Energy & Fuels 2008, 22, 1739–1746
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Selective Adsorption of Thermal Cracked Heavy Molecules Lante Carbognani, Manuel F. González,† Francisco Lopez-Linares, Clementina Sosa Stull, and Pedro Pereira-Almao* Schulich School of Engineering, UniVersity of Calgary, Calgary, Alberta, T2N 1N4 Canada ReceiVed NoVember 16, 2007. ReVised Manuscript ReceiVed February 14, 2008
The production of modified heavy molecules via thermal cracking (visbreaking) and their corresponding adsorption over macroporous silica–alumina, such as kaolin, is described. The characterization of cracked products in terms of hydrocarbon type SARA distributions and stability indexes (P value) is discussed. Improving the properties of visbreaking products after adsorption over kaolin adsorbent with the quantification of organic adsorbates is presented. Preliminary insights on the nature of those organic adsorbates are described. The feasibility of including an adsorption step after thermal cracking for process improvement is demonstrated in this article.
Introduction Increased reliance on heavy/extra-heavy oils (HO and XHO) is globally expected for the foreseeable future. Before global energy demand can be provided by alternative/emerging sources and technologies, HO and XHO will find extended use as substitutes for declining light oils.1 Development of costeffective upgrading schemes for heavy hydrocarbon reserves is a must due to its intrinsic heavy nature. HO and XHO typically contain more than 50 wt % of components remaining within distillation vacuum residues. Upgrading these feedstocks is technologically challenging and energy intensive. Moreover, viscosity improvement for enhanced production and transportation is frequently achieved by dilution processes. The increase on bitumen production could face a potential bottleneck due to the increase of solvent requirements and the future diluents availability, since HO and XHO are devoid of these fractions. In addition, several upgrading technologies rely on hydrogen addition. Generation of this expensive upgrading component is always an issue. So far, the most common hydrogen generation process used for upgrading heavy hydrocarbons is steam reforming of natural gas and/or naphtha. Based on the expected increase demand of diluents and hydrogen, it is possible to forecast an important constraint in the HO and XHO production and refining industry. An alternative cost-effective way of producing hydrogen and the release of naphtha and natural gas consumption could be an integrated process which comprises three steps: (1) thermal cracking of vacuum residua from HO and XHO, (2) adsorption step which may selectively capture at least a fraction of the heaviest hydrocarbon molecules, those most instable, and (3) low-temperature catalytic steam gasification (CSG) of the adsorbed compounds. For this study, visbreaking (VB), a mild version of thermal cracking processes, was the selected option for molecular modification of residua.2 Under VB conditions, residues are partitioned into low molecular weight (MW) * To whom correspondence should be addressed. Telephone: +1 (403) 220-4799. Fax: +1 (403) 284-4852. E-mail:
[email protected]. † Present address: Jacobs Consultancy Canada Inc., 400S, 8500 Macleod Trail S., Calgary, AB, Canada, T2H 2N7. (1) Roberts, P. The End of Oil: On the Edge of a Perilous New World; Mariner Books: Wilmington, MA, 2005.
