Nickel-iron modified natural ore oxygen carriers for chemical looping steam methane reforming to produce hydrogen

Chemical looping steam methane reforming (CL-SMR) is a promising and efficient method to produce hydrogen and syngas. However, oxygen carrier (OC) prepared by synthesis are complex, expensive and poor mechanical performance, while natural ore OCs are low activity and poor selectivity. In order to avoid these problems, Ni/Fe modification of natural ores were proposed to improve the reactivity and stability of OC to CL-SMR. The results indicated that the modified calcite recombined and improved the structural phase during the reaction, enhancing performance and inhibiting agglomeration. Moreover, high ratio of iron to nickel was easy to sinter and decline the OC performance. In addition, with the increase of steam flow, both CH₄ conversion and carbon deposition decreased. Thereinto, the highest H₂ concentration, CH₄ conversion efficiency and H₂ yield were obtained when the ratio of steam to OC was 0.05. Furthermore, CH₄ flow rate had a great impact on CL-SMR performance. When the ratio of CH₄ to OC was 0.04, it achieved the highest CH₄ conversion efficiency of 98.96%, the highest H₂ concentration of 98.83% and the lowest carbon deposition of 3.23%. However, the carbon deposition increased with the increase of CH₄ flow rate. After a long-time chemical looping process, the Ni/Fe modified calcite showed a consistently stable performance with average H₂ concentration of 93.08%, CH₄ conversion efficiency of 88.03%, and carbon deposition of 2.15%.     

Techno-economic assessment of a chemical looping reforming combined cycle plant with iron and tungsten based oxygen carriers

Chemical looping reforming (CLR) is an efficient technology that transforms hydrocarbons into hydrogen (H₂) and carbon dioxide (CO₂) with the use of an oxygen carrier. The three-reactor CLR (TRCLR) uses natural gas as fuel similar to a conventional steam-methane reforming (SMR) process. In the current study, two of the most suitable oxygen carriers with base metals iron (Fe) and tungsten (W) are investigated. The model of the CLR unit integrated with a combined cycle power plant is developed using Aspen Plus. The results show that the W-based TRCLR plants are 4 %-points more efficient in terms of H₂ production efficiency. In terms of electrical efficiency, the Fe-based TRCLR plant produces excess power at an efficiency of 1.6% whereas the W-based plant requires 3% of extra power from the grid. As a result, the Fe-based plant is 2.6 %-points more efficient than the W-based plant in terms of global efficiency. The costs of H₂ production for the Fe and W-based plants are estimated to be $1.66/kg and $16.92/kg, respectively. Compared to the SMR process, the cost of H₂ production from the Fe-based TRCLR plant is about 31% lower.     

Sustainable iron-based oxygen carriers for Chemical Looping for Hydrogen Generation

We report a detailed reactor study of two sustainable Fe-based oxygen carriers (OC) prepared by spray drying. We compare Fe₂O₃ supported on Al₂O₃ and MgFeAlO_x in isothermal Chemical Looping for Hydrogen Generation. In this process, CH₄ is converted into syngas (H₂ + CO) and H₂O is used as the oxidant that reduces to pure H₂. We noticed that the Al₂O₃ supported OC deactivates quickly while the MgFeAlO_x supported OC withstands >60 cycles. We will show that the irreversible formation of an inactive FeAl₂O₄ phase is responsible for the deactivation of the alumina supported OC. We show detailed information on all the transient stages of the process and the different crystalline forms that are created, and combine this information into a full chemical looping cycle for both OC. Moreover, we evaluate the crushing strength of the oxygen carriers within a full chemical looping cycle and during long-term operation and we investigated the conversion of H₂O and the selectivity to H₂-production during long-term oxygen carrier regeneration. The MgFeAlO_x support with an extra Fe-based active phase is a promising material to replace the typical Ni-based oxygen carriers, as it forms a sustainable non-toxic, stable and green alternative for hydrogen generation by chemical looping.     

