Optimising chlorine compression design with vapour phase nitrogen trichloride destruction

Nitrogen trichloride (NCl₃) is a by‐product of electrolytic chlorine manufacture, produced when the brine is contaminated with ammonia. A common treatment method is a thermal destruction process in which the NCl₃ is absorbed in a solvent (CHCl₃) using a distillation column with no liquid bottoms product. The chlorine gas is cooled through direct contact with liquid chlorine, which flashes and condenses the solvent and NCl₃ vapours. The condensate drains through trays to a reboiler in which the NCl₃ decomposes while the chlorine, solvent, NCl₃ solution boils. This process is well‐known and widely practiced but is known to experience catastrophic detonations. A vapour phase thermal decomposition of NCl₃ does occur, particularly when the heat added through compression is considered. The known data on this decomposition reaction have been collected and converted in a rate expression that allows for integration within an ASPENPLUS process model. Different options for the compressor, precooler, intercooler and liquefier operations are considered, and their impact on the compressor and liquefier duties is reported. A different approach to the design and operation for a chlorine compression/liquefaction train is presented and discussed. © 2013 Canadian Society for Chemical Engineering     

Inhibition of Methane–Oxygen Flames by Organophosphorus Compounds

For CH₄/O₂ flames doped with trimethyl phosphate (TMP), the flame structure is examined and the velocity of flame propagation is determined with the aim of studying the mechanism of inhibition of flames doped with organophosphorus compounds. The structure of a methane–oxygen flame doped with TMP stabilized on a flat burner at a pressure of 1 atm was studied. The dependence of flame propagation velocity on the concentration of TMP is measured using a Mache–Hebra burner to determine the effectiveness of a number of MP as a flame inhibitor. The mechanism of destruction of TMP in flames was used to model the flame structure and calculate the velocities of propagation of a methane–air flame as functions of the initial concentration of TMP. Calculation and experimental results are compared.     

Ignition and flame propagation in halocarbon-chlorine mixtures subject to UV radiation

Ignition and flame propagation in halocarbon (difluoromethane, 1,1-difluoroethane) mixtures with chlorine subject to UV radiation is investigated. Depending on initial conditions, the ignition of C₂F₂H₄+Cl₂ mixtures was observed at different distances from the irradiated end of the reaction cell. Data on flame propagation velocities are reported.Moscow. Novosibirsk. Translated from Fizika Goreniya i Vzryva, Vol. 29, No. 3, pp. 82–84, May–June, 1993.     

Factors of Surface and Volumetric Reactions in Glass Technology Processes

Various phenomena and processes in glass production are considered taking into account surface and volumetric factors. Kinetic analysis of reactions of K₂O – PbO – SiO₂ system glasses with a reducing flame and the molding process under isothermal and non-isothermal conditions is carried out. The data obtained can be used for analysis and calculations of technological processes.     

Kinetic study of the degradation of a new aromatic polyethersulfone

The degradation of a new thermoplastic polyethersulfone containing more than one SO₂ group in the repeating unit was carried out in both dynamic and isothermal heating conditions, under N₂ flow and in a static air atmosphere. The experiments indicated that the polymer degraded by initial random chain scission, followed by branching and crosslinking in an inert atmosphere and complete degradation in an oxidative environment. Apparent activation energy values associated with the first degradation stage were calculated and suggested that the first degradation stage was not affected by the experimental conditions. Results indicated for the investigated polymer a thermal stability higher than those of some previously investigated polyethersulfones containing only one SO₂ group in their repeating units.     

Existence of Critical Conditions of Chain Thermal Explosion in Flames

The paper discusses the possibility of the existence of two kinetic regimes and critical conditions of thermal chain explosion during wave propagation of flame over hydrogen–air and methane–air mixtures. It is shown that experimental data do not confirm the existence of t he two kinetic regimes. For fuel mixtures in sealed vessels under gravity, two combustion regimes exist that are not related to kinetic characteristics.     

Kinetic Regimes of Developed Chain Combustion

It is shown that chain thermal explosion is an inherent property of chain branching combustion that is due to simultaneous action of a chain avalanche and self-heating, which under certain conditions also becomes a progressively accelerating process. An attempt to deny this phenomenon is in fact equivalent to denying thermal explosion. This phenomenon is also observed in the absence of convection. The chain branching reaction mechanism is involved in all regimes of gas-phase combustion of hydrogen-containing compounds with oxygen. This results in inhibition or promotion of flame propagation, indicating the necessity of taking into account competition between reaction chain branching and termination.     

