Experimental study of fuel decomposition and hydrocarbon growth processes for practical fuel components in nonpremixed flames: MTBE and related alkyl ethers

Fuel decomposition and hydrocarbon growth processes of methyl tert‐butyl ether (MTBE) and related alkyl ethers have been studied experimentally in soot‐producing nonpremixed flames. Temperature, C1–C12 hydrocarbons, and major species were measured in coflowing methane/air flames whose fuel was separately doped with 5000 ppm of MTBE, n‐butyl methyl ether (NBME), sec‐butyl methyl ether (SBME), ethyl tert‐butyl ether (ETBE), and tert‐amyl methyl ether (TAME; =1,1‐dimethylpropyl methyl ether). The consumption rates of the dopants, several simple kinetic calculations, and the dependence of the observed products on fuel composition indicate that the dominant decomposition process was unimolecular dissociation, not H‐atom abstraction. The dominant dissociations were four‐center elimination of alcohols for the doubly branched ethers (MTBE, ETBE, and TAME) and C? O fission for the linear ether (NBME), while four‐center elimination and C? O fission were comparably important for the singly branched ether (SBME). These dissociations produced alkenes which further reacted to produce alkadienes/alkynes, alkenynes, acetylenic compounds, and aromatics. The dependence of the maximum benzene mole fractions on fuel composition was consistent with benzene formation through reactions of highly‐unsaturated C3 and/or C4 hydrocarbons (C₃H₃, n‐C₄H₃, C₄H₄, n‐C₄H₅, etc.). © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 345–358, 2004     

专用测定汽油中含氧化合物气相色谱仪的研制和开发

采用气相色谱分析技术,可快速、准确地测定清洁汽油中的含氧化合物含量.参照ASTM D4815及SH/T0663的要求,在上海市计算技术研究所自主研制生产的气相色谱仪上开发此专用分析方法,分析汽油中C1～C4醇、甲基叔丁基醚(MTBE)、乙基叔丁基醚(ETBE)、叔戊基甲基醚(TAME)等组分,测试范围:醇,0.1%(M/M)～12.0%(M/M);醚,0.1%(M/M)～20.0%(M/M).再结合开发的专用色谱分析软件,力求给用户提供性价比更高、操作更加便捷的分析系统.     

Dual capillary gas chromatographic analysis of alcohols and methyl tert-butyl ether in gasolines

A gas chromatographic method has been developed for the identification and direct determination of alcohols and methyl tert-butyl ether (MTBE) in gasolines. The technique involves simultaneous injection of the gasoline without any sample preparation onto two fused silica capillary columns of differing polarities. The method permits simultaneous determinations of methanol, ethanol, 2-propanol, tert-butanol, 1-propanol, sec-butanol, 1-butanol, and MTBE. By using an automatic sampler in combination with electronic pressure programming and BASIC programming, the determinations were performed automatically and reproducibly with a relatively short analysis time.     

Determination of low level methyl tert-butyl ether, ethyl tert-butyl ether and methyl tert-amyl ether in human urine by HS-SPME gas chromatography/mass spectrometry

Methyl tert-butyl ether (MTBE), ethyl tert-butyl ether (ETBE) and tert-amyl methyl ether (TAME) are oxygenated compounds added to gasoline to enhance octane rating and to improve combustion. They may be found as pollutants of living and working environments. In this work a robotized method for the quantification of low level MTBE, ETBE and TAME in human urine was developed and validated. The analytes were sampled in the headspace of urine by SPME in the presence of MTBE-d12 as internal standard. Different fibers were compared for their linearity and extraction efficiency: carboxen/polydimethylsiloxane, polydimethylsiloxane/divinylbenzene, and polydimethylsiloxane. The first, although highly efficient, was discarded due to deviation of linearity for competitive displacement, and the polydimethylsiloxane/divinylbenzene fiber was chosen instead. The analysis was performed by GC/MS operating in the electron impact mode. The method is very specific, with range of linearity 30-4600 ng L⁻¹, within- and between-run precision, as coefficient of variation, <22 and <16%, accuracy within 20% the theoretical level, and limit of detection of 6 ng L⁻¹ for all the analytes. The influence of the matrix on the quantification of these ethers was evaluated analysing the specimens of seven traffic policemen exposed to autovehicular emissions: using the calibration curve and the method of standard additions comparable levels of MTBE (68-528 ng L⁻¹), ETBE (<6 ng L⁻¹), and TAME (<6 ng L⁻¹) were obtained.     

