Study of vacuum gasoil cracking over high-acid ZrO -SiO mixed oxide Текст научной статьи по специальности «Химические науки»

CHEMICAL SCIENCES

STUDY OF VACUUM GASOIL CRACKING OVER HIGH-ACID ZRO2-SIO2 MIXED OXIDE

Prudius S.

PhD in chemistry, senior researcher, Institute for Sorption and Problems of Endoecology, the National

Academy of Science of Ukraine, 03164 Kyiv, Ukraine

Inshina O.

PhD in chemistry, junior researcher, Institute for Sorption and Problems of Endoecology, the National

Academy of Science of Ukraine, 03164 Kyiv, Ukraine

Khomenko K.

PhD in chemistry, senior researcher, Institute for Sorption and Problems of Endoecology, the National

Academy of Science of Ukraine, 03164 Kyiv, Ukraine

Popov V.

Engineer, State Scientific-Production Enterprise "Zirconium", 51900Kamenskoe, Ukraine

Brei V.

Doctor of chemical sciences, Corresponding Member the NAS of Ukraine, Directorof Institute for Sorption and Problems of Endoecology, the National Academy of Science of Ukraine, 03164 Kyiv, Ukraine

Abstract

High-acid ZrO2-SiO2 mixed oxides, including samples prepared on the basis of natural zircon concentrate, have been tested in cracking of industrial gasoil at 480-550 °C under WHSV = 4 h-1 using flow reactor with fixed bed of catalyst. It was shown that zirconosilicates provide the higher gasoil conversion and gasoline yield in comparison with industrial aluminosilicate catalyst. Also, zirconosilicates produce more isoparaffins and less aromatic hydrocarbons and olefins than aluminosilicate catalyst. The reason of high cracking activity of ZrO2-SiO2 mixed oxide is discussed.

Keywords: gasoil cracking, acid catalysts, zirconia-silica mixed oxide, aluminosilicates

INTRODUCTION

Fluid catalytic cracking (FCC) of vacuum gasoil is one of the most important conversion processes in a petroleum refinery [1]. The main cracking product is high-octane gasoline. Traditionally, acid aluminosilicate catalysts are used in FCC process [1-4]. Typical cracking catalyst contains of H-Y faujasite (15-20 %), kaolin or bentonite (20-30 %), alumina (15-30 %), amorphous aluminosilicate (20-45 %), an obligatory additive of rare earth (up to 2 % Ln2O3), and a small amount of platinum (20-50 ppm) as catalyst for oxidation of CO to CO2 in the regenerator [1-3]. Additive of deficient lanthanides improves the activity and hydrothermal stability of zeolite catalyst [2].

Based on our experience on synthesis of high acid ZrO2-SiO2 mixed oxide and on the results of its testing in several reactions with a proton transfer [5-7], we decided to use this material for cracking of vacuum gasoil. In this communication the data on testing of zirconosilicates, prepared from natural zircon, in cracking of industrial gasoil are presented. The reason of high cracking ability of ZrO2-SiO2 is discussed also.

EXPERIMENTAL

Catalyst Preparation

The strongly acid ZrO2-SiO2 (ZrSi) mixed oxides have been prepared using two methods [5-8].

1) A mixture of tetraethylorthosilicate (TEOS), deionized water, ethanol and nitric acid (molar ratio

nC2H5OH/nTEOS = 0.7,

nH2O/nTEOS = 65 and

nHNO3/nTEOS = 0.1), stirred at room temperature for about 30 min, was added to 1 mol/L aqueous solution of zirconyl nitrate (for synthesis of ZrSi) or mixture of zirconyl and aluminum nitrates (for synthesis of

ZrSiAl). Then, urea was added with a molar ratio n(NH2)2CO/n(TEOS+ZrO(NO3)2+Al(NO3)3) = 3. The formed gel was aged for 2 days at 93 °C, washed with water, dried in oven at 120 °C for 24 h and calcined at 750 °C for 2 h. The ZrSi and ZrSiAl samples are denoted as ZrxSiy or ZrxSiyAlz, where x, y and z represented the atomic percentage of cations.

