Resource-efficient technologies are essential for economically viable biodiesel production. This work focuses on conversion of microalgal lipids and vegetable oils into fatty acid alkyl esters or biodiesel. Transesterification of waste cooking oil (WCO) and extractive-transesterification of wet microalgal biomass were investigated using microwave and ultrasound irradiations through several process parametric evaluation studies to elucidate the effects of different alcohols and catalyst types (homogeneous and heterogeneous), reaction time, and reaction temperatures. First, a brief overview of process steps involved in microalgal biodiesel production and associated energy consumption and research needs were discussed. Next, energy analysis of microalgal biocrude production via extractive-transesterification under microwave and ultrasound irradiations (individually) was performed. Then, the synergistic effect of microwave and ultrasound irradiations on extractive-transesterification of microalgal lipids was evaluated through a process optimization study using response surface methodology to determine the best process conditions. For this study, a maximum biocrude conversion of 51.2% was obtained when 20 g of algal paste was treated with 30 mL methanol, 1 wt.% catalyst, 7 min reaction time, and 140 W for MW and US (280 W total). Further, biocrude yield kinetics study revealed that the activation energy for this reaction was around 17, 298 J mol-1 K-1. A series of experimental studies were conducted to understand the roles and effects of various process related conditions including the power output and power density of microwave and ultrasound irradiations in biodiesel production. The two non-conventional heating techniques were compared for their process intensification effects. Ultrasound was applied either in continuous or pulse mode. Pulse sonication was found to be more suitable for simple transesterification reaction of WCO with a 98% biodiesel yield in 2.5 min (9:1 methanol to oil ratio, 1.25% catalyst, and 150 W power output) over 82% yield for continuous sonication under the same conditions. Followed by this, a detailed study was conducted to determine optimum pulse (ON and OFF time) sonication conditions. A 99% conversion yield was obtained for a pulse ON-OFF combination of 7s-2s. Additionally, the effect of different alcohols (ethanol, methanol, and ethanol-methanol mixtures) using pulse sonication was evaluated.
| Identifer | oai:union.ndltd.org:MSSTATE/oai:scholarsjunction.msstate.edu:td-5753 |
| Date | 07 May 2016 |
| Creators | Martinez-Guerra, Edith Lorena |
| Publisher | Scholars Junction |
| Source Sets | Mississippi State University |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | Theses and Dissertations |
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