A COMPARISON OF THE SOFTENING POINTS OF SOME FOREIGN AND AMERICAN PYROMETRIC CONES1

This paper is a report of results obtained from a study of the softening points of pyrometric cones as made in England, France, Germany, and America. The results are briefly discussed and are also shown photographically so that interested readers can best obtain the specific information they desire from a study of these photographs. The data obtained further indicate that the temperature at which the cones most used in the trade (Nos. 1 to 20) soften can be determined with an accuracy of ±15°C in laboratory kilns of the gas-fired type, provided good pyrometric equipment is used and reasonable precautions are taken to maintain definite rates of heating. Errors of as much as ±25° can be expected in the determination of temperatures at which cones less refractory than No. 1 or more refractory than No. 20 soften. In the case of more refractory cones this is due principally to the difficulty of maintaining definite rates of heating while, in the case of the less refractory cones Nos. 022 to 01 inclusive, inaccuracies can be attributed both to difficulty of maintaining definite heating rates and to the sensitiveness of the softening behavior of the cones to furnace atmospheres. This is particularly true of the “red series” (cones 010 to 01) the softening points of which are materially affected by changes of a few per cent in the CO₂ and SO₂ content of furnace gases.     

THE OXIDATION OF CERAMIC WARES DURING FIRING.—I. SOME REACTIONS OF A WELL KNOWN FIRE CLAY1

After a review of the literature, a chemical laboratory study is made of the gases evolved on heating a lower Kittanning fire clay at various rates to various temperatures in a current of pure oxygen. The rates of evolution of CO₂, SO₂, and SO₃ are determined under varying conditions. Determinations of the remaining sulphur in the clay after heating are made. Possibilities as to the chemical mechanism of sulphur evolution are suggested. Plans for continuation of the work are outlined.     

TEMPERATURE MEASURING CONES *

A series of pyrometric cones that measure temperature independent of the rate of heating has been developed. These cones are mixtures of inorganic salts and melt congruently. Melting-point data are presented for the three binary systems MgSO₄-Li₂SO₄, K₂SO₄-KBr, and Na₂SO₄-NaBr.     

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.     

Effect of preparation conditions on the structure and catalytic activity of carbon-supported platinum for the electrooxidation of methanol

Carbon-supported platinum catalysts (Pt/C) were prepared by treatment of PtO₂/C under different conditions: (a) heating at 380°C in air, argon and hydrogen; (b) electrochemical reduction in H₂SO₄; and (c) reduction with NaBH₄. The effect of the preparation conditions on the structure and the catalytic activity of the catalysts for the electrooxidation of CH₃OH in acid media was studied. The highest activity was achieved for the catalyst treated in air. The activity is determined by the crystal faces exposed at the particle surface as well as particle size and the partial oxidation of the carbon support.     

Burning and nodulization process of clinker in the rotary kiln as viewed from the fine textures of the constituent minerals

Portland cement clinkers from the rotary kiln vary with their grain size in both chemical compositions and microscopic textures, according to the wide variation in the burning and nodulization environment in the kiln. The dense interior of large clinker nodules, first formed at high heating rates on and near the surface of the moving raw mix mass, is enriched with K₂O and SO₃ and made up from coarse-grained components of the raw mix. The alite crystals consist mostly of the M₃ phase with inclusions in the core. By contrast, the porous exterior, formed inside the mass at lower heating rates and firing temperatures, is less in K₂O and SO₃ content and made up from fine-grained components of the raw mix. The alite crystals are generally zoned with M₁ occurring in the core. Clinker nodules of medium size, similar in both the chemical composition and the fine textures of alite, are formed concurrently with the exterior of large nodules. Fine clinker nodules come from the core of the mass where the radial motion is stagnant and are formed, due to the large temperature gradient in the mass, at low heating rates and firing temperatures. Dust components comprise, besides small fragments of clinkers, separate alite and belite grains in quantity, indicating that they are separated mostly in the quenching cooler from the porous surface layers of the large clinker nodules. K₂O and SO₃, as well as the fine textures of alite, are useful as an indicator of the progress of firing and nodulization in the kiln.     

