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AZ9RBAYCAN KIMYA JURNALI № 1 2016
97
UDC 541.128+542.943 +544.47: 544.476.
INVESTIGATION OF CATALYTIC PROPERTIES OF NANO-PARTICULATED TITANIUM DIOXIDE IN OXIDATION OF ISOPROPYLBENZENE
E.B.Zeynalov, Y.M.Nagiyev, M.Ya.Magerramova
Nagiyev Institute Catalysis and Inorganic Chemistry of Azerbaijan NAS
Received 09.12.2015
Catalytic properties of nano-grade titanium dioxide of mean size 5-10 nm have been studied in a model isopropylbenzene (cumene) oxidation. The kinetic data obtained indicate the significant catalytic activity of nano-TiO2 for fairly broad concentration interval. The deep catalytic oxidation of cumene for 6 hours at 1000C affords mainly cumene hydroperoxide. The results can be used to prepare effective catalytic systems for oxidation of aromatic hydrocarbons.
Keywords: air oxidation, isopropylbenzene, nano-grade titanium dioxide, naphthenate Co, naphthenate
Mn, cumene hydroperoxide.
Introduction
The aerobic oxidation processes of hydrocarbons directed to produce valuable chemical products imply as inalienable factor in the use of catalysts. The catalysts are usually compounds of transitional metals [1-4] which enable to decompose hydroperoxides by radical way to develop the oxidation chains and afford necessary products. As far as the oxidation is chain reaction there are many routes to reach desired outputs. For instance, if one wants to obtain a hydroperoxide - this is comparatively simple task to be realized against harder one to reach synthesis of carbonyl-, alcohol-, carboxyl- or ether-groups-containing compounds. Rise of temperature onset does not give the satisfactory results, the use of catalysts is obligatory, especially such active as metallcomplex and biomimetic ones [57]. Moreover, nano-grade catalysts there should also be specially mentioned since they are able to impart a higher activity, yield, selectivity, even at temperatures close to the ambient [8, 9]. Thus, there are many challenges in this field and they are not completed yet, i.e. this is a really abundant area for further research efforts.
Seeking new catalysts for the processes of alkylaromatic hydrocarbons selective oxidation at moderate temperatures has remained in force since this line is closely connected with the "Hock" and "Halcon" processes which are targeted to production of the respective industrially valuable products.
This account is further development of our previous work [10] to use nano-titanium dioxide (nano-TiO2) as a promising catalyst for the aerobic oxidation of cumene.
Cobalt and manganese naphthenates are known as commercial catalysts for oxidation of oil hydrocarbons [11, 12] and were involved in the oxidation as reference additives.
Experimental part
The employed cumene was of 99% purity ("Alfa Aesar"). The model oxidation of cumene (RH) was conducted at 600C and constant oxygen pressure PO =20 KPa (air). The deep oxidation
"3
was conducted at [RH] = 6.6 mol/l (25 cm ), [nano-TiO2] = 4 g/l, temperature - 1000C, in the air stream for 6 hours. The titanium dioxide used in this investigation was experimental grade prepared in the laboratories of Millennium Inorganic Chemicals, Grimsby, UK. The titanium dioxide characteristics are given in Table 1.
Table 1. Properties of a nano-grade titanium dioxide used in this work
Sample-allotropic form BET surface area, m2/g Particles, s size, nm Surface treatment
PC-500/nano anatase 329.1 5-10 none
Naphthenates of M(Mn,Co)= [M(RCOO)2] were synthesized at the laboratory by the subsequent interaction:
RCOOH + NaOH ^ RCOONa + H2O, 2 RCOONa + MSO4 ^ M(RCOO)2 + Na2SO4 .
Figure 1. Represents micrograph (A) and corresponding spectrum (B) of the nano-TiO2 sample.
Here: RCOOH is distilled naturally occurring petroleum acids with acidity index - 250 mg KOH/g and molecular weight M ~ 220 g/mol; sodium hydroxide - 10% aqueous solution; RCOONa - sodium salt of the petroleum acid.
The saponification of the natural petroleum acid by 10% of the sodium hydroxide aqueous solution was carried out at 60-800C and under continuous stirring. The reaction is considered to be completed when the value of the acid number of the reaction mix reaches 3-5 mg KOH/mg.
The rate of oxidation was evaluated from the amount of oxygen consumed that was measured volumetrically with the simple equipment as described in [12-14]. Oxidation rates were assessed from slopes of a kinetic curve of oxygen consumption. Experiments were carried out at least in triplicate and the correctness of the oxidation rate values determined was within the
м -
у = 0,05051-0,0389
Time (mio).
range of 5-7%.
Deep oxidation experiments were conducted in the oxidation cell [15] under continuous air stream. Products of oxidation were analyzed using IR and NMR spectrometers (Thermo SCIENTIFIC).
Results and Discussion
Results of kinetic experiments are exemplified in Fig. 2. The profile of kinetic dependences of the oxygen uptake for cumene oxidation in the presence of nano-TiO2-PC-500 demonstrates good linear approximation. Kinetic data obtained are accumulated in Table 2. They show that the nano-TiO2 considerably accelerates the reaction while the oxidation rates without catalyst and in the presence of naphthenates Mn and Co[M(RCOO)2] are nearly zero.
