- Email: [email protected]
Characterization of asphaltenic material obtained by treating of vacuum residue with different reactive molecules
Fuel 149 (2015) 8–14
Contents lists available at ScienceDirect
Fuel journal homepage: www.elsevier.com/locate/fuel
Characterization of asphaltenic material obtained by treating of vacuum residue with different reactive molecules S.K. Maity ⇑, S. Kumar, M. Srivastava, A.S. Kharola, K.K. Maurya, S. Konathala, A.K. Chatterjee, M.O. Garg Indian Institute of Petroleum, Dehradun, Uttarakhand 248005, India
h i g h l i g h t s Modification and separation of asphaltene from natural bitumen have been discussed. How the asphaltenes are formed and how it changes the final properties of modified bitumen have been highlighted. Modified asphaltenes have been characterized in details.
a r t i c l e
i n f o
Article history: Received 26 March 2014 Received in revised form 27 October 2014 Accepted 4 November 2014 Available online 21 November 2014 Keywords: Bitumen Asphaltene Modifier XRD SEM
a b s t r a c t Natural bitumen which is generally used for highway paving has a short life cycle, due to traffic load and drastic change of pressure and temperature. To get the appropriate physical properties of this bitumen, it is generally modified by using reactive molecules. In this study, glycerol, styrene, methyl methacrylate (MMA), hydroquinone (HQ), and C18 acrylate molecules are used as modifiers. The required amounts of the modifier and bitumen are heated at 200 °C for 8 h with continuous stirring. The asphaltene is extracted from these modified bitumen by soxhlet process. The physical properties of the dried asphaltene are characterized by XRD, SEM and TGA. Results show that the hardness properties, like penetration, softening point, ductility of the natural bitumen are substantially improved after treatment with the modifiers. XRD results indicate that asphaltenes extracted from the modified bitumens become more compact than the asphaltene from the natural bitumen. The results also show that the number of aromatic sheets increases due to the treatment of natural bitumen with the modifiers. The asphaltene derived from C18-acrylate modified bitumen has the maximum number of aromatic sheets. The presence of vinyl double bond and –COOR functional group in C18-acrylate helps effectively the polymerization reaction between the modifier and the natural bitumen. SEM and TGA results also support the presence of a high degree of polymerization/structural arrangement in the asphaltene obtained from this modified bitumen. Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction Natural bitumen is mainly used for highway paving. However, this base bitumen obtained directly from refinery does not have sufficient strength to withstand sudden stress of excessive loading or stress from low temperature during winter. This bitumen should also be hard enough so that it should not deform at high temperature. To get these properties of the natural bitumen several modifiers or binders are used. It is found in the literature, that air blowing was industrially used for the modification of soft bitumen for hardening. However, it was later found that air blowing increased fragility of the binders as well as higher aging susceptibility which was ⇑ Corresponding author. Tel.: +91 1352525724; fax: +91 135 2660098. E-mail address: [email protected] (S.K. Maity). http://dx.doi.org/10.1016/j.fuel.2014.11.002 0016-2361/Ó 2014 Elsevier Ltd. All rights reserved.
not good for paving purposes [1–3]. Rheological modification of a bitumen with maleic anhydride and dicarboxylic acids was studied by Herrington et al. [4]. It was found that the visco-elastic property of the bitumen changed at lower concentration of the modifiers. It was proposed that this change mainly took place due to the formation of transient networks of bitumen species, linked by hydrogen bonding and dipole–dipole interactions. The aggregation of asphaltenes has been studied by in situ with small angle neutron scattering [5]. Maya, Khafji and Iranian light were used for the different sources of the asphaltene. Around 5 wt% of asphaltene obtained from these sources was mixed with different solvent like decalin, 1-methylnaphthalene and quinoline. The shape and size of these asphaltene aggregates at various temperatures were investigated. It was noted that the size and shape of asphaltene-aggregates changed depending on the source, solvent
9
S.K. Maity et al. / Fuel 149 (2015) 8–14
Nomenclature A B N g s mma hq acl An Bn Ins P25
asphaltene bitumen natural glycerol (CH2OHCHOHCH2OH) styrene (C6H5CH@CH2) methyl methacrylate (CH2@C(CH3)COOCH3) hydroquinone (C6H4(OH)2) C18-acrylate (C21H40O2) asphaltene derived from natural bitumen natural bitumen insoluble penetration at 25 °C
and temperature. Maya asphaltene in decalin solvent forms a fractal network and this network sustains at high temperature like 350 °C, indicating the high coking tendency of Maya crude. Due to the presence of high aromaticity, the Iranian light asphaltene precipitates comprehensively in decline even at lower temperature. In their other studies, Tanaka et al. [6] reported a three main hypothetical aggression of asphaltene as (i) core aggregates are formed by p–p stacking of asphaltene molecules (20 Å size), (ii) medium aggregates are formed by secondary aggregation of core aggregates that result from interactions with maltenes, oils or solvents (50–500 Å) and (iii) fractal aggregates are secondary aggregates of core aggregates that results from diffusion limited cluster aggregation or reaction limited cluster aggregation (which is independent of any media) (size > 1000 Å). It was also concluded by the authors that this model of asphaltene aggregate was a highly simplified model. The usefulness of other recycled waste materials like glass, steel slag, tyres, rubbers and plastics for bitumen pavements has been discussed in detail in the literature [7–11]. Regardless of the chemical used, the reaction conditions and sources of a bitumen, the modification increases asphaltene content in the bitumen cluster and hence the soft property of the bitumen becomes hard. The degree of hardening depends on several factors like-source of bitumen, chemical use and reaction conditions, etc. Although several research work are found in the literature for modification of a bitumen by chemical reaction, still the formation of asphaltenic material and its nature are so complex, that there is no clear explanation of how asphaltenes are formed and how it changes the rheology of the bitumen. But it is proved as stated above that the presence of asphaltene molecules in the bitumen improves significantly its properties and hence it can be used for paving or other purposes. Therefore, in this study, different bitumen modifiers are used and the effects of these modifiers on asphaltene’s properties are examined. For these reasons, glycerol, styrene, methyl methacrylate (MMA), hydroquinone (HQ) and C18-acrylate are used as modifiers. The asphaltenes extracted from these modified bitumen are characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), and thermogravimetric analysis (TGA).
2. Experimental
D27 Kv Mwt FT dm dc Lc M G0 G00 G⁄ d
ductility at 27 °C kinematic viscosity molecular weight fail temperature layer distance between aromatic sheets interchain layer distance average height of stack aromatic sheets molecules of aromatic sheets in a stacked cluster storage modulus loss modulus complex modulus phase angle
quantity of modifier was added and the mixture was stirred for a period of 8 h. All chemicals except C18-acrylate were of commercial grade. C18-acrylate was synthesized in our laboratory according to the procedure given elsewhere [12]. Asphaltene was extracted from the modified bitumen by soxhlet process. In this process the modified bitumen was taken with n-heptane (ten times of bitumen) solvent into a round bottle. The mixture was then refluxed for a period of 6 h. The insoluble portion was separated and dried in a vacuum oven at 110 °C. A flow diagram of the separation of asphaltene is presented in Fig. 1. 2.2. Characterization of modified bitumens and asphaltenes The physical properties like-penetration, ductility, softening point of the untreated and treated bitumens were measured by standard methods. The penetration is determined by a standard method (ASTM D5) with a penetrometer. In this method, a needle loaded with 100 g was brought to the sample surface at right angle, allowed to penetrate the sample for 5 s at 25 °C. The penetration is measured in deci-millimeter (dmm). The ductility of a sample is measured by ASTM D113 method. In this method a sample was pulled apart at a uniform rate of 5 cm/min. at 27 °C until it ruptured. The elongation or stretch of the sample in centimeter was measured. The softening point was determined by ASTM D 36 method by using ring and ball apparatus. The average molecular weight of the natural and modified bitumen were also measured by Agilent Gel Permeation Chromatography (GPC) using model 1260. The dynamic shear rheometer of TA instrument of model AR 1500eX was used to characterize visco-elastic behavior of natural and modified bitumens. Rheological study was carried out at minimum instrument inertia of 16.85 lN m2 as per ASTM D7175-05. Different rheological parameters like G⁄, d, G⁄/Sin d at 1.1 kPa gives the fail temperature. It is the temperature at which bituminous
Vacuum residue Reaction with chemical at 200OC for 8 hrs Modified Bitumen Soxhlet reflux with n-heptane
2.1. Modification of bitumen and asphaltene separation Vacuum residue (VR, 540 °C+) procured from the Indian refinery (Panipat) was used as a base material (bitumen). Around 200 g of the base material was heated into a flask with continuous mechanical stirring. After getting desired temperature, the required
Asphaltene (Insoluble fraction) Fig. 1. Separation of asphaltenes from vacuum residue.
