Article pubs.acs.org/EF
Cite This: Energy Fuels 2017, 31, 11640-11650
Role of HZSM‑5 Aluminosilicates on Asphaltenes Deposition by High-Throughput in Situ Characterizations of a Microreservoir Bruno Pinho,† Karishma Minsariya,† Andrew Yen,‡ Nikhil Joshi,§ and Ryan L. Hartman*,† †
Department of Chemical and Biomolecular Engineering, New York University, Brooklyn, New York 11201, United States Nalco Champion, An Ecolab Company, Sugar Land, Texas 77478, United States § Anadarko Petroleum Corporation, The Woodlands, Texas 77380, United States ‡
S Supporting Information *
ABSTRACT: Hydrocarbon reservoirs are complex in their mineralogy and chemistry. Microfluidics offers an effective platform for rapid, in situ characterizations at experimental conditions that intend to simulate sandstone reservoirs (near wellbore, in production time scale). We have begun to examine the influence of the Al2O3/SiO2 ratio (an important characteristic of reservoir mineralogy) on asphaltenes precipitated in quartz packed-bed microreactors using in situ Raman spectroscopy (2D to 3D mapping), UV−vis spectroscopy, and pressure sensors. The reservoir matrix was created by injecting 707 nm·aggregate−1 HZSM-5 zeolite fine particles (a model aluminosilicate available with Al2O3/SiO2 ratios of 1/91 and 1/26) on a quartz bed. The methodologies were developed to identify the effect of the chemical interactions, giving insights about asphaltenes’ sheet size (nm) and bed occupancy variations. Our results show that, in the precipitation process, an Al2O3/SiO2 ratio of 1/26 leads to 13% higher asphaltenes’ sheet size and >10% higher bed occupancy compared to a bed with no Al2O3 particles. When increasing the ratio, the number of pore volumes required to plug the pore throats increases, leading to greater deposit thickness. Our findings support that the Al2O3 content delays asphaltenes’ nanoaggregation and has higher selectivity toward bigger molecules. asphaltenes in capillary flow by experiment and simulation. Schneider et al.26 designed a microfluidic apparatus and a UV−vis intrument to correlate absorbance with asphaltenes’ weight content. Hu et al.27 designed a microfluidic reservoir with quartz packing and characterized damage to it by asphaltenes. The effect of the chemical environment on asphaltenes has been studied for: salinity,29 salinity + aluminosilicates,30 acidity,31and oxides,5,21,24 etc. In this study, we attempted to scale down a reservoir (μReservoir; near wellbore, in production time scale) replica of a rock formation chemical matrix (sand and clay) and study the impact of aluminosilicates. This was successfully achieved by assembling a porous quartz packing and incorporating aluminosilicates fine particles (HZMS-5) with different Al2O3/SiO2 content. The effect of the Al2O3/SiO2 ratio (0 [bed without fine particles], 1/91, and 1/26; chemical environment) on asphaltenes bed damaging was investigated using UV−vis spectroscopy, pressure sensors, and in situ Raman spectroscopy. The UV−vis and the pressure drop gave us insight into how Al2O3 content affects bed porosity and the asphaltenes adsorption mechanism. To understand the interaction between asphaltenes and Al2O3 content, two Raman spectroscopy methodologies were developed to further characterize the precipitated asphaltenes. μReservoirs were 2D and 3D mapped for asphaltenes sheet size and asphaltenes occupancy on the quartz surface. We shall see that these characterization methods allow us to add additional highthroughput information to a geological laboratory device, going from molecular scale to microscale. This helps obtain more reliable data by adding a whole new microscopic frame of reference.
