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PROCEEDINGS OF UNIVERSITIES. APPLIED CHEMISTRY AND BIOTECHNOLOGY 2019 Vol. 9 No. 2 _ИЗВЕСТИЯ ВУЗОВ. ПРИКЛАДНАЯ ХИМИЯ И БИОТЕХНОЛОГИЯ 2019 Том 9 N 2_
Оригинальная статья / Original article УДК 66.061
DOI: http://dx.doi.org/10.21285/2227-2925-2019-9-2-313-319
Comparative analysis of petroleum and coal pitches using 1H and 13C NMR spectroscopy
© Ivan O. Doshlov, Igor A. Ushakov
Irkutsk National Research Technical University, Irkutsk, Russian Federation
Abstract: Petroleum and coal pitches are known to be among the most important sources of raw materials for the production of carbon materials, including electro-carbon, heat- and chemical-resistant structural products, metal-carbon and carbon-carbon composite materials, graphite electrodes, self-baking anode paste, carbon fibres, blast furnace and cupola coke. The quality of the pitches is determined by the elemental and group composition, as well as their structural and physical-chemical properties. The study of the molecular structure and group composition of the organic components of the pitch and the identification of the effect of the composition on the performance of the products is of great interest for assessing the prediction of the behaviour of pitches during processing and the properties of the products obtained from them. The present work is devoted to the study of the group composition of two petroleum and two coal pitches using high-resolution NMR spec-troscopy. The data of the 1H and 13C NMR spectra allow the composition of the pitch product to be estimated without separation into fractions, which, in turn, combined with the accuracy of the method and the recording speed of the 1H NMR spectra, increases the rapidity of this method of analysis. The combination of 1N and 13C NMR data allows additional information on the correlation of physical parameters and pitch composition to be established. The calculation of the (Ha/Ha) parameter, corresponding to the ratio of the integral intensities of signals of aromatic and aliphatic hydrogen atoms, provides the possibility of using it as a structural characteristic for a particular sample. In order to ensure the correct contribution to the integral intensity of the signals, 13C NMR spectra were recorded in a pulse sequence with suppression of the spin-spin proton interaction only for the period of data reading for the purposes of minimising the nuclear Overhauser effect. The relaxation delay between pulses was set to 10 s. The study of petroleum and coal pitches using NMR spectroscopy showed the proton spectra of NMR data to be sufficiently informative and suitable for monitoring the technological process of pitch production.
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Keywords: petroleum pitch, coal pitch, aromatic compounds, NMR spectroscopy, С NMR, softening point
Information about the article: Received October 19, 2018; accepted for publication June 7, 2019; available online June 28, 2019.
1 13
For citation: Doshlov I.O., Ushakov I.A. Comparative analysis of petroleum and coal pitches using H and C NMR spectroscopy. Izvestiya Vuzov. Prikladnaya Khimiya i Biotekhnologiya [Proceedings of Universities. Applied Chemistry and Biotechnology]. 2019, v. 9, no. 2, pp. 313-319. (in Russian). DOI: 10.21285/2227-2925-2019-9-2-313-319
Сравнительный анализ нефтяных и каменноугольных пеков методами 1H и 13C ЯМР-спектроскопии
© И.О. Дошлов, И.А. Ушаков
Иркутский национальный исследовательский технический университет, г. Иркутск, Российская Федерация
Резюме: Нефтяные и каменноугольные пеки являются одним из важных источников сырья для производства углеродных материалов: электроугольных, жаро- и химостойких конструкционных изделий, металл-углеродных, углерод-углеродных композиционных материалов, графитированных электродов, самообжигающихся анодных масс, углеродных волокон, доменного и литейного кокса. Качество пеков определяется элементным и групповым составом, его структурой и физико-химическими свойствами. Наибольший интерес для оценки прогнозирования поведения пеков при переработке и свойств получаемой из них продукции представляет изучение молекулярного строения и
группового состава органических компонентов пека и выявление влияния состава на практические свойства продукции. Представляемая работа посвящена исследованию группового состава двух нефтяных и двух каменноугольных пеков методами спектроскопии ЯМР высокого разрешения. Данные спектров ЯМР 1Н и 13С позволяют оценивать состав пековой продукции без разделения на фракции, что в сочетании с точностью метода и скоростью записи спектров ЯМР 1Н повышает экспрессность такого метода анализа. Совместное использование данных ЯМР 1Н и 13С позволяет извлекать дополнительную информацию, по которой можно устанавливать корреляцию с физическими параметрами составов пеков. Вычисление параметра (Нар/Нал) соответствующего отношению интегральных интенсивностей сигналов от ароматических атомов водорода к алифатическим атомам водорода, позволяет использовать его в качестве структурной характеристики для конкретного образца. Для обеспечения корректного вклада в интегральную интенсивность сигналов спектры ЯМР 13С регистрировались в импульсной последовательности с подавлением спин-спинового взаимодействия с протонами только на период считывания данных для минимизации ядерного эффекта Оверхаузера. Релаксационная задержка между импульсами задавалась равной 10 с. Проведенное исследование нефтяных и каменноугольных пеков методом ЯМР-спектроскопии показало достаточную информативность данных протонных спектров ЯМР, что может быть использовано при мониторинге технологического процесса производства пека.
