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In situ preparation of alumina nanoparticles in heavy oil and their performance towards thermal cracking Maen M. Husein, and Salman J. Alkhaldi Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/ef5012963 • Publication Date (Web): 05 Sep 2014 Downloaded from http://pubs.acs.org on September 5, 2014

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In situ preparation of alumina nanoparticles in heavy oil and their performance towards thermal cracking Maen M. Husein* and Salman J. Alkhaldi Department of Chemical and Petroleum Engineering, University of Calgary, Calgary, AB, Canada T2N 1N4 ABSTRACT This work details a technique for the in situ preparation of alumina nanoparticles in heavy oil and explores their activity towards mild thermal cracking. In principle, in situ prepared nanoparticles display high level of dispersion, which should improve their catalytic activity. Dispersed alumina nanoparticles of 17±5 nm mean diameter were successfully prepared at 300oC and characterized using XRD, TEM and EDX. The thermal cracking experiments were carried out in a batch reactor setup under two stages of heating at 300oC and 350oC. The pressure buildup in the reactor and the viscosity and oAPI gravity of the resultant oil were taken as measures for the extent of thermal cracking. Although there was a general shift towards higher oAPI gravity, it still fill within the level of uncertainty probably due to agglomeration at 350oC which limited nanoparticle activity. Higher viscosity was obtained for the liquid fraction due to crosslinking. Furthermore, hydrocarbon uptake by the in situ prepared nanoparticles was compared with commercial alumina nanoparticles. Uptake values with and without n-heptane or DCM washing suggest different adsorbed species onto the two types of particles.

Keywords: nanoparticle, Al2O3, heavy oil, thermal cracking, asphaltene, adsorption, uptake *Corresponding author phone (403) 220-6691; Fax (403) 282-3945; e-mail: [email protected]

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1. Introduction Unconventional oils, which include heavy oil, extra heavy oil and bitumen, are characterized by their high viscosities and densities1,2 owing to their high molecular weight and high sulfur, heavy metal and asphaltenes contents. Unconventional oil must undergo upgrading processes before it can be utilized. These processes involve converting heavy fractions into light fractions with higher H/C ratio and removing heteroatoms such as sulfur, nitrogen and metals, which ultimately improve the combustion characteristics and reduce the environmental impact of fuel combustion.3 Major upgrading processes involve two routes: (1) producing coke which has low H/C ratio while producing distillate material having high H/C ratio, or (2) increasing the yield of the liquid product while reducing the coke yield by adding hydrogen. Thermal cracking, visbreaking and coking are examples of carbon rejection processes and hydrocracking is an example of hydrogen addition processes.4 The main target of the thermal cracking processes is to maximize the yield of lighter distillates.5 A main concern, on the other hand, is the stability of the product. Thus, the choice of operating temperature is decisive, since too low temperature will lead to lower recovery of light to middle distillates from the heavy oil, whereas, too high temperature will result in asphaltenes precipitation from the oil product during storage5 Higher temperatures in the range of 455-540°C are used at pressure of 100-300 psig to increase the fraction of lighter products.6,7 The atmospheric or vacuum residue is the feedstock of this process, whereas the major product is gas oil.7 Asphaltenes are the most problematic fraction of the heavy oil. A workable definition of asphaltenes is the component of oil that is soluble in light aromatic hydrocarbons such as benzene and toluene, while insoluble in saturated hydrocarbons such as n-pentane and nheptane.1,8-10 Asphaltenes molecules portray the highest molecular weight, polarity and surface


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activity of all the different fractions of the crude.11,12 Therefore, asphaltenes display the highest tendency to adsorb onto surfaces and their adsorption can have detrimental effects. For example, asphaltenes adsorb onto rocks, hence changing rock wettability from water-wet to oil-wet,13-17 which poses its own challenges during oil recovery.12,13,15-18 Furthermore, the metallic heteroatoms of adsorbed asphaltenes lead to catalyst poisoning during petroleum refining and upgrading.11,19-21 Consequently, removal of asphaltenes from crude oil improves the quality of the crude. Several researches have studied the adsorption of asphaltenes onto metallic surfaces such as gold,22,23 stainless steel,24 metal oxide surfaces such as Fe3O4, Al2O3 and TiO2,25,26 mineral surfaces such as clays27 and metal oxide nanoparticles.19,25,28-30 The use of alumina as catalyst and/or support material has been widely reported in the literature;31-33 in particular, the use of alumina nanoparticles as a promoter for the oxidation of adsorbed asphaltene.25,30 Moreover, asphaltenes adsorption from toluene model solutions onto commercial alumina nanoparticles was very fast.25 Nickel oxide supported on alumina nanoparticles displayed an even higher asphaltenes adsorption compared with alumina nanoparticles.19 In this paper we detail an approach for in situ preparation of dispersed alumina nanoparticles in heavy oil and explore their role towards mild thermal cracking at 350oC. Our previous work on in situ preparation of vanadium and nickel oxides28,34 demonstrated the ability to produce highly dispersed nanoparticles in heavy oil with appreciable surface area. As such, these particles potentially serve as very good catalysts. In addition, we evaluate the adsorption of asphaltenes, and other hydrocarbons, onto the in situ prepared alumina particles and compare it with commercial Al2O3 nanoparticles. The efficacy of the nanoparticles towards thermal


