JP4626965B2 - Method for analyzing sulfur compounds - Google Patents

Description

The present invention relates to a method for analyzing sulfur compounds contained in kerosene and light oil.

  In recent years, when hydrocarbons are used as the hydrogen source of fuel cells, which are attracting attention as a highly efficient and clean technology, sulfur that becomes a catalyst poison for reforming catalysts in the hydrogen production process and further degrades the performance of the fuel cell body. It is necessary to remove it strictly. For example, when fuel oil such as naphtha, kerosene, and light oil is used as the hydrogen source of the fuel cell, it is necessary to reduce the sulfur content in the fuel oil to ppb or less.

  However, flame photometric detector (FPD) -gas chromatograph (GC), atomic emission detector (Atomic Emission Detector), which has been conventionally used for qualitative and quantitative analysis of sulfur compounds in hydrocarbons. AED) -GC and Sulfur Chemiluminescence Detector (SCD) -GC are insensitive to sulfur concentrations below ppb. Even in recent years, GC-Inductively Coupled Plasma Mass Spectrometer (ICP-MS), which has been applied to qualitative and quantitative analysis of sulfur compounds in gasoline, cannot be said to have sufficient sensitivity. 3ppb was the limit (see Non-Patent Document 1). Furthermore, the conventional examination (Non-patent Document 1) relates to gasoline, and there is no examination of kerosene or light oil having a higher boiling point.

On the other hand, when xenon (Xe) gas is used as the collision gas for ICP-MS, although the detection intensity of sulfur is reduced, spectral interference caused by coexisting oxygen diatomic ions ( ³² O ₂ ⁺ ) can be reduced. In particular, it is known that the lower limit of determination of sulfur can be lowered. However, when GC is directly connected, it is considered that the influence of oxygen diatomic ions is not significant, and further, there is a demerit that the detection intensity of sulfur is reduced by introducing a collision gas. -Introducing collision gas to ICP-MS also considered that device manufacturers had no effect.

Steven M.M. Wilbur and Emmett Sofity: Agilent Technologies Technical Report “Quantification and Charactarization of Sulfur in Low-Sulfur Reformed MSP”

Then, the objective of this invention is providing the qualitative and quantitative analysis method of the sulfur compound contained in kerosene or light oil with a low detection minimum and a minimum of determination.

  As a result of diligent research to solve the above problems, the present inventors have significantly reduced the background even in GC-ICP-MS by using xenon gas as the collision gas. It was found that the lower limit of quantification was lowered, but a smaller amount of sulfur content could be quantified although the detection intensity of the slag decreased. Further, the supply amount of xenon gas as a collision gas is effective at 0.05 mL / min or more, preferably in the range of 0.05 to 1.00 mL / min, more preferably in the range of 0.10 to 0.50 mL / min, and 0.20 to 0.30 mL / min. It has been found that more xenon gas is preferably supplied to a sulfur compound having a higher molecular weight, particularly a sulfur compound having a molecular weight higher than that of benzothiophene.

That is, the present invention provides a qualitative and quantitative analysis by GC-ICP-MS, relates analytical method of sulfur subjected to inhibition of oxygen 2 atomic ions, the method analyzes of sulfur compounds of the present invention, sulfur kerosene or gas oil benzothiophene and / or gas chromatograph with large molecular weight sulfur compounds than the benzothiophene is included as a compound - during the qualitative and quantitative analysis by inductively coupled plasma mass spectrometer, supplying xenon gas as the collision gas 0.10 mL / min or more It is characterized by doing.

According to the present invention, in qualitative and quantitative analysis by GC-ICP-MS of benzothiophene and / or a sulfur compound having a molecular weight higher than that of benzothiophene contained in kerosene or light oil as a sulfur compound, oxygen coexisting in the analysis system Sulfur can be analyzed with high sensitivity by removing oxygen diatomic ions generated by decomposition and recombination of molecules, water, siloxane, etc. with a collision gas made of xenon gas.

  The present invention is described in detail below. In the qualitative and quantitative analysis method for sulfur compounds according to the present invention, in the analysis by GC-ICP-MS, xenon gas can be used as a collision gas to remove oxygen diatomic ions and detect sulfur with high sensitivity. it can.

