Optimization Study on Oxidative Desulfurization of Crude Oil under Electric Field

Transcription

1 Process Research China Petroleum Processing and Petrochemical Technology 2011,Vol. 13, No. 3, pp September 30, 2011 Optimization Study on Oxidative Desulfurization of Crude Oil under Electric Field Liu Lin; Lü Hong; Meng Fanfei; Wang Ning; He Yiyi (Liaoning Province Key Laboratory for Synthesis and Application of Functional Compounds, Bohai University, Jinzhou ) Abstract: Oxidative (ODS) of Azeri crude oil was studied under the electric field. By means of orthogonal experiments, the optimum conditions for of crude oil were identified, while the effect of oxidative under the electric field was compared with that of the single oxidative method. The test results showed that the reaction taking place under the electric field would be better than the traditional method. The rate of crude oil could reach up to 77.06% at 115 at a distilled water amount of 10 m%, a desulfurizer dosage of 200 μg/g, and a demulsifier dosage of 50 μg/g. Key words: crude oil; oxidative ; electric field; orthogonal experiment 1 Introduction In recent years with increasingly stringent environmental requirements and the shortage of oil resources [1], the processing of high-sulfur crude oil has become an inevitable trend of the oil refining industry [2-3]. However, it is important to minimize the sulfur content of crude oil before refining. The first process of oil processing is desalting, which is mainly aimed at removing salt and water from crude oil. The feed oil under the electric field that is used in the pre- process for crude oil is heated under intensive agitation and mixed with the desulfurizing agent added thereby. Then the sulfides that are removed after reaction are discharged to the wastewater treatment system [4-5]. The process is carried out in the electric desalting unit, which performs the functions of, desalting and dehydration at the same time, and does not need to change the existing process for modifying the original harsh operating conditions to provide such advantages as less time-consuming operation, less amount of agent needed, investment cost saving, low energy consumption, and operating costs reduction. The pre- process for treating the crude oil can alleviate the equipment corrosion problems resulted from processing of sour crude oil, reduce the total sulfur content in oil, and prevent catalyst poisoning, which will herald the broad application prospects of this process. 2 Experimental 2.1 Instruments and materials Instruments used in the experiments included: a SH-II type electrical desalting unit (manufactured by the Equipment Research Institute of Luoyang Petrochemical Engineering Company of Sinopec), a TSN-2000 type ultraviolet fluorescence sulfur/nitrogen analyzer (manufactured by the Jiangsu Jiangfen Electroanalytical Instrument Co., Ltd.); and a CHI660D electrochemical workstation (manufactured by the Shanghai Chenhua Instrument Co., Ltd.). Materials used in the experiments included: the Azeri crude oil, the desulfurizer (oxidant), and the demulsifier. 2.2 Experimental methods In this paper, crude oil by oxidation method, in which the oxidant was described as the desulfurizer, was carried out according to the orthogonal tests of five factors and four levels of L 16 (4 5 ) [6]. The influences of the four main factors, including the desulfurizer dosage, the oil bath temperature, the distilled water injection rate, Corrresponding Author: Dr. Liu Lin, Telephone: ; liulinln@163.com 59

2 China Petroleum Processing and Petrochemical Technology 2011,13(3):59-63 and the demulsifier dosage, on the rate were studied, and the factors are shown in Table 1. The total sulfur content in oil sample was determined according to the SH/T method (and also the national standard GB/T 4756). Table 1 and levels Levels A (Desulfurizer dosage), μg/g B (Temperature), C (Distilled water injection rate), m% D (Demulsifier dosage), μg/g A definite amount of crude oil sample was put into the micro-electric desalting drum, in which a certain amount of distilled water, demulsifier, and desulfurizer at a specified ratio was also added. After having switched on power to the electrical desalting unit, the desalting unit was preheated for a certain time until a specified temperature was reached, while the reaction mixture was fully mixed. The electric field intensity of the weak electric field and the strong electric field was regulated to the required value prior to commencement of the reaction, which should be conducted in a specified period of time. The micro-electric desalter drum was removed and cooled down after reaction, and then the bottom of the jacket was opened, with water and oil sample being separately discharged through the micro-valve. During the post-treatment, the total sulfur content in oil was determined, and the corresponding relationship between the sulfur content and the corrosion degree before and after oil was analyzed by the detector creating the electrochemical corrosion polarization curves. The processing equipment is presented in Figure 1. 3 Results and Discussion 3.1 Orthogonal test results and analysis Table 2 shows that the rate of crude oil reached m%, and Table 3 shows the influences of four investigated factors on rate that decreased in the following order: distilled water injection rate> desulfurizer dosage> oil bath temperature> demulsifier dosage. And the most optimum conditions were identified at a distilled water injection rate of 10 m%, a desulfurizer dosage of 200 μg/g, and a demulsifier dosage of 50 μg/g at an oil bath temperature of 115. Table 2 The design and results of orthogonal experiments Tests Figure 1 A schematic diagram of processing steps for oil A B C D Desulfurization rate, m%

