Pyrolysis of atmospheric residue of petroleum (ATR) usingAlSBA-15 mesoporous material by TG and Py-GC/MS

Kesia K. V. Castro • Aneliese L. Figueiredo • Amanda D. Gondim •

Ana C. F. Coriolano • Ana P. M. Alves • Valter J. Fernandes Jr. •

Antonio S. Araujo

Received: 31 March 2013 / Accepted: 14 March 2014

� Akademiai Kiado, Budapest, Hungary 2014

Abstract The mesoporous material AlSBA-15 with Si/Al

molar ratio of 25 was synthesized by the hydrothermal

method and characterized by X-ray diffraction and nitrogen

adsorption. This is a promising material in the field of

catalysis, particularly for petroleum refining, since their

mesopores facilitate the accessibility of large hydrocarbon

molecules to the active sites of AlSBA-15, producing light

hydrocarbons. In order to evaluating the catalytic activity

of AlSBA-15, a sample of ca. 10 % in mass of this solid

was physically mixed with atmospheric residue of petro-

leum (ATR) and heated in a thermobalance from room

temperature up to 900 �C, under nitrogen atmosphere.

From TG curves, it was observed a reduction in the onset

temperature, when AlSBA-15 was used as catalyst for the

degradation process of ATR. The kinetic model proposed

by Ozawa–Flynn–Wall yielded some kinetic parameters to

determine the apparent activation energy of the degrada-

tion, evidencing the efficiency of the mesoporous material,

since there was a decrease in the activation energy for the

catalytic degradation. The ATR alone and mixed with

AlSBA-15 was also heated in a pyrolysis reactor coupled to

a gas chromatograph and mass spectrometer (Py-GC/MS).

From the chromatograms, it was observed an increase in

the yield of hydrocarbons in the range of gasoline and

diesel derived from the catalytic process. These results are

due to the combination of the mesoporosity and acidity of

the AlSBA-15 for application in the process of pyrolysis of

hydrocarbons molecules constituents of the ATR.

Keywords Atmospheric residue of petroleum �Thermogravimetry � Pyrolysis � AlSBA-15

Introduction

Porous inorganic solids have been used as catalysts and

adsorbents for many industrial applications. The presence

of porosity allows molecules access to large surface areas,

which are associated with high adsorptive and catalytic

activities [1–3]. The oil refineries use catalysts to obtain

light products from heavy oil fractions, since the demand

for such products is growing more each day.

During the past decades, thermal analysis has been used

for characterization of oil and its derivatives. For crude oils,

the techniques usually used to evaluate its decomposition are

pyrolysis and combustion. In the case of catalytic degrada-

tion, lower temperatures are required and chemical product

distribution is fewer than in thermal degradation, leading to

more valuable products [4]. In general, the kinetics of these

processes was monitored by TG, using integral dynamic

curves at multiple heating rates, and the activation energy

was estimated from the Flynn–Wall kinetic model [5, 6].

Catalytic pyrolysis is one of the most popular processes

used by oil refinery industry, breaking, and transforming

great hydrocarbon molecules into smaller and lighter ones.

Compared with the conventional thermal pyrolysis, cata-

lytic pyrolysis has the potential of reducing energy costs by

operating at lower temperatures and using a variety of

feedstock. Heavy oil is a relatively low value refinery

feedstock. The challenge is to add value to this feedstock

[7]. Compared with conventional steam pyrolysis, catalytic

K. K. V. Castro � A. L. Figueiredo � A. D. Gondim �A. P. M. Alves � V. J. Fernandes Jr. � A. S. Araujo (&)

Institute of Chemistry, Federal University of Rio Grande do

Norte, Natal, RN 59078-970, Brazil

e-mail: araujo.ufrn@gmail.com

A. C. F. Coriolano

Potiguar University, Laureate International Universities, Av.

Nascimento de Castro, 1597, Natal, RN 59056-450, Brazil

123

J Therm Anal Calorim

DOI 10.1007/s10973-014-3757-8

pyrolysis can not only reduce reaction temperature and

energy cost but also allows to flexibly adjust the product

distribution. In addition, catalytic pyrolysis produce light

olefins from a wide range of low-quality feedstock, such as

heavy oils [8].