I
nvestigating the interactions between inorganic compounds and asphaltenes is key to understanding oil precipitation, deposition, and remediation. There is a vast amount of research that has been conducted to explain the effect of the chemical environment on asphaltenes deposition.1−6 The chemical environment infers chemical composition, molecular structure,7−9 bed porosity, pressure, and temperature. It affects other research fields, such as solubility,10−12 aggregation and flocculation,13−17 adsorption/desorption,17−20 and so on. It is not uncommon to encounter inorganic compounds during the extraction process. The sandstone reservoir matrix is often composed of a vast number of oxides, such as ZrO2, CaCO3, TiO2, SiO2, MgO, Al2O3, and CeO2.5,21 Changes in the reservoir’s matrix (composition) affects aggregation and deposition on rock formations, wellbores, flowlines, and contact surfaces.22,23 In addition, changes in the asphaltenes type studied lead to different interactions, due to heteroatoms, such as nitrogen, sulfur, oxygen, nickel, and vanadium.4 As an example, TiO2 nanoparticles enhance the stability of asphaltenes’ nanoaggregates through the formation of hydrogen bonds at acidic conditions.5 Insight on the effect of the chemical environment would help the oil industry to implement better remedial processes, thereby increasing the productivity of oil and efficiency in the unit processes and operations. There is significant potential to better understand the chemical environment effect on asphaltenes by using transparent devices (i.e., lab-on-a-chip device). They are an interesting solution because of their reduced scales, enhanced mixing of multiphase flows, controlled and reproducible environment, and faster experiments. A significant number of studies have been done on asphaltenes aggregation/flocculation/deposition in porous media using microfluidic devices.1,19,24−27 A few examples can be cited. Boek et al.28 studied the deposition and aggregation of colloidal © 2017 American Chemical Society
Received: June 20, 2017 Revised: September 29, 2017 Published: September 29, 2017 11640
DOI: 10.1021/acs.energyfuels.7b01748 Energy Fuels 2017, 31, 11640−11650
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microfluidic device (III). Two Teledyne 65DM syringe pumps were used to precipitate asphaltenes: one for 4 g·L−1 asphaltenes dissolved in toluene and another for n-heptane or 15.2 μg·L−1 HZSM-5 dispersed on isopropanol. For the RTD experiments, a Harvard Apparatus PHD 2000 syringe pump with two 5 mL glass syringes (Hamilton 1010C) was used to inject n-heptane (carrier) and acetone (tracer). The tubing used in the setup is made of PEEK and stainless steel, having 1/50 in inner diameter and 1/16 in outer diameter. At the module block (II), each fluid was filtered with a stainless steel frit with 20 μm pore size, IDEX Health & Science and purged with a series of on/off valves to prevent contamination. A series of check valves were added to prevent leakages and backflows. They act when ΔP > 0.03 bar. The asphaltenes dissolved in toluene were mixed with n-heptane in a stainless steel T-union within an ultrasonic bath (VWR International) to prevent asphaltenes aggregation prior to the μPBR. From the mixing point to the device there is 49 μL of swept volume. Two pressure transducers (Honeywell SPT4 V0500PG5W02; maximum 32 bar; accuracy, ±0.25%) were placed before the T-union. No pressure transducer or back-pressure regulator was placed downstream from the μPBR. By monitoring both pressure transducers, it is possible to perform pressure drop analysis and check anomalies on the mixing point. Regarding the module block (II) for RTD experiments, a microscale injector (8125, IDEX Health & Science) with a 5 μL sample loop was used. The absorbance was measured at the process downstream (IV), using an online UV−vis spectroscopy cell (Ocean Optics) placed at a wavelength of 277 nm20 for maximizing signal-to-noise ratio, and the acquisition time was set to 0.1 s. The UV light source was allowed to warm up for at least 20 min before performing the experiments. Experimental Procedure. To characterize the μPBR before and after damaging, six sets of experiments were performed: (I) determine void volume by RTD measurements on an empty (EμBPR) and quartzpacked μReservoir (μPBR), (II) inject zeolites fine particles (H-ZSM-5) on the μReservoir packed with quartz (μBPR+Z), (III) perform asphaltenes deposition (DμBPR and DμBPR+Z), (IV) perform RTD measurements to quantify changes in the μReservoir void volume, (V) dry the μReservoir by natural convention, and (VI) characterize the