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cracking and the effect of asphaltenes removal on the properties of the heavy oil were assessed by measuring the viscosity and oAPI gravity of the resultant oil.

2. EXPERIMENTAL METHODS 2.1 Nanoparticle preparation The heavy oil medium was prepared by mixing Athabasca vacuum gas oil, VGO, with Athabasca vacuum residue, VR, at a mass ratio of 80:20. Dispersed alumina, Al2O3, nanoparticles were prepared in situ via thermal decomposition of aqueous Al(NO3)3 precursor (98% pure powder, Sigma-Aldrich Fine Chemical, Toronto, ON) as follows. First, and since dispersed water pools in oil media behave similar to bulk aqueous phases,34,35 the thermal decomposition of bulk aqueous Al(NO3)3 solution was carried out in order to establish the required temperature and time. A volume of 10 mL of 150 g/L aqueous Al(NO3)3 was used. It is worth noting that bulk Al2O3 was prepared by different researchers from the isothermal decomposition of Al(NO3)3 powder at temperatures ranging between 300oC and 1100oC for times ranging between 2 to 10 h.36-38 This suggests that at temperature as low as 300oC and appropriate time duration, 5 to 8 h were chosen in this study, there should be no thermodynamic or kinetic limitations towards the thermal decomposition of aqueous aluminium nitrate to alumina. The following reaction was proposed by El-Shereafy39 to describe the thermal decomposition of solid Al(NO3)3.

Al(NO ) Al O + NO + NO + O

(R1)

In case of the dispersed particles, 2.5 mL of 540 g/L aqueous Al(NO3)3 solution were added to 50 mL of the heavy oil matrix and mixed very well in a vortex mixer, since effective mixing is a key to ensuring the formation of very small water pools to serve nanoparticle preparation, 4 ACS Paragon Plus Environment

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followed by shaking at 200 rpm and 70oC for 5 min in an incubator shaker. The mixture was visually inspected for any phase separation before it could be placed in an oven at 300oC for 8 h to carry out the thermal decomposition. The as-prepared particles were either collected for characterization or left in the dispersed form to evaluate their performance during thermal cracking. 2.2 Particle Characterization For characterization purposes, particle recovery from the heavy oil medium involved addition of toluene at a volume ratio of 7 mL toluene/1 mL heavy oil, followed by centrifugation at 5000 rpm for 15 min, and washing several times with toluene to remove adsorbed materials. The final powder was dried, ground using a mortar and pestle and introduced to Ultima III Multipurpose Diffraction System (Rigaku Corporation, The Woodland, TX, USA) for XRD analysis. The instrument employs a Cu-Kα radiation that operates at 40 kV and 44 mA with a θ-2θ goniometer. The structure of the particles was identified by comparing the patterns with database provided by JADE program, ©Materials Data XRD Pattern Processing Identification & Quantification as well as literature.40,41 In order to estimate the surface area, the final powder was further washed with dichloromethane (DCM) (anhydrous ≥ 99.8% Sigma-Aldrich Fine Chemical, Toronto, ON). The particles were, then, thoroughly dispersed in methanol using sonication, and one drop of the resulting suspension was deposited on a copper grid covered with holey carbon film. The grid was shaken for few seconds in order to remove excess suspension to avoid aggregation during evaporation, and was left to evaporate overnight. Images from different locations on the grid were collected on a Philips Tecni transmission electron microscope (TEM) (FEI USA Inc., Hillsboro, OR) equipped with 200 kV Field Emission Gun and Gatan Imaging Filter (GIF) with a


