Catalytic Aquaprocessing of Arab Light Vacuum Residue via Short

ARTICLE pubs.acs.org/EF

Catalytic Aquaprocessing of Arab Light Vacuum Residue via Short Space Times Mazin M. Fathi* and Pedro Pereira-Almao Department of Chemical and Petroleum Engineering, Schulich School of Engineering, University of Calgary, Calgary, Alberta, T2N 1N4, Canada ABSTRACT: Finding new economic means of upgrading residuals is becoming increasingly important. In this work, the upgrading of Arabian Light vacuum residue under asphaltene stability limit by steam catalytic cracking using unsupported ultra-dispersed (UD) alkali and a non-noble transition metals catalyst is investigated in a continuous open tubular reactor pilot plant. The experiments are conducted with K/Ni UD catalyst under 260 psig at process temperatures of 430
445 °C and LHSV of 5
10.5 h
1. Experimental results showed a relative increase in the residual oil conversion of 13% by Aquaprocessing at the minimum asphaltene stability limit when compared to conventional thermal cracking. With the use of O18 labeled water, it is confirmed that the UD catalyst during reaction is capable of dissociating water into hydrogen and oxygen radicals at near visbreaking conditions.

1. INTRODUCTION The choices for many refineries to process and carry out the upgrading of residual oil have been mainly focused on conventional thermal processing technologies such as delayed coking and visbreaking,1 because of their high reliability and ability to economically produce desirable products. However, these processes are characterized by low conversion (i.e., visbreaking), and a large percentage of undesirable byproduct such as coke (i.e., delayed coking), which requires proper disposal procedures.2 Improved conversion residual oil upgrading technologies that are routinely applied in the refining industry but incur high operating costs include hydroconversion and deasphalting processes.3 Hydroconversion processes necessitate a large hydrogen supply due to a high hydrogen partial pressure requirement and hydrogen consumption necessary to complete the conversion process and reduce coke formation.4 The deasphalting processes utilize precipitant solvents, such as propane and pentane, that are subject to losses either due to process related issues or simply due to evaporation.5 The purpose of this work is to investigate an alternative means that increases upgradability of Arab light vacuum residue (ALVR) at the minimum asphaltene stability limit, providing enhanced conversions than thermal processes and being more economical than the hydroprocessing and deasphalting processes without the requirement of major equipment investment. In this study, the upgrading of ALVR by a novel technology known by the trade mark Aquaconversion, hereinafter called “Aquaprocessing” in a generic term, is reported for the first time with this type of residual oil. The study presented in this work on ALVR has never been presented for that novel process. There is relevant information and an original set of conditions with respect to the ones proposed by the patents and literature on the process, which extends beyond previous knowledge the windows of operability of that process. The conditions tested in this work were found to be sufficiently different in terms of space velocity with respect to the published results thus far on this process. From the literature review there has been no much work published on Aquaconversion experimentally other than ones r 2011 American Chemical Society

presented in the patent.6 Furthermore, there has been no reported literature on the applicability of Aquaprocessing or Aquaconversion to paraffinic residuum such as ALVR. It is well-known that the paraffinic nature of these residues and the relative instability of its asphaltenes limit the yield to distillates attainable via visbreaking with these residues in comparison with naphthenic residua. Therefore, it could be expected that the application of Aquaprocessing to ALVR and obtaining added yields over visbreaking is challenging. Aquaprocessing consists of a steam catalytic cracking (SCC) using unsupported ultra-dispersed (UD) alkali and a non-noble transition metal catalyst, first patented by Pereira et al.6 This process aims to increase the yield of light hydrocarbons with respect to those attainable with conventional visbreaking technologies for a minimal incremental investment, with the additional advantage of still producing a stable converted product. The unique feature of this novel technology is the addition of steam and oil dispersed metal precursors. It is believed the catalyst precursors decompose once subjected to high temperature at reaction conditions and produce unsupported catalytic particles for in situ (in reactor) hydrogen generation through the dissociation of steam. However, no unequivocal evidence have so far been presented on these aspects. The advantages of unsupported UD catalysts over conventional supported catalysts for processing heavy feedstocks include elimination of catalyst pore plugging issues, increasing the accessibility of highly dispersed active sites by large size reactant molecules, minimizing diffusion control,7 and more flexibility in handling used catalysts. Aquaprocessing would involve a reaction mechanism where the alkali metal, potassium in this case, is believed to promote water dissociation into hydrogen and oxygen radicals. The presence of highly reactive free radicals enhances the hydrocarbon cracking reactions, which commences simultaneously. The non-noble transition metal, nickel in this case, is believed to promote water dissociation as well as minimize the condensation reactions by Received: June 26, 2011 Revised: September 20, 2011 Published: September 28, 2011 4867

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Table 1. HTSD of Arab Light VR wt % off

°C

distillates (204
455 °C)

IBP

302

VGO (455
540 °C)

5

455.1

10

507.5

15

529.1

residue (540 °C+)

18.3

540

81.7

540+

promoting the hydrogen addition to the hydrocarbon free radicals. The proposed reaction sequence proceeds by catalytic dissociation8 of water into hydrogen radicals and hydroxyl radicals, as shown by eq 1. This reaction is accompanied by simultaneous cleavage of molecular bonds between the heavy oil molecules and their alkyl appendages by the effect of thermal energy, which produces hydrocarbon free radicals, as represented by eq 2. The UD catalyst promotes hydrogen and oxygen radicals addition to the produced free radicals and olefins, which are typical thermal cracking products. This results in hydrocarbons with lower molecular weights in addition to CO2 production, as represented by eqs 3 and 4 2H2 O f 2H• þ 2OH•

