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Disposable filtering facepiece respirators (FFRs) include a wide range of products that may be certified or non-certified. Many of these respirators are being produced with activated carbon claiming nuisance level organic vapor (OV) relief. OV includes a wide range of volatile organic compounds (VOCs) which have been linked to major and minor health discomfort such as headaches, upper extremity discomfort, nausea, respiratory irritation, asthma nervous system complications, hearing loss, cancer, and death. Common industries that have been identified that may expose employees to nuisance level OV, resulting in minor symptoms, include beautician salons, dry cleaning operations, and pesticide applications. FFRs with activated carbon (FFR-AC) may provide a more convenient alternative for reusable respirators which could also protect employees from OV exposure. This study investigated the adsorption capabilities of one certified respirator (3M) and two alternatively designed respirators (RZ Hunting Mask, Surgical Mask) with activated carbon filtering media. The three FFRs were tested to determine the 50% breakthrough time for two hydrocarbons and one non-carbon-based vapor. 50% breakthrough was chosen because we felt that reducing nuisance level exposures by half would still be protective. Non-certified respirators were exposed to 15 parts per million (ppm) and 50 ppm for all three vapors. Concentrations of 15 ppm and 50 ppm were standardized to achieve similar mass per time exposures across all contaminants and because these values represented the range of nuisance level exposure documented in literature. The 3M respirator was exposed to 15 and 50 ppm of acetone and ammonia, and perchloroethylene was evaluated at 50 ppm. Perchloroethylene was not evaluated at 15 ppm because breakthrough was longer than 8 hours. 3M respirators were also evaluated at 95% relative humidity using 50 ppm of acetone, ammonia, and perchloroethylene. The total number of trials was 43 (n=43). These contaminants and concentrations were chosen based on published data on occupational exposures. The non-certified respirators, (RZ Hunting Mask and Surgical Mask) , were ineffective for all vapors and offered less than 10 minutes of protection before 50% breakthrough occurred. Respirators performed poorly, when exposed to ammonia, with breakthrough less than 5 mins at 50 ppm and 10 minutes at 15 ppm. The 3M respirator had the longest breakthrough times for all trials. Acetone breakthrough occurred at 121 minutes for 50 ppm and 233 minutes at 15 ppm. Perchloroethylene took over 400 minutes to achieve 50% breakthrough at 50 ppm. When acetone at 50 ppm and perchloroethylene at 50 ppm were evaluated with 95% R.H. breakthrough times decreased to 39 and 144 minutes respectively, a nearly 70% decrease in time for both vapors. The results of this study show that non-certified respirators advertised as nuisance level relief may not offer protection for OV. Certified respirators show much more promise, but their performance is highly dependable upon the characteristics of the vapor and environment the respirators are being used in. Additional research is needed to increase our understanding of FFR-ACs performance under more conditions.

Many industrial processes handling organic solvents produce volatile organic compounds (VOCs). These VOCs not only cause environmental pollution, but also represent an economic loss. VOC removal and recovery have become a big issue that needs to be addressed. Traditional techniques for VOCs removal include carbon adsorption, condensation, and absorption, and none is efficient enough to meet every need. Membrane separation has emerged as an excellent alternative or complementary technology for VOC separation. Separation of VOCs from nitrogen by composite hollow fiber membranes is studied in this thesis. Microporous hollow fiber membranes were spun from polyvinylidene fluoride (PVDF) using the phase inversion method, and the hollow fibers were coated with a thin layer of poly(ether block amide) (PEBA), thereby forming composite membranes. PVDF was chosen as the substrate material because of its excellent thermal and chemical stabilities and good mechanical strength, and PEBA was selected as the active separating layer because of its good permselectivity and film forming properties. In PEBA polymer, the hard polyamide blocks provide high mechanical strength, and the soft polyether blocks provide flexibility and elasticity. This study is focused on the preparation and characterization of PEBA/PVDF composite hollow fiber membranes. The membranes were tested for the removal of representative VOCs including hexane, heptane and cyclohexane, which are the main components of gasoline, and dimethyl carbonate (DMC), ethanol, methanol, and methyl t-butyl ether (MTBE) that are the oxygenates and octane number enhancers of gasoline. The separation of gasoline vapor from nitrogen was also investigated. It was found that the PEBA/PVDF composite hollow fiber membranes are effective for the separation of hydrocarbon vapors from nitrogen. The effects of hollow fiber membrane preparation conditions on the membrane performance were studied, and the separation performance of the composite hollow fiber membranes at various operating conditions (e. g. feed concentration, operating temperature) was evaluated.

