Gas evolution during oil shale pyrolysis. 2. Kinetic and stoichiometric analysis

Nonisothermal rate measurements for the evolution of H₂, CH₄, C₂ hydrocarbons and C₃ hydrocarbons during the pyrolysis of Colorado oil shale have been analysed using the recent kinetic theory of Antony and Howard AIChE J. 1976, 22, 625. This analysis yields a simple set of rate expressions, which can be used for modelling kerogen pyrolysis under typical retort heating conditions. A stoichiometric representation of kerogen pyrolysis is also developed. These results are then used to derive a simple mechanistic picture of oil shale pyrolysis between 25 and 900 °C.     

Gas evolution kinetics of two coal samples during rapid pyrolysis

Quantitative gas evolution kinetics of coal primary pyrolysis at high heating rates is critical for developing predictive coal pyrolysis models. This study aims to investigate the gaseous species evolution kinetics of a low rank coal and a subbituminous coal during pyrolysis at a heating rate of 1000 °C s^− 1 and pressures up to 50 bar using a wire mesh reactor. The main gaseous species, including H₂, CO, CO₂, and light hydrocarbons CH₄, C₂H₂, C₂H₄, C₂H₆, C₃H₆, C₃H₈, were quantified using high sensitivity gas chromatography. It was found that the yields of gaseous species increased with increasing pyrolysis temperature up to 1100 °C. The low rank coal generated more CO and CO₂ than the subbituminous coal under similar pyrolysis conditions. Pyrolysis of the low rank coal at 50 bar produced more gas than at atmospheric pressure, especially CO₂, indicating that the tar precursor had undergone thermal cracking during pyrolysis at the elevated pressure.     

Study on pyrolysis of oil sludge with microalgae residue additive

The pyrolysis of oil sludge (OS) with microalgae residue (MR) additive was conducted with a TGA and a tube furnace. The pyrolysis process of OS with the MR additive can be divided into three stages: 1) water evaporation, 2) the release of light groups of hydrocarbon compounds, the cracking of heavy groups, and carbon decomposition, and 3) minerals decomposition. With the MR addition ratio increasing, the yield of oil and gas increased, and oil to gas ratio increased during OS pyrolysis. The MR addition improved the quality of pyrolysis oil and gas from OS pyrolysis. The proportion of light oil increased from 38 % with a 5 % MR addition ratio to 45 % with a 30 % addition ratio. Major components of pyrolysis gas included H₂, CO, CO₂, and C_xH_y. With the increase of the MR blending ratio, CO and CO₂ contents increased, while H₂ and C_xH_y contents decreased. Adding MR favoured the transformation of heavy hydrocarbons (C₆₊), resulting in a high content of light hydrocarbons. This work can help promote massive synergistic treatment of OS and microalgae biomass.

     

Prediction of gaseous products from biomass pyrolysis through combined kinetic and thermodynamic simulations

Due to the nonhomogeneous characteristics of biomass constituent, it has been known to be difficult to apply directly any simulation work to the pyrolysis of biomass for a precise prediction of gaseous products. In this study, two computation codes (HSC Chemistry for thermodynamic and Sandia PSR for kinetic simulations) were employed, to consider the integrated effects of thermodynamic and kinetic phenomena occurring in biomass pyrolysis on the distribution of gaseous products. The principle of simulation applied in this study was to extract substitutable gas phase compositions from HSC calculations, which were predicted thermodynamically. Then, the gas phase compositions were inputted into the Sandia PSR code to consider the potential constrains of kinetics involving in the pyrolysis and finally to get the distributions of gas products which should be closer to the realistic situation. Palm oil wastes, a local representative biomass, were studied as sample biomass. The gaseous products obtained from HSC calculations were mainly H₂, CO₂, CO, CH₄ and negligible C₂₊ hydrocarbons. After applying these products into PSR program, the final products developed into H₂, CO₂, CO, CH₄, C₂H₂, C₂H₄, C₂H₆ and C₃H₈ which are more realistic products in the modern fast pyrolysis.     

Ultrapyrolysis of automobile shredder residue

A fast pyrolysis (Ultrapyrolysis) process was employed to convert automobile shredder residue (ASR) into chemical products. Experiments were conducted at atmospheric pressure and temperatures between 700 and 850°C with residence times between 0.3 and 1.4 seconds. Pyrolysis products included 59 to 68 mass% solid residue, 13 to 23 mass% pyrolysis gas (dry) and 4 to 12 mass% pyrolytic water from a feed containing 39 mass% organic matter and 2 mass% moisture. No measurable amounts of liquid pyrolysis oil were produced. The five most abundant pyrolysis gases, in vol%, were CO (18–29), CO₂ (20–23), CH₄ (17–22), C₂H₄ (20–22) and C₃H₆ (1–11), accounting for more than 90% of the total volume. The use of a higher organic content ASR feed (58 mass%) resulted in less solid residue and more pyrolysis gas. However, no significant changes were noted in the composition of the pyrolysis gas.     