ð1Þ

R
CH2
Rn f R • þ • CH2
Rn

ð2Þ

R • þ H• f RH

ð3Þ

2OH• þ • CH2
Rn f CO2 þ 2H2 þ RnH

ð4Þ

R
CH2
Rn þ 2H2 O f RH þ CO2 þ HRn þ 2H2 ð5Þ The overall reaction eq 5 and the balanced reaction steps eqs 1
4 are provided as general representations of the upgrading mechanism. These provided possible reactions are only a small part of the complex reaction system simultaneously occurring during Aquaprocessing. The entire reaction sequence improves the heavy oil stability by effectively reducing coke precursor’s formation and asphaltene condensation reactions, which allows increasing process severity to enhance the heavy hydrocarbon conversion yield. In order to establish a baseline to measure the upgrading gain by the combined effect of UD catalyst and steam during Aquaprocessing of ALVR, noncatalytic thermal and steam cracking experiments are conducted for at least one condition of Aquaprocessing. Then, the products from the three processes are compared in terms of stability, quality, and the amount of 540 °C + hydrocarbon conversion.

2. EXPERIMENTAL PROCEDURE 2.1. Feedstock Preparation Procedure. The feedstock is ALVR provided by Saudi Aramco Oil Company. The feedstock consists of 18.3 wt % VGO and 81.7 wt % 540 °C+ residual hydrocarbons, as indicated in Table 1, with an average total acid number (TAN) of 0.5 mg KOH/g. The feedstock is prepared with the main objective of efficiently dispersing and suspending 600 ppm of catalytic metal particulates within the residual oil medium at a metals weight ratio of 3:1 (K/Ni) following the procedure developed by Pereira et al.6 Figure 1 illustrates the feedstock preparation process schematic for Aquaprocessing experiments. The feedstock is

Figure 1. Feedstock preparation schematic. prepared at 40 °C in the form of water in oil (W/O) catalytic emulsion that is composed of 94 wt % ALVR as the continuous phase, 5 wt % distilled water, 1 wt % surfactant, 140 ppm nickel precursor salt, and 460 ppm potassium precursor salt dissolved in the 5 wt % water . ALVR is highly viscous at 40 °C and cannot be emulsified with the catalytic metals precursors at this temperature. As a result, before the emulsification process is started, 25 wt % naphtha (ASTM D-86, 25
220 °C) is blended with the ALVR to bring down its viscosity from 36 100 cP to a mixture viscosity of 300 cP at 40 °C. The ALVR and naphtha blend is kept at 40 °C and stirred at a rate of 800 rpm with a mixer until the catalytic emulsion preparation process is complete. The emulsifying procedure started by gradually adding 1 wt % by weight surfactant to the low-viscosity oil to enhance its distribution inside the oil. The surfactant used is HLB-8, which is a combination of TWEEN 80 (35%) and SPAN 80 (65%). Then, potassium hydroxide (85% Sigma Aldrich) aqueous solution with a final metallic concentration of 460 ppm is emulsified with the blend oil. The aqueous potassium hydroxide solution neutralizes the residual oil indigenous naphthenic acids to potassium naphthenic salts, which are considered natural surfactants. This in situ naphthenic acid neutralization is referred to as natural surfactant activation.9 Ensuing, nickel(II) acetate tetrahydrate (98% Sigma Aldrich) aqueous solution with a final metallic concentration of 140 ppm is emulsified with the blend oil containing potassium in the form of natural surfactants. The catalytic emulsion is stirred at a rate of 800 rpm to homogenize the system for 1 h. During this time, water droplets containing the nickel salt are dispersed throughout the oil medium by mixing and are surrounded by the HLB-8 and potassium naphthenic salt surfactants, which enhance their dispersion and prevent coalescence. Next, the catalytic emulsion is decomposed in a 4 cm3 upflow decomposition reactor at 350 °C, and atmospheric pressure within a space time of 2 min to form the catalytic suspension, where naphtha and water are vaporized from the emulsion and collected in a cold separator, leaving behind the particulates of the catalytic metals suspended within the residual oil medium. This procedure produces highly dispersed suspended fine catalytic metal particles in the oil media, which improves their accessibility and reactivity. For the remaining naphtha removal, the catalytic suspension is sent to a hot separator set up at 240 °C and under atmospheric pressure, with a supply of nitrogen stream to aid in removing any traces of naphtha trapped within the oil, as shown in Figure 1. The naphtha removal procedure is sufficient to bring back the residual oil to its original composition as indicated by high-temperature simulated distillation (HTSD) being the results determined for the residual oil samples collected prior to naphtha blending and after its removal shown in Figure 2. Table 2 shows the mass balance of the catalytic suspension preparation. 2.2. Reactivity Tests Plan and Procedure. The experimental plan involves characterization of the original and converted ALVR and 4868

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Figure 2. SimDist of ALVR before and after UD catalyst incorporation.

