CC BY
22DOI: 10.6060/ivkkt.20226509.6535
УДК: 66.092-977-922
КАТАЛИЗАТОРЫ ДЕСТРУКЦИИ УГЛЕВОДОРОДНОГО СЫРЬЯ НА ОСНОВЕ ХЛОРИДА БАРИЯ
С.Р. Сахибгареев, М.А. Цадкин, А.Д. Бадикова, Э.Ф. Гумерова
Самат Рифович Сахибгареев (ORCID 0000-0002-4653-0897)*
Факультет общенаучных дисциплин, Уфимский государственный нефтяной технический университет, ул. Космонавтов, 1, Уфа, Республика Башкортостан, Российская Федерация, 450062 E-mail: [email protected]
Михаил Авраамович Цадкин (ORCID 0000-0001-7585-5802), Эльмира Фаиловна Гумерова (ORCID 00000002-7821-5146)
Кафедра высокомолекулярных соединений и общей химической технологии, Башкирский государственный университет, ул. Заки Валиди, 32, Уфа, Российская Федерация, 450076 E-mail: [email protected], [email protected]
Альбина Дарисовна Бадикова (ORCID 0000-0003-4696-4342)
Кафедра физической и органической химии, Уфимский государственный нефтяной технический университет, ул. Космонавтов, 1, Уфа, Российская Федерация, 450062 E-mail: [email protected]
Эффективным катализатором пиролиза углеводородного сырья в олефинсодержа-щий газ при сравнительно невысоких температурах является барийсодержащий катализатор. В работе исследовали применение новых катализаторов пиролиза прямогонного бензина, рафината платформинга, бензинов термического крекинга на основе хлорида бария. Исследованы прочностные свойства таблетированных катализаторов с добавками графита, диэтаноламида СЖК (синтетические жирные кислоты), фенолфурановой смолы и глины. При формовании катализаторов сравнительно легко осуществляется введение добавок, модифицирующих активность. Получены результаты экспериментальных данных на катализаторе хлориде бария с данными модифицирующими добавками. Эти данные свидетельствуют о том, что производство катализаторов на основе хлорида бария экономически целесообразно, так как основано на использовании недорогих и доступных химических реагентов, а это в свою очередь способствует повышению эффективности использования природного невозобновляемого сырья и энергосбережению в процессах его переработки. Для катализаторов, формованных с добавлением тетрахлоралю-мината натрия, характерно появление каталитической активности в процессах крекинга и изомеризации. Проведены испытания на определение длительности срока службы катализаторов с различными модификациями. Получены результаты: в течение 700 ч работы при температуре 500 °С катализатор, сформованный с 3,0% мас. графита, сохраняет активность по газообразованию и выходу низших олефинов при данных режимах работы. При этом выход кокса на пропущенное сырье для всех модификаций катализаторов не превышает 2,5% мас. за 30 чработы при температуре 700 °С Примечательно, что катализатор, содержащий NaAlCU характеризуется относительно невысоким коксооб-разованием.
Ключевые слова: катализаторы пиролиза, электрофильные добавки, каталитическая активность, бензиновая фракция, тетрахлоралюминат натрия
Для цитирования:
Сахибгареев С.Р., Цадкин М.А., Бадикова А.Д., Гумерова Э.Ф. Катализаторы деструкции углеводородного сырья на основе хлорида бария. Изв. вузов. Химия и хим. технология. 2022. Т. 65. Вып. 9. С. 64-73. DOI: 10.6060/ivkkt.20226509.6535.
For citation:
Sakhibgareev S.R., Tsadkin M.A., Badikova A.D., Gumerova E.F. Catalysts for destruction of hydrocarbon raw materials based on barium chloride. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2022. V. 65. N 9. P. 64-73. DOI: 10.6060/ivkkt.20226509.6535.
