Thermogravimetric study of the devolatilization of hydropyrolysis chars

The devolatilization of hydropyrolysis (HyPy) chars formed at 485–850 °C under 3 MPa and chars formed at 580 °C under 0–5 MPa of H₂ and 3 MPa He is investigated in a thermobalance coupled to two gas chromatographs. The H₂, CH₄ and CO₂ released are analysed every 4 min and all are analysed at the end of the experiment. The amount of residual volatile matter in the chars decreases rectilinearly with the HyPy temperature, whereas their decrease is asymptotic with the HyPy pressure. The char formed under He contains 45% more residual volatile matter than that formed in the same conditions under H₂. The HyPy temperature must be limited if the char is to be burned in a boiler. The CH₄ formation is strongly dependant of the HyPy temperature.     

Formation and gasification of carbon deposits on NiSiO2 catalysts

The deposition of carbon from CH₄ and CO on $\text{Ni}\text{SiO}{}_2$ catalysts was studied in pulse-flow experiments as well as volumetrically with a low-field magnetic permeameter. It was found that carbon, deposited from CH₄ according to: CH₄ → C + 4H, gave rise to the formation of nickel carbide, Ni₃C, only at the surface of the nickel particles (T< 300 °C). However, carbon, deposited from CO according to: 2CO → C + CO₂, led to the formation of a bulk nickel carbide as well as dissolution of carbon interstitially. The reactivity of the carbon thus deposited was studied with both H₂ and H₂O. The rate of reaction with hydrogen appeared to be a function of temperature: the rate passed through a maximum at 200 °C and dropped steeply above 300 °C. The only product of the reaction was CH₄. The reaction with H₂O produced besides CH₄, CO₂ and (at low carbon surface coverages) H₂.     

Tri-reforming of surrogate biogas over Ni/Mg/ceria–zirconia/alumina pellet catalysts

The performance of catalytic tri-reforming under industrially relevant situations (e.g., pellet catalysts, pressurized reactor) was investigated using surrogate biogas as the feedstock. Tri-reforming using Ni/Mg/Ce_0.6Zr_0.4O₂/Al₂O₃ pellet catalysts was studied in a bench scale fixed-bed reactor. The feed molar ratio for CH₄:CO₂:air was fixed as 1.0:0.70:0.95. The effects of temperature (800–860°C), pressure (1–6?bar), and H₂O/CH₄ molar feed ratio (0.23–0.65) were examined. Pressure has substantial impact on the reaction and transport rates and equilibrium conversions, making it a key variable. At 860°C, CO₂ conversion increased from 4 to 61% and H₂/CO molar ratio decreased from 2.0 to 1.1 as the pressure changed from 1 to 6?bar. CO₂ conversion and H₂/CO molar ratio were also influenced by the temperature and H₂O/CH₄ molar ratio. At 3?bar, CO₂ conversion varied between 4 and 43% and the H₂/CO molar ratio varied between 1.2 and 1.9 as the temperature changed from 800 to 860°C. At 3?bar and 860°C, CO₂ conversion decreased from 35 to 8% and H₂/CO molar ratio increased from 1.7 to 2.4 when the H₂O/CH₄ molar ratio was increased from 0.23 to 0.65. This work demonstrates that the tri-reforming technology is feasible for converting biogas under scaled-up conditions in a fixed-bed reactor.     

Hydrogen formation from a real biogas using electrochemical cell with gadolinium-doped ceria porous electrolyte

The electrochemical cell consisting of a gadolinium-doped ceria (GDC, Ce_0.9Gd_0.1O_1.95) porous electrolyte, Ni–GDC cathode and Ru–GDC anode was applied for the dry-reforming (CH₄+CO₂→2H₂+2CO) of a real biogas (CH₄ 60.0%, CO₂ 37.5%, N₂ 2.5%) produced from waste sweet potato. The composition of the supplied gas was adjusted to CH₄/CO₂=1/1 volume ratio. The supplied gas changed continuously into a H₂–CO mixed fuel with H₂/CO=1/0.949–1/1.312 vol ratios at 800 °C for 24 h under the applied voltage of 1–2 V. The yield of the mixed fuel was higher than 80%. This dry-reforming reaction was thermodynamically controlled at 800 °C. The application of external voltage assisted the reduction of NiO and the elimination of solid carbon deposited slightly in the cathode. The decrease of heating temperature to 700 °C reduced gradually the fraction of the H₂–CO fuel (61.3–18.6%) within 24 h. Because the Gibbs free energy change was calculated to be negative values at 700–600 °C, the above result at 700–600 °C originated from the gradual deposition of carbon over Ni catalyst through the competitive parallel reactions (CH₄→C+2H₂, 2CO→C+CO₂). The application of external voltage decreased the formation temperature of carbon by the disproportionation of CO gas. At 600 °C, the H₂–CO fuel based on the Faraday's law was produced continuously by the electrochemical reforming of the biogas.     

