Thermodynamic performance of O2/CO2 gas turbine cycle with chemical recuperation by CO2-reforming of methane

This paper proposes a novel power cycle system composed of chemical recuperative cycle with CO₂–NG (natural gas) reforming and an ammonia absorption refrigeration cycle. In which, the heat is recovered from the turbine exhaust to drive CO₂–NG reformer firstly, and then lower temperature heat from the turbine exhaust is provided with the ammonia absorption refrigeration system to generate chilled media, which is used to cool the turbine inlet gas except export. In this paper, a detailed thermodynamic analysis is carried out to reveal the performance of the proposed cycle and the influence of key parameters on performance is discussed. Based on 1 kg s⁻¹ of methane feedstock and the turbine inlet temperature of 1573 K, the simulation results shown that the optimized net power generation efficiency of the cycle rises up to 49.6% on the low-heating value and the exergy efficiency 47.9%, the new cycle system reached the net electric-power production 24.799 MW, the export chilled load 0.609 MW and 2.743 kg s⁻¹ liquid CO₂ was captured, achieved the goal of CO₂ and NO_x zero-emission.     

Adsorption and separation of CH4/CO2/N2/H2/CO mixtures in hexagonally ordered carbon nanopipes CMK-5

Adsorption and separation of N₂, CH₄, CO₂, H₂ and CO mixtures in CMK-5 material at room temperature have been extensively investigated by a hybrid method of grand canonical Monte Carlo (GCMC) simulation and adsorption theory. The GCMC simulations show that the excess uptakes of pure CH₄ and CO₂ at 6.0 MPa and 298 K can reach 13.18 and 37.56 mmol/g, respectively. The dual-site Langmuir–Freundlich (DSLF) model was also utilized to fit the absolute adsorption isotherms of pure gases from molecular simulations. By using the fitted DSLF model parameters and ideal adsorption solution theory (IAST), we further predicted the adsorption separation of N₂–CH₄, CH₄–CO₂, N₂–CO₂, H₂–CO, H₂–CH₄ and H₂–CO₂ binary mixtures. The effect of the bulk gas composition on the selectivity of these gases is also studied. To improve the storage and separation performance, we finally tailor the structural parameters of CMK-5 material by using the hybrid method. It is found that the uptakes of pure gases, especially for CO_2, can be enhanced with the increase of pore diameter D_i, while the separation efficiency is apparently favored in the CMK-5 material with a smaller D_i. The selectivity at D_i=3.0 nm and 6.0 MPa gives the greatest value of 8.91, 7.28 and 27.52 for S_CO2/N2, S_CH4/H2 and S_CO2/H2, respectively. Our study shows that CMK-5 material is not only a promising candidate for gas storage, but also suitable for gas separation.     

Effect of H2/O2 addition in increasing the thermal efficiency of a diesel engine

Using hydrogen as an additive to enhance the conventional diesel engine performance has been investigated by several researchers and the outcomes are very promising. However, the problems associated with the production and storage of pure hydrogen currently limits the application of pure hydrogen in diesel engine operation. On-board hydrogen-oxygen generator, which produces H₂/O₂ mixture through electrolysis of water, has significant potential to overcome these problems. This paper focuses on evaluating the performance enhancement of a conventional diesel engine through the addition of H₂/O₂ mixture, generated through water electrolysis. The experimental works were carried out under constant speed with varying load and amount of H₂/O₂ mixture. Results show that by using 4.84%, 6.06%, and 6.12% total diesel equivalent of H₂/O₂ mixture the brake thermal efficiency increased from 32.0% to 34.6%, 32.9% to 35.8% and 34.7% to 36.3% at 19 kW, 22 kW and 28 kW, respectively. These resulted in 15.07%, 15.16% and 14.96% fuel savings. The emissions of HC, CO₂ and CO decreased, whereas the NO_x emission increased.     

Effects of microwave,UV, and O3 on propylene gas degradation via photocatalytic reaction with CVD TiO2 films

A microwave/UV/ozone/TiO₂ photocatalyst hybrid process system, which is a combination of various propylene gas treatment techniques, is evaluated for use as an advanced, efficient technology for air pollution treatment. TiO₂ photocatalyst balls were prepared using low-pressure metal-organic chemical vapor deposition. The microwave/UV/TiO₂ photocatalyst hybrid process exhibited the higher degradation efficiency than the microwave/UV/alumina ball hybrid system. The degradation efficiency increased almost linearly with increasing ozone dose. The lower the propylene inlet concentration was the higher degradation efficiency. The double bond of propylene is broken by ozone and OH, resulting in production of CH₄ and C₂H₆. These two intermediate products are mineralized into CO₂, H₂O, and CO. C₂H₄ and C₃H₈ may be produced from CH₄, whereas C₂H₆ and C₃H₆ are produced by microwave irradiation.     