Utilization of laterite ore as an oxygen carrier in chemical looping reforming of methane for syngas production

Growing energy demands in various sectors have resulted in overusing fossil fuel sources and rise in greenhouse gases in the atmosphere. This necessitates the need for reducing greenhouse gases and shifting to cleaner, renewable energy sources like H₂. Chemical looping is one such renewable method to produce clean H₂. The efficiency of this process depends on the oxygen carrier. Generally, oxygen carriers (OC) are transition metal oxides (Fe₂O₃ or NiO) or some complex metal oxides like spinel or perovskites, but usage of these OCs are restricted due to their availability and redox performance. One solution for selecting OCs can be using industrial waste like slag or low-grade ores because of their composition, which consists of metal oxides. One such low-grade ore is Ni-laterite ore or chromite overburden, a mining waste found in the chromite mines of Sukinda (India). In this work, we have focused on utilizing this laterite ore as an OC for the chemical looping reforming of methane to produce syngas. The reactivity analysis of laterite ore with CH₄ was performed in DSC-TG and the reaction products were analyzed in gas chromatography along with microscopy and spectroscopic techniques. Results showed the formation of H₂ and CO gases along with reduced metallic phases. The total H₂ yield at 750 °C is determined to 53.67 (±1.09) ml/g of OC which is comparable or even higher than existing CeO₂ based OCs. Further, thermodynamic calculations are presented to calculate the theoretical yield for our process and compared with the experimental H₂ yield. This study effectively demonstrates the performance of laterite ore as an OC for generating clean and renewable energy through chemical looping technique.     

Chemical looping gasification of cotton stalk with bimetallic Cu/Ni/olivine as oxygen carrier

Bimetallic Cu/Ni/olivine oxygen carriers (OCs) were prepared using olivine as support material for chemical looping gasification (CLG). The cyclic redox behaviors and oxygen carrying capacity (R_o) of OCs were evaluated by thermo-gravimetric analysis. The effect of Cu/Ni ratio, gasification temperature, steam to biomass ratio (S/B), oxygen carrier to biomass ratio (OC/B) on CLG of cotton stalk has been studied in a fixed bed. The OCs characterized using BET surface area, scanning electron microscopy (SEM), X-ray diffraction (XRD), temperature-programmed reduction (TPR) to investigate the physicochemical property of OCs during CLG. Result shows that the sintering problem of OC was progressively alleviated with the increasing Cu/Ni ratio. The olivine behaves as suitable OC support with oxygen carrying capacity of 1.07%. The redox reactivity of all of the OCs kept well during multiple redox cycles. The R_o of OCs progressively increased with the Cu/Ni ratio. By comparing the product gas concentration, carbon conversion, H₂ + CO yield and gas yield over the invested OCs, the Cu9/Ni6/O was found to demonstrate better comprehensive CLG performance due to the synergistic effect of Cu and Ni. The maximum gas yield, H₂ + CO yield and carbon conversion with Cu9/Ni6/O can be obtained at the S/B of 0.8 and OC/B of 2. Compared to theoretical value, 65% of lattice oxygen has been supplied by Cu9/Ni6/O during actual CLG process. The OC displayed better reactivity due to basic crystalline phase being preserved well during multiple CLG cycles.     

Advances in the application of active metal-based sorbents and oxygen carriers in chemical looping biomass steam gasification for H2 production

Active metal-based materials (AMMs) as CO₂ sorbents or oxygen carriers (OCs) have been investigated to enhance hydrogen production during various biomass-based chemical looping processes. CaO-based sorbents and Fe-based OCs are widely used in this field; therefore, these two types of materials will be the focus of this review. CaO-based sorbents can promote the water-gas shift reaction towards H₂ generation with in-situ CO₂ removal. OCs partly oxidise biomass, releasing CO – a reactant in the water-gas shift reaction. The use of Fe-based OCs boosts H₂ yield via iron-steam reactions. AMMs possess catalytic activity for tar cracking, generating more H₂. However, these AMMs suffer from sintering over cycles, which hinders their utilisation at industrial scales. The addition of support materials aims to overcome this issue. This review first assesses the impacts of CaO sorbents and OCs on H₂ production, and then examines the material behaviour, cyclic performance and applications in biomass-based chemical looping processes. The mechanism of support materials as a reactivity enhancer and sintering inhibitor is proposed in the review. The effects of operating conditions on H₂ yield are summarised and provided in the Supplementary materials.     

Study of the reactivity by pulse of CH4 over NiO/Fe-doped MgAl2O4 oxygen carriers for hydrogen production

The reactivity of Ni-based oxygen carrier (OC) was studied by CH₄ pulse test. The MgAl₂O₄ spinel was synthesized by microwave assisted combustion method and Ni and Fe were added by wet impregnation method. The results of CH₄ pulse test revealed that the OCs were more reactive for partial oxidation reaction. The XRD analysis of OCs after the test confirms the presence of NiO and MgAl₂O₄ without the secondary phases like NiAl₂O₄ and FeAl₂O₄. Among the OCs, Ni15Fe2MA was the most reactive producing the highest amounts of H₂ and exhibiting good re-oxidation capacity, illustrating its potential for use in Chemical Looping Reforming (CLR). The high reactivity is associated to a change on the NiO-support interaction.     