10
S.K. Maity et al. / Fuel 149 (2015) 8–14
binder lost its binding/adhesive property. Complex modulus (G⁄) is the resultant of storage modulus (G0 ) and loss modulus (G00 ) and is calculated by the following equations.
qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi G ¼ G02 þ G002 G ¼
qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 2 2 ðG cos dÞ þ ðG sin dÞ
ð1Þ ð2Þ
where d is the phase angle. All the rheological parameters G0 , G00 , d and G⁄/sin d are temperature dependent and were determined to define performance of a bitumen. In this study all rheological parameters were measured at angular frequency of 10 rad/s and at controlled constant percentage strain of 12.0%. These measurements were taken in the temperature range of 42–82 °C with an increment of 6 °C. G⁄ define resistance to deformation and is a function of G0 , G00 and d in the viscoelastic region (0 < d < 90). X-ray diffraction (XRD) of asphaltene was studied in the powder samples by using a model Rigaku Denki. For this analysis Cu K1 radiation operating at 40 kV and 30 mA in the range of 2–60° of 2h was used. The crystalline parameters, like layer distance between aromatic sheets were calculated by using the Bragg equation.
dm ¼
k 2 sin h
ð3Þ
The distance between the saturate portion of the molecules or interchain layer distance was calculated by using an equation:
dc ¼
5k 8 sin h
ð4Þ
The average height of the stack aromatic sheets perpendicular to the plane of the sheets was calculated by using the following equation.
Lc ¼
0:45 B1=2
ð5Þ
where B1/2 is the full width at half maximum (FWHM), obtained from the graphene band. The molecules of aromatic sheets in a stacked cluster (M) were also calculated from Eqs. (3) and (5) as
M¼
Lc þ1 dm
ð6Þ
The morphology of asphaltene samples was also determined by using SEM, model quanta 200F. The asphaltenes obtained from the natural and modified bitumens were also characterized by thermogravimetric analysis by using Perkin-Elmer model TGA-4000. In this experiment around 10 mg of the bitumen sample was heated from room temperature to 900 °C at a rate of 10 °C/min in the presence of air (flow 50 mL/min). 3. Results and discussion 3.1. Physical properties of modified bitumen In this study the reference material i.e. bitumen was collected from Indian refinery and its properties were given in Table 1. Table shows that our reference bitumen (Bn) contains 11.4 wt% insoluble. The penetration value of this unmodified bitumen is 130 dmm. This material is also comparatively soft in nature and its softening point (SP) is as low as 38 °C. This bitumen was treated with different reactive molecules to get appropriate physical properties. Almost all the treatment was performed in the presence of glycerol as co-additive. Changes of physical properties of the treated bitumen have been compared with untreated bitumen in Table 2. Sample Bg is the modified bitumen with 0.3 wt% glycerol.
Table 1 Physico-chemical characteristics of natural bitumen (Bn). Properties
Value
Density (15 °C) API gravity Flash point (°C) Viscosity (cSt at 135 °C) Aromaticity (by NMR) Saturates (wt%) Naphthenic aromatics (wt%) Polar aromatics (wt%) Asphaltene (wt%)
1.0134 8.05 252 182 0.44 6.18 55.03 27.37 11.42
It is noticed from Table 2 that the percentage of asphaltene like aggregate molecules (Ins) increases from 11.4 to 20.7 wt%. The softening point is also improved (from 38 to 48 °C). The sample Bg also becomes hard in nature and this can be seen from the penetration value. P25 value of the natural bitumen is 130 dmm and it decreases to 50 dmm after treatment with glycerol. Formation of the maximum amount of asphaltene is noticed in sample Bacl which is treated with C18-acrylate. Its asphaltene percentage is as high as 91 wt%. P25 value of this sample is reduced substantially. The samples Bhq which is obtained by treatment of bitumen with hydroquinone also has a high percentage of asphaltene aggregate. And therefore, their P25 and SP values are also improved significantly. The kinematic viscosity at 135 °C of Bn, Bmma and Bacl samples were measured and given in Table 2. The viscosity values also indicate the presence of large molecules in the modified bitumen. The molecular weight values also support this fact. The molecular weight of natural bitumen increases from 1730 to 2862 g/mol when it is treated with C18-acrylate. Similarly the fail temperature (FT) that gives indication of visco-elastic behavior of bitumen, also increases due to the reaction of natural bitumen with modifiers. From these studies, it is clear that with increased percentage of asphaltene aggregate, penetration value decreases whereas SP values increase. Improvement of both these properties is required in bitumen so that it can be used for paving or other purposes. It is also found in the literature that maleic anhydride improves significantly temperature sensitivity [4]. The viscoelastic properties (complex modulus, G⁄ and phase angle, d) as a function of temperature for samples Bn, Bmma and Bacl were measured and presented in Fig. 2. The complex modulus G⁄ decreases with increase in temperature due to decrease in magnitude of G⁄/sin d and increase in phase angle d with temperature. The modified bitumens have high G⁄ than natural bitumen at the same temperature. Data shows that G⁄ of methyl methacrylate modified bitumen is 6677 Pa at 60 °C while that of natural bitumen is 2570 Pa. This indicates that complex modulus increases when natural bitumen is modified with methyl methacrylate even it increases substantially in case of C18-acrylate modified bitumen. This concludes that modified bitumens are more resistant to permanent deformation and have good storage stability in comparison of natural bitumen [7,9,13]. The softening point is higher in the bitumen having high asphaltene-aggregates. Therefore, it is the asphaltene cluster that most significantly affects the strength and softening point of a bitumen [14,15]. A considerable research was carried out in the past few years for the modification of bitumen by several others molecules. Among them the use of styrene is well known. It is believed that styrene–butadiene–styrene copolymer absorbs the oil fraction (maltenes) of the bitumen and it leads to swelling of the bitumen. It makes a rubber–elastic network within the modified binder. The nature of network and finally its effect on the bitumen properties depends on the base bitumen, the nature and content of the polymer, bitumen–polymer compatibility. It is very important to aggregate the appropriate amount of polymer into the
11
S.K. Maity et al. / Fuel 149 (2015) 8–14 Table 2 Physical characteristics of natural bitumen (Bn) and modified bitumens. Name
Modifiers (wt%) g
Bn Bg Bs Bmma Bhq Bacl
0.3 0.3 0.3 – 0.3
s
Physical properties mma
hq
acl
0.45 2.3 0.2 0.8
Ins (wt%)
P25 (dmm)
SP (°C)
11.4 20.7 27.5 48.2 80.3 90.8
130 50 45 33 13 12
38 48 49 57 72 70
D27 (cm)
+90 61.5 6.5
Mwt (g/mol)
FT (°C)
182
1730
66
745
2432
72
2153
2862
96
kV cSt at 135 °C
3.2. X-ray diffraction
bitumen, otherwise phase separation between maltenes and asphaltene can occur. This phase separation can be considered as incompatibility between styrene and bitumen [16]. It is found that paraffinic bitumen shows a greater degree of polymerization than naphthenic bitumen. It is also said that during reaction of a bitumen with a polymer, two phases like structure is formed-one is polymer-rich phase and other is asphaltene rich phase. This asphaltene rich phase mostly contributes to characteristics of a bitumen. A similar explanation can be given in this study also. From Table 2, it is found that the percentage of insoluble material increases substantially, however, the hardness of these insoluble phases does not increase proportionately. For an example, sample Bhq contains 80 wt% of insoluble and its P25 value is 13. This value does not improve significantly with further increase of insoluble content. It can explain that all insoluble parts do not contribute to the formation of asphaltene. There may be some naphthenic (polymerized) material which is also insoluble in n-heptane. These naphthenic material may not be as hard as asphaltene. It was categorically stated in the literature [1], that the solid particles insoluble in n-heptane was significantly higher than the true asphaltene content in bitumen. It was said that n-heptane was not exactly a solvent equivalent to the maltenes. Therefore, the solid phase in a bitumen was actual asphaltene and adsorbed resins and hence the amount of insoluble (asphaltene + adsorbed resins) was much higher than actual asphaltene present in a bitumen. The percentage of insoluble material in our case is very high after reaction. Therefore, it is likely that not only resin but also naphthenic compounds present in vacuum residue also contribute as n-heptane insoluble material. It can be concluded that in the presence of reactive molecules like glycol, styrene, C18-acrylate, the insoluble material from vacuum residue is separated in a certain order form. These reactive molecules help to form a three dimensional network by linking one asphaltenic structure to another and thus it improves the hardness of the bitumen.
Iintensity (a.u)
Fig. 2. Complex modulus as a function of temperature for natural and modified bitumens.