Simultaneous determination of methyl tert-butyl ether, its degradation products and other gasoline additives in soil samples by closed-system purge-and-trap gas chromatography-mass spectrometry

A new protocol for the simultaneous determination of methyl tert-butyl ether (MTBE); its main degradation products: tert-butyl alcohol (TBA) and tert-butyl formate (TBF); other gasoline additives, oxygenate dialkyl ethers: ethyl tert-butyl ether (ETBE), tert-amyl methyl ether (TAME) and diisopropyl ether (DIPE); aromatics: benzene, toluene, ethylbenzene and xylenes (BTEX) and other compounds causing odour events such as dicyclopentadiene (DCPD) and trichloroethylene (TCE) in soils has been developed. On the basis of US Environmental Protection Agency (EPA) method 5035A, a fully automated closed-system purge-and-trap coupled to gas chromatography/mass spectrometry (P&T-GC/MS) was optimised and permitted to detect microg/kg concentrations in solid matrices avoiding losses of volatile compounds during operation processes. Parameters optimised were the sampling procedure, sample preservation and storage, purging temperature, matrix effects and quantification mode. Using 5 g of sample, detection limits were between 0.02 and 1.63 microg/kg and acceptable method precision and accuracy was obtained provided quantification was performed using adequate internal standards. Soil samples should be analysed as soon as possible after collection, stored under -15 degrees C for not longer than 7 days if degradation products have to be analysed. The non-preservative alternative (empty vial) provided good recoveries of the most analytes when freezing the samples up to 7 day holding time, however, if biologically active soil are analysed the preservation with trisodium phosphate dodecahydrate (Na(3)PO(4).12H(2)O or TSP) is strongly recommended more than sodium bisulphate (NaHSO(4)). The method was finally applied to provide threshold and background levels of several gasoline additives in a point source and in sites not influenced by gasoline spills. The proposed method provides the directions for the future application on real samples in current monitoring programs at gasoline pollution risk sites where till now little monitoring data for MTBE in soils are available.     

Quantitative Determination of BTEX and Total Aromatic Compounds in Gasoline by Comprehensive Two-Dimensional Gas Chromatography (GC×GC)

Comprehensive two-dimensional gas chromatography (GC×GC) has been applied to the quantitative analysis of benzene, toluene, ethylbenzene, xylenes (BTEX), and all heavier aromatic compounds in gasoline. The two-dimensional chromatographic separation used volatility selection on the first-dimension column and polarity selection on the second-dimension column. In the resulting GC×GC chromatogram, aromatic species were resolved from other compound classes. Moreover, structurally related aromatics were grouped in a manner that facilitated identification and integration. The response of a flame ionization detector to each major aromatic group in gasoline was calibrated using internal standards. Quantitation produced results directly comparable with ASTM standard methods. The present GC×GC method can be expanded to analyze other gasoline components.     

Simultaneous determination of gasoline oxygenates and benzene, toluene, ethylbenzene and xylene in water samples using headspace-programmed temperature vaporization-fast gas chromatography-mass spectrometry