Reduction and oxidation properties of Fe2O3/ZrO2 oxygen carrier for hydrogen production

Fe₂O₃ is a promising oxygen carrier for hydrogen production in the chemical-looping process. A set of kinetic studies on reduction with CH₄, CO and H₂ respectively, oxidation with water and oxygen containing Ar for chemical-looping hydrogen production was conducted. Fe₂O₃ (20 wt.%)/ZrO₂ was prepared by a co-precipitation method. The main variables in the TGA (thermogravimetric analyzer) experiment were temperatures and gas concentrations. The reaction kinetics parameters were estimated based on the experimental data. In the reduction by CH₄, CO and H₂, the reaction rate changed near FeO. Changes in the reaction rate due to phase transformation were observed at low temperature and low gas concentration during the reduction by CH₄, but the phenomenon was not remarkable for the reduction by CO and H₂. The reduction rate achieved using CO and H₂ was relatively faster than achieved using CH₄. The Hancock and Sharp method of comparing the kinetics of isothermal solid-state reactions was applied. A phase boundary controlled model (contacting sphere) was applied to the reduction of Fe₂O₃ to FeO by CH₄, and a different phase boundary controlled model (contacting infinite slab) was fit well to the reduction of FeO to Fe by CH₄. The reduction of Fe₂O₃ to Fe by CO and H₂ can be described by the former phase boundary controlled model (contacting sphere). This phase boundary controlled model (contacting sphere) also fit well for the oxidation of Fe to Fe₃O₄ by water and FeO to Fe₂O₃ by oxygen containing Ar. These kinetics data could be used to design chemical-looping hydrogen production systems.     

Effects of hydrogen on carbon nanotube formation in CH4/H2 plasmas

Carbon nanotubes (CNTs) were synthesized using CH₄/H₂ plasmas and plasmas simulated using a one-dimensional fluid model. The thinnest and longest CNTs with the highest number density were obtained using CH₄/H₂ = 27/3 sccm at 10 Torr. These conditions allowed CNTs to grow for 90 min without any meaningful loss of catalyst activity. However, an excess H₂ supply to the CH₄/H₂ mixture plasma made the diameter distribution of the CNTs wider and the yield lower. Hydrogen concentration is considered to affect catalyst particle size and activity during the time interval before starting CNT growth (=incubation period). With CH₄/H₂ = 27/3 sccm for a growth time of 10 min efficient CNT growth was achieved because the amount of carbon atoms in the CNTs and that calculated from simulation showed good agreement. The effect of hydrogen etching on CNTs was analyzed by scanning electron microscopy and X-ray photoelectron spectroscopy by observing CNTs treated by H₂ plasma after CNT growth. It was confirmed that (a) multi-walled CNTs were not etched by the H₂ plasma, (b) the C 1s XPS spectra of the CNTs showed no chemical shift after the treatment, and (c) C-H bonds were produced in CNTs during their growth.     

Autothermal Reforming of Methane with Integrated CO2 Capture in a Novel Fluidized Bed Membrane Reactor. Part 2 Comparison of Reactor Configurations

The reactor performance of two novel fluidized bed membrane reactor configurations for hydrogen production with integrated CO₂ capture by autothermal reforming of methane (experimentally investigated in Part 1) have been compared using a phenomenological reactor model over a wide range of operating conditions (temperature, pressure, H₂O/CH₄ ratio and membrane area). It was found that the methane combustion configuration (where part of the CH₄ is combusted in situ with pure O₂) largely outperforms the hydrogen combustion concept (oxidative sweeping combusting part of the permeated H₂) at low H₂O/CH₄ ratios (<2) due to in situ steam production, but gives a slightly lower hydrogen production rate at higher H₂O/CH₄ ratios due to dilution with combustion products. The CO selectivity was always much lower with the methane combustion configuration. Whether the methane combustion or hydrogen combustion configuration is preferred depends strongly on the economics associated with the H₂O/CH₄ ratio.     