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slow scan CCD camera. Energy dispersive X-ray (EDX) was also collected by zooming on a given location on the grid. Scanning electron microscopy (SEM) (Philips XL30 ESEM, USA) photographs were collected to provide further analysis of the particles. Unlike the TEM sample preparation, SEM sample preparation did not involve any dispersion. In addition, the surface area of the in situ prepared Al2O3 nanoparticles was estimated by means of N2 adsorption and desorption at 77 K using a Micromeritics Tristar 3020 surface area analyzer (Micromeritics Instrument Corporation, USA). As part of the sample preparation procedure, and in order to study the effect of degassing temperature on the area calculation,28 the Al2O3 sample was degassed at 200oC or 300oC under N2 flow overnight. The surface area was calculated by the instrument using the Brunauer-Emmet-Teller (BET) equation. The external surface area was obtained from the t-plot provided by the instrument. Pore volume was estimated using BarrettJoyner-Halenda (BJH) adsorption model. 2.3 Amount of the adsorbed species The mass of the adsorbed species was determined using thermogravimetric analysis, TGA (Q600 SDT, TA Instruments, Inc., USA), following Abu Tarboush and Husein.28 TGA analysis involved heating a few mg of the sample from 25oC to 1000oC at a constant temperature ramp of 10oC/min under a constant flow of air of 100 cm3/min. The amount of adsorbed species was calculated from the mass loss provided by the TGA, while accounting for any mass loss associated with the in-house prepared and commercial Al2O3 as control samples. The in-house Al2O3 particles were prepared from thermal decomposition of bulk aqueous Al(NO3)3 at 350oC, which is the same as the thermal cracking temperature. The amount of adsorbed species onto the in-situ prepared nanoparticles was compared with the amount of the adsorbed species onto commercial Al2O3 nanoparticles (dp < 50 nm, 99.8%, Sigma-Aldrich Fine Chemical, Toronto,


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ON). Moreover, for the experiments involving determining the chemisorbed and total adsorbed asphaltenes, some samples were washed with DCM or n-heptane (99.8% Sigma-Aldrich Fine Chemical, Toronto, ON), respectively, and allowed to dry for 12 h at room temperature. Three different replicates were prepared for some of the samples and the standard error was around 1%. 2.4 Thermal cracking performance The performance of the as-prepared particles towards thermal cracking reaction was assessed using a cylindrical 100 mL batch reactor setup (4590 Micro Bench top Reactor, Parr Instrument Company, IL, USA). For each experiment, 50 mL of the oil matrix containing 1 mL of dispersed aqueous Al(NO3)3 solution of different concentrations, such that 2000 ppm, 3000 ppm or 4000 ppm Al2O3 in the final oil matrix is produced, was added to the reactor. Heating commenced in two stages, both under 160 rpm of continuous stirring, using a heating coil wrapped around the reactor unit. In the first stage, the reactor was heated from room temperature to 300°C at 5oC/min and was maintained at this temperature for 5 h in order to form the Al2O3 nanoparticles. A separate experiment of thermal decomposition for 5 h confirmed the in situ formation of dispersed Al2O3 nanoparticles. The second stage involved increasing the temperature to 350°C, at the same temperature ramp, and maintaining the final temperature for a total of 7 h. The corresponding pressure buildup inside the reactor was monitored and recorded at specific time intervals. Control samples composed of the oil matrix with and without 1 mL deionized water were subjected to the same heat treatment, and the pressure buildup was also reported. Samples from the gas space were periodically collected and analyzed using gas chromatography (SRI GC with multiple detection systems, Model: SRI-8610-0070, CA, USA). At the end of the experiment, the reactor was cooled down to room temperature and the liquid phase was centrifuged and collected for analysis. Viscosity and oAPI gravity of the liquid phase were


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measured using BrookField Digital viscometer (Model: LVDV-1 PRIME, Brookfield Engineering Laboratories Inc, MA, USA) and specific gravity bottle, pycnometer (Thomas Scientific, NJ, USA), respectively. Figure 1 below summarizes the experimental methods and the relationship among the different experiments.

Al2O3 Preparation Bulk: o

Dispersed:

o

o

300 C, 350 C

300 C; 7 h

o

Al2O3 nanoparticle characterization: XRD, TEM, EDX

or 700 C; 8 h

Confirm Al2O3

Thermal cracking: o

formation: XRD

300 C; 5 h o

350 C; 7 h

Al2O3 particles characterization: XRD, TEM, EDX, SEM, surface area, adsorbed hydrocarbons

Liquid phase characterization: viscosity, oAPI Figure 1: Block diagram illustrating the experiments, conditions and characterization involved in this study.

3. RESULTS AND DISCUSSION 3.1 Bulk alumina particles Given the fact that dispersed water pools in oil media portray similar behavior as bulk aqueous phases,34 the thermal decomposition of bulk aqueous Al(NO3)3 solution was carried in order to establish the required temperature and time. Figure 2a-c shows the X-ray diffraction patterns of 8 ACS Paragon Plus Environment

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the powder collected following thermal decomposition of 10 mL of 150 g/L (0.4 M) bulk aqueous Al(NO3)3 solution at 300oC, 350oC and 700oC. The figure confirms the formation of amorphous Al2O3 as previously reported in the literature.40,41 Figure 2d shows the X-ray diffraction pattern of the commercial alumina nanoparticles used in this study. Although no sharp peaks could be obtained, this material is most likely Al2O3, as suggested by the JADE program.

