PARTⅠ PYROLYSISPYROLYSIS OF MIXED PLASTICS IN THE FLUIDIZED BED
USING HARD BURNT LIME AS BED MATERIAL
Shotaro Matsumoto, Guido Grause, Tomohito Kameda, Toshiaki Yoshioka*
Graduate School of Environmental Studies, Tohoku University,Aramaki Aza Aoba 6-6-07,
Aoba-ku, Sendai 980-8579, Japan
yoshioka@env.che.tohoku.ac.jp
Abstract: A mixture consisting of 40 wt% PS, 20 wt% PE, 20 wt% PP and 15 wt% PET were
pyrolyzed in the presence of both steam and nitrogen, using a fluidized bed reactor with hardburnt lime (HBL) as bed material. The experiments were carried out at 600 °C and 700 °C. In
opposite to soft burnt lime, HBL showed good fluidizing properties and little erosion. Sinceboth CaO and Ca(OH)2 are widely used as aggregates in order to fix HCl and catalyze thedegradation of organic acids, the purpose of this research was the investigation of the impact
on the product distribution and the ability of HBL to support the degradation of PET.
Compared with experiments applied in the presence of quartz sand, the gas yield increased,
while the wax fraction was strongly reduced. In the presence of HBL, the benzene yield rosestrongly due to the decarboxylation of PET.
1. Introduction
The pyrolysis of mixed plastics is one of the useful feedstock recycling techniques.
Waste plastics consist mainly of poly(ethylene) (PE), poly(propylene) (PP), poly(styrene)(PS), and poly(ethylene terephthalate) (PET). Polyolefines, such as PE, and PP, and PS, canbe converted into oil via thermal decomposition. However, the thermal decomposition of PET
causes not only corrosion and blocked pipes, but also the reduction of the oil yield by thegeneration of sublimating substances, such as terephthalic acid (TPA) and benzoic acid. As acountermeasure against these difficulties, hydrated lime (Ca(OH)2)was introduced into theprocess in order to avoid the problems mentioned above [1]. On the other hand, the pyrolysisof PET in a steam atmosphere in contact with Ca(OH)2 or CaO at above 520°C led to a highyield of benzene without the production of sublimating substances[2,3]. We suggest that theapplication of this reaction to the pyrolysis of mixed plastics, using a fluidized bed reactorwith hard burnt lime (HBL) as bed material, might also be able to eliminate the problems,caused by sublimating materials.

- 47 -The 5th ISFR (October 11-14, 2009, Chengdu, China)
2. Experimental
2.1 Material
The material used in these experiments was mixed virgin plastics, consisting of 40 wt%
PS, 20 wt% PE, 20 wt% PP, and 15 wt% PET (Aldrich) with the particle sizes of less than
500 mm. HBL was received from Okutama Kougyou.
2.2 Pyrolysis experiment
The experiments were carried out in a fluidized bed reactor (Fig.1) at 600 °C and 700 °C
in nitrogen and steam atmosphere (0, 70 vol%, 7.5 l min-1 at room temperature). The steam
was generated at 250 °C and piped through an isolated tube into the reactor. The sample (200g) was fed into the hot reactor at 70-123 g h-1. HBL (500 g) with a particle size of 300-500mm was used as bed material. The product oil and wax were gathered in cooling units, cooledwith water and ethanol, and an electrostatic precipitator. The collected oil and wax waredistilled, using the fluorine cut at 295 °C. Gas samples were collected in a gas bags. The gascomposition was analyzed by GC-TCD, using a packed column. The distilled oil wasanalyzed qualitatively by GC-MS with a HP-5MS capillary column. The quantitative analysis
was carried out by GC-FID with capillary column of the same type. The wax was fractions
were analyzed by FT-IR. The bed material was analyzed by XRD.