Table 2. ALVR Catalytic Suspension Preparation Mass Balance total feed (g)

2500

water (w/w) naphtha (w/w)

0.05 0.25

potassium (ppm)

460

nickel (ppm)

140

surfactant (w/w)

0.01

surfactant added (g)

25.00

potassium added (g)

1.1500

nickel added (g)

0.3500

water added (g) naphtha added (g)

125.00 625.00

total emulsion before decomposition (g)

3276.50

total collected water + naphtha (g)

761.00

total catalytic suspension collected (g)

2501.50

total vented (by difference) (g)

14.00

investigation on its upgrading reactivity in response to changes in process severities in terms of space velocity and temperature. Thermal and steam cracking experiments are conducted near Aquaprocessing conditions, in order to compare their performances. The reactivity tests are carried out in a pilot plant provided with an upflow open tubular 100 cm3 isothermal reactor, as shown in Figure 3. The plant is flushed with nitrogen before starting each experiment to ensure no oxygen is present inside the system. Residue from the feed tank maintained at 100 °C is fed into the unit with a Zenith Precision Metering Gear Pump model H-9000. In the case of Aquaprocessing and steam cracking, 5 wt % steam is coinjected before the reactor by an Alltech HPLC pump model 426. Then, the combined feed is sent to the reactor after passing through a preheating section maintained at 355 °C. It is worth mentioning that the same preheating protocol is followed for the three processes TC, SC, and SCC. The temperatures of the preheating zone and downstream from the preheater including the reactor are raised to 300 °C at a heating rate of 15 °C/5 min. After that, the temperature downstream of the preheating zone and upstream from the reactor is increased gradually at a heating rate of 10 °C/5 min to a maximum temperature of 355 °C. For SC and SCC, the steam lines are heated to 330 °C to generate super heated steam after which the water pump is initiated to the required flow rate. The reactor temperature is increased to the reaction temperature at the heating rate of 10 °C/5 min and then finetuned. After reaching the reaction, temperature and pressure in the reactor

Figure 3. Experimental process pilot plant. are allowed to stabilize. The upgraded oil exiting the reactor is sent to a hot separator where the 320 °C+ heavy product is collected at the bottom. The lighter fraction is sent to a condenser where the condensed liquid is collected at room temperature, and the noncondensable gases are sent to a gas chromatography unit for compositional analysis and then to a Wet Test Meter (WTM) model W-NK, supplied by Shinagawa Precision, for gas volume measurement. The collected liquid products and recorded gas volume and composition are used to close the mass balance in a predetermined period of time. Aliquots from the heavy product are tested for asphaltene stability, which is repeated at each severity level investigated to decide the next incremental severity level. Asphaltene stability is defined in the oil analysis subsection below. Initially, Aquaprocessing, thermal, and steam cracking experiments are executed at the same operating conditions of 430 °C, 5 h
1, and 260 psig. Upon first indications of product improvement, the Aquaprocessing pilot plant experiments are extended to examine its performance under higher severities in order to comprehend the optimum upgrading temperature at which the conversion of 540 °C+ hydrocarbons is maximized under the minimum asphaltene stability limit. With the intention of examining Aquaprocessing under higher temperatures, 12 points of liquid hourly space velocities are selected in the range of 5
10.5 h
1, with an increment of 0.5 h
1, using five temperature set points, as shown in Figure 4. The first column of Figure 4 shows the experimental temperature points selected at which the residual oil is tested at 5 h
1. The ALVR Aquaprocessing experiments are conducted at different temperature points at 5 h
1 in order to inspect optimum temperature that gives the highest conversion at the minimum asphaltenes stability limit. In the other columns of Figure 4, the LHSVs are fixed while the temperatures are varied to reach the optimum conversion at the minimum asphaltenes stability limit to gather enough data points to develop a 4869

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kinetic model for ALVR upgrading via Aquaprocessing. The examined experimental conditions for thermal cracking are shown in Figure 5, where the conditions are selected targeting the highest conversion at the minimum asphaltene stability limit. Three temperature points (400, 405, and 408 °C) are selected at LHSVs of 2 and 2.5 h
1 under thermal cracking conditions to generate the specific reaction rates that are to be used in the kinetic model for comparison purposes. The procedure of developing the kinetic modeling as well as the modeling results will be published in a

separate article. The numbers shown in bold italic in Figures 4 and 5 represent the minimum asphaltene stability limits, after which the asphaltene condensation reactions accelerate. It is worth mentioning that the LHSVs of steam cracking and Aquaprocessing shown in Figure 4 are the residua liquid hourly space velocities only (excluding steam).

