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.     

Brown coal conversion under the action of supercritical water

A test bench was developed and the conversion of the organic matter of coal (OMC) in supercritical water (SCW) was studied under conditions of a continuous supply of a water-coal suspension to a vertical flow reactor at 390–760°C and a pressure of 30 MPa. From 44 to 63% OMC was released as liquid and gaseous products from coal particles (from the water-coal supension) during the time of fall to the reactor. This stage was referred to as the dynamic conversion of coal. The particles passed through the stage of the dynamic conversion of coal did not agglomerate in the reactor in the subsequent process of batch conversion in a coal layer at T = 550–760°C. The volatile products of the overall process of the dynamic and batch conversion of coal included saturated hydrocarbons (CH₄ and C₂H₆), aromatic hydrocarbons (C₆H₆, C₇H₈, and C₈H₁₀), synthesis gas (H₂ and CO), and CO₂. At T < 600°C, CO₂ and CO were the degradation products of oxygen-containing OMC fragments, whereas they also resulted from the decomposition of water molecules at higher temperatures in accordance with the reaction (C) + H₂O = CO + H₂. The mechanisms were considered, and the parameters responsible for the dynamic conversion of coal were calculated.     

Hydropyrolysis of a high-sulphur,high-calcite Italian Sulcis coal: 3. Pyrite behaviour

The chars obtained from hydtopytolysis of Sulcis coal were examined by scanning electron microscopy coupled with an energy dispersion analyser. Under 3 MPa of He at 540 °C, pyrite is transformed into FeS_1.5. Under H₂ pressure, pyrite reduction depends on the temperature. At 780 °C, pyrite is completely reduced to iron. The complete reduction is made possible because the H₂S formed reacts with the caleite of this coal and thus does not limit the reducing reaction.     

Hydropyrolysis of a high-sulphur-high-calcite Italian Sulcis coal. 2. Importance of the mineral matter on the sulphur behaviour

The sulphur distribution among the char, oil and gas obtained after hydropyrolysis of a high-sulphur (4.3 wt%) and high-calcite (7.3 wt%) coal has been investigated. The chars were examined by scanning electron microscopy coupled with an energy dispersion analyser and by X-ray diffraction. The proportion of the combustible and non-combustible sulphur in the char has been determined. Hydrogen pressure promotes reaction with sulphur but the sulphur content of the chars increases from 3 to 4.5 wt% when the temperature is increased from 616 to 845 °C. This increase in sulphur is a consequence of the reaction between hydrogen sulphide, produced during hydropyrolysis of coal, with the alkaline-earth mineral matter to produce alkaline-earth sulphide. The SEM and X-ray diffraction images show that in the char formed at 780 °C the sulphur, calcium and magnesium are localized in the same compounds. This is not the case when hydropyrolysis is performed at lower temperature. Combustion of the chars produces only <0.6 S0₂ MJ^?1 compared to 2.2 g S0₂ MJ^?1 for untreated coal. X-ray diffraction has shown that the sulphur in the char is oxidized and fixed in the ashes mainly as CaS0₄ and also some as MgS0₄. Although sulphur remains partly in the chars after hydropyrolysis, 75% of it is non-combustible. The hydropyrolysis of a high-sulphur coal containing calcite, produces a char which may be used as a clean fuel.     

An active iron catalyst containing sulfur for Fischer-Tropsch synthesis

A precipitated iron catalyst containing sulfur for Fischer-Tropsch (F-T) synthesis was prepared by means of a novel method using a ferrous sulfate as precursor. Both fixed bed reactor (FBR) and continues stirred tank slurry reactor (STSR) were used to test long-term F-T reaction behaviors over the catalyst. A stability test (1600 h) in FBR showed that the catalyst was active even after 1500 h of time-on-stream with CO conversion of 78% and with C₅⁺ hydrocarbon selectivity of 72 wt% at 250 °C, 2.0 MPa, 2.0 NL/g-cat/h, and H₂/CO=2.0. The test (550 h) in STSR indicated that the catalyst exhibited relatively high activity with CO conversion of 70-76% and C₅⁺ selectivity of 83-86 wt% in hydrocarbon products under the conditions of 260 °C, 2.0 MPa, 2.0 NL/g-cat/h, and H₂/CO=0.67. The deactivation rate of the catalyst was low, accompanied by surprisingly low methane selectivity of 2.0-2.9 wt%. It is shown that a small amount of sulfur (existing as SO₄²⁻) may promote the catalyst by increasing activity and improving the heavier hydrocarbon selectivity. It is also comparable with other typical iron catalysts for F-T synthesis.     

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.     

