Article Cite This: Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
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Using Separate Kinetic Models to Predict Liquid, Gas, and Coke Yields in Heavy Oil Hydrocracking Guillermo Feĺ ix†,‡ and Jorge Ancheyta*,‡ †
Ind. Eng. Chem. Res. Downloaded from pubs.acs.org by UNIV OF LOUISIANA AT LAFAYETTE on 04/24/19. For personal use only.
Instituto Politécnico Nacional, Centro de Investigación en Ciencia Aplicada y Tecnología Avanzada, Unidad Legaria. Legaria 694, Col. Irrigación, 11500 Ciudad de México, Mexico ‡ Instituto Mexicano del Petróleo, Eje Central Lázaro Cárdenas 152, San Bartolo Atepehuacan, 07730 Ciudad de México, Mexico ABSTRACT: A kinetic model based on distillation curves for predicting the liquid fractions composition (residue, vacuum gas oil, middle distillates, and naphtha) in heavy crude oil hydrocracking was developed, whereby the yield of each liquid fraction can be calculated. The experiments were carried out in a 1.8 L batch reactor at reaction temperature of 360−400 °C, hydrogen pressure of 3.9 MPa, and reaction times of 2−5 h, using a heavy crude oil as feed and mineral catalyst. This kinetic model was combined with another one based on SARA, gas, and coke composition, and with both models the yield of the different liquid fractions, gas, and coke can be predicted with good accuracy. Based on the values of the reaction rate coefficients, it was determined that some reaction pathways do not occur at low temperature. The average absolute error between experimental and calculated composition was lower than 3.3% indicating the high accuracy of the proposed kinetic model.
1. INTRODUCTION Since the light crude oil reserves have been depleting and the demand of high value products such as gasoline and diesel is increasing, the upgrading of heavy crude oils has emerged as one of the most attractive technological options. Among all of the available alternatives, slurry-phase hydrocracking is well-recognized to be the choice to upgrade feedstocks with large amounts of impurities such as metals and asphaltenes.1−3 Differently to other technologies in development and close to commercial application, which operate at high reaction severity conditions4,5 (pressure of 7−27 MPa and temperature of 380− 525 °C) with the consequent elevated residue conversion (70− 95%), the Mexican Institute of Petroleum has recently developed a slurry-phase process for hydrocracking of heavy oils using mineral catalysts aimed at producing upgraded oil with reduced viscosity to facilitate the transportation.6 In continuation with the development of this technology, a series of experimental studies have been carried out to determine the reaction kinetics. In a previous work,7 SARA (saturates, aromatics, resins, and asphaltenes) fractions of the heavy oil feed were used to predict the composition of these fractions in the liquid upgraded oil as well as coke and gas formation. The liquid upgraded oil can also be characterized by simulated distillation, from which different lumps can be defined based on boiling point ranges such as naphtha, middle distillates, vacuum gas oils, and vacuum residue.7−13 This liquid composition can be used to generate kinetic models based on lumping approach. The literature reports some lumping kinetic models for heavy oil hydrocracking that have been reviewed elsewhere.14−18 All of the literature kinetic © XXXX American Chemical Society
models were obtained with experimental data at severe operating conditions using nonmineral catalyst, which include various liquid lumps and gases and coke produced by several reaction pathways from the liquid fractions. The objective of this work is to use experimental data obtained at low severity reaction conditions with mineral catalyst to develop a new lumped kinetic model for predicting the yields of the liquid upgraded oil during hydrocracking of heavy oils in slurry phase. The proposed kinetic model is coupled with the previously developed model based on SARA fractions to be able to predict simultaneously the yields of the liquid fractions, gases, and coke, as well as the SARA composition of the liquid upgraded oil.
2. EXPERIMENTAL SECTION To define the operating conditions at which intrinsic kinetic parameters can be calculated, a series of experiments were carried out with the heavy crude oil (360 g) as feed and 5000 ppm of Mo-based catalyst.19,20 The following reaction conditions were kept constant: temperature of 380 °C, pressure of 3.9 MPa, and reaction time of 4 h, while stirring rate was varied at 400, 600, 800, and 1000 rpm, in order to evaluate the magnitude of external diffusion. Other experiments were also conducted by varying the particle size (22.5, 63.5, 127, and 335 μm) keeping all previous conditions constants to determine the catalyst size at which internal diffusion is insignificant. Received: Revised: Accepted: Published: A
February April 10, April 15, April 15,
15, 2019 2019 2019 2019 DOI: 10.1021/acs.iecr.9b00904 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
Article
Industrial & Engineering Chemistry Research
measure the volume of gas product with an online gasometer. A sample of gas product is taken in a syringe to measure its composition following the UOP539 method for refinery gases. The properties of the feedstock are listed in Table 1. The dispersed mineral catalyst was molybdenite with an average particle size of 63.5 μm and a Mo content of 54.52 wt %. All experiments were carried out at reaction times of 2−5 h and temperatures of 360−400 °C. The liquid products were analyzed by kinematic viscosity (ASTM D7042 method), sulfur content (ASTM D4294 method), and simulated distillation (ASTM D7169 method). The latter provides the distillation curve, from which the composition of different fractions (pseudocomponents) can be obtained. The method to separate and measure coke content is reported elsewhere,7 which in summary consists of separating the solid part from the upgraded oil by vacuum filtration, washing with n-heptane and then washing with toluene in a Soxhlet apparatus. The separated solids are placed into an oven and weighed to obtain the amount of coke.
Table 1. Properties of the Heavy Crude Oil property
value
API gravity kinematic viscosity (cSt) at 25.0 °C 37.8 °C 54.4 °C sulfur content (wt %) metals content (ppm) Ni V simulated distillation (wt %) naphtha (538 °C) SARA composition (wt %) saturates aromatics resins asphaltenes
11.97 43233 9521 2082 5.618 81 415 6.98 17.30 34.45 41.27 13.02 36.25 29.44 21.29
3. KINETIC MODELING The reaction scheme shown in Figure 1 involves four lumps and different pathways in series and in parallel. The lumping kinetic model derived from this reaction scheme is based on distillation curve and takes into account the following fractions in the liquid phase: vacuum residue (VR, >538 °C), vacuum gasoil (VGO, 343−538 °C), middle distillates (MD, 204−343 °C), and naphtha (N,