Verfahrenstechnische und wirtschaftliche Aspekte der Verarbeitung verdünnter SO2-Gase zu Schwefelsäure

Chemical engineering and economic aspects of converting dilute SO₂ gases into sulphuric acid. In the contact process for production of concentrated sulphuric acid the lowest limit for the autothermal processing of dilute SO₂ gases lies at around 2 vol.-% SO₂ provided that a pre-drying concentrating system is in use. Yet more dilute SO₂ gases can be processed by Ciba Geigy's nitrogen oxide/sulphuric acid process – a modern version of the well-known lead chamber process – which is already producing 70 to 75% H₂SO₄ from molybdenum disulfide roasting waste gases of ca. 1 vol.-% SO₂ on an industrial scale. The paper considers not only the specific boundary conditions, and chemical engineering characteristics of the two fundamentally different processes but considers above all the economics of processing low-concentration SO₂ gases for sulphuric acid.     

Reduction of phosphogypsum for SO2 production: Insights into the release characteristics of SO2 following the solid–solid reaction of CaS and CaSO4 under different atmospheres

Phosphogypsum (PG) severely pollutes the environment and is difficult to recycle. PG is primarily composed of CaSO₄ · 2H₂O. In this study, the characteristics of SO₂ released from the solid–solid reaction between calcium sulphide (CaS) and CaSO₄ were thoroughly investigated using thermodynamic calculations. Experiments were performed by tuning the molar ratio of CaS to CaSO₄, reaction atmosphere (S, CH₄, N₂, and air), and the heating rate. As shown by the phase diagram, high reaction temperatures favour CaO stability, and the corresponding maximum SO₂ equilibrium partial pressure increases. The total SO₂ production significantly increased with increasing molar ratio and slightly increased when the ratio exceeded 1:3. The SO₂ productions were ranked from highest to lowest as follows: S, CH₄, N₂, CO, and air. The total SO₂ production decreased with increasing heating rate. For the reaction between CaS and CaSO₄, a higher molar ratio of CaS to CaSO₄ no less than 1:3, both S and CH₄ reductive atmospheres, and a lower heating rate (2°C/min) favour the total SO₂ emission.     

A STUDY OF PROCESSES THAT GOVERN THE MAINTENANCE OF AEROSOLS IN THE MARINE BOUNDARY LAYER

We systematically evaluate the relative influence of sources and sinks of particles in the remote marine boundary layer (MBL) to elucidate the principal factors that govern MBL aerosol behavior. Processes considered include: (1) surface flux of dimethyl sulfide (DMS); (2) gas-phase oxidation of DMS to SO₂; (3) gas-phase oxidation of SO₂ to H₂SO₄; (4) mass transfer of SO₂ and H₂SO₄ to pre-existing particles; (5) homogenous nucleation of H₂SO₄/H₂O; (6) entrainment of air from the free troposphere; (7) deposition to the sea surface; (8) cycling of air through clouds and rain scavenging; (9) oxidation of SO₂ in sea salt aerosols and cloud droplets; and (10) sea-salt particle production at sea surface. The average aerosol number concentration is found to be quite sensitive to the rate of entrainment of aerosol-containing air from the free troposphere. The path that leads to the greatest accumulation of non-sea-salt (nss) sulfate involves SO₂ (rather than H₂SO₄) absorption into existing particles. Because of scavenging of SO₂ and H₂SO₄ by sea-salt aerosol, a considerable fraction of nss-sulfate is internally mixed with sea-salt aerosol. Under the conditions assumed in this study, MBL aerosol number concentration is dominated by free tropospheric aerosol under virtually all conditions, 89% in the base case, and even 69% at a 17 m s^-1 wind speed. Aerosol mass, on the other hand, is dominated by sea-salt particles, 62% in the base case and 98% at a wind speed of 17 m s^-1. Evaporation of cloud droplets provides 4.6% of the particle number in the base case, but 28% of the particle mass. At the high nucleation rate case considered here, there is notably little change in the overall contributions to aerosol number and mass from the base case; only about 5% of the total particle number is provided by nucleation events. Variation in precipitation frequency also has only a minor effect on the overall contributions. One concludes that the MBL aerosol is remarkably robust in the face of ever-changing conditions. Free tropospheric aerosol entrainment tends to sustain particle number concentrations, and sea-salt emissions maintain most of the aerosol mass. Cloud processing, while not a major contributor to aerosol number, does provide, except under high wind conditions, the order of 20% of the aerosol mass. Although nucleation occurs only infrequently and does not contribute appreciably to long-term average aerosol number or mass, nucleation is, nonetheless, the mechanism that replenishes aerosol number in brief, intense episodes when aerosol surface area levels are substantially reduced by precipitation.     