Ключевые слова: нефтяные пеки, каменноугольные пеки, ароматические соединения, ЯМР-спектро-скопия, ЯМР 13С, температура размягчения
Информация о статье: Дата поступления 19 октября 2018 г.; дата принятия к печати 7 июня 2019 г.; дата онлайн-размещения 28 июня 2019 г.
Для цитирования: Дошлов И.О., Ушаков И.А. Сравнительный анализ нефтяных и каменноугольных пеков методами 1H и 13C ЯМР-спектроскопии // Известия вузов. Прикладная химия и биотехнология. 2019. Т. 9, N 2. С. 313-319. DOI: 10.21285/2227-2925-2019-9-2-313-319
INTRODUCTION
Petroleum and coal pitches are one of the most important sources of raw materials for the production of carbon materials, such as electro-carbon, heat and chemical resistant structural products, metal-carbon and carbon-carbon composite materials, graphite electrodes, self-baking anode paste, carbon fibres, blast furnace and cupola coke, formed solid propellants, etc. [1]. The quality of the pitches is determined by the elemental and group composition, as well as its structure and physical-chemical properties. The study of the molecular structure and group composition of the organic components of the pitch and the identification of the effect of the composition on the performance of the products is of great interest for assessing the prediction of the behaviour of pitches during processing and the properties of the products obtained from them [2-5]. A large number of publications are devoted to this problem, whose authors typically report using EPR and IR spectroscopy, GLC, and thermogravimetric methods of analysis [6-9]. For these purposes, NMR spectroscopy is used relatively rarely [10-12], although this method has significant advantages when using quantitative techniques for recording spectra on 1H and 13C nuclei [13].
The present work is devoted to the study of the group composition of two petroleum and two coal pitches using high-resolution NMR spectroscopy. Due to the complexity of the chemical composition, pitches are typically characterised by the group composition of its fractions having various solubility
in isooctane (petroleum ether), toluene and quino-line. According to the selectivity of dissolution, the pitches are divided into the following fractions [14]:
- a-fraction comprising substances insoluble in toluene and including two groups;
- a1-fraction involving substances insoluble in quinoline, having the properties of a polymer, but with two temperature transitions. In other words, these fractions represent a set of polymers, determine the possibility of a mesophase formation and are responsible for the graphitising properties of pitch;
- a2-fraction presented by substances soluble in quinoline, but not soluble in toluene. The insoluble part exhibits properties typical of crystallographite;
- p-fraction, presented by compounds soluble in toluene, but not soluble in petroleum ether, involving a polymer fraction and determining the binding properties of the pitch;
- /-fraction, presented by substances soluble in petroleum ether, is a mixture of compounds of the aromatic and heterocyclic series. With the temperature increases, the Y-fraction transforms into an isotropic liquid, which determines the impregnating properties of the pitch.
The 1H and 13C NMR spectra data allow the composition of the pitch production being estimated to be transformed into fractions without separation, which, in turn, combined with the accuracy of the method and the recording speed of the 1H NMR spectra, increases the rapidity of this method of analysis.
Fragmental analysis of the molecular structure of the pitches is associated with the need to select
solvents and ensure the high reproducibility of the results. The authors [12] believe that carbon disul-phide is the only acceptable solvent having both a sufficiently high dissolving power and the absence of signals in the analytical spectral regions. However, CS2 does not contain deuterium atoms, which inhibits the use of the internal field stabilisation of spectrometer, especially during long-term experiments. In our work, deuterochloroform was used as a solvent, in which all fractions dissolve quite well. The problem of the presence of residual solvent signals in proton spectra (7.25 ppm) was solved by taking into account the contribution from the solvent to the total integral intensity of the spectrum. In the 13C NMR spectra, the solvent signal does not overlap the significant spectral regions, additionally providing its calibration (77.1 ppm).