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Figure 2: XRD pattern of bulk alumina powder collected following thermal decomposition of 10 mL of 0.4 M Al(NO3)3 at (a) 300oC; (b) 350oC; (c) 700oC for 8 h and (d) commercial alumina nanoparticles employed in this study 3.2 Dispersed Al2O3 particles The XRD, TEM and EDX results for the particles collected following thermal decomposition of aqueous Al(NO3)3 originally dispersed in the oil matrix at 300oC are shown in Figure 3a-c. The XRD pattern includes noise, especially at low values of 2θ, and no sharp peaks. Comparison with Figure 2 suggests the formation of amorphous Al2O3 particles. The lack of crystallinity did


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not allow particle/crystal size estimation from the XRD pattern.42 The EDX spectrum shows peaks for aluminum and oxygen, while the copper peak is attributed to the copper grid. The extra peaks appearing in the XRD pattern and the EDX spectrum can be attributed to adsorbed material,28

as detailed below. Assuming spherical particles, the mean particle diameter

calculated from the TEM photographs averaged over 34 particles was 17±5 nm. In light of nanoparticle synthesis in water-in-oil microemulsions, the size of the resultant particles may reflect the size of the parent water pools at the given experimental conditions. Due to the complex nature of the heavy oil system, estimation of the size of the water pools was not possible, nevertheless. It should be noted that most of the mixing was provided by the vortex mixer, and the stirring during the experiment probably helped maintaining the original dispersion intact. Since no significant reactions took place at 300oC, the temperature for thermal cracking was further increased to 350oC. In order to provide analysis of the particles utilized during thermal upgrading, the TEM and EDX photographs of the in situ prepared Al2O3 particles following the two-stage heating at 300oC and 350oC were collected. Figure 3d,e depicts the TEM and EDX photographs for these particles following thorough washing with DCM in order to remove adsorbed material. As can be seen in Figure 3d, significant agglomeration took place after heating at 350oC, probably owing to the higher temperature treatment as well as the nature and amount of adsorbed species. Therefore, no reliable particle size could be estimated from the TEM photographs for the dispersed particles employed during thermal cracking. The elemental analysis of Figure 3e confirms the presence of aluminium and oxygen in these agglomerates, nonetheless. The disappearance of copper between Figure 3c and 2e is worth noting, and may be attributed to much less background interference due to the higher extent of agglomeration.


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Energy (keV)

Figure 3: (a) XRD pattern; (b) TEM photographs and (c) EDX spectrum of in situ prepared Al2O3 particles at 300oC. (d) TEM photograph and (e) EDX spectrum of in situ prepared Al2O3 particles following the two-stage heating at 300oC and 350oC. The surface area of the in situ prepared nanoparticles involved in the thermal cracking experiments calculated by BET and external surface area equations as well as the pore volume, following degassing the sample at 200oC and 300oC, are shown in Table 1. As can be seen from Table 1, the surface area depends on the degassing temperature, which suggests the existence of adsorbed species, even after DCM washing.28 It appears that heat treatment during degassing made pores within the agglomerated structure available for adsorption, and hence, larger pore volume was obtained at higher degassing temperature as shown in Table 1. The fact that the external surface area was very low, nearing zero, relative to the BET calculated area further confirms an agglomerated structure. The SEM images of the in situ prepared Al2O3 following DCM and n-heptane washing are shown in Figure 4. Mainly spherical particles with average sizes of 10±2 and 8±2 µm were 14 ACS Paragon Plus Environment

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obtained for the DCM and n-heptane washed samples, respectively. Even though there is no statistical difference between the surface area estimation following DCM and n-heptane washing, it appears that the n-heptane washed particles display higher aggregation relative to the DCM washed ones. TGA analysis, below, suggests different nature of some adsorbed species following washing with the two solvents. The significant difference in surface area estimates by Micromeritics Tristar following degassing at 200oC (4.8 m2/g) and 300oC (9.6 m2/g) as well as TEM (0.9±0.5 m2/g) and SEM estimates (0.2 m2/g), and given the fact that TEM preparation step involves dispersing the suspension, while SEM does not, leads to the conclusion that none of the methods employed provides good estimate of the surface area of the as-prepared particles. It is believed that agglomeration encountered, in part, during particle collection led to uncertainties arising from collection method-dependent pore volume. These pores are believed to establish themselves within the agglomerated structure rather than within the nanoparticles.28 On the other hand, dynamic light scattering (DLS), which is typically used to estimate sizes of dispersed particles, cannot be employed for heavy oil media, due to their high capabilities of adsorbing light.43 (a)


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(b)

Figure 4: SEM images of in situ prepared Al2O3 particles collected from 2000 ppm alumina in heavy oil following the two-stage heating at 300oC and 350oC after (a) DCM and (b) n-heptane washing. Table 1: Surface area estimate of the in-situ prepared Al2O3 particles following the two-stage heating at 300oC and 350oC as calculated by Micromeritics Tristar 3020.