Propagation and quenching of premixed flames in narrow channels

The shape and propagation of unsteady premixed flames in narrow channels with adiabatic and isothermal walls are numerically investigated in the present study. The flame chemistry is modelled by an one-step overall reaction, which simulates the reaction of a stoichiometric acetylene-air mixture. The numerical results show that both ignition methods and thermal boundary conditions affect flame formation and its shape. The flame keeps a single tulip shape in the whole process of propagating through the channel if plane ignition is used and a single mushroom shape if spark ignition is used. For isothermal cold walls, the flame cannot keep a single tulip shape or mushroom shape all the time. Under plane ignition, a transition from a tulip-shaped flame to a mushroom-shaped flame occurs as flames propagate from one end of channel to the other. Under spark ignition, the process is just the contrary. It is also shown that the heat loss at the cold walls has a dual effect on the formation of a tulip-shaped flame. Flame propagation and quenching in narrow channels of different heights are analyzed systematically, and a criterion is proposed to judge the flame states of partial extinction and total extinction. It is called the criterion of flame propagation and quenching in narrow channels. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 3, pp. 27–36, May–June, 2006.     

Flame Propagation in a Variable–Section Channel with Gas Filtration

A one–dimensional unsteady model is proposed, which describes gas–flame propagation in a narrow variable–section channel with a gas counterflow and takes into account heat propagation over the channel walls. The case of the channel cross section changing slowly at a distance of the order of the thermal thickness of the combustion wave is considered. It is shown that various regimes of flame propagation are possible in such a system: a regime of flame propagation with a high velocity (of the order of the burning velocity of the flame), a regime of flame propagation with a low velocity as in the case of filtrational gas combustion in a porous medium, and an intermittent regime of combustion, where the flame has a high velocity in the wide section of the channel and a low velocity in the narrow section. A simple analytical model of flame oscillations in such a system is constructed. The possibility of these oscillations was predicted by numerical simulation results. The simple model considered is an attempt to take into account the large–scale inhomogeneity of the porous medium in simulation of filtrational combustion of gases.     

Promotion and inhibition of a hydrogen—oxygen flame by the addition of trimethyl phosphate

This paper gives results of numerical modeling of a laminar hydrogen—oxygen flame doped with trimethyl phosphate at various pressures and compositions of the combustible mixture. The calculations were performed using the PREMIX and CHEMKIN-II software packages. It was found that phosphorus-containing additives promoted the flame at subatmospheric pressures and inhibited it at atmospheric pressure. Kinetic analysis showed that catalytic recombination reactions were responsible for both phenomena. In the case of subatmospheric pressures, the promoting effect and its enhancement with increasing additive concentration were related to a flame temperature rise in the chemical-reaction zone due to catalysis of the recombination reactions by phosphorus-containing compounds. Increasing the additive concentration led to an increase in both the rate of the branching reaction H + O₂ = OH + O and the rate of the chain termination reaction, but the increase in branching reaction rate prevails, resulting in an increase in the flame velocity. In the case of atmospheric-pressure flames, where the reaction-zone temperature is close to the adiabatic equilibrium value, the additive led to an increase in the rate of decay of active flame species and, hence, to a decrease in the flame propagation velocity with increasing additive concentration. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 5, pp. 3–13, September–October, 2006.     

Deterioration Mode of Barium-Containing NOx Storage Catalyst

Barium-containing NO _x storage catalyst showed serious deactivation under thermal exposure at high temperatures. To elucidate the thermal deterioration of the NO _x storage catalyst, four types of model catalyst, Pt/Al₂O₃, Ba/Al₂O₃, Pt–Ba/Al₂O₃, and a physical mixture of Pt/Al₂O₃ + Ba/Al₂O₃ were prepared and their physicochemical properties such as BET, NO TPD, TGA/DSC, XRD, and XPS were evaluated while the thermal aging temperature was increased from 550 to 1050°C. The fresh Pt–Ba/Al₂O₃ showed a sorption capacity of 3.35 wt%/g-cat. but the aged one revealed a reduced capacity of 2.28 wt%/g-cat. corresponding to 68% of the fresh one. It was found that this reduced sorption capacity was directly related to the deterioration of the NO _x storage catalyst by thermal aging. The Ba on Ba/Al₂O₃ and Pt–Ba/Al₂O₃ catalysts began to interact with alumina to form Ba–Al solid alloy above 600°C and then transformed into stable BaAl₂O₄ having a spinel structure. However, no phase transition was observed in the Pt/Al₂O₃ catalyst having no barium component, even after aging at 1050°C.     

Relation between velocity of propagation of isothermal flame and parameters of CS2+O2 mixtures

Based on a review of four mechanisms for the chemical kinetics in the study of controlled combustion of CS₂+O₂ mixtures, expressions were derived, based on the stoichiometric composition, relating the velocity of propagation of a laminar flame and the temperature and pressure of the mixture. The expressions were in good agreement with the experimental data.Moscow. Translated from Fizika Goreniya i Vzryva, Vol. 27, No. 6, pp. 60–62, November–December, 1991.     