Opposite effect of gas phase H2O2 on photocatalytic oxidation of acetone and benzene vapors

The effect of additions of gas phase H₂O₂ was measured for gas phase photocatalytic oxidation of organic vapors. Photocatalytic oxidation of benzene vapor over TiO₂ in a flow reactor resulted in a quick catalyst deactivation. Additions of gas phase H₂O₂ into the reactor feed provided enhanced and sustained oxidation of benzene vapor. The increase of inlet H₂O₂ vapor concentration from 0 to about 1000 ppm led to the one order of magnitude growth of benzene vapor complete oxidation rate. The highest rate of 1.1 nmol/s was observed at C₆H₆ concentration 124 ppm and H₂O₂ concentration 1000 ppm. In the case of acetone vapor photocatalytic oxidation, the rate of complete oxidation in the flow reactor decreased with an increase of gas phase H₂O₂ inlet concentration. TiO₂ Degussa P25 provided higher oxidation rate in the presence of H₂O₂ than pure anatase TiO₂.     

Molecular simulation studies of separation of CH4/H2 mixture in metal-organic frameworks with interpenetration and mixed-ligand

In our previous work, we have investigated the adsorption selectivity of CH₄/H₂ in three pairs of isoreticular metal-organic frameworks (IRMOFs) with and without interpenetration to study the effect of interpenetration on gas mixture separation through Monte Carlo simulation. In addition, the self-diffusivities and the diffusion mechanism of single H₂ and CH₄ in these MOFs were examined by molecular dynamics simulations. In this work, we extend our previous work to mixed-ligand MOFs to investigate the effects of interpenetration as well as mixed-ligand on both equilibrium-based and kinetic-based gas mixture separation. We found that methane adsorption selectivity is much enhanced in the selected mixed-ligand interpenetrated MOFs compared with their non-interpenetrated counterparts, similar to what we found before for IRMOFs with single-ligand. At room temperature and atmospheric pressure, molecular-level segregation was observed in the mixed-ligand MOFs, and the extent of the effects of interpenetration is comparable for single-ligand and mixed-ligand MOFs. In addition, we found that the diffusion selectivity in the interpenetrated MOFs is similar to the one in their non-interpenetrated counterparts, while the permeation selectivity in the former is much higher than that in the latter, which corroborates our expectation that interpenetration is a good strategy to improve the overall performance of a material as a membrane in separation applications based only on the single component diffusion results. Furthermore, the CH₄ permeability of the selected MOF membrane was also evaluated.     

Investigation in the role of hydrogen on the properties of diamond films grown using Ar/H2/CH4 microwave plasma

The transition of diamond grain sizes from micron- to nano- and then to ultranano-size could be observed when hydrogen concentration is being decreased in the Ar/CH₄ plasma. When grown in H₂-rich plasma (H₂ = 99% or 50%), well faceted microcrystalline diamond (MCD) surface with grain sizes of less than 0.1 μm are observed. The surface structure of the diamond film changes to a cauliflower-like geometry with a grain size of around 20 nm for the films grown in 25% H₂-plasma. In the Ar/CH₄ plasma, ultrananocrystalline diamond (UNCD) films are produced with equi-axed geometry with a grain size of 5-10 nm. The H₂-content imposes a more striking effect on the granular structure of diamond films than the substrate temperature. The induction of the grain growth process, either by using H₂-rich plasma or a higher substrate temperature increases the turn-on field in the electron field emission process, which is ascribed to the reduction in the proportion of grain boundaries.     

Oxy-CO2 reforming of methane to syngas over CoOx/MgO/SA-5205 catalyst

The oxy-CO₂ methane reforming reaction (OCRM) has been investigated over CoO_x supported on a MgO precoated highly macroporous silica–alumina catalyst carrier (SA-5205) at different reaction temperatures (700–900 °C), O₂/CH₄ ratios (0.3–0.45) and space velocites (20,000–100,000 cc/g/h). The reaction temperature had a profound influence on the OCRM performance over the CoO/MgO/SA-5205 catalyst; the methane conversion, CO₂ conversion and H₂ selectivity increased while the H₂/CO ratio decreased markedly with increasing reaction temperature. While the O₂/CH₄ ratio did not strongly affect the CH₄ and CO₂ conversion and H₂ selectivity, it had an intense influence on the H₂/CO ratio. The CH₄ and CO₂ conversion and the H₂ selectivity decreased while the H₂/CO increased with increasing space velocity. The O₂/CH₄ ratio and the reaction temperature could be used to manipulate the heat of the reaction for the OCRM process. Depending on the O₂/CH₄ ratio and temperature the OCRM process could be operated in a mildly exothermic, thermal neutral or mildly endothermic mode. The OCRM reaction became almost thermoneutral at an OCRM reaction temperature of 850 °C, O₂/CH₄ ratio of 0.45 and space velocity of 46,000 cc/g/h. The CH₄ conversion and H₂ selectivity over the CoO/MgO/SA-5205 catalyst corresponding to thermoneutral conditions were excellent: 95% and 97%, respectively with a H₂/CO ratio of 1.8.     

