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TOLEDO (SPAIN)RECYCLING OF TANNERY WASTES BY PYROLYSIS IN A VERTICAL LAB SCALEREACTORA. Marcilla1, A. N. García1 M. León2, P. Martínez2 and E. Bañón2
1 Chemical Engineering Department, University of Alicante. Apartado 99. Alicante Spain
2 Technological Institute for Footwear and Related Industries (INESCOP). Polígono Industrial Campo Alto P.O. Box 253 E-e-mail:03600 Elda, Spainantonio.marcilla@ua.esAbstract
The thermal degradation of a chromium-tanned waste (bobine split leather) under inert atmosphere has been carried out in a
vertical reactor. Process conditions have been selected to optimize the liquid fraction obtained (bio-oil). Flash pyrolysis at
three different temperatures (450, 500 and 550ºC) and slow pyrolysis up to 725ºC have been performed. Experiments withcollagen were also carried out. Although tannery waste is a biomass that can be valorized through thermal degradation
processes, the results reveal the complexity of the gas and liquid fractions generated, which include a significant proportionof oxygenated, nitrogenated and sulphured gases. A clear relationship was observed between the weight loss of the sample
during its thermal degradation and the evolution of pyrolytic gases detected. From the three fractions obtained, char fraction
has the highest calorific value, followed by the gas evolved. The heating value of the liquid fraction is about 20% of that of
the original leather. Further treatments of the bio-oil obtained would be needed to improve its fuel potential.

Keywords: Flash and slow pyrolysis, chromium-tanned wastes, GC-MS, Thermogravimetric analysis, vertical reactor

1. Introduction
Wide literature about leather waste treatment andrecycling can be found: mechanical recycling, protein
recuperation and chromium reutilization [1,2], orenergetic use (combustion). However, specificinformation related to the pyrolysis of tannery wastes is
scarce [3,4].
Pyrolysis presents an interesting alternative to theconventional combustion process. Gas and liquid
fractions are also susceptible to generate usefulchemicals. Moreover as a fuel, used alone or mixed withother fuels, the char obtained can also be used as acheap adsorbent.
In this paper, pyrolysis of chromium-tanned wastes is
proposed to convert these wastes into a gas or liquid
fuel, trying to optimize the production of liquid fraction.

2. Materials and Methods
The experiments were carried out on a chromium-tanned
waste (bobine split leather) supplied by Palomares Piel,S.L. and collagen powder from the Achilles tendon of abovine species supplied by SIGMA-ALDRICH without
any tanning treatment. Table 1 shows the ultimate
analysis of these materials.
Table 1. Ultimate Analysis.
LeatherCollageninteriores libro.indd 63

N
12.94
12.82

C
41.49
48.14

H
6.85
7.25S
0.83
0The leather was subjected to thermal degradation withTG analysis in nitrogen atmosphere using a heating rateof 10ºC/min until 800ºC.
The experiments were carried out in a fluidized bed
reactor (71cm x 5.8cm) under different conditions:- flash pyrolysis at 450ºC, 500ºC and 550ºC (leather)- slow pyrolysis (10 ºC/min) up to 725ºC (leather)- flash pyrolysis 500ºC sand bed (leather and collagen)Gas fractions were collected in tedlar bags. In the case ofslow pyrolysis, specific gas samples were collected atintervals of 50ºC approximately. Condensed volatiles
were collected in glass traps. Gas and liquid compounds
were identified by GC-MS.

