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Energy & Fuels 2004, 18, 918-923
Study on the Deferrization and Desalting for Crude Oils Guiling Liu, Xinru Xu,* and Jinsheng Gao Research Institute of Petroleum Procession, East China University of Science and Technology, Meilong Road 130, 200237, Shanghai, People’s Republic of China Received June 17, 2003. Revised Manuscript Received December 22, 2003
Three high-iron crude oils were studied for iron distributions, deferrization, and desalting in the desalting process. Observations showed that ∼48%-75% of the iron in crude oil exists as organacid salts, and ∼6%-40% exists as an iron complex. Four deferric agents were synthesized for the testing. Deferric agents TE-3 and TE-4 of the polyamine carboxylate types had a better deferrization effect than TE-1 and TE-2 of the organophosphate types. In regard to the polyamine carboxylate type, TE-4 that was synthesized with polyamine yielded a better result than TE-3 that was synthesized with monoamine. The deferric agent TE-4 can remove most of the iron from crude oil, which decalcifying agents cannot do, and also can effectively remove calcium, sodium, and magnesium, as well as some of the nickel and vanadium. The addition of deferric agents did not affect the salt content of the oils in the desalting process. The dosage of deferric agent TE-4 had an optimal value, at which inorganic and organacid iron in high-iron crude oils could effectively be removed. The mechanism of deferrization also was discussed.
1. Introduction Recently, with the excessive exploitation of many oil fields, the properties of crude oils are more and more inferior; that is, the amount of crude oils with higher acid value, viscosity, and salt content is increasing. Moreover, with the need for deep processing of crude oil and hydrogenation, metals such as iron in crude oil are causing problems in petroleum processing. The concentration of metal in each crude oil is different. For example, the calcium content in one oil is relatively high, whereas the iron content in another is relatively higher. In fact, the iron content in some crude oils is increasing. For example, in Shengli crude oil (from PRC), from 1984 to 2000, the salt content increased from 6.4 mg/L to 14.96 mg/L, the density increased from 882.5 mg/L to 915.6 mg/L, and the iron content increased from 5.85 µg/g to 53.12 µg/g. All crude oil contains impurities (such as metals species) that can contribute to corrosion, heat exchanger fouling, furnace coking, catalytic deactivation, and product degradation in refining and other processes. Iron in crude oils is harmful in the refining process. For example, iron reacts with hydrogen sulfides from the petroleum hydrogenation process and produces iron sulfide, which covers the catalyst surface and degrades the activity and selectivity of the catalyst.1 This reaction can be represented as
Fe(RCOO)2 + H2S + 6H2 f FeS + 2RCH3 + 4H2O (1) After distillation, the majority of the iron remains in residual and heavy stocks. During the catalytic cracking of heavy oil, iron deposits on the catalyst, which causes * Author to whom correspondence should be addressed. E-mail address:
[email protected].
trouble in feedstock conversion. Research demonstrated2 that the loss of conversion ratio of feedstock was 10% for serious iron deposits that form during the catalytic cracking. For these reasons, the present methods for resolving the aforementioned problems include magnetic separation, iron passivation, iron absorption, and hydroprocessing for deferrization. Magnetic separation technology, for iron and its compounds that have a stronger magnetism, was used to separate iron from petroleum through the use of a magnetic separator; however, the average deferric rate of such a method is ∼43%. Akzo Nobel3 developed an iron passivator to inhibit iron deposition on the surface of catalysts; however, ∼15%20% of the installed capacity must be guaranteed to restore the activity of the catalyst. Iron adsorption technology, which was developed by Chevron,3 uses sulfur in a fiber material to react with iron in crude oil and produce iron sulfide that deposits on the fiber; the presence of the iron sulfide then further accelerates the reaction between sulfur and iron. The disadvantage of this technology is that it a long-term operation and sulfur-containing feedstock is required; in addition, the deferric rate is >75% only when the reaction is run continuously for ∼100 h, and its industrialization is difficult. Hydroprocessing for deferrization is a catalytic process that is used to remove iron, calcium, and sodium from hydrocarbon oil that had a metals content of >1 (1) Herna´ndez-Beltra´n, F.; Moreno-Mayorga, J. C.; Quintana-Solo´rzano, R.; Sa´nchez-Valente, J.; Pedraza-Archila, F.; Pe´rez-Luna, M. Sulfur Reduction in Cracked Naphtha by a Commercial Additive: Effect of Feed and Catalyst Properties. Appl. Catal., B 2001, 34, 137148. (2) Dunn, J. P.; Strenger, H. G., Jr.; Wachs, I. E. Molecular Structure-Reactivity Relationships for the Oxidation of Sulfur Dioxide over Supported Metal Oxide Catalysts. Catal. Today 1999, 53, 543556. (3) Lu Y. Poisoning of FCC Catalyst by Iron and Countermeasures. Pet. Refin. Eng. 2002, 32, 42-46.
