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74 AZ9RBAYCAN KIMYA JURNALI № 3 2018 ISSN 2522-1841 (Online)
ISSN 0005-2531 (Print)
UDC 547.554.2f022:665.652.095.2
ALKYLATION OF ETHYLBENZENE BY ETHANOLE ON H-ULTRASIL ZEOLITE
CATALYST, MODIFIED BY LANTANUM
T.O.Gakhramanov, S.E.Mammadov, E.LAkhmedov
Baku State University taleh bdu@mail. ru Received 02.02.2018
The modified H-ultrasil zeolite maintained high crystallinity and high specific surface areas precursors testified by XRD, BET and NH3-TPD analysis. Effect of lanthanum concentration on the adsorptive, acidic and catalytic properties of H-ultrasil in the ethylbenzene ethylation reaction was investigated. Influence of modifying on catalytic properties of H-ultrasil zeolite is studied in a 300-400°C temperature interval. Under these conditions, selectivity of /»-diethylbenzene in H-ultrasil is 42.1-44.4%. It is established that increasing concentration of lanthanum on H-ultrasil makes reduction of porous volume, essential decrease in concentration of the strong acid centers that in turn leads to increase selectivity on p-diethylbenzene. By the increase in concentration of lanthanum in H-ultrasil to 5.0 wt. % selectivity onp-diethylbenzene increases to 74.5%.
Keywords: H-ultrasil, zeolite, modification, p-selectivity, lanthanum, ethylation, ethylbenzene, ethanol.
Introduction
Aromatics find a wide variety of applications in petrochemical and chemical industries [1]. Benzene, toluene and xylene are the three basic materials that serve as intermediates of commodity chemicals of aromatic derivatives. Dialkyl benzenes such as xylene, diethylben-zene and dipropylbenzene are used for the production of polyesters, engineering plastics, as solvents, photodevelopers, antioxidants and etc. [2-4]. Diethylbenzene is used as solvent and precursor for cross-linking agents in producing resins. 1,4-Diethylbenzene (p-DEB) is a desor-bent for parex process of universal oil products (UOP) [5]. H-ultrasil zeolite could be the best catalyst for the reaction of ethylbenzene ethylation by ethanol to /»-DEB because of its special shape selectivity and surface acidity. Many processes have been developed to modify its surface property in order to promote para-selectivity for alkylation and prevent coking deposition: for example, loading with oxide of P, Mg or B [6-12], coking by methanol [11-13], silylation by silicon alkoxide [14, 15] using H-ultrasil zeolites of different crystal sizes [16, 17] and use of metallosilicate zeolites with the MFI structure [18-20]. Modified H-ultrasil zeolites exhibit high /-»¿//'¿/-selectivity than the parent zeolite. The mechanism for the improvement of para-selectivity of the modified H-ul-
trasil zeolites has also been reported. Kaeding et al. proposed that the high para-selectivity of modified H-ultrasil zeolites for the alkylation or disproportionation was due to product shape selectivity, that is, the intracrystalline diffusivi-ty of the /»-isomer was much higher than that other two isomers [7, 8, 10]. Proparatto et al. reported that the /»-isomer was found selectively inside the H-ultrasil channels in the ethylation of toluene while the isomeration of the /»-isomer proceeded just on the external surfaces and that the improvement in /-»¿//'¿/-selectivity by the modification was due to the inactivation of the acid sites on the external surfaces [16, 17, 21, 22] Yashima et al. proposed that the primary product in the alkylation was only the /»-isomer due to restricted transition-state shape selectivity and that the improvement in /-»¿//'¿/-selectivity by the modification of H-ultrasil was due to suppression of the isomerization of primarily produced /»-isomer [6-9, 19]. According to Vinek et al. [23] phosphorus treatment results in a decrease in the strength of both Bronsted and Lewis acids sites, while Jaumain et al. [24] stated that when H-ultrasil catalyst was modified with phosphorus, both Lewis and Bronsted acids sited of various strengths were decreased, and when modified by magnesium, the stronger acid sites were eliminated while the weaker Lewis acid sites increased. It is still uncertain
АЗЕРБАЙДЖАНСКИЙ ХИМИЧЕСКИЙ ЖУРНАЛ № 3 2018
whether the modifying agent is deposited only on the extremal surface of the zeolite crystallites or is penetrating the channels as well; it is also controversial whether the deposition of the modifier occurs without or with the interaction between the acid sites and the modifier precursor inducing changes in the density and strength of the acid sites. The aim of this work was to investigate the effect of the location of the lanthanum species in the catalytic mass, the concentration and strength of the acid sites of the La-H-ultrasil zeolites on their activity and para-selectivity in the ethylation of ethylbenzene.
