Effect of catalyst addition on gasification reactivity of HyperCoal and coal with steam at 775-700 °C

HyperCoal is a clean coal with ash content <0.05 wt%. HyperCoal was prepared from a bituminous coal by solvent extraction method with an extraction yield of 66.7%. Effect of K₂CO₃ loading and temperature on steam gasification rate of HyperCoal and parent raw coal was investigated. Experiments were carried out at 775 and 700 °C for both HyperCoal and coal with 0-25% catalyst loading. Gasification rates increased with increased catalyst loading and reached a value above which rates did not change with catalyst loading. The catalyst loadings were 6% for HyperCoal and 20% for coal. The difference is most likely due to the difference in ash content of HyperCoal and coal and not due to the effect of H₂ inhibition on the rate. In the presence of catalyst effect of temperature was only on gasification rate and total gas yield and gas composition were unaffected.     

Lime enhanced gasification of solid fuels: Examination of a process for simultaneous hydrogen production and CO2 capture

The lime enhanced gasification (LEGS) process uses CaO as a CO₂ carrier and consists of two coupled reactors: a gasifier in which CO₂ absorption by CaO produces a hydrogen-rich product gas, and a regenerator in which the sorbent is calcined producing a high purity CO₂ gas stream suitable for storage. The LEGS process operates at a pressure of 2.0 MPa and temperatures less than 800 °C and therefore requires a reactive fuel such as brown coal. The brown coal ash and sulfur are purged from the regenerator together with CaO which is replaced by fresh limestone in order to maintain a steady-state CaO carbonation activity (a_ave). Equilibrium calculations show the influence of process conditions and coal sulfur content on the gasifier carbon capture (>95% is possible). Material balance calculations of the core process show that the required solid purge of the sorbent cycle is mainly attributed to the necessary removal of ash and CaSO₄ if the solid purge is used as a pre-calcined feedstock for cement production. The decay in the CaO capture capacity over many calcination–carbonation cycles demands a high sorbent circulation ratio but does not dictate the purge fraction. A thermodynamic analysis of a LEGS-based combined power and cement production process, where the LEGS purge is directly used in the cement industry, results in an electric efficiency of 42% using a state of the art combined cycle.     

Three‐stage well‐mixed reactor model for a pressurized coal gasifier

Three Canadian coals of different rank were gasified with air‐steam mixtures in a 0.1 m diameter spouted bed reactor at pressures to 292 kPa, average bed temperatures varying between 840 and 960°C, and steam‐to‐coal feed ratios between 0.0 and 2.88. In order to analyze gasifier performance and correlate data, a three‐stage model has been developed incorporating instantaneous devolatilization of coal, instantaneous combustion of carbon at the bottom of the bed, and steam/carbon gasification and water gas shift reaction in a single well mixed isothermal stage. The capture of H₂S by limestone sorbent injection is also treated. The effects of various assumptions and model parameters on the predictions were investigated. The present model indicates that gasifier performance is mainly controlled by the fast coal devolatilization and char combustion reactions, and the contribution to carbon conversion of the slow char gasification reactions is comparatively small. The incorporation of tar decomposition into the model provides significantly closer predictions of experimental gas composition than is obtained otherwise.     

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.     

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.     

Effect of rice husk ash addition on CO2 capture behavior of calcium-based sorbent during calcium looping cycle

Rice husk ash/CaO was proposed as a CO₂ sorbent which was prepared by rice husk ash and CaO hydration together. The CO₂ capture behavior of rice husk ash/CaO sorbent was investigated in a twin fixed bed reactor system, and its apparent morphology, pore structure characteristics and phase variation during cyclic carbonation/calcination reactions were examined by SEM-EDX, N₂ adsorption and XRD, respectively. The optimum preparation conditions for rice husk ash/CaO sorbent are hydration temperature of 75 °C, hydration time of 8 h, and mole ratio of SiO₂ in rice husk ash to CaO of 1.0. The cyclic carbonation performances of rice husk ash/CaO at these preparation conditions were compared with those of hydrated CaO and original CaO. The temperature at 660 °C–710 °C is beneficial to CO₂ absorption of rice husk ash/CaO, and it exhibits higher carbonation conversions than hydrated CaO and original CaO during multiple cycles at the same reaction conditions. Rice husk ash/CaO possesses better anti-sintering behavior than the other sorbents. Rice husk ash exhibits better effect on improving cyclic carbonation conversion of CaO than pure SiO₂ and diatomite. Rice husk ash/CaO maintains higher surface area and more abundant pores after calcination during the multiple cycles; however, the other sorbents show a sharp decay at the same reaction conditions. Ca₂SiO₄ found by XRD detection after calcination of rice husk ash/CaO is possibly a key factor in determining the cyclic CO₂ capture behavior of rice husk ash/CaO.     

