5-7 OCTOBERISFR2011

73

TOLEDO (SPAIN)CATALYTIC CRACKING OF WAXES FROM POLYOLEFINS UNDER FCC
OPERATING CONDITIONS
J.M. Arandes1, I. Torre1, M.J. Azkoiti2, M. Olazar1, J. Ereña1 and J.Bilbao1
1University of the Basque Country. Chemical Engineering Department, Apdo. 644, 48080 Bilbao, Spain
2University of the Basque Country. Chemical and Environmental Engineering Department, Plaza de la Casilla 3, 48012

e-mail:Bilbao, Spain
josemaria.arandes@ehu.esAbstract
The catalytic cracking of polyolefin pyrolysis waxes has been carried out in an FCC riser simulator in the 500-550ºCrange, with a catalyst/feed ratio of 5.5 and contact times between 3 and 12 s. The effect of the operating conditions on
the yields and composition of products has been studied. The results have been compared with those of a vacuum gas oil(VGO) and a mixture of VGO (80 wt%) and waxes (20 wt%) catalytic cracking. The results show that the yields andcomposition of products are acceptable by refineries without any special modification of operating conditions. The effectof HZSM-5 incorporation on the yields and composition of product streams has also been studied.

Keywords: Waste polyolefins, catalytic cracking, FCC, waxes

1. Introduction
A way for upgrading waste plastics lies in theirincorporation into refineries following different operating
strategies. The most straightforward solution consists ina single-step treatment by incorporating them into arefinery process, such as the catalytic cracking unit,FCC, or the hydrocracking unit. This paper studies a twostep strategy: (1) pyrolysis at the location where theplastics are collected; (2) incorporation of the product(waxes) to a conventional FCC feed.
A study is carried out on the cracking of waxes underconditions similar to those of an FCC unit. The results
are complementary to those obtained in previous papers,
where polyolefins dissolved in VGO, either in purearomatics or in LCO (light cycle oil) were cracked under
FCC conditions [1].

2. Materials and Methods
The waxes have been obtained by flash pyrolysis ofpolypropylene (PP) at 500ºC. The pyrolysis reactor is aconical spouted bed [2] that allows obtaining wax yields
higher than 90 wt%. A vacuum gas oil has been used asa reference feed. The simulated distillation of VGO andof the waxes are shown in Table 1. A number averagemolecular weight of 363 and a weight average molecularweight of 2405 have been determined for the waxes bygel permeation chromatography. A clearly olefinic nature
has been determined by FTIR.
The behaviour of two catalysts (Table 2) has beenstudied. CAT-1 is an equilibrated catalyst used in aSpanish FCC unit. CAT-H is a hybrid catalyst preparedby mixing CAT-1 (75 wt%) with a catalyst based on
HZSM-5 zeolite (SiO2/Al2O3 = 50), CAT-Z.

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Table 1. Properties of the VGO and Waxes.
Properties
Density, g cm-3 (at 15ºC)
Conradson C, wt%
Simulated distillation, ºC
IP
5 wt%
10 wt%
30 wt%
50 wt%
70 wt%
90 wt%
95 wt%EP
Paraffins, wt%
Naphthenes, wt%
Aromatics, wt%
Sulfur compounds, wt%

VGO
0.90070.61Waxes
0.8902
---

264
--378
434
469
505
553
--627
6.8
35.6
41.1
16.5

182
241
275
362
440
512591618-----------The reaction device is a riser simulator reactor. It is aninternally circulating reactor specially designed forcatalytic cracking and has been previously described [3].
The runs have been carried out at 2-3 atm, in the 500550ºC range, with a catalyst/feed ratio of C/O=5.5 byweight and a value of contact time between 3-12 s. The
low value of contact time minimizes the contribution ofthermal cracking.
Product analysis has been carried out by means of asampling device connected to a 6890 Agilent GC.
Product identification was carried out by GC-MS (Agilent
6890 GC–MS Engine with electronic ionization). The
product identification was confirmed by using PIANO
standards in the C5-C12 range.

