Search Results (6,268)

Abstract: In 2020, China put forward the national energy and economic development strategy goal of “carbon peak and carbon neutrality”; in this context, the hydrogenation of carbon dioxide into clean energy and high-value-added chemicals can effectively alleviate the current environmental pressure. This process represents a crucial avenue for the advancement of green energy and the realisation of a sustainable energy development strategy. Among the efficient catalysts designed for CO₂ hydrogenation reactions, transition metal cobalt has garnered extensive attention from researchers due to its relatively abundant reserves and low economic cost. This paper first introduces the thermodynamic process of carbon dioxide hydrogenation and discusses methods to improve the efficiency of the catalytic reaction from a thermodynamic perspective. It then briefly describes the reaction mechanism of cobalt-based catalysts in the carbon dioxide hydrogenation reaction. Based on this understanding, this paper reviews recent research on the application of cobalt-based catalysts in the hydrogenation of carbon dioxide to produce methane, hydrocarbon chemicals, and alcohols. Finally, the methods to improve the catalytic efficiency of these catalysts are discussed, and future research directions are proposed. Full article

The role of coastal mangrove wetlands in sequestering atmospheric carbon dioxide has been increasingly investigated in recent years. While studies have shown that mangroves are weak sources of methane (CH₄) emissions, measurements of CH₄ fluxes from these ecosystems remain scarce. In this study, we examined the temporal variation and biophysical drivers of ecosystem-scale CH₄ fluxes in China’s northernmost mangrove ecosystem based on eddy covariance measurements obtained over a 3-year period. In this mangrove, the annual CH₄ emissions ranged from 6.15 to 9.07 g C m⁻² year⁻¹. The daily CH₄ flux reached a peak of over 0.07 g C m⁻² day⁻¹ during the summer, while the winter CH₄ flux was negligible. Latent heat, soil temperature, photosynthetically active radiation, and tide water level were the primary factors controlling CH₄ emissions. This study not only elucidates the mechanisms influencing CH₄ emissions from mangroves, strengthening the understanding of these processes but also provides a valuable benchmark dataset to validate the model-derived carbon budget estimates for these ecosystems. Full article

This study investigates the reservoir physical properties, present-day stress, hydraulic fracturing, and production capacity of No. 3 coal in the Shizhuang south block, Qinshui Basin. It analyzes the control of in situ stress on permeability and hydraulic fracturing, as well as the influence of geo-engineering parameters on coalbed methane (CBM) production capacity. Presently, the direction of maximum horizontal stress is northeast–southwest, with local variations. The stress magnitude increases with burial depth, while the stress gradient decreases. The stress field of strike-slip faults is dominant and vertically continuous. The stress field of normal faults is mostly found at depths greater than 800 m, whereas the stress field of reverse faults is typically found at depths shallower than 700 m. Permeability, ranging from 0.003 to 1.08 mD, is controlled by in situ stress and coal texture, both of which vary significantly with tectonics. Hydraulic fracturing design should consider variations in stress conditions, pre-existing fractures, depth, structural trends, and coal texture, rather than employing generic schemes. At greater depths, higher pumping rates and treatment pressures are required to reduce fracture complexity and enhance proppant filling efficiency. The Shizhuang south block is divided into five zones based on in situ stress characteristics. Zones III and IV exhibit favorable geological conditions, including high porosity, permeability, and gas content. These zones also benefit from shorter gas breakthrough times, relatively higher gas breakthrough pressures, lower daily water production, and a higher ratio of critical desorption pressure to initial reservoir pressure. Tailored fracturing fluid and proppant programs are proposed for different zones to optimize subsequent CBM development. Full article