  ICP-MS has been more than 20 years since it was commercialized in the 1980s, and is now widely used in various industries. In particular, it is widely used in the semiconductor industry, and is used as an analytical method for quality control of high-purity substances that are becoming increasingly demanding with the times. In addition, it is expected to be applied to the analysis of trace amounts of toxic metals in environmental samples, and recently, in order to cope with the decrease in environmental standard values and drainage standard values accompanying revision of various official laws in the environmental field, ICP-MS is adopted.

ICP-MS is extremely sensitive with detection limits of most elements on the order of ppt to ppq, allows simultaneous multi-element analysis, enables rapid qualitative and quantitative analysis, has a wide dynamic range, and isotope ratio measurement. It has various features such as being possible. The ICP-MS includes an ion source (ICP), a sampling interface, an ion lens, a mass spectrometer (MS) meter, and a detector. Further, argon (Ar) is used as the plasma gas (make-up gas). ICP, which is an ion source, is ideal as an ionization source for MS analysis, and many elements are ionized by 90% or more. Ions generated in the ICP are guided to the MS analysis section through the sampling interface. The sampling interface section is composed of a conical shape made of two metals, a sampling cone and a skimmer cone, and the space between the two is exhausted to about several hundred Pa by a rotary pump. Ions drawn through the sampling cone and the skimmer cone are converged on the MS analyzer by the ion lens. The ion lens and the mass analysis unit are exhausted to 10 ⁻³ Pa and 10 ⁻⁴ Pa, respectively, by a turbo molecular pump. The ions subjected to mass selection by the mass spectrometer are detected by an ion detector.

  One of the problems of ICP-MS is spectral interference in which polyatomic ions having the same mass number as the target element overlap and cause interference. In addition to polyatomic ions (ArO, ArH, ArOH, ArN, ArCl, ArC, ArAr, etc.) derived from argon, polyatomic ion interference is derived from oxygen diatomic ions and nitrogen molecules derived from oxygen molecules in the air. Nitrogen diatomic ions etc.

  The collision (collision) gas used in the analysis method of the present invention is a gas for reducing the amount of unnecessary polyatomic ions detected by colliding with unnecessary polyatomic ions at the interface section. Conventionally, collision gases such as hydrogen gas and helium gas have been used, but in recent years it has been found that xenon gas is effective in removing oxygen diatomic ions.

  Since MS used in the analysis method of the present invention is detected for each mass number, those having the same molecular weight cannot be distinguished. Here, the mass number of the oxygen diatomic ion is 32, which is the same as the atomic weight 32 of sulfur. Therefore, if oxygen diatomic ions are mixed in MS, they are detected together with sulfur. When the sulfur content is high, even if a very small amount of oxygen diatomic ions is added, there is no big problem. However, in the analysis at the ppb level, the amount of oxygen diatomic ions relative to the amount of sulfur is at a level that cannot be ignored. Oxygen diatomic ions are detected as a background when analyzing a liquid that does not contain any sulfur, and in general, about 1/10 of the background is the lower limit of quantification. In order to enable analysis, the background needs to be about 10 ppb.

In the case where ICP-MS is directly connected to GC, when a capillary column necessary for detailed qualitative analysis is used, since the amount of sample introduced into the GC column is small, the detection intensity of sulfur is inevitably reduced. On the other hand, oxygen diatomic ions generated by decomposition and recombination of oxygen molecules, water, siloxane, etc. in plasma are diluted with a carrier gas such as helium or separated from sulfur compounds in the column. For this reason, it has been considered that almost no detection has been made. In addition, by introducing collision gas into ICP-MS, oxygen diatomic ions can be removed, but at the same time, part of the sulfur ions ( ³² S ⁺ ) are also removed, and the detection intensity of sulfur is reduced. End up. Therefore, since it was thought that almost no oxygen diatomic ions existed through the GC, introducing a collision gas in the GC-ICP-MS only reduces the detection intensity of sulfur. It was considered ineffective.

