Subscriber access provided by Gothenburg University Library
Article
Removal of Sulfur and Nitrogen Compounds from Diesel Oil by Adsorption using Clays as Adsorbents Luana Ventura Baia, Wallace C. Souza, Ricardo José Faustino de Souza, Claudia de Oliveira Veloso, Sandra Shirley X. Chiaro, and Marco A.G. Figueiredo Energy Fuels, Just Accepted Manuscript • Publication Date (Web): 05 Oct 2017 Downloaded from http://pubs.acs.org on October 5, 2017
Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
Energy & Fuels is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.
Page 1 of 62
Energy & Fuels
Intensity (a.u.)
Clay A
2 (degrees)
Intensity (a.u.)
Clay B
2 (degrees)
Intensity (a.u.)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58
Clay C
2 (degrees) ACS Paragon Plus Environment
Energy & Fuels
C la y A
)
C la y B
Q u a n tity a d s o rb e d (m m o l g
-1
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 2 of 62
C la y C
A lu m in a
0 .0
0 .2
0 .4
0 .6
R e la tiv e p re s s u re (p /p 0) ACS Paragon Plus Environment
0 .8
1 .0
Page 3 of 62
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels
103x132mm (150 x 150 DPI)
ACS Paragon Plus Environment
Energy & Fuels
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
111x130mm (150 x 150 DPI)
ACS Paragon Plus Environment
Page 4 of 62
Page 5 of 62
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels
107x129mm (150 x 150 DPI)
ACS Paragon Plus Environment
Energy & Fuels
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
111x129mm (150 x 150 DPI)
ACS Paragon Plus Environment
Page 6 of 62
Page 7 of 62
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels
117x128mm (150 x 150 DPI)
ACS Paragon Plus Environment
Energy & Fuels
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
112x129mm (150 x 150 DPI)
ACS Paragon Plus Environment
Page 8 of 62
Page 9 of 62
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels
119x130mm (150 x 150 DPI)
ACS Paragon Plus Environment
Energy & Fuels
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
119x129mm (150 x 150 DPI)
ACS Paragon Plus Environment
Page 10 of 62
Page 11 of 62
Energy & Fuels
0 .2 0
0 .1 0
q
e
(m o l S k g
a d so rb e n t
)
0 .1 5
-1
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44
0 .0 5
0 .0 0 0
5 0
1 0 0
1 5 0
2 0 0
ACS Paragon Plus Environment
T im e (m in )
2 5 0
3 0 0
3 5 0
Energy & Fuels
a d so rb e n t
0 .1 0
0 .0 5
q
e
(m o l N k g
-1
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44
)
0 .1 5
Page 12 of 62
0 .0 0 0
5 0
1 0 0
1 5 0
2 0 0
ACS Paragon Plus Environment
T im e (m in )
2 5 0
3 0 0
3 5 0
Page 13 of 62
Energy & Fuels
0 .2 0
a d so rb e n t
-1
)
A lu m in a
q t (m o l S k g
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44
0 .2 0
C la y A
0 .1 5
0 .1 5
0 .1 0
0 .1 0
0 .0 5
0 .0 5
0 .0 0
0 .0 0 0
5
1 0
1 5
2 0
0
5
1 0
1 5
2 0
0 .2 0 0 .1 5 0 .1 5 0 .1 0 0 .1 0 0 .0 5 0 .0 5 0 .0 0
C la y B
C la y C
0 .0 0 0
5
1 0
1 5
2 0
0
ACS Paragon Plus Environment
T im e
1 /2
(m in
1 /2
)
5
1 0
1 5
2 0
Energy & Fuels
0 .1 5
0 .1 5
C la y A
0 .1 0
0 .1 0
0 .0 5
0 .0 5
q t (m o l N k g
a d so rb e n t
)
A lu m in a
-1
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44
Page 14 of 62
0 .0 0
0 .0 0 0
5
1 0
1 5
2 0
0
0 .1 5
0 .1 5
0 .1 0
0 .1 0
0 .0 5
0 .0 5
5
1 0
1 5
C la y B
2 0
C la y C
0 .0 0
0 .0 0 0
5
1 0
1 5
2 0
0
5
1 / 2 Environment 1 /2 ACS Paragon Plus
T im e
(m in
)
1 0
1 5
2 0
Page 15 of 62
Energy & Fuels
4 0 0 0
A
C la y A C la y B
B
C la y A C la y B
4 0 0 3 5 0 0
)
3 0 0 3 0 0 0 2 0 0
C
e
(m o l k g
-1
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44
5 0 0
2 5 0 0 1 0 0
2 0 0 0
0 0 .0
0 .2
0 .4
0 .6
0 .8
0 .0
ACS Paragon Plus Environment
A d so rb e n t d o se (g m L
0 .2 -1
)
0 .4
0 .6
0 .8
Energy & Fuels
0 .6
0 .4 0 .3 0 .2
q
e
(m o l S k g
a d so rb e n t
)
0 .5
-1
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44
Page 16 of 62
0 .1 0 .0 0 .0 5
0 .0 6
0 .0 7
0 .0 8
ACS Paragon Plus Environment
C
e
(m o l S L
-1
)
0 .0 9
0 .1 0
Page 17 of 62
0 .4
q e(m o l N k g
a d so rb e n t
)
0 .3
-1
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44
Energy & Fuels
0 .2
0 .1
0 .0 0 .0 0
0 .0 1
0 .0 2 ACS Paragon Plus Environment
C
e
(m o l N L
-1
)
0 .0 3
Energy & Fuels
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 18 of 62
Removal of Sulfur and Nitrogen Compounds from Diesel Oil by Adsorption using Clays as Adsorbents Luana V. Baia†, Wallace C. Souza†, Ricardo J. F. de Souza‡, Cláudia O. Veloso†,*, Sandra S.X. Chiaro‡, Marco Antonio G. Figueiredo†
†
Institute of Chemistry, Rio de Janeiro State University, Campus Maracanã, PHLC, Rua São Francisco
Xavier, 524, Rio de Janeiro RJ, 20550-900, Brazil. ‡
PETROBRAS - CENPES - Research and Development Center, Av. Horácio Macedo, 950, Rio de
Janeiro RJ, 21941-915, Brazil.
1 ACS Paragon Plus Environment
Page 19 of 62
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels
ABSTRACT Stringent specifications for sulfur compounds content and the need to use oils with large amount of nitrogen compounds are challenges for fuel producers. Adsorption is an alternative process to remove sulfur and nitrogen compounds and clays are promising adsorbents for this removal. In this work, the adsorption performance of different commercial clays, Clay A (attapulgite), B (bentonite), C (bentonite), for removing sulfur and nitrogen compounds from a real diesel stream was studied through kinetic and isotherm experiments. The bentonite clays showed the best adsorptive capacity for sulfur and nitrogen compounds removal probably due to the presence of Brønsted acid sites. The highest adsorption capacity was observed for Clay B, 0.174 mol kg-1 for sulfur compounds and 0.127 mol kg-1 for nitrogen compounds. Clay A was more selective to nitrogen compound removal. Equilibrium data showed that adsorbate-absorbate and adsorbate-surface interactions predominate for sulfur and nitrogen compounds, respectively, for Clay A and B.
