CC BY
103
ISSN 2522-1841 (Online) ISSN 0005-2531 (Print)
AZ9RBAYCAN KIMYA JURNALI № 2 2018
15
UDC 66.097.3:546.74
STUDY OF COKE FORMATION LAWS AND MECHANICAL STABILITY OF CATALYSTS ON NATURAL CARRIERS USED IN HYDROGENATED PROCESSING OF LIQUID PYROLYSIS PRODUCTS
Z.Ch.Salayeva, R.M.Mustafayeva, Kh.G.Isayev, N.A.Zeynalov*, G.A.Mammadaliyev
"Olefin Scientific-research and production center "OJS olefin-merkez@mail.ru *M.Nagiyev Institute of Catalysis and Inorganic Chemistry, NAS of Azerbaijan
Received 24.05.2017
The paper provides the results of practical research work on coke formation laws on catalysts produced on the basis of natural clays and clinoptilolite. To study the amount and character of coke deposition products on the surface of catalysts, as well as determination of optimum conditions for their oxidizing regeneration the samples of selected catalysts were investigated by the methods of Differential Thermal and Thermo-gravimetric analyses. Mechanical stability of catalysts prepared from natural carriers was studied. Introduction of natural bentonite clay (~20%) as a binding component into carrier gives catalysts of high mechanical stability. Study of activity and mechanical stability of catalysts showed their practical use in production of benzene by hydrogenated processing of aromatic concentrates.
Keywords: hydrodealkylation-hydrocracking catalyst, clinoptilolite, coke deposition, differential-thermal and thermogravimetric analyses, mechanical stability.
Introduction
Unlike applied traditional catalytic systems for hydrogenated processing of liquid pyrolysis products (LPP) the preparation of new catalysts on the basis of zeolites and natural carriers is economically and ecologically prospective [1-4].
Natural zeolite clayish minerals such as montmorillonite, vermiculite, bentonite and others are much cheaper than their synthetic analogues.
The possibility of their using in different processes petroleum chemistry is always an urgent topic in the researches of many scientists. Earlier whitening and catalytic property of ben-tonite clays from deposits of Azerbaijan in treatment process of oil products has been studied by well-known scientists (V.S.Gutirya [5], R.G.Ismayilov [6] and others).
It is known that chemical activation of natural bentonite clays causes a considerable change of their porous-structural characteristics. Acidic activation of bentonite clays increases specific surface, total capacity and average radius of pores.
The work [2] provides the results on the development of catalysts based on activated bentonite clays from two - Dash-Salakhly (Azerbaijan) and Cherkaske (Ukraine) deposits - which have similar practical activity and selectivity by end reaction of hydrogenated processing of LPP, including benzene-toluene-
xylene (BTX) fraction for the production of benzene. Catalysts with different content of active components based on clinoptilolite, as well as active clay of Khanlar deposit (khanlarite) and natural clay of Dash-Salakhly deposit (Azerbaijan) were tested under hydrogenated processing to select optimum catalyst and content of active components - iron and molybdenum. It should be noted that more than 70% of Dash-Salakhly clay consists of montmorillo-nite [2]. The present paper provides the results of research of coke formation laws on catalysts derived from natural clays and clinoptilolite.
Experimental part
Artificial-model mixture imitating BTX fraction of pyrocondensate toluene:n-octane= 80:20+0.05% of thiophene was used as a raw material for testing catalysts. The conditions of the process are as follow: temperature - 600625 C, pressure - 4 MPa, volumetric rate =1.0 h-1, mol ratio - H2:raw material = 5:1. Developed catalysts were tested in short and long-term experiments (5.20 and 200 hours). Catalysts based on clinoptilolite and activated clay (khanlarite) in hydrocracking and hydrodesulfu-rizing activity are not inferior to foreign catalysts of a similar purpose, but for hydrodealkyl-ation activity they considerably exceed them (Table 1).
