Effect of ethane addition on propane pyrolysis

Pyrolysis of propane/argon mixture in the presence of trace quantities (0.1% and 0.9%) of ethane was investigated at reflected shock wave temperatures between 1200 and 2000K. Traces of ethane accelerated propane decomposition at high temperature. However, increase in the quantity of ethane added to propane/argon mixture did not result in the same increase of its accelerating influence. Ethylene, methane and acetylene were the main hydrocarbon reaction products, with small quantities of propylene and ethane detected only at lower temperatures. Below 1500K, addition of ethane slightly enhanced the yields of ethylene and methane at the expense of propylene and ethane respectively. The selectivity for acetylene increased with increasing temperature and with the decline of those for the other products. For none of the products, did the presence of ethane alter the relationship between product formation rates and temperature. The influence of ethane addition on propane pyrolysis at high temperatures was explained in terms of increased radical concentrations, especially hydrogen atoms and vinyl radicals, formed at high conversions. These accounted for the rapid acceleration of propane decomposition and the high yield of acetylene at high temperatures.     

Preparation of C/C composites by the chemical vapor infiltration (CVI) of propane pyrolysis

The preparation of C/C composites by the chemical vapor infiltration (CVI) of the pyrolysis carbon from propane was studied. Pyrolysis carbon was deposited at 30 torr and at temperatures between 1,173 and 1,233 K. The rate of carbon deposition increased slightly with time. The main gas products in the exit gas were methane, ethylene, and acetylene. The fraction of ethylene decreased and that of acetylene increased with the reaction temperature and the propane concentration. The produced propyl radicals reacted further at a high temperature and at a high propane concentration. These trends were similar to those of the reported data. Changes of the shapes of deposited carbon in the pores of preform were confirmed with SEM photos. The mathematical modeling of the system with the deposition rate constant from the reference estimated experimental data well.     

Pyrolysis of methane in a single pulse shock tube

The thermal decomposition of methane has been studied in a chemical shock tube at pressures up to 20 atm over a temperature range of between 1750 and 2700 K and for reaction times up to 2.5 ms. Attention is drawn to some of the experimental features of the shock tube and to the fact that reaction temperatures were measured. Optimum conditions for the production of acetylene from methane are suggested, and the relatively small effect of pressure on the acetylene yields is noted. Values for activation energy (93.6 kcal/mol) and frequency factor (3.8 × 10¹³ s^?1 for methane decomposition are given. The experimental results obtained are discussed in connection with suggested mechanisms of decomposition. In the discussion attention is drawn to the difficulty of predicting acetylene yields arising from the incomplete understanding of the mechanism of acetylene decomposition and of “carbon” formation under the conditions employed.     

The attapulgus clay-catalysed thermal decomposition of terphenyls

The kinetics of the pyrolysis of pure o-, m- and p-terphenyl and of material mixed with Attapulgus clay were studied. 10 to 12 times more o-, m- and p-terphenyl was decomposed in the clay-catalysed experiments and a strong isomerisation of o- into m- and p-, and m- into p-terphenyl appeared. Twice as much benzene and biphenyl was formed, in the runs to which clay had been added. Similar differences were obtained for the quaterphenyl, triphenyl and triphenylbenzene formations. From the catalysed experiments 50 times as much total gas was found consisting of 41% hydrogen, 19% methane, 7% ethane, 2% propane, 1·5% n-pentane, 3·8% isopentane, 2·5% ethylene, 0·4% acetylene, 0·9% propene and 32% butenes. The uncatalysed runs yielded 82% hydrogen, 4% methane, 1% ethane, 0·4% propane 0·2% n-pentane, 0·3% isopentane, 10% ethylene, 2·8% acetylene, 1·2% propene and 2% butenes. It is suggested that the thermal decomposition of pure terphenyls follows a radical mechanism while the clay-catalysed pyrolysis follows a carbonium ion mechanism.     

