Direct synthesis of formic acid as hydrogen carrier from CO2 for cleaner power generation through direct formic acid fuel cell

The objective of this work is to develop a process flow modeling for the synthesis of formic acid from CO₂ and H₂ for energy storage and transport purposes. The use of formic acid as an energy storage medium is promising due to difficulties in hydrogen storage, where formic acid can be stored for a longer time with less losses, and then can be utilized in a direct formic acid fuel cell for cleaner power generation. The process flow is developed using Aspen Plus and Engineering Equation Solver to obtain the energy and mass balances, efficiencies, fuel utilization, and Nernst voltage of the direct formic acid fuel cell. The model is validated against data available in the literature for operating parameters. The results show that the operation parameters such as formic acid formation rate, heat duty, and work values, fuel cell efficiency have a significant influence on the overall performance. The proposed system forms formic acid from gaseous H₂ and CO₂ with an energy efficiency of about 19%. The formed formic acid is initially stored in a tank for energy storage and then used in a direct formic acid fuel cell to produce about 168 kW power with an energy efficiency of 16% at 0.7 V, 25 °C and 1 bar.     

Two-step catalytic dehydrogenation of formic acid to CO2 via formaldehyde

Formic acid has been decomposed into hydrogen and carbon dioxide through a two-step process involving the formation of formaldehyde. This allows the formation of carbon dioxide and hydrogen in two different steps, negating the need for gas separation. A novel system for the catalytic disproportionation of formic acid into formaldehyde and carbon dioxide was thus far developed using monoclinic bismuth chromate hydroxide proto-catalyst, m-Bi(OH)CrO₄. The catalytically active species, BiCrO₄, was isolated and its activity assessed for thermal disproportionation of formic acid under mild conditions (200–300 °C, tube furnace). A maximum formaldehyde production rate of 0.065 mmol/mmol catalyst/hour was observed using bismuth chromate at 250 °C. The formaldehyde produced through this method was selectively dehydrogenated to formate by an IrCl₃ catalyst at room temperature under basic conditions, with a dehydrogenation rate of 20.1 mmol of hydrogen/mmole catalyst/hour. This completes a step-by-step and yet efficient cycle of formic acid dehydrogenation.     

Catalytic hydrolysis of alkaline sodium borohydride solution for hydrogen evolution in a micro-scale fluidized bed reactor

An investigation was conducted into the generation of hydrogen from catalytic hydrolysis of alkaline sodium borohydride solution in a micro-scale fluidized bed. In this work, the Cobalt loaded on walnut shell activated carbon was applied as the catalyst. The impact of NaBH₄ concentration, the diameter of catalyst particle, the rate of reaction fluid flow, and the temperature of initial reaction fluid on the process of hydrogen generation was explored, and the optimum reaction conditions were determined. It was found out that the maximum length of stable hydrogen generation (58.46% of the total reaction time) is obtainable under the following conditions. The concentration of NaBH₄ is 2 wt%, the flow rate is 3.00 × 10⁻³ m·s⁻¹, and the flow temperature is 25°C. In addition, a comparison was performed between the batch reactor and micro-fluidized bed reactor during the process of hydrogen generation. Moreover, when the concentration of NaBH₄ reached 1 and 2 wt%, the efficiency and stability of the micro-fluidized bed reactor were identified as superior to those of the batch reactor.     

Improved dark fermentation of cane molasses in mesophilic and thermophilic anaerobic fluidized bed reactors by selecting operational conditions

