Development of chromatographic methods by using direct-sampling procedure for the quantification of cyclic and linear volatile methylsiloxanes in biogas as perspective for application in online systems.

By empirically examining the persistent theme, we hope to produce a more complete understanding of methods for determination of volatile methylsiloxanes in biogas stream. Therefore, we made an attempt to investigate a rapid and sensitive method for simultaneous analysis of linear and cyclic volatile methylsiloxanes in sewage biogas in the context of the perspective for application in online systems. The gas chromatographic (GC) parameters were optimised, and sampling of volatile methylsiloxanes from biogas was performed using novel direct sampling procedure with applying of three kinds of liquid-media. Through application of well-established gas chromatography technique coupled with two types of detector – flamed ionisation detector and mass spectrometer detector – we developed the characterisation of the presented methods. Moreover, during the samples preparation the extraction procedure was consistently excluded, as well as the time of analysis was significantly reduced. The analyses were carried out by applying special constructed sampling train where the absorbed VMSs were trapped and analysed directly by GC technique, afterwards. The instrumental analytical protocol was found to yield a linear calibration in the range 0.1–55.13 (µg g^?1) with R² values 0.996 and in the range from 0.1 to 65.17 µg g^?1) with R² values > 0.99 for GC-FID and GC-MS method respectively. In all analysed samples linear and cyclic VMSs were found in sewage gas with quantities exceeding 4.6 mg Nm^?3 and 19.9 mg Nm^?3, respectively Furthermore, estimation of VMSs solvent absorption efficiency was tested and the highest absorption efficiency was obtained when acetone was used as a primary solvent. High range of linearity (0.1–65.17 µg/g), and low values of limit of detection (0.01 µg/g), limit of quantification (0.04 µg/g) clearly indicate that the analysis can be successfully repeated in other independent laboratory. The proposed method creates the real perspective for analyis of VMSs in on-line system.     

An experimental approach for the development of direct-absorption sampling method for determination of trimethylsilanol and volatile methylsiloxanes by the GC-MS technique in landfill gas

This paper reports on an absorption method used for the determination of six target volatile methylsiloxanes and trimethylsilanol existing in raw biogas samples by means of a special and portable sampling train system. After biogas sampling (no accurate pump needed), the samples obtained were analysed by gas chromatography-mass spectrometry (GC-MS). The optimisation of the used solvent was carried out, and acetone was selected as the preferred liquid medium for trapping the siloxanes. The results clearly showed that using pure acetone and a mixture of acetone and water (97/3% = v/v) ensures very good solvation of silicon-contained molecules; thus the sampling procedure was more accurate. Replicate samples showed that the relative standard deviation of the method was less than 5.7% and 6.3% for methylsiloxanes as well as less than 2.1% and 2.4% for trimethylsilanol analysed 24 and 72 hours after sampling, respectively. Furthermore, limits of detection were determined theoretically and experimentally. The limits of detection for siloxanes and trimethylsilanol were in the range 0.04–0.11 mg/Nm³ and 0.08–0.12 mg/Nm³, respectively. The limit of quantification for trimethylsilanol was 0.1 mg/Nm³, whereas the limit for siloxanes ranged from 0.1 to 0.13 mg/Nm³. Finally, raw biogas samples were successfully analysed by the developed method. Trimethylsilanol and methylsiloxanes were found in the concentrations of 34.5 mg/Nm³ and 1.7–20 mg/Nm³ in the analysed raw biogas, respectively.     

Development of a method for determination of VOCs (including methylsiloxanes) in biogas by TD-GC/MS analysis using Supel™ Inert Film bags and multisorbent bed tubes

An analytical method based on TD-GC/MS was developed and validated for the determination of volatile organic compounds (VOCs), including linear and cyclic volatile methylsiloxanes (VMSs), in biogas. Biogas was first sampled in Supel? Inert Film bags and subsequently dynamically sampled onto multisorbent bed tubes (Carbotrap, Carbopack X and Carboxen 569) using portable pump equipment. Two sample volumes, 100 and 250 ml, were evaluated. Desorption efficiency values for both volumes are in the range of 99–100% for almost all studied compounds while breakthrough values (%VOC on sample tube back section) are below 1% for most evaluated VOCs. However, acetaldehyde, carbon disulphide, ethanol and 1,3-butadiene have breakthrough values higher than 5%. Method detection limits were in the range of 0.01–0.8 ng per sample. The most abundant VOCs in biogas were terpenes with concentrations between 500 and 700 mg m^?3. Other important families were ketones, aromatic hydrocarbons and alkanes, with concentrations in the range of 36–46 , 20–35 and 14–16 mg m^?3, respectively. VMSs presented average concentrations of 4.9 ± 0.4 mg m^?3. Additionally, the Supel? Inert Film bags were evaluated for stability for 4 days at room temperature. Although several VOC families’ concentrations in the bag increased or decreased significantly (t-test; p ≤ 0.01, n = 5) 2 days after collection, recoveries were around 70–130% for most studied VOCs. The results shown demonstrate that the presented methodology is reliable and satisfactory for the evaluation of VOCs in biogas and presents an alternative to the currently existing biogas analytical techniques.     

