Volatile Silicon Compounds Research Articles

Elemental Concentrations of Natural Graphite and Steelmaking Slag: Development of Microwave-Assisted Acid Digestion

To develop more sustainable purification and recovery processes, it is critical to accurately determine inorganic impurities of natural graphite (NG) and valuable elements present in low concentrations in steelmaking slag. This study applied three microwave-assisted acid digestion methods for basic oxygen furnace (BOF) slag, NG, and NG ash. Nitric acid (HNO3), hydrochloric acid (HCl), and hydrogen fluoride (HF) were used in method 1. In method 2, method 1 was followed by microwave-assisted boric acid (H3BO3) digestion. In method 3, acids (HNO3, HCl, HF, and H3BO3) were added simultaneously. Concentrations were measured using inductively coupled plasma–optical emission spectrometry. Analytical performance was evaluated using spiking recovery tests (NG) and certified reference (slag) material (CRM). Spiking recoveries for Al, Ca, Fe, K, Mg, Na, and Si were between 5% and 116% (method 1) and 94%–116% (methods 2 and 3). CRM recoveries for Al, Ca, Fe, Mg, Mn, P, Si, Ti, and V were between 2% and 102% (method 1) and 92%–103% (methods 2 and 3). The unsuitability of method 1 was evident due to the low recoveries. Methods 2 and 3 digested Ca- and Si-containing BOF slag completely without visible residue. The sufficient recoveries verified the adequacy of the methods. The suitability of method 3 probably depended on the phases of samples, as quartz was not completely digested from the NG. Method 2 completely digested the inorganic material of NG, and the spiking test showed no loss of volatile silicon compounds. These methods have not been published for NG or NG ash and validated for slag before.

Adsorptive purification of volatile methyl siloxanes in a digester biogas stream

AbstractBACKGROUNDSiloxanes, one of the various impurity contaminants contained in biogas, comprise a group of volatile organic silicon compounds that pose a major obstacle to biogas application as a consequence of their potential to severely damage energy conversion equipment. Therefore, volatile methyl siloxanes (VMSs) need to be effectively removed from biogas before application.RESULTSThe concentration profile of octamethlytrisiloxane (L3), octamethylcyclotetrasiloxane (D4) and decamethylcyclopentasiloxane (D5) in a biogas were determined. Then in order to investigate the adsorption characteristics of these three siloxane compounds, two commercial granular activated carbons (ACs) were tested for the removal of L3, D4 and D5 in a dynamic adsorption column using biogas streams. The observed concentrations of L3, D4 and D5 in the wastewater treatment plant biogas were 0.62 ± 0.20, 3.07 ± 0.66 and 4.67 ± 1.02 mg m−3, respectively. The best adsorption capacities of L3, D4 and D5 were calculated as 4, 22 and 107 mg g−1, respectively, in real biogas.CONCLUSIONThe adsorption capacity of AC2 was found to be higher than AC1 adsorbents for each siloxane compounds studied. Although the elemental and physical structure of the ACs were similar, and AC1's surface area was higher than AC2, AC2 was more effective in siloxane removal due to high mesoporosity causing excess Van der Waals interaction. The relatively higher mesoporous volume and lower rate of mesh size of AC2 resulted in higher adsorption of siloxane compounds. The order of the breaking points was determined as L3 < D4 < D5 in both AC types. © 2021 Society of Chemical Industry (SCI).

The core microbiome is responsible for volatile silicon and organic compounds degradation during anoxic lab scale biotrickling filter performance

Volatile silicon compounds present in the biogas of anaerobic digesters can cause severe problems in the energy recovery systems, inducing costly damages. Herein, the microbial community of a lab-scale biotrickling filter (BTF) was studied while testing its biodegradation capacity on octamethylcyclotetrasiloxane (D4) and decamethylcyclopentasiloxane (D5), in the presence of toluene, limonene and hexane. The reactor performance was tested at different empty bed residence times (EBRT) and packing materials. Community structure was analysed by bar-coded amplicon sequencing of the 16S rRNA gene. Microbial diversity and richness were higher in the inoculum and progressively decreased during BTF operation (Simpson's diversity index changing from 0.98–0.90 and Richness from 900 to 200 OTUs). Minimum diversity was found when reactor was operated at relatively low EBRT (7.3 min) using a multicomponent feed. The core community was composed of 36 OTUs (accounting for 55% of total sequences). Packing material played a key role in the community structure. Betaproteobacteriales were dominant in the presence of lava rock and were partially substituted by Corynebacteriales and Rhizobiales when activated carbon was added to the BTF. Despite these changes, a stable and resilient core microbiome was selected defining a set of potentially degrading bacteria for siloxane bioremoval as a complementary alternative to non-regenerative adsorption onto activated carbon.