2 ACS Paragon Plus Environment
Energy & Fuels
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 20 of 62
1. INTRODUCTION The producers of fuels for transport are now facing challenges such as more stringent specifications for sulfur compounds content to reduce the emission of sulfur oxides and therefore atmospheric pollution and the need to use heavier oils with large amount of nitrogen compounds.1 The removal of sulfur and nitrogen compounds from refinery streams is carried out through hydrotreatment process (HDT) that includes hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) processes. The sulfur compounds are converted into H2S and hydrocarbons in the presence of a heterogeneous catalyst at high temperature and pressure, and under hydrogen atmosphere. The presence of refractory sulfur compounds and nitrogen compounds present in heavy crude oils hampers the HDS process. Nitrogen compounds are much less reactive than sulfur compounds and strongly adsorb on the active sites of the catalyst hindering the adsorption of sulfur compounds.2-4 Adsorption is an alternative process to remove sulfur and nitrogen compounds in order to minimize the above mentioned HDT technical difficulties. An association of adsorption and HDT units can be a possible solution for the production of cleaner fuels under less severe conditions and reducing process cost.5 Several adsorbents have been used for desulfurization and denitrogenation of liquid fuels such as modified oxides,6,7 activated carbon,8,9 mesopourous,10-12 and microporous13,14 molecular sieves, and clays.15-22 The latter group of adsorbents is distinguished by their absorptive, adsorptive and catalytic capacities15 and it is highly employed in oil industry for various separation and adsorption processes.18 Clays are composed by minerals that are hydrous silicates of aluminum and/or magnesium. Iron, nickel, chromium and other cations can be also present in the crystalline structure as an isomorphic substitution. The physicochemical properties of clays are dependent on its structure and composition. These properties also influence the adsorption and/or catalytic behavior of clays. The most used clays are bentonite and attapulgite. Bentonite is a clay mainly comprising to montmorillonite 3 ACS Paragon Plus Environment
Page 21 of 62
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels
group (Na-montmorillonite or Ca-montmorillonite), that is, aluminosilicate clay minerals designated as a 2:1 layer mineral composed of two silica tetrahedral sheets with a central aluminum octahedral sheet. Palygorskite and attapulgite are synonymous terms for the same hydrated magnesium aluminosilicate material, which chemical composition is (MgAl)5Si8O20(OH)2(H2O)4.4H2O. Like other clay minerals, attapulgite has tetrahedral (silica) and octahedral (alumina) sheets as its basic building block. These units are connected to one another by shared oxygen atoms.23 There are just a few papers about adsorption of sulfur and/or nitrogen compounds from model and real oil fractions using clays as adsorbent. Mambrini et al. used hydrophobic bentonite clay for treating dibenzothiophene and quinoline solutions. Adsorption capacities of 38.7 mg g-1 and 54.5 mg g1
were obtained for sulfur and nitrogen compounds, respectively.15 In another study, Zn-containing
montmorillonite clay was used as adsorbents achieving 76 % (kerosene) and 77 % (diesel) of desulfurization. The authors suggested that these results were due to the increase in area, volume and diameter of pores caused by the presence of Zn.18 Montmorillonite, kaolinite, vermiculite and palygorskite were employed for the removal of sulfur compounds from petroleum fractions.16 The kaolinite showed the highest removal level, reaching desulfurization of 60, 76 and 64 % in crude oil, kerosene, and diesel samples, respectively. Ha evaluated the removal of sulfur compounds (2,4dimethyldibenzothiophene and dibenzothiophene) from model fuels by modified clays.24 The most attractive results are those obtained by clays modified with benzyltrimethylammonium salts, due to its similarity with pollutants (aromatic compounds). The maximum adsorption capacity for 2,4dimethyldibenzothiophene was 11.3 mg g-1 in model gasoline and 31.3 mg g-1 in model diesel. It is important to highlight that no information about the adsorption of nitrogen compounds using clays was found. Therefore, aiming at understanding the removal process of sulfur and nitrogen compounds using three commercial clays, Clay A (attapulgite), B (bentonite), C (bentonite), as adsorbents, an adsorption 4 ACS Paragon Plus Environment
Energy & Fuels
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 22 of 62
study through kinetic and isotherm experiments was carried out. For comparative purposes, an activated alumina was also used due to their promising properties as adsorbent of various substances.25
2. Experimental 2.1. Adsorbent characterization. Four commercial adsorbents were used, that is, an amorphous alumina, one attapulgite clay, and two bentonite clays, named Alumina, Clay A, Clay B, Clay C, respectively. The elemental composition of the adsorbents was determined by X-ray fluorescence (XRF) using a Philips PW2400 WXRF spectrometer with a rhodium X-ray tube. The SuperQ/Quantitative PW2450 software, version 2.1d (Philips) was used to analyze the results. The crystalline phases of the adsorbents were identified by X-ray diffraction (XRD) using a Philips PW1710 spectrometer equipped with copper anode and graphite single crystal. The diffractometer operated at 40 kV and 20 mA using Cu Kα radiation over the range of 5-70 ° with 4 ° min-1 scan rate. The samples were dried at 120 °C for 12 h before being used. The textural analysis of the studied adsorbents involves the determination of specific area (Brunauer-Emmett-Teller method), microporous volume (t-plot method), mesoporous volume (BarretJoyner-Halenda method), and pore diameter (Barret-Joyner-Halenda method). Textural properties were determined by N2 adsorption-desorption at -196 °C using an ASAP 2400 (Micromeritics). Samples were degassed under vacuum (50 mTorr) at 300 °C for 1 h. The density and strength distribution of acid sites were determined by temperature-programmed desorption (TPD) of ammonia (2.91 mol% NH3 in He) using an AutoChem 2900 instrument (Micromeritics). The adsorbents were pretreated at 500 °C for 1 h using a 10 °C min-1 heating rate under a He flow (30 mL min-1). Then, the sample was cooled to 30 °C and saturated with ammonia.
5 ACS Paragon Plus Environment
Page 23 of 62
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels
The temperature was then raised to 100 °C for 2 h. Afterwards the sample was heated to 500 °C at 10 °C min-1. Desorption products were monitored by an OmniSTAR™ mass spectrometer (Pfeiffer). The nature of acid sites was determined by pyridine adsorption on adsorbents using Fourier transform infrared spectroscopy (FTIR). The samples were dried at 500 °C using a heating rate of 5 °C min-1. After thermal treatment, the sample was cooled down to 150 °C and exposed to a stream of pyridine / He (30 mL min-1) for 1 min. Then, the sample was outgassed under vacuum for 1 h at 150 °C. The spectra were recorded before pyridine adsorption and after desorption step. The spectra were acquired with a FTIR Spectrum 100 spectrometer from Perkin Elmer equipped with an MCT-A detector and a high temperature chamber (Harrick) with ZnSe windows and scanned using 60 scans with a resolution of 4 cm-1.
2.2. Kinetic experiments. Straight-run diesel oil from a Brazilian refinery, whose composition was 3906 mg kg-1 of sulfur and 522 mg kg-1 of nitrogen representing Arabian crudes was used to study the adsorption properties of the chosen adsorbents. Kinetic tests were carried out in a Dubnoff reciprocal shaking bath using a shaking frequency of 150 rpm at 40 °C. Seven flasks containing 10 mL of diesel and 2 g of adsorbent were used and samples were taken at 10, 30, 60, 120, 180, 240 and 300 min. All adsorbents were pretreated at 150 °C for 1 h to remove adsorbed compounds.
2.3. Isotherm experiments. Adsorption experiments were carried out at 40 and 70 °C using a Dubnoff reciprocal shaking bath. 10 mL of diesel and different adsorbent amount 6.0, 4.0, 2.0, 1.0, 0.5, 0.33, 0.2 g were used for each equilibrium point after 480 min. All adsorbents were pretreated at 150 °C for 1 h before the experiments. The concentration of total sulfur and nitrogen compounds in liquid phase was analyzed using an Elemental Analyzer 9000 (Antek). 6 ACS Paragon Plus Environment
Energy & Fuels
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 24 of 62
2.4. Experimental data treatment. First order, pseudo-first order, pseudo-second order models were used to adjust adsorption kinetic data. An intra-particle diffusion model was also tested to study the adsorbate transport from solution to adsorbent surface. The first model is composed by two differential equations of first-order usually used for reaction kinetic model, where adsorbate sorption from liquid phase to solid phase can be considered as a reversible reaction with an equilibrium being established between two phases.26,27 This model neglects diffusion parameter and is composed of two differential equations of first-order. The EulerCauchy numerical solution with a spreadsheet was used to solve the equations.28 The differential equations are shown in eqs 1 and 2. They were rearranged and numerically integrated giving eqs 3 and 4, where Ct (mol L-1) and qt (mol kg-1) are sulfur or nitrogen compounds concentrations in liquid and solid phase at time "t", respectively; k1 is the adsorption coefficient (min-1); k-1 is the desorption coefficient (min-1); ma is the adsorbent weight (kg); v is solution volume (L); t is time (min); ∆t is time variation (min).
dC m = − k1C + k−1q a dt v
(1)
dq v = k1C − k−1q dt ma
(2)
m Ct + ∆t = Ct − kCt ∆t + k−1qt ∆t a v
(3)
v qt + ∆t = qt − k −1qt ∆t + kCt ∆t ma
(4)
The second model is a pseudo-first order rate Lagergren model.29,30 It describes solid-liquid adsorption based on solid capacity. It considers that the adsorbate removal rate along time is directly 7 ACS Paragon Plus Environment
Page 25 of 62
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels
proportional to the difference in saturation concentration and the number of active sites in solid.31 It suggests film diffusion is the rate-limiting step.32 This model has been chosen because it is one of the most applied model in the literature for kinetics data.25,29 Eq 5 describes this model and eq 6 is the former equation rearranged and numerically integrated using Euler-Cauchy numerical solution, where qt is sulfur or nitrogen compounds concentration in solid phase at time "t" (mol kg-1); qe is sulfur or nitrogen compounds concentration in solid phase at equilibrium (mol kg-1); and k2 is the adsorption coefficient (min-1). k2 (qe − q ) =
dq dt
(5)
qt + ∆t = qt + k2 (qe − qt )∆t
(6)
The third model is a pseudo-second order rate model.29,30 It is used for describing chemisorption involving the valence force by sharing or exchanging of electrons between adsorbent and adsorbate. The reaction velocity depends on the solute quantity adsorbed on the adsorbent surface and the quantity adsorbed at equilibrium.27 It suggests chemisorption is the rate limiting step and it takes account of all the steps of adsorption including external film diffusion, intraparticle diffusion and adsorption.32 This model has been chosen because it is also largely used in the literature for kinetics data.30 Eq 7 represents this model and it was rearranged and numerically integrated using Euler-Cauchy numerical solution (eq 8), where qt is the concentration of sulfur or nitrogen compounds in solid phase at time "t" (mol kg-1); qe is the concentration of sulfur or nitrogen compounds in solid phase at equilibrium (mol kg-1); and k3 is the adsorption coefficient (kg mol-1 min-1).
k3 (qe − qt )2 =
dq dt
(7)
qt + ∆t = qt + k3 (qe − qt )2 ∆t
(8) 8
ACS Paragon Plus Environment
Energy & Fuels
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 26 of 62
Besides the three kinetic models presented above, the adsorbate diffusion within the adsorbent pores applying intraparticle diffusion model was investigated (eq 9).25 In this model, qt is the concentration of sulfur or nitrogen compounds in solid phase at time "t" (mol kg-1); kid is the intraparticle diffusion rate constant (mol kg-1 min-1/2); and values of I (mol kg-1) give an idea about the thickness of the boundary layer.
