科研之友
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摘要
To study the characteristics of biochar products from biomass pyrolysis, cotton stalk and rapeseed straw were used as raw materials to prepare pyrolytic biochar samples under various temperatures (350, 550, 750, 950°C). The combustion characteristics, hydrating properties, CO2adsorption characteristics, phenol adsorption characteristics and antioxidant abilities of different biochar samples (marked as CS350, CS550, CS750, CS950, RS350, RS550, RS750, RS950) were compared. A thermo gravimetric analyzer (STA409, NETZSCH) was used to investigate the combustion behavior of char. In the thermogravimetric experiment, approximately 10 mg of sample was heated in TG equipment at a heating rate of 20°C/min from room temperature to 900°C. TG-DTG tangent method was employed to determine the combustion characteristic indexes, including ignition temperature (Ti), burnout temperature (Tf) and the maximum mass loss rate (DTGmax). Results showed that the Tiand Tfvalue of char was increased with pyrolysis temperature increment, and CS550 and RS750 had better combustion characteristics due to their higher heating values and faster combustion rates, and they were appropriate for use as fuel char. Water absorption characteristics of char were conducted in a constant temperature and humidity box (Temperature: 30°C, Humidity: 90%), and an oven setting at 55°C was used to test the dehydration characteristics of the chars. Gravimetric method was used to describe the water absorption and dehydration process of char and soil. The test results showed that CS350 and RS550 had higher water absorbing capacity and water retaining capacity than soil and other chars, and they were appropriate for biochar. CO2adsorption characteristics of char were measured in an automatic adsorption equipment (Micromeritics, ASAP 2020, USA) at 273 K. Before the adsorption measurements, the sample was degassed at 150°C under a vacuum (pressure of 50 lmHg) for 10 h. The test results showed that the pyrolysis char had a good CO2adsorption ability, varying from 25 mg/g to 115 mg/g. This capacity was proportional to the micropore volume of biochar, which was 4 to 30 times higher than that of soil. These chars can be used as biochar to reduce CO2concentration of underground environment, but also can be used as CO2absorbent to improve the quality of syngas in biomass pyrolysis system. Phenol was used as a model compound to investigate the water purification ability of char. UV-visible spectrophotometer (Lambda 35, PerkinElmer, America) was used to measure the concentrations of the filtered and blank sample. Results showed that the phenol adsorption capacity of char was proportional to their micropore volume. CS750 and RS950 had strong capacity of phenol adsorption, and they were appropriate for use as the activated carbon to remove contaminants of water. The investigation methods of antioxidant abilities of biochar were the same with combustion behavior research. A parameter, R50was employed to evaluate the carbon sink of char. R50can be expressed as: R50=Tbiochar,50/Tgraphite,50, where Tbiochar,50and Tgraphite,50are the corresponding temperature to the 50% mass loss of char and graphite in TGA experiment, respectively. Results showed that the R50value of biochar increased with pyrolysis temperature increment, which indicated that the char prepared at high temperature was difficultly to be decomposed in aerobic environment. Meanwhile, the cotton stalk derived char had a larger R50value than that of rapeseed straw. This demonstrated that the cotton stalk char had a more stable structure compared with rapeseed straw char. In conclusion, pyrolysis temperature had a strong impact on properties of biochar made from cotton stalk and rapeseed straw.
- 出版日期2014
- 单位华中科技大学
