Year: 2013
Type: article
Abstract: Brian McConnell, BS Honors Thesis, University of New Hampshire (UNH), May 2013 Kinetics of the Lipid Extraction from Microalgae Major advisor: Dr. Ihab H. Farag, Professor, Chemical Engineering (UNH) The lipid extraction from microalgae is relatively energy-intensive, time-consuming and costly. Hexane is traditionally the extraction solvent of choice. However, hexane is toxic. Clearly it is highly desirable to develop a faster and environmentally safer microalgal lipid extraction technique. This is the focus of this project. The aims are: 1Evaluate heptane as a substitute for hexane. Both are non-polar, but heptane is less toxic than hexane. Our data confirmed that hexane and heptane extract very similar material, so heptane is a possible replacement for hexane. 2Collect experimental data on the rate of extraction of lipids from microalgae using hexane and heptane then use the data to determine the kinetics of the extraction process. A first order model was adopted, τ dY/dt = (K-Y), where Y is the g of lipid extracted per 100 g dry algae (initially at t = 0, Y = 0), K is the maximum g of lipid which can be extracted in the process per 100 g dry algae, t is the extraction time (min), and is the time constant for the process (min). Solving the differential equation gives . The maximum yield (K) and time constant (τ) depend on the solvent used and the solvent to dry algae ratio (R, mL of solvent used per g dry algae). The effect of the solvent to dry algae ratio (R) on the lipids extracted (Y) was studied. It was important to establish the validity of the first order kinetics model for both solvents and a large range of R. Microalgae was grown and harvested to supply enough dry algae for lipid extractions. Experimental data of Y vs. t were collected on a bench scale batch extractor, using hexane and heptane with R = 5 and 30. The extraction process was found to follow the assumed first order model. The maximum yield and time constant were determined from a least square error fit of the data to the proposed model. The results show that the diffusion of lipids from the algae into hexane is slow with time constants of 10-20 minutes. Heptane extraction was faster with time constants of 27 minutes. For an R of 5, hexane’s time constant was five times that of heptane (hexane was 10 min and heptane was 2 min). For an R of 30, hexane’s time constant was a little less than triple that of heptane (hexane was 20 min while heptane was 7 min). These values confirm that the heptane extraction is faster than the hexane extraction. Increasing R from 5 to 30 (factor of 6), roughly doubled the time constant for hexane (10 min to 20 min), more than tripled the time constant for hexane (2 min to 7 min), increased hexane’s maximum yield by 42% (2.75 to 3.90 g lipid extracted/100 g algae), and increased heptane’s maximum yield by 45% (1.80 to 2.61 g lipid extracted/100 g algae). For R = 5 hexane’s maximum yield was 53% larger than heptane’s maximum yield (2.75 vs. 1.80 g lipid extracted/100 g algae). For R = 30, hexane’s maximum yield was 49% larger than heptane’s maximum yield (3.90 vs. 2.61 g lipid extracted/100 g algae). The results show that while hexane is slower at extracting the algae lipids, it extracts more lipids than heptane. Similarly, increasing the solvent to algae ratio (R) slows down the extraction, but increases the yield. Technically, heptane offers a potential safer alternative to hexane for microalgae oil extraction. From an engineering standpoint, further research is needed to determine if heptane is economically superior to hexane, and the optimum R.
Authors: McConnell, Brian, Nichols, Brendan
Institution: University of New Hampshire
Language: English
Field: Energy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W394413853