Search

The present study aimed to investigate the feasibility of blended amine absorbents in improving the CO2 alkanolamine-based absorption of multicycle integrated absorption–mineralization (multicycle IAM) under standard operating conditions (20–25 °C and 1 atm). Multicycle IAM is a promising approach that transforms CO2 emissions into valuable products such as carbonates using amine solvents and waste brine. Previously, the use of monoethanolamine (MEA) as an absorbent had limitations in terms of CO2 conversion and absorbent degradation, which led to the exploration of blended alkanolamine absorbents, such as diethanolamine, triethanolamine, and aminomethyl propanol (AMP) combined with MEA. The blended absorbent was evaluated in terms of the absorption performance and carbonate production in continuous cycles of absorption, precipitation/regeneration, and preparation. The results showed that the fourth cycle of the blend of 15 wt.% AMP and 5 wt.% MEA achieved high CO2 absorption and conversion efficiency, with approximately 87% of the absorbed CO2 being converted into precipitated carbonates in 43 min and a slight degradation efficiency of approximately 45%. This blended absorbent can improve the efficiency of capturing and converting CO2 when compared to the use of a single MEA, which is one of the alternative options for the development of CO2 capture and utilization in the future. [ABSTRACT FROM AUTHOR]

Making accurate prediction of methanol price is great important for intelligent coking plant production scheduling, and it is essentially a time-series prediction problem. Efficient extraction of temporal and spatial features of methanol price data is conducive to improve the prediction accuracy of the future methanol price, and there are cyclical influences in methanol price prediction. Considering the advantages of convolutional neural networks (CNN) and gated recurrent unit (GRU) in extracting temporal and spatial features, a novel methanol price prediction method based on multicycle CNN-GRU and attention mechanism is proposed, abbreviated MCGAT. In the model construction, a parallel hybrid network architecture is designed. First, CNN is used for extracting static spatial features of methanol price data, and GRU is employed to mine its dynamic temporal features; then, the attention mechanism is utilized to fuse the static spatial and dynamic temporal features attained by CNN and GRU; finally, the methanol price prediction model-based multicycle CNN-GRU is constructed to probe into the cyclical influences. Experimental results on two real methanol price datasets in the past six years manifest the proposed MCGAT outperforms other state-of-the-art methods, and it provides a useful prediction tool of future methanol price for intelligent coking plant. [ABSTRACT FROM AUTHOR]

The amount of ultimately recoverable resources and/or timing of peak production have been the central purpose of numerous studies. One broadly applied method is Hubbert modeling, subsequently extended as multicyclic Hubbert modeling. This paper explores a modification to conventional multicyclic Hubbert modeling that we term "cycle‐jumping" wherein the overlap of multiple curves is limited and explicitly accounted for. The model is designed in a way that each curve is described by the same three parameters as a multicyclic Hubbert model, and every two curves are connected through an explicit transition. The transition width indicates the time of the shift from one curve to the next and is controlled by a weighting parameter for the respective curves. Cycle‐jumping provides a superior data fit compared to the conventional cycle‐addition model and, more important, reflects historical production data more realistically as socioeconomic and political factors important to resource production vary in time. Recommendations for Resource ManagersConventional multicyclic Hubbert modeling poorly reflects transitions in production trends.Cycle‐jumping with a finite transition period practically and mathematically provides a superior model for historical resource production by limiting the overlap of multiple curves.Cycle‐jumping with a finite transition period reflects more realistically the production profile affected by external factors including capturing inherent asymmetry in different cycles. [ABSTRACT FROM AUTHOR]

Microwave-assisted post-synthetic detemplating method was applied to remove successfully the occluded organic template from the mesoporous silica frameworks of as-synthesized SBA-15 within a short period of time compared to a conventional method, such as furnace calcination. The nitrogen adsorption/desorption isotherm studies showed that the resultant detemplated SBA-15 had a very high specific surface area of 1,271 m2/g, large pore size of 9.21 nm and high pore volume of 2.10 cm3/g; while the powder X-ray diffraction patterns and high-resolution TEM images of these support materials revealed the presence of highly ordered mesopores without any structural shrinkage. Both the microwave power and time during post-synthetic microwave irradiation were found to influence the morphological structure of the SBA-15 support. To evaluate the adsorption performance of the microwave-irradiated SBA-15 support, CO2 adsorption uptake was measured after functionalizing it with different loadings of polyethyleneimine (PEI) under 9.7% CO2/N2 mixture at 75oC. The maximum CO2 uptake was 3.63 mmol CO2/g (0.16 g/g), with an optimum PEI loading of 70 wt%. Because of the significant improvement in structural characteristics, the microwave-irradiated SBA-15 supports facilitated more PEI incorporation that contributed to about 15% higher CO2 uptake than that of conventional furnace calcined one. In addition, the sorbent demonstrated very good cyclic stability when tested over 25 cycles and for a total duration of 20 h in humid conditions. [ABSTRACT FROM AUTHOR]

