5-7 OCTOBERISFR2011

13TOLEDO (SPAIN)FEEDSTOCK RECYCLING OF NITROGEN CONTAINING POLYMERS BY FLUIDIZEDBED PYROLYSIS
W. Kaminsky
University of Hamburg, Institute for Technical and Macromolecular Chemistry
Bundesstr.45, 20146 Hamburg, Germany
e-mail: kaminsky@chemie.uni-hamburg.deAbstract
The increasing use of plastics and the high crude oil price prefer the research to pyrolyze mixed plastics into gas and oil.
Well established are the use of polyolefins, PMMA, PET, and polystyrene as feedstocks for recycling by pyrolysis. Oneproblem for cracking mixed plastics into suitable products is the contamination of nitrogen containing polymers. Thesematerials produce by higher pyrolysis temperatures high amounts of toxic components, such as HCN and nitriles. Purepolyamides (Pa 6 and Pa 6.6) and polyuretanes (PUR) were used as feedstock in a fluidized bed pyrolysis process bytemperatures of 810°C. Acryl nitrile butadiene styrene copolymers (ABS) were pyrolyzed by 800°C in a plant with athroughput of 3 kg/h. It was one goal of the study to investigate the concentration of HCN and nitiles in the pyrolysisproducts. In mixed plastics pyrolysis the concentration of HCN and nitiles decrease lineary with the amount ot nitrogencontaining polymers. That makes it possible to calculate the amount of hazard compounds.

Keywords: Fluidized bed pyrolysis, polyamide, nitrogen containing polymers, gas and oiland contaminated the waste, the more difficult it is torecycle it mechanically. The pyrolytic route is favoredbecause of the high rates of conversion into oil and gas
which can be obtained. The gas with a high caloric value
may be used as fuel for heating in the process. Someprocesses to recycle plastics by pyrolysis are near to becommercialized such as pyrolysis in vessels, autoclaves,rotary kilns and fluidized bed reactors (1,2).

1. Introduction
The pyrolysis of mixed plastics is receiving attention
since the crude oil price is increasing rapidly and as aroute for the disposal of the large quantities of plastic
wastes collected by different systems. Mechanicalrecycling can be preformed solely on single polymer
plastic waste since a market can be found only if therecycled products show a high quality. The more complex

PIRMTIRTIRPIRTIR
EtOH
Coil Condenser

CyclonePIR

Polymer
Storage

Cyclone

PIR

TIR

TIR

Steel Condenser
TIR
PIR

M

TIR

Fluidized Bed Reactor
Metering Screw

HeaterM

TIR

Electrostatic Filter

EtOH

TIR

Coil Condenser

StorageTank(Solids)

Drag-in Screw
TIR
PIR

Preheater

PI

Storage
Tank(Liquids)

StorageTank(Liquids)

StorageTank(Liquids)

Storage
Tank(Liquids)

PI

Compressor

Gas Meter

TIR

PI

FlareTIR

PIR

Gas Meter

Check Valve

Vacuum Pump
N2

Gas Samples

Fig. 1. Flow scheme of the used fluidized bed process.

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6th International Symposium on Feedstock Recycling of Polymeric Materials

For the commercial use it is necessary to know thecontent of toxic compounds in the gas and oil products
which are produced by pyrolysis of mixed plastics.
Beside PVC as feedstock which produces high amountsof HCl, the content of nitrogen containing products are ofinterest, such as brussic acid (HCN), nitriles, andisocyanates. These compounds are produced fromnitrogen containing polymers.