The catalytic effect of both oxygen-bearing functional group and ash in carbonaceous catalyst on CH<Subscript>4</Subscript>-CO<Subscript>2</Subscript> reforming

A kind of new catalyst—carbonaceous catalyst—for CH₄-CO₂ reformation has been developed in our laboratory. The effect of both oxygen-bearing functional group such as phenolic hydroxyl, carbonyl, carboxyl, and lactonic, and ash such as Fe₂O₃, Na₂CO₃, and K₂CO₃ in the carbonaceous catalyst on the CH₄-CO₂ reforming has been investigated with a fixed-bed reactor. It has been found that the carbonaceous catalyst is an efficient catalyst on CO₂-CH₄ reforming. With the decrease of oxygen-bearing functional group, the catalytic activity of carbonaceous catalyst decreases quickly. The oxygen-bearing functional groups play a significant role in the carbonaceous-catalyzed CO₂-CH₄ reforming; the ash components in carbonaceous catalyst also have an important influence on the CO₂-CH₄ reforming. Fe₂O₃, Na₂CO₃, and K₂CO₃ in the ash can catalyze the CO₂-CH₄ reforming reaction; CaO has little effect on CO₂-CH₄ reforming reaction. CaO can catalyze the gasification between carbonaceous catalyst and CO₂; Al₂O₃ and MgO inhibit the CO₂-CH₄ reforming.     

Steam gasification of coal with salt mixture of potassium and nickel in a fluidized bed reactor

Australian coal loaded with a mixed catalyst of K₂SO₄+Ni(NO₃)₂ has been gasified with steam in a fluidized bed reactor of 0.1 m inside diameter at atmospheric pressure. The effects of gas velocity (2-5 U_g/U_mf), reaction temperature (750-900 °C), air/coal ratio (1.6-3.2), and steam/coal ratio (0.63-1.26) on gas compositions, gas yield and gas calorific value of the product gas and carbon conversion have been determined. The product gas quality and carbon conversion can be greatly improved by applying the catalyst; they can also be enhanced by increasing gas velocity and temperature. Up to 31% of the catalytic increment in gas calorific value could be obtained at higher temperatures. In the experimental runs with variation of steam/coal ratio, the catalytic increments were 16-38% in gas calorific value, 14-57% in carbon conversion, 5-46% in gas yield, and 7-44% in cold gas efficiency. With increasing fluidization gas velocity and reaction temperature, the unburned carbon fraction of cyclone fine for catalytic gasification decreased 4-18% and 13-16%, respectively, compared to that for non-catalytic gasification. Presented at the Int’l Symp. on Chem. Eng. (Cheju, Feb. 8–10, 2001), dedicated to Prof. H. S. Chun on the occasion of his retirement from Korea University.     

Catalytic steam gasification of Yallourn coal using sodium hydridotetracarbonyl ferrate

Catalytic steam gasification of Yallourn coal using sodium hydridotetracarbonyl ferrate was carried out in a semi-flow-type fixed-bed reactor at 873 and 973 K at atmospheric and high pressures. With Na[HFe(CO)₄] (Fe 1.67 wt%, Na 0.68 wt%), the steam gasification of the coal was more highly promoted than with Na₂CO₃ (Na 2.17%) and the coal was almost completely burnt out. The gasification rate decreased with increasing carbon burnoff with or without catalyst at 873 K, but increased in the presence of the catalyst at 973 K. Under pressurized steam (0.4 MPa), the catalyst exhibited higher activity. The char, obtained from Yallourn coal under argon at 823 K for 2 h, gasified under steam partial pressures of 0.4 and 0.8 MPa behaved the same as the original coal and no increase in gasification rate with steam pressure was observed. X-ray diffraction analysis showed that Na[HFe(CO)₄] was converted to Fe₃O₄ and Na₂CO₃ during the reaction.     

HYDROTHERMAL REACTION OF FLY ASH/HYDRATED LIME: CHARACTERIZATION OF THE REACTION PRODUCTS

Class F coal fly ash was slurried with hydrated lime at 90°C in 1/3, 5/3, 9/3, and 15/3 weight ratios and for 3, 5, 7, and 9 hours of hydration, in a process to prepare sorbents for SO₂ removal. The amounts of aluminum, silicon, and calcium in the product of the pozzolanic reaction were determined in order to study the evolution of product composition with the initial raw materials ratio and hydration time and to relate this composition to the desulfurization capability of the material. Al, Si, and Ca were present in the solid product for any raw materials ratio and hydration time, showing that calcium silicates, calcium aluminates, and/or calcium aluminum silicates were obtained simultaneously. The products formed show a nearly constant molar ratio of Al₂O₃/SiO₂ independent of the experimental conditions tested and similar to the Al₂O₃/SiO₂ ratio in the fly ash. The SiO₂/CaO molar ratio in the products decreased as the initial fly ash/Ca(OH)₂ ratio decreased, being approximately constant for each ratio with respect to hydration time after 5 hours of hydration. The maximum moles of CaO, SiO₂, and Al₂O₃ per gram of sorbent in the reaction product were found for any hydration time for the 5/3 sorbents, meaning that at this initial ratio the pozzolanic reaction takes place at the highest rate. The capacity of the sorbent for SO₂ removal depends not only on the amount of products produced by the pozzolanic reaction but also on the specific surface area of the sorbent.     