EXPERIMENTAL SECTION
Chemicals and Materials. n-Heptane (HPLC grade, 99% purity) was purchased from Alfa Aesar. Toluene (HPLC grade, >99.9% purity) was purchased from BDH Chemicals VWR. Ethanol (absolute, >99.5% purity), isopropanol (HPLC, 99.7% purity), and acetone (HPLC grade, 99.8% purity) were obtained from Millipore. The previous chemicals were used without further purification. Quartz sand (420−590 μm) was purchased from VWR International. The zeolites HZSM-5 (Al2O3/SiO2 molar ratio of 1/26 and 1/91) were purchased from ACS Material, having a water content Al2O3 (4.32 × 102 kJ·mol−1) > SiO2 (2.09 × 102 kJ·mol−1). Taking into account that in μReservoirs the early pore throat plugging is caused by hydrodynamic bridging of large asphaltenes aggregates, the addition of HZSM-5 seems to destabilize the asphaltenes aggregation process. This may be seen as a decrease in the fouling rate (lower collision efficiency between growing asphaltenes aggregates). Between the zeolites tested, the impact in the early plugging is allied with the number of Al2O3 active sites present in the HZSM-5.3,5,18 When Al2O3 substitutes the SiO2 in a tetrahedral zeolite framework, a cation is required to satisfy the Al2O3 tetrahedron. Adding Al2O3 content in the zeolite framework makes the number of Brønsted acid sites increase linearly with the Al2O3 content.49 The number of Brønsted active sites ranges from 0.24 to 0.71 mol·kg−150 for Al2O3/SiO2 of 1/91 and 1/26, respectively.51 Although the Al2O3 content present on the bed delays pore throat plugging (Figure 6), it was previously seen (Figure 5; Table 1) that there is twice the amount of asphaltenes deposited on a DμPBR+Z with Al2O3 than on a DμPBR. This is expected because higher fluid content flows through the μReservoir without having early pore throat plugging. Al2O3 may also have a role in regulating the multilayer of asphaltenes on the SiO2 deposits.
Table 1. Void Volume, Porosity, and Asphaltenes’ Mass Deposited on the Different μReservoirs reservoir
void vol (μL)
ε
mass deposited (mg)
EμPBR μPBR μPBR+Z DμPBR DμPBR+Z (Al2O3/SiO2 = 1/91) DμPBR+Z(Al2O3/SiO2 = 1/26)
53.0 ± 0.8 26.5 ± 0.9 24.5 ± 1.3 22.5 ± 3.7 13.5 ± 2.7 14.7 ± 5.5
1.00 0.50 ± 0.01 0.45 ± 0.03 0.40 ± 0.07 0.27 ± 0.04 0.29 ± 0.10
0.00 0.00 0.00 2.39 ± 2.15 6.57 ± 1.44 5.58 ± 3.23
As the number of asphaltenes layers deposited on the bed surface increases, the different color contrast appears. Dark brown means that the quartz particle reaches the maximum number of layers for the maximum pressure drop imposed. The effective deposited thickness ranges from δ* to δmax (later estimated). The white means that no layer was yet deposited at the quartz surface. To better understand and characterize these zones, each bed (Figure 5) was characterized according to its pressure drop (ΔP, bar), asphaltenes sheet size (La, nm), and asphaltenes occupancy on the quartz surface (ϖQ). Pressure Drop Measurements during Asphaltenes Deposition. Measuring the pressure drop across the μPBR and μPBR+Z during asphaltenes deposition helps uncover information about molecular interactions: asphaltenes-to-asphaltenes, -to-quartz, and -to-zeolite. Through monitoring pressure over time for several replicates [up to 6 bar (ΔPtotal)], it is possible to evaluate the impact of different Al2O3/SiO2 ratios. Before proceeding with the asphaltenes deposition, n-heptane was first injected at 40 μL·min−1 across the μPBR and μPBR+Z, and the pressure drop (ΔP0) was monitored from 33 min, having a value of 0.037 ± 0.005 bar. The ΔP0 will be later used to make pressure dimensionless. Figure 6 shows the pressure drop behavior during asphaltenes deposition for different Al2O3/SiO2 molar ratios: 0, 1/91, and 1/26. Deposition is often associated with polydispersity, wettability, steric colloid formation, aggregation, and electrokinetics, leading 11645
