Effect of iron enrichment with GIC or FeCl3 on the pore structure and reactivity of coking coal

The effect of a Lewis acid addition to a coking coal on the porosity and reactivity towards steam of the resulting iron enriched coal chars are studied. GIC (FeCl₃ graphite intercalation compound) or free FeCl₃ are used as iron containing additives. Coal iron enrichment was performed using either directly FeCl₃ in vapour phase, or by mixing of coal and additives in decaline or by common grinding of coal and additives under argon. Iron enriched coals were carbonized at 750°C (heating RATE = 5°C min) and activation made with pure steam at 800°C to a burn-off off of 50 wt%. The pore structures of coal chars before and after activation were evaluated on the basis of CO₂ and C₆H₆ sorption at 25°C. A significant development of the microporosity is observed in the iron enriched char before activation and its steam reactivity is also increased. After activation, BET surface area values are increased in presence of iron, and porosity is mainly microporous.     

CO2 and steam gasification of a grapefruit skin char

A kinetic study on the gasification of carbonised grapefruit (Citrus Aurantium) skin with CO₂ and with steam is presented. The chars from this agricultural waste show a comparatively high reactivity, which can be mostly attributed to the catalytic effect of the inorganic matter. The ash content of the carbonised substrate used in this work falls around 15% (db) potassium being the main metallic constituent. The reactivity for both, CO₂ and steam gasification, increases at increasing conversion and also does the reactivity per unit surface area, consistently with the aforementioned catalytic effect. Lowering the ash content of the char by acid washing leads to a decrease of reactivity thus confirming the catalytic activity of the inorganic matter present in the starting material. Saturation of this catalytic effect was not detected within the conversion range investigated covering in most cases up to 0.85-0.9. Apparent activation energy values within the range of 200-250 kJ/mol have been obtained for CO₂ gasification whereas the values obtained for steam gasification fall mostly between 130 and 170 kJ/mol. These values become comparable with the reported in the literature for other carbonaceous raw materials including chars from biomass residues and coals under chemical control conditions.     

The phenol steam reforming reaction towards H2 production on natural calcite

The steam reforming of phenol towards H₂ production was studied in the 650–800 °C range over a natural pre-calcined (air, 850 °C) calcite material. The effects of reaction temperature, water, hydrogen, and carbon dioxide feed concentrations, and gas hourly space velocity (GHSV, h⁻¹) were investigated. The increase of reaction temperature in the 650–800 °C range and water feed concentration in the 40–50 vol% range were found to be beneficial for catalyst activity and H₂-yield. A similar result was also obtained in the case of decreasing the GHSV from 85,000 to 30,000 h⁻¹. The effect of concentration of carbon dioxide and hydrogen in the phenol/water feed stream was found to significantly decrease the rate of phenol steam reforming reaction. The latter was probed to be related to the reduction in the rate of water dissociation as evidenced by the significant decrease in the concentration of adsorbed bicarbonate and OH species on the surface of CaO according to in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS)-CO₂ adsorption experiments in the presence of water and hydrogen in the feed stream. Details of the CO₂ adsorption on the CaO surface at different reaction temperatures and gas atmospheres using in situ DRIFTS and transient isothermal adsorption experiments with mass spectrometry were obtained. Bridged, bicarbonate and unidentate carbonate species were formed under CO₂/H₂O/He gas mixtures at 600 °C with the latter being the most populated. A substantial decrease in the surface concentration of bicarbonate and OH species was observed when the CaO surface was exposed to CO₂/H₂O/H₂/He gas mixtures at 600 °C, result that probes for the inhibiting effect of H₂ on the phenol steam reforming activity. Phenol steam reforming reaction followed by isothermal oxygen titration allowed the measurement of accumulated “carbonaceous” species formed during phenol steam reforming as a function of reaction temperature and short time on stream. An increase in the amount of “carbonaceous” species with reaction time (650–800 °C range) was evidenced, in particular at 800 °C (4.7 vs. 6.7 mg C/g solid after 5 and 20 min on stream, respectively).     