To date, microwave radiation has been successfully used to support the chemical hydrolysis of organic substrates in the laboratory. There is a lack of studies on large-scale plants that would provide the basis for a reliable evaluation of this technology. The aim of the research was to determine the effectiveness of using microwave radiation to support the acidic and alkaline thermohydrolysis of lignocellulosic biomass prior to anaerobic digestion on a semi-industrial scale. Regardless of the pretreatment options, similar concentrations of dissolved organic compounds were observed, ranging from 99.0 ± 2.5 g/L to 115.0 ± 3.0 in the case of COD and from 33.9 ± 0.92 g/L to 38.2 ± 1.41 g/L for TOC. However, these values were more than twice as high as the values for the substrate without pretreatment. The degree of solubilisation was similar and ranged between 20 and 28% for both monitored indicators. The highest anaerobic digestion effects, ranging from 99 to 102 LCH4/kgFM, were achieved using a combined process consisting of 20 min of microwave heating, 0.10–0.20 g HCl/gTS dose, and alkaline thermohydrolysis. For the control sample, the value was only 78 LCH₄/kgFM; for the other variants, it was between 79 and 94 LCH₄/kgFM. The highest net energy gain of 3.51 kWh was achieved in the combined alkaline thermohydrolysis with NaOH doses between 0.10 and 0.20 g/gTS. The use of a prototype at the 5th technology readiness level made it possible to demonstrate that the strong technological effects of the thermohydrolysis process, as demonstrated in laboratory tests to date, do not allow for positive energy balance in most cases. This fact considerably limits the practical application of this type of solution. Full article

3-Nitrooxypropanol (3-NOP) is a nitrooxy compound that specifically targets methyl-coenzyme M reductase (MCR), ultimately resulting in a reduction in methane production. In this study, we undertook an in vitro investigation of the effects of different dosages of 3-NOP on ruminal fermentation parameters, methane production, and the microbial community. A single-factor completely randomized design was adopted, comprising a control treatment (C), where no 3-NOP was added to the fermentation substrate, and three 3-NOP treatments, where 0.025 mg (low-dose treatment, LD), 0.05 mg (medium-dose treatment, MD), or 0.1 mg (high-dose treatment, HD) was added to 1 g of fermentation substrate (DM basis), followed by incubation for 24 h in vitro. The results showed that, compared with the control treatment, the three dosages of 3-NOP reduced total gas production, methane production, and acetate production (all p < 0.01). In contrast, 3-NOP treatment increased H₂ production and the molar proportions of propionate and butyrate (all p ≤ 0.02), resulting in a decrease in the acetate-propionate ratio (p < 0.01). Meanwhile, the microbial profiles were not altered by the treatments, but the relative abundances of Prevotella, Methanobrevibacter, and Ophryoscolex were increased by the MD and HD treatments (all p < 0.01), whereas those of Methanosarcina, Methanosaeta, Sphaerochaeta, RFN20, Entodinium, and Diplodinium were decreased by the HD treatment (all p ≤ 0.03). Moreover, the results of a correlation analysis showed that there was a certain correlation between these microorganisms and total gas production, methane production, H₂ production, acetate, propionate, and butyrate. In summary, under in vitro conditions, the addition of 3-NOP to the diet affected the microbial community structure, thereby altering the ruminal fermentation pattern and reducing methane production. Our results indicated that 0.05 mg per g of dietary DM is the recommended inclusion ratio for 3-NOP in the diet of lambs. Full article

Anaerobic digestion (AD) of food waste (FW) is considered an environmentally sustainable process that can divert the disposal of FW to landfill and prevent greenhouse gas (GHG) emissions in managing the FW. Although several studies have attempted to demonstrate the AD of FW, low methane yields and a high incidence of process instability have been reported due to the rapid generation and accumulation of volatile fatty acids (VFAs). This paper reviews the recent research and development with high variation in FW composition, such as the carbon-to-nitrogen (C/N) ratio and, consequently, the effect of its physicochemical composition on process performance and methane yields. The paper highlights the significance of optimizing the anaerobic co-digestion (AcoD) of FW with carbon-rich substrates such as garden waste (GW) and/or the addition of trace elements as strategies that can improve the process performance and methane yields from FW. This review focuses on the factors effecting the feasibility of food organics and garden organics (FOGO) as a substrate for methane production. The review also critically analyses the prospects of enhancement of biomethane yield by optimizations of the impactful parameters. The progress in research related to these methods and identifying existing limitations to efficient AD of FOGO are the key findings of this review. This review also assesses the impact of nanotechnology on the process performance of the digester. The integration of FO and GO in AD processes has demonstrated enhanced biogas yields, improved process stability, and better waste management outcomes compared to the digestion of either substrate alone. Despite these advantages, challenges such as feedstock variability, process optimization, and the need for advanced pretreatment methods remain. Addressing these issues through continued research and technological innovations will be crucial for maximizing the efficiency and scalability of AD systems. Moreover, the economic feasibility and policy frameworks supporting AD need further development to promote broader adoption. Full article