EXPERIMENTAL PART
1 13
N and C NMR spectra of the pitch working solutions in CDCl3 with a concentration of 5 and
1 13
10% for H- and C-analyses, respectively, were recorded by the Bruker DPX250 NMR spectrometer in the pulse mode at the working frequencies of 250 MHz (1N) and 63 MHz (13C) using internal stabilisation of resonance conditions on the 2N channel, quadrature phase detection and 90a read pulses with a sweep width of 10 kHz (1N) and 15 kHz (13C). 13C NMR spectra were recorded in a pulse sequence with suppression of the proton spin-spin interaction for the period of data reading due to minimisation of the nuclear Overhauser effect. Relaxation delay was
set to 10 s in order to ensure the correct contribution
•io
to the integral intensity of the signals [13]. C NMR spectra were obtained in 10K passes. Spectra processing in all cases included Fourier transform using the weighting function, phase adjustment, baseline correction and automatic digital signal integration.
The following numbering was assigned to the studied samples: petroleum pitch - 1 (Angarsk, Russia); pitch of pyrolysis resin - 2 (Angarsk, Russia); coal pitch - 3 (Zaporozhe), coal pitch - 4 (Russia).
A comparison of the obtained 1N NMR spectra (Fig. 1) for petroleum (1, 2) and coal (3, 4) pitches detected a significant difference in the contributions to the integral intensity of signals from aromatic hydrogen atoms EHar (range 6-9.5 ppm) and aliphatic hydrogen atoms EHal with the integration of signals carried out in the range of 0-5 ppm (Table 1). The total integral intensity of the spectrum in all cases was normalised to 100 units, Table 1 presents the corresponding contributions. The Har/Hal ratio allowed the proportion of the corresponding aromatic and aliphatic fragments in the mixture to be quantified.
To obtain detailed information, the spectral ranges were divided into fragments corresponding to the resonance regions of methyl, methylene and me-thine hydrogen atoms [12, 13] (see Table 1). Additionally, the low-field resonance region (2.0-5.0 ppm) corresponds to hydrogen atoms in a-position relative to the aromatic fragment, while the 0-2.0 ppm region corresponds to hydrogen atoms in p- and Y-position of the aliphatic chain.
9.5 9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0
ppm
1
Fig. 1. H NMR spectra of pitch samples 1-4 Рис. 1. Спектры ЯМР1Н образцов пеков 1-4 315 ХИМИЧЕСКАЯ ТЕХНОЛОГИЯ / CHEMICAL TECHNOLOGY =
Table 1
Spectral intensity contributions of signals in various ranges, %, in accordance to the 1H NMR spectra
Таблица 1
Вклады спектральных интенсивностей сигналов различных диапазонов, %,
по данным спектров ЯМР Н
Sample Spectral range, ppm ZHal Spectral range, ppm ZHar Har/Hal
0-1.0 1.0-2.0 2.0-3.0 3.0-5.0 6.0-8.5 8.5-9.5
1 11.6 40.7 18.7 5.9 76.9 19.8 3.3 23.1 0.30
2 1.7 9.4 20.5 11.9 43.5 51.9 4.6 56.5 1.30
3 0.1 1.1 8.8 4.8 14.8 75.5 9.7 85.2 5.76
4 0.1 2.1 7.3 5.1 14.6 74.3 11.1 85.4 5.85
As a result of analysis of the data presented in the Table 1, for the studied coal pitches of various origin (3, 4), spectral parameters are noted to be close in magnitude. Well-resolved 1N NMR spectra indicate the low molecular weight composition of the pitch components with a predominance of aromatic and polyaromatic structures having a low content of aliphatic functional groups.
Distinct 1H NMR spectra data are observed for the petroleum pitch samples. These spectra are characterised by broadened lines characteristic of multicomponent mixtures. In the sample 1, the main components contributing to the integral of the aliphatic part are the resonances of methylene groups of saturated fragments (1.0-2.0 ppm), corresponding to long chains (-CH2-)n (n> 3). In sample 2 (pyrolysis resin), signals of hydrogen atoms in a-position relative to the aromatic cycles contribute significantly to the intensity of the aliphatic part of the spectrum. For pitch samples 1 and 2, the relative contribution of the aliphatic part of the spectrum to the total integrated intensity differs significantly, as reflected in the integral value of EHal and Har/Hal ratio. Undoubtedly, these differences in the 1N NMR spectra indicate the different component composition of the pitches having an effect on their physical properties. For sample 1, the softening point is lower than for sample 2. Table 2 shows the physical-chemical properties of the investigated petroleum and coal pitches.
