Catalytic Hydrotreatment of Crude Waxes from Different Sources over

6854

Ind. Eng. Chem. Res. 2008, 47, 6854–6861

Catalytic Hydrotreatment of Crude Waxes from Different Sources over a Ni-W/-Al2O3 Catalyst Jesu´s Sa´nchez E.TSI Minas, UniVersidad Polite´cnica de Madrid, C/Rı´os Rosas, 21, 28003 Madrid, Spain

Marı´a Fernanda Tallafigo E.TSI Caminos Canales y Puertos, UniVersidad Polite´cnica de Madrid, Ciudad UniVersitaria, 28040 Madrid, Spain

Miguel A. Gilarranz* A´rea de Ingenierı´a Quı´mica, Facultad de Ciencias, UniVersidad Auto´noma de Madrid, 28049 Madrid, Spain

Francisco Rodrı´guez Departamento de Ingenierı´a Quı´mica, Facultad de Quı´mica, UniVersidad Complutense de Madrid, 28040 Madrid, Spain

The hydrotreatment of crude wax from the dewaxing of spindle, light neutral, medium neutral, heavy neutral, and brightstock oil was studied to obtain refined paraffins that are suitable for high-grade applications. The runs were performed using an alumina-supported catalyst with 5.9 wt % of nickel (as NiO) and 16.2 wt % of tungsten (as WO3) that was used for >6000 h. The ease of treatment was ranked as follows: spindle > light neutral > medium neutral > heavy neutral . brightstock. The use of high temperatures and pressures was needed to obtain a convenient reduction in the color of the heavier feedstocks. Spindle feedstock required a temperature of 548 K and a pressure of 9.81 MPa, whereas 623 K and 13.7 MPa were needed for heavy neutral feedstock to obtain refined paraffins with a Saybolt color of >+30. Introduction Wax is an organic, plastic-like substance that is solid at ambient temperature and becomes liquid when melted. The term “wax” is applied to a large number of chemically different materials. Petroleum is the major source of commercial waxes, given that most petroleum waxes are obtained as a byproduct of the manufacture of lubricating oil, where the lubricating oil fractions obtained from the vacuum distillation of the heavy portions of crude oil are subjected to solvent extraction to remove substances that are not desired, because of their poor lubricating properties. The term “paraffin wax” is usually applied for those waxes that are derived from light lubricating oil distillates. Paraffin waxes contain predominantly straight-chain hydrocarbons, with an average chain length of 20-30 C atoms, although the number of carbons can extend past 60.1 Branched paraffins (isoparaffins) and cycloparaffins are present in a lower and variable extent. Microcrystalline wax is obtained from vacuum residual and crude-storage tank bottoms by extraction and dewaxing. Microcrystalline waxes differ from paraffin waxes in that they have a poorly defined crystalline structure, darker color, and generally higher viscosities and melting points. Because of the small size of the crystals, a higher percentage of oil is occluded by microcrystalline paraffins. The crude waxes obtained in oil refineries have a characteristic smell and are represented as a homogeneous mass that has a white to yellowish color, in the case of paraffin wax, or is dark brown, in the case of microcrystalline wax. For industrial * To whom correspondence should be addressed. Fax: +34 91 497 35 16. E-mail address: [email protected].

