Amphipathic Solvent-Assisted Synthetic Strategy for Random Lamellae of the Clinoptilolites with Flower-like Morphology and Thinner Nanosheet for Adsorption and Separation of CO2 and CH4.

The random lamellae of the synthetic CP were synthesized with a hydrothermal approach using o-Phenylenediamine (OPD) as a modifier. The decreases in the order degree of the CP synthesized in the presence of the OPD resulted from the loss of long-range order in a certain direction. Subsequently, the ultrasonic treatment and washing were conducive to further facilitate the disordered arrangements of its lamellae. The possible promotion mechanism regarding the nucleation and growth behaviors of the sol-gel particles was proposed. The fractal evolutions of the aluminosilicate species with crystallization time implied that the aluminosilicate species became gradually smooth to rough during the crystallization procedures since the amorphous structures transformed into flower-like morphologies. Their gas adsorption and separation performances indicated that the adsorption capacity of CO2 at 273 K reached up to 2.14 mmol·g-1 at 1 bar, and the selective factor (CO2/CH4) up to 3.4, much higher than that of the CPs synthesized without additive OPD. The breakthrough experiments displayed a longer breakthrough time and enhancement of CO2 uptake, showing better performance for CO2/CH4 separation. The cycling test further highlighted their efficiency for CO2/CH4 separation.

Rapid Identification Method for CH4/CO/CH4-CO Gas Mixtures Based on Electronic Nose.

The inherent cross-sensitivity of semiconductor gas sensors makes them extremely challenging to accurately detect mixed gases. In order to solve this problem, this paper designed an electronic nose (E-nose) with seven gas sensors and proposed a rapid method for identifying CH4, CO, and their mixtures. Most reported methods for E-nose were based on analyzing the entire response process and employing complex algorithms, such as neural network, which result in long time-consuming processes for gas detection and identification. To overcome these shortcomings, this paper firstly proposes a way to shorten the gas detection time by analyzing only the start stage of the E-nose response instead of the entire response process. Subsequently, two polynomial fitting methods for extracting gas features are designed according to the characteristics of the E-nose response curves. Finally, in order to shorten the time consumption of calculation and reduce the complexity of the identification model, linear discriminant analysis (LDA) is introduced to reduce the dimensionality of the extracted feature datasets, and an XGBoost-based gas identification model is trained using the LDA optimized feature datasets. The experimental results show that the proposed method can shorten the gas detection time, obtain sufficient gas features, and achieve nearly 100% identification accuracy for CH4, CO, and their mixed gases.

Conversion mechanism of thermal plasma-enhanced CH4-CO2 reforming system to syngas under the non-catalytic conditions.

Thermal plasma activation of CH4-CO2 reforming (CRM) to syngas under non-catalytic conditions is an efficient and clean technology for the large-scale utilization of hydrocarbon resources and the conversion of greenhouse gases. This study investigates the equilibrium state and transformation mechanism of a CRM reaction system activated by thermal plasma through experimental, thermodynamic, and kinetic analyses. The experimental results illustrated that the CO2 conversion rate and H2 selectivity showed a downward trend with an increase in the CO2/CH4 molar ratio, whereas the CH4 conversion rate and CO selectivity showed the opposite trend. When CO2/CH4 molar ratio was 6/4, the selectivity for CO and H2 increased to 87.0 % and 80.8 %, respectively. Excess CO2 promotes the partial oxidation of CH4 to eliminate carbon deposition, resulting in an H2/CO molar ratio value closer to 1. Thermodynamic results show that the thermal-plasma-initiated CRM reaction can reach thermodynamic equilibrium more easily than the conventional catalyzed reactions, achieving much higher feedstock gas conversion without carbon deposition. The kinetic results obtained from the PSR model revealed that CH4 and CO2 were cleaved to form free radicals at the instant of contact with the plasma flame. O, H, and other particles generated in the form of free radicals rapidly collided with each other and transformed into CO and H2, accelerating the reaction process. The results presented in this study will help reveal the transformation mechanism of the CRM reaction activated by thermal plasma under non-catalytic conditions and provide a new perspective for studying CRM reactions.

Study on key influencing factors of competitive adsorption of coalbed methane by carbon dioxide displacement.