Sugarcane molasses is a carbohydrate-rich carbon source with potential to develop the biorefinery model in the sugarcane industry. Two of the most well-known renewable products from the dark fermentation of cane molasses are succinic acid and biohydrogen, with both having valuable applications in different industries. However, the continuous dark fermentation of cane molasses is a process regulated by many operational conditions, like reactor temperature and hydraulic retention time. It is important to control these conditions to shift metabolic pathways in order to increase production rates and yields. Thus, this research evaluates the response of mesophilic and thermophilic dark fermentation of cane molasses by mixed culture on hydrogen and succinic acid generation in fluidized bed reactors by changing the hydraulic retention time (8, 6, 4, 2, and 1 hour). In the thermophilic reactor (55°C), higher hydraulic retention times (from 8 to 4 hours) favored the succinate production (molar fractions between 75.0% and 81.4%). Similarly, in the mesophilic reactor (30°C), the molar fractions of succinate were 45.5% at the hydraulic retention time of 8 hours and 74.7% at 6 hours. The reduction of the hydraulic retention time to 1 hour decreased the succinic acid concentration to undetectable values and increased the hydrogen yield in both reactors. The lower hydraulic retention time also enhanced the hydrogen productivity to 171.1 mL/L_bed·h in the mesophilic reactor and to 303.4 mL/L_bed·h in the thermophilic reactor. These values were coincident with the predominant production of butyric and acetic acids. All of these points to the fact that the hydraulic retention time is an efficient parameter to control and select the production of hydrogen or succinic acid by mixed cultures under different temperatures.     

Effect of temperature on the fast pyrolysis of organic-acid leached pinewood; the potential of low temperature pyrolysis

In this paper, we have evaluated the potential of organic acid (mixture of acetic, formic and propionic acid) leaching of biomass and subsequent fast pyrolysis to increase the organic oil, sugars and phenols yield by varying the fluidized bed temperature between 360 °C and 580 °C (360 °C, 430 °C, 480 °C, 530 °C, and 580 °C). The pyrolysis of acid leached pinewood resulted in more organic oil and less water and residue compared to untreated pinewood over the whole temperature range. Below 500 °C the difference was most profound; for acid leached pinewood at 360 °C the organic oil was already 650 g kg⁻¹ pine with a sugar yield of 230 g kg⁻¹ pine. At this low pyrolysis temperature no bed agglomeration was observed for acid leached pine whereas at the higher temperatures tested agglomerates were found, which were identified to be clusters of fluidization sand glued together by sticky pyrolysis products (melt). Low reactor temperatures also favored the production of monomeric phenols, though their absolute yields remained low for both untreated and leached pine (maximum: 23 g kg⁻¹ pine, 80 g kg⁻¹ lignin). GPC, GC/MS and UV-fluorescence spectroscopy showed that acid leaching did not influence significantly the yield and molecular size of the aromatic fraction in the produced pyrolysis oils. Back impregnation of the removed AAEMs into leached biomass revealed that the effects of the applied acid leaching, both with respect to the product yields and bed agglomeration, can be mainly assigned to the removal of AAEMs.     

Catalytic supercritical water gasification of black liquor along with lignocellulosic biomass

Supercritical water gasification (SCWG) is a novel technology for environmental pollution management and hydrogen production from biomass and wastes. In this study, the SCWG of black liquor (BL) which is high-potential biomass and rich in alkalis was investigated. The experiments were conducted in a batch reactor at 350–400 °C, reaction time of 1–60 min, and constant concentration of 9 wt% of BL in the absence and presence of heterogeneous catalysts (3–5 wt%), lignocellulosic biomass, and formic acid (5 and 7 wt %) in three parts. First, the SCWG of BL was performed without any additive. The experimental results showed that the maximum production of H₂, CO₂, and CH₄ was obtained at the highest temperature and reaction time; 400 °C and 60 min. The hydrogen yield was also enhanced by increasing the temperature, and reached 3.51 mol H₂/kg dry ash free-black liquor (DAF-BL) at 400 °C. Reaction time increment improved the gas product and gasification efficiency up to 28.03 mmol and 21.73%, respectively. Subsequently, three heterogeneous catalysts (MnO₂, CuO, and TiO₂) were used, however 5 wt% of MnO₂ was the best catalyst, significantly improving the hydrogen yield compared to the same condition of BL gasification without a catalyst. Hydrogen yield reached 5.09 mol H₂/kg (DAF-BL) at 400 °C and the reaction time of 10 min. Finally, BL with poplar wood residue as a lignocellulosic biomass and formic acid was gasified separately and the highest hydrogen yield was obtained in the case of 5 wt% of formic acid (10.79 mol H₂/kg (DAF-BL)). Overally, SCWG dramatically reduced the chemical oxygen demand of BL to 76% using 5 wt% of formic acid.     