CATALYSTS FOR DESTRUCTION OF HYDROCARBON RAW MATERIALS BASED
ON BARIUM CHLORIDE
S.R. Sakhibgareev, M.A. Tsadkin, A.D. Badikova, E.F. Gumerova
Samat R. Sakhibgareev (ORCID 0000-0002-4653-0897)
Faculty of General Scientific Disciplines, Ufa State Petroleum Technological University, Kosmonavtov st., 1,
Ufa, 450062, Russia
E-mail: [email protected]
Mikhail A. Tsadkin (ORCID 0000-0001-7585-5802), Elmira F. Gumerova (ORCID 0000-0002-7821-5146)
Department of High-molecular Compounds and General Chemical Technology, Bashkir State University, Zaki
Validi st., 32, Ufa, 450076, Russia
E-mail: [email protected], [email protected]
Albina D. Badikova (ORCID 0000-0003-4696-4342)
Department of Physical and Organic Chemistry, Ufa State Petroleum Technological University, Kosmonavtov st., 1, Ufa, 450062, Russia E-mail: [email protected]
A barium-containing catalyst is the new effective catalyst for the pyrolysis of hydrocarbons into olefin-containing gas at relatively low temperatures. This article discusses options for the development of new straight-run gasoline pyrolysis catalysts, platformer raffinates and barium chloride-based thermal cracking gasolines. The strength properties of tableted catalysts with the addition of graphite, FAS (fatty acid synthesis) diethanolamide, phenol-furan resin and clay were studied. When forming the catalysts, the introduction of activity modifying additives is relatively easy. The results of experimental data on a barium chloride catalyst with these modifying additives were obtained. These data indicate that the production of barium chloride-based catalysts is economically feasible, since it is based on the use of inexpensive and affordable chemical reagents, and this in turn helps to increase the efficiency of using natural non-renewable raw materials and energy saving in the processes of its processing. The catalysts formed with the addition of sodium tetra-chloroaluminate are characterized by catalytic activity in cracking and isomerization processes. Tests were carried out to determine the duration of the catalyst lifetime with various modifications, and the following results were obtained: during 700 h of operation at a temperature of 500 °C, the catalyst formed with 3.0% wt. graphite, retains activity on gas formation and the yield of lower olefins. In this case, the coke yield on the skipped feedstock for all catalyst modifications does not exceed 2.5% wt. for 30 h of operation at a temperature of 700 °C. It is noteworthy that the catalyst containing NaAlCl4 is characterized by a relatively low coke formation.
Key words: pyrolysis catalysts, electrophilic additives, catalytic activity, gasoline fraction, sodium tetrachloroaluminate
mally cracked gasoline, straight-run gasoline, plat-forming raffinate also replenish the market of second-
Catalytic pyrolysis seems to be an important ary hydrocarbon raw materials, the use of which can direction in the group of secondary oil refining pro- and should more effectively serve as a powerful addi-cesses for solving of the task of yield increasing of use- tional source of raw materials. Until now, attempts to ful hydrocarbon products. Such processes make it pos- use some types of such low-quality secondary raw ma-sible to expand the range of hydrocarbon feedstock in- terials [1-5], in particular, and cracked gasolines, have volved to obtain gaseous hydrocarbons, represented not opened up the possibility of their inclusion in the mainly by ethane-ethylene, propane-propylene frac- traditional processing scheme. In this regard, it seems tions, which are valuable raw materials for petrochem- promising to involve them in the stage of catalytic pro-ical industries and the production of consumer goods, cessing to obtain gaseous products. With creation of especially plastics. Liquid products formed in the main effective catalytic forms for pyrolysis processes, it thermal cracking processes, in particular, such as ther- would be possible to solve the problem of processing
secondary fractions into useful hydrocarbon products. This determines the need to find active forms of new catalytic systems and establish experimental conditions for their high efficiency. In accordance with the task set, the ongoing research should be aimed at identifying the patterns of changes in the activity of the catalyst under conditions of variation of both the experimental parameters and the composition of the processed secondary raw materials.
Development of a technologically acceptable catalyst modification is a condition for industrial implementation of gasoline catalytic pyrolisis in eth-ylene/propylene in the presence of BaCh [1-3]. The use of a finely divided powder catalyst leads to a number of undesirable processes, such as an increase in hy-drodynamic resistance in a catalyst fixed-bed reactor, which subsequent coking makes a fixed bed impassable or powder particles with gasoline processed are entrained in a catalyst fluid-bed reactor. Therefore, barium chloride as a crystal powder cannot be used in an industrial process.
