Pyrolysis kinetics of hydrochars produced from brewer’s spent grains

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

Influence of hydrothermal pretreatment on the pyrolysis of spent grains

Hydrothermal carbonization process (HTC) is a thermochemical process which operates at elevated temperature and pressure, where liquid water is used as a reaction medium [1]. The biomass is converted into a lignite-like solid product called hydrochar [2]. The advantage of hydrothermal treatment is a possibility to convert high moist bio-waste streams without thermal drying. A two-step carbonization process (Figure 5) consisting of HTC and pyrolysis may improve the properties of final biochar (e.g., carbon content, surface area, and electrical conductivity). Hydrothermal conversion occurs using different mechanisms (e.g., hydrolysis and polymerization of intermediates) compared to pyrolysis, due to the liquid water environment, which also improves the heat transfer across the particles [1,3]. Hydrochar can be easily mechanically dewatered, due to higher hydrophobicity than the initial feedstock [2]. The mass of initial biomass is also reduced according to the HTC yield, which results in a lower mass flow of material for pyrolysis reactor and previous drying step. The two-step carbonization concept may spread the range of feedstocks used for biochar production and improve the overall energy efficiency as well as economic feasibility of pyrolysis, using wet biomass streams. Please click Additional Files below to see the full abstract

Hydrothermal carbonization coupled with ultrasound assisted extraction for recovery of phenolic compounds

Since the world average population is expected to grow during the next years, also coffee production and consumption is going to increase as well. This makes necessary to find a valuable way to valorize the residues generated by instant coffee production called exhausted or spent coffee ground (SCG). SCG is a wet organic material with lignocellulosic structure (Silva et al. 1998), containing a high amount of valuable compounds, such as polysaccharides, proteins, lipids, aliphatic acids, alkaloids, tannins, polyphenols (Campos-Vega et al. 2015) and high calorific value. Thus aims to find a proper way to treat SCG to produce value-added products and/or use the remaining solid for a suitable application, depending on the specific scenario. Hydrothermal carbonization (HTC) is a promising technology for the treatment of wet feedstock (up to 80 wt.%), at temperatures between 180 to 260 °C during a reaction time between 30 min to several hours. The main product of HTC is hydrochar, and a co-product called process water (PW). Ultrasound assisted extraction (UAE) is an eco-friendly technology suitable for the extraction of valuable compounds in the SCG, such as phenols and tannins. The target of this study is the production of hydrochar and the quantification of the total phenolic content (TPC) (mg GAE/g dry solid) after HTC and UAE. With this objective SGC is initially treated by HTC under different temperatures (200, 230, 260 °C) and reaction times (1 and 3 h). Afterwards, it was applied a UAE to the produced hydrochars at determined as the optimum operating conditions to extract maximum phenolic compounds, 40°C, 40 min, S-L (1:25, g/ml), three solvents (water, methanol, water: methanol, 50:50) and an ultrasonic bath of 100W. The results of the study may be summarized as follow: a) The increase of the severity during HTC produces an increment of 71 wt. % of the fuel ratio (fixed carbon/volatile matter). Additionally, the low ash content 2.38 wt. % and 33.17 (MJ/kg) of the hydrochars make suitable to use them as co-fuel. b) TPC (mg GAE/g dry solid) in the PW after HTC decrease with the increment of the severity during HTC. c) The results obtained after the UAE of the produced hydrochars shows that the use of methanol as solvent increases the yield of extraction of the TPC (mg GAE/g dry solid) and hydrochars produced at 200 °C during 1h reaction time contains the highest amount of TPC (mg GAE/g dry solid). References Silva, M. A.; Nebra, S. A.; Machado Silva, M. J.; Sanchez, C. G. (1998): THE USE OF BIOMASS RESIDUES IN THE BRAZILIAN SOLUBLE COFFEE INDUSTRY. In Biomass and Bioenergy 14 (5-6), pp. 457–467. DOI: 10.1016/S0961-9534(97)10034-4. Campos-Vega, Rocio; Loarca-Piña, Guadalupe; Vergara-Castañeda, Haydé A.; Oomah, B. Dave (2015): Spent coffee grounds. A review on current research and future prospects. In Trends in Food Science & Technology 45 (1), pp. 24–36. DOI: 10.1016/j.tifs.2015.04.012

Do you BET on routine? The reliability of N2 physisorption for the quantitative assessment of biochar’s surface area