Performance prediction of a coupled metal hydride based thermal energy storage system

The present study discusses the thermodynamic compatibility criteria for the selection of metal hydride pairs for the application in coupled metal hydride based thermal energy storage systems. These are closed systems comprising of two metal hydride beds – a primary bed for energy storage and a secondary bed for hydrogen storage. The performance of a coupled system is analyzed considering Mg₂Ni material for energy storage and LaNi₅ material for hydrogen storage. A 3-D model is developed and simulated using COMSOL Multiphysics® at charging and discharging temperatures of 300 °C and 230 °C, respectively. The LaNi₅ bed used for hydrogen storage is operated close to ambient temperature of 25 °C. The results of the first three consecutive cycles are presented. The thermal storage system achieved a volumetric energy storage density of 156 kWh m⁻³ at energy storage efficiency of 89.4% during third cycle.     

Dark fermentative biohydrogen production from confectionery wastewater in continuous-flow reactors

The production of biohydrogen from industrial wastewater through the dark fermentation (DF) process has attracted increased interest in recent years. To implement a DF process on a large scale, a thorough knowledge of laboratory scale process control is required. The operating parameters and design features of the reactors have a great influence on the efficiency of the process. In this work, the possibility of continuous production of biohydrogen from confectionery wastewater was evaluated. The DF process was carried out at 37 ± 1 °C in two different reactors: an upflow anaerobic filter (AF) and a fluidized bed reactor (AFB). Polyurethane foam (PU) was used to immobilize the biomass. The DF process was studied at four hydraulic retention times (HRT) (1.5, 2.5, 7.5 and 15 days) and the corresponding organic loading rates (OLR) (9.21, 6.12, 2.04 and 1.02 g COD_init/(L day)). The highest hydrogen yield (HY) (44.73 ml/g COD_init) and hydrogen production rate (HPR) (92.5 ml/(L day)) was observed in AFB at HRT of 7.5 days and 2.5 days, respectively. The highest concentration of hydrogen in biogas was 34% in AF and 36% in AFB at HRT of 7.5 days. In contrast to AF, the COD removal efficiency in AFB increased with increasing HRT. The pH of the effluent was low (3.95–4.38). However, due to the use of PU for biomass immobilization, it is possible that there were local zones in the reactor that were optimal for the functioning of not only acidogens, but also methanogens. This was evidenced by a rather high content of methane in biogas (2.5% in AF and 9.6% in AFB at HRT of 15 days). These results provide valuable data for optimizing the continuous DF of wastewater from confectionery and other food industries to produce biohydrogen or biohythane.     

Kinetics and microstructural changes during fluidized reduction of magnetite with hydrogen at low temperatures

Hydrogen reduction has received much attention in reducing carbon dioxide emissions and becoming carbon neutral in the iron and steel industry. In this study, the low-temperature hydrogen reduction (H₂: N₂ = 80%: 20%) process of natural magnetite in a fluidized bed was investigated. The reduction kinetics, phase transformation, and microstructure changes were characterized using chemical analyses, X-ray diffraction, Brunauer–Emmett–Teller method, and scanning electron microscopy. The results revealed that the magnetite was reduced to metallic iron in one step in the temperature range of 495 °C to 570 °C, and the reaction rate increased with increasing temperature. The one-step reduction of magnetite was controlled by the phase boundary reaction, and the apparent activation energy was 29.76 kJ/mol. Microstructural analysis indicated that as the reduction reaction progressed, micropores and cracks on the surface of the solid particles gradually developed. The dense magnetite core was wrapped by the porous metallic iron, which promoted the penetration of hydrogen into the particles and continued the reaction.     

Gasification of preheated coal: Experiment and thermodynamic equilibrium calculation

A new process integrating a circulating fluidized bed (CFB) reactor and an entrained bed reactor was proposed for gasification of preheated coal. The CFB reactor as a preheater was successfully used in clean coal combustion. In this study, gasification of preheated coal was tested in a bench-scale test rig, which consisted of a CFB preheater and a down flow bed (DFB) gasifier. The effects of operating parameters of the preheater and gasifier were revealed via thermodynamic equilibrium calculations. A stable preheating process was obtained in the CFB preheater at the O₂/C molar ratio of 0.31 and higher gasification reactivity was gained in preheated char owing to the improvement in intrinsic reactivity, specific surface area and total pore volume. Effective gasification of preheated char was achieved in the DFB gasifier at 1100 °C and the total O₂/C molar ratio of 0.67, meanwhile the CO + H₂ yield and carbon conversion increased. Thermodynamic equilibrium calculations revealed when the gasification reaction rates varied little above 1100 °C and the same carbon conversion was achieve in gasifier, lowering the temperature would lead to an increase in cold gas efficiency and a decrease in O₂ demand.     

