Biomass char production at low severity conditions under CO₂and N₂environments

Abstract

In a perspective of biomass value addition, biomass char, a thermochemical product, long time considered as a residue, is now getting attention and may represent a vector in the sustainability of the whole biomass sector. Some char types were shown to have great potential as a solid fuel or precursor for further transformations as well as having attributes for storage and transportation. Other types showed potential as a soil carbon sequestration technique and soil amendment enhancing biomass yields. Depending on several factors, but mostly on biomass and production conditions, biomass char physico-chemical characteristics may vary tremendously. Therefore, in order to be used in accordance for specific utilizations, its characteristics must be carefully understood and controlled. In this study, chars with varying properties were produced in a custom-made lab-scale fixed bed reactor. Along these experiments, various biomass chars were produced under CO 2 and N 2 for temperatures of 300 and 500 °C. Char was produced from switchgrass (Panicum virgatum L.) an energy crop grown in Canada. It was then characterized for ultimate and proximate analysis as well as for calorific value. In addition, specific surface was characterized by Brunauer-Emmett-Teller (BET) technique. Char organic content composition was verified by Soxhlet extractions using dichloromethane and extracts were analysed by GC-MS.

Pyrolysis of Switchgrass (Panicum virgatum L.) at Low Temperatures within N2and CO2Environments: Product Yield Study

“…As reported in a preliminary study on the subject, in the presence of CO 2 , higher specific surface had been observed in the presence of CO 2 (189 vs 82 m 2 /g in CO 2 and N 2 environments, respectively; Table ). The possible reasons leading to this important difference may be related to the two reactors designs and operating conditions which imply: the superficial velocity of gas environment is lower in this study (0.24 vs 0.54 m/s; for 500 °C, at 1 atm), the amount of material varies mostly (25 vs 1 g), and there was a contact with air after the test within the preliminary study . In order to verify whether the gas environment (N 2 or CO 2 ) followed by air contact had an effect on char porosity, two additional tests were conducted specifically for 500 °C conditions at which high surface area were observed .…”

“…The possible reasons leading to this important difference may be related to the two reactors designs and operating conditions which imply: the superficial velocity of gas environment is lower in this study (0.24 vs 0.54 m/s; for 500 °C, at 1 atm), the amount of material varies mostly (25 vs 1 g), and there was a contact with air after the test within the preliminary study . In order to verify whether the gas environment (N 2 or CO 2 ) followed by air contact had an effect on char porosity, two additional tests were conducted specifically for 500 °C conditions at which high surface area were observed . The results obtained in both cases lead to chars with similar surface area 183 and 198 m 2 /g for N 2 + air and CO 2 + air environments, respectively (Table ).…”

“…After air treatment, the reactor was left cooling as for the previous tests. These two tests were carried in order to compare with results obtained within a previous analysis, which were in contact with ambient air after the pyrolysis reaction . Since these tests were conducted especially for BET measurements, only char yields and BET analyses were conducted.…”

“…In this study, switchgrass (Panicum virgatum L.) was pyrolyzed within two respective gas environments (CO 2 and N 2 ) using a fixed bed batch type reactor that was operated at three temperatures (300, 400, and 500 °C) for a 2.5 min residence time. Two additional tests were also performed at 500 °C (CO 2 and N 2 environments, respectively) with a special air quench following the above process at 500 °C for 2.5 min in order to compare the actual work with a preliminary study presented in the work of Pilon and Lavoie …”

Integration of Biomass Torrefaction and Gasification based on Biomass Classification: A Review

“…The sample pretreated with CO 2 had a higher surface area than the one torrefied with N 2 , and the average aperture radius was much higher than the average diameter of CO 2 and N 2 molecules; thus CO 2 and N 2 molecules can more easily diffuse into the biomass particle voids. Pilon and Lavoie [91] and Gray et al [92] reached a similar conclusion. However, Ibrahim et al [85] surveyed the surface area of willow and eucalyptus samples using the Brunauer-Emmett-Teller (BET) method and did not find any significant pore development during torrefaction.…”