Figure 2. Profile of kinetic dependences of oxygen-uptake for aerobic oxidation of cumene in the presence of the nano-grade titanium dioxide PC-500; reaction mixture volume 10 ml, oxygen pressure: P0 = 20 kPa (air), temperature - 600C; [TiO2] • 102, mol/l: 1= 0, 2= 3.1, 3= 6.25
Table 2. Oxidation rates of the liquid-phase oxidation of cumene; reaction mixture volume: 10 ml, oxygen
pressure P 0 = 20 kPa (air), temperature - 600C.
-1
Catalyst, g/l w O mm3O2/min wo xl°6' mol O 2 TV
without 2 0.14
[TiO2] = 2.5 27 1.8
[TiO2] = 5.0 51 3.5
[M(RCOO)2] = 5.0 0 0
Reaction mixture after the cumene catalytic oxidation conducted in reaction cell under conditions specified in the Experimental Part was analyzed by IR, 13C and 1H NMR spectroscopy (Figs. 3, 4). The IR spectrum shows the absorption peaks in three regions responsible for C-H vibrations in aromatic
structures - 1) valence vibrations in 3000 cm region, 2) deformation vibrations below 900 cm-1 and 3) absorption bands 1604-1493cm-1. The presence of oxygen-containing groups is seen from region near 1750 cm-1 - stretching vibrations of C=O group, 1400-1000 cm-1 are vibrations connected with C-O-H grouping and 3500-3200 cm-1 - valence vibrations of O-H group. The absorption bands observed within the region 2360 and 2341 cm-1 are related to carbon dioxide that is inevitably at the analysis.
IR spectrum confirms the formation of oxygen-containing compounds while the NMR spectra directly denote obtaining of cumene hydroperoxide.
Wave number (cm"1)
Figure 3. IR spectrum of the reaction mixture obtained after aerobic oxidation of cumene (RH); [RH] = 6.6 mol/l (25 cm3), [nano-TiO2] = 4 g/l, temperature 1000C, air streаm, reaction time is 6 hours.
13 C (NMR)
X
o
-V7 l
1 ' 1 30 160 ■ i ■ 140 I 1 I 120 100 80 6 0 40 20 ppm
PMR('H)
J
A
B
Figure 4. NMR spectra of the reaction mixture obtained after aerobic oxidation of cumene (RH); [RH] = 6.6 mol/l (25 cm3), [nano-TiO2] = 4 g/l, temperature - 100oC, air stream, reaction time is 6 hours.
Conclusions
1. The air oxidation of cumene is considerably accelerated by the addition of nano-grade TiO2-PC-500 at moderate temperatures - rates of oxidation are increasing tenfold in the presence of the catalyst.
2. Cumene hydroperoxide is main product formed at the aerobic dynamic oxidation of cumene at 100° C for 6 hours.
3. The catalyst tested is very affordable and may be recommended as active accelerant of alkyl- aromatic hydrocarbons oxidation to be considered for industrial purposes.
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ИССЛЕДОВАНИЕ КАТАЛИТИЧЕСКИХ СВОЙСТВ НАНО-ГРАНУЛИРОВАННОГО ДИОКСИДА
ТИТАНА В ОКИСЛЕНИИ ИЗОПРОПИЛБЕНЗОЛА
Э.Б.Зейналов, Я.М.Нагиев, М.Я.Магеррамова
Каталитические свойства нано-диоксида титана (нано-ТЮ2) со средним размером частиц 5-10 нм изучены на модельной реакции окисления изопропилбензола (кумола). Полученные кинетические данные указывают на значительную каталитическую активность нано-ТЮ2 в достаточно широком интервале концентраций. Глубокое каталитическое окисление кумола в течение 6 ч и 1000С приводит в основном к получению гидропероксида кумола. Полученные результаты могут быть использованы при создании новых эффективных каталитических систем для окисления ароматических углеводородов.
Ключевые слова: окисление кислородом воздуха, изопропилбензол, нано-диоксид титана, нафтенат Со, нафтенат Mn, гидропероксид кумола.
iZOPRORiLBENZOLUN OKSiDLO§MO PROSESiNDO NANO-TiTAN DiOKSiD HiSSOCiKLORiNiN
KATALiTiK TOSiRiNiN TODQiQi
E.B.Zeynalov,Y.M.Nagiyev, M.Ya-Maharramova
izopropilbenzolun (kumolun) oksidla§ma prosesinda 5-10 nm orta ölgülü nano-titan dioksidin (nano-TiO2) katalitik tasiri tadqiq edilmi§dir. Alinan kinetik malumatlara asasan müayyan olunmu§dur ki, nano-TiO2 müxtalif qatiliqlarda aktiv katalitik tasira malikdir. Oksidla§ma prosesi 1000C temperaturda 6 saat müddatinda aparilmi§ va asas mahsulun kumolhidroperoksid olmasi a§kar edilmi§dir. Alinmi§ naticalar aromatik karbohidrogenlarin oksidla§ma prosesi ügün effektiv katalitik sistemlarin hazirlanmasinda istifada edila bilar.
Agar sözlzr: hava oksigeni ih oksidh§ma, izopropilbenzol, nano ölgülü titandioksid, Co naftenat, Mn naftenat, kumolhidroperoksid.
