Estimation of methane production for batch technology – A new approach

In the case of agricultural biogas plants it is the living microorganisms (mainly archaea) that determine the amount of methane produced. If the conditions in the digester are not adequate or the substrates are selected incorrectly, the microorganisms will not be able to develop properly and methane production will also be low or none. Therefore, in the first place the influence of individual factors on the production of methane was analysed. Next, based on the conclusions drawn from the analysis of the factors, a mathematical model was developed that will facilitate the selection of appropriate substrates and process parameters by future investors building agricultural biogas plants. The aim of the study was to demonstrate the impact of the factors on the production of methane and to present a mathematical model for estimating methane production for batch technology used in agricultural biogas plants (this kind of production is also used in laboratories for testing specific substrates). The model presented in the paper has been developed and tested on a group of over seventy substrates of agricultural origin. The inclusion of many factors determining methane production in the model is not complicated as each of the factors is easy to measure.     

Simple synthesis of Cu2O–CoO nanoplates with enhanced catalytic activity for hydrogen production from ammonia borane hydrolysis

The development of inexpensive and high performing catalysts for ammonia borane (NH₃BH₃) hydrolysis is crucial for hydrogen production. In our research, a high-performance plate-like Cu₂O–CoO nanocomposite catalyst for NH₃BH₃ hydrolysis has been developed for the first time. In the hydrolytic reaction, both Cu₂O and CoO are separately inactive, while Cu₂O–CoO nanoplates show a high turnover frequency of 34.1 mol_hydrogen min⁻¹ mol_cat⁻¹, which is attributed to the synergistic effect between Cu₂O and CoO. It is interesting to discover that the induction time for the hydrolytic reaction is reduced to null when a small amount of Cu₂O is introduced into CoO. The reaction kinetics of NH₃BH₃ hydrolysis catalyzed by Cu₂O–CoO is also investigated. This work may provide other researchers some valuable insights into designing inexpensive and synergistic catalysts with enhanced catalytic activity for NH₃BH₃ hydrolysis for hydrogen production.     

Transition metal tuned semiconductor photocatalyst CuCo/β-SiC catalyze hydrolysis of ammonia borane to hydrogen evolution

In the study, a novel approach of Cu, Co tuned photocatalyst β-SiC catalyze hydrolysis of ammonia borane was proposed as a means to boost H₂ evolution. Electronic properties including band structure and DOS of β-SiC and CuCo/β-SiC are calculated. In addition, the hydrolysis mechanism of AB and photocatalytic boosting mechanism of AB hydrolysis on the catalyst CuCo/β-SiC are discussed. The systematic investigation showed that the transition metal atom (Cu, Co) can tune the electronic properties of the β-SiC, and reduce the band gap of semiconductor catalyst β-SiC from the value of 2.739eV–0.535eV. Which makes the β-SiC response to the wider UV–Vis spectrum, and transition metal atom (Cu, Co) tuned β-SiC can help to boost the photocatalytic quantum efficiency of photocatalytic AB hydrolysis reaction. In the process of CuCo/β-SiC catalyzed AB hydrolysis, the reaction path can be described in three key steps: At first, CuCo/β-SiC bond to B of AB, induce the BH bond activation, then H₃B- attacked by a H₂O molecule, which contributes to the concerted dissociation of BN bond. Finally, via BH₃ hydrolysis and produce the borate ion accompanied by the H₂ produce. In the reaction of AB hydrolysis, the reaction barrier step is the step of H₂O molecule attack BH₃, and its energy barrier is 31.44 kcal/mol. In addition, the synergistic hydrolyze and photolyze AB to H₂ evolution mechanism was first proposed due to AB can be photocatalyzed by semiconductor photocatalyst β-SiC and conventional catalyzed by the metal catalyst.     