The SBA-15 (Santa Barbara Amorphous number 15)

materials were synthesized by the end of the 90s by

researchers of the University of California—Santa Barbara,

using Pluronic P123 triblock co-polymer as structural tem-

plate. These materials present mesopore with diameters from

2 to 30 nm interconnected with micropores, as shown in

Fig. 1. Due to the properties of high surface area, pore size

diameter, and high thermal stability, it is a promising material

for processing of voluminous molecules, such as hydrocar-

bons present in the atmospheric residue of petroleum (ATR).

In a previous paper [1], we studied the effect of the

AlMCM-41 mesoporous material on the catalytic pyrolysis

of ATR, by means of thermogravimetry (TG) using mul-

tiple heating rate. From TG, using Ozawa–Flynn–Wall

(OFW) model, the average value of activation energy was

ca. 161 kJ mol-1, for the pure ATR, and ca. 71 kJ mol-1

for ATR containing AlMCM-41. The main objective of this

work was to study the thermal degradation kinetics of ATR

mixed with AlSBA-15 mesoporous catalyst by non-iso-

thermal multiple heating rates, from TG. The values of

activation energy were compared with that for ATR with-

out catalyst. The obtained products obtained were analyzed

from pyrolysis coupled to chromatography and mass

spectrometry (Py-GC/MS).

Experimental

Synthesis

The AlSBA-15 material was synthesized by the hydro-

thermal method, using a gel with molar composition: 1.0

TEOS:0.017 P123:0.02 Al2O3:5.7 HCl:193 H2O, with Si/

Al molar ratio equal to 25. TEOS represents the tetraethyl

orthosilicate, corresponding to the source of silicon; P123

is a triblock copolymer Pluronic-123, and was used as a

template for the sample; 37 % HCl was used as an acid;

H2O was the solvent, and pseudobohemite was the source

of aluminum. A typical procedure of synthesis has been

previously reported [9].

For the synthesis, firstly a solution was prepared by

mixing the amounts of P123, HCl, and the water, keeping

the mixture stirring at 35 �C. When the temperature was

reached, the silicon and aluminum sources were added. The

final mixture was kept under stirring for 24 h at 35 �C,

keeping the pH below 1 in order to obtain a homogeneous

gel. This mixture was placed in a Teflon stainless steel

autoclave and was afterward kept over a period of 48 h at a

temperature of 100 �C. After the hydrothermal treatment,

the material was filtered and washed with anhydrous eth-

anol to remove part of the template (P123). After this

procedure, the material was dried at room temperature

overnight. Then, the sample was submitted to calcination at

500 �C with nitrogen for 1 h, and subsequently for one

additional hour under air atmosphere.

Characterizations

The powder X-ray diffraction is the most commonly

method used to characterize mesoporous materials [10]. In

this work, X-ray diffraction was carried out in a Shimadzu

XRD-6000 using CuKa radiation and a nickel filter,

respectively, with a voltage and tube current of 30 kV and

30 mA. The specific surface area was determined by

adsorption of N2 at 77 K, using Quantachrome NOVA-

2000 equipment, according to the Brunauer–Emmett–

Teller (BET) method in the relative pressure P/P0 in the

range of 0.05–0.95. The samples were previously out-

gassed by treatment at 300 �C for 3 h under vacuum. The

pore size diameter (Dp) was calculated according to Bar-

rett–Joyner–Halenda (BJH) algorithm [11].

TG experiments

To evaluate the catalytic activity of the material, a sample of

ATR, obtained from the Petrobras refinery, at Guamare, Rio

Grande do Norte State, Brazil. The TG curves and kinetic

parameters for degradation of the ATR alone and mixed with

catalyst (ATR/AlSBA-15) were determined by thermo-

gravimetry (TG/DTG) using a thermobalance DTG-60

model from Shimadzu Instruments, in the temperature range

25–900 �C, with heating rates of 5, 10, and 20 �C min-1

under atmosphere of nitrogen flowing at 50 mL min-1.