Thick coal seams recorded abundant petrological, geochemical, and mineralogical information regarding their formation, which in turn can reflect the characteristics of the coal-forming environments, provenance attributes, paleoclimate, and so on. In order to explore the geochemical and lead isotope characteristics of thick coal seams, the No. 7 coal seam in the Datun mining area, Jiangsu Province of China, was selected as the research object. In this work, 29 samples (including coal, roof, and floor rock samples) were collected from three coal mines in the Datun mining area. Through an analysis of the mineral composition and element geochemical characteristics in the coal samples, the enrichment degree of trace elements and modes of rare earth elements were determined. The genetic mechanism of abnormal enrichment of enriched elements is discussed, especially the modes of occurrence and isotope characteristics of Pb. The results showed the following: (1) The main minerals in the coal samples include quartz, potassium feldspar, plagioclase, calcite, dolomite, pyrite, gypsum, and clay minerals, with clay minerals, calcite, quartz, and dolomite being the most common. (2) The major element oxides in coal mainly include SiO₂, Al₂O₃, Fe₂O₃, MgO, CaO, Na₂O, K₂O, TiO₂, P₂O₅, and FeO. In the vertical direction, the variation of SiO₂, Al₂O₃, Fe₂O₃, MgO, K₂O, and FeO in coal samples from the three coal mines is consistent. The average value of Al₂O₃/TiO₂ in the samples of Kongzhuang, Longdong, and Yaoqiao coal mines is 28.09–50.52, which basically locates the samples in the felsic source area, such that the sediment source is considered to be felsic source rock. (3) Elements U, La, Pb, and other elements are more enriched in Kongzhuang coal mine samples; elements Th, U, La, Pb, and other elements are more enriched in the Longdong coal mine samples; and elements Th, U, La, Pb, and other elements are more enriched in the Yaoqiao coal mine samples. Furthermore, W is enriched in Yaoqiao mine samples and is highly enriched in Longdong mine samples. The mining area is generally rich in the elements U, La, and Pb. The distribution curves of rare earth elements in the three mines are inclined to the right, with negative Eu anomalies. The enrichment is of the light rare earth enrichment type. (4) Pb isotope data show that the samples from the three mines are mainly distributed in the orogenic belt and the subduction zone lead source areas, where the upper crust and the mantle are mixed, with individual sample points distributed in the mantle and upper crust lead source areas. Full article

In order to clarify the gas-phase carrying capacity after the atomization of water from the bottom of deep coalbed wells, considering characteristics of atomization-assisted production and the dynamic equilibrium principle of gas–liquid two-phase flow in the wellbore, the gas-phase liquid-carrying drop model was established, and the solution method of the upstream and downstream driving force of liquid drop flow was studied. We also verified the theoretical model through physical simulation. Then, the law for the influence of droplet size, wellbore inclination, wellbore diameter, and wellhead back pressure of the critical liquid-carrying velocity in the gas phase is analyzed using the model. The results show the following: ① the larger the diameter of atomized droplets, the greater the gravity force applied to it, the worse the ability to be carried by the gas phase, a onefold increase in droplet diameter corresponds to the increase in the minimum critical velocity of the gas phase by 1.45 times; ② with the increase in wellbore inclination, the liquid-carrying capacity of the gas phase decreases, and the minimum critical liquid-carrying velocity of equal diameter droplets increases by 0.01438 m/s or 1.27 times for the increase in wellbore inclination by 10°; ③ with the increase in wellbore diameter, both the driving force of a droplet of equal diameter and the flow resistance through the gas phase in the wellbore decrease within the range of a driving pressure difference of 0.2 Mpa; the decrease in liquid-carrying velocity caused by the decrease in received flow resistance can reach the maximum value of 0.0473 m/s; ④ with the increase in wellhead back pressure, the driving force of equal-diameter droplets decreases, the resistance against passing through the high-concentration gas phase increases, and the gas-phase-carrying droplets start the game; ⑤ the atomization-assisted production has the function of drainage gas recovery, and the adoption of atomization-assisted production technology can increase the production time of a coalbed gas flowing well, enabling the wells to have a good transition time interval for the conversion of flowing wells to pumping ones, which provides a precise production dynamic basis for the efficient design and implements the overall strategy of drainage gas recovery by deep-well pumping. In short, this technology has the high-efficiency liquid-carrying function of “water atomization to help liquid-phase flow and increase gas production”, as well as obvious technical advantages, which can provide a new idea for the development of deep coalbed methane wells and other types of gas wells with water. Full article