Highlights • The application of fly ash in integrated CO 2 absorption and mineralisation for energy efficient CO 2 sequestration. • Low energy penalty and cost. • Detailed investigation of amine regeneration by mineralisation. Abstract The most critical challenge for the large-scale implementation of amine-based carbon dioxide (CO 2) capture is the high energy consumption of absorbent thermal regeneration. To reduce the energy requirement, absorbent thermal regeneration can be replaced by a chemical method that integrates amine scrubbing, chemical regeneration and CO 2 mineralisation in one process. However, the mechanisms of the process and the application of industrial waste as feedstocks have not been fully investigated. In the present work, we studied the integrated CO 2 absorption–mineralisation process using the benchmark solvent monoethanolamine (MEA) as an amine absorbent and fly ash as a chemical regeneration agent. We investigated the mechanism involved in the mineralisation in detail and studied the performance of MEA in regeneration by mineralisation of calcium oxide (CaO) at various CO 2 -loadings. The performance stability of MEA was verified in multicycle CO 2 absorption–mineralisation experiments. We also investigated the technical feasibility of using fly ash as a feedstock for absorbent regeneration. Our results show that MEA can be regenerated after a carbonation reaction with both calcium oxide and fly ash at 40 °C, and that the CO 2 absorbed by MEA is precipitated as calcium carbonate. Compared with traditional thermal regeneration-based CO 2 capture, the integrated CO 2 absorption–mineralisation process displays a similar cyclic CO 2 -loading (0.21 mol/mol) but has great advantages in energy reduction and capital cost savings due to the smaller energy requirement of amine regeneration and the limitation of CO 2 compression and pipeline transport. This technology has great potential for industrial application, particularly with CaO-containing wastes such as fly ash and carbide slag. [ABSTRACT FROM AUTHOR]

In this work, ordered mesoporous SBA-15 was synthesized and functionalized by polyethyleneimine (PEI). The morphological properties were characterized by N2 adsorption/desorption, field-emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HR-TEM) and Fourier transform infrared (FTIR) spectroscopy methods. The carbon dioxide (CO2) uptake on the sorbents, kinetics of CO2 adsorption/desorption and long-term multicycle stability of PEI-impregnated sorbent were measured. An optimal amine loading of 50 wt.% showed a CO2 adsorption capacity ~3.09 mmol g−1 using 10% pre-humidified CO2 at 75°C. The presence of moisture in flue gas showed a promoting effect in CO2 sorption capacity. The temperature swing adsorption/desorption cycles showed excellent multicycle stability over 60 cycles during 65 h of operations under humid CO2. [ABSTRACT FROM AUTHOR]

This paper discusses the use of one of the safest isotopes known isotopes, Kr-85, as a candidate fuel source for deep space missions. This isotope comes from 0.286% of fission events. There is a vast quantity of Kr-85 stored in spent fuel and it is continually being produced by nuclear reactors. In using Kr-85 with a novel Dual Cycle Conversion System (DCCS) it is feasible to boost the system efficiency from 26% to 45% over a single cycle device while only increasing the system mass by less than 1%. The Kr-85 isotope is the ideal fuel for a Photon Intermediate Direct Energy Conversion (PIDEC) system. PIDEC is an excellent choice for the top cycle in a DCCS. In the top cycle, ionization and excitation of the Kr-85:Cl gas mixture (99% Kr and 1% Cl) from beta particles creates KrCl* excimer photons which are efficiently absorbed by diamond photovoltaic cells on the walls of the pressure vessels. The benefit of using the DCCS is that Kr-85 is capable of operating at high temperatures in the primary cycle and the residual heat can then be converted into electrical power in the bottom cycle which uses a Stirling Engine. The design of the DCCS begins with a spherical pressure vessel of radius 13.7 cm with 3.7 cm thick walls and is filled with a Kr-85:Cl gas mixture. The inner wall has diamond photovoltaic cells attached to it and there is a sapphire window between the diamond photovoltaic cells and the Kr-85:Cl gas mixture which shields the photovoltaic cells from beta particles. The DCCS without a gamma ray shield has specific power of 6.49 W/kg. A removable 6 cm thick tungsten shield is used to safely limit the radiation exposure levels of personnel. A shadow shield remains in the payload to protect the radiation sensitive components in the flight package. The estimated specific power of the unoptimized system design in this paper is about 2.33 W/kg. The specific power of an optimized system should be higher. The Kr-85 isotope is relatively safe because it will disperse quickly in case of an accident and if it enters the lungs there is no significant biological half-life. [ABSTRACT FROM AUTHOR]