use, crude waxes can be refined by treatment with adsorbents such as clay, which yields relatively color-stable, odorless, and tasteless materials. To upgrade wax to higher-valued products with the purity required for the food and medicinal grades, an additional chemical treatment is needed. Color and oil content are among the most important properties used to estimate the quality and purity of paraffins. As in the case of other oil fractions, wax color is related to the presence of heteroatoms that are associated to hydrocarbons in a variety of compounds.2 In food-grade paraffins, colorless and totally transparent materials are required. In addition to this, good color stability is desired, which is indicative of very low levels of color promoters, such as unsaturated compounds and heteroatoms.3 The term “oil” refers to the low-molecular-weight paraffins that are contained in waxes. Food and medicinal paraffins are usually employed in wax paper, fruit coatings, paper cups, chewing gum, cheese coating, lipsticks, medicine seals, etc. Recently, an important growth in the consumption of high-quality waxes has happened, because of the occurrence of more-strict quality standards in applications. For instance, the manufacture of candles, which represents ∼50% of the petroleum wax use,4 has increased the consumption of food-grade paraffin, because of concerns about indoor air pollution.5 Thus, important plant expansions have occurred for the production of upgraded paraffins, especially in Asia, in addition to a strengthening of the trend toward vegetal wax.6 An alternative to petroleum waxes are synthetic waxes. Fischer-Tropsch waxes are obtained from the Fischer-Tropsch process as a heavy fraction. These waxes require decolorization by chemical treatment and are mainly used in adhesives and hot-melt coatings,7 although it has been shown that they can

10.1021/ie800014u CCC: $40.75  2008 American Chemical Society Published on Web 08/07/2008

Ind. Eng. Chem. Res., Vol. 47, No. 18, 2008 6855 8

be upgraded for use in higher-quality applications. Lowmolecular-weight polyethylenes are also referred as synthetic waxes; their uses include being mixed with other waxes as a mold and extrusion aid and as color dispersant for plastics.9 The hydrotreatment of oil wax feedstocks is the most important process for the production of high-grade paraffins, displacing the formerly used sulfuric acid process, because of advantages such as continuous operation, high products yield, flexibility with regard to feedstocks, hydrogenation of aromatics, degradation of sulfur and nitrogen compounds, low corrosion, and reduced environmental impact.10 The main purpose of wax hydrotreatment is the removal of unsaturated compounds and heteroatoms that are associated with hydrocarbons that confers dark color.3,11 Thus, the colorless and totally transparent materials of good color stability and low oil content that are required for food-grade applications can be obtained. Similarly, the removal of heteroatoms and the conversion of aromatics to naphthenes and paraffins stabilize the product and prevent its aging.12,13 In the hydrotreatment processes, the waxes are contacted with hydrogen at high temperatures and relatively elevated pressures in the presence of a catalyst. Under these conditions, several reactions such as isomerization, cracking, dehydrocyclization, cyclization, aromatization, and hydrogenolysis occur, because the extension of such reactions is influenced by the characteristics of the raw paraffin feedstock, the reaction conditions, and the catalytic system used.14 As a result of such reactions, the heterocyclic compounds are hydrogenated and the heteroatoms contained in the feedstock are either removed in the gas phase (H2S, NH3, H2O) or deposited on the catalyst surface (NiSx, VSx).15 On the other hand, large hydrocarbon molecules are hydrogenated and cracked. In the case of n-paraffins, skeletal isomerization to give branched iso-paraffins can also be important,16 which lowers the melting point and reduces the stiffness of the treated paraffin.17 The higher tendency of multibranched isoalkanes to crack dictates a relatively low occurrence of multibranched compounds.17 Cracking is a major concern in the hydrotreatment of waxes, because it reduces the yield of long-chain paraffins and increases the content of low-molecular-weight compounds, which are usually grouped by the term “oil”. When linear paraffins are subjected to hydrotreatment, cracking reactions always occur, to a certain extent.18,19 It has been reported that increasing the temperature and reaction time results in higher cracking, together with a higher conversion to iso-paraffins, because of a higher contribution of isomerization reactions.20 Similarly, high temperatures shift the thermodynamic equilibrium toward the formation of aromatics.21 On the other hand, the cracking of long-chain linear paraffins has been reported to occur, to a smaller extent, at high pressure, in contrast to the behavior that has been observed for light paraffins.18,22 The catalysts used for hydroprocessing must exhibit activity for reactions such as hydrodesulfurization, hydrodenitrogenation, hydrodeoxygenation, hydrodemetallization, and the hydrogenation of aromatics.23 The majority of the catalysts used are bimetallic,23-26 with those that are based on nickel, cobalt, tungsten, and molybdenum being more suitable for feedstocks with a high concentration of sulfur.18 Presulfurization of the catalysts is a common practice to promote the activity in the removal of heteroatoms.27,28 A variety of supports based on alumina, silica, active carbon, titanium dioxide, zeolites, and silicopaluminosphosphates have been proposed, although alumina, especially R-Al2O3 and γ-Al2O3, is, by far, the most employed, because of the active role of this support in reactions such as hydrodesulfurization.11,19,24,28-30