Conversion of syngas to hydrocarbons in a tube-wall reactor using CoFe plasma-sprayed catalyst: experimental and modeling studies

Catalyst activity and product selectivity studies of the conversion of synthesis gas to various hydrocarbon fractions were performed in a single-tube tube-wall reactor (TWR) using a CoFe plasma-sprayed catalyst with the operating conditions: temperature 250–275°C, pressure 0.1–1.03 MPa, exposure velocity 139–722 μms⁻¹, and a H₂:CO ratio of 2.0. The catalyst activity in terms of CO conversion was highest (98.5% m/m) at an exposure velocity of 139 μms⁻¹, temperature of 275°C, and in the pressure range 0.69–1.03 MPa. The selectivity to hydrocarbons was 43–50% (m/m) in the pressure range 0.69–1.03 MPa whereas the selectivity to C₅ + hydrocarbons was over 40% of the total hydrocarbons produced. The production of propylene was higher than ethylene under similar process conditions. The performance of the TWR was predicted by a numerical model. The model is based on the complete two-dimensional transport equations and reaction rate equations, developed for the CoFe catalyst. Predictions are made for the temperature along the axis of the reactor, for CO and H₂ conversions as functions of the reactor length and the exposure velocity, and the axial H₂O and CO₂ concentrations.     

Decomposition of ammonia with iron and calcium catalysts supported on coal chars

Decomposition of NH₃ to N₂ with Fe and Ca catalysts supported on brown coal chars has been studied with a cylindrical quartz reactor from a viewpoint of hot gas cleanup. The catalyst is prepared by pyrolyzing a brown coal with Fe or Ca ions added. In the decomposition of 2000 ppm NH₃ diluted with He at 750 °C and at a space velocity of 45,000 l/h, 2-6 wt% Fe catalysts are more active than not only 6 wt% Ca catalyst but also 8 wt% Fe catalyst loaded on a commercial activated carbon. The transmission electron microscope observations show that fine iron particles with the sizes of 20-50 nm account for the higher catalytic performances. When reaction temperature is increased to 850 °C, all of Fe and Ca catalysts on the chars achieve complete decomposition of NH₃. The co-feeding of H₂ with 2000 ppm NH₃ improves the performance of the 2% Fe catalyst at 750 °C, but contrarily the coexistence of syngas (CO/H₂=2) deactivates it remarkably, whereas the addition of CO₂ to syngas restores the catalytic activity of the Fe to the original state without syngas. The powder X-ray diffraction and temperature programmed desorption measurements strongly suggest that the Fe and Ca catalysts promote NH₃ decomposition through cycle mechanisms involving the formation of N-containing intermediate species and the subsequent decomposition to N₂.     

Hydrogen production from coal by separating carbon dioxide during gasification

Hydrogen generation during the reaction of a coal/CaO mixture with high pressure steam was investigated using a flow-type reactor. Coal, CaO and CO reactions with steam, and CO₂ absorption by Ca(OH)₂ or CaO occurred simultaneously in the experiment. It was found that H₂ was the primary resultant gas, comprising about 85% of the reaction products. CO₂ was fixed into CaCO₃ and CO was completely converted to H₂. Pyrolysis of the coal/CaO mixture carried out in N₂ was also examined. The pyrolysis gases were compared with gases produced by general coal pyrolysis. While general coal pyrolysis produced about 14.7% H₂, 50.5% CH₄, 12.0% CO and 12.0% CO₂, the gases produced from coal/CaO mixture pyrolysis were 84.8% H₂, 9.6% CH₄, 1.6% CO₂ and 1.1% CO.     

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.     

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.     

Hydropyrolysis of Alberta coal and petroleum residue using calcium oxide catalyst and toluene additive

Hydropyrolysis of a mixture of Alberta coal and Athabasca bitumen was carried out in a batch reactor using calcium oxide as an alternate catalyst and the results were compared with those of widely used iron oxide and well-known NiMo/Al₂O₃ catalysts. Most of the reactions were done at temperatures of 500–540°C, residence time of 1 min and hydrogen pressure of 3.4 MPa. Maximum distillable oil (below 523°C) yield of 55 wt% and pitch conversion of 62 wt% were obtained in the presence of CaO or Fe₂O₃ and these values were higher than those without catalyst, although NiMo/Al₂O₃ catalyst gave much higher oil yield and pitch conversion. Catalyst concentration (above 2 wt%) has no consequence upon the distribution of various product fractions.

In another study, addition of 15% toluene to the feed in the absence of catalyst led to higher distillable oil yield (68 wt%) and pitch conversion (72 wt%) in the hydroconversion of coal and bitumen mixture. Increase in toluene concentration from 15 to 50 wt% had no positive effect on the product yields.     