Preferential CO Oxidation in the Presence of H2, H2O and CO2 at Short Contact-times

High selectivities and conversions in the preferential oxidation of CO in the presence of large quantities of H₂, H₂O and CO₂ are demonstrated on noble metal catalysts at millisecond contact times (~10–15 ms) for temperatures between 150 and 500 °C. With a simulated water-gas shift product stream containing 0.5% CO and varying amounts of H₂, H₂O and CO₂, we are able to achieve ~90% CO conversions on a Ru catalyst at temperatures of ~300 °C using a stoichiometric amount of O₂ (0.25%). Experiments with and without O₂ and with varying H₂O reveal that significant water-gas shift occurs on Pt and Pt-ceria catalysts at temperatures between 250 and 400 °C, while significant CH₄ is formed on Ru and Rh catalysts at temperatures greater than 250 and 350 °C, respectively. The presence of H₂O blocks H₂ adsorption and allows preferential CO oxidation at higher temperatures where rates are high. We propose that a multistage preferential oxidation reactor using these catalysts can be used to bring down CO content from 5000 ppm at the reactor entrance to less than 100 ppm at very short contact-times.     

Gas evolution during oil shale pyrolysis. 1. Nonisothermal rate measurements

The rate of evolution of CH₄, CO, CO₂, H₂, C₂ hydrocarbons, and C₃ hydrocarbons during pyrolysis of Colorado oil shale between 25 and 900 °C is reported. All experiments were performed nonisothermally using linear heating rates varying from 0.5 to 4.0 °C min^?1. Hydrogen is the major noncondensable gas produced by kerogen pyrolysis. The amount of H₂ released is influenced, via the shift and Boudouard reactions, by the CO₂ evolved from mineral carbonates. Lesser amounts of C₁, C₂, and C₃ hydrocarbons are produced. On the basis of heat content, however, the combined C₁ to C₃ hydrocarbons contribute twice as much as H₂ to the heating value of the pyrolysis gas. The evolution of H₂ and CH₄ involves processes that are interpreted as a ‘primary’ pyrolysis of the kerogen to generate oil, and a higher temperature ‘secondary’ pyrolysis of the carbonaceous residue. The CO formed is a product of the Boudouard reaction; nearly complete conversion of the carbon residue to CO via this reaction is observed.     

Chemical‐looping combustion process: Kinetics and mathematical modeling

Chemical Looping Combustion technology involves circulating a metal oxide between a fuel zone where methane reacts under anaerobic conditions to produce a concentrated stream of CO₂ and water and an oxygen rich environment where the metal is reoxidized. Although the needs for electrical power generation drive the process to high temperatures, lower temperatures (600–800°C) are sufficient for industrial processes such as refineries. In this paper, we investigate the transient kinetics of NiO carriers in the temperature range of 600 to 900°C in both a fixed bed microreactor (WHSV = 2‐4 g CH₄/h/g oxygen carrier) and a fluid bed reactor (WHSV = 0.014‐0.14 g CH₄/h per g oxygen carrier). Complete methane conversion is achieved in the fluid bed for several minutes. In the microreactor, the methane conversion reaches a maximum after an initial induction period of less than 10 s. Both CO₂ and H₂O yields are highest during this induction period. As the oxygen is consumed, methane conversion drops and both CO and H₂ yields increase, whereas the CO₂ and H₂O concentrations decrease. The kinetics parameter of the gas–solids reactions (reduction of NiO with CH₄, H₂, and CO) together with catalytic reactions (methane reforming, methanation, shift, and gasification) were estimated using experimental data obtained on the fixed bed microreactor. Then, the kinetic expressions were combined with a detailed hydrodynamic model to successfully simulate the comportment of the fluidized bed reactor. © 2010 American Institute of Chemical Engineers AIChE J, 2010     