Hydrothermal synthesis and crystal structure of a novel cyanide-bridged double helical copper(I) coordination polymer [Cu3(CN)3(phen)]n

Hydrothermal reaction of CuCN, K₃[Fe(CN)₆] and 1,10-phenanthroline affords a novel cyanide-bridged copper(I) coordination polymer [Cu₃(CN)₃(phen)]_n (1). The complex displays an interesting one-dimensional neutral double helical framework with (phen)Cu–CN– side-arms as interchain bridges. The double helical chains are close packed in a parallel fashion, and the phen ligands stack in an interpenetrating mode, which leads to π–π interactions between parallel phen planes. The thermal stability and fluorescent property have also been investigated.     

Self-propagating chain combustion with formation of ultradispersed powders

We have investigated the possibility of realizing the self-propagating combustion regime for a gaseous mixture of SiH₄–NH₃–O₂ and SiH₄-2 with an oxygen content of 0–2%. Calculation of the equilibrium composition indicates the possibility that the target products Si and Si₃N₄ are formed. We have established experimentally that propagation of the chemical reaction front in the self-sustaining regime with formation of the above-indicated products occurs only in the presence of oxygen. We show that chemical induction, leading to consumption of up to 60% of the initial monosilane, is a chain reaction.Institute of Structural Macrokinetics, Russian Academy of Sciences, Chernogolovka 142432. Translated from Fizika Goreniya i Vzryva, Vol. 30, No. 4, pp. 85–91, July–August, 1994.     

Role of atomic hydrogen diffusion in a hydrogen flame

A numerical modeling study of the propagation of a laminar flat homogeneous gas flame has shown that in a hydrogen-air flame, a rapid increase in the concentration of OH radicals begins in the range of low temperatures and the concentration profile has two maxima. The first maximum in the low-temperature region of the front is related to the diffusion of H atoms, formation of HO₂ radicals, and the quadratic branching reaction H + HO₂ → OH + OH. The second maximum in the OH concentration profile is due to the classical high-temperature branching reactions H + O₂ → OH + O and O + H₂ → OH + H. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 2, pp. 3–9, March–April, 2007.     

Stereoregular Polysiloxanes via Ring-Opening Polymerization, a Review

Although polysiloxanes are not ordinarily considered stereoregular, a few references describe ring-opening polymerizations of cyciosiloxanes that can produce polymers enriched in stereoregularity. Most are made from the cis-isomers of unsymmetrically substituted strained cyclosiloxanes by methods where ring–chain and chain–chain equilibria are suppressed. The monomers insert randomly at the reactive chain ends with equal probabilities of forming new meso (m) or raceme (r) siloxane links while preserving the stereoconfiguration of the original monomer. The resulting polysiloxanes are enriched in isotactic configurations but are limited in their run lengths by the new randomly configured siloxane links formed between the original monomer units. One citation, however, describes a ring–chain equilibrium where the isotactic conformation was the preferred conformation. Another illustrates the profound influence of stereoregularity on the mechanical properties of a silicone elastomer.     

Investigation of concentration limits of flame propagation in ammonia-based gas mixtures

The concentration limits of flame propagation inNH ₃-O ₂,NH ₃-H ₂-O ₂,NH ₃-O ₂-N ₂,and NH ₃-H ₂-O ₂-N ₂ mixtures at temperatures of up to70°C and pressures of up to1.0 MPa were studied experimentally. The lower concentration limit of propagation of ammonia flame in oxygen decreases significantly at elevated temperature and pressure, the effect of temperature being stronger than for organic combustible substances. It is shown that the Le Chatelier rule for the limits ofN ₂-NH ₃-O ₂ mixtures is satisfied with sufficient accuracy.Translated from Fizika Goreniya i Vzryva, Vol. 32, No. 5, pp. 3–7, September–October, 1996.     

Existence of stationary self-maintained combustion of porous and channel propellants

It is shown theoretically that in channel and porous propellants there exists a stationary self-maintained regime of propagation of a convective flame front. The existence of a spherical structure of the combustion zone results in the appearance of a qualitatively new propagation regime — subsonic relative to the condensed phase and supersonic relative to the gas phase ahead of the front. The final states of the reaction products lie on the branch of the detonation adiabat corresponding to weak detonation. It is shown that in a propellant with constant average density and thermal conductivity the velocity of the wave is variable and can be regulated by adjusting the size of the individual channels.Moscow. Translated from Fizika Goreniya i Vzryva, Vol. 27, No. 4, pp. 18–24, July–August, 1991.     

The structure of the [Et2In(μ,λ-O2C)–C6H4–2–NH2]∞ coordination polymer: Competition of intramolecular hydrogen bonding with metal–ligand coordination preferences in determining the molecular and crystal structure

The X-ray structure analysis of [Et₂In(μ,λ-O₂C)–C₆H₄–2–NH₂]_n (1) reveals an extended one-dimensional chain comprised of an array of five-coordinate indium centers. The chain unit repeated along two-fold screw axis is defined by the diethylindium moiety chelated asymmetrically by the carboxylate group with one of the two carboxylate oxygens acting as bridge to the next indium center in the chain. The NH₂ group does not participate in the coordination of the metal center but is involved in an intermolecular hydrogen bond.