Analysis of dynamic CO2 capture over 13X zeolite monoliths in the presence of SOx,NOx and humidity

In this investigation, the CO₂ capture performances of zeolite 13X monoliths with 600 and 800 cells per square inch (cpsi) in the presence of SO₂/NO impurities under dry and humid conditions were evaluated and compared with that of 13X beads. Dynamic breakthrough tests demonstrated a drastic reduction in CO₂ capture capacity and deterioration of kinetics under dry-clean conditions, whereas, upon switching the feed from a clean gas to contaminated gas which contained SO₂ and NO, different adsorption performance was observed. Specifically, in dry-contaminated mode, the adsorbents retained their capture capacities with comparable kinetics to that of dry-clean feed conditions, however, in humid-contaminated mode, the adsorbents experienced improved CO₂ uptake and CO₂/N₂ selectivity, albeit at the expense of deteriorated kinetics. These findings indicate that the presence of SO₂ and NO contaminants, especially SO₂ contaminants, lead to dramatic changes in the adsorption performance of zeolite 13X monoliths, indicating the importance of evaluating adsorbent materials under realistic conditions.     

XPS evidence for molybdenum nitride formation in ZSM-5

Microwave plasma-assisted catalytic reduction of SO₂ by CO was studied over four catalysts. The activities of the four catalysts under microwave plasma decreased in the order of CoO/γ-Al₂O₃>>SnO₂> copper wires > iron wires, which was consistent with the results under conventional heating. By comparing the activity of CoO/γ-Al₂O₃ catalyst in the microwave plasma mode with that in the conventional mode, it is demonstrated that the temperature at which the full SO₂ conversion was obtained in the microwave plasma mode was about 200 °C lower than that under the conventional heating mode. Moreover, an increase of space velocity had little effect on SO₂ conversion and sulfur selectivity under microwave plasma; while under conventional heating mode, both SO₂ conversion and sulfur selectivity significantly decreased with an increase of space velocity.     

A decision support tool formulti‐pollutants reduction incement industry using analytic hierarchy process (AHP)

Several energy intensive industries are contributing to air pollution problems. Cement industry, as an example, is one of these significant sources of several air pollutants and these must be monitored and controlled. This paper deals with five air pollutants from cement plants and these are SO₂, NO_x, CO₂, dust, and volatile organic compounds (VOC). The purpose of this study is to evaluate several available technologies to control each pollutant. Analytic hierarchy process (AHP) technique is used as a decision support tool to find the best technology for each pollutant under multi‐criteria. These criteria are: cost, efficiency, lifetime or duration, and industry acceptability. The technique is illustrated in a case study from St. Marys Plant, located in St. Marys, Ontario, Canada. The results show that adsorption on activated coke technology will be recommended for SO₂ reduction. For NO_x reduction, the AHP suggests to apply selective non‐catalytic reduction (SNCR) technology based on the four criteria defined. Carbon capture and sequestration (CCS) using MEA technology is chosen for CO₂ reduction. For dust reduction, bag filters should be used and increase oxygen concentration at the kiln inlet is the selected technology for VOC reduction. The current paper covers the set of criteria weights considered typical for cement plants. The results presented here are illustrative and user defined weighting is required to make this study valuable for a specific group of users.     

Mixed-Gas Separation Properties of Phosphazene Polymer Membranes

Abstract

In this paper the mixed-gas separation properties of poly[bis(phenoxy)phosphazene] based polymers are reported. Transport behavior was determined using the variable volume technique. Test gases were run as mixed-gas pairs including SO₂/N₂, H₂S/CH₄, and CO₂/CH₄. Transport of these gases was found to be a sorption controlled process since these gases significantly deviated from the diffusion controlled permeability-size correlation. Membranes were prepared using solution casting techniques. Solvent evaporation rate during the casting and subsequent curing processes was controlled to provide a consistent membrane microstructure. We have observed that polyphosphazene membranes can effectively be used to separate acid gases from various waste streams in harsh, chemically aggressive environments.     