Coffee husks gasification using high temperature air/steam agent

Analyses made on the world's biomass energy potential show that biomass energy is the most abundant sustainable renewable energy. The available technical biomass energy potential surpasses the total world's consumption levels of petroleum oils, coal and natural gas. In order to achieve a sustainable harnessing of the biomass energy potential and to increase its contribution to the world's primary energy consumption, there is therefore a need to develop and sustain contemporary technologies that increase the biomass-to-energy conversion. One such technology is the high temperature air/steam gasification (HTAG) of biomass. In this paper we present findings of gasification experimental studies that were conducted using coffee husks under high temperature conditions. The experiments were performed using a batch facility, which was maintained at three different gasification temperatures of 900 °C, 800 °C, and 700 °C. The study findings exhibited the positive influence of high temperature on increasing the gasification process. Chars left while gasifying at 800 °C and 700 °C were respectively 1.5 and 2.4 times that for the case of 900 °C. Furthermore, increased gasification temperature led to a linear increment of CO concentration in the syngas for all gasification conditions. The effect was more pronounced for the generally poorly performing gasification conditions of N₂ and 2% oxygen concentration. When gasification temperature was increased from 700 °C to 900 °C the CO yield for the 2% O₂ concentration increased by 6 times and that of N₂ condition by 2.5 times. The respective increment for the 3% and 4% O₂ conditions were only twofold. This study estimated the kinetic parameters for the coffee husks thermal degradation that exhibited a reaction mechanism of zero order with apparent activation energy of 161 kJ/mol and frequency factor of 3.89 × 10⁴/min.     

Effect of pre-oxidation on reactivity of chars in steam

The effects of pre-oxidation of char from Taiheiyo coal, a non-caking bituminous coal, in the 400–550 °C temperature range on its gasification reactivity with N₂-H₂O at 0.1 MPa (steam partial pressure of 13.2 kPa) have been investigated. The pre-oxidation of char markedly enhances gasification rates at temperatures between 800 and 900 °C. Reactivity is found to parallel the burn-off level during preoxidation at low temperatures (400–430 °C), whereas at relatively high temperatures (480–550 °C), the burn-off level only affects the reactivity slightly. The amount of CO and CO₂ evolved from the preoxidized char by heat treatment is proportional to the burn-off level at low temperatures (400–430 °C), being closely related to the enhancement of the gasification reactivity in steam.     

Catalytic gasification of char from co-pyrolysis of coal and biomass

The catalytic gasification of char from co-pyrolysis of coal and wheat straw was studied. Alkali metal salts, especially potassium salts, are considered as effective catalysts for carbon gasification by steam and CO₂, while too expensive for industry application. The herbaceous type of biomass, which has a high content of potassium, may be used as an inexpensive source of catalyst by co-processing with coal. The reactivity of chars from co-pyrolysis of coal and straw was experimentally examined. The chars were prepared in a spout-entrained reactor with different ratios of coal to straw. The gasification characteristics of chars were measured by thermogravimetric analysis (TGA). The co-pyrolysis chars revealed higher gasification reactivity than that of char from coal, especially at high level of carbon conversion. The influence of the alkali in the char and the pyrolysis temperature on the reactivity of co-pyrolysis char was investigated. The experimental results show that the co-pyrolysis char prepared at 750 °C have the highest alkali concentration and reactivity.     

Experimental comparison of biomass chars with other catalysts for tar reduction

In this paper the potential of using biomass char as a catalyst for tar reduction is discussed. Biomass char is compared with other known catalysts used for tar conversion. Model tar compounds, phenol and naphthalene, were used to test char and other catalysts. Tests were carried out in a fixed bed tubular reactor at a temperature range of 700–900 °C under atmospheric pressure and a gas residence time in the empty catalyst bed of 0.3 s. Biomass chars are compared with calcined dolomite, olivine, used fluid catalytic cracking (FCC) catalyst, biomass ash and commercial nickel catalyst. The conversion of naphthalene and phenol over these catalysts was carried out in the atmosphere of CO₂ and steam. At 900 °C, the conversion of phenol was dominated by thermal cracking whereas naphthalene conversion was dominated by catalytic conversion. Biomass chars gave the highest naphthalene conversion among the low cost catalysts used for tar removal. Further, biomass char is produced continuously during the gasification process, while the other catalysts undergo deactivation. A simple first order kinetic model is used to describe the naphthalene conversion with biomass char.     

Mechanism of water vapour gasification of carbon—A new model

The mechanism of water vapour gasification of carbon was studied by temperature-programmed desorption measurements of carbon monoxide from polyvinyl chloride cokes of different heat treatment temperatures, which were pregasified in water vapour atmospheres, and quenched before desorption in an inert atmosphere. A new mechanism of water vapour gasification of coal, coke or carbon is proposed, which assumes condention of hydroxyl groups formed by dissociation of water at active sites. The resulting ether groups which are already formed at the ‘carbon’ surface by 500°C are extremely stable (desorption of carbon monoxide in inert atmosphere above 900°C). The onset of gasification by 700°C is explained by an equilibrium shift from the ether groups prevailing at the lower temperatures to desorbable hydroxyl groups by interaction with water vapour. The subsequent steps are identical to those proposed in the generally discussed mechanism of water vapour gasification.     