In a former work,31 alumina-supported catalysts that were based on a Ni-Mo and Ni-W active phase were evaluated for the hydrogenation of crude microcrystalline wax from the dewaxing of heavy neutral oil. Ni-W catalysts were determined to require lower temperature to achieve acceptable Saybolt color and oil content values. In another approach,32 several Ni-W catalysts that were supported on alumina were tested. The increase in the metal load led to a higher catalytic activity when the porosity of the support was simultaneously increased. Optimum results were found for a catalyst with a nickel and tungsten load of 5.9 wt % (as NiO) and 16.2 wt % (as WO3), respectively, and with a surface area of 169 m2/g. In the current work, such a catalyst is evaluated for the upgrading of commercial crude waxes from different sources. The color, sulfur content, oil content, and carbonizable substances content were considered to evaluate the treated paraffins, because these properties are of paramount importance to assess the quality of the paraffins for high-grade applications. The study of the behavior of different feedstocks is essential for the development of a paraffin hydrotreatment process, because the characteristics of the feedstock is a major factor, together with the catalyst that is used and the reaction conditions.14 Thus, recent works8,32 have shown that the behavior of Fischer-Tropsch waxes and oil-derived waxes can be significantly different under equivalent hydrogenation conditions. Experimental Section A schematic diagram of the pilot plant used in the experiments for the hydrotreatment of the raw paraffins is shown in Figure 1. The reactor consisted of fixed bed with an inner diameter (ID) of 0.027 m and a length of 2 m, of which ∼1.3 m in the central part was packed with the catalyst and the rest was packed with silicon carbide. The reactor was designed for concurrent downflow operation (trickle bed reactor). The reaction temperature was controlled by means of eight independent heating sections, each of which was provided with temperature measurement and control, thanks to thermocouples inserted in the catalyst bed. The liquid feeding section consisted of a vessel, where the raw wax was melted and stored, and a pump, which passed the molten paraffin though a filter to remove solid impurities. The melted wax was preheated together with a hydrogen stream and fed into the reactor. The reaction products were filtered and sent to a high-pressure gas-liquid separator. The liquid products were sent to a stabilization column, where the volatile reaction products (mainly hydrogen sulfide and ammonia) were stripped with nitrogen. The gas leaving the gas-liquid separator was sent to the hydrogen recovery unit. Most of the reaction runs were performed at a hydrogen pressure of 9.81 MPa, although, in some experiments, a pressure of 13.7 MPa was used. The temperature ranged between 523 K and 623 K. The catalyst was diluted with silicon carbide of the same particle size, to improve wetting and to obtain liquid hourly space velocity (LHSV) values in the range of 0.33-1.0 h-1 (m3/h of paraffin per cubic meter of catalyst). A hydrogen-toliquid-wax volumetric ratio of 500 was used. Five different crude waxes were used. They correspond to the wax separated in the dewaxing of different oil fractions produced in vacuum distillation: spindle (SP), light neutral (LNP), medium neutral (MNP), heavy neutral (HNP), and brightstock (BSP). The samples studied are representative of the commercial stocks obtained in oil refineries. The main characteristics of crude waxes are summarized in Table 1. The Ni-W catalyst studied was prepared via the coimpregnation of alumina cylindrical extrudates 0.0025 m in