The extraction of coal bed methane (CBM) by injecting CO2 into deeply buried unmined coal seams in competition with CH4 adsorption to provide a clean fuel is known as enhanced coal bed methane recovery (ECBM) and has proven to be an effective technological strategy to address global warming. The study of the interaction of coal with CO2 and CH4 under multi-physical field conditions is particularly necessary. In this work, a series of experiments were conducted on a home-made test system to investigate the competing sorption patterns of high and medium ash coal samples subjected to variables such as gas pressure, temperature, nodulation and lateral limit constraints. The results show that there is a sorption isotherm relationship between coal samples and exposure time. The adsorption capacity sorption of CH4/CO2 varied considerably for different ash coal samples. As the CO2 pressure increased from 2.3 to 5.5 MPa, the strain on the coal samples increased from 0.082 to 0.4%. The deformation in the vertical laminae direction is always greater than that in the parallel laminae direction. A correlation coefficient K exists between 1 and 2, and there is an internal expansion pattern in the adsorption deformation of coal. This paper can contribute to the improvement of ECBM efficiency.

[Temporal and Spatial Variation Characteristics of Methane, Carbon Dioxide, and Nitrous Oxide Concentrations and the Influencing Factors in Small Aquaculture Pond].

As an important source of greenhouse gases, the changes in greenhouse gas concentrations of aquaculture ponds are not only the basis for accurate quantification of greenhouse gases emissions but are also important for identifying their influencing factors. The spatial and temporal variation characteristics of CH4, CO2, and N2O concentrations and the influencing factors in a typical small aquaculture pond in the Yangtze River Delta were analyzed based on the headspace equilibrium-gas chromatograph method. Except in spring, the concentrations of CH4, and N2O appeared high at noon or afternoon and were influenced by water temperature. Impacted by water temperature and aquatic plant photosynthesis, the concentrations of CO2 were high in the morning when photosynthesis was weak. The concentrations of CH4 and CO2 were the highest in autumn and the lowest in winter. The mean concentrations of CH4 in autumn and winter were 176.34 nmol·L-1 and 32.75 nmol·L-1, respectively, which were mainly affected by air temperature, water temperature, and dissolved oxygen. The average CO2 concentrations in autumn and winter were 134.37 µmol·L-1 and 23.10 µmol·L-1, respectively, and were mainly affected by aquatic vegetation photosynthesis and pH. N2O concentration was the highest in summer and the lowest in winter, with mean values of 97.05 nmol·L-1 and 19.41 nmol·L-1, respectively, which were mainly affected by air temperature and water temperature. In terms of the vertical spatial variations of the three greenhouse gases, the concentration of CH4decreased with water depth in summer, and the concentration differences between the surface layer and the bottom and middle layers were 71.28 nmol·L-1 and 42.80 nmol·L-1, respectively. The concentration of CH4 increased with water depth in autumn, and the concentration difference between the bottom layer and surface layer was 163.94 nmol·L-1. The CO2 concentration increased with water depth in summer and autumn. The concentration differences between the bottom and surface concentrations were 18.69 µmol·L-1 and 29.90 µmol·L-1, respectively. N2O concentration showed no obvious change in the vertical direction. For the horizontal variations, the concentrations of CH4, CO2, and N2O in the feeding area in summer and in chicken manure in spring were approximately 1.34-1.98 times and 1.95-2.42 times those in other areas, respectively, and the concentrations of N2O and CO2 in spring and summer were approximately 1.13-1.26 times and 1.39-1.74 times those in other areas.

Biogas Conversion to Syngas Using Advanced Ni-Promoted Pyrochlore Catalysts: Effect of the CH4/CO2 Ratio.

Biogas is defined as the mixture of CH4 and CO2 produced by the anaerobic digestion of biomass. This particular mixture can be transformed in high valuable intermediates such as syngas through a process known as dry reforming (DRM). The reaction involved is highly endothermic, and catalysts capable to endure carbon deposition and metal particle sintering are required. Ni-pyrochlore catalysts have shown outstanding results in the DRM. However, most reported data deals with CH4/CO2 stoichiometric ratios resulting is a very narrow picture of the overall biogas upgrading via DRM. Therefore, this study explores the performance of an optimized Ni-doped pyrochlore, and Ni-impregnated pyrochlore catalysts in the dry reforming of methane, under different CH4/CO2 ratios, in order to simulate various representatives waste biomass feedstocks. Long-term stability tests showed that the ratio CH4/CO2 in the feed gas stream has an important influence in the catalysts' deactivation. Ni doped pyrochlore catalyst, presents less deactivation than the Ni-impregnated pyrochlore. However, biogas mixtures with a CH4 content higher than 60%, lead to a stronger deactivation in both Ni-catalysts. These results were in agreement with the thermogravimetric analysis (TGA) of the post reacted samples that showed a very limited carbon formation when using biogas mixtures with CH4 content <60%, but CH4/CO2 ratios higher than 1.25 lead to an evident carbon deposition. TGA analysis of the post reacted Ni impregnated pyrochlore, showed the highest amount of carbon deposited, even with lower stoichiometric CH4/CO2 ratios. The later result indicates that stabilization of Ni in the pyrochlore structure is vital, in order to enhance the coke resistance of this type of catalysts.