Analysis of products of high-temperature pyrolysis of various hydrocarbons

Ethane, ethylene, acetylene, propane and neopentane have been pyrolyzed at 1173 K, and methane at 1372 K in a flow system, and the volatile pyrolysis products analyzed. Eleven aromatic hydrocarbons, containing 14 or fewer carbon atoms, accounted for 98 + % of the liquid products recovered in each case. Benzene was the main product, followed by naphthalene. No compounds with branched chains or multiple substituents were present, and compounds containing even numbers of carbons comprised 93–99% of each mixture. Acetylene was a major component of the gaseous effluent from each of the initial hydrocarbons. The effect of temperature on the composition of the gaseous effluent during pyrolysis of methane, ethane and ethylene was determined. Carbon film deposition from methane commenced at about 1273 K; from ethane at 1015 K and from ethylene at 1100 K, in each instance coinciding with the appearance of acetylene in the effluent. As the temperature was raised, at first the increase in the rate of carbon deposition closely followed the increase in the concentration of acetylene in the effluent. It is proposed that acetylene may be a common factor in the pyrolysis of aliphatic hydrocarbons, perhaps acting as the precursor of both surface carbon and aromatic hydrocarbons by a process of head-to-tail linkage of two-carbon units at active surface sites to form chains that then undergo dehydrogenation to carbon or cyclization and desorption as aromatic species.     

Heavy oil processing in steam and hydrogen plasmas

Heavy oil in the form of finely divided spray was reacted with steam and hydrogen plasmas respectively. The heavy oil was preheated to 473 K at a pressure of 2 MPa and fed through pressure atomizers at flow rates between 0.002 and 0.08 m³/h into a dc plasma jet contained in a reactor 20 cm in diameter and 1.5 m long. The hydrogen and steam plasmas had maximum initial temperatures of 6000 K and 3450 K respectively and specific net energy inputs between 0.4 and 12.6 kWh/kg oil were used. With a hydrogen plasma, the heavy oil reacted to form acetylene, ethylene, methane, soot, and pitches, while with a steam plasma, carbon monoxide and dioxide were formed as well. Light liquid hydrocarbons were not in evidence. Increases in the hydrogen (or steam)-to-oil ratio and specific energy consumption increased the oil-to-gas conversions.     

A direct catalytic conversion of natural gas to C2+ hydrocarbons by microwave plasma

Methane, the major constituent of natural gas, was converted to higher hydrocarbons by a microwave plasma. The yield of C2+ products increased from 29.2 % to 42.2% with increasing plasma power and decreasing flow rate of methane. When catalysts were used in the plasma reactor, the selectivities of ethylene and acetylene increased, while the yield of C2+ remained constant. Among various catalysts used, Fe catalyst showed the highest ethylene selectivity of 30 %. And when the actual natural gas was introduced, more C2+ products were obtained (46%). This is due to the ethane and propane in the natural gas. Applying electric field inductance for evolving the high plasma, we obtained high C2+ products of 63.7 % when Pd-Ni bimetal catalyst was used.     

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.     

Methane conversion to ethane in the presence of iron‐ and manganese‐promoted sulfated zirconia

Sulfated zirconia promoted with 1.0 wt% Fe and 0.5 wt% Mn converts methane into ethane with traces of ethylene and acetylene. The initial reaction rate at 723 K and a methane partial pressure of 20 kPa was found to be about 10^-9 mol(CH ₄) (g s)^-1, and deactivation was rapid, with the reaction rate declining to half the maximum rate within an hour. This revised version was published online in July 2006 with corrections to the Cover Date.     

A kinetic study on the conversion of methane to higher hydrocarbons in a radio-frequency discharge

This study investigated methane conversion with direct current discharge at low pressure in a radio frequency. The main gaseous products of the reaction were ethane, ethylene, acetylene and propane. This study was concentrated on the influence of discharge conditions on the conversion of methane to higher hydrocarbons. Reaction temperature, electron density and mean residence time were calculated from experimental data and mathematical relations. The maximum conversion of the methane was about 45% with the pure methane as a reactant. Ethane was the main product when the reaction occurred in the glow discharge. Ethane selectivity decreased with the increase of the gas temperature. The kinetics of reactions was also analyzed from possible reaction equations and various rate constant data. Consequently, the dissociation constant and the density of radicals could be obtained at any experimental conditions.     

