Water-washing to reduce metals in oils extracted from Nannochloropsis algae for potential FCC feedstock

Abstract

Abstract Algae cultivation offers the potential to produce biofuels with much higher productivity than conventional soil-based crops. Organic oils can be extracted from algae using solvents such as alcohols and paraffins. A challenge is to define the most economical means to process these extracted oils into products such as chemical intermediates and liquid fuels. One approach is to add algal oils directly into the petroleum-based feeds to existing refinery processes such as fluid catalytic cracking (FCC) or hydroprocessing. Maximum acceptable levels were defined for contaminants such as sodium, potassium, calcium, phosphorus, and nitrogen in the feed to an FCC unit, based on refinery experience. Cracking runs in a laboratory unit confirmed the large decrease in conversion for high levels of sodium and potassium. For a laboratory sample of Nannochloropsis algae, the level of metals was far too high in the whole algae or in oils extracted from the algae using ethanol or n-heptane to allow their inclusion in FCC feedstock, even at a level of 2% algal product in the FCC feed. Washing the extracted oil with water removed only modest amounts of metals. It was found that washing the algae with water first, and then doing solvent extractions, resulted in oils with metals levels low enough for co-feeding to an FCC unit at a level of 2%. The oil yields by mass from the starting algae from this route were 21% for ethanol solvent, and 10% for heptane solvent. If an FCC unit were completely dedicated to bio-feeds without the necessity of co-processing petroleum feedstocks, the unit might operate with a different catalyst and different set of operating constraints, but that is beyond the scope of this study.