2.3. Investigation on Water Splitting Role of the UD Catalyst. Evidence on water splitting when the catalyst was used in the presence of steam and hydrocarbons under reaction conditions is essential to the validation of the Aquaprocessing mechanism. Water is expected to be split on some transition metals as well as on alkali doped transition metals.8 In the presence of hydrocarbons, as suggested by Pereira et al.,6 the water dissociation reactions are accompanied by simultaneous production of hydrocarbon free radicals by the homolytic cleavage of heavy oil molecular bonds. It has been advanced by the same author that the UD catalyst in Aquaprocessing promotes hydrogen and oxygen radicals’ availability to hydro-saturate the produced free radicals and olefins and to oxidize a primary carbon resulting from the hydrocarbon cleavage. This results in hydrocarbons with lower molecular weights in addition to CO2 by the oxidation/reforming of hydrocarbon radicals. The validation of this mechanism could be attempted by monitoring via marked isotope; the origin of oxygen in the CO2 produced using water labeled with isotope O18. There is extremely poor oxygen scrambling between water and the oxygen contained in the heterocompounds present in the oil, as our results showed. It would suffice to find a significant increase of the CO2 masses 46 (C
O16O18) and 48 (C
O18O18) when replacing normal water with H2O18. Analysis of the gas products with gas chromatography (GC) should be sufficient proof, and analysis of oxygen in the liquids is not necessary, which is extremely more difficult and has poor accuracy. The research group of Dr. Pereira-Almao has produced this evidence (unpublished results yet) using vacuum gas oil from naphthenic bitumen (Athabasca) and catalytic steam cracking conditions. However, the ALVR feedstock is chemically different and the catalyst could be passivated or could follow a different mechanistic path. The most convenient would be to gather the same kind of evidence for this specific feedstock during Aquaprocessing conditions. For the purpose, a quadrupole mass spectrometer (QMS) (Pfeiffer OmniStar mass spectrometer) was used to analyze the gas product coming from the pilot plant, and a mixture of 50
50 vol %/vol % of H2O16 (normal distilled water) and H2O18 obtained from (Marshall Isotopes) is used. The QMS is an analytical method that determines the mass to charge ratio (m/e) of constituents of a gaseous sample after ionization.10 The OmniStar mass spectrometer is a compact benchtop analysis system. The analysis systems consist of an inlet system, a PrismaPlus mass spectrometer, a dry-compressing diaphragm vacuum pump, and a

Figure 4. Aquaprocessing experimental conditions.

Figure 5. Thermal cracking experimental conditions.

Table 3. Original and Upgraded AL VR Characterization Results condition

original AL VR

temperature (°C)
1

LHSV(h )

steam cracking (SC)

aquaprocessing (SCC)

408

410

430

430

430

432

435

440

445

2

2.5

5

5

5

5

5.5

6.5

8

conversion (wt %)

0

23.6

25.6

28.5

26.8

28.9

29.9

30.5

33.5

33.3

P-value

2.9

1.2

1.2

1.2

1.2

1.35

1.2

1.2

1.2

1.2

MCR (wt %)

18.8

24.1

23.3

23.9

23.7

23.7

21.1

22.3

22.9

saturates wt %

6.1

9.4

9.2

9.4

9.3

9.8

9.2

10.3

9.8

aromatics wt %

60.3

63.1

62.8

61.9

62.6

64.6

64.3

66.4

65.6

resins wt % asphaltenes wt %

23.5 10.1

13.3 14.1

13.7 14.2

13.6 15.1

14.1 13.9

12.5 13.2

12.2 14.3

10.4 12.9

11.2 13.3

o

API

viscosity (cP)a a

thermal cracking (TC)

6.1

6.7

6.5

6.9

6.9

7.2

7.1

7.3

7.2

36091

9223

9129

8293

8586

9025

7422

7377

7553

Measured at 60 °C. 4870

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Figure 6. ALVR AQP 320 °C+ heavy product samples P-values as a function of % conversion.

Figure 7. ALVR AQP 320 °C+ heavy product samples dynamic viscosities as a function of % conversion.

HiPace turbopump. The gas inlet is equipped with a stainless steel capillary that can be heated up to 350 °C. The heated capillary prevents vapors from condensing during analysis of the process gas. The mass spectrometer software enables analyses to be performed on mass ranges of 1
300 amu. Samples of the evolved gases are stored in the stainless steel Swagelok sample cylinder equipped with a pressure gauge and a needle valve with a Swagelok fitting at the outlet. This fitting is attached to a small piece of 1/8 stainless steel tubing having another needle valve attached at the other end and a pressure gauge to measure pressure of the gas in the tubing. The inlet of the QMS is attached to the other end of the 1 /8 stainless steel tubing. To draw a gas sample, the needle valve of the 1 /8 is closed and the needle valve connected to the gas cylinder is opened slowly to allow the gas to pass into the 1/8 stainless steel tubing until 30 psi is read on the gauge after which the valve is closed. Then, the second needle valve attached to the QMS inlet is opened to allow the gases to flow into the system for the analysis. In this way, a controlled amount of gas was injected each time. The QMS allows monitoring the molecular weight of each gas component injected into the QMS chamber. Specifically in this case, monitoring the masses 44, 46, and 48 during the process at steady state conditions allows validating water splitting and the oxygen transfer role of the catalyst in the process. The scope of the analysis is to detect the labeled CO218 originating from the generated isotopic oxygen O18 radicals by the dissociation of the labeled water. The experimental procedure involves upgrading of ALVR by Aquaprocessing, at 7 h
1, 440 °C, and 260 psi, utilizing the oxygen-18 labeled water diluted with distilled water at a volumetric ratio of 1:1. Then, the process is repeated with the introduction of unlabeled water. Samples from the generated reaction gases are analyzed by GC. In addition, online gas samples are also collected downstream the reactor and stored in a stainless steel Swagelok sample cylinder and analyzed with the QMS to measure CO2 species generated by the labeled and unlabeled waters. A normal CO2 molecule, with two O16, has a molecular ion 44, which corresponds to its molecular weight. The labeled CO2 can be generated from one isotopic oxygen atom (O18), thus having a molecular ion of 46, and/or from two isotopic oxygen atoms, thus having a molecular ion of 48. In addition, in order to provide further proof of the catalyst role in water splitting, the ALVR is subjected to steam cracking without the catalyst following the same procedure of using labeled and unlabeled water.

