Reactions of different food classes during subcritical water gasification for hydrogen gas production

The reactions of different food classes during alkaline subcritical water gasification have been investigated with a view on hydrogen gas production. Experiments were conducted with sub-stoichiometric amounts of H₂O₂ for partial oxidation. NaOH was added to aid sample decomposition, reduce char/tar formation and to promote water–gas shift reaction. In general, hydrogen gas production depended on the class of food wastes including their chemical structure. Carbohydrate-rich food waste (glucose, molasses, tropical fruit mixture, whey powder) produced higher H₂ gas yields than others (proteins and lipids). Lipid-rich samples were the most difficult to decompose into gasifiable intermediates and therefore produced the lowest H₂ yield. Generally, the addition of NaOH led to higher H₂ generation from all sample types. However, two separate side reactions namely, neutralization and saponification involving NaOH with protein- and lipid-rich samples, respectively were significant. Hydrogen production from carbohydrate-rich samples was most suited for the reaction conditions applied.     

Utilization of palm kernel cake as a renewable feedstock for fermentative hydrogen production

Fermentative hydrogen generation was studied using palm kernel cake (PKC) as sustainable cellulosic biomass. PKC was subjected to an acid hydrolysis approach using dilute H₂SO₄ (7% v/v). PKC hydrolysate obtained was then diluted (70%) and used as a substrate for hydrogen generation. Chemical analysis showed that the main fermentable sugars in diluted PKC hydrolysate were glucose, xylose and mannose with the concentrations of 2.75 g/L, 2.60 g/L and 27.75 g/L, respectively. Hydrogen production was carried out by the cultivation of Clostridium acetobutylicum YM1 on PKC hydrolysate. The effect of incubation temperature, the initial pH of culture medium and microbial inoculum size on hydrogen production was studied using a statistical model. The analysis of the model generated showed that the initial pH value of the culture medium and inoculum size had significant effects on the hydrogen production. The study showed that the optimum conditions for the biohydrogen production were 30.57 °C temperature, pH 5.5 and 20% inoculum size. A verification experiment was performed in the optimum conditions determined. Experimental results of the verification test showed that a cumulative hydrogen volume of 1575 ml/L was generated with consuming 2.75 g/L glucose, 2.20 g/L xylose and 16.31 g/L mannose.     

Co-gasification of catechol and starch in supercritical water for hydrogen production

Hydrogen production from waste feedstocks using supercritical water gasification (SCWG) is a promising approach towards cleaner fuel production and a solution for hard to treat wastes. In this study, the catalytic co-gasification of starch and catechol as models of carbohydrates and phenol compounds was investigated in a batch reactor at 28 MPa, 400–500 °C, from 10 to 30 min. The effects of reaction conditions, and the addition of calcium oxide (CaO) as a carbon dioxide (CO₂) sorbent and TiO₂ as catalyst on the gas yields and product distribution were investigated. Employing TiO₂ as a catalyst alone had no significant effect on the H₂ yield but when combined with CaO increased the hydrogen yield by 35% and promoted higher total organic carbon (TOC) reduction efficiencies. The process liquid effluent was characterized using GC–MS, with the results showing that the major non-polar components were phenol, substituted phenols, and cresols. An overall reaction scheme is provided.     

Research on hydrogen production and degradation of corn straw by circular electrolysis with polyoxometalate (POM) catalyst

Converting corn straw into high-value chemicals and H₂ energy is of great significance to the effective utilization of biomass resources. Based on the proton exchange membrane electrolysis technology, a circular electrolysis system for H₂ evolution and corn straw degradation was built using polyoxometalate (POM) catalysts as redox media and charge carriers. Under mild conditions (80 °C), the influence of factors such as reaction temperature, reaction time, catalyst concentration, and current density on the research system was explored. As a result, the efficient use of corn straw has been realized. The degradation rate of corn straw was as high as 63.48%, and the Faraday efficiency of H₂ production by electrolysis reaches 94.54%. The degradation products of corn straw were characterized and analyzed by SEM, FT-IR, XPS, GC-MS, and 2D HSQC NMR. This technique provides a potentially new pathway for H₂ production and corn straw processing.     

