Hydrogen Gasification Efficiency Research Articles

Thermochemical conversion of guaiacol with supercritical CO2: Experimental insights

The excessive CO2 in the environment resulting from the combustion of fossil fuels has posed a significant challenge in terms of its conversion and utilization. In this work, the thermochemical conversion of guaiacol under supercritical CO2 (scCO2) was proposed, which not only enabled the consumption of CO2 but also facilitated the conversion of biomass into valuable products. It was concluded that the carbon gasification efficiency (CE) and hydrogen gasification efficiency (HE) were 37.10 % and 51.77 %, respectively, when the CO reached the maximum of 8.72 ± 0.28 mol/kg at 700 °C for 20 min. The addition of catalyst promoted the production of H2 and increased CE, the H2 yield of guaiacol gasification under different catalysts was ordered as Al2O3 > KOH > without catalyst > KCl. As the reaction temperature increased, the unreacted guaiacol and phenol decreased and were gradually converted to liquid products such as pyrene and benzo[c]phenanthrene. With the increase in reaction temperature, the more fully guaiacol was reacted, the easier it was to carbonize and form more carbon microspheres. In addition, reaction pathways for free radicals were proposed, including cleavage of free radicals, isomerization of free radicals, secondary cleavage of free radicals and recombination of free radicals. In short, degrading guaiacol using scCO2 is a feasible approach, which provides a new direction for the disposal and energy recovery of biomass in the future.

Experimental study of diphenylmethane gasification with supercritical CO2

Supercritical carbon dioxide (SCCO2) gasification reaction is one of the current popular research fields with wide application prospects in green chemical synthesis, environmental protection and energy conversion. This work aimed to investigate the effects of different conditions on the gas–liquid-solid three-phase products during the reaction of SCCO2 gasification of diphenylmethane. As a result, the carbon gasification efficiency (CE) and the hydrogen gasification efficiency (HE) were 25.99 % and 21.97 % respectively at 700 ℃ for 40 min, in which the CO reached the maximum of 15.64 ± 0.16 mol/kg. As the temperature and residence time increased, the apparent morphology of solid products became more homogeneous. In addition, based on the theories of cleavage of free radicals, secondary cleavage of free radicals and binding of free radicals, three pathways for the generation of fluorene, biphenyl and m-terphenyl were postulated. The experimental results provide fundamental data and theoretical support for an in-depth understanding of the reactions mechanism under the SCCO2 atmosphere, which is of great significance for deepening our knowledge of supercritical carbon dioxide reduction reactions and promoting green chemical synthesis research.

Effects of the supported FeOOH on catalyzing gasification of oily sludge in supercritical water

FeOOH/AC-, FeOOH/Al2O3- and FeOOH/ZnO-supported catalysts were synthesized by immersion, hydrothermal hydrolysis, and hydrothermal methods, and used for supercritical water gasification (SCWG) of oily sludge. Under the same conditions, compared to FeOOH/Al2O3 and FeOOH/ZnO, the catalytic effect of FeOOH/AC was superior. When the concentration is 5% and the loading is 10%, the hydrogen production rate with FeOOH/AC composite is the highest, which is 4.638 mmol/g, and the hydrogen gasification efficiency (HE) is 89.50%. The reaction mechanism of FeOOH composites in the SCWG was also investigated. These results indicate that FeOOH composites are potential catalysts for oily sludge treatment.

Hydrogen-rich gas production from hydrothermal gasification of fuel pellets obtained from co-pelletization of agricultural residues

Hydrothermal gasification of fuel pellets obtained from co-pelletized agricultural residues such as barley straw, canola hull and oat hull was performed in a batch reactor. The effects of process conditions such as temperature (300–500 °C), reaction time (20–60 min) and feed-to-water mass ratio (1:05–1:15) were investigated to optimize the gasification process for large gas yields. The maximum yield of gas was attained at the temperature, reaction time and feed-to-water mass ratio of 500 °C, 60 min and 1:10, respectively. The highest hydrogen gasification efficiency (113%), hydrogen selectivity (52%), cold gasification efficiency (41%) and heating value of gas (920 kJ/Nm3) were found for the hydrothermal gasification of canola hull pellet at the optimal conditions. The temperature was the most paramount variable followed by reaction time and feed-to-water mass ratio. Physicochemical characterization of hydrochar produced at higher gasification temperatures revealed higher carbon content, thermal stability, alkalinity and structural deformity. The liquid products obtained from hydrothermal gasification of canola hull pellets also showed the presence of partially degraded or reformed organic compounds, which can be extracted as precursors for value-added chemicals.