As a result of intensive studies, the present inventors have found that the lower limit of determination of sulfur can be lowered by introducing a collision gas also in GC-ICP-MS, and it can be determined up to about 1 ppb. In particular, by supplying xenon gas as a collision gas at 0.10 mL / min or more, preferably 0.10 to 1.00 mL / min, more preferably 0.10 to 0.50 mL / min, and even more preferably 0.20 to 0.30 mL / min, the effect is improved. Become huge. If too much xenon gas is supplied as collision gas, sulfur ions ( ³² S ⁺ ) will be removed and the detection intensity of sulfur will be reduced, so the xenon gas supply rate will be 1.00 mL / min or less. It is preferable to do. In particular, for a sulfur compound having a lower molecular weight, such as a compound having a lower molecular weight than benzothiophene, it is more effective to set the supply amount of xenon gas as a collision gas to 0.10 to 0.3 mL / min. For sulfur compounds having a higher molecular weight, for example, sulfur compounds having a molecular weight higher than benzothiophene, it is more effective to supply xenon gas as a collision gas at 0.10 mL / min or more, preferably 0.20 mL / min or more. I found out. The reason for this is not clear, but liquid hydrocarbons with a high boiling point have high viscosity, so dissolved oxygen molecules are likely to be entrained in the GC, and oxygen contained in the column at a temperature at which high-boiling compounds flow out of the GC column. It is conceivable that the compound also flows out.

The sulfur compound analysis method of the present invention is applied to kerosene or light oil.

The kerosene and light oil can be used as a hydrogen source for fuel cells and the like, but sulfur contained in kerosene and light oil becomes a catalyst poison of the reforming catalyst in the hydrogen production process, and further reduces the performance of the fuel cell body. Therefore, it must be removed strictly. For example, when using kerosene, gas oil as the hydrogen source, the sulfur content of the kerosene and gas oil, several mass ppb or less, it is necessary to preferably reduced to less than 1 ppb by weight.

The kerosene is mainly composed of hydrocarbons having about 12 to 16 carbon atoms, has a density (15 ° C.) of about 0.790 to 0.850 g / cm ³ and a boiling point range of about 150 to 320 ° C. The kerosene contains a large amount of paraffinic hydrocarbons, but contains about 0 to 30% by volume of aromatic hydrocarbons and about 0 to 5% by volume of polycyclic aromatics. Specific examples include Japanese Industrial Standards JIS No. 1 kerosene, which is used as fuel for lighting, heating, and kitchen. The quality of the kerosene is as follows: flash point 40 ° C or higher, 95% distillation temperature 270 ° C or lower, sulfur content 0.008% by mass or lower, smoke point 23mm or higher (21mm or higher for cold weather), copper plate corrosion (50 ° C, 3 hours) 1 or less, color (Saebold) +25 or more. The kerosene contains a sulfur content of several ppm to 80 ppm or less and a nitrogen content of several ppm to several tens of ppm.

The light oil is mainly composed of hydrocarbons having about 16 to 20 carbon atoms, has a density (15 ° C.) of about 0.820 to 0.880 g / cm ³ and a boiling point range of about 140 to 390 ° C. The light oil contains a large amount of paraffinic hydrocarbons, but contains about 10 to 30% by volume of aromatic hydrocarbons and about 1 to 10% by volume of polycyclic aromatics. The light oil contains a sulfur content of several ppm to 100 ppm or less and a nitrogen content of several ppm to several tens of ppm.

The sulfur compound analyzed by the method of the present invention is preferably selected from sulfur compounds contained in kerosene and light oil. The sulfur in the sulfur compound has four natural isotopes, specifically, ³² S (94.93%), ³³ S (0.76%), ³⁴ S (4.29%) and ³⁶ S (0.02%). Consists of. Usually, the mass number 32 is measured for quantitative determination with high sensitivity. On the other hand, oxygen has natural isotopes of ¹⁶ O (99.76%), ¹⁷ O (0.038%), and ¹⁸ O (0.205%), so even if you select the measured mass number of sulfur, If the generation of ions occurs in a free combination, it cannot escape from interference. In the present invention, the measurement of the mass number 32 is mainly performed, but the measurement of the mass number 34 or the like is not excluded.

