Pyrolytic characteristics of microalgae as renewable energy source determined by thermogravimetric analysis

Two kinds of autotrophic microalgae, Spirulina platensis (SP) and Chlorella protothecoides (CP) were pyrolyzed at the heating rates of 15, 40, 60 and 80 degreesC/min up to 800 degreesC in a thermogravimetric analyzer to inves tigate their pyrolytic characteristics. Three stages (dehydration, devolati lization and solid decomposition) appeared in the pyrolysis process. SP and CP mainly devolatilized at 190-560 degreesC and 150-540 degreesC, respecti vely. A total volatile yield of about 71% was achieved from each microalga. As the heating rate increased, a lateral shift to higher temperatures was observed in their thermograms, and the instantaneous maximum and average re action rates in the devolatilization stage were increased while the activat ion energy was decreased. The value of activation energy for CP pyrolysis w as 4.22-5.25 x 10(4), lower than that of SP (7.62-9.70 x 10(4)), and the ch ar in final residue of CP was 14.00-15.14%, less than that of SP by 2-3%. T his indicated that CP is preferable for pyrolysis over SP. The experimental results may provide useful data for the design of pyrolytic processing sys tems using planktonic microalgae as feedstock. (C) 2001 Elsevier Science Lt d. All rights reserved.