Gasification Biochar Research Articles

Carbon Dioxide Gasification of Biochar: A Sustainable Way of Utilizing Captured CO2 to Mitigate Greenhouse Gas Emission

This study proposes CO2 gasification of biochar as a potential carbon utilization pathway for greenhouse gas emission reduction. It aims to evaluate the effects of CO2 concentration on carbon and CO2 conversion and output CO yield. It also performs kinetic analysis, using the volume reaction model, to determine the activation energy and pre-exponential factor. The operating conditions utilized include gasification temperatures of 700, 800, and 900 °C; inlet CO2 concentrations of 15%, 30%, 45%, and 60% by volume (N2 balance); and a CO2 flow rate of 5 L/min. Carbon dioxide gasification of biochar was performed in a fixed bed batch reactor, and the composition of the output gases was analyzed. Increases in the temperature and inlet CO2 concentration both resulted in an increase in carbon conversion, with the maximum carbon conversion of 57.1% occurring at 900 °C and a 60% inlet CO2 concentration. The results also showed that CO2 conversion increased against temperature but decreased with an increasing inlet CO2 concentration. The maximum CO2 conversion of 76% was observed at 900 °C and a 15% inlet CO2 concentration. An activation energy in the range of 109 to 117 kJ/mol and a pre-exponential factor in the range of 63 to 253 s−1 were determined in this study.

Analytical evaluation of the performance of pyrolysis-gasification (Py-Gs) combination within hybrid thermochemical-biological biorefinery

Thermochemical treatments like pyrolysis and gasification, were proposed to circumvent hydrolysis bottleneck of conventional 2nd generation biorefineries. Within this big-picture, the target of this article was to establish the type and amount of bioavailable matter that can be obtained through intermediate pyrolysis of biomass followed by gasification of biochar. To establish the amount of “chemical energy” partitioned among different products’ chemical oxygen demand (COD), which is proportional to higher heating value (HHV) and often utilized for biological systems, was applied for the evaluation of thermochemical conversion of a lignocellulosic feedstock (fir wood). The most abundant product of intermediate pyrolysis was biochar, which retains from 33 % to 40 % of feedstock COD (with temperatures starting from 450 °C). The yield of water-soluble pyrolysis products (WS) slightly increases from 24 % at 450 °C to 27 % at 650 °C, whereas the yield of WI increases considerably with the same temperature. Pyrolysis temperature showed a minor effect on the composition of WS as revealed by GC-MS analysis of main compounds and size exclusion chromatography. Preliminary gasification experiments, performed at 850 °C under CO2 atmosphere, provided gasification rates for different biochars, which was equal to 0.004, 0.005, 0.006 min−1 for biochars obtained at 650, 550, and 450 °C respectively. Syngas obtained from gasification of 450 °C and 550 °C biochar was almost tar-free, whereas gasification of 650 °C biochar yielded a detectable amount of tars (0.4 %). Increasing the gasification temperature to 950 °C sharply increases the gasification rate of biochar obtained at 450 °C, allowing to obtain 55% conversion yield. Within the scope of hybrid thermochemical-biological (HTB) processes, the obtained results show that intermediate pyrolysis, when coupled with subsequent 950 °C CO2 gasification of biochar, can deliver 64% of chemical energy (by COD basis) of the lignocellulosic feedstock as bioavailable constituents, which are defined to syngas and WS based on recent biological studies. Whereas downstream fermentation can process syngas and WS materials in an effective way, such yields could surpass the holocellulose-targeted methods based on hydrolysis.

Development of multiple alkali metals doped La-Ni based perovskites for CO2 gasification of biochar to produce CO rich syngas