2) The natural zircon (ZrSiO4) concentrate, as the source of silicon and zirconium (Zr:Si = 1), was sintered with sodium carbonate (1:1 mol) at around 1000 °C for 2 h under static condition. Baked mass was leached with 6M HNO3 (L/S = 4:1) under reflux for 1 h results in 100 % Zr(IV) dissolution. For preparation of ternary ZrSiAl oxide or to obtain the ratio Zr:Si < 1 to the resultant solution calculated amount of aluminum nitrate or aqueous-alcohol solution of TEOS were added. Next, it was cooled and adjusted to pH ~ 2-3 by dropwise addition of ammonium hydroxide and followed by addition of urea. The mixture was heated to 60 °C and kept 2 h to form a gel, which was washed with water, dried and calcined at 700 °C for 2 h. The samples prepared from zircon are denoted as ZrSi-Z and ZrSiAl-Z.

Catalyst Characterization

Total number of acid sites was determined by reverse titration using n-butylamine solution in cyclohex-ane with bromthymol blue as an indicator. The acid strength (H0) and concentration-strength acid site distribution were examined by the Hammett indicators method using 0.1 % solution of the corresponding indicator in cyclohexane [9].

The X-ray powder diffraction (XRD) analysis was performed using DRON-4-07 diffractometer (CuKa).

Nitrogen isotherms were measured using a Quantachrome Nova 2200e Surface Area and a Pore Size Analyzer.

The prepared ZrSi samples and industrial alumi-nosilicate catalyst (IAC) were tested using laboratory unit with a flow fixed bed steel reactor (inner diameter 12 mm, length 160 mm). The reactionary zone (7090 mm), filled with 8 g (8-10 cm3) of a catalyst, was separated by fiber glass from the lower and top part of reactor filled with granulated quartz. The industrial, rather heavy vacuum gasoil with melting temperature of 30 °C was used (Table 1). Heated to 50 °C gasoil was injected by a syringe pump (Orion M361) in the reactor under argon flow (30 ml min-1) at atmospheric pressure. The cracking products passed the pre-condenser with a temperature of 35 °C and were condensed in the receiver of liquid fraction cooled to -20 °C.

Catalytic cracking experiments were performed in the temperature range of 480-550 °C under WHSV = 4 h-1 (4 g of gasoil on 1 g of catalyst per hour).

_Properties of vacuum gasoil (Oil refinery

Duration of experiment was 30 min. After that, a catalyst was regenerated in air flow (200 cm3min-1) at 600 °C for 90 min, and then an experiment was repeated. The stable activity of ZrSi samples was kept after carrying out 20-25 experiments. Amount of coke was calculated as a weight difference between coked-up catalyst before and after its calcination at 600 °C for 90 min.

The distillation of liquid cracking products was carried out in two steps. The first fraction with end boiling point EBP = 100 °C was distillated at atmospheric pressure. Distillation of the second fraction was carried out under vacuum (17 kPa) according to ASTM D 1160-03. The final temperature of distillation of 146 °C corresponded to EBP = 200 °C of gasoline fraction under normal pressure as it was defined for m-cresol (Tb = 202 °C). Detailed hydrocarbon group analysis, distribution of products and calculation of research octane number (RON) were performed according to the test procedure based on ASTM D 6729 using "Kristall 5000.1" Chromatograph.

Table 1

"Ukrtatnafta", Kremenchug, Ukraine)_

Density (kg m-3)

Fractional composition (°C)

IBP

10 %

50 %

87 %

90 %

Melting Sulfur temperature content, (°C) g/g

900.5

258

347

436

500

508

30

1.910-3

RESULTS AND DISCUSSION

According to the X-ray analysis, all synthesized ZrSi are amorphous. In spite of the crystalline structure of initial zircon, the samples synthesized on its basis are characterized by amorphous structure similar to the solgel ZrSi and ZrSiAl samples (Figure 1). The nitrogen adsorption-desorption isotherms and pore distributions

for samples are shown in Figure 2. Table 2 summarizes the textural and acidity properties of prepared ZrSi and ZrSiAl samples. The specific surface area decreases with the increase of zirconia content (Table 2). ZrSi and ZrSiAl samples that are prepared from nitrates and TEOS are characterized by the highest surface area.

13 d

(/) c 0

13 03

W

c 0

10 20 30 40 50 60 70

10 20 30 40 50 60 70

29, grad 29,grad

Figure 1. XRD patterns for original zircon concentrate and ZrSi (a), ZrSiAl (b) samples.

