Determination of total carbon and total organic carbon from volatile air pollutants

Summary The method developed based on the determination of TC and TOC in the form of the total amount of CO₂ requires application of the proper techniques for the final determination of CO₂. The possibility of using a stream of carrier gas at a convenient flow-rate for desorbing quantitatively CO₂ concentrated on a molecular sieve permits use of a wide variety of known analytical techniques for the final determination of CO₂. Various methods were compared on the basis of both absolute and calibration measurements. The absolute methods chosen were gravimetric (classical or an automated version based on application of a gravimetric automat and automatic recording balance), thermogravimetric analysis and coulometry. The calibration methods included thermal conductivity, the flame-ionization detector (after conversion of CO₂ into methane) and infrared absorption. Usefulness of the methods was evaluated on the basis of comparative statistical analysis of experimental data with respect to precision (Snedecor'sF-test and Bartlett'sU ²-test) and accuracy (Student'st-test).

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Zusammenfassung Das entwickelte Verfahren zur Bestimmung des TC- und TOC-Gehaltes in Form der gesamten Menge CO₂ erfordert die Anwendung geeigneter Analysentechniken zur Endbestimmung dieser Verbindung. Die Möglichkeit einer Desorption des am Molekularsieb angereicherten CO₂ in einem Gasstrom mit geeignetem Durchfluß erlaubt zur Endbestimmung von CO₂ die Anwendung einer Reihe verschiedener Analysenverfahren. Die Anwendbarkeit verschiedener, auf Absolutverfahren und auch auf relativen Messungen beruhender Methoden wurde vergleichend untersucht. Die folgenden Methoden zur CO₂-Bestimmung wurden gewählt: die Gravimetrie (klassische oder automatisierte unter Einsatz eines Wägeautomaten und einer registrierenden Waage), die Thermogravimetrie und die Coulometrie. Von den relativen Methoden wurden die Thermokonduktometrie, der Flammenionisationsdetektor (nach Umsetzung von CO₂ zu Methan) und das IR-Absorptionsmeßverfahren geprüft. Die Anwendbarkeit der Methoden wurde mit Hilfe statistischer Prüfverfahren beurteilt, wobei die Präzision (SnedecorsF-Test und BartlettsU ²-Test) und die Genauigkeit (Studentst-Test) der erhaltenen Analysenwerte verglichen wurden.

     

Optimisation of a photochemical sensor for total organic carbon measurement

A new tool for the measurement of TOC based on the heterogeneous photocatalysis activated by two different light sources has been planned. The instrument is constituted by a cell where the degradation occurs thanks to both the UV irradiation and the presence of a powered catalyst and by a measurement cell lodging CO2 gas permeable membrane electrode (detector), thermometer, inlet and outlet ways for the samples. One of the sources has a maximum emission at 254nm, while the other simulates the solar spectrum. A suspension (1 g/L) of titanium dioxide (Degussa P25) has been used to catalyse the process. A magnetic stirrer and a circulating pump avoid the deposition of the catalyst on the bottom of the reactor. The online measurement of produced CO2 was performed on 11 molecules (commercial names: Parachlorophenol, D-Glucose, Acid Blue 29, Atraton, Aspirin, Dimethoate, Aldicarb sulfone, Hydroquinone, (R)-Propranolol, Citric acid, Atrazine) to test the system efficiency. The experimental CO2 value was compared with the theoretical TOC value calculated by means of the structure's formula.     

Organic-free water for total organic carbon determination

Commercially available “organic-free” water is compared with water cleaned by ultraviolet (u.v.) radiation for applicability to total organic carbon determinations. The u.v.-treated water contains an organic carbon concentration less than the detection limit of the method used (0.056 mg C l^-1). The commercially processed water lacks the consistently low blank level required for use in TOC determinations.     

Photocatalytic oxidation for total organic carbon analysis

A new method and apparatus for the determination of organic carbon in water are described. Photocatalytic oxidation of organic matter by near-UV illuminated titanium dioxide is used to convert organic carbon to carbon dioxide. Atmospheric oxygen is the oxidant. The light source is a 20-W black-light fluorescent tube. The carbon dioxide equilibrates between the reaction loop and a conductivity detection loop and the recirculated air forms the interface between the two loops. The method is suitable for analysis of water containing 0.1–30 μg ml^?1 organic carbon and sample volumes of 1–40 ml. Higher concentrations can be determined after appropriate dilution. Times for 99% oxidation of organic solutes to carbon dioxide are of the order of 10 min or less. The main advantages of the apparatus are low cost and ease of operation.     

