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DOI - 10.32743/UniTech.2024.129.12.18885
THE ROLE OF THE CATALYST IN THE AROMATIZATION PROCESS OF PARAFFIN FRACTIONS FROM SYNTHETIC PETROLEUM
Javohir Toshqobilov
Employee, Uzbekistan GTL LLC, Uzbekistan, Karshi E-mail: [email protected]
РОЛЬ КАТАЛИЗАТОРА В ПРОЦЕССЕ АРОМАТИЗАЦИИ ПАРАФИНОВЫХ ФРАКЦИЙ
СИНТЕТИЧЕСКОЙ НЕФТИ
Тошцобилов Жавохир
сотрудник, Uzbekistan « ООО GTL», Республика Узбекистан, г. Карши
ABSTRACT
Scientific research has been carried out on the processes of producing benzene from light paraffinic hydrocarbons from naphtha, the process is carried out using aluminum-nickel-molybdenum catalyst modified with bentonite. The possibilities of processing normal paraffin hydrocarbons of naphtha composition into aromatic products were investigated. The composition and physicochemical characteristics of a mixture of paraffin hydrocarbons of local raw materials were studied. The quantitative ratio of the resulting aromatic hydrocarbons depends on the composition and structure of the original hydrocarbon and reaction conditions.The feasibility of obtaining aromatic hydrocarbons from the С5-С8 fraction using dehydrogenation methods on bifunctional catalysts has been established.
АННОТАЦИЯ
Прoвeдeны Hay4Hbie исслeдoвaния npo^ccoB пoлучeния бeнзoлa из лeгких пaрaфинoвых углeвoдoрoдoв из гафты, npo^cc oсyщeствляeтся с испoльзoвaниeм aлюмoникeлмoлибдeнoвым KaTaOT3aropoM, мoдифицирoвaнным 6eHTOHmoM. Hcrae^DBaHbi вoзмoжнoсти nepepa6oTKH HopManbHbix пaрaфиювых yraeBo^3po^3B нaфтoвoгo cocraßa в apoMaTH4ecKue продукты. №y4eHbi cocTaB и физикo-xимичecкиe xapaKTep^rara смeси пaрaфинoвыx yrae-вoдoрoдoв MecTHoro с^1рья. Кoличecтвeннoe cooтнoшeниe oбрaзyющиxcя apoмaтичecкиx yглeвoдoрoдoв зaвиcит ot cocTaBa и cтрoeния raxoAroro yглeвoдoрoдa и ycлoвий прoвeдeния рeaкции. Уcтaнoвлeнa вoзмoжнocть пoлyчeния apoMaTH4ecKHx yглeвoдoрoдoв из фрaкции С5-С8 мeтoдaми дeгидрирoвaния га бифyнкциoнaльныx кaтaлизaтoрax.
Kеywоrds: Cyclization, Bentonite, Pentasil, Paraffinic hydrocarbons, Arenes, Benzene, Toluene, Xylene.
Ключевые слова: Циклизaция, Бeнтoнитoм, Пeнтacил, Пapaфинoвыe yглeвoдopoды, Аpeны, Бeнзoл, Тoлyoл, Кcилoл.
Introduction
Plans for "green" and inclusive economic growth in the Republic of Uzbekistan include further expanding the use of renewable energy sources, saving resources in all sectors of the economy, including studying the possibilities of transitioning to the use of "green" technologies in resource technologies. It consists in ensuring the use of economical technologies, waste-free production technologies that enable waste processing, safe chemicals, as well as renewable energy and their implementation [1].
Most petrochemical processes use practically pure compounds - hydrocarbons of relatively low molecular weight. The main liquid fractions of oil that are used as raw materials for petrochemicals are low-octane gasolines obtained by topping natural associated gases
or cracking gases, and light gasolines of primary distillation or cracking.
The main direction of development of the oil refining industry is the deepening of oil and natural gas processing. Thus, the rate of development of hydrocatalytic processes in production is steadily increasing, including the cyclization of paraffin hydrocarbons into cycloalkanes and arenes - valuable components of fuels and oils.
Cyclization reactions underlie important catalytic processes for the production of aromatic hydrocarbons, mainly toluene, benzene and xylenes, as well as gasolines characterized by increased detonation resistance [2].
Aromatic hydrocarbon production accounts for 21% of global petrochemical production. Global trends in the
Библиографическое описание: Toshqobilov J. THE ROLE OF THE CATALYST IN THE AROMATIZATION PROCESS OF PARAFFIN FRACTIONS FROM SYNTHETIC PETROLEUM // Universum: технические науки : электрон. научн. журн. 2024. 12(129). URL: https://7universum.com/ru/tech/archive/item/18885
development of production and consumption of petrochemical products indicate an increase in the need for aromatic hydrocarbons [3].
