Basic Gases Research Articles

Emission characteristics and control efficiency of acidic and basic gases and aerosols from packed towers

Large amount of acidic liquids, such as H 2 SO 4 , HF, HCl and HNO 3 , and basic NH 3 liquid are used in high-tech industries in cleaning and etching processes in the Hsinchu Science-Based Industrial Park in Taiwan. The industries use packed towers (or scrubbers) to control emission of these inorganic pollutants, in which acidic gases but not particles are regulated by the Taiwan EPA’s strict emission standard for semiconductor industry. To understand whether the emission standard is met and to investigate the emission rates, emission profiles, emission factors, and control efficiencies of various gaseous/aerosol species, measurement of pollutants before and after the packed towers was conducted using a sensitive porous metal sampler during January 2001 to February 2003. Results show that the pollutants are mainly in the gaseous phase, and the control efficiency of pollutants is low and variable when the inlet concentration is low. In addition to the control efficiency data, emission factors before the control device for various gas and particle species have also been developed for estimating the emission rates.

Integrating nephelometer measurements for the airborne fine particulate matter (PM 2.5) mass concentrations

This work describes the application of integrating nephelometer measurements for the determination of airborne fine particulate matter (PM 2.5) mass concentrations. In response to over 150 complaints (spanning a period of 20 years) from local citizens of irritant fogs and pungent odors, the North Carolina Division of Air Quality conducted a monitoring program, in collaboration with the Washington Regional Air Quality Office and PCS Phosphate, Inc., to characterize air quality in the Pamlico River airshed of eastern North Carolina. The continuous monitoring from 1 May through 31 October 2000 at four sites, involved collection of air samples and subsequent quantification for reactive acidic and basic gases, aerosols and fine particulate matter (PM 2.5) using a 7-day Annular Denuder System (ADS). Additionally, the airborne concentration of the fine particulate matter (PM 2.5) was concurrently (to the ADS) monitored using a tapered element oscillating micro-balance (TEOM). Relevant meteorological data were obtained from conventional sensors installed at each sampling site. An integrating nephelometer was used for the regional visibility measurements. An integrating nephelometer was used to measure light scattering (a surrogate for visibility) continuously for 24-h per day over a 6-month period at the four sites. A linear relationship has been found for the nephelometer (Beta scat) measurements and mass data (PM 2.5) obtained both from the TEOM and ADS. The calculated correlation coefficient results between nephelometer and ADS and nephelometer and TEOM are satisfactory and close to one. This indicates that in this region, the nephelometer measurements have the potential to be a surrogate for the determination of regional airborne fine particle (PM 2.5) mass concentrations. The ratios for each of the four sampling sites using 24-h averages of nephelometer data and PM 2.5 concentrations from the ADS units and the TEOM gave an average ratio of 0.32±0.02. This value implies that the physical properties of the fine particulate (PM 2.5) mass at each of the four sites were similar. The precision of nephelometer measurements (as Beta scat) has been demonstrated by collocating three nepehlometers for continuous 24-h measurements for 10 days at one of the four sampling sites. Percent difference among the three instruments ranged from 0.42% to 4.41% and the inter-correlation produced R 2 values of 0.9833, 0.9874 and 0.9943, respectively. This study results demonstrates that the integrating nephelometer is a simple, inexpensive and a sensitive instrument that can be used in field studies. Furthermore, data on both light scattering (for visibility) and fine particulate (PM 2.5) mass concentrations can be obtained reliably and importantly in a time effective manner for a rapid assessment of fine particle (PM 2.5) air pollution.

Acidic and basic gas adsorption properties in composites of layered double hydroxide/aluminosilicate xerogels

Composites of Mg–Al LDH and ASG were prepared by various methods, and their acidic and basic gas adsorption properties were investigated by CO 2 and NH 3 gas TPD. Of the various preparation methods, composite samples prepared by precipitation of LDH in an ASG sol solution showed a superior adsorption for both acidic and basic gases. The adsorption was higher than the arithmetic mean of the LDH, which mainly adsorbs acidic gas and the ASG, which mainly adsorbs basic gas. These composites could be good candidates as adsorbents and deodorants for the simultaneous uptake of acidic and basic adsorbates, i.e. materials with dual function adsorption properties.