Low-temperature hydropyrolysis of coal under pressure of H2-CH4 mixtures

Hydropyrolysis of a Beringen bituminous coal (VM, 32.8wt%) has been studied in a fixed bed reactor with different gas flows of H₂-CH₄ and H₂-N₂ mixtures. At 580 °C, various hydrogen partial pressures between 0 and 1 MPa were used with a total pressure of 1 and 4 MPa. Oil yield increased significantly with increasing hydrogen partial pressure. However, if the difference between partial and total pressure is too large, the oil yield is affected more by the total than the hydrogen partial pressure. Similar effects are observed for the yields of BTX, PCX and naphthalenes except that for the latter the total pressure does not have a significant effect. In the conditions investigated the methane is chemically inert. Thus it is possible to recycle the gas during coal hydropyrolysis with only a slight decrease of the yields.     

A novel nickel/carbon catalyst for CH4 and H2 production from organic compounds dissolved in wastewater by catalytic hydrothermal gasification

A novel Ni/carbon catalyst recently developed by the authors was used to gasify organic compounds dissolved in the wastewater with TOC concentration from 0.2 to 2%. The process removes the organic compounds by gasifying them into high calorific gases like methane and hydrogen. The investigations were focused on the efficiency of the Ni/carbon catalyst in terms of carbon conversion, conversion of big organic molecules, and catalyst deactivation due to sintering. The preliminary results showed that up to 99% carbon conversion can be achieved at 360 °C, and 20 MPa. A conversion mechanism was suggested which consists of: first, decomposition of big molecules to small molecules on the metal surface, steam gasification of small molecules to produce CO and H₂ followed by CO methanation and CO shift reaction to produce CH₄ and CO₂. The catalyst was found to be highly active and stable and no sintering was observed even after 100 h of reaction time.     

The effect of synthesis gas composition on the Fischer–Tropsch synthesis over Co/γ-Al2O3 and Co–Re/γ-Al2O3 catalysts

The Fischer–Tropsch synthesis over Co/γ-Al₂O₃ and Co–Re/γ-Al₂O₃ was investigated in a fixed-bed reactor at 20 bar and 483 K using feed gases with molar H₂/CO ratios of 2.1, 1.5 and 1.0 simulating synthesis gas derived from biomass. With lower H₂/CO ratios in the feed, the CO conversion and the CH₄ selectivity decreased, while the C₅₊ selectivity and olefin/paraffin ratio for C₂–C₄ increased slightly. The water–gas shift activity was low for both catalysts, resulting in high molar usage ratios of H₂/CO (close to 2.0), even at the lower inlet ratios (i.e. 1.5 and 1.0). For both catalysts, the drop in the production rate of hydrocarbons when shifting from an inlet ratio of 2.1 to 1.5 was significant mainly because the H₂/CO usage ratio did not follow the change in the inlet ratio. The hydrocarbon selectivities were rather similar for inlet H₂/CO ratios of 2.1 and 1.5, while significantly deviating from those for an inlet ratio of 1.0. With the studied catalysts, it is possible to utilize the advantages of an inlet ratio of 1.0 (higher selectivity to C₅₊, lower selectivity to CH₄, no water–gas shifting of the bio-syngas needed prior to the FT reactor) if a low syngas conversion is accepted.     

Wilson parameters for the system H2, N2, CO,CO2, CH4, H2S,CH3OH,and H2O

Parameters for the Wilson equation have been determined for 24 of the 28 binary pairs in the system: H₂, N₂, CO, CO₂, CH₄, H₂S, CH₃OH, and H₂O. The data for eleven pairs were fit using the symmetric convention, with the remaining pairs satisfying the unsymmetric convention. Coefficients for the missing pairs could be estimated from Henry's Law constants. References have been included for the heat capacities of liquid methanol and carbon dioxide. Heats of mixing were also found in the literature. This information, plus readily available gas heat capacities, provides sufficient information to calculate multicomponent material and energy balances for the columns used in the separation of H₂S and CO₂ by cold methanol absorption.     