Catalytic decomposition of biomass tars with iron oxide catalysts

Catalytic gasification of wood (Cedar) biomass was carried out using a specially designed flow-type double beds micro reactor in a two step process: temperature programmed non-catalytic steam gasification of biomass was performed in the first (top) bed at 200–850 °C followed by catalytic decomposition gasification of volatile matters (including tars) in the second (bottom) bed at a constant temperature, mainly 600 °C. Iron oxide catalysts, which transformed to Fe₃O₄ after use possessed catalytic activity in biomass tar decomposition. Above 90% of the volatile matters was gasified by the use of iron oxide catalyst (prepared from FeCl₃ and NH_3aq) at SV of 4.5 × 10³ h^?1. Tar was decomposed over the iron oxide catalysts followed by water gas shift reaction. Surface area of the iron oxide seemed to be an important factor for the catalytic tar decomposition. The activity of the iron oxide catalysts for tar decomposition seemed stable with cyclic use but the activity of the catalysts for the water gas shift reaction decreased with repeated use.     

Investigation on the reactions influencing biomass air and air/steam gasification for hydrogen production

Hydrogen could be the energy carrier of the next world scene provided that its production, transportation and storage are solved. In this work the production of an hydrogen-rich gas by air/steam and air gasification of olive oil waste was investigated. The study was carried out in a laboratory reactor at atmospheric pressure over a temperature range of 700 ­ 900 °C using a steam/biomass ratio of 1.2 w/w. The influence of the catalysts ZnCl₂ and dolomite was also studied at 800 and 900 °C. The solid, energy and carbon yield (%), gas molar composition and high heating value of the gas (kJ NL^− 1), were determined for all cases and the differences between the gasification process with and without steam were established. Also, this work studies the different equilibria taking place, their predominance in each process and how the variables considered affect the final gas hydrogen concentration. The results obtained suggest that the operating conditions were optimized at 900 °C in steam gasification (a hydrogen molar fraction of 0.70 was obtained at a residence time of 7 min). The use of both catalysts resulted positive at 800 °C, especially in the case of ZnCl₂ (attaining a H₂ molar fraction of 0.69 at a residence time of 5 min).     

Platinum,barium and platinum-barium catalysed gasification of graphite in steam and CO2

The concept of forming a bifunctional catalyst system for the gasification of carbon was investigated using controlled atmosphere electron microscopy. Platinum and barium were chosen as the catalyst components and their effect has been studied, both in separate and combined forms, on the gasification of graphite in steam and CO₂. Platinum was found to operate in both systems primarily by the channelling mode but was not very active and was susceptible to deactivation at temperatures 900 °C in a steam environment. This deactivation phenomenon is believed to arise from carbon deposition or precipitation during the reaction. In contrast, previous studies have shown that barium is a relatively active catalyst for both these reactions and operates predominantly by the edge recession mode. The mixed platinum-barium catalyst only exhibited channelling activity, but the intrinsic rate indicated that it probably functions as a true bifunctional catalyst with barium increasing the oxygen reactivity, and platinum the carbon reactivity. The results of this study demonstrate the potential of multicomponent catalysts in which the components are selected by their ability to enhance the rate of one particular step in the reaction scheme.     

Catalytic decomposition of methane over a wood char concurrently activated by a pyrolysis gas

The catalytic activity of a wood char towards CH₄ decomposition in a pyrolysis gas was investigated in a fixed bed reactor for maximising hydrogen production from biomass gasification. Wood char is suggested to be the cheapest and greenest catalyst for CH₄ conversion as it is directly produced in the pyrolysis facility. The conversion of methane reaches 70% for a contact time of 120 ms at 1000 °C. Because steam and CO₂ are simultaneously present in the pyrolysis gas, the carbon catalyst is continuously regenerated. Hence the conversion of methane quickly stabilises. Such a phenomenon is shown to be possible through the oxidation of the char by CO₂ and H₂O at high temperature, which prevents the blocking of the mouth of pores by the concurrent pyrolytic carbon deposition. In the experimental conditions, oxygenated functional surface groups are continuously formed (by steam and CO₂ oxidation) and thermally decomposed. The active sites for CH₄ chemisorption and decomposition are suggested to be the unsaturated carbon atoms generated by the evolution of the oxygenated functions at high temperature.     