Research methods
Aromatic hydrocarbons in oils contain 15-20%, and in aromatic oils their content reaches 35%. Gasoline fractions up to 200 0C contain only benzene homologues [4]. The bulk of straight-run gasolines have a low octane number, not exceeding 40-60 according to the motor method (MM). In order to obtain a high-octane component of automobile fuels from low-octane gasoline, they are subjected to a catalytic reforming process at temperatures of 470-530 °C and a pressure of 0.7-3.0 MPa in the presence of hydrogen-containing gas on oxide catalysts containing platinum or platinum with rhenium additives as an active component, and promoted by chlorine or fluorine.
The catalytic reforming process is designed to increase the knock resistance of gasoline and produce individual aromatic hydrocarbons - benzene, toluene, xylenes. Catalytic reforming processes involve the formation of aromatic hydrocarbons due to the dehydrocyclization of paraffinic hydrocarbons (C5- or C6-dehydrocyclization). The transformation of paraffin hydrocarbons into aromatic hydrocarbons is a reversible reaction that occurs with an increase in volume and heat absorption. The process is carried out on bifunctional catalysts that combine acid and hydrogenation-dehydrogenation functions. The acid function in industrial reforming catalysts is performed by a carrier, which is aluminum oxide. To enhance and regulate the acidic function of the carrier, a halogen is introduced into the catalyst: fluorine or chlorine. The quality of reforming feedstock is determined by the fractional and chemical composition of gasoline. The fractional composition of the raw material is selected depending on the intended purpose of the process. If the process is carried out with the aim of obtaining individual aromatic hydrocarbons, then to obtain benzene, toluene and xylenes, fractions containing hydrocarbons C6 (62...85 °C), C7 (85...105 °C) and Cb (105...140 °C) are used, respectively. To produce the high-octane component of gasoline, fractions of85 - 180°C and 105 - 180°C are used; for the production of individual hydrocarbons: benzene - fraction 60 - 85°C, toluene -85 -105°C, xylenes - 105 - 140°C; mixtures of benzene, toluene, xylenes - 62 - 140°C, and with the simultaneous production of arenes and high-octane gasoline - fraction 62 - 180°C. [5] The yield of stable reformate is up to 84-88% wt. for raw materials.
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Currently, the plants process synthetic liquid fuels obtained using the Fischer-Tropsch method (FFM). The main products are liquefied gases, naphtha (fractions of straight-run gasoline), diesel fuel, high molecular weight paraffins. Naphtha produced by the Fischer-Tropsch method does not contain aromatic hydrocarbons and sulfur. The favorable composition of such naphtha allows the use of high-quality raw materials for petrochemical synthesis [6].
Dehydrocyclization of paraffin hydrocarbons is the main direction of their transformation under catalytic reforming conditions. An increase in temperature, along with an increase in the yield of arenes, accelerates the splitting reactions of hydrocarbons, mainly paraffin. The temperature during the process should not exceed 530 °C [7]. By analogy with the dehydrocyclization of paraffins containing 6 or more carbon atoms, bifunctional supported metal reforming catalysts, which have dehydrogenating activity, are used to convert light alkanes.
The mechanisms of cyclization of paraffinic hydrocarbons of aromatic compounds are considered as follows:
• C6 - catalytic dehydrocyclization of alkanes -elimination of hydrogen with simultaneous ring closure. The catalyst can be platinized carbon at 300 °C, as well as oxides of chromium, molybdenum, and vanadium. The most commonly used is chromium oxide on aluminum oxide at 500 °C and 3 MPa [8,9].
• C6-cyclization, in which alkanes are converted into cyclohexanes, occurring on charged surface complexes of platinum group metals.
• C5-cyclization of alkanes to saturated cyclopentane hydrocarbons, occurring on the surface of metals (Pt) in excess of hydrogen.
• C5-dehydrocyclization proceeds through the stage of formation of surface compounds containing a cyclopentadiene ring [2].
The choice of the most probable cyclization paths is facilitated by the fact that the content of some hydrocarbons in the reaction products, as well as the selectivity of the reaction, strongly depends on the process conditions, in particular, the concentration of hydrogen in the reaction mixture (Fig. 1). According to the authors, maximum amounts of benzene are formed even at low partial pressures of H2, which is due to the fact that intermediate surface compounds through which benzene is formed must contain more unsaturated bonds than intermediate compounds characteristic of C5 cyclization.
