CC BY
23
KMYA PROBLEML9RÎ № 2 2017
173
UDC 541.183:661.183.2 EXPERIMENTAL EVIDENCE OF DIRECT INFLUENCE OF THE COMPOSITION AND PREPARED CONDITIONS ON THE ACTIVITY AND SELECTIVITY OF
HYDROTREATING CATALYSTS
Kh.A.Nasullaev, Sh.T.Gulomov, U.Kh.Sayidov, Z.A.Teshabaev, M.P.Yunusov
Uzbek scientific-research chemical- pharmaceutical institute. Durmon Yuli 40, Tashkent, 100125, Republic of Uzbekistanst E-mail: [email protected]
Synthesis questions of oxides Ni-Mo, Co - Ni-Mo and Co-Mo catalysts for processes of hydrodesulfurization and hydrogenation of aromatic hydrocarbons in the composition of kerosene, deasphaltisate and natural gas are considered.
Keywords: Catalysts, activity, hydro-process, aluminum oxide, adsorbent, oil, gas, model systems.
Introduction
Processing raw hydrocarbons into different types of commercial-grade fuel and oil involves environmental, economic and quality issues. Insufficient refining of fuel from sulfur and aromatic hydrocarbon causes environmental pollution. Sour sulfur contained in natural gas causes active corrosion of pipelines and equipment to result in enormous economic losses. Compositions based on compounds of Mo, Co and Ni, applied on y-Al2O3 are typical for a great number of catalysts in hydro-processing oil products to comply with up-to-date requirements of residual content of sulfur and aromatic compounds [1]. Rather promising is the single soaking with joint solutions and complexing agents, as well as the coating with nickel or cobalt in the composition of molybdenum heteropoly compounds. Noteworthy is the combination of nickel and cobalt in the composition of Co-Mo/y-Al203 hydro-treating catalysts [2; 3]. Nickel as (co) promoter helps
with "containment" of cobalt cations in the CoMoS phase, and the synergistic improving catalysts' activity is typical for the reactions of hydrogenation and hydrodesulphurization.
The paper focuses on various aspects of the application of non-traditional component carriers in the synthesis of elements of multilayer catalyst systems comprised of catalysts of hydro-desulphurization and hydro-dearomatization for processing fractions of highly resinous oil with the sulfur in high content, as well as for the removal of mercaptan from natural gas given the availability of CO2 and H2O. The paper examines the influence of additives to developed aluminum oxide adsorbent, waste of Al2O3 -TiO2 carrier and kaolin clay in the process of synthesis, both physical and chemical, as well as catalyst properties of CoMo, Ni-Mo, Co-Mo-Fe, Ni-Fe-Mo and Co-Ni-Mo catalysts when hydro-processing liquid and gaseous raw hydrocarbons.
Experiment
Carriers and catalysts were synthesized in line with our own technology [3]. A sample (Carrier №-1) was made up of a mixture of 55% of industrial aluminum hydrate (pseudo-boehmite prepared on the basis of gibbsite by alkaline deposition; Ryazan, Russia), 10 % of kaolin ("Angren Kaolin" Ltd.) and 35 % of Al2O3 (developed adsorbent of the Shurtan
Gas and Chemical Complex) followed by peptization with boric acid and hydrogen nitrate as well as shaping as Raschig rings or trefoil. Carrier №-2 was prepared in the same manner as a mixture of 45% of pseudo-boehmite (Russia), 10% of kaolin, 10% waste of AI2O3 -TiO2 Carrier ("Himex", Uzbekistan) and 35 % of developed adsorbent. Carrier №-3
was prepared in the same way but on the basis of a mixture of 55% of pseudo-boehmite Sasol SB alcoholate-derivative (Sasol SB Pural GmbH, Germany), 10% of kaolin and 35% of developed adsorbent.
Note that shaped carriers were calcinated at 823K, and after cooling soaked in a joint stabilized phosphoric acid solution of ("P") series or citric acid (C1 series). Various catalysts of C2 series were prepared on the basis of citric acid and soaked by means of consistently wet method with varied values of pH. The molybdenum was applied first out of aqueous solution of ammonium
heptamolybdate (Mo/№-1). Then the base of Mo/№-1 was soaked in a joint solution of nickel nitrate (cobalt, iron) - citric acid with an appropriate pH. An actual content of molybdenum, nickel, cobalt and iron in various catalysts is shown in the Table attached.
The diffraction patterns were obtained on the diffractometer DRON-3 using filtered CuKa, voltage - 30 kV, current -20mA. Electron spectrums were obtained using the spectrophotometer Hitachi-330 Raman- AND X.