Hydrolytic cleavage of ammonia-borane complex for hydrogen production

A new process for generating hydrogen via near room temperature hydrolysis of AB complex using small amounts of platinum group metal catalyst has been studied. Using in situ ¹¹B NMR spectroscopy, the overall rate of K₂Cl₆Pt catalyzed hydrolysis of AB complex was calculated to be third-order. The pre-exponential factor (A) and the activation energy (E_a) of Arrhenius equation, ln k = ln A − E_a/RT, were determined to be: A = 1.6 × 10¹¹ L mol⁻¹ s⁻¹ and E_a = 86.6 kJ mol⁻¹ for temperature range of (25–35 °C). X-ray photoelectron spectroscopy of the residue suggested that the platinum salt was reduced from Pt⁴⁺ to Pt⁰ within the course of the reaction and X-ray diffraction analysis pattern for the residue showed crystallized single-phase boric acid.     

Existing large steam power plant upgraded for hydrogen production

This paper presents and discusses the results of a complete thermoeconomic analysis of an integrated power plant for co-production of electricity and hydrogen via pyrolysis and gasification processes fed by various coals and mixture of coal and biomass, applied to an existing large steam power plant (ENEL Brindisi power plant – 660 MW_e). Two different technologies for the syngas production section are considered: pyrolysis process and direct pressurized gasification. Moreover, the proximity of a hydrogen production and purification plants to an existing steam power plant favors the inter-exchange of energy streams, mainly in the form of hot water and steam, which reduces the costs of auxiliary equipment. The high quality of the hydrogen would guarantee its usability for distributed generation and for public transport. The results were obtained using WTEMP thermoeconomic software, developed by the Thermochemical Power Group of the University of Genoa, and this project has been carried out within the framework of the FISR National project “Integrated systems for hydrogen production and utilization in distributed power generation”.     

A study of combined biomass gasification and electrolysis for hydrogen production

An integrated system for the production of hydrogen by gasification of biomass and electrolysis of water has been designed and cost estimated. The electrolyser provides part of the hydrogen product as well as the oxygen required for the oxygen blown gasifier. The production cost was estimated to 39 SEK/kg H₂ at an annual production rate of 15?000 ton, assuming 10% interest rate and an economic lifetime of 15 years. Employing gasification only to produce the same amount of hydrogen, leads to a cost figure of 37 SEK/kg H₂, and for an electrolyser only a production cost of 41 SEK/kg H₂. The distribution of capital and operating cost is quite different for the three options and a sensitivity analyses was performed for all of these. However, the lowest cost hydrogen produced with either method is at least twice as expensive as hydrogen from natural gas steam reforming.     

An investigation into steam gasification of biomass for hydrogen enriched gas production in presence of CaO

Biomass steam gasification could be an attractive option for sustainable hydrogen production. Biomass, regarded as carbon neutral emitter, could be claimed as carbon negative emitter if carbon dioxide produced is captured and not allowed to emit to the environment during the process. Thus here an experimental study is carried out to find out the potential of hydrogen production from steam gasification of biomass in presence of sorbent CaO and effect of different operating parameters (steam to biomass ratio, temperature, and CaO/biomass ratio). Product gas with hydrogen concentration up to 54.43% is obtained at steam/biomass = 0.83, CaO/biomass = 2 and T = 670 °C. A drop of 93.33% in carbon dioxide concentration was found at CaO/biomass = 2 as compared to the gasification without CaO. Mathematical model based on Gibbs free energy minimization has been developed and is compared with the experimental results.     