The high energy penalty of absorbent regeneration remains the most critical challenge hindering the large-scale application of amine-based carbon dioxide (CO 2 ) capture. To overcome this challenge, we developed an integrated CO 2 absorption-mineralisation (IAM) process in which the amine sorbent can be regenerated by a chemical method rather than the traditional thermal method. We investigated the technical feasibility of IAM and the associated mechanisms by adding calcium oxide or fly ash into CO 2 -loaded amine solutions, including the five commonly used amines: monoethanolamine, diethanolamine, piperazine (PZ), N-methyldiethanolamine and 2-amino-2-methy-1-propanol. The performance stability of the optimised amine was verified in multicycle experiments. We also investigated the technical feasibility of IAM in practical applications using fly ash as a feedstock for absorbent regeneration. The CO 2 absorption and mineralisation experiments were performed in a bubble column and a stirred reactor respectively. Acid titration was used to measure the CO 2 -loading of solid and liquid sample. FT-IR spectroscopy was used to analyse the species changes in the amine solutions during regeneration. The crystalline phases present in fresh and carbonated fly ash samples were determined by X-ray diffraction analysis. The results indicate that CO 2 absorbed by the five amine solutions was sequestered into carbonate precipitates at a moderate temperature (40 °C) and the amine absorbents were regenerated after carbonation reactions. PZ exhibited the largest cyclic loading (0.72 mol/mol) and regeneration efficiency (91%) among the five amines. PZ also achieved stable cyclic loading, regeneration efficiency and kinetic performance over five cycles of IAM experiments. When the industrial waste, fly ash was used, PZ displayed a cyclic loading of 4.2 mol/mol, lower than that of CaO but still 1.1 times higher than that of the thermal regeneration-based process. Compared with the traditional thermal regeneration-based CO 2 capture, the IAM process has great advantages in energy reduction and capital savings due to a larger cyclic CO 2 capacity, a requirement for less energy for amine regeneration and no need for CO 2 compression and pipeline transport. This technology has great potential for industrial applications, particularly with CaO-containing wastes, such as fly ash and other alkaline wastes. [ABSTRACT FROM AUTHOR]

Microwave-assisted post-synthetic detemplating method was applied to remove successfully the occluded organic template from the mesoporous silica frameworks of as-synthesized SBA-15 within a short period of time compared to a conventional method, such as furnace calcination. The nitrogen adsorption/desorption isotherm studies showed that the resultant detemplated SBA-15 had a very high specific surface area of 1,271 m2/g, large pore size of 9.21 nm and high pore volume of 2.10 cm3/g; while the powder X-ray diffraction patterns and high-resolution TEM images of these support materials revealed the presence of highly ordered mesopores without any structural shrinkage. Both the microwave power and time during post-synthetic microwave irradiation were found to influence the morphological structure of the SBA-15 support. To evaluate the adsorption performance of the microwave-irradiated SBA-15 support, CO2 adsorption uptake was measured after functionalizing it with different loadings of polyethyleneimine (PEI) under 9.7% CO2/N2 mixture at 75oC. The maximum CO2 uptake was 3.63 mmol CO2/g (0.16 g/g), with an optimum PEI loading of 70 wt%. Because of the significant improvement in structural characteristics, the microwave-irradiated SBA-15 supports facilitated more PEI incorporation that contributed to about 15% higher CO2 uptake than that of conventional furnace calcined one. In addition, the sorbent demonstrated very good cyclic stability when tested over 25 cycles and for a total duration of 20 h in humid conditions. [ABSTRACT FROM AUTHOR]