Auto-Oxidation of a Volatile Silicon Compound: A Theoretical Study of the Atmospheric Chemistry of Tetramethylsilane.

Volatile silicon compounds (VOSiCs) are air pollutants present in both indoor and outdoor environments. Here, tetramethylsilane (TMS) is selected as a model to study the photochemical oxidation mechanisms for VOSiCs using ab initio and RRKM theory/master equation kinetic modeling. Under tropospheric conditions, the radical (CH3)3SiCH2• reacts with O2 to produce a stabilized peroxyl radical, which is expected to ultimately yield the alkoxyl radical (CH3)3SiCH2O•. At combustion-relevant temperatures, however, a well-skipping reaction to (CH3)3SiO• + HCHO dominates. Importantly, the (CH3)3SiCH2O• radical is predicted to rearrange to (CH3)3SiOCH2• with a very low reaction barrier, enabling an auto-oxidation process involving addition of a second O2. Subsequent oxidation reaction mechanisms of (CH3)3SiOCH2• have been developed, with the major product predicted to be the trimethylsilyl formate (CH3)3SiOCHO, an experimentally observed TMS oxidation product. The production of substantially oxygenated compounds following a single radical initiation reaction has implications for the ability of VOSiCs to contribute to ozone and particle formation in both outdoor and indoor environments.

Sources of Carbon Impurities in the Preparation of High-Purity Monoisotopic 28Si by a Hydride Method

This paper examines sources of carbon impurities in polycrystalline monoisotopic 28Si prepared by a hydride method. Analytical data on the concentrations of carbon-containing impurities in volatile silicon compounds (28SiH4 and 28SiH4), process gases (Ar and H2), and polycrystalline 28Si are used to identify the major sources of carbon in the polycrystalline 28Si prepared by the hydride method. These are the starting 28SiH4 and calcium hydride used in 28SiH4 conversion into 28SiH4. The rate of carbon intake into polycrystalline silicon from the apparatus material during the monosilane pyrolysis process does not exceed 9 × 1011 cm–2 h–1. Polycrystalline silicon has been precipitated from monosilane with different concentrations of hydrocarbon impurities. At hydrocarbon concentrations in the range 10–4 to 10–3 mol %, the carbon concentration in the monosilane correlates with that in the silicon obtained from it. High-purity monosilane has been used to prepare polycrystalline 28Si samples with concentrations of carbon impurities in the range (0.8–2.3) × 1015 cm–3. Based on calculations of the carbon impurity distribution along the length of a zone-refined ingot, we examine the effect of the initial carbon concentration in the starting polycrystal on the yield of single-crystal monoisotopic 28Si. Requirements are formulated for the carbon concentration in polycrystalline 28Si which ensure a high yield of single crystals with parameters suitable for metrological applications.

Comparison of adsorbents for H2S and D4 removal for biogas conversion in a solid oxide fuel cell

Biogas contains trace compounds detrimental for solid oxide fuel cell (SOFC) application, especially sulphur-containing compounds and volatile organic silicon compounds (VOSiCs). It is therefore necessary to remove these impurities from the biogas for fuelling an SOFC. In this paper, dynamic lab-scale adsorption tests were performed on synthetic polluted gas to evaluate the performance of a polishing treatment to remove hydrogen sulphide (H2S – sulphur compound) and octamethylcyclotetrasiloxane (D4 – VOSiC). Three kinds of adsorbents were tested: an activated carbon, a silica gel (SG) and a zeolite (Z). Z proved to be the best adsorbent for H2S removal, with an adsorbed quantity higher than at the SOFC tolerance limit. However, as concerns D4 removal, SG was the most efficient adsorbent, with an adsorbed quantity of about 184 mgD4/gSG at the SOFC tolerance limit. These results could not be explained by structural characteristics of the adsorbents, but they were partly explained by chemical interactions between the adsorbate and the adsorbent. In these experiments, internal diffusion was the controlling step, Knudsen diffusion being predominant to molecular diffusion. As Z was also a good adsorbent for D4 removal, competition phenomena were investigated with Z for the simultaneous removal of H2S and D4. It was shown that H2S retention was dramatically decreased in the presence of D4, probably due to D4 polymerization resulting in pore blocking.