Carbon nanotubes and hydrogen production from the reforming of toluene

Catalytic steam reforming of liquid hydrocarbons is one of the promising alternatives for hydrogen production. However, coke deposition on the reacted catalyst results in catalyst deactivation and also CO₂ emission during reforming are among the main challenges in the process. In this work, the production of high-value carbon nanotubes (CNTs) during hydrogen production from catalytic reforming of toluene has been investigated. Thus, less carbon emission and higher product values can be expected from the process. A two-stage fixed bed pyrolysis-reforming reactor was used in this work. The results showed that the addition of a Ni–Mg–Al catalyst, with an additional downstream stainless steel mesh, increased hydrogen production from 24.8 to 54.8 (mmol H₂ g⁻¹ toluene), when water (steam) was injected at a rate of 0.01 g min⁻¹. CNTs were also produced in the process in the presence of the Ni–Mg–Al catalyst and with a water injection rate of 0.01 g min⁻¹ had the highest band ratio of G′/G when analyzed by Raman spectrometry, indicating the highest purity of CNTs. In addition, Raman spectra of the generated CNTs showed that the purity of CNTs was reduced with the addition of water for reforming without the Ni–Mg–Al catalyst. The presence of the Ni–Mg–Al catalyst significantly increased the yield of CNTs formed on the surface of the stainless steel mesh and also improved the quality of the CNTs in relation to the distribution of diameters and their length.     

Challenges for renewable hydrogen production from biomass

The increasing demand for H₂ for heavy oil upgrading, desulfurization and upgrading of conventional petroleum, and for production of ammonium, in addition to the projected demand for H₂ as a transportation fuel and portable power, will require H₂ production on a massive scale. Increased production of H₂ by current technologies will consume greater amounts of conventional hydrocarbons (primarily natural gas), which in turn will generate greater greenhouse gas emissions. Production of H₂ from renewable sources derived from agricultural or other waste streams offers the possibility to contribute to the production capacity with lower or no net greenhouse gas emissions (without carbon sequestration technologies), increasing the flexibility and improving the economics of distributed and semi-centralized reforming. Electrolysis, thermocatalytic, and biological production can be easily adapted to on-site decentralized production of H₂, circumventing the need to establish a large and costly distribution infrastructure. Each of these H₂ production technologies, however, faces technical challenges, including conversion efficiencies, feedstock type, and the need to safely integrate H₂ production systems with H₂ purification and storage technologies.     

Evaluation of greenhouse residues gasification performance in hydrogen production

In this study, a modeling study was carried out to investigate the potential of hydrogen production from greenhouse tomato and pepper residues blending in different rates (0%, 25%, 50%, 75% and 100%) by air-steam gasification. The numerical model developed for the gasification system assumes that all carbon in the mixture is gasified. Air to fuel rate and steam to fuel rates are 0.05 due to high content of O₂ in biomass residues. The gasifier temperature is 877 °C (1150 K) for developed model. According to the result of this study, increasing tomato residues blending rate increases hydrogen content of syngas. It is mainly caused by the content of O₂ in tomato residues being higher than content of O₂ in pepper residues. This study shows that the O₂ content of greenhouse residues is an important factor in syngas production, especially in H₂ production.     

Hydrogen rich gas production by thermocatalytic decomposition of kenaf biomass

Kenaf (Hibiscus cannabinus L.), a well known energy crop and an annual herbaceous plant grows very fast with low lodging susceptibility was used as representative lignocellulosic biomass in the present work. Thermocatalytic conversions were performed by aqueous phase reforming (APR) of kenaf hydrolysates and direct gasification of solid biomass of kenaf using 5% Pt on activated carbon as catalyst. Hydrolysates used in APR experiments were prepared by solubilization of kenaf biomass in subcritical water under CO₂ gas pressure.     

Role of sodium hydroxide in the production of hydrogen gas from the hydrothermal gasification of biomass

The role of sodium hydroxide as a promoter of hydrogen gas production during the hydrothermal gasification of glucose and other biomass samples has been investigated. Experiments were carried out in a batch reactor with glucose and also in the presence of the alkali from 200 °C, 2 MPa to 450 °C, 34 MPa at constant water loading. Without sodium hydroxide, glucose decomposed to produce mainly carbon dioxide, water, char and tar. Furfural, its derivatives and reaction products dominated the ethyl acetate extract of the water (organic fraction) at lower reaction conditions. This indicated that the dehydration of glucose to yield these products was unfavourable to hydrogen gas production. In the presence of sodium hydroxide however, glucose initially decomposed to form mostly alkylated and hydroxylated carbonyl compounds, whose further decomposition yielded hydrogen gas. It was observed that at 350 °C, 21.5 MPa, half of the optimum hydrogen gas yield had formed and at 450 °C, 34 MPa, more than 80 volume percent of the gaseous effluent was hydrogen gas, while the balance was hydrocarbon gases, mostly methane (≥10 volume percent). Other biomass samples were also comparably reacted at the optimum conditions observed for glucose. The rate of hydrogen production for the biomass samples was in the following order; glucose > cellulose, starch, rice straw > potato > rice husk.     