200-

^ 160 -| o

■O

CD

120

o w

T3 <

0) 80-| E

_=3

o >

40-

Zr Si

0,0

1,5 2,0 2,5 Pore Radius, nm

1-1-1-1-1-1-1-1-1—r

0,0 0,2 0,4 0,6 0,8 1,0

Relative pressure, p/p0

200-,

r>

E

o

CD 120 H .Q

O W

T3 <

CD

E

o >

^35^12

80-

40-

0,0

1,5 2,0 2,5 Pore Radius, nm

T-1-1-1-1-1-1-1-1—r

0,0 0,2 0,4 0,6 0,8 1,0

Relative pressure, p/p

Figure 2. Nitrogen adsorption-desorption isotherms and pore distributions for ZrSi (a) and ZrSiAl (b) samples.

It is known [6,7], that the maximal content of acid Zr36Si53Aln-Z), are similar to Ho of the samples ob-sites in ZrSi mixed oxides was achieved at Si4+/Zr4+ = 2 tained from TEOS by sol-gel method (Table 2). As re-and it is confirmed by our results (Table 2). The used gards the mixed ZrSiAl oxide, that addition of Al3+ ions sol-gel method allows synthesizing ZrSi samples with to the ZrO2-SiO2 matrix leads to increasing of acid sites

strength of this ternary oxide on three orders from Ho = -11.35 to -14.52 (Table 2). The highest acid sites strength of -14.52 is observed on the Zr35Si53Ali2 surface.

Table 2

1.7 mmol g-1 of acid sites at their strength up to Ho > -11.35 (Table 2). The obtained results demonstrate that acid site strength (Ho) of ZrSi and ZrSiAl, prepared from zircon (Zr50Si50-Z, Zr33Si67-Z,

Sample BET surface area (m2 g-1) Pore volume (cm3 g-1) Average pore diameter (nm) [HB] (mmol g H0 max

Zr50Si50 250 0.14 2.2 1.0 -8.2

Zr33Si67 405 0.32 3.2 1.7 -11.35

Zr25Si75 420 0.30 2.9 1.5 -8.2

Zr20Si80 445 0.32 2.9 1.4 -8.2

Zr50Si50-Z 200 0.12 2.4 0.7 -8.2

Zr33Si67-Z 390 0.25 2.6 1.4 -11.35

Zr35Si53Al12 370 0.29 3.2 1.4 -14.52

Zr24Si72Al4 360 0.32 3.6 1.3 -13.16

Zr36Si53Aln-Z* 370 0.24 2.6 1.2 -13.16

IAC** 124 0.17 1.0 0.7 -8.2

samples prepared from zircon "industrial aluminosilicate catalyst

The concentration-strength acid site distributions -12.14 > Ho > -16.04, and 17 % — the medium acid

for ZrSi and ZrSiAl oxides show a wide range of acid strength with -8.2 > Ho > -12.14. On the surface of

strength (Figure 3). About 66 % of Zr3sSi53Ali2 acid Zr33Si67 oxide the less acidic sites with

sites correspond to superacid range -5.6 > Ho > -12.14 are detected (Figure 3).

[HB], mmol/g 0,8

0,6

0,4

0,2

0,0

Zr35Si53Al12

Zr33Si67

Zr50Si50

H

-2 -4 -6 -8 -10 -12 -14

Figure 3. Concentration-strength acid site distributions for Zr35Si53Al12, Zr33Si67 and Zr50Si50 oxides.

The results on comparative testing of prepared zir-conosilicates and industrial aluminosilicate catalyst in cracking of vacuum gasoil at 500 °C are presented in Table 3. At whole, all tested ZrSi and ZrSiAl oxides provide the higher gasoil conversion and gasoline yield than the aluminosilicate catalyst IAC (Table 3). For instance, Zr33Si67 mixed oxide produces 51 % of gasoline

at 69 % gasoil conversion in comparison with 40 % gasoline content at 58 % gasoil conversion for IAC. Zr33Si67-Z sample, prepared from zircon, provides some less gasoline yield (46 %) (Table 3). However at whole, high-acid zirconosilicates produce some more cracking gases C<4 and coke than aluminosilicate catalyst (Table 3).