The lower the concentration of the sulfur compound contained in the kerosene or light oil , the greater the effect of the present invention.For example, the concentration of the sulfur compound contained in the kerosene or light oil is preferably 50 mass ppm or less as sulfur. More preferably, it is at most ppm by mass.

The organic sulfur compounds contained in the kerosene or light oil can be classified into six types: mercaptans, chain sulfides, cyclic sulfides, thiophenes, benzothiophenes, and dibenzothiophenes.

  The mercaptans are sulfur compounds having a mercapto group (—SH) (RSH: R is a hydrocarbon group such as an alkyl group or an aryl group), and are also called thiols or thioalcohols. The mercapto group is highly reactive and reacts particularly easily with metals. Typical mercaptans include methyl mercaptan, ethyl mercaptan, propyl mercaptan, butyl mercaptan (including tertiary butyl mercaptan), pentyl mercaptan, hexyl mercaptan, heptyl mercaptan, octyl mercaptan, nonyl mercaptan, decyl mercaptan, and thiophenol. (Also called phenyl mercaptan and benzenethiol), thiocresol (also called mercaptotoluene), thiolenol (also called mercaptoxylene and dimethylphenyl mercaptan), thiocarbachlor (2-mercapto-p-cymene, 5-isopropyl-2- Also called methylthiophenol), dithiocatechol (o-phenylene dimercaptan, o-mercaptobenzene, 1,2-disulfhydrylbenze) Dithiohydroquinone (also called dithiohydroquinone, p-phenylene dimercaptan, p-dimercaptobenzene, 1,4-disulfhydrylbenzene), dithioresorcin (m-phenylene dimercaptan, m-dimercaptobenzene, 1 , 3-disulfhydrylbenzene), dithiol (also called toluene-3,4-dithiol, 3,4-dimercaptotoluene), trithiophloroglucin and other thiophenols (Ar-SH: Ar is an aryl group) Furthermore, thionaphthol (also referred to as naphthyl mercaptan and mercaptonaphthalene), thiobenzhydrol (also referred to as benzhydryl mercaptan and α-mercaptodiphenylmethane), and derivatives thereof can be mentioned.

  The sulfides are also called thioethers, and are a general term for alkyl sulfides and aryl sulfides, and sulfur represented by the general formula R—S—R ′ (R and R ′ are hydrocarbon groups such as alkyl groups and aryl groups). A compound. The sulfides are compounds in which two hydrogen atoms of hydrogen sulfide are substituted with an alkyl group or the like. In the present invention, disulfides are also included in the above sulfides. The disulfide means a disulfide, and is a general term for alkyl disulfide and aryl disulfide, and is represented by a general formula R—S—S—R ′ (R and R ′ are hydrocarbon groups such as an alkyl group). It is a sulfur compound. A disulfide bond (SS) is one of the oxidation stages of a mercapto group (-SH), and is naturally present in proteins. The sulfides can be classified into chain sulfides and cyclic sulfides.

  The above-mentioned chain sulfides are sulfur compounds having no heterocyclic ring containing a sulfur atom as a different atom among sulfides. Typical chain sulfides include dimethyl sulfide, methyl ethyl sulfide, methyl propyl sulfide, diethyl sulfide, methyl butyl sulfide, ethyl propyl sulfide, methyl pentyl sulfide, ethyl butyl sulfide, dipropyl sulfide, methyl hexyl sulfide, ethyl pentyl. Sulfide, propyl butyl sulfide, methyl heptyl sulfide, ethyl hexyl sulfide, propyl pentyl sulfide, dibutyl sulfide, dimethyl disulfide, methyl ethyl disulfide, methyl propyl disulfide, diethyl disulfide, methyl butyl disulfide, ethyl propyl disulfide, methyl pentyl disulfide, ethyl butyl disulfide, Dipropyl disulfide, methyl hex Thioketones such as disulfide, ethylpentyl disulfide, propylbutyl disulfide, methylheptyl disulfide, ethylhexyl disulfide, propylpentyl disulfide, dibutyl disulfide, thioanisole (also called methylphenyl sulfide), thiophenetol (also called ethylphenyl sulfide), thiobenzophenone (RCSR ′: R and R ′ are hydrocarbon groups such as an alkyl group and an aryl group) and derivatives thereof.