Determination of total carbon and total organic carbon from volatile air pollutants. Part II

Summary The possibility of specific removal of carbon monoxide from a stream of air in the presence of vapours of volatile organic compounds was investigated. Weighed samples of oxalic acid were pyrolyzed to obtain standard mixtures of CO with air. Carbon monoxide present in the stream of air (at the flow rate of 700 cm³/ min) is quantitatively oxidized to CO₂ by a layer of the Körbl catalyst (diameter=12 mm, length=35 mm) heated to 90° C. The CO₂ formed can be specifically bound by a heated layer of ascarite⁴⁶. On the basis of model experiments it was concluded that under the conditions described in the paper the degree of oxidation of 16 various organic compounds ranged from 0.7 to 8.7%. Thus, the developed method can be applied as a mean of practically specific removal of CO from a stream of analyzed air in the course of determination of total organic carbon (TOC).

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Zusammenfassung Die Möglichkeit einer spezifischen Entfernung von Kohlenoxid neben Dämpfen flüchtiger, organischer Verbindungen aus dem Luftstrom wurde untersucht. Zur Herstellung von CO-Luftstandardgemischen dienten gewogene Mengen Oxalsäure, die thermisch zersetzt wurden. Das im Luftstrom (700 cm³/Minute) anwesende CO wird an einer auf 90° C erhitzten Körblkatalysatorschicht von 35 mm Länge und 12 mm Durchmesser quantitativ zu Kohlendioxid oxydiert, das dann an einer erhitzten Ascariteschicht⁴⁶ spezifisch gebunden wird. Bei Modellversuchen mit 16 verschiedenen organischen Verbindungen wurde festgestellt, daß der Oxydationsgrad unter den angegebenen Bedingungen 0,7–8,7% beträgt. Das entwickelte Verfahren kann somit zur praktisch spezifischen Entfernung von Kohlenoxid aus dem analysierten Luftstrom bei der Bestimmung des TOC-Gehaltes aus flüchtigen, organischen Verunreinigungen nach ihrer Oxydation Anwendung finden.

     

Determination of total carbon and total organic carbon from volatile air pollutants. Part III

Summary The possibility of selective oxidation of volatile organic compounds in the presence of methane was investigated. Thermal decomposition of a mixture of CH₃COONa and NaOH was used as the source of methane introduced into a stream of purified air. Oxidation of the methane present in a stream of air on a layer of the Körbl catalyst is only slight and does not exceed 10%, even in the case of simultaneous presence of acetic acid, which is completely oxidized under identical conditions. Other volatile organic compounds also undergo complete oxidation. It was found that the degree of oxidation of 16 organic compounds is 97.5%. The detection limit of the developed method depends primarily on the effective removal of the so-called carbon background of the air sample, resulting from the presence of CO₂, CO and CH₄. The developed method of selective oxidation can be used for specific elimination of the effect of methane on the results of determinations of TOC in volatile air pollutants.

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Zusammenfassung Die Möglichkeit einer selektiven Oxydation flüchtiger organischer Verbindungen neben Methan wurde untersucht. Methan wurde im gereinigten Luftstrom durch thermische Zersetzung eines Gemisches von CH₃COONa und NaOH hergestellt. Die Oxydation des Methans im Luftstrom an einer Körbl-Katalysatorschicht ist gering und überschreitet nicht 10%, sogar bei gleichzeitiger Anwesenheit von Essigsäure, welche unter diesen Bedingungen — wie andere flüchtige, organische Verbindungen — vollständig oxydiert wird. An 16 organischen Verbindungen wurde festgestellt, daß der Oxydationsgrad97,5% beträgt. Die Erfassungsgrenze der entwickelten Methode zur TOC-Bestimmung ist vor allem von einer effektiven Beseitigung des sogenannten Kohlenstoffblindwertes abhängig, der durch Anwesenheit von CO₂, CO und CH₄ in der Luftprobe verursacht wird. Das entwickelte, selektive Oxydationsverfahren kann somit zur spezifischen Eliminierung des Einflusses von Methan auf die Bestimmungsresultate des TOC-Gehaltes aus flüchtigen Luftverunreinigungen Anwendung finden.