Under the background of carbon neutrality, there is an urgent need for the production of high-valued syngas from renewable carbon resources. This work focused on the evaluation of multiple alkali metals doping on the catalytic activity of La-Ni based perovskite catalysts in CO2 gasification of biochar. The structure and property evolution of samples were analyzed by XRD, SEM, TEM, XPS, Raman spectra, CO2-TPD, etc. The experiment results found that Li+ exhibited a stronger catalytic gasification promotion effect than K+ and Na+, owing to the high mobility of the smallest radius ions in the lattice. Among the samples, La0.4K0.2Na0.2Li0.2NiO3 possessed the best catalytic performance with the maximum release rates of CO of 116.76 mL min−1·g−1 and 3.25 times in reactivity indexes in contrast to the LaNiO3. Correspondingly, it also showed significant resistance to ash in the cycle gasification experiments. Deep substitution with multiple alkali metals at A-site produced more active oxygen species ([O]) on the oxygen vacancies (Ov) and increased the proportion of Ni3+ of the La0.4K0.2Na0.2Li0.2NiO3, resulting in excellent catalytic CO2 gasification capacity. Furthermore, the adsorption and activation capacity of CO2 were also enhanced by the surface basic active sites generated by alkali metals substitution. Based on the experiments and characterization results, the redox recycling between Ni2+−Ov and Ni3+−[O] were proposed as the main reaction mechanisms for CO2 gasification of biochar. This study provides a valuable exploration for the complex substitution of perovskite catalysts and high-efficiency CO2 gasification of biochar.

Seeking the synergistic potential of biochar integration in municipal composting plants for techno-economic and environmental leverage

This work comprehensively investigates the technological, economic, and environmental implications of biochar application to a municipal composting facility through various combinations of in situ gasification or biochar trading. The aim is to find the optimal solution to minimize environmental impacts and to maximize resource utilization over the year. The study hybridizes an existing composting facility using various gasification plants chosen in between the commercial SynCraft model, resulting in a pioneering study where a gasifier is integrated in a composting plant. The techno-economic feasibility of each scenario is obtained calculating the payback time, estimating the annual biomass demand, evaluating the seasonal variability of biomass, and setting as a key-point the amount of produced electrical energy and gasification biochar. The scenarios differ in the installed gasifier sizing (500 kW, 1 MW and 1.7 MW) and the supplementary amount of biochar that may be purchased, applied at a 3 % w/w rate on the treated organic mix. Economic results reveal that a purchase of all necessary biochar is infeasible; therefore, the installation of a gasifier for biochar self-production should be always considered. For the 500-kW gasifier a 25-year payback (weighted average cost of capital = 10 %) that reduces to 14 or 12 years for the 1 MW gasifier, respectively with and without purchase of supplementary biochar. The 1.7 MW gasifier is the most cost-effective option, but it requires high initial investments. Additionally, this work studies both the carbon dioxide equivalent storage, thanks to the biochar utilization, quantifying the corresponding Carbon Credits in 3652 credits for the best scenario (through VERRA method), and the reduction of methane emissions during composting that are abated by nearly half in the best scenarios. Aiding biochar into composting operations emerges as a promising way for waste management optimization, balancing economic viability and environmental sustainability. On the other hand, some operational issues are identified and discussed in this work, but the findings highlight the significance of innovative approaches in shaping the future of composting facilities and advancing the circular economy.

Investigation of physicochemical and chemical properties of biochar activated with carbonate, nitrate, and borohydride

AbstractActivation of biomass before pyrolysis with various chemicals significantly affects the surface area and porosity, chemical composition, and formation and distribution of functional groups on the surface of the biochar produced. For this purpose, raw tea waste (RTW) was mixed with potassium nitrate (KNO3), potassium sodium carbonate (NaKCO3), and sodium borohydride (NaBH4) in solid form and pyrolyzed at 500 °C for 1 h. The effects of the chemical activators on biomass char formation were investigated using DTA-TGA and DSC. Compared to conventional pyrolysis, carbonate, nitrate, and hydrides increase the gasification of biochar by catalyzing the decomposition of cellulose and lignin. The effect of NaBH4 on graphitization and deoxidation of carbon is higher than that of carbonates and nitrides. In addition, all prepared biochar samples were characterized by XRD, SEM, FT-IR, elemental analysis, and N2 adsorption–desorption. While treatment of RTW with KNO3 and NaKCO3 increased the hydroxylation of the biochar, treatment with NaBH4 decreased hydroxylation by increasing dehydrogenation and dehydroxylation. Increasing boron content led to hydroxylation of the material with hydratation of NaBO2. The surface area and pore distribution results showed that nitrates and carbonates have insignificant effect on the surface area of biochar, while NaBH4 almost doubles the surface area and total pore volume of biochar by forming hydrogen.