Using three chemical looping reactors in ammonia production process – A novel plant configuration for a green production

Production of three pure streams of H₂, N₂ and CO₂ makes the chemical looping reactors as an attractive intermediate technology to provide the feedstock of ammonia synthesis loop. As a goal of paper, for the first time, a novel and green plant configuration using three chemical looping reactors is proposed for ammonia production in which needed hydrogen and nitrogen are produced by means of a process simpler than the conventional technologies. Due to the reduction in plant units and also 30% increase in production ratio and simultaneously production of economically valuable by-products of H₂, N₂ and CO₂, significant potential for investment cost reduction along with CO₂ capture and storage can be anticipated. Moreover, the proposed plant for ammonia production is very flexible in terms of adjusting the desired main products.     

An effective synthesis route for improving the catalytic activity of carbon-supported Co–B catalyst for hydrogen generation through hydrolysis of NaBH4

A novel method for synthesis of carbon-supported cobalt boride catalyst was developed for hydrogen generation from catalytic hydrolysis of NaBH₄ solution. The activated carbon and carbon black supported catalysts prepared by “reduction–precipitation” method were found to be much more active than those prepared by conventional “impregnation–reduction” method inspite of the same Co content. A maximum hydrogen generation was achieved using carbon black supported Co–B, which lowers the activation energy to 56.7 kJ mol⁻¹. The effects of NaOH concentration (1–15 wt.%), NaBH₄ concentration (5–20 wt.%) and reaction temperature (25–40 °C) on the performance of the most active catalyst (Co–B/C_B) were investigated in detail. The results indicated that this catalyst can be used in a hydrogen generator for mobile applications such as PEMFC systems due to its high catalytic activity and simple preparation method.     

Technoeconomics of large-scale clean hydrogen production – A review

Hydrogen is widely used in many industries, yet its role in the clean energy transition goes beyond being an element of these industries. Near-term practical large-scale clean hydrogen production can be made available by involving nuclear, solar, and other renewable energy sources in the process of hydrogen production, and coupling their energy systems to sustainable carbon-free hydrogen technologies. This requires further investigation and assessment of the different alternatives to achieve clean hydrogen using these pathways. This paper assesses the technoeconomics of promising hydrogen technologies that can be coupled to nuclear and solar energy systems for large-scale hydrogen production. It also provides an overview of the design, status and advances of these technologies.     

Synthesis of Cu@FeCo core–shell nanoparticles for the catalytic hydrolysis of ammonia borane

Non-noble Cu@FeCo core–shell nanoparticles (NPs) containing Cu cores and FeCo shells have been successfully in situ synthesized via a facile chemical reduction method. The NPs exerted composition-dependent activities towards the catalytic hydrolysis of ammonia borane (NH₃BH₃, AB). Among them, the Cu_0.3@Fe_0.1Co_0.6 NPs showed the best catalytic activity, with which the max hydrogen generation rate of AB can reach to 6674.2 mL min⁻¹ g⁻¹ at 298 K. Kinetic studies demonstrated that the hydrolysis of AB catalysed by Cu_0.3@Fe_0.1Co_0.6 NPs was the first order with respect to the catalyst concentration. The activation energy (Ea) was calculated to be 38.75 kJ mol⁻¹. Furthermore, the TOF value (mol of H₂. (mol of catalyst. min)⁻¹) of Cu_0.3@Fe_0.1Co_0.6 NPs was 10.5, which was one of the best catalysts in the previous reports. The enhanced catalytic activity was largely attributed to the preferable synergistic effect of Cu, Fe and Co in the special core–shell structured NPs.     