     

Determination of total carbon and total organic carbon from volatile air pollutants. Part I

Summary A new method of collection of representative air samples for the determination of TC and TOC from volatile air pollutants has been developed. The organic substances undergo combustion and only the carbon dioxide produced is concentrated on molecular sieve 5 A at ambient temperature. The CO₂ is subsequently liberated by thermal desorption at ca. 380°C in a stream of purified gas. Atmospheric CO₂ must be removed first and this can be done (at the sample flow rate of 700 ml/min) by a layer of Ascarite heated at 90° C. Organic compounds passing through the layer are then combusted by a dynamic method utilizing Körbl catalyst and the CO₂ formed is concentrated on a molecular sieve 5 A, followed by thermal desorption and final determination. Organic acids are also retained by the first CO₂ absorber. A diffusion cell for preparation of the mixtures of purified air with vapours of organic compounds is described.

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Zusammenfassung Eine neue Anreicherungsmethode zur Gewinnung representativer Luftproben zur Bestimmung des Gesamtkohlenstoffgehaltes und des Gehaltes an organischem Kohlenstoff (TOC) aus flüchtigen Luftverunreinigungen wurde entwickelt. Während der Probenahme werden die flüchtigen Verunreinigungen verbrannt und nur das entstandene Kohlendioxid bei Zimmertemperatur am Molekularsieb 5A angereichert. Anschließend wird CO₂ bei ca. 380° C im gereinigten Gasstrom thermisch desorbiert. Bei der TOC-Bestimmung muß atmosphärisches CO₂ vorangehend aus dem Luftstrom entfernt werden und wird an einer auf 90° C erwärmten Ascariteschicht gebunden. Die durchfließenden organischen Verbindungen werden dann im dynamischen System am Körblkatalysator oxydiert, das entstandene CO₂ am Molekularsieb 5A angereichert, thermisch desorbiert und einer Endbestimmung zugeführt. Organische Säuren werden gleichfalls durch den ersten CO₂-Absorber gebunden. Eine Diffusionszelle zur Herstellung von Gemischen gereinigter Luft mit Dämpfen organischer Verbindungen wurde beschrieben.

     

Electrical conductivity of carbon black filled ethylene-vinyl acetate copolymer as a function of vinyl acetate content

The electrical conductivity of carbon black filled ethylene-vinyl acetate copolymer was measured as a function of carbon and vinyl acetate (VAc) content. For the composites whose matrices contain less than 32 wt% ofVAc content, a sharp break point of the relation between carbon content and conductivity was observed. The conductivity jumps as much as ten orders of magnitude at the break point. The critical carbon content corresponding to the break point can essentially be predicted by our previous model. This model was derived under certain assumptions, the most important of which is that when the interfacial excess energy introduced by carbon particles into the polymer matrix reaches a universal value,g ^*, the carbon particles begin to coagulate so as to avoid any further increase of energy and to form networks which facilitate electrical conduction. On the other hand, for the composites whose matrices contain more than 32 wt% ofVAc content, a sharp break of the relation between the carbon content and conductivity cannot be observed and conductivity increases continuously with increasingVAc content. In this region ofVAc content, carbon particles were dispersed well in theVAc rich matrices. This is because the presence of polar groups in aVAc component enhances its bonding to conductive fillers. In this case, the interfacial excess energy,g, seems to be the caseg0. Better dispersibility of fillers in this region ofVAc content can be shown from an electron micrograph (TEM).     

Mechanical and rheological properties of poly(ethylene-co-ethyl acrylate) as a function of carbon black content

Carbon black (CB) filled poly(ethylene-co-ethyl acrylate) (EEA-CB) is used as conductive phase in conductive polymer composites (CPC). Electrical conductivity of CPC obtained from blends of immiscible polymers results from CB particles localization within the material, which depends on composition and processing conditions. It is particularly important to control viscosity of such systems as this parameter determines both the phase morphology and conductive pathway structure. The small scale, at which CB particle aggregation/dispersion phenomena occur within CPC, makes direct observations difficult. But the effect of carbon black particles/polymers interactions is clearly visible by means of rheological measurements. A strong reinforcing effect of CB on CPC in both solid and liquid states has been noticed. This phenomenon has been analyzed using classical models as a function of temperature and CB content. The results confirm the necessity of CPC rheology control especially during the process to achieve good reproducibility of electrical properties.     

Automated quantitative and isotopic (13C) analysis of dissolved inorganic carbon and dissolved organic carbon in continuous-flow using a total organic carbon analyser

A method for the automated (13)C analysis of dissolved inorganic and organic carbon species has been developed to operate on a continuous-flow isotope ratio mass spectrometer (CF-IRMS). For natural and anthropogenic carbon species, the (13)C stable isotope has proven to be an excellent environmental tracer. Analytical performance tests were carried out on various organic compounds from easily oxidisable (sugar) to difficult (humic acid). A set of natural samples was also analysed to confirm the flexibility of the system. Analytical precision (2sigma) is typically <0.20 per thousand with sample reproducibility from 0.10-0.35 per thousand depending on reactivity of material. We believe this to be the first successful use of a total organic carbon (TOC) analyser for both dissolved inorganic and, specifically, dissolved organic species for (13)C stable isotope analysis in an automated CF-IRMS system. Routine analysis is achieved fairly quickly, is relatively simple with little or no sample manipulation, and will allow new and exciting studies for stable isotope research in both natural abundance and organic tracer studies not easily achieved before.     