Results and discussion
Stable joint solutions of ammonium heptamolybdate with one or two transition metal nitrates were obtained at pH=1.3-2.5 (stabilization H3PO4) and pH=0.5 (stabilization C3H8C7H20). Polymeric ions of molybdenum
in such conditions while in contact with ions
2+ 2+
of Co or Ni , may form heteropolyanions [4]. As a result, hydrated molybdates of MeMoO4 type and heteropolyanions [NiH6Mo6024]4-, [CoH,Mo6O24]4-, together with appropriate cations of Co2+, Ni2+, NH4+
- -3
and anions of NO3" and PO4" coexisted in joint solutions. X-ray studies revealed stabilized H3P04, a number of amorphous and crystal phases in the composition of concentrated or dried at 393K joint solutions. Diffraction patterns of dried catalysts of "P" series, in
addition to the broad lines from y"-Al2O3 and narrower lines of quartz have shown the halo effect in the area of d= 8.0-2.6A. Note that a diffraction pattern of the catalyst №7/H-2-P has shown lines of anatase and rutile.
Also, appearance of a wide halo was due to the overlapping of many weak lines which correspond to nickel and cobalt molybdate previously identified in the model systems as follows:
NiMo04H20 -d=0.820 (23); 0.431(7); 0.401(3); 0.325 (100); 0.300(90); 0.280(5); 0.20 (12); 0.190(10) A; x- NiO Mo03y^0 -d=0.672(20); 0.379(18); 0.335(23); 0.326 (17) A; NiMo04 - d= 0.615 (5); 0.37(3); 0.34 (20); 0.307(50); 0.272(30); 0.206(10); 0.191(4 A
CoMo04H20 -d = 0.633 (15); 0.383(33); 0.350 (23); 0.338 (100); 0.338(43); 0.314 (26) A; CoMo04 -d =0.623(13); 0.354(22); 0.313 (26) A. Note that percentage point terms are given inside brackets. Diffraction patterns of NiMo, NiCoMo and FeNiMo catalysts within "P" series against halo effects have shown lines from NiMo04H20 and x NiO Mo03 yH20. Lines of weaker intensity (d =11.0(3); 5.11(5); 3.03(2) A) from
(NH4)4[Ni(0H)6Mo6018]-5H20 have been revealed only through the use of XFA NiMo catalysts. XFA analysis of catalysts №2/H-1-P and №3/H-1-P (dried under 393K) also revealed several strong peaks against the halo effect. Such diffraction peaks are typical for crystal phases CoMo04 H20 u (NH4)4[Co(OH)6Mo6018] 5H2O (d =10,87(4); 11.02 (3); 5.72(7); 5.12(9); 3.73(2) A). As opposed to the «P» series, in case of dried catalysts of «C1» and «C2» series, the source lines were detected in the diffraction patterns only. However, Raman spectrums of all dried catalysts proved to be the same, all of them containing bands 955-952 (intense), 900 (shoulder) 570-565, 355 and 220 sm-1. These bands were in keeping with poly-molybdates.
Diffraction patterns of all catalysts (series «P», «C1» and «C2») calcinated under 823K have shown the line of quartz strongly extended by moderate intensity as per line Al203 and corresponded to the metal molybdate against the halo effect in the area d=6.4-2.3 A. No oxide phases have been
EXPERIMENTAL EVIDENCES OF THE DIRECT INFLUENCE
175
detected (FeMo04, M0O3 or C0AI2O4, NiAl204, FeAl204). The XFA analysis has revealed the presence of crystallite mixture y -and <x-Fe2O3 (d= 4.81; 2.94; 2.69; 2.48; 2.31; 2.22 A) in the content of catalyst agents №1/H-1-P and №2/H-1-P. The great intensity of halo in case of catalyst within the "P" series has shown their lower dispersion.
Results of the XFA analysis in regard to a greater catalyst dispersity of "C1" and "C2" series coincided with the data of the Raman spectroscopy. A degree of polymerization of molybdate structures decreased in a row as follows: №9/H-1-C1 > №10/H-1-C1 > №13/H-1-C2 > №14/H-1-C2 > №6/H-1-P > №4/H-1-P > №7/H-2-P > №12/H-1-C2.
