Non-catalytic Thermal Decomposition Research Articles

Experiment and simulation of non-catalytic thermal decomposition of CH4 for CO2-free hydrogen production in a vertical tube

To address climate change issues, there has been growing interest in low-carbon H2 production technologies with the potential for zero-CO2 emissions. Non-oxidative CH4 pyrolysis is a promising method for producing H2 and solid carbon without generating CO2 emissions. This study presents experimental and numerical studies on non-catalytic CH4 pyrolysis using a vertical tube reactor (28 mm in diameter and 1800 mm in height). A three-dimensional (3D) Eulerian computational fluid dynamics (CFD) model coupled with chemical reaction and heat transfer was developed and validated against the experimentally determined axial temperature profiles and methane conversion (XCH4). The hydrodynamics, reaction kinetics, and heat transfer characteristics were investigated using the validated CFD model. The highest XCH4 of 99% was achieved at 1200 °C with a gas flow rate of 0.5 LPM. Heat transfer combined with natural and forced convection was confirmed by the CFD simulation of the tubular reactor. The heat transfer coefficient in the reaction zone ranged from 43 to 46 W/m2/°C. The CFD simulation served as a viable tool for examining the influence of the hydrodynamics, heat transfer, and reaction kinetics on the performance of the reactor with a given geometry and under specified operating conditions in non-catalytic CH4 pyrolysis.

Non-catalytic thermal decomposition of naphthenic acids of petroleum crudes

Non-catalytic thermal decomposition of naphthenic acids of petroleum crudes

Impact of Carbon Dioxide on the Non-Catalytic Thermal Decomposition of Methane

Economically and ecologically, the thermal decomposition of methane is a promising process for large scale hydrogen production. In this experimental study, the non-catalytic decomposition of methane in the presence of small amounts of carbon dioxide was analyzed. At large scales, natural gas or biomethane are possible feedstocks for the thermal decomposition and can obtain up to 5% carbon dioxide. Gas recycling can increase the amount of secondary components even further. Experiments were conducted in a packed flow reactor at temperatures from 1250 to 1350 K. The residence time and the amounts of carbon dioxide and hydrogen in the feed were varied. A methane conversion of up to 55.4% and a carbon dioxide conversion of up to 44.1% were observed. At 1300 K the hydrogen yield was 95% for a feed of methane diluted in nitrogen. If carbon dioxide was added to the feed at up to a tenth with regard to the amount of supplied methane, the hydrogen yield was reduced to 85%. Hydrogen in the feed decreases the reaction rate of the methane decomposition and increases the carbon dioxide conversion.

Coupled hydrodynamic and kinetic model of liquid metal bubble reactor for hydrogen production by noncatalytic thermal decomposition of methane

Industrial-scale implementation of liquid metal bubble reactors (LMBRs) to produce hydrogen by methane decomposition will require large gas holdups (e.g., 20–30 vol%) and elevated gas pressures (>20 bar) to allow for practical reactor sizes. A realistic reactor design must account for the coupling between reaction kinetics and hydrodynamic effects. The gas holdup is predicted from the superficial gas velocity with a drift flux model that was experimentally corroborated in gas-molten metal mixtures. Large superficial gas velocities (>0.40 m s−1) are required to achieve gas holdups of about 25 vol% in liquid metal baths (LMBs). A noncatalytic kinetic model is developed to provide thermodynamically consistent decomposition rates at methane conversions approaching equilibrium. The coupled model optimizes the LMB dimensions (diameter and length) and the inlet pressure to minimize the volume of liquid metal when the hydrogen production rate, bath temperature, methane conversion, metal composition, and maximum gas holdup are specified. For example, 200 kt a−1 of hydrogen can be produced in an LMBR containing at least 96.5 m3 of molten tin held at 1100 °C in a bath measuring 3.50 m in diameter and 14.3 m in length, with an inlet methane pressure of 57.8 bar resulting in an average gas holdup of 29.7 vol% and a methane conversion of 65%.