Table 2. Results of continuous testing of catalyst 5% Fe-1.5% Mo-"khanlarite" in hydrogenated processing of BTX fraction of pyrocondensate. Conditions: T=6250C, P =6.0 MPa, volumetric rate - 1.0 h-1, molar ratio H2:raw material - 5:1
Table 1. Results of comparative testing catalysts based on natural carriers - clinoptilolite and bentonite clays in hydrogenated processing of BTX fraction of pyrocondensate. Conditions: T=6250C, P = 4 MPa, volumetric rate - 1.5 h-1, molar ratio H2:raw material - 5:1_
Catalyst Conversion, % Output of benzene from converted aromatic C7-C8, % mol
С7-С8 aromatic С6-С8 non-aromatic organosulfur
5%Fe+0.5% Mo+clinoptilolite 80%+na-tural clay 20% 75.0 99.5 98.0 95.7
5% Fe+natural Dash-Salakhly clay 66.7 99.0 97.7 97.7
5% Fe+1.5% Mo+khanlarite 80%+na-tural clay 20% 74.3 99.6 98.5 96.7
Catalyst of the process "pyrotol" USA 65.9 98.8 97.3 97.4
Catalyst of the process "detol" USA 66.7 98.4 97.0 97.9
Conversion, % Output of benzene
Duration of catalyst work*, from converted aro-
hour С7-С8 aromatic С6-С8 non-aromatic organosulfur matic C7-C8, mol %
1 83.3 100 98.9 94.3
5 82.0 100 98.3 94.6
25 80.1 99.9 98.6 95.3
50 78.6 99.8 99.0 96.8
75 79.3 100 97.9 97.0
100 77.8 99.9 98.1 96.7
150 80.9 100 97.7 96.9
200 78.3 99.7 99.3 97.0
After oxidizing regeneration 81.3 99.7 98.9 97.2
* 20% of Dash-Salakhly clay contains as a binding agent
As it is known coke deposition on catalysts' active surface plays the main role in deactivation their. Formation of a coke in the processes of catalytic processing of hydrocarbons results from dehydrogenation, cyclization, condensation and other reactions and has the following feature: at the beginning of process a coke deposition proceeds more intensively, and then slows down. In most cases blocking of an external surface of the zeolite crystals deactivates catalyst with coke. Condensation level of a coke is defined by topology of active centers on the external surface of catalysts. Coked substances with two or three condensed aromatic rings are adsorbed, as a rule, on Broensted acidic sites which are located on the external surface of catalysts [7-9].
Catalyst of high temperature hydro processing of aromatic concentrates in benzene is exposed to the impact of high temperature (600-6500C) and high pressure (to 6 MPa).
That's why stable activity and mechanical density are in the list of requirements to catalysts of hydrodealkylation-hydrocracking [9, 10].
According to the results of testing activity of catalysts prepared on the basis of natural carriers it was confirmed that under the process the latter are not poisoned (with sulphur and other compounds in the composition of raw material) and the main factor impacting on long-term activity of a catalyst is deposition of coke deposition products on its surface.
For studying the amount and character of coke deposition products on the surface of catalysts and determining optimum conditions for their oxidizing regeneration the samples of selected catalysts were studied using the methods of Differential Thermal and Thermogravimetric (DTA and TGA) analyses.
Figure 1 shows thermograms of primary clinoptilolite and catalyst samples processed after testing and prepared on clinoptilolite. Con-
sidering DTA and TGA curves of processed catalyst it can be noted that coke deposition products on the surface of a catalyst have a complex character and obviously consist of light (polyphenyl, polymeric and other) products and heavy coke. That's why DTA curves have three peaks.
T, 0C
Fig. 1. A thermogram of the initial clinoptilolite and the spent (in the conditions of hydrogenation processing of the BTX pyro-condensate fraction) of the catalyst prepared on its basis: 1 - initial clinoptilolite, 2 - spent catalyst Fe (5%) + Mo (0.5%) clinoptilolite (after a continuous 200-hours run).
During oxidizing regeneration from the surface of a catalyst the light products are first removed. Maximum of exo-effect of these products corresponds to 2150С.