Hydrogen gas yield and trace pollutant emission evaluation in automotive shredder residue (ASR) gasification using prepared oyster shell catalyst

This work examines the hydrogen gas yield and trace pollutants partitioning in automobile shredder residue (ASR) catalytic gasification by fixed bed and fluidized bed gasifier with controlling at equilibrium ratio (ER) 0.2, temperature 900 °C, and 5%–15% prepared catalyst addition. Oyster shell (OS) is a valuable resource due to its higher calcium content that it could prepare as a catalyst for enhancing the hydrogen production in ASR gasification. In the case of the fixed bed gasifier experiments, the highest lower heating value (LHV) and syngas production were found at 900 °C and 10% OS catalyst addition. The maximum H₂ and CO composition were 6.57% and 5.97%, respectively. The LHV of syngas was approximately 4.43 MJ/Nm³. The fluidized bed gasifier could provide a good ASR decomposition and heat transfer behavior. The syngas yield results indicated the maximum H₂ and CO composition were 12.12% and 10.59%, respectively. It was obviously showed that the syngas production and energy conversion efficiency were enhanced by applying fluidized bed gasifier. The maximum produced gas LHV was 10.77 MJ/Nm³ as well as the cold gas efficiency (CGE) of produced gas was 71.62%. On the other hand, the volatile sulfur and chlorine speciation formed in ASR gasification were mainly partitioned in the solid and/or liquid phase. It implied that tested OS catalysts could inhibit the volatile sulfur and chlorine speciation emission in the produced gas as well as enhance the produced gas quality. In summary, this research could provide basic insight into enhanced syngas production and quality in ASR catalytic gasification using the prepared OS catalyst.     

Synthesis of low-cost catalyst NiO(111) for CO2 hydrogenation into short-chain carboxylic acids

Reducing gaseous carbon dioxide to valuable chemicals and fuels by using gaseous hydrogen can decrease the concentration of greenhouse gases that contribute to global warming. Carbon dioxide conversion into fuels such as methane, methanol, and formic acid is a good hydrogen-storage method. In this paper, a comparative study of CO₂ conversion into formic and acetic acids on alumina-supported nickel oxide with and without the presence of carbon is reported. NiO (111) with high surface area was synthesized through a simple and one-pot fusion solid-state method at 550 °C and 700 °C. The synthesized catalysts were tested in carbon dioxide hydrogenation reaction in a batch slurry reactor at 130 °C and under mild pressure. Interestingly, the optimum condition of the reaction also successfully produced C₂ carboxylic acid in significant amounts. The highest levels of formic acid and acetic acid production were 8.13 and 7.63 mmol/L, respectively.     

Efficient photocatalytic hydrogen production from formic acid on inexpensive and stable phosphide/Zn3In2S6 composite photocatalysts under mild conditions

Developing an efficient, stable and low-cost photocatalytic hydrogen production from formic acid is a daunting challenge and has attracted the intense interest of many of researchers. In this paper, we report the synthesis of novel composite photocatalysts (Ni₂P/Zn₃In₂S₆ (ZIS6) and MoP/ZIS6) and their catalytic performance for H₂ production reaction from formic acid under visible light irradiation, in which Ni₂P and MoP were used as cocatalysts to enhance hydrogen generation activity of ZIS6. The photocatalytic hydrogen production rates of the optimized 1.5 wt% Ni₂P/ZIS6 (45.73 μmol·h⁻¹) and 0.25 wt% MoP/ZIS6 (92.69 μmol·h⁻¹) were 3.5 times and 7.2 times higher than that of the pure ZIS6 (12.88 μmol·h⁻¹), respectively. The apparent quantum efficiency at wavelength λ = 400 ± 10 nm for the two photocatalysts was about 1.8% and 6.4%, respectively. Significantly, it was found that the remarkable improvement of hydrogen production performance is attributed to the introduction of the phosphide cocatalysts, which can serve as a charge separation center and an active site for photocatalytic hydrogen production from the decomposition of formic acid. The reaction mechanism of photocatalytic hydrogen production from formic acid was also proposed.     