TDI- and MDI-analysis during fire simulation tests — filter- and high-volume impinger-sampling

The sampling and HPLC-determination methods for TDI (toluene diisocyanate) and MDI (diphenylmethane diisocyanate) during fire simulation tests have been given in detail. The preparation of the sampling filters with derivatizing reagents and the high-volume impinger sampling techniques have been demonstrated. The measured TDI- and MDI-values were in the range of about 8 to 15 mg TDI/m³ and about 18 mg MDI/m³ fire gases during “steady” fire conditions. The values reflect the kinetics of the fire tests in a plausible way. This work was part of an International Isocyanate Institute project, the results of which are published elsewhere [1], [3].     

Suitability of Tedlar gas sampling bags for siloxane quantification in landfill gas

Landfill or digester gas can contain man-made volatile methylsiloxanes (VMS), usually in the range of a few milligrams per normal cubic metre (Nm³). Until now, no standard method for siloxane quantification exists and there is controversy with respect to which sampling procedure is most suitable. This paper presents an analytical and a sampling procedure for the quantification of common VMS in biogas via GC-MS and polyvinyl fluoride (Tedlar^®) bags. Two commercially available Tedlar bag models are studied. One is equipped with a polypropylene valve with integrated septum, the other with a dual port fitting made from stainless steel. Siloxane recovery in landfill gas samples is investigated as a function of storage time, temperature, surface-to-volume ratio and background gas. Recovery was found to depend on the type of fitting employed. The siloxanes sampled in the bag with the polypropylene valve show high and stable recovery, even after more than 30 days. Sufficiently low detection limits below 10 μg Nm⁻³ and good reproducibility can be achieved. The method is therefore well applicable to biogas, greatly facilitating sampling in comparison with other common techniques involving siloxane enrichment using sorption media.     

“Badge-type” passive sampler for monitoring ambient ammonia concentrations

A passive “badge-type” sampling device for the determination of gaseous ammonia was developed. The collection substrate is phosphoric acid. The sampler can be used for outdoor and indoor sampling of ammonia in the concentration range from 0.05 μg/m³ to 10 mg/m³. The performance was tested in the laboratory and in the field against an annualar denuder, a filter pack and an impinger technique. The intercalibration showed that the passive sampler compares very well with active samplers (r²=0.99; k=1.05). The average reproducibility of the sampler was 8%. Hence the badge sampler is well suited for the determination of ammonia in a wide range of concentrations and particularly for application under rural background conditions. The sampling rate of the device was calculated according to a simple multi-layer model.     

Determination of aliphatic amines in air by membrane enrichment directly coupled to a gas chromatograph

Summary A method is described for the determination of shortchain aliphatic amines in ambient air based on impinger sampling in dilute H₂SO₄, selective enrichment across a PTFE gas membrane and quantification by gas chromatography. The enrichment step is carried out in a flow system directly connected to the chromatograph. The separation is performed on a packed column with nitrogen selective detection. The enrichment per sample volume was in the range 7.3 to 8.2 mL^–1 for C₁–C₆ amines. Detection limits were ca 3–10 nM with enrichment of a 2.9 mL liquid sample. After impinger sampling of 5 m³ air in 10 mL absorption solution, this corresponds, to 0.4–0.8 ng/m³ (ca 0.2–0.5 ppt by volume) in air.     

GC-MS Analysis of Organic Vapours Emitted from Polyurethane Foam Insulation

Abstract

The vapours emitted by rigid polyurethane foam at 40° and 80° in dry and in humid (90% RH) air were trapped with a Tenax TA sampling tube and, after thermal desorption, analyzed by high resolution gas chromatography – mass spectrometry. The chromatograms obtained demonstrate a certain characteristic pattern. The qualitative composition of the effluent mixture is basically independent of both temperature and humidity of the foam. Over seventy compounds were identified as polyurethane foam off-gases. Among them the most numerous are hydrocarbons. The most abundant is the blowing agent, trichlorofluoromethane. The most interesting are cyclic acetals, aldehydes, cyclic ethers, alcohols, chloroform and chlorobenzene. The headspace concentration of the majority of them is below 10mg/m³, there are, however, several compounds with the concentration exceeding 100mg/m³.     