Chemisorption of C3 hydrocarbons on cobalt silica supported Fischer–Tropsch catalysts

Chemisorption of propene and propane was studied in a pulse reactor over a series of cobalt silica-supported Fischer–Tropsch catalysts. It was shown that interaction of propene with cobalt metal particles resulted in its rapid autohydrogenation. The reaction consists in a part of the propene being dehydrogenated to surface carbon and CH_x chemisorbed species; hydrogen atoms released in the course of propene dehydrogenation are then involved in hydrogenation of remaining propene molecules to propane at 323–423 K or in propene hydrogenolysis to methane and ethane at temperatures higher than 423 K. The catalyst characterization suggests that propene chemisorption over cobalt catalysts is primarily a function of the density of cobalt surface metal sites. A correlation between propene chemisorption and Fischer–Tropsch reaction rate was observed over a series of cobalt silica-supported catalysts. No propane chemisorption was observed at 323–373 K over cobalt silica-supported catalysts. Propane autohydrogenolysis was found to proceed at higher temperatures, with methane being the major product of this reaction over cobalt catalysts. Hydrogen for propane autohydrogenolysis is probably provided by adsorbed CH_x species formed via propane dehydrogenation. Propene and propane chemisorption is dramatically reduced upon the catalyst exposure to synthesis gas (H₂/CO = 2) at 323–473 K. Our results suggest that cobalt metal particles are probably completely covered by carbon monoxide molecules under the conditions similar to Fischer–Tropsch synthesis and thus, most of cobalt surface sites are not available for propene and propane chemisorption.     

Kinetic modeling of oxidative dehydrogenation of propane with CO2 over MoOx/La2O3–Al2O3 in a fluidized bed

A 4-step kinetic model of CO₂-assisted oxidative dehydrogenation (ODH) of propane to C₂/C₃ olefins over a novel MoO_x/La₂O₃–γAl₂O₃ catalyst was developed. Kinetic experiments were conducted in a CREC Riser Simulator at various reaction temperatures (525–600 °C) and times (15–30 s). The catalyst was highly selective towards propylene at all combinations of the reaction conditions. Langmuir-Hinshelwood type kinetics were formulated considering propane ODH, uni- and bimolecular cracking of propane to produce a C₁-C₂ species. It was found that the one site type model adequately fitted the experimental data. The activation energy for the formation of propylene (67.8 kJ/mol) is much lower than that of bimolecular conversion of propane to ethane and ethylene (303 kJ/mol) as well as the direct cracking of propane to methane and ethylene (106.7 kJ/mol). The kinetic modeling revealed the positive effects of CO₂ towards enhancing the propylene selectivity over the catalyst.     

Vapor phase reactions of graphite with light hydrocarbons

The pyrolysis of ethane and propane has been performed in the presence of carbon vapor at temperatures between 2,000°K and 5,000°K. This high energy environment is obtained by an electric arc struck between two graphite electrodes. The quenched gases are analyzed by gas chromatography. The major reaction products are acetylene and hydrogen. C₂H₂ yields are a function of the C/H₂, ratio, the power input, the reaction temperature and the total pressure. Power levels between 10 and 50 kw. and gas flow rates of 1.5 to 20 liters per minute have been used. The electric arc process of hydrocarbon cracking is compared with conventional methods of acetylene production.     