As a consequence, an edge of a broad sheet of charge transfer in the oxygenated complexes Mo6+ within the electron spectrums
appr. 270-285 nm showed a joint presence of
2+
MoO4 and polymerized molybdate-ions within the structure of catalysts № 3-5, 7 of series «P». An exact location of such bands displays a local symmetry of Mo6+ environment which depends on factors of coordination and physical form. Isolated (particles) of molybdates within the tetrahedral site (MoTd) found characteristic band of absorption about 250 nm, whereas a signal from poly-molybdates within the octahedral state (MoOh) is observed in the area between 260 and 330 nm depending on the degree of agglomeration of these particles. In addition, both types of particles Mo6+ show two strong bands of absorption of approx.200-220 nm. The deconvolution Spectrum Ni-Mo of the catalyst clearly indicates the presence of molybdenum particles within the octahedral and tetrahedral states [4]. The ratio of intensity of MoOh (275-330 nm) and MoTd (200-275 nm) can provide qualitative information about poly-molybdate MoOx centers on the surface of various catalysts. From this it follows that when transiting to higher percent catalysts the band's edge shifted to 300 nm (№8/H-3-P, №11/H-1-C2, №12/H-1-C2) and further to 330 nm (№9/H-1-C1, №13/H-1-C2) due to the increase in polymerization level of molybdate-anions.
The UV-visible electron spectrums of cobalt solutions were received following the
dissolution of ammonium heptamolybdate and cobaltous nitrate in sour aqua solutions to demonstrate the same cobalt varieties in the aqueous solution with bands having been formed under 460-465, 513-520 and 615-619 nm.
These bands are typical for Co(II) d-d
of electron transitions in the hexaaqua
2+
complexes [Co (H2O)6] . Meanwhile, bands which were localized within 645-658, 730-735 and 1065 nm and classified as structures with nickel ions [3]. A comparison of relationship (respective) between d-d transitions of nickel and cobalt in treating solutions and Ni (Co) Mo samples of "P" series showed their stability. It was indicative of the persistence of hydrated ion [Ni(H2O)6]2+ and [Co(H2O)6]2+ while drying, and the interaction of metals with the carrying base caused by electrostatic
adsorption. On the contrary, d-d transitions of
2+
Ni in dried samples of «C2» series have shown a red shift Ni2+: 653 nm—>660 nm, 395 nm—>400 nm; Co2+: 653 nm—>660 nm, 395 nm—>400 nm) caused by the increase in bond strength of ligands. According to a spectrochemical row, this bathochromic shift was related to the replacement of water ligands in hydrated ion of nickel with weaker surface ligands that form complexes with nickel ions in the inner coordination sphere, AlO-Ni-Citrate. A predominant complex formation of about pH 3-8 manifested itself under maximum mol fraction at pH 3.3 ant pH 5.8, respectively [Ni(HCit)(Cit)(H2O)4]3- and [Ni(Cit)2(H2O(H2O)4]4- respectively [5]. A simple pale green nickel nitrate solution in the water (pH 3.7) consisted only of hexahydrate
nickel [Ni(H2O)6]2-. At pH 0.3 and mol
2+
fraction of [Ni ]= 0.63M as well as mol ratio
3+ 2+
Cit /Ni =2, the solution color remained pale green. On the contrary, at pH 3.4, the mol fraction [Ni2 ] = 0.63M and mol ratio
3+ 2+
Cit /Ni =2, the solution color turned to be green-blue. In accordance with the article [5] and due to the increase in pH, the replacement of citrate ligand in the complex [Ni(Cit)2(H2O(H2O)4]4+ ammonium and the rise in the mol fraction of uncoordinated citric acid has occurred.
Blue shift (701^676 nm) of the band of d-d nickel that followed in the spectrum of
samples №9/H-1-C1, and №14/H-1-C2 in comparison with spectrums of other catalysts of "C2" series showed a greater strength of coordination bonds with the ligand.
These observations showed that applied nickel in the complex NiMo-Citr (pH>3.4) is subject to be retained wholly or partly together with the citrate of complexes [Ni(H
Citr)(Citr)(H20)4]3- or [Ni(Citr)2(H20)4]4-.
Whereas in case of №9/H-1-C1, and №14/H-1-C2 catalysts, no surface ligands can be water ones and weaker than citrates. In order to study the coordination of citric acid upon drying (393K), infrared spectrums of «C2» series catalysts have been obtained. The type of coordination of citric acid showed that it spectroscopically coincided with the results of the UV-visible spectrography. Infrared spectrum of the Ni-Citr solution ad pH=0.5 has shown bands identical to the ones in samples (citric acid and nickel nitrate) which indicate that carboxylic acid in the residue of citric acid is neither dissociated, nor connected. However, the rise of pH in the solution resulted in the deprotonation of carboxylic groups while reducing the intensity of absorption bands of carboxylic acid. The
intensity of marked unsymmetrical (Yas -absorption bands at 1602 and 1567 cm-) and quite strong symmetrical oscillations of carboxylates (vs-absorption band ad 1413 cm-1) rose simultaneously which led to the coordination of deprotonated carboxylic groups with metal. An intense broad band 1500-1700 cm-1 appeared in the spectrum which was related to the adsorbed water on the basis of aluminum oxide as a part of the structure, the latter can be overlapped with signals from the carboxylate, for the band 1335 cm-1 came to be associated with the
bands of 5 (C-H) and 1401 cm-1 Ys due to the oscillations of carboxylate. The preservation of absorption bands went to show the coordination of carboxyl groups. In accordance with the results of UV-VIS DR, the adsorbed nickel in hard №14/H-1-C2 fails
to form citrates as Ys absorption from carboxylates and does not manifest itself in the
infrared spectrum as distinct from other NiMo-Citr (pH=3.4^8.7) samples.