Experimental part
Catalyst preparation. The protonic parent H-ultrasil zeolite was obtained by ion-exchange of the commercially available ZSM-5 (Nizhego-rodskie sorbenty Ltd., Russia, Si/Al=61) with NH4CI and following calcinations this, 5.0 g H-ultrasil was refluxed twice in 100 ml of 1.0 M NH4CI solution for 6 h and then calcined (in air) at 550°C for 4 h. Prior to the use as catalyst, zeolite was granulated by pressing without any filler
n
or binder a maximum pressure of 2.5-10'Pa, and sieved to obtain particles with a diametre of 0.2-0.3 mm. The impregnated La/HZSM-5 zeolite was prepared similarly to the in the 0.03-0.30 g/10 ml aqueous solution of lanthanum nitrate La(N03)3-5 H20 at 70-80°C for 24 h. The impregnated powder was dried at 110°C for 4 h and then calcined at 550°C for 4 h in air to obtain 1.0 wt% La/H-ultrasil, in which 10.0 wt% denotes the load of La. The thus prepared crude La/H-ultrasil was pressed, crushed, and solted to get particles of 0.2-0.3 mm as indicated above for H-ultrasil.
Catalyst Characterization. The La-loading of the catalyst was measured by atomic absorption spectrophotometer (AAS TJA, Atomsan 16) XRD pattern of the catalyst was collected by powder X-Ray diffractometer with Cu/T,,-radiation (k= 0.15046 nm) operated at 40 kV and 30 raA to identify the structure of the catalyst N2 isotherme adsorption-desorption characterization of the sample was performed at liquid nitrogen adsorption of 77 K using Micromeri-tics ASAP-2010 instrument. Degassing was
0 3
done for 8 h under vacuum at 250 C and 1x10" Pa for 4 h before the measurement of data. The specific surface area was calculated according to BET method. The volume of pores was evaluated by plot analysis of the adsorption isotherm. Acid properties of the method of ammonia thermodesorption along the procedure described in [12].
Catalytic Test. The catalytic experiments were carried out in a fixed bed: continuous down flow tubular quarts reactor (1.0 cm I.D and 16 cm long) was placed inside a microprocessor controlled furnace preceded by a pre-heater and followed by a condenser. The sample reactive tube was used in all the experiments. In a typical run, about 2.0 g at catalyst was charge into the reactive and the reaction was carried out of atmospheric pressure in the presence of hydrogen in the temperature range 300-400°C with feeding of lh"1 volume rate and mole ratio C7H8:C2H5OH:H2=2:l:2 using unmodified as were as modified H-ultrasil catalysts. The catalysts were activated for lh atmosphere and hydrogen before the experiments runs were started. The vapours of products along with unreacted reactants were condensed in the condenser and the liquid samples collected were analyzed by gas chromatography using a Agilent HP-capillary column (100 mx0.25 mmx0.5 (j,m) and a flame ionization detector. The program used was follows. Initial temperature was °C and then held for 2 min. After that, the temperature was increased to 200°C with a ramp rate of 10°C/min. Again in stayed at 200°C for 1 min. The detector and injection temperature were 250°C. Flow rate of air, hydrogen was 35 ml/min, respectively. From gas chromatography results, the selectivity and diethylbenzene in the products were calculated. The conversion of toluene was also noted for modified as well as unmodified H-ultrasil catalysts.
Result and discussion
The La-loading of these catalysts was measured by ASS. It can be seen from Table 1 that the final La loading at this catalyst was lower than the La loading calculated by this catalyst preparation. Table 1 shows BET speci-
fic surface area (<Sbet) and pore volume (Fpore) of La/H-ultrasil with the different loadings of La. Both 1.0 wt %, La/H-ultrasil and 2.0 wt % showed Sbet and Fpore similar to the parent H-ultrasil. These results suggest that the addition of La up to the 2.0 wt % has no influence on either the BET surface area or the mesopore volume of the catalyst. When the La loading was more than 2.0 wt %, ^bet of La/H-ultrasil decreased with the increase of La loading simi-lary, Fpore of this catalyst presented reduction tendency. Figure 1 shows XRD patterns of La/H-ultrasil and H-ultrasil as reference. Characteristic diffraction peaks of H-ultrasil (29= 7.8°, 8.8° 23.1°, 23.8°, 24.2° were found from these La/H-utrasil catalyst. On the other hand, the new peaks presented at 29 =23.3° and 23.6° were detected from La/H-ultrasil comparing
with the parent H-ultrasil. The peaks at 2 9=23.3° slightly shifted to the high 29 and the peaks 29 =23.6° slightly shifter to low 29 with the increase of La-loading. These phenomena are tentcively due to the interaction of La with H-ultrasil framework. On the other hand, no diffraction peaks belonging to La and La oxides were detected from these catalysts, indicating that La species might highly disperse on H-ultrasil surface. For La/H-ultrasil, the diffraction peaks intensity of H-ultrasil became weak with the increase of La-loading compared with the parent H-ultrasil. The phenomenon was possibly due to the parent H-ultrasil. The phenomenon was possibly due to the increase in the coverage of La species on H-ultrasil and or the reduction in the crystallinity with the increase of La-loading.