Adsorption of octamethylcyclotetrasiloxane on silica gel for biogas purification

Biogas can be used as a fuel for electricity conversion. However, volatile organic silicon compounds (including siloxanes) in biogas severely damage combustion engines or solid oxide fuel cells. Three adsorbents of different nature were tested for octamethylcyclotetrasiloxane (D4) removal and silica gel (SG) proved to be the most efficient. It was shown that SG adsorption capacity is in the order of 250mgD4/gSG and the adsorbent bed height has little influence on this adsorption capacity. In the presence of water (relative humidity of 70%), the adsorption capacity was lowered by 90% due to competitive effects and preferential adsorption of water. An increase of the temperature of roughly 20°C also lowered the adsorption capacity but the decrease was less than 15%. Moreover, SG regeneration by heating was only partial, probably due to siloxane polymerization on SG.

Volatile organic silicon compounds in biogases: development of sampling and analytical methods for total silicon quantification by ICP-OES.

Current waste management policies favor biogases (digester gases (DGs) and landfill gases (LFGs)) valorization as it becomes a way for energy politics. However, volatile organic silicon compounds (VOSiCs) contained into DGs/LFGs severely damage combustion engines and endanger the conversion into electricity by power plants, resulting in a high purification level requirement. Assessing treatment efficiency is still difficult. No consensus has been reached to provide a standardized sampling and quantification of VOSiCs into gases because of their diversity, their physicochemical properties, and the omnipresence of silicon in analytical chains. Usually, samplings are done by adsorption or absorption and quantification made by gas chromatography-mass spectrometry (GC-MS) or inductively coupled plasma-optical emission spectrometry (ICP-OES). In this objective, this paper presents and discusses the optimization of a patented method consisting in VOSiCs sampling by absorption of 100% ethanol and quantification of total Si by ICP-OES.

휘발성 유기규소화합물의 기액 물질전달 특성: 흡수용매의 영향

휘발성 유기규소화합물의 기액 물질전달 특성: 흡수용매의 영향

GC-FID 분석을 이용한 휘발성 유기규소화합물 혼합가스의 검량특성

GC-FID 분석을 이용한 휘발성 유기규소화합물 혼합가스의 검량특성

Hydrolysis of polydimethylsiloxane fluids in controlled aqueous solutions

Accelerated degradation tests were performed on polydimethylsiloxane (PDMS) fluids in aqueous solutions and in extreme chemical conditions (pH 2-4 and 9-12). Results confirmed that silicones can be degraded by hydrolysis. Higher degradation levels were achieved in very acidic and alkaline conditions. Degradation products are probably polar siloxanols. In alkaline conditions, the counter-ion was found to have a strong influence on degradation level. Degradation kinetic studies (46 days) were also performed at different pH values. Supposing zeroth-order kinetics, degradation rate constants at 24 °C were estimated to 0.28 mgSi L(-1) day(-1) in NaOH solution (pH 12), 0.07 mgSi L(-1) day(-1) in HCl solution (pH 2) and 0.002 mgSi L(-1) day(-1) in demineralised water (pH 6). From these results, the following hypothesis was drawn: PDMS hydrolysis could occur in wastewater treatment plants and in landfill cells. It may be a first step in the formation of volatile organic silicon compounds (VOSiCs, including siloxanes) in biogas: coupled to biodegradation and (self-) condensation of degradation products, it could finally lead to VOSiCs.