The UV-VIS DR -spectra of all catalysts of similar composition ("P", "C1" and "C2" series calcinated at 823 K proved to be similar. A degree of interaction of the carrier with cobalt ions on calcination was determined
through the bands triplet intensity of 555; 602
2+
and 667 nm from CoTd ions. Note that appearance of the diffuse reflection of the
characteristic doublet of 595 and 633 nm from
2+
NiTd ions after calcination at 823K in the electron spectra clearly indicates the formation of a nickel-aluminum spinel. The wide absorption band at 510 nm with a shoulder around 469 nm corresponds to CoTd2+ ions in the cobalt molybdate structure. The cobalt-molybdenum and nickel-molybdenum associates were identified by the presence of absorption bands in the zone of 312-345 nm [3]. Note that bands of 417-435 nm and
approx. 735-758 nm [3] are in keeping with
2+
NiTd nickel ions in the structure closer to NiMo04. The number of non-active spinel structures changed in a row as follows: "P"series > "C2"series > "C2" series >
Before testing their activity, the "F" series catalysts were calcinated at 823 K and the "C1> and "C2" series dried catalysts sulphided ex situ in a tube reactor at 400°C for 4 hours in a stream of 10 vol. % H2S in H2 of atmospheric pressure.
Hydrogenating and desulphuring function of samples were evaluated through comparing changes in the content of total sulphur (ESulphur as shown in the Table), polycyclic aromatic hydrocarbons (PAC), and mercaptan (RSH) in hydrogenation product with a flowing unit obtained due to the feed stock process.
Activity in hydrodesulphurization and hydrogenation of polyaromatic compounds in the composition of deasphaltizate and kerosene fraction has been examined on the flowing unit under a pressure of 4.0-4.5 MPa and temperature of 573-593 K while the natural gas under a pressure of 2.5-3.0 MPa and at a temperature of 573 K.
Ti№ Influence of composition and preparation method on activity and selectivity of catalysts
pH of solutions The actual content, in oxides equivalent (after oolcbatkn aiS23K) PAH and ail fur compounds concentration in the hjdrogenation products of various K>'drocaibonst%
JfcPfygt Mo + Co (NiT Fe) HA Mo C7H1O, Co>Ni Kerosene Deaspliattisate Natural gas
OriguiaJ Dried
Mo Ni Co Fe PAC ESutfar PAC ESulfar RSH RSH*
Concentration of sulfur* PAH and mercaptans in t ic fced stock; 16.9 0.25 32.4 1.32 0,005 0,004
tél/H-1-P 1.6 12,3 3,1 0,9 14.7 0,068 30, & 0,370 0,00023 0,00021
1.7 12.1 0 3.2 1.0 14.7 0,066 31.0 0.361 0,00020 0,00019
tffl/H-l-P 2,5 II .H 3.& 14 & 0.070 30 5 0,372 0.00021 0.00020
№4/H-l-P 14 12,1 3,9 14 .4 0,072 27,7 0,3*1 0,00025 0,00024
14 12,2 0,9 3.2 14.5 0,070 27,9 0.37& 0,00024 0,00023
№6/1 M»P U 164 46 10 0.056 25 1 0362 0.00021 0 00020
№7/H-2-P 14 12,1 3J M.I 0.064 26,S 0.373 0,00023 0,00020
««/H-a-p M 16,5 4.7 7.S 0,054 25,5 0.340 0,00020 0,00019
№9/H-l-C, 0 5 166 4 5 6.R 0042 23.il 0263 0.0001 S 000017
№10/H*1*CJ 0.6 16,1 0,9 3.2 7.0 0,035 24,2 0.252 0,00017 0,00017
5.5 3.5 16.1 4J Í.S 0,032 23,3 0.234 0,00014 0,00013
Jfel2/ H-I-Ci 5.5 3.6 16.2 LI 3.3 5.9 0,030 23,6 0.203 0,00012 0,00011
№I3/H-I*C2 5 5 3.4 16.0 0 4.5 5.9 0.025 23,J 0.200 0.00012 0.00012
.V M H-I-Ci 0.5 3.5 16.4 4.1 6.2 0.034 23,7 W.V. 0,00015 0.00014
E.