Table 3

Effect of catalyst on gasoil cracking at 500 °C and WHSV = 4 h-1._

Catalyst [HB] (mmol g 1) H0 max Conversion X (%)* Gas C<4 (%) Coke (%) Gasoline (%) EBP = 200 °C Residual gasoil >200 °C (%)

Zr50Si50 1.0 -8.2 68.9 14.5 7.8 46.6 31.1

Zr33Si67 1.7 -11.35 69.3 10.3 8.0 51.0 30.7

Zr25Si75 1.5 -8.2 64.9 14.4 4.6 45.9 35.1

Zr20Si80 1.4 -8.2 63.5 10.2 5.2 48.1 36.5

Zr50Si50-Z 0.7 -8.2 64.5 11.6 5.9 47.0 35.5

Zr33Si67-Z 1.4 -11.35 66.2 12.1 7.7 46.4 33.8

Zr35Si53Al12 1.4 -14.52 65.1 10.1 8.5 46.5 34.9

Zr24Si72Al4 1.3 -13.16 69.6 16.5 6.2 46.9 30.4

Zr36Si53Aln-Z" 1.2 -13.16 69.9 12.4 9.2 48.3 30.1

IAC*** 0.7 -8.2 57.9 13.8 4.1 40.0 42.1

*X = 100 % - residual gasoil, %

**samples prepared from zircon

***industrial aluminosilicate catalyst

At raising temperature from 480 °C to 550 °C con- yield on zirconosilicates is observed at 500 °C (Fig-

version of gasoil increases, but the maximal gasoline ure 4).

Gasoline, %

60 -,

50-

40- 1

30- 1

20- 1

10- 1

0- »

I480oC

<Б>ч<эЬ

^500oC 550 C

.0

Figure 4. Yield of gasoline at different temperatures (WHSV = 4 h-1).

The compositions of gasoline obtained on different catalysts at 500 °C and WHSV = 4 h-1 are presented in Table 4. The gasoline, formed over ZrSi and ZrSiAl oxides, contains more i-paraffins. In contrast, aluminosilicate catalyst produces more aromatic hydrocarbons

and olefins (Table 4). The calculated research octane number of gasoline obtained on ZrSi and ZrSiAl is a little higher than for aluminosilicate gasoline.

Gasoline fractions obtained on different catalysts (500 °C, WHSV = 4 h 1).

Table 4

Hydrocarbons (%) Zr33Si67 Catalyst Zr35Si53Al12 IAC*

n-paraffins 5.4 4.5 3.9

i-paraffins 43.4 43.5 33.3

cycloparaffins 13.4 14.0 14.0

olefins 12.0 11.1 17.2

aromatic hydrocarbons 25.9 26.9 31.6

benzene 0.5 0.6 0.5

Research Octane Number (RON) 82 82 79

'industrial aluminosilicate catalyst

Among 262 hydrocarbons identified in the gasoline, the 10 hydrocarbons shown in Table 5 have the highest content.

Typical hydrocarbons in obtained gasoline fractions

Hydrocarbons (%)

'industrial aluminosilicate catalyst

Catalyst

Zr33Si6

Zr35Si53Äll2

IAC*

Table 5

i-pentane 8.4 8.5 4.3

2-methylpentane 5.1 5.3 3.3

3-methylpentane 3.6 3.7 2.1

methylcyclopentane 2.7 2.7 1.9

2-methylhexane 3.9 4.4 3.2

3-methylhexane 3.1 3.4 2.2

methylcyclohexane 1.8 2.0 1.8

toluene 2.4 2.7 3.0

m-xylol 2.6 2.8 3.3

1,2,4-trimethylbenzene 2.6 2.8 3.1

The high activity of studied zirconosilicates in vacuum gasoil cracking (Table 3) could be explained by their higher acidity in comparison with aluminosilicate catalyst (Table 2). It is well known [1,3,4,10,11], that B- or L- acid sites of a catalyst provide formation of intermediate carbonium and carbenium ions in catalytic cracking of hydrocarbons. The superacids, as HF-SbFs, with of Ho < -20 are necessary for protonation of n-alkanes at usual conditions [9]. Obviously, the studied oxides are not capable to activate alkanes at usual temperatures. However, at temperature rising, an ability of solid acids to protonation of organic compounds considerably increases as it was shown for H-Y faujasite and Zr33Si67 oxide [6,12]. It was determined that change of Hammett function values at increasing temperature is described by the equation Ho = -(a + 0.06T) [6,12], where T - temperature (°C), aH-Y = 4, aZrSi = 9.8. So, at cracking temperature of 500 °C, calculated HoH-Y = -34 and HoZrSl = -40, and both these solid acids become capable to produce al-kane ions. Thus, the strength of acid sites (H0) should not be considered as the main reason of different cracking ability of alumino- and zirconosilicates. Obtained results are agreed with this conclusion because there are not correlations between gasoline yield or gasoil conversion and strength or content of acid sites on the surface of studied ZrSi samples (Table 2, 3).