Catalytic gasification of indole in supercritical water with non-noble bimetallic catalysts

Indole is commonly reported as a N-containing heterocyclic compounds in biomass supercritical water gasification (SCWG), and is difficult to be degraded to small molecule substances. In this work, Ni/AC, Ni–Cu/AC, Ni–Co/AC, Ni–Ce/AC were prepared and tested for catalytic SCWG of indole. The results showed that Ni–Cu/AC had the highest activity for converting indole and producing gases, leading to the highest hydrogen gasification efficiency (135.1%) and carbon gasification efficiency (33.1%). During the catalytic SCWG of indole, the addition of auxiliary metal Cu in multi-component catalyst showed synergistic effects by changing reaction pathways and reaction rates. It significantly promoted water-gas shift and steam reforming reactions, so forming the highest H2 yield of 2.62 mol mol−1. Furthermore, large specific surface, Ni reduction and high catalyst stability point to potential advantages of the Ni–Cu/AC catalyst for catalytic SCWG of recalcitrant N-containing compounds.

Partial oxidation gasification kinetics of indole in supercritical water for hydrogen production

Indole is one of refractory intermediate products in hydrothermal conversion of biomass, and its decomposition significantly restricts the improvement of gasification efficiency and hydrogen production in biomass supercritical water gasification (SCWG). In order to improve gasification efficiency of indole and moderate reaction conditions for hydrogen production in biomass SCWG, indole (0.25 mol/L) was gasified in supercritical water at 540–600 °C, 25 MPa, 0–0.8 of oxidation coefficients (OC) in min-batch reactors. Corresponding pathways and kinetics of partial oxidation of indole in supercritical water for hydrogen production were explored. The results showed that the addition of oxidant (hydrogen peroxide) promoted steam reform and decomposition, especially ring-opening reactions, so increasing the gasification efficiency of indole and the yields of H2 and CO2 in gaseous products. The maximum hydrogen gasification efficiency could reach up to 60.3% at OC = 0.6, which was about twice that of non-oxidant. Moreover, 29 groups of reaction rate constants, activation energies and Arrhenius constants were obtained in the established kinetic model.

Optimize hydrogen production from chicken manure gasification in supercritical water by experimental and kinetics study

In this work, H2 production from supercritical water gasification (SCWG) of chicken manure in a high heating rate batch reactor under different temperatures (500–620 °C) and residence times (1–12 min) was studied, and a quantitative kinetic model was employed to study the reaction mechanism and optimize the H2 production. The H2 yield, hydrogen gasification efficiency (HE) and carbon gasification efficiency (CE) were promoted with the growth of temperature and residence time. The maximum H2 yield, HE and CE reached 22.47 mol/kg, 174.53% and 81.34% at 620 °C and 12 min, respectively. The results of kinetic model indicated that higher temperature accelerated the reaction rate and more intermediates were converted into gas products. H2 was mainly produced by the steam reforming reaction and the generation rate of each gas decreased to be negligible after 10 min. High temperature from nearly 580 °C was preferred to accelerate water gas shift reaction (WGSR) to promote H2 production in SCWG of chicken manure. Hydrolysis reaction of chicken manure has a very important effect on H2 production.