Determination of the activation energy and intrinsic rate constant of methane gas hydrate decomposition

Experimental data on the kinetics of methane gas hydrate decomposition are reported. The isothermal/isobaric semi‐batch stirred‐tank reactor, used by Kim et al. (1987), was modified to include an on‐line particle size analyzer. The experiments were conducted at temperatures ranging from 274.65 K to 281.15 K and at pressures between 3.1 and 6.1 MPa. The model of Clarke and Bishnoi (1999, 2000) was used to determine the intrinsic rate constant. It was found that the activation energy for methane hydrate decomposition is 81 kJ/mol and the intrinsic rate constant of decomposition is 3.6 × 10⁴ mol/m² Pa.s.     

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.     

Methane aromatization on Zn-modified zeolite in the presence of a co-reactant higher alkane: How does it occur?

By using ¹³C solid-state NMR and GC–MS, the analysis of the ¹³C-label transfer from methane-¹³C into the products of methane and propane co-aromatization on Zn/H-BEA zeolite at 823–873 K has been performed. A high degree involvement of ¹³C-carbon atoms of methane into aromatic products (benzene, toluene, xylenes) has been demonstrated. The main pathway of methane conversion into aromatics has been determined to consist in the methylation of aromatics, which is produced exclusively from propane, by methane. The methoxy species formed by the dissociative adsorption of methane on ZnO species of the zeolite is responsible for the methylation.     

Partial Oxidation of Propane over Rubidium-Promoted MoO3/SiO2 Catalyst

Silica-supported Rb₂MoO₄ and rubidium-promoted MoO₃ were used as catalysts for the partial oxidation of propane in a fixed-bed continuous-flow reactor at 770–823 K using N₂O as oxidant. The main hydrocarbon products of the reaction were propylene, ethylene, propanal and methane. Addition of various compounds of rubidium to the MoO₃/SiO₂ greatly enhanced the conversion of propane and promoted the formation of propanal at the expense of ethylene and propylene. The highest yield for the production of this compound was found over Rb₂MoO₄/SiO₂ catalyst.     

Stability of acetylene/methane and acetylene/hydrogen/methane gas mixtures at elevated temperatures and pressures

Hydrogen-enriched natural gas (HENG) containing a mixture of acetylene, hydrogen, and methane is produced from natural gas feedstock in our plasma dissociation process. Storage of this HENG fuel at pressures up to 4000 psig is required for rapid vehicle refueling. Little information on the stability of acetylene mixtures at elevated pressures is presently available; therefore we have performed stability testing on gas mixtures that simulate our HENG fuel. This report describes the stability testing of binary gas mixtures of acetylene and methane containing up to 10%(v) acetylene, and a ternary gas mixture of 4%(v) acetylene, 20%(v) hydrogen, and 76%(v) methane, at pressures up to 3600 psig and temperatures up to 200 °C. The mixtures tested were found to be stable to rapid spontaneous decomposition at all test conditions; however, some degree of hydrogenation of acetylene to ethylene may have occurred in an intermediate mixture of acetylene and hydrogen while preparing the highest pressure ternary test mixture.     

Ethylene dimerization over a model Sn/Pt(111) catalyst

The dimerization reaction of ethylene was studied over Pt(111) and (3×3)R30°-Sn/ Pt(111) model catalysts at moderate pressures (20–100 Torr). The catalyst surfaces were prepared and characterized in a UHV surface analysis system and moderate pressure catalytic reactions were conducted with an attached batch reactor. The overall catalytic activity of the (3×3)R30°-Sn/Pt(111) surface alloy for C₄ products was slightly higher than that at Pt(111). In addition to the dimerization reaction, hydrogenolysis of ethylene to propane and methane was also observed, with the (3×3)R30°-Sn/Pt(111) surface alloy less active than Pt(111). Among the C₄ products, butenes andn-butane were the major components. Carbon buildup was observed to be significant above 500 K with the (3×3)R30°-Sn/Pt(111) surface alloy much more resistant than Pt(111). The dimerization of ethylene was not eliminated by the presence of surface carbonaceous deposits and even at significant surface coverages of carbon the model catalysts exhibited significant activities. The results are discussed in terms of the surface chemistry of ethylene and the previously reported catalytic reactions of acetylene trimerization andn-butane hydrogenolysis at these surfaces.