Table 1. Specific Surface Area Volume of these Catalysts
Catalyst Lanthanum content, wt% La-loading, wt% »SBET- nr/g J' v pore? cm3/g
H-ultrasil - - 268.5 0.23
La/H-ultrasil 1.0 0.91 266.8 0.22
La/H-ultrasil 3.0 2.89 238.5 0.19
La/H-ultrasil 5.0 4.93 225.6 0.18
La/H-ultrasil 10.0 9.74 213.7 0.17
Fig. 1. XRD pattern of parent and modified H-ultrasil catalysts. АЗЕРБАЙДЖАНСКИЙ ХИМИЧЕСКИЙ ЖУРНАЛ № 3 2018
Table 2 lists the data on activity and selectivity of H-ultrasil in the reaction of et-hylbenzene ethylation. The reaction temperature did not affect the ethanol conversion that remained on the level 92-100%, the toluene conversion raised with temperature from 31.5 to 44.6 wt %. A long side toluene and diethylben-zene (DEB) in the hydrocarbon fraction of the catalyzate were detected aliphatic hydrocarbons C>5, benzene, ethylbenzene, xylenes ant other aromatic hydrocarbons. In gaseous products were detected saturated and unsaturated hydrocarbons (C1-C4). At lower temperature the process was complicated with formation of aliphatic hydrocarbons C>5, at higher temperature by the increase in the yield of side aromatic hydrocarbons and decrease in selectivity on /?-DEB As seen from the Figure 2 and the data in
the zeolite with a solution of lanthanum nitrate followed by decomposition of the salt at 550°C leads to substantial changes in catalytic and physicochemical properties of the catalyst: its activity in the alkylation and toluene dispropor-tionation reactions falls while selectivity of p-DEB formation grows.
Selectivity on /»-DEB on H-ultrasil at 300-400°C corresponds to 42.1-44.4%. Modification of H-ultrasil with La provides the increasing of selectivity on /»-DEB. Increasing of La concentration into H-ultrasil up to 5.0 mas % leads to increasing of selectivity on /»-DEB up to 74.5%. The future increasing of La concentration into H-ultrasil provides higher para-selectivity up to 82.7%, however in these conditions the conversion of ethylbenzene decrease from 19.5 to 12.7%.
Table 3 insertion of lanthanum by impregnating Table 2. Composition of the product of ethylbenzene alky lation with ethanol on the H-ultrasil form
Conversion.% Selectivity 011 the products in catalyzate, % Selectivity for /9-DEB ' %
T, °c EB EtOH benzene toluene p-DEB «/-DEB o-DEB xylenes *PAH Aliphatic hydrocarbon c5+
300 31.5 93.8 5.4 0.3 33.7 39.5 1.8 5.8 1.6 11.5 44.4
350 39.8 100 7.1 0.8 32.4 40.6 2.9 6.7 2.0 7.3 42.3
400 44.6 100 8.6 1.7 32.8 42.5 3.4 2.2 3.1 4.8 42.1
PAH - Polvaromatic hydrocarbons
a
ox 40-
%
CP 30-
W
C
.g <s> 20-
b 0 10-
u
O
<P 100
80
60
40
%
cq w P
1
e
o
g
J
>
Fig 2. Plot of ethylbenzene a (wt.%) and selectivity cp (%) on /»-DEB on the lanthanum content (wt. %).
10
<D OA
Table 3. Adsorption of water, heptane and benzene vapors with the H-ultrasil modified with lanthanum
Zeolite Lanthanum content, wt% Adsorption, cnrVg
HoO /7-C7H16 o,a,
H-ultrasil 0 0.073 0.164 0.08
La-H-ultrasil 1 0.070 0.156 0.072
La-H-ultrasil 3 0.063 0.127 0.064
La-H-ultrasil 5 0.057 0.094 0.056
La-H-ultrasil 10 0.052 0.068 0.041
The higher /^//'¿/-selectivity of the lanthanum-containing H-ultrasil can be a result of decrease in the strength of Bronsted and Lewis acid centers in the zeolite [12, 24] and by the change in size of the canals in the catalyst structure and hence, in its adsorption: desorption and diffusion characteristics. Actually, at the modification the modifier reacts with the zeolite that leads to affecting the accessibility of the structural canals of the zeolite catalysts. This is confirmed by the fact of decrease in sorption capacity of the samples when lanthanum content in
their compositions increases (Table 3). The changes in the H-ultrasil activity and para-selectivity at modification it with lanthanum is also a result of changes in concentration of acid centers (Table 4).