one to calculate the amount of 540 °C+ residue using the ASTM D7169-05 method. Details were presented before by Carbognani et al.12 Microcarbon residue (MCR) measurement is used to determine the coke formation potential of the oils and is determined using a muffle furnace method developed by Hassan et al.13 Vacuum residue asphaltene stability measurement by the P-value is decisive to determine the maximum achievable conversion limit. The P-value is a measurement of the intrinsic stability between the asphaltenes and maltene fractions of the residual oil, herein determined using a procedure described by DiCarlo et al.14 The P-value measurements are based on the fact that asphaltenes tend to precipitate in an oil medium when it is titrated with n-paraffins. The P-value of the product is determined by titration of multiple samples of the product with n-cetane at 100 °C. After that, a single drop of the titration mixture is spotted over a microscope slide and pressed tightly with a cover slide to force the drop into a thin film. Then, after ambient temperature is reached, samples slides are placed under an optical digital microscope model DC3163 provided by National, with a camera and Motic Images Plus 2.0 software. The samples images are enlarged, captured by the camera, and stored in the database. The following equation shows the relationship between the P-value and n-cetane ! mL ðn-cetaneÞ ð6Þ P-value ¼ 1 þ g sample

2.4. Feedstock and Products Characterization Analysis. Feed and product samples are collected and analyzed for gathering the required information. Water content is measured by the Karl Fischer titration method in a Mettler-Toledo model DL-32, as recently published.11 Viscosity at 40 °C is determined with a Brookfield viscometer model DV-II + Pro. High-temperature simulated distillation is carried out with an Agilent 6890 GC instrument modified by Separation Systems Inc., which allows

First a P-value is assumed, and then the milliliters of n-cetane that need to be added to the preweighed sample are determine by the following equation ððP-valueÞ
1Þg sample ¼ mL ðn-cetaneÞ

ð7Þ

In this manner, multiple P-values are assumed (at a 0.05 P-value step) and then n-cetane titrated oils are examined under the microscope until the optimum P-value is reached just before onset of asphaltene precipitation. Petroleum heavy oil with a P-value in the range of 1
1.15 refers to a residual oil that has already precipitated asphaltenes. The minimum P-value at which oil is considered stable is 1.20. The error in the P-value measurement is (0.05. The P-value measurements are repeated at least twice, and the final value considered when the difference between the two P-values of the same sample does not exceed (0.05. Saturates, aromatics, resins, and asphaltenes (SARA) hydrocarbon group type distribution analysis is conducted to acquire further upgrading details of the reactivities of thermal cracking and catalytic cracking. This analysis is done according to a procedure published by Carbognani et al.15 API gravity is calculated from specific gravity measurement by pycnometry.16 The percent weight conversion refers to the conversion of the 540 °C+ hydrocarbons that are found in the original feed to lighter products. The calculation is made by first determining the weight of the 540 °C+ hydrocarbons (HC) in the feed 4871

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Figure 8. ALVR Aquaprocessing 320 °C+ heavy product sample spots under a digital microscope for P-value measurements.

Figure 9. ALVR upgrading profiles with thermal cracking and Aquaprocessing determined from 540 °C+ heavy products at different space times. and in the heavy product from the hot separator bottom, then using eq 8 to achieve the conversion ð540 °C þ Þ HC feed ðgÞ
ð540 °C þ Þ HC in heavy product ðgÞ conversion ¼ ð540 °C þ Þ HC in feed ðgÞ

ð8Þ The relative percentage difference between Aquaprocessing and thermal cracking conversions is calculated with eq 9, which is used to show the relative gain in conversion % difference ¼

% conversionSCC
% conversionTC  100 ð% conversionSCC þ % conversionTC Þ=2 ð9Þ

3. RESULTS AND DISCUSSION 3.1. Experimental Upgrading and Characterization Results. The liquid and gas products yields are within 93
95% and 7
5% ranges, respectively, depending on the process severity. Table 3 shows the results of upgrading and characterization of converted and unconverted ALVR via Aquaprocessing, thermal cracking, and steam cracking under varying conditions. From Table 3 it is observed that ALVR is rich in aromatics and resins and low in paraffin despite the fact the Arab light crude oil is highly paraffinic. It is also observed that MCR, aromatics, saturates, and asphaltenes increase gradually while resins, P-value, and dynamic viscosity decrease as the conversion level increases. Comparison between the products of thermal cracking and Aquaprocessing shows that the 4872

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UD catalyst incorporation with the residue in the presence of steam has reduced asphaltene and MCR generation17 and improved the API and P-value while producing more saturates and aromatics at the expense of resin. This is likely due to an increase in dealkylation, heavy aromatics cracking, and ring saturation reactions by the effect of UD catalysts in the presence of steam. This is an explicit indication of the stability and upgrading gain achieved using UD unsupported catalyst. Upgrading comparison between thermal cracking and Aquaprocessing at 430 °C and 5 Table 4. CO2 and CH4 Products of SC and SCCa gas type

a

C3H8

CO2

normal water SCC (wt %)

0.940

0.405

isotopic water SCC (wt %)

0.972

0.417

isotopic water SC (wt %)

0.944

0.276

Experimental conditions: 440 °C, 7 h
1.