distillates and hydrogen-deficient bottoms (visbroken residues). Further, insoluble heavy molecules and coke are generated when the process is carried at more severe conditions.3,4 VB yield is controlled by the stability of the visbroken product, which is grossly determined by the asphaltene precipitation. Under typical VB conditions, upper conversion limits typically reach values of 30 wt % for highly aromatic feedstocks. At this conversion level, product stability reaches a minimum critical value, commonly expressed by a peptization parameter (P value) ∼1.1.5 The continuous trend toward instability conditions along a VB process is derived from several simultaneous effects such as the following: (1) aromatic molecules lose rapidly their alkyl appendages, increasing their aromaticity; (2) solubilizing maltene phase becomes enriched in alkyl compounds which are not properly suited for maintaining aromatic compounds in solution;4 and (3) reduction in the resins/asphaltene ratio which means the reduction of the capacity of asphaltene to remain dispersed or solubilized.6 For the second step, a potential adsorbent that also acts as catalyst was designed aiming the retention of thermally modified heavy hydrocarbon molecules in order to be gassified later for hydrogen production at low cost. Clays are solid substrates that have been studied for adsorption of polar hydrocarbons.7–12 The existence of natural clay-organics composite materials within heavy oil was recently reported.13,14 If the adsorptive properties of clays can be improved by modifying their textural properties such as surface area and pore size, an optimized route for the removal of modified large MW polar compounds is open. Incorporation of iron oxides can improve organics retention over solid adsorbents.15 Also, the incorporation of active metals for catalytic steam gasification16–19 (2) Speight, J G.; Ozum, B. Petroleum Refining; Marcel Dekker: New York, 2002. (3) Omole, O.; Olieh, M. N.; Osinovo, T. Fuel 1999, 78, 1489. (4) Singh, J.; Kumar, M. M.; Saxena, A. K.; Kumar, S. Chem. Eng. Sci. 2004, 59, 4505. (5) diCarlo, S.; Janis, B. Chem. Eng. Sci. 1992, 47, 2695. (6) Koots, J. A.; Speight, J. G. Fuel 1975, 54, 179. (7) Lopez-Linares, F.; Sosa Stull, C.; Gonzalez, M. F.; Pereira-Almao, P. Prepr. Am. Chem. Soc., DiV. Fuel Chem. 2005, 50, 786. (8) Charlesworth, J. M. Geoch. Cosmochim. Acta 1986, 50, 1431. (9) Bantignies, J. L.; Cartier dit Moulin, C.; Dexpert, H.; Frank, A. M.; Williams, G. C. R. Acad. Sci., Paris, Ser. II 1995, 320–699. (10) Cooper, W. J.; Hayes, J. M. J. Chromatogr. 1984, 314, 111.
10.1021/ef700690v CCC: $40.75 2008 American Chemical Society Published on Web 04/11/2008
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is also desired in order to produce hydrogen from those fractions. This alternative for hydrogen production at upgrading facilities expectedly will be attractive for both installed and future units. Such a potential application would benefit the quality of the synthetic crude being produced since heavy compounds like asphaltene contribute considerably to its quality limitations as well as the reduction on the amount of diluents required for transportation. Additionally, hydrogen resulting from the gasification of these heavy compounds could either be used for refining purposes or for in situ reservoir upgrading of HO. In this paper, we present the results concerning to the thermal modification of Athabasca vacuum residue, using visbreaking as thermal process. Then, adsorption of the more unstable fractions in a modified natural silica–alumina such as kaolin is studied. Kaolins are designed with enhanced macroporosity in order to minimize physical constraints for the access of the molecules to the surface of the adsorbent. Description of the methodology used as well as the main results and preliminary conclusions are presented. Experimental Section Materials. Toluene, n-heptane, dichloromethane (spectrophotometric grade, Sigma-Aldrich), n-hexadecane, and chloroform (HPLC grade, Sigma-Aldrich) were used as received. A vacuum residue from Athabasca bitumen provided by Suncor was studied in this work. This feedstock contains 26 wt % distillable fractions (545 °C-), as determined by gas chromatography simulated distillation (SimDist).20 An amount of about 0.7 wt % of insoluble materials in chlorinated solvents (methylene chloride and/or chloroform) was