Availability of BaCl2, an active component, enables to consider simpler and effective ways for obtaining industrial modifications of catalysts. Granules (tablets) obtained by moulding are an optimal form to fixed-bed reactors. Thus, the purpose of this paper is to develop ways for obtaining industrial modifications of barium-containing catalysts using the introduction of additives, i.e. from textural components, which relieve forming, up to components, which are able to perform co-catalytic functions.
EXPERIMENTAL
Barium chloride salt (GOST 4108-72-Barium chloride 2-aqueous) was used as a basic form of pyrol-ysis catalyst. By drying the salt for 20 h at a temperature of 171-175 °C, the bound water was evaporated from the crystalline hydrate, then the salt was subjected to heating at a temperature of 350 °C in a muffle furnace. To prepare catalyst samples, anhydrous barium chloride was mixed with various additives: diethanola-mides of the FFA fraction (TU 38-107-250-83), phe-nolfuran resin (FF-65C), clay of the montmorillonite group (Kuganak deposit), graphite powder (OSCH 8- 4, GOST 23463-79). NaCl (GOST 4233-77) and AlCl3 (GOST 4452-66) were sintered at 154 ± 1 °C in a stoichiometric ratio to obtain the double salt NaCl-AlCh. The double salt in the form of a melt was applied onto a powdered barium chloride (BaCh) preliminarily heated at 350 °C.
The catalytic charge was used to form tablets 5x3 mm in size on a RTM-41 M2V tablet machine. Tableting was carried out by pressing at a temperature of 25 °C, then the carriers were impregnated.
Experimental technique. The oil feedstock was fed from the measured raw material tank with preheating, using a peristaltic pump of the RR-2-1B type to the preheating furnace, from where it entered the upper part of the reactor with a stationary catalyst bed. The reaction zone was heated using a PTF 12/50/250 laboratory tube furnace. Temperature control was carried out using thermocouples in the temperature range from 500 to 750 °C. The degradation products condensed in the condensing system, and the liquid product entered the receiver for liquids. Gaseous products, having passed through the trap, enter the drum counter with a liquid seal. The composition of the products was determined on a Shimadzu GCMS-QP2020 chromato-mass spectrometer with Rxi-5 ms capillary column.
The low-temperature nitrogen adsorption-desorption method (77 K) was used to determine the characteristics of the porous structure of the catalyst on an ASAP-2020 Micromeritics sorbtometer. Prior to analysis, the samples were subjected to evacuation for 6 h at a temperature of 350 °C. The specific surface area was calculated using the BET method at a relative partial pressure P/P0 = 0.2. The total (total) pore volume was determined by the BJH (Barrett-Joyner-Halend) method at a relative partial pressure P/P0 = 0.95.
A granular catalyst was obtained in the shape of cylindrical tablets 5x6 mm in size by forming on a high capacity-tableting machine.
The conditions for base catalysts, which conform to the technological requirements, were defined based on experimental data researches on granule forming of various sizes.
The study of BaCh finely-divided powder showed that the best tablet strength properties are observed for 0.25-0.50 mm fraction (Table 1). Granule mechanical stability is also increased more when performing prior thermal processing of a mixture with post-calcination of granules. Powder fraction preliminary thermal processing at 175-300 °C, i.e. it is above the temperature of crystal water evaporation from BaCl2 crystalline hydrates, increases the strength of ready granules by 5 times.
Variability in characteristics of a particle contact for BaCh in a powder form when forming catalysts, for instance, adhesive strength between particles, has a great impact on structural and mechanical properties of granules.
Adhesion reliability can be regulated by surface energy attenuation in friction zones as a result of formation of SAA (surface active agent) adsorbed beds introduced into a catalyst system [4-7]. The use of lubricated agents, which lower concentration of subsurface stresses in areas of pressed mixture particles contact, ensures strengthening of ready granules. A reinforcing effect of specific additives, for example, when
using polymer resins, is explained by formation of a space skeleton in the shape of a chemically cross-linked network [8-10].