Characterization of silicon species issued from PDMS degradation under thermal cracking of hydrocarbons: Part 1 – Gas samples analysis by gas chromatography-time of flight mass spectrometry

Silicon species are becoming emergent contaminants in the oil and gas industry due to their severe poisoning effect on the hydrotreatment (HDT) catalysts. Using an experimental pilot plant, fresh and representative samples of PDMS degradation under thermal cracking of hydrocarbons were produced. To follow the evolution of silicon species, the gas fraction was immediately analyzed by GC/TOFMS after the production and also after 4months of storage at 4°C. Cyclic siloxanes (Dn) as the major products of PDMS thermal degradation were characterized in the gas phase but these compounds are mainly present in the liquid fraction. Five volatile silicon compounds belonging to the families of silanes, siloxanes and silanols were characterized and quantified in the thermal cracking samples depending on the operating conditions applied in degradation tests. Under coking or visbreaking conditions (long residence time, absence of steam), silanes and siloxanes were preferentially formed. Under evaluated steam cracking conditions (short residence time and presence of steam), trimethylsilanol (TMSOH) was mainly produced by the hydrolysis of PDMS. The formation of the linear siloxane (L2) after several month of storage at 4°C by the self-condensation of TMSOH was also observed. The suspected poisoning effects of these molecules were discussed and could explain the deactivation of catalysts taking place in the refining of the light petroleum cuts. The new identified volatile silicon compounds could affect the performance of the catalyst by the reaction of hydroxyl groups potentially present at the surface of the support with reactive silicon molecules, more specifically silanols.

Organic silicon compounds in biogases produced from grass silage, grass and maize in laboratory batch assays

In the present study the occurrence of volatile organic silicon compounds in biogas produced from grass silage, grass and maize in laboratory batch assays was analyzed and methane potentials were determined. Inoculum from a mesophilic farm digester was used, and its effects were subtracted. Methane yields from grass silage, grass and maize were 0.38, 0.42 and 0.34 m3CH4/kg – volatile solids added (VSadd), respectively. Trimethyl silanol, hexamethylcyclotrisiloxane (D3), octamethylcyclotetrasiloxane (D4) and decamethylcyclopentasiloxane (D5) were detected from all the biogases. Higher yields of volatile organic silicon compounds in the grass (from 21.8 to 37.6 μg/kgVSadd) were detected than in grass silage or maize assays (from 14.7 to 20.4 and from 7.4 to 12.1 μg/kgVSadd, respectively). Overall, it is important to consider silicon-containing compounds also in biogases in energy crop digestion as the number of biogas plants using energy crops as feeding material increases and some biogas applications are sensitive to organic silicon compounds.

Transmission electron microscopy investigation of crystalline silicon surface irradiated by femtosecond laser pulses in different background atmospheres

This article aims to obtain structural and compositional characteristics of a crystalline silicon surface irradiated by femtosecond laser pulses in SF6, N2, air, and vacuum background atmospheres by performing transmission electron microscopy observation of 〈110〉 cross-sectional specimens. Conical microstructures covered with defective outer layers were formed in SF6 gas. The elemental sulfur dopants in the surface microstructure, which located in close proximity to defects, were mainly concentrated at the tip region of the microcones, and about several hundred nanometers thick. In N2 atmosphere, the defects produced regularly on the silicon surface were of the same types with those formed in SF6 gas and confirmed to be stacking faults and overlapped twins. Furthermore, silicon crystalline grains with different orientations were observed on the silicon surface irradiated in N2, air, and vacuum atmospheres. Especially, β-Si3N4 crystalline grains were found to be formed in N2 and air as chemical products when elemental nitrogen exists, and the SiO2 amorphous phase was formed in air by the oxidation effect. Based on these experimental results, the relevant interaction mechanisms between pulsed laser and crystalline silicon were suggested to be mainly attributed to laser-assisted chemical etching and laser ablation, i.e., if volatile silicon compounds can be produced in a reactive gas atmosphere (e.g., SF6), the strong laser-assisted chemical etching dominates over the laser irradiation process. Otherwise, laser ablation is the dominant mechanism such as in N2, air, and vacuum.

Determination of Siloxanes and other Volatile Silicon Compounds in Biogas Samples Using Sample Preconcentration with GC-MS and GC-ICP-MS.

Determination of Siloxanes and other Volatile Silicon Compounds in Biogas Samples Using Sample Preconcentration with GC-MS and GC-ICP-MS.