The use of NiO as an oxygen carrier in chemical-looping combustion

The feasibility of using NiO as an oxygen carrier during chemical-looping combustion has been investigated. A thermodynamic analysis with CH₄ as fuel showed that the yield of CH₄ to CO₂ and H₂O was between 97.7 and 99.8% in the temperature range 700–1200 °C, with the yield decreasing as the temperature increases. Carbon deposition is not expected as long as sufficient metal oxide is supplied to the fuel reactor. Hydrogen sulfide, H₂S, in the fuel gas will be converted partially to SO₂ in the gas phase, with the degree of conversion increasing with temperature, but decreasing as a function of pressure. There is the possibility of sulfide formation as Ni₃S₂ at higher partial pressures of H₂S+SO₂ in the reactor. The reactivity of freeze granulated particles of NiO with NiAl₂O_4, MgAl₂O₄, TiO₂ and ZrO₂ sintered at different temperatures was investigated in a small fluidized bed reactor by exposing them cyclically to 50% CH₄/50% H₂O and 5% O₂ at 950 °C. During the reducing period, the NiO initially reacted with the CH₄ to form CO₂ and H₂O. However, there were always minor amounts of CO from the outlet of the reactor even at high concentrations of CO₂, which was due to the thermodynamic limitations. Here, the ratio CO/(CO₂+CO+CH₄) was between 1.5 and 2.5% at 950 °C for the oxygen carriers with alumina based inert. A small amount of CH₄ was released from the reactor at high degrees of oxidation of the NiAl₂O₄ and MgAl₂O₄-based carriers. As the time under reducing conditions increased, steam reforming of CH₄ to CO and H₂ became considerable, with Ni catalyzing this reaction. Whereas the ZrO₂ particles showed similar behavior as the alumina-based carriers, the TiO₂-based particles showed a markedly different reaction behavior, likely due to the complex interaction between NiO and TiO₂.     

Catalysis of gasification of coal-derived cokes and chars

Calcium is the most important in-situ catalyst for gasification of US coal chars in O₂, CO₂ and H₂O. It is a poor catalyst for gasification of chars by H₂. Potassium and sodium added to low-rank coals by ion exchange and high-rank coals by impregnation are excellent catalysts for char gasification in O₂, CO₂ and H₂O. Carbon monoxide inhibits catalysis of the CH₂O reaction by calcium, potassium and sodium; H₂ inhibits catalysis by calcium. Thus injection of synthesis gas into the gasifier will inhibit the CH₂O reaction. Iron is not an important catalyst for the gasification of chars in O₂, CO₂ and H₂O, because it is invariably in the oxidized state. Carbon monoxide disproportionates to deposit carbon from a dry synthesis gas mixture (3 vol H₂ + 1 vol CO) over potassium-, sodium- and iron-loaded lignite char and a raw bituminous coal char, high in pyrite, at 1123 K and 0.1 MPa pressure. The carbon is highly reactive, with the injection of 2.7 kPa H₂O to the synthesis gas resulting in net carbon gasification. The effect of traces of sulphur in the gas stream on catalysis of gasification or carbon-forming reactions by calcium, potassium, or sodium is not well understood at present. Traces of sulphur do, however, inhibit catalysis by iron.     

Dynamic behavior of trace elements during pyrolysis of coals

Release behavior of sodium and potassium was followed during pyrolysis of coals in a nitrogen stream up to 1200 °C. Sodium and potassium in coal and char were classified into five fractions by a serial dissolution method with H₂O, CH₃COONH₄, HCl, H₂SO₄ and HF solutions. Distribution of selenium in coal matrix and its release behavior were observed for density-separated samples during pyrolysis. The results showed that lower temperature release of potassium was observed during pyrolysis comparing to the sodium release. Fractions of H₂O soluble and CH₃COONH₄ soluble decreased, and fractions of H₂SO₄ soluble increased with heat treatments for both alkali metals. Selenium was distributed unevenly in the coal matrix and its content was correlated well with pyritic sulfur content but not with organic sulfur content.     