It is of importance to note that finely divided mixture moisturization (up to 5% water) helps to increase the efficiency of mechanical performance for a ready catalyst, but at the same time strength spread is observed in various modifications. The introduction of a SAA (surface active agent), such as FAS (fatty acid synthesis) diethanolamide of C10-C13 fraction in the amount of 0.25-3.0% wt. has no effect on strength. Highly dispersed graphite may serve as an effective shaping additive in the amount of no more than 5.0% wt. (to a mixture). A narrow spread in strength values of 8-16 kg/tablet is observed by the content of graphite 3.0% wt. (to a mixture). When optimizing characteristics, such as composition, a dispersion component
value, conditions for raw material preparation, the best performance by granule fracture strength is achieved axially and radially by 55 and 35 kg/tablet, respectively and it is considered to be in compliance with the use of such catalysts in production.
Considering reduced strength of granules radially, leading to catalyst damage when in loading-unloading thermally reactive components should be applied as auxiliary additives, ensuring catalyst modifications isotropic in strength.
The effect of phenol-furan resin as an auxiliary additive was studied. Tablets of a catalyst were obtained containing phenol-furan resin 0.5-5.0% wt. and calcined at 300-400 °C within 30-60 min, which strength reaches 50-60 kg/tablet both axially and radially (Table 1).
Table 1
Strength properties of BaCh-Based tablet catalysts
Catalyst weight Conditions of thermal processing Crushing stren gth, kg/tablet
BaCl2 powder fraction, mm Additive, % wt. T, °C t, h Axially Radially
0.16-1.00 unfractioned - - - 0.7-1.6 0.6-0.9
0.5-1.00 - - - 0.4-0.8 0.2-0.5
0.16-0.25 - - - 8.0-1.6 0.2-0.6
0.25-0.50 - - - 1.4-2.0 0.8-1.3
0.25-0.50 - 175 10 8.0-12.0 2.0-9.0
0.25-0.50 - 175 20 10.0-15.0 4.0-9.0
0.25-0.50 - 175 25 10.0-16.0 4.0-9.0
0.25-0.50 - 300 10 10.0-16.0 9.0-14.0
0.25-0.50 - 400 10 10.0-16.0 9.0-12.0
0.25-0.50 - 500 10 10.0-16.0 9.0-12.0
Graphite
0.16-1.00 3.00 - - 19.0-23.0 16.0-21.0
0.16-0.25 0.25 - - 21.0-24.0 7.0-13.0
0.16-0.25 1.00 - - 34.0-48.0 20.0-27.0
0.16-0.25 3.00 - - 45.0-65.0 32.0-37.0
0.16-0.25 5.00 - - 39.0-50.0 31.0-38.0
0.25-0.50 3.00 - - 38.0-43.0 30.0-37.0
FAS (fatty acid synthesis) diethanolamide
0.25-0.50 0.25 - - 10.0-16.0 0.5-3.0
0.25-0.50 0.50 - - 4.0-6.0 1.0-3.0
0.25-0.50 3.00 - - 2.0-3.0 1.0-4.0
Phenol-furan resin
0.25-0.50 0.5 - - 1.0-1.3 0.5-1.3
0.25-0.50 0.25 - - 0.6-0.9 0.6-0.8
0.25-0.50 5.0 - - 1.0-1.2 0.5-1.2
0.25-0.50 0.5 300 0.5 6.0-9.0 5.0-9.0
0.25-0.50 2.5 300 0.5 10.0-15.0 4.0-12.0
0.25-0.50 5.0 300 0.5 20.0-24.0 18.0-24.0
0.25-0.50 5.0 400 0.5 50.0-64.0 47.0-60.0
0.25-0.50 5.0 500 0.5 55.0-61.0 55.0-60.0
0.25-0.50 5.0 600 0.5 56.0-66.0 51.0-65.0
Clay
0.25-0.50 5.0 - - 59.0 38.0
RESULTS AND DISCUSSION
In addition to affecting the strength properties, calcination and introduction of thermally reactive components into a catalytic mixture allows changing granule structural characteristics, such as a specific surface area and pores volume. Calcination of original BaCh with subsequent calcination of ready granules leads to the growth in the specific surface area (Fig. 1). Adding water, graphite and FAS (fatty acid synthesis) diethan-olamide significantly reduces the specific surface area as compared with the original catalyst.
pores volume is observed when adding graphite in the amount of 1.0% wt., as compared with the granules formed without calcination and in no additives. A subsequent increase in the content of graphite leads to a decrease in the porosity of granules.