Investigation of the interaction between intermediates from gasification of biomass in supercritical water: Formaldehyde/formic acid mixtures

Supercritical water gasification (SCWG) is a promising technology for converting wet biomass and waste into renewable energy. While the fundamental mechanism involved in SCWG of biomass is not completely understood, especially hydrogen (H₂) production produced from the interaction among key intermediates. In the present study, formaldehyde mixed with formic acid as model intermediates were tested in a batch reactor at 400 °C and 25 MPa for 30 min. The gas and liquid phases were collected and analyzed to determine a possible mechanism for H₂ production. Results clearly showed that both gasification efficiency (GE) and hydrogen efficiency (HE) increased with addition of formic acid, and the maximum H₂ yield reached 17.92 mol/kg with a relative formic acid content of 66.67% in the mixtures. The total organic carbon removal rate and formaldehyde conversion rate also increased to 67.33% and 89.81% respectively. The reaction pathways for H₂ formation form mixtures was proposed and evaluated, formic acid promoted self-decomposition of formaldehyde to generate H₂, and induced a radical reaction of generated methanol to produce more H₂.     

CO2-free hydrogen production via microwave-driven methane pyrolysis

Hydrogen will play an integral role in achieving net-zero emissions by 2050. Many studies have been focusing on green hydrogen, but this method is highly electricity intensive. Alternatively, methane pyrolysis can produce hydrogen without direct CO₂ emissions and with modest electricity inputs, serving as a bridge from fossil fuels to renewable energies. Microwaves are an efficient method of adding the required energy for this endothermic reaction. This study introduces a new method of CO₂-free hydrogen production via non-plasma methane pyrolysis using microwaves and carbon products of this process. Carbon particles in the fluidized bed absorb microwave energy and create a hot medium (>1200 °C) in contact with flowing methane. As a result, methane decomposes into hydrogen and solid carbon achieving over 90% hydrogen selectivity with ∼500 cumulative hours of experiments This modular pyrolysis system can be built anywhere with access to natural gas and electricity, enabling distributed hydrogen production.     

Integrated design of hydrogen production and thermal energy storage functions of Al-Bi-Cu composite powders

In recent years, the hydrolysis of Al-based composite powders to produce hydrogen has become a hot topic in the field of hydrogen energy research. However, the hydrogen generation products of Al-based alloys have not been reasonably utilized. For this purpose, this study proposed a novel research idea to achieve the integrated design of hydrogen production and thermal energy storage functions of Al-based composite powders. Specifically, Al-Bi-Cu composite powders with stable hydrogen production were taken as research objects. The hydrogen was obtained by the reaction of Al-Bi-Cu alloy powders with H₂O for different reaction times, and then the hydrogen generation products were directly sintered at high temperature to obtain Al-Cu alloy based composite phase change thermal energy storage materials. The results indicated that at 50 °C, the hydrogen yield of Al-Bi-Cu alloy powders in 100min, 200min and 400min are 319.9 mL/g, 428.5 mL/g and 665.8 mL/g, respectively. Importantly, the Al-Cu alloy based composite phase change thermal energy storage materials prepared by the hydrogen generation products exhibited an adjustable phase change temperature (577.3 °C ∼ 598.2 °C), high thermal energy storage density (44.1J/g ∼ 153.5J/g), good thermal cycling stability and structural stability.     