Design and Testing of a Personal Porous-Metal Denuder

A personal denuder made of porous-metal disc has been designed and tested. The entire casing and substrate support are made of Teflon, and the sampling flow rate is 2 L/min. The sampler consists of a two-stage cascade impactor (having cut-off aerodynamic diameters of 9.5 and 2.0 μm, respectively) to collect liquid particles and two porous-metal discs (diameter: 2.54 cm; pore size: 100 μm; thickness: 0.317 cm) to collect basic and acidic gases, respectively. The denuder was tested for gas collection efficiency and capacity at a gas concentration of two times the permissible exposure limit (PEL, promulgated by Taiwan Institute of Occupational Safety and Health (IOSH)), with relative humidity (RH) of 80 ± 5% and temperature of 30 ± 3°C. The test data indicate that the gas collection efficiency is high, and the capacity is sufficient for the acidic/basic gas sampling in the workplace. Using 5% (w/v, g/mL) sodium carbonate/1% (w/v) glycerol coating on the porous-metal disc, the collection efficiency is 91.2 ± 0.26% (average ± standard deviation), 95.08 ± 0.06% and 100 ± 0.04%, and the capacity is 4.47, 7.2, and 2.5 mg for HNO 3 , HCl and HF, respectively. The collection efficiency for NH 3 for the porous-metal disc with 4% (w/v) citric acid coating is 96.39 ± 0.13%, and the capacity is 33.6 mg.

Development of an automated, simultaneous and continuous measurement system by using a diffusion scrubber coupled to ion chromatography for monitoring trace acidic and basic gases (HCl, HNO3, SO2 and NH3) in the atmosphere

An automated simultaneous measurement system for monitoring acidic and basic gases such as HCl, HNO3, SO2 and NH3 in the atmosphere was developed by using a diffusion scrubber coupled to an ion chromatograph (DS-IC system). Acidic and basic gases were effectively collected by the diffusion scrubber which consisted of a hydrophobic porous polytetrafluoroethylene (PTFE) tube disposed concentrically within a Pyrex-glass tube. De-ionized water was used as a scrubbing solution for collecting the acidic and basic gases such as HCl, HNO3, SO2 and NH3, which were dissociated to ion species (Cl–, NO3–, SO32–, SO42– and NH4+, respectively). After the collection of gases, the total anions and cations in the scrubbing solution were preconcentrated in anion and cation concentrator columns connected in series. All the analyte ions were separated and determined by ion chromatography. All operations relating to the air sampling, the preconcentration and the ion chromatographic analysis were controlled by a sequencer. Automated simultaneous continuous measurement could be performed at 60 min intervals. The collection efficiencies of the acidic and basic gases were higher than 97% at an air flow rate of 1 l min–1. The detection limits (3ς of the blank value) of HCl, HNO3, SO2 and NH3 were less than 0.01 ppbv for a 52 l of air sampling volume. The interference from co-existing NO2 for measuring HNO3 was negligible. The concentrations of SO2 measured by this automated measurement (DS-IC) system showed good agreement with those obtained with a pulse-fluorescence meter.

Effect of surface chemistry on gas-phase adsorption by activated carbon prepared from oil-palm stone with pre-impregnation

Effects of surface chemistry (acidity or basicity) on gas-phase adsorption (NO2 or NH3) by activated carbons prepared from oil-palm stones pre-impregnated with various solutions (ZnCl2, H3PO4 and KOH) were studied in this paper. Textural and chemical characterizations of these activated carbons were carried out. High solid density and hardness, fairly high BET surface area and predominant microporosity (as shown in the pore size distributions) of the oil-palm-stone activated carbons suggested their potential applications in gas-adsorbing processes. Chemical characterization showed that impregnation affected significantly the surface chemistry, i.e. surface functional group. The samples pre-treated with H3PO4 presented acidic groups such as phenols and carboxylic acids, whereas those with KOH impregnation showed basic groups likely to be pyrones (cyclic ketone) and other keto-derivatives of pyran. From adsorption tests of NO2 and NH3, it was found that the activated carbons pre-treated with KOH could adsorb more NO2 but less NH3 than those pre-treated with H3PO4, even though they had almost identical BET surface areas. This indicated that the adsorptive capacity of the activated carbon was not only determined by its textural characteristics, but also related to the surface chemistry, which was relevant to the type of impregnating agent, concentration of impregnation solution and activation temperature. In general, the activated carbons prepared from oil-palm stones impregnated with H3PO4 and KOH are suitable for adsorbing basic (NH3) and acidic (NO2) gases, respectively.

