Highest Hydrogen Yield Research Articles

Metal boride-decorated CoNi layered double hydroxides supported on muti-walled carbon nanotubes as efficient hydrolysis catalysts for sodium borohydride

Without effective and secure hydrogen production, it is impossible to utilize hydrogen energy on a large scale. Whereas hydrogen emission from NaBH4 hydrolysis with high hydrogen yield is an impressively efficient hydrogen supply method. However, it is affected by sluggish hydrogen production kinetics and low yields, therefore it is required to develop hydrolysis catalysts with good performance under alkaline conditions. In this study, a composite of unique CoNi layered double hydroxide (CoNi-LDH) nanosheets interconnected by muti-walled carbon nanotubes (MWCNTs) was prepared for the first time, and the surface was modified with metal borides produced by in-situ reduction. Among them, CoNi-LDH nanosheets are created when CoNi-MOF spontaneously derivates in alkaline electrolytes. The successful preparation of CoB-LDH-CNT has been confirmed by SEM, TEM, EDS, XRD, and XPS characterization. The hydrolysis experiments show that it has good catalytic activity with an optimal hydrogen generation rate (HGR) of 5167.72 mL·min−1·g−1 and low activation energy (Ea) of 29.93 kJ·mol−1. After ten cycles of experiments, it still has 75.4% of the initial performance, showing excellent stability, which may be attributed to the fact that MWCNTs can help to reconnect broken nanosheets during the reaction. This interconnected multistage structure offers a new methodology for enhancing the catalytic performance of metal boride and metal hydroxide materials.

Degradation of rubber waste into hydrogen enriched syngas via microwave-induced catalytic pyrolysis

Microwave-induced catalytic pyrolysis of end-of-life tires was conducted for the purpose of producing hydrogen-enriched syngas. Tire derived char (TDC) was employed as the catalyst due to its superiorities of excellent microwave-absorbing ability, remarkable catalytic effect, and cost-effectiveness. The effects of the carbon structure, microwave power, and tire-to-catalysts ratio on the hydrogen yield and conversion rate were investigated. TDC had two functions in promoting the production of hydrogen in microwave-induced pyrolysis (MP). One was facilitating the degradation of tar into gas, and the other was initiating the catalytic reforming of light hydrocarbons into hydrogen. The highest hydrogen yield (27.81 mmol/g) and conversion rate (85.57%) were obtained under optimal experimental conditions. The as-generated TDC in MP could be reused as a catalyst for MP, thus improving the economics of this method significantly. This research provides an efficient and economical strategy for the microwave-induced pyrolysis of end-of-life tires to produce hydrogen-rich syngas.

Co–solvent effects on hydrothermal co–gasification of coal/biomass mixtures for hydrogen production

The use of low–rank coals for hydrogen production by gasification can create advantageous options to overcome a potential energy crisis. In this study, the effects of 8 different solvents on gasification and hydrogen yield in coal/biomass co–solvent hydrothermal gasification were investigated. The most effective co–solvent on product conversion and high hydrogen yield was found N–methyl pyrrolidone (NMP) and tetrahydrofuran (THF). Total gas volumes and hydrogen yields obtained from the co–solvent gasification of coal/sorghum blends were higher than the arithmetical sum of the average values of the yields from individual solvent and coal/sorghum blend gasifications. The increase in the hydrogen yield was 11 mol H2/kg feed with the co–solvent THF due to the synergistic effects of THF on hydrogen production. Solvent concentration was effective on both total gas volumes and hydrogen yields. In the catalytic (K2CO3/CaO) runs with a concentration of 20 % (v/v) NMP co–solvent 98.8 ± 0.1 mol H2/kg feed was achieved with a dramatic decrease of CO content in the produced gas mixture. The comparison of the results obtained from subcritical and supercritical water conditions showed that in catalytic processes co–solvent was more effective towards feedstock conversion and almost the same hydrogen yields obtained at lower pressures under the subcritical water conditions.