Получение изоцианатов на примере бутилизоцианата термолизом карбаматов

Butyl isocyanate is widely distributed as a precursor for the production of a number of biologically active substances: fungicides, preservatives, insecticides, personal care products, etc. Nowadays, there are a number of methods for the preparation of isocyanates, which can be divided into liquid phase and gas phase. One of the perspective methods for the production of isocyanates is the thermolysis of carbamate and/or the actions of various reaction activating agents, accompanied by the elimination of alcohol, but this process is reversible, which greatly complicates its use in industry. The paper presents the results of studies of non-catalytic thermal decomposition of N-alkylcarbamates with the formation of alkylisocyanates on the example of butylisocyanate in the gas phase, flow reactor in a wide temperature range (200 to 450 °C). In addition, a series of experiments was carried out using a catalyst, dibutyltin dilaurate, in order to reduce the thermolysis temperature and increase the yield of the final product. To implement the isocyanate production process, an experimental laboratory setup, consisting of a gas flow meter (argon) regulator, a packed column (for heating) and a sorption solution tank, was developed and tested. The thermolysis of N-n-butylcarbamate was carried out in two variations: the preparation of an individual n-butylisocyanate and the passage of reaction products through a sorption solution linking the n-butyl isocyanate to N-n-butyl-N '-(1-phenylethyl)urea, which allows to estimate the yield of the target n-butylisocyanate without additional losses. The analysis of the obtained substances was carried out by high performance liquid chromatography with a UV detector (target product) and a mass detector (analysis of by-products). According to the results of research, a modification of the laboratory facility was proposed, as well as n-butylisocyanate was obtained with a yield of 49% on the basis of a new technique.

Hydrogen production by methane decomposition on Pt/γ-alumina doped with neodymium catalysts and its kinetic study

Abstract This paper presents results for the catalytic decomposition of methane using Pt/γ-Al2O3 and Pt/γ-Al2O3-Nd2O3 catalysts for the hydrogen production. All catalysts were prepared by wet impregnation using Nd(NO3)3⋅6H2O and H2 PtCl6.6H2O as precursor salts. The concentrations of the catalysts were Pt, 1.0 wt%, and Nd, 1.0 and 10.0 wt%. The reaction was carried out from 400 to 750 °C. All the catalysts reduced methane decomposition temperature by 400–750 °C relative to noncatalytic thermal decomposition, which is carried out at 1300 °C. The Pt catalysts supported on γ-alumina doped with neodymium exhibited higher activity than Pt supported on alumina alone. All catalysts showed high activity and selectivity at 750 °C, with conversions around 57–80%vol and hydrogen productions of 0.29, 0.27 and 0.19 mmoles of H2/min*gcat for PtANd10, PtANd1 and PtA catalysts respectively also were observed in the output stream, traces of C2H4 y C2H6 (less than 1%) and unconverted methane. This work includes a kinetic study of methane cracking, for this purpose two experiments were carried out, the first one consisted of varying the amount of catalyst, keeping the feed flow constant, in the second experiment the flow rate was varied, keeping the mass of the catalyst constant. The activation energy of methane cracking is estimated at 35.5, 37.9 and 33 kJ/mol for the Pt/A, Pt/ANd1 and Pt/ANd10 catalysts, respectively. The characterization was done by X-ray diffraction, N2 adsorption-desorption, H2-TPR, FTIR of CO adsorption, FTIR of Pyridine adsorption, XPS, HRTEM, catalytic activity and TPO (Temperature programed Oxidation) analysis after reaction.

Study of non-catalytic thermal decomposition of triglyceride at hydroprocessing condition

Non-catalytic thermal decomposition of triglyceride is studied between 300 and 410°C at 0.1 and 5MPa in the presence of H2 or inert gas. This test is carried in tubular reactor filled with inert material (borosilicate glass pellet). The qualitative and analytical results showed that n-alkanes and alkenes with oxygenated olefins were primary products, consistent with thermal cracking to lighter hydrocarbons. The resulting outlet fuel gas obtained mainly from the radical reaction and had high concentration of CO, ethylene and methane. The decomposition forms a large number of radical compounds containing acids, aldehydes, ketones, aliphatic and aromatic hydrocarbon groups. Lighter fraction contains mostly naphthenic group, and heavy fraction contains straight chain paraffinic hydrocarbons. When H2 partial pressure raised, the cracking of heavy fractions is low, and products contain low concentration of the lighter and gasoline fractions. Here, the thermal decomposition of triglyceride yields lighter fractions due to cracking, decarboxylation and decarbonylation.