The effect of steam on pyrolysis and char reactions behavior during rice straw gasification

Steam gasification of biomass can generate hydrogen-rich, medium heating value gas. We investigated pyrolysis and char reaction behavior during biomass gasification in detail to clarify the effect of steam presence. Rice straw was gasified in a laboratory scale, batch-type gasification reactor. Time-series data for the yields and compositions of gas, tar and char were examined under inert and steam atmosphere at the temperature range of 873-1173 K. Obtained experimental results were categorized into those of pyrolysis stage and char reaction stage. At the pyrolysis stage, low H₂, CO and aromatic tar yields were observed under steam atmosphere while total tar yield increased by steam. This result can be interpreted as the dominant, but incomplete steam reforming reactions of primary tar under steam atmosphere. During the char reaction stage, only H₂ and CO₂ were detected, which were originated from carbonization of char and char gasification with steam (C + H₂O→CO + H₂). It implies the catalytic effect of char on the water-gas shift reaction. Acceleration of char carbonization by steam was implied by faster hydrogen loss from solid residue.     

Synthesis of LiFePO4/carbon composite from nano-FePO4 by a novel stearic acid assisted rheological phase method

LiFePO₄/carbon composite was synthesized at 600 °C for 4 h in an Ar atmosphere by a stearic acid assisted rheological phase method using amorphous nano-FePO₄ as the iron source. XRD, SEM and TEM observations show that the LiFePO₄/carbon composite has good crystallinity, ultrafine and well-dispersed particles of 60–150 nm size and in situ carbon coated on the surface of LiFePO₄ crystallites. The synthesized LiFePO₄/carbon composite shows a high discharge capacity of 160 mAh g⁻¹ and 155 mAh g⁻¹ at rates of 0.5 C and 1 C, respectively. Even at a high current density of 30 C, the material still presents a discharge capacity of 93 mAh g⁻¹ and exhibits an excellent cycling performance.     

Pressurized gasification of woody biomass—Variation of parameter

Pressurized gas produced from biomass is a renewable resource that is attracting a great deal of attention due to its wide range of industrial applications, such as the production of hydrogen, chemicals or high grade fuels. Therefore, the Vienna University of Technology in cooperation with BioEnergy 2020+ is operating a bubbling pressurized gasification plant. The pressurized research unit (PRU) is able to perform the gasification of wood chips, wood pellets, coal and other solid fuels with gasification agents air, steam, oxygen or carbon dioxide. This paper gives the results of parameter variation at this plant with regard to the producer gas composition. The feedstock was wood pellets and as bed material olivine was used with an average particle size of 0.5 mm. The parameters varied were temperature (720-900 °C), pressure (1-5 bar), air ratio (0.2-0.4), gasification agent (air, steam, oxygen), biomass feed input (4.5-8 kg/h) and the fluidization conditions of the reactor fluidized bed (fluidization number (3-7)).     

Drastic changes in biomass char structure and reactivity upon contact with steam

An Australian cane trash biomass was pyrolysed by heating at a slow heating rate to 700-900 °C in an inert gas atmosphere. The chars were then gasified in situ with steam. Our results indicate that the gasification of char with steam, even only for 20 s when the char conversion was minimal, resulted in drastic reduction in the intrinsic reactivity of char with air at 400 °C. The decreases in the char reactivity were not mainly due to the possible volatilisation of inherent catalysts during gasification in steam. Instead, the FT-Raman spectroscopy of the chars showed that the gasification of char with steam resulted in drastic changes in char structure including the transformation of smaller ring systems (3-5 fused rings) to large ring systems (?6 fused rings). It is believed that the intermediates of char-steam reactions, especially H, penetrated deep into the char matrix to induce the ring condensation reactions.     

