Study On Microalgae Cell Disruption By Cavitation Technology

Microalgae cell disruption is the key step to extract the intracellular lipids and is a bottleneck problem in the microalgae oil industry for a long time. The mechanism of ultrasonic cavitation and hydraulic cavitation method is to form cavitation effect in the liquid medium to damage the periplasm near the cell membrane. When compared with other cell disruption methods,the two methods have obvious advantage of low energy consumption, broken evenly, easy to operate, and is expected to disrupt cells continuous and on large scale.In this paper,the chlorella cells were disrupted with the method of ultrasonic cavitation. The results showed that the factors of lipid extraction yield influence order was: power, cell density, processing time, temperature, dispersant concentration. The optimal combination of the parameters with comprehensive consideration of influence on lipid extraction rate and energy consumption was: ultrasonic power 220 W, temperature 25 ℃, the processing time of 6 min, cell density of 0.2 g/ml, sample throughput of 120 ml and dispersant concentration of 0.4 g/ml.As to the hydraulic cavitation, this paper integrated porous plate, venturi tube and trailing vortex cavitation technology into one hydraulic cavitation cell disruption system with reference of numerical simulation software FLUENT. The results of numerical simulation showed that: For porous plate, reduce pore size and increase the orifice plate thickness and the number of hole will enhance the cavitation intensity; The cavitation effect of circular cross hole distribution is superior to the circular array distribution. For venturi tube, sharp-angled venturi has stronger cavitaion effect; With the increase of the throat diameter, the cavitation effect decreases, but has no effect on the position where bubbles begin to collapse; The change of tapered section length has little effect on cavitation effect, but has significant effect on the position where bubbles begin to collapse; The increase of diverging section length and decrease of pipeline diameter will enhance the cavitation effect and the position where bubbles begin to collapse becomes more close to the throat. Then, this paper took cell disruption experiment with the hydrodynamic cavitation system. The results showed that, to various microalgae cell suspension, the cell disruption rate could exceed 90% when the processing time reached 30 minutes, whereas the cell disruption effect declined. The cell disruption rate would increase about 30% when the inlet pressure increased from 0.1MPa to 0.2MPa. The cell disruption rate would increase about 20% when the rotate speed of cavitator increased from 0 to 1200rad/min. Compared with ultrasonic cavitation, the cell disruption of hydrodynamic cavitation was more even and sufficient, and the processing capacity was much higher.Finally,this paper made biodiesel preparation of microalgae crude oil and microalgae powder with the method of ultrasonic alkali catalysis to generate ester exchange reaction, and made physical and chemical comparation between biodiesel and 0# diesel. The results showed that chlorella biodiesel conversion rate increased by about 90% with the cell disruption treatment; The microalgae biodiesel had similar elemental composition and the physical and chemical properties with 0 # diesel oil; Compared with one-step biodiesel preparation, two-step method got lower length of carbon chain, but was still higher than that of petroleum diesel which made its viscosity and condensation point higher than that of petroleum diesel.