Fast pyrolysis of cellulose with reactive methane gas in a single-pulse shock tube

A shock tube technique was employed to study the fast pyrolysis of cellulose with methane under conditions of high temperature, high heating rate, short reaction time, and rapid quenching. The effects of temperature, methane atmosphere, and reaction time are investigated. Experiments were carried out at temperatures between 700 and 2200°C in 1% methane (diluted in argon), and comparisons in the yields of major gas products are made with the results obtained in pure argon atmosphere. The total gas yield decreased about 25–30% in methane. The principal gas products—carbon monoxide, carbon dioxide, and acetylene, except ethylene—were significantly decreased in methane as compared to the yields in pure argon. An increase of about 25% in ethylene yield in methane over argon was observed. The onset of the decomposition of cellulose and the evolution of major pyrolysis products were changed with the reaction times, which also affected the amplitude and the distribution of the pyrolysis products. © 1994 John Wiley & Sons, Inc.     

Effects of methane concentration on hydrocarbon release during the pyrolysis of coal

The weight-loss characteristics of Longkou lignite were studied by means of thermogravimetric analysis in methane ambience. Pyrolysis experiments of the sample coal in different concentrations of methane were carried out on a tube reactor to study the characteristics of hydrocarbon released. The results show that methane can promote the pyrolysis of lignite in a certain temperature range and the coal can also improve the pyrolysis of methane further. The influence of methane concentration on hydrocarbon release during the pyrolysis of coal is obvious. The hydrocarbon released from the pyrolysis of lignite is intensive within the temperature range from 400°C to 500°C and the release of hydrocarbon components dramatically increased as the concentration of methane decreased. This indicates that the release of C₂, C₃ and C₄ has a close relationship with methane pyrolysis and proves that a synergistic effect does exist between the coal and methane.     

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.     

碳五烷烃裂解制低碳烯烃反应性能的分析

考察了碳五烷烃的热裂解和催化裂解反应性能,发现正戊烷和异戊烷的裂解反应产物存在差异;进一步分析了正戊烷和异戊烷的裂解反应机理,以及裂解生成低碳烯烃和甲烷的区别。结果表明,在热裂解条件下,正戊烷的（乙烯+丙烯）选择性高于异戊烷,异戊烷的丁烯和甲烷选择性高于正戊烷;650℃时,正戊烷和异戊烷的热裂解产品中（乙烯+丙烯）、丁烯、甲烷的选择性分别为37.48%、7.23%、6.75%和19.57%、25.16%、9.36%。而在催化裂解条件下,异戊烷的（乙烯+丙烯）、丁烯、甲烷选择性均高于正戊烷;650℃时,正戊烷和异戊烷的催化裂解产品中（乙烯+丙烯）、丁烯、甲烷的选择性分别为37.16%、9.11%、7.80%和47.70%、14.45%、13.79%。此外,发现在高温裂解条件下异构烷烃比正构烷烃容易裂解生成丁烯和甲烷。     

Coal flash pyrolysis: 1. An indication of the olefin precursors in coal by CP/MAS 13C n.m.r. spectroscopy

The results reported indicate that the low molecular weight olefins (ethylene, propylene and butadiene) which are major gaseous hydrocarbon products of flash pyrolysis of coal derive from the same precursors in coal, whereas methane, benzene and other pyrolysis products are mainly formed from different components in the coal. CP/MAS ¹³C n.m.r. spectra suggest that the olefin precursors are long-chain polymethylene structures (chemical shift 31 ppm), either chemically bound or mechanically trapped in the coal and thus not solvent-extractable.     

Coal flash pyrolysis: 2. Polymethylene compounds in low temperature flash pyrolysis tars

Pyrolysis of coals at low temperatures (< 600 °C) produces tars containing the precursors of the low molecular weight aliphatic hydrocarbons, such as ethylene and propylene, observed on flash pyrolysis of the coals at higher temperatures (700–800 °C). This is shown by further pyrolysis of these low temperature tars at high temperatures. Various methods, including isolation by h.p.l.c. were used to confirm the presence of straight chain paraffin and olefin pairs (C₁₄C₂₆ and above) in the low temperature tars. Pyrolysis of pure paraffins and olefins in this molecular weight range at temperatures > 700 °C produce ethylene, propylene and other cracking products similar to those obtained on flash pyrolysis of coal.     