Nitrogen transformation during gasification of livestock compost over transition metal and Ca-based catalysts

Catalytic gasification of a pig compost (PC) was investigated over transition metal catalysts (TMCs, including limonite, CoMo/Al2O3, Ni/Al2O3, and nickel loaded on lignite char) and Ca-based catalysts (dolomite and CaO) in a two-stage fixed-bed reactor to understand the effects of catalyst, temperature, and steam on nitrogen distributions. Non-catalytic thermal decomposition (TD) of PC volatiles below 750°C is not effective for decomposing the entire volatile nitrogen species (VNSs) to N2. NH3 was found to be the predominant nitrogenous gas under inert conditions used in this investigation, and its yield increased with raising TD temperature. The N yield in HCN is lower than 5% below 550°C, and sharply increased to 13.9% at 750°C due to TD of volatiles. Most of VNSs were converted to N2 over TMCs, especially over Ni-based ones. The TMCs proved to be quite active not only for tar reduction, but also for VNSs decomposition at 450–650°C. On the contrary, CaO-based catalysts, especially dolomite, significantly promoted the conversion of VNSs to NH3. Ni/Al2O3 effectively promoted the conversion of NH3 and HCN to N2 at 550°C. Steam introduced mainly prevented HCN decomposition over dolomite and coke deposition over Ni/Al2O3. This study provides a basic insight into the nitrogen transformations during catalytic gasification of PC, which would benefit the clean utilization of PC as an energy source.

Low-temperature catalytic gasification of sewage sludge-derived volatiles to produce clean H2-rich syngas over a nickel loaded on lignite char

Catalytic gasification (CG) of sewage sludge-derived volatiles (SSDVs) was investigated over a prepared nickel loaded on Loy Yong lignite char (Ni/LYLC) in a two-stage fixed-bed reactor to understand the effects of the catalyst, temperature, and steam on the gas yields and nitrogen transformations. Non-catalytic thermal decomposition of SSDVs below 650 °C is not effective for decomposing the tar and converting the volatile nitrogen species (VNSs) to N2. Ni/LYLC proved to be quite active not only for tar reduction, but also for the conversion of VNSs to N2 at 650 °C. CG of SSDVs over Ni/LYLC produced significant amount of clean H2-rich syngas. CG above 650 °C results in the increase of nickel crystallite size and the deactivation of Ni/LYLC for tar decomposition. The study revealed the possibility of using Ni/LYLC as a potential catalyst for low-temperature CG of sewage sludge to produce clean H2-rich syngas.

High-temperature hydrodechlorination of ozone-depleting chlorodifluoromethane (HCFC-22) on supported Pd and Ni catalysts

The hydrodechlorination of chlorodifluoromethane (HCFC-22) was performed by a catalytic reaction and noncatalytic thermal decomposition at high temperatures of 400–800°C. After 47 h of time-on-stream on a supported palladium (Pd) catalyst, the gas-phase composition of difluoromethane (HFC-32) is 41.0%, with 4.9% of the HCFC-22 remaining, indicating the conversion of up to 95.1% of HCFC-22. The supported nickel catalyst's deactivation is significant as it exhibits the low conversion of HCFC-22 under the same reaction conditions. The deactivation of the catalyst is caused by the polymerization of adsorbed methyl radicals, which competes with the formation of HFC-32. With concentrated reactants at high reaction temperatures, there was an increase in the catalytic activity; however, unwanted tar, methane, and trifluoromethane (HFC-23) by-products are also produced. The use of catalyst suppresses the formation of these by-products. Considering the compositions of the products of the catalytic and noncatalytic reactions, we demonstrate that the use of the supported-metal catalysts and hydrogen flow suppresses tar formation and lowers the required reaction temperature.