Defected tungsten disulfide decorated CdS nanorods with covalent heterointerfaces for boosted photocatalytic H2 generation

Owing to their intrinsic and pronounced charge carrier transport when facing the formidable challenge of inhibiting severe surface charge recombination, one-dimensional (1D) CdS nanostructures are promising for advancing high-yield hydrogen production. We herein demonstrate an efficient strategy of boosting interfacial carrier separation by heterostructuring 1D CdS with defective WS2. This process yields solid covalent interfaces for high flux carrier transfer that differ distinctively from those reported structures with physical contacts. As a nonnoble cocatalyst, WS2 can accept photogenerated electrons from CdS, and the sulfur vacancies existing at its edges can effectively trap electrons as active sites for H2 evolution. Moreover, due to its strong negative property, the H+ from the aqueous solution can gather around WS2. WS2 possesses a lower reaction barrier than CdS, which expedites the kinetic process for the reaction. The optimized sample exhibits a high photocatalytic H2 evolution rate of 183.4 µmol/h (10 mg photocatalyst), which is as far as we know among the top in the records for CdS-based photocatalysts. We believe this present work will be inspiring in addressing the interfacial charge carrier transfer by constructing covalent heterointerfaces.

Combined Bio-Hydrogen, Heat, and Power Production Based on Residual Biomass Gasification: Energy, Exergy, and Renewability Assessment of an Alternative Process Configuration

Bio-hydrogen from residual biomass may involve energy-intensive pre-treatments for drying and size management, as in the case of wet agro-industrial residues. This work assesses the performance of an alternative process layout for bio-hydrogen production from citrus peel gasification, with the aim of cogenerating heat and power along with hydrogen, using minimal external energy sources. The process consists of an air-steam fluidized bed reactor, a hydrogen separation unit, a hydrogen compression unit, and a combined heat and power unit fed by the off-gas of the separation unit. Process simulations were carried out to perform sensitivity analyses to understand the variation in bio-hydrogen production’s thermodynamic and environmental performance when the steam to biomass ratios (S/B) vary from 0 to 1.25 at 850 °C. In addition, energy and exergy efficiencies and the integrated renewability (IR) of bio-hydrogen production are evaluated. As main results, the analysis showed that the highest hydrogen yield is 40.1 kgH2 per mass of dry biomass at S/B = 1.25. Under these conditions, the exergy efficiency of the polygeneration system is 33%, the IR is 0.99, and the carbon footprint is −1.9 kgCO2-eq/kgH2. Negative carbon emissions and high values of the IR are observed due to the substitution of non-renewable resources operated by the cogenerated streams. The proposed system demonstrated for the first time the potential of bio-hydrogen production from citrus peel and the effects of steam flow variation on thermodynamic performance. Furthermore, the authors demonstrated how bio-hydrogen could be produced with minimal external energy input while cogenerating net heat and power by exploiting the off-gas in a cogeneration unit.

Single step microwaves assisted catalytic conversion of plastic waste into valuable fuel and carbon nanotubes

The deconstruction of plastic waste into hydrogen, carbonaceous materials and hydrocarbons is an attractive way of meeting the global energy demand. This paper presents single-step microwave pyrolysis of high-density plastic waste using different catalysts to produce hydrogen and carbon nanotubes (CNTs). For catalytic pyrolysis, NiFe2O4, Al2O3, and Fe2O3 catalysts were prepared through a facile sol-gel method. The highest hydrogen yield was recorded with NiFe2O4 catalyst, which is about 57 mmol.g−1. The hydrogen production efficiency was about 93 wt.%. In comparison to polypropylene (PP) and high-density polyethylene (HDPE), the polystyrenes (PS) produced the highest yield of solid carbon (73 wt.%) with NiFe2O4 catalyst. The produced CNTs were characterized through XRD, TEM, SEM, TGA and RAMAN spectroscopy. The NiFe2O4 catalyst produced relatively pure and well-structured CNTs as compared to Al2O3 and Fe2O3 catalysts.

