This works focuses on the initial stage of the synergistic processes of acoustic treatment of biochar in water saturated with CO2 (AIChE Journal, 2014;60:1054-1065). Switchgrass was pyrolyzed in high purity helium with a temperature sweep from room temperature to 550 oC at 5 oC/min heating rate and 10 min holding time. The solution containing 3 grams of biochar and 50 ml of water in an 100 ml Karter beaker was bubbled with CO2 for 30 min before sonication by a 20 kHz, 700 W Qsonica Q700 transducer pointing downward in the solution. Sonication was conducted with 2 different levels of power strength (30 and 100% amplitudes) for different time lengths in order to capture the dynamics in the early stages of the treatment. This is critically important for practical reactor design. The biochar weight changes during treatment with the two series of power amplitudes revealed that the process includes a fast weight loss phenomenon, followed by a relatively slow weight gain process. Elemental and ash analyses of biochar suggest that weight loss is caused mainly by leaching of minerals and removal of a small amount of acidic organic compounds. The subsequent weight gain is attributable to C and H attachments from CO2 and H2O, respectively. Interestingly, biochar is observed to reject the O atoms from CO2 and H2O during the process. The loss of mineral matter, and additions of C and H results in a desirable gain of biochar’s heating value (HV). The process is reasonably fast. For instance, biochar was observed to gain 6.1% of HV (or 350.0 cal/g of biochar) after 15 s of treatment with a total ultrasound consumption 81.4 cal/g of biochar. It should be mentioned that a large amount of ultrasound energy is dissipated in the environment and the observed synergism can be optimized by changing the biochar/water ratio, reactor design, and pyrolysis severity. Moreover, the internal surface area of biochar increases notably, thus signifying a potential for application in pollution abatement. Both ultrasound and CO2 are needed to acquire the synergism.

Synergistic processes in early-etage acoustic treatment of biochar in CO2 and water

254th National Meeting (2017)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.