qt = kid t1 / 2 + I
(9)
The adsorption isotherm parameters were estimated using Langmuir–Freundlich and BrunauerEmmett-Teller (BET) isotherm models according to experimental data. Brunauer–Emmett–Teller (BET) isotherm is a theoretical equation, widely applied in the gas– solid equilibrium systems. It was developed considering physical adsorption with overlapping layers33 (eq 10), where Ce (mol L-1) and qe (mol kg-1) are concentrations of sulfur and nitrogen compounds in liquid and solid phases at equilibrium time; qs is the adsorption capacity of the adsorbent for the first layer (mol kg-1); K1 is the adsorption constant during contaminant-adsorbent interaction (formation of monolayer) (L mol-1); and Ka is the adsorption constant during contaminant-contaminant interaction (formation of next layers) (L mol-1).
qe =
qs K1Ce (1 − K aCe )(1 − K aCe + K1Ce )
(10)
Langmuir–Freundlich isotherm (eq 11) is a combined form of Langmuir and Freundlich expressions. This isotherm can circumvent the limitation of the rising adsorbate concentration 9 ACS Paragon Plus Environment
Page 27 of 62
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels
associated with Freundlich isotherm model and predict the heterogeneous adsorption systems that are not included in Langmuir equation. K C nS S e qe = qmax S 1 + K C nS S e
(11)
where Ce (mol L-1) and qe (mol kg-1) are concentrations of sulfur and nitrogen compounds in liquid and solid phases at equilibrium time, KS (L mol-1), qmaxS (mol kg-1) and nS (dimensionless) are the Langmuir–Freundlich characteristic parameters. Microsoft® Office Excel 2007 was used to solve both kinetic and equilibrium models through data adjustment by minimizing objective function (eq 12) for resolution of eq 1 and objective function (eq 13) for resolution of eq 2, it was possible to determine the parameters using SOLVER tool from the cited software. n
(
)
n
(
)
OF = ∑ Cexp i − Ccalci 2 + ∑ qexp i − qcalci 2 i =1
n
(12)
i =1
(
)
OF = ∑ qexp i − qcalci 2
(13)
i =1
3. RESULTS AND DISCUSSION 3.1. Adsorbent characterization. Four adsorbents were studied for the desulfurization and denitrogenation of a commercial diesel, that is, Clay A (attapulgite), Clay B (bentonite), Clay C (bentonite) and an Alumina. Bentonite is a clay mainly comprising to montmorillonite group that is an aluminosilicate clay minerals designated as a 2:1 layer mineral. Bentonite particles present cation exchange capacity, and high surface area.23 Attapulgite is a hydrated magnesium aluminosilicate material that has tetrahedral (silica) and octahedral (alumina) sheets as its basic building block. These units are connected to one another by shared oxygen atoms.23 The chemical composition of the 10 ACS Paragon Plus Environment
Energy & Fuels
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 28 of 62
adsorbents (Table 1) is given in oxides weight percent. The Alumina adsorbent contains 0.3 wt% of Na2O. Clay samples present alkaline earth metals mainly MgO. Clay A contained 23.6 wt% of alkaline earth oxides (MgO and CaO). Clay B and C showed the same Si/Al molar ratio, while Clay A presented a very high ratio. The crystalline phases of clay adsorbents were determined using X-ray diffraction (Figure 1). Clay B and C are mainly composed by montmorillonite (ICCD 13-0135) (Figure S1).34,35 However, the X-ray diffractogram of Clay C indicates the presence of minor amounts of quartz, K-feldspar, and plagioclase.35 X-ray diffraction pattern of Clay A shows that the major mineral is attapulgite, with characteristic diffraction peaks at 8.4°, 13.9°, 19.8°, 20.8°, 28.0°, and 28.8°. Besides attapulgite (ICCD 31-0783) (Figure S2), the presence of quartz and dolomite was identified by the peaks around 26.6° 3638
and at 30.8°,39 respectively. According to the supplier, Alumina sample is an amorphous adsorbent. As can be seen in Table 2, Alumina is the adsorbent with the highest specific area, while Clay A
(attapulgite type) showed the smallest area. Clays B and C (bentonite type) present similar specific areas that are higher than Clay A specific area, indicating that these clays were chemically treated by the suppliers.40 The acid treatment leads the leaching of cations from octahedral and tetrahedral sheets, dissolves impurities, and replaces exchangeable cations with hydrogen ions. It also opens the edges of the platelets. All these changes result in increased specific area and pore diameter. The pore volume and diameter of Alumina and Clays B and C are similar, while a higher value of these properties was observed for Clay A. The N2 adsorption/desorption isotherms of the adsorbents are illustrated in Figure 2 and they were identified according to IUPAC or BDDT (Brunauer, Deming, Deming and Teller) classification. All isotherms showed hysteresis loops that are usually associated with the filling and emptying of mesopores by capillary condensation. The bentonite clays, Clay B and Clay C, presented similar isotherms classified as Type IV that is characteristic of mesoporous solids41 with H4 type hysteresis 11 ACS Paragon Plus Environment
Page 29 of 62
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels
loops representing slit shaped pores and plate-like particles with spaces between the parallel plates.42 Caglar et al. found similar isotherm profiles.43 On the other hand, Clay A, an attapulgite clay, presented a type V isotherm, corresponding to a weak adsorbent-adsorbate interaction and saturation of the adsorbed amount at high pressures.44 A steep increase of adsorbed amount is observed for Clay A at p/po = 0.9 that is probably related to filling of voids among particles. Similar N2 isotherms for attapulgite samples were observed in the literature.45-47 The N2 adsorption/desorption isotherm of Alumina sample is type IV with H3 hysteresis loop, which is usually observed with aggregates of platelike particles giving rise to slit-shaped pores.48,49 The determination of density, strength, and type of acid sites exposed on the surface of a solid is a useful tool to understand the adsorption capacity of adsorbents. Temperature-programmed desorption (TPD) of ammonia was used to measure total density and strength of acid sites on the surface of the studied samples, while acid site type was identified using pyridine adsorption. The acid site densities were measured by TPD of ammonia and the results are shown in Table 2. Alumina is the adsorbent with the highest density, while Clay A is the adsorbent with the lowest density. The following sequence was observed: Alumina > Clay B > Clay C > Clay A. For all adsorbents, a broad peak with temperature maximum around 222-237 °C was observed, indicating that these are mainly weak acid sites. IR spectra of the samples in OH stretching region are shown in Figure 3. The hydroxyl stretching region of Clay A is complex with bands at 3739, 3718, 3673, 3638, 3619, and 3587 cm-1. According to the literature,50-52 bands below 3600 cm-1 are assigned to hydroxyl stretching vibrations of water, while bands above 3600 cm-1 are associated with coordinated hydroxyl groups. Frost et al. attributed bands at 3731 and 3710 cm-1 to hydroxyls attached to tetrahedral silicon in the attapulgite structure.50 They suggested that the first band is due to non-hydrogen bonded hydroxyl group and the second band is associated to hydrogen bonded hydroxyl on the tetrahedral silicon. These bands are 12 ACS Paragon Plus Environment
Energy & Fuels
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 30 of 62
frequently observed in layered silicates and zeolites, and are assigned to terminal Si–OH groups. The remaining four bands are attributed to hydroxyl stretching vibrations of octahedral magnesium or equivalent cation.50 A band around 3616 cm-1 is always observed for palygorskite50,53,54 and it is related to the contribution of stretching vibrations of OH in (Fe, Mg)–OH and (Al, Mg)–OH. The band at 3580 cm-1 was assigned to Al–Fe3+–OH or Al–Mg–OH bonds,55 while Chahi et al. attributed it to Al–Fe–OH stretching.53 Clays B and C FTIR spectra of hydroxyl region are shown in Figure 3. These samples are bentonites mainly composed of montmorillonite. The major bands observed for Clays B and C are 3743 and 3631 cm-1, and 3742 and 3636 cm-1, respectively. The former band is ascribed to Al-O-Si-OH that resembles the hydroxyl on silica and the latter band is associated to hydroxyl groups (AlOH).34,56,57 Shoulders at 3666, 3655 and 3625 cm-1 were observed for Clay C and are ascribed to OH stretching of structural hydroxyl groups associated to aluminum. On Alumina sample, bands at 3779, 3730, and 3693 cm-1 were observed. According to the literature,58 bands at 3779 and 3730 cm-1 are assigned to terminal OH that shows acidic character, and activity in adsorption. The band centered in 3693 cm-1 is likely due to bridging species. Probe molecules are widely used to determine the characteristics of the surface of different materials. Acid site type, Lewis or Brønsted sites, can be discriminated by the interaction of pyridine with these sites due to the specific IR vibrational bands observed for each mode of interaction between pyridine and material surface. The main interactions are: pyridine coordinated to surface Lewis acid sites produces bands around 1621, 1614, 1590, 1577, 1493, and 1452 cm-1; pyridine protonated on Brønsted acid sites (pyridinium ions) generates bands near 1640, 1620, around 1540-1548, and at 1490 cm-1; hydrogen-bonded pyridine is identified by bands in the ranges of 1440-1447 and 1590-1600 cm-1, and also at 1490 cm-1.56,59 A clear identification of hydrogen-bonded pyridine and pyridine adsorbed at Lewis and Brønsted acid sites is possible due to the low thermal stability of hydrogen-bonded pyridine 13 ACS Paragon Plus Environment
Page 31 of 62
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels
that allows the desorption of hydrogen-bonded species and the identification of Lewis and Brønsted acid sites.60,61 Figure 4 shows the spectra of pyridine chemisorption on all samples at 150 °C. The spectra for Alumina (1616, 1599, 1576, 1492, 1451 cm-1) and Clay A (1621, 1610, 1577, 1494, 1448 cm-1) showed the presence of only Lewis acid sites. Alumina sample showed a band at 1599 cm-1 that is related to a labile species ascribed to hydrogen-bounded pyridine,56 and the band at 1616 cm-1 was assigned to Al3+ sites in octahedral symmetry.62,63 On the other hand, the spectra of Clay B and Clay C indicated the presence of Brønsted (1638, 1545, 1491 cm-1, and 1637, 1545, 1491 cm-1, respectively) and Lewis acid sites (1622, 1576, 1491, 1455 cm-1, and 1622, 1612, 1577, 1491, 1454 cm-1, respectively). Similar IR spectra were observed in the literature.43,64 Bodoardo et al.56 ascribed the formation of pyridinium ions on (AlOH) hydroxyl species, while Lewis acid sites were related to Al centers. At least two types of Lewis sites can be observed, one at 1622 cm-1 associated to Al sites on pillars and the other one at 1614 cm-1 associated to Al sites in the tetrahedral layer. 3.2. Adsorption kinetics. The adsorption kinetics describes the rate of adsorbate retention on an adsorbent indicating adsorption efficiency. The adjusting of batch adsorption kinetics is useful for designing adsorption columns. The kinetic profiles for the adsorption of sulfur compounds on studied adsorbents are depicted in Figure 5. Clay A and Alumina achieved equilibrium after less than 10 min, while Clays B and C required 60 min to reach equilibrium. Thus, all batch experiments were conducted with a contact time of 480 min under vigorous stirring. The rate of sulfur compounds adsorption was very rapid during the initial 10 min, and thereafter, it decreases. Srivastav and Srivastava observed the same behavior for adsorptive removal of dibenzothiophene (DBT) in the presence of alumina.25 They highlighted that at initial adsorption stage a large number of vacant surface sites were available, but after a period of time, the further adsorption on the remaining vacant surface sites was difficult due to repulsive forces between the solute molecules on the solid and bulk phases. According to Shakirullah et 14 ACS Paragon Plus Environment
Energy & Fuels
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 32 of 62
al., for clays, the adsorption process starts on upper surface layer and lower basal layers as contact time increases it takes place on middle layers.16 So the access for middle layers is easier for Clay A, and for Clay B and C it is more difficult. Considering adsorption capacity, Clay B showed the highest adsorption capacity to remove sulfur compounds, while Clay A was the adsorbent with the smallest adsorption capacity. The following adsorption capacity sequence was observed: Clay B (0.174 mol kg-1) > Clay C (0.128 mol kg-1) > Alumina (0.059 mol kg-1) > Clay A (0.018 mol kg-1). Clays B and C are commercial bentonites that exhibit similar chemical composition (Si and Al are the major elements) and specific area. These samples exhibit Brønsted and Lewis acid sites. Alumina sample presents only aluminum, high specific area and acid site density; however, only Lewis acid sites were noticed. Clay A, an attapulgite clay, shows low specific surface area and acid site density, and as Alumina only Lewis acid sites were observed. The main element in its chemical composition is silicon and the presence of Ca and Mg was also observed. It is important to highlight that the presence of Brønsted acid sites seems to be crucial to a better performance in the adsorption of sulfur compounds as Clays B and C showed the higher values of adsorption capacity. However, the interaction of Lewis acid sites with sulfur and nitrogen compounds cannot be denied as Alumina and Clay A that have only this type of acid site are able to remove these compounds. The type of acid site, Brønsted or Lewis, is more important than acid site density. Shakirullah et al. have studied kaolinite, montmorillonite, palygorskite and vermiculite natural clays as adsorbents for selective adsorption of sulfur compounds present in crude oil, kerosene, and diesel oil.16 Kaolinite exhibited the higher removal of sulfur compounds, 64 %, at 40 °C after 6 h. The authors explained that the highest desulfurization capacity of kaolinite clay is attributed to its larger specific area, small porous structure and its mineralogical composition, which shows only aluminum and silicon in the framework. Khalili et al. have studied raw, treated, and acid activated bentonites as adsorbents to the desulfurization of a diesel fuel.17 The acid activated bentonite sample has been treated 15 ACS Paragon Plus Environment
Page 33 of 62
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels
with HCl (3.0 mol L-1) was added to the suspension. The suspension was stirred under reflux for 12 h at 70 °C, filtered, washed with water, and dried at 105 °C. The best adsorption capacity achieved was 4.78 mg S / g acid activated bentonite using 15 mL of diesel fuel (initial concentration = 8700 ppm S) mixed with 0.5 g of bentonite and shaken for 5 h. On the other hand, an adsorption capacity of 5.60 mg S / g of Clay B was obtained in this work using 10 mL of diesel fuel (3906 mg kg-1 of sulfur) and 2 g of adsorbent at 40 °C stirred at 150 rpm for 5 h. The parameters of first-order, pseudo-first order, and pseudo-second order kinetic models for sulfur compounds adsorption are showed in Table 3. For all adsorbents and kinetic models, qe,exp and qe,cal values are very similar. For Alumina, the best model was the first-order model (model 1) with the highest value of coefficient of determination (R2). In the case of Clay A, all three kinetic models showed low coefficient of determination due to dispersion of experimental data. Clay B kinetic data was fitted by first-order and pseudo-second order model (model 1 and 3), while for Clay C, the pseudosecond order model (model 3) showed the highest R2. The adsorption of sulfur compounds on Clay C and B can be considered a two-step mechanism, that is, diffusion of adsorbate towards adsorbent surface followed by physical interaction between adsorbates molecules and the surface sites. This model suggests that chemisorption is the rate-limiting step and it takes account of all the steps of adsorption including external film diffusion, intraparticle diffusion and adsorption.32 The kinetic profiles for the adsorption of nitrogen compounds on studied adsorbents are depicted in Figure 6. Considering adsorption capacity, Clays B and C presented the highest adsorption capacity to remove nitrogen compounds. On the other hand, Alumina achieved the smallest adsorption capacity. The following adsorption capacity sequence was observed: Clay B (0.127 mol kg-1) > Clay C (0.109 mol kg-1) > Clay A (0.078 mol kg-1) > Alumina (0.059 mol kg-1). As for sulfur compounds, Clays B and C exhibit better adsorption capacity indicating that Brønsted acid sites are crucial. It is important to highlight that Clay A is more selective to nitrogen compounds adsorption (0.078 mol kg-1) as compared 16 ACS Paragon Plus Environment
Energy & Fuels
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 34 of 62
to sulfur ones (0.018 mol kg-1). The equilibrium was first reached by Clay A after 20 min, on the other hand the other three adsorbents attained the saturation after 120 min. To the best of our knowledge, no information on the adsorption of nitrogen compounds on clay adsorbents is available in the literature. The parameters of first-order, pseudo-first order, and pseudo-second order kinetic models for nitrogen compounds adsorption are showed in Table 4. For all adsorbents and kinetic models, qe,exp and qe,cal values are very similar. For Alumina, the best fit was observed with first order model, with higher value of R2. In the case of the Clay A, the pseudo-first order model showed the best results, this model suggests film diffusion is the rate-limiting step.32 For Clay B, first order and pseudo-first order models showed the same fit, while for Clay C pseudo-second order model presented highest R2, this model suggests chemisorption is the rate-limiting step and it takes account of all the steps of adsorption including external film diffusion, intraparticle diffusion and adsorption.32 The complete adsorption process is composed of one or more steps, that is, film or external diffusion, pore diffusion, surface diffusion and adsorption on the pore surface, or a combination of different steps. The influence of intraparticle diffusion was evaluated using Weber-Morris diffusion model,25,65-67 expressed by a plot of qt versus t1/2. When sole intraparticle diffusion controlled the adsorption process a linear relation of experimental data that passes through the origin is observed. However, multi-linear plots indicate that two or more steps influence the adsorption process. Figure 7 shows the Weber-Morris plot for the adsorption of sulfur compounds. All adsorbents showed multi-linear relations. Clay B and C presented three linear portions. The first sharp line represented the diffusion of adsorbate from solution to external surface of adsorbent or boundary layer diffusion. The second linear portion is attributed to the gradual adsorption stage controlled by intraparticle diffusion. The third stage is the final equilibrium stage, where intraparticle diffusion starts to slowdown due to the extremely low adsorbate concentration left in the solution.25 The desulfurization of a model solution containing dibenzothiophene in n-heptane was carried out using 17 ACS Paragon Plus Environment
Page 35 of 62
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels
untreated, acid activated and magnetite nanoparticle loaded bentonites as adsorbents. The plot of the intraparticle diffusion model of all adsorbents showed three different linear steps.19 For Alumina and Clay A, only the first and the third stages were identified. Srivastav and Srivastava used a commercial activated alumina as adsorbent to remove dibenzothiophene (DBT) dissolved in n-hexane and observed that more than one process is controlling adsorption as three stages were identified in Weber-Morris plots.25 In a similar way, Neubauer et al. studied the desulfurization a jet-A1 fuel enriched with benzothiophene and dibenzothiophene using an Ag-Al2O3 adsorbent and identified three-stage behavior for these sulfur compounds.65 Weber-Morris plots for the adsorption of nitrogen compounds are depicted in Figure 8. Only one stage was observed for Alumina indicating that the adsorption process is controlled by intraparticle diffusion. Clays A, B and C showed two steps. For Clay A, the first and the third steps were noted; similarly to the result obtained for sulfur compound adsorption. On the other hand, stages one and two described the adsorption process for Clays B and C in the tested time range.
