Fethi Zagrouba

Impact of different catalysis supported by oyster shells on the pyrolysis of tyre wastes in a single and a double fixed bed reactor

The treatment and disposal of tyres from vehicles has long been of considerable environmental importance. Studies have been undertaken to reduce their environmental impact. In this study, an alternative gas was produced from automobile tyre wastes by the means of a controlled pyrolysis. To do so, a novel catalytic system was designed with the aim of increasing the rate of conversion and improving the quality of the pyrolysis products. This work aimed also to reduce the severity of the overall reactions, by using powder catalysts (MgO, Al2O3, CaCO3, and zeolite ZSM-5) uniformly distributed on two layers of oyster shells (OS) particles. The catalyst/tyres mass ratio was kept for all the tests at 1/30. The pyrolysis reactor was maintained at 500°C and the influence of each catalyst and of the number of shell beds (0, 1 or 2), on the yield and composition of the derived products, was examined. The gas yields could contribute by 1.2% of total consumption in Tunisia. Furthermore, some combinations could upgrade the derived gas and made it possible to use it as such or with the minimum of post-treatment. It was found that, with the use of supported catalyst, the gas produced is 45% greater compared to classical thermal pyrolysis. The Heating value of the produced gas was also improved by the use of supported catalysts; it was found 16% greater with the use of Al2O3/OS compared to non-catalytic pyrolysis. When compared to the gas obtained from only one catalytic supported bed, the sulfur content was reduced by 80% with the use of CaCO3/OS on two catalytic beds.

Energy and monomer recovery from polymer wastes

In this paper the products obtained through thermochemical processing of several polymer-based wastes are characterised. The influence of chemical composition of raw materials on the characteristics of obtained products has been investigated by using fixed bed reactor. The aim of this work is to identify the best use of products recovered after pyrolysis of plastic wastes collected from chemical and biochemical laboratories. This work is developed in a laboratory bench installation design to perform O2-free processing at atmospheric pressure. The process parameters such as pyrolysis temperature and adapted heating rate have been determined through the transposition of thermal and kinetic information provided by thermogravimetric analysis (TGA). Gas-chromatography techniques have been used to identify the chemical composition of gases (GC/TCD) and liquids (GC/FID-MS). It was established that polymer wastes can led to a valuable liquid products, with encouraging energetic properties that allow their blending with fuels currently used without altering the performances of burning devices.

Study on hydrogen and hydrogen-carriers production during rubbery wastes cracking

There is much interest in producing hydrogen from various materials, including rubbery wastes to help in the fulfilment of the predicted hydrogen economy of the future. In this paper thermal and catalyzed cracking processes have been investigated for their suitability in producing gaseous compounds during thermochemical decomposition of polymer-based materials. Hydrogen and hydrogen-carriers production through rubbery wastes cracking was carried out into a laboratory bench scale installation using a fixed bed reaction system. Experiments were conducted at 500 °C with a catalyst/waste ratio of 1/30. Catalysts influences on rubber decomposition were characterized using a variety of methods, including thermogravimetric analysis (TGA). The results indicated that the gas yield varied from 17 to 31 wt.% with addition of different catalysts. The potential of H2 production was significantly increased from 14 to 32 wt.% by using MgO-based catalytic bed. Moreover, it was found that the higher heating value (HHV) of gases varied from 10 to 44 MJ/Nm3, and the use of catalysts led to an increasing HHV especially in the first stage of cracking (250-350°C). This work highlights the evolution of hydrogen and hydrogen-carriers during thermal and catalyzed cracking, too.

Waste tyres pyrolysis: Managing the environmental hazards of scrap tyres

Thinking on environmental hazards, images of chemicals in waters, or air pollution coming out of industrial furnaces are most often seen. There are some hazards that are overlooked and one of them is scrap tires. Without a good management, scrap tires treatment can threaten not only our environment, but the public health as well. For instant, run-off from scrap tire fires can contaminate groundwater and surface water, and scrap tire sites are an ideal habitat for the breeding of insects carrying disease. In this paper we present an experimental approach on understanding and managing the environmental hazards of co-products resulted during energy recovery processes applied on scrap tyres. As tyre combustion faces serious problems related to harmful emissions, pyrolysis appears as a process that allows the management of toxic compounds. The experimental data were used to highlight the influence of textile and metal tyre compounds and provided worthy and substantive information on the issues to conduct and manage the thermochemical process in order to maximize the interest product yield. Thus, for the reactions occurs during pyrolysis and combustion of tyres organic matters the main intensive degradation thermal ranges have been established. The work was carried out by coupling thermogravimetric analysis (TGA) of tyre samples with bench scale reactor in order to identify the relationships between thermochemical behaviour and products distribution. TGA results afford the study of the kinetics parameters while the laboratory facilities allow the comprehension of tyres behaviours in real conditions. The processing temperature was limited at 700°C and the measures focused on the mass balance determination and gaseous products analysis. It was found that the three obtained products have a good energetic potential: the solid (20-32 MJ/kg), the liquid (41-43 MJ/kg) and the gas (32-36 MJ/m3). Nevertheless, the liquid need to be upgrading in order to be used as Diesel-like fuel and gases should be treated to remove sulphur compounds. With this purpose some catalysts, known for their ability to increase gaseous fraction have been studied in TGA and an important shift of degradation peaks was identified and discussed.