A H2SO4 Loaded Polybenzimidazole (PBI) Membrane for High Temperature PEMFC

Sulfuric acid loaded polybenzimidazole (PBI) membranes were prepared with loading levels up to 10.58 (acid molecule per repeat unit of PBI) and characterized with Fourier transform infrared spectroscopy. Ionic conductivity of the PBI–H₂SO₄ membrane was found greater than that of the PBI–H₃PO₄ membrane. Through plane conductivity of a PBI–H₂SO₄ membrane with loading level 9.65 was >0.2 S cm^–1 at 150 °C. However, the conductivity of PBI–H₂SO₄ membrane increased greatly with increasing relative humidity. Membrane electrode assemblies using PBI–H₂SO₄ membrane exhibited better power density performances with pre‐humidified H₂ and air than that with none‐humidified gases. Polymer electrolyte membrane fuel cells with PBI–H₂SO₄ membrane in a single cell fixture demonstrated a peak power density >0.35 W cm^–2 with H₂ and air.     

Development and reactivity tests of Ce-Zr-based Claus catalysts for coal gas cleanup

Claus reaction (2H₂S + SO₂ ↔ 3/nS_n + 2H₂O) was used to clean the gasified coal gas and the reactivity of several metal oxide-based catalysts on Claus reaction was investigated at various operating conditions. In order to convert H₂S contained in the gasified coal gas to elemental sulfur during Claus reaction, the catalysts having the high activity under the highly reducing condition with the moisture should be developed. CeO₂, ZrO₂, and Ce_1−xZr_xO₂ catalysts were prepared for Claus reaction and their reactivity changes due to the existence of the reducing gases and H₂O in the fuel gas was investigated in this study. The Ce-based catalysts shows that their activity was deteriorated by the reduction of the catalyst due to the reducing gases at higher than 220 °C. Meanwhile, the effect of the reducing gases on the catalytic activity was not considerable at low temperature. The activities of all three catalysts were degraded on the condition that the moisture existed in the test gas. Specifically, the Ce-based catalysts were remarkably deactivated by their sulfation. The Ce-Zr-based catalyst had a high catalytic activity when the reducing gases and the moisture co-existed in the simulated fuel gas. The deactivation of the Ce-Zr-based catalyst was not observed in this study. The lattice oxygen of the Ce-based catalyst was used for the oxidation of H₂S and the lattice oxygen vacancy on the catalyst was contributed to the reduction of SO₂. ZrO₂ added to the Ce-Zr-based catalyst improved the redox properties of the catalyst in Claus reaction by increasing the mobility of the lattice oxygen of CeO₂.     

Effect of different acids during the synthesis of urea-formaldehyde adhesives and the mechanical properties of medium-density fiberboards bonded with them

The characteristics of urea-formaldehyde (UF) adhesives condensed by catalysis with four different acids, namely formic (HCOOH), hydrochloric (HCl), phosphoric (H₃PO₄), and sulfuric (H₂SO₄) acids, under alkaline–acidic–alkaline conditions at a molar ratio F/U = 1.12 were studied. The thermal curing properties of UF adhesives catalyzed with acid were characterized by differential scanning calorimetry at 10 °C/min heating rate. The resin structure examined by ¹³C-NMR spectroscopy showed that the resin catalyzed with HCl had a lower proportion of methylol groups, resulting in a lower level of formaldehyde emission. It was interesting to note that HCOOH resulted in the best overall mechanical properties of the medium-density fiberboard (MDF) panels. The HCl catalyst resulted in the poorest performance, providing the lowest internal bond strength, modulus of elasticity, and thickness swelling, with the exception of the free formaldehyde content. The resin catalyzed with H₂SO₄ had the highest free formaldehyde and the highest formaldehyde emission. H₂SO₄ and H₃PO₄ resulted in MDF mechanical properties relatively lower than for HCOOH. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47256.     