Applying the Flynn–Wall multiple heating rate kinetic

model, the values of activation energy for the process were

Microporous

Mesoporous

Fig. 1 Unidimensional Structure of SBA-15 material, showing the

hexagonal system of the mesopores interconnected by micropores

K. K. V. Castro et al.

123

determined. All experiments were carried out using alu-

mina crucibles of 900 lL, containing ca. 10 mg of sample.

The AlSBA-15 was added to ATR in a concentration of ca.

10 % in mass.

Pyrolysis-GC/MS

The pyrolysis process of RAT was carried out using the

fast pyrolysis method in a Single-Shot Pyrolyzer equip-

ment, PY-2020iS model from Frontier Lab, with a tubular

reactor coupled online to a CG/MS QP 2010 Plus from

Shimadzu. The pyrolysis reactions were accomplished on

quartz filler tube (62 mm length, 6 mm i.d.) at 500 �C by

approximately 3 s, with a mass of ca. 0.5 mg of sample of

ATR containing 10 mass% of AlSBA-15 mesoporous

catalyst.

For identification of the reaction products, the injector

temperature was kept at 250 �C. The chromatographic

separation was performed using a capillary column UA5-

30M-0.25F (30 m 9 0.25 mm i.d., 0.25 lm film thick-

ness). Helium (99.999 %) was used as gas carrier with a

constant flow rate of 3.0 mL min-1 and a 1:400 split ratio.

The oven was heated using the following temperature

program: heat up 40 �C and keep at this temperature for

2 min, then heat up to 300 �C, at rate of 10 �C min-1 and

keep for 10 min. The temperature of the GC/MS interface

was kept at 300 �C and the mass spectrometer was oper-

ated in electron ion (EI) mode at 70 V of ionization volt-

age, 0.80 kV of detector and temperature of ion source of

280 �C. The mass spectra were obtained from m/z 29 to

600 with scan speed of 588 amu/s. The obtained results

were an average of two runs for each experiment. The

identification of the products from the pyrolysis was car-

ried out from a research of the database of the National

Institute of Standards of Technology (NIST) library, using

software installed in the GC/MS system, in which the

fragment standards of known mass of the constituents of

the fragments were considered.

Results and discussion

The hydrothermal method used for the synthesis and cal-

cination of SBA-15 was efficient for obtaining active

materials. With the introduction of aluminum on its

structure, the aluminosilicate mesoporous material was

nominated as AlSBA-15. The formation of acid sites is due

to co-ordination of aluminum to silicon by oxygen bond, as

shown below:

O O O O

SiSi Al

H+–δ –δ

The X-ray diffractogram of the synthesized material

AlSBA-15 is shown in Fig. 2. This technique shows that

the hexagonal array of mesoporous AlSBA-15 was formed

after calcination of the material. In the X-ray diffraction

patterns, the Miller indexes are represented in its simplified

form through the reflection planes (100), (110), and (200)

which confirms the quality of the material with well-

defined mesoporous structure [9, 10].

Figure 3 illustrates the N2 adsorption–desorption iso-

therms at 77 K. The sample showed the type IV isotherm,

characteristic of mesoporous materials, according to the

BET classification and hysteresis type I. These results are

consistent with the XRD patterns of these samples and

intensify the idea that the addition of aluminum in SBA-15

samples did not cause destructive changes in the structure

of the molecular sieve studied. The textural and structural

10

1000

2000

3000

4000

5000

6000

7000

(100

)

(110

)(2

00)

8000

2

Inte

nsity

/a.u

.

3

2θ/°4 5

Fig. 2 X-ray diffractogram of the AlSBA-15 nanostructured mate-

rial, showing the miller indexes (100), (110), and (200)

0.00

100

200

300

400

500

600

AdsorptionDesorption

0.2 0.4 0.6

Relative pressure/P/P0

Am

ount

ads

orbe

d/cm

3 g–

1

0.8 1.0

Fig. 3 N2 adsorption and desorption isotherms at 77 K for the

AlSBA-15 material

Pyrolysis of atmospheric residue of petroleum (ATR)

123

properties of the AlSBA-15 obtained from the results of

XRD and N2 adsorption–desorption are summarized in

Table 1. The determination of specific surface area, pore

diameter (Dp), and total pore volume (Vt) were obtained, by

BET and BJH methods, respectively.