Devolatilization characteristics of high volatile coal in a wire mesh reactor

A wire mesh reactor was used to investigate the devolatilization process of coal particle during entrained flow gasification. Coal from Indonesia East Kalimantan mine, which has high moisture and high volatile matter, was chosen as a sample. Experiments were carried out at the heating rate of 1,000 °C/s and isothermal condition was kept at peak temperature under atmospheric pressure. The char, tar and gas formation characteristics of the coal as well as the composition of the gas components at peak temperatures were determined. The experimental results showed that devolatilization process terminated when temperature reached above 1,100 °C. Most of tar was formed at about 800 °C, while the rate of tar formation decreased gradually as the temperature increased. CH₄ was observed at temperatures above 600 °C, whereas H₂ was detected above 1,000 °C. The amount of formed gases such as H₂, CO, CH₄ and C _n H _m increased as the temperature increased. From the characteristics of devolatilization with residence time, it was concluded that devolatilization terminated within about 0.7 second when the temperature reached 1,000 °C. As the operating temperature in an entrained flow gasifier is higher than ash melting temperature, it is expected that the devolatilization time of high volatile coal should be less than one second in an entrained flow gasifier.     

Thermodynamic Equilibrium Calculations for the Reforming of Coke Oven Gas with Gasification Gas

Thermodynamic analyses of the reforming of coke oven gas with gasification gas for syngas were investigated as a function of coke oven gas‐to‐gasification gas ratio (1–3), oxygen‐to‐methane ratio (0–1.56), pressure (25–35 bar) and temperature (700–1100 °C). Thermodynamic equilibrium results indicate that the operating temperature should be approximately 1100 °C and the oxygen‐to‐methane ratio should be approximately 0.39, where about 80 % CH₄ and CO₂ can be converted at 30 bar. Increasing the operating pressure shifts the equilibrium toward the reactants (CH₄ and CO₂); increasing the pressure from 25 to 35 bar decreases the conversion of CO₂ from 73.7 % to 67.8 %. The conversion ratio of CO₂ is less than that in the absence of O₂. For a constant feed gas composition (7 % O₂, 31 % gasification gas, and 62 % coke oven gas), a H₂/CO ratio of about 2 occurs at temperatures of 950 °C and above. Pressure effects on the H₂/CO ratio are negligible for temperatures greater than 750 °C. The steam produced has an effect on the hydrogen selectivity, but its mole fraction decreases with temperature; trace amounts of other secondary products are observed.     

High-temperature in situ FTIR spectroscopy study of LaOF and BaF2/LaOF catalysts for methane oxidative coupling

In situ FTIR spectroscopy was used to characterize the oxygen adspecies and its reactivity with CH₄ over LaOF and 15 mol% BaF₂/LaOF catalysts at OCM temperature (750-800°C). It was found that gas-phase oxygen was activated on the surface of LaOF and 15 mol% BaF₂/LaOF, which had been pretreated under vacuum at 750 or 800°C, forming O ₂ ^- species at high temperature (750-800°C). At 750°C, the adsorbed O ₂ ^- species can react with pure CH₄ accompanied by formation of gas-phase C₂H₄ and CO₂, and there is a good correlation between the rate of disappearance of surface O₂and the rate of formation of gas-phase C₂H₄. The O ₂ ^- species was also observed over the catalysts under working condition, and it reacted with CH₄ in a manner that was consistent with its role in a catalytic cycle. These results suggest that O ₂ ^- may be the active oxygen species for OCM reaction over these catalysts. This revised version was published online in July 2006 with corrections to the Cover Date.     

Catalytic carbon deposition-oxidation over Ni,Fe and Co catalysts: A new indirect route to store and transport gas hydrocarbon fuels

In this work, a new two-step route to store and transport associated natural gas, promoted by Ni, Fe and Co supported catalyst was presented. Initially, CH₄ is converted into carbon deposits (M/C composite), being Fe catalyst the most active catalyst. In Step 2, M/C composite reacts with H₂O producing H₂, CO and CH₄. TPO experiments showed that efficiency and selectivity of oxidation depends on the metal. Ni catalyst produced mainly H₂ and CO, while Fe system was more selective to convert carbon into CH₄. The formation of C₂ and C₃ compounds suggests the presence of a Fischer Tropsch like process.     