A Continuous Monitoring System for Strong Acidity in Aerosols

Inhalation of acid aerosols is believed to be a major source of respiratory ailments. A fully automated instrument that can measure acidity levels meaningful to real situations is described. A 5−10 L/min sampling rate is used. First, coarse particles are removed by a cyclone, followed by the removal of acid and basic gases with a parallel plate wet denuder. Aerosols are then collected with a vapor condensation aerosol collection system (VCACS). The VCACS provides an aqueous liquid effluent in which all soluble constituents are present in the dissolved form and the undissolved material remains suspended. The effluent is concentrated sequentially on a cation exchanger and an anion exchanger, which respectively constitute the injection loops of cation and anion analysis subsystems. In the first system, non-H+-cations (primarily NH4+) are conductometrically determined as the corresponding hydroxide by elution with a strong acid plug and conductivity suppression with a hydroxide-form anion exchanger. In the se...

Fabrication of a gas sensor using pentacene thin films as a detector

AbstractHighly sensitive gas sensors for both acidic and basic gases were fabricated based on conducting thin films of polyacene compounds. Gas sensors formed with pentacene thin films deposited on various kinds of substrates were found to exhibit high sensitivity in detecting subppm concentrations of NO2 or Cl2 by monitoring the conductivity of the thin film. Improvements in the conductance and duration period for detection were achieved by changing the shape of electrodes and substrate. The sensors with PEN thin films initially doped with iodine could detect ppm concentrations of ammonia gas, since iodine molecules were dedoped upon exposure to ammonia, causing the reduction of the conductivity.

Sensors for Acid-Base-Active Gases

AbstractThe theoretical background for potentiometric and conductometric (bulk and surface) sensors is briefly discussed with regard to the usual application, viz. the detection of redox-active gases, and the importance of understanding chemical diffusion is stressed in this context. It is then shown how the analogous concept applied to acid-base interactions leads to powerful possibilities to measure partial pressures of acid-base active gases such as CO2, NH3 and H2O. Two examples of novel sensor principles are discussed: i) The response of the surface ionic conductivity of AgCl or CaF2 upon changes of partial pressures of (Lewis) basic or acid gases can be used to sense NH3 and BF3. ii) In the major part of the paper it is shown how the deliberate use of overall acid-base cell reactions in potentiometric arrangements leads to a fast and precise CO2-sensor. For this purpose, open reference electrodes based on Na2Ti6O13 or Na2SnO3 have been constructed. Owing to the criteria developed in the text the whole cell can be exposed to a CO2 and O2 containing atmosphere without the necessity of sealing. Detailed results are given.

Studies on Harmful Gas Adsorbents Containing Chiefly Gas Adsorption Resins.

Two kinds of harmful gas (such as malodorous gas) adsorbent containing gas adsorption resins were developed. One is a polystyrene polyamine metal (Co) chelating resin capable of adsorbing more than 90% of sulfur-containing (C2H5SH and H2S etc.) or acidic gases (SOx, NOx and HCl etc.) within 60 minutes. The other is a polystyrene polysulfonic acid resin that can adsorb more than 90% of basic gases such as NH3 within 60 minutes. Thus, both resins have large gas adsorption capacity and their stability is good. The harmful gas adsorbents obtained by mixing both resins with active charcoal can adsorb a wide range of harmful gases. Both resins are very economical since they can be regenerated. The practical application of these resins are as follows. (1) Both can be used to remove specific harmful gases. (2) The harmful gas adsorbent is placed in a gas circulating device. (3) The gas adsorption sheet comprising of many corrugated layers of gas adsorbent can be hung from a wall. It should thus be possible to use these resins in many places such as lavatories, childcare rooms, hospitals, building and cars, factories and tunnels and be used to prevent corrosion of precision instruments.

Transducer mechanisms for optical biosensors. Part 1: The chemistry of transduction

The first stage of optical biosensor transduction involves a chemical interaction between the analyte and an indicator phase to produce an optically detectable signal. This stage is critical because it determines stability, selectivity and sensitivity as well as establishing the wavelengths required for the optical measurement. Several types of analyte/ indicator interaction are possible. Direct indicators such as those used in optical pH sensors are in equilibrium with the analyte in the sample. They may be used for continuous measurements and can be coupled to the sensing of other analytes such as acidic and basic gases like carbon dioxide and ammonia. Integrating reagents react irreversibly with analyte and require that the rate of product formation be measured. Sensors based on catalysis by an immobilised enzyme involve a steady-state measurement of optically detectable substrate or product. High selectivity can be achieved using antibodies as reagents and basing sensing on competitive binding; however, response time is a serious problem. A variety of methods have been employed to immobilise the indicator phase including adsorption on solid substrates, covalent bonding to a substrate and confinement by membranes permeable to analyte but not to indicator.

Characterization and reconstruction of historical London, England, acidic aerosol concentrations.