3.3. Adsorbent dose. Two adsorbents were chosen to study equilibrium adsorption, Clay A and Clay B. According to adsorption kinetics, Clay A has shown a high selectivity for nitrogen compounds, while Clay B presented the highest adsorption capacity of sulfur and nitrogen compounds. The influence of adsorbent amount on the removal of adsorbates is associated to the availability and accessibility of adsorption sites. Figure 9 depicts the effect of adsorbent dose in the adsorption of sulfur and nitrogen compounds present in a diesel sample. For sulfur compounds (Figure 9A), Clay A and Clay B showed different behaviors. In the presence of Clay A sulfur compounds removal increased until adsorbent dose equal to 0.4 g mL-1, thereafter this removal remained constant. This trend can be due to aggregation of adsorbent particles hindering the access to adsorbent active sites. On the other hand, for Clay B the removal of sulfur compounds increased constantly when adsorbent dose increased. 18 ACS Paragon Plus Environment
Energy & Fuels
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 36 of 62
This behavior can be attributed to the availability of larger specific area and adsorbent sites for sulfur compounds adsorption. For nitrogen compounds (Figure 9B), Clay A and Clay B showed similar behavior, that is, the removal increased constantly when adsorbent dose increased. 3.4. Adsorption isotherm. The adsorption process in liquid phase involves a competition between solvent and solute that has to be considered for an accurate discussion of the process. The adsorption of a solute on an adsorbent at a liquid-solid interface is commonly followed by measuring the solute concentration at an equilibrium point.68 The adsorption isotherm is a correlation of the amount of adsorbed solute by unit mass of solid and the remaining equilibrium concentration of the solute at a specific temperature. It is important for describing the adsorption mechanism pathways and designing of the adsorption systems. The adsorption performance of a solid is influenced by the accessibility of adsorption sites and the surface properties of the adsorbent. The equilibrium results are expressed as sulfur or nitrogen mol per adsorbent mass, in order to allow the comparison between sulfur and nitrogen removals. Figure 10 illustrates the results for sulfur compounds adsorption isotherm with the selected adsorbents at 40 and 70 °C. Due to the profile of the isotherm data, only BET isotherm model was used to adjust the experimental results. The isotherm constants for BET model along with R2 values, which shows adjustment quality, are shown in Table S1. The BET model is the suitable equation for representing the adsorption isotherm data for sulfur compounds on Clay A and B at 40 and 70 °C. Regardless of adsorption temperature and adsorbent, all isotherms for sulfur compounds were classified as type S, according to Giles et al..69 Two interactions are important to the adsorption process, that is, adsorbate-adsorbent and adsorbate-adsorbate interactions. Type S isotherm is observed when adsorbate-adsorbate interactions significantly contribute to increase adsorption, indicating a continuous progression with increasing loading from monolayer to multilayer adsorption. An increase of adsorption capacity in high range of concentration confirms the difficulty in sulfur adsorption. Both 19 ACS Paragon Plus Environment
Page 37 of 62
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels
adsorbents presented isotherms with unfavorable profile, indicating that at low concentrations there is a small contaminant removal. At 40 °C, Clay B achieved lower equilibrium concentration and higher adsorption capacity for sulfur adsorption in the concentration range used, indicating that this is a better adsorbent for sulfur compounds removal. As expected, the increase of adsorption temperature led to higher equilibrium concentration and lower adsorption capacity, suggesting that the interaction of sulfur compounds and adsorption sites on Clay B is weak and also that the adsorptive forces between adjacent molecules of the adsorbed phase are also weak. The results for nitrogen compounds adsorption isotherms with the selected adsorbents are presented in Figure 11. The isotherm constants for Langmuir-Freundlich and BET models along with R2 values, which show adjustment quality, are shown in Table S2. The experimental data for the adsorption of nitrogen compounds on Clay A at 40 and 70 °C was fitted by BET model, while on Clay B at 40 and 70 °C the best model was Langmuir-Freundlich. According to Giles et al.,69 the four isotherms were classified as Type L that shows a concave to the concentration axis near the origin. This type of isotherm usually indicates that molecules are adsorbed on the surface, and, sometimes, they can show a strong intermolecular attraction resulting in a vertically adsorption. A well-defined plateau can also be observed and it is associated to the formation of a monolayer of the adsorbate. The isotherms obtained for Clay B at 40 and 70 °C were assigned to sub-group 1, while Clay A isotherms at both adsorption temperatures were classified as sub-group 3. The sub-groups of the isotherm classes are defined according to the shape of the curves away from the origin, plateaus and changes of slope are considered. The sub-group 1 curves do not show a plateau or an inflection indicating a clearly incomplete isotherm, that is, the saturation of the surface has not been reached. For sub-group 3 isotherms, a plateau and an inflection point are observed. The plateau is formed when adsorbed molecules cover the surface and the possible sites are filled. A short plateau, as 20 ACS Paragon Plus Environment
Energy & Fuels
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 38 of 62
can be seen for Clay A isotherms, means that after the adsorbate interacts with the adsorbent surface forming an adsorbate layer on the surface, the adsorbate in the solution shows the similar affinity to the adsorbent surface and to the adsorbate layer built on the adsorbent surface. The greater the attraction for the adsorbate layer is, the curve rises steadily and a second rise is noted. Nitrogen compounds present in the studied diesel showed a good interaction with Clay B adsorption sites as the highest adsorption capacity for nitrogen compounds was observed for this adsorbent. As mentioned above, the plateau of the type L isotherm was not achieved throughout the concentration range indicating that adsorption sites are still available on the surface. The adsorption capacity of Clay B at 70 °C was higher than that at 40 °C; this increase is due to the increase of fluidity of liquid phase, allowing the diffusion of the adsorbate into adsorbent pores. Clay A presented a lower adsorption capacity for nitrogen compounds comparing to Clay B, indicating that Clay A surface has less adsorption sites for nitrogen than Clay B. The isotherm shape, type L and sub-group 3, suggested that nitrogen compounds had a better attraction to each other than to the adsorption sites on Clay A. The increase of adsorption temperature from 40 to 70 °C did not influence the adsorption capacity of Clay A until the sharp rise in curve steepening due to multilayer adsorption. The increase of temperature did not influence the nitrogen compounds adsorption in the region of the initial rise and plateau, indicating that these compounds strongly interact with adsorption sites. On the other hand, the adsorbate-adsorbate attraction is a weak interaction, because when adsorption temperature increases the adsorption capacity decreases. Analyzing characterization results and adsorption isotherms, it is not simple to establish a correlation between higher contaminant removal capacity and adsorbent properties. Although the adsorption is a surface phenomenon, it was not possible to establish a direct correlation with specific area. In this case, Alumina showed the worst performance, although it had the highest specific area. On
21 ACS Paragon Plus Environment
Page 39 of 62
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels
the other hand, acid site type (Brønsted sites) seems to be more important than acid site density for sulfur compounds adsorption.
4. CONCLUSION The bentonite clays (Clay B and C) showed promising adsorptive capacity for nitrogen and sulfur compounds probably due to the presence of Brønsted acid sites and also higher specific area, whereas the attapulgite clay (Clay A) was selective to nitrogen compounds, whose adsorption can be influenced by chemical composition, that is, a high Si/Al molar ratio. Clays were more effective than Alumina for sulfur and nitrogen compounds removal from a real diesel stream. For Clay A, the adsorption process for sulfur and nitrogen compounds can be describe by the diffusion of adsorbate from solution to external surface of adsorbent, and the equilibrium stage, where low adsorbate concentration is present in the solution. It is important to highlight that Clay A showed the highest pore volume. On the other hand, Clays B and C presented different adsorption steps for sulfur and nitrogen compounds. For sulfur compounds the three steps (diffusion of adsorbate from solution to external surface of adsorbent or boundary layer diffusion; intraparticle diffusion; final equilibrium stage) were observed, while for nitrogen compounds only diffusion of adsorbate from solution to external surface of adsorbent, and the equilibrium stage were noted. From equilibrium data, it was noted that adsorbate-absorbate and adsorbate-surface interactions predominate for sulfur and nitrogen compounds, respectively, for Clay A and B.
AUTHOR INFORMATION Corresponding author * E-mail:
[email protected] Notes 22 ACS Paragon Plus Environment
Energy & Fuels
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 40 of 62
The authors declare no competing financial interest.
ACKNOWLEDGEMENTS The authors thank Petrobras S.A. for financial support.