Effect of early stages of coal oxidation on its reaction with elemental sulphur

The present research shows how mild oxidation of coal mostly affects the evolution of H₂S produced in the reaction of coal with elemental sulphur. Coal samples oxidized at 30, 50, 80 and 150°C were reacted with sulphur in a temperature-programmed reactor. The H₂S produced in the reaction is very sensitive to the initial stage of the oxidation of coal. The strongest reduction in the amount of H₂S evolved was observed in the samples oxidized at 30°C. This temperature is lower than the one found in most coal storage places. The reaction with elemental sulphur could be used to monitor the initial stages of coal oxidation, which otherwise would be difficult to follow by conventional analytical methods.     

Relation of the chemical structure of coal to its hydropyrolysis

The hydropyrolysis of Illinois No. 6 coal has been studied in a batch reactor, in which the reactions were initiated by explosion of $\text{H}{}_2\text{O}{}_2$ mixtures. The ratio of H₂ to O₂ was kept at 8, while the total pressure of the gas mixture was changed to vary the reaction temperature. The heating rate was ≈ 50 000 °C s^?1, and the reaction time was < 50 ms. The conversion of the feed coal increased from 19% at 620 °C to 81%at ? 1500 °C. At conversions < 50%, the gaseous product consisted of mainly CH₄ and CO in almost equal proportions, and at conversions ? 60% the concentration of CO increased. Comparison with results from a large flow reactor revealed that comparable conversions were obtained in the present batch reactor, although product distributions were markedly different from each other. The dissimilar product distribution is attributed to different reacting media: preburning of H₂ and O₂ in the flow reactor versus in situ burning of the mixture in the batch reactor. The H/C ratios of solid residues after the hydropyrolysis decreased linearly as the conversion increased, revealing that the portions of coal having high H/C ratios were preferentially gasified. This observation was substantiated by a high H/C ratio, 1.74 of the first portion of coal gasified, and by a sharp decrease in H/C ratio in subsequent gasified portions. These data indicated that aliphatic side chains (or linkages) and single-ring aromatic clusters in the feed coal were gasified first, followed by larger aromatic clusters. Semi-quantitative determination of the distribution of different aromatic clusters showed good agreement with current structural information on coal. Thus, the effects of reaction variables were explained in terms of the structural features of coal, and the ratelimiting steps in the hydropyrolysis process were identified.     

Thermodynamic analysis of the gasification of coal from the Daurskoe deposit

The equilibrium composition of the products of the fluidized-bed pressure gasification of brown coal from the Daurskoe deposit in Transbaikalia krai for the production of process gas (in particular, synthesis gas) was calculated with the use of a method of chemical thermodynamics. The gasification was performed at P = 0.1 MPa and the blast coefficient α₁ = 0.3–0.35 in the presence of 36 wt % of water vapor in a temperature range of 100–1500°C. It was found that, at a Cl₀ pressure of 0.1 MPa, a temperature of 850°C, and the air-steam blast composition of α₁ = 0.3 and α₀ + 36 wt % H₂O, the gasification products of the organic matter of coal (OMC) mainly consisted of CO and H₂.     

Thermal and catalytic upgrading of a biomass‐derived oil in a dual reaction system

The thermal and catalytic upgrsding of bio‐oil to liquid fuels was studied at atmospheric pressure in a dual reactor system over HZSM‐5, silica‐alumina and a mixed catalyst containing HZSM‐5 and silica‐alumina. This bio‐oil was produced by the rapid thermal processing of the maple wood. In this work, the intent was to improve the catalyst life. Therefore, the first reactor containing no catalyst facilitated thermal cracking of blo‐oil whereas the second reactor containing the desired catalyst upgraded the thermally cracked products. The effects of process variables such as reaction temperature (350°C to 410°C), space velocity (1.8 to 7.2 h^?1) and catalyst type on the amounts and quality of organic liquid product (OLP) were investigated, In the case of HZSM‐5 catalyst, the yield of OLP was maximum at 27.2 wt% whereas the selectivity for aromatic hydrocarbons was maximum at 83 wt%. The selectivities towards aromatics and aliphatic hydrocarbons were highest for mixed and silica‐alumina catalysts, respectively. In all catalyst cases, maximum OLP was produced at an optimum reaction temperature of 370°C in both reactors, and at higher space velocity. The gaseous product consisted of CO and CO₂, and C₁‐C₆ hydrocarbons, which amounted to about 20 to 30 wt% of bio‐oil. The catalysts were deactivated due to coking and were regenerated to achieve their original activity.     

Catalytic liquefaction of various coals using a mixture of carbon monoxide and water

In a batch-autoclave, twenty coals were liquefied using a cobalt-molybdenum oxide catalyst with a mixture of CO and H₂0 at 400 °C with or without vehicle oil. Furthermore, lignite and peat were liquefied on tungsten oxide catalyst at 300 °C in the absence of CO. The reactivity of coal in this liquefaction is found to depend strongly on its rank. The vehicle oil significantly influences the extent of the water-gas shift reaction, especially when bituminous coals are liquefied, by dissolving such coals. Liquefaction of coal by this process is considered to take place via three routes: hydrogenolysis by the nascent hydrogen produced from the shift reaction; dissolution of coal into the vehicle oil which is an initial stage of hydrogenolysis; and a solvolytic reaction with H₂O, such as hydrolysis.     