Figures 4 and 5 present the mass loss versus temperature

of ATR and mixture of AlSBA-15/ATR at three different

heating rates. The TG curves show two events that occur in

different temperature ranges, as shown in the DTG curves.

For ATR without catalyst, the first loss was observed in the

range of 100–440 �C, which was attributed to the distilla-

tion of light materials and the second range, 440–500 �C is

due to the cracking of hydrocarbons of high molecular

mass. In presence of catalyst (AlSBA-15), the losses

occurred at lower temperature ranges, evincing the cata-

lytic effect for the process of catalytic degradation. In

addition, for AlSBA-15/ATR, was observed a mass loss

from room temperature up to 120 �C, which was attributed

to the presence of water physically adsorbed on the cata-

lyst. Considering the region of cracking, the maximum

temperatures of the mass losses occurred in the range of

440–470 �C for ATR alone and at 310–425 �C for AlSBA-

15/ATR. Comparing these two ranges of temperature, it

was verified the catalytic effect of the mesoporous material

AlSBA-15 for the process of ATR degradation.

The kinetic study of the thermal degradation of the

materials by TG is a useful tool for calculating the kinetic

parameters involved in the process. Some factors are deci-

sive for these calculation parameters, such as the experi-

mental conditions (mass sample, type of sample support,

heating rate, and atmosphere) and the calculation method

employed. The profile of thermal pyrolysis of the residue

(ATR alone) and the catalytic pyrolysis (ATR mixed with

AlSBA-15) depends on several factors, being the main ones:

the temperature and the catalyst added to the system.

0 100 200 300 400 500 600 700 800 900

0

20

40

60

80

100

β = 5 °C min–1

β = 10 °C min–1

β = 20 °C min–1

Mas

s lo

ss/%

Temperature/°C

0 100 200 300 400 500 600 700 800 900

Temperature/°C

–0.025

–0.020

–0.015

–0.010

–0.005

0.000

DT

G/m

g s–

1

β = 5 °C min–1

β = 10 °C min–1

β = 20 °C min–1

Fig. 4 TG (above) and DTG (below) curves for degradation of ATR

without catalyst, at different heating rates

0 100 200 300 400 500 600 700 800 9000

20

40

60

80

100

β = 5 °C min–1

β = 10 °C min–1

β = 20 °C min–1

Mas

s lo

ss/%

Temperature/°C

0 100 200 300 400 500 600 700 800 900

Temperature/°C

–0.010

–0.008

–0.006

–0.004

–0.002

0.000

DT

G/m

g s–

1β = 5 °C min–1

β = 10 °C min–1

β = 20 °C min–1

Fig. 5 TG (above) and DTG (below) curves for degradation of ATR

with 10 % of AlSBA-15 catalyst, at different heating rates

Table 1 Physicochemical properties of AlSBA-15 mesoporous

material

Sample a0/nm Dp/nm Wt/nm Vp/cm3 g-1 SBET/m2 g-1

AlSBA-15 10.2 6.2 4.0 1.1 826

a0, unit cell parameter, Dp, pore diameter, SBET BET surface area, Vt,

total pore volume

Wt, silica wall thickness (Wt = a0-Dp)

K. K. V. Castro et al.

123

In general, the reaction rate and others kinetic parameters

for each system should be determined through experimental

data, however, due to complexity of the hydrocarbons deg-

radation reactions, the conventional methods for determin-

ing kinetic data are difficult to apply [11]. In order to obtain

the kinetic parameters, the use of non-isothermal procedure

was adopted. The calculated parameters are dependent on the

calculation method used. In this study, we used a method

based on the OFW model [12, 13].

