Subscriber access provided by READING UNIV
Article
An exploratory study for the upgrading of transport properties of heavy oil by disperse phase hydrocracking Alexander Quitian, Carolina Leyva, Sergio Ramirez, and Jorge Ancheyta Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/ef501577d • Publication Date (Web): 18 Dec 2014 Downloaded from http://pubs.acs.org on December 26, 2014
Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
Energy & Fuels is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.
Page 1 of 28
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels
An exploratory study for the upgrading of transport properties of heavy oil by slurry-phase hydrocracking Alexander Quitian1,2, Carolina Leyva3, Sergio Ramírez1, Jorge Ancheyta1* 1
Instituto Mexicano del Petróleo, Eje Central Lázaro Cárdenas Norte 152 Col. San Bartolo Atepehuacan, Mexico D.F. C.P 07730, Email:
[email protected] 2
Facultad de Química, Universidad Nacional Autónoma de México, Ciudad Universitaria, Coyoacán, Mexico D.F. CP 04510
3
Centro de Investigación en Ciencia Aplicada y Tecnología Avanzada - Unidad Legaria IPN, Legaria 694, Col. Irrigación, Mexico City 11500, Mexico
ABSTRACT The partial hydrocracking of a crude oil of 13 °API and viscosity of 6100 cSt at 37.8 °C was carried out in a batch reactor using a dispersed catalyst. The operating conditions were varied in the following ranges: hydrogen pressure of 40-100 kg/cm2, temperature of 360400 °C, and reaction time of 3-5 hours. Molybdenum trioxide of analytical grade was employed as dispersed catalyst, and its concentration was modified from 0 to 2 wt%. The obtained results showed that the most favorable reaction conditions to obtain an upgraded crude oil with the required specifications for transportation by pipeline are 40 kg/cm2, 380 °C, 4 hours of reaction, and a catalyst concentration of 0.75 wt%. At these operation conditions no coke formation was observed. Keywords:
slurry catalyst, dispersed catalyst, heavy crude oil, upgrading oil,
hydrocracking
1 ACS Paragon Plus Environment
Energy & Fuels
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
1.
Page 2 of 28
INTRODUCTION
The petroleum industry has changed significantly in recent years. The production of light crude oil has declined worldwide, while production of heavy crude oil has increased. This situation has brought several problems in the production, transportation, storage and refining of the heavy crude oil. Due to its properties of high specific gravity (low API gravity) and high viscosity, it is required the application of different procedures and technologies to maintain the smooth flow of heavy crude oil, in order to transport it from production facilities to distribution centers or refineries, which are typically located hundreds of miles away. The problem is even worse when heavy oil needs to be transported from offshore facilities to producers, who face many difficulties such as heating the pipeline, easy access and use of diluents, reduced area for installing large plants, among others, which limit the application of the same technologies used in ground surface. The most important property is the viscosity, which defines whether a heavy crude can be transported or not. The API gravity is also used as transportability parameter of a heavy oil; however, its minimum value depends on the source and nature of the crude oil. Typically, for transportation purposes, a crude oil requires API gravity value greater than 16 and a viscosity less than 250 cSt at 37.8 °C to be pumped and to achieve low operating and investment costs in the pumping1. The current solutions to solve the problems of transportation of heavy crude oils in pipelines can be classified into two groups: (1) lowering the viscosity of heavy crude oil and (2) reducing the friction of the oil within the pipeline. To improve the transport properties of heavy crude oils, particularly the viscosity, and the following methods are
2 ACS Paragon Plus Environment
Page 3 of 28
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels
reported: (1) heating, (2) dilution, (3) formation of emulsions, among others. Each option can apply different methods and technologies2,3,4. The most common method is blending the heavy crude oil with some light crudes, distillates or solvents, however, availability of diluent fluids in proximity of the production site is crucial, although doing so, will affect somehow the final product properties3. However, these approaches have a number of technical and economical drawbacks so that their application is limited because they may increase the cost of production of heavy crude oil. Thus, the oil transportation issue must be solved at a cost that will still produce a profit5,6.