After increasing regeneration temperature, as it was noted, first light, and then heavy products of coke deposition (exo-effect peaks were at 4100С and 530 С, correspondingly) burn. As it is seen burning of a heavy coke begins at 5000С and ends at 6000С. Weight loss of a catalyst sample from burning of light and heavy products of coke deposition makes up 1.2%.
Results and discussion
The results of thermogravimetric analysis of pure (after hydrogen activation) and processed catalyst samples on the basis of activated
"khanlarite" and natural (80:20) clay are provided in Figure 2.
T, °c
Fig. 2. Thermogram of fresh and spent (in the conditions of hydrogenation processing of BTX pyrocondensate fraction) catalyst samples Fe (5%) + Mo (1.5%) -"khanlarit": 1 - fresh catalyst (activated in H2 current), 2 - the spent catalyst (after a continuous 200-hour run).
As Figure 2 shows DTA curve of a pure catalyst sample has several peaks - at temperatures of 240, 320, 350 and 4700С. exo-Effects at 240, 320 and 3500С, as it is seen, are related to the oxidation of metallic iron till different oxide forms, exo- effect at 4700С is probably associated with the oxidation of МоО to МоО3.
As it is seen, thermograms of processed and pure (after hydrogen activation) catalyst samples are very similar by the character of DTA, however, exo-peaks of DTA curves of processed sample are shifted to higher temperature region. Thus, exo-peak at 5100С most likely corresponds to oxidizing regeneration of coke deposition products on the surface of a catalyst. Burning down of a coke, as in the case of clinoptilolite, takes place at 6000С.
Study of catalysts' activity based on activated clay "khanlarite" at relatively low temperatures (550-5700С) showed that their activity considerably falls in time. After increasing the
temperature to 600-6250C fall of activity a catalyst in time is not practically observed.
This is corrected by the data of thermo-gravimetric study of processed catalyst samples, in which it is seen that at moderate temperatures (550-5750C) the amount of coke depositions on the surface of a catalyst is considerably high and reaches 13-14% (Figure 3).
One of the requirements to catalysts for using in the processes with stationary layer of a catalyst is their mechanical strength. Mechanical strength of catalysts prepared on the basis of natural carriers is sufficiently high and considerably exceeds mechanical strength of most of the heterogeneous catalysts in industry.
For giving catalysts mechanical strength, prepared on the basis of clinoptilolite and chemically activated clays, it is sufficient to add 20% of natural bentonite clay into the composition of a barrier as a binding agent.
The results of studies on mechanical strength of pure, processed and regenerated samples of catalysts on the basis of natural carriers are provided in Table 3 (mechanical strength of catalysts was determined on PPK-1).
As Table 3 shows, catalysts do not decrease the required mechanical strength during hydrogenated processing and after oxidizing regeneration.
T, 0C
Fig.3. A thermogram of the spent (in the conditions of hydrogenation processing of the BTX pyro-condensate fraction) and the regenerated catalyst sample Fe (5%) + Mo (1.5%) - "khanlarit": 1 - spent catalyst, 2 -regenerated catalyst.
Table 3. Averaged values of mechanical strength of pure, processed and regenerated samples of the catalysts on the basis of natural carriers
Catalyst Mechanical strength of a catalyst, kg per grain
pure processed regenerated
5% Fe + natural Dash-Salakhly clay 13.8 14.0 (after 20 hours range) 14.0
5% Fe + 1.5% Mo+activated "khanlarite" 5.2 5.5 (after 200 hours range) 5.3
5% Fe + 0.5% Mo + clinoptilolite 4.5 4.6 (after 200 hours range) 4.4
NOTE: Catalysts based on activated clay "khanlarite" and clinoptilolite as a binding agent contain 20% natural Dash-Salakhly clay.
Conclusion
According to the results it was recommended to use a catalyst containing 5% Fe + 1.5% Mo + activated clay with binding agent (80% of "khanlarite" and 20% of natural clay) in production process of benzene of hydrogen-ated processing of aromatic concentrates.