Steady-state conversion of methane to C4+ aliphatic products in high yields using an integrated recycle reactor system

Conversion of methane in high yields to C₄₊ nonaromatic hydrocarbons was demonstrated in a recycle system. The principal components of the recycle system included an oxidative coupling reactor with a Mn/Na₂WO₄/SiO₂ catalyst at 800°C for conversion of methane to ethylene, and a reactor with an H-ZSM-5 zeolite at 275°C for subsequent conversion of ethylene to higher hydrocarbons. Total yields of C₄₊ products were in the range of 60–80%, and yields of C₄₊ nonaromatic hydrocarbons were in the range of 50–60%. This revised version was published online in July 2006 with corrections to the Cover Date.     

The effects of oxygen on the yields of the thermal decomposition products of catechol under pyrolysis and fuel-rich oxidation conditions

In order to investigate the effects of oxygen on the distribution of thermal decomposition products from complex solid fuels, pyrolysis and fuel-rich oxidation experiments have been performed in an isothermal laminar-flow reactor, using the model fuel catechol (ortho-dihydroxybenzene), a phenol-type compound representative of structural entities in coal, wood, and biomass. The gas-phase catechol pyrolysis experiments are conducted at a residence time of 0.3 s, over a temperature range of 500-1000 °C, and at oxygen ratios ranging from 0 (pure pyrolysis) to 0.92 (near stoichiometric oxidation). The pyrolysis products are analyzed by nondispersive infrared analysis and by gas chromatography with flame-ionization and mass spectrometric detection. In addition to an abundance of polycyclic aromatic hydrocarbons, catechol pyrolysis and fuel-rich oxidation produce a range of C₁-C₅ light hydrocarbons as well as single-ring aromatics. Quantification of the products reveals that the major products are CO, acetylene, 1,3-butadiene, phenol, benzene, vinylacetylene, ethylene, methane, cyclopentadiene, styrene, and phenylacetylene; minor products are ethane, propyne, propadiene, propylene and toluene. Under oxidative conditions, CO₂ is also produced. At temperatures <850 °C, increases in oxygen concentration bring about increases in catechol conversion and yields of C₁-C₅ and single-ring aromatic products—in accordance with increased rates of pyrolytic reactions, due to the enhanced free-radical pool. At temperatures >850 °C, catechol conversion is complete, and increases in oxygen bring about drastic decreases in the yields of virtually all hydrocarbon products, as oxidative destruction reactions dominate. Reactions responsible for the formation of the C₁-C₅ and single-ring aromatic products from catechol, under pyrolytic and oxidative conditions, are discussed.     

Toward more cost‐effective and greener chemicals production from shale gas by integrating with bioethanol dehydration: Novel process design and simulation‐based optimization

A novel process design for a more cost‐effective, greener process for making chemicals from shale gas and bioethanol is presented. The oxidative coupling of methane and cocracking technologies are considered for converting methane and light natural gas liquids, into value‐added chemicals. Overall, the process includes four process areas: gas treatment, gas to chemicals, methane‐to‐ethylene, and bioethanol‐to‐ethylene. A simulation‐optimization method based on the NSGA‐II algorithm for the life cycle optimization of the process modeled in the Aspen HYSYS is developed. An energy integration model is also fluidly nested using the mixed‐integer linear programming. The results show that for a “good choice” optimal design, the minimum ethylene selling price is $655.1/ton and the unit global‐warming potential of ethylene is 0.030 kg CO₂‐eq/kg in the low carbon shale gas scenario, and $877.2/ton and 0.360 kg CO₂‐eq/kg in the high carbon shale gas scenario. © 2014 American Institute of Chemical Engineers AIChE J, 61: 1209–1232, 2015     

Upgrading biomass pyrolysis gas by conversion of methane at high temperature: Experiments and modelling

Biomass gasification at temperatures below 1273 K produces gas which contains methane and too much tar for Fischer-Tropsch synthesis. The aim of this study is to investigate methane conversion at high temperature. Experimental tests were performed between 1273 and 1773 K, with a mixture of gas representative of wood pyrolysis at 1100 K (main components only: CO, CO₂, CH₄, H₂, H₂O). Two different kinetic schemes were used to predict the gas composition, and PAH molecules formation. For a residence time of 2 s in the reactor, the gas must be heated to at least 1650 K to reach a methane conversion rate of 90%. A parametric study was performed at 1453 K, by varying the initial methane, steam and hydrogen contents, so as to find out which components are the most influent on methane conversion and soot production.     