Agricultural waste-derived biochars from co-hydrothermal gasification of rice husk and chicken manure and their adsorption performance for dimethoate

This study aimed to combine energy utilisation of agricultural wastes with the dimethoate (DT) adsorption from agricultural wastewater via hydrogen and biochar production using co-hydrothermal gasification (CHTG). The gasification behaviour after CHTG of five ratios of rice husk (RH) and chicken manure (CM) and the corresponding adsorption performance of biochars on DT were evaluated. The results demonstrated that the feedstock of 3RH+ 1CM achieved the maximum gas yield and hydrogen gasification efficiency (HGE), and the highest adsorption capacity of the derived biochars was 3.57 mg g−1. Surface characterisation and elemental analysis showed that the biochar derived under different C/N ratios varied considerably. The results of the isotherm and kinetic simulation showed that the Langmuir model and pseudo-first-order model best fitted the experimental data. The superior performance of agricultural waste-derived biochars (AWB) over five cycles of regeneration and adsorption indicated that AWB is a green and stable adsorption material for farmland tailwater. In addition, the degradation pathway of DT during hydrothermal gasification (HTG) regeneration of the spent adsorbent was comprehensively discussed. The CHTG treatment enhanced the yield of gaseous products from RH and CM and produced AWBs with high adsorption capacities for DT. This provides a green and efficient technology for resource utilisation of agricultural waste and treatment of agricultural wastewater using pesticide residues.

Partial oxidation of phenolic wastewater using NaOH and Ni addition for hydrogen production and phenolics degradation in supercritical water

Phenolic wastewater is a challenge for traditional microbial treatment because of complex pollutant constituents and high concentration of aromatic hydrocarbons. Using H2O2 as oxidant, partial oxidation of phenolic wastewater using NaOH and Ni addition for hydrogen production and phenolics degradation in supercritical water was explored. It was found that higher oxygen ratio was advantageous for phenolics and other organic pollutants converting to gaseous products from supercritical water partial oxidation without any catalyst addition, but hydrogen production peaked at 0.5 oxygen ratio. Hydrogen gasification efficiency were raised to 75.68% within 0.5 oxygen ratio and 3.0% NaOH addition. Although separate Ni catalyst effectively enhanced the production of the gasifiable intermediate, hydrogen gasification efficiency appeared to a balance due to the enhancement of hydrogenation and methanation reactions. Both organic pollutants removal and hydrogen production enhancement were significantly improved under the combined NaOH-Ni catalyst, 85.24% TOC removal and 86.39% hydrogen gasification efficiency achieved within 1.0 NaOH + 2.0 Ni catalyst. There was very little cyclic compounds detected in liquid phase from combined NaOH-Ni catalytic partial oxidation, compared with individual addition. S, O and Si elements deposited in the surface of Ni catalyst, which have some negative effect on reuse. The positive effect of combined NaOH-Ni catalyst on organic pollutants removal and hydrogen production enhancement was demonstrated, which provided novel results and information that help to solve the problems in the process of toxic and high concentration organic wastewater treatment and facilitate the engineering application of supercritical water partial oxidation technology in the future.

Enhancement of depolymerization slag gasification in supercritical water and its gasification performance in fluidized bed reactor

Supercritical water gasification (SCWG) can achieve efficient utilization of solid wastes, including depolymerization slag, biomass, municipal sludge, and others, and can produce hydrogen-rich gas. But phenolic intermediates produced during the gasification process are difficult to be gasified. It restricted the increase of conversion efficiency. Thus, in this paper, two effective schemes were put forward to raise the gasification efficiency of depolymerization slag. The first one was to add oxidants to promote the decomposition of hydrolysates. Carbon gasification efficiency (CGE) and hydrogen gasification efficiency (HGE) reached 71% and 74% respectively at the time of 1200 s. They raised by 41.6% and 60.5%, separately compared with non-oxidants addition. The second one was to raise the reaction temperature since a higher temperature can accelerate the reaction rate and obtain a high hydrogen yield. The results showed that hydrogen percentage increased by 32.82% and CGE and HGE increased by 35.39% and 219.85%, respectively when the reaction temperature raised by 200 °C. Based on the obtained gasification mechanism, the catalytic gasification.