Supporting Information. Isotherm constants for BET and Langmuir-Freundlich models and R2 values for adsorption experimental data on Clay A and B at 40 and 70 °C; and ICCD cards: 13-0135 (montmorillonite-15A) and 31-0783 (palygorskite) are shown in Supporting Information. This material is available free of charge via the Internet at http://pubs.acs.org.
REFERENCES (1) Koriakin, A.; Ponvel, K. M.; Lee, C. Denitrogenation of Raw Diesel Fuel by Lithium-Modified Mesoporous Silica. J. Chem. Eng. 2010, 162, 649-655. (2) Laredo, G.; Vega-Merino, P.; Trejo-Zárraga, F.; Castillo, J. Denitrogenation of Middle Distillates using Adsorbent Materials towards ULSD Production: A Review. Fuel Process. Technol. 2013, 106, 21-32. (3) Sano, Y.; Choi, K.; Korai, Y.; Mochida, I. Adsorptive Removal of Sulfur and Nitrogen Species from a Straight Run Gas Oil over Activated Carbons for its Deep Hydrodesulfurization. Appl. Catal. B 2004, 49, 219-225. (4) Sano, Y.; Choi, K.; Korai, Y.; Mochida, I. Effects of nitrogen and refractory sulfur species removal on the deep HDS of gas oil. Appl. Catal. B 2004, 53, 169-174. (5) Lee, S.; Ryu, J. W.; Min, W. SK Hydrodesulfurization (HDS) Pretreatment Technology for Ultralow Sulfur Diesel (ULSD) Production. Cat. Surv. Asia 2003, 7, 271-279.
23 ACS Paragon Plus Environment
Page 41 of 62
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels
(6) Silveira, E.; Veloso, C.; Costa, A.; Henriques, C.; Zotin, F.; Paredes, M.; Reis, R.; Chiaro, S. Influence of Metal Oxides Impregnated on Silica–Alumina in the Removal of Sulphur and Nitrogen Compounds from a Hydrotreated Diesel Fuel Stream. Adsorpt. Sci. Technol. 2015, 33, 105-116. (7) Silva, J.; Silveira, E.; Veloso, C.; Costa, A.; Henriques, C.; Zotin, F.; Paredes, M.; Reis, R.; Chiaro, S. Influence of the Chemical Composition of Silica-Alumina Adsorbents in Sulfur and Nitrogen Compounds Removal from Hydrotreated Diesel. Ind. Eng. Chem. Res. 2014, 53, 16000-16014. (8) Seredych, M.; Bandosz, T. J. Adsorption of Dibenzothiophenes on Nanoporous Carbons: Identification of Specific Adsorption Sites Governing Capacity and Selectivity. Energy Fuels 2010, 24, 3352-3360. (9) Schmitt, C.; Chiaro, S.; Tanobe, V.; Takeshita, E.; Yamamoto, C. Regeneration of Activated Carbon from Babassu Coconut Refuse Applied as a Complementary Treatment to Conventional Refinery Hydrotreatment of Diesel Fuel. J. Cleaner Prod. 2017, 140, 1465-1469. (10) Li, W.; Tang, H.; Zhang, T.; Li, Q.; Xing, J.; Liu, H. Ultra-Deep Desulfurization Adsorbents for Hydrotreated Diesel with Magnetic Mesoporous Aluminosilicates. AIChE J. 2009, 56, 1391-1396. (11) Wang, Y.; Yang, R.T.; Heinzel, J.M. Desulfurization of Jet Fuel by π-complexation Adsorption with Metal Halides Supported on MCM-41 and SBA-15 Mesoporous Materials. Chem. Eng. Sci. 2008, 63, 356-365.
(12) Santos, F.; Alsina, O.; Carvalho, M., Barbosa, C., Chiaro, S. Use of AIPO and MeAPO as Adsorbents in a Cyclohexene-Propanethiol Mixture for Sulfur Content Reduction. Braz. J. Pet. Gas 2008, 2, 17-26. (13) Lee, K.; Valla, J. Investigation of Metal-Exchanged Mesoporous Y Zeolites for the Adsorptive Desulfurization of Liquid Fuels. Appl. Catal. B 2017, 201, 359-369. (14) Tian, F.; Shen, Q.; Fu, Z.; Wu, Y.; Jia, C. Enhanced Adsorption Desulfurization Performance Over Hierarchically Structured Zeolite Y. Fuel Process. Technol. 2014, 128, 176-182. 24 ACS Paragon Plus Environment
Energy & Fuels
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 42 of 62
(15) Mambrini, R.V.; Saldanha, A.L.M.; Ardisson, J.D.; Araujo, M.H.; Moura, F.C.C. Adsorption of Sulfur and Nitrogen Compounds on Hydrophobic Bentonite. Appl. Clay Sci., 2013, 83-84, 286-293. (16) Shakirullah, M.; Ahmad, W.; Ahmad, I.; Ishaq, M.; Khan, M. Desulphurization of Liquid Fuels by Selective Adsorption through Mineral Clays as Adsorbents. J. Chil. Chem. Soc. 2012, 57, 1375-1380. (17) Khalili, F.I.; Sultan, M.; Robl, C.; Al-Ghouti, M.A. Insights into the Remediation Characterization of Modified Bentonite in Minimizing Organosulphur Compounds from Diesel Fuel. J. Ind. Eng. Chem. 2015, 28, 282-293. (18) Ahmad, W.; Ahmad I.; Ishaq, M.; Ihsan, K. Adsortive Desulfurization of Querosene and Diesel Oil
by
Zn
Impregnated
Montmorollonite
Clay.
Arabian
J.
2014.
Chem.
http://dx.doi.org/10.1016/j.arabjc.2013.12.025. (19) Ishaq, M.; Sultan, S.; Ahmad, I.; Ullah, H.; Yaseen, M.; Amir, A. Adsorptive Desulfurization of Model Oil using Untreated, Acid Activated and Magnetite Nanoparticle Loaded Bentonite as Adsorbent. J. Saudi Chem. Soc. 2017, 21,143-151. (20) Tang, X.; Meng, X.; Shi, L. Desulfurization of Model Gasoline on Modified Bentonite. Ind. Eng. Chem. Res. 2011, 50, 7527-7533.
(21) Zhang, Y.; Yang, X.; Li, D.; Na, P. Adsorptive Desulfurization of Model Gasoline on Organic – Inorganic Modified Montmorillonite. Adv. Mat. Res. 2014, 875-877, 237-241. (22) Zhang, Y.; Chen, A.; Li, C.; Luo, M.; Xu, Z. On the Effect of Modifications to Montmorillonite for the Desulphurization of Synthetic Gasoline. Adsorpt. Sci. Technol. 2011, 29, 197-209. (23) Emam, E. A. Clays as Catalysts in Petroleum Refining Industry. ARPN J. Sci. Technol. 2013, 3, 356-375. (24) Ha, J.H. Remarkable removal of sulfur-containing compounds from model fuels with modified clays. Department of Chemistry, New York University, 2011.
25 ACS Paragon Plus Environment
Page 43 of 62
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels
(25) Srivastav, A.; Srivastava, V. C. Adsorptive Desulfurization by Activated Alumina. J. Hazard. Mater. 2009, 170, 1133-1140.
(26) Bhattacharya, A.; Venkobachar, C. Removal of Cadmium (II) by Low Cost Adsorbents. J. Environ. Eng. 1984, 110, 110-122.
(27) Ho, Y.S.; McKay, G. Pseudo-Second Order Model for Sorption Processes. Process Biochem. 1999, 34, 451-465. (28) Coe, D. Numerical Solutions of Kinetic Equations on a Spreadsheet. J. Chem. Educ. 1987, 64, 496-497. (29) Muzic, M.; Sertic-Bionda, K.; Gomzi, Z.; Podolski, S.; Telen, S. Study of Diesel Fuel Desulfurization by Adsorption. Chem. Eng. Res. Des. 2010, 88, 487-495. (30) Kumar, K. V. Linear and Non-Linear Regression Analysis for the Sorption Kinetics of Methylene Blue onto Activated Carbon. J. Hazardous Mater. 2006, 137, 1538-1544. (31) Ho, Y.S. Citation Review of Lagergren Kinetic Rate Equation on Adsorption Reactions. Scientometrics 2004, 59, 171-177.
(32) Licthfouse, E.; Schwarzbauer, J.; Robert, D. Green Materials for Energy, Products and Depollution; Springer Science and Business Media: Dordrecht, 2013.
(33) Suzuki, M., Adsorption Engineering, Kodansha LTD: Tokio, and Elsevier Science Publishers B. V.: Amsterdam, 1990. (34) Liu, D.; Yuana, P.; Liu, H.; Cai, J.; Tan, D.; He, H.; Zhu, J.; Chen, T. Quantitative Characterization of the Solid Acidity of Montmorillonite using Combined FTIR and TPD Based on the NH3 Adsorption System. Appl. Clay Sci. 2013, 80-81, 407-412. (35) Malfoy, C.; Pantet, A.; Monnet, P.; Righi, D. Effects of the Nature of the Exchangeable Cation and Clay Concentration on the Rheological Properties of Smectite Suspensions. Clays Clay Miner. 2003, 51, 656-663. 26 ACS Paragon Plus Environment
Energy & Fuels
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 44 of 62
(36) Xavier, K.; Santos, M.; Santos, M.; Oliveira, M.; Carvalho, M.; Osajima, J.; Silva Filho, E. Effects of Acid Treatment on the Clay Palygorskite: XRD, Surface Area, Morphological and Chemical Composition. Mater. Res. 2014, 17, 3-8. (37) Wang, J.; Chen, D. Mechanical Properties of Natural Rubber Nanocomposites Filled with Thermally
Treated
Attapulgite.