6856 Ind. Eng. Chem. Res., Vol. 47, No. 18, 2008

Figure 1. Simplified scheme of the paraffin hydrogenation pilot plant. Table 1. Properties of the Raw Waxes Studied propertya oil content (wt %) [ASTM-D-721] viscosity at 372 K (cSt) [ASTM-D-445] Saybolt color [ASTM-D-156] ASTM color [ASTM-D-1500] needle penetration at 298 K (mm) [ASTM-D-1321] carbonizable substances test [ASTM-D-612] specific gravity, 343/277 K melting point (K) [ASTM-D-938] refractive index, at 353 K [ASTM-D-1747] absorptivity at 290 nm (L/(g cm)) [ASTM-D-2008] sulfur content (ppm) [UOP-357-802] a

sample SP

sample LNP

sample MNP

sample HNP

sample BSP

0.37-0.9

0.08

0.03-0.4

0.36-1.12

1.06

3.05-3.06

3.78

4.84-4.95

5.84-6.70

15.71

+30 0.37 0.21

523 0.75 +28 0.37 -0.01

548 0.8 >+30 0.90 -0.01

573 1.0 >+30 0.90 0.00

pass 3-4 0.31

pass 1-2 0.20

pass 1-2 0.19

pass 3-4 0.35

not pass 6 0.57

pass 3 0.29

pass 2-3 0.26

Pressure, 9.81 MPa; catalyst age, 2660-2995 h (1330-1570 kg wax/kg catalyst).

substances, which was performed by treatment with concentrated sulfuric acid, as described by ASTM-D-612. For a qualitative estimation of the content of carbonizable substances, test variants B and C of the CFR method, which is based on standard test method ASTM-D-612, were applied. The oil content of the paraffins, which is representative of the presence of lowmolecular-weight paraffins and cracking products, was determined as indicated by standard test method ASTM-D-721. The sulfur content was determined according to the Nickel-Raney method (using standard test method UOP 357-80). In this method, the paraffin sample is treated with Nickel-Raney, to convert sulfur to nickel sulfide. Further treatment with hydrochloric acid releases sulfur in the form of hydrogen sulfide, which is absorbed with an alkaline solution and titrated with mercury acetate, using dithizone as an indicator. The FDA test for petroleum wax34 was performed to check if the refined paraffins from different sources fulfill the requirements for their use in food applications and food packaging. Other properties measured for the crude wax included the kinematic viscosity (standard test method ASTM-D-445), needle penetration at 25 °C (standard test method ASTM-D-1321), specific gravity, melting point (standard test method ASTM-D-938), refractive index (standard test method ASTM-D-1747), and absorptivity at 290 nm (standard test method ASTM-D-2008). Results and Discussion All the experiments described in this work were performed using the same catalyst; therefore, it was necessary to test the time-on-stream behavior, to confirm that the results from different experiments can be compared. Table 3 shows the results obtained when an experiment that consisted of the hydrotreatment of HNP at 623 K, 9.81 MPa, and a space velocity of 0.5 h-1 was repeated after different time-on-stream values in the range of 1690-6090 h. The catalyst showed excellent behavior and good reproducibility of the Saybolt color, despite the long period of time that was considered. In industrial practice, the gradual deactivation of the catalysts is compensated by constantly increasing the temperature.2 In the current work, after 6000 h on stream, the catalyst maintained the initial activity and was still able to produce a perfectly transparent and brilliant

