合成氨空压机的运行维护管理

从合成氨装置新空压机在运行中的日常运行维护、停机保护和机组常见故障几个方面进行阐述，对故障发生的原因进行了分析，提出了解决方法，以实现机组的安全、稳定运行。     

Amino-group and space-confinement assisted synthesis of small and well-defined Rh nanoparticles as efficient catalysts toward ammonia borane hydrolysis

Hydrogen evolution from ammonia borane (AB) hydrolysis is of great importance considering the ever-increasing demand for green and sustainable energy. However, the development of a facile and efficient strategy to construct high-performance catalysts remains a grand challenge. Herein, we report an amino-group and space-confinement assisted strategy to fabricate Rh nanoparticles (NPs) using amino-functionalized metal-organic-frameworks (UiO-66-NH₂) as a NP matrix (Rh/UiO-66-NH₂). Owing to the coordination effect of amino-group and space-confinement of UiO-66-NH₂, small and well-distributed Rh NPs with a diameter of 3.38 nm are successfully achieved, which can be served as efficient catalysts for AB hydrolysis at room temperature. The maximum turnover frequency of 876.7 min^?1 is obtained by using the Rh/UiO-66-NH₂ with an optimal Rh loading of 4.38 wt% and AB concentration of 0.2 M at 25 °C, outperforming most of the previously developed Rh-based catalysts. The catalyst is also stable in repetitive cycles for five times. The high performance of this catalyst must be ascribed to the structural properties of UiO-66-NH₂, which enable the formation of small and well-dispersed Rh NPs with abundant accessible active sites. This study provides a simple and efficient method to significantly enhance the catalytic performance of Rh for AB hydrolysis.     

One-step synthesis of Cu@FeNi core–shell nanoparticles: Highly active catalyst for hydrolytic dehydrogenation of ammonia borane

This paper investigates a facile and one-step synthesis of trimetallic magnetic Cu@FeNi core–shell nanoparticles, which are composed of crystalline Cu cores and amorphous FeNi shells, at room temperature under ambient atmosphere within 2 min. It is found that among the Cu@FeNi system, Cu_0.4@Fe_0.1Ni_0.5 shows the best synergistic performance for catalyzing the hydrolytic dehydrogenation of ammonia borane with the activation energy of 32.9 kJ/mol, being lower than most of the reported data, and the catalytic activity of Cu_0.4@Fe_0.1Ni_0.5 is much better than its monometallic, bimetallic and trimetallic counterparts whether in states of pure metals, alloys or physical mixtures. Further, the present catalyst has a good recycle stability with an easy magnetic separation method.     

Evaluation of hydrogen producing cultures using pretreated food waste

In order to enhance bio-hydrogen production from food waste, pretreatment methods are widely used. The influence of the initial pH and autoclaving were investigated in batch experiments. Fermentative studies showed that pure cultures like Clostridium beijerinckii could directly utilize raw food waste to produce hydrogen, while other cultures (Clostridium butyricum and Clostridium pasteurianum) could produce hydrogen only after pH adjustment. In this case, the optimal starting pH of the culture was found to be 7. Autoclaving could further enhance hydrogen yields due to increased hydrolysis of food waste. The maximum hydrogen yield was achieved by C. butyricum (38.9 mL-H₂/g-VS_added) after autoclaving food waste with pH adjustment at 7. In addition, the ratio acetic to butyric acid was decreased by autoclaving pretreatment, because butyrate metabolic pathway was favored in the fermentation process. However, suitable pH for bacteria growth and the low ammonia production could be achieved from autoclaving food waste.     