Assessment of supercritical water gasification of food waste under the background of waste sorting: Influences of plastic waste contents

Waste sorting is being gradually implemented as a key measure for circular and sustainable development in China, food waste will be separately collected and separated from municipal solid waste (MSW), thus the plastic content in food waste also will be reduced. In this study, supercritical water gasification (SCWG) of food waste with different contents of plastic (0–3.5 wt%) was experimentally investigated to simulate the influence of waste sorting on the food waste treatment. The results showed that lower plastic content in food waste favored higher gas yield and gasification efficiencies. The highest H2 yield and total gas yield were 3.11 mol/kg and 8.41 mol/kg in the plastic-free case, respectively. When the plastic content decreased from 3.5 wt% to 0 wt%, the cold gas efficiency (CGE), carbon conversion efficiency (CE) and hydrogen gasification efficiency (HE) increased by 125.97%, 173.48% and 94.09%, respectively. However, lower plastic content negatively affected the quality of produced syngas through decreasing H2 mole fraction and LHV. The solid residues from SCWG of food waste with lower plastic content had higher ratio of fixed carbon to volatile matter (FC/VM). Based on the analysis of pyrolysis properties and combustion behavior, decreasing the plastic content in food waste helped to improve the thermal stability of solid residues. Moreover, lower plastic content resulted in a decrease of total organic carbon (TOC) concentration in liquid effluent, which is favorable for further treatment of liquid effluent.

Partial oxidation of phenol in supercritical water with NaOH and H2O2: Hydrogen production and polymer formation

The catalytic supercritical water partial oxidation of phenol using H2O2 as oxidant in the presence of NaOH was explored to enhance hydrogen production and inhibit phenol polymerization. The results indicated that H2 production was enhanced in the presence of NaOH when phenol supercritical water oxidation was controlled at a lower O/C ratio. Compared with the individual catalytic partial oxidation of phenol, the reaction with NaOH and H2O2 simultaneously enhanced H2 production and inhibited polycyclic polymer generation at O/C ratios below 0.5. A peak hydrogen gasification efficiency value of 62.35% was observed at an O/C ratio of 0.3 with 1.0 wt% NaOH, and a phenol removal efficiency of nearly 75% was reported. Phenol polymerization was effectively inhibited for reaction times limited to 50 s. Moreover, other phenol reaction pathways reported in the literature were compared with the partial oxidation of phenol in supercritical water with NaOH and H2O2.

Production of H2-rich syngas from gasification of unsorted food waste in supercritical water

In China, waste sorting practice is not strictly followed, plastics, especially food packaging, are commonly mixed in food waste. Supercritical water gasification (SCWG) of unsorted food waste was conducted in this study, using model unsorted food waste by mixture of pure food waste and plastic. Different operating parameters including reaction temperature, residence time, and feedstock concentration were investigated. Moreover, the effect of three representative food additives namely NaCl, NaHCO3 and Na2CO3 were tested in this work. Finally, comparative analysis about SCWG of unsorted food waste, pure food waste, and plastic was studied. It was found that higher reaction temperature, longer residence time and lower feedstock concentration were advantageous for SCWG of unsorted food waste. Within the range of operating parameters in this study, when the feedstock concentration was 5 wt%, the highest H2 yield (7.69 mol/kg), H2 selectivity (82.11%), total gas yield (17.05 mol/kg), and efficiencies of SCWG (cold gas efficiency, gasification efficiency, carbon gasification efficiency, and hydrogen gasification efficiency) were obtained at 480 °C for 75 min. Also, the addition of food additives with Na+ promoted the SCWG of unsorted food waste. The Na2CO3 showed the best catalytic performance on enhancement of H2 and syngas production. This research demonstrated the positive effect of waste sorting on the SCWG of food waste, and provided novel results and information that help to overcome the problems in the process of food waste treatment and accelerate the industrial application of SCWG technology in the future.