Catalytic decomposition of liquid hydrocarbons in an aerosol reactor: A potential solar route to hydrogen production

Catalytic decomposition of liquid fuels (n-octane, iso-octane, 1-octene, toluene and methylcyclohexane) is achieved in a continuous tubular aerosol reactor as a model for the solar initiated production of hydrogen, and easily separable CO free carbonaceous aerosol product. The effects of fuel molecular structure and catalyst concentration on the overall hydrogen yield were studied. Iron aerosol particles used as the catalysts, were produced on-the-fly by thermal decomposition of iron pentacarbonyl. The addition of iron catalyst significantly decreases the onset temperature of hydrogen generation as well as improves the reaction kinetics by lowering the reaction activation energy. The activation energy without and with iron addition was 260 and 100 kJ/mol, respectively representing a decrease of over 60%. We find that with the addition of iron, toluene exhibits the highest hydrogen yield enhancement at 900 °C, with a 6 times yield increase over thermal decomposition. The highest H 2 yield obtained was 81% of the theoretical possible, for n-octane at 1050 °C. The general trend in hydrogen yield enhancement is that the higher the non-catalytic thermal decomposition yield, the weaker the catalytic enhancement. The gaseous decomposition products were characterized using a mass spectrometer. An XRD analysis was conducted on the wall deposit to determine the product composition and samples for electron-microscopic analysis were collected exiting the furnace by electrostatically precipitating the aerosol onto a TEM grid.

Hydrogen production by thermocatalytic decomposition of butane over a carbon black catalyst

Catalytic activity of carbon black for decomposition of butane was investigated for CO 2-free hydrogen production. The carbon black employed was a rubber black and the range of reaction temperature was from 500 to 1100 °C. Although the primary decomposition of butane occurred mostly by non-catalytic thermal decomposition, the butane conversion and the hydrogen yield obtained in the presence of the carbon black were higher than those obtained by non-catalytic thermal decomposition. This is mainly due to the catalytic effect of carbon black which accelerates decomposition of butane as well as subsequent decomposition of propylene, ethylene and methane that have been produced by the primary decomposition. The catalytic decomposition of ethylene was pronounced from 750 °C and that of methane from 950 °C. A variety of products such as methane, ethylene, ethane, propylene and propane were formed, but in the presence of carbon black ethane, propylene and propane were negligible above 900 °C and ethylene was so at and above 1000 °C. Deactivation of the catalyst was not observed at least for 200 min in spite of carbon deposition.

A lumped model for thermal decomposition of urea. Uncertainties analysis and selective non-catalytic reduction of NO

A two-step mechanism for non-catalytic thermal decomposition of urea was investigated. It involves a first order reaction for the thermolysis of urea and a pseudo-first order reaction for hydrolysis of isocyanic acid. Rate constants of these reactions were tuned on experimental measurements of NH 3 and HNCO concentrations at 423–723 K and 1083–1383 K in isothermal flow reactors made of aluminum and ceramic, respectively. A regression analysis by taking the uncertainties in the kinetic parameters into account shown that the resultant pairs of Arrhenius expressions for thermo-hydrolyzing urea were different with a 90% confidence when obtained from the different sets of experimental data. Additional results of ammonia concentration from experiments of urea solution decomposition reported in the literature revealed the reliability of the Arrhenius expressions tuned on the reaction rates obtained in the highest range of temperature in the ceramic reactor. The consistency of these equations was also verified by a comparison between calculated and experimental rates of selective non-catalytic reduction of nitric oxide with urea as reducing agent. A statistical analysis based on the identification of possible tendencies in these residuals again evidences the weakness of the Arrhenius expressions based on the experiments performed at lower temperatures, which was attributed to a non-expected catalytic effect of aluminum reactor walls on reactions rates of urea thermal decomposition.

One-Step Synthesis of Polycrystalline Carbon Nanofibers with Periodic Dome-Shaped Interiors and Their Reversible Lithium-Ion Storage Properties

Carbon nanofibers and carbon nanotubes continue to draw unwavering interest from industrial and academic communities because of their fascinating properties and their projected application values. This paper reports a one-step synthesis of high-purity carbon nanofibers with dome-shaped interiors by the noncatalytic thermal decomposition of acetylene over a copper surface at atmospheric pressure. These uniquely shaped carbon nanofibers were impurity free, and their dome-shaped interiors could be repeated with high periodicity throughout the length. In addition, Y-junction and forklike carbon nanofibers with the same internal structure were also formed as byproducts. The growth of these unique carbon nanomaterials could be rationalized by a mechanism based on the autocatalytic chemical vapor deposition of 3D graphene flakes. Preliminary electrochemical measurements indicated that the carbon nanofibers could be used as the active anode material for lithium-ion batteries, delivering good cyclability and a reversible capacity of ∼260 mAh/g at the high specific current of 100 mA/g.

