Production & Supply Chain
Hydrothermal conversion of lignin and black liquor for phenolics with the aids of alkali and hydrogen donor
Jun 2019
Publication
"The potentials of phenolic productions from lignin and black liquor (BL) via hydrothermal technology with the aids of alkalis and hydrogen donors were investigated by conducting batch experiments in micro-tube reactors with 300 °C sub-critical water as the solvent. The results showed that all the employed alkalis improved lignin degradation and thus phenolics production and the strong alkalis additionally manifested deoxygenation to produce more phenolics free of methoxyl group(s). Relatively hydrogen donors more visibly facilitated phenolics formation. Combination of strong alkali and hydrogen donors exhibited synergistically positive effects on producing phenolics (their total yield reaching 22 wt%) with high selectivities to phenolics among which the yields of catechol and cresols respectively peaked 16 and 3.5 wt%. BL could be hydrothermally converted into phenolics at high yields (approaching 10 wt% with the yields of catechol and cresols of about 4 and 2 wt% respectively) with the aids of its inherent alkali and hydrogen donors justifying its cascade utilization."
A comparison of steam reforming concepts in solid oxide fuel cell systems
Mar 2020
Publication
Various concepts have been proposed to use hydrocarbon fuels in solid oxide fuel cell (SOFC) systems. A combination of either allothermal or adiabatic pre-reforming and water recirculation (WR) or anode off-gas recirculation (AOGR) is commonly used to convert the fuel into a hydrogen rich mixture before it is electrochemically oxidised in the SOFC. However it is unclear how these reforming concepts affect the electrochemistry and temperature gradients in the SOFC stack. In this study four reforming concepts based on either allothermal or adiabatic pre-reforming and either WR or AOGR are modelled on both stack and system level. The electrochemistry and temperature gradients in the stack are simulated with a one-dimensional SOFC model and the results are used to calculate the corresponding system efficiencies. The highest system efficiencies are obtained with allothermal pre-reforming and WR. Adiabatic pre-reforming and AOGR result in a higher degree of internal reforming which reduces the cell voltage compared to allothermal pre-reforming and WR. Although this lowers the stack efficiency higher degrees of internal reforming reduce the power consumption by the cathode air blower as well leading to higher system efficiencies in some cases. This illustrates that both stack and system operation need to be considered to design an efficient SOFC system and predict potentially deteriorating temperature gradients in the stack.
Dynamic modelling of a direct internal reforming solid oxide fuel cell stack based on single cell experiments
May 2018
Publication
Direct internal reforming enables optimal heat integration and reduced complexity in solid oxide fuel cell (SOFC) systems but thermal stresses induced by the increased temperature gradients may inflict damage to the stack. Therefore the development of adequate control strategies requires models that can accurately predict the temperature profiles in the stack. A 1D dynamic modelling platform is developed in this study and used to simulate SOFCs in both single cell and stack configurations. The single cell model is used to validate power law and Hougen-Watson reforming kinetics derived from experiments in previous work. The stack model based on the same type of cells accounts for heat transfer in the inactive area and to the environment and is validated with data reported by the manufacturer. The reforming kinetics are then implemented in the stack model to simulate operation with direct internal reforming. Although there are differences between the temperature profiles predicted by the two kinetic models both are more realistic than assuming chemical equilibrium. The results highlight the need to identify rate limiting steps for the reforming and hydrogen oxidation reactions on anodes of functional SOFC assemblies. The modelling approach can be used to study off-design conditions transient operation and system integration as well as to develop adequate energy management and control strategies.
