Date of Award
Master of Science
Lignocellulosic feedstocks are the most abundant biomass on earth with a high potential of producing fuels and the shortage of fossil fuels and environmental pollution resulting from burning fossil fuels have boosted interest in lignocellulose in the past few decades. Hydrothermal Liquefaction (HTL) is a process where the biomass is heated at a high temperature and high pressure to produce bio-oil. Sweet sorghum bagasse has been used in our research for this process because of its abundance in the world and in the United States. HTL of sweet sorghum bagasse was carried out under varying conditions of temperature, catalyst concentration and reaction time. This study aimed to find out the optimum condition that can lead to maximum yield of bio-oil. By testing each variable at three levels, the Box Behnken design necessitated a total of 17 runs. Among these conditions, the highest bio-oil yield of 45.28% was observed at 300oC with K2CO3 at 1M and a residence time of 60 minutes. The obtained bio-oil yields under different operating conditions could be fitted well by a cubic model. This model predicted that a maximal bio-oil yield of 57% could be achieved if the HTL is conducted at 320oC with K2CO3 at 1M and a reaction time of 60 minutes. To confirm this model, HTL performed using the optimal condition led to a bio-oil yield of 52.215%. Under the same optimal condition, two more runs were carried out without the use of K2CO3 as a catalyst. The average bio-oil yield was 7.517%, which was much lower than those with the catalyst. Therefore, the presence of K2CO3 increased yield of bio-oil significantly. The CHNS/O analysis was conducted for selected bio-oil samples. The results indicated that bio-oil samples derived from HTL with K2CO3 had a high content of carbon and a very low content of sulfur and nitrogen. The oxygen content, however, was quite high. Thus, further upgrading the HTL bio-oil is needed to improve its heat content and fuel quality.
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