Pyrolysis Kinetics of Hydrochars Produced from Brewer’s Spent Grains

Abstract

The current market situation shows that large quantities of the brewer’s spent grains (BSG)—the leftovers from the beer productions—are not fully utilized as cattle feed. The untapped BSG is a promising feedstock for cheap and environmentally friendly production of carbonaceous materials in thermochemical processes like hydrothermal carbonization (HTC) or pyrolysis. The use of a singular process results in the production of inappropriate material (HTC) or insufficient economic feasibility (pyrolysis), which hinders their application on a larger scale. The coupling of both processes can create synergies and allow the mentioned obstacles to be overcome. To investigate the possibility of coupling both processes, we analyzed the thermal degradation of raw BSG and BSG-derived hydrochars and assessed the solid material yield from the singular as well as the coupled processes. This publication reports the non-isothermal kinetic parameters of pyrolytic degradation of BSG and derived hydrochars produced in three different conditions (temperature-retention time). It also contains a summary of their pyrolytic char yield at four different temperatures. The obtained KAS (Kissinger–Akahira–Sunose) average activation energy was 285, 147, 170, and 188 kJ mol−1 for BSG, HTC-180-4, HTC-220-2, and HTC-220-4, respectively. The pyrochar yield for all hydrochar cases was significantly higher than for BSG, and it increased with the severity of the HTC’s conditions. The results reveal synergies resulting from coupling both processes, both in the yield and the reduction of the thermal load of the conversion process. According to these promising results, the coupling of both conversion processes can be beneficial. Nevertheless, drying and overall energy efficiency, as well as larger scale assessment, still need to be conducted to fully confirm the concept.

HTC of Wet Residues of the Brewing Process: Comprehensive Characterization of Produced Beer, Spent Grain and Valorized Residues

“…Similar findings were reported by Olszewski et al [82], and the peak found exclusively for the raw spent grain at 293 • C was also attributed to hemicellulose [82]. The peak that is common for pyrolysis of raw spent grain and hydrochars, located approximately at 350 • C, was explained by decomposition of cellulose [9,82]. A similar explanation could be given for the existence of the peak present for both types of raw spent grain at 340 • C. However, it seems that it could not be attributed exclusively to cellulose and the influence of the proteins should not be overlooked, as the DTG peaks of different proteins can be found in the literature within similar temperature range [83].…”

“…Arauzo et al [9] also attributed the large peak, present at 287 • C for pyrolysis of raw BSG and absent for pyrolysis of corresponding hydrochars, to the decomposition of the hemicellulose [9]. Similar findings were reported by Olszewski et al [82], and the peak found exclusively for the raw spent grain at 293 • C was also attributed to hemicellulose [82]. The peak that is common for pyrolysis of raw spent grain and hydrochars, located approximately at 350 • C, was explained by decomposition of cellulose [9,82].…”

Acid Hydrolysis of Lignocellulosic Biomass: Sugars and Furfurals Formation

“…After pretreatment with sulphuric acid, a new, broad peak at approximately 415 • C is generated in the thermogram. The peak is still weak at a pretreatment temperature of 180 • C, but becomes more abundant at a pretreatment temperature of 200 • C. The emergence of a new peak in the region of 410-420 • C was also observed in the sulphuric acid-catalysed pretreatment of miscanthus, as well as in the hydrothermal carbonisation of various lignocelluloses [63][64][65]. It can be assumed that the 415 • C peak is an inert pseudo lignin formed by solid-to-solid transformations of the polysaccharides [66].…”

A Comprehensive Review on Hydrothermal Carbonization of Biomass and its Applications

“…The pure carbohydrate can either exist in the form of monosaccharides such as glucose and fructose, or the form of disaccharides and polysaccharides such as maltose, [175,177] xylose, sucrose, amylopectin, and starch. Some carbohydrates derivatives, such as hydroxymethyl furfural and furfural, can also be used to prepare carbon-rich substances for feedstock [111,112,154]. The carbonization reaction mainly comprises of three steps, as reported by [90].…”

“…Cellulose would then decompose into glucose and at the same time, lignin gets fragmented and dissolves with an increase in the reaction time. GC-MS results have shown that 5-HMF, furfural and phenolic derivatives are the characteristic products of cellulose, hemicellulose, and lignin respectively [111,112]. In the acidic media, furfural compounds undergo condensation reaction and the opening of the hydrolytic ring.…”