Apart from conventional and unconventional (i.e. emerging) technologies, traditional upgrading technologies may be used to reach the properties for crude oil transportation. Nevertheless, each upgrading technology exhibits disadvantages, which limit its application, for instance5-8:
•
Visbreaking is not suitable for feeds with high content of asphaltenes and Conradson carbon residue.
•
Delayed coking produces a high amount of coke with elevated amount of impurities and it requires a big size of coking drums.
•
Solvent deasphalting produces a high metal and sulfur content pitch, which is also viscous and of low commercial value.
•
High severity hydrocracking uses catalysts and hydrogen at elevated pressure and temperature; it is most useful for total conversion of heavy feeds.
These and other processes are certainly applicable for the upgrading of heavy oils which purpose is the total conversion of bottom-of-barrel in refineries, but their application for
3 ACS Paragon Plus Environment
Energy & Fuels
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 4 of 28
producing transportable oil (low conversion) is questionable technically and economically speaking, particularly in off-shore facilities9. The technologies that are based on high severity hydrocracking and the use of disperse catalyst (VCC, HDH plus, SOC, EST, HCAT, etc.) operate at 420-460 °C and 150-200 kg/cm2. These processes can achieve conversions of the residue higher than 90 %10,11,12. A few years ago, there was a race of the developers of these technologies to achieve almost 100 % conversion, but recently it seems that it has finished, and now developers are most focused on the promotion of their commercial applications in different parts of the world. All technologies and process reported in the literature that use disperse catalyst are focused on refining of residue or heavy crude oils. The presence of disperse catalyst and hydrogen prevents coke formation and leads to more stable products10,13,14,15. As the catalyst is uniformly distributed, the hydrocracking of the high molecular weight hydrocarbons is more efficient and can be controlled only to reduce the viscosity at low pressure and temperature 16- 18. One attractive alternative presented in this study is to use hydrocracking with a dispersed catalyst for upgrading of transport properties of heavy and extra-heavy crude oils at low severity operating conditions. This experimental investigation reports an exploratory study carried out in a batch reactor for the partial hydrocracking of heavy oils using molybdenum oxide as dispersed catalyst. The aim is to achieve the properties required for transportation by pipeline of a heavy crude oil of an API gravity of 13° and a viscosity at 37.8 °C of 6110 cSt.
4 ACS Paragon Plus Environment
Page 5 of 28
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels
2.
EXPERIMENTAL
2.1.
Materials and feedstock
Molybdenum trioxide (MoO3) from Sigma-Aldrich Co. with a purity of 99.5 % was used as dispersed catalyst. The main properties of this catalyst are reported in Table 1. A heavy crude oil of 13° API was employed as feedstock and its properties are presented in Table 2. 2.2.
Experimental set up
Hydrocracking tests were carried out in a Parr batch reactor model 4843 equipped with a control system for temperature, pressure and stirring rate. The scheme of the reaction system is shown in Figure 1. 2.3.
Operating conditions
The reactor operation was isothermal and batch, hence hydrogen pressure decay was not compensated during the reaction. The operating conditions were varied in the following ranges: initial hydrogen pressure of 40-100 kg/cm2, reaction time of 3-5 hours, and temperature of 360-400 °C. The stirring rate was kept constant at 750 rpm. The ranges of pressures and temperatures were chosen because it is well known that at these conditions, hydrocracking reactions occur and there is not precipitation of sediments12,19. During each experiment, the reactor was loaded with 200 grams of a heavy crude oil, after this; appropriate of MoO3 was then loaded depending on the desired concentration that was varied between 0 to 2%wt, which is equal to a concentration of active metal-based catalyst of 13,333 ppm of Mo. 2.4.
Analysis of products
After each experiment, liquid and solid samples were discharged and the obtained quantities of upgraded crude oil, gas and coke or sediment were measured. Gas samples
5 ACS Paragon Plus Environment
Energy & Fuels
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 6 of 28
were analyzed and quantified by gas chromatography using and Agilent Gas Chromatograph Model 6890 according to the UOP-539 standard for refinery gases. Liquid samples were analyzed in terms of API gravity, viscosity, sulfur and metals content. Determinations of viscosity and density of the upgraded crude oil were performed in an Anton Parr viscometer/densimeter model SVM3000. While, sulfur content (ASTM D4294) was quantified using a Horiba sulfur-in-oil analyzer model SLFA-2100/2800. Additionally, the analyses of Ni and V content in the upgraded crude oil were carried out in Thermo Electron Atomic Absorption Spectrometer model SOLAAR series S following the ASTM D 5863-00a method. The reported values of the product properties correspond to an average of five experiments carried out at the same operating conditions. The maximum experimental standard deviations of the data are ±0.5, 10 cSt, 0.2 wt% and 50 ppm for API gravity, viscosity, sulfur content and metals content respectively.