Integrated adsorption steam gasification for enhanced hydrogen production from palm waste at bench scale plant

The generation of hydrogen-enriched synthesis gas from catalytic steam gasification of biomass with in-situ CO₂ capture utilizing CaO has a high perspective as clean energy fuels. The present study focused on the process modeling of catalytic steam gasification of biomass using palm empty fruit bunch (EFB) as biomass for hydrogen generation through experimental work. Experiment work has been carried out using a fluidized bed gasifier on a bench-scale plant. The established model integrates the kinetics of EFB catalytic steam gasification reactions, in-situ capturing of CO₂, mass and energy balance calculations. Chemical reaction constants have been calculated via the parameters fitting optimization approach. The influence of operating parameters, mainly temperature, steam to biomass, and sorbent to biomass ratio, was investigated for the hydrogen purity and yield through the experimental study and developed model. The results predicted approximately 75 vol% of the hydrogen purity in the product gas composition. The maximum H₂ yield produced from the gasifier was 127 gH₂/kg of EFB via experimental setup. The increase in both steam to biomass ratio and temperature enhanced the production of hydrogen gas. Comparing the results with already published literature showed that the current system enables to produce a high amount of hydrogen from EFB.     

Apparatus for the production of hydrogen from sodium borohydride in alkaline solution

Extended application of hydrogen as energy carrier demands an economical, safe and reliable technology for storage. In particular, chemical hydrides appear as capable and promising to overcome the issues related to hydrogen safety and handling and to be considered competitive with respect to conventional fuels.     

Parametric analysis and assessment of a coal gasification plant for hydrogen production

The purpose of this paper is to conduct a parametric study to show the best steam to carbon ratio that produces the maximum system performance of an integrated gasifier for hydrogen production. The study focuses on the energy and exergetic efficiency of the system and hydrogen production. The work is completed using computer simulation models in Engineering Equation Solver software package. This software is used for its extensive thermodynamic properties library. An equilibrium based model is used to determine the performance of the system. The data is presented in graphs which show the chemical composition in molar fractions of the syngas, the overall energy and exergy efficiency of the system, and the hydrogen production rates. A study of these parameters is conducted by varying the steam to carbon ratio entering the gasifier and the ambient temperature. It is observed that the higher the steam to carbon ratio that is achieved the more hydrogen and more power the plant is able to produce. Because of this, the exergy and energy efficiency of the system increases as the steam to carbon ratio increases as well. It is also observed that the system favors a lower ambient temperature for maximum exergy efficiency and hydrogen production.     

Exploring the technological maturity of hydrogen production by hydrolysis of sodium borohydride

Sodium borohydride NaBH₄ (SB) has been rediscovered in the late 1990s and been presented as a promising hydrogen storage material owing to its high gravimetric hydrogen density of 10.8 wt% and ability to produce H₂ by hydrolysis at ambient conditions. This looked promising, but soon hydrolysis of SB encountered numerous obstacles. In 2015, a progress report (Int J Hydrogen Energy 2015; 40:2673–91) showed that the 2000–2014 research did not overcome all of the obstacles, making SB far from being technologically mature. Eight years have passed since 2015. Have we put more effort into all aspects relating to hydrolysis of SB? If so, do we have produced scaled-up technologies and prototypes, of which we would have a better knowledge? Have we been able to gain in technological readiness level? Answering these questions is the main objective of this article. A secondary objective is to summarize the newly acquired knowledge. Five main observations stand out. First, the 2015–2022 period is regrettably similar to the 2000–2014 since, again, catalysts have dominated the field and the other aspects (e.g. recycling of the by-product to regenerate SB, scale-up and implementation) have received little attention. Second, hydrolysis of SB still runs into numerous obstacles, some of the obstacles being known since a long time and other ones being relatively new and unknown. Third, there has been little gain in terms of technological readiness level while few research groups have shown that there is room for new ideas and innovation. Fourth, energy, exergy and economic analyses are needed to evaluate the overall cost of H₂ from SB. Fifth, SB has not effectively thought from the end user perspective. In conclusion, many obstacles remain to be overcome before hydrolysis of SB can be a commercial solution for carrying and producing H₂. However, all efforts should be dedicated to (i) construct, operate and optimize H₂ production systems (i.e. prototypes and demonstrators), (ii) handle SB at the gram-to-kilogram scale, (iii) make production of SB even more efficient, and (iv) overcome all obstacles while thinking from the end user perspective.     

