A thesis submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy.
Johannesburg
10th of October 2016 / Thermal pyrolysis is one of the viable technologies suitable for the management of organic solid waste, which has become a global challenge over the years. This is due to the non-biodegradability of these materials and their continuous usage across all segments of man’s daily activities. Effectiveness of the method is in converting these materials under controlled process conditions, that enable the optimization of the fraction of interest, such as the liquid fraction also referred to as pyrolytic oil with a near zero pollution effect on the environment.
The main setback in the production of the liquid fraction include low yield, presence of sulphur and other aromatic compounds which have been linked to environmental pollution and health complications. This study focuses on improving the liquid fraction yield and composition obtainable from pyrolysis process. Latex natural rubber (obtained from Hevea Brasiliensis) was pyrolysed and its products compared with that of the used tyres.
The production of pyrolytic oil from used tyres and natural rubber was performed using thermal and catalytic pyrolysis processes. The operating temperature range of 375 to 750 oC (at an interval of 75 oC) at a heating rate of 15oC/min and feed material particle sizes of 2, 4, 6, 8 and 10 mm were used. In addition, Zeolite NaY was synthesized from Lawani Benin River Kaolin (LBK) at a synthesis time and temperature of 9 h and 100 oC respectively, using hydrothermal synthesis method, and used for catalytic pyrolysis.
The chemical characterisation revealed pyrolytic oil composition to be a complex mixture of aliphatic, aromatics, polycyclic aromatic hydrocarbons and other oxygen, nitrogen, sulphur and
chlorinated compounds in small proportions. The non-catalysed and catalysed pyrolysis using natural rubber resulted in pyrolytic oil with 80 and 66% of aliphatic, 12 and 15% aromatic (with polycyclic aromatic hydrocarbons concentration of 2 and 1%). The non-catalysed and catalysed pyrolysis using used tyres yielded pyrolytic oil with 42 and 32% of aliphatic, 34 and 39% aromatic (with polycyclic aromatic hydrocarbons concentrations of 18 and 23%).
The kinetics of the thermal degradation with the aid of a thermogravimetry and differential thermogravimetry analyzer was performed over a temperature range of 30 to 800 oC at a heating rate of 15, 20 and 30oC/min. Results showed that natural rubber displayed higher activation energy than used tyres, with respect to the heating rates. This is an indication that natural rubber is more difficult to thermally decompose than used tyres.
The distillation temperature of the distillates was within the temperature range of the conventional petrol and diesel. The composition of the distillates revealed carbon chain length of C5-C30 with majority being C8 – C10. A spark ignition generator engine was used to perform the combustion tests for the various pyrolytic oil distillates and petrol blended in the ratio 0, 5, 10, 15 and 20% successfully without engine modification. For the fuel consumption with respect to generator run time, it was observed that an optimum of 20% natural rubber pyrolytic oil distillates (NRPD)-Petrol blend gave comparative fuel consumption behavior with that of commercial petrol. Furthermore, the 20% NRPD distillates gave optimum fuel consumption and power. Hence, a significant yield improvement and combustion performance were observed for the pyrolytic oil derived from natural rubber than that of used tyres. Further treatment of the
pyrolytic oil distillates could pave the way for effective use of the oil as chemical feedstock for
industries, or as substitutes for fossil fuel.
It was also requisite to develop a mathematical model which adopts thermogravimetry analyser
(TGA) as a dynamic apparatus to predict weight change of a material as it degrades with time at
a fixed temperature. The proposed models were in three consecutive phases which were
classified into three time zones 0 ≤ t ≤ t1, t1 ≤ t ≤ t2 and t ≤ t2.
The general model equation for the first phase of degradation was
2
0
1 2
0 ( )
t T
w t w e
, while the
second phase model was
and at the third phase, it is assumed
that the limit of weight loss (in the second phase equation) as t tends to ∞ gives a value k , at
which change in weight loss with time is negligible. The proposed model was used to plot graph
of weight loss versus time at different fixed temperature which fitted well with the experimental
TGA and had a characteristic pattern fitted closely to the second phase degradation of the fixed
bed reactor. / MT2017
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/22447 |
| Date | January 2016 |
| Creators | Osayi, Julius Ilawe |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | Online resource (xxvi, 293 leaves), application/pdf, application/pdf, application/pdf |
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