Retention of sulphur by laboratory-prepared ash from low-rank coal

A procedure similar to that of Knudsen and Holm⁷ was applied to 195 measurements of ash from high sulphur subbituminous and lignite coals from New Zealand. Sulphur reaction by coal ash was not catalysed by iron oxide and no effect of MgO, Na₂, K₂O or CaO was observed.     

Catalytic gasification of coal using eutectic salts: identification of eutectics

Different eutectic salt mixture catalysts for the gasification of Illinois No. 6 coal were identified and various impregnation or catalyst addition methods to improve catalyst dispersion were evaluated in this study. In addition, the effects of major process variables such as temperature, pressure, and steam/carbon ratio were investigated in a thermogravimetric analyzer (TGA) and fixed-bed bench scale reactor systems. The TGA studies showed that the eutectic catalysts increased CO₂ gasification rate significantly. The methods of catalyst preparation and addition had significant effect on the catalytic activity and coal gasification. Based on the TGA studies of several eutectic systems, the 43.5% Li₂CO₃-31.5% Na₂CO₃-25% K₂CO₃ and 39% Li₂CO₃-38.5% Na₂CO₃-22.5% Rb₂CO₃ ternary eutectics, the 29% Na₂CO₃-71% K₂CO₃ binary eutectic and the K₂CO₃ single salt catalysts were selected for the fixed-bed studies. The catalyst loading increased the gasification rate and almost complete conversion of carbon was observed when 10 wt.% of catalyst was added to the coal. Upon further increasing the catalyst amount to 20 wt.% and above, there was no significant rise in gasification rate.     

Sorption properties of lithium carbonate doped CaO and its performance in sorption enhanced methane reforming

In-house prepared lithium carbonate doped CaO was tested for its CO₂ sorption properties and suitability as a CO₂ sorbent for sorption-enhanced reforming of methane. The new material demonstrated CO₂ capacity at the temperatures above the equilibrium for CaO recarbonation reaction. However, the capacity was unstable and decreased during carbonation–regeneration cycles. After sufficiently large number of cycles Li dopant escaped from the sorbent and its sorption behavior resembled to that of CaO. The main route of escape is, probably, a crossover of liquid Li₂CO₃ onto crucible in TG experiments and onto catalyst in SER tests. Sorption enhanced methane reforming at 2 bar pressure, 750 °C and H₂O to CH₄ ratio of 4 using novel sorbent yielded as high as 99.8 vol% pure hydrogen during the first cycle. In subsequent cycles the hydrogen purity drastically decreased as a result of severe catalyst poisoning by Li.     

Influence of technological parameters on the epoxidation of 1‐butene‐3‐ol over titanium silicalite TS‐2 catalyst

BACKGROUND: The influence of technological parameters on the epoxidation of 1‐butene‐3‐ol (1B3O) over titanium silicalite TS‐2 catalyst has been investigated. Epoxidations were carried out using 30%(w/w) hydrogen peroxide at atmospheric pressure. The major product from the epoxidation of B3O was 1,2‐epoxybutane‐3‐ol, with many potential applications. RESULTS: The influence of temperature (20–60 °C), 1B3O/H₂O₂ molar ratio (1:1–5:1), methanol concentration (5–90%(w/w)), TS‐2 catalyst concentration (0.1–6.0%(w/w)) and reaction time (0.5–5.0 h) have been studied. CONCLUSION: The epoxidation process is most effective if conducted at a temperature of 20 °C, 1B3O/H₂O₂ molar ratio 1:1, methanol concentration (used as the solvent) 80%(w/w), catalyst concentration 5%(w/w) and reaction time 5 h. Copyright © 2009 Society of Chemical Industry     

Palladium on Carbon‐Catalyzed Cross‐Coupling using Triarylbismuths

Simple and efficient protocols for the 10% palladium on carbon (Pd/C)‐catalyzed cross‐coupling reactions between triarylbismuths and aryl halides have been developed. A variety of iodo‐ and bromobenzenes possessing an electron‐withdrawing group on the aromatic nucleus were smoothly cross‐coupled in the presence of 10% Pd/C, sodium phosphate dodecahydrate (Na₃PO₄⋅12 H₂O) and 1,4‐diazabicyclo[2.2.2]octane (DABCO) in heated N‐methyl‐2‐pyrrolidone (NMP) as the solvent. For the arylations of iodobenzenes, the reactions effectively proceeded under the combined use of caesium fluoride (CsF) and 2,2′‐biquinoline. Furthermore, a ligand‐free 10% Pd/C‐catalyzed cross‐coupling reaction between the aryl iodides and triarylbismuths was also established by the addition of tetra‐n‐buthylammonium fluoride trihydrate (TBAF⋅3 H₂O) in which the palladium metals were hardly leached from the catalyst into the reaction media.     