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6th International Symposium on Feedstock Recycling of Polymeric Materials

Table 2. Catalysts properties
CAT-1
14
123
89
7.8
146
24.27
890
2186
0.018
125-140
6.3

50

CAT-Z
25
182
63
5.5
103
------0.024<120
1.9bGasoline composition (wt%)

Properties
Zeolite percentage, wt%
BET surface area, m2 g-1
Zeolite area, m2 g-1
Micropore diameter, ÅMesopore diameter, ÅUCS, ÅNi, ppm
V, ppm
Acidity, mmol NH3 g-1Acid strength, kJ mol-1 NH3Bronsted/Lewis ratio

3. Results and Discussion
Figure 1 shows as an example the conversion of waxes
and VGO at different temperatures and contact times.
Wax conversion is higher at all the conditions studied, as
they are more olefinic and liable to catalytic cracking thanVGO, which is mainly aromatic.
80Conversion (wt%)

403020100

The coke deposited on the catalyst was measured bythermogravimetric analysis in a Setaram TG-DSC 111.
The spent catalyst was dried at 110ºC in nitrogen stream
and subjected to combustion with air at a programmedtemperature (5ºC min-1) up to 700ºC.

500 ºC
525 ºC
550 ºC

70Waxes
VGO
VGO+waxes

60

5040csatiomArsnesthephNa

ffin

ara

n-pnsefi

Ols

ffin

ara

i-p

Fig. 2. Comparison of gasolines obtained by cracking
different feedstocks.
The gasoline from wax cracking has a higher content ofolefins, naphthenes and paraffins, with less aromatics
and more isoparaffins than that obtained by cracking theVGO.
At high temperatures and contact times the mixture ofVGO with waxes shows a synergistic effect, giving way toan increase in the yield of gasoline and LPG, which isprobably due to the reactivity of C2-C4 radicals generated
in the primary cracking of waxes.
A catalyst based on HZSM-5 leads to a decrease in theconversion of waxes due to the shape selectivity of theHZSM-5 zeolite. This lower conversion involves a lower
yield of LPG, dry gases and coke, although the yield ofgasoline is higher than using the base catalyst.
The gasoline obtained using the hybrid catalyst has ahigher concentration of naphthenes, n-paraffins andolefins and a higher concentration of aromatics and ofisoparaffins than the gasoline corresponding to the basecatalyst.

4. Conclusions

3003

691215Time (s)Fig. 1. Conversion of waxes (white points) and of VGO(black points).
Likewise, Figure 2 also shows as an example the resultsof gasoline composition obtained in the catalytic cracking
of waxes, VGO and VGO+wax mixtures at severe
conditions (550ºC and t = 12 s).
A comparison of VGO cracking with wax cracking showsthat the latter gives way to a gasoline with a higher
content of olefins, naphthenes, paraffins, andisoparaffins. This is a consequence of wax composition,with olefinic linear chains, and of VGO composition,
which is conditioned by its aromatic nature.
The octane number, RON, of the gasoline obtained in thecracking of waxes (between 95 and 98) is suitable forbeing added to the refinery gasoline pool.
The LPG obtained by cracking waxes has propene as themain component and its olefinicity increases astemperature is increased.

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Polyolefin pyrolysis waxes provide satisfactory results forrefineries when used as an FCC feed. Given that thecompounds present in the waxes are more easily
cracked than those in VGO, its conversion is higher inthe whole range of temperatures and contact times.
The FCC unit is sufficiently versatile for co-feeding thewaxes without operational problems, which contributes tothe large-scale valorisation of waste plastics and to theintensification of crude valorisation.

References[1] J.M. Arandes, I. Abajo, D. López-Valerio, I.
Fernández, M.J. Azkoiti, M. Olazar, J. Bilbao.
Transformation into Fuels of Several Plastic Wastes byCatalytic Cracking. Ind. Eng. Chem. Res. 36 (1997)
4523-4529.
[2] R. Aguado, M. Olazar, B. Gaisán, R. Prieto. Kinetic
Study of Polyolefins Pyrolysis in a Conical Spouted Bed
Reactor. Ind. Eng. Chem. Res. 41 (2002) 4559-4566.
[3] H.I. de Lasa. US Patent 5,102,628 (1992).

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