5-7 OCTOBER

ISFR

2011

89

TOLEDO (SPAIN)

DECHLORINATION OF PVC IN CATALYTIC PYROLYSIS OF PACKAGING PLASTICWASTES
A. López, I. de Marco, B.M. Caballero, A. Adrados, M.F. Laresgoiti
Chemical and Environmental Engineering Department, School of Engineering of Bilbao, University of the Basque Country
e-mail: alex.lopez@ehu.esAbstract
PVC is frequently present in plastic wastes giving rise to the presence of chlorine in pyrolysis products, which is rather
detrimental for their potential applications mainly due to chlorine environmental hazards. The use of zeolites has been
proved to be beneficial for the pyrolysis process and it has been demonstrated that a low temperature dechlorination stepprior to the pyrolysis process significantly reduces the chlorine content in the liquid products. In this paper the combination ofboth, catalyst and dechlorination step, is explored. A mixture of PE, PP, PS, PET and PVC has been pyrolysed in a 3.5 dm 3
semi-batch reactor at 440 ºC for 30 min using a ZSM-5 zeolite as catalyst. A previous low temperature (300 ºC)
dechlorination step has been carried out both with and without catalyst. It has been proved that the application of suchdechlorination gives rise to a 75 wt% reduction of chlorine in the liquid fraction. However, such step has a negative influenceon the catalyst, which loses some catalytic activity. The optimum procedure in terms of quality and chlorine content of theproducts is first a low temperature step and then the catalytic pyrolysis step.

Keywords: stepwise pyrolysis, feedstock recycling, catalytic decomposition, plastic wastes, dechlorination.

1. Introduction
PVC is one of the most widely used polymers. However,the presence of chlorine in the PVC backbone is the key
concern when it comes to waste PVC management, due
to the chlorinated compounds which can arise during
waste treatment operations as a consequence of themolecular instability of PVC towards heat and light [1].
Pyrolysis is a process which has received renewed
attention in the last years for recycling plastic wastes,
converting them in potentially useful liquids and gases. In
the pyrolysis process (heating in an oxygen freeatmosphere), the organic components of the material aredecomposed generating liquid and gaseous products
while the inorganic ingredients (fillers, metals, etc.)
remain practically unaltered in the reactor. When PVC
containing samples are pyrolysed, the pyrolysis process
can be improved by means of a previous low
temperature step in order to remove chlorine from theoriginal sample as HCl, which evolves as a gas at
temperatures around 300 ºC, preventing the generationof chlorinated compounds in the liquid fraction [2]. On theother hand, it is well known that the use of catalysts
enhances the quality of pyrolysis products. Therefore, theobjective of this paper is to study the effectiveness of theprevious dechlorination step when catalyst is used in thepyrolysis process, in order to obtain high quality pyrolysis
liquids with low contents of chlorine.

2. Materials and Methods
A mixture of 40 wt% PE, 35 wt% PP, 18 wt% PS, 4 wt%
PET and 3 wt% PVC in pellet size (≈3 mm) was used forthe pyrolysis experiments. The catalyst used was ainteriores libro.indd 89

commercial ZSM-5 zeolite; in all the experiments it wasused as received and in a plastic/catalyst ratio of 10/1.
The pyrolysis experiments were carried out using an
unstirred stainless steel 3.5 dm3 reactor in semi-batch
operation. In all the experiments, 100 g of plastic sample
were placed into the reactor; nitrogen was passed
through at a rate of 1 dm3 min-1 through all the run, andthe vapours leaving the reactor flowed to a series ofrunning water cooled gas-liquid separators where thecondensed liquids were collected. The uncondensed
products were passed through an activated carbon
column and collected as a whole in Tedlar plastic bags.
Three different pyrolysis methods were explored. 1)“Conventional catalytic pyrolysis”, in which the plastic
sample was mixed with the catalyst and the system washeated at a rate of 20 ºC min-1 to 440 ºC, and maintained
there for 30 min. 2) “Catalytic stepwise pyrolysis”, inwhich the plastic sample was mixed with the catalyst, aprevious dechlorination step was carried out at 300 ºC
during 60 min and then the temperature was raised at 20ºC min-1 to 440 ºC to complete the pyrolysis process. 3)“Non catalytic dechlorination step + catalytic pyrolysis”, inwhich the dechlorination step was applied to the plastic
sample alone (without catalyst) and then the catalyst wasadded, carrying out the final pyrolysis as in the othermethods. The amount of solids remaining in the reactor
and the liquids condensed in the gas-liquid separators
were weighed after pyrolysis and the pyrolysis yields
were calculated as weight percentage with respect to theraw material pyrolysed. Gas yields were normallydetermined by difference. Method 5050 of theEnvironmental Protection Agency (EPA) of the UnitedStates was used for chlorine determination. Additionally,pyrolysis liquids were also analysed by GC-MS.