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Energy & Fuels To have an insight on this phenomenon, Raman mapping of the damaged μReservoir was performed (asphaltenes sheet characterization). The deposition mechanism is outside the scope of this work. Estimation of the Maximum Deposited Effective Thickness. The maximum effective deposited thickness (δmax) was estimated for the maximum pressure drop imposed. This value will be useful to later help us estimate the minimum thickness that fully blocks light transmission (δ*). The minimum theoretical value for hydraulic radius (rH, min) was estimated considering the following: (i) the pore network as a network of ideal capillaries (Hagen−Poiseuille’s equation),1 (ii) the flow distribution not affected during the asphaltenes deposition through the pore network, and (iii) no mechanical entrapment associated. We are aware that these assumptions are greatly simplified and that they might not even be true; nevertheless, it will give us information toward understanding the ranges where δ* is placed (using eqs 9 and 10, based on Lawal et al.1). rH,0 4 μt ΔPt = ΔP0 μ0 rH, t 4
(9)
rH, t = rH,0 − δt max
(10)
content, 0 to 1/26, going from shades of blue (∼2.44 nm) to shades of green (∼2.76 nm). By observation, the sheet size is homogeneously distributed on the DμPBR (Figure 7 A1) and DμPBR+Z (Figure 7 B1,C1). This indirectly means that the Al2O3/SiO2 content injected, in a form H-ZSM5, are homogeneously distributed throughout the μReservoir. Based on the asphaltenes sheet size maps, several histograms were created per trial and Al2O3/SiO2 ratio (Figure 7 A2,B2,C2). Among all the trials, the histograms seem normally distributed. Concerning the histograms per Al2O3/SiO2 ratio, the standard deviation slightly changes between trials, having deviations up to 25% of the average value. We presume that this is related to (i) stochastic behavior of the flow distribution inside the reactor, due to molecular entrapment and adsorption/desorption mechanisms, and (ii) polydispersity of the molecules layered on top of the mineral bed surface. Panels A and B of Figure 8 show the average and standard deviations of the asphaltenes sheet size, Panels C and D of Figure 8 show the average and standard deviations of fwhm ratio. At high Al2O3/SiO2 content, 1/26, asphaltenes deposited have 2.76 ± 0.82 nm and fwhm ratio of 0.42 ± 0.09. In opposition, when no Al2O3/SiO2 is present, the molecules are 13% smaller, being 2.44 ± 0.51 nm, and have fwhm ratio of 0.38 ± 0.05 (the molecular weight can be related to the size of typical asphaltenes molecules; refer to the Support Information). These results can be attributed to the morphology and surface chemistry of the different types of HZSM-5 with Al2O3 used. The effect of the HZSM-5 structure and morphology on the sheet size deposition is minimal, indicated by the close results between Al2O3/SiO2 of 0 and 1/91, Figure 8A,B. This implies that the nature of HZSM-5 surface chemistry (Al2O3 active sites) plays a significant role in the aggregation process (nanoaggregation, clustering, and flocculation, as proposed by the modified Yen model54) and deposition process. Panels A and B of Figure 8 show that the higher the Al2O3 content, the larger asphaltenes deposited. We argue that Al2O3 acts as a selective sieve toward larger asphaltenes structures. This is further supported when comparing the asphaltenes sheet size prior to the μPBR (2.63 μm) and inside the μPBR (2.44, 2.53, and 2.76 μm; obtained for different Al2O3/SiO2 ratios), which is between the sheet sizes obtained on the μPBR. There are two associated effects that can explain the sheet size variation: (i) Al2O3 active sites have higher affinity toward molecules with a higher number of functional