Insights into biomass mild gasification based on mass-energy balance: Establishing condition, thermodynamic mechanisms, and product properties

To alleviate the challenge of gas and char quality competition arising from over oxidation during the biomass gasification. A new concept of biomass mild gasification based on mass and energy balance was proposed, wherein the energy produced during the oxidation stage precisely equals the energy consumed in the pyrolysis and reduction stages. An energy balance index (EBI), obtained through the combined use of TG-DSC-MS-FTIR and Gaussian model fitting to represent the relationship between mass loss and endothermic/exothermic properties among different reaction stages, was optimized by response surface methodology (RSM) to obtain the critical conditions of biomass mild gasification. Under two typical mild gasification conditions, the quality characteristics of mild gasification biochar were analyzed and the gas evolution characteristics and sequence were determined through the combination of two-dimensional correlation spectroscopy (2D COS). The results indicated that mild gasification can be achieved within a heating rate range of 21 °C/min to 26 °C/min, with the oxidation temperature ranging from 776 °C to 869 °C. Under mild gasification conditions, the biochar produced at 850 °C-20 °C/min had higher COOH content, which can regulate soil pH, promote organic matter degradation, and enhance biological activity. Under the 800 °C-25 °C/min mild gasification condition, more CO and CH4 were generated during the pyrolysis stage, but slightly more CO2 was also produced during both the pyrolysis and oxidation stages. This work provides comprehensive thinking on the precious control of gasification process, which lays a foundation for co-generation of high-quality char and gas.

Effect of Alkali and Alkaline Earth Metallic Species on Gas Evolution and Energy Efficiency Evolution in Pyrolysis and CO2-Assisted Gasification

Abstract In this study, the same moles of alkali and alkaline earth metallic species were introduced into pine wood to investigate their effects on biomass pyrolysis and carbon dioxide-assisted gasification. First, thermogravimetric analysis was conducted to examine the pyrolytic behavior of pine wood loaded with alkali and alkaline earth metallic species. A semi-batch fixed bed platform was used to quantify gaseous product parameters, including gas mass flowrate, gas yield, recovered energy, energy efficiency, and net carbon dioxide consumption. Thermogravimetric results indicated that the loading of alkali and alkaline earth metallic species promoted the thermal decomposition of pine wood at low temperatures, but an inhibitory effect was observed at high temperatures. In terms of pyrolysis, adding alkaline earth metals increased syngas yields, and recovered energy, as well as energy efficiency, whereas alkali metals had the opposite effect. For the gasification, the loading of alkali metals showed a stronger catalytic than the pine wood loaded with alkaline earth metals. Based on the evolution of carbon monoxide, the effects of alkali and alkaline earth metallic species on enhancing the biochar's gasification reactivity were in the sequence of sodium > potassium > calcium > magnesium. In addition, the addition of alkali metals exhibited a stronger capacity for carbon dioxide consumption, which contributed to the management of the greenhouse gas. Considering only energy efficiency, adding alkaline earth metals in biomass pyrolysis is an optimal choice due to the higher overall energy efficiency obtained in less time.

Biochar gasification: Insights from pyrolysis atmospheres and gasification heating rates

Gasification is a promising technology for the synthesis of syngas and hydrogen, with char reactivity being a pivotal factor in the design of industrial gasifiers. Despite extensive studies on the gasification characteristics of biochar, the influence of the pyrolysis atmospheres on the evolution of biochar pore structure and its reactivity in gasification remains poorly understood. This study aims to bridge this gap by comprehensively investigating the effects of char preparation atmospheres (i.e., CO2, H2O, and N2) on ensuring gasification reactivities at varied heating rates. Biochars were synthesized in a horizontal tube furnace at 700 °C with a low heating rate (10 °C min−1) under three different atmospheres: N2, CO2, and H2O. Subsequent gasification reactivities were investigated using i) a thermogravimetric analyzer (TGA) at a low heating rate (10 °C min−1) and ii) a wire mesh reactor (WMR) at a high heating rate (1000 °C s−1), both under CO2 atmosphere at 950 °C. The results showed that the presence of an active atmosphere (CO2 and H2O) during pyrolysis significantly impacts the biochar’s aromaticity, crystalline structure, and surface morphology. The functional group concentration and surface area trends indicated that CO2 and H2O atmospheres during pyrolysis enhance biochar reactivity compared to the N2 atmosphere, with the highest reactivity observed for biochars produced under H2O. Furthermore, biochar gasification reactivity was markedly higher using the WMR compared to TGA, underscoring the pronounced effects of heating rate on gasification behavior. The high heating rate in WMR preserved the biochar’s porous and amorphous structure, whereas the TGA gasification encountered diffusional limitations and thermal annealing effects. These insights underscore the need to consider pyrolysis atmosphere and heating rate in gasification studies, offering a more comprehensive understanding of biochar’s behavior under practical gasification conditions.