Capture‐Transport Double Enhancement Strategy to Construct High‐efficiency Photo‐catalysts with p‐n Junction for Hydrogen Production under Visible‐light Irradiation

AbstractThe conversion of solar energy into chemical energy by photo‐hydrolysis is considered as an effective way to solve current energy and environmental problems. The preparation of photo‐catalysts with excellent activity is expected to promote the rapid development of photo‐catalytic hydrogen production research. A two‐step strategy is used to obtain a CdS‐based photo‐catalyst with enhanced photo‐hydrogen production efficiency by improving the electron transport efficiency and the intrinsic electric field to promote electron separation. The CdS/Ag2S/NiS nanocomposites were prepared by a two‐step method in this work. After characterization of the structure, optical properties and surface chemical state by XRD, EDS, XPS, TEM and UV‐vis, it is found that Under visible light exposure (λ=420 nm), when the ratio of NiS is 11 %, the sample got the highest hydrogen yield (3280 μmol ⋅ g−1 ⋅ h−1), which is 2.8 times of CdS/Ag2S material, and also showing good cycle stability. The improved catalytic efficiency can be attributed to two points: the introduction of Ag2S provides more electro‐chemical active sites and routes for nano‐materials; the introduction of NiS builds an internal electric field to promote the transmission and separation of optical electrons and holes, and improve aquatic hydrogen capacity.

Hydrogen Production from Enzymatic Hydrolysates of Alkali Pre-Treated Giant Reed (Arundo donax L.)

The perennial rhizomatous grass giant reed (Arundo donax L.) can be exploited to produce hydrogen by dark fermentation. This implies a high availability of simple sugars, like glucose and xylose, and, thus, a pre-treatment is necessary to remove lignin and expose the holocellulose to enzymatic attack. This study aimed at evaluating the hydrogen production from giant reed hydrolysates. Giant reed dry meal was pre-treated with diluted NaOH (1.2% weight/weight), then the solid fraction was separated from the alkaline black liquor by filtration, enzymatically hydrolyzed with a cellulase blend (Cellic CTec2), and fermented in mesophilic batch conditions with a microbial consortium derived from pig slurry. The impact on hydrogen yield of initial pH was evaluated by comparing the hydrogen production from hydrolysates with not adjusted (5.3) or adjusted initial pH (8.7) using NaOH or alkaline black liquor. The highest hydrogen yield, 2.0 mol/mol of hexoses, was obtained with alkaline initial pH 8.7, regardless of how the pH adjustment was managed. The yield was 39% higher than that obtained in reactors with initial pH 5.3. In conclusion, thermo-alkaline pre-treatment followed by enzymatic saccharification and initial pH adjustment at 8.7 with the black liquor remaining after pre-treatment is a promising strategy to produce hydrogen from giant reeds in dark fermentation.

Investigation of Hydrogen Production from Sodium Borohydride in the Presence of Ni/Al2O3

With the increasing trend towards the use of renewable energy and the encouragement of international agreements due to environmental effects, the world tends to provide the energy it needs from renewable sources. Hydrogen is an environmentally friendly energy carrier that is produced from various energy sources and can be a sustainable solution to energy needs. Catalyst evaluation studies are carried out in studies that release high purity hydrogen by hydrolysis of metal hydrides such as sodium borohydride (NaBH4), and potassium borohydride (KBH4). In this study, Al2O3 supported Ni catalysts were synthesized by the impregnation method and the catalysts were characterized by applying X-Ray Diffractometry (XRD), X-Ray Fluorescence (XRF), Scanning Electron Microscopy (SEM), and Brunauer-Emmett-Teller (BET) methods. The performance of the catalysts was evaluated in the production of hydrogen by the hydrolysis of sodium borohydride. The influences of reaction temperature (20, 40, and 60 °C) and Ni content of the catalyst (20, 30, and 40 %) on the hydrolysis reaction was investigated under experimental conditions of 100 mg NaBH4, 100 mg catalyst, 5 mL 0.25 M NaOH. The highest hydrogen yield (100%) and hydrogen production rate (364.3 mL/gcat.min) was obtained with 40% Ni/Al2O3 catalyst at 60 °C reaction temperature.