  On the other hand, the cyclic sulfides have a heterocyclic ring containing one or more sulfur atoms as hetero atoms among the sulfides, and have no aromaticity (a 5-membered ring or a 6-membered ring with 2 double bonds). Sulfur compounds that do not have more than one heterocyclic ring. Typical cyclic sulfides include thioketones (RCSR ′: R and R ′) such as tetrahydrothiophene (also called tetramethylene sulfide), thiochroman (also called dihydrobenzothiopyran), thiaadamantane, trithioacetone, and dithioacetone. Are hydrocarbon groups such as alkyl groups and aryl groups), trimers of thiobenzaldehyde, 1,4-dithiane (also referred to as diethylene disulfide), dithiolane, and derivatives thereof.

  Among the heterocyclic compounds containing one or more sulfur atoms as heteroatoms, the thiophenes have a five-membered or six-membered heterocyclic ring and have aromaticity (two double bonds in the heterocyclic ring). In addition, sulfur compounds in which the heterocycle is not condensed with the benzene ring and derivatives thereof, and compounds in which the heterocycles are condensed are also included. Thiophene is also called thiofuran, and other typical thiophenes include methylthiophene (also called thiotolene), thiopyran (also called penthiophene), thiobutene, tetraphenylthiophene (also called thionesal), dithienylmethane, and these. And derivatives thereof.

  Among the heterocyclic compounds containing one or more sulfur atoms as heteroatoms, the above benzothiophenes have a five-membered or six-membered heterocyclic ring and have aromaticity (a double bond in the heterocyclic ring has 2 And a sulfur compound in which a heterocyclic ring is condensed with one benzene ring and derivatives thereof. Benzothiophene is also called thionaphthene or thiocoumarone, and other typical benzothiophenes include methylbenzothiophene, dimethylbenzothiophene, trimethylbenzothiophene, tetramethylbenzothiophene, pentamethylbenzothiophene, hexamethylbenzothiophene, methyl Ethylbenzothiophene, dimethylethylbenzothiophene, trimethylethylbenzothiophene, tetramethylethylbenzothiophene, pentamethylethylbenzothiophene, methyldiethylbenzothiophene, dimethyldiethylbenzothiophene, trimethyldiethylbenzothiophene, tetramethyldiethylbenzothiophene, methylpropylbenzo Thiophene, dimethylpropylbenzothiophene, trimethylpropylben In addition to alkylbenzothiophenes such as thiophene, tetramethylpropylbenzothiophene, pentamethylpropylbenzothiophene, methylethylpropylbenzothiophene, dimethylethylpropylbenzothiophene, trimethylethylpropylbenzothiophene, tetramethylethylpropylbenzothiophene, thiochromene (benzothio- (also referred to as γ-pyran), dithiaphthalene and derivatives thereof.

  Among the above-mentioned dibenzothiophenes, among heterocyclic compounds containing one or more sulfur atoms as hetero atoms, the heterocyclic ring is a 5-membered or 6-membered ring and has aromaticity (a double bond is formed in the heterocyclic ring). And a sulfur compound in which a heterocyclic ring is condensed with two benzene rings and derivatives thereof. Dibenzothiophene is also called diphenylene sulfide, biphenylene sulfide, and diphenylene sulfide. Among the above dibenzothiophenes, 4-methyldibenzothiophene and 4,6-dimethyldibenzothiophene are well known as difficult desulfurization compounds in hydrorefining. ing. Other representative dibenzothiophenes include trimethyldibenzothiophene, tetramethyldibenzothiophene, pentamethyldibenzothiophene, hexamethyldibenzothiophene, heptamethyldibenzothiophene, octamethyldibenzothiophene, methylethyldibenzothiophene, dimethylethyldibenzothiophene, Trimethylethyldibenzothiophene, tetramethylethyldibenzothiophene, pentamethylethyldibenzothiophene, hexamethylethyldibenzothiophene, heptamethylethyldibenzothiophene, methyldiethyldibenzothiophene, dimethyldiethyldibenzothiophene, trimethyldiethyldibenzothiophene, tetramethyldiethyldibenzothiophene, Pentamethyldiethyldibenzo Offene, hexamethyldiethyldibenzothiophene, heptamethyldiethyldibenzothiophene, methylpropyldibenzothiophene, dimethylpropyldibenzothiophene, trimethylpropyldibenzothiophene, tetramethylpropyldibenzothiophene, pentamethylpropyldibenzothiophene, hexamethylpropyldibenzothiophene, heptamethylpropyl In addition to alkyldibenzothiophene such as dibenzothiophene, methylethylpropyldibenzothiophene, dimethylethylpropyldibenzothiophene, trimethylethylpropyldibenzothiophene, tetramethylethylpropyldibenzothiophene, pentamethylethylpropyldibenzothiophene, hexamethylethylpropyldibenzothiophene, and thiant Emissions (also called diphenylene disulfide), thioxanthene (dibenzo thiopyran, also referred to as diphenylmethane sulfide), and derivatives thereof.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples.