Effect of Chemical Compositions on Ash Fusibility Characterization of a Jincheng Anthracite during Combustion and Gasification

The ash melting temperature of coal ash has an important effect during the fluidized bed combustion and gasification process, which affects the slagging and deposition characteristics of the boiler. Experiments on the effects of chemical components on the ash fusion behaviors have been completed on the ash fusion temperatures (AFTs) analyzer under typical gasification and combustion atmospheres. Meanwhile, calculations on the variation of minerals in ash with ash composition were conducted using the FactSage software. The results indicated that the AFTs under gasification were a little higher than those under the combustion atmosphere. On increasing the Fe₂O₃, CaO, and Na₂O contents under the combustion and gasification atmospheres, the four temperatures deformation temperature (DT), softening temperature (ST), hemispherical temperature (HT), and flow temperature (FT) decreased dramatically and the generation and transformation of minerals occurred. The iron-containing minerals, such as hercynite and fayalite, formed with increase in the content of Fe₂O₃; the Ca-bearing feldspar minerals, like gehlenite and anorthite, started appearing on increasing the CaO content, and the Na-containing feldspar minerals, like carnegieite, were detected as the Na₂O was increased. These three minerals can form low-temperature eutectics, decreasing the fusion temperature.     

Natural Calcium‐Based Residues for Carbon Dioxide Capture in a Bubbling Fluidized‐Bed Reactor

Used clamshells (Paphia undulata), as a precursor of calcium oxide (CaO) sorbents, were employed for carbon dioxide (CO₂) adsorption in a bubbling fluidized‐bed reactor. To find the optimal calcination conditions, a 2^k experimental design was used to vary the ground clamshell particle size, heating rate, and calcination time at 950 °C under a nitrogen atmosphere. The heating rate was the most significant factor affecting the CO₂ adsorption capacity of the obtained CaO sorbent. The maximum CO₂ adsorption capacity of the CaO obtained under these study conditions was higher than that of commercial CaO.     

气化参数对气流床粉煤气化影响实验研究

为评价和优化中国高、低灰熔点煤气化运行参数对气流床气化特性的影响,在1600℃的一维常压沉降式气流床气化实验系统上,着重研究了中国典型高、低灰熔点煤在1200～1600℃温度范围内、O／C摩尔比在0．9～1.2范围内的干煤粉气化特性。结果表明：随着温度的升高,产气中CO、H2含量逐渐增多,CO2、CH4含量逐渐减少,碳转化率有很大提高;随着O／C的增加,CO、H2含量不断减少,CO2逐渐增加;煤的灰熔融性也是影响煤气组分一个重要因素,当气化反应温度接近煤灰熔点温度时,煤气组分（CO＋H2＋CH4）达到一个最大值。     

Steam gasification of coal char using alkali and alkaline-earth metal catalysts

The catalytic effect of alkali and alkaline-earth metal salts or oxides on the gasification of Chinese Linnancang coal char was investigated at atmospheric pressure and a temperature of 800 °C. The order of catalytic activity is K₂SO₄ or K₂CO₃ Na₂CO₃ KCl NaCl CaCl₂ or CaO. The effect of amount of catalysts added on catalytic activity was studied. The distribution of K₂CO₃ or CaO catalysts on the coal char surface for different methods of catalyst loading was examined by an electron microprobe analyser. The relation between the catalytic activity and distribution of catalysts were illustrated. The loading method of K₂CO₃ has little effect on its catalytic activity but that of CaO influences the activity significantly.     

Correlation between potassium losses and mineral matter composition in catalytic coal steam gasification

The utilization of potassium as catalyst in coal steam gasification suffers due to difficulty in its quantitative recovery from gasification residues. This is due to the formation of non-leachable compounds with the mineral matter of coal. The reactivity of K₂CO₃ with some mineral constituents of coal has been evaluated at 973 K; after reaction, residues were analysed by XRD and leached with water to test the potassium solubility. Subsequently, through investigation of the interaction of potassium with 8 carbonaceous matrices from four differen ccoals, an attempt was made to establish a correlation between ash characteristics and quantity of non-recoverable potassium. It was also possible to identify some compounds formed by reaction between potassium and mineral matter.