3.
RESULTS AND DISCUSSION
3.1.
Experiments without catalyst
A series of experiments were performed with the objective to analyze the effect of pressure and temperature without catalyst at a reaction time of 4 hours in the presence of hydrogen, then these experiments are similar to the hydrovisbreaking process but at mild conditions. The evolution of the API gravity and viscosity at 37.8 °C of the upgraded crude oil as function of pressure and temperature is observed in Figure 2a. The API gravity enhances when the temperature increases and slightly decreases as the pressure increases. API
6 ACS Paragon Plus Environment
Page 7 of 28
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels
gravity always has a value greater than 19° in the entire range of pressures and temperatures studied. The viscosity of the obtained upgraded crude oil at 37.8 °C decreases as the reaction temperature raises and it lowers slightly as the reaction pressure is reduced. In all ranges of pressure and temperature studied, the obtained upgraded oils have a viscosity between 50220 cSt (Figure 2a). The volumetric expansion, measured at room temperature and defined as the volume of upgraded oil divided by the volume of feed minus one, is a process parameter that gives an indication of the level of hydrogenation/hydrocracking. Since hydrogen is added, volumetric expansion must be higher than 100%. This process parameter is also used to perform mass balances, which are further employed to determine equipment capacities for economic study purposes. Volumetric expansion depends strongly on temperature and slightly on pressure. The values range between 3.8-4.9 vol% at 360 °C and 8.7-9.4 vol% at 380 °C, at the studied range of hydrogen pressures (Figure 2b). In the case of sulfur content, it was reduced from 5.2 wt% to 4.5-4.8 wt% at 360 °C, and to 3.8-4.3 wt% at 380 °C in the obtained upgraded crude oils at pressure of 40-100 kg/cm2, which means maximum sulfur removal of 27 % (Figure 2c). Even when the upgraded crude oils produced in absence of catalyst have appropriate properties for pipeline transportation and that the thermal cracking is favored without the presence of a catalyst, there is a high production of coke and gas which enhances at higher temperature, with the consequent reduction of the yield of upgraded oil (Figure 2d). It is well-known, that thermal cracking reactions occur by a free radical mechanism and that they are favored at low pressure (350 °C).
7 ACS Paragon Plus Environment
Energy & Fuels
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 8 of 28
However, without the presence of catalyst in the system, the hydrogenation reactions cannot be promoted and the thermal cracking produces a large amount of light hydrocarbons, hydrogen sulfide (Table 3) and coke, because the hydrocracking reactions without catalyst break a larger number of C-S bonds19-21. The high production of coke and hydrocracking gases (rich in C1-C4 compounds) reduces the upgraded crude oil yield in spite of the good volumetric expansion obtained in the liquid products. These problems make the non-catalyzed hydrocracking reaction not commercially viable. 3.2. Effect of temperature and pressure with catalyst To study the effect of temperature and pressure on the quality of the product obtained by partial catalytic hydrocracking, a series of experiments were conducted using a reaction time of 4 hours and molybdenum trioxide as catalyst at concentration of 1 wt%. As seen in the Figure 3a, the API gravity of the obtained upgraded crude oils is increased as the temperature rose and the pressure is diminished. API gravity has an approximately constant value of 14° at 360 °C, while at 380 °C it reaches values between 19.5° and 18° in the studied pressure range. The viscosity at 37.8 °C of the obtained upgraded crude oils decreases with pressure and temperature (Figure 3a). The viscosity at 360 °C reaction temperature has values of 18002300 cSt, whereas at 380 °C, it varies slightly between 170-190 cSt. The small variation of the API gravity and viscosity is due to the low temperature (>360 °C) and low pressure (