The OFW method involves measurements of tempera-

tures corresponding to fixed values of degree of conversion

(a) at different heating rates (b). As general approach for

kinetic analysis from TG data, a mathematical function of

degree of conversion f(a) should be considered as the

extent of reaction with time, (at) defined as:

at ¼mi � mt

mi � mf

; ð1Þ

where mi and mf are the mass percent at certain time t and

mf is the final mass percent, respectively, directly obtained

from TG curves. For non-isothermal decomposition kinet-

ics, the most frequently equation used to describe the

reaction rate is:

dadt¼ f ðaÞ � kðTÞ; ð2Þ

where a is the extent of conversion, t is decomposition or

degradation time, and T is the absolute temperature of the

process. In Eq. (2), d(a)/d(t) is used to express the reaction

rate. The function f(a) is a mathematical expression of the

kinetic model and k(T) is the rate constant as a function of

temperature. Replacing k(T) in Eq. (2) with the Arrhenius

equation, gives:

dadt¼ A exp � E

RT

� �� f ðaÞ; ð3Þ

where A is the frequency of pre-exponential factor, E is the

activation energy, and R is the universal gas constant.

Considering the TG measurements at multiple heating

rates, b = dT/dt, for the non-isothermal experiments, and

the reaction rate d(a)/d(t) can be expressed by:

dadT¼ A

b

� �exp � E

RT

� �� f ðaÞ: ð4Þ

Equation 4 shows that for non-isothermal data, the

E values as a function of a, may be obtained using the

isoconversional method of OFW [14, 15], using the linear

approximation of Doyle [16] of the temperature integral

p(x), where x = E/RT is valid in the conversion range of

20–60 %. It is assumed that the reaction rate at constant

extent of conversion (a) depends only on the temperature.

For multi-step processes of decomposition, such as pyro-

lysis and catalytic degradation of ATR, the E varies with a

due to the contributions of the several decompositions steps

on the overall reaction rate [17].

Applying the OFW method, a new function g(a) is now

considered as the integral form of the f(a) function, and the

activation energy at any particular value of degree of

conversion can be determined by the equation:

log b ¼ logAE

RgðaÞ

� �� 2:315� 0:4567

E

RT

� �: ð5Þ

Finally, from the obtained experiments using multiple

heating rates (b), at a certain degree of conversion (a), the

plot of log b versus 1/T gives a straight line, and from its

slope, the activation energy (E) can be estimated, inde-

pendently of the kinetic model adopted, as stated in the

following equation:

d log bð Þs 1=Tð Þ ¼ 0:4567

E

R

� �: ð6Þ

In summary, the rate for catalytic cracking of ATR

depends on the parameters of conversion (a), temperature

(T) and time of reaction (t). For each degradation step on

the process, the reaction velocity is given as a function of

the conversion f(a) and can be determined from experi-

mental data. In this study, the non-isothermal data based on

the OFW method were successfully applied in order to

determine the activation energy for the reaction of ATR

degradation in the presence of catalyst without the need of

a model of reaction rate in function of the reactants

concentrations.

The use of a solid catalyst for residue of petroleum

catalysis requires information concerning the kinetic

parameters, and mainly the energy of activation relating to

the process. Reliable methods for determination of the

activation energy using dynamic integral TG curves at

several heating rates have been proposed [14]. It could be

stated that OFW method works well in any conversion

degree. Figure 6 presents the activation energies as a

function of degree of conversion for ART and ATR mixed

with the AlSBA-15 catalyst. The values of the E of each

conversion were determined and used to observe the ten-

dency of the activation energy along the process of pyro-

lysis of ATR alone and in the presence of catalyst (ATR/

AlSBA-15).

According to Fig. 6, for a given level of conversion, the

degradation process using the catalyst occurred at energies

below the thermal decomposition, evidencing the catalytic

activity of the AlSBA-15 mesoporous material. Curiously,

in the conversion degree ranging from of 20 to 60 %, the

tendencies of curves were similar, suggesting parallel and

consecutive reactions for degradation of the ATR. The

range for these conversions is in agreement of the Doyle’s

approximation for OFW method. The incorporation of

aluminum aimed to increase the acidity of the material,

Pyrolysis of atmospheric residue of petroleum (ATR)

123

since acid sites allow adsorption and subsequent catalytic

cracking of the high hydrocarbons to light fractions [11].