A large amount of vegetable waste generated by farms is currently damaging the environment and public health. Anaerobic fermentation is a mature technology that significantly contributes to the recovery of energy and resources from tail vegetables and the control of environmental pollution. However, most vegetable wastes have not been utilized due to poor performance of biogas production, lack of optimal solid contents, and multiple other reasons. Herein, the anaerobic digestion biogas production performance of tail vegetables treated with different total solid (TS) content was studied using solanaceous and leafy vegetables as raw materials. Results showed that there was no acidification in all trials except for treatment with TS of 6%. The optimal TS for anaerobic fermentation of vegetable waste was determined to be around 20% in terms of methane production and biogas production efficiency. The cumulative methane production per unit of volatile solids (VSs) reached 241.7 mL CH₄/g of VS, and the methane content was about 65% during the peak period of biogas production. Theoretically, the value of methane production based on anaerobic fermentation of tail vegetables is as high as 1.8 × 10¹³~4.6 × 10¹³ L in China. This research provides advice for screening specific and efficient parameters to promote the biogas production rate by tail vegetable anaerobic fermentation. Full article

Urochloa spp. are the most important grasses for ruminants in Brazil and contain secondary metabolites, mainly saponins. Urochloa brizantha extracts (ethanolic EE and hydroalcoholic HE with 3.62 and 5.38 mg protodioscin mL⁻¹, respectively) were developed to verify their potential as additives for ruminant nutrition. The in vitro gas production technique was used to evaluate ten treatments in a completely randomized factorial arrangement (2 × 4 + 2), where the main effects were two extracts (EE and HE); four levels (50, 100, 150, and 200 mL of the extract kg⁻¹ of DM), plus two controls (one positive with 25 ppm of monensin and another with no additives). The extracts EXT (EE and HE) produced a higher proportion of acetate (C2) and lower propionate (C3) than CTL, reflected in a 31% higher C2:C3 ratio. However, there was no significant difference (p > 0.05) between the treatments for methane production parameters. Archaea and Ruminococcus’ relative gene expressions were higher in EE than in HE; however, the protozoa opposite occurred, HE was higher than EE. Fibrobacter succinogenes were 33% lower in EXT than in CTL. The addition of these extracts in a sheep diet increased the production of SCFA and decreased Fibrobacter succinogenes without altering the methane and archaeal population. Full article

In this study, the impact of bioplastic design on anaerobic digestion for biogas production was investigated. This research aims to facilitate the integration of bioplastics into a circular economy, which is why our study proposes considering not only aspects related to their degradation in the formulation but also ensuring efficient behavior in anaerobic digestion plants. Thermoplastic starch (TPS) samples, derived from different starch sources and formulated with varying concentrations of calcium carbonate and thicknesses, were subjected to anaerobic digestion tests. Three key parameters were explored: the influence of filler concentration, the effect of sample thickness, and the role of starch origin. Biogas production and kinetics were assessed using biochemical methane potential (BMP) tests. The results reveal that calcium carbonate concentration negatively influenced the methane production rate, reaching 30 NmL/gVS/day for the filler-free sample, highlighting the importance of understanding filler effects on anaerobic digestion. Additionally, thicker samples exhibited slower biogas production, with a rate of 25 NmL/gVS/day compared to 30 NmL/gVS/day for the thinnest sample, emphasizing the relevance of sample thickness in influencing digestion kinetics. The starch origin did not yield significant differences in biogas production, providing valuable insights into the feasibility of using diverse starch sources in bioplastic formulations. This study enhances our understanding of bioplastic behavior during anaerobic digestion, offering essential insights for optimizing waste management strategies and advancing circular economy practices. Full article