determined to be present within the sample. Solid Adsorbent/Catalysts Synthesis and Characterization. The adsorbent was prepared in order to achieve important macropores proportions with an average diameter higher than 50 nm, in order to allow the penetration of large molecules like asphaltene. The preparation starts with kaolin as primary component (Al2O3 ∼ 39.0 wt %, SiO2 ∼ 43.5 wt %) which is combined with a binder and porogen material in order to modify the textural properties. The resulted material is then calcined up to 650 °C for 8 h. After the preparation of the absorbent, characterization was performed (pore volume, surface area, pore diameter, etc.) by BET method using a CHEMBET-3000 equipment and mercury porosimetry from Quantachrome Instruments. The prepared macroporous kaolin has a maximum pore volume lower than 1 cm3/g and surface area lower than 20 m2/g.7 Each sample was dried at 150 °C prior adsorption experiments and stored in desiccators for further use. The adsorbent acidity was determined by NH3 thermal program desorption (TPD), being 520.4 µmol NH3/g adsorbent. Metal-loaded catalysts for CSG applications16–19 were prepared by incipient wet impregnation with the desired metal salts over the macroporous kaolin. Catalysts were calcined up to 650 °C for 8 h. Adsorption of visbroken materials (11) Murgich, J.; Rodríguez, J.; Izquierdo, A.; Carbognani, L.; Rogel, E. Energy Fuels 1998, 12, 339. (12) van Duin, A. C. T.; Larter, S. R. Org. Geochem. 2001, 32, 143. (13) Strausz, O. P.; Lown, E. M. In The Chemistry of Alberta Oil Sands, Bitumens and HeaVy Oils; Alberta Energy Research Institute: Calgary, AB, Canada, 2003; Chapter 8. (14) Tu, Y.; Kingston, D.; Kung, J.; Kotlyar, L. S.; Sparks, B. Pet. Sci. Technol. 2006, 24, 327. (15) Carbognani, L. Pet. Sci. Technol. 2000, 18, 335. (16) Pereira, P.; Csencsits, R.; Somorjai, G. A.; Heinemann, H. J. Catal. 1990, 123, 463. (17) Carrazza, J.; Tysoe, W. T.; Heinemann, H.; Somorjai, G. A. J. Catal. 1985, 96, 234. (18) Delanay, F.; Tysoe, W. T.; Heinemann, H.; Somorjai, G. A. Appl. Catal. 1984, 10, 111–123. (19) Domazetis, G.; Liesegang, J.; James, B. D. Fuel Process. Technol. 2005, 86, 463. (20) Carbognani, L.; Lubkowitz, J.; Gonzalez, M. F.; Pereira-Almao, P. Energy Fuels 2007, 21, 2831.
Carbognani et al. over several of these catalysts is reported in this work; however, catalytic steam gasification will be a topic for future communications. Vacuum Residue Thermal Cracking. Visbreaking of the Athabasca VR was carried out at 380 °C, under ambient pressure. Varying reaction times allowed collecting products with diverse conversion levels, up to 35 wt %. The end of experiments was determined when the desired precalculated amount of distillates was collected. VB was carried out under an inert atmosphere (N2), the light products being carried away by applying a slight N2 sweep. The reactions were carried out in a three-neck 500 mL round-bottom flask provided with N2 inlet, thermometer, and condenser. Depending on the reaction scale, 250 or 400 g of VR is employed and the reaction mixture is stirred with a magnetic bar. Yields and conversion levels were determined by weighing the reactor contents before and after VB. Stability of the products was determined by titration with n-cetane at 100 °C, the appearance of precipitated asphaltene being detected by visible-light microscopy carried out at ambient temperature. One drop of the titration mixture was poured over a microscope slide and, while still warm, tightly pressed with a cover slide in order to produce a thin film. After reaching ambient temperature, samples were observed within an optical microscope. A National Model DC3-163 microscope provided with a camera system and Motic Images 2000 software (version 1.3) was used. Monitoring was generally performed with a magnifying power of 40× and adoption of the camera enhanced mixtures observation. Sample stability was determined according to former reported procedures relying on n-cetane P values.5 The error for P value determinations, according to the standarized methodology, is 0.05 for samples within the 1 to 300 °C) were selected for adsorption experiments carried out during 1 h. At the end of (21) Carbognani, L; Gonzalez, M. F.; Pereira-Almao, P. Energy Fuels 2007, 21, 1631. (22) González, M. F.; Sosa Stull, C.; López-Linares, F.; Pereira-Almao, P. Energy Fuels 2007, 21, 234.