The study on catalysts containing clay of a montmorillonite group, Kuganak deposit (Republic of Bashkortostan) as a binder, based on aluminosilicates of xAhOsxyS^nftO structure, was conducted. Satisfactory strength and ease through the tableting process can be achieved by introducing up to 5.0% wt. to a clay mixture (Table 1). With a high clay content in the catalyst (30.0 or 50.0% wt.), extrusion forming of a pre-wetted catalyst up to 25% wt. should be carried out. Catalysts with crushing strength of 178240 kg/granules axially and 140-205 radially are produced by thermal processing at 350-400 °C. Catalysts forming with clay addition (up to clay 30.0% wt.) improves structural characteristics (Fig. 2a, b).
Fig. 1. Specific surface area (■) Sw (m2-g-1), pores specific volume (□) Vw (cm3-g-1) of barium-containing catalyst 1-12. 1 - original catalyst; 2 - tablets calcined at 175 °С; 3 - with preliminary calcination of the mixture at 175 °С; 4 - tablets calcined at 300 °С; 5 - with preliminary calcination of the mixture at 300 °С; additive component (wt. %): 6 - 1 of graphite, 7 - 3 of graphite, 8 - 5 of graphite, 9 - 1 of diethanolamide, 10 - 5 of water, 11 - 0.25 of graphite + 1
of water, 12 - 5 of phenol-furan resin Рис. 1. Удельная поверхность (■) Sw (м2т-1), удельный объем пор (□) Vw (см3т-1) барийсодержащих катализаторов 1-12. 1 - исходный катализатор; 2 - таблетки, прокаленные при 175 °С; 3 - с предварительным прокаливанием шихты при 175 °С; 4 - таблетки, прокаленные при 300 °С; 5 - с предварительным прокаливанием шихты при 300 °С; добавка (% ма^): 6 - 1 графита, 7 - 3 графита, 8 - 5 графита, 9 - 1 диэтаноламида, 10 - 5 воды, 11 - 0,25 графита + 1 воды, 12 - 5 фенолфурановой смолы
During the application of various additives to the surface of barium chloride, layers are formed that prevent the penetration of raw material particles to the active center of the catalyst. As a result, the specific surface area and pore volume of the catalyst support are reduced.
The ambiguous effect of these factors on the surface-pore structure of granules is monitored. As a rule, thermal processing of an original material and formed catalyst increases the pores volume, but when used with various additives, the effect is of more complex nature, and the reaction of the agents introduced already significantly depends on the nature and concentration of additives. Thus, diethanolamide introduction (1.0% wt.) significantly increases the pores volume, water introduction up to 5.0% wt., does not effeсt this value, on the contrary. A slight increase in the
b
Fig. 2а. Dependence of specific surface area (■) Sw (m2-g-1) on pores specific volume (□) Vw (cm3-g-1) of barium-containing catalysts: 1 - catalyst without additives; clay addition as a binder (wt.%): 2 - 1.0; 3 - 5.0; 4 - 10.0; 5 - 20.0; 6 - 30.0; 7 - 45.0 Fig. 2b. Dependence of mechanical performance (■) P on specific pore volume (□) Vw (cm3-g-1) of barium-containing catalysts: 1 - catalyst without additives; clay addition as a binder (wt.%): 2 - 1.0;
3 - 5.0; 4 - 10.0; 5 - 20.0; 6 - 30.0; 7 - 45.0 Рис. 2а. Зависимость удельной площади поверхности (■) Sw (м2т-1) от удельного объема пор (□) Vw (см3т-1) барийсодержащих катализаторов: 1 - катализатор без добавки; добавка глины в качестве связующего (% мас.): 2 - 1,0; 3 - 5,0; 4 - 10,0;
5 - 20,0; 6 - 30,0; 7 - 45,0 Рис. 2b. Зависимость механической прочности (■) P от удельного объема пор (□) Vw (см3т-1) барийсодержащих катализаторов: 1 - катализатор без добавки; добавка глины в качестве связующего (% мас.): 2 - 1,0; 3 - 5,0; 4 - 10,0; 5 - 20,0; 6 - 30,0; 7 - 45,0
The extrusion method allows granules to be formed into uninterrupted regular macroscopic lattice or honey-combed structures from a catalyst plastic mass. Such structural modification, as a rule, optimizes the reactor gas-dynamic operating mode. Pressuriza-tion in a reactor for more than 0.1 MPa leads to a decrease in the yield of desired products and growth of methane yield [11, 12]. The form and size of a catalyst are influencing parameters of the pressure and its differences in a reaction area during the movement of a reaction gas mixture through a catalyst bed. In the catalyst bed, a large pressure drop is accompanied by the process using tableted granules in the form of cylindrical solid particles, where the drop is 1.5-1.7 times greater than in the bed layer in the form of Raschig rings in average. The ethylene yield in average of 0.50.1% higher is observed at 790-795 °C in the catalyst bed based on potassium vanadate modified with boron compounds produced in the form of Raschig rings than
when using a cylindrical catalyst. A regular honeycombed or lattice structure creates the most optimal gas-dynamic mode undoubtedly [13-15].
