Study on Removal of Naphthenic Acids from White Oil by [BMIM]Br-AlCl 3

Transcription

1 Scientific Research China Petroleum Processing and Petrochemical Technology December 30, 2010 Study on Removal of Naphthenic Acids from White Oil by [BMIM]Br-AlCl 3 Li Jing; Sun Yu; Shi Li (The State Key Laboratory of Chemical Engineering, East China University of Science and Technology, Shanghai ) Abstract: The removal of acid compounds (naphthenates) from acidic oil with ionic liquids was systematically investigated. [BMIM]Br-AlCl 3