X-ray diffraction of asphaltene samples was analyzed and the diffractogram of selected samples are presented in Fig. 3. Figure shows that most of the peaks appear at around 2h value of 20° and 25°. The doublet of c peak appears at around 20° = 2h which is mainly due to the aliphatic chains or condensed saturated rings. Peak at around 25° = 2h is graphene band. These graphenes are formed by the staging of aromatic molecules present in the asphaltenic structure. There are also possibilities to appear other two peaks at a higher 2h value and that are due to the reflection of first (1 0 0) and second (1 1 0) nearest neighbors in the ring structure [17–20]. And the peak intensities due to these bands are very week compared with two main bands of c and graphene as stated above. It is observed from figure that the doublet c peak appears at 19.25 = 2h of the natural asphaltene (An). The 2h values vary in between 19.25 and 22.65 for other modified asphaltenes. For an example, it appears at 21.5° = 2h for sample Ag whereas it is at 22.65° for Aacl. From figure it is also found that the peak intensities of c and graphene in sample Ahq are more compared with the reference sample An. The different crystalline parameters calculated from the graphene bands of asphaltene are summarized in Table 3. The average layer distance between the sheets (dm) of natural asphaltene (An) is 3.7 Å which decreases to 3.5X Å (X = 4 or 5 or 6) for the modified asphaltenes. This suggests that when the natural bitumen is treated with a modifier, during the reaction asphaltene becomes more compact. These results are consistent with the results documented in the literature [6,17,20]. Similarly, average inter-chain layer distance (dc) also reduces from 4.63 to 4.4X Å (X = 2 or 4 or 6). So it
Aacl
Ahq
An
40
20
2Ɵ Fig. 3. X-ray diffractograms of natural and modified asphaltenes.
12
S.K. Maity et al. / Fuel 149 (2015) 8–14
Table 3 Crystallite parameters of different asphaltenes. Sample
An Ag As Amma Ahq Aacl
Crystallite parameters dm (Å)
dc (Å)
Lc (Å)
M
3.7 3.54 3.55 3.56 3.76 3.54
4.63 4.42 4.44 4.46 4.70 4.41
18.18 23.06 33.7 36.01 39.85 43.85
5.91 7.52 10.49 11.1 11.61 13.42
also suggests that both the condensed aromatic as well as aliphatic layer becomes more compact due to aging reaction with reactive molecules. Siddiqui et al. [17] have also reported that during short term aging both aromatic ring and aliphatic chain of the asphaltene becomes compact and condensed. However, with further aging the compactness of asphaltene structure does not change. This compactness of the asphaltene also improves the hardness property of the bitumen. The average stack height of the aromatic sheets perpendicular to the plane (Lc) has also been calculated and it is within the range of 18.18–43.85 Å. The number of aromatic sheets in a stacked asphaltene cluster is 5.91 for natural asphaltene and it increases after the treatment with functional molecules. The maximum number of aromatic sheet is found in the sample that is derived from bitumen treated with C18-acrylate. It indicates that the functional group or groups present in the reactive molecule take part in the polymerization reaction. The degree of polymerization is the maximum when the natural bitumen reacts with C18-acrylate molecule and as a result, the number of aromatic sheet is more in this modified bitumen. When natural bitumen is treated with glycol (the smallest molecule having only OH group) the number
of aromatic sheet increases from 5.91 to 7.52 but this value reaches maximum 13.42 when this bitumen is treated with the C18-acrylate (the biggest molecule having both C@C and ACOOR functional groups). Therefore, it also suggests that the degree of polymerization not only depends on the molecular weight but also on the functional groups present in the modifier. 3.3. Scanning electron microscope The surface images of different asphaltene molecules are taken by SEM and are presented in Fig. 4. Fig. 4 (An) shows that asphaltene is similar to the colloidal particles. It suggests that the asphaltene particles are mixed with some resin molecules. Fig. 4 (An) also shows that the presence of cavities which are the precursor of pores. The sizes of the cavities vary from 14.12 to 22.10 lm and the colloidal particle sizes are around 21.3 to 27.97 lm. So, the images clearly show that the asphaltene obtained from natural bitumen is still not a matured state. The colloidal behavior of the asphaltene molecules in a bitumen has been detailed discussed by Lesueur [1]. In another word, it can be said that small amount resin (which is liquid) may also present with the asphaltene. As it has been stated earlier that the solid phase in a bitumen is actual asphaltene and adsorbed resins and hence the amount of insoluble (asphaltene + adsorbed resins) is high. The formation of asphaltene particles however is observed in Fig. 4 (Ag). The image is cauliflower like structure and the colloidal type particle structure are not present. The formation of cauliflower like structure has also been reported by others [21–26]. This image also reveals the inhomogeneity of the asphaltene particles. The different size and shape of the particles are clearly noticed. It is worth to mention that this asphaltene is extracted from the bitumen that is treated with glycerol. A complete different type of images for asphalting particles are noticed in Fig. 4 (Amma) for the sample which was obtained after
An
Ag
Amma
A acl
Fig. 4. SEM images of natural asphaltene An, and modified asphaltenes Ag, Amma and Aacl.
S.K. Maity et al. / Fuel 149 (2015) 8–14
treatment of bitumen with methyl methacrylate. The image appears like a cloud. The image also indicates inhomogeneity of the asphaltene particles. The formation of porous structure which is reported by other [21,22] is not clearly observed in this case. Only some pore cavities with a size of 1.36–4.10 lm are noticed. A smooth surface with several layers can be observed in Fig. 4 (Aacl). The growth of different shape and size of asphaltene particles is noticed. The asphaltene in this case is obtained from bitumen, which is treated with the heaviest reactive molecule, C18-acrylate. From the above discussion, it is established that the surface structure of asphaltenes are different for the asphaltenes obtained from the different modified bitumens. The surface heterogeneity is everywhere with respect to size, shape and appearance. Although there are pore cavities in some cases, but a usual pore structure in asphaltene is absent in this present work. Quantitative analysis of different elements present in asphaltene has also been studied by SEM-EDX and the results are presented in Table 4. The data given here is an average value of the elements analyzed at different locations. Carbon, oxygen and sulfur are the most abundant elements found in the asphaltene samples. The percentage of oxygen present in asphaltene increases when the bitumen is treated with oxygen containing compounds, i. e. glycerol, methyl methacrylate, C18-acrylate, etc. The O/C ratio has also been calculated and the same increasing trend is observed. A plausible reason for the presence of extra oxygen in asphaltene is from the bitumen’s modifiers. However, it is not so simple; the degree of polymerization also needs to be considered. The O/C ratios of samples Ag and Aacl are 0.07 and 0.11 respectively, but the present of oxygen (with respect to carbon) in chemical structure in glycerol is much more than that in C18 acrylate. It explains that since the degree of polymerization in sample Aacl is much higher than that in sample Ag hence more oxygen is present in sample Aacl. It is also noticed that the percentage of sulfur decreases due to treatment of the natural bitumen. It is due to the presence of more oxygen and carbon present in the modified asphaltenes. It is also possible that sulfur is removed from the system [1]. 3.4. Thermogravimetric analysis (TGA) Weight loss due to combustion of asphaltenes derived from natural bitumen (An) and modified bitumens has been measured by thermogravimetric analysis and it is presented in Fig. 5(a). This figure shows that around 97 wt% of An is burned in the presence of air. However, other two samples (Amma and Aacl) are completely burned at around 630 °C. The weight loss respect to temperature for these two samples are identical. The derivatives of weight loss with temperature are also presented in Fig. 5(b). All derivative curves clearly show two principal weight losses at around 460 °C and at 580 °C, indicating that there are two types of asphaltenes are present. One is burned at lower temperature, named as soft asphaltene and other at higher temperature, named as hard asphaltene. Both of the peaks are sharp in nature. The presence of two types of coke (obtained mainly polymerization of asphaltene) is also reported in the literature [27,28]. First asphaltene combustion temperature (Tm) of An is 465 °C and it is shifted towards lower temperature for Amma and Aacl. However, 2nd Tm of the reference sample appears at 581 °C and it is shifted to the higher temperature of the sample Table 4 Elements distribution in different asphaltenes measured by SEM-EDX.
C (wt%) O (wt%) S (wt%) O/C
An
Ag
Amma
Aacl
91.4 5.3 3.3 0.06
91.7 6.4 1.9 0.07
88.9 9.1 2.0 0.10
89.2 9.7 1.1 0.11
13
Fig. 5. TGA curves of (a) weight loss, and (b) derivative weight of asphaltene derived from bitumens.