For the experiments were used polyamide 6 (PA 6),
polyamide 6.6 (PA 6.6), polyurethane (PUR), andacrylonitrile-butadiene-styrene copolymers (ABS).Thenitrogen content in PA 6 and PA 6.6 was 12 wt% in ABS
3 wt%.
The pyrolysis experiments were carried out in alaboratory scale fluidized bed reactor with a throughput of
1-3 kg/h of polymers (Figure 1). The reactor consist of asteel tube (length 770 mm, 154 mm inside diameter). Thegas distributor is a steel plate with 108 tubes. The
fluidized bed of fine sand (0.3-0.5 mm) is heatedindirectly by electricity. Nitrogen or steam are used as
fluidizing gas, but during the experiments it is displacedby gaseous pyrolysis products. The feed material isinserted into the reactor, using two screw conveyers. The
product gases are cooled in different separation units.
Carbon black and fine sand are precipitated in a cyclone.
The product fractions obtained were analyzed by different
capillary GC-columns and registered with TCD_ and FIDdetectors. The reactor sand used and the precipitates in
the cyclone were combusted in a furnace to constantweight. The loss in weight was balanced as carbon blackand inorganic fillers. All results of the analysis of theorganic product fractions were combined together to forma total mass balance.

3. Results and Discussion
Table 1 gives an overview on the product composition ofthe different polymers pyrolyzed.
Table 1. Pyrolysis of PA, PUR, ABS.
Feed:

PA 6

PA 6.6 PUR

Pyrolysis T

810 °C

810 °C 750 °C 800 °C

ABS

Fluidizing gas pyro-gas steam steam pyro-gas
Products:
5252

Table 2. Pyrolysis gas of PA, PUR, ABS
Feed:

PA 6

PA 6.6 PUR

Pyrolysis T

810 °C

810 °C 750 °C 800 °C

ABSHydrogen

0.6

1.2

1.3

3.2CO

2631

46.7

5.7

CO2

2.1

3.4

3.7

3.0

Methane

12.4

16.1

24.7

45.9

Ethene

22.6

21.3

10.3

10.0

Ethane

2.8

3.1

0.8

1.0

Propene

1.9

2.4

0.4

0.9

HCN

18.4

18.9

2.0

18.3

Others

13.2

2.6

10.1

12.0

Products:wt%

2. Materials and Methods

Gas (wt%)

The gas fraction (Table 2) contains mainly CO, methane,
ethane and HCN. The HCN concentration reaches valuesof over 18 wt% for PA and ABS as feedstock.

5332

HCN

8.5

8.7

0.5

5.9

Nitriles

9.2

9.0

8.0

4.1Oil

25.4

26.2

19.8

44

Tar/C

22.6

21.8

27.2

24

Main components in the oil are by a pyrolysis
temperatures of 750 -810°C benzene, toluene,naphthalene and nitriles. Table 3 shows theconcentrations of some nitriles in the product oil.
Table 3Nitriles concentration in the oil fraction
Feed:

PA 6

PA 6.6 PUR

Pyrolysis T810 °C

810 °C 750 °C 800 °C

ABSAcetonitrile

1.4

1.2

0.9

Acrylonit.

2.4

3.4

0.3

0.4

Benzonit.

0.4

1.0

5.9

2.8

Propionit.

0.3

0.8

0.1

0.1

Products:wt%1.3All nitriles together give a concentration of 5-8 wt% in theproducts. Mixed plastics collected by household waste
separation contain about 2 wt% of PA, PUR; and ABS.
The concentration of toxic HCN and nitriles can becalculated to be less than 0.2 wt% in pyrolysis products.

References[1] J. Scheirs, W. Kaminsky, Feedstock Recycling andPyrolysis of Waste Plastics, Wiley Series in Polymer
Science, Chichester 2006.
[2] W. Kaminsky, C. Mennerich, Z. Zhang , J. Anal. Appl.
Pyrolysis 85, (2009) 334.

Gas with over 50 wt% is the main fraction for polyamides
and polyurethane as feedstock by a pyrolysis
temperature of 810°C. Using ABS the main productfraction with 44 wt% is oil. HCN formed reaches 8.5 or
8.7 wt% for PA 6 or PA 6.6 while this is only o.5 wt% for
PUR and 5.9 wt% for ABS.

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