A sensitive method is presented for the fast analysis of seven fuel oxygenates (methanol, ethanol, tert-butyl alcohol (TBA), methyl tert-butyl ether (MTBE), ethyl tert-butyl ether (ETBE), tert-amyl methyl ether (TAME) and diisopropyl ether (DIPE)) and benzene, toluene, ethylbenzene and p-xylene (BTEX) in water samples. The applicability of a headspace (HS) autosampler in combination with a GC device equipped with a programmable temperature vaporizer (PTV) and a MS detector is explored. The proposed method achieves a clear improvement in sensitivity with respect to conventional headspace methods due to the use of the PTV. Two different packed liners with materials of different trapping strengths (glass wool and Tenax-TA) were compared. The benefits of using Tenax-TA instead of glass wool as packed material for the measurement of the 11 compounds emerged as better signal-to-noise ratios and hence better detection limits. The proposed method is extremely sensitive. The limits of detection are of the order of ng/L for six of the compounds studied and of the order of microg/L for the rest, with the exception of the most polar and volatile compound: methanol. Precision (measured as the relative standard deviation for a level with an S/N ratio close to 3) was equal to or lower than 15% in all cases. The method was applied to the determination of the analytes in natural matrixes (tap, river and sea water) and the results obtained can be considered highly satisfactory. The methodology has much lower detection limits than the concentration limits proposed in drinking water by the US Environmental Protection Agency (EPA) and the European Union for compounds under regulation.     

Determination of fuel dialkyl ethers and BTEX in water using headspace solid-phase microextraction and gas chromatography-flame ionization detection

A simple procedure for the determination of methyl tert-butyl ether (MTBE), ethyl tert-butyl ether (ETBE), ethyl butyl ether (EBE), tert-amyl methyl ether (TAME), benzene, toluene, ethylbenzene, and xylenes (BTEX) in water using headspace (HS) solid-phase microextraction (HS-SPME) was developed. The analysis was carried out by gas chromatography (GC) equipped with flame ionization detector (FID) and 100% dimethylpolysiloxane fused capillary column. A 2 Plackett-Burman design for screening and a central composite design (CCD) for optimizing the significant variables were applied. Fiber type, extraction temperature, sodium chloride concentration, and headspace volume were the significant variables. A 65 microm poly(dimethylsiloxane)-divinylbenzene (PDMS-DVB) SPME fiber, 10 degrees C, 300 g/l, and 20 ml of headspace (in 40 ml vial) were respectively chosen for the best extraction response. An extraction time of 10 min was enough to extract the ethers and BTEX. The relative standard deviation (R.S.D.) for the procedure varied from 2.6 (benzene) to 8.5% (ethylbenzene). The method detection limits (MDLs) found were from 0.02 (toluene, ethylbenzene, and xylenes) to 1.1 microg/l (MTBE). The optimized method was applied to the analysis of the rivers, marinas and fishing harbors surface waters from Gipuzkoa (North Spain). Three sampling were done in 1 year from June 2002 to June 2003. Toluene was the most detected analyte (in 90% of the samples analyzed), with an average concentration of 0.56 microg/l. MTBE was the only dialkyl ether detected (in 15% of the samples) showing two high levels over 400 microg/l that were related to accidental fuel spill.     

Method for determination of methyl tert-butyl ether in gasoline by gas chromatography

A simple method for the determination of methyl tert-butyl ether (MTBE) in gasoline has been developed. The separation of MTBE from other analytes was controlled by the use of gas chromatography–mass spectrometry in the full scan mode using the characteristic primary, secondary and tertiary ions m/z 73, 57 and 43. The sample mass spectrum did not show any superimposition of other analytes. The separation from the common gasoline component 2-methylpentane was sufficient for reliable quantitation. An application of the developed conditions using gas chromatography with flame ionization detection was performed by the analysis of regular, euro super, super premium unleaded and ‘Optimax’ gasoline from petrol stations in the area of Frankfurt/Main, Germany. Regular unleaded gasoline shows an average MTBE content of 0.4% (w/w), whereas the MTBE content in euro super gasoline varies between 0.4 and 4.2% (w/w). The blending of MTBE to super premium has increased from 8.2% (w/w) in 1998 to 9.8% (w/w) on average in 1999. The recently introduced gasoline ‘Optimax’ shows an average MTBE content of 11.9% (w/w). The presented method might also be used for the analysis of other ethers, such as ethyl tert-butyl ether, which requires the use of another internal standard.     