Synthesis of a new self-supported Mgy(CuxNi0.6-xMn0.4)1-yFe2O4 oxygen carrier for chemical looping steam methane reforming process

Novel self-supported Mg_y(Cu_xNi_0.6-xMn_0.4)_1-yFe₂O₄ with (y = 0, 0.05, 0.1, 0.15, and x = 0, 0.15, 0.3, 0.45, 0.6) oxygen carriers (OCs) are synthesized through the co-precipitation method. The synthesized OCs’ properties are characterized by X-ray powder diffraction (XRD), Raman spectra, transform infrared spectroscopy (FT-IR), Brunauer-Emmett-Teller (BET), transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDX), and Thermogravimetric Analysis (TGA). The synthesized OCs are assessed in Chemical Looping Steam Methane Reforming (CL-SMR) process subject to different mesh sizes, reaction temperatures, Steam/Carbon (S/C) molar ratios, Mg concentrations, and Cu and Ni concentrations. The characterization of the OCs and process results indicate the contributive effect of Mg incorporation on the Cu_xNi_0.6-xMn_0.4Fe₂O₄ support structure. The redox results reveal that Mg_0.1(Cu_0.3Ni_0.3Mn_0.4)_0.9Fe₂O₄ OC is of the highest activity, even at low reduction temperatures. This OC exhibits the highest activity and stability with lowest coke deposition during 24 redox cycles at 650 °C and S/C = 2.5. The highest CH₄ conversion of about 99.4% and H₂ yield of about 84.4% are obtained.     

Metal modified hexaaluminates for syngas generation and CO2 utilization via chemical looping

Chemical looping CH₄CO₂ reforming (CLDR) is an emerging technology for the generation of Fischer-Tropsch ready syngas and CO₂ utilization, which is strongly dependent upon the improvement in the design of efficient oxygen carriers (OCs). In this present work, different metal additives (Si, Zr and Ce ions) were introduced into Fe-based hexaaluminates and used OCs for CLDR. The microstructure and reactivity of BaFe_2.8M_0.2Al₉O₁₉ (M = Fe, Si, Zr, and Ce) OCs were found greatly influenced by the metal additives and CH₄/CO₂ redox treatment. Pure Fe and Ce doped OCs showed the co-existence of both β-Al₂O₃ and MP hexaaluminate phases, while the introduction of Si and Zr in the hexaaluminate structure led to the phase transformation from β-Al₂O₃ into MP. During the CH₄/CO₂ redox process, large amounts of Fe species in both BaFe_2.8Si_0.2Al₉O₁₉ and BaFe_2.8Zr_0.2Al₉O₁₉ OCs were gradually stabilized in sintering FeAl₂O₄ with low oxygen-storage capacity, which resulted in low CH₄ reactivity and weak cyclic stability. However, Ce-doped BaFe_2.8Ce_0.2Al₉O₁₉ OC showed good reactivity and stability during the 10 redox cycles with CH₄ conversion of 93%, H₂/CO ratio of ∼2, high syngas yield of 2.2 mmol/g, and high CO₂ activation ability of 0.95 mmol/g, which was associated with the preservation of hexaaluminate main phase, the formation of CeFe_xAl_1-xO₃ and the abundant oxygen vacancies.     

Thermodynamic analysis of plant-wide CLC-SESMR scheme for H2 production: Studying the effect of oxygen carrier supports

Sorption enhanced steam methane reforming (SESMR) integrated with chemical looping combustion (CLC) is one of the most capable greener technologies that allows co-generation of H₂ from natural gas together with CO₂ capture. The performance of CLC mainly depends on the sustained reactivity, strength and durability of oxygen carriers (OCs). A suitable combination of active OCs with optimal inert composition is essential to meet the overall thermal demand of integrated CLC-SESMR process. In this work, the effect of inert OC supports on the performance of CLC-SESMR has been studied through thermodynamic analysis based on steady-state plant wide models developed using ASPEN plus. Ni-based OCs are considered with two different support materials, SiC/Al₂O₃ and MgAl₂O₄ at different inert compositions ranging from 0 to 70% by weight. The sensitivity analysis results revealed that H₂ purity and CO₂ captured are directly proportional to the inert composition while H₂ yield is inversely proportional. The optimal inert compositions are found to be 30% and 40% by weight for the respective cases of SiC/Al₂O₃ and MgAl₂O₄. In both the cases, the overall performance of CLC-SESMR is found to be nearly same, i.e., with 97% overall methane conversion, 96% CO₂ captured, 98.3% H₂ purity, 2.24 H₂ yield, and 71.4% net plant efficiency.     