Promotion effect of proton-conducting oxide BaZr0.1Ce0.7Y0.2O3−δ on the catalytic activity of Ni towards ammonia synthesis from hydrogen and nitrogen
Aug 2018
Publication
In this report for the first time it has been observed that proton-conducting oxide BaZr0.1Ce0.7Y0.2O3−δ (BZCY) has significant promotion effect on the catalytic activity of Ni towards ammonia synthesis from hydrogen and nitrogen. Renewable hydrogen can be used for ammonia synthesis to save CO2 emission. By investigating the operating parameters of the reaction the optimal conditions for this catalyst were identified. It was found that at 620 °C with a total flow rate of 200 mL min−1 and a H2/N2 mol ratio of 3 an activity of approximately 250 μmol g−1 h−1 can be achieved. This is ten times larger than that for the unpromoted Ni catalyst under the same conditions although the stability of both catalysts in the presence of steam was not good. The specific activity of Ni supported on proton-conducting oxide BZCY is approximately 72 times higher than that of Ni supported on non-proton conductor MgO-CeO2. These promotion effects were suspected to be due to the proton conducting nature of the support. Therefore it is proposed that the use of proton conducting support materials with highly active ammonia synthesis catalysts such as Ru and Fe will provide improved activity of at lower temperatures.
Interfacial confinement of Ni-V2O3 in molten salts for enhanced electrocatalytic hydrogen evolution
Apr 2020
Publication
Implementation of non-precious electrocatalysts is key-enabling for water electrolysis to relieve challenges in energy and environmental sustainability. Self-supporting Ni-V2O3.electrodes consisting of nanostrip-like V2O3.perpendicularly anchored on Ni meshes are herein constructed via the electrochemical reduction of soluble NaVO3 in molten salts for enhanced electrocatalytic hydrogen evolution. Such a special configuration in morphology and composition creates a well confined interface between Ni and V2O3. Experimental and Density-Functional-Theory results confirm that the synergy between Ni and V2O3.accelerates the dissociation of H2O for forming hydrogen intermediates and enhances the combination of H* for generating H2.
The effect of intermolecular hydrogen bonding on the planarity of amides
Jul 2012
Publication
Ab initio and density functional theory (DFT) calculations on some model systems are presented to assess the extent to which intermolecular hydrogen bonding can affect the planarity of amide groups. Formamide and urea are examined as archetypes of planar and non-planar amides respectively. DFT optimisations suggest that appropriately disposed hydrogen-bond donor or acceptor molecules can induce non-planarity in formamide with OCNH dihedral angles deviating by up to ca. 20° from planarity. Ab initio energy calculations demonstrate that the energy required to deform an amide molecule from the preferred geometry of the isolated molecule is more than compensated by the stabilisation due to hydrogen bonding. Similarly the NH2 group in urea can be made effectively planar by the presence of appropriately positioned hydrogen-bond acceptors whereas hydrogen-bond donors increase the non-planarity of the NH2 group. Small clusters (a dimer two trimers and a pentamer) extracted from the crystal structure of urea indicate that the crystal field acts to force planarity of the urea molecule; however the interaction with nearest neighbours alone is insufficient to induce the molecule to become completely planar and longer-range effects are required. Finally the potential for intermolecular hydrogen bonding to induce non-planarity in a model of a peptide is explored. Inter alia the insights obtained in the present work on the extent to which the geometry of amide groups may be deformed under the influence of intermolecular hydrogen bonding provide structural guidelines that can assist the interpretation of the geometries of such groups in structure determination from powder X-ray diffraction data.
Effect of syngas fuel compositions on the occurrence of instability of laminar diffusion flame
Dec 2020
Publication
The paper presents a numerical investigation of the critical roles played by the chemical compositions of syngas on laminar diffusion flame instabilities. Three different flame phenomena – stable flickering and tip-cutting – are formulated by varying the syngas fuel rate from 0.2 to 1.4 SLPM. Following the satisfactory validation of numerical results with Darabkhani et al. [1] the study explored the consequence of each species (H2 CO CH4 CO2 N2) in the syngas composition. It is found that low H2:CO has a higher level of instability which however does not rise any further when the ratio is less than 1. Interestingly CO encourages the heat generation with less fluctuation while H2 plays another significant role in the increase of flame temperature and its fluctuation. Diluting CH4 into syngas further increases the instability level as well as the fluctuation of heat generation significantly. However an opposite effect is found from the same action with either CO2 or N2. Finally considering the heat generation and flame stability the highest performance is obtained from 25%H2+75%CO (81 W) followed by EQ+20%CO2 and EQ+20%N2 (78 W).