Analytical methodology for sampling and analysing eight siloxanes and trimethylsilanol in biogas from different wastewater treatment plants in Europe

Siloxanes and trimethylsilanol belong to a family of organic silicone compounds that are currently used extensively in industry. Those that are prone to volatilisation become minor compounds in biogas adversely affecting energetic applications. However, non-standard analytical methodologies are available to analyse biogas-based gaseous matrixes. To this end, different sampling techniques (adsorbent tubes, impingers and tedlar bags) were compared using two different configurations: sampling directly from the biogas source or from a 200 L tedlar bag filled with biogas and homogenised. No significant differences were apparent between the two sampling configurations. The adsorbent tubes performed better than the tedlar bags and impingers, particularly for quantifying low concentrations. A method for the speciation of silicon compounds in biogas was developed using gas chromatography coupled with mass spectrometry working in dual scan/single ion monitoring mode. The optimised conditions could separate and quantify eight siloxane compounds (L₂, L₃, L₄, L₅, D₃, D₄, D₅ and D₆) and trimethylsilanol within fourteen minutes. Biogas from five waste water treatment plants located in Spain, France and England was sampled and analysed using the developed methodology. The siloxane concentrations in the biogas samples were influenced by the anaerobic digestion temperature, as well as the nature and composition of the sewage inlet. Siloxanes D₄ and D₅ were the most abundant, ranging in concentration from 1.5 to 10.1 and 10.8 to 124.0 mg Nm⁻³, respectively, and exceeding the tolerance limit of most energy conversion systems.     

Hydrosilylation of m-TMI: New siloxane based aliphatic polyisocynates

Well-characterized polyfunctional aliphatic isocyanates were obtained in high purity and quantitative yield by the hydrosilylation of m-isopropenyl-α,α-dimethylbenzyl isocyanate (m-TMI) with cyclic and acyclic hydrogementhylsiloxance. The products were characterized by ¹H- and ¹³C-NMR, IR, and GPC, and all result exclusively from ß-addition to m-TMI. Polymers with SiH Groups are also effective hydrosilylating agents of m-TMI. The isocyanato siloxanes can be used as precursors for star and network polymers as well as other poly-functional reagents, and examples of reactions with methoxy polyethylene glycol and with amine-containing compounds are discussed.     

Effect of catalyst structure on the reaction of α-methylstyrene with 1,1,3,3-tetramethyldisiloxane

Reaction of α-methylstyrene with 1,1,3,3-tetramethyldisiloxane in the presence of the complexes of platinum(II), palladium(II) and rhodium(I) is explored. It is established that in the presence of platinum catalyst predominantly occurs hydrosilylation of α-methylstyrene leading to formation of β-adduct, on palladium catalysts proceeds reduction of α-methylstyrene, on rhodium catalysts both the processes take place. In the reaction mixture proceeds disproportion and dehydrocondensation of 1,1,3,3-tetramethyldisiloxane that leads to formation of long chain linear and cyclic siloxanes of general formula HMe₂Si(OSiMe₂) _n H and (-OSiMe₂-)m (n = 2–6, m = 3–7), respectively. Platinum catalysts promotes formation of linear siloxanes, while both rhodium and palladium catalysts afford linear and cyclic siloxanes as well. Structure of intermediate metallocomplexes is studied.     

Determination of airborne methyl isocyanate as dibutylamine or 1-(2-methoxyphenyl)piperazine derivatives by liquid and gas chromatography