Direct formation of H2O2 from H2 and O2 and decomposition/hydrogenation of H2O2 in aqueous acidic reaction medium over halide-containing Pd/SiO2 catalytic system

Formation of H₂O₂ from H₂ and O₂ and decomposition/hydrogenation of H₂O₂ have been studied in aqueous acidic medium over Pd/SiO₂ catalyst in presence of different halide ions (viz. F⁻, Cl⁻ and Br⁻). The halide ions were introduced in the catalytic system via incorporating them in the catalyst or by adding into the reaction medium. The nature of the halide ions present in the catalytic system showed profound influence on the H₂O₂ formation selectivity in the H₂ to H₂O₂ oxidation over the catalyst. The H₂O₂ destruction via catalytic decomposition and by hydrogenation (in presence of hydrogen) was also found to be strongly dependent upon the nature of the halide ions present in the catalytic system. Among the different halides, Br⁻ was found to selectivity promote the conversion of H₂ to H₂O₂ by significantly reducing the H₂O₂ decomposition and hydrogenation over the catalyst. The other halides, on the other hand, showed a negative influence on the H₂O₂ formation by promoting the H₂ combustion to water and/or by increasing the rate of decomposition/hydrogenation of H₂O₂ over the catalyst. An optimum concentration of Br⁻ ions in the reaction medium or in the catalyst was found to be crucial for obtaining the higher H₂O₂ yield in the direct synthesis.     

Pure and mixed gas CH4 and n-C4H10 permeability and diffusivity in poly(1-trimethylsilyl-1-propyne)

Pure and mixed gas n-C₄H₁₀ and CH₄ permeability coefficients in poly(1-trimethylsilyl-1-propyne) (PTMSP) are reported at temperatures from −20 to 35 °C. CH₄ partial pressures range from 1.1 to 14.6 atm, and n-C₄H₁₀ partial pressures range from 0.02 to 1.8 atm. CH₄ permeability decreases with increasing n-C₄H₁₀ upstream activity (f/f_sat) in the feed. For example, at −20 °C, CH₄ permeability decreases by more than an order of magnitude, from 52,000 to 1700 Barrer, as n-C₄H₁₀ activity increases from 0 to 0.73. In contrast, n-C₄H₁₀ mixed gas permeability is essentially unaffected by the presence of CH₄. The depression of CH₄ permeability in mixtures is a result of competitive sorption and blocking effects, which reduce both CH₄ mixture solubility and diffusivity, respectively. Diffusion coefficients of n-C₄H₁₀ and CH₄ in mixtures were calculated from mixture permeability and mixture solubility data. The CH₄ concentration-averaged diffusion coefficient generally decreases as n-C₄H₁₀ activity increases. On the other hand, the n-C₄H₁₀ diffusion coefficient is essentially unaffected by the presence of CH₄. Pure and mixed gas activation energies of permeation and diffusion of CH₄ and n-C₄H₁₀ are reported. The mixed gas n-C₄H₁₀/CH₄ permeability selectivity increases with increasing n-C₄H₁₀ activity and decreasing temperature, and it is higher than pure gas estimates would suggest. Mixture diffusivity selectivity also increases with increasing n-C₄H₁₀ activity. The difference between pure and mixed gas permeability selectivity arises from both solubility and diffusivity effects. The dual mode mixed gas permeability model describes the mixture permeability data reasonably well for n-C₄H₁₀. However, the model must be modified to accurately describe the methane data by accounting for the decrease in methane diffusivity due to the presence of n-C₄H₁₀ (i.e., blocking). Even though the penetrant concentrations are rather significant at some of the conditions considered, no evidence is observed for phenomena such as multicomponent coupling that would require a model more complex than the binary form of Fick's law. That is, Fick's law in its simplest form adequately describes the experimental data.     