Electric system management through hydrogen production – A market driven approach in the French context

Hydrogen is usually presented as a promising energy carrier that has a major role to play in low carbon transportation, through the use of fuel cells. However, such a development is not expected in the short term. In the meantime, hydrogen may also contribute to reduce carbon emissions in diverse sectors among which methanol production. Methanol can be produced by combining carbon dioxide and hydrogen, hence facilitating carbon dioxide emission mitigation while providing a beneficial tool to manage the electric system, if hydrogen is produced by alkaline electrolysis operated in a variable way driven by the spot and balancing electricity markets. Such a concept is promoted by the VItESSE² project (Industrial and Energy value of CO₂ through Efficient use of CO₂-free electricity - Electricity Network System Control & Electricity Storage). Through the proposed market driven approach, hydrogen production offers a possibility to help managing the electric system, together with an opportunity to reduce hydrogen production costs.     

Flow characteristics of refrigerants flowing through capillary tubes – A review

A comprehensive review of the literature on the flow of various refrigerants through the capillary tubes of different geometries viz. straight and coiled and flow configurations viz. adiabatic and diabatic, has been discussed in this paper. The paper presents in chronological order the experimental and numerical investigations systematically under different categories. Flow aspects like effect of coiling and effect of oil in the refrigerants on the mass flow rate through the capillary tube have been discussed. Furthermore, the phenomenon of metastability and the correlations to predict the underpressure of vaporization have also been discussed. The paper provides key information about the range of input parameters viz. tube diameter, tube length, surface roughness, coil pitch and coil diameter, inlet subcooling and condensing pressure or temperature. Other information includes type of refrigerants used, correlations proposed and methodology adopted in the analysis of flow through the capillary tubes of different geometries operating under adiabatic and diabatic flow conditions. It has been found from the review of the literature that there is a lot more to investigate for the flow of various refrigerants through different capillary tube geometries.     

Electrochemical template synthesis of Ni–Cu bilayer hollow microtubes for green hydrogen production through electrocatalytic reforming of ethanol

This article is devoted to the investigation of the processes occurring at the synthesis of Ni–Cu hollow tubes (NC-HT) and their application as an electrocatalyst in the hydrogen evolution reaction from water-ethanol solution. The reactions at the electrochemical reduction of CuO to Cu and during the electrodeposition of nickel were investigated by chronopotentiometry. Depending on the thickness of the nickel layer, morphology (SEM) and chemical composition (EDX-mapping, XRD) of tubes, as well as electrocatalytic activity (CVA, ECSA, TOF, and stability tests) were studied. The synthesized materials have a structure with a high electrochemically active surface area (ECSA) from 1.38 to 3.50 m²g^-1, which makes it possible to fulfill low activation overpotential values equal to ?86 and ?250 mV at 10 and 50 mAcm^?2 after 100 cycles. The stability test results demonstrate the overpotential values ?160, ?183, ?265 mV for NC-HT15, NC-HT30, and NC-HT60, respectively, after 24 h examinations.     

Information and communication technologies – A new round of household electrification

Information and communication technologies (ICTs) increasingly permeate everyday life in industrialized societies. The aim of this paper is to explore ICT-related transformations of everyday practices and discuss the implications, particularly for residential electricity consumption. The present socio-technical changes are seen in a historical perspective, and it is argued that the integration of ICT into everyday practices can be seen as a new round of household electrification, comparable to earlier rounds that also led to higher electricity consumption. A case study carried out in Denmark in 2007–2008 explores the present changes in everyday life. Based on qualitative interviews, the study focuses on people's ways of integrating ICTs into their everyday practices, on any significant changes in these practices, and on the influence of the changed practices on electricity consumption. The paper concludes with a discussion on the implications for energy policy.     

Biodiesel resources and production technologies – A review

The environmental concern and availability of fuels are greatly affecting the trends of fuels for transportation vehicles. Biodiesel is one of the options as alternative transport fuel. This can be produced from straight vegetable oils (SVOs), oils extracted from various plant species and animal fats. Amongst many resources, availability and cost economy are the major factors affecting the large scale production of the biodiesels. The transesterification is one of the production processes for biodiesel, but incomplete esterification of all fatty acids in the starting material, lengthy purification methods such as water washing, relatively long reaction times, contamination and separation difficulties associated with co-production of glycerol and saponification of the starting material under certain reaction conditions are still being major challenges in the biodiesel production. Technological advancement and enhanced production methods are the demand of present time for large scale and sustainable production of biodiesel. In the present paper, comprehensive review on its production process, feed stock and its applications have been made. From many case studies it was concluded that engine performance with B20 biodiesel blends, and mineral diesel were found comparable.     