Photocatalytic Degradation of Ethyl tert‐Butyl Ether in Aqueous Solution Mediated by TiO2 Suspensions: Parameter and Reaction Pathway Investigations

Degradation of ethyl tert‐butyl ether (ETBE) with UV/TiO₂ was studied by solid‐phase microextraction and gas chromatography‐mass spectrometry. The complete removal of 0.1 g L^?1 of ETBE was achieved after 20 h of treatment. Factors such as pH of the system, catalyst and substrate concentration, and the presence of anions influenced the degradation rate. Establishment of the degradation pathway was made possible by a thorough analysis of the reaction mixture, which identified the main intermediate products generated. The possible degradation pathways were proposed and discussed in this research. The attack on the C–H bond in ETBE by ·OH forms an alkyl radical, which consequently produces a peroxyl radical upon reaction with oxygen. Peroxyl radicals react with one another and produce an alkoxy radical. The β‐bond fragmentation of the alkoxy radical produces different intermediates.     

Trace Analysis of Methyl Tert‐butyl Ether in Water Samples Using New Ultrasound‐assisted Dispersive Liquid‐liquid Microextraction and Gas Chromatography‐flame Ionization Detection

In this study, simple and efficient ultrasound‐assisted dispersive liquid‐liquid microextraction combined with gas chromatography (GC) was developed for the preconcentration and determination of methyl‐tert‐butyl ether (MTBE) in water samples. One hundred microliters of benzyl alcohol was injected slowly into 10 mL home‐designed centrifuge glass vial containing an aqueous sample with 30% (w/v) of NaCl that was located inside the ultrasonic water bath. The formed emulsion was centrifuged and 2 μL of separated benzyl alcohol was injected into a gas chromatographic system equipped with a flame ionization detector (GC‐FID) for analysis. Several factors influencing the extraction efficiency such as the nature and volume of organic solvent, extraction temperature, ionic strength and centrifugation times were investigated and optimized. Using optimum extraction conditions a detection limit of 0.05 μg L^‐1 and a good linearity (r² = 0.998) in a calibration range of 0.1‐500 μg L^‐1 were achieved. This proposed method was successfully applied to the analysis of MTBE in tap, well and a ground water sam ple contaminated by leaking gasoline from an underground storage tank (LUST) in a gasoline service station.     

Kinetics of liquid phase synthesis of ethyl tert‐butyl ether from tert‐butyl alcohol and ethanol catalyzed by β‐zeolite supported on monolith

This paper compared the performance of β‐zeolite and Amberlyst‐15 catalysts on a liquid phase synthesis of ethyl tert‐butyl ether (ETBE) from ethanol (EtOH) and tert‐butyl alcohol (TBA) β‐Zeolite was synthesized and deposited on monolith support. Its structure was confirmed by an XRD measurement and its composition was analyzed by an XRF measurement. It was found that even though the catalytic activity of β‐zeolite was lower than that of Amberlyst‐15, the selectivity of ETBE was much higher than that of Amberlyst‐15, resulting in almost the same level of ETBE yield. The dehydration of TBA to isobutene (IB) was the major side reaction. The kinetic study of the reaction catalyzed by β‐zeolite supported on monolith was carried out by using a semibatch reactor. The effect of external mass transfer was investigated by varying stirring speeds. The activity‐based rate expressions were developed taking into account of water inhibition. Three temperature levels of 323, 333, and 343 K were performed in the study to obtain the parameters in the Arrhenius's equation and the Van't Hoff's equation. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 292–299, 2002     