The usefulness of a glass fibre filter method to collect airborne methyl isocyanate (MIC) was studied in laboratory experiments and in a workplace during manufacture of mineral wool insulation material. Filter collection was based on derivatisation in situ with 1-(2-methoxyphenyl)piperazine (2MP). 2MP impinger sampling was also evaluated in the workplace. Impinger sampling with dibutylamine (DBA) was used as an independent method. The samples were analysed by liquid and gas chromatography using various detection techniques: mass spectrometry, ultraviolet and electrochemical detection (LC-MS, LC-UV, LC-EchD and GC-MS). The sampling efficiency of 2MP filters for MIC varied with the origin of the glass fibre filter. Two Whatman filters (diameter 25 mm) with altogether 21 mumol of 2MP collected 100% of 9.8 micrograms of MIC during 30 min at an airflow rate of 1 l min-1. The workplace measurements were performed at two concentration levels, 0.003 and 0.09 mg m-3. The theoretical amounts of derivatisation reagent were 42 mumol (2MP filter), 52 mumol (2MP impinger) and 100 mumol (DBA). MIC concentrations were 20% lower by the 2MP methods compared with the DBA method (statistically significant difference). Breakthrough was 6% for the DBA method and 9% for the 2MP impinger method. To trap both MIC and isocyanic acid, which was also present in the workplace samples, a tenfold molar amount of 2MP reagent was used. The precision of sample preparation, expressed as relative standard deviation, was 3.5% (0.17 microgram ml-1, n = 6). The precision of sampling in the workplace was 15% (0.002 mg m-3, n = 6). The limit of quantification was 0.0006 mg m-3 for 30 l of air by the 2MP impinger method and 0.03-0.05 mg m-3 by the 2MP filter method. Hence, airborne MIC can be determined using 2MP as derivatisation reagent. Impinger sampling is preferable when low concentration levels are expected.     

In situ Removal of Hydrogen Sulfide During Biogas Fermentation at Microaerobic Condition

In this paper, rice straw was used as a raw material to produce biogas by anaerobic batch fermentation at 35 °C (mesophilic) or 55 °C (thermophilic). The hydrogen sulfide in biogas can be converted to S⁰ or sulfate and removed in-situ under micro-oxygen environment. Trace oxygen was conducted to the anaerobic fermentation tank in amount of 0.5, 1.0, 2.0, 3.0, 4.0, 5.0, or 10.0 times stoichiometric equivalence, respectively, and the control experiment without oxygen addition was carried out. The results showed that the initial H₂S concentrations of biogas are about 3235?±?185 mg/m³ (mesophilic) or 3394?±?126 mg/m³ (thermophilic), respectively. The desulfurization efficiency is 72.3 % (mesophilic) or 65.6 % (thermophilic), respectively, with oxygen addition by stoichiometric relation. When the oxygen feeded in amount of 2～4 times, theoretical quantity demanded the removal efficiency of hydrogen sulfide could be over 92 %, and the oxygen residue in biogas could be maintained less than 0.5 %, which fit the requirement of biogas used as vehicle fuel or combined to the grid. Though further more oxygen addition could promote the removal efficiency of hydrogen sulfide (about 93.6 %), the oxygen residue in biogas would be higher than the application limit concentration (0.5 %). Whether mesophilic or thermophilic fermentation with the extra addition of oxygen, there were no obvious changes in the gas production and methane concentration. In conclusion, in-situ desulfurization can be achieved in the anaerobic methane fermentation system under micro-oxygen environment. In addition, air could be used as a substitute oxygen resource on the situation without strict demand for the methane content of biogas.     

Cyclolinear polysiloxanes. I. Synthesis and characterization

The synthesis and characterization of two novel cyclic siloxanes, diacetoxydiethyltetramethylcyclotetrasiloxane and diacetoxytriethylpentamethylcyclopentasiloxane, and cyclolinear polymers synthesized from these monomers are presented. The cyclic siloxanes were synthesized from tetramethylcyclotetrasiloxane and pentamethylcyclopentasiloxane, respectively, by acetylation followed by ethylation. The cyclic monomers were characterized with ¹H NMR spectroscopy. Subsequently, the cyclic siloxanes were self‐condensed into cyclolinear polysiloxanes and cocondensed (extended) with silanol‐terminated polydimethylsiloxane into high‐molecular‐weight polymers containing cyclic units withlinearpolydimethylsiloxane spacers (extended cyclolinear polysiloxanes). The molecular weights of both the cyclolinear polysiloxanes and extended cyclolinear polysiloxanes were determined. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4039?4052, 2006     

Analysis of t-Butyldimethylsilyl Derivatives of Chlorophenols in the Atmosphere of Urban and Rural Areas in East of France