Several past studies of the historical London air pollution record have reported an association between daily mortality and British Smoke levels. However, this pollution index does not give direct information on particulate mass or its chemical composition. A more specific particulate matter index, aerosol acidity, was measured at a site in central London, and daily data are available for the period 1963-1972. British Smoke and SO2 were also measured at the same site. Also, meteorological parameters were routinely measured at a nearby British Meteorological Office. Thus, daily fluctuation of the acidic aerosols was characterized in terms of other environmental parameters. Each of the other parameters analyzed seems necessary, but not sufficient to explain a high level of acidic aerosol. Overall, about half of the variance of log-transformed daily fluctuations of acidic aerosols can be explained by a combination of parameters including SO2 and British Smoke concentrations, temperature, ventilation by wind, and humidity. The rest of the variance cannot be explained by the parameters included in this analysis. Potential factors responsible for this unique variance would be variations in the availability of basic gases to cause neutralization and variation in the availability of catalytic metal salts. Because the acidic aerosol has a unique component of variation, it may be possible to distinguish health effects due to this specific pollutant from other available pollution indices or environmental factors.

Interfacial Effects of Plasma Treatment on Fiber Pull-Out

AbstractSurface modification of organic reinforcement fibers by exposure to certain plasmas appears to have considerable potential as a means for improving the performance of composites. Such treatments can change fiber surface properties, leaving the core of the fiber virtually unaffected so that the mechanical properties of the fibers remain unaltered. Previous studies [1–5] have shown that plasma treatment of polymeric fibers can modify surface energetics and that the acid/base characteristics of a fiber surface can be altered by exposure to plasmas of acidic or basic gases. Although several publications [6,7] have reported that the mechanical properties of composites reinforced with plasma-treated fibers are enhanced, there has been no direct evidence to show the impact of fiber surface plasma treatment on interfacial shear strength.

Reaction of microparticles by the diffusion of reactive gases through porous shells

A new experimental technique, single-particle electrodynamic balance (SPEB), was used to study the heterogeneous reaction between single acid droplets and basic gases. Experiments with phosphoric acid droplets and ammonia gas show that the droplet reaction dynamics are sequentially controlled by surface-phase, gas-phase diffusion-controlled, and porous-shell diffusion-controlled reactions. Gas-phase diffusion-controlled reactions terminate when ammonium phosphate crystallizes at the droplet surface, and porous-shell diffusion-controlled reactions become rate limiting. We derive a semiempirical model to describe the porous-shell diffusion-controlled reaction of acid droplets with surface layers of crystallized solids. The model is parametrized with an effective porous-shell diffusion coefficient to describe the transport of reactive gases through the porous shell. The model is compared to reaction data obtained from the SPEB for the reaction of phosphoric acid droplets layered with shells of ammonium phosphate. The characteristic pore radius of the porous shell is determined as a function of reaction condition.

Theoretical and experimental study of the removal of dust particles from flue gases using two-phase steam-water droplet mixtures

The removal of dust particles using two-phase steam-water droplet mixtures has been studied. Two-phase steam-water droplet jets obtained by the flashing expansion of subcooled water, through convergent/divergent nozzles, have been characterized. The water droplet sizes and velocities were measured through the use of stroboscopic photography and laser-doppler velocimetry, respectively. A theoretical model using one-dimensional mass, momentum, and energy balances together with the concept of a critical Weber number criterion was developed to predict water droplet sizes and velocities. The agreement between measurements and predictions was reasonable. A theoretical model for predicting dust collection efficiencies of a two-phase scrubber was developed. It was determined that dust collection efficiencies exceeding 99 pct for basic oxygen furnace flue gases could be obtained using a two-phase scrubber.

The photochemistry of a remote marine stratiform cloud

The coupled gas‐ and aqueous‐phase photochemistry of a stratiform cloud in a remote region of the marine atmosphere is investigated with a time‐dependent box model. Both scavenging of ambient acidic aerosols and gases as well as aqueous‐phase chemical reactions within droplets are found to be important sources of acidity to cloud water and can lead to pH levels in cloud water in the remote marine atmosphere well below 5.6. The major sources of acidity via aqueous‐phase chemical reactions are the generation of sulfuric acid from dissolved SO2 and the generation of formic acid from dissolved formaldehyde. In both cases, aqueous‐phase free radicals can play a significant role either directly by oxidizing dissolved SO2 and HCHO or indirectly by producing the aqueous‐phase oxidant H2O2. The rate of SO2 conversion to sulfuric acid is sensitive to a variety of parameters including the accommodation or sticking coefficient for SO2, H2O2, HO2, and OH, the liquid water content, and the ambient levels of SO2, HNO3, and other acidic or basic gases. Because high levels of SO2 tend to deplete cloud water of H2O2, the possibility exists that the pH of precipitation in polluted regions will respond nonlinearly to reduced SO2 emissions.