3 Liu Lin, et al. Optimization Study on Oxidative Desulfurization of Crude Oil under Electric Field Table 3 Results of orthogonal experiment date analysis Tests A B C D K K K the electric field intensity for the electrical desalting unit) could realize a better crude oil effect. Meanwhile, a weak electric field intensity of 400V/cm could also achieve a better effect on crude oil rate (as evidenced by Figure 4). K k k k k R Major influence minor influence C>A>B>D Optimal level A 2 B 3 C 4 D 3 Optimal combination C 4 A 2 B 3 D Reproducibility of test results As the results of orthogonal experiments had determined the optimal process combinations to be C 4 A 2 B 3 D 3, repeated tests were carried out to determine the accuracy of experimental data, with the results shown in Table 4. The oil rate could reach m%. Figure 2 Effect of oxidative under electric field and electric field-free oxidative at different temperatures Without electric field; With electric field Table 4 Desulfurization rate under the optimal conditions of orthogonal experiments Combination of optimal process conditions Test No. Desulfurization rate, m% C 4 A 2 B 3 D Comparison on the effect of ODS with and without electric field and the effect of electric field intensity on the rate The effect of oxidative of oil at different temperatures in the presence of an electric field was compared with that without using the electric field. Figure 2 shows that the oxidative rate in the presence of an electric field was higher than that achieved by the oxidative process without using an electric field. Figure 3 shows that a strong electric field with a intensity of 1700 V/cm (the maximum setting of Figure 3 Effect of strong electric field intensity on crude oil rate Figure 4 Effect of weak electric intensity on crude oil rate 61

4 China Petroleum Processing and Petrochemical Technology 2011,13(3): Evaluation of basic physical and chemical properties of crude oil before and after Since Table 5 indicates that the density and viscosity of crude oil were decreased with the removal of sulfur compounds, it was interesting to know if the oil impurities, or a small part of the heavy constituents, or the cyclic compounds in crude oil were also removed, then the role of electric field for oil would be questioned. Since other basic properties of crude oil were little affected after process as evidenced by the data listed in Table 5, the method of oxidative under the electric field would not affect the quality of downstream products except for reducing the total sulfur content of crude oil. Table 5 Physical and chemical properties of crude oil before and after Analysis item Before Analytical data After Density (20 ), g/cm Viscosity (50 ), mm 2 /s Viscosity (80 ), mm 2 /s Acid number, mgkoh/g Solidification point, -8-8 Sulfur content, m% Analysis of electrochemical corrosion polarization curves The corrosion polarization curves were measured using a three-electrode system, with the platinum sheet serving as the auxiliary electrode, the saturated calomel electrode (SCE) as the reference electrode, and the silver strip as the working electrode. The analysis of electrochemical corrosion in a potentiostat by means of Tafel polarization curves was carried out in the CHI660D electrochemical workstation. Figure 5 shows the electrochemical corrosion polarization curves of silver strip in the crude oil before and after. It can be seen from the curves that the free corrosion potential of the silver strip in the crude oil after was higher. Generally speaking, the corrosion current for silver strip dipped in crude oil after was less than that for silver strip in oil before, which indicated the corrosion rate of silver strip in desulfurized crude oil was reduced. Fig 5 Electrochemical corrosion polarization curves of crude oil before and after 1 before ; 2 after 4 Conclusions (1) Oxidative of crude oil under electric field demonstrated an obviously enhanced effect than that achieved by the single oxidative method without using electric field. (2) The influence of the four investigated factors on the oil rate decreased in the following order: distilled water injection rate> desulfurizer dosage> oil bath temperature> demulsifier dosage. And the most optimum conditions were achieved at a distilled water injection rate of 10 m%, a desulfurizer dosage of 200 ppm, and a demulsifier dosage of 50 ppm at an oil bath temperature of 115. (3) The oxidative of oil in the presence of an electric field had little influence on the basic physical and chemical properties of crude oil. (4) The free corrosion potential of the silver strip in the crude oil after was higher. And the corrosion current for silver strip dipped in crude oil after was less than that of the case using crude oil before, and the corrosion rate of silver strip was also reduced. Acknowledgement: The authors are grateful to financial supports from the Science and Technology Office of Liaoning Province (Project number: ) and the Liaoning Provincial Office of Education for Innovation Team (Project number: 62