Modified HeaVy Molecules Via Thermal Cracking adsorption experiments, the organic phase was poured into vials and the adsorbent covered with the remaining organics was transferred with methylene chloride (DCM) washings into a Soxhlet thimble. Physisorbed materials were removed from the adsorbent until no color was visually observed in the Soxhlet extractor. The extracted solid adsorbent containing chemisorbed organics was dried inside vacuum desiccators. Dynamic adsorber experiments were carried out with a packed column containing about 9 g of adsorbent. A sample/adsorbent ratio 5/1 w/w was initially targeted (i.e., about 45 mL of residua was scheduled for percolation through the packed adsorber). However, only 2–3 fractions of about 7–8 mL were collected from the adsorber exit, since P value improvements were routinely observed for the first of these collected effluents. The system was entirely built with stainless steel (SS) parts. Adsorber dimension was 17.8 cm long × 1 cm internal diameter (i.d.). Adsorbent extrudates (rods ca. 5 mm long × 1 mm diameter) were retained with SS screens. A heated (150 °C) SS tube (25 cm long × 2.2 cm i.d.) was used for liquefied sample storage. Sample was delivered to the adsorber with an LDC-Milton Roy single piston mini-pump, maintained at 150 °C. Before entering the adsorber, a preheater coil brought samples to operating temperature (>300 °C). The adsorber body and connecting tubings (1/8 in. outer diameter (o.d.)) were heated with wrapped-around heating stripes, the whole system being covered with fiberglass insulation fabric. Temperatures for tested zones were monitored with thermocouples. Experiments were run up-flow, effluents from the adsorber being collected from a u-tube connected to the column exit. Flow during the adsorption experiments was set at 2.5 mL/min. For this phase of the study the focus was on the properties of the visbroken materials after contacting adsorbents and, consequently, the packed material containing adsorbed materials was not further analyzed. Quantification of Macroporous Kaolin Chemisorbed Organics. The extracted and dried adsorbents were analyzed for chemisorbed materials contents by thermogravimetric analysis (TGA). Thermograms under oxidizing atmosphere (air) were carried out with an SDT Q 600 system from Thermal Analysis Instruments Co. Sample losses between 150 and 900 °C were registered as total chemisorbed materials. The blank value for pure kaolin/catalyst substrate was subtracted in all cases from the determined weight losses. It was found that pure macroporous kaolin and catalysts formulated with basis on this material, loss about 0.5% w/w within the 150–900 °C range in TGA experiments run under air atmosphere. These losses were presumed to derive from the presence of remaining carbonized porogen added during the macroporous kaolin synthesis. Isolation and Characterization of Macroporous Kaolin Chemisorbed Organics. Isolation of chemisorbed organics within macroporous kaolin adsorbent was carried out by solid matrix destruction with HCl/HF. Variables affecting this procedure have been reviewed for kerogen isolation.23 About 1 g of sample (weighed to the nearest 0.1 mg) and polymeric laboratoryware was routinely used for these studies. Aqueous HCl digestion followed by aqueous HF digestion released the organics which were collected by filtering through 0.45 µm Teflon membranes. After the isolated organics were weighed, they were mixed with methylene chloride (about 50 mg of sample in 80 mL of solvent), separating the soluble portion from the insoluble one by filtering as described before. Isolated organics were characterized by Fourier transformed infrared spectroscopy (FTIR). Spectra were recorded in a Nicolet Avatar 380 spectrophotometer. Isolation of the Insoluble Mineral-Organic Solids Present in the Vacuum Residue and Visbroken Products. About 20 g aliquots of vacuum residue were diluted with 40 mL of methylene chloride. The solution was poured inside capped centrifuge Teflon test tubes and centrifuged at 3500 rpm for 60 min, the sequentially collected supernatants being pooled for recovery of the solids free residue. The procedure was repeated until clear supernatants were (23) Vandenbroucke, M. Oil Gas Sci. Technol.-ReV. IFP 2003, 58, 243.