Figure 1. Dependence of the yield ofproducts on the hydrogen content in the carrier gas (helium) during the conversion of n-hexane (pulse mode, temperature 375 0C, catalyst - palladium black): ♦ - benzene; □ -
methylcyclopentane; A - hexane isomers; • - olefins
Dehydrocyclization on catalysts occurs through several different mechanisms:
• bifunctional catalysis with dehydrogenation on a metal and cyclization on acid sites;
• monofunctional dehydrogenation and cyclization on a metal, which reactions occur only on metal centers; dehydrocyclization on a metal occurs without the participation of acid centers [10].
The process of aromatization of n-paraffin hydrocarbons with 6 or more carbon atoms in the chain on bifunctional catalysts, in particular, platinum on acidic supports, includes dehydrogenation of an n-alkane on a metal followed by cyclization of the dehydrogenated molecule on acid sites. Both C5 and C6 cyclization take place; the ratio of these processes strongly depends on the length of the hydrocarbon chain and its branching.
On monofunctional platinum systems, two possible paths are most likely: C6 cyclization on the platinum surface with cleavage of the C-H bond at the primary and secondary atom, followed by dehydrogenation
of cycloalkanes into arenes (C5 cyclization contributes to a lesser extent to the formation of aromatic compounds), or C6-dehydrocyclization (aromatization) of alkanes by sequential elimination of hydrogen atoms from a linear molecule with the formation of olefins, dienes, trienes and subsequent thermal cyclization [2, 11].
The expansion of the C5 to C6 ring on bifunctional catalysts occurs much faster (the reaction rate is -10 times greater) than on monofunctional ones. The reaction of benzene formation at temperatures from 460 to 500 °C and hexane supply rates from 0.4 to 1.6 wt /hour per 1 wt of catalyst with grain sizes of 0.25-0.50 and 2.0-3.0 mm occurs in kinetic region. The dependences of benzene yield on temperature and feed rate during the dehydrocyclization of n-hexane were determined.
The n-octane molecule cyclizes in two directions -into o-xylene or ethylbenzene. During consecitive dehydrogenation, two intermediate octatrienes and, accordingly, two aromatic products are formed: octatriene-1,3,5 will give ethylbenzene, and octatriene-2,4,6 o-xylene (FIGURE 2).
Figure 2. Formation of aromatic products of consucutive dehydrogenation
In the presence of an alumina-platinum catalyst, an increase in hydrogen pressure changes the direction of C6 dehydrocyclization, and an increase in hydrogen pressure leads to an increase in the o-xylene/ethylbenzene ratio. If there is little hydrogen on the metal surface, then the surface complex is formed by abstraction of the hydride ion and adsorption at the primary C atoms.
As the concentration of platinum and the size of its particles decrease, the electron deficit of platinum catalysts increases; with a decrease in the platinum content, the yield of o-xylene increases, and at low concentrations of platinum, the yield of p-xylene from 3-methylheptane doubles. [12].
Results
Uzbekistan produced synthetic oil in the history of the republic's petrochemical industry. The Uzbekistan GTL
plant produces synthetic oil. The resulting synthetic oil is the main raw material for the production of synthetic diesel fuel, jet fuel, naphtha and liquefied gas [13]. In the industrial sector of the Uzbekistan GTL plant, the need to consistently continue work on establishing the production of synthetic fibers, polyester resins, polymers, aromatic hydrocarbons, which are in demand in the construction, automotive and pharmaceutical industries [14].
Scientific research relates to the processes of producing benzene from light paraffinic hydrocarbons from naphtha, the process is carried out using aluminum-nickel-molybdenum catalyst modified with bentonite. The hydrocarbon composition of paraffin fractions, determined by GLC method [15], is given in Tаblе 1.
Table 1.
Cоmpоsitiоn оf ой which is rеcеivеd аt Uzbеkistаn GTL
Entеrprisеs ЗД^е^: оf f^ct^ns, % mаss
С3 С4 С5 С6 С7 С8
Uz GTL 1,17 5,38 10,95 13,92 15,15 15,45
The condudsd rеsеаrch wаs аimеd аt studying Ше possibility of procеssing light рагаЕйтс hydrocаrbons into rnphto compositions into аготайс products.
Light раМЕт hydrocаrbons аге а mixture of liquеfiеd hydrocаrbon gаsеs аМ light gаsolinе.