Syngas production by chemical looping gasification of rice husk using Fe-based oxygen carrier

The chemical looping gasification (CLG) of rice husk was conducted in a fixed bed reactor to analyze the effects of the ratio of oxygen carrier to rice husk (O/C), temperature, residence time and preparation methods of Fe-based oxygen carriers. The yield of gas, H₂/CO, lower heating value of syngas (LHV), conversion efficiency and performance parameters were analyzed to obtain CLG reaction characterization and optimal reaction conditions. Results showed that when O/C increased from 0.5 to 3.0, the gas production, H₂/CO, CO₂ yield and carbon conversion efficiency gradually increased, while the yield of H₂, CO and CH₄ and LHV gradually decreased. At the same time, a highest gasification efficiency was obtained when O/C was 1.5. As increasing temperature, the gas production, CO yield, carbon conversion efficiency and gasification efficiency gradually increased, while the yield of H₂, CH₄ and CO₂, H₂/CO and LHV gradually decreased. Sintering and agglomeration was obvious when the temperature was higher than 850 °C. When the reaction time increased from 10 min to 60 min, the gas production, CO yield, carbon conversion efficiency and gasification efficiency gradually increased, but the yield of H₂, H₂/CO and LHV decreased, among which 30 min was the best reaction residence time. In addition, coprecipitation was the best preparation method among several preparation methods of oxygen carrier. Finally, O/C of 1.5, 800 °C, 30 min and coprecipitation preparation method of oxygen carrier were the optimal parameters to obtain a gasification efficiency of 26.88%, H₂ content of 35.64%, syngas content of 56.40%, H₂/CO ratio of 1.72 and LHV of 12.25 MJ/Nm³.     

Interaction between bimetallic composite oxygen carriers and coal and its contribution to coal direct chemical looping gasification

Coal direct chemical looping gasification (CDCLG) to produce synthesis gas was investigated with Fe-based bimetallic composite oxygen carriers (Fe–M oxides, M = Ba, Ca, Cu, Ni and Co). Thermogravimetric-mass spectrum analysis and fixed-bed tests indicated that reaction between coal and Fe-based composite oxygen carriers via direct contact could not be negligible in the CDCLG process. The contribution of the reaction between the two solid particles to the carbon conversion was estimated. Furthermore, the yields of synthesis gas production were also conducted to evaluate performance for the prepared samples. Of the five investigated Fe-based bimetallic composite oxygen carriers (OCs), Fe–Ni oxides/Al₂O₃ presented high reactivity with coal and high selectivity for synthesis gas during coal-OC steam gasification, which made it attractive for the CDCLG process. By comparing with the main phases of the Fe-based OCs after cycling and the raw samples before test, it could be observed that there were no significant changes in material phases. Combined with the SEM images of the Fe-based OCs samples, we can conclude that the prepared OCs showed a good heat-resistant property, which was beneficial for keeping a stable performance in the CDCLG experiment.     

Syngas production from chemical looping gasification of rice husk-derived biochar over iron-based oxygen carriers modified by different alkaline earth metals

Oxygen carrier (OC) is a key factor in chemical looping gasification (CLG). Iron oxide is a promising OC due to advantages regarding cost and environment; however, its reactivity with biochar requires improvement to increase syngas production. The novelty of this work is to compare the performance of alkaline earth metals (AEMs: Ca, Ba, and Mg) ferrites and iron oxide OCs for enhancing syngas production from CLG of biochar. The thermogravimetric analyzer and fixed bed system were used to investigate OCs performance. The results demonstrated that the AEMs ferrites have good gasification performance, and BaFe₂O₄ showed highest syngas yield through solid-solid reaction. Furthermore, CLG was conducted under steam addition, and the results revealed that all AEMs ferrites had improved the performance compared to iron oxide, as syngas yield increased by 39.2%, 15.7%, and 13.8% for BaFe₂O₄, CaFe₂O₄, and MgFe₂O₄, respectively. The highest syngas produced by BaFe₂O₄ reached 0.07 mol/g of biochar.     