Degassing temperature (°C)

Specific surface area per BET model (m2/g)

External surface area (t-Plot) (m2/g)

Pore volume (BJH adsorption model)(m3/g)

200 300

4.8 9.6

~0 ~0

0.16×10-6 0.60×10-6

3.3 Thermal cracking performance of the as-prepared Al2O3 particles In this study, we attempted thermal cracking at a lower temperature; namely 350oC, than the visbreaking process, 44 which is deemed as a mild thermal cracking process, in order to explore the efficacy of the nanoparticles as promoters for such reactions. The pressure buildup versus time for the samples containing 0, 2000, 3000 and 4000 ppm of the as-prepared alumina particles is depicted in Figure 5. Following 5 h of heating at 300oC, the relatively small difference in the pressure buildup between the control sample initially containing no water or precursor and the experimental samples suggests no appreciable thermal


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cracking at this temperature. Therefore, the temperature was increased to 350oC following the first heating stage and maintained there for 7 h. Nonetheless, the first 5 h were sufficient for the formation of the Al2O3 nanoparticles. A comparison between the control samples with and without water reveals a role for water in the reactions taking place. At the temperature of the system, aquathermolysis is the most likely reaction.45 The major products of aquathermolysis are H2, CH4, CO2, H2S, C2H6 and C3C7.46 In the presence of the as-prepared Al2O3 nanoparticles, the pressure buildup is more significant. Gas evolution during thermal cracking correlates to coke formation. A complete investigation on coke formation during thermal cracking in the presence of alumina nanoparticles will be communicated shortly. A representative GC analysis confirmed the formation of 10 vol% H2 and 51 vol% CH4 as the major gaseous products. Nevertheless, the pressure buildup does not seem to be affected by the particle concentration and the pressure profiles fill within the experimental error for all the samples containing the nanoparticles. It seems likely that Al2O3 particles have promoted the pyrolysis reaction,47 however their effect was limited by particle agglomeration. Particle agglomeration induced large degree of uncertainty as can be seen in the error bars of Figure 5, which, should to be representative of the uncertainty in all other runs. It appears that particle agglomeration within the oil phase is inevitable at 350oC, even under the 160 rpm stirring.


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Figure 5: Pressure buildup in the batch reactor during the two-stage heating at 300oC and 350oC of: (∆) control sample initially containing no deionized water or aqueous precursor; (▲) control sample initially containing 1 mL deionized water; (○) oil containing aqueous precursor for 2000 ppm Al2O3; (●) oil containing aqueous precursor for 3000 ppm Al2O3; (◊) oil containing aqueous precursor for 4000 ppm Al2O3. Experimental condition: 160 rpm stirring. Following thermal cracking, the viscosity and oAPI gravity of the resultant oil were measured and reported in Table 2. The table suggests a significant drop in the viscosity of the feed by virtue of heat treatment alone. Carbon rejection methods tend to concentrate the carbon in the coke product, meanwhile use the hydrogen to terminate the free radicals. This, in turn, lowers the viscosity of the liquid fraction. An even lower viscosity was achieved in the absence of DI-water and nanoparticles, whereas in the presence of DI-water and nanoparticles there seems to be no statistical difference in the values of viscosity between the samples. Abu Tarboush and Husein28 reported an increase in the viscosity, relative to control samples, in the 18 ACS Paragon Plus Environment

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presence of NiO nanoparticles. They attributed this observation to a role nanoparticles play in cross linking the different constituents of the oil.28 It appears that such an effect overshadows any decrease in viscosity arising from possibly more effective upgrading in the presence of the nanoparticles. This conclusion finds support in the oAPI gravity values of Table 2, which suggest an overall shift towards higher oAPI in the presence of the in situ prepared Al2O3 particles. Table 2: Viscosity and oAPI gravity for oil samples involved in this study at 23oC. Samples and controls were subjected to the same two-stage heat treatment at 300oC and 350oC. Sample Original Feed Control sample initially containing no precursor or DI-water Control sample initially containing DI-water Sample 2000 ppm Al2O3 Sample 3000 ppm Al2O3 Sample 4000 ppm Al2O3