white product at 623 K when the reaction pressure was increased to 13.7 MPa. A slight increase was observed in the oil content for a time-on-stream longer than 5400 h, which could indicate a higher tendency of the catalyst to promote the cracking of the paraffin. Similarly, some isomerization and a certain amount of chain-length shortening can be expected, because nickel-based catalysts catalyze hydroenolysis reactions. However, the results obtained in the tests for carbonizable substances do not indicate an important generation of low-molecular-weight compounds. Therefore, it was assumed that the catalyst shows convenient conditions for its use in the comparison of the hydrotreatment of different crude waxes. Table 4 shows the results for the hydrotreatment of the crude wax obtained in the dewaxing of spindle oil (SP). This crude paraffin is the lightest among the five types of feedstocks studied, and the results indicate that it can be easily hydrotreated to obtain a product that is suitable for high-grade applications, such as food paraffin. Although Saybolt color values of >+30 can be obtained for temperatures as low as 523 K (run 1), an increase in temperature up to 548-573 K (runs 2 and 3) improves the hydrogenation of aromatics and the isomerization of isoparaffins,and, hence, a reduction in the carbonizable substances content. It has also been shown that, in the hydrogenation of tetratlin over a Pt/Al2O3 at 8.1 MPa, the conversion increases dramatically for temperatures at >523 K.35 Run 4 shows that the use of higher temperatures causes greater paraffin cracking, which leads to higher oil and carbonizable substances contents. Similarly, the acidic properties of sulfided metallic hydrotreating catalysts has been shown to catalyze the hydroisomerization of paraffins.36 Oil content is also an important parameter for highquality applications of paraffins, where oil contents of +30 to +28, because of insufficient removal of the sulfur, nitrogen, and aromatic compounds that contribute to the dark color. The

6858 Ind. Eng. Chem. Res., Vol. 47, No. 18, 2008 Table 5. Characteristics of the Hydrotreated Paraffin Obtained from LNP Stocka Value

a

parameter

run 8

run 9

run 10

run 11

run 12

run 13

run 14

temperature (K) space velocity (h-1) Saybolt color initial oil content (wt %) oil content increase, ∆ (wt %) carbonizable substances tests ASTM-D-612 CFR-LN-6 T, variant B CFR-LN-6 T, variant C

548 0.5 +30 0.08 0.21

548 1.0 +6 0.08 0.09

573 0.5 >+30 0.08 0.19

623 0.5 >+30 0.08 0.37

573 0.75 >+30 0.08 0.15

573 1.0 +19 0.08 0.04

623 1.0 >+30 0.08 0.19

pass +30 0.02 -0.02

598 9.81 1.0 +12 0.46 -0.01

623 9.81 1.0 +21 0.40 0.01

598 13.7 0.5 >+30 0.55 -0.03

623 13.7 1.0 >+30 0.43 0.01

pass +30 0.56 0.42

623 13.7 >+30 0.46 0.10

643 13.7 >+30 0.36 0.10

pass 1 0.10

pass 1-2 0.16

pass 3-4 0.39

not pass 6-7 0.73

pass 1-2 0.21

pass 3-4 0.72

Catalyst age, 3600-4450 h (1590-2410 kg wax/kg catalyst); space velocity, 0.5 h-1.

Table 8. Characteristics of the Hydrotreated Paraffin Obtained from BSP Stocka Value

a

parameter

run 32

run 33

run 34

run 35

temperature (K) space velocity (h-1) color ASTM-D-1500 initial oil content (wt %) oil content increase, ∆ (wt %) carbonizable substances test, ASTM-D-612