Synergistic conversion of iron ore sintering dust and waste biochar to produce direct reduction iron and syngas: Gasification, reduction behavior and thermodynamic analysis

Waste biochar from biomass power generation and sintering dust from ferrous metallurgy were skillfully used to produce direct reduced iron (DRI) and syngas via a synergetic conversion in this study. The thermodynamic analysis of their related reactions, biochar conversion and reduction behavior of sintering dust were investigated. The biochar gasification and reduction of sintering dust were coupled and promoted by each other at 1000 °C for 60 min with 1.2 mol (C/Fe). For biochar conversion, adding sintering dust deepened the pyrolysis of the volatiles in the waste biochar to generate more CH4, and it provided more oxygen atoms, gasifying carbon atoms in the fixed carbon to generate more CO. The CO and CH4 yield from biochar conversion with iron oxides of sintering dust increased by 633.8% and 41.5% to its pyrolysis alone. For the reduction of sintering dust, the whole conversion process of sintering dust was the generation, aggregation and growth of the iron grains, including the generation of metallic iron grains, forming curved bars and composite flocculent metallic iron, and its larger lumps particles finally. A DRI with a 92.4% metallization ratio, meeting the requirements of the subsequent electric arc furnaces, was obtained at 1000 °C for 60 min with 1.2 mol (C/Fe). This study achieves an efficient and reciprocal conversion of these two solid waste resources. It offers an essential research reference for fuel gasification and DRI processes.

Synergistic catalytic biomass-H2O gasification for H2 production and biochar etching mechanism: Experimental and DFT studies

Biomass-H2O gasification facilitated by multi-metal synergistic catalysis for H2 production. Oxygen transfer, carbon dissolution, lateral/vertical etching mechanism, and hydrogen production capacity of biomass self-contained K and added Ni catalytic gasification were studied through biomass loaded with K and Ni pyrolysis, biochar gasification experiments, and DFT calculations. The H2 yield from KNi catalytic gasification was 67.09 mmol/g (increased by 13.51%). Driven by *OH, K migrates and transforms from the inside of the carbon matrix to form active sites (CK), increasing carbon defects (40–50%) and reactivity. The vertical etching ability of Ni on biochar is enhanced from outside to inside (forming NiC and CK to reduce carbon dissolution energy barrier) and the gasification reaction rate is increased. The competition between the strong attraction of Ni on OH and the van der Waals force of K on OH leads to a 7.7% increase in the energy barrier of the rate-determining step (H transfer). The work enhances the understanding of the multi-metal catalytic gasification of rich H2 and provides a foundation for developing catalytic gasification technology.

The conductivity dilemma: How biochar grain’s chemical composition and morphology hinder the direct measurement of its electrical conductivity

Although electrical conductivity is one of biochar’s fundamental properties that affects the way it interacts with microorganisms in soil applications, however its measurement is not univocal. This work starts from the results of a testing campaign on gasification biochar as the basis for a larger discussion on the parameters that affect the conductivity measurement and, therefore, the limits of the most widely used compression measuring approach. Different samples were obtained by combining sifting and grinding on a single batch of biochar. The samples were tested in a PTFE cylinder with conductive plunger and cap in a range of pressures up to 25 bar. The same biochar prepared in different ways showed different conductivity behaviors, with variation up to 85%, proving that the testing condition can strongly affect the measurement. These findings encourage the scientific community to further investigate the meaning of the results obtained with a further recommendation to properly describe the sample preparation and the testing conditions when a compression method is used. The final point of this discussion hypothesizes that neither one of the obtained conductivities truly represents the conductivity perceived by the microorganism that interacts with the char in soil applications.