Procеssing of pаrаffin hydrocаrbons of this composition is possiblе in two directions [16]:
1. Sеpаrаtion of gаs gаsolinе from thе rаw mаtеriаl with Ше procеssing of light hydrocаrbons Сз - С4 to obtаin stаblе аromаtic products;
2. Cаtаlytic procеssing of аИ n-pаrаffin hydrocаrbons into nаphthа.
Whеn implеmеnting Ше sеcond direction, thеrе is а nееd to study thе possibility of ob^ning аromаtic products from а mixture of С3-С8 hydrocаrbons.
Thе procеss of аromаtizаtion of pаrаffin frаctions wаs studiеd in геаСоге with а cаtаlyst loаding of 100 cm3, аt а tеmpеrаturе in thе rеаction zore of 480 °C, а wеight fееd rаtе of liquid raw mаtеriаl of 450 h-1 аМ аtmosphеric prеssurе. Thе аctivity of cаtаlysts in thе аromаtizаtion of propаnе is low, which is аssociаtеd with thе low rеаction tеmpеrаturе. As thе molеculаr wеight of pаrаffins incrеаsеs, thе dеgrее of convеrsion аlso incrеаsеs. On Ше IK-30/4% ALNiMO+ bentonite cаtаlyst, thе convеrsion of normаl hеxаnе аnd hеptаnе incrеаsеs to 84.7 аМ 88.2%, rеspеctivеly. Thе yiеld
of C6-C9 arenes also increases with increasing molecular weight of the raw material, 20.0 and 24.8.
It can be concluded that there is a clear relationship between the increase in the degree of conversion, selectivity and arene yield with an increase in the molecular weight of the original paraffin.
Considering the selectivity curves for the formation of arenes (Fig. 3) depending on the length of the n-paraffin molecule, one can also see a similar nature of their passage. The selectivity for the formation of benzene has a minimum during the aromatization of n-butane, then an increase in the concentration of benzene is observed during the conversion of hexane and heptane. The data obtained confirm an increase in the activity of n-paraffins in the aromatization reaction with increasing molecular weight of paraffins. In the table, we can see that when we heat n-paraffins at 55 °C, C3-C4 make up to 7.98% of the total product, C5 - 50.65%, C6 - 21.31%, C7 - 2.74% C8 - 0.29, C9 - 0.04%. The sample is shown in line 1. Residual temperature when heated at 80 °C is up to 3.81% of the total product to C3-C4, C5 - 46.32%, C6 -13.54%, C7 - 5.25%, C8 - 1.28, C9- 0 ,13%. Sample is reflected in line 2. The residual product is up to 0.001% of the total product up to C3-C4, C5 - 1.67%, C6 - 10.04%, C7 - 21.51%, C8 - 22.65, C9- 16.12%. The sample is shown in 3 lines.
•Samplel
Sample2
Sample3
60
cN 21
& £ 3
50
40
30
20
10
6 7
Carbon number
0
4
5
8
9
Figure 3. Formation of C4-C9 n-paraffin hydrocarbons in naphtha
The results obtained show that the dependence of the composition of arenes on the initial molecule of the raw material manifests itself during the conversion of propane-butane.
When comparing the composition of arenes obtained from the conversion of n-paraffins C4-C8, the same benzene content is at the level of 20.0 -22.2% wt. during the transformation of paraffins with very different molecular weights, the formation of benzene from n-hexane as a result of the classical dehydrocyclization reaction [17,18,20]:
It can be concluded that in cracking reactions the composition of products is formed during the conversion of n-paraffins [19,21]. Our study showed that n-pentane did not cyclize like all its studied homologues, while n-hexane cyclized like n-octane. Thus, at 350 °C and a space velocity of 0.2 h-1, n-pentane remained unchanged on the freshly prepared catalyst, while n-hexane and n-octane were converted to 3.5-4.5% aromatic hydrocarbons (Table 2).
n-C6Hi4 = C6H6 + 4H2
(1)
Table 2.
Chromatographic results of the obtained samples
Experience Mono-aromatic hydrocarbons mass fraction% Di-aromatic hydrocarbons mass fraction% Anthracene hydrocarbons mass fraction%
1 3,96 0,87 1,63
2 3,02 2,47 2,06
Conclusion
New catalytic systems were developed for the conversion and synthesis of synthetic naphtha samples (1), (2) into aromatic hydrocarbons. When Cr2O7 catalyst was used with AlNiMo+bentonite catalyst, it was proven
that the samples converted to aromatic hydrocarbons in the first pass. The combined use of these catalysts resulted in high yields of mono-aromatic hydrocarbons from a mixture of naphtha hydrocarbons with a high mass fraction of n-hexane, n-heptane, and n-octane, and demonstrated excellent selectivity for this synthesis.
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