Ammonia borane thermolytic decomposition in the presence of metal (II) chlorides

In the present work, we studied the effect of metal chlorides, MCl₂, on the thermal decomposition of ammonia borane NH₃BH₃ (AB). Some metals from row n = 4 of the periodic table were chosen and used as MCl₂: namely, FeCl₂, CoCl₂, NiCl₂, CuCl₂, and ZnCl₂. In addition, three metals from column VIII of the periodic table were considered: NiCl₂, PdCl₂ and PtCl₂. The AB decomposition was followed by TGA and DSC; the decomposition gases analyzed by μGC/MSD coupling, and the solid by-products identified by XRD, IR and XPS. We observed that the presence of CuCl₂ in AB is beneficial, making the decomposition occur in much milder conditions than for pristine AB; for example, the dehydrogenation of CuCl₂-doped AB started at 25 °C, with the sample losing about 14 wt% at 85 °C. However, MCl₂ does not hinder the evolution of the undesired borazine; it only contributes to a decrease in its content compared to pristine AB. To rationalize the better performance of CuCl₂, we propose that Cu offers an optimal doping activity with intermediate binding energies for the intermediates: i.e. with H not too strongly bonded but optimally bonded to the N of AB. The germ Cu?NH₂–BH₂, then formed, acts as a Lewis acid through B and has an optimized reactivity towards a new AB molecule (head-to-tail dehydrocoupling). This is discussed herein.     

The flame propagation characteristics and detonation parameters of ammonia/oxygen in a large-scale horizontal tube: As a carbon-free fuel and hydrogen-energy carrier

As a carbon-free fuel and a hydrogen-energy carrier, ammonia is a potential candidate for future energy utilization. Therefore, in order to promote the application of ammonia in detonation engines and to evaluate the safety of ammonia related industrial process, DDT experiments for ammonia/oxygen mixtures with different ERs were carried out in a large-scale horizontal tube. Moreover, pressure transducers and self-developed temperature sensors were applied to record the overpressure and the instantaneous flame temperature during DDT process. The results show that the DDT process in ammonia/oxygen mixtures contains four stages: Slow propagation stage, Flame and pressure wave acceleration stage, Fast propagation and detonation wave formation stage, Detonation wave self-sustained propagation stage. For stoichiometric ammonia/oxygen mixtures, flame front and the leading shock wave propagate one after another with different velocity, until they closely coupled and propagated together with one steady velocity. At the same time, it is found that an interesting retonation wave propagates backward. The peak overpressure, detonation velocity, and flame temperature of the self-sustained detonation are 2 MPa, 2000 m/s and 3500 K, respectively. With the ER increased from 0.6 to 1.6, the detonation velocities and peak overpressures ranged from 2310 m/s to 2480 m/s and 25.6 bar–28.7 bar, respectively. In addition, the detonation parameters of ammonia were compared with those of methane and hydrogen to evaluate the detonation performance and destructiveness of ammonia.     

The dispersed SiO2 microspheres supported Ru catalyst with enhanced activity for ammonia decomposition

Ru nanoparticles supported on SiO₂ microspheres (Ru/SiO₂-GUS) were prepared by the glucose-urea-metallic salt method and applied in the decomposition of ammonia. In the glucose-urea-metallic salt method, glucose as the carbon template plays a significant role in the formation of diffusion-beneficial structural properties of Ru/SiO₂-GUS, and also induceds the modification of the electronic state of Ru. Ru/SiO₂-GUS exhibited higher catalytic activity compared with the catalyst prepared with the impregnation method. The catalytic performance of Ru/SiO₂-GUS was further enhanced with the addition of either K or Cs——the addition order and amount strongly affecting the catalytic performance. When the ratio of K/Cs to Ru is 2, the alkali metal (KOH/CsOH) solution is added in the homogeneous solution of glucose, urea, RuCl₃ and the colloidal silica, the promotion effect of K/Cs is the strongest, particularly under lower reaction temperatures. However, the promotion effects of K and Cs are different as reveled by the combined results of H₂-TPR, XPS and NH₃-TPSR. More NH₃ can be absorbed on K–Ru/SiO₂-GUS and the electron density of Ru decreased. By contrast, more metallic Ru formed on Cs–Ru/SiO₂-GUS, facilitating N₂ recombination.     