Study of the reactivity of Double-perovskite type oxide La1−xMxNiO4 (M = Ca or Sr) for chemical looping hydrogen production

La_2-xM_xNiO₄ perovskite oxygen carriers (OC) doped with Ca and Sr (x = 0.05 and 0.20) in the site La were prepared by microwave assisted combustion method and calcined at 800 °C for 2 h. A reactivity study was carried out applying pulses of H₂, O₂ and CH₄. The reactions involved in each step, as well as H₂ production, were studied to evaluate the redox properties of each OC. The crystalline structure, morphology, reduction and oxidation profiles were determined by XRD, SEM and TPR/TPO cycles, respectively. The results indicate that the dopant (Ca or Sr) strongly affect the structure and reactivity of the OC. The increase in dopant concentration increased the degree of crystallinity and the amount of the A₂BO₄ phase formed. The increase in dopant concentration decreased the reducibility of the perovskite. OCs doped with Ca showed higher conversion percentages, and also higher H₂ production. In carriers doped with Sr no coke formation was observed.     

Hydrogen production via chemical looping steam reforming of ethanol by Ni-based oxygen carriers supported on CeO2 and La2O3 promoted Al2O3

This work studies the effects of Ce⁴⁺ and/or La³⁺ on NiO/Al₂O₃ oxygen carrier (OC) on chemical looping steam reforming of ethanol for hydrogen production - alternating between fuel feed step (FFS) and air feed step (AFS). Suitable amount of Ce- and La-doping increases OC carbon tolerance. The solubility limit is found at 50 mol% La in solid solution. At higher La-doping, La₂O₃ disperses on the surface and adsorbs CO₂ forming La₂O₂CO₃ during FFS. From the 1st cycle, 12.5 wt%Ni/7 wt%La₂O₃-3wt%CeO₂–Al₂O₃ (N/7LCA) displays the highest averaged H₂ yield (3.2 mol/mol ethanol) with 87% ethanol conversion. However, after the 5th cycle, 12.5 wt%Ni/3 wt%La₂O₃-7wt%CeO₂–Al₂O₃ (N/3LCA) exhibits more stability and presents the highest ethanol conversion (88%) and H₂ yield (2.7 mol/mol ethanol). Amorphous coke on the OCs decreases with increasing La³⁺ content and can be removed at 500 °C during AFS; nevertheless, fibrous coke and La₂O₂CO₃ cannot be eliminated. Therefore, after multiple redox cycles, highly La-doped OCs exhibits rather low stability.     

Comparison of metallic oxide,natural ore and synthetic oxygen carrier in chemical looping combustion process

As one of clean coal combustion ways, chemical looping combustion (CLC) showed high CO₂ capture efficiency with lower energy penalty. But these processes were limited by the low reaction rate between oxygen carriers (OCs) with coal char. This study evaluated the performances of Cu-based OCs with coal in in-situ gasification chemical-looping combustion (iG-CLC) and chemical-looping with oxygen uncoupling (CLOU) process. CuO modified by iron ore and chrysotile were employed as OCs which the addition of chrysolite improved the char gasification and iron ore enhanced the stability of CuO at high temperature. Results showed that CuO supported by ores (chrysolite and iron ore) had better H₂ and CO conversion under H₂O atmosphere than CuO and iron ore. Chrysolite decorated CuO can convert almost all H₂ to H₂O at 850 °C. Synthetic OCs showed better stability and high temperature tolerance during 10 redox cycles.     

Identifying the roles of MFe2O4 (M=Cu,Ba, Ni,and Co) in the chemical looping reforming of char,pyrolysis gas and tar resulting from biomass pyrolysis

Biomass chemical looping gasification (BCLG), which employs oxygen carriers (OCs) as the gasification agent, is drawing more attention for its low cost and environmental friendliness. However, the complex products of biomass pyrolysis and the reactions between OCs and the pyrolysis products constrain its development. In this study, MFe₂O₄ (M = Cu, Ba, Ni and Co) ferrites synthesized via the sol-gel method were investigated as OCs in BCLG for hydrogen-rich syngas production. The properties of the as-prepared and spent OCs were characterized by X-ray diffraction (XRD), H₂-temperature programmed reduction (TPR), scanning electron microscopy (SEM), and automatic surface area porosimetry (BET). The three-phase products (char, pyrolysis gas and toluene) derived from biomass pyrolysis were employed as the reactants to investigate the reactivity of the ferrites. Then, BCLG experiments using biomass were conducted on the four ferrites to further determine their performance. The characterization results suggested that the four ferrites are all attractive for the chemical looping process, exhibiting good oxygen transferability and wide distributions of metal cations because of their metal synergistic effects in the spine structure. Reactions with pyrolysis gas and biomass char indicated that BaFe₂O₄ has a higher reactivity via a solid-solid reaction but a lower reactivity with pyrolysis gas, which make it very favorable for the production of hydrogen-rich syngas. Furthermore, BaFe₂O₄ showed excellent performance for toluene catalytic cracking with small amounts of carbon deposition. The synergetic effects between Ba and Fe metals considerably enhanced selective oxidation to produce 26.72% more H₂ than CoFe₂O₄ and 13.79% more H₂ than NiFe₂O₄ and CuFe₂O₄ for biomass gasification. The hydrogen yield produced by BaFe₂O₄ with the assistance of steam for biomass gasification can reach 41.8 mol/kg of biomass.     