Plasmonic nickel nanoparticles decorated on to LaFeO3 photocathode for enhanced solar hydrogen generation
Nov 2018
Publication
Plasmonic Ni nanoparticles were incorporated into LaFeO3 photocathode (LFO-Ni) to excite the surface plasmon resonances (SPR) for enhanced light harvesting for enhancing the photoelectrochemical (PEC) hydrogen evolution reaction. The nanostructured LFO photocathode was prepared by spray pyrolysis method and Ni nanoparticles were incorporated on to the photocathode by spin coating technique. The LFO-Ni photocathode demonstrated strong optical absorption and higher current density where the untreated LFO film exhibited a maximum photocurrent of 0.036 mA/cm2 at 0.6 V vs RHE and when incorporating 2.84 mmol Ni nanoparticles the photocurrent density reached a maximum of 0.066 mA/cm2 at 0.6 V vs RHE due to the SPR effect. This subsequently led to enhanced hydrogen production where more than double (2.64 times) the amount of hydrogen was generated compared to the untreated LFO photocathode. Ni nanoparticles were modelled using Finite Difference Time Domain (FDTD) analysis and the results showed optimal particle size in the range of 70–100 nm for Surface Plasmon Resonance (SPR) enhancement.
Kinetics study and modelling of steam methane reforming process over a NiO/Al2O3 catalyst in an adiabatic packed bed reactor
Dec 2016
Publication
Kinetic rate data for steam methane reforming (SMR) coupled with water gas shift (WGS) over an 18 wt. % NiO/α-Al2O3 catalyst are presented in the temperature range of 300–700 °C at 1 bar. The experiments were performed in a plug flow reactor under the conditions of diffusion limitations and away from the equilibrium conditions. The kinetic model was implemented in a one-dimensional heterogeneous mathematical model of catalytic packed bed reactor developed on gPROMS model builder 4.1.0®. The mathematical model of SMR process was simulated and the model was validated by comparing the results with the experimental values. The simulation results were in excellent agreement with the experimental results. The effect of various operating parameters such as temperature pressure and steam to carbon ratio on fuel and water conversion (%) H2 yield (wt. % of CH4) and H2 purity was modelled and compared with the equilibrium values.
Design of experiment to predict the time between hydrogen purges for an air-breathing PEM fuel cell in dead-end mode in a closed environment
Feb 2021
Publication
Fuel cells are promising technologies for zero-emission energy conversion. They are used in several applications such as power plants cars and even submarines. Hydrogen supply is crucial for such systems and using Proton Exchange Membrane Fuel Cell in dead-end mode is a solution to save hydrogen. Since water and impurities accumulate inside the stack purging is necessary. However the importance of operating parameters is not well known for fuel cells working in closed environments. A Design of Experiment approach studying time between two purges and cell performance was conducted on an air-breathing stack in a closed environment. The most influential parameters on the time between two purges are the relative humidity and the current load. Convection in the closed environment can decrease the stability of the fuel cell. A linear model with interactions between these last three parameters was found to accurately describe the studied responses.
Study of the co-production of butanol and hydrogen by immobilizing Clostridium acetobutylicum CICC8012
Mar 2019
Publication
Three kinds of carrier materials activated carbon bagasse and brick were used as immobilizing carriers during fermentation by Clostridium acetobutylicum CICC8012. Compared with cell suspended fermentation enhanced fermentation performance was achieved during immobilizing cell fermentation with shorter fermentation time required. During the experiments hydrogen and butanol appear to be competitive events. The best fermentation performance of butanol was obtained in the case of bagasse as immobilizing carrier (5.804g/L of butanol production 0.22g/g of yield and 0.44g/L/h of productivity) while the hydrogen yield was just 1.41 mol/mol. The highest hydrogen productivity (402mL/L/h) and yield (1.808mol/mol glucose) could be obtained in the case of brick as immobilizing carrier while the butanol yield was 0.18 g/g. The highest hydrogen concentration of 66.76 % was obtained in the case of activated carbon as immobilizing carrier.