By introducing BaCh into the original plastic clay mass, catalyst blocks with low strength and mechanical instability to high temperatures were obtained. An impregnation with an aqueous solution of barium chloride of a formed aluminum ceramic block may increase BaCh content up to 45%. But it is worth noting that such blocks are destroyed when calcined at 800 °C. It is possible to prevent this process without changing the surface pore parameters of the aluminum ceramic matrix by reducing the content of barium chloride up to 18.0% wt.
For a catalyst containing NaAlCU 10% wt., the temperature range from 650 to 750 °C was determined experimentally, at which a change in the nature of the process is observed.
Table 2
The yield of gaseous* gasoline pyrolysis products on various forms of barium-containing catalysts Таблица 2. Выход газообразных* продуктов пиролиза бензинов на различных формах барийсодержащих
T, °C V ** h-1 Yield of products, % wt. on passed feedstock
CH4+ H2 C2H4 C3H6 C3H8 XC4H8 XC4H10 C5 Total
Straight-run gasoline/ tableted catalyst with clay 30% wt.
650 0.5 9.1 28.2 10.0 14.9 2.0 6.5 0.8 71.5
700 0.5 12.6 29.1 7.3 15.1 1.1 9.1 0.7 75.0
725 0.5 17.6 32.9 7.2 13.8 0.9 7.0 0.1 79.5
750 0.5 25.2 34.9 7.1 12.0 0.8 5.5 0.1 85.6
Straight-run gasoline/ tableted catalyst with NaAlCL 10% wt.
650 0.5 6.8 12.5 6.4 17.5 0.9 13.7 - 57.8
650 1.0 6.9 10.9 6.9 18.2 0.2 14.4 - 57.5
700 0.5 12.4 28.4 28.0 7.0 18.3 1.0 14.8 81.5
700 1.0 11.5 21.4 8.1 23.4 0.9 14.9 - 80.2
725 0.5 19.8 32.9 7.0 18.9 0.8 3.0 - 82.4
725 1.0 17.0 30.0 9.1 18.3 1.2 3.5 - 81.1
750 0.5 25.7 38.9 6.2 12.2 0.6 0.4 - 84.0
750 1.0 20.0 33.1 8.0 17.2 0.7 4.8 - 83.8
Straight-run gasoline/ honey-combed catalyst with BaCl2 18% wt.
