“Thermochemical conversion of biomass waste is a high potential option for increasing usage of renewable energy sources and transferring wastes into the circular economy. This work focuses on the evaluation of the energetic and adsorption properties of solid residue (char) of the gasification process. Gasification experiments of biomass wastes (wheat straw, hay and pine sawdust) were carried out in a vertical fixed bed reactor, under a CO2 atmosphere and at various temperatures (800, 900 and 1000 °C). The analysis of the energy properties of the obtained chars included elemental and thermogravimetric (TGA) analysis. TGA results indicated that the chars have properties similar to those of coal; subjected data were used to calculate key combustion parameters. As part of the analysis of adsorption properties, BET, SEM, FTIR and dynamic methanol vapor sorption tests were conducted. The specific surface area has risen from 0.42–1.91 m2/g (biomass) to 419–891 m2/g (char). FTIR spectroscopy confirmed the influence of gasification on the decomposition of characteristic chemical compounds for biomass. Methanol sorption has revealed for the 900 °C chars of pine sawdust the highest sorption capacity and its mass change was 24.15% at P/P0 = 90%. Selected chars might be an appropriate material for volatile organic compounds sorption.”
A Mettler Toledo TGA/DSC 1 Star System thermogravimetric analyzer (TGA) was used to study the combustion process of the raw materials and the obtained chars. The analyses took place in air atmosphere and started from the ambient temperature up to 800 °C with a heating rate of 10 K/min. The mass sample was around 5 mg and placed in the platinum crucible.
The comparison of the mass loss (TG curves) and the differential mass loss (DTG curves) of raw biomass and its chars during the combustion process is presented in . During the analysis, the combustion reaction occurred in different temperature zones for raw biomass samples than for chars obtained from it. There can be distinguished two stages of combustion in the case of raw biomass [
41]: the first stage is related to the combustion of volatile matter and appeared in temperature zones of 160–330 °C for ABW, 135–330 °C for ABH and 160–360 °C for WBP, which can be observed based on DTG curves. The second stage appeared in temperature ranges 330–457 °C, 330–484 °C, 260–490 °C for ABW, ABH and WBP, respectively. The fact that the combustion process of the chars is missing the first stage is related to the fact that volatile matter was released during gasification. Its second stage appeared in approximate temperature ranges of 244–494 °C, 255–486 °C and 340–620 °C for ABW, ABH and WBP, correspondingly. When comparing the second stages of combustion of raw materials and chars, we can see a higher intensity at DTG peaks in this area for chars than for raw biomass. It is related to the fact that char contains a higher content of carbon, resulting in high-intensity combustion of carbon compounds at this stage. During combustion of raw material, volatiles start to evolve at a lower temperature and then burn in an area of higher temperature by reaching ignition temperature. Generated heat during volatile combustion influences the start of the combustion process of fixed carbon [
42,
43]. As the volatile matter was removed from the chars, it can be observed that only one peak is detected at the DTG curve, where the mass loss at the TG curve is moved to higher temperature areas.