Achieving high-rate hydrogen recovery from wastewater using customizable alginate polymer gel matrices encapsulating biomass
Jul 2018
Publication
In addition to methane gas higher-value resources such as hydrogen gas are produced during anaerobic wastewater treatment. They are however immediately consumed by other organisms. To recover these high-value resources not only do the desired phenotypes need to be retained in the anaerobic reactor but the undesired ones need to be washed out. In this study a well-established alginate-based polymer gel with and without a coating layer was used to selectively encapsulate hydrogen-producing biomass in beads to achieve high-rate recovery of hydrogen during anaerobic wastewater treatment. The effect of cross-linking agents Ca2+ Sr2+ and Ba2+ as well as a composite coating on the beads consisting of alternating layers of polyethylenimine and silica hydrogel were investigated with respect to their performance specifically their mass transfer characteristics and their differential ability to retain the encapsulated biomass. Although the coating reduced the escape rate of encapsulated biomass from the beads all alginate polymer matrices without coating effectively retained biomass. Fast diffusion of dissolved organic carbon (DOC) through the polymer gel was observed in both Ca-alginate and Sr-alginate without coating. The coating however decreased either the diffusivity or the permeability of the DOC depending on whether the DOC was from synthetic wastewater (more lipids and proteins) or real brewery wastewater (more sugars). Consequently the encapsulation system with coating became diffusion limited when brewery wastewater with high chemical oxygen demand was fed resulting in a lower hydrogen production rate than the uncoated encapsulation systems. In all cases the encapsulated biomass was able to produce hydrogen even at a hydraulic residence time of 45 min. Although there are limitations to this system the used of encapsulated biomass for resource recovery from wastewater shows promise particularly for high-rate systems in which the retention of specific phenotypes is desired.
Anchoring of turbulent premixed hydrogen/air flames at externally heated walls
Oct 2020
Publication
A joint experimental and numerical investigation of turbulent flame anchoring at externally heated walls is presented. The phenomenon has primarily been studied for laminar flames and micro-combustion while this study focuses on large-scale applications and elevated Reynolds number flows. Therefore a novel burner design is developed and examined for a diverse set of operating conditions. Hydroxyl radical chemiluminescence measurements are employed to validate the numerical method. The numerical investigation evaluates the performance of various hydrogen/air kinetics Reynolds-averaged turbulence models and the eddy dissipation concept (EDC) as a turbulence-chemistry interaction model. Simulation results show minor differences between detailed chemical mechanisms but pronounced deviations for a reduced kinetic. The baseline k-ω turbulence model is assessed to most accurately predict flame front position and shape. Universal applicability of EDC modelling constants is contradicted. Conclusively the flame anchoring concept is considered a promising approach for pilot flames in continuous combustion devices.
Pyrolysis-gasification of wastes plastics for syngas production using metal modified zeolite catalysts under different ratio of nitrogen/oxygen
Jun 2020
Publication
The aim of this study was the syngas production by the gasification of plastic waste (polyethylene polypropylene and terephthalate polyethylene). Ca Ce La Mg and Mn were used to promote the Ni/ZSM-5 catalyst in order to enhance the production of higher syngas yield. The modified catalysts can enhanced the reaction rate of the pyrolysis process and resulting in high syngas in the product yields. Especially cerium lanthanum promoted catalysts can enhance the yield of syngas. The effect of the reaction temperature and nitrogen/oxygen ratio of the carrier gas was also investigated. The maximum syngas production was obtained with lanthanum catalyst (112.2 mmol/g (95%N2 and 5%O2) and 130.7 mmol/g (90%N2 and 10%O2) at 850 °C. Less carbon depositions was found at 850 °C or even by the using of catalyst and more oxygen in the carrier gas. The oxygen content of the pyrolysis-gasification atmosphere had a key role to the syngas yield and affects significantly the carbon-monoxide/carbon-dioxide ratio. Catalysts can also accelerate the methanization reactions and isomerize the main carbon frame. Increasing in both temperature and oxygen in the atmosphere led to higher n-paraffin/n-olefin ratio and more multi-ring aromatic hydrocarbons in pyrolysis oils. The concentration of hydrocarbons containing oxygen and branched compounds was also significantly affected by catalysts.