While comparing the spectral characteristics
of coal and petroleum pitches, it is necessary to note the insignificant contribution of aliphatic functional groups to the total spectrum intensity for coal pitches 3 and 4, reflecting in the Har/Hal parameter. the low value of the integral for signals in the range of 0-2.00 ppm evidences the absence of saturated hydrocarbon chains in the structures of the coal pitches. In the spectral region of 8.5-9.5 ppm for pitches 3 and 4, a more complex character is observed for the signals, belonging to protons constituting complex polyaromatic structures of the phenic type.
An analysis of the obtained 13C NMR spectra provides the qualitative features of the structure of the components of the pitches 1-4. First of all, this consists in the absence of signals in the range of 150-200 ppm. This fact allows for the absence of carbonyl and carboxyl-containing fragments in the structures of the pitch components to be established with confidence. Moreover, this absence can be applied to O-alkyl and O-aryl functional groups characterised by signals in the spectral region of 50-60 and 145-160 ppm, respectively (Fig. 2).
For petroleum pitch 1 in the 1 C NMR spectrum, narrow intense signals are observed in the range of 10-30 ppm, characteristic of saturated linear aliphatic chains. According to the relative integral intensity of these signals, the length of such fragments can be estimated as 7-8 carbon atoms. The
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integrated intensities of all signals in the C NMR spectra were normalised to 100 units (Table 3).
Table 2
Physical-chemical properties of petroleum and coal pitches
Таблица 2
Физико-химические свойства нефтяных и каменноугольных пеков
Sample Viscosity at 185 °C, cPs, not more than Softening point,°C (Mettler apparatus) Substances, insoluble in toluene (a-fraction), % Yield of volatile substances, mass %
1 1800 123.1 25.3 56.9
2 1630 142.6 24.7 52.0
3 407.2 111.2 34.5 54.3
4 395.4 110.5 33.6 57.1
Doshlov I.O., Ushakov I.A. Comparative analysis of petroleum and coal... Дошлов И.О., Ушаков И.А. Сравнительный анализ нефтяных и каменноугольных..
J. •J^L
3 Jk ,
A il ,
210 190 170 150 130 110 90 80 70 60 50 40 30 20 10 0
ppm
13
Fig. 2. C NMR spectra of pitch samples 1-4 (The intense signal of 77 ppm pertains to the solvent)
Рис. 2. Спектры ЯМР13С образцов пеков 1-4 (интенсивный сигнал 77 м.д. принадлежит растворителю)
For petroleum pitches 1 and 2, compared to the data for coal pitches, a greater contribution of 13C signals in the region of 130-150 ppm is observed. This region of the spectrum corresponds to the resonances of the quaternary atoms of aromatic structures directly connected with aliphatic fragments (Car-alkyl groups). In established terms of mass spectrometry, the composition of the pitch is characterised by its separation by mass of oligomeric products into monomers with m/z ranging from 200 to 400, dimers (m/z = 400-650), trimers (m/z = 650-950) and tetramers (m/z = 950-1600). In the main composition, even compounds with m/z ranging 800-900 present condensed aromatic systems containing
10-12 benzene rings [15, 16]. Such systems incorporate a set of non-equivalent quaternary carbon atoms contributing to the 13C NMR spectra in the region of 130-140 ppm.
As well as the proton spectra, the 13C NMR spectra of coal pitches 3 and 4 are better resolved by additionally indicating the simpler composition of the pitch components. The signal broadening in 13C NMR spectra of samples 1 and 2 indicates the presence of polymer products (ai-fraction) in their composition, which are formed due to the polymerisation of poly-condensed aromatic molecules during catalytic cracking. Such polymerisation reactions can lead to products having a molecular weight from 200 to 2000 or more [1, 15].
Table 3
Spectral intensity contributions of signals in various ranges, %, in accordance to the 13C NMR spectra
Таблица 3
Вклады спектральных интенсивностей сигналов от различных диапазонов, %,
по данным спектров ЯМР13С
Sample
0-17
Spectral range, ppm
17-25
25-40
40-60
ZCal
Spectral range, ppm
90-133
133-160
4.1 0.7 0.7 1.6
8.2 4.2 1.5 2.5
23.5 7.9 2.6 2.6
5.2
3.2 1.2
2.3
41 16 6 9
43.0 61.5 84.5
87.1
16.0 22.5 9.5 3.9
59 84 94 91
ar
CONCLUSIONS
A study of petroleum and coal pitches using NMR spectroscopy showed that the proton spectra of 1H NMR data are sufficiently informative and can be used to monitor the technological process of pitch production. A combination of 1N
13
and C NMR spectral data results in additional information being obtained, on which a correlation of the composition and physical parameters of the pitches can be established. In particular, the origin of the pitches (petroleum, coal), is uniquely determined by Har/Hal, T,Cal and Y.Car parameters.