10.1021/ef030127k CCC: $27.50 © 2004 American Chemical Society Published on Web 05/21/2004
Deferrization and Desalting for Crude Oils
Figure 1. Schematic diagram of the PDY-1 instrument used for the electric desalting of crude oil. Legend: 1, controller; 2, transformer; 3, coaxial electrode; 4, test bottle; and 5, heater.
mg/L. Although such technology has been industrialized, a huge equipment investment and rigorous operation conditions (such as higher temperature and pressure) are required. However, the deferrization and desalting technology of crude oil uses present desalting units, by adding a deferric agent into the crude oil, to cause the deferric agent to react with organic iron compounds that are dissolved in the oil and produce substances that dissolve in water; at that point, along with the other inorganic salts, most irons can be separated from crude oil by demulsification and settlement. Such technology is simple and effective, which relieves the subsequent units of load and does not require a catalyst and other additional investment. In this paper, three high-iron crude oils were chosen to conduct the experiment of desalting and deferrization, to determine the distribution of iron in crude oils and thus synthesize and evaluate deferric agents to maximize iron removal from oils and finally lay a foundation for the future industralizaton. 2. Experimental Section 2.1. Decalcifying Agents. Oxalic acid (ST-99), sodium tripolyphosphate (LY-1), and calgon (LY-2) were used as decalcifying agents. 2.2. Synthesis of Deferric Agents. 2.2.1. Synthesis of Organophosphates. At ∼100-120 °C, and using a small amount of catalyst, organophosphates were synthesized with methanol, ethanol, phosphoric acid, succinic acid, and acrylic acid at a proper molar ratio in a 500-mL glass flask that had four necks and was fitted with a condenser, a mechanical stirrer, and a thermometer. The final product could be obtained via the hydrolysis of an acid catalyst. 2.2.2. Synthesis of Polyamine Carboxylates. Acetic acid or monochloroacetic acid and a certain amount of water were added into a 500-mL flask; polyamine then was added dropwise at 20 °C. After the temperature was increased to 80 °C, a certain proportion of epichlorohydrin was added into the flask. 2.3. Process of Electric Desalting for Crude Oil. An electric desalting instrument (PDY-1) was used in the experiment. The oil sample, after preheating and uniform stirring, was delivered into the mixer, in which a certain amount of washing water was also added, and then stirred at 9000 rpm for 1 min. The emulsion, appropriate demulsifier, and deferric agent then were placed into test bottles. The bottles, which were equipped with electrodes, were fixed in an oscillator, shaken for 1 min, and then stored in a constant-temperature bath at 85 ( 2 °C for 10 min (Figure 1); the sample bottles were placed in an electric field for 20 min and allowed to settle for another 10 min. The volume of separated water was recorded every 5 min. Finally, the metal and salt contents in the oil after desalting were analyzed.
