Article pubs.acs.org/EF
Novel Propylene Production Route: Utilizing Hydrotreated Shale Oil as Feedstock via Two-Stage Riser Catalytic Cracking Xiaobo Chen,*,† Nan Li,† Yiqing Yang,‡ Chaohe Yang,† and Honghong Shan† †
State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Qingdao, Shandong 266580, People’s Republic of China ‡ Lanzhou Petrochemical Research Center, PetroChina, Lanzhou, Gansu 730060, People’s Republic of China ABSTRACT: In this paper, a novel propylene production route is proposed. Hydrotreated shale oil was first used as a feedstock for fluid catalytic cracking (FCC) to increase the propylene yield because of its abundant aliphatic hydrocarbons. The catalytic cracking performance of hydrotreated shale oil was investigated in detail via two-stage riser catalytic cracking (TMP). The results of the pilot-plant-scale TMP indicated that hydrotreated shale oil blended with 30 wt % Daqing vacuum residue could not only maximize the propylene yield but also showed a more desirable product distribution than conventional FCC feedstock. The yield of liquid products (including liquefied petroleum gas, gasoline, and diesel) was as high as 84.93 wt %, and the propylene yield reached 23.62 wt %, whereas the dry gas yield was only 6.06 wt %. This study may provide a novel route to reasonably use shale oil.
1. INTRODUCTION
alternative feedstock for FCC to produce propylene because of its abundant aliphatic hydrocarbons. This paper proposes a novel propylene production route. Hydrotreated shale oil was used for the first time as the feedstock of FCC to maximize the propylene yield. The catalytic cracking performance of hydrotreated shale oil was investigated in detail via two-stage riser catalytic cracking (TMP). The results obtained here could be of interest in the study of refining shale oil and may provide a novel route to reasonably use shale oil.
Shale oil, similar to conventional crude oil, is derived from oil shale retorting. Shale oil is often used as a fuel or further converted into gasoline, diesel, and petrochemicals; thus, it is expected to be a highly important alternative to conventional petroleum resources.1,2 Some previous works have demonstrated that shale oil is a rather complex liquid organic mixture, containing thousands of hydrocarbons and nitrogen-, oxygen-, and sulfur-containing organic compounds.3−7 These heteroatom compounds result in some problems in the storage and refining of shale oil, such as discoloration, increased viscosity, poisoning of catalysts, gum formation, and emissions of NOx and SOx.8,9 Therefore, it is necessary to remove heteroatoms during shale oil refining processes. At present, hydrotreatment is considered the most efficient method to remove S, N, and O atoms from shale oil. After hydrotreatment, the heteroatom content of shale oil decreases to a low level and the hydrotreated shale oil becomes a fraction containing a large amount of aliphatic hydrocarbons.10−12 Aliphatic hydrocarbons are excellent feedstocks to produce propylene through fluid catalytic cracking (FCC), which provides 30% of the global supply of propylene.13−15 In recent years, some FCC processes have employed novel technologies and special catalysts to maximize the propylene yield. Several processes have been developed and applied to commercial units, such as Saudi Aramco’s HS-FCC,16 Shell’s MILOS,17 Sinopec’s DCC,18,19 CPP,20 HCC,21 and FDFCC,22 and China National Petroleum Corporation (CNPC)’s two-stage riser catalytic cracking for maximizing the propylene yield (TMP).23−25 Besides employing an additive of ZSM-5 zeolite,26 a shared feature of these FCC technologies is that their feedstocks contain abundant aliphatic hydrocarbons, e.g., paraffinic vacuum gas oil (VGO), paraffinic atmospheric residue, hydrotreated VGO, and Fischer−Tropsch naphtha.27 Consequently, hydrotreated shale oil may be an appropriate © 2015 American Chemical Society
2. EXPERIMENTAL SECTION 2.1. Feedstocks and Catalysts. The hydrotreated shale oil (feedstock A) used in this study was provided by Fushun Mining Group, China. Its properties are listed in Table 1. The properties of conventional feedstock with Daqing VGO blended with 30 wt % Daqing vacuum residue (feedstock B) and hydrotreated shale oil blended with 30 wt % Daqing vacuum residue (feedstock C) are also shown in Table 1. Feedstock B is a representative paraffinic base feedstock, which is a relatively excellent feedstock to produce light olefins through FCC,13,23,25 and it was obtained from the Daqing Oilfield, China. Shale oil was hydrotreated in a fixed-bed scale unit over a Ni−Co/Al2O3 catalyst. The conditions of hydroprocessing were as follows: reaction pressure of 10 MPa, reaction temperature of 360 °C, space velocity in volume of 1.0 h−1, and hydrogen/shale oil of 800 (v/v).8 Conradson carbon residue (CCR) was analyzed using the Chinese standard analytical method for the determination of the carbon residue, GB/T 268-87, which agreed with ISO 6615-1983. The element content was measured by a Vario EL III elemental analyzer (Elementar Co., Ltd., Germany). The group compositions were analyzed using the Chinese standard analytical method for the petroleum and natural gas industry, SY/T 5119-2008.28 A mixture of two commercial equilibrium FCC catalysts were used, including the catalyst LTB-2 (50 wt %) with an active component of Received: September 15, 2015 Revised: October 21, 2015 Published: October 23, 2015 7190
DOI: 10.1021/acs.energyfuels.5b02076 Energy Fuels 2015, 29, 7190−7195
Article
Energy & Fuels
percentage of H 2 and N 2 and the mass content of C 1 −C 6 hydrocarbons. The liquid product was weighed and then analyzed by simulated distillation (ASTM D2887) using an Agilent 6890N gas chromatograph to determine the yields of gasoline [from initial boiling point (IBP) to 204 °C], diesel (from 205 to 350 °C), and heavy oil (above 350 °C). To provide sufficient feedstocks for second-stage catalytic cracking experiments, the liquid product was fractionated to gasoline, diesel, and heavy oil by the true boiling point distillation. The coke yield was determined by measuring the content of CO and CO2 and the volume of flue gas.
Table 1. Properties of Feedstocks items feedstock
feedstock A hydrotreated shale oil
848.4 density at 20 °C (kg/m3) CCRa (wt %) 0.02 carbon (wt %) 85.88 hydrogen (wt %) 13.70 sulfur (wt %)
