Catalytic Effect of Inorganic Elements on Steam Gasification Biochar Properties from Agrowastes

Abstract

Steam gasification chars from lignocellulosic agrowastes are highly microporous materials with specific surface areas between 500 and 1000 m 2 /g, comparable to that of activated carbons. Nevertheless, the analysis and comparison of gasification chars from different feedstocks revealed the important effect of the raw biomass inorganic composition on their physicochemical properties. In particular, it was found that the catalytic effect of alkali and alkaline earth metals (AAEM) on the steam gasification reactions resulted in higher char specific surface areas, with greater proportions of surface oxygen-containing functional groups. In contrast, this effect was not observed for Si and P rich samples. In accordance, the biomass inorganic ratio K/(Si + P) proved to be a valuable indicator of the steam gasification char reactivity, giving a new insight for the engineering of useful value-added materials from lignocellulosic agrowastes. The mechanisms presented in this work could be an important reference for real gasification applications working with different kind of residues when the valorization of the solid byproduct is targeted.

CO2 Gasification of Sugarcane Bagasse Char: Consideration of Pyrolysis Temperature, Silicon and Aluminum Contents, and Potassium Addition for Recirculation of Char

“…The gasification rates for char samples prepared at temperatures up to 850 °C monotonically decreased with conversion, with the exception of the char sample prepared at 900 °C, which underwent maximum gasification at ∼10% conversion. This type of gasification behavior has been previously observed for char materials that, like SCB, have Si as the most abundant ash species. , As shown in Figure a, above 30% conversion, the gasification rates were similar and complete gasification required approximately 140 min for all samples. A time of 50 min was reported for the nonisothermal (with a heating rate of 20 °C min –1 ) CO 2 gasification of SCB char prepared at 500, 800, and 900 °C but with smaller initial particle sizes in the range of 180–450 μm (compared to the average particle size of 793 μm used herein, Figure a) and higher gasification temperatures (up to 1300 °C compared to 850 °C used herein) …”

“…This type of gasification behavior has been previously observed for char materials that, like sugarcane bagasse, have Si as the most abundant ash species. 44,45 As shown in Figure 5a, above 30% conversion, the gasification rates were similar and complete gasification required approximately 140 min for all samples. A time of 50 min was reported for the non-isothermal (heating rate of 20 °C min -1 ) CO2 gasification of sugarcane bagasse char prepared at 500, 800, and 900 °C but with smaller initial particle sizes in the range of 180-450 μm (compared to the average particle size of 793 μm used herein, Figure , the labels on the curves refer to the pyrolysis temperatures used to prepare the samples.…”

Characterization of Steam Gasification Biochars from Lignocellulosic Agrowaste Towards Soil Applications

“…Biomass gasification experiments were performed in a semicontinuous laboratory-scale fluidized bed gasifier, described in detail in a previous work [3]. For all the experiments, 80 g of biomass with particle size between 1 mm and 3 mm were placed inside the reactor and heated to 850 °C, under nitrogen, with a heating rate of 20 °C/min.…”

“…The repeatability of the TPD tests was found to be satisfactory with a maximum calculated standard deviation below 10% for at least three replicates. To determine the contribution of each type of oxygen complex, both the CO and CO 2 desorption curves were deconvoluted using six Gaussian peaks according to the procedure proposed by Zhou et al [34], and detailed in a previous work [3]. The fitting error found between the experimental and the deconvoluted curve was always below 8%.…”

“…However, in most cases, agrowastes are barely valorized and remain underexploited. In this context, steam gasification could be an interesting process for the simultaneous production of high heating value fuel gases for heat or power generation, and a porous carbon-based by-product, also called biochar, that could be valorized [1][2][3].…”