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БИБЛИОГРАФИЧЕСКИМ СПИСОК
1. Morgan P. Carbon fibers and their composites. London: Taylor and Francis, 2005. 1200 p. DOI: https://doi.org/10.1201/9781420028744
2. Мухамедзянова АА., Хайбуллин А.А., Теля-шев Э.Г., Гимаев Р.Н. Получение нефтяного пека из остатков переработки нефти // Химия и технология топлив и масел. 2011. N 2 (564). С. 10-13.
3. Kuznetsov P.N. Kamenskiy E.S., Kuznetso-va L.I. Comparative Study of the Properties of the Coal Extractive and Commercial Pitches // Energy and Fuels. 2017. Vol. 31. No. 5. P. 5402-5410. DOI:
10.1021/acs. energyfuels.7b00158
4. Kim H.G., Park M., Kim H.-Y., Kwac L.K., Shin H.K. Characterization of pitch prepared from pyrolysis fuel oil via electron beam irradiation // Radiation Physics and Chemistry. 2017. Vol. 135. P. 127-132. https://doi.org/10.1016/j.radphyschem.2017.01.040
5. Lou B., Liu D., Duan Y., Hou X., Zhang Y., Li Z., Wang, Z., Li M. Structural Modification of Petroleum Pitch Induced by Oxidation Treatment and Its Relevance to Carbonization Behaviors // Energy and Fuels. 2017. Vol. 31. No. 9. P. 9052-9066.
6. Валинурова Э.Р., Кудашева Ф.Х. Исследование фазовых превращений во фракциях нефтяного пека методом обращенной газовой хроматографии // Доклады Башкирского университета. 2017. Т. 2. N 5. С. 713-718.
7. Лебедева МА, Колесник В.Д., Машуков В.И., Егоров А.В. Хроматографическое определение химического состава тяжелых смол пиролиза // Известия Томского политехнического университета. 2010. Т. 316. N 3: Химия. С. 102-105.
8. Mochida I., Korai Y., Ku Ch., Watanabe F., Sakai Y. Chemistry of synthesis, structure, preparation and application of aromatic-derived mesophase pitch // Carbon. 2000. Vol. 38. Issue 2. P. 305-328. https://doi.org/10.1016/S0008-6224(99)00176-1.
9. Qian S.A., Xiao Y.X., Gu Y.D. Study on chemical composition and formation mechanism of some typical pitch feedstocks using field desorption mass spectrometry // Fuel. 1987. Vol. 66. Issue 2. P. 242-249. https://doi.org/10.1016/0016-2361 (87) 90249-3
10. Murakami K., Okumura M., Yamamoto M., Sanada Y. Structural analysis of mesophase pitch with high-resolution, high- temperature 13C-NMR // Carbon. 1996. Vol. 34. No. 2. P. 187-192. DOI: 10.1016/0008-6223(96)00168-6
11. Dickinson E.M. Structural comparison of petroleum fractions using proton and 13C n.m.r. spec-
Contribution
Ivan O. Doshlov, Igor A. Ushakov carried out the experimental work, on the basis of the results summarized the material and wrote the manuscript. Ivan O. Doshlov, Igor A. Ushakov have equal author's rights and bear equal responsibility for plagiarism.
Conflict of interests
The authors declare no conflict of interests regarding the publication of this article.
AUTHORS' INDEX
Ivan O. Doshlov, El
Postgraduate Student,
Irkutsk National Research Technical University, e-mail: doshlov125@mail.ru
Igor A. Ushakov,
Ph.D. (Chemistry), Associate Professor, Irkutsk National Research Technical University, e-mail: igor-papa71@mail.ru.
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Критерии авторства
Дошлов И. О., Ушаков И. А. выполнили экспериментальную работу, на основании полученных результатов провели обобщение и написали рукопись. Дошлов И. О., Ушаков И. А. имеют на статью равные авторские права и несут равную ответственность за плагиат.
Конфликт интересов
Авторы заявляют об отсутствии конфликта интересов.
СВЕДЕНИЯ ОБ АВТОРАХ
Дошлов Иван Олегович, СЕН
аспирант,
Иркутский национальный исследовательский технический университет, e-mail: doshlov125@mail.ru
Ушаков Игорь Алексеевич,
к.х.н., доцент,
Иркутский национальный исследовательский технический университет, e-mail: igor-papa71@mail.ru.