Economic Viability and Environmental Efficiency Analysis of Hydrogen Production Processes for the Decarbonization of Energy Systems
Aug 2019
Publication
The widespread penetration of hydrogen in mainstream energy systems requires hydrogen production processes to be economically competent and environmentally efficient. Hydrogen if produced efficiently can play a pivotal role in decarbonizing the global energy systems. Therefore this study develops a framework which evaluates hydrogen production processes and quantifies deficiencies for improvement. The framework integrates slack-based data envelopment analysis (DEA) with fuzzy analytical hierarchy process (FAHP) and fuzzy technique for order of preference by similarity to ideal solution (FTOPSIS). The proposed framework is applied to prioritize the most efficient and sustainable hydrogen production in Pakistan. Eleven hydrogen production alternatives were analyzed under five criteria including capital cost feedstock cost O&M cost hydrogen production and CO2 emission. FAHP obtained the initial weights of criteria while FTOPSIS determined the ultimate weights of criteria for each alternative. Finally slack-based DEA computed the efficiency of alternatives. Among the 11 three alternatives (wind electrolysis PV electrolysis and biomass gasification) were found to be fully efficient and therefore can be considered as sustainable options for hydrogen production in Pakistan. The rest of the eight alternatives achieved poor efficiency scores and thus are not recommended.
Membrane based purification of hydrogen system (MEMPHYS)
Feb 2019
Publication
A hydrogen purification system based on the technology of the electrochemical hydrogen compression and purification is introduced. This system is developed within the scope of the project MEMPHYS. Therefore the project its targets and the different work stages are presented. The technology of the electrochemical purification and the state of the art of hydrogen purification are described. Early measurements in the project have been carried out and the results are shown and discussed. The ability of the technology to recover hydrogen from a gas mixture can be recognized and an outlook into further optimizations shows the future potential. A big advantage is the simultaneous compression of the purified hydrogen up to 200 bar therefore facilitating the transportation and storage.
Photocatalytic hydrogen production by biomimetic indium sulfide using Mimosa pudica leaves as template
Jan 2019
Publication
Biomimetic sulfur-deficient indium sulfide (In2.77S4) was synthesized by a template-assisted hydrothermal method using leaves of Mimosa pudica as a template for the first time. The effect of this template in modifying the morphology of the semiconductor particles was determined by physicochemical characterization revealing an increase in surface area decrease in microsphere size and pore size and an increase in pore volume density in samples synthesized with the template. X-ray photoelectron spectroscopy (XPS) analysis showed the presence of organic sulfur (Ssingle bondO/Ssingle bondC/Ssingle bondH) and sulfur oxide species (single bondSO2 SO32− SO42−) at the surface of the indium sulfide in samples synthesized with the template. Biomimetic indium sulfide also showed significant amounts of Fe introduced as a contaminant present on the Mimosa pudica leaves. The presence of these sulfur and iron species favors the photocatalytic activity for hydrogen production by their acting as a sacrificial reagent and promoting water oxidation on the surface of the templated particles respectively. The photocatalytic hydrogen production rates over optimally-prepared biomimetic indium sulfide and indium sulfide synthesized without the organic template were 73 and 22 μmol g−1 respectively indicating an improvement by a factor of three in the templated sample.