h
1 at the minimum asphaltene stability limit in Table 3 shows an improvement in the P-value via Aquaprocessing. This additional stability allowed more room for upgrading by raising the temperature to 432 °C at the 5 h
1, which increased the conversion to 29.9% at the minimum P-value of 1.2. ALVR steam cracking at 430 °C and 5 h
1 did not result in an improved conversion when compared to AQP, which indicates that the steam does not dissociate in the absence of UD catalyst. Figures 6 and 7 show the P-value and dynamic viscosity of the liquid products of AQP at 435, 440, and 445 °C, respectively. From both figures it is observed that the dynamic viscosities substantial improvement is accompanied by a drop in the heavy product’s P-values as expected. This is a common behavior observed for the ALVR that is upgraded via Aquaprocessing and thermal cracking. This is caused by the breaking of the larger molecules into smaller molecules through the breaking of the alkyl appendages and aliphatic molecules. This in turn

Figure 10. Gases QMS analysis of AL VR SCC at 440 °C, 7.0 h
1, and 260 psi with unlabeled CO2.

Figure 11. Gases QMS analysis of AL VR SCC at 440 °C, 7.0 h
1, and 260 psi with labeled CO2. 4873

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Figure 12. Gases QMS analysis of ALVR SC at 440 °C, 7.0 h
1, and 260 psi with unlabeled CO2.

Figure 13. Gases QMS analysis of ALVR SC at 440 °C, 7.0 h
1, and 260 psi with labeled CO2.

makes the oil medium less solvating for asphaltenes, which causes a simultaneous drop in the P-value of the upgraded oil. Higher severities beyond the stability limit are expected to improve the oil viscosities but would deteriorate its P-value and cause asphaltene precipitation eventually. Figure 8 illustrates microscopic images of spotted heavy oil samples on glass sheets. Oil samples are collected from the 320 °C + hydrocarbon products from TC, SC, and SCC at 430 °C and LHSVs of 5 h
1 with the indicated P-values. In order to accurately detect the asphaltenes aggregates, the images are usually taken at the liquid edges enclosed in-between the glass sheets, where the asphaltenes particles mostly collect. The absence of these black dots in the sample indicates that the product’s P-value is at least 1.20. Comparison between the three images shown in Figure 8 indicates that the heavy product of SCC inherits the highest

asphaltene stability limit at the similar percent conversions under the same severity as of those of TC and SC. Figure 9 presents compilation of the progression of ALVR conversion data with respect to space time at different temperatures for both thermal cracking and Aquaprocessing. The standard deviations of percent conversions from multiple pilot plant experiments are in the range of 0.08
0.3. The continuous blue and red dotted curves in the middle of Figure 9 correspond to the maximum Aquaprocessing and thermal cracking upgrading profiles achieved at the minimum asphaltene stability limit, respectively. The two curves are located at the boundaries between asphaltene condensation and stability regions. They trace the optimum ALVR upgrading threshold, on the basis of asphaltene stability and maximum output, via Aquaprocessing and thermal cracking. One can choose to either operate at the stability limit 4874

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8 h
1

4875

0.10 0.31% 33.22

relative standard deviation

(% conversion) final % conversion

(% conversion)

33.22

standard deviation

1.20

P-value

average (% conversion)

33.29

(540 °C+) % conversion

2.90

56.51

70.47

(540 °C + HC) wt % in total product

in heavy product

(540 °C + HC) wt %

81.7

82

18

18

291.73

total product (g)

(540 °C + HC) wt % in feed

4.94 291.73

feed water % total feed (g)

(540 °C
HC) wt % in feed

13.74

feed water (g)

277.99

6.93

gas % yield

total hydrocarbon product (g)

93.07 19.26

gas products (g)

total liquid product (g)

liquid hydrocarbon % yield

57.37 272.47

light product weight (g)

277.99 215.10

AL VR

total hydrocarbon feed pumped (g) heavy product weight (g)

fluid type (grams)

(0.10

1.25

33.14

70.56

82

18

287.42

301.53

4.91 301.53

14.11

7.00

20.11

93.00

281.42

58.82

287.42 222.60

(2) 8 h
1

28.38

1.45%

0.41

28.38

1.30

28.67

58.39

71.22

82

18

349.36

365.56

4.64 365.56

16.20

6.35

22.19

93.65

343.37

57.38

349.36 285.99

8.5 h
1

(0.41

1.30

28.09

72.50

82

18

342.42

359.45

4.97 359.45

17.03

6.38

21.86

93.62

337.59

59.97

342.42 277.62

(2) 8.5 h
1

26.03

0.47%

0.12

26.03

1.35

26.12

59.69

71.84

82

18

355.97

373.47

4.91 373.47

17.50

6.07

21.61

93.93

351.86

52.61

355.97 299.25

9 h
1

(0.12

1.30

25.94

71.00

82

18

360.38

378.30

4.97 378.30

17.92

5.76

20.74

94.24

357.56

50.31

360.38 307.25

(2) 9 h
1

Table 5. Process Experimental Data for Upgrading ALVR via AQP at 445 °C and 8
10.5 h
1