Amma and Aacl. It suggests that the hard asphaltene of the natural bitumen becomes harder when this is treated with the modifiers. This is also in agreement with of our other physical properties of the bitumens. Other than these two principal peaks, a small peak at lower temperature (around 400 °C) is also observed in all three samples. The intensity of this small peak is high for the An sample and this intensity decreases in the asphaltene obtained from modified bitumens. It is also clearly observed from this figure that the intensity of 1st main peak is higher than that of 2nd peak in sample An. But the reverse trend is noticed in the other two samples, i.e. the intensity of the 2nd peak in Amma and Aacl samples is higher than that of 1st peak. It indicates that the concentration of hard asphaltene increases due to the modification of natural bitumen with reactive molecules. From our TGA results it can be concluded that there is no new material is formed due to the reaction of active modifier with natural bitumen. However, the nature of asphaltenes derived from modified bitumens become harder. This is with the good agreement with the other physical properties presented in this work. Asphaltene is one of the components present in the petroleum crude and defined as insoluble in n-heptane but soluble in toluene. It contains millions of different molecules, including heteroatoms such as nitrogen, oxygen, sulfur and metals, mainly iron, nickel and vanadium. It is so complex molecule that the structure of it is not well known so far. However, it remains in the center of the research for many years to understand its behavior during refinery processes and its visco-elastic building role in a bitumen. It is a condensed aromatic rings in a planer form which can be associated through pi bonding to form graphite-like structure [1]. The nature of natural bitumen is different and it depends on its source. This bitumen is comparatively soft in nature and is not suit-
14
S.K. Maity et al. / Fuel 149 (2015) 8–14
able for its application in road-paving. However, hardness properties of this bitumen can be improved by chemical reaction with foreign molecules or even by air blowing. Moschopedis and Speight [29] observed that the asphaltenes molecular weight increased by 3/2 of its original value upon air blowing at moderate temperature. It was observed by the authors that due to the air blowing, the ratios of H/C, N/C and S/C were decreased while the ratio of O/C was increased, indicating that oxygen uptake in the asphaltenes was developed whereas nitrogen and sulfur were released from the system. It was concluded that asphaltenes were produced during air blowing by polymerization reaction [29–31]. The modification of visco-elastic properties of a bitumen by reaction with a small amount of maleic anhydride, succinic anhydride and dicarboxylic acid was observed by Herrington et al. [4]. It was assumed by the authors that improvement of visco elastic properties of the bitumen occurred due to the hydrogen bonding and dipolar interaction of the bitumen spices. The presence of dipolar interaction has also been reported by others [32]. It was stated that asphaltene in a bitumen was colloidal in nature, consisting of a well packed insoluble asphaltene core and a loose packed periphery, which is more active and easily accessible to solvent or reactive molecules [1]. It is confirmed from this study and other studies reported in the literature that asphaltene mainly contributes the hardness properties of the bitumen. Our XRD, SEM and TGA results and physical properties suggest that the improvement of the hardness properties of a bitumen is mainly due to (i) increase in asphaltene content, (ii) compactness of asphaltene and (iii) the degree of polymerization. Increase in number of graphene layers into the treated bitumen suggests that the reactive molecules help to form a three dimensional networking by linking one asphaltene structure to another may be pi-bonding [5]. This type of networking structure is more when the reactive molecule bigger is in size like C18-acrylate. The presence of both AC@CA and ACOOR may have an important role in polymerization reaction, since C18 acrylate has both these functional groups whereas glycerol has only OH group. Even from our quantitative analysis by SEM shows that the ratio of O/C is more in asphaltene derived from C18-acrylate modified bitumen, indicating a high degree of the polymerization reaction. 4. Conclusions To improve the hardness properties of the natural bitumen, several modifiers like, glycerol, styrene, methyl methacrylate, hydroquinone and C18-acrylate have been used. Results show that hardness properties, like penetration, softening point, ductility of natural bitumen are substantially improved after treatment with reactive molecules. Crystallite properties show that asphaltene cluster becomes more compact due to the modification. The number of aromatic sheets is augmented with the treatment and the maximum number of sheets is found in asphaltene obtained after treatment with C18-acrylate. SEM and TGA results also support the high degree of polymerization for C18-acrylate molecule indicating that the presence of vinyl double bonds and ACOOR functional groups help effectively in this polymerization process. It is also observed that asphaltene cluster is of inhomogeneous nature. During the chemical reaction with reactive molecules, the hardness of the bitumen is improved considerably due to the increasing percentage of highly compact asphaltene. Acknowledgement Authors thank to the director of IIP for his financial support of this work. The authors also thank to Panipat refinery for providing the bitumen.
References [1] Lesueur D. The colloidal structure of bitumen: consequences on the rheology and on the mechanisms of bitumen modification. Adv Colloid Interface Sci 2009;145:42–82. [2] Gorbatovskii AA, Rozental DA, Dronov SV. Structure and composition of polymer–bitumen composites. Russ J Appl Chem 2007;80(5):838–41. [3] Agrawala M, Yarranton HW. An asphaltene association model analogous to liner polymerization. Ind Eng Chem Res 2001;40:4664–72. [4] Herrington PR, Wu Y, Forbes C. Rheological modification of bitumen with maleic and hydride and dicarboxylic acids. Fuel 1999;78:101–10. [5] Tanaka R. Aggregates structure analysis of petroleum asphaltenes with small angle neutron scattering. Energy Fuels 2003;17:127–34. [6] Tanaka R, Sato E, Hunt JE, Winans RE, Sato S, Takanohashi T. Characterization of asphaltene aggregates using X-ray diffraction and small angle X-ray scattering. Energy Fuels 2004;18:1118–25. [7] Lu X, Isacsson U. Chemical and rheological evaluation of ageing properties of SBS polymer modified bitumens. Fuel 1998;77:916–72. [8] Morales MG, Partal P, Navarro FJ, Boza FM, Gallegos C, Gonzalez N. Linear visco-elasticity of recycled eva modified bitumen. Energy Fuels 2004;18:357–64. [9] Morales MG, Partal P, Navarro FJ, Boza FM, Gallegos C, Gonzalez N. Viscous properties and microstructure of recycled eva modified bitumen. Fuel 2004;83:31–8. [10] Huang Y, Bird RN, Heidrich O. A review of the use of recycled solid waste materials in asphalt pavements. Resour Conserv Recycl 2007;52. 85-73. [11] Kumar K, Singh A, Maity SK, Negi S. Use of polymers/waste rubber in road network development in Uttarakhand state. IOSR-JAC 2014;7(6):28–35. [12] Chatterjee AK, Phatak AD, Murthy PS, Joshi GC. Comb-type polymers and their interaction with wax crystals in waxy hydrocarbon fluids: wide-angle X-ray diffraction studies. J Appl Polym Sci 1994;52:887–94. [13] Kumar P, Mehndiratta HC, Singh KL. Rheological properties of crumb rubber modified bitumen-A lab study. J Sci Ind Res 2009;68:812–6. [14] Yen TF, Erdman JG, Pollack S. Investigation of the structure of petroleum asphaltenes by X-ray diffraction. Anal Chem 1961;33:1587–93. [15] Habib NZ, Kamaruddin I, Napiah M, Tan IM. Rheological properties of polyethylene and polypropylene modified bitumen. Int J Civil Environ Eng 2011;3(2):96–100. [16] Airey GD. Rheological properties of styrene butadiene styrene polymer modified road bitumens. Fuel 2003;82:1709–19. [17] Siddiqui MN, Ali MF, Shirokoff J. Use of X-ray diffraction in assessing the aging pattern of asphalt fractions. Fuel 2002;81:51–8. [18] Ebert LB, Scanion JC. Average structure determination for heavy ends in fossil fuels. Liquid Fuel Technol 1984;2(3):257–86. [19] Shirokoff JW, Siddiqui MN, Ali MF. Characterization of the structure of Saudi crude asphaltenes by X-ray diffraction. Energy Fuels 1997;11:561–5. [20] Nazar ARS, Bayandory L. Investigation of asphaltene stability in the Iranian crude oils. Iran J Chem Eng 2008;5(1):3–12. [21] Trejo F, Ancheyta J, Rana MS. Structural characterization of asphaltenes obtained from hydroprocessed crude oils by SEM and TEM. Energy Fuels 2009;23:429–39. [22] Hernández RP, Anaya DM, Galicia GM, Espinosa ME, Lugo VR, Lozada M, et al. Microstructural study of asphaltene precipitated with methylene chloride and n-hexane. Fuel 2003;82:977–82. [23] Berna ACS, Moran VC, Guzmán ETR, Yacamán MJ. Asphaltene aggregation from vacuum residue and its content of inorganic particles. Petrol Sci Technol 2006;24:1055–66. [24] Bragado CGA, Santiago P, Almazo M, Espinosa M, Romero ET, Murgich J, et al. Fullerenic structures derived from oil asphaltenes. Carbon 2002;40: 2761–6. [25] Morales MG, Partal P, Navarro FJ, Gallegos C. Effect of waste polymer addition on the rheology of modified bitumen. Fuel 2006;85:936–43. [26] Litao W, Chen H, Yang L, Suoqi Z, Yahe Z, Chunming X, et al. Effect of experimental conditions on the molecular composition of maltenes and asphaltenes derived from oil sands bitumen: characterized by negative-ion ESI FT-ICR MS. Sci China Chem 2013;56(7):863–73. [27] Maity SK, Blanco E, Ancheyta J, Alonso F, Fukuyama H. Early stage deactivation of heavy crude oil hydroprocessing catalysts. Fuel 2012;10:17–23. [28] Sahoo SK, Ray SS, Singh ID. Structural characterization of coke on spent hydroprocessing catalysts used for processing of vacuum gas oils. Appl Catal A: Gen 2004;278. 83-1. [29] Moschopedis SE, Speight JG. The effect of air blowing on the properties and construction of a natural bitumen. J Mater Sci 1977;12:990–8. [30] Corbett LW, Swarbrick RE. Composition analysis used to explore asphalt hardening. Proc Assoc Asphalt Paving Technol 1960;29:104–12. [31] Kats BI, Glotova NA, Kudryashova AI. Study of aging of asphalts from Romashkino and Ust’-Balyk under natural conditions. Chem Technol Fuels Oils 1976;12:121–4. [32] Cimenoglu MA. Dynamic nuclear polarization in suspensions of asphaltene obtained from MC-20 liquid asphalt. Fuel 2001;80:2014–47.