Methods and equipment for testing gas analyzers for the basic industrial gases

Methods and equipment for testing gas analyzers for the basic industrial gases

The sweetest cures

This is the age of innovation not only new ways of doing things but new ways of thinking. The versatility of many resources is being put to test as space and economy become determining factors. It is no longer easy to fit things or roles into old categories. Substances are synthesized to products unlike themselves, yet more important, new uses are found for old products. For example, fiber plants, such as cotton, become food plants. Garbage items are recycled and municipal wastes subjected to "pyrolysis a system of reducing refuse to basic chemicals, liquids, and gases which have commercial value" (7). And, now, the subject of this report is that an old and familiar food item becomes a medicine. The use of sugar in man's diet dates back to earliest times and its continuing popularity is ascertained by the per capita consumption of over one hundred pounds in at least ten countries in the world, namely (and in order of use), Ireland, Netherlands, Australia, United Kingdom, New Zealand, Denmark, Israel, Switzerland, United States, and Canada (8). In spite of such impressive figures, the humming bird has been, and still is, the best promotion agent the sugar industry has. There are 319 species of these "glittering fragments of the rainbow", and each day the individual bird locates and consumes half its body weight in sugar (12). Sugars are the simplest of organic foods. They exist in several forms, yet sucrose is the one of greatest significance in commerce and use. It is a disaccharide, known as granulated sugar and derived from sugar cane or sugar beets. Chemically, it is made up of one molecule of glucose and one molecule of fructose,

Mass filter studies of gases in a 90-liter getter-ion vacuum system

The basic residual gases present in a 90-liter titanium getter-ion vaccum system operating under different conditions are determined with the aid of a quadrupole-field mass filter. Mass spectra of gases in the system during successive temperature increases of molybdenum and tungsten filament heaters over a temperature range from 25°C to 1050°C for molybdenum and 25°C to 1250°C for tungsten are presented. Possible sources of the gases are discussed primarily in terms of outgassing characteristics of materials and interaction between gases and the surfaces on which they impinge. Fragments resulting from the introduction of solvents commonly used in cleaning vacuum hardware (acetone and isopropyl alcohol) are presented. Results show that major residual gases present in the getter-ion system are carbon monoxide, nitrogen, argon, hydrogen, methane, and water vapor, with their order of prominence variable depending upon conditions. The introduction of hot tungsten or molybdenum filament heaters does not alter the gas profile appreciably until their surface temperatures reach about 1000°C, at which point outgassing from surrounding surfaces becomes appreciable. Carbon dioxide, carbon, and a host of hydrocarbons then play increasingly important roles. When acetone and isopropyl alcohol are introduced into the vacuum system, they dissociate quite readily and completely into several smaller components, in particular CH +, CH 3 +, C 2H 3 +, C 2H 5 +, and C 3H 3 +.

276. Noise reduction in microwave tubes by getter-ion-pumping: N. W. W. Smith, Vacuum, 10, 106–109, 1960

The basic residual gases present in a 90-liter titanium getter-ion vaccum system operating under different conditions are determined with the aid of a quadrupole-field mass filter. Mass spectra of gases in the system during successive temperature increases of molybdenum and tungsten filament heaters over a temperature range from 25°C to 1050°C for molybdenum and 25°C to 1250°C for tungsten are presented. Possible sources of the gases are discussed primarily in terms of outgassing characteristics of materials and interaction between gases and the surfaces on which they impinge. Fragments resulting from the introduction of solvents commonly used in cleaning vacuum hardware (acetone and isopropyl alcohol) are presented. Results show that major residual gases present in the getter-ion system are carbon monoxide, nitrogen, argon, hydrogen, methane, and water vapor, with their order of prominence variable depending upon conditions. The introduction of hot tungsten or molybdenum filament heaters does not alter the gas profile appreciably until their surface temperatures reach about 1000°C, at which point outgassing from surrounding surfaces becomes appreciable. Carbon dioxide, carbon, and a host of hydrocarbons then play increasingly important roles. When acetone and isopropyl alcohol are introduced into the vacuum system, they dissociate quite readily and completely into several smaller components, in particular CH+, CH3+, C2H3+, C2H5+, and C3H3+.