Spatial distribution of greenhouse gases (CO2 and CH4) on expressways in the megacity Shanghai, China.

Carbon dioxide (CO2) and methane (CH4) are the two major greenhouse gases (GHGs) in the atmosphere that contribute to global warming. Vehicle emissions on expressways cannot be neglected in the megacity Shanghai because oil accounts for 41% of the total primary energy consumption, and the expressway network carries 60% of the total traffic volume. The spatial distributions of CO2 and CH4 concentrations were monitored in situ on the expressways and in road tunnels using a mobile vehicle. The average CO2 and CH4 concentrations were 472.88 ± 34.48 ppm and 2033 ± 54 ppb on the expressways and 1308.92 ± 767.48 ppm and 2182 ± 112 ppb in the road tunnels in Shanghai, respectively. The highest CO2 and CH4 concentrations appeared on the Yan'an Elevated Road and the North-South Elevated Road, respectively, while their lowest values both occurred on the Huaxia Elevated Road passing through the suburban area. The hotspots of CO2 and CH4 were not consistent, suggesting that they have different sources. Tunnels had a "push-pull effect" on GHGs, and the traffic-congested Yan'an East Road Tunnel showed a dramatically increasing trend of GHG concentration from the entrance to the exit. This traffic-congested tunnel could accumulate a very high concentration of GHGs as well as other pollutants, which could introduce unhealthy conditions for both drivers and passengers. Significant correlations between CO2 and CH4 mostly appeared on the expressways and in the tunnels in Shanghai, suggesting the influences of vehicle exhaust. ΔCH4/ΔCO2 (the slope of the linear regression between CH4 and CO2) and the CH4/CO2 ratio could be used as indicators of vehicle exhaust sources because it increases from sources (e.g., road tunnels) to the observatories in the urban area.

The peculiar role of C/N and initial pH in anaerobic digestion of lactating and non-lactating water buffalo manure.

Manure from lactating and non-lactating water buffaloes was separately collected from a single dairy farm and anaerobically digested under mesophilic conditions in batch mode to produce biogas. This substrate, scarcely studied in the literature, showed two peculiarities regarding two fundamental parameters in the digestion processes: C/N ratio and initial pH. Typically, optimal C/N varies from 20 to 30, but in this work an almost negligible role of this ratio is observed. We demonstrated it by investigating a very large C/N interval, from 9.7 to 50.1, not by adding selected nutrients to the system, but exploiting the natural variation of the substrate. Concerning the pH, we show that also typically considered unfavorable conditions are feasible for this substrate. In fact, though neutral-basic initial pH is proved to be optimal to run the digestion process, in line with many other kinds of dungs, also acid initial pH leads to satisfactory CH4 yield. This is principally related to the capability of water buffalo manure of auto-modifying the pH to neutrality during the digestion, when initial pH of 5.0 and 6.0 are considered. This aspect may be relevant in co-digestion processes with acid wastes, since it may allow not adding neither a buffer, nor a pH regulator to the system. All the digestion conditions are separately tested with lactating and non-lactating water buffaloes and no statistical meaningful differences exist between the two kinds of cattle.

Process of CH4-CO2 reforming over Fe/SiC catalyst under microwave irradiation.

In this work, the properties of the CH4-CO2 reforming reaction over the Fe/SiC catalyst during the whole process were studied under microwave irradiation and the reaction process was analyzed by mass spectrometry and Fourier transfer infrared spectrometry in real time. The effects of microwave power on the gas composition, conversion of reactants, and selectivity of products in the reaction were investigated. It was found that the microwave dry reforming reaction can be divided into a rapid reaction stage, slow reaction stage, and reaction equilibrium stage. The conversion of reactants and selectivity of products in the slow reaction stage were both higher than 95% under 90 W/g. In the long-term (~50 h) stability test, a combination of SEM, XRD, BET, and TG analyses found that the catalyst activity did not reduce significantly and the amount of carbon deposits (which was mainly Cγ) was negligible (~0.78 wt%). The results indicate that the cheap Fe-based catalyst has good catalytic activity and stability under microwave irradiation and hence has a promising application.