Pyrolysis of coal and iron oxides mixtures. 2. Reduction of iron oxides

The reduction of iron oxides during the pyrolysis of blends of coal and iron oxides on a laboratory scale, has been studied. The pyrolysis of blends of bituminous coal and 30 wt% of magnetite or hematite has been studied by thermogravimetry and analysis of gases, using a heating rate of 3.2 K min^?1. The state of iron in ferrocoke has been established by X-ray diffraction. A primary reduction by hydrogen and carbon monoxide of the hematite has been observed at between 400 °C and 500 °C, but hidden in thermogravimetric measurements by primary volatilization of the coal. At ≈600 °C magnetite is progressively reduced to wustite and then to iron. This reduction starts a little earlier if the heating rate is slow and the coal rank is low and progresses more rapidly when using hematite. Except for higher heating rates in the coal-magnetite blends, the reduction is complete at 1000 °C. The reductants are H₂ and CO, with production of H₂O and CO₂. When the temperature is increased the reduction by CO becomes of increasing importance, being mainly produced from the coke by the Boudouard reaction. The consumption of coke for the reduction of iron oxides is therefore more important at higher temperatures. Lignite is clearly a better reducing agent than the other coals, because of larger quantities of CO produced from the start of its pyrolysis, and the good reactivity of its char towards CO₂ and H₂O.     

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.     

Pyrolysis of used sunflower oil in the presence of sodium carbonate by using fractionating pyrolysis reactor

Pyrolysis of used sunflower oil was carried out in a reactor equipped with a fractionating packed column (in three different lengths of 180, 360 and 540 mm) at 400 and 420°C in the presence of sodium carbonate (1, 5, 10 and 20% based on oil weight) as a catalyst. The use of packed column increased the residence times of the primer pyrolysis products in the reactor and packed column by the fractionating of the products which caused the additional catalytic and thermal reactions in the reaction system and increased the content of liquid hydrocarbons in gasoline boiling range. The conversion of oil was high (42–83 wt.%) and the product distribution was depended strongly on the reaction temperature, packed column length and catalyst content. The pyrolysis products consisted of gas and liquid hydrocarbons, carboxylic acids, CO, CO₂, H₂ and water. Increase in the column length increased the amount of gas and coke–residual oil and decreased the amount of liquid hydrocarbon and acid phase. Also, increase of sodium carbonate content and the temperature increased the formation of liquid hydrocarbon and gas products and decreased the formation of aqueous phase, acid phase and coke–residual oil. The major hydrocarbons of the liquid hydrocarbon phase were C₅–C₁₁ hydrocarbons. The highest C₅–C₁₁ yields (36.4%) was obtained by using 10% Na₂CO₃ and a packed column of 180 mm at 420°C. The gas products included mostly C₁–C₃ hydrocarbons.     

煤快速热解固相和气相产物生成规律

利用能有效避免二次转化反应的高频炉热解装置对3种不同变质程度的煤进行了600～1200℃条件下的快速热解,考察了在煤热解最初阶段焦产率、焦-C产率、热解气产率、热解气4种主要组分H₂、CO、CH₄和CO₂的比例以及热解气热值随煤阶和热解温度的变化规律。结果表明,焦的产率和焦-C的产率均随煤阶的升高而升高,热解气的产率随煤阶的升高而降低;热解温度的提高能显著降低煤焦和焦-C的产率并提高热解气的产率。热解气组分以H₂相似文献   

Pyrolysis kinetics for Green River oil shale from the saline zone

The nature of the organic and mineral reactions during the pyrolysis of Saline-zone Colorado oil shale containing large amounts of nahcolite and dawsonite has been determined. Results reported include a material-balanced Fischer assay and measurements of gas evolution rate of CH₄, C₂H_x, H₂, CO and CO₂, Stoichiometry and kinetics of the organic pyrolysis reactions are similar to oil shale from the Mahogany zone. X-ray diffraction and thermogravimetric analysis results are used to help determine the characteristics of the mineral reactions. Kinetic expressions are reported for dawsonite decomposition, and it is demonstrated that the temperature of dolomite decomposition is substantially lower than for Mahogany-zone shale because of the presence of the sodium minerals.     

Calculation of the solubilities of gases in paraffin hydrocarbons

A semiempirical equation is proposed to calculate the solubilities of gas systems containing H₂, CO, CO₂, N₂, Ar, CH₄, C₂H₆, and C₃H₈ in normal paraffin hydrocarbons from C₅ to C₂₀ and higher over wide temperature and pressure ranges. The applicability of the equation proposed is evaluated.     