J.
Nanomater.
2013,
article
ID
496584,
http://dx.doi.org/10.1155/2013/496584. (38) Oliveira, R. N.; Acchar, W.; Soares, G. D. A.; Barreto, L. S. The Increase of Surface Area of a Brazilian Palygorskite Clay Activated with Sulfuric Acid Solutions Using a Factorial Design. Mater. Res. 2013, 16, 924-928. (39) Pushpaletha, P.; Lalithambika M. Modified Attapulgite: An Efficient Solid Acid Catalyst for
Acetylation of Alcohols Using Acetic Acid. Appl. Clay Sci. 2011, 51, 424-430. (40) Diaz, F.; Santos, P. Studies on the Acid Activation of Brazilian Smectitic Clays. Quim. Nova 2001, 24, 345-353. (41) Gregg, S.J.; Sing, K.S.W. Adsorption, Surface Area and Porosity; Academic Press: New York, 1991. (42) Lowell, S.; Shields, J.E.; Thomas, M.A.; Thommes, M. Characterization of Porous Solids and Powders: Surface Area, Pore Size and Density; Kluwer Academic Publishers: Dordrecht, 2004.
(43) Caglar, B.; Cubuk, O.; Demir, E.; Coldur, F.; Catir, M.; Topcu, C.; Tabak, A. Characterization of AlFe-Pillared Unye Bentonite: A Study of the Surface Acidity and Catalytic Property. J. Mol. Struct. 2015, 1089, 59-65. (44) Rouquerol, F.; Rouquerol J.; Sing, K.S.W.; Maurin G.; Llewellyn, P. Adsorption by Powders and Porous Solids: Principles, Methodology and Applications; Elsevier: Amsterdam, 2014. (45) Xue, A.; Zhou, S.; Zhao, Y.; Lu, X.; Han, P. Effective NH2-Grafting on Attapulgite Surfaces for
Adsorption of Reactive Dyes. J. Hazard. Mater. 2011, 194, 7-14. 27 ACS Paragon Plus Environment
Page 45 of 62
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels
(46) Zhang, J.; Wang, Q.; Chen, H.; Wang, A. XRF and Nitrogen Adsorption Studies of AcidActivated Palygorskite. Clay Miner. 2010, 45, 145-156. (47) Zhang, J.; Zhang, L.; Lu, J.; Zhou, S.; Chen, H.; Zhao, Y.; Wang, X. Exceptional Visible-Light-
Induced Photocatalytic Activity of Attapulgite–BiOBr–TiO2 Nanocomposites. Appl. Clay Sci. 2014, 90, 135-140.
(48) Phung, T.; Herrer, C.; Larrubi, M.; García-Diéguez, M.; Finocchio, E.; Alemany, L.; Busca, G. Surface and Catalytic Properties of Some γ-Al2O3 Powders. Appl. Catal. A 2014, 483, 41-51. (49) Shen, J.; Li, Z.; Wu, Y.; Zhang, B.; Li, F. Dendrimer-Based Preparation of Mesoporous Alumina Nanofibers by Electrospinning and their Application in Dye Adsorption. Chem. Eng. J. 2015, 264, 4855. (50) Frost, R.L.; Cash, G. A.; Kloprogge, J.T. ‘Rocky Mountain Leather’, Sepiolite and Attapulgite An Infrared Emission Spectroscopic Study. Vib. Spectrosc. 1998, 16, 173-184. (51) Boudriche, L.; Calvet, R.; Hamdi, B.; Balard, H. Surface Properties Evolution of Attapulgite by IGC Analysis as a Function of Thermal Treatment. Colloids Surf. A 2012, 399, 1-10. (52) Suárez, M.; García-Romero, E. FTIR Spectroscopic Study of Palygorskite: Influence of the Composition of the Octahedral Sheet. Appl. Clay Sci. 2006, 31, 154-163. (53) Chahi, A.; Petit, S.; Decarreau, A. Infrared Evidence of Dioctahedral–Trioctahedral Site Occupancy in Palygorskite. Clays Clay Miner. 2002, 50, 306-313. (54) Blanco, C.; Herrero, L. J.; Mendioroz, S.; Pajares, J. A. Infrared Studies of Surface Acidity and Reversible Folding in Palygorskite. Clays Clay Min. 1988, 36, 364-368. (55) Serna, C.; Van Scoyoc, G.E.; Ahlrichs, J.L. Hydroxyl Groups and Water in Palygorskite. Am. Mineral. 1977, 62, 784-792.
(56) Bodoardo, S.; Figueras, F.; Garrone, E. IR Study of Brønsted Acidity of Al-Pillared Montmorillonite. J. Catal. 1994, 147, 223-230. 28 ACS Paragon Plus Environment
Energy & Fuels
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 46 of 62
(57) Madejova, J.; Komadel, P. Baseline Studies of the Clay Minerals Society Source Clays: Infrared Methods. Clays Clay Miner. 2001, 49, 410-432. (58) Busca, G. The Surface of Transitional Aluminas: A Critical Review. Catal. Today 2014, 226, 213. (59) Breen, C.; Deane, A. T.; Flynn, J. J. The Acidity of Trivalent Cation-Exchanged Montmorillonite. Temperature-Programmed Desorption and Infrared Studies of Pyridine and N-Butylamine. Clay Miner. 1987, 22, 169-178. (60) Kalevaru, V.N.; Benhmid, A.; Radnik, J.; Pohl, M.M.; Bentrup, U.; Martin, A. Marked Influence of Support on the Catalytic Performance of PdSb Acetoxylation Catalysts: Effects of Pd Particle Size, Valence States, and Acidity Characteristics. J. Catal. 2007, 246, 399-412. (61) Volckmar, C.; Bron, M.; Bentrup, U.; Martin, A.; Claus, P. Influence of the Support Composition on the Hydrogenation of Acrolein over Ag/SiO2–Al2O3 Catalysts. J. Catal. 2009, 261, 1-8. (62) Crépeau, G.; Montouillout, V.; Vimont, A.; Mariey, L.; Cseri, T.; Maugé, F. Nature, Structure and Strength of the Acidic Sites of Amorphous Silica Alumina: An IR and NMR Study. J. Phys. Chem. B 2006, 110, 15172-15185. (63) Zaki, M.I.; Hasan, M.A.; Al-Sagheer, F.A.; Pasupulety, L. In Situ FTIR Spectra of Pyridine
Adsorbed on SiO2-Al2O3, TiO2, ZrO2 and CeO2: General Considerations for the Identification of Acid Sites on Surfaces of Finely Divided Metal Oxides. Colloids Surf., A 2001, 190, 261-274. (64) Gil, A.; Vicente, M.A.; Korili, S.A. Effect of the Si/Al Ratio on the Structure and Surface Properties of Silica-Alumina-Pillared Clays. J. Catal. 2005, 229, 119-126. (65) Neubauer, R.; Husmann, M.; Weinlaender, C.; Kienzl, N.; Leitner, E.; Hochenauer, C. Acid Base Interaction and its Influence on the Adsorption Kinetics and Selectivity Order of Aromatic Sulfur Heterocycles Adsorbing on Ag-Al2O3. Chem. Eng. J. 2017, 309, 840-849.
29 ACS Paragon Plus Environment
Page 47 of 62
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels
(66) Randhawa, N.S.; Das, N.N.; Jana, R.K. Adsorptive Remediation of Cu(II) and Cd(II) Contaminated Water using Manganese Nodule Leaching Residue. Desalin. Water Treat. 2014, 52, 4197-4211. (67) Allen, S.J.; McKay, G.; Khader, K.Y.H. Intraparticle Diffusion of a Basic Dye during Adsorption onto Sphagnum Peat. Environ. Pollut. 1989, 56, 39-50. (68) Rouquerol, F., Rouquerol, J., Sing, K. Adsorption by Powders and Porous Solids. Principles, Methodology and Applications; Academic Press: London, 1999.
(69) Giles, C.; Macewans, T.; Nakhwaa, S.; Smith, N. Studies in Adsorption. Part XI. A System of Classification of Solution Adsorption Isotherms, and its Use in Diagnosis of Adsorption Mechanisms and in Measurement of Specific Surface Areas of Solids. J. Chem Soc. 1960, 3973-3993.