As seen from the data in Table 4, increase in lanthanum content decrease almost eight times in the concentration of strong acid centers (from 528 to 62 (j,mol/g), that probably is one of the principal causes changing catalytic activity and selectivity of the zeolites modified with lanthanum.
Table 4. Acidic properties of the H-ultrasil modified with lanthanum
Catalyst Lanthanum content, wt% Temperature at the peak of ammonia desorption maximum, °C Concentration of acid centers, |imol/g
I II Q c2
H-ultrasil - 195 408 625 528
La-H-ultrasil 1.0 192 352 405 289
La-H-ultrasil 3.0 186 321 295 154
La-H-ultrasil 5.0 175 292 158 94
La-H-ultrasil 10.0 168 261 112 62
Ci and C2 are concentrations of acid in I and II forms, respectively.
Conclusions
Chemical modification by lanthanum of H-ultrasil decreases considerably concentration of strong acid centers and adsorption capacity of the zeolite that leads to increase in selectivity of the catalyst for /»-DEB in the reaction of ethylbenzene alkylation by ethanol. 9
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АЛКИЛИРОВАНИЕ ЭТИЛБЕНЗОЛА ЭТАНОЛОМ НА ЦЕОЛИТНОМ КАТАЛИЗАТОРЕ Н-УЛЬТРАСИЛ, МОДИФИЦИРОВАННОМ ЛАНТАНОМ
Т.О.Гахраманов, С.Э.Мамедов, Э.И.Ахмедов
Методами РФА, БЕТ и ТРД аммиака установлены высокая степень кристалличности и высокие удельные поверхности модифицированных ультрасилов. Исследовано влияние концентрации лантана на адсорбционные, кислотные и каталитические свойства Н-ультрасилов модифицированных лантаном, в реакции этилирования этилбензола. Влияние модификации на каталитические свойства цеолита Н-ультрасил изучено в интервале температур 300-400°С. В этих условиях на Н-ультрасиле селективность по и-диэтилбензолу составляет 42.1-44.4%. Установлено, что увеличение концентрации лантана в Н-ультрасиле приводит к уменьшению объема пор, существенному снижению концентрации сильных кислотных центров, что в свою очередь приводит к увеличению селективности по и-диэтилбензолу. При увеличении концентрации лантана в Н-ультрасиле до 5.0 мае % селективность по и-диэтилбензолу увеличивается до 74.5%
Ключевые слова: Н-ультрасил, цеолит, модифцироеание, лантан, п-селектиеностъ, этилирование, этилбензол, этанол.
LANTANLA MODÍFÍKASIYA OLUNMUÍ? H-ULTRASÍL SEOLÍT KATALÍZATORUNDA ETÍLBENZOLUN ETANOLLA ALKÍLLOSMOSI
T.O.Qohromanov, S.E.Mommodov, E.I.Bhmodov
Ammonyakin TPD, RFA va BET metodlan ib modifikasiya olunmus ultrasillorin viiksok kristallasma dorocosino va xüsusi sotho malik olmasi тйэууэп cdilmisdir. Etilbenzolun ctillosmo reaksiyasinda lantanla modifikasiya olunmus H-ultrasilin katalitik, tursu va adsorbsion xassolorino lantanin qatiligimn tosiri todqiq cdilmisdir. H-ultrasilin katalitik xassolorino modifikasiyamn tosiri 300-400°C temperatur intervalinda ôvrnilmisdir. Bu soraitdo H-ultrasildo p-dietilbenzola goro selektivlik 42.1-44.4 % toskil edir. Мйэууэп cdilmisdir ki, H-ultrasildo lantamn miqdanmn artmasi ib mosamolorin hocminin kicilmosi. güclü tursu morko/lorinin ohomivvotli azalmasi bas verirmosi noticodo p-dietilbenzola goro selektivlik artir. Torkibindo lantamn miqdan 5.0 küt % oían H-ultrasildo /j-dietilbenzola goro selektivlik 74.5 % olur.
Acar sozbr'. H-ultrasil, seolit, modifikasiya, lantan, p-selektivlik, еШ1э§тэ, etilbenzol, etanol.