Contents lists available at ScienceDirect
Fuel journal homepage: www.elsevier.com/locate/fuel
Characterization of asphaltenic material obtained by treating of vacuum residue with different reactive molecules S.K. Maity ⇑, S. Kumar, M. Srivastava, A.S. Kharola, K.K. Maurya, S. Konathala, A.K. Chatterjee, M.O. Garg Indian Institute of Petroleum, Dehradun, Uttarakhand 248005, India
h i g h l i g h t s Modification and separation of asphaltene from natural bitumen have been discussed. How the asphaltenes are formed and how it changes the final properties of modified bitumen have been highlighted. Modified asphaltenes have been characterized in details.
a r t i c l e
i n f o
Article history: Received 26 March 2014 Received in revised form 27 October 2014 Accepted 4 November 2014 Available online 21 November 2014 Keywords: Bitumen Asphaltene Modifier XRD SEM
a b s t r a c t Natural bitumen which is generally used for highway paving has a short life cycle, due to traffic load and drastic change of pressure and temperature. To get the appropriate physical properties of this bitumen, it is generally modified by using reactive molecules. In this study, glycerol, styrene, methyl methacrylate (MMA), hydroquinone (HQ), and C18 acrylate molecules are used as modifiers. The required amounts of the modifier and bitumen are heated at 200 °C for 8 h with continuous stirring. The asphaltene is extracted from these modified bitumen by soxhlet process. The physical properties of the dried asphaltene are characterized by XRD, SEM and TGA. Results show that the hardness properties, like penetration, softening point, ductility of the natural bitumen are substantially improved after treatment with the modifiers. XRD results indicate that asphaltenes extracted from the modified bitumens become more compact than the asphaltene from the natural bitumen. The results also show that the number of aromatic sheets increases due to the treatment of natural bitumen with the modifiers. The asphaltene derived from C18-acrylate modified bitumen has the maximum number of aromatic sheets. The presence of vinyl double bond and –COOR functional group in C18-acrylate helps effectively the polymerization reaction between the modifier and the natural bitumen. SEM and TGA results also support the presence of a high degree of polymerization/structural arrangement in the asphaltene obtained from this modified bitumen. Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction Natural bitumen is mainly used for highway paving. However, this base bitumen obtained directly from refinery does not have sufficient strength to withstand sudden stress of excessive loading or stress from low temperature during winter. This bitumen should also be hard enough so that it should not deform at high temperature. To get these properties of the natural bitumen several modifiers or binders are used. It is found in the literature, that air blowing was industrially used for the modification of soft bitumen for hardening. However, it was later found that air blowing increased fragility of the binders as well as higher aging susceptibility which was ⇑ Corresponding author. Tel.: +91 1352525724; fax: +91 135 2660098. E-mail address: [email protected] (S.K. Maity). http://dx.doi.org/10.1016/j.fuel.2014.11.002 0016-2361/Ó 2014 Elsevier Ltd. All rights reserved.
not good for paving purposes [1–3]. Rheological modification of a bitumen with maleic anhydride and dicarboxylic acids was studied by Herrington et al. [4]. It was found that the visco-elastic property of the bitumen changed at lower concentration of the modifiers. It was proposed that this change mainly took place due to the formation of transient networks of bitumen species, linked by hydrogen bonding and dipole–dipole interactions. The aggregation of asphaltenes has been studied by in situ with small angle neutron scattering [5]. Maya, Khafji and Iranian light were used for the different sources of the asphaltene. Around 5 wt% of asphaltene obtained from these sources was mixed with different solvent like decalin, 1-methylnaphthalene and quinoline. The shape and size of these asphaltene aggregates at various temperatures were investigated. It was noted that the size and shape of asphaltene-aggregates changed depending on the source, solvent
9
S.K. Maity et al. / Fuel 149 (2015) 8–14
Nomenclature A B N g s mma hq acl An Bn Ins P25
asphaltene bitumen natural glycerol (CH2OHCHOHCH2OH) styrene (C6H5CH@CH2) methyl methacrylate (CH2@C(CH3)COOCH3) hydroquinone (C6H4(OH)2) C18-acrylate (C21H40O2) asphaltene derived from natural bitumen natural bitumen insoluble penetration at 25 °C
and temperature. Maya asphaltene in decalin solvent forms a fractal network and this network sustains at high temperature like 350 °C, indicating the high coking tendency of Maya crude. Due to the presence of high aromaticity, the Iranian light asphaltene precipitates comprehensively in decline even at lower temperature. In their other studies, Tanaka et al. [6] reported a three main hypothetical aggression of asphaltene as (i) core aggregates are formed by p–p stacking of asphaltene molecules (20 Å size), (ii) medium aggregates are formed by secondary aggregation of core aggregates that result from interactions with maltenes, oils or solvents (50–500 Å) and (iii) fractal aggregates are secondary aggregates of core aggregates that results from diffusion limited cluster aggregation or reaction limited cluster aggregation (which is independent of any media) (size > 1000 Å). It was also concluded by the authors that this model of asphaltene aggregate was a highly simplified model. The usefulness of other recycled waste materials like glass, steel slag, tyres, rubbers and plastics for bitumen pavements has been discussed in detail in the literature [7–11]. Regardless of the chemical used, the reaction conditions and sources of a bitumen, the modification increases asphaltene content in the bitumen cluster and hence the soft property of the bitumen becomes hard. The degree of hardening depends on several factors like-source of bitumen, chemical use and reaction conditions, etc. Although several research work are found in the literature for modification of a bitumen by chemical reaction, still the formation of asphaltenic material and its nature are so complex, that there is no clear explanation of how asphaltenes are formed and how it changes the rheology of the bitumen. But it is proved as stated above that the presence of asphaltene molecules in the bitumen improves significantly its properties and hence it can be used for paving or other purposes. Therefore, in this study, different bitumen modifiers are used and the effects of these modifiers on asphaltene’s properties are examined. For these reasons, glycerol, styrene, methyl methacrylate (MMA), hydroquinone (HQ) and C18-acrylate are used as modifiers. The asphaltenes extracted from these modified bitumen are characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), and thermogravimetric analysis (TGA).
2. Experimental
D27 Kv Mwt FT dm dc Lc M G0 G00 G⁄ d
ductility at 27 °C kinematic viscosity molecular weight fail temperature layer distance between aromatic sheets interchain layer distance average height of stack aromatic sheets molecules of aromatic sheets in a stacked cluster storage modulus loss modulus complex modulus phase angle
quantity of modifier was added and the mixture was stirred for a period of 8 h. All chemicals except C18-acrylate were of commercial grade. C18-acrylate was synthesized in our laboratory according to the procedure given elsewhere [12]. Asphaltene was extracted from the modified bitumen by soxhlet process. In this process the modified bitumen was taken with n-heptane (ten times of bitumen) solvent into a round bottle. The mixture was then refluxed for a period of 6 h. The insoluble portion was separated and dried in a vacuum oven at 110 °C. A flow diagram of the separation of asphaltene is presented in Fig. 1. 2.2. Characterization of modified bitumens and asphaltenes The physical properties like-penetration, ductility, softening point of the untreated and treated bitumens were measured by standard methods. The penetration is determined by a standard method (ASTM D5) with a penetrometer. In this method, a needle loaded with 100 g was brought to the sample surface at right angle, allowed to penetrate the sample for 5 s at 25 °C. The penetration is measured in deci-millimeter (dmm). The ductility of a sample is measured by ASTM D113 method. In this method a sample was pulled apart at a uniform rate of 5 cm/min. at 27 °C until it ruptured. The elongation or stretch of the sample in centimeter was measured. The softening point was determined by ASTM D 36 method by using ring and ball apparatus. The average molecular weight of the natural and modified bitumen were also measured by Agilent Gel Permeation Chromatography (GPC) using model 1260. The dynamic shear rheometer of TA instrument of model AR 1500eX was used to characterize visco-elastic behavior of natural and modified bitumens. Rheological study was carried out at minimum instrument inertia of 16.85 lN m2 as per ASTM D7175-05. Different rheological parameters like G⁄, d, G⁄/Sin d at 1.1 kPa gives the fail temperature. It is the temperature at which bituminous
Vacuum residue Reaction with chemical at 200OC for 8 hrs Modified Bitumen Soxhlet reflux with n-heptane
2.1. Modification of bitumen and asphaltene separation Vacuum residue (VR, 540 °C+) procured from the Indian refinery (Panipat) was used as a base material (bitumen). Around 200 g of the base material was heated into a flask with continuous mechanical stirring. After getting desired temperature, the required
Asphaltene (Insoluble fraction) Fig. 1. Separation of asphaltenes from vacuum residue.