> »
O Cd
r
M
S r
QJ
a
£
N> K» O
I—' -4
Raw natural gas contained (vol.%) mercaptan - 0.005 (in S equivalent), hydrogen sulphide - 0.06 vol. carbon dioxide - 3.99, nitrogen 0.043 and water vapor. In order to evaluate the influence of water and C02, activity of catalysts in natural gas hydrodemercaptanization before and after passing through the adsorbent dryer has been tested in parallel. Results obtained are marked in italics in the Table.
Within each series, the desulphuri-zation of liquid and gaseous hydrocarbons proved to be higher on Co-Mo catalysts, and upon hydrogenation of PAH in the composition of fuels and oils on Ni-Mo. Tri-metallic catalysts occupied an intermediate position. It revealed that the catalyst activity increases with the addition of citric acid due to the activity of catalysts of the same composition together with phosphoric acid added.
Conclusion
Given the results above, one can conclude as follows:
1. Carriers obtained through the use of kaolin clay, developed alumina adsorbent and waste of Al203 -Ti02 carrier together with pseudoboehmite of varied origin may be used for preparation of active catalysts.
2. Activity and stability of any catalysts in question are commensurable to the best commercial catalysts for oil products with low sulfur content.
3. Maximum desulfurizing effect was achieved on a catalyst №13/H-1-C2, where the complex of [Ni(Citr)2(H20)4]4- is detected spectrally.
References
1. Tomina N.N., Nikulshin P.A., Pimerzin Al.A. Influence of compounds of molybdenum on the activity of Mo/y-Al2O3 and NiMo/y-Al2O3 hydrofining of catalysts. Kinetika i kataliz -Kinetics and catalysis. 2008, vol.49, no №5, pp. 684693. (In Russian).
2. Mozhaev A.V., Nikulshin P.A., Pimerzin A.A., Konovalov V.V. Activity of CO (Ni) MoS/Al2O3 catalysts obtained on base salts Co (Ni) H6[Co2Moio038H4] in hydrogenolysis of thiophen and hydrofining of diesel fraction. // Neftehimiya - Petroleum Chemistry. 2012, vol.52, no.1, pp. 45-53. In Russian).
3. Yunusov MP., Saidahmedov Sh.M., Jalalova Sh.B., Nasullaev Kh.A. Synthesis
and study of Ni-Mo-Co catalysts for hydro-processing of oil fractions. Catal. Sustain. Energy. 2015, no.2, pp. 43-56.
4. Mohan S.Rana, S.K. Maity, J. Ancheyta, G. Murali Dhar. MoCo(Ni)/Zr02-Si02 hydrotreating catalysts: physico-chemical characterization and activities studies. Applied catalysis A: General. 2004, vol.268, issues 1-2, pp.89-97.
5. Suarez-Toriello V.A., Santolalla-Vargas C.E., J.A. de los Reyes, Vazquez-Zavala A., Vrinat M, Geantet C. Influence of pH solution on impregnation of citric acid and activity of Ni/W/Al203 catalysts. Journal of Molecular Catalysis A: Chemical.404 2015, vol. 404, pp.36-46.
EXPERIMENTAL EVIDENCES OF THE DIRECT INFLUENCE
179
ЭКСПЕРИМЕНТАЛЬНОЕ ДОКАЗАТЕЛЬСТВО ВЛИЯНИЯ СОСТАВА И УСЛОВИЙ ПРИГОТОВЛЕНИЯ НА АКТИВНОСТЬ И СЕЛЕКТИВНОСТЬ КАТАЛИЗАТОРОВ ГИДРОПРОЦЕССОВ
Х.А.Насуллаев, Ш.Т.Гуломов, У.Х.Сайидов, З.А.Тешабаев, М.П.Юнусов
Узбекский научно-исследовательский химико-фармацевтический институт 100125, Республика Узбекистан, Ташкент, ул. Дурмон йули 40, e-mail: [email protected]
Рассматриваются вопросы синтеза оксидов Ni-Мо, Co-Ni-Мо и Co-Mo-катализаторов для процессов гидродесульфуризации и гидрирования ароматических углеводородов в составе керосина, деасфальтизата и природного газа. Ключевые слова: катализатор, активность, гидрообработка, оксид алюминия, адсорбент, нефть, газ, модельные системы.
Поступила в редакцию 25.05.2017.