Production and purification of hydrogen by biogas combined reforming and steam-iron process

Cobalt ferrite and hematite with minor additives have been tested for production and purification of high purity hydrogen from a synthetic biogas by steam-iron process (SIP) in a fixed bed reactor. A catalyst based in nickel aluminate has been included in the bed of solids to enhance the rate of the reaction of methane dry reforming (MDR). The reductants resulting from MDR are responsible for reducing the oxides based on iron that will, in the following stage, be oxidized by steam to release hydrogen with less than 50 ppm of CO. Coke minimization along reduction stages forces to operate such reactors above 700 °C for reductions, and as low as 500 °C for oxidations to avoid coke gasification. To avoid problems such as reactor clogging by coke in reductions and/or contamination of hydrogen by gasification of coke along oxidations, steam in small proportions has been included in the feed with the aim of minimizing or even avoiding formation of carbonaceous depositions along the reduction stage of SIP. Since steam is an oxidant, it exerts an inhibiting effect upon reduction of the oxide, that slows down the efficiency of the process. It has been proved that co-feeding low proportions of steam with an equimolar mixture of CH₄ and CO₂ (simulating a poor heating value desulphurized biogas) is able to avoid coke deposition, allowing the operation of both, reductions and oxidations, in isothermal regime (700 °C). Empirical results have been contrasted with data found in literature for similar processes based in MDR and combined (or mixed) reforming process (CMR), concluding that the combination of MDR + SIP proposed in this work, taking apart economic aspects and complex engineering, shows similar yields towards hydrogen, but with the advantage of not requiring a subsequent purification process.     

Photocatalytic hydrogen generation over alkaline-earth titanates in the presence of electron donors

The efficiency of alkaline-earth titanate-based compounds (Ca, Sr, Ba) for catalysts in photocatalytic hydrogen generation has been investigated. In this report, we have shown that the addition of organic donors (such as formic acid, acetic acid, methanol, 2-propanol and formaldehyde) enhanced the efficiency of the studied process. The systematic study has shown that the most efficient organic donor in regards to its hydrogen generation efficiency is formic acid. Of the catalysts explored, the highest photocatalytic activity was shown by SrTiO₃:TiO₂. Additionally, the effects of photocatalyst quantity and formic acid concentration on hydrogen evolution have been investigated.     

Fundamental design of a continuous biomass gasification process using a supercritical water fluidized bed

A novel biomass gasification (first stage of hydrogen production from biomass) process using a supercritical water fluidized bed was proposed and the fundamental design of the process was conducted. The flow rate was determined by evaluating the minimum fluidization velocity and terminal velocity of alumina particles enabling fluidization with the thermodynamic properties of supercritical water. Three cases were examined: a bubbling fluidized bed in which water was used mainly as the fluidized medium and biomass were added for gasification, a bubbling fluidized bed fluidized by biomass slurry feed alone, and a fast fluidized bed fluidized by biomass slurry feed alone. According to calculations of the residence time and thermal efficiency assuming heat recovery with a heat exchanger efficiency of 0.75, the bubbling fluidized bed fluidized by biomass slurry alone was appropriate for continuous biomass gasification using a fluidized bed.     

Extracting high-purity hydrogen via sodium looping-based formic acid dehydrogenation

Formic acid (FA) has been considered as a prospective hydrogen carrier for its potentials to realize hydrogen storage, transportation, and in-situ supply under mild conditions. However, the application of FA dehydrogenation is limited by its unsatisfactory hydrogen concentration and carbon monoxide selectivity. Herein, a sodium looping-based (Na₂CO₃?NaHCO₃) formic acid dehydrogenation (SLFAD) system is proposed for high-purity hydrogen production with ultra-low CO generation via the Na₂CO₃?NaHCO₃ looping. The SLFAD system consists of three parts, which are FA dehydrogenation reactor (FADR), sorption-enhanced carbon oxide removal reactor (CORR), and sodium-based sorbent regeneration reactor (SSRR). Experimental results proved that no sodium formate and sodium oxalate was formed under NaHCO₃ reduction by H₂. A comprehensive assessment of the system was carried out to preliminary verify the feasibility and optimize the operation parameters of the SLFAD system. Results indicated that a maximum hydrogen concentration of 97.905 vol%, a minimum CO concentration of 11.97 ppm, and a high hydrogen production rate of 0.99989 kmol H₂ h^?1 can be obtained under the conditions of atmospheric pressure, FADR temperature at 80 °C, H₂O/HCOOH = 1.2, CORR temperature at 80 °C, and Na₂CO₃/HCOOH = 1.0.