10
S.K. Maity et al. / Fuel 149 (2015) 8–14
binder lost its binding/adhesive property. Complex modulus (G⁄) is the resultant of storage modulus (G0 ) and loss modulus (G00 ) and is calculated by the following equations.
qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi G ¼ G02 þ G002 G ¼
qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 2 2 ðG cos dÞ þ ðG sin dÞ
ð1Þ ð2Þ
where d is the phase angle. All the rheological parameters G0 , G00 , d and G⁄/sin d are temperature dependent and were determined to define performance of a bitumen. In this study all rheological parameters were measured at angular frequency of 10 rad/s and at controlled constant percentage strain of 12.0%. These measurements were taken in the temperature range of 42–82 °C with an increment of 6 °C. G⁄ define resistance to deformation and is a function of G0 , G00 and d in the viscoelastic region (0 < d < 90). X-ray diffraction (XRD) of asphaltene was studied in the powder samples by using a model Rigaku Denki. For this analysis Cu K1 radiation operating at 40 kV and 30 mA in the range of 2–60° of 2h was used. The crystalline parameters, like layer distance between aromatic sheets were calculated by using the Bragg equation.
dm ¼
k 2 sin h
ð3Þ
The distance between the saturate portion of the molecules or interchain layer distance was calculated by using an equation:
dc ¼
5k 8 sin h
ð4Þ
The average height of the stack aromatic sheets perpendicular to the plane of the sheets was calculated by using the following equation.
Lc ¼
0:45 B1=2
ð5Þ
where B1/2 is the full width at half maximum (FWHM), obtained from the graphene band. The molecules of aromatic sheets in a stacked cluster (M) were also calculated from Eqs. (3) and (5) as
M¼
Lc þ1 dm
ð6Þ
The morphology of asphaltene samples was also determined by using SEM, model quanta 200F. The asphaltenes obtained from the natural and modified bitumens were also characterized by thermogravimetric analysis by using Perkin-Elmer model TGA-4000. In this experiment around 10 mg of the bitumen sample was heated from room temperature to 900 °C at a rate of 10 °C/min in the presence of air (flow 50 mL/min). 3. Results and discussion 3.1. Physical properties of modified bitumen In this study the reference material i.e. bitumen was collected from Indian refinery and its properties were given in Table 1. Table shows that our reference bitumen (Bn) contains 11.4 wt% insoluble. The penetration value of this unmodified bitumen is 130 dmm. This material is also comparatively soft in nature and its softening point (SP) is as low as 38 °C. This bitumen was treated with different reactive molecules to get appropriate physical properties. Almost all the treatment was performed in the presence of glycerol as co-additive. Changes of physical properties of the treated bitumen have been compared with untreated bitumen in Table 2. Sample Bg is the modified bitumen with 0.3 wt% glycerol.
Table 1 Physico-chemical characteristics of natural bitumen (Bn). Properties
Value
Density (15 °C) API gravity Flash point (°C) Viscosity (cSt at 135 °C) Aromaticity (by NMR) Saturates (wt%) Naphthenic aromatics (wt%) Polar aromatics (wt%) Asphaltene (wt%)
1.0134 8.05 252 182 0.44 6.18 55.03 27.37 11.42
It is noticed from Table 2 that the percentage of asphaltene like aggregate molecules (Ins) increases from 11.4 to 20.7 wt%. The softening point is also improved (from 38 to 48 °C). The sample Bg also becomes hard in nature and this can be seen from the penetration value. P25 value of the natural bitumen is 130 dmm and it decreases to 50 dmm after treatment with glycerol. Formation of the maximum amount of asphaltene is noticed in sample Bacl which is treated with C18-acrylate. Its asphaltene percentage is as high as 91 wt%. P25 value of this sample is reduced substantially. The samples Bhq which is obtained by treatment of bitumen with hydroquinone also has a high percentage of asphaltene aggregate. And therefore, their P25 and SP values are also improved significantly. The kinematic viscosity at 135 °C of Bn, Bmma and Bacl samples were measured and given in Table 2. The viscosity values also indicate the presence of large molecules in the modified bitumen. The molecular weight values also support this fact. The molecular weight of natural bitumen increases from 1730 to 2862 g/mol when it is treated with C18-acrylate. Similarly the fail temperature (FT) that gives indication of visco-elastic behavior of bitumen, also increases due to the reaction of natural bitumen with modifiers. From these studies, it is clear that with increased percentage of asphaltene aggregate, penetration value decreases whereas SP values increase. Improvement of both these properties is required in bitumen so that it can be used for paving or other purposes. It is also found in the literature that maleic anhydride improves significantly temperature sensitivity [4]. The viscoelastic properties (complex modulus, G⁄ and phase angle, d) as a function of temperature for samples Bn, Bmma and Bacl were measured and presented in Fig. 2. The complex modulus G⁄ decreases with increase in temperature due to decrease in magnitude of G⁄/sin d and increase in phase angle d with temperature. The modified bitumens have high G⁄ than natural bitumen at the same temperature. Data shows that G⁄ of methyl methacrylate modified bitumen is 6677 Pa at 60 °C while that of natural bitumen is 2570 Pa. This indicates that complex modulus increases when natural bitumen is modified with methyl methacrylate even it increases substantially in case of C18-acrylate modified bitumen. This concludes that modified bitumens are more resistant to permanent deformation and have good storage stability in comparison of natural bitumen [7,9,13]. The softening point is higher in the bitumen having high asphaltene-aggregates. Therefore, it is the asphaltene cluster that most significantly affects the strength and softening point of a bitumen [14,15]. A considerable research was carried out in the past few years for the modification of bitumen by several others molecules. Among them the use of styrene is well known. It is believed that styrene–butadiene–styrene copolymer absorbs the oil fraction (maltenes) of the bitumen and it leads to swelling of the bitumen. It makes a rubber–elastic network within the modified binder. The nature of network and finally its effect on the bitumen properties depends on the base bitumen, the nature and content of the polymer, bitumen–polymer compatibility. It is very important to aggregate the appropriate amount of polymer into the
11
S.K. Maity et al. / Fuel 149 (2015) 8–14 Table 2 Physical characteristics of natural bitumen (Bn) and modified bitumens. Name
Modifiers (wt%) g
Bn Bg Bs Bmma Bhq Bacl
0.3 0.3 0.3 – 0.3
s
Physical properties mma
hq
acl
0.45 2.3 0.2 0.8
Ins (wt%)
P25 (dmm)
SP (°C)
11.4 20.7 27.5 48.2 80.3 90.8
130 50 45 33 13 12
38 48 49 57 72 70
D27 (cm)
+90 61.5 6.5
Mwt (g/mol)
FT (°C)
182
1730
66
745
2432
72
2153
2862
96
kV cSt at 135 °C
3.2. X-ray diffraction
bitumen, otherwise phase separation between maltenes and asphaltene can occur. This phase separation can be considered as incompatibility between styrene and bitumen [16]. It is found that paraffinic bitumen shows a greater degree of polymerization than naphthenic bitumen. It is also said that during reaction of a bitumen with a polymer, two phases like structure is formed-one is polymer-rich phase and other is asphaltene rich phase. This asphaltene rich phase mostly contributes to characteristics of a bitumen. A similar explanation can be given in this study also. From Table 2, it is found that the percentage of insoluble material increases substantially, however, the hardness of these insoluble phases does not increase proportionately. For an example, sample Bhq contains 80 wt% of insoluble and its P25 value is 13. This value does not improve significantly with further increase of insoluble content. It can explain that all insoluble parts do not contribute to the formation of asphaltene. There may be some naphthenic (polymerized) material which is also insoluble in n-heptane. These naphthenic material may not be as hard as asphaltene. It was categorically stated in the literature [1], that the solid particles insoluble in n-heptane was significantly higher than the true asphaltene content in bitumen. It was said that n-heptane was not exactly a solvent equivalent to the maltenes. Therefore, the solid phase in a bitumen was actual asphaltene and adsorbed resins and hence the amount of insoluble (asphaltene + adsorbed resins) was much higher than actual asphaltene present in a bitumen. The percentage of insoluble material in our case is very high after reaction. Therefore, it is likely that not only resin but also naphthenic compounds present in vacuum residue also contribute as n-heptane insoluble material. It can be concluded that in the presence of reactive molecules like glycol, styrene, C18-acrylate, the insoluble material from vacuum residue is separated in a certain order form. These reactive molecules help to form a three dimensional network by linking one asphaltenic structure to another and thus it improves the hardness of the bitumen.
Iintensity (a.u)
Fig. 2. Complex modulus as a function of temperature for natural and modified bitumens.