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Figure 1. Visbreaking of Athabasca vacuum residue. Stability (P value) is plotted as a function of visbreaking severity for two sets of experiments carried out with varying sample amounts.
visually observed. Precipitated solids were dried inside vacuum desiccators for further characterization and tests.
Results and Discussion Generation and Characterization of Modified Heavy Molecules by Mild Thermal Cracking. Visbreaking (VB) was chosen as a simple and convenient thermal cracking process for modification of heavy molecules existing in vacuum residua, aiming at their retention over a solid adsorbent. Two sets of experiments employing 250 or 400 g of Athabasca VR/run were carried out. The criterion selected for ending the reaction as well as to define the level of conversion was the amount of distillate yield previously calculated. Figure 1 presents the results from these VB experiments. The two sets of runs carried out with different sample sizes were observed to proceed following a common trend of stability reduction due to the increase of conversion. The limiting stability P value of 1.1 was reached when conversion approaches 30 wt %, agreeing with former reported studies.3–5 Recombination of free radicals produced during the thermal cracking reactions might be ascribed for the observed asphaltene increases and sample’s instability. However, under the setup experimental conditions (mild cracking carried out in all-glass equipment), coke was determined to reach pretty low levels (300 °C) batch adsorption experiments. P values determined by titration with n-hexadecane and optical microscopy detection. Empty circle: P value for the “solids free” 28.5% visbroken product after contacting macroporous kaolin adsorbent (see detailed explanation within the discussion).
montmorillonite that, despite having larger surface areas, showed lower adsorption uptakes in comparison with the macroporous kaolin.33 It seems that other factors could drive the adsorption such as aromaticity or heteroatom contents in a similar way as observed recently for Athabasca-C7-asphaltene,22 indicating that the rate of adsorption may depend on specificities of the molecules being adsorbed. Nevertheless, the impact of such parameters on the adsorption of this type of fractions over different solids is currently under investigation. Having shown how this macroporous kaolin adsorbs visbroken fractions from diluted toluene solutions of Athabasca vacuum residue at ambient temperature, high-temperature adsorption experiments were then performed. Bulk residua (no solvents) were studied in batch adsorption experiments, using a ratio of sample/adsorbent 5/1 w/w. The results presented in Figure 5 shows that stability P values do not improve for the VB products obtained at lower conversions (8.7–23.3%) after being contacted with macroporous kaolin. However, the most severely visbroken product was observed to improve its stability after the adsorption process, increasing its stability from a P value of 1.1 to 1.2. The micrographs presented within Figure 5 illustrate these findings. These results show that stability detection relying on P value determinations for similar samples are pretty difficult, usually depending to a considerable degree on the operator. Monitoring with a camera system provided with a specialized software improves this aspect. The method’s accepted error is (0.05 P value units for samples falling within the 1 to 300 °C) dynamic adsorption experiments. (A) P values determined by titration with n-hexadecane and optical microscopy detection. Repeatabilities for P value determinations shown ((0.05 units). (B) Micrographs for sample studied on Exp.#3, before adsorption. (C) Micrographs for sample studied on Exp.#3, after adsorption. Black solids highlighted (“X”): native organoclay particles from mined produced bitumen.
carried out within a dynamic adsorber tower for verifying these important findings. Results are presented in Figure 7. From the findings presented in Figure 7, it is observed that thermal cracked samples processed up to P values ranging from 1.05 to 1.15 showed stability improvements after passing through the macroporous kaolin packed bed that was able to retain the most unstable compounds from the visbroken residua. Consistently, 0.1 P value units were determined within this series of experiments. Typical repeatabilities for the technique can cast doubts on the observed improvements. However, the experiment discussed above related to the solids free 28.5% visbroken product is deemed to support the claim from this paper that adsorption of visbroken products is able to remove residua components primarily responsible for sample stability. The micrograph examples included in Figure 7 show the appeareance of titrated samples before and after contacting the adsorber
Carbognani et al.