22.68

1.12%

0.25

22.68

1.45

22.86

61.05

72.11

82

18

346.63

363.81

4.96 363.81

17.18

5.58

19.35

94.42

344.46

41.39

346.63 303.07

9.5 h
1

SCC 445 °C

(0.25

1.45

22.50

72.99

82

18

350.12

367.42

4.94 367.42

17.30

5.47

19.14

94.53

348.28

44.45

350.12 303.83

(2) 9.5 h
1

21.11

0.69%

0.15

21.11

1.55

21.01

61.69

72.63

82

18

382.94

401.71

4.90 401.71

18.77

5.07

19.41

94.93

382.30

41.89

382.94 340.41

10 h
1

(0.15

1.55

21.21

72.98

82

18

377.10

395.75

4.95 395.75

18.65

4.94

18.64

95.06

377.11

44.35

377.10 332.76

(2) 10 h
1

20.56

1.57%

0.32

20.56

1.60

20.34

61.95

73.17

82

18

385.40

404.22

4.88 404.22

18.82

5.54

21.36

94.46

382.86

39.87

385.40 342.99

10.5 h
1

(0.32

1.60

20.79

72.47

82

18

381.40

400.37

4.97 400.37

18.97

5.51

21.00

94.49

379.37

38.65

381.40 340.72

(2) 10.5 h
1

Energy & Fuels ARTICLE

dx.doi.org/10.1021/ef200936k |Energy Fuels 2011, 25, 4867–4877

Energy & Fuels for maximum upgrading to maximize profit or, as a precautionary measure, at a higher stability to prevent asphaltene condensation reactions due to unanticipated feed composition variations. While the extension of the thermal cracking profile predicts a maximum possible conversion of 29.5%, Aquaprocessing demonstrated a higher conversion of 33.5%. The relative percentage difference between these conversions demonstrates a 13% relative gain in the ALVR conversion in favor of Aquaprocessing. In addition, since the UD catalyst best performs at high temperatures, it is noticed from Figure 9 that higher ALVR conversions by Aquaprocessing are favored by combinations of short space times and high temperatures. As a result, one should seek process temperatures higher than 430 °C, which require higher throughput as well to prevent asphaltene aggregation and precipitation. This is considered advantageous for refiners seeking high throughput. The enclosed cross-hatched area between the red and blue curves represents the potential increase in percent conversion of ALVR achievable through Aquaprocessing. The set of conditions described in the few papers and patents for Aquaprocessing when applied to ALVR does not allow noticeable improvements in yields as shown in Figure 9. However, for naphthenic residua, the literature shows that the reaction conditions can be brought to 430 °C or more at a space velocity of 2
3 h
1 without reaching the asphaltenes minimum stability limit and under Aquaprocessing produce significantly higher yields than visbreaking.7 3.2. Evidences of Water Splitting by the UD Catalyst. Table 4 shows the Aquaprocessing and steam cracking (no catalyst) gaseous products analyses results by GC. The errors in the GC gas analysis results are found to be less than 5%. Propane is a hydrocarbon gas with a similar molecular weight of CO2 (44). On the basis of gas chromatography, analysis of the process gas has consistently been found in Aquaprocessing experiments that while propane production does not show noticeable differences between SCC and SC, CO2 production showed a significant increase via SCC. This is an indication of the water splitting and oxygen (therefore hydrogen) transfer role of the UD catalyst. Figures 10 and 11 illustrate the QMS analysis result of the gaseous products of Aquaprocessing with unlabeled and labeled water, respectively. In these figures, the horizontal axis (x-axis) is the radio frequency cycle (measuring cycle) and the vertical axis (y-axis) is the current of a specific mass to charge ratio (m/e). Since the propane compositions are identical in the gaseous products of both experiments, as shown in Table 3, their m/e measurements with the QMS are presumably identical as well. Therefore, differences in the m/e measurements of molecular ion 46 between the gaseous products of both experiments can only be attributed to the presence of labeled CO2 of one isotopic oxygen atom. The ratios of molecular ion 44 net m/e to net m/e of molecular ions 46 (Δ44/Δ46) and 48 (Δ44/Δ48) are found to be 32 for each with unlabeled water, as shown in Figure 10. The aforementioned ratios dropped 3-fold to 10 and 11, respectively, when the unlabeled water was replaced with the labeled water, as shown in Figure 11. This drop in the ratios Δ44/Δ46 and Δ44/ Δ48 can only be due to the increase in the labeled CO2 (CO16O18 and CO218). These results indicate that the labeled water is dissociated by the effect of the UD catalyst. From the above rational and that the conversion in both cases is noticed (ALVR AQP with labeled and unlabeled waters), the catalyst role in splitting water is proven viable regardless of the acidic effect that might be inherited by the labeled water as suggested by Thornton.18

ARTICLE

The CO2 in gaseous products of ALVR steam cracking did not show any significant difference when the normal water is replaced with labeled water. Figures 12 and 13 show the QMS analysis result of the gaseous products of steam cracking with unlabeled and labeled water, respectively. The ratios Δ44/Δ46 and Δ44/ Δ48 are found to be 51 and 19 with unlabeled water, respectively, as shown in Figure 12. The ratios Δ44/Δ46 and Δ44/Δ48 are found to be 46 and 20 with labeled water, respectively, as shown in Figure 13. The Δ44/Δ46 and Δ44/Δ48 ratios of SC with unlabeled and labeled waters are in close agreement. The small drop in the ratio Δ44/Δ46 when labeled water is used is possibly due to the limited water dissociation caused by the indigenous materials present in the oil. However, the difference of 5 between the Δ44/Δ46 ratios of both SC with unlabeled and labeled waters is negligible when compared to the counterpart differences of 22 shown in the case of Aquaprocessing. This can only indicate that the water does not dissociate effectively without the incorporation of UD catalyst. This constitutes the most intimate mechanistic and sound proof of the role of the catalyst during the Aquaprocessing of heavy oils. It proves cracking occurs as C for CO2, and additional production can only come from C
C scission beyond the levels of noncatalytic steam cracking SC and it also proves water splitting and oxygen transfer as labeled oxygen was introduced into the system via steam exclusively.