气相色谱法测定车用汽油中含氧化合物和苯胺类化合物

利用中心切割技术和双毛细管色谱柱系统,采用两次进样的方式,建立了气相色谱测定车用汽油中含氧化合物和苯胺类化合物的分析方法。第一次进样分析,组分首先进入非极性DB-1色谱柱(30 m×0.32 mm×1.0μm),按沸点由低到高的顺序分离,通过电磁阀切换将沸点小于2-己酮的组分切割至强极性GS-OxyPLOT色谱柱(10 m×0.53 mm×10μm)或CP-Lowox色谱柱(10 m×0.53 mm×10μm),其余重烃组分通过阻尼柱进入FID检测器。在GS-OxyPLOT或CP-Lowox色谱柱上,烃类组分与含氧化合物分离并进入检测器检测,消除了大量的烃类组分对含氧化合物测定的影响。第二次进样分析,设定电磁阀切换时间为间-甲基苯胺从非极性色谱柱流出的时间,苯胺类化合物在GS-OxyPLOT或CP-Lowox色谱柱上与烃类和含氧化合物分离并进入检测器检测。以乙二醇二甲基醚为内标化合物进行内标法定量。实现了在一套系统上同时测定车用汽油中添加的甲基叔丁基醚(MTBE)、甲醇、甲缩醛、乙酸仲丁酯、乙酸乙酯、苯胺、邻/间/对-甲基苯胺和N-甲基苯胺的含量,各组分的检测范围为0.01%~10%(质量分数),回收率为86.0%~102.6%。该法可以为车用汽油的质量控制提供有效的检测手段。     

Application of Comprehensive Two‐Dimensional Gas Chromatography (GC×GC) to the Qualitative Analysis of Essential Oils

This paper investigates the separation of moderately complex samples by comprehensive two‐dimensional gas chromatography (GC×GC). The analysis of peppermint (Mentha piperita) and spearmint (Mentha spicata) essential oil components, including acetates, alcohols, furans, ketones, sesquiterpenes, and terpenes, was achieved by one‐dimensional gas chromatography with quadrupole mass spectrometry detection (GC/MSD) and GC×GC with flame ionization detection. Peppermint essential oil was found to contain 89 identifiable peaks by GC×GC compared to 30 peaks in the GC/MSD chromatogram. Likewise, 68 peaks were found in the GC×GC chromatogram of spearmint (compared to 28 in GC/MSD). Plots of the first dimension versus second dimension retention times provided a fingerprint of the two essential oils, which revealed 52 similar compounds between the two essential oils as opposed to 18 matches by 1D GC.     

全二维气相色谱-飞行时间质谱对催化裂化汽油的定性与定量分析

采用全二维气相色谱-飞行时间质谱(GC×GC-TOF MS)对催化裂化汽油全馏分进行了定性与定量分析,建立了相应的分析方法.结果表明,汽油族组成中的烷烃、烯烃、环烷烃、芳烃在全二维点阵谱图中呈分区域、带状的分布特点.GC×GC-TOF MS根据催化裂化汽油组分内分子的沸点及极性差异对其进行两个维度分离,极大地避免了普通色谱法分析过程中沸点相似化合物共流的弊端,实现催化裂化汽油组分的精确分离和准确定性分析.通过引入响应因子,修正了不同性质的烃类在电离源上电离效率的差异,使得TOF对催化裂化汽油族组成的定量结果与普通气相色谱法的定量结果的相关性较好,且应用GC×GC-TOF MS方法获得了催化裂化汽油更为精确的族组成信息.GC×GC-TOF MS为催化裂化汽油精确表征提供了一种有效方法.     

Projection of multidimensional GC data into alternative dimensions—exploiting sample dimensionality and structured retention patterns

Comprehensive multidimensional gas chromatography (GC×GC) is a powerful separation technique. One of the features of this technique is that it offers separations with more apparent structure than that offered by conventional one-dimensional GC (1-D GC). While some previous studies have alluded to this structure, and used structured retention patterns for some simple classifications, the topic of structured retention in GC×GC has not been studied in any great detail. Using the separation of fatty acid methyl esters (FAME) on both nonpolar/polar and polar/nonpolar column sets, the interaction between the separation dimensions and the sample dimensions is explored here. The GC×GC separation of a series of compounds is presented as a projection of the sample from sample space, a p-dimensional space with dimensions defined by the dimensionality of the sample, into separation space: for GC×GC, a two-dimensional plane passing through the sample space in an orientation defined by the separation conditions. Using this conceptual model and some a priori knowledge of the sample, it is shown how the image of the sample in the separation space can be used to construct an image of the sample in alternate dimensions, such as second dimension retention factor (²k) vs. chain length in the case of FAME. These projections into alternate dimensions should facilitate the interpretation of the complex patterns found within the GC×GC chromatogram for the identification and classification of compounds.     

