Porosity and pore size distribution of biochar from straw biomass - data for DOE
Description
Biochar is produced by pyrolyzing biomass in the absence of oxygen and has considerable promise as a sorbent or carbon sequestration material. Despite several investigations on biochar properties, the biochar porosity and sorption properties achieved with varied pyrolysis settings remain mostly unknown. The goal of this work was to evaluate the interrelationships between temperature, material grain size, heating rate, and retention duration, as well as the effects of these interactions on the surface morphology of wheat straw biochar. Biochars made at various pyrolytic temperatures were tested for sorption, porosity, and pore size distribution. Elemental analysis, BET-N2 surface area analysis, ICP-OES, and Fourier transform infrared spectroscopy were used to evaluate 19 wheat straw biochars produced through pyrolysis at various temperatures (500 to 700 °C), heating rates (20 and 30 °C/min), and residence periods (5 and 15 min). The best settings for wheat straw pyrolysis and the variables that have a statistically significant effect on biochar quality were established using a full factorial design technique and variance analysis. At 700 °C, with a grain size of 0.5-1.0 mm and a heating rate of 20 °C/min and a residence period of 5 minutes, a high surface area of 400 m2/g and an average pore size of roughly 2.34 nm were produced.
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Three samples of various particle sizes, namely, 0.5–1, 1–2, and 2–3.15 mm, were subjected to pyrolysis under various temperatures between 500 and 700 °C, with steps of 100 °C. Pyrolysis tests were conducted at heating rates of 20, 25, and 30 °C/min and residence times of 5, 10, and 15 min using a TGA-701 LECO. In each pyrolysis test, a 1-g sample was placed in a ceramic crucible and pyrolysed in a nitrogen atmosphere. The 19 samples were prepared at the same time and analysed under the same pyrolysis conditions. The porous structure of the biochar was characterized by nitrogen adsorption at 77 K. Prior to this analysis, the samples were outgassed under vacuum at 200 °C for at least 24 h to obtain a residual pressure below 50 mTorr; to record the adsorption isotherms, a 3-Flex instrument, Micromeritics, USA, was used. All samples were analysed in triplicate. The pore characteristics of the studied materials were analysed for three pore size ranges: micropores with pore sizes less than 2 nm, mesopores with pore diameters between 2 and 50 nm, and macropores with diameters larger than 50 nm. The following porosity and pore size distribution parameters were evaluated: volume and percentage ratio of micro, meso- and macropores, total volumes of pores, SBET (Brunauer‒Emmett‒Teller (BET) equation), and pore size. The nitrogen adsorption and desorption isotherms were determined in the relative pressure range p/po = 0.01 to 0.96, allowing for the determination of micropore, mesopore, and total pore volumes. The specific pore area SBET was determined from the Brunauer‒Emmett‒Teller (BET) equation. The total pore volume was calculated from Gurvitch's law based on the amount of adsorbed gas at a relative pressure p/po = 0.96. The average pore width (davarage) was determined using the following equation: davarage = 4VT/SBET.