X-ray diffraction of asphaltene samples was analyzed and the diffractogram of selected samples are presented in Fig. 3. Figure shows that most of the peaks appear at around 2h value of 20° and 25°. The doublet of c peak appears at around 20° = 2h which is mainly due to the aliphatic chains or condensed saturated rings. Peak at around 25° = 2h is graphene band. These graphenes are formed by the staging of aromatic molecules present in the asphaltenic structure. There are also possibilities to appear other two peaks at a higher 2h value and that are due to the reflection of first (1 0 0) and second (1 1 0) nearest neighbors in the ring structure [17–20]. And the peak intensities due to these bands are very week compared with two main bands of c and graphene as stated above. It is observed from figure that the doublet c peak appears at 19.25 = 2h of the natural asphaltene (An). The 2h values vary in between 19.25 and 22.65 for other modified asphaltenes. For an example, it appears at 21.5° = 2h for sample Ag whereas it is at 22.65° for Aacl. From figure it is also found that the peak intensities of c and graphene in sample Ahq are more compared with the reference sample An. The different crystalline parameters calculated from the graphene bands of asphaltene are summarized in Table 3. The average layer distance between the sheets (dm) of natural asphaltene (An) is 3.7 Å which decreases to 3.5X Å (X = 4 or 5 or 6) for the modified asphaltenes. This suggests that when the natural bitumen is treated with a modifier, during the reaction asphaltene becomes more compact. These results are consistent with the results documented in the literature [6,17,20]. Similarly, average inter-chain layer distance (dc) also reduces from 4.63 to 4.4X Å (X = 2 or 4 or 6). So it
Aacl
Ahq
An
40
20
2Ɵ Fig. 3. X-ray diffractograms of natural and modified asphaltenes.
12
S.K. Maity et al. / Fuel 149 (2015) 8–14
Table 3 Crystallite parameters of different asphaltenes. Sample
An Ag As Amma Ahq Aacl
Crystallite parameters dm (Å)
dc (Å)
Lc (Å)
M
3.7 3.54 3.55 3.56 3.76 3.54
4.63 4.42 4.44 4.46 4.70 4.41
18.18 23.06 33.7 36.01 39.85 43.85
5.91 7.52 10.49 11.1 11.61 13.42
also suggests that both the condensed aromatic as well as aliphatic layer becomes more compact due to aging reaction with reactive molecules. Siddiqui et al. [17] have also reported that during short term aging both aromatic ring and aliphatic chain of the asphaltene becomes compact and condensed. However, with further aging the compactness of asphaltene structure does not change. This compactness of the asphaltene also improves the hardness property of the bitumen. The average stack height of the aromatic sheets perpendicular to the plane (Lc) has also been calculated and it is within the range of 18.18–43.85 Å. The number of aromatic sheets in a stacked asphaltene cluster is 5.91 for natural asphaltene and it increases after the treatment with functional molecules. The maximum number of aromatic sheet is found in the sample that is derived from bitumen treated with C18-acrylate. It indicates that the functional group or groups present in the reactive molecule take part in the polymerization reaction. The degree of polymerization is the maximum when the natural bitumen reacts with C18-acrylate molecule and as a result, the number of aromatic sheet is more in this modified bitumen. When natural bitumen is treated with glycol (the smallest molecule having only OH group) the number
of aromatic sheet increases from 5.91 to 7.52 but this value reaches maximum 13.42 when this bitumen is treated with the C18-acrylate (the biggest molecule having both C@C and ACOOR functional groups). Therefore, it also suggests that the degree of polymerization not only depends on the molecular weight but also on the functional groups present in the modifier. 3.3. Scanning electron microscope The surface images of different asphaltene molecules are taken by SEM and are presented in Fig. 4. Fig. 4 (An) shows that asphaltene is similar to the colloidal particles. It suggests that the asphaltene particles are mixed with some resin molecules. Fig. 4 (An) also shows that the presence of cavities which are the precursor of pores. The sizes of the cavities vary from 14.12 to 22.10 lm and the colloidal particle sizes are around 21.3 to 27.97 lm. So, the images clearly show that the asphaltene obtained from natural bitumen is still not a matured state. The colloidal behavior of the asphaltene molecules in a bitumen has been detailed discussed by Lesueur [1]. In another word, it can be said that small amount resin (which is liquid) may also present with the asphaltene. As it has been stated earlier that the solid phase in a bitumen is actual asphaltene and adsorbed resins and hence the amount of insoluble (asphaltene + adsorbed resins) is high. The formation of asphaltene particles however is observed in Fig. 4 (Ag). The image is cauliflower like structure and the colloidal type particle structure are not present. The formation of cauliflower like structure has also been reported by others [21–26]. This image also reveals the inhomogeneity of the asphaltene particles. The different size and shape of the particles are clearly noticed. It is worth to mention that this asphaltene is extracted from the bitumen that is treated with glycerol. A complete different type of images for asphalting particles are noticed in Fig. 4 (Amma) for the sample which was obtained after
An
Ag
Amma
A acl
Fig. 4. SEM images of natural asphaltene An, and modified asphaltenes Ag, Amma and Aacl.
S.K. Maity et al. / Fuel 149 (2015) 8–14
treatment of bitumen with methyl methacrylate. The image appears like a cloud. The image also indicates inhomogeneity of the asphaltene particles. The formation of porous structure which is reported by other [21,22] is not clearly observed in this case. Only some pore cavities with a size of 1.36–4.10 lm are noticed. A smooth surface with several layers can be observed in Fig. 4 (Aacl). The growth of different shape and size of asphaltene particles is noticed. The asphaltene in this case is obtained from bitumen, which is treated with the heaviest reactive molecule, C18-acrylate. From the above discussion, it is established that the surface structure of asphaltenes are different for the asphaltenes obtained from the different modified bitumens. The surface heterogeneity is everywhere with respect to size, shape and appearance. Although there are pore cavities in some cases, but a usual pore structure in asphaltene is absent in this present work. Quantitative analysis of different elements present in asphaltene has also been studied by SEM-EDX and the results are presented in Table 4. The data given here is an average value of the elements analyzed at different locations. Carbon, oxygen and sulfur are the most abundant elements found in the asphaltene samples. The percentage of oxygen present in asphaltene increases when the bitumen is treated with oxygen containing compounds, i. e. glycerol, methyl methacrylate, C18-acrylate, etc. The O/C ratio has also been calculated and the same increasing trend is observed. A plausible reason for the presence of extra oxygen in asphaltene is from the bitumen’s modifiers. However, it is not so simple; the degree of polymerization also needs to be considered. The O/C ratios of samples Ag and Aacl are 0.07 and 0.11 respectively, but the present of oxygen (with respect to carbon) in chemical structure in glycerol is much more than that in C18 acrylate. It explains that since the degree of polymerization in sample Aacl is much higher than that in sample Ag hence more oxygen is present in sample Aacl. It is also noticed that the percentage of sulfur decreases due to treatment of the natural bitumen. It is due to the presence of more oxygen and carbon present in the modified asphaltenes. It is also possible that sulfur is removed from the system [1]. 3.4. Thermogravimetric analysis (TGA) Weight loss due to combustion of asphaltenes derived from natural bitumen (An) and modified bitumens has been measured by thermogravimetric analysis and it is presented in Fig. 5(a). This figure shows that around 97 wt% of An is burned in the presence of air. However, other two samples (Amma and Aacl) are completely burned at around 630 °C. The weight loss respect to temperature for these two samples are identical. The derivatives of weight loss with temperature are also presented in Fig. 5(b). All derivative curves clearly show two principal weight losses at around 460 °C and at 580 °C, indicating that there are two types of asphaltenes are present. One is burned at lower temperature, named as soft asphaltene and other at higher temperature, named as hard asphaltene. Both of the peaks are sharp in nature. The presence of two types of coke (obtained mainly polymerization of asphaltene) is also reported in the literature [27,28]. First asphaltene combustion temperature (Tm) of An is 465 °C and it is shifted towards lower temperature for Amma and Aacl. However, 2nd Tm of the reference sample appears at 581 °C and it is shifted to the higher temperature of the sample Table 4 Elements distribution in different asphaltenes measured by SEM-EDX.
C (wt%) O (wt%) S (wt%) O/C
An
Ag
Amma
Aacl
91.4 5.3 3.3 0.06
91.7 6.4 1.9 0.07
88.9 9.1 2.0 0.10
89.2 9.7 1.1 0.11
13
Fig. 5. TGA curves of (a) weight loss, and (b) derivative weight of asphaltene derived from bitumens.