Viscosity (cP) 1485±95

Gravity (oAPI) 16.8±2.2

400±80

18.5±4.2

590

15.2

525±50 575 605

17.2±2.4 19.4 19.4

3.4 Uptake of adsorbed species Table 3 depicts the mass of adsorbed species per g of the in situ prepared and commercial Al2O3 nanoparticles. These calculations are based on the thermogravimetric, TG, results of Figure 6 for nanoparticles recovered from the heavy oil matrix, while accounting for mass loss associated with the nanoparticles.28 The oil was subjected to the two-stage heating at 300oC for 5 h followed by 350oC for 7 h and contained 2000 ppm of the in situ prepared or commercial Al2O3 particles. Table 3 shows that more species were adsorbed onto the commercial Al2O3 nanoparticles versus the in situ prepared ones. This difference may arise from different degree of agglomeration within the heavy oil matrix, which is difficult to assess, and/or the higher degree of crystallinity of the commercial Al2O3 particles, as evident from the XRD pattern of Figure 2. Yan et al.48 reported that amorphous Fe nanoparticles improved the rate of H2 generation from 19 ACS Paragon Plus Environment

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ammonia borane to a higher extent than crystalline Fe nanoparticles. Nevertheless, they reported that catalytic activity of both samples degraded due to particle agglomeration. Hermanek et al.,49 on the other hand, assessed the catalytic activity of synthesized nanoparticles by tracking the decomposition of hydrogen peroxide and concluded that the highest activity of the nanocatalyst corresponded to the highest degree of crystallinity. Nassar et al.,30 reported higher adsorption of C7-asphaltenes from toluene model solutions onto Al2O3 and attributed their findings to the higher acidity. Table 3: Species uptake by the in situ prepared and commercial Al2O3 particles recovered from 2000 ppm alumina in heavy oil system following the two-stage heat treatment with and without DCM or n-heptane Washing. Sample

Uptake (g/g) In-situ prepared Al2O3

Uptake (g/g) Comercial Al2O3

No Washing DCM Washing

0.62 0.22±0.04

1.48 0.18

n-Heptane Washing

0.15

0.35

Generally, higher uptake was reported for the unwashed samples, as shown in Table 3. In heavy oil systems, asphaltenes display the highest polarity and, therefore, the highest surface activity.45,46 Resins are less polar than asphaltenes, however, are likely to interact with the adsorbed asphaltenes, since resins typically adsorb onto asphaltenes nanoaggregates in crude oil providing stability to the colloidal aggregates.50-53 Moreover, some heavy paraffins and waxes may also deposit onto surfaces54,55 as well as lighter materials which may get enmeshed within the depositing heavier species. DCM washing removes the physically adsorbed species, which arise from van der Waals interaction with the surface or other adsorbed species, whereas it leaves behind materials adhering to the surface through chemical bonds56 and coke. The uptake values of Table 3 following DCM washing suggest high extent of physical adsorption onto the two


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types of nanoparticles, which can be explained by the low crystallinity reported for the two types of particles. n-Heptane washing, on the other hand, leaves behind asphaltenes,57 coke as well as chemically adsorbed species. Comparing the uptake values following n-heptane and DCM washing suggests the existence of physisorbed asphaltenes onto the commercial Al2O3 nanoparticles, whereas the existence of some non-asphaltenic chemically adsorbed species in the case of the in situ prepared Al2O3 particles. The difference in nature of adsorbed species between the DCM and n-heptane washed samples may explain the higher degree of agglomeration noted earlier in the case of n-heptane washed in situ prepared Al2O3 particles, as evident in Figure 6. The low mass loss beyond 550oC, suggest low percentage of coke. 100

7 90

8 3

1

80

6 Mass loss %

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2

70

5

3

4

60 4

50

5

40

6

2

7

30

1 8

20 0

200

400

600

800

1000

Temperature (oC)

Figure 6: Rate of mass loss versus temperature for species adsorbed onto particles recovered from the 2000 ppm alumina in heavy oil following the two-stage heat treatment: 1) commercial Al2O3 unwashed; 2) in-situ prepared Al2O3 unwashed; 3) commercial Al2O3 DCM washed; 4) insitu Al2O3 DCM washed (95% CI); 5) commercial Al2O3 n-heptane washed and 6) in-situ prepared Al2O3 n-heptane washed. Control samples: 7) commercial Al2O3; 8) in-house prepared Al2O3. TGA parameters: heating rate = 10 °C/min; air flow = 100 cm3/min.