Comparative investigations of coal pyrolysis under inert gas and H2 at low and high heating rates and pressures up to 10 MPa

Five German hard coals of 6–36 wt% volatile matter yield (maf) were pyrolysed at pressures up to 10 MPa, using two different apparatuses, which mainly differ in the heating rates. One consists of a thermobalance where a coal sample of ≈ 1.5 g is heated at a rate of 3 K min ^?1 under a gas flow of 3 I min^?1. The other apparatus is constructed for rapid heating (10²?10³ K s^?1) of a small sample of ≈10 mg of finely-ground coal distributed as a layer between the folded halfs of a stainless-steel screen, heated by an electric current. The product gas composition was determined by quantitatively analysing for H₂, CH₄, C₂H₄, C₂H₆, CO, CO₂ and H₂O. The amounts of tar and char were measured by weighing. The heating rate, pressure and gas atmosphere were varied. Under an inert gas atmosphere, high heating rates result in slightly higher yields of liquid products, e.g. tar. The yields of light hydrocarbon gases remain the same. With increasing pressure, the thermal cracking of tar is intensified resulting in high yields of char and light hydrocarbon gases. Under H₂, pyrolysis is influenced strongly at elevated pressure. Additional amounts of highly aromatic products are released by hydrogenation of the coal itself, particularly between 500 and 700°C. This reaction is less effective at higher heating rates because of the shorter residence time and diffusion problems of H₂. The yield of light gaseous compounds CH₄ and C₂H₆ increases markedly under either heating condition owing to gasification of the reactive char.     

Investigation of Fischer-Tropsch synthesis performance and its intrinsic reaction behavior in a bench scale slurry bubble column reactor

A bench scale slurry bubble column reactor (SBCR) with active-Fe based catalyst was developed for the Fischer-Tropsch synthesis (FTS) reaction. Considering the highly exothermic reaction heat generated in the bench scale SBCR, an effective cooling system was devised consisting of a U-type dip tube submerged in the reactor. Also, the physical and chemical properties of the catalyst were controlled so as to achieve high activity for the CO conversion and liquid oil (C₅₊) production. Firstly, the FTS performance of the FeCuK/SiO₂ catalyst in the SBCR under reaction conditions of 265 °C, 2.5 MPa, and H₂/CO = 1 was investigated. The CO conversion and liquid oil (C₅₊) productivity in the reaction were 88.6% and 0.226 g/g_cat-h, respectively, corresponding to a liquid oil (C₅₊) production rate of 0.03 bbl/day. To investigate the FTS reaction behavior in the bench scale SBCR, the effects of the space velocity and superficial velocity of the synthesis gas and reaction temperature were also studied. The liquid oil production rate increased up to 0.057 bbl/day with increasing space velocity from 2.61 to 3.92 SL/h-g_Fe and it was confirmed that the SBCR bench system developed in this research precisely simulated the FTS reaction behavior reported in the small scale slurry reactor.     

Catalytic decomposition of ammonia gas with metal cations present naturally in low rank coals

A novel hot gas cleanup method to decompose a low concentration of NH₃ to N₂ with metal cations present inherently in low rank coals has been studied with a quartz reactor under the conditions of 750–850 °C, 0.1 MPa and high space velocity of 45,000 h⁻¹. Each coal is pyrolyzed at 900 °C to prepare the char, which is subjected to the decomposition of 2000 ppm NH₃ after pretreatment with H₂. All of five chars examined promote NH₃ decomposition in inert gas, but the promotion effect depends strongly on the kind of char and can correlate more closely with the Fe content than with the Ca content. This result may indicate that the Fe plays a crucial role in the reaction. A commercial activated carbon with a very low Fe content of <0.05 wt% exhibits lower conversion of NH₃ to N₂ than five chars. The TEM pictures reveal the formation of nanoscale particles of Fe and Ca components on a brown coal char that provides the largest catalytic performance. The char maintains the high conversion level of 80% during 25 h reaction at 750 °C and achieves the complete decomposition of NH₃ at 850 °C. The co-feeding of a mixture of H₂, CO, and CO₂ does not change significantly the catalytic activity of the char at a steady state, whereas the coexistence of 2000 ppm H₂S lowers it in the whole range of time on stream. It is proposed by combining the XRD and TPD observations with our previous results that the catalytic decomposition of NH₃ in inert gas with the chars derived from low rank coals proceeds through two cycle mechanisms involving iron metal, iron nitrides, CaO and CaCN₂.