The pyrolysis of individual plastics and a plastic mixture in a fixed bed reactor

Six thermoplastics, which represent more than two-thirds of all polymer production in western Europe, were pyrolysed in a static batch reactor in a nitrogen atmosphere. These were high density polyethylene (HDPE), low density polyethylene (LDPE), polystyrene (PS), polypropylene (PP), polyethylene terephthalate (PET) and polyvinyl chloride (PVC). The heating rate used was 25°C min⁻¹ to a final temperature of 700°C. These six plastics were then mixed together to simulate the plastic fraction of municipal solid waste found in Europe. The effect of mixing on the product yield and composition was examined. The results showed that the polymers studied did not react independently, but some interaction between samples was observed. The product yield for the mixture of plastics at 700°C was 9·63% gas, 75·11% oil, 2·87% char and 2·31% HCl. The gases identified were H₂, CH₄, C₂H₄, C₂H₆, C₃H₆, C₃H₈, C₄H₈, C₄H₁₀, CO₂ and CO. The composition of oils were determined using Fourier Transform infra-red spectrometry and size exclusion chromatography. Analysis showed the presence mainly of aliphatic compounds with small amounts of aromatic compounds. ©1997 SCI     

Structural characterization and thermal behaviour of block copolymers of polydimethylsiloxane and polyamide having trichlorogermyl pendant groups

Block copolymers having a pendant trichlorogermyl group as a part of polyamide segment? (CO? R′? CO? NH? Ar? NH? )_xCO? R′? CO? and polydimethylsiloxane of general formula [(? CO? R′? CO? HN? Ar? NH)_x? CO? R′? CO? NH(CH₂)₃SiO(CH₃)₂ ((CH₃)₂SiO)_ySi(CH₃)₂(CH₂)₃ NH? ]_n (where R′ = CH₂CH(GeCl₃), CH(CH₃)CH(GeCl₃), CH(GeCl₃)CH(CH₃); Ar = C₆H₄, (? C₆H₃? CH₃)₂, (? C₆H₃? OCH₃)₂, 2,5‐(CH₃)₂? C₆H₂, C₆H₄? O? C₆H₄) were prepared by a polycondensation reaction and characterized using CHN and Ge analysis, Fourier transform infrared (FTIR) and ¹H NMR spectroscopy, thermogravimetric analysis (TGA) and molecular weight determination. They have a lamellar structure with weight‐average molecular weight in the range 1.21 × 10⁵–4.79 × 10⁵ g mol^?1. These copolymers display two glass transition temperatures and have an average decomposition temperature of 489 °C. TGA, FTIR and gas chromatography/mass spectrometry studies indicate that degradation of these block copolymers results in carbon monoxide, oligomeric siloxanes and polyamide fragments. They are thermally stable due to the hydrogen bonded interlinked chains of polyamide, while they absorb water due to the presence of Ge? Cl bonding. Copyright © 2010 Society of Chemical Industry     

Effect of gas permeation temperature and annealing procedure on the performance of binary and ternary mixed matrix membranes of polyethersulfone,SAPO‐34, and 2‐hydroxy 5‐methyl aniline

This study investigated the effect of annealing time and temperature on gas separation performance of mixed matrix membranes (MMMs) prepared from polyethersulfone (PES), SAPO‐34, and 2‐hydroxy 5‐methyl aniline (HMA). A postannealing period at 120°C for a week extensively increased the reproducibility and stability of MMMs, but for pure PES membranes no post‐annealing was necessary for stable and reproducible performance. The effect of operation temperature was also investigated. The permeabilities of H₂, CO₂, and CH₄ increased with increasing permeation temperature from 35°C to 120°C, yet CO₂/CH₄ and H₂/CH₄ selectivities decreased. PES/SAPO‐34/HMA ternary and PES/SAPO‐34 binary MMMs exhibited the highest ideal selectivity and permeability values at all temperatures, respectively. For H₂/CO₂ pair, when temperature increased from 35°C to 120°C, selectivity increased from 3.2 to 4.6 and H₂ permeability increased from 8 to 26.5 Barrer for ternary MMM, demonstrating the advantage of using this membrane at high temperatures. The activation energies were in the order of CH₄ > H₂ > CO₂ for all membranes. PES/SAPO‐34/HMA membrane had activation energies higher than that of PES/SAPO‐34 membrane, suggesting that HMA acts as a compatibilizer between the two phases. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40679.     