Energy & Fuels, Vol. 18, No. 4, 2004 919 2.4. Analysis of Salt Content in Crude Oil. A microcoulometric detector (WC-2) was used to detect the salt content in the crude oil. The principle of the detector is that crude oil that was mixed with a polar solvent was heated to extract the salt and then centrifuged. A small amount of extracted liquid was delivered into the detector, so that the Cl- ion of the sample could react with the Ag ion in the detector. According to Faraday’s laws (of electrolysis), the salt content in the sample will be obtained by measuring the change in the supply of Ag ions. 2.5. Detection of Metal Elements in Crude Oil. An inductively coupled plasma-atomic emission spectroscopy (ICP-AES) method4 was used to detect the metal elements in the oil sample. The sample, after pretreatment, was injected into an ICP system. The characteristic spectral line and intensity of elements then were analyzed using the spectradetecting system and the data process system. The detection instrument used was produced by Thermo Elemental (model IRIS 1000). 2.6. Measure for Inorganic Iron in Crude Oil. One hundred grams of crude oil, after uniform preheating and stirring, was delivered into the mixer, in which 25 mL of washing water was also added, and then stirred at 9000 rpm for 10 s. The emulsion then was placed into a test bottle. The bottle was placed in a constant-temperature bath at 85 ( 2 °C for 300 min, and the separated water was removed from the container. The extraction process was repeated several times. All the separated water was collected and used to analyze the iron content in the crude oil. 2.7. Extraction of Organic Acid Iron in Crude Oil. One hundred grams of crude oil, after preheating, was vigorously mixed with a 4% NaOH solution and then placed in a constanttemperature bath at 85 ( 2 °C for 300 min. The lower water component was separated by an injector. The caustic extraction was repeated several times. The upper oil phase then was mixed with 17% HCl and the separated water was also gathered. The HCl extraction was repeated several times. The lower water component that was mentioned previously was analyzed to detect the metal-element content in water. The difference between the results of this extraction method and that for the inorganic iron in crude oil is the organacid iron content. 2.8. Measurement of Refractive Index, Viscosity, and Density of Deferric Agents, as well as Infrared Spectroscopy. An Abbe refractive instrument was used to measure the refractive index of the sample, based on the reflection and refraction laws of light rays on the two different transparent media. The viscosity and density of the sample were measured using an Ostwald viscometer and Westphal balance instrument. A Fourier transform infrared (FTIR) spectrometer (Nicolet Magna, model IR-550) was used to analyze the structure of the deferric agent.
3. Results and Discussion 3.1. Distribution of Iron in Crude Oils. Metals in crude oil may be inorganic or organometallic compounds, which consist of hydrocarbon combinations with iron, vanadium, nickel, etc. Iron exists in petroleum and its products as ferric chlorides, oxides, sulfides, oilsoluble iron naphthenates, and its complexes (iron porphyrin), in which some inorganic irons that are dissolved in oil (such as iron oxides, sulfides, and chlorides, mainly from pipelines and reserve tanks) are dispersed in oil as very fine particles, whereas organic irons mainly originate from feedstock and reaction of the corrosive components such as naphthenic acid.5 It (4) Montaser, A.; Golightly, D. W. Inductively Coupled Plasmas in Analytical Atomic Spectrometry; VCH: New York, 1987; pp 17-56.
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butions in crude oils (Table 2), four deferric agents (Table 3) were synthesized and used for desalting and deferrization. Through evaluation of the electric field intensity, the demulsifiers, and its dosages for three crude oils, processing parameters were obtained; these parameters are shown in Table 4. Crude oils (see Table 1) were used to perform desalting and deferrization. Here, the desalting and deferric rates are used to evaluate the capabilities of the demulsifier and the deferric agent, respectively:
Table 1. Properties of Three Crude Oils property
Luning (1)
Rocalya (2)
Shengli (3)
density at 20 °C (g/cm3) viscosity (mm2/s) at 50 °C at 100 °C freezing point (°C) acid value (mg of OH/g) sulfur content (%) wax content (%) colloids content (%) asphaltenes content (%) salt concentration (mg/L) metals content (µg/g) iron calcium magnesium sodium nickel vanadium
0.9108
0.9263
0.9156
90.96 14.49 21 1.02 0.21 12.34 32.06 2.52 6.97
36.71 3.34