Either B- or L-sites of cracking catalysts are capable to activate alkane molecules mainly, this question was repeatedly discussed [3,4,11]. It was well known, that the concentration of B-sites on aluminosilicates and on other acid oxides decreases at raising temperature whereas the concentration of L-sites respectively increases [9]. The same situation is observed for the ZrSi and ZrSiAl oxides [6,7]. Namely coordination-un-saturated Zr4+ ions, as strong L-sites, provide the high acidity of these oxides [6]. Therefore, we suppose that at rather high temperature of cracking process of 450550 °C the main role is played by acid L-sites of ZrSi

oxides. According to known scheme [1,3,4,10], such strong L-sites could be capable to tear off hydride ions from alkane molecules with formation of carbenium ions. After p-scission of these ions or their isomeriza-tion, a catalyst returns H- ions.

However, kinetics of alkane ion formation should not limit the cracking of heavy vacuum gasoils [3]. The transformation of light hydrocarbons of vacuum gasoil can be limited to kinetics, but cracking of heavy hydrocarbons — by their diffusion in pores of a catalyst, as it is typical for gas-phase reactions over porous catalysts at high temperatures [3]. Here, studied mesoporous ZrSi oxides with pore diameter of 2.2 - 3.6 nm have advantage before aluminosilicate catalyst with Dp = 1.0 nm (Table 2). Perhaps, it is a reason of the higher cracking activity of ZrSi samples (Table 3).

CONCLUTIONS

The mixed ZrO2-SiO2 oxides, including samples prepared from natural zircon concentrate, have been tested in the cracking of vacuum gasoil. The zirconosil-icates, without lanthanide additive, are high active in the hydrocarbon cracking. The ZrO2-SiO2 mixed oxides produce more i-alkanes and less aromatic hydrocarbons and olefins in comparison with the aluminosil-icate catalyst.

REFERENCES:

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5. S.V. Prudius, A.V. Melezhyk, V.V. Brei, Synthesis and catalytic study of mesoporous WO3-Z1O2-SiO2 solid acid. Stud. Surf. Sci. Catal, 2010, 175, 233236. https://doi.org/10.1016/S0167-2991(10)75031-X

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7. O. I. Inshina, A. M. Korduban, G. M. Telbiz, V. V. Brei, Synthesis and study of superacid ZrO2-

SiO2-Al2O3 mixed oxide Adsorpt. Sci. Technol. 2017, 35, 339. https://doi.org/10.1177/0263617417694887

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THE PRINCIPLE OF SUBSTANCE STABILITY CREATES THE DESIGN OF LIVING BEINGS AND

SYSTEMS

Gladyshev G.

Doctor of chemical sciences, professor Principal scientist N. N. Semenov Institute of Chemical Physics Russian Academy of Sciences, Russian Academy of Arts, Moscow

PHYSICAL, CHEMICAL AND BIOLOGICAL SCIENCES ПРИНЦИП СТАБИЛЬНОСТИ ВЕЩЕСТВА СОЗДАЕТ ДИЗАЙН ЖИВЫХ СУЩЕСТВ И СИСТЕМ

Гладышев Г.П.

Доктор химических наук, профессор Главный научный сотрудник Институт химической физики им. Н. Н.Семенова Российская Академия наук, Российская Академия Художеств, Москва

Abstract

The laws and principles of thermodynamics, regardless of the particularities of the formulations, describe the evolution and design of material objects, including living beings and systems of all hierarchical levels. Evolutionary development of organisms subjects to the principle of substance stability, which manifests itself in the form of a general thermodynamic mechanism for the mutual transformation of the hierarchical structures of the living world.

Аннотация

Законы и принципы термодинамики, независимо от особенностей формулировок, описывают эволюцию и дизайн материальных объектов, включая живые существа и системы всех иерархических уровней. Эволюционное развитие организмов подчиняется действию принципа стабильности вещества, который проявляется в виде общего термодинамического механизма взаимного преобразования иерархических структур живого мира.

Keywords: thermodynamics, hierarchy, biology, the origin of life, evolution, aging, Darwinism, design, stability, the principle of substance stability.

Ключевые слова: термодинамика, иерархия, биология, возникновение жизни, эволюция, старение, дарвинизм, дизайн, стабильность, принцип стабильности вещества .