Pyrolysis of tire powder: influence of operation variables on the composition and yields of gaseous product

The pyrolysis of tire powder was studied experimentally using a specially designed pyrolyzer with high heating rates. The composition and yield of the derived gases and distribution of the pyrolyzed product were determined at temperatures between 500 and 1000 °C under different gas phase residence times. It is found that the gas yield goes up while the char and tar yield decrease with increasing temperature. The gaseous product mainly consists of H₂, CO, CO₂, H₂S and hydrocarbons such as CH₄, C₂H₄, C₂H₆, C₃H₆, C₃H₈, C₄H₈ and C₄H₆ with a little other hydrocarbon gases. Its heating value is in the range of 20 to 37 MJ/Nm³. Maximum heating value is achieved at a temperature between 700 and 800 °C. The product distribution ratio of gas, tar and char is about 21:44:35 at 800 °C. The gas yield increases with increasing gas residence time when temperature of the residence zone is higher than 700 °C. The gas heating value shows the opposite trend when the temperature is higher than 800 °C. Calcined dolomite and limestone were used to explore their effect on pyrolyzed product distribution and composition of the gaseous product. It is found that both of them affect the product distribution, but the effect on tar cracking is not obvious when the temperature is lower than 900 °C. It is also found that H₂S can be absorbed effectively by using either of them. About 57% sulfur is retained in the char and 6% in the gas phase. The results indicated that high-energy recovery could not be achieved if fuel gas is the only target product. In view of this, multi-use of the pyrolyzed product is highly recommended.     

Hydrogen production through dry reforming of biogas using a porous electrochemical cell: Effects of a cobalt catalyst in the electrode and mixing of air with biogas

This paper reports the performance of porous Gd-doped ceria (GDC) electrochemical cells with Co metal in both electrodes (cell No. 1) and with Ni metal in the cathode and Co metal in the anode (cell No. 2) for CO₂ decomposition, CH₄ decomposition, and the dry reforming reaction of a biogas with CO₂ gas (CH₄ + CO₂ → 2H₂ + 2CO) or with O₂ gas in air (3CH₄ +?1.875CO₂ +?1.314O₂ → 6H₂ +?4.875CO +?0.7515O₂). GDC cell No. 1 produced H₂ gas at formation rates of 0.055 and 0.33?mL-H₂/(min?m²-electrode) per 1?mL-supplied gas/(min?m²-electrode) at 600?°C and 800?°C, respectively, by the reforming of the biogas with CO₂ gas. Similarly, cell No. 2 produced H₂ gas at formation rates of 0.40?mL-H₂/(min?m²) per 1?mL-supplied gas/(min?m²) at 800?°C from a mixture of biogas and CO₂ gas. The dry reforming of a real biogas with CO₂ or O₂ gas at 800?°C proceeded thermodynamically over the Co or Ni metal catalyst in the cathode of the porous GDC cell. Faraday's law controlled the dry reforming rate of the biogas at 600?°C in cell No. 2. This paper also clarifies the influence of carbon deposition, which originates from CH₄ pyrolysis (CH₄ → C + 2H₂) and disproportionation of CO gas (2CO → C + CO₂), on the cell performance during dry reforming. The dry reforming of a biogas with O₂ molecules from air exhibits high durability because of the oxidation of the deposited carbon by supplied air.     

Gaseous products of the thermolysis of brown coal impregnated with potassium hydroxide

The yields of gaseous products (H₂, CO, CO₂, and C _n H_2n + 2 at n = 1−4) from brown coal and brown coal-KOH compounds were determined under conditions of nonisothermal heating (4°C/min) to 800°C followed by an isothermal exposure (1 h, 800°C). It was found that, in the presence of the alkali, the yields of H₂, CO, C₂H₆, and C₃H₈ increased; the yields of CO₂ and CH₄ decreased; and the formation of isobutane was completely suppressed. Changes in the gas compositions were explained by the alkali degradation of C-C bonds in the organic matter of coal and by the thermally initiated dehydrogenation and dealkylation reactions of arene and alkane structural fragments, in which KOH molecules served as H-atom donors in the formation of H₂ and alkanes.