A large specific surface area is one of the structural characteristics which makes biochar a promising material for novel applications in agriculture and environmental management. However, the high complexity and heterogeneity of biochar's physical and chemical structure can render routine surface area measurements unreliable. In this study, N-2 and CO2 characterization of twelve biochars from three feedstocks with production temperatures ranging from 400 degrees C to 900 degrees C were used to evaluate materials with varying structural properties. The results indicate that the frequently reported peak in the surface area of biochars around 650 degrees C is an artefact of N-2 measurements and not confirmed by CO2 analysis. Contradicting results indicate an influence of the structural rigidity of biochar on N-2 measurements due to pore deformation in certain biochars. Pore non-specific calculation models like the Brunauer-Emmett-Teller method do not allow for adjustments to these changes. Instead, the use of a pore specific model and the exclusion of pores smaller than 1.47 nm was found to achieve more representative results. The proposed calculation was validated on an external dataset to highlight the applicability of the method. Our results provide novel insights for understanding the structural evolution of biochar related to production temperature

Hydrothermal Carbonization Brewer’s Spent Grains with the Focus on Improving the Degradation of the Feedstock

Hydrochar is a very interesting product from agricultural and food production residues. Unfortunately, severe conditions for complete conversion of lignocellulosic biomass is necessary, especially compared to the conversion of sugar compounds. The goal of this work is to improve the conversion of internal carbohydrates by application of a two-steps process, by acid addition and slightly higher water content. A set of experiments at different temperatures (180, 200, and 220 °C), reaction times (2 and 4 h), and moisture contents (80% and 90%) was performed to characterize the solid (high heating value (HHV), elemental) and liquid product phase. Afterwards, acid addition for a catalyzed hydrolysis reaction during hydrothermal carbonization (HTC) and a two-steps reaction (180 and 220 °C) were tested. As expected, a higher temperature leads to higher C content of the hydrochar and a higher fixed carbon (FC) content. The same effect was found with the addition of acids at lower temperatures. In the two-steps reaction, a primary hydrolysis step increases the conversion of internal carbohydrates. Higher water content has no significant effect, except for increasing the solubility of ash components

Adsorption mechanism of different dyes on chemical activated carbon as quantitative assessment for wastewater treatment : comparative study between ZnCl2 and its eutectic

A recent development in the field of activated carbon is chemical activation via physical mixing using molten salts. Previous research discussed the differences in characteristics of activated carbons from pinewood created by pure ZnCl2 and its eutectic mixture of ZnCl2-KCl-NaCl (60:20:20 mol %). Herein a contrast in mesoporous pore size distribution and its corresponding surface area was discovered. ZnCl2 generates a higher surface area over a broad pore range whereas the eutectic creates lower surface area but with a distinctive narrow peak in the larger mesopores. The question remains whether this difference in pore distribution and surface area has an impact on the adsorption mechanism. For this instance, the effect of varying pH on adsorption was tested for methylene blue (cationic), neutral red (neutral) and methyl orange (anionic). Next to that, the adsorption kinetics and equilibrium were investigated using methyl orange and brilliant blue FCF. The latter is also anionic but larger in size and molecular weight compared to the former. A variety of adsorption models were compared to the obtained adsorption data. The pseudo-second-order model provided the best description of adsorption kinetics with both dyes. Highest adsorption in this case was noted for carbons activated with the eutectic mixture, amounting to 229.6 mg/g for methyl orange and 121.8 mg/g for brilliant blue FCF. Regarding the adsorption equilibrium, adsorption of methyl orange obtained the best fit with the Langmuir model. Adsorption of brilliant blue on the other hand had the best correlation with the Fowler-Guggenheim model, which accounts for lateral interactions between adsorbate molecules. Again, the eutectic treated carbons showed the most promising results, amounting to 447.5 mg/g and 146.4 mg/g for methyl orange and brilliant blue FCF, respectively. Furthermore, removal efficiency was determined and mass transfer resistance that might have occurred during adsorption, were investigated for both anionic dyes. Finally, regeneration of the carbons was examined. After 3 cycles, the carbons treated with the eutectic mixture maintained 60.7 and 49.1 % of their original adsorption capacity of methyl orange and brilliant blue, respectively, while this amounted to 65.9 and 46.3 % for the ZnCl2 activated carbons. This research shows that adsorption capacity not solely relies on the adsorbents surface area but is also dependent on the pore distribution. Bearing this in mind, it can be stated that eutectic salt mixtures can serve as useful activating agents for tailor-made activated carbons suitable for wastewater treatment

Adsorptive carbons from pinewood activated with a eutectic mixture of molten chloride salts : influence of temperature and salt to biomass ratio

The current market searches for technologies allowing for efficient and sustainable production of biomass-based activated carbons for their further application in the adsorption of pollutants. Chemical activation of biomass in a bed of molten salts is a novel and promising technology in that regard. However, an in-depth understanding of the process mechanism is low and optimal production conditions must be substantiated. Therefore, this study investigates the relationship between molten bed process conditions and properties of derived activated carbons. Pinewood shavings (ca. 1 mm) were mixed with three different ratios of an eutectic mixture of ZnCl2-KCl-NaCl (60:20:20 mol %) and subsequently treated at 400, 500 and 600 degrees C under an inert atmosphere. After washing, the properties of activated carbons were characterised with elemental and proximate analysis, FTIR, gas adsorption (N2, CO2) and adsorption of iodine and methylene blue. The pore size distribution of activated carbons indicates that the presence of molten salts during conversion enhances micropore and mesopore formation. At 400 degrees C with a salt to biomass ratio of 5, the optimal structural properties of activated carbon with a specific surface area of 844 m2/g, was obtained. Its adsorption capacity of methylene blue (144 mg/g) and iodine (725 mg/g) were also satisfactorily high. This study confirms that optimum parameters for chemical activation with molten salts (temperature and salt to biomass ratio) towards functional materials can be achieved. Further process development may lead to a novel and efficient technology for the production of bio-based activated carbons