Experimental study on potassium catalyzed gasification of large particle size biomass with CO2

Candlenut wood with large particle size is selected to investigate the biomass gasification catalyzed by potassium. The sample pore structure, the spatial distribution of potassium, and the effects of potassium salt species on the biomass gasification with CO2 are examined. The results show that the large particle candlenut wood exhibits obvious spatial anisotropy and that the pore structure is mainly distributed along the axial direction. Large particle candlenut wood has a more uniform distribution of potassium salts along the axial direction. Part of the potassium salt releases outward during the gasification, which reduces the potassium salt content in the sample center. The average potassium contents of sample loaded with KCl and biochar of sample loaded with KCl are 9.273% and 7.745%, respectively. The synthesis of polycyclic aromatic hydrocarbons in tar could be inhibited by potassium, which could also catalyze the gasification and methane removal reactions of biochar and facilitate the formation of CO and H2. Compared to raw sample (28.99%), the syngas yields from the gasification of sample loaded with KCl, sample loaded with K2CO3, and sample loaded with K2SO4 are 40.22%, 52.16%, and 41.72%, separately. The catalysis of potassium is closely related to its occupation of the active sites on biochar. The chemical bonds formed by potassium and biochar are repeatedly broken and formed during the gasification, which promotes the decomposition of organic matter. Compared with KCl and K2SO4, K2CO3 has a better catalytic effect.

Techno-economic assessment of an autothermal poly-generation process involving pyrolysis, gasification and SOFC for olive kernel valorization

The present work elaborates on the simulation and techno-economic analysis of a proposed MW-scale hybrid scheme that enables the production of different marketable products (i.e., electric energy and bio-oil) from the thermochemical exploitation of olive kernel residual biomass. In this regard, detailed calculations for mass and energy balances, process simulation in Aspen Plus and economic analysis with complementary sensitivity scenarios were conducted, with the aim to model and assses the feasibility of an integrated process for electricity and crude bio-oil co-generation via subsequent stages of biomass pyrolysis, bio-char gasification, syngas-fed SOFC and steam turbine. Notably, it was demonstrated that the provision of 20 tn/day of raw olive kernel resulted in a net electricity generation of 1685 kWel as well as production of 3.4 tn/day of bio-oil, without the need for external heating. Equally importantly, the overall electric efficiency and the combined bio-oil/power co-generation efficiency of the integrated process were equal to 46.8% and 77.0%, respectively, being amongst the highest values reported in relevant works. Moreover, economic analysis revealed that syngas clean-up and SOFC units account for 75% of the total fixed capital investment as well as for 62% of the annual operation costs. Nonetheless, increased unit cost is largely counterbalanced by the fact that electricity generation accounts for ∼85% of total profits. Also, it was found that the proposed venture is not profitable considering current market values for electricity and bio-oil. However, sensitivity analysis revealed that a main equipment cost reduction of 70% is a prerequisite for the break-even electricity price to attain the current market values. Moreover, profitability can be marginally improved further by accounting for a state subsidization of more than half of the initial investment and by the increase of the crude bio-oil price at 700 €/tn.

Investigation of BaFe2O4 oxygen carrier modified by supports in chemical looping gasification of biochar

BaFe2O4 (BF) is a promising oxygen carrier (OC) for chemical looping gasification (CLG), but its stability is low due to serious sintering. The novelty of this work is to investigate the potential of adding different supports (Al2O3, MgAl2O4, and ZrO2) with BF to enhance performance and stability in the CLG of biochar. The results demonstrated that the addition of the supports had enhanced sintering resistance, surface area, pore properties, and oxygen vacancies on the surface simultaneously with positive effects on CLG performance. Among all supports, MgAl2O4 with 50% content displayed the greatest syngas yield (0.088 mol/g) and carbon conversion (80.76%), attributed to the highest surface area and total pore volume, as confirmed by BET results. Moreover, despite the slight decline in the reactivity due to ash deposition, the BF/MgAl2O4 showed stable CLG performance during the multiple cycles, which can be ascribed to the resistance of sintering provided by MgAl2O4.