Figure 8. Athabasca visbroken products adsorption over macroporous kaolin adsorbents. Adsorbates uptake determined by TGA under air atmosphere.
particles within the dynamic adsorber. One additional outcome from these micrographs is the filtering effect brought by the adsorbed packed bed. This is evidenced by the decreased amount of mineral organoclay particles evidenced after percolation of the visbroken residue (compare Figure 7, B and C). Further studies are currently under way both in batch and flow experiments, related to bitumens produced via SAGD (steamassisted gravity drainage) which are devoid a mineral fines and vacuum residua isolated from oils produced from foreign reservoirs. Results have been additionally confirmed by microcarbon residue tests (MCR) before and after contacting adsorber beds. This set of new findings is the topic for upcoming articles, the one devoted to MCR method development being already submitted for publication.34 The fact that the most severely visbroken products were able to improve their properties after adsorption over macroporous kaolin adsorbents confirmed the hypothesis that modification of heavy molecules can selectively produce hydrocarbon mixtures with increased adsorptive properties. The adsorption uptake of organics produced during VB further support these findings, an aspect that will be discussed in the ensuing paragraph. Quantities of organics adsorbed over macroporous kaolin and/ or catalysts based on this solid were determined by TGA conducted under oxidizing atmosphere. Samples from batch adsorption experiments were analyzed in this regard. Results are presented in Figure 8. The largest amount of adsorbed materials was of the order of 34 ( 3 mg of adsorbate/g of solid. This amount agrees with values formerly reported in the open literature.7–9 Though the amount of adsorbed materials was deemed not very high with the experiments described above, it was found to depend closely on the severity of the process giving origin to the adsorbates. About twice the amount of organic adsorbates was found within the adsorbents contacting the highseverity visbroken product, compared to the less severe TC product. Several series of enhanced adsorbent/catalysts based on macroprous kaolin have been additionally produced, showing up to 4 times the cited adsorption uptakes. Optimizing engineering properties for these materials is currently under development and, eventual publication of these findings will require cleareance from the research sponsors. One aspect investigated during this study was the possible effect on the adsorption process derived from the already mentioned presence of organomineral composite solids These materials account for about 0.7% w/w of the studied Athabasca residue. Its FTIR spectrum is presented in Figure 9. Typical clay bands for Si-O (1032 cm-1) and O-H bands (3695 and (34) Hassan, A.; Carbognani, L.; Pereira-Almao, P. Development of an alternative set up for the estimation of microcarbon residue. Submitted for publication in Fuel.
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Figure 9. FTIR spectrum of the organomineral composite solid present within Athabasca VR. KBr compressed pellet.