Chemical reduction of sulphur dioxide to free sulphur with lignite and coal. 1. Steady-state reaction chemistry and interaction of volatile components

The chemical reduction of SO₂ with North Dakota lignite has been discovered to be a facile reaction which occurs at a relatively low temperature of 600–650 °C. Under optimum conditions, the reaction chemistry can be controlled to allow 85–90% conversion of SO₂ to free sulphur in a single-stage reaction. Major by-products of the reaction are CO₂, H₂O and a free-flowing ash. The high sulphur yield from this reaction exceeds the calculated thermodynamic gas phase equilibrium value of 66–70%. The higher experimental yield was found to be due in part to a catalysed re-equilibration of the gaseous products in the exit line. With lignite and low-rank coals, the mechanism of SO₂ reduction appears to involve reaction of hydrocarbons within the pores structure and thus allows complete conversion of the volatile matter with no tar formation. Volatilization and tar formation successfully compete with SO₂ reduction in bituminous coals under the same reaction conditions.     

Infrared spectroscopic study of thermal transformations of polyacrylonitrile in gas media

Conclusions Optical densities of the main absorption bands have been compared in the IR spectra of specimens of polyacrylonitrile fibre which have been treated in the presence of SO₂ by keeping them at constant temperature for 30 min and by rapid (15 min) elevation of temperature to higher values. It has been found that no fundamental differences are observed in the processes which take place in the fibre.From a comparison of the changes in optical density of the main absorption bands in the IR spectra of fibres which have been treated in air, in nitrogen, and in SO₂ under otherwise equal conditions, it follows that treatment in air is characterized mainly by oxidation reactions. Treatment in SO₂ is characterized by the generation of absorption bands at 1130 and 1680 cm^–1, which are assignable to sulfur-containing functional groups.The suggestion has been made that sulfur-containing bridge bonds are the main reason for the thermal stability of fibres treated in SO₂.It has been shown that stretching loads accelerate many reactions which take place in the fibre on heating in various media, and can therefore be used to accelerate the thermal stabilization process.Translated from Khimicheskie Volokna, No. 2, pp. 21–24, March–April, 1989.     

Dynamic adsorption on activated carbons of SO2 traces in air: I. Adsorption capacities

Sulphur dioxide is an atmospheric pollutant which, among numerous others, has to be eliminated by habitacle filters. Breakthrough curves of low concentration SO₂ streams through beds of activated carbons have been obtained. Two carbons were studied, an activated PAN fiber (CF) and a granulated activated carbon (CN) under SO₂ concentrations lower than 100 ppm. Carbon CN used ‘as received’ is able to trap SO₂ in air at concentrations as low as 2.5 ppm. At this concentration, the adsorption of SO₂ is essentially irreversible. The fraction of reversibly adsorbed SO₂ rapidly increases when SO₂ content in air increases from 2.5 to 100 ppm. As expected, the amounts of SO₂ adsorbed per gram of carbon are much smaller than in the case of high SO₂ contents in air (>1000 ppm). The presence of water in carbon micropores enhances both reversible and irreversible adsorption of SO₂. The reversibly adsorbed part is physisorbed while the irreversibly adsorbed part results in oxidation of SO₂ at the carbon surface. This oxidation was evidenced by TPD from carbon samples after adsorption. The mechanism of SO₂ adsorption is discussed in relation to the mechanisms proposed in literature for high SO₂ contents (>1000 ppm).     

Function of sulfur dioxide in the kinetic mechanism of oxidation of carbon

Retardation of the gasification reaction of carbon with oxygen by SO₂ was observed. Rates of oxidation were determined by thermal gravimetric analysis (TGA) of a nuclear graphite in the temperature range of 550–700°C, and of a coconut charcoal in the temperature range of 400–505°C. The oxidant gases were dry air containing 0–6% SO₂. Reduction of the rate by SO₂ varied with burn-off. Differential thermal analysis (DTA) was also applied to detect the retardation effect of SO₂. The technique of infrared internal reflection spectroscopy (IRS) was used to examine the surface species of reacted charcoal samples. Absorption bands were assigned to surface carbonyls, lactones, and a chemisorbed SO₂ in the form of sulfate. Chemisorption of SO₂ was attributed to cause the retardation of the oxidation reaction.