Air gasification of high-ash sewage sludge for hydrogen production: Experimental,sensitivity and predictive analysis

In this work, air gasification of sewage sludge was conducted in a lab-scale bubbling fluidized bed gasifier. Further, the gasification process was modeled using artificial neural networks for the product gas composition with varying temperatures and equivalence ratios. Neural network-based prediction will help to predict the hydrogen production from product gas composition at various temperatures and equivalence ratios. The gasification efficiency and lower heating values were also established as a function of temperatures and equivalence ratios. The maximum H₂ and CO was recorded as 16.26 vol% and 33.55 vol%. Intraileally at ER 0.2 gas composition H₂, CO, and CH₄ show high concentrations of 20.56 vol%, 45.91 vol%, and 13.32 vol%, respectively. At the same time, CO₂ was lower as 20.20 vol% at ER 0.2. Therefore, optimum values are suggested for maximum H₂ and CO yield and lower concentration of CO₂ at ER 0.25 and temperature of 850 °C. A predictive model based on an Artificial Neural network is also developed to predict the hydrogen production from product gas composition at various temperatures and equivalence ratios. The network has been trained with different topologies to find the optimal structure for temperature and equivalence ratio. The obtained results showed that the regression coefficients for training, validation, and testing are 0.99999, 0.99998, and 0.99992, respectively, which clearly identifies the training efficiency of the trained model.     

Thermodynamics research on hydrogen production from biomass and coal co-gasification with catalyst

A model comprises two sub-models, i.e. combustion and gasification models, is developed to simulate a single fluidized bed two-step gasification process and to predict H₂ production under different conditions. The combustion sub-model which consists of volatile precipitation and char combustion sub-models. The combustion sub-model is used to forecast residual char. The gasification sub-model, based on the mass and energy balance, is used to examine thermodynamically the effect on the hydrogen production of calcium oxide as the catalyst. Moreover, the effects of the operational conditions on the hydrogen production such as biomass/coal (mass ratio), temperature, steam/coke, and calcium/coke, are simulated. The results indicate that the addition of calcium oxide at certain conditions can significantly improve hydrogen production and lower the required temperature for gasification. The model predicts that the maximum hydrogen production of 60% can be achieved under the conditions of temperature in the range of 800-850 °C, calcium/coke, steam/coke, and coal/biomass (mass ratio) are 0.5, 1.8, and 1/4, respectively. The model predictions are in good agreement with the experimental data.     

Influence of catalyst and temperature on gasification performance of pig compost for hydrogen-rich gas production

The catalytic steam gasification of pig compost (PC) for hydrogen-rich gas production was conducted in a fixed-bed reactor. The influence of the catalyst and reactor temperature on yield and product composition was studied at the temperature range of 700–850 °C, for weight hourly space velocity (WHSV) in the range of 0.30–0.60 h⁻¹. The results indicate that the developed NiO on modified dolomite (NiO/MD) catalyst reveals better catalytic performance on the tar elimination and hydrogen yield than calcined MD or NiO/γ-Al₂O₃ catalyst. Meanwhile, the lower WHSV and higher reactor temperature can contribute to more hydrogen production and gas yield. Moreover, the char from catalytic steam gasification of PC has a highest ash content of 75.84% at 850 °C. In conclusion, pig compost is a potential candidate for hydrogen gas production through catalytic steam gasification technology.