Effect of wood gasification biochar on soil physicochemical properties and enzyme activities, and on crop yield in a wheat-production system with sub-alkaline soil

Biochar may have beneficial effects on soil depending on its properties and pedoclimatic conditions. Highly sloping soils are prone to erosion and organic matter depletion, and biochar can be useful to restore soil fertility and quality, and crop yields. To test the effect of wood gasification biochar (WGB), we conducted a field experiment applying 0 and 60 Mg ha−1 of WGB only (no fertilizer) to a sub-alkaline and fine-textured soil under Mediterranean climate conditions. The effect of WGB on the soil physicochemical properties and on 12 enzyme activities involved in the C, N, P, and S cycles was monitored during a wheat-growing season along with its effect on grain yield. The results show that WGB was rather recalcitrant, and the application of a high dose of it had no effect on most of the soil physicochemical properties, enzyme activities and wheat grain yield. Since enzyme activities involved in the C cycle were similar in WGB-treated and not-treated soils, WGB failed to stimulate organic matter mineralization during the monitored period, with no contribution to N and P supply. Since WGB can contribute to soil C stock with no detrimental effects on wheat yield, wood gasification can allow recycling waste woody materials of urban origin to produce energy and return biochar back to agricultural soils. We suggest that future studies on WGB focus on the effect of its aging in soil on soil physicochemical and biochemical properties, and on crop performances.

Catalytic calcium-looping gasification of biochar with in situ CO2 utilization with improved energy efficiency

Capture and conversion of CO2 from optimal-scenarios into fuels or chemicals provide a viable solution to combat climate change in reducing greenhouse gas emissions. Here, we propose and experimentally demonstrate that synergistic integration (Catalytic calcium-looping (CaL) gasification of biochar) can realize the capture and in situ conversion of CO2. Thermodynamic and kinetic estimations, catalytic conversion and cyclic tests and microstructure characterizations showed that by using a mixture of limestone and K2CO3-impregnated biochar, calcination fully coupled with the reverse Boudouard reaction can shift thermodynamic equilibrium and simultaneously induce the synergetic catalysis between CaCO3 and K2CO3, allowing for accelerating decarbonation kinetics, enhancing CO yield and maintaining stable cyclic CO2 conversion at lower temperatures (850 °C), as compared to the individual CaL and gasification processes. Theoretical calculations further revealed that the activation energy barriers for the monatomic C-assisted CO2 dissociation were lower than its desorption energy for CO2 on the K-doped CaO surface, demonstrating superior conversion reactivity. Importantly, the process is demonstrated in terms of practical scalability using a renewable and cost-effective reductant (biochar), a cheap catalyst (K2CO3) and inexpensive natural CO2 sorbents (limestone and dolomite) in an energy-efficient manner, therefore opening a unique direction for net-negative emission for large CO2 stationary sources eliminating the need for sequestration.

Extension of the layer particle model for volumetric conversion reactions during char gasification

The so-called “layer model” or “interface-based model” is a simplified single particle model, originally developed for shorter computation time during computational fluid dynamics (CFD) simulations. A reactive biomass particle is assumed to consist of successive layers, in which drying, pyrolysis and char conversion occur sequentially. The interfaces between these layers are the reaction fronts. The model has already been validated for drying, pyrolysis and char oxidation. Layer models in the literature have commonly employed surface reactions at the reaction front to describe char conversion. In this work, the suitability of this surface reaction concept is assessed when gasifying biochar. It is shown that a particular layer model, already available, which originally employed surface reactions, was unable to adequately describe the mass loss during gasification of a biochar. In order to overcome this incapability, the model was extended to consider volumetric reactions in the char layer. The influence of intraparticle diffusion was considered through an effectiveness factor. The model is easily adaptable for different gas-solid kinetic rate laws, while still allowing for comparably fast solutions of the model equations. The extended model was validated using theoretical calculations and experimental measurements from literature. It was demonstrated that intraparticle diffusion can significantly slow down the biochar gasification process. A general guideline for when to employ volumetric reactions, rather than surface reactions, and when to consider intraparticle diffusion is provided based on the Thiele modulus as the criterion.