A new frontier of nanofluid research – Application of nanofluids in heat pipes

Nanofluid is a new kind of working fluid with special properties to enhance the heat transfer of heat pipes. This paper reviews and summarizes the research done on heat pipes using nanofluids as working fluids in recent years. The effect of characteristics and mass concentrations of nanoparticles on the thermal performance in various kinds of heat pipes with different base fluids under various operating conditions have been discussed. The mechanism of enhancement or degradation of heat transfer utilizing nanofluids in the investigated heat pipes has been explained. The paper discusses the relative reduction of the total heat resistance for various heat pipes with nanofluids in comparison with the existing ones and also presents a perspective on possible future research applications.     

Nanocrystalline cobalt–nickel–boron (metal boride) catalysts for efficient hydrogen production from the hydrolysis of sodium borohydride

Innovative metal boride nanocatalysts containing crystalline Co–Ni based binary/ternary boride phases were synthesized and used in the hydrolysis of NaBH₄. All the as-prepared catalysts were in high-purity with average particle sizes ranging between ~51 and 94 nm and consisting of different crystalline phases (e.g. CoB, Co₂B, Co₅B₁₆, NiB, Ni₄B₃, Ni₂Co_0·67B_0.33). The synergetic effect of the different binary/ternary boride phases in the composite catalysts had a positive role on the catalytic performances thus, while the binary boride containing phases of unstable cobalt borides or single Ni₄B₃ were not showing any catalytic activity. The Co–Ni–B based catalyst containing crystalline phases of CoB–Ni₄B₃ exhibited the highest H₂ production rate (500.0 mL H₂ min^?1 g_cat^?1), with an apparent activation energy of 32.7 kJ/mol. The recyclability evaluations showed that the catalyst provides stability even after the 5th cycle. The results suggested that the composite structures demonstrate favorable catalytic properties compared to those of their single components and they can be used as alternative and stable catalysts for efficient hydrogen production from sodium borohydride.     

Preparation and catalytic activity of thin-film cobalt–tungsten–boron for the hydrolysis of ammonia borane

In this work, cobalt–tungsten–boron nanoparticles (Co–W–B) have been successfully deposited on foam Ni to manufacture thin-film catalysts by electroless plating technique and applied in hydrogen generation from ammonia borane (NH₃BH₃) hydrolysis. Physicochemical properties of Co–W–B nanoparticles are characterized by XRD (Powder X–ray diffraction), SEM (Scanning electron microscopy), and EDS (Energy dispersive X–ray spectroscopy). It is observed that Co–W–B showed irregular spherical structure on the surface of foam Ni substrate. An increase of depositional pH value in the preparation process leads to the change of particle size. When the pH value is equal to 11.5, as-synthesized Co–W–B exhibits the smaller particle size, which suggests that depositional pH value has directly impacted the nucleation and growth of catalysis particles. The optimized Co–W–B catalyst displays higher catalytic activity toward NH₃BH₃ hydrolysis with a specific rate of hydrogen generation of 12933.3 mL min^?1·g^?1 at room temperature. Moreover, the lower apparent activation energy of 47.3 kJ mol^?1 is achieved. Compared with previously reported catalysts, the as-obtained catalytic performance is situated at the better rank. Moreover, the reusability has been investigated under the mild NH₃BH₃ hydrolysis conditions. It reveals that as-fabricated thin-film Co–W–B maintains excellent durability after five cycles. A possible mechanism for the released hydrogen from NH₃BH₃ hydrolysis using Co–W–B catalyst has been proposed.     