This study elucidates the geological and physical factors that produce polymodal grain size distributions in two dunes systems in southeastern Oaxaca, Mexico. The dune systems are characterized by (1) small embryo vegetated, transverse and undeveloped dunes; and (2) tall types identified as barchanoid, parabolic, climbing and falling dunes. We performed a best-fit statistical Weibull distribution model with data obtained by laser granulometry to determine the polymodal trends of the coastal dune sands distribution. Polymodal distributions in small dunes arise from coarse and fine-grained sands mainly derived from the erosion of alluvial deposits composed of granitic and metasedimentary rock fragments (e.g., schists, orthogneiss and paragneiss). The medium- to fine-grained sands result from wind deflation, producing a heavy mineral lag. Conversely, the polymodal grain size distributions in the tall dunes are mainly derived from the physical weathering of granites, andesitic-tuff-lava flow marine sandstones (ATLMS), alluvial deposits, and metasedimentary rock fragments (e.g., schists, orthogneiss and paragneiss) due to the frequent storms and intense winds. We constructed binary plots of grain size parameters to compare the dune sand systems in Oaxaca with some others in Mexico. Based on the sedimentary results and the Weibull distributions, we conclude that the grain sizes of the coastal dune sands from Oaxaca, Mexico, are controlled by the sand composition, wind patterns, hydrodynamic conditions, weathering effects, and physical characteristics, regardless of the dune geomorphology. Evidence of multicycle aeolian transport of sand particles in the Oaxaca coastal dunes is supported by the compositional framework of the sands and the roundness of sand grains. [Display omitted] • Oaxaca's coastal dunes in Mexico develop under complex geological and physical conditions. • The Weibull analysis supports the polymodal distributions in the Oaxaca's coastal dune sands. • Dune morphology seems not to control the diversity in grain sizes of the coastal dune sands. [ABSTRACT FROM AUTHOR]

Abstract: Multicycle optimization was carried out by assuming power sharing of each fuel batch as an independent parameter; that is, the power sharing of each fuel batch was considered as an optimization variable. The steepest descent method was used to optimize the power sharing for multiple cycles. Two different optimizations were carried out, i.e., multicycle and successive single-cycle optimizations. In the former, the power sharing of each fuel batch in each cycle was simultaneously optimized for multiple cycles. In the latter, optimization of the power sharing in a cycle was carried out, and then optimization in the next cycle was carried out. Maximization of discharge burnup and minimization of the number of fresh fuel assemblies were considered as the objective functions. The calculation results qualitatively and quantitatively clarify the implicit adverse effect of the single-cycle optimization, which is usually used in current core designs. Under the calculation conditions of the present study, the difference in the number of fresh fuel assemblies between multicycle and successive single-cycle optimizations is 2–3 fuel assemblies per cycle. Comparison of the power sharing obtained by both methods would provide insights to correct the adverse effect of the single-cycle optimization. [Copyright &y& Elsevier]

The sealing capacity of the caprock of a gas-reservoir-type underground gas storage (UGS) directly affects the safe storage and efficient utilization of natural gas, especially during a high rate of multicycle injection-withdrawal under different pressure ranges. In order to determine the safety threshold, we propose an in-situ stress-fluid coupling simulation and evaluation method to analyze the dynamic breakthrough pressure of caprock, and use the caprock samples from three UGSs to explore the evolution of the sealing capacity at alternating stress and the critical sealing capacity. We find that the fatigue effect caused by multicycle injection-withdrawal can change the pore-throat structure and enhance the in-situ sealing capacity of the caprock. Increasing gas injection pressure leads to the decline of breakthrough pressure, and the failure of capillary sealing occurs before mechanical failure. Our results show that the sealing capacity of caprock changes dynamically under in-situ effective stress during injection-withdrawal periods, and the dynamic sealing mechanism reveals the risk timing of the caprock, and guides to release the full potential of an UGS. • A novel method to evaluate dynamic sealing capacity of UGS caprock is proposed. • Safe threshold of caprock is found under in-situ stress-fluid coupling condition. • Sealing capacity of caprock changes dynamically during injection-withdrawal. • Capillary sealing failure is more likely to cause leakage than mechanical failure. [ABSTRACT FROM AUTHOR]

Abstract: The first step of forming hydrogen from carbonaceous solid fuels (coal, biomass) is gasification, followed by water gas shift reaction and separation of the carbon dioxide and hydrogen. Several processes, such as the HyP-RING process, reaction swing methodology by SIU (Southern Illinois University), chemical looping processes, etc., have been developed for hydrogen production involving the use of CaO as the carbon dioxide acceptor. In an effort to increase the purity of hydrogen in the product stream by separation of the product gases from gasification, a new process to produce Ca-based carbon dioxide sorbent with enhanced sorption capacities and life has been developed. Samples with mean sizes ranging from 5 to were produced. Repetitive calcination–carbonation reactions in pure nitrogen and carbon dioxide, respectively, were performed. Correlation of the removal efficiencies with BET surface area, pore size distribution, and particle size distribution are presented. The uptake by commercial CaO was less than 40%, while that by the commercial calcium carbonate decreased monotonously from an initial value of 52% to nearly 20% after 11 cycles. On the other hand, the uptake by the laboratory synthesized samples showed nearly 100% conversions with only a 5% decrease after 50 cycles. The reactivities of the lab-synthesized removal agents were found to be greater than 10 times that of the commercially available Ca-based sorbents. [Copyright &y& Elsevier]