One-stage H2 and CH4 and two-stage H2 + CH4 production from grass silage and from solid and liquid fractions of NaOH pre-treated grass silage

In the present study, mesophilic CH₄ production from grass silage in a one-stage process was compared with the combined thermophilic H₂ and mesophilic CH₄ production in a two-stage process. In addition, solid and liquid fractions separated from NaOH pre-treated grass silage were also used as substrates. Results showed that higher CH₄ yield was obtained from grass silage in a two-stage process (467 ml g⁻¹ volatile solids (VS)_original) compared with a one-stage process (431 ml g⁻¹ VS_original). Similarly, CH₄ yield from solid fraction increased from 252 to 413 ml g⁻¹ VS_original whereas CH₄ yield from liquid fraction decreased from 82 to 60 ml g⁻¹ VS_original in a two-stage compared to a one-stage process. NaOH pre-treatment increased combined H₂ yield by 15% (from 5.54 to 6.46 ml g⁻¹ VS_original). In contrast, NaOH pre-treatment decreased the combined CH₄ yield by 23%. Compared to the energy value of CH₄ yield obtained, the energy value of H₂ yield remained low. According to this study, highest CH₄ yield (495 ml g⁻¹ VS_original) could be obtained, if grass silage was first pre-treated with NaOH, and the separated solid fraction was digested in a two-stage (thermophilic H₂ and mesophilic CH₄) process while the liquid fraction could be treated directly in a one-stage CH₄ process.     

Gasification of landfill leachate in supercritical water: Effects on hydrogen yield and tar formation

Landfill leachate was gasified in supercritical water (SCW) in a batch reactor made of 316 SS. The effects of temperature, pressure, reaction time and oxidation coefficient (OC) on the pollutant removal efficiencies and gasification characteristics were investigated. To observe the formation of tar and char visually, a capillary quartz reactor was also used. Results indicated that CO₂, H₂ and CH₄ were the most abundant gaseous products. Temperature has an appreciable effect on the gasification process. Increasing temperature enhanced the H₂ yield (GY_H2) and TOC removal efficiency (TRE) significantly. Although the influence of reaction time on the fractions of gaseous products was negligible at time above 300 s, the yields of H₂, CH₄, and CO₂ increased with reaction time whereas the CO, C₂H₄ and C₂H₆ yields decreased. Tar and char formation was evident on the interior surface of capillary quartz reactor. Adding a little oxidant could increase H₂ and CH₄ yields and decrease tar and char formation. GY_H2 reached up to the maximum of 231.3 mmol L^?1 leachate at 500 °C, 25 MPa, 600 s and 0.2 OC, which was 2.4 times of that without oxidant.     

Design of a novel biohythane process with high H2 and CH4 production rates

A biohythane process based on wheat straw including: i) pretreatment, ii) H₂ production using Caldicellulosiruptor saccharolyticus, iii) CH₄ production using an undefined consortium, and iv) gas upgrading using an amine solution, was assessed through process modelling including cost and energy analysis. According to simulations, a biohythane gas with the composition 46–57% H₂, 43–54% CH₄ and 0.4% CO₂, could be produced at high production rates (2.8–6.1 L/L/d), with 93% chemical oxygen demand (COD) reduction, and a net energy yield of 7.4–7.7 kJ/g dry straw. The model was calibrated and verified using experimental data from dark fermentation (DF) of wheat straw hydrolysate, and anaerobic digestion of DF effluent. In addition, the effect of gas recirculation was investigated by both wet experiments and simulation. Sparging improved H₂ productivities and yields, but negatively affected the net energy gain and cost of the overall process.