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6th International Symposium on Feedstock Recycling of Polymeric Materials

3. Results and Discussion
The liquid, gas and solid yields (weight %), obtained withthe three mentioned pyrolysis methods are presented inTable 1.
Table 1. Pyrolysis yields (wt%)
Method 1
Method 2
Method 3

Liquids
56.9
69.0
56.8

Gases
40.4
29.0
41.2

Solids3.2
2.0
2.0

If the pyrolysis yields of methods 1 and 2 are compared,
when the previous dechlorination step is carried out inpresence of the catalyst an increase in liquid yield and adecrease in gas yield compared with the conventional
catalytic experiment is produced. This fact suggests thatthe zeolite losses some activity during the dechlorination
step. In addition, Table 4 shows that when the catalyst isadded to the sample after the dechlorination step, almost
the same yields as in the conventional catalytic
experiment are obtained, which confirms that thedechlorination step caused the loss of activity of thezeolite.
Figure 2 shows all the compounds identified in thepyrolysis liquids by GC-MS grouped in three categories
according to their carbon number: C5–C9, C10–C13 and>C13.
C5-C9C10-C13>C1390,080,070,060,050,040,030,020,010,00,0Method 1

Method 2

Method 3

Fig. 1. C5-C9, C10-C13 and >C13 fractions of thepyrolysis liquids (% area).
As it can be seen, C5-C9 is the main fraction of thepyrolysis liquids in a conventional catalytic experiment,
ranging more than 80% area. The formation of lighthydrocarbons in the pyrolysis of polyolefinic plastic
wastes in presence of ZSM-5 zeolite has been reported
before [3], and it is very interesting since C5-C9 is thegasoline carbon number range. When the dechlorination
step is carried out in presence of the zeolite, thepercentage of light (C5-C9) and medium (C10-C13)hydrocarbons significantly decrease (75.5 and 1.5% area
respectively), and the yield of heavy hydrocarbons
increases up to 9.5% area. This fact is in agreement withthe previously mentioned loss of activity of the catalyst
that is produced during the previous step. In fact, when
the catalyst is added after the dechlorination step, theC5-C9 yield is quite similar to that of the conventional
catalytic run.

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Table 8 shows the percentage of chlorine in the products
obtained after each experiment.
Table 2. Chlorine in the pyrolysis fractions (wt%)
Method 1
Method 2
Method 3

Liquids
1.2
0.3
0.3

Gases
1.0
3.0
2.2

Solids0.4
0.4
0.4

It can be seen that the chlorine content of the liquids after
a conventional catalytic pyrolysis run is 1.2 wt%, which isquite high and may condition the potential application ofsuch liquids. When the dechlorination step is applied, thechlorine content of the liquids decreases in both cases(from 1.2 to 0.3 wt%), which is equivalent to a 75%
reduction of chlorine in the liquids with respect to theconventional catalytic pyrolysis liquids. Since chlorine
evolves as HCl (mainly generated in the first step), Table
8 shows higher contents of chlorine in the gases when
the previous dechlorination step is used (2.2 - 3.0 wt%)
than that obtained in conventional catalytic pyrolysis (1.0wt%). As it has been mentioned before, the objective of
this previous step is precisely to separate the chlorine asHCl, since in an industrial process HCl could beabsorbed in alkaline solutions by means of wet scrubbers
and the gases generated in the subsequent pyrolysis
step would be free of chlorine.

4. Conclusions
Catalytic pyrolysis is an attractive alternative for recycling
mixed plastic wastes. However, the presence of PVC inthe original sample leads to the generation of chlorinatedchemicals which are part of the pyrolysis liquids, and thisis very detrimental for their potential applications. Theliquids chlorine content can be reduced up to more than
75 wt% compared to conventional catalytic pyrolysis bymeans of a previous dechlorination step at 300º C during
60 min. However, the authors have proved that when thecatalyst is mixed with the sample from the beginning of
the process, the previous dechlorination step significantly
decreases the catalyst activity, giving rise to liquids witha higher content of heavier hydrocarbons. On the other
hand, the addition of the catalyst after the thermal
dechlorination step has been found to be an efficientmethod to obtain almost the same results as in theconventional catalytic process, in terms of products yieldand quality, and at the same time the high reduction inthe chlorine content of the liquids.

References[1] European Commission. Green Paper: Environmental
issues of PVC (2000) 469.
[2] A. López, I. de Marco, B.M. Caballero, A. Adrados,M.F. Laresgoiti. Dechlorination of fuels in pyrolysis ofPVC containing plastic wastes, Fuel Process. Technol.
92 (2011) 253-260.
[3] D.P. Serrano, J. Aguado, J.M. Escola, J.M.
Rodríguez. Influence of nanocrystalline HZSM-5 externalsurface on the catalytic cracking of polyolefins. J Anal
Appl Pyrolysis 74 (2005) 353-360.

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