Читать книгу Encyclopedia of Renewable Energy - James Speight G., James G. Speight - Страница 73

Algae fuels can be recovered by three processes: (i) physical extraction or (ii) chemical extraction, and (iii) enzymatic extraction.

In the first step of physical extraction, the oil must be separated from the rest of the algae. The simplest method is mechanical crushing. When algae are dried it retains its oil content, which can then be recovered using an oil press. Many commercial manufacturers of vegetable oil use a combination of mechanical pressing and chemical solvents in extracting oil. Since different strains of algae vary widely in their physical attributes, various press configurations (such as the screw, expeller, and piston configurations) work better for specific algae types. Often, mechanical crushing is used in conjunction with chemical solvents.

Ultrasonic extraction is a type of physical extraction that can greatly accelerate extraction processes. Using an ultrasonic reactor, ultrasonic waves are used to create cavitation bubbles in a solvent material. When these bubbles collapse near the cell walls, the resulting shock waves and liquid jets cause those cells walls to break and release their contents into a solvent. Ultrasonication can enhance basic enzymatic extraction. The combination sono-enzymatic treatment accelerates extraction and increases yields.

In chemical extraction, chemical solvents are often used in the extraction of the oils. A common choice of chemical solvent is hexane, although other hydrocarbon solvents can also be used. Another method of chemical solvent extraction is Soxhlet extraction in which oils from the algae are extracted through repeated washing, or percolation, with an organic solvent, under reflux in specialized equipment. The value of this technique is that the solvent is reused for each cycle.

Supercritical carbon dioxide can also be used as a solvent. In this method, carbon dioxide is liquefied under pressure and heated to the point that it becomes supercritical (having properties of both a liquid and a gas), allowing it to act as a solvent.

Enzymatic extraction uses enzymes to degrade the cell walls with water acting as the solvent. This makes fractionation of the oil much easier. The enzymatic extraction can be supported by ultrasonication.

See Algae, Algae Fuels, Aquatic Plants, Biomass.