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Conclusions Dispersed alumina nanoparticles were prepared in situ within heavy oil system composed of Athabasca vacuum gas oil, VGO, and Athabasca vacuum residue, VR, by means of thermal decomposition of dispersed aqueous precursor. Heat treatment at 300oC resulted in the formation of finely dispersed Al2O3 nanoparticles of 17±5 nm mean diameter. However, when the particles were subjected to further heat treatment at 350oC, in order to enable appreciable thermal cracking, significant agglomeration took place which limited thermal cracking capabilities of the resultant particles. A general trend towards higher oAPI gravity was reported in the presence of the in situ prepared Al2O3 particles, although not very clear due to the high level of uncertainty. Moreover, higher viscosity, which may have resulted from crosslinking, was obtained. Evaluation of hydrocarbon uptake on the in situ prepared and the commercial Al2O3 nanoparticles following DCM and n-heptane washing revealed different types of chemi and physisorbed hydrocarbons.

Acknowledgment The authors would like to acknowledge the financial support of the Natural Sciences and Engineering Research Council of Canada (NSERC), the financial support of Saudi Aramco in the form of a scholarship awarded to Mr. Alkhaldi, and the help of Dr. Azfar Hassan with the TGA analyses.


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References (1) Cortés, F.B.; Mejía, J.M.; Ruiz, M.A.; Benjumea, P.; Riffel, D.B. Energy Fuels 2012, 26, 17251730. (2) Franco, C.; Patiño, E.; Benjumea, P.; Ruiz, M.A.; Cortés, F.B. Fuel 2013, 105, 408-414. (3) Tian, K.P.; Mohamed, A.R.; Bhatia, S. Fuel 1998, 77, 1221-1227. (4) Speight, J.G. Catal. Today 2004, 98, 55-60. (5) Pilviol, O.; Juha Vilhunen, J.T. ACS Division of Fuel Chemistry, Preprints 1998, 43, 310-313. (6) Speight, J. G. The Chemistry and Technology of Petroleum, CRC Press/Taylor & Francis, Boca Raton, FL, USA, 2007. (7) Jones, D. S., Pujadó, P. R. Eds. Handbook of petroleum processing; Springer: Dordrecht, Netherlands, 2006. (8) Bouhadda, Y.; Bormann, D.; Sheu, E.; Bendedouch, D.; Krallafa, A.; Daaou, M. Fuel 2007, 86, 1855-1864. (9) Liao, Z.; Zhou, H.; Graciaa, A.; Chrostowska, A.; Creux, P.; Geng, A. Energy Fuels 2005, 19, 180-186. (10)

Yen, T. F., Chilingarian, G. V. Asphaltenes and asphalts. 2; Elsevier Science B.V:

Amsterdam, Netherlands, 2000. (11)

Syunyaev, R.Z.; Balabin; R.M.; Akhatov, I.S.; Safieva, J.O. Energy Fuels 2009, 23,

12301236. (12)

Sayyouh, M. H.; Hemeida, A.M.; Al-Blehed, M.S.; Desouky, S.M. J. Pet. Sci. Eng. 1991,

6, 225-233. (13)

Amroun, H.; Tiab, D. In SPE Rocky Mountain Petroleum Technology Conference,

Keystone, CO, USA January 2001. (14)

Al-Maamari, R.; Buckley, J. In SPE/DOE Improved Oil Recovery Symposium, Tulsa, OK,

USA, January 2000. (15)

Yan, J.; Plancher, H.; Morrow, N. In International symposium on oilfield chemistry,

Houston, TX, abruary 1997; pp. 259-266. (16)

González, G.; Moreira, M.B. Colloids Surf.1991, 58, 293-302.

(17)

Crocker, M.; Marchin, L. J. Pet. Technol. 1988, 40, 470-474.

(18)

González, M.F.; Stull, C.S.; López-Linares, F.; Pereira-Almao, P. Energy Fuels 2006, 21,

234-241. 24 ACS Paragon Plus Environment

Page 24 of 27

Page 25 of 27

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

(19)

Franco, C.A.; Nassar, N.N.; Ruiz, M.A.; Pereira-Almao, P.; Cortés, F.B. Energy Fuels

2013, 27, 2899-2907. (20)

Balabin, R.M.; Syunyaev, R.Z.; Schmid, T.; Stadler, J.; Lomakina, E.I.; Zenobi, R.

Energy Fuels 2010, 25, 189-196. (21)

Takahashi, T.; Higashi, H.; Kai, T. Catal. Today 2005, 104, 76-85.

(22)

Xie, K.; Karan, K. Energy Fuels 2005, 19, 1252-1260.

(23)

Ekholm, P.; Blomberg, E.; Claesson, P.; Auflem, I.H.; Sjöblom, J.; Kornfeldt, A. J. Colloid

Interface Sci. 2002, 247, 342-350. (24)

Abdallah, W.; Taylor, S. Nucl. Instrum. Methods Phys. Res., Sect. B 2007, 258, 213-217.

(25)

Nassar, N.N. Energy Fuels 2010, 24, 4116-4122.