A method using GC-MS and derivatization with N-(t-butyldimethylsilyl)-N-ethyltrifluoroacetamide (MTBSTFA) was developed for the analysis of 19 chlorophenols compounds in atmospheric samples (gas and particles). Air sampling was carried out using a Hi-Vol sampler with glass fibre filter and XAD-2 resin at a flow rate of 60 m³ h⁻¹. The particle and gas phases were collected separately over a period of 4 h. Samples were Soxhlet extracted, evaporated to dryness under nitrogen and refilled with acetonitrile. 100 mL of these extracts were derivatized with 100 μL of MTBSTFA at 80 °C for 1 h under strong stirring. Sylylated chlorophenols were injected into a GC-MS in splitless mode and quantified as their TBDMS derivatives in the SIM mode. Mass spectral analysis of the derivatives of the 19 compounds studied indicates that the spectra are highly specific showing an ion at [M - 57]⁺ which is useful for structure confirmation or analysis at low levels using selected ion monitoring. Quantification limits varied between 5 μg L⁻¹ and 10 μg L⁻¹ which correspond to 20 pg m⁻³ and 40 pg m⁻³ for 250 m³ of air sampled. This method was successfully applied to atmospheric samples collected simultaneously in winter 2004 in an urban (Strasbourg) and rural (Erstein) areas in east of France.     

Reaction of Organylchlorosilanes with Dimethyl Sulfoxide in the Presence of Octamethyltrisiloxane

Dichloro(methyl)(vinyl)silane reacts with DMSO in the presence of octamethyltrisiloxane to form cyclooligomethyl(vinyl)siloxanes(MeViSiO) _n (n = 3-6). The reaction involves disproportionation of octamethyltrisiloxane into hexamethyldisiloxane and decamethyltetrasiloxane. Along with the latter two products, insertion products of methyl vinyl silanone into both permethyloligosiloxanes were identified. Alkyltrichlorosilanes RSiCl₃ (R = Me, Et) react with DMSO in the presence of octamethyltrisiloxane to form cyclic oligoalkyltrichlorosiloxanes (RClSiO) _m (m = 3-6).     

Anaerobic Digestion of Sugarcane Vinasse Through a Methanogenic UASB Reactor Followed by a Packed Bed Reactor

The anaerobic treatment of raw vinasse in a combined system consisting in two methanogenic reactors, up-flow anaerobic sludge blanket (UASB) + anaerobic packed bed reactors (APBR), was evaluated. The organic loading rate (OLR) was varied, and the best condition for the combined system was 12.5 kg COD m^?3day^?1 with averages of 0.289 m³ CH₄ kg COD r^?1for the UASB reactor and 4.4 kg COD m^?3day^?1 with 0.207 m³ CH₄ kg COD r^?1 for APBR. The OLR played a major role in the emission of H₂S conducting to relatively stable quality of biogas emitted from the APBR, with H₂S concentrations <10 mg L^?1. The importance of the sulphate to COD ratio was demonstrated as a result of the low biogas quality recorded at the lowest ratio. It was possible to develop a proper anaerobic digestion of raw vinasse through the combined system with COD removal efficiency of 86.7% and higher CH₄ and a lower H₂S content in biogas.     

Volatile organic compounds in landfill odorant emissions on the island of Mallorca

This study provides data on the occurrence of volatile organic compounds (VOCs) in the biogas emission from a landfill located on the island of Mallorca (Balearic Islands, Spain), where 200,000 tonnes of urban solid wastes are dumped every year. Three different sampling cells, of differing waste ageing were investigated in August 2008, during the main tourist season and the warmest possible weather conditions. Samples were collected in Nalophan? bags according to the standard European method EN 13725 followed by VOCs adsorption onto Carboxen 1000? and Tenax TA? materials prior to thermal desorption and analysis by GC-MS. In total 42 VOCs were analysed, using external standards, out of which 36 were positively identified. Detected VOCs in µg?m^?3 were alkanes (19–62), aldehydes (65–98), ketones (78–129), alcohols (67–78), esters (25–33), BTEX (83–106), halogenated compounds (16–39), terpens (1.4–2.4) and reduced sulphur compounds (2.6–4.2), showing different concentrations on each one of the three cells. Emitted VOCs showed some similarities with other previous studies from China and Turkey, while large differences to an Italian study. The benzene-to-toluene ratio (B:T) showed values in the range of 0.13 to 0.20 characteristic of biogas. H₂S and NH₃ gases emitted by the landfill were measured in-situ utilising Dräger? Tubes for Short-Term-Measurements, showing concentration levels of ≤800?µg?m^?3 and <300?µg?m^?3, respectively, which is higher than the determined VOCs in accordance with previous studies. Samples were examined with dynamic olfactometry following standard European method EN 13725, to determine a potential statistical linear correlation between odour and VOC concentrations. Such correlations were not observed probably owing to the large number of compounds emitted from garbage which are not quantified, yet causing positive results in olfactometry.