Performance analysis of the adsorptive separation of ethylene downstream of an oxidative coupling of methane (OCM) process, being an alternative process for converting methane content of natural gas or other methane-rich sources to ethylene, was studied in this research for a production capacity of 1 Mt/yr. This was motivated by observing promising adsorption characteristics and efficiency in the selective adsorption of ethylene using 13X zeolite-based sorbent. The energy and economic performance of alternative scenarios for retrofitting the adsorption unit into an integrated OCM process were analyzed. Simulations of the integrated OCM process scenarios include OCM unit, CO₂-hydrogenation, ethane dehydrogenation and methane reforming sections. The use of efficient ethylene adsorption separation enabled the improvement of the economic and energy efficiency of the integrated OCM process under specific operating conditions. For instance, the invested amount of energy and the associated energy cost per ton of ethylene in the cryogenic ethylene-purification section of the integrated process using adsorption unit are, respectively, 75% and 89% lower than the reference integrated OCM process. Under the conditions considered in this analysis, the return on investment for the final proposed integrated OCM process structure using adsorption separation was found to be less than 9 years, and the potential for further improvement was also discussed. Full article

The physical characteristics of coal reservoirs are important factors affecting the occurrence status of coalbed methane, as well as key factors restricting the production capacity. Therefore, taking 3# coal in Qinnan region of China as the research object, based on the actual production data of 200 coalbed methane wells in the research area, experimental testing combined with simulation analysis was used to explore the physical properties of medium and high-order reservoirs and their impact on the occurrence and production of coalbed methane. The characteristics of coalbed methane reservoir formation and production capacity changes in the research area were revealed, and the factors restricting the production capacity of coalbed methane wells were calculated using the gray correlation analysis method. The results indicate that the micropores in the coal reservoir in the study area are well-developed, while the macropores and mesopores (exogenous fractures) are underdeveloped, the surface of the micropores is complex, and the connectivity of the micropores is poor, resulting in reservoirs with high gas adsorption characteristics and low permeability. The fractal characteristics of pores and fractures can reflect the permeability characteristics of reservoirs. Permeability is positively correlated with macropores (exogenous fractures) and mesopores, and negatively correlated with micropores. There is a positive correlation between permeability and productivity, and the reservoir in the study area has a stress-sensitive boundary. The main factors restricting productivity under the complex pore and fracture system of high-rank coal reservoir were identified, and the gray relational analysis method was used to evaluate the development effect of the research area. This study provides guidance for the development of coalbed methane production in high-rank coal reservoirs. Full article

Three experiments were performed investigating bovine enteric methane (CH₄) production inhibition using a proprietary kelp blend product (PKBP) containing a halogenated methane analog (i.e., bromoform). Calves were fed a corn-silage basal diet top-dressed with the assigned treatment, with rations provided at 1.5 × NE_m in Experiments 1 and 2 (n = 12 and 6 steers, respectively) and ad libitum in Experiment 3 (n = 9 steers). In Experiment 1, we evaluated bromoform’s potency in decreasing CH₄. Dry matter intake (DMI) was not affected by treatment (p ≥ 0.11; 0 vs. 52.5 ± 10.5 ppm bromoform), whereas bromoform supplementation decreased CH₄ (p < 0.01). In Experiments 2 and 3, treatments were 0, 9.5 ± 1.5, or 20 ± 3 ppm bromoform. In Experiment 2, we examined CH₄ recovery following bromoform removal from the ration. Bromoform treatments were fed on d1, but not the subsequent 8 d, to investigate residual effects. On d1, CH₄ was below limits of detection for 20 ppm bromoform inclusion. Across days, a cubic response (p < 0.01) was observed with 20 ppm bromoform inclusion, but not with 0 and 9.5 ppm inclusion levels. Experiment 3 (30 d finishing trial) tested bromoform effects on feeder calves. DMI (p = 0.53), average daily gain (p = 0.55), and gain:feed (p = 0.82) were not influenced by bromoform inclusion. Bromoform residues were undetectable in liver, kidney, adipose, and muscle samples collected at harvest. These experiments demonstrated that cattle fed PKBP experience short-term reductions in CH₄ without tissue accumulation of bromoform and without evidence of effects on animal growth or feed consumption. Full article