Insight into the application of biochars produced from wood residues for removing different fractions of dissolved organic material (DOM) from bio-treated wastewater

The primary aim of this study was to conduct a comparative analysis of four distinct biochar types, which were derived from wood residues through varied production methods. To assess their efficacy in removing dissolved organic matter (DOM) from bio-treated wastewater, this study examines the capacity of these biochars to extract DOM fractions from wastewater sourced from landfill leachate. Three types of the biochar were raw gasification biochar , and gasification biochars activated with H2O and CO2 respectively. The other one was a pyrolytic biochar produced from wood residues. To evaluate the biochars’ performance in DOM removal, various wastewater DOM components were analyzed. The study found that the production method significantly impacted the biochars’ ability to remove DOM while the activation technique showed slight impact on the biochars’ performance in DOM removal. Activated gasification biochars exhibited superior DOM removal compared to pyrolytic biochar. 78% of the wastewater COD was removed by activated gasification biochars while the raw biochar only removed 48% of the COD, at 7 gL−1 of the biochars. Pyrolytic biochar could remove 64% of the wastewater COD at 7 gL−1 of the biochar and showed better fluorescent compounds adsorption. Further analysis revealed that pyrolytic biochar was more selective in removing higher molecular weight compounds. In contrast, activated gasification biochars removed compounds with a broad range of molecular weights. The biochars’ adsorption efficiency were attributed to changes in specific biochar characteristics, such as pore size distribution and changes in functional groups. This study suggests that the gasification biochars have great capability in DOM removal.

Chemical looping pyrolysis-gasification staged conversion of microalgae biomass with Ca-Fe composite oxygen carrier

Chemical looping pyrolysis-gasification staged conversion (CL-PGSC) of biomass was proposed in this work, which involves the separation of chemical looping gasification into two stages: biomass pyrolysis stage and bio-char gasification stage at different temperature. Pyrolysis and gasification behavior of Nannochloropsis sp., a microalga, with Ca-Fe composite oxygen carrier was investigated in a tubular reactor at varying temperatures and Ca-Fe molar ratios. The results indicate that all Ca-Fe composite oxygen carriers are capable of catalytically upgrading the quality of bio-oils in-situ during the pyrolysis stage. The complex metal oxides calcium ferrites facilitate the formation of aromatics and ketones, while both Fe2O3 and CaO components promote the production of alcohols. As for oxygen carrier with Ca-Fe molar ratio 1:1, the total peak area percentage of hydrocarbons and ketones reaches 66.5 area% within bio-oils, with 28.7 area% being toluene and 18.8 area% being 2-heptadecanone. Moreover, at the gasification stage, clean CO-rich or H2-rich syngas were generated from bio-chars produced at various pyrolysis temperatures with or without steam as a gasifying agent. In the proposed CL-PGSC process, Ca-Fe composite oxygen carrier serves as a catalysis for in-situ upgrading pyrolytic bio-oils, then as an oxygen donor for the gasification of pyrolytic char to achieve the simultaneous production of valuable pyrolytic bio-oils and clean syngas free from tar contamination. This provides a promising strategy for the full utilization of biomass.

Insights into direct reduction iron using bamboo biomass as a green and renewable reducer: Reduction behavior study and kinetics analysis

Biochar is a renewable, carbon-neutral energy source that can replace traditional fossil fuels for iron and steel production, so it is of great significance to reduce carbon emissions and reduce pollution. In this paper, the reaction characteristics and kinetics between biomass (bamboo powder) pyrolysis gas, biochar, and iron ore powder are studied by a thermogravimetric analyzer (TG). Comparing the samples with four different C/O ratios (C/O = 0.375, 0.5, 1, 3), it is found that the sample with C/O = 1 can completely reduce hematite. The mass loss process is divided into the following four stages: de-crystal water, hematite to magnetite, magnetite to wustite, and wustite to metallic iron. Among them, the latter three stages are following the kinetic model of random nucleation (n = 1, 2) and three-dimensional diffusion, and the activation energy of the three stages increases and then decreases. Through scanning electron microscopy (SEM), the surface of hematite particles changed from relatively flat to porous and finally the reduced metal iron aggregated, and connected into large pieces. By using online Thermogravimetry-Fourier Transform Infrared Reflection (TG-FTIR), when the reduction temperature is lower than 700 °C, biochar plays a leading role. On the contrary, the CO produced by biochar gasification plays a leading role.