groups and heteroatoms, which is more often present in larger molecules, and (ii) Al2O3 stabilizes the media, preventing asphaltenes aggregation by steric repulsion between aliphatic side chains, avoiding asphaltenes in T-shape configurations. It makes the self-assembling of nanoaggregates composed by small structures less likely [less aromatic cores ⇒ smaller molecular weight ⇒ lower dimerization free energy (ΔG)55,56], and therefore, less prone to aggregate and to deposit (aggregation number > 2555). According to molecular simulations reported by Sedghi et al.55 for asphaltenes in n-heptane, when a cluster is not stable enough to flocculate, nanoaggregates tend to attach and detach continuously (oscillations). This holds true to asphaltenes−bed interactions. Interestingly, pressure oscillations are more pronounced for Al2O3/SiO2 ratio of 1/26 than for no Al2O3 (Figure 6), which endorses this point. The work of Mohammadi et al.5 is also in agreement with the reduction of the average size of the aggregates by the presence of an oxide, in their case TiO2. Even knowing that the sheet size helps one understand the effect of Al2O3 on asphaltenes deposition, it is important to
where ΔPt and ΔP0 (bar) refers to the pressure drop across a pore throat before and after the asphaltenes deposition at t time, rH (μm) refers to the hydraulic radius, μ (mPa·s) refers to the fluid viscosity, and δt max (μm) refers to the effective asphaltenes deposited thickness. For the 0 subscript, n-heptane was used instead of the mixture of asphaltenes on toluene/ n-heptane. The properties of the fluid mixture (toluene/n-heptane) were calculated using PRO/II SIMSCI correlation, based on Twu52) with Peng−Robinson 78 thermodynamic package, being 792.2 and 0.49 mPa·s (293 K and 1 bar (gauge)). n-Heptane has 679.6 kg·m−3 and 0.38 mPa·s. Theoretically, when the μReservoir is fully damaged, its (minimum) hydraulic radius is ∼1.18 μm, and δt max is ∼3.43 μm· particle−1. Knowing that the bed was never 100% damaged (the overall occupancy ϖ < 1), δ* is probably between 2.05 (δt for Al2O3/SiO2 of 1/26) and 3.43 μm·particle−1 (δt max ). Asphaltenes Sheet Size Characterization. To better explain why Al2O3 content prevents earlier deposition and leads to higher content deposited, the deposited layers were evaluated using in situ Raman spectroscopy. Our Raman methodology was used to characterize the asphaltenes (aromatic) sheet size on the entire DμPBR and DμPBR+Z. For each spectrum acquired, the sheet size evaluated corresponded to the diameter of the most typical asphaltenes structure present.39,53 The fwhm ratio was used to further validate the La trend in case of low signal-to-noise ratio (greatly affects La measurements, but has virtually no impact on fwhm ratio. These data exclude the chemical environment (Raman inactive or weak), which accounts for the impacts of molecular aggregation by hydrogen and van der Waals bonds, which only affects the peak shift position. Only the strength of chemical bonds, covalent (C−C bond stretching) and ionic, are Raman active and can be accounted toward the sheet size (spectral intensities).40 The asphaltenes sheet size at the source (before μPBR) is 2.63 ± 0.53 nm (see Supporting Information). Panels A1, B1, and C1 of Figure 7 show a map of the asphaltenes sheet size for different Al2O3/SiO2 ratios: 0, 1/91, and 1/26. The sheet size is displayed between 2.44 and 2.76 nm, and the fwhm ratio is between 0.38 and 0.42. A close inspection of Figure 7 reveals color changes when increasing the Al2O3/SiO2 11646
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Figure 7. (A1−A3) 2D maps of the asphaltenes sheet size (La) against Al2O3/SiO2 ratios: 0, 1/91, and 1/26. Only the first trials for each Al2O3/SiO2 ratio were displayed. (B1−B3) Histograms of the asphaltenes sheet size against Al2O3/SiO2 ratio. All the data were acquired at 298 K. (C1−3) Histograms of the fwhm ratio (eq 4) against Al2O3/SiO2 ratio. Three trials were plotted per Al2O3/SiO2 ratio studied, and the average and standard deviation are present for all the trials.