Preparation of Co-Ce-O catalysts and its application in auto-thermal reforming of acetic acid

The well-dispersed Co species which partly incorporated into the lattice of CeO 2 (nanorod) was successfully synthesized, and a higher proportion of Ce 3+ /(Ce 3+ + Ce 4+ ) and enhanced oxygen mobility were thus obtained, which accounts for the high reactivity in auto-thermal reforming of acetic acid. • Well-dispersed Co species partly doped into the lattice of CeO 2 (nanorod). • Enhanced oxygen mobility and higher Ce 3+ was observed over Co-Ce-O (nanorod). • Co-Ce-O (nanorod) presents high hydrogen yield of 2.69 mol-H 2 /mol-HAc at 600 °C. As the preparation method was vital to modify the structure of catalysts, Co-Ce-O oxides were fabricated via different hydrothermal methods and evaluated in auto-thermal reforming (ATR) of acetic acid (HAc) for hydrogen production. Results of characterizations, including XRD, BET, H 2 -TPR, SEM and XPS, indicated the structure and electronic characteristics of each catalyst varied with different synthesis methods. In the case of CC-R with the morphology of nanorod, well-dispersed Co species were partly incorporated into the lattice of CeO 2 support, resulting in a higher proportion of Ce 3+ /(Ce 3+ + Ce 4+ ) and enhanced oxygen mobility. Consequently, it exhibited a promising catalytic performance in a 10-h testing in ATR of HAc: HAc conversion maintained at 96.8% with hydrogen yield recorded at 2.69 mol-H 2 /mol-HAc at 600 °C, while almost no by-product was detected, demonstrating its potential for hydrogen production.

Obtaining High Yield Hydrogen from Sewage Sludge by Two-Stage Gasification: Alkaline Pyrolysis Coupled with Catalytic Reforming

Municipal sludge is a sizable byproduct of sewage treatment plants, and its treatment and disposal need to agree with both environmental protection and resource utilization policies. In this study, municipal sludge was treated to produce hydrogen as a resource. A two-stage reactor was employed, and alkaline pyrolysis was coupled with ex-situ catalytic gasification and optimized to promote hydrogen production from sludge. The gas production characteristics were analyzed under different gasification parameters, and the catalyst was characterized following the reaction. Optimal gasification conditions were found at a steam flow of 5 mL h–1 in which 34.23 mmol g–1 of hydrogen was produced from dry sludge. Results suggested that the increased amount of hydrogen produced was due to promoting the water gas shift reaction. A brief economic analysis showed that this process is feasible for use in future industrial applications and provides an effective process route for the resource treatment of sludge.

Carbon nanotubes and (Mg10Ni)85Ce15 synergistically activate Mg-Al alloy waste for efficiently hydrolysis hydrogen generation

Hydrogen generation via Mg-Al alloy waste (MA) hydrolysis is regarded as a potential and promising strategy for portable hydrogen generators. An efficient modification method to obtain rapid kinetics and high yield for hydrolysis H2 generation needs to be further explored. At present, it is difficult to achieve rapid and high-yield hydrogen production process while maintaining high capacity. In this work, carbon nanotubes (CNTs) and (Mg10Ni)85Ce15 (MNC15) were creatively employed as additives to synergistically activate MA. Different content of additives was respectively or simultaneously employed through high energy ball milling process to investigate their synergistic effect. The results show that the simultaneous addition of MNC15 and CNTs can significantly improve the hydrolysis kinetics and hydrogen yield of MA. MA-5CNTs-10MNC15 can generate 806.6 mL·g−1 H2 with 0.92 yield at 328 K with initial 10 min. The thermodynamic behaviors of MA and activated MA were investigated in detail and the rate-controlling steps were further analysed via different hydrolysis stages. When 10 wt% CNTs added, Ea decreases from 33.6 kJ·mol−1 to 8.1 kJ·mol−1. The Ea of MA-5CNTs-10MNC15 can reach to 15.8 kJ·mol−1. The rate-controlling steps were confirmed to transform from three-dimensional interface to one dimensional-diffusion process. The synergistic activation effect was creatively explained by nucleation and growth up mechanism on the basis of the increased nucleation rate by MNC15 and enlarged growth space by CNTs. This work may provide a novel and efficient modified strategy for transforming Mg alloy waste into pure H2, which may pave way for the application of portable hydrogen generators.