Excess molar enthalpies of the ternary system mtbe+ethanol+hexane

Excess molar enthalpies of the ternary mixture {x₁ tert-butyl methyl ether (MTBE)+x₂ ethanol+(1–x₁–x₂) hexane} and, the involved binary mixtures {x tert-butyl methyl ether (MTBE)+(1–x) ethanol}, {x tert-butyl methyl ether (MTBE)+(1–x) hexane} and {x ethanol+( 1–x) hexane} have been measured at 298.15 K and atmospheric pressure, over the whole composition range, using a Calvet microcalorimeter. The results were fitted by means of different variable degree polynomials.     

Simultaneous measurement of methyl tert‐butyl ether and tert‐butyl alcohol in human serum by headspace solid‐phase microextraction gas chromatography–mass spectrometry

The abundant production of methyl tert‐butyl ether (MTBE) and its widespread use have led to an increase in the potential for human exposure. This work described a simple, fast, sensitive, reliable and low‐cost method for the simultaneous measurement of MTBE and its metabolite, tert‐butyl alcohol (TBA) in human serum by headspace solid‐phase microextraction gas chromatography–mass spectrometry. Extraction conditions were optimized and 40 °C, 10 min, 250 rpm and 0.3 g NaCl for a 1 mL sample were the optimal conditions. This method showed good analytical performance in terms of sensitivity with limits of detection in serum (1 mL) of 0.03 µg/L for MTBE and 0.05 µg/L for TBA, accuracy (mean recovery values) from 75.8% to 85.8%, precision (relative standard deviations) <10% and sample stability (biodegradation) <10% after 28 days. A verification experiment proved the reproducibility and stability of this method as well. Finally the method was used to detect 212 specimens, and the internal dose levels for MTBE in human serum were presented in China. Copyright © 2015 John Wiley & Sons, Ltd.     

Rapid separation of cyanidin‐3‐glucoside and cyanidin‐3‐rutinoside from crude mulberry extract using high‐performance countercurrent chromatography and establishment of a volumetric scale‐up process

This study describes the rapid separation of mulberry anthocyanins; namely, cyanidin‐3‐glucoside and cyanidin‐3‐rutinoside, using high‐performance countercurrent chromatography, and the establishment of a volumetric scale‐up process from semi‐preparative to preparative‐scale. To optimize the separation parameters, biphasic solvent systems composed of tert‐butyl methyl ether/n‐butanol/acetonitrile/0.01% trifluoroacetic acid, flow rate, sample amount and rotational speed were evaluated for the semi‐preparative‐scale high‐performance countercurrent chromatography. The optimized semi‐preparative‐scale high‐performance countercurrent chromatography parameters (tert‐butyl methyl ether/n‐butanol/acetonitrile/0.01% trifluoroacetic acid, 1:3:1:5, v/v; flow rate, 4.0 mL/min; sample amount, 200–1000 mg; rotational speed, 1600 rpm) were transferred directly to a preparative‐scale (tert‐butyl methyl ether/n‐butanol/acetonitrile/0.01% trifluoroacetic acid, 1:3:1:5, v/v; flow rate, 28 mL/min; sample amount, 5.0–10.0 g; rotational speed, 1400 rpm) to achieve separation results identical to cyanidin‐3‐glucoside and cyanidin‐3‐rutinoside. The separation of mulberry anthocyanins using semi‐preparative high‐performance countercurrent chromatography and its volumetric scale‐up to preparative‐scale was addressed for the first time in this report.