Electrochemical reduction of high pressure CO2 at a Cu electrode in cold methanol

The electrochemical reduction of high pressure CO₂ with a Cu electrode in cold methanol was investigated. A high pressure stainless steel vessel, with a divided H-type glass cell, was employed. The main products from CO₂ by the electrochemical reduction were methane, ethylene, carbon monoxide and formic acid. In the electrolysis of high pressure CO₂ at low temperature, the reduction products were formed in the order of carbon monoxide, methane, formic acid and ethylene. The best current efficiency of methane was of 20% at −3.0 V. The maximum partial current density for CO₂ reduction was approximately 15 mA cm⁻². The partial current density ratio of CO₂ reduction and hydrogen evolution, i(CO₂)/i(H₂), was more than 2.6 at potentials more positive than −3.0 V. This work can contribute to the large-scale manufacturing of fuel gases from readily available and inexpensive raw materials, CO₂-saturated methanol from industrial absorbers (the Rectisol process).     

Oxidative Coupling of Methane in a Negative DC Corona Reactor at Low Temperature

Oxidative coupling of methane (OCM) in the presence of DC corona is reported in a narrow glass tube reactor at atmospheric pressure and at temperatures below 200°C. The corona is created by applying 2200V between a tip and a plate electrode 1.5 mm apart. The C₂ selectivity as well as the methane conversion are functions of methane‐to‐oxygen ratio, gas residence time, and electric current. At CH₄/O₂ ratio of 5 and the residence time of about 30 ms, a C₂ yield of 23.1% has been achieved. The main products of this process are ethane, ethylene, acetylene as well as CO and CO₂ with CO/CO₂ ratios as high as 25. It is proposed that methane is activated by electrophilic oxygen species to form methyl radicals and C₂ products are produced by a consecutive mechanism, whereas CO_x is formed during parallel reactions.     

Electrochemical reduction of carbon dioxide to ethylene with high Faradaic efficiency at a Cu electrode in CsOH/methanol

The electrochemical reduction of CO₂ with a Cu electrode in CsOH/methanol-based electrolyte was investigated. The main products from CO₂ were methane, ethylene, ethane, carbon monoxide and formic acid. A maximum Faradaic efficiency of ethylene was 32.3% at −3.5 V vs. Ag/AgCl saturated KCl. The best methane formation efficiency was 8.3% at −4.0 V. The ethylene/methane current efficiency ratio was in the range 2.9–7.9. In the CsOH/methanol, the efficiency of hydrogen formation, being a competitive reaction against CO₂ reduction, was depressed to below 23%.     

Integrated coal pyrolysis with CO2 reforming of methane over Ni/MgO catalyst for improving tar yield

A new process to integrate coal pyrolysis with CO₂ reforming of methane over Ni/MgO catalyst was put forward for improving tar yield. And several Chinese coals were used to confirm the validity of the process. The experiments were performed in an atmospheric fixed-bed reactor containing upper catalyst layer and lower coal layer to investigate the effect of pyrolysis temperature, coal properties, Ni loading and reduction temperature of Ni/MgO catalysts on tar, water and char yields and CH₄ conversion at fixed conditions of 400 ml/min CH₄ flow rate, 1:1 CH₄/CO₂ ratio, 30 min holding time. The results indicated that higher tar yield can be obtained in the pyrolysis of all four coals investigated when coal pyrolysis was integrated with CO₂ reforming of methane. For PS coal, the tar, water and char yield is 33.5, 25.8 and 69.5 wt.%, respectively and the CH₄ conversion is 16.8%, at the pyrolysis temperature of 750 °C over 10 wt.% Ni/MgO catalyst reduced at 850 °C. The tar yield is 1.6 and 1.8 times as that in coal pyrolysis under H₂ and N₂, respectively.     

The pyrolysis of natural gas: A study of carbon deposition and the suitability of reactor materials

This study of methane pyrolysis was designed to look at carbon deposition on the internal reactor and wafer surface during CH₄ pyrolysis. The rate of carbon deposition on the internal reactor surfaces could be reduced with: lower methane/oxygen ratios, shorter residence times, and lower temperatures. The type of carbon formed appeared to have a significant effect on the pyrolysis process. Pyrolytic carbon with a lower order structure produces a higher selectivity for carbon formation compared to carbon with a higher order structure. Form a process perspective, there are two obvious means of addressing this: deposited carbon could be regularly removed; and/or pyrolysis conditions are selected that produce carbon with a higher order structure. From the results, it is very clear that any development of a commercial process for natural gas pyrolysis in ceramic reactor systems would have to carefully address the selection of reactor material. © 2018 American Institute of Chemical Engineers AIChE J, 65: 1035–1046, 2019     