5 Liu Lin, et al. Optimization Study on Oxidative Desulfurization of Crude Oil under Electric Field 2009T002). References [1] Yuan Qingtang. Progress and outlook on technologies for processing inferior crude oil in China[J]. China Petroleum Processing and Petrochemical Technology, 2008(1): 1-7. [2] Shi Yahua. Desulphurization in Petroleum Processing Process[M]. Beijing: China Petrochemical Press, 2009: 13 (in Chinese). [3] Qian Jianhua, Zhou Yuenan, Liu Lin, et al. Study on kinetics for of model diesel[j]. China Petroleum Processing and Petrochemical Technology, 2009(2): [4] Lin Zhiping, Yin Shuhua, Jiang Tianyan, et al. Desulphurization process for high-sulfur crude oil and the agent: CN [P] (in Chinese). [5] Liu Guiling. Research on application of fine chemicals of petroleum in processes for pretreatment of crude oil[d]. Shanghai: East China University of Science and Technology, 2004 (in Chinese). [6] Department of Math, Peking University. Experiment Design[M]. Beijing: Petrochemical Industry Press, 1976 (in Chinese). Successful Development of PIA Integrated Process Unit By Tianhua Institute The SINOPEC development project Development of integrated process and equipment for filtration, washing and pre-drying of pure isophthalic acid (PIA) undertaken by the Tianhua Chemical Machinery and Automation Research and Design Institute has passed the appraisal organized by the Sinopec Corp. This institute after having studied and analyzed the existing filtration process and technology of the PIA purification unit has developed an integrated continuous pressurized drum filter press encompassing filtration, washing, pre-drying, and discharging of materials with independent intellectual property rights. This pressurized filter press has adopted the one-step filtration in place of the existing separation process comprising centrifuge-pulping in tank-separation by centrifugation, resulting in a simplified process flow scheme. It is said that this project has its innovation nature with one technique being granted a Chinese patent. At present the newly developed filter press has been successfully applied in commercial scale at the 50 kt/a PIA unit of the SINOPEC Yanshan Branch Company. The operating results have revealed that the machinery operates smoothly with low failure rate. The water content of the target product is stabilized at around 12% with good quality that can meet the needs of production process. The equipment of this technology requires a smaller plot area and lower energy consumption, and its maintenance is easier. This technology can be disseminated and applied in the PIA production process. Construction of First DMTO Unit Kicked off at Yanchang Oil Field On July 3, 2011 the construction of the first in the Yanchang Oilfield DMTO unit was kicked off in the Jingbian Energy Chemical Park. The EPC (engineering, procurement and construction) of this project have been granted to the SINOPEC Luoyang Petrochemical Engineering Company (LPEC) as the major contractor, and the mechanical completion of this project is scheduled for June It is learned that the feedstock distributor, the largediameter heat compensation device for piping, the novel expansion joint, the cyclones, and the vertical heat exchangers will be fabricated using the patented technology owned by LPEC. The integrated DMTO unit is a key unit among those for starting up the Jingbian Energy Chemical Park, and is an important link for the coal-to-olefins process route. The construction of the DMTO unit will symbolize the complete commencement of construction of major projects at the Jingbian Energy Chemical Park. 63