Fig.1 Experimental setup
3. Result and Discussion
Fig. 2 shows the yields of the pyrolysis of mixed plastics at 600 °C and 700 °C. In thecase of HBL was used in place of sand as bed material in N2 atmosphere at 600 °C, the yieldof wax was decreased from 35.8 wt% to 10.0 wt%. On the other hand, the yields of the gases- 48 -

PARTⅠ PYROLYSIS
rose from 17.4 wt% to 40.9 wt%. The addition of HBL caused also the degradation of PET,
increasing the benzene yield from 0.01 wt% to 3.6 wt%. Fig.3 shows the FT-IR spectra ofwax (a) using HBL as bed material, in N2 atmosphere, (b) HBL, in steam (c) sand, in N2 (d)Sand, in steam, and (e) TPA, each obtained at 600 °C. The FT-IR spectra of (c), (d) and (e)display the absorption bands of the C=O stretching vibrations (around 1150 cm-1) and the C-O
stretching vibrations (around 1700cm-1) derived from TPA. These were not visible it theFT-IR spectra of (a) and (b), indicating the degradation of TPA derived from PET in thepresence of HBL. In the presence of HBL, the amount of waxes decreased by 25.8 wt%. Since
the degradation of the TPA, derived from PET, can be accounted for a maximum of 12.8 wt%
in the absence of HBL, another 13.0 wt% of waxes, derived from other plastics, wereconverted into lighter compounds.

Fig.2 Yields of the pyrolysis of mixed plastics with different
bed materials and fludizing gases at 600℃ and 700℃
There is a possibility that PET inhibits the decomposition of other plastics. Under thisconsideration, HBL prevents the inhibition of the degradation of plastics by PET. Assumingthat benzene was derived solely from PET, the change of the benzene amount from 0.01 wt%
to 3.6 wt% means that the benzene yield increased from 0.06 % to 24 %. When steam wasused as fluidizing gas, the yields of waxes and solids decreased due to steam cracking.
Moreover in the case of using HBL as bed material, steam addition increased the benzene
yield from 24% to 35 %, caused by the hydrolysis of PET promoting the production ofterephthalic acid which was decomposed to benzene and CO2.

- 49 -

The 5th ISFR (October 11-14, 2009, Chengdu, China)

Fig.3 FT-IR spectra of wax(a) HBL N2(b) HBL Steam(c) Sand N2 (d)Sand Steam(e)TPA
At 700 °C, the yields of the pyrolysis of mixed plastics with different bed materials andfluidizing gases (Fig.2), did not indicate significant changes in the presence of HBL,
assuming that the degradation of TPA to benzene and other component at 700 °C was little
affected by HBL. When steam was added, decreasing yields of waxes and solids wereobserved, comparable to the reaction at 600 °C. However, another rise of the benzene yield
was not observed indicating that at this temperature the pyrolysis rate is faster than hydrolysis
rate.

Fig.4 XRD of the HBL before and after the reaction and the cyclone fraction
Fig.4 shows the XRD of the HBL before and after the reaction and the cyclone fraction,
obtained after the experiment at 600 °C in steam atmosphere. The HBL, obtained from the- 50 -PARTⅠ PYROLYSIS
cyclone, consisted of CaO, Ca(OH)2, and CaCO3. CaO formed Ca(OH)2 in the presence ofsteam. CaCO3 was produced by the absorption of CO2 after the degradation of TPA. However,the HBL that remained in the bed did not show any changes due to the regeneration of CaCO3
after the end of the experiment during the cooling down procedure. The high dynamic of thisprocess, shows that HBL can be used for long reaction cycles, without being replaced orregenerate.
4. Conclusion
Using HBL as bed material and steam as fluidizing gas can reduce the yields of waxes
and increase the yields of gases. When HBL is used as bed material at 600 °C, the yields ofuseful products, such as oils and gases, becomes comparable to those at 700 °C. This indicatesthat HBL is an efficient catalyst for the feedstock recycling of mixed plastics by pyrolysis.
Possibility of reuse of HBL was confirmed.
References[1] M. Shioya, K. Wakai, M. Fukushima, and H. Ibe, Towards maximizing recycling rate in
Sapporo plastics liquefaction plant, the 4th ISFR 2007.
[2] T. Yoshioka, E. Kitagawa, T. Mizoguti and A. Okuwaki, Chemistry Letters, 2004,
33,282-283.
[3] T. Yoshioka,T. Handa , G. Grause,Z. Lei, H. Inomata, T. Mizoguchi ,J. Anal. Appl.
Pyrolysis, 2005,73,139–144.

- 51 -