Hydrogen balance for catalytic pyrolysis of atmospheric residue

The catalytic pyrolysis of atmospheric residue over the commercial catalytic pyrolysis process catalyst (Al₂O₃/Fe₂O₃/Na₂O (46.3, 0.27 and 0.04 wt.%, respectively)) was investigated in a confined fluidized bed reactor. The yield of light olefins was above 37 wt.% at reaction temperature above 600 °C and it reached a maximum of 47 wt.% at 660 °C. The main components in light olefins were ethylene and propylene, and those in liquid samples were aromatics. The main components in light alkanes were propane and i-butane at low reaction temperature (600 °C), and those were methane and ethane at high reaction temperature (700 °C). The hydrogen content of light olefins was about 14.27 wt.%, that of light alkanes was above 18.5 wt.%, that of gasoline was below 12.5 wt.%, and that of diesel was below 7.8 wt.%. The percentage of the hydrogen in light alkanes to total hydrogen was above 29% and that in light olefins was above 40%. The effective utilization ratio of hydrogen decreased from 66.60% at 600 °C to 61.44% at 700 °C.     

Low temperature catalysts for oxidative coupling of methane

A simple review is given to the recent work of the oxidative coupling of methane at low temperature. Emphasis is laid on the different systems of low-temperature catalysts under conventional CH₄/O₂ co-feed conditions, and on the investigations of low-temperature oxidative coupling of methane in the presence of steam in the feed. Other approaches, e.g. oxidative coupling of methane at elevated pressure and moderate temperature, preparing ethylene by oxidative coupling reaction of methane on laser-activated solid surface, are also included.     

Coal flash pyrolysis: 5. Pyrolysis in an atmosphere of methane

Flash pyrolysis of coal at temperatures above 700°C and in the presence of methane produces substantially more ethylene and other low molecular weight hydrocarbons than are produced by pyrolysis of coal in the presence of nitrogen alone. Evidence is presented to show that the increase is due to pyrolysis of the methane quite independently of the coal, except with the possible catalysis by the coal, coke or mineral matter in the coal ash. This is contrary to recent reports in the literature.     

Electrochemical reduction of carbon dioxide to ethylene at a copper electrode in methanol using potassium hydroxide and rubidium hydroxide supporting electrolytes

The electrochemical reduction of CO₂ with a Cu electrode was investigated in methanol using potassium hydroxide and rubidium hydroxide supporting salts. The main products from CO₂ were methane, ethylene, carbon monoxide and formic acid. The maximum current efficiency for ethylene was of 37.5%, at −4.0 V versus Ag/AgCl, saturated KCl in KOH/methanol. The typical ratios of current efficiency for ethylene/methane, r_f(C₂H₄)/r_f(CH₄), were 2.3 and 6.7, in KOH/methanol and RbOH/methanol-based electrolytes, respectively. In KOH/methanol, the efficiency of hydrogen formation, a competing reaction of CO₂ reduction, was depressed to below 3.3%. On the basis of this work, the high efficiency electrochemical CO₂-to-ethylene conversion method appears to be achieved. Future work to advance this technology may include the use of solar energy as the electric energy source. This research can contribute to the large-scale manufacturing of fuel gases from readily available and inexpensive raw materials, CO₂-saturated methanol from industrial absorbers (the Rectisol process).     

Conversion of methane to higher hydrocarbons in pulsed DC barrier discharge at atmospheric pressure

Conversion of methane to C₂/C₃ or higher hydrocarbons in a pulsed DC barrier discharge at atmospheric pressure was studied. Non-equilibrium plasma was generated in the barrier discharge reactor. In this plasma, electrons which had sufficient energy collided with the molecules of methane, which were then activated and coupled to C₂/C₃ or higher hydrocarbons. The effect of the change of applied voltage, pulse frequency and methane flow rate on methane conversion, selectivities and yields of products was studied. Methane conversion to higher hydrocarbons was about 25% as the maximum. Ethane, propane and ethylene were produced as primary products, including a small amount of unidentified C₄ hydrocarbons. The selectivity and yield of ethane as a main product came to about 80% and 17% as the highest, respectively. The selectivities of ethane and ethylene were influenced not by the change of pulse frequency but by the change of applied voltage and methane flow rate. However, in case of propane, the selectivity was independent of those condition changes. The effect of the packing materials such as glass and A1₂O₃ bead on methane conversion was also considered, showing that A1₂O₃ played a role in enhancing the selectivity of ethane remarkably as a catalyst.