Many industrial processes handling organic solvents produce volatile organic compounds (VOCs). These VOCs not only cause environmental pollution, but also represent an economic loss. VOC removal and recovery have become a big issue that needs to be addressed. Traditional techniques for VOCs removal include carbon adsorption, condensation, and absorption, and none is efficient enough to meet every need. Membrane separation has emerged as an excellent alternative or complementary technology for VOC separation. Separation of VOCs from nitrogen by composite hollow fiber membranes is studied in this thesis. Microporous hollow fiber membranes were spun from polyvinylidene fluoride (PVDF) using the phase inversion method, and the hollow fibers were coated with a thin layer of poly(ether block amide) (PEBA), thereby forming composite membranes. PVDF was chosen as the substrate material because of its excellent thermal and chemical stabilities and good mechanical strength, and PEBA was selected as the active separating layer because of its good permselectivity and film forming properties. In PEBA polymer, the hard polyamide blocks provide high mechanical strength, and the soft polyether blocks provide flexibility and elasticity. This study is focused on the preparation and characterization of PEBA/PVDF composite hollow fiber membranes. The membranes were tested for the removal of representative VOCs including hexane, heptane and cyclohexane, which are the main components of gasoline, and dimethyl carbonate (DMC), ethanol, methanol, and methyl t-butyl ether (MTBE) that are the oxygenates and octane number enhancers of gasoline. The separation of gasoline vapor from nitrogen was also investigated. It was found that the PEBA/PVDF composite hollow fiber membranes are effective for the separation of hydrocarbon vapors from nitrogen. The effects of hollow fiber membrane preparation conditions on the membrane performance were studied, and the separation performance of the composite hollow fiber membranes at various operating conditions (e. g. feed concentration, operating temperature) was evaluated.

This study investigated the effects of temperature and humidity on the photocatalytic oxidation of volatile organic compound (VOCs) over titanium dioxide. Benzene, methyl tert-butyl ether (MTBE), perchloroethylene (PCE), and toluene were selected to investigate the influences of temperature and humidity on photocatalytic conversion. Among these four VOCs, benzene and MTBE were selected for the investigation of reaction pathways and kinetics. This work employed a self-designed annular packed-bed photocatalytic reactor to determine the conversion and reaction rates during photocatalytic degradation of VOCs. Degussa P-25 TiO2 was used as the photocatalyst and a 15 W near-UV lamp (350 nm) served as the light source. Benzene conversions increased with temperature below 160 ºC, but decreased above 160 ºC. Moreover, the conversions of MTBE increased with temperature from 30 to 120 ºC, and the thermocatalytic reaction began above 120 ºC. The conversions of PCE decreased as the temperature increased from 120 to 200 ºC. Toluene conversions almost remained constant at 100~200 ºC. Based on the gas-solid catalytic reaction theory, raising the reaction temperature could promote the chemical reaction rate and reduce reactant adsorption on TiO2 surfaces. The overall reaction rate increased with temperature, indicating that the reduction of reactant adsorption did not affect the overall reaction, and thus the chemical reaction was the rate-limiting step. As the chemical reaction rate gradually increased and the reactant adsorption decreased with temperature, the rate-limiting step could shift from the chemical reaction to the reactant adsorption, while the overall reaction rate decreased with temperature. Additionally, the competitive adsorption between VOCs and water for the active sites on TiO2 resulted in VOCs influent concentration and humidity promoting or inhibiting the reaction rate. The mineralization of benzene and the selectivity of CO and CO2 were not obviously affected under various temperatures, humidities, and influent benzene concentrations. The benzene mineralization ratios ranged from 0.85 to 1.0, to which CO and CO2 contributed approximately 5~20% and 80~95%, respectively. Temperature and humidity variation did not influence the photocatalytic reaction pathway of benzene. Acetone (AC) and tert-butyl alcohol (TBA) were two major organic products for the photocatalysis of MTBE. The addition of water transferred the reaction pathway from producing AC to TBA, while the temperature increase transferred the reaction pathway from producing TBA to AC. A modified bimolecule Langmuir-Hinshelwood kinetic model was developed to simulate the temperature and humidity related promotion and inhibition of the photocatalysis of benzene and MTBE. The competitive adsorption of VOCs and water on the active sites resulted in VOCs influent concentration and humidity promoting or inhibiting the reaction. The reaction rate constant increased with temperature while the adsorption equilibrium constants decreased, confirming that increasing reaction temperature enhanced the chemical reaction, but reduced the adsorption of VOCs and water. Furthermore, the correlation developed here was also used for determining the apparent activation energy of photocatalytic oxidation of VOCs and the adsorption enthalpies of benzene, MTBE, water vapor, and oxygen.

The oxidation of a range of Volatile Organic Compounds (VOCs) has been studied, from small alkenes (e.g. ethene C2) to larger sesquiterpene species (e.g. β-caryophyllene C15). The gas-phase reactions of these VOCs, largely emitted from biogenic sources, can form oxidation products with high mass and low volatility to contribute to aerosol formation, namely for monoterpene and sesquiterpene species. These organic aerosols formed from chemical reactions in the atmosphere are secondary organic aerosols (SOA). Aerosols can have a profound impact on both climate and health issues at regional and global scales. Processes that govern these gas-to-particle phase reactions are still not fully understood. This thesis presents detailed gas-phase composition data from the various VOCs examined, and tries to highlight important gas-phase species involved in the processes for SOA formation in the atmosphere. The gas-phase composition was measured in real-time utilising the University of Leicester Chemical Ionisation Reaction-Time of Flight-Mass Spectrometer (CIR-ToF-MS). Experiments were conducted under two different environments, “dark” ozonolysis experiments were studied at the EUropean PHOtoREactor (EUPHORE) atmospheric simulation chamber (Valencia, Spain) whilst “light” photooxidation experiments were conducted at the Manchester Aerosol Chamber (MAC) facility (Manchester, UK). The ozonolysis experiments focused around small alkene species (ethene, isobutene, and trans-2-butene), isoprene and monoterpenes (myrcene, α-pinene and limonene) in the absence of NOx and investigated with and without radical scavengers in order to suppress side reactions. Under dry conditions the primary oxidation products for smaller alkene ozonolysis averaged yields for formaldehyde (HCHO) as 1.56 ± 0.09, 1.21 ± 0.03 and 0.15 ± 0.01 for ethene, isobutene and trans-2-butene respectively. Other major gas phase product yields were recorded. Under wet conditions HCHO yields increased dramatically for ethene ozonolysis, to 3.09 ± 0.12 and 1.94 ± 0.31 for isobutene, but no substantial difference was observed for trans-2-butene with an average yield of 0.19 ± 0.04. Observations on gas-phase composition varied little based on the latter and model comparisons were made using the Master Chemical Mechanism (MCMv3.1). Photolysis experiments were conducted for isoprene, monoterpenes (limonene, α-pinene and myrcene) and a sesquiterpene, β-caryophyllene. This led to a direct comparison of composition and yields were obtained for certain oxygenated VOCs (oVOCs). The major gas phase products of isoprene ozonolysis, methacrolein (MACR) recorded average yields of 0.24 ± 0.16 and methyl-vinyl ketone (MVK) at 0.15 ± 0.01 for dry conditions, whilst yields of 0.36 ± 0.04 and 0.17 ± 0.02 were observed for wet conditions respectively. Similar yields were observed for photolysis conditions. The highest average yields in the gas phase for all monoterpene species were the primary aldehyde species formed (e.g. pinonaldehyde for α-pinene), ranging averaged yields from 0.115 to 0.583 for ozonolysis reactions and 0.119 to 0.270 under photolysis conditions. Where applicable, SOA yields were determined using a Differential Mobility Particle Sizer (DMPS) and composition of the particle phase made off-line using Liquid chromatography-ion trap mass spectrometry (LC-MSn). A unique method of organic seed formation was also constructed for photolysis