characterize the asphaltenes dispersion throughout the μReservoir (ϖ, asphaltenes bed occupancy). Asphaltenes Bed Occupancy Characterization. Figure 9 shows the asphaltenes bed occupancy (ϖ) obtained from Raman analyzes for the different Al2O3/SiO2 ratios studied: 0, 1/91, and 1/26. According to Figures 9 and 10, asphaltenes are heterogeneously dispersed independently on the Al2O3 content. As an example, ϖ histograms for the μPBR without Al2O3 have considerable differences between trials (Figure 9A1), going from a bimodal distribution, ϖ = 0.42 (trial I), to a unimodal distribution, ϖ = 0.62 (trial III). Changes on the flow distribution overtime are responsible for the heterogeneity on the asphaltenes deposition (Figure 9A1−A3). At the early stage of asphaltenes deposition, the flow distribution is similar over the porous network. This is supported by low deviations on the porosity for undamaged μPBR and μPBR+Z, and by the presence of asphaltenes deposits all over the DμPBR and DμPBR+Z (Figure 10) (minimum, ϖ = 0.1). The flow distribution changes significantly over time, and the pore throats are heterogeneously plugged by molecular entrapment or chemical adsorption, changing local permeability, and consequently the flow distribution. The zones with higher occupancy on Figure 10 are direct evidence of changes in flow distribution during asphaltenes deposition. It is expected that inferior overall flow distribution across the bed leads to higher occupancy contrasts. It was found that by increasing Al2O3 content, the mean occupancy across the bed increases (Δϖ > 0.1), being 0.71 ± 0.11 and 0.64 ± 0.14 for
Al2O3/SiO2 of 1/91 and 1/26, when compared to 0.55 ± 0.16 for a bed without Al2O3 content (Figure 9B). This behavior shows that the overall flow distribution is less affected during deposition when Al2O3 content is present. This outcome is in good agreement with our earlier results, which support higher affinity of Al2O3 toward molecules with a higher number of functional groups and heteroatoms. It is also in agreement with flow visualization experiments on transparent rectangular microchannels, where it is stated that the asphaltenes deposition is not homogeneous but a function of the distance from the microfluidic entrance,1,28,57 having a highly nonuniform axial deposit. Depth Bed Characterization: Asphaltenes Sheet Size and Occupancy. To better understand if the channel depth has impact on the sheet size and occupancy results, 3D maps [ϖ vs x (μm) vs y (μm); La (μm) vs x (μm) vs y (μm)] were done for the bed (Figure 11), ranging from 0 to 200 μm. This range helps account for “hills” and “valleys” of the bed, which leads to enhancements (laser acquires more information when zooming on “valley”) and reductions on the signal (laser defocus when zooming on a “hill”, providing less information). Since, the present bed is compact to a εDμPBR+Z of 0.27 ± 0.04 (Al2O3/SiO2 = 1/91) (Figure 10), little signal enhancement (void surface area fraction ≈ 0.27) and more reductions of the hills (occupied surface area fraction ≈ 0.73) are expected. Figure 11 shows that depth does not influence the occupancy values, staying constantly at 0.89 ± 0.07. The asphaltenes sheet size (La) slightly changes, going from 2.79 to 2.46 nm. This result can be considered as an artifact, because the overall intensity of 11647
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Figure 9. (A1−A3) Histograms of the asphaltenes bed occupancy against Al2O3/SiO2 ratio. Three trials were plotted per Al2O3/SiO2 ratio studied, and the average and standard deviation are present in all of the trials. (B) Mean occupancy per Al2O3/SiO2 ratio studied. All the data were acquired at 298 K.
Figure 8. (A) Average asphaltenes sheet size (La) against Al2O3/SiO2 ratio. (B) Asphaltenes sheet size standard deviation (std) against Al2O3/ SiO2 ratio. (C) Asphaltenes fwhm ratio against Al2O3/SiO2 ratio. (D) Asphaltenes fwhm ratio standard deviation (std) against Al2O3/ SiO2 ratio. The blue lines displayed in panels A−D are trend lines. Al2O3/SiO2 ratio of 0 means no Al2O3 and no zeolites present on the μReservoir bed. The asphaltenes’ structures8,21 are present as an example. Their dimensions were estimated using a force field in a gas phase.