Addressing Concerns With Volatile Organic Silicon Compounds (VOSC) Using Reciprocating Engines in Biosolids to Energy Projects

Addressing Concerns With Volatile Organic Silicon Compounds (VOSC) Using Reciprocating Engines in Biosolids to Energy Projects

Volatile organic silicon compounds: the most undesirable contaminants in biogases

Recently a lot of attention has been focused on volatile organic silicon compounds (VOSiC) present in biogases. They induce costly problems due to silicate formation during biogas combustion in valorisation engine. The cost of converting landfill gas and digester gas into electricity is adversely affected by this undesirable presence. VOSiC in biogases spark off formation of silicate deposits in combustion chambers. They engender abrasion of the inner surfaces leading to serious damage, which causes frequent service interruptions, thus reducing the economic benefit of biogases. It is already known that these VOSiC originate from polydimethylsiloxanes (PDMS) hydrolysis. PDMS (silicones) are used in a wide range of consumer and industrial applications. PDMS are released into the environment through landfills and wastewater treatment plants. There is a lack of knowledge concerning PDMS biodegradation during waste storage. Consequently, understanding PDMS behaviour in landfill cells and in sludge digester is particularly important. In this article, we focused on microbial degradation of PDMS through laboratory experiments. Preliminary test concerning anaerobic biodegradation of various PDMS have been investigated. Results demonstrate that the biotic step has an obvious influence on PDMS biodegradation.

Development of a gas filter against wire chamber ageing for the MDT chambers in ATLAS

Drift chamber ageing is a serious concern for the operation of the Monitored Drift Tube chambers (MDT) in the ATLAS muon system. Therefore systematic studies of ageing effects have been carried out at the University of Freiburg. It has been shown that tiny contaminations with volatile silicon compounds, which are found in many components supplied by industry, cause a severe degradation of the drift tube performance. Since the ATLAS MDT system contains many thousands of commercial components the cleanliness of all parts cannot be guaranteed. Therefore gas filters with zeolites have been developed in Freiburg, which remove these impurities efficiently. They will be employed in the gas system for the MDT chambers.

Preparation of High-Purity Silicon for Solar Cells

This article addresses the problems in the preparation of high-purity silicon for solar cells. The growing application field of silicon solar cells requires a substantial reduction in the cost of semiconductor-grade silicon, which is currently produced by the classical trichlorosilane process. Here, we analyze alternative processes for the preparation of solar-grade silicon: the reduction of volatile silicon compounds, refining of metallurgical-grade silicon, reduction of silicon fluorides, and reduction of silicon dioxide. We believe that carbothermal reduction followed by the refining of melted silicon is the most attractive process from the viewpoint of manufacturing cost.

Analysis of cosmetic products by gas chromatography/mass spectrometry and fast‐atom bombardment mass spectrometry: when a combined approach is successful

Fast-atom bombardment mass spectrometry (FAB-MS, both in the positive-and negative-ion modes) and gas chromatography/mass spectrometry (GC/MS) were applied for the rapid identification of the main ingredients of two widely employed cosmetic products, a mascara and a semipermanent hair dye. FAB-MS, on the untreated product (hair dye) or on a crude methanol extract (mascara) gives an unequivocal fingerprint of involatile constituents, i.e. surfactants, anionic (cetyl/stearyl soaps) in mascara and cationic (polyethoxylated oleyl/linoleyl/ricinoleyl-methyl ammonium chloride) in the hair dye. GC/MS (n-hexane and chloroform extracts), detects hydrocarbons, volatile silicon compounds, perfume components, preservatives and antioxidants in mascara and fatty acids (C8–C18), dye solvents and 4 colouring agents: 2-amino-5-nitrophenol, HC Yellow 2 (N-2-hydroxyethyl-o-nitroaniline); O-(2-hydroxyethyl)-4-amino-3-nitrophenol and HC Red3, N-(2-hydroxyethyl)-2-nitro-p-phenylendiamine in the hair dye. These results demonstrate that the combined FAB-MS and GC/MS approaches, enabling a complete picture of the constituents of the cosmetic matrix, provide an invaluable analytical tool for the quality control of cosmetics, a subject that has been rather neglected to date. © 1997 John Wiley & Sons, Ltd.