Experimental investigations were carried out on a 50-I.D. multicycle pulse detonation engine (PDE) model, and liquid fuel (gasoline) was used. The average of pressure peak, as measured by piezoelectricity pressure transducer, increased versus distance to thrust wall before fully-developed detonation came into being. According to the pressure history, the pressure in detonation tube would not rise abruptly until the flame front advanced a certain distance downstream the spark. Just at that moment, two compression waves spreading to opposite direction were formed. One was enforced by combustion and became detonation rapidly. The other was weakened because of obstacles and insufficiency of fuel. Two methods were used to determine the induction length of two-phase detonation wave through the pressure history. Ignition delay time was found to be longer than deflagration-to-detonation transition (DDT) time, and the sum of the two would change little as cycle frequency increased. So they could be the most important factors controlling two-phase PDE frequency. Filling process and blowdown process were also analyzed. [ABSTRACT FROM AUTHOR]

This study aimed to investigate the influence of cyclic hot/cold shock on the change in the permeability of coal sample under different temperature gradients. The low permeability of Chinese coal seams has always hindered the exploitation and use of coalbed methane resources. In the present study, bituminous coal produced from the Xutuan Mine was selected as the test coal sample. The hot/cold shock experiments of single, multiple cycles treatment under the same temperature gradient, different temperature gradients were carried out by heating of samples in a drying oven, followed by a low-temperature treatment using liquid nitrogen. The fixed-point photography and nitrogen percolation tests were carried out on the coal samples at various stages of exposure. The results showed that the cracking effect of coal was proportional to the number and the temperature gradient of the cycle hot/cold shock treatment. After two treatments, the maximum increment of the permeability of coal samples reached 1129.79%. The permeability increment of coal sample with heating temperature of 100 °C is 2.89–6.44 times that of coal sample with 20 °C. This paper used a quadratic function to fit and discuss the seepage results of coal samples. The influence of hot/cold shock treatment on the Klinkenberg effect of nitrogen flow in coal was also analyzed. • The cracking effect of coal is proportional to the number and the temperature gradient of the hot/cold shock treatment. • The permeability curves of coal under multi-group gas pressure, confining pressure were obtained. • The influence of hot/cold shock treatment on the Klinkenberg effect of N 2 flow in coal was analyzed. [ABSTRACT FROM AUTHOR]

Flexizymes, highly flexible tRNA aminoacylation ribozymes, have enabled charging of virtually any amino acid (including non-proteogenic ones) onto tRNA molecules. Coupling to a custom-made in vitro translation system, namely the flexible in vitro translation (FIT) system, has unveiled the remarkable tolerance of the ribosome toward molecules, remote from what nature has selected to carry out its elaborate functions. Among the very diverse molecules and chemistries that have been ribosomally incorporated, a plethora of entities capable of mediating intramolecular cyclization have revolutionized the design and discovery of macrocyclic peptides. These macrocyclization reactions (which can be spontaneous, chemical, or enzymatic) have all served as tools for the discovery of peptides with natural-like structures and properties. Coupling of the FIT system and mRNA display techniques, known as the random non-standard peptide integrated discovery (RaPID) system, has in turn allowed for the simultaneous screening of trillions of macrocyclic peptides against challenging biological targets. The macrocyclization methodologies are chosen depending on the structural and functional characteristics of the desired molecule. Thus, they can emanate from the peptide's N-terminus or its side chains, attributing flexibility or rigidity, or even result in the installation of fluorescent probes.

In this paper, we prove that every vertex-transitive graph can be expressed as the edge-disjoint union of symmetric graphs. We define a multicycle graph and conjecture that every vertex-transitive graph can be expressed as the edge-disjoint union of multicycles. We verify this conjecture for several subclasses of vertex-transitive graphs, including Cayley graphs, multidimensional circulants, and vertex-transitive graphs with a prime or twice a prime number of nodes. We conclude with some open questions of interest.