623 0.5 4- 5 1.07 0.20 not pass

643 0.33 +30 at 9.81 MPa, although the use of such a temperature also leads to a severe increase in the oil and carbonizable substances contents and a failure in the ASTM-D-612 test. The important increase in oil content observed for the reaction at 648 K (run 29) is not in accordance with the trend observed in the 588-623 K range, where a negligible increase in oil content occurred. Thus, the high oil generation in run 29 may be related to the high initial oil content of the crude HNP sample that is used, probably because of long storage time in the liquid state. Nevertheless, an alternative for the reduction of the color of HNP is increasing the pressure: when the crude paraffin was treated at 13.7 MPa and 643 K (run 31), the generation of oil was reduced substantially, in relation to run 29. The reduction in oil can be partially attributed to the inhibitory effect of pressure, because it has been shown that, during the catalytic hydrogenation of lineal paraffins, the rate constant for cracking reactions is inversely proportional to hydrogen pressure,17,19 which is contrary to the behavior displayed by lighter paraffins;22 however, the lower initial oil content of the crude paraffin sample that is used can also play a role. Despite the good results for oil content, the carbonizable substances content for the sample obtained in run 31 can be considered to be high, which may be related to the occurrence of isomerization reactions at high temperature, as it has been described by Calemma et al.,18 who found that the extent of isomerization reactions increases with temperature, resulting in a higher iso/n-paraffin ration and also promoting the formation of polybranched paraffins. According to the difficulties observed for the use of high temperatures, the most favorable conditions to achieve a Saybolt color

value of >+30 from HNP would be to increase the pressure to 13.7 MPa while using a temperature of 623 K (run 30). Table 8 summarizes the results obtained in the treatment of the wax from the dewaxing of a brightstock (PWB), which is the oil fraction obtained in refineries as the residue of vacuum distillation. PWB is the heaviest of the waxes studied in this work, and it is characterized by a very high viscosity, a high melting point, and an important sulfur content. The PWB feedstock was observed to be very difficult to refine via hydrotreatment, and the treated samples obtained were characterized by an intense color that made it impossible to use the Saybolt scale; therefore, the results in Table 8 for color are referenced to the ASTM color scale. Because of the aforementioned difficulty in the treatment of PWB, all the runs were conducted at a pressure of 13.7 MPa and temperatures of >623 K. Similarly, space velocities of +30 0.00 pass 2 0.004 pass 0.767 323 3.40 15

573 9.81 0.75 >+30 0.15 pass 3 0.004 pass 0.775 331 3.74 12

573 9.81 0.5 >+30 0.01 pass 4 0.004 pass 0.782 334 4.80 17

623 13.7 0.5 >+30 0.10 pass 5 0.009 pass 0.793 338 6.37 20

643 13.7 0.5 0.5a 0.32 not pass 40 0.04 not pass 0.799 345 14.14 27

a

Using ASTM-D-1500.

oil content is an important drawback for their application. The initial oil content of the crude was already excessive (∼1%), and additional oil is generated during the hydrotreatment. Therefore, the production of high-grade paraffin from PWB would require an additional or alternative treatment, such as sulfuric acid treatment and adsorption. Table 9 summarizes the most-convenient reaction conditions for the treatment of each of the feedstocks studied, together with the characteristics of the treated paraffins obtained under such conditions. As previously commented, the hydrotreatment of heavier feedstocks requires the use of higher temperatures and pressures. Paraffins of high quality, even those suitable for food applications, can be obtained from SP, LNP, MNP, and HNP feedstocks. For these feedstocks, the amount of aromatics, naphthenes, and heteroatoms can be reduced to very low concentrations, which makes it possible to pass the carbonizable substances (ASTM-D-612) and FDA tests. Similarly, the sulfur content and the absorptivity at 290 nm show very low values. The generation of oil under the reaction conditions indicated is low, although the oil content of the hydrotreated samples also is dependent on the initial oil content, which is greater for heavier feedstocks, because of the microcrystalline nature of the crystallized paraffin. In the case of BSP, the hydrotreatment studied cannot provide a suitable degree of refinement and the properties of the treated paraffin are far from those required for high-quality applications. No significant changes are observed for the specific gravity and the melting point of the paraffins, and their ranges are suitable for commercial applications. The viscosity of all the samples was reduced slightly during the hydrotreatment. This phenomenon can also be responsible for the increase in needle penetration, which denotes a lower stiffness of paraffins. Conclusions The alumina-supported Ni-W catalyst that has been used showed excellent time-on-stream behavior for more than 6000 h and enabled the comparison of five crude wax feedstocks during their refinement by hydrotreatment. The use of heavier feedstocks required the use of more-severe hydrogenation conditions (i.e., an increase in temperature and pressure) to obtain a convenient reduction in the color of the paraffins. Although a higher temperature enables an easier reduction of color, excessive temperature can lead to greater cracking of the paraffins and the generation of oil and carbonizable substances. Thus, for heavy neutral oil (HNP) and brightstock oil (BSP), the increase in temperature was combined

