Extraction and Evaluation of the Fuel Properties of Tyre Pyrolysis Oil

Abstract

The environmental degradation as a result of waste disposal and the energy crisis are some of the problems mankind is currently facing. It has resulted in the utilization of appropriate technologies that enable energy recovery from non-conventional sources. These may include recycling of waste material to get energy. Worn-out tyres are some of the waste material around us. Whereas they can’t be remolded to any form, they contain high amounts of energy that can be recovered. The objective of this research was to extract and evaluate the fuel properties of oil obtained by pyrolising waste tyres. A batch type pyrolysis system was designed and fabricated. It was then used in the extraction of tyre pyrolysis oil. Waste tyres were collected and cut into pieces with cross-sections of 2-3 cm wide and then fed into the reactor chamber. It was locked and then heated by a crucible furnace to a temperature between 530 0C and 570 0C. Heating was continued till no visible flow of gases was observed. This ensured that all possible gaseous and liquid products had exited the reactor, indicating completion of pyrolysis. The gases were condensed to obtain a liquid fraction of the pyrolysis gases, while the non-condensable fraction was fed back to the furnace as fuel. The collected pyrolytic oil was then weighed. To evaluate the effect of catalyst on the pyrolysis products, the same procedure was repeated with feed material being mixed with sodium carbonate as a catalyst in percentages of 1.5 %, 2.5 %, 5 %, 7.5 % and 10 %. The chemical and physical properties of tyre pyrolysis oil were assessed. Evaluation of the effects of a catalyst on the collected oil samples was carried out as well. Specific gravity was found to increase with the increase in catalyst from 0.92167 to 0.95071 while calorific value, flash point, sulphur content, and Cetane index were decreased 40.431 to 39.182 MJ/kg, 51 to 32 0C, 8443 to 1689 mg/kg and 12.72 to 3.66 respectively. Kinematic viscosity was decreasing with the increase of catalyst up to when the catalyst was 2.5 % from 3.04924 to 2.51894 cSt and started to increase proportionally with it, while pH was increasing with the increase of catalyst up to when the catalyst was 5 % 6.93 to 8.12 and started to decrease. The analysis of hydrocarbons present in the resulting tyre pyrolysis oil was carried out by the use of a gas chromatography and mass spectrometry (GC-MS) test. Functional groups were also analyzed using Fourier transformation analysis (FTIR). It was found from FTIR and GC-MS analyses, that the TPO samples produced by both catalytic and thermal pyrolysis were complex mixtures of aliphatic, aromatics, nitrogen and oxygen containing compounds with carbon content ranging between C4 and C45. The TPO was found to contain aliphatic compounds that were similar to the ones contained in diesel fuel. The use of a catalyst was found to increase the oil yield and reduce the amount of Sulphur content in the oil. The change of the structure of the oil was found to make the oil not fit for its usage in a diesel engine when considering its Cetane index. Ways of improving the structure e.g. hydrogenation can be explored for its usability in a diesel engine.