(26)

Marczewski, A.W.; Szymula, M. Colloids Surf., A 2002, 208, 259-266.

(27)

Marlow, B.; Sresty, G.; Hughes, R.; Mahajan, O. Colloids and Surf. 1987, 24, 283-297.

(28)

Abu Tarboush, B.J.; Husein, M.M. J. Colloid Interface Sci. 2012, 378, 64-69.

(29)

Nassar, N.N.; Hassan, A.; Pereira-Almao, P. Colloids Surf., A 2011, 384, 145-149.

(30)

Nassar, N.N.; Hassan, A.; Pereira-Almao, P. J. Colloid Interface Sci. 2011, 360, 233-

238. (31)

Wang, X.; Lu, G.; Guo, Y.; Wang, Y.; Guo, Y. Mater. Chem. Phys. 2005, 90, 225-229.

(32)

Melo Faus, F.; Grange, P.; Delmon, B. Appl. Catal. 1984, 11, 281-293.

(33)

Pines, H.; Haag, W.O. Alumina: Catalyst and Support. I. J. Am. Chem. Soc. 1960, 82,

2471-2483. (34)

Abdrabo, A.E.; Husein, M.M. Energy fuels 2012, 26, 810-815.

(35) Rabie, H.R.; Helou, D.; Weber, M.E.; Vera, J.H. J. Colloid Interface Sci. 1997, 189, 208215. (36)

YI, J.H.; SUN, Y.Y.; GAO, J.F.; XU, C.Y. T. Nonferr. Metal. Soc. 2009, 19, 1237-1242.

(37)

Yao, N.; Xiong, G.; Zhang, Y.; He, M.; Yang, W. Catal. Today 2001, 68, 97-109.

(38)

Zeng, W.; Gao, L.; Guo, J. Nanostruct. Mater. 1998, 10, 543-550.

(39)

El-Shereafy, E.; Abousekkina, M.M.; Mashaly, A.; El-Ashry, M. J. Radioanal. Nucl.

Chem.1998, 237, 183-186 (40)

Kim, S.; Liu, B.; Zachariah, M. Chem. Mater. 2002, 14, 2889-2899.

(41)

Pacewska, B.; Keshr, M. Thermochim. Acta 2002, 385, 73-80.

(42)

Patterson, A. Phys Rev. 1939, 56, 978.

(43)

Nassar, N.N.; Husein, M.M. Fuel Process. Technol. 2010, 91, 164-168.

(44)

Rana, M.S.; Sámano, V.; Ancheyta, J.; Diaz, J.A. Fuel 2007, 86, 1216-1231.


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

(45)

Page 26 of 27

Song, G.; Zhou, T.; Cheng, L.; Wang, Y.; Tian, G.; Pi, J.; Zhang, Z. Pet. Sci. 2009, 6,

289-293. (46)

Hongfu, F.; Yongjian, L.; Liying, Z.; Xiaofei, Z. Fuel 2002, 81, 1733-1738.

(47) Ali, M.F.; Saleem, M. Fuel Sci.Technol. Int. 1991, 9, 461-484. (48) Yan, J. M.; Zhang, X.B.; Han, S.; Shioyama, H.; Xu, Q. Angew. Chem. Int. Ed. 2008, 47, 2287-2289. (49) Hermanek, M.; Zboril, R.; Medrik, I.; Pechousek, J.; Gregor, C. J. Am. Chem. Soc. 2007, 129, 10929-10936. (50) Speight, J.G. Oil Gas Sci Technol. 2004, 59, 467-477. (51)

Spiecker, P.M.; Gawrys, K.L.; Trail, C.B.; Kilpatrick, P.K. Colloids Surf., A 2003, 220, 9-

27. (52)

Acevedo, S.; Ranaudo, M.A.; Escobar, G.; Gutiérrez, L.; Ortega, P. Fuel 1995, 74, 595-

598. (53)

Espinat, D.; Ravey, J.C.; Guille, V.; Lambard, J.; Zemb, T.; Cotton, J.P. J. Phys. IV 1993,

3, 181-184. (54)

García, M.D.C.; Carbognani, L. Energy Fuels 2001, 15, 1021-1027.

(55)

Speight, J.G. J. Pet. Sci. Eng. J. Pet. Sci. Eng 1999, 22, 3-15.

(56) Gaspard, J.P. In Interfacial Aspects of Phase Transformations; Springer: Netherlands, 1982; pp. 103-118 (57)

Goual, L.; Firoozabadi, A. AIChE J. 2002, 48, 2646-2663.


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Al2O3 Al2O3

Al3+ NO3-

Heating 300oC

Al2O3

Heating 350oC

Al2O3

Al2O3 Al2O3 Al2O3

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