3620 cm-1) can be clearly observed and agree with recently published results.14 Contribution of Fe2O3 for these solids is also deduced from the absorption bands observed at 538 and 472 cm-1.15 Finally, organic compounds participating within these complexes are responsible for the IR bands appearing at 2920, 2850, 1626, 1454, 800, and 696 cm-1. One important outcome from experiments carried out with organoclay particles was achieved when these insoluble organomineral composites were dispersed in toluene and contacted with the macroporous kaolin adsorbent. Negligible adsorption was determined both by TGA and gravimetric analysis, suggesting that the insoluble organominerals require a synergistic effect from other organic components in order to adsorb over kaolin adsorbents. These organomineral composites were totally removed with asphaltene when these compounds were precipitated with heptane. The observed red iron staining of asphaltene remaining ashes from the TGA analysis is due to the coprecipitated insoluble composites. The facts already presented and discussed within this section suggest that visbroken products having limiting stability properties (P value ≈1.1) can be upgraded in terms of intrinsic stability by adsorption over solid adsorbents as those selected in this study, based on macroporous kaolin. Native organomineral complexes present in residues were observed to influence the adsorption process and particularly the optical determination of P value stability indexes. Studies are currently underway in order to improve the comprehension of these complex interactions. All the findings already discussed suggest that the envisaged combined process is worth further evaluation under large scale dynamic and, ideally, field conditions. Preliminary Insights into the Nature of Chemisorbed Organics over Macroporous Kaolin. The inorganic matrices of macroporous kaolin adsorbents carrying adsorbates from batch adsorption experiments were destroyed by HCl-HF sequential treatments. The presumed “organic” adsorbates were further discriminated into soluble/insoluble portions. The results presented in Figure 10 illustrate the findings obtained to date. Inorganic materials were observed to contribute to the insoluble portions for the tests conducted so far. The distribution trends observed are not easy to understand, appearing that soluble amounts are inversely proportional to insoluble materials. No attempts have been performed for elucidating the nature of the inorganic materials. One possible reason for their presence is encapsulation within organic materials, being protected in that way toward the action of the acids. This phenomenon has been discussed recently by others.14 Some clues on the nature of the isolated fractions were derived from their FTIR spectra. These are presented in Figure 11. All the soluble portions displayed spectra that are almost exactly the same. Their IR absorption bands are those of typical
Figure 10. Athabasca visbroken products: distribution of adsorbed materials isolated from macroporous kaolin after contacting the residua samples at high temperature. Adsorbates isolation made possible by mineral matrix digestion with aqueous HCl-HF.
Figure 11. FTIR spectra of isolated adsorbates from Athabasca visbroken products. Mineral matrix from macroporous Kaolin adsorbents was destroyed by aqueous HCl-HF sequential treatment.
polar compounds as exemplified by many of the Athabasca polars published recently.35 The studied insoluble portions also resemble very much among them and, according to their FTIR spectra, they consist of mixtures of organics and inorganics (Figure 11). A striking resemblance with the original ironbearing organoclays can be established by comparing the FTIR for the insoluble from Figure 11 with the FTIR spectrum for the insoluble material presented in Figure 9. Probing the precise nature of the adsorbates studied in this work, namely the organic soluble/insoluble portions and the inorganic contributors, is a topic worth demanding further efforts. Other research groups are also studying these materials14 and one of the intriguing aspects derived from the present work is the synergistic nature that appears to influence the adsorption properties of the mixtures. Conclusions A conceived process combining thermal cracking generation of unstable molecules followed by adsorption has been presented showing that near-unstable residues (P value ≈1.1) can be upgraded in terms of intrinsic stability with additional potential conversion improvement in a visbreaking process. The adsorption uptake of heavy molecules on macroporous kaolin depends on the level of thermal cracking and is related (35) Strausz, O. P.; Lown, E. M. In The Chemistry of Alberta Oil Sands, Bitumens and Heavy Oils; Alberta Energy Research Institute: Calgary, AB, Canada, 2003; Chapter 12, p 261.
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to the resins/asphaltene ratio and product stability. The adsorption experiments confirm that the pore size developed in this material is large enough to accommodate those heavy molecules. Native organomineral complexes existing within vacuum residues participate in the adsorption process and influence the separation of solid phases from near unstable visbroken products. Preliminary findings show that organic adsorbates from visbroken products within macroporous kaolin adsorbents are complex mixtures of soluble polar compounds and insoluble organomineral composites.
Carbognani et al. Acknowledgment. Research grants provided by AERI (Alberta Energy Research Institute, Canada), AIF (Alberta Ingenuity Fund). Scholar support provided to P.P.-A. and NSERC (National Science and Engineering Research Committee of Canada) are acknowledged. Dr. Josefina Perez-Zurita from Central University of Venezuela and Professor Otto Strausz from University of Alberta (Edmonton) are thanked for helpful discussions. Luis A. Pineda is acknowledged for experimental support. EF700690V
