Article pubs.acs.org/EF
Single- and Multi-stage Counter-current Solvent Extractions of Bitumen from Xinjiang Oil Sand Kai Yu,† Zhenbo Wang,*,†,‡ Youhai Jin,†,‡ Zhiqian Sun,† Yang Liu,† Jiajia Yang,† and Yaomin Cai† †
College of Chemical Engineering, and ‡State Key Laboratory of Heavy Oil, China University of Petroleum, Qingdao, Shandong 266580, People’s Republic of China ABSTRACT: Non-aqueous solvent extraction is best characterized by higher bitumen recovery and minimal water consumption. In this study, single- and multi-stage counter-current solvent extractions of bitumen from Xinjiang oil sands were investigated. The particle size distributions of original oil sand samples, suspended particles, and extracted sands were analyzed. The results indicate that oil sand particles should be broken down to a size range of less than 450 μm and the median particle diameter should be approximately 268 μm. Bitumen recoveries for both the two- and three-stage counter-current processes are more than 93.5%, and the two-stage process is more effective for recovering bitumen than the single- and threestage extractions based on a series of evaluation methods. The majority of the suspended solid particles are under 21 μm, and the residual solvent can be efficiently recovered through heating. The multi-stage counter-current solvent extraction has beneficial effects on the exploitation and utilization of Xinjiang oil sand ores. bitumen recoveries.7 Painter et al. found that bitumen could be recovered from Utah tar sands efficiently when an ionic liquid (IL) together with an organic solvent was used. The extraction process could take place at approximately 25 °C, and the bitumen recovery could exceed 90%.8 It should be noted, however, that once water is introduced into the extraction process, so are most of the problems associated with hot-water extraction.12 As an alternative technique to the hot-water extraction process, non-aqueous bitumen extraction has been investigated since the mid-1960s. This type of technology is more promising because (i) non-aqueous solvent is used, which decreases the consumption of water, (ii) bitumen recovery is high (more than 90%), and (iii) little solvent will leave in extracted sands.1,11,12 Several non-aqueous solvent extraction processes have been researched. Li et al. used a mixture solvent of n-heptane and toluene (3:1, v/v) to recover bitumen and found that bitumen recovery could reach 99 wt % when multi-stage extraction was implemented.1 Wu et al. studied the multi-stage extractions of bitumen, and several solvents (n-pentane, hexane, cyclopentane, a mixture of n-pentane and cyclopentane, and toluene) were used. They found that the bitumen recoveries could exceed 90 wt %, and cyclopentane was the best solvent among the given solvents.12 U.S. Patent 3,475,318 described a solvent extraction process. Solvent was separated from the extracted bitumen through distillation, and the recovered solvent could be used circularly. The extracted bitumen was then transported to a vacuum flasher to obtain naphtha and asphaltene.13 U.S. Patent 4,046,668 presented an oil-sand-treating process, and a light naphtha/methanol solvent system was used to recover bitumen. The nonpolar organic ingredients would dissolve in naphtha; the more polar soluble ingredients could be recovered
1. INTRODUCTION With the gradually rising energy consumption and approaching depletion of traditional fossil fuels, humans are trying to find new forms of energy media. As one type of alternate energy source, the importance of oil sands is increasing.1,2 China has enormous oil sand resources. The reserves of oil sands in China are 59.7 × 108 tons, and 22.58 × 108 tons can be exploited according to a report from the Ministry of Land and Resources of People’s Republic of China. These reserves can provide a reliable energy supply for our country. The utilization of oil sands resources can relieve the energy shortage of China and promote the development of our economy. Therefore, the study of oil sands utilization technology is of crucial importance. Several methods are used to extract bitumen from oil sand, such as hot-water extraction, water-based extraction, ionic liquid extraction, non-aqueous bitumen extraction, etc.3−6 The most common commercial method is hot-water extraction. However, it has several shortcomings, such as a large requirement of fresh water, high energy consumption, and large yields of extracted sands (tailing).7 In addition, the hotwater extraction technology is not suitable for disposing the oilwet oil sand ores.8 To alleviate those disadvantages, water-based extraction (aqueous−non-aqueous hybrid process) and ionic liquid extraction were developed. Hupka et al. considered that organic solvent was needed to reduce the bitumen viscosity but the amount of solvent that could be accepted by the oil sand was determined by the oil sand porosity.9 To reduce the oil sand processing temperature and increase bitumen recovery, Harjai et al. proposed a robust aqueous−non-aqueous hybrid bitumen extraction process. They found that kerosene could augment bitumen liberation kinetics and ameliorate bitumen aeration.10 Long et al. found that temperature played a pivotal role in improving bitumen recovery. It would exacerbate the bitumen recovery when the processing temperature was lower than 35 °C, and some kinds of chemical additives could be used at lower temperatures to maintain comparatively higher © 2013 American Chemical Society
Received: July 11, 2013 Revised: October 14, 2013 Published: November 4, 2013 6491
dx.doi.org/10.1021/ef4013196 | Energy Fuels 2013, 27, 6491−6500
Energy & Fuels
Article
by methanol; and the insoluble asphaltenes could be found at the interface of the two solvents.14 U.S. Patent 4,046,669 used trichloroethylene to recover bitumen.15 U.S. Patent 4,139,450 described a sophisticated solvent extraction process. The oil sands−solvent mixture was separated into two phases of fines and coarse sand to increase separation efficiency.16 U.S. Patent 4,347,118 disclosed an oil sand treatment process. A low boiling solvent (20−70 °C) was used, and a two-stage fluidizedbed drying zone was selected to recover the residual solvent from the extracted sands.17 To date, however, few studies have been performed to investigate the influences of the oil sands particle size on bitumen recovery and solid contents in the supernatant. In this research, a new process (multi-stage counter-current solvent extractions) for solvent extraction of bitumen from Xinjiang oil sands was investigated, and five disparate nonaqueous organic solvents (toluene, cyclohexane, diesel oil, No. 93 gasoline, and No. 97 gasoline) were studied. This study sought to do the following: (i) determine a comparatively better solvent from the given solvents; (ii) determine the optimal particle size range for organic solvent extraction; (iii) set a series of assessment criteria to investigate the effectiveness of multi-stage (two- and three-stage) counter-current solvent extractions in terms of bitumen recovery, distribution of bitumen in the supernatant, extracted sands, and suspended particles, solid contents in the supernatant, bitumen contents in suspended particles and residual solvent, and bitumen in extracted sands; (iv) determine the optimal extraction stage and preferable solvent/oil sand ratio (V/M) for each stage of the multi-stage counter-current extraction; (v) analyze the particle size distribution of the original oil sand ores, suspended particles, and extracted sands; and (vi) simulate the recovery of the residual solvent through heating. To keep the consistency of the concepts, bitumen in the supernatant, extracted sands, and suspended particles was referred to as dissolved bitumen, residual bitumen, and suspended bitumen, respectively.
Table 1. Composition of Xinjiang Oil Sand Ores bitumen (wt %)
water (wt %)
solids (wt %)
fines (≤44 μm) (wt %)
12.1
2.2
85.7
2.3
stage counter-current solvent extraction, the oil sand ores were divided into four different particle sizes. The particle size distributions of the four samples measured by the Beckman Coulter LS230 are shown in Figure 1 and Table 2. The overwhelming majority of the particles of sample 1 are distributed from 1600 to 1000 μm, followed by sample 2 (1000−450 μm), sample 3 (