with an increase in pressure to promote the hydrogenation of colored compounds and prevent cracking. It was found that the generation of oil can also be controlled using a higher space velocity, which reduces cracking, because of limitations in the access of high-molecular-weight paraffins to the active sites of the catalyst. Important differences in behavior were found within a single feedstock, depending on the initial oil content of the raw paraffin, which indicates the importance of the control of cracking during their melting and storage. High-quality paraffins with a Saybolt color value of >+30, which are suitable for food applications, were obtained from spindle oil (SP), light neutral oil (LNP), medium neutral oil (MNP), and HNP stocks. However, serious difficulties were encountered for the refinement of BSP, which requires the use of an additional or alternative treatment. Literature Cited (1) Musser, B. J.; Kilpatrick, P. K. Molecular characterization of wax isolated from a variety of crude oils. Energy Fuels 1998, 12, 715–725. (2) Furimsky, E.; Massoth, F. E. Deactivation of hydroprocessing catalysts. Catal. Today 1999, 52, 381–495. (3) Bergeron, I.; Charland, J. P.; Ternan, M. Color degradation of hydrocracked diesel fuel. Energy Fuels 1999, 13, 686–693. (4) De Guzman, D. US petroleum wax market hurt by slowing economy & imports. Chem. Mark. Rep. 2001, (April 23), 10–11. (5) EPA. Candles and Incense as Potential Sources of Indoor Air Pollution: Market Analysis and Literature ReView. Report prepared by National Risk Management, Research Laboratory, January 2001. (6) Growth initiatives for wax industry discussed at NPRA. Chem. Mark. Rep. 2001, (December 3), 18-19. (7) Rase, H. F. Handbook of Commercial Catalysts: Heterogeneous Catalysts; CRC Press: Boca Raton, FL, 2000. (8) Bolder, F. H. A. Fischer-Tropsch Wax Hydrogenation over a Sulfided Nickel-Molybdenum Catalyst. Energy Fuels 2007, 21, 1396–1399. (9) Class, J. A. Natural resins. In Encyclopedia of Polymer Science and Engineering; Wiley-Interscience: New York, 1988. (10) Koog, W. Trends in Lube Oil and Wax Production. Uhde Edeleanu GmbH Report: Alzeanu, 1999. (11) Ancheyta, J.; Rana, M. S.; Furimsky, E. Hydroprocessing of heavy petroleum feeds: Tutorial. Catal. Today 2005, 109, 3–15. (12) Callejas, M. A.; Martı´nez, M. T. Hydroprocessing of a Maya residue. Intrinsic kinetics of sulfur-, nitrogen-, nickel-, and vanadiumremoval reactions. Energy Fuels 1999, 13, 629–636. (13) Singh, H. High quality lubricants through advanced technologies. Hydrocarbon Asia 2003, (January/February), 40-46. (14) Ali, L. I.; Ali, A. A.; Aboul-Fotouh, S. M.; Aboul-Gheit, A. K. Hydroconversion of n-paraffins in light naphtha using PT/Al2O3 catalysts promoted with noble metals and/or chlorine. Appl. Catal., A 2001, 205, 129–146. (15) Eijbouts, S. Deactivation, regeneration and recycling of hydroprocessing catalysts. In EnVironmental Catalysis; Imperial College Press: London, 1999.

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ReceiVed for reView January 3, 2008 ReVised manuscript receiVed June 16, 2008 Accepted June 24, 2008 IE800014U