Simulations and experimental investigations of the competitive adsorption of CH4 and CO2 on low-rank coal vitrinite.

The mechanism for the competitive adsorption of CH4 and CO2 on coal vitrinite (DV-8, maximum vitrinite reflectance R o,max = 0.58%) was revealed through simulation and experimental methods. A saturated state was reached after absorbing 17 CH4 or 22 CO2 molecules per DV-8 molecule. The functional groups (FGs) on the surface of the vitrinite can be ranked in order of decreasing CH4 and CO2 adsorption ability as follows: [-CH3] > [-C=O] > [-C-O-C-] > [-COOH] and [-C-O-C-] > [-C=O] > [-CH3] > [-COOH]. CH4 and CO2 distributed as aggregations and they were both adsorbed at the same sites on vitrinite, indicating that CO2 can replace CH4 by occupying the main adsorption sites for CH4-vitrinite. High temperatures are not conducive to the adsorption of CH4 and CO2 on vitrinite. According to the results of density functional theory (DFT) and grand canonical Monte Carlo (GCMC) calculations, vitrinite has a higher adsorption capacity for CO2 than for CH4, regardless of whether a single-component or binary adsorbate is considered. The equivalent adsorption heat (EAH) of CO2-vitrinite (23.02-23.17) is higher than that of CH4-vitrinite (9.04-9.40 kJ/mol). The EAH of CO2-vitrinite decreases more rapidly with increasing temperature than the EAH of CH4-vitrinite does, indicating in turn that the CO2-vitrinite bond weakens more quickly with increasing temperature than the CH4-vitrinite bond does. Simulation data were found to be in good accord with the corresponding experimental results.

Predicting methane emissions of lactating Danish Holstein cows using Fourier transform mid-infrared spectroscopy of milk.

Enteric methane (CH4), a potent greenhouse gas, is among the main targets of mitigation practices for the dairy industry. A measurement technique that is rapid, inexpensive, easy to use, and applicable at the population level is desired to estimate CH4 emission from dairy cows. In the present study, feasibility of milk Fourier transform mid-infrared (FT-IR) spectral profiles as a predictor for CH4:CO2 ratio and CH4 production (L/d) is explained. The partial least squares regression method was used to develop the prediction models. The models were validated using different random test sets, which are independent from the training set by leaving out records of 20% cows for validation and keeping records of 80% of cows for training the model. The data set consisted of 3,623 records from 500 Danish Holstein cows from both experimental and commercial farms. For both CH4:CO2 ratio and CH4 production, low prediction accuracies were found when models were obtained using FT-IR spectra. Validated coefficient of determination (R2Val) = 0.21 with validated model error root mean squared error of prediction (RMSEP) = 0.0114 L/d for CH4:CO2 ratio, and R2Val = 0.13 with RMSEP = 111 L/d for CH4 production. The important spectral wavenumbers selected using the recursive partial least squares method represented major milk components fat, protein, and lactose regions of the spectra. When fat and protein predicted by FT-IR were used instead of full spectra, a low R2Val of 0.07 was obtained for both CH4:CO2 ratio and CH4 production prediction. Other spectral wavenumbers related to lactose (carbohydrate) or additional wavenumbers related to fat or protein (amide II) are providing additional variation when using the full spectral profile. For CH4:CO2 ratio prediction, integration of FT-IR with other factors such as milk yield, herd, and lactation stage showed improvement in the prediction accuracy. However, overall prediction accuracy remained modest; R2Val increased to 0.31 with RMSEP = 0.0105. For prediction of CH4 production, the added value of FT-IR along with the aforementioned traits was marginal. These results indicated that for CH4 production prediction, FT-IR profiles reflect primarily information related to milk yield, herd, and lactation stage rather than individual milk fatty acids related to CH4 emission. Thus, it is not feasible to predict CH4 emission based on FT-IR spectra alone.

Responses of greenhouse gas fluxes to experimental warming in wheat season under conventional tillage and no-tillage fields.