Recent advancements in chemical looping water splitting for the production of hydrogen
Oct 2016
Publication
Chemical looping water splitting or chemical looping hydrogen is a very promising technology for the production of hydrogen. In recent years extensive research has enabled remarkable leaps towards a successful integration of the chemical looping technology into a future hydrogen infrastructure. Progress has been reported with iron based oxygen carriers for stable hydrogen production capacity over consecutive cycles without significant signs of degradation. The high stability improvements were achieved by adding alien metal oxides or by integrating the active component into a mineral structure which offers excellent resistance towards thermal stress. Prototype systems from small μ-systems up to 50 kW have been operated with promising results. The chemical looping water splitting process was broadened in terms of its application area and utilization of feedstocks using a variety of renewable and fossil resources. The three-reactor system was clearly advantageous due to its flexibility heat integration capabilities and possibility to produce separate pure streams of hydrogen CO2 and N2. However two-reactor and single fixed-bed reactor systems were successfully operated as well. This review aims to survey the recently presented literature in detail and systematically summarize the gathered data.
A novel exergy-based assessment on a multi-production plant of power, heat and hydrogen: integration of solid oxide fuel cell, solid oxide electrolyzer cell and Rankine steam cycle
Feb 2021
Publication
Multi-production plant is an idea highlighting cost- and energy-saving purposes. However just integrating different sub-systems is not desired and the output and performance based on evaluation criteria must be assessed. In this study an integrated energy conversion system composed of solid oxide fuel cell (SOFC) solid oxide electrolyzer cell (SOEC) and Rankine steam cycle is proposed to develop a multi-production system of power heat and hydrogen to alleviate energy dissipation and to preserve the environment by utilizing and extracting the most possible products from the available energy source. With this regard natural gas and water are used to drive the SOEC and the Rankine steam cycle respectively. The required heat and power demand of the electrolyzer are designed to be provided by the fuel cell and the Rankine cycle. The feasibility of the designed integrated system is evaluated through comprehensive exergy-based analysis. The technical performance of the system is evaluated through exergy assessment and it is obtained that the SOFC and the SOEC can achieve to the high exergy efficiency of 84.8% and 63.7% respectively. The designed system provides 1.79 kg/h of hydrogen at 125 kPa. In addition the effective designed variables on the performance of the designed integrated system are monitored to optimize the system’s performance in terms of technical efficiency cost-effectivity and environmental considerations. This assessment shows that 59.4 kW of the available exergy is destructed in the combustion chamber. Besides the techno-economic analysis and exergoenvironmental assessment demonstrate the selected compressors should be re-designed to improve the cost-effectivity and decline the negative environmental impact of the designed integrated energy conversion system. In addition it is calculated that the SOEC has the highest total cost and also the highest negative impact on the environment compared to other designed units in the proposed integrated energy conversion system.
Achievements of European projects on membrane reactor for hydrogen production
May 2017
Publication
Membrane reactors for hydrogen production can increase both the hydrogen production efficiency at small scale and the electric efficiency in micro-cogeneration systems when coupled with Polymeric Electrolyte Membrane fuel cells. This paper discusses the achievements of three European projects (FERRET FluidCELL BIONICO) which investigate the application of the membrane reactor concept to hydrogen production and micro-cogeneration systems using both natural gas and biofuels (biogas and bio-ethanol) as feedstock. The membranes used to selectively separate hydrogen from the other reaction products (CH4 CO2 H2O etc.) are of asymmetric type with a thin layer of Pd alloy (<5 μm) and supported on a ceramic porous material to increase their mechanical stability. In FERRET the flexibility of the membrane reactor under diverse natural gas quality is validated. The reactor is integrated in a micro-CHP system and achieves a net electric efficiency of about 42% (8% points higher than the reference case). In FluidCELL the use of bio-ethanol as feedstock for micro-cogeneration Polymeric Electrolyte Membrane based system is investigated in off-grid applications and a net electric efficiency around 40% is obtained (6% higher than the reference case). Finally BIONICO investigates the hydrogen production from biogas. While BIONICO has just started FERRET and FluidCELL are in their third year and the two prototypes are close to be tested confirming the potentiality of membrane reactor technology at small scale.
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