Catalytic supercritical water gasification of aqueous phase directly derived from microalgae hydrothermal liquefaction

Microalgae (N. chlorella) hydrothermal liquefaction (HTL) was conducted at 320 °C for 30 min to directly obtain original aqueous phase with a solvent-free separation method, and then the supercritical water gasification (SCWG) experiments of the aqueous phase were performed at 450 and 500 °C for 10 min with different catalysts (i.e., Pt-Pd/C, Ru/C, Pd/C, Na2CO3 and NaOH). The results show that increasing temperature from 450 to 500 °C could improve H2 yield and TGE (total gasification efficiency), CGE (carbon gasification efficiency), HGE (hydrogen gasification efficiency), TOC (total organic carbon) removal efficiency and tar removal efficiency. The catalytic activity order in improving the H2 yield was NaOH > Na2CO3 > None > Pd/C > Pt-Pd/C > Ru/C. Ru/C produced the highest CH4 mole fraction, TGE, CGE, TOC removal efficiency and tar removal efficiency, while NaOH led to the highest H2 mole fraction, H2 yield and HGE at 500 °C. Increasing temperature and adding proper catalyst could remarkably improve the SCWG process above, but some N-containing compounds were difficult to be gasified. This information is valuable for guiding the treatment of the aqueous phase derived from microalgae HTL.

Catalytic supercritical water gasification of glucose with in-situ generated nickel nanoparticles for hydrogen production

Hydrogen production from catalytic supercritical water gasification of glucose with in-situ generated nickel nanoparticles in a quartz tube reactor is demonstrated. The effects of various operating parameters such as the presence of catalyst, resident time, reaction temperature and feed concentration on the gasification performances are studied. The results show that both the carbon gasification efficiency and the hydrogen gasification efficiency of glucose in supercritical water were improved with in-situ generated nickel nanoparticles as catalyst compared to those without catalyst. The catalyst promotes the water-gas shift reaction and CO methanation reaction, resulting in increased yields of H2, CH4 and CO2 and decreased yield of CO. At the presence of catalyst, 10 wt% glucose solution exhibits the best gasification performances at 500 °C. Highly dispersed nickel nanoparticles identified by high resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS) are assumed to be generated via supercritical hydrothermal synthesis through hydrolysis, dehydration and in-situ reduction. However, the in-situ generated nano-nickel catalyst underwent an activation to deactivation transition due to carbon deposition on the surface of nickel nanoparticles. Regeneration strategies of the deactivated catalysts need further study for practical application.

Hydrothermal gasification of microalgae over nickel catalysts for production of hydrogen-rich fuel gas: Effect of zeolite supports

A series of Ni catalysts with different zeolites were prepared by wet impregnation method and used to catalyze supercritical water gasification (SCWG) of microalgae for production of hydrogen-rich fuel gas under conditions of 430 °C, 60 min, ρH₂O = 0.162 g/cm3, 2 g/g Ni/zeolites. Compared with noncatalytic SCWG, the presence of Ni/zeolite could increase the hydrogen gasification efficiency and carbon gasification efficiency by promoting water–gas shift and steam reforming reactions which are mainly affected by the amount of strong acid sites and Ni, respectively. The highest carbon gasification efficiency (CGE) and hydrogen gasification efficiency (HGE) of 23.61% and 23.55% were achieved with Ni/HY (Na2O, 0.8%). The gaseous produced mainly consisted of H2 and CO2. The H2 content in the gaseous products varied from 27.15 to 40.51% depending on the Ni/zeolites and increased with increasing the SiO2/Al2O3 molar ratio of HZSM-5, which is 2.3–3.6 times higher than that of produced without catalyst. The H2 yield varied between 2.57 and 3.61 mmol/g depending on the Ni/zeolites and increased from 2.19 to 5.61 mmol/g with increasing the SiO2/Al2O3 molar ratio from 50:1 to 170:1, which is 3.6–7.8 times higher than that of produced without catalyst. Coke formation, surface area loss, and sintering of Ni could decrease the activity of the Ni/zeolites.

Supercritical water gasification of microalgae over a two-component catalyst mixture