Hydrogen Production by Catalytic Decomposition of Methane

Traditionally, hydrogen is produced by reforming or partial oxidation of methane to produce synthesis gas, followed by the water-gas shift reaction to convert CO to CO2 and produce more hydrogen, followed in turn by a purification or separation procedure. This paper presents results for the catalytic decomposition of undiluted methane into hydrogen and carbon using nanoscale, binary, Fe−M (M = Pd, Mo, or Ni) catalysts supported on alumina. All of the supported Fe−M binary catalysts reduced methane decomposition temperature by 400−500 °C relative to noncatalytic thermal decomposition and exhibited significantly higher activity than Fe or any of the secondary metals (Pd, Mo, and Ni) supported on alumina alone. At reaction temperatures of approximately 700−800 °C and space velocities of 600 mL g-1 h-1, the product stream was comprised of over 80 volume % of hydrogen, with the balance being unconverted methane. No CO, CO2, or C2 and higher hydrocarbons were observed in the product gas. High-resolution SEM and TEM characterization indicated that almost all carbon produced in the temperature range of 700−800 °C is in the form of potentially useful multiwalled nanotubes. At higher temperatures (>900 °C), hydrogen production decreases and carbon is deposited on the catalyst in the form of amorphous carbon, carbon flakes, and carbon fibers. In the noncatalytic thermal decomposition mode, at temperatures above 900 °C, graphitic carbon film is deposited everywhere in the reactor. Thus, the morphology of the carbon produced may be the controlling parameter in catalytic decomposition of methane. The efficient removal of the carbon from the catalyst surface in the form of nanotubes may be the key factor influencing catalyst performance.

Reaction mechanism of methanol dehydrogenation on a sodium carbonate catalyst

The aim of this study is to identify the reaction mechanism of methanol dehydrogenation on sodium carbonate catalyst. Quantitative analyses of the products of methanol dehydrogenation on sodium carbonate catalyst at 963 K indicate that methane is formed in parallel with formaldehyde, while carbon monoxide is mainly produced from further decomposition of formaldehyde. In a specially designed fixed-bed reactor, more than half of the methanol conversion takes place in the post-catalytic space, where the selectivity for formaldehyde is in the same range as for the reaction in the catalyst bed. It is therefore suggested that free radicals produced on the catalyst surface play an important role in methanol dehydrogenation. Temperature-programmed desorption of methanol on sodium carbonate and transient isotope experiments show that a hydrogen species is strongly adsorbed on the catalyst, but carbon-containing species are weakly adsorbed. Temperature-programmed reaction experiments indicate that non-catalytic thermal decomposition of formaldehyde is more significant than the surface reaction at high temperatures. Based on these facts, it is proposed that chemisorbed methanol is dissociated on the catalyst surface into adsorbed hydrogen and a gas-phase <d CH 2OH radical. Recombination and desorption of the former is rate-determining, and the latter initiates a series of homogeneous reactions that result in the final reaction products. The proposed mechanism is useful for further improving the catalyst.

On-line process control of a fluidized bed reactor with non-catalytic gas/solid reaction

In a bench-scale, stainless steel reactor, experiments were carried out to investigate fluidized bed behavior by means of on-line process control. The non-catalytic thermal decomposition of sodium hydrogen carbonate to sodium carbonate, carbon dioxide and water was used a model reaction. The experimental equipment was provided with control systems and reulating units which were connected to a PDP 11/40 computer by means of suitable analogue and digital input/output interfaces. The operating conditions are highly influenced by the chemical reaction as well as by the fluid-dynamical behavior of the reactor. Several experiments were carried out to evaluate the kinetics of the model reaction. The fluid-dynamics was investigated by means of on-line experiments with and without chemical reaction. Based on the experimental results, a model was developed to describe the whole process so that model simulations should yield information on the process itself. With this model, strategies are tested before they are applied to the process computer for on-line process control.