Process modeling for parametric study on oil palm empty fruit bunch steam gasification for hydrogen production

Biomass steam gasification with in-situ carbon dioxide capture using CaO exhibits good prospects for the production of hydrogen rich gas. The present work focuses on the process modeling for hydrogen production from oil palm empty fruit bunch (EFB) using MATLAB for parametric study. The model incorporates the reaction kinetics calculations of the steam gasification of EFB (C_3.4H_4.1O_3.3) with in-situ CO₂ capture, as well as mass and energy balances calculations. The developed model is used to investigate the effect of temperature and steam/biomass ratio on the hydrogen purity, yield and efficiency. Based on the results, hydrogen purity of more than 76.1 vol.% can be achieved. The maximum hydrogen yield predicted at the outlet of the gasifier is 102.6 g/kg of EFB. It is found that increment in temperature and steam/biomass ratio promotes hydrogen production. However, it is also predicted that the efficiency decreases when using more steam. Due to the still on-going empirical work, the results are compared with published literatures on different systems. The comparison shows that the results are in agreement to some extent due to the different basis.     

Improvement in hydrogen production from hard-shell nut residues by catalytic hydrothermal gasification

The hydrothermal gasification of some hard-shell nut residues (hazelnut, walnut and almond shells) was performed in a batch type reactor at temperature and pressure ranges of 300–600 °C and 88–405 bar, respectively. The biomass samples were converted into gaseous product (hydrogen, carbon dioxide, methane, carbon monoxide and C₂–C₄ compounds), aqueous product (carboxylic acids, furfurals, phenols, aldehydes and ketones) and solid products after hydrothermal gasification. Hydrogen production was improved by using natural mineral catalysts (Trona, Dolomite and Borax). The activity of selected natural mineral catalysts in hydrothermal gasification can be ordered as being Trona [Na₃(CO₃)(HCO₃)·2H₂O] > Borax [Na₂B₄O₇·10H₂O] > Dolomite [CaMg(CO₃)₂]. The most effective catalyst was found to be Trona at 600 °C leading enhancement in hydrogen yields (mol H₂/kg C in biomass) for hazelnut, walnut and almond shells as 82.4%, 74.1% and 42.4%, respectively.     

Modeling of catalytic gasification kinetics of coal char and carbon

Calcium- and potassium-catalyzed gasification reactions of coal char and carbon by CO₂ are conducted, and the common theoretical kinetic models for gas-carbon (or char) reaction are reviewed. The obtained experimental reactivities as a function of conversion are compared with those calculated based on the random pore model (RPM), and great deviations are found at low or high conversion levels as predicted by theory. Namely, calcium-catalyzed gasification shows enhanced reactivity at low conversion levels of <0.4, whereas potassium-catalyzed gasification indicated a peculiarity that the reactivity increases with conversion. CO₂ chemisorption analysis received satisfactory successes in both interpreting catalytic effects and correlating the gasification reactivity with irreversible CO₂ chemical uptakes (CCU_ir) of char and carbon at 300 °C. In details, calcium and potassium additions led to significant increases in CCU_ir and correspondent high reactivities of the char and carbon. Furthermore, CCU_ir of char and carbon decreased with conversion for calcium-catalyzed reaction but increased for potassium-catalyzed one, corresponded to the tendency of their reactivity. The RPM is extended and applied to these catalytic gasification systems. It is found that the extended RPM predicts the experimental reactivity satisfactorily. The most important finding of this paper is that the empirical constants in the extended RPM correlate well with catalyst loadings on coal.     

Fe/赤泥催化水蒸气气化煤焦的反应性与微结构特性

利用固定床反应器和自制Fe/赤泥（RM）、RM催化剂,进行了900℃煤焦/催化剂不同质量比的水蒸气气化实验,并采用原位红外（FTIR）、物理吸附仪（BET）、拉曼光谱（Raman）等测试手段,分析了催化气化过程中不同阶段煤焦的气化反应性、表面官能团、孔隙结构和碳微晶结构的演变规律。结果表明,Fe1/RM2催化剂可显著提高煤焦-水蒸气的气化反应性。在Fe1/RM2/煤焦-水蒸气反应过程中,煤焦表面形成-CH₂、-COOH、酚羟基等活性官能团并与Fe1/RM2活性组分相互作用,形成新的小分子基团或化合物;煤焦的比表面积先增大后减小（6.98～323.22m²/g）,平均孔径呈现相反的变化趋势（2.91～11.25nm）;碳有序化程度先降低后提高,碳转化率为36%煤焦中无定形碳的相对含量最高（0.371）。在煤焦-Fe1/RM2-水蒸气反应初期（X_C<36%）,煤焦表面活性基团增多、比表面积增大、有序化程度降低,综合提高了煤焦-水蒸气气化反应性;降低36%≤X_C≤62%阶段的碳有序化程度,对煤焦气化反应性的提高具有显著意义。