Supercritical water gasification (SCWG) of the microalga Chlorella pyrenoidosa was examined with a catalyst mixture of Ru/C and Rh/C in a mass ratio of 1:1. The influences of temperature (380–600°C), water density (0–0.197g/cm3), and catalyst loading (0–20wt%) on the yields and composition of the gaseous products and the gasification efficiency were examined. The temperature and water density significantly affected the SCWG of the microalgae. The hydrogen gasification efficiency was more dependent on the temperature, while the carbon gasification efficiency was more dependent on the water density. The gaseous products mainly consisted of CH4, H2, CO, and CO2, with smaller amounts of C2-C3 hydrocarbons. CH4 made up half of the mole fraction of the gaseous products under most reaction conditions. A synergistic effect between Ru/C and Rh/C existed during the SCWG of the microalgae, and this effect favored the production of CH4. The role of the catalyst mixture became indistinct at higher temperatures. Hydrogen atoms from the water were transferred to the gaseous products during the SCWG, leading to hydrogen gasification efficiencies that exceeded 100%. The main components of the bio-oil were aromatics and nitrogen-containing compounds, and the main aromatics consisted of azulene and anthracene. The nitrogen-containing compounds are potential poisons to the catalyst mixture.

Gasification of Iranian walnut shell as a bio-renewable resource for hydrogen-rich gas production using supercritical water technology

Gasification in supercritical water (SCW) media is known as an efficient and promising technology for obtaining hydrogen-rich gas from dry and wet bio-renewable materials. Gasification of walnut shell as the main hard nutshell produced in Kurdistan Province of Iran was investigated using a stainless steel batch micro-reactor. Effects of reaction time in the range of 10–30 min, feed loading in the range of 0.06–0.18 g, and temperature in the range of 400–440 °C were investigated to determine the condition for maximum hydrogen yield. Furthermore, carbon gasification efficiency (CGE) and hydrogen gasification efficiency (HGE) were calculated according to the elemental analysis and the yields of gaseous products. Total gas yield and hydrogen yield were directly correlated with temperature. Steam reforming of walnut shell was favored at higher temperatures. Also, walnut shell loading was inversely correlated with total gas and hydrogen yields while production of methane was favored by higher loading of walnut shell. Furthermore, hydrogen yield increased first, when reaction time increased from 10 to 20 min, and then decreased. Maximum hydrogen yield of 4.63 mmol/g of walnut shell was obtained at 440 °C, walnut shell loading of 0.06 g and reaction time of 20 min.

Testing the constrained equilibrium method for the modeling of supercritical water gasification of biomass

Most of the modeling approaches for supercritical water gasification (SCWG) of biomass involve the global thermodynamic equilibrium approach which shows the thermodynamic limits of the gasification process. However, the constrained equilibrium method can be a useful tool for the modeling of SCWG of biomass processes for local equilibrium conditions. This study aims to determine the additional constraints for the Gibbs free energy minimization method and test the constrained equilibrium method for the modeling of supercritical water gasification of biomass. Using two different approaches: i) treating the fluid phase as it is composed of one “pseudo” gas phase and one “pseudo” aqueous solution phase (approach I) and ii) treating the fluid phase as one single phase (approach II). Additional constraints including carbon gasification efficiency (CGE), hydrogen gasification efficiency and constrained amounts for specific compounds have been introduced as process dependent values to predict the local equilibrium state compounds. CGE appears to be the most important additional constraint. Setting a constant amount for a specific compound as another constraint improves the accuracy of the model on predicting the composition of the gas products. The model not only predicts the gas formation behavior, but also gives insight into limiting reaction pathways taking place.

Gasification of sugarcane bagasse in supercritical water; evaluation of alkali catalysts for maximum hydrogen production

Sugarcane bagasse is one of the major resources of agricultural wastes in the Khuzestan Province of Iran. With the aim of maximum hydrogen production, supercritical water gasification of lignocellulosic feedstock was studied in a batch reactor at the constant pressure of 25 MPa. The effect of catalyst (five different alkali salts, Raney nickel, and activated carbon) and reaction temperature (400–800 °C) on gas yield and composition, gas heating value, carbon gasification efficiency (CGE), and hydrogen gasification efficiency (HGE) was investigated. An increase in reaction temperature led to significant improvement in hydrogen yield. The highest amount of hydrogen (75.6 mol kg−1) was achieved at 800 °C with the presence of KOH as catalyst where the complete gasification of bagasse took place. The annual potential of hydrogen production in the Khuzestan Province of Iran was roughly estimated to be 470 millions of Nm3 and this calculation showed that this figure is capable of substituting the need of 6550 ha of sugarcane farms to chemical fertilizer.