650 0.5 3.59 3.9 2.7 26.1 0.1 8.3 4.61 49.3
700 0.5 17.5 22.0 3.9 25.9 0.8 12.5 4.2 84.8
725 0.5 22.4 28.9 4.4 19.0 0.4 12.7 0.1 87.9
725 1.0 19.9 27.1 1.0 22.9 0.3 16.4 0.2 87.8
725 2.0 13.7 23.4 4.0 24.8 0.2 19.3 0.3 85.7
725 2.5 13.6 23.2 4.0 24.9 0.1 19.1 0.3 85.2
750 0.5 26.3 31.0 0.4 12.6 0.1 10.1 0.1 80.6
Note: *С5 hydrocarbons condense in the refrigerator along with liquid products; **V - bulk feed rate
Примечание: *углеводороды С 5 конденсируются в холодильнике вместе с жидкими продуктами; **V - массовая скорость подачи
Straight-run gasoline pyrolysis at 650-700 °C gives a lower yield of ethylene as compared with the yields of propylene and butylenes (Table 2), while the
content of butylenes in a pyrolysis gas mixture is significantly higher than in a thermal process. The composition of the gaseous products of the process is con-
sistent with the literature data on the cracking of hydrocarbons with the predominant formation of C4 olefins using NaAlCl4. However, the composition of products changes at a temperature of 725 °C and above, an increase in ethylene content occurs, and the content of butylene is reduced. The yield of ethylene reaches 38% and higher, with a gas formation rate of 80% on the introduced raw materials. In general, the composition of the products becomes typical for a high-temperature radical process [15].
According to the data [6, 16], low-temperature catalytic decomposition of hydrocarbons requires the introduction of water or other hydrogen donors into the system to activate electrophilic catalysts based on complex metal chlorides. The role of water in the activation of MAlCl4 is based on its ability to dissociative adsorption on the surface of the catalyst. Thus, catalytically active metal chlorides under these conditions exhibit the properties of Brensted acids.
Statistical treatment of the results of analysis of the catalytic cracking straight run gasoline performed using «STATISTICA» program. The diagrams show the desirability responses of ethylene and propylene versus temperature and feed rate.
It can be seen from the figures that increase in temperature, the formation of ethylene, propylene is observed at a low feed rate, and with an increase in the feed rate of straight-run gasoline, the temperature decreases.
As a rule, the yield of ethylene varies depending on the degree of dilution of the feedstock with superheated water vapor (Table 3). A significant increase in the gas formation and the yield of ethylene is observed when steam is supplied up to 75% wt. from the feedstock. In addition, carbon oxide is identified in the composition of gases [17-19].
Liquid pyrolysis products contain aromatic hydrocarbons (Table 4).
a b
Fig. 3. The response of the "desirability" of the formation of a) C2H4, б) C3H6 from straight-run gasoline using a catalytic system of barium
chloride tableted with 10% wt. NaAlCU Рис. 3. Реакция "желательности" образования а) C2H4, б) СзНб из прямогонного бензина с использованием каталитической системы хлорида бария, таблетированного с 10% масс. NaAlCU
Table 3
The yield and composition of gaseous products of straight-run gasoline pyrolysis on granular catalysts upon dilution of the feedstock with water vapor (temperature 725 °С, bulk feed rate 0.5 h-1) Таблица 3. Выход и состав газообразных продуктов пиролиза прямогонного бензина на гранулированных катализаторах при разбавлении сырья водяным паром (температура 725 °С, объемная скорость подачи
Dilution, % wt. on the feedstock Yield of gas % wt. on the passed feedstock
CH4+H2 C2H4 C2H6 C3H6 С3Н8 С4Н8 С4Н10 Carbon oxides Total
Catalyst with graphite 3% wt.
- 19.1 31,6 7.9 10.9 0.7 5.5 0.2 - 75.9
50 20.8 32,5 4.6 12.9 1.0 6.5 0.1 1.2 79.6
100 25.0 31,9 4.0 12.0 0.6 4.0 0.8 1.9 80.2
Catalyst with clay 3% wt.