The cost of production and storage of renewable hydrogen in South Africa and transport to Japan and EU up to 2050 under different scenarios

The decarbonisation of hard-to-abate sectors globally will require significant volumes of carbon-free hydrogen. An investigation has been performed to determine the cost at which hydrogen can be generated by electrolysis using renewable electricity in South Africa between 2020 and 2050; stored in suitable carriers: liquid organic hydrogen carrier (LOHC), cryogenic liquid hydrogen, and ammonia; then shipped to Japan and EU. Renewable electrolysis hydrogen is produced at lowest cost in South Africa using electricity generated by a hybrid fleet of wind and single-axis tracking PV power plants, using large-scale alkaline electrolyser plants. Hydrogen is converted and stored at lowest cost as LOHC, but delivered to Japan at lowest cost as ammonia. It may be delivered to Japan at or below the Japanese target cost of US $3/kg or €2.50/kg by 2030 (when bulk imports are planned to begin) in one of two ways: firstly by reconverting the ammonia carrier to gaseous hydrogen, provided that concessionary finance allows a maximum weighted average cost of capital (WACC) of 3% the for renewable power and electrolyser infrastructure, or secondly as ammonia for direct use (without reconversion to gaseous hydrogen), provided concessionary finance allows a maximum WACC of 6%. In any event, the landed target price may be met for gaseous hydrogen by 2040 (when hydrogen imports must be carbon-free) at a WACC of up to 6%.     

Modeling and optimization of ammonia process: Effect of hydrogen unit performance on the ammonia yield

The main object of this research is the development of a mathematical framework to simulate a commercial ammonia plant and obtaining the optimal operating conditions of process at steady state condition. The considered ammonia plant consists of steam and autothermal reforming reactors, low and high temperature shift converters, hydrogen purification section, methanation, and ammonia synthesis reactors. The catalytic reactors are heterogeneously modeled based on the mass and energy balance equations considering heat and mass transfer resistances in the gas and catalyst phases. In addition, an equilibrium model is applied to simulate the absorption column. Then, the accuracy of developed framework is investigated against plant data. The results show that the internal mass transfer resistance in the commercial catalyst limits the syngas production in the reforming section. In the second step, an optimization problem is formulated to enhance the ammonia production considering safety and operating limitations. The formulated optimization problem is handled employing the genetic algorithm. The results show that more syngas production in the optimized hydrogen unit is one of the main reasons for higher ammonia synthesis in the considered plant. Applying optimal conditions on the process increases ammonia production potential from 1890 to 2179 mol s⁻¹.     

Hierarchically alloyed Pd–Cu microarchitecture with tunable shapes: Morphological engineering,and catalysis for hydrogen evolution reaction of ammonia borane

Some uniquely microstructured bi/poly-metal alloys containing lesser or no noble metal have been testified to be cost-effective catalysts suitable for solvolytic dehydrogenation of ammonia borane, which expects the intensive study on their morphological engineering and synergistic mechanism. To this, we here introduce a facile and flexible fabricating protocol, i.e. stepwise wet-chemical reduction route, to purposefully modulate the orientated growth of Pd–Cu alloyed crystals via joint operation of adding suitable additives and adjusting temperature. The characterization of phase composition and evaluation of catalytic ability regarding as-fabricated Pd–Cu nanocrystals with diverse morphological features (e.g. concave tetrahedron, cube, polyhedron, nanosphere, nanowire, worm-like, seaurchin-like, flower-like, etc.) demonstrates that the nanocrystals have homogeneous alloyed phase, holding significantly enhanced catalytic activity and durability. The formation of synergistic effect due to charge transfer from Cu to Pd gives rise to electron enrichment around Pd atomic nucleus, facilitating the adsorption of H to form metal-H species, thus promoting the dehydrogenation of ammonia borane. The difference of catalytic activity of the Pd–Cu nanocrystals with different shapes reveals their morphologic dependent nature, endowing the uniquely shaped bimetal nanocrystals with exceptional catalytic performance. The concave tetrahedron shaped Pd–Cu alloyed nanocrystals hold the excellent catalytic activity almost equivalent to that of noble metal Pd, catalyzing hydrolytic reaction of ammonia borane at 298 K with the apparent activation energy of 31.18 kJ/mol, and maintaining 89% of the incipient catalytic ability after 5 recycling runs. Theoretically, the suggested morphologic tuning strategy can be also applied in fabricating other bi/poly metal alloy catalysts, with great practical potential and development prospects.