H2 rich gas production from agricultural waste mixture over Ni/kaolin and Ni/bentonite catalyst by gasification

Biomass gasification is an attractive technology in order to utilize agricultural waste which is the mixture of oil extracted sunflower seeds (pulp), tea, and tobacco waste. In this study, natural clay-based catalysts were synthesized using the impregnation method with the different Ni loading amounts (10, 20, 30 wt%), different support materials (kaolin and bentonite). The catalysts were characterized by Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray fluorescence (XRF), Scanning electron microscopy (SEM), and Brunauer–Emmett–Teller analysis (BET). Gasification of biomass mixture was performed using air as the gasification agent using an updraft tubular gasifier. Studies were carried out at 650–850 °C and the time range of 15–30 min without a catalyst, and the studies with catalyst were carried out at a constant temperature of 650 °C. The highest hydrogen yield was obtained as 6.86 mol/kg biomass at 650 °C, 15 min with 30% Ni/Calcined Kaolin.

Effects of pretreatment in a vortex layer apparatus on the properties of confectionery wastewater and its dark fermentation

Pretreatment prior to anaerobic digestion is an effective option for increasing the biodegradability of organic waste. Vortex layer apparatus (VLA) is considered one of the promising types of equipment for pretreatment. In this work, confectionery wastewater (CW) was pretreated in VLA for 1 and 3 min before dark fermentative hydrogen production in anaerobic upflow biofilters. The pretreatment resulted in a slight increase in soluble chemical oxygen demand (COD), soluble sugars and acetic acid, and a decrease in the concentration of propionic, butyric and caproic acids. Due to the abrasion of steel needles in VLA, the concentration of iron in the pretreated CW increased by 2.57 times. Hydraulic retention time in anaerobic upflow biofilters was gradually reduced from 5.6 to 1.8 and 1.3 days, which corresponded to organic loading rate of 2.0, 6.3 and 8.8 kg COD/(m3 day). Although the highest hydrogen yield (96.2 ± 8.1 ml/g COD) was obtained for non-pretreated CW, the pretreatment contributed to a significant increase in methane yield (39.2 ± 2.5 ml/g COD), possibly due to higher iron content (1.8 ± 0.3 mg/L). The highest energy production rate (4407 J/(L day)) was achieved after 3 min CW pretreatment. Thus, pretreatment in VLA can be a promising method for improving the biohythane production process.

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 CODinit/(L day)). The highest hydrogen yield (HY) (44.73 ml/g CODinit) 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.

Sustainable and Highly Efficient Recycling of Plastic Waste into Syngas via a Chemical Looping Scheme.

Converting plastic waste into valuable products (syngas) is a promising approach to achieve sustainable cities and communities. Here, we propose for the first time to convert plastic waste into syngas via the Fe2AlOx-based chemical looping technology in a two-zone reactor. The Fe2AlOx-based redox cycle was achieved with the pyrolysis of plastic waste in the upper zone, followed by the decomposition and thermal cracking of hydrocarbon vapors, and the oxidation and water splitting in the lower zone (850 °C) enabled a higher carbon conversion (81.03%) and syngas concentration (92.84%) when compared with the mixed feeding process. The iron species could provide lattice oxygen and meanwhile act as the catalyst for the deep decomposition of hydrocarbons into CO and the accumulation of deposited carbon in the reduction step. Meanwhile, the introduced water would be split by the reduced iron and deposited carbon to further produce H2 and CO in the following oxidation step. A high hydrogen yield of 85.82 mmol/g HDPE with a molar ratio of H2/CO of 2.03 was achieved from the deconstruction of plastic waste, which lasted for five cycles. This proof of concept demonstrated a sustainable and highly efficient pathway for the recycling of plastic waste into valuable chemicals.