Porous MoxCy/SiO2 Material for CO2 Hydrogenation

The synthesis and characterization of an inexpensive porous Mo_xC_y/SiO₂ material is presented, which was obtained by mixing ammonium hexamolybdate, sucrose, and a mesoporous silica (SBA-15), with a subsequent heat treatment under inert atmosphere. This porous material presented a specific surface area of 170 m²/g. The catalytic behavior in CO₂ hydrogenation was compared with that of Mo₂C and α-MoC_1?x obtained from ammonium hexamolybdate and sucrose, using different Mo/C ratios. CO₂ hydrogenation tests were performed at moderate (100 kPa) and high pressures (2.0 MPa), and it was found that only CO, H₂O and CH₄ are formed at moderate pressures by the three materials, while at higher pressures, methanol and hydrocarbons (C₂H₆, C₃H₈) are also obtained. Differences in selectivity were observed at the high pressure tests. Mo₂C presented higher selectivity to CO and methanol compared with MoC_1?x, which showed preferential selectivity to hydrocarbons (CH₄, C₂H₆). The porous Mo_xC_y/SiO₂ material showed the highest CO₂ hydrogenation activity at high temperatures (270 and 300 °C), being a promising material for the conversion of CO₂ to CO and CH₄.

     

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.     

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.     

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.     

Biomass pyrolysis experiments in an analytical entrained flow reactor between 1073 K and 1273 K

Experiments are performed in an entrained flow reactor to better understand the kinetic processes involved in biomass pyrolysis under high temperatures (1073-1273 K) and fast heating condition (>500 K s⁻¹). The influence of the particle size (0.4 and 1.1 mm), of the temperature (1073-1273 K), of the presence of steam in the gas atmosphere (0 and 20 vol%) and of the residence time (between 0.7 and 3.5 s for gas) on conversion and selectivity is studied. Under these conditions, the particle size is the most crucial parameter that influences decomposition. For 1.1 mm particles, pyrolysis requires more than 0.5 s and heat transfer processes are limiting. For 0.4 mm particles, pyrolysis seems to be finished before 0.5 s. More than 70 wt% of gas is produced. Forty percent of the initial carbon is found in CO; less than 5% is found in CO₂. The hydrogen content is almost equally distributed among H₂, H₂O and light hydrocarbons (CH₄, C₂H₂, C₂H₄). Under these conditions, the evolution of the produced gas mixture is not very significant during the first few seconds, even if there seems to be some reactions between H₂, the C₂ and tars.     

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.     

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     

Coupling and reforming of methane by means of low pressure radio-frequency plasmas

Non-oxidative coupling of CH₄/H₂ mixtures was carried out by means of radio frequency (rf) glow discharges for the first time. A central composite design was employed to determine the best experimental conditions for methane transformation into higher hydrocarbons and to fit the experimental data. rf power was the factor showing the highest effect on the results while CH₄/H₂ mole ratio showed the lowest. Conversion was 46.4% at 100 W, 0.07 mbar and CH₄/H₂ mole ratio of 1/2. Selectivity was 56.9% for C₂, 6.9% for C₃, and 36.2% for C₄ hydrocarbons. Least squares fits of quadratic equations yielded approximating functions permitting to predict results of random experiments with errors of about 5%. The same rf system was used for the reforming of methane with CO₂, O₂, and steam plasmas, respectively. The highest oxidation was observed with oxygen whilst steam plasma produced the best results. H₂/CO mole ratio was adjusted by setting specific experimental parameters of the latter. CO₂ free synthesis gas was produced at higher H₂O and CH₄ flow rates, i.e. 0.8 mmol/h and higher power, i.e. 100 W. CO₂ and CO free H₂ was produced at 0.3 and 0.6 mmol/h flow rates of H₂O and CH₄, respectively, and 50 W.     

Catalytic Synthesis of Methanethiol from H2S-rich Syngas Over Sulfided SiO2-supported Mo-based Catalysts

The synthesis of methanethiol from H₂S-rich syngas was investigated over sulfided Mo-based catalysts supported on SiO₂. At CO/H₂/H₂S = 1/1/2, 0.2 MPa, 3,000 h⁻¹, and 300 °C, mainly CH₃SH, COS, and CO₂ were formed, along with small amounts of hydrocarbons and thioethers over potassium-promoted Mo-based catalysts. Studies of the reaction pathway show that COS is a primary product, which is hydrogenated to CH₃SH and H₂O. Most of CO₂ originates from water-gas shift reaction. The hydrocarbons and thioethers originate from the hydrogenation of CH₃SH.