experiments for isoprene and limonene using β-caryophyllene as a precursor for the organic seed. Finally mesocosm experiments of direct emissions from tree species Ficus cyathistipula, Ficus benjamina and Caryota millis (to simulate tropical Asian conditions) and Betula Pendula (to encompass European environments). The tropical monoterpene producing species formed SOA, whereas the European isoprene dominant species did not. Implications of this are further discussed along with the difference observed in gas-phase composition and yields of oxidation products produced from all experiments. An Am241 source and a newly developed hollow cathode source was utilised in both campaigns so instrumental sensitivity, in particular for lower mass species is also discussed. Evidence from the experiments shows that SOA formation is only observed from monoterpene and sesquiterpene compounds. Here isoprene did not form any substantial SOA and we argue it can inhibit SOA formation. Important gas phase species for SOA contribution were those of C10 or higher, in particular the primary aldehyde oxidation products of monoterpenes that were observed in both gas and particulate phase.

Real time detection of Volatile Organic Compounds (VOCs) using Selected Ion Flow Tube – Mass Spectrometry (SIFT-MS) provides a unique opportunity for research into breath testing for clinical diagnosis. However, before engaging in research into breath analytes as markers of disease, appropriate breath collection methods are required. Collection of breath for SIFT-MS instruments fall into two categories, direct breath collection into the instrument and the remote breath collection onto a storage medium. This thesis describes the development and validation of both methods of breath collection equipment for SIFT-MS analysis. Development of the direct breath collection device involved standardising and optimising the way in which breath is sampled by SIFT-MS. Design considerations include ergonomics, patient safety, breathing resistance, materials, and appropriate operating conditions of the device. Results from materials testing showed that all materials emit VOCs and the best approach is to minimise VOC emission by careful material selection. To minimise flow resistance experienced by the patient, the capillary from which the SIFT-MS instrument samples, is placed as close as possible to the users mouth. The optimal operating temperature of the device was found to be 100°C - 120°C, which ensures that water vapour will not condense inside the capillary causing blockage. In order to ensure patient safety the device is adequately insulated using stagnant air which also minimises VOC emission from insulation materials. Because a SIFT-MS instrument is large and cannot be easily shifted around a hospital, a system of remote sample collection is required. It is also important to separately collect and analyse breath from the respiratory alveolar region. For this reason the remote breath collection device designed also fractionates collected breath samples into the breath from the upper airways and alveolar breath. The storage medium chosen for the collected breath samples is a gas sampling bag made from Tedlar™. Collection of breath into Tedlar™ bags allows breath to be stored as a whole air sample, the ideal form for analysis with the SIFT-MS technique. Alveolar breath is fractionated from deadspace gasses by measuring a subject's exhalation and collecting the portion of interest. The breath exhalation is measured by an averaging Pitot tube and pressure transducer. Signal processing and automation of the remote breath collection device is controlled by a Cypress Microsystems PSoC microcontroller. To validate the device isoprene and acetone concentrations in fractionated breath samples were compared with a whole breath sample. Results showed that the alveolar breath fraction had a higher concentration of acetone than the upper airway fraction, indicating that the breath was successfully fractioned. However, isoprene concentrations were lower in both fractions due to hyperventilation of the subject causing a dilution effect of alveolar VOCs. Therefore, a higher sample collection volume is required per exhalation, and regulating subjects' breathing rate will avoid the dilution effect observed in collected breath samples. Overall, this thesis had designed, developed and validated two forms of breath collection systems for use with SIFT-MS technology.