Effective catalytic steam reforming of naphthalene over Ni-modified ZSM-5 via one-pot hydrothermal synthesis

Ni-modified ZSM-5 catalysts are prepared by a one-pot hydrothermal synthesis method and applied to the steam reforming of naphthalene as a tar model compound. The effects of the reaction temperature, silica-alumina ratio (Si/Al) and metal content on the catalytic performance for reforming naphthalene are investigated. Characterization results indicate that the Ni-modified ZSM-5 catalysts maintain the original MFI structure of ZSM-5 and a portion of Ni is successfully introduced into the zeolite structure. When the reaction temperature is 800 °C, the conversion efficiency of naphthalene achieves 91.5% with a high yield (6.75%) of hydrogen. Zeolite catalysts with higher Si/Al ratios improve the conversion of naphthalene to syngas, demonstrating their better catalytic activity. An appropriate active metal content (2.4 wt%) contributes to the catalytic performance of the catalyst owing to the strong metal-support interaction, resulting in resistance to sintering and carbon deposition. The reaction mechanism involved in the catalytic reforming of naphthalene is proposed. The application of a novel one-pot hydrothermal synthesis method greatly promoted the catalytic activity of Ni@ZSM-5, which provided an appropriate and universal approach for the improvement and optimization of tar reforming catalysts.

α-Fe2O3 Nanoparticles/Iron-Containing Vermiculite Composites: Structural, Textural, Optical and Photocatalytic Properties

Vermiculite two-dimensional mixed-layer interstratified structures are a very attractive material for catalysis and photocatalysis. The iron-containing vermiculite from the Palabora region (South Africa) and its samples, which calcined at 500 and 700 °C, were studied in comparison with the α-Fe2O3 nanoparticles/vermiculite composites for the first time as photocatalysts of methanol decomposition, which is an organic pollutant and an efficient source for hydrogen production. The aim of the work was to characterize their structural properties using X-ray fluorescence, X-ray diffraction, infrared spectroscopy, nitrogen physisorption, diffuse reflectance UV-Vis spectroscopy and photoluminescence spectroscopy to explain the photocatalytic effects. The photocatalytic test of the samples was performed in a batch photoreactor under UV radiation of an 8W Hg lamp. The photocatalytic activity of vermiculite–hydrobiotite–mica-like layers at different water hydration states in the interstratified structure and the substitution ratio of Fe(III)/Al in tetrahedra can initiate electrons and h+ holes on the surface that attack the methanol in redox processes. The activity of α-Fe2O3 nanoparticle photocatalysts stems from a larger crystallite size and surface area. The hydrogen production from the methanol–water mixture in the presence of vermiculites and α-Fe2O3 nanoparticles/vermiculite composites was very similar and higher than the yield produced by the commercial TiO2 photocatalyst Evonik P25 (H2 = 1052 µmol/gcat.). The highest yield of hydrogen was obtained in the presence of the Fe/V–700 composite (1303 µmol/gcat after 4 h of irradiation).

Development and application of Ni–M/sepiolite (M=Ce, Pr, and La) catalysts in biomass pyrolysis for syngas production

The proposed Ni–M/sepiolite (SEP) catalysts (M=Ce, Pr, and La) were developed to improve syngas production in biomass pyrolysis. A homogeneous precipitation method was used to synthesize these catalysts. These catalysts were characterized using X-ray fluorescence, X-ray diffraction, scanning electron microscopy/energy-dispersive X-ray spectroscopy, and the Brunauer–Emmett–Teller method. A series of experiments were conducted to investigate the effects of catalyst types and M loading on gas composition and content in gas production. Simultaneously, the catalyst’s stability was tested. The experiments showed that the synthesized Ni–La/SEP catalyst with 12 wt% La and 20 wt% Ni loading had a high catalytic activity of improving gas quality compared with Ni–Pr/SEP, Ni–Ce/SEP, and Ni/SEP, giving a high hydrogen yield (41.18 vol.%) and CO yield (32.23 vol.%).

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.