  Tetrahydrothiophene (reagent special grade, manufactured by Kanto Chemical Co., Inc.), diethyl disulfide (reagent special grade, manufactured by Wako Pure Chemical Industries, Ltd.) and benzothiophene (reagent special grade, manufactured by Kanto Chemical Co., Ltd.), toluene (reagent special grade, Kanto Chemical Co., Ltd.) Company) and diluted to 100 mass ppb as sulfur. Next, qualitative and quantitative analysis of the sulfur compound was performed under the analysis conditions shown in Table 1. In addition, as GC-ICP-MS, the system which connected 6890N type GC made from Agilent, and 7500cs type ICP-MS with the transfer line was used. The results are shown in FIG.

  As shown in Figure 1, by supplying xenon gas as collision gas, the background equivalent concentration (BEC), which is the sulfur content with the same detection intensity as the background, is almost halved, and the lower limit of quantification is reduced to about half. It turns out that it falls. In the case of tetrahydrothiophene and diethyl disulfide, when the xenon gas supply amount is 7% or more (actual flow rate: 0.14 mL / min) or more, there is little effect of further reducing BEC even if the xenon gas supply amount is increased. It can be seen that benzothiophene having a higher molecular weight has the effect of further reducing BEC by increasing the xenon gas supply amount even when the xenon gas supply amount is 10% or more (actual flow rate: 0.20 mL / min). For sulfur in benzothiophene, the BEC is about 10 mass ppb with the indicated value of xenon gas supply amount of 10%, and the lower limit of quantification is about 1 mass ppb when the lower limit of quantification is considered 1/10 of the background. .

  Kerosene (manufactured by Japan Energy, boiling range 158.5-270.0 ° C, 5% distillation point 170.5 ° C, 10% distillation point 175.0 ° C, 20% distillation point 181.5 ° C, 30% distillation point 188.0 ° C, 40% distillation 194.5 ° C, 50% distilling point 202.5 ° C, 60% distilling point 211.0 ° C, 70% distilling point 221.0 ° C, 80% distilling point 232.0 ° C, 90% distilling point 245.5 ° C, 95% distilling point 256.5 ℃, 97% Distillation point 263.5 ℃, Density (15 ℃) 0.7982g / ml, Aromatic content 17.5% by volume, Saturated content 82.5% by volume, Sulfur content 13.3ppm, Benzothiophenes 8.8ppm, Dibenzothiophenes 4.5ppm, Qualitative and quantitative analysis was performed by GC-ICP-MS in the same manner as in Example 1 by supplying 0.20 mL / min of xenon gas as a collision gas for sulfur compounds contained in nitrogen content of 1 ppm or less. As a result, about 1 mass ppb of sulfur could be detected in kerosene, and the effect of the collision gas composed of xenon gas could be confirmed.

It is a graph which shows the relationship between the collision gas supply amount (valve instruction | indication value of collision gas) and background equivalent density | concentration in Example 1. FIG.

Claims (1)

Benzothiophene and / or large sulfur compound having a molecular weight than the benzothiophene gas chromatograph contained as a sulfur compound in kerosene or gas oil - in qualitative and quantitative analysis by inductively coupled plasma mass spectrometer, a xenon gas as collision gas 0.10 A method for analyzing sulfur compounds, characterized by supplying at least mL / min .

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