- 17.6 32.9 7.2 13.8 0.9 7.0 0.1 - 79.5
50 18.1 34.8 9.1 16.8 1.0 7.0 0.3 1.4 88.5
100 20.0 34.0 8.0 16.1 0.4 5.1 0.1 2.0 85.7
-1
Table 4
The composition of the light fraction of straight-run gasoline pyrolysis resin in the presence of barium-containing
catalysts (bulk feed rate 0.5 h-1) Таблица 4. Состав лёгкой фракции смолы пиролиза прямогонного бензина в присутствии
Pyrolysis condensate component Catalyst I Catalyst II Catalyst III
Composition, % wt. at pyrolysis temperature, °С
650 700 725 750 650 700 725 750 650 700 725 750
Paraffin-naphthene olefinic part 43.5 41.6 41.2 39.9 44.7 41.7 41.4 39.4 44.4 43.9 43.7 49.0
Benzene 15.9 16.1 16.9 12.0 12.7 13.6 16.9 15.6 12.1 10.9 9.3 9.9
Toluene 10.9 10.7 10.0 9.3 12.0 10.9 10.3 9.9 16.0 16.3 15.2 15.7
Ethylbenzene 2.1 2.0 1.1 0.9 4.3 3.7 3.4 3.1 3.4 7,.3 7.0 4.8
Xylenes 8.9 7.0 4.3 4.0 7.0 6.4 5.2 4.0 7.1 7.2 8.4 3.0
Cumene 3.8 3.5 3.3 2.9 7.5 3.5 1.9 0.8 1.2 0.9 0.4 0.6
Styrene 4.5 7.5 8.8 15.2 2.8 5.2 12.4 15.3 6.5 7.6 11.0 14.9
Indin 2.0 3.7 8.2 10.0 2.7 6.6 7.0 7.3 4.3 3.9 4.3 9.9
Unidentified components 8.4 7.9 6.2 5.8 6.5 8.4 1.5 4.6 5.0 2.0 0.7 2.2
Note: Catalyst 1 - formed, graphite 3.0% wt.; Catalyst 2 - formed, clay 30.0% wt.; Catalyst 3 - formed, NaAlCU 10.0% wt Примечание: Катализатор 1 - сформирован с 3,0% масс. графита; Катализатор 2 - сформирован с 30,0% масс. глины; Катализатор 3 - сформирован с 10,0% масс. NaAlCU
The study of the structure of both pure BaCh and its modifications obtained by applying various additives showed that under the studied temperature conditions from 500 to 750 °C, the solid structure of the BaCh catalyst undergoes some physical and chemical changes. In particular, the macro- and microstructures of the catalyst undergo certain physical changes. With prolonged exposure to temperature under operating conditions, recrystallization occurs, leading to a reduction in the specific surface of the catalyst or a decrease in the number of active catalytic centers per unit of its surface. However, when adding additives to the surface of the BaCh catalyst base, such as graphite, FFA dieth-anolamide (synthetic fatty acids), phenolfuran resin, and clay, which do not have their own catalytic activity or have relatively little activity, it has been shown that the recrystallization rate of the active component of the catalyst decreases. The low proportion of compaction and coking processes on the surface of both pure and modified catalyst determines its activity during the long studied exposure period up to 700 h.
Interestingly, that the introduced raw materials for all structural modifications of the catalyst account for 2.5% wt. and less than the coke yield for 30 h of operation at a temperature of 700 °C. It is also noteworthy that processes using a NaAlCl4-based catalyst are characterized by relatively low coking.
The study of the spent catalyst, in particular, the surface on the sections of tablets, showed that the distribution of coke deposits mainly occurs only in a
thin surface layer. The pores structure and specific surface area of the granules were almost unchanged. As a result, in particular, the specific surface of the original and coked catalyst at 500 °C are 3.62 and 3.43 m2/g, and the pores volume is 0.22 and 0.28 cm3/g, respectively. In this regard, a certain decrease in the rate of coke deposition on the catalyst can be explained by partial desorption of intermediate compaction products - coke precursors into the gas phase [20]. This leads to a certain increase in the yield of heavy resins when reducing the yield of coke and it does not affect the yield of the desired gaseous pyrolysis products.
CONCLUSION
Catalysts based on barium chloride are promising in terms of obtaining light olefins during pyroly-sis of gasoline fractions, and they also fully meet the level of requirements for thermal pyrolysis catalysts. The results obtained during the experiments indicate that the production of barium catalysts is economically feasible, since it is based on the use of inexpensive and affordable chemical reagents, and this in turn contributes to increasing the efficiency of using natural non-renewable raw materials and energy saving in its processing processes.
The authors declare the absence a conflict of interest warranting disclosure in this article.
Авторы заявляют об отсутствии конфликта интересов, требующего раскрытия в данной статье.
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Поступила в редакцию 18.10.2021 Принята к опубликованию 22.06.2022
Received 18.10.2021 Accepted 22.06.2022