Amma and Aacl. It suggests that the hard asphaltene of the natural bitumen becomes harder when this is treated with the modifiers. This is also in agreement with of our other physical properties of the bitumens. Other than these two principal peaks, a small peak at lower temperature (around 400 °C) is also observed in all three samples. The intensity of this small peak is high for the An sample and this intensity decreases in the asphaltene obtained from modified bitumens. It is also clearly observed from this figure that the intensity of 1st main peak is higher than that of 2nd peak in sample An. But the reverse trend is noticed in the other two samples, i.e. the intensity of the 2nd peak in Amma and Aacl samples is higher than that of 1st peak. It indicates that the concentration of hard asphaltene increases due to the modification of natural bitumen with reactive molecules. From our TGA results it can be concluded that there is no new material is formed due to the reaction of active modifier with natural bitumen. However, the nature of asphaltenes derived from modified bitumens become harder. This is with the good agreement with the other physical properties presented in this work. Asphaltene is one of the components present in the petroleum crude and defined as insoluble in n-heptane but soluble in toluene. It contains millions of different molecules, including heteroatoms such as nitrogen, oxygen, sulfur and metals, mainly iron, nickel and vanadium. It is so complex molecule that the structure of it is not well known so far. However, it remains in the center of the research for many years to understand its behavior during refinery processes and its visco-elastic building role in a bitumen. It is a condensed aromatic rings in a planer form which can be associated through pi bonding to form graphite-like structure [1]. The nature of natural bitumen is different and it depends on its source. This bitumen is comparatively soft in nature and is not suit-
14
S.K. Maity et al. / Fuel 149 (2015) 8–14
able for its application in road-paving. However, hardness properties of this bitumen can be improved by chemical reaction with foreign molecules or even by air blowing. Moschopedis and Speight [29] observed that the asphaltenes molecular weight increased by 3/2 of its original value upon air blowing at moderate temperature. It was observed by the authors that due to the air blowing, the ratios of H/C, N/C and S/C were decreased while the ratio of O/C was increased, indicating that oxygen uptake in the asphaltenes was developed whereas nitrogen and sulfur were released from the system. It was concluded that asphaltenes were produced during air blowing by polymerization reaction [29–31]. The modification of visco-elastic properties of a bitumen by reaction with a small amount of maleic anhydride, succinic anhydride and dicarboxylic acid was observed by Herrington et al. [4]. It was assumed by the authors that improvement of visco elastic properties of the bitumen occurred due to the hydrogen bonding and dipolar interaction of the bitumen spices. The presence of dipolar interaction has also been reported by others [32]. It was stated that asphaltene in a bitumen was colloidal in nature, consisting of a well packed insoluble asphaltene core and a loose packed periphery, which is more active and easily accessible to solvent or reactive molecules [1]. It is confirmed from this study and other studies reported in the literature that asphaltene mainly contributes the hardness properties of the bitumen. Our XRD, SEM and TGA results and physical properties suggest that the improvement of the hardness properties of a bitumen is mainly due to (i) increase in asphaltene content, (ii) compactness of asphaltene and (iii) the degree of polymerization. Increase in number of graphene layers into the treated bitumen suggests that the reactive molecules help to form a three dimensional networking by linking one asphaltene structure to another may be pi-bonding [5]. This type of networking structure is more when the reactive molecule bigger is in size like C18-acrylate. The presence of both AC@CA and ACOOR may have an important role in polymerization reaction, since C18 acrylate has both these functional groups whereas glycerol has only OH group. Even from our quantitative analysis by SEM shows that the ratio of O/C is more in asphaltene derived from C18-acrylate modified bitumen, indicating a high degree of the polymerization reaction. 4. Conclusions To improve the hardness properties of the natural bitumen, several modifiers like, glycerol, styrene, methyl methacrylate, hydroquinone and C18-acrylate have been used. Results show that hardness properties, like penetration, softening point, ductility of natural bitumen are substantially improved after treatment with reactive molecules. Crystallite properties show that asphaltene cluster becomes more compact due to the modification. The number of aromatic sheets is augmented with the treatment and the maximum number of sheets is found in asphaltene obtained after treatment with C18-acrylate. SEM and TGA results also support the high degree of polymerization for C18-acrylate molecule indicating that the presence of vinyl double bonds and ACOOR functional groups help effectively in this polymerization process. It is also observed that asphaltene cluster is of inhomogeneous nature. During the chemical reaction with reactive molecules, the hardness of the bitumen is improved considerably due to the increasing percentage of highly compact asphaltene. Acknowledgement Authors thank to the director of IIP for his financial support of this work. The authors also thank to Panipat refinery for providing the bitumen.
References [1] Lesueur D. The colloidal structure of bitumen: consequences on the rheology and on the mechanisms of bitumen modification. Adv Colloid Interface Sci 2009;145:42–82. [2] Gorbatovskii AA, Rozental DA, Dronov SV. Structure and composition of polymer–bitumen composites. Russ J Appl Chem 2007;80(5):838–41. [3] Agrawala M, Yarranton HW. An asphaltene association model analogous to liner polymerization. Ind Eng Chem Res 2001;40:4664–72. [4] Herrington PR, Wu Y, Forbes C. Rheological modification of bitumen with maleic and hydride and dicarboxylic acids. Fuel 1999;78:101–10. [5] Tanaka R. Aggregates structure analysis of petroleum asphaltenes with small angle neutron scattering. Energy Fuels 2003;17:127–34. [6] Tanaka R, Sato E, Hunt JE, Winans RE, Sato S, Takanohashi T. Characterization of asphaltene aggregates using X-ray diffraction and small angle X-ray scattering. Energy Fuels 2004;18:1118–25. [7] Lu X, Isacsson U. Chemical and rheological evaluation of ageing properties of SBS polymer modified bitumens. Fuel 1998;77:916–72. [8] Morales MG, Partal P, Navarro FJ, Boza FM, Gallegos C, Gonzalez N. Linear visco-elasticity of recycled eva modified bitumen. Energy Fuels 2004;18:357–64. [9] Morales MG, Partal P, Navarro FJ, Boza FM, Gallegos C, Gonzalez N. Viscous properties and microstructure of recycled eva modified bitumen. Fuel 2004;83:31–8. [10] Huang Y, Bird RN, Heidrich O. A review of the use of recycled solid waste materials in asphalt pavements. Resour Conserv Recycl 2007;52. 85-73. [11] Kumar K, Singh A, Maity SK, Negi S. Use of polymers/waste rubber in road network development in Uttarakhand state. IOSR-JAC 2014;7(6):28–35. [12] Chatterjee AK, Phatak AD, Murthy PS, Joshi GC. Comb-type polymers and their interaction with wax crystals in waxy hydrocarbon fluids: wide-angle X-ray diffraction studies. J Appl Polym Sci 1994;52:887–94. [13] Kumar P, Mehndiratta HC, Singh KL. Rheological properties of crumb rubber modified bitumen-A lab study. J Sci Ind Res 2009;68:812–6. [14] Yen TF, Erdman JG, Pollack S. Investigation of the structure of petroleum asphaltenes by X-ray diffraction. Anal Chem 1961;33:1587–93. [15] Habib NZ, Kamaruddin I, Napiah M, Tan IM. Rheological properties of polyethylene and polypropylene modified bitumen. Int J Civil Environ Eng 2011;3(2):96–100. [16] Airey GD. Rheological properties of styrene butadiene styrene polymer modified road bitumens. Fuel 2003;82:1709–19. [17] Siddiqui MN, Ali MF, Shirokoff J. Use of X-ray diffraction in assessing the aging pattern of asphalt fractions. Fuel 2002;81:51–8. [18] Ebert LB, Scanion JC. Average structure determination for heavy ends in fossil fuels. Liquid Fuel Technol 1984;2(3):257–86. [19] Shirokoff JW, Siddiqui MN, Ali MF. Characterization of the structure of Saudi crude asphaltenes by X-ray diffraction. Energy Fuels 1997;11:561–5. [20] Nazar ARS, Bayandory L. Investigation of asphaltene stability in the Iranian crude oils. Iran J Chem Eng 2008;5(1):3–12. [21] Trejo F, Ancheyta J, Rana MS. Structural characterization of asphaltenes obtained from hydroprocessed crude oils by SEM and TEM. Energy Fuels 2009;23:429–39. [22] Hernández RP, Anaya DM, Galicia GM, Espinosa ME, Lugo VR, Lozada M, et al. Microstructural study of asphaltene precipitated with methylene chloride and n-hexane. Fuel 2003;82:977–82. [23] Berna ACS, Moran VC, Guzmán ETR, Yacamán MJ. Asphaltene aggregation from vacuum residue and its content of inorganic particles. Petrol Sci Technol 2006;24:1055–66. [24] Bragado CGA, Santiago P, Almazo M, Espinosa M, Romero ET, Murgich J, et al. Fullerenic structures derived from oil asphaltenes. Carbon 2002;40: 2761–6. [25] Morales MG, Partal P, Navarro FJ, Gallegos C. Effect of waste polymer addition on the rheology of modified bitumen. Fuel 2006;85:936–43. [26] Litao W, Chen H, Yang L, Suoqi Z, Yahe Z, Chunming X, et al. Effect of experimental conditions on the molecular composition of maltenes and asphaltenes derived from oil sands bitumen: characterized by negative-ion ESI FT-ICR MS. Sci China Chem 2013;56(7):863–73. [27] Maity SK, Blanco E, Ancheyta J, Alonso F, Fukuyama H. Early stage deactivation of heavy crude oil hydroprocessing catalysts. Fuel 2012;10:17–23. [28] Sahoo SK, Ray SS, Singh ID. Structural characterization of coke on spent hydroprocessing catalysts used for processing of vacuum gas oils. Appl Catal A: Gen 2004;278. 83-1. [29] Moschopedis SE, Speight JG. The effect of air blowing on the properties and construction of a natural bitumen. J Mater Sci 1977;12:990–8. [30] Corbett LW, Swarbrick RE. Composition analysis used to explore asphalt hardening. Proc Assoc Asphalt Paving Technol 1960;29:104–12. [31] Kats BI, Glotova NA, Kudryashova AI. Study of aging of asphalts from Romashkino and Ust’-Balyk under natural conditions. Chem Technol Fuels Oils 1976;12:121–4. [32] Cimenoglu MA. Dynamic nuclear polarization in suspensions of asphaltene obtained from MC-20 liquid asphalt. Fuel 2001;80:2014–47.