4. CONCLUSIONS Arab light vacuum residue upgrading by Aquaprocessing is investigated experimentally. Experimental comparisons between Aquaprocessing and thermal cracking processes showed that using Aquaprocessing, there is a noticeable increase in ALVR upgrading in terms of increased residual oil conversion with improved product stability, which can be achieved without major investments. This enhancement is obtained with the higher productivity region when compared to thermal cracking, which implies more throughputs at equivalent space times. Characterization of original and converted ALVR, in terms of P-value, HTSD, SARA, MCR, API, and dynamic viscosity are performed. The percent conversions of the 540 °C+ hydrocarbons processed at LHSV of 5 h
1 at the minimum stability limit of 1.20 P-value are found to be 28.5 and 29.9% under thermal cracking and Aquaprocessing at 430 and 432 °C, respectively. The maximum percent conversions of the 540 °C+ hydrocarbons by thermal cracking and Aquaprocessing schemes are found 29.5 and 33.5%, respectively, with a relative gain in conversion of 13% in favor of Aquaprocessing. The incorporation of ultradispersed catalyst thus improved asphaltene stability and increased heavy hydrocarbons percent conversion. Upgrading comparison between thermal cracking and Aquaprocessing upgrading profiles shows an area of further potential for ALVR upgradability, achievable by Aquaprocessing. With the use of labeled water, it was evidenced that the ultradispersed catalyst is capable of dissociating water molecules into oxygen and hydrogen radicals, being labeled oxygen radicals found within the produced CO2 species. The experimental results obtained in this work have indicated that the Aquaprocessing performance is confirmed for upgrading ALVR beyond the thermal cracking limitation without incurring major investment on equipment. The set of conditions described in the few papers and patents on Aquaprocessing, when applied to ALVR, do not allow noticeable improvements in yields; whereas for naphthenic residua the 4876

dx.doi.org/10.1021/ef200936k |Energy Fuels 2011, 25, 4867–4877

Energy & Fuels literature indicates that these can be brought to 430 °C or more at 2
3 h
1 without reaching the asphaltenes stability limit and under Aquaprocessing produce significantly higher yields than thermal cracking. It is observed that one major reason for the above limitation is that in the Aquaprocessing of ALVR the catalyst responsible for water dissociation is not active at temperatures lower than 430 °C. In order to increase the reaction temperature while keeping asphaltenes relatively stable in the reaction media, higher space velocities are needed (shorter residence times), which are investigated in this work. On the other hand, the asphaltenes in naphthenic residua are still suspended in the media at temperatures higher than 430 °C at 2
3 h
1; therefore, the limitation of the catalyst was not evidenced in previous literature reports with naphthenic residua.7 This finding along with the evidence of water dissociation when the catalyst is used clearly opens the path for an extended and more precise application of the Aquaprocessing concept to many different types of hydrocarbon heavy fractions. Table 5 shows the process data along with mass balances on the indicated process conditions for ALVR upgrading via AQP. To show the repeatability of the pilot plant experiments, the standard deviation is calculated for a number of the experiments.

’ AUTHOR INFORMATION Corresponding Author

*Address: 912 Harris Place NW, Calgary, AB, Canada, T3B 2 V4. Phone: (403)2102766. E-mail: [email protected].

’ ACKNOWLEDGMENT This work is supported by Saudi Aramco who provided oil samples and academic financial support. It is also supported by Alberta Ingenuity Fund, now Alberta Innovates, via a Scholar award provided to Dr. Pereira-Almao. The authors acknowledge Drs. Lopez-Linares, Hassan, and Carbognani particularly for help in feedstock preparation, mass spectrometry, and SimDist analysis, respectively, and fruitful discussions. Help from R. Gomez and several members of the Catalysis for Bitumen Upgrading and Hydrogen Production (CBUHP) group from the University of Calgary in analytical and technical matters is also acknowledged.

ARTICLE

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18), 3631–3639. (14) Di Carlo, S.; Janis, B. Composition and visbreakability of petroleum residues. Chem. Eng. Sci. 1992, 47 (9
11), 2695–2700. (15) Carbognani, L.; Gonzalez, M. F.; Pereira-Almao, P. Characterization of Athabasca Vacuum Residue and Its Visbroken Products. Stability and Fast Hydrocarbon Group-Type Distributions. Energy Fuels 2007, 21 (3), 1631–1639. (16) Carbognani, L.; Lopez-Linares, F.; Carbognani, L. A.; PereiraAlmao, P. Solution Pycnometry for Density (API) Determination of Asphaltenes and Vacuum Residua. Prepr.
Am. Chem. Soc., Div. Pet. Chem. 2011, 56. (17) Speight, J. G. The Chemistry and Technology of Petroleum, 4th ed.; CRC Press/Taylor & Francis: Boca Raton, FL, 2007; p 945. (18) Thornton, E. R. Solvent Isotope Effects in H2O16 and H2O18. J. Am. Chem. Soc. 1962, 84 (13), 2474–2475.

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dx.doi.org/10.1021/ef200936k |Energy Fuels 2011, 25, 4867–4877