abstract: A wireless hybrid device for detecting volatile organic compounds (VOCs) has been developed. The device combines a highly selective and sensitive tuning-fork based detector with a pre-concentrator and a separation column. The selectivity and sensitivity of the tuning-fork based detector is optimized for discrimination and quantification of benzene, toluene, ethylbenzene, and xylenes (BTEX) via a homemade molecular imprinted polymer, and a specific detection and control circuit. The device is a wireless, portable, battery-powered, and cell-phone operated device. The device has been calibrated and validated in the laboratory and using selected ion flow tube mass spectrometry (SFIT-MS). The capability and robustness are also demonstrated in some field tests. It provides rapid and reliable detection of BTEX in real samples, including challenging high concentrations of interferents, and it is suitable for occupational, environmental health and epidemiological applications. / Dissertation/Thesis / M.S. Electrical Engineering 2011

Please read the abstract in the section 00front of this document / Dissertation (MSc)--University of Pretoria, 2010. / Chemistry / unrestricted

Biotreatment for air pollution control can generally be categorized as biofilter, bioscrubbing and biotrickling filter systems. Generally, biotreatments could be effective and more economical treatment for containment waste gas if designed and operated properly. A two stage down-flow biofilter (2.18 m in height and 0.4 m¡Ñ0.4 m in cross-sectional area) was constructed to develop a biofilter packed only with fern chips for the removal of air-borne propylene glycol monomethyl ether acetate (PGMEA). Both stages were packed with fern chips of 0.30 m in height and 0.40 m ¡Ñ0.40 m in cross section. Fern chips could avoid the shortcomings of traditional media, such as compaction, drying, and breakdown, which lead to the performance failure of the biofilters. In addition, the fern chip medium has the following merits: (1) simplicity in composition, (2) low pressure drop for gas flow (< 20 mmH2O m-1), (3) simple in humidification, nutrient addition, pH control, and metabolite removal, (4) economical (USD$ 174 ¡V 385 m-3), and (5) low weight (wet basis around 290 kg m-3). Results indicate that with operation conditions of media moisture content controlled in the range of 50 ¡V 74%, media pH of 6.5 ¡V 8.3, EBRT (empty bed retention time) of 0.27 ¡V 0.4 min, influent PGMEA concentrations of 100 to 750 mg m-3, volumetric organic loading of < 170 g m-3 h-1, and nutrition rates of Urea-N 66.0 g m-3.day-1, KH2PO4-P 13.3 g m-3.day-1 and milk powder 1.0 g m-3 day-1, the fern-chip packed biofilter could achieve an overall PGMEA removal efficacy of around 94%. Instant milk powder or liquid milk was essential to the good and stable performance of the biofilter for PGMEA removal. An activated sludge aeration basin (20 cm i.d., 140 cm height) equipped with either a coarse air diffuser (a plastic pipe perforated with 56 orifices of 2 mm in diameter) or a fine diffuser (porous plastic type with 100-micrometer pores) was utilized to treat an air-borne hydrophobic VOC (toluene, 700 ¡V 800 mg m-3). The purposes of this study were to test the influences of both MLSS and diffuser type on the VOC removal efficiency. Results show that higher MLSS (mixed liquor suspended solids) such as 10,000 ¡V 40,000 mg L-1 in the mixed liquor did not enhance greatly the transfer and removal of the introduced toluene. Instead, activated sludge basins with a normal MLSS (e.g., 2,000 ¡V 4,000 mg L-1) in the mixed liquor and an efficient gas diffusion system with volumetric VOC transfer coefficient of around 10 ¡V 15 h-1 can be used for the removal of hydrophobic VOCs from the introduced gas. For achieving a removal of over 95% of the introduced toluene or similar hydrophobic VOCs, commercial air diffusers for aerobic biological wastewater treatment basins can be used with a submerged liquid depth of over 0.40 m over the diffusers and an aeration intensity (air flow rate/basin cross-sectional area) of lower than 5.0 m3 m-2 h-1.