3. Results and Discussion
The fraction distribution obtained in the experiments
carried out is shown in Table 2.
Table 2. Product distribution

F 450ºC
F 500ºCF 550ºC
S 725ºCFB leather
FB collagenGas (%)*

Liquid (%)

Solid (%)

20.47
25.08
26.62
41.83
12.05
9.81

41.01
44.52
42.34
29.61
53.49
55.36

38.52
30.40
31.04
28.56
34.03
34.83

F Flash; S Slow; FB Flash sand bed 500ºC(*) Calculated by difference26/9/11 13:12:55

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6th International Symposium on Feedstock Recycling of Polymeric Materials

For the leather, there are not significant differences
between gas products generated from flash and slow
pyrolysis, although the yields obtained in each casedepend on the heating rate and the process temperature.
The major components found are hydrocarbons(methane, ethane, ethylene, propane, propylene,isobutene), although a high number of oxygenatedcomponents are also identified. It has to be noticed thesignificant proportion of nitrogenated and sulphured
gases, such as HCN, acetonitrile and CH3SH as well asother minor sulphured and chlorated components suchas COS, H2S and ClCH3.
In the slow pyrolysis, it is observed that the evolution ofvolatiles is comparable with the weight loss obtained inthermogravimetric analysis.
Figure 1 shows the DTG curve obtained in the TG and
the evolution of gases (CO, CO2 and other gases such as
light hydrocarbons) in the slow pyrolysis reactor. As canbe seen, the weight loss at around 250-360ºC is mainly
due to the CO2 formation together with a small
contribution of CO. In the range 360-450ºC, the evolutionof other gases different from carbon oxides plays animportant role in the weight loss of the sample. CO 2
generation is also detected in this range. Above thattemperature, the solid seems not to suffer further
reactions, however gases are detected in the reactor
experiments (CO mainly and hydrocarbons). These
results show that in a slow pyrolysis gases formed above
540ºC are due to secondary reactions of heavy volatiles
that remain in the hot zone of the reactor but they do notcome from the decomposition of the solid.

Fig. 2. Percentages of groups of liquid compound
obtained in flash pyrolysis at 500 º C
The presence of sand in the reactor has reduced its freevolume, thus reducing the residence time of the volatiles
in the reactor. As a consequence, the gas yields in theexperiments have diminished. By comparing results frompyrolysis of collagen and leather, higher yields of ketones
and paraffins and olefins has been found in collagen.

4. Conclusions
Tannery waste is a biomass that can be valorizedthrough pyrolysis process. The maximum evolution ofpyrolytic condensable volatiles is produced in the range
400 - 500ºC. The major products obtained in gas fraction
are hydrocarbons although nitrogenated, oxygenated andsulphured compounds need to be taken into account.
Ketones and amines are the major functional groups
detected in the liquid fraction, although a wide distributionof heterocompounds are also found in minor proportions.

Acknowledgements
Co-financial support for this investigation has been
provided by IMPIVA, Generalitat Valenciana, and FEDER
for research within the field of pyrolysis flash of leather
waste.

ReferencesFig. 1. DGT and % gas compounds of slow pyrolysis
In liquid fraction, the spectrum of compounds found ismainly formed by aromatics and heteroatoms containing
compounds. Figure 2 shows the yields of the groups
obtained on the flash pyrolysis (500ºC) of chromium
leather: ketones, phenol derivatives, nitro-aromatics,
esters, paraffins and olefins, aromatics, sulphurs andalcohols. Derivatives of naphthalene (aromatics) andpyridine (nitro-aromatics) seem to be morecharacteristics of slow than flash pyrolysis.

interiores libro.indd 64[1] Mu, W. Lin, M. Zhang, Q. Zhu. Towards zero
discharge of chromium-containing leather waste throughimproved alkali hydrolysis. Waste Manage 23 (2003)
835.
[2] Cabeza, L.F., Taylor, M.M., Brown, E.M., Marmer;
W.N. Chemical and physical properties of protein
products isolated from chromium-containing leather
waste using two consecutive enzymes. J. Soc. Leather
Techvol. Chem., 82(5) (1998) 173.
[3] Font, R., Caballero, J.A, Esperanza, M.M., Fullana, A.
Pyrolytic products from tannery wastes. Journal of
Analytical and Applied Pyrolysis 49 (1999) 243.
[4] Yilmaz, O., Kantarli, I.C., Yuksel, M., Saclam, M.,
Yanik, J. Conversion of leather wastes to usefulproducts. Resources, Conservation and Recycling 49(2007) 436-448.

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