30 ACS Paragon Plus Environment
Energy & Fuels
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 48 of 62
FIGURES
Figure 1
31 ACS Paragon Plus Environment
Page 49 of 62
Clay A
Quantity adsorbed (mmol g )
Clay B
-1
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels
Clay C
Alumina
0.0
0.2
0.4
0.6
0.8
1.0
Relative pressure (p/p0)
Figure 2
32 ACS Paragon Plus Environment
Energy & Fuels
3739
3631
3673
3743
3718
3638 3619
3700 3600 3500 Wavenumber (cm-1)
Clay B
Absorbance
Absorbance
3587
Clay A
3800
3800
3400
3700 3600 3500 Wavenumber (cm-1)
3400
3693 3636
3730
3625 3655 3666
Clay C
3742
3800
3700 3600 3500 Wavenumber (cm-1)
3400
Alumina
Absorbance
Absorbance
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 50 of 62
3779
3900
3800 3700 3600 3500 Wavenumber (cm-1)
3400
Figure 3
33 ACS Paragon Plus Environment
Page 51 of 62
1451
Clay A
Alumina Absorbance
1448
Absorbance
1616
1599 1576
1610
1492
1494
1621
1700 1650 1600 1550 1500 1450 1400 1350 Wavenumber (cm-1)
1577
1543
1700 1650 1600 1550 1500 1450 1400 1350 Wavenumber (cm-1) 1622
Clay B
1638
Clay C 1612
Absorbance
1622
Absorbance
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels
1491 1455
1454
1491
1637
1545
1545
1576
1577
1650 1600 1550 1500 1450 1400 1350 Wavenumber (cm-1)
1700 1650 1600 1550 1500 1450 1400 1350 Wavenumber (cm-1)
Figure 4
34 ACS Paragon Plus Environment
Energy & Fuels
0.20
0.15
-1
qe (mol S kgadsorbent)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 52 of 62
0.10
0.05
0.00 0
50
100
150
200
250
300
350
Time (min)
Figure 5
35 ACS Paragon Plus Environment
Page 53 of 62
0.15
0.10
-1
qe (mol N kgadsorbent)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels
0.05
0.00 0
50
100
150
200
250
300
350
Time (min)
Figure 6
36 ACS Paragon Plus Environment
Energy & Fuels
0.20
0.20
Alumina
-1
qt (mol S kgadsorbent)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 54 of 62
Clay A
0.15
0.15
0.10
0.10
0.05
0.05
0.00
0.00 0
5
10
15
20
0
5
10
15
20
0.20 0.15 0.15 0.10 0.10 0.05 0.05 0.00
Clay B
Clay C
0.00 0
5
10
15
20 1/2
0
5
10
15
20
1/2
Time (min )
Figure 7
37 ACS Paragon Plus Environment
Page 55 of 62
0.15
0.15
Clay A
Alumina 0.10
0.10
0.05
0.05
-1
qt (mol N kgadsorbent)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels
0.00
0.00 0
5
10
15
20
0
0.15
0.15
0.10
0.10
0.05
0.05
5
10
Clay B
15
20
Clay C
0.00
0.00 0
5
10
15
20 1/2
0
5
10
15
20
1/2
Time (min )
Figure 8
38 ACS Paragon Plus Environment
Energy & Fuels
4000
A
500
Clay A Clay B
B
Clay A Clay B
400 3500 300
-1
Ce (mol kg )
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 56 of 62
3000 200 2500 100
2000 0.0
0.2
0.4
0.6
0.8
0 0.0
0.2
0.4
0.6
0.8
-1
Adsorbent dose (g mL )
Figure 9
39 ACS Paragon Plus Environment
Page 57 of 62
0.6 0.5 0.4
-1
qe (mol S kgadsorbent)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels
0.3 0.2 0.1 0.0 0.05
0.06
0.07
0.08
0.09
0.10
-1
Ce (mol S L )
Figure 10
40 ACS Paragon Plus Environment
Energy & Fuels
0.4
0.3
-1
qe(mol N kgadsorbent)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 58 of 62
0.2
0.1
0.0 0.00
0.01
0.02
0.03
-1
Ce (mol N L )
Figure 11
41 ACS Paragon Plus Environment
Page 59 of 62
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels
FIGURE CAPTIONS
Figure 1. X-ray diffractograms of Clays A, B, and C. () attapulgite, () quartz, () dolomite, () montmorillonite, () plagioclase. Figure 2. Nitrogen adsorption/desorption isotherms of Clay A (), Clay B (), Clay C (), and Alumina (). Figure 3. Infrared spectra in the OH stretching region for Alumina, Clay A, Clay B, and Clay C. Figure 4. Infrared spectra of pyridine adsorbed on Alumina, Clay A, Clay B and Clay C at 150 °C. Figure 5. Adsorption kinetics of sulfur compounds on Alumina (), Clay A (), Clay B (), Clay C (). Experimental conditions: 10 mL of diesel and 2 g of adsorbent under stirring of 150 rpm at 40 °C. Alumina, Clay A and Clay B adjusted with first-order model; Clay C adjusted with pseudo-second order model. Figure 6. Adsorption kinetics of nitrogen compounds on Alumina (), Clay A (), Clay B (), Clay C (). Experimental conditions: 10 mL of diesel and 2 g of adsorbent under stirring of 150 rpm at 40 °C. Alumina adjusted with first-order model; Clay A and Clay B adjusted with pseudo-first order model; Clay C adjusted with pseudo-second order model. Figure 7. Weber-Morris intraparticle diffusion plot for sulfur compounds adsorption on Alumina (), Clay A (), Clay B (), Clay C (). Experimental conditions: 10 mL of diesel and 2 g of adsorbent under stirring of 150 rpm at 40 °C. Figure 8. Weber-Morris intraparticle diffusion plot for nitrogen compounds adsorption on Alumina (), Clay A (), Clay B (), Clay C (). Experimental conditions: 10 mL of diesel and 2 g of adsorbent under stirring of 150 rpm at 40 °C.
42 ACS Paragon Plus Environment
Energy & Fuels
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 60 of 62
Figure 9. Effect of adsorbent dose on the adsorption of sulfur (A) and nitrogen (B) compounds on Clay A () and Clay B (). Experimental conditions: 10 mL of diesel and 6.0, 4.0, 2.0, 1.0, 0.5, 0.33, 0.2 g of adsorbent under stirring of 150 rpm at 40 °C. Figure 10. Adsorption isotherm of sulfur compounds in diesel using Clay A and Clay B as adsorbents. Experimental conditions: 10 mL of diesel; 40 (: Clay A;
:
Clay B) and 70 (: Clay A; : Clay B)
°C; 8 h; atmospheric pressure.
Figure 11. Adsorption isotherm of nitrogen compounds in diesel using Clay A and Clay B as adsorbents. Experimental conditions: 10 mL of diesel; 40 (: Clay A; : Clay B) and 70 (: Clay A; : Clay B) °C; 8 h; atmospheric pressure.
43 ACS Paragon Plus Environment
Page 61 of 62
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels
TABLES Table 1. Adsorbents chemical composition. Chemical composition (wt%) Sample
Si/Al molar ratio SiO2
Al2O3
CaO
MgO
Fe2O3
-
99.6
-
-
-
-
Clay A
68.7
1.1
10.0
13.6
3.9
53
Clay B
74.9
16.3
-
5.6
1.5
3.9
Clay C
72.1
16.1
-
6.1
2.3
3.8
Alumina
Table 2. Textural and acid properties of the adsorbents.
Sample
Specific area (m2 g-1)
Mesoporous volume(a) (cm3 g-1)
Microporous volume(b) (cm3 g-1)
Pore diameter (nm)
Acid site density(c) (µmol NH3 g-1)
Alumina
357
0.34
0.02
5
297
Clay A
95
0.45
0.01
22
74
Clay B
198
0.21
0.01
6
127
Clay C
273
0.30
0.02
9
88
(a)
: BJH method;
(b)
(c)
: t-plot method; : measured by TPD of NH3.
44 ACS Paragon Plus Environment
Energy & Fuels
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 62 of 62
Table 3. Kinetic parameters for each adsorbent for sulfur compounds adsorption. Model 1: firstorder; Model 2: pseudo-first order; Model 3: pseudo-second order. qe,exp and qe,cal (mol kg-1), k1 (min-1), k-1 (min-1L-1), k2 (min-1), k3 (kg g-1 min-1). Model 1 Adsorbent
Model 2
Model 3
qe,exp
k1
k-1
qe,cal
R2
k2
qe,cal
R2
k3
qe,cal
R2
Alumina
0.056
0.081
0.645
0.059
0.937
0.860
0.057
0.928
2.426
0.057
0.927
Clay A
0.018
0.359
10.0
0.018
0.595
2.000
0.018
0.595
10.00
0.018
0.573
Clay B
0.179
0.152
0.310
0.174
0.987
0.415
0.184
0.966
0.121
0.183
0.987
Clay C
0.128
0.064
0.205
0.126
0.998
0.260
0.128
0.997
0.128
0.127
0.999
Table 4. Kinetic parameters for each adsorbent for nitrogen compounds adsorption. Model 1: first-order; Model 2: pseudo-first order; Model 3: pseudo-second order. qe,exp and qe,cal (mol kg-1), k1 (min-1), k-1 (min-1L-1), k2 (min-1), k3 (kg g-1 min-1). Model 1 Adsorbent
qe,exp
k1
k-1
qe,cal
Model 2 R2
k2
qe,cal
Model 3 R2
k3
qe,cal
R2
Alumina
0.063 0.005 0.011
0.058
0.9571 0.016 0.058
0.9570 0.041
0.054
0.9537
Clay A
0.079 0.070 0.081
0.074
0.992
0.118 0.078
0.996
0.192
0.077
0.987
Clay B
0.125 0.013 0.033
0.125
0.989
0.016 0.126
0.989
0.017
0.114
0.973
Clay C
0.114 0.013 0.005
0.116
0.965
0.020 0.114
0.965
0.031
0.108
0.968
45 ACS Paragon Plus Environment