Comparative study on the effect of ZnCl2, a 60:20:20 mol % eutectic of ZnCl2-NaCl-KCl and CO2 during activation of pinewood

Chemical activation in molten salts is a recent development in the field of tailoring activated carbon, where a combination of activating agents is used rather than a single compound. However, a comprehensive understanding of differences in catalytic activity is lacking. So, the question remains which chemical activation method is more beneficial. This research compares the catalytic effect of ZnCl2 as a single activating agent and its eutectic mixture of ZnCl2-KCl-NaCl (60:20:20 mol %). Pinewood shavings were chemically activated at 400 degrees C in a mass ratio of 5 to 1 (salt to biomass) and then washed to remove the activating agent. Obtained materials were subsequently physically activated using CO2 at 800 degrees C in an attempt to further increase their surface area. Properties of obtained carbons were characterized by elemental and proximate analyses, ICP-AES, FTIR, gas adsorption (N-2, CO2), and adsorption (iodine, methylene blue, and molasses). Chemical activation with ZnCl2 and the eutectic mixture resulted in a surface area of respectively 910 m(2)/g and 917 m(2)/g with significant differences in porosity. The eutectic mixture created a greater proportion of micropores. ZnCl2 was more beneficial for mesoporosity which was formed over a broad range, whereas the eutectic mixture created mesopores in a narrower size range (19-27 nm). Subsequent CO2 gasification widened the pores and lowered the surface area, decreasing the adsorption capacity. This study illustrates that employing mixtures of molten salts has several advantages over a single activating agent and might lead to further development of tailor-made activated carbons

Heteronuclear (Co–Ca, Co–Ba) 2,3-pyridinedicarboxylate complexes: synthesis, structure and physico-chemical properties

Three pyridine 2,3-dicarboxylate complexes have been synthesized and characterized by IR spectroscopy, thermal analysis and single crystal X-ray diffractometry. Their magnetic properties have also been studied by EPR and magnetisation measurements. The decomposition of such complexes in air leads to the generation of mixed metal oxides, as confirmed by powder X-ray diffraction.J.B. gratefully acknowledges financial aid from MICINN projects MAT08/1077 and MAT2008-03461/MAT, as well as DGA projects E33 and E34. George Filoti deeply ackowledges the financial support of Contract 235/2007 via IDEI Program of Romania. R. Luque is grateful to Ministerio de Ciencia e Innovacion, Gobierno de España for the provision of a Ramon y Cajal contract (ref. RYC-2009-04199).Peer Reviewe

The feasibility of activated carbon derived from waste seaweed via molten salt activation in a eutectic mixture of ZnCl2-NaCl-KCl for adsorption of anionic dyes

A recent development in activated carbon research is molten salt activation involving the combined use of activating agents. Preceding research indicated that a 60:20:20 mol% eutectic mixture of ZnCl2-KCl-NaCl as activating agents on pinewood holds several advantages over pure ZnCl2. Especially noteworthy was the characteristic pore development in the mesopores with the eutectic. Nevertheless, biomass precursors for activated carbon require sustainability and abundancy. Furthermore, a uniform product with similar porosity is desired. For this instance, this study investigates whether it is possible to generate activated carbon from waste feedstocks with a completely different biocomposition compared to pinewood such as macroalgae and if the employed ZnCl2-KCl-NaCl eutectic stimulates the same pore development. Brown seaweed (Sargassum horneri) and green seaweed (Ulva pertusa) were treated with a 60:20:20 mol% mixture of ZnCl2-KCl-NaCl as an activating agent at 400 and 600 °C. Characteristics of obtained carbons were determined via elemental and proximate analysis, FTIR, gas adsorption (N2, CO2) and chemical adsorption of iodine and several dyes (methylene blue, methyl orange, rose bengal and brilliant blue FCF). All ZnCl2-KCl-NaCl treated samples treated obtained a tailored pore size distribution with a sharp distinctive peak around 22 nm, which is analogous to previous research with pinewood. This showcases the usefulness of eutectic salt mixtures as activating agents for tailor-made activated carbons. The best results were obtained at 400 °C with green seaweed; the surface area amounted to 504 m2/g with a yield of 36.1 wt% and the highest adsorption capacity of 175.7 mg/g with methyl orange