool for the preparation ofacidic Al-SBA-15 supports. Microporous Mesoporous
Mat. 85: 297-304.DOI:10.1016/j.micromeso.2005.06.031

6th International Symposium on Feedstock Recycling of Polymeric Materials (ISFR2011), Toledo, Spain
5 – 7 October 2011