Simplifying biodiesel production: The direct or in situ transesterification of algal biomass

The in situ esterification/transesterification of algal biomass lipids to produce FAME for potential use as biodiesel was investigated. Commercial algal biomass was employed, containing 20.9 wt% hexane extractable oil. This consisted of 35.1 wt% free fatty acids (FFA), 18.2 wt% TAG, and 8.8 wt% MAG, accounting for 62.1% of the extractable material. Other constituents of the hexane extractable material, accounting for 37.9% of the extracts, were not further characterized. The predominant fatty acids in the oil were palmitic (42.4 wt%), oleic (30.6 wt%), linoleic (22.8 wt%), and linolenic (16.1 wt%). Small amounts of 10-keto 16:0 and 10-OH 16:0 fatty acids were also present. Statistical experimental design was employed to coordinately examine the effects of the amounts of methanol, sulfuric acid, and reaction temperature (23–65°C) on the yield of FAME in 2 h reactions. Three methods of feedstock preparation were examined – as received, oven dried, and water-washed/dried. For all feedstocks conditions could be identified which were predicted to yield greater than 90% maximum theoretical FAME production. Oven drying the feedstock reduced the amount of methanol required, with 83% of maximum yield obtained at a methanol/fatty acid molar ratio of 220:1 (4 mL methanol/g substrate). Water washing the biomass did not reduce the methanol required for high level transesterification. Practical applications: In biodiesel production by the conventional method of alkali-catalyzed transesterification of a refined vegetable oil/the combination of feedstock and process costs threatens the economic viability of biofuel production. In situ esterification/transesterification is a method for producing biodiesel wherein a lipid-bearing material is directly treated with reagents that catalyze fatty acid alkyl ester production from FFA and acylglycerols. By eliminating the need to isolate and refine the feedstock lipid, this approach to biodiesel production eliminates some of the processing steps required by contemporary methods. This could provide a welcome reduction in the cost of biodiesel production. There is presently considerable interest in the possibility of biofuel production from algal biomass. This study describes the application and optimization of in situ transesterification to a lipid-bearing algal biomass. Application of this technology could facilitate the economical production of biodiesel from algal biomass.