School of Chemical and Bio Engineering

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Browsing School of Chemical and Bio Engineering by Author "Abdulhafiz, Yishak"

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    Liquid Fuel Production Through Pyrolysis of Khat and plastic waste mixture
    (Addis Ababa University, 2014-02) Abdulhafiz, Yishak; Kiflie, Zebene(PhD)
    A good portion of the Ethiopian population, especially of the youth, has taken up the habit of chewing Khat (scientific name: Catha edulis Forsk). Growing use of the stimulant is obviously generating a huge amount of waste making the already-bad situation of solid waste management in Addis Ababa worse. On the other hand, the disposal of plastics is also affecting the environment negatively and in no less a degree. With the expected increase in the consumption of both items, the problem will certainly grow correspondingly especially given the trend that khat is almost always sold in plastic bags. This study investigated the potentials of khat waste to be mixed with high-density polyethylene (HDPE) for use as a raw material in pyrolysis to produce liquid fuel. The results showed that khat waste can be used in pyrolysis, solely and in a mixture with waste HDPE, to yield liquid fuel. A maximum of 26%.wt of liquid yield was achieved. Produced data on characteristics of khat waste that were not available until now showed that khat waste had 76.3% moisture (as discarded); 5.31% ash (dry basis); 59% cellulose; 31.7% lignin; 47.12% C; 6% H; 45.65% O; 1.23% N; HHV of 17.5 MJ/kg; and LHV of 12.6 MJ/kg. A dark brownish liquid that had smoky odor was produced from all runs. An average liquid yield of 15.57% was obtained while the minimum and maximum values were 3% and 26%, respectively. The experiment studied respective influences from varying amount of khat in feed; pyrolysis temperature; and total pyrolysis time. It was seen that pyrolyzing khat waste alone and in higher percentages gave better results. Lower amount of khat (30%) in the feed composition led to higher yield at 550OC. However, pyrolysis at the remaining temperatures studied (650OC and 750OC) showed corresponding increase in yield with increasing amount of khat (70% and 100%). As respective decomposition of its lignocellulosic components took place at higher temperatures (> 300OC for cellulose, and > 500OC for lignin), more amount of khat in the feed led to increased amount of liquid yield. Variation in the total pyrolysis time between 30 and 60 min did not have any significant effect. Following the similarity between elemental composition of bio-oil from pyrolysis and the parent biomass, the HHV and LHV of liquid product were calculated to be 17.1 MJ/kg and 15.05 MJ/kg, respectively. In general, the expected enhancement in liquid yield from presence of plastic was not observed. In the study, pyrolysis of khat waste alone (0% HDPE) gave the maximum percentage yield for liquid product. However, it would not be plausible to conclude that addition of plastic does not bring any benefit at all – only percentage yields but not qualities of liquid produced with and without HDPE in the feed were compared.