Biodiesel production from microalgae: co-location with sugar mills

Co-location of algae production facilities with sugarcane mills in Louisiana was investigated as a way to address the bottlenecks for algal biodiesel production. Using the process modeling software Sugars™, an algal biodiesel production process was integrated with the operation of a typical-sized 10,000 metric tons/day (11,000 short tons/day) sugarcane mill to evaluate material and energy balances. A process is proposed wherein alga production is supplemented with energy, water, and CO2 available from a sugarcane mill. The Energy Return on Invested, EROI (a ratio of the energy produced/energy required) of the proposed algal biodiesel production process was 1.25; meaning 25% more energy can be produced than is required by the process. A sensitivity analysis showed that this number ranged from 0.8 to 1.4 when the range of values for oil content, CO2 utilization, oil conversion and harvest density reported in the literature were evaluated. A locally sourced alga, Louisiana strain, was evaluated for its suitability as a biodiesel feedstock and to justify some of the assumptions used in the model. Hexane and ethanol were compared as neutral and polar solvents for extracting oil from the alga in order to establish a range for oil yield; it was found that 5% and 37% by wt. of the alga could be extracted as ’crude oil’ by the two solvents, respectively. The crude oil was subjected to an acid catalyzed esterification to produce fatty acid methyl esters (FAME, i.e. biodiesel). Using gas chromatography mass spectrometry (GC-MS) it was determined that 17-19% of the crude oil was converted FAME for both solvents; therefore ethanol is a more effective solvent. By incorporating the lab-generated results into the assumptions of the computer model, biodiesel yield was projected to be 920,000 liters biodiesel/yr (240,000 gallons biodiesel/year) on 440 hectares (1,100 acres) with an EROI of 0.91