Recommended catalyst prepared on the basis of activated clay "khanlarite" and natural Dash-Salakhly clay operated under hydrogenat-ed processing of BTX fraction of pyroconden-sate for 200 hours, as well as after oxidizing regeneration preserves the required mechanical strength.
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PÍROLÍZÍN MAYE MOHSULLARININ HÍDROGENLO§DÍRÍCÍ EMALINDA ÍSTÍFADO OLUNAN TOBÍÍ DA§IYICILAR OSASINDA KATALÍZATORLARIN MEXANÍKÍ DAVAMLILIGI VO KOKSOMOLOGOLMO QANUNAUYGUNLUGUNUN todqíqí
Z.^.Salayeva, R.M.Mustafayeva, X.Q.Ísayev, N.A.Zeynalov, H.A.Mamm3d3liyev
Maqalada tabii gil va klinoptilolit asasinda alinan katalizatorlarin koksamalagalma qanunauygunluqlarinin tadqiqina aid tacrübi i§larin naticalari verilmi§dir Katalizatorun sathinda koksamalagalma (koksyigilma) mahsullarinin xarakteri va miqdari, hamginin onlarin oksidla§diriri regenerasiyasinin optimal ¡jaraitinin tadqiqi nóqteyi-nazardan segilan katalizator nümunalari differensial-termoqravimetrik analiz metodu (DTA va DTQ) ila óyranilmi¡jdir. Hidrogenla§ma -hidrokrekinq katalizatorlarina qoyulan asas talab katalizatorlarin mexaniki davamliligi va aktivliyi oldugu ügün, tabii da§iyicilar asasinda hazirlanmi§ katalizatorlarin mexaniki davamliligi óyranilmi¡jdir. Da§iyicinin tarkibina alaqalandirici komponent kimi xam bentonit gilinin (~20%) daxil edilmasi katalizatora yüksak mexaniki davamliliq verir. Stabilliyin, aktivliyin va mexaniki davamliligin tadqiqi, onlarin aromatik konsentratlarin hidrogenla§dirici emali ila benzolun alinmasi prosesinda istifadasinin praktiki mümkünlüyünü góstarir.
Agar sozlar: hidroalfáÜ3§m3-hidrokrekmq katalizatoru, klinoptilolit, koksyigilma, differensial-termoqravimetrik analiz, mexaniki davamliliq.
ИССЛЕДОВАНИЕ ЗАКОНОМЕРНОСТИ КОКСООБРАЗОВАНИЯ И МЕХАНИЧЕСКОЙ ПРОЧНОСТИ КАТАЛИЗАТОРОВ НА ОСНОВЕ ПРИРОДНЫХ НОСИТЕЛЕЙ, ИСПОЛЬЗУЕМЫХ В ГИДРОГЕНИЗАЦИОННОЙ ПЕРЕРАБОТКЕ ЖИДКИХ ПРОДУКТОВ ПИРОЛИЗА
З.Ч.Салаева, Р.М.Мустафаева, Х.Г.Исаев, Н.А.Зейналов, Г.А.Мамедалиев
Приведены результаты исследования закономерности коксообразования на катализаторах, полученных на основе природных глин и клиноптилолита. С целью изучения количества и характера продуктов коксоотложения на поверхности катализаторов, а также определения оптимальных условий их окислительной регенерации, образцы выбранных катализаторов изучали методом дифференциально-термогравиметрического анализа (ДТА и ДТГ). Изучена механическая прочность катализаторов, приготовленных на основе природных носителей. Введение в состав носителя в качестве связующего компонента сырой бентонитовой глины (~20%) придает катализаторам высокую механическую прочность. Исследование активности и механической прочности катализаторов показало их практическую возможность использования в процессе получения бензола гидрогенизационной переработкой ароматических концентратов.
Ключевые слова: катализатор гидродеалкилирования-гидрокрекинга, клиноптилолит, коксоотложение, дифференциально-термогравиметрический анализ, механическая прочность.