According to the chromatograms showed in Figs. 7 and

8, it was determined the catalytic activity of the AlSBA-15

material for the pyrolysis process, observing that there was

a decreasing in the retention times of many peaks when

compare with the pyrolysis process without catalyst. Based

on the chromatograms was determined the yield of frac-

tions of oil, and the hydrocarbon compositions were divi-

ded in three groups: composition of C6–C12 (gasoline

range); composition of C13–C18 (diesel range); and com-

position C19? (gasoil, lubricants and waxes).

Table 2 summarizes the yield of fractions obtained by

pyrolysis of ATR with and without AlSBA-15, emphasizing

that those ranges of hydrocarbons is interesting, for obtaining

gasoline and diesel, which are products with higher value,

from the pyrolysis of ATR. Heavy oil, such as atmospheric

residues, tends to contain smaller amount of these products,

and technological innovations are necessary.

Conclusions

In order to demonstrate the use of TG in the kinetic analysis,

the study of thermal pyrolysis of ATR and catalytic degra-

dation in the presence of AlSBA-15 mesoporous material

(ATR/AlSBA-15) were carried out. By the application of

OFW isoconversion method, the activation energy values

were obtained. It was found that the activation energy values

for ATR alone were lower than ATR/AlSBA-15, in any

range of conversion degree. It was demonstrated that the

OFW approach is a powerful tool to estimate the activation

energy (E) of decomposition process of ATR alone or in the

presence of solid catalyst. In conclusion, from non-isother-

mal TG data, it was determined the E values with good

accuracy, and the obtained results evidence the catalytic

performance of the AlSBA-15.

The catalyst activity on the pyrolysis of residues was

clearly evidenced by a decrease of the activation energy of

100

50

100

150

200

250

300

350RAT

RAT + Al-SBA-15 (Si/Al = 25)

20 30 40 50 60

Conversion/%

Ea/

kJ m

ol–1

70 80 90

Fig. 6 Activation energy as a function of the degree of conversion

calculated from the Ozawa–Flynn–Wall method, for decomposition

process of ATR and ART mixed with AlSBA-15 catalyst

0 5

C6 C8

C12

C13C14

C16

C18

C19C20

C22

C24

C26

C28

C30

C32

C34

C36C38

C40

10 15 20 25Retention time/min

Abs

olut

e in

tens

ity/a

.u.

30 35 40

Fig. 7 Chromatogram obtained by thermal pyrolysis of ATR (reac-

tion conditions: temperature of the pyrolysis reactor: 500 �C; mass of

ATR sample: 3 mg; flow of He: 3.0 mL min-1)

0 5 10 15 20 25Retention time/min

30 35 40

Abs

olut

e in

tens

ity/a

.u.

C6C8

C10

C13

C12

C14

C16C15

C18

C20 C22

C24

C26C28

C30

C32

C34

C36

C38

Fig. 8 Chromatogram obtained by catalytic pyrolysis of ATR with

10 % of AlSBA-15 catalyst (reaction conditions: temperature of the

pyrolysis reactor: 500 �C; mass of AlSBA-15/ATR sample: 5 mg;

flow of He: 3.0 mL min-1)

Table 2 Yield of fractions obtained by pyrolysis of ATR and cata-

lytic degradation of ATR/AlSBA-15

Sample C6–C12/% C13–C18/% [C19/%

ATR 1.75 5.35 92.9

AlSBA-15/ATR 9.05 25.00 65.95

K. K. V. Castro et al.

123

the process when the AlSBA-15 was used. When AlSBA-

15 was used as catalyst, was obtained a better result in

terms of yield of light fractions of hydrocarbons, in the

range of middle distillate. The mesoporous AlSBA-15

presented catalytic activity for the pyrolysis of ATR, and

selectivity for obtaining products in the diesel range

(C13–C18), besides the formation of heavy fractions ([C19).

This result was satisfactory and expected since the amount

of aluminum incorporated into the structure of AlSBA-15

promote a considerable acidity and consequently a better

breaking of the molecules present on the ATR. The

selectivity for diesel in the pyrolysis process was due a

combination of acidity with the mesoporosity of the AlS-

BA-15, while the amount of fraction in the range of C6–C12

was attributed to the presence of micropores.

Acknowledgements The authors acknowledge the financial support

from Brazilian Agencies: ANP, CAPES, CNPq, FINEP, and Petrobras

S/A.

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