Design of the metal hydride reactors – A review on the key technical issues

The metal hydride reactors are widely used in many industrial applications, for example, hydrogen storage, heat pump, thermal compression, gas separation, etc. The performance of the reactor is greatly affected by its design, which deserves careful study. Given the complicated nature of the hydride formation/decomposition processes, a series of technical issues are involved in the design of metal hydride reactors, such as primary configuration, thermal management, hydrogen transfer and mechanistic strength. These issues should be well addressed to fulfil the requirement of specific application. In this paper, the representative achievements with regards to the design issues so far were reviewed in detail, and some comments were made accordingly. It was concluded that an optimized reactor design comes from integrated considerations of numerous factors, particularly requirements for the applications and characteristics of the metal hydride system. The analytic hierarchy process was recommended for use in the selection of the optimum reactor scheme.     

Hydrogen production from ammonia decomposition using Co/γ-Al2O3 catalysts – Insights into the effect of synthetic method

Chemical hydrogen storage in molecules such as ammonia (>17 wt% H₂) have the unique potential to overcome the current storage and transport limitations of the H₂ economy. However, sustainable on-demand production of hydrogen via ammonia decomposition, requires the development of novel transition metal-based catalysts beyond the current use of highly active but expensive ruthenium to ensure economic feasibility. In this paper, we provide fundamental understanding of the effects of a range of synthetic methods of Co/γ-Al₂O₃ catalysts on the resulting ammonia decomposition activity. The main activity determining factors are collectively the reducibility of the cobalt species and their particle size. This systematic work demonstrates that decreasing the cobalt particle size enhances the ammonia decomposition catalytic activity. However, a careful balance is required between a strong metal-support interaction leading to small particle sizes (promoted by precipitation methods) and the formation of inactive cobalt aluminate species (encouraged by adsorption methods). In addition, impurities such as boron and chloride remaining from particular synthetic methods were found to have detrimental effects on the activity.     

Continuous fermentative hydrogen production from cheese whey – new insights into process stability

Continuous dark fermentation experiments for hydrogen production from synthetic cheese whey were conducted at different HRTs and OLRs. The study mainly aimed at developing a novel criterion to quantitatively assess stability and relating it to the evolution of microbial pathways and associated metabolic products.For HRTs = 6–8 h and OLRs = 65–97.5 g TOC/(L·d), the best hydrogen generation performance was attained, yielding 42–50 L H₂/kg TOC. Instead of using a stability index for the entire test length, accounting for the fluctuations of hydrogen production over 1-HRT periods (dynamic stability index) provided a more accurate assessment of process stability showing a clear correlation with the hydrogen yield. The analysis of the metabolic reactions provided evidence of a competition among acidogenic, hydrogen-consuming and hydrogen-neutral microbial species. This explained the lower process performance in comparison to the theoretical yield expected, pointing out at the need for further investigation on suitable strategies to effectively inhibit undesired metabolic pathways.     

In situ synthesized Fe–Co/C nano-alloys as catalysts for the hydrolysis of ammonia borane

Composite catalysts Fe_0.3Co_0.7-doped carbon aerogel have been in situ synthesized by chemical reduction method and successfully employed in the hydrolysis of NH₃BH₃ (AB) at room temperature. The mass percent of the doped Fe_0.3Co_0.7 alloys can reach to the maximum value of 40 wt%. The prepared catalysts exhibit excellent catalytic activity, especially for the specimen of 40 wt% Fe_0.3Co_0.7/C, which shows high catalytic activity and long durability. Its maximum hydrogen generation rate is as high as 13,695.6 ml min⁻¹ g⁻¹ at 298 K and the activation energy is only 20.83 kJ mol⁻¹. Besides, this catalyst possesses preferable cycling stability at room temperature. The low cost, high catalytic activity and enhanced cycling stability can make it have a bright future in the application field of fuel chemistry.