We successfully created a reproduction of a porous rock reservoir (near wellbore, in production time scale) chemical matrix on a microscale, by adding inorganic oxides (fine particles of HZSM-5) to a quartz bed. The effects of different Al2O3/SiO2 ratios, 0, 1/91, and 1/26, on asphaltenes deposition throughout the bed were carefully studied using different characterization techniques, such as RTD (residence time distribution), pressure drop, sheet size, and bed occupancy. Residence time distribution experiments were designed effectively to determine the volume of quartz, zeolite, and asphaltenes inside the microreactor. Reproducible and stable packings of quartz particles with aluminosilicates (HZSM-5) with a porosity of ∼0.45 ± 0.03 were designed. It was shown that the Al2O3/SiO2 ratio influences the deposition process in several ways (i−iv). (i) Al2O3 acts as a preventive agent in the asphaltenes deposition process by reducing early pore throat plugging, which reduces asphaltenes aggregation, and mechanical entrapment. Al2O3/ SiO2 ratio of 1/26 requires 2.5 times more pore volumes when compared to no Al2O3. (ii) The mass of asphaltenes entrapped across the bed increases with the Al2O3 content, being at least twice for 1/91 and 1/26 Al2O3/SiO2 ratio. (iii) The average asphaltenes sheet size entrapped increases 10% with the increase of Al2O3/SiO2 ratio, 0 to 1/26, which indicates higher selectively of Al2O3 toward bigger molecules. (iv) Raman occupancy
the spectra decreases, which leads to less intensity for the G and D1 bands. Therefore, the D1 band gets smaller; consequently, the noise has higher impact, which makes the area obtained from the peak deconvolution less accurate. Therefore, when applying eq 3, the IG becomes higher than ID1. This explanation is supported by having almost no difference between fwhm ratio results for 0 and 100 μm. This zone can be considered as the optimal channel depth to do mapping analysis. In the present work, the depth of 30 μm is where there is optical focus.
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CONCLUSION The possibility to investigate asphaltenes deposition on a microfluidic scale offers access to high-throughput screening and characterization methodologies. In this work, we developed methodologies to further characterize a damaged μReservoir with in situ Raman techniques; the aim is to map the μReservoir for molecular information about the asphaltenes sheet size, and for the distribution of asphaltenes deposits (defined as bed occupancy). 11648
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mapping of a dried bed show higher bed occupancy and lower channeling during asphaltenes deposition when adding Al2O3 content.
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ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.energyfuels.7b01748. Derivation of occupancy expression; dynamic light scattering results of HZMS-5 (Figure 1S); calibration curve for Raman spectroscopy (Figure 2S); process module for RTD and deposition experiments (Figure 3S); estimated molecular weight size against molecular weight (Figure 4S); asphaltenes sheet size for the asphaltenes source (Figure 5S); and molecular structures and size estimates (Table 1) (PDF)
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Figure 10. 2D maps of the asphaltenes bed occupancies against Al2O3/ SiO2 ratios: 0, 1/91, and 1/26. The maps were obtained using Raman mapping and eq 7.
AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. ORCID
Ryan L. Hartman: 0000-0002-5364-9933 Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS We gratefully acknowledge Nalco Champion, an Ecolab company, and Anadarko Petroleum Corp. for funding. We also acknowledge Weiqi Chen for his help with the in-house code for analyses.
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ABBREVIATIONS DμPBR = damaged (with asphaltenes) micro packed-bed (quartz) reservoir DμPBR+Z = damaged (with asphaltenes) micro packed-bed reservoir with zeolites EμPBR = empty micro packed-bed reservoir fwhm = full width at half-maximum RTD = residence time distribution μPBR = micro packed-bed (quartz) reservoir μPBR+Z = micro packed-bed reservoir with zeolites REFERENCES
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Figure 11. 3D maps [ϖ vs y (μm) vs x (μm)] of the occupancy against the bed depth analyzed. The information regarding occupancy, the sheet size (La) and the fwhm ratio are shown in the figure for each depth. Only the occupancy 3D information is presented. 11649
DOI: 10.1021/acs.energyfuels.7b01748 Energy Fuels 2017, 31, 11640−11650
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DOI: 10.1021/acs.energyfuels.7b01748 Energy Fuels 2017, 31, 11640−11650