The role of activated carbon as a catalyst in GAC/iron oxide/H2O2 oxidation process

The catalytic properties of granular activated carbon (GAC) in GAC/iron oxide/hydrogen peroxide (H₂O₂) system was investigated in this research. Batch experiments were carried out in de-ionized water at the desired concentrations of ethylene glycol and phenol. Rate constants for the degradation of hydrogen peroxide and the formation rate of iron species were determined and correlated with mineralization of ethylene glycol at various GAC concentrations. The observed first order degradation rate of hydrogen peroxide in the absence of iron oxide and organic matter increases linearity with the increasing of the GAC concentration. The decomposition rate of hydrogen peroxide was suppressed significantly as the solution pH became acidic or by reducing the surface area of the GAC. The reduction of the surface area was obtained by loading an organic compound (such as phenol) on the GAC or by using the oxidizing agent (H₂O₂). The addition of both chemicals, phenol and H₂O₂, affects mainly the surface area of the small pores, resulting in reducing the catalytic activity inside the micropores.The catalytic properties of the GAC were used to accelerate the formation rate of the ferrous ions, which is known in the literature to be the limiting rate reaction in the classic Fenton like reagent. It was shown that the ethylene glycol mineralization rate was increased by more than 50%.Finally, optimization of the GAC consumption leading to the fastest mineralization of the ethylene glycol, resulting in decreasing of the decomposition rate of H₂O₂ while enhancing the generation rate of ferrous ions.     

Conversion of CO2 into CH4 by methane-producing bacterium FJ10 under a pressurized condition

In this study, fresh water methane-producing bacterium (MPB), strain FJ10, which used H₂ as an electron donor and CO₂ as an electron acceptor, was isolated and chosen as the primary methanogen for the conversion of CO₂ into CH₄. Improvements to culture medium to increase methane production were investigated using a fractional factorial design in 32 experiments with six variables under consumption of H₂/CO₂ at ratios of 4 and 1. The tested nutrient compositions were NaCl, NH₄Cl, FeSO₄, MgCl₂, H₂PO₄ and yeast extract. Experimental results indicate that yeast extract was essential for the growth of strain FJ10 to impact the conversion of CO₂ into CH₄. Strain FJ10 generated maximum CH₄ production with 5.0 g/l of yeast extract. Moreover, optimal culture conditions for methane production by strain FJ10 were 40 °C and pH 8. Approximately 22-25% of CO₂ conversion into CH₄ was achieved at an H₂/CO₂ ratio of 4 and roughly 2.5-6% of CO₂ conversion into CH₄ was obtained at an H₂/CO₂ ratio of 1 under different pressurized conditions of 1 atm, 50 atm and 100 atm. Under 100 atm, about 6780 μM CH₄ was produced with an H₂/CO₂ ratio of 4 and 4240 μM CH₄ was produced with an H₂/CO₂ ratio of 1 under the steady state condition. The kinetic model for H₂/CO₂ utilization and CH₄ production under different pressures was verified by experimental data. Model predictions are in good agreement with experimental results. The experimental and modeling approaches in this study can be applied to evaluate the conversion of CO₂ into CH₄ as an energy source by geo-microorganisms in geological sequestration.     

A novel Ni-Mg-Al-CaO catalyst with the dual functions of catalysis and CO2 sorption for H2 production from the pyrolysis-gasification of polypropylene

A novel Ni-Mg-Al-CaO catalyst/sorbent has been prepared by integration of the catalytic and CO₂ absorbing properties of the material to maximise the production of hydrogen. The prepared catalyst was tested for hydrogen production from the pyrolysis-gasification of polypropylene by using a two-stage fixed-bed reaction system. X-ray diffraction (XRD), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM)-energy dispersive X-ray spectrometry (EDXS) were used to characterize the prepared Ni-Mg-Al-CaO catalyst/sorbent. Ni-Mg-Al-CaO and calcined dolomite showed a stable carbonation conversion after several cycles of carbonation/calcination, while CaO showed a certain degree of decay. The calcined dolomite showed low efficiency for hydrogen production from pyrolysis-gasification of polypropylene. Increasing the gasification temperature resulted in a decrease of H₂/CO ratio for the Ni-Mg-Al catalyst mixed with sand; however, a stable H₂/CO ratio (around 3.0) was obtained for the Ni-Mg-Al-CaO catalyst. An increased Ni-Mg-Al-CaO catalyst/polypropylene ratio promoted the production of hydrogen from the pyrolysis-gasification of polypropylene. Approximately 70 wt.% of the potential H₂ production was obtained, when the Ni-Mg-Al-CaO catalyst/polypropylene ratio and gasification temperature were 5 and 800 °C, respectively.