Pervaporation selectivity as a function of pressure and sorption properties of a polymeric film membrane

Results obtained in an experimental study of the pervaporation of binary solutions with a cellulose hydrate (cellophane) nonporous film membrane are discussed. A primary attention is given to the sorption and the effect of the residual pressure of the permeate on the separation characteristics.     

Orientation of a benzene molecule inside a carbon nanotube

Benzene molecules confined in carbon nanotubes of varying radii are employed as semiconductors in electronic nanodevices, and their orientation determines the electrical properties of the system. In this paper, we investigate the interaction energy of all the possible configurations of a benzene molecule inside various carbon nanotubes and then we determine the equilibrium configuration. We adopt the continuous approach together with the semi-empirical Lennard-Jones potential function to model van der Waals interaction between a benzene molecule and a carbon nanotube. This approach results in an analytical expression, which accurately approximates the interaction energy and can be readily used to generate numerical data. We find that horizontal, tilted and perpendicular configurations on the axis of the carbon nanotube are all possible equilibrium configurations of the benzene molecule when the radius of the carbon nanotube is less than 5.580 Å. However, when the radius of the carbon nanotube is larger than 5.580 Å an offset horizontal orientation is the only possible equilibrium configuration of the benzene molecule. In the limiting case, the orientation of a benzene molecule on a graphene sheet can be derived simply by letting the radius of the carbon nanotube tend to infinity.     

薄膜电导率法总有机碳分析仪的校准

探索薄膜电导率法总有机碳分析仪的校准方法.对薄膜电导率法总有机碳分析仪的性能参数进行调查统计,从示值误差、测量重复性、线性误差、检出限和记忆效应5个方面对仪器进行校准.采用500μg/L的蔗糖标准溶液、响应值分别达量程50％、80％对应的蔗糖溶液,以测量值的相对误差最大者作为仪器的相对示值误差,该项建议值为±10％;以...     

Simultaneous sorption of benzene and heavy metals onto two organoclays

An experimental study was performed to determine the feasibility of using hexadecyltrimethylammonium bentonite clay (HDTMA-clay) and benzyltriethylammonium bentonite clay (BTEA-clay) for simultaneous sorption of benzene and one of four heavy metals (Pb, Cd, Zn and Hg). Specifically, the role of competition between benzene and each heavy metal was studied. The sorption of Pb, Cd, and Zn on both BTEA- and HDTMA-clay decreases in the presence of benzene relative to the sorption obtained without benzene present. This indicates that there is competition between Pb, Cd, and Zn and organic compounds during sorption onto both organoclays. On BTEA-clay, Cd, Pb and Zn sorption was reduced by 24, 37, and 51%, respectively. On HDTMA-clay, Cd, Pb, and Zn sorption was reduced by 25, 30, and 57%, respectively. Hg sorption was not affected either by the presence of benzene or by the organoclays used. The sorption of benzene onto BTEA-clay in the presence of Hg, Zn, Pb, and Cd was less than the sorption observed when no heavy metal was present. The presence of Hg resulted in the most significant decrease in sorption, causing a 59% reduction in benzene sorption. The presence of Zn, Pb, and Cd caused a 41, 35, and 31% reduction in benzene sorption, respectively. In general, sorption of benzene onto HDTMA-clay was not affected by the presence of the heavy metals, indicating there are no competitive effects observed with Zn, Cd, and Hg when HDTMA-clay was the sorbent. However, the presence of Pb did cause a 20% reduction in benzene sorption to HDTMA-clay. Both organoclays tested had dual sorptive properties for both heavy metals and an organic contaminant. While the competitive effects were greater for the BTEA clay, both organoclays are capable of simultaneously removing benzene and either Zn, Cd, Hg, or Pb from aqueous solution.     

Propane transformation on H-GaZSM-5 as a function of Ga content

Gallosilicates with different contents of gallium have been studied in propane aromatization reaction. Catalytic evaluations were carried out at atmospheric pressure, varying temperature and reactant flow. The best results in yield to BTX products were obtained for samples with gallium contents of 3–5 wt. %.