2011). The high content of neutral oils also may eliminate the need for solvent extraction. These types of innovations are important for energy balance.
Phosphorus (P) within the organism in the form of phospholipids presents additional complexity in processing algae into fuels. These molecules are detrimental to downstream processing and in end-use can inhibit or poison catalysts used in fuel conversion and can damage vehicle catalytic converters (Fan et al., 2010). ASTM D6751-11b, which is the standard specification for biodiesel fuel blend stock for middle distillate fuels, specifies maximum P content allowable in biodiesel blend stock. P compounds are removed using the degumming technology developed for use with seed oils (Lurgi GmbH; AlfaLaval, 2010). Most commonly, phospholipids are converted to immiscible solids that are then removed by centrifugation. Methods of extracting phospholipids include water, acid, or enzymatic degumming. The most commonly used acid is phosphoric acid. Any of these methods produces a crude gum stream for disposal or alternative use. Acid and enzymatic degumming, while truly catalytic, require acid and enzyme additions.
The next pathway, illustrated in Figures 3-6 and 3-7, assumes that the algal biomass has sufficient value so that it provides a significant revenue stream. This pathway assumes that the biomass has value in the unprocessed and dewatered state, and that subsequent processing to recover minor valuable components is not done.
FIGURE 3-6 Alternative pathway #1: Open raceway pond producing green diesel, a pure hydrocarbon fuel with coproduct for sale.