Understanding the effects of warming on greenhouse gas (GHG, such as N2O, CH4 and CO2) feedbacks to climate change represents the major environmental issue. However, little information is available on how warming effects on GHG fluxes in farmland of North China Plain (NCP). An infrared warming simulation experiment was used to assess the responses of N2O, CH4 and CO2 to warming in wheat season of 2012-2014 from conventional tillage (CT) and no-tillage (NT) systems. The results showed that warming increased cumulative N2O emission by 7.7% in CT but decreased it by 9.7% in NT fields (p<0.05). Cumulative CH4 uptake and CO2 emission were increased by 28.7%-51.7% and 6.3%-15.9% in both two tillage systems, respectively (p<0.05). The stepwise regressions relationship between GHG fluxes and soil temperature and soil moisture indicated that the supply soil moisture due to irrigation and precipitation would enhance the positive warming effects on GHG fluxes in two wheat seasons. However, in 2013, the long-term drought stress due to infrared warming and less precipitation decreased N2O and CO2 emission in warmed treatments. In contrast, warming during this time increased CH4 emission from deep soil depth. Across two years wheat seasons, warming significantly decreased by 30.3% and 63.9% sustained-flux global warming potential (SGWP) of N2O and CH4 expressed as CO2 equivalent in CT and NT fields, respectively. However, increase in soil CO2 emission indicated that future warming projection might provide positive feedback between soil C release and global warming in NCP.

Improvement in CH4/CO2 ratio and CH4 yield as related to biomass mix composition during anaerobic co-digestion.

Sixteen data sets (two of which were measured in this study) with a combined total of 145 measurements of ultimate methane yield (UMY) during mono- and co-digestion of ternary biomass mixtures were used to assess impact of co-digestion on the relative change in UMY (ΔUMY) as a function of biomass mix composition. The data involved 9 biomass materials (brewery spent grains, chicken manure, cow manure, fresh grass clippings, pig manure, primary sewage sludge, vegetable food waste, wheat straw, and rice straw). Results of the assessment shows that co-digestion in 85% of yields positive values of ΔUMY regardless of the biomass materials used, however, a smaller fraction (15%) resulted in negative ΔUMY during co-digestion. The data further indicate that for each set of ternary biomass material mixtures there exists an optimal biomass mix composition at which ΔUMY is at a maximum. Statistical analyses based on the data used here indicate that the maximum value of ΔUMY (ΔUMYmax) is always positive regardless of biomass materials being co-digested.

Improving biogas quality and methane yield via co-digestion of agricultural and urban biomass wastes.

Impact of co-digestion versus mono-digestion on biogas and CH4 yield for a set of five biomass materials (vegetable food waste, cow dung, pig manure, grass clippings, and chicken manure) was investigated considering 95 different biomass mixes of the five materials under thermophilic conditions in bench-scale batch experiments over a period of 65days. Average biogas and CH4 yields were significantly higher during co-digestion than during mono-digestion of the same materials. This improvement was most significant for co-digestion experiments involving three biomass types, although it was independent of the specific biomasses being co-digested. Improvement in CH4 production was further more prominent early in the digestion process during co-digestion compared to mono-digestion. Co-digestion also appeared to increase the ultimate CH4/CO2 ratio of the gas produced compared to mono-digestion although this tendency was relatively weak and not statistically significant.

Sono-synthesis and characterization of bimetallic Ni-Co/Al2O3-MgO nanocatalyst: Effects of metal content on catalytic properties and activity for hydrogen production via CO2 reforming of CH4.

Sono-dispersion of Ni, Co and Ni-Co over Al2O3-MgO with Al/Mg ratio of 1.5 was prepared and tested for dry reforming of methane. The samples were characterized by XRD, FESEM, PSD, EDX, TEM, BET and FTIR analyses. In order to assess the effect of ultrasound irradiation, Ni-Co/Al2O3-MgO with Co content of 8% prepared via sonochemistry and impregnation methods. The sono-synthesized sample showed better textural properties and higher activity than that of impregnated one. Comparison of XRD patterns indicated that the NiO peaks became broader by increasing Co content over the support. The FESEM images displayed the particles are small and well-dispersed as a result of sonochemistry method. Also, EDX analysis demonstrated better dispersion of Ni and Co as a result of sonochemistry method in confirmation of XRD analysis. The sono-synthesized Ni-Co/Al2O3-MgO as a superior nanocatalyst with Co content of 3% illustrates much higher conversions (97.5% and 99% for CH4 and CO2 at 850 °C), yields (94% and 96% for H2 and CO at 850 °C) and 0.97 of H2/CO molar ratio in all samples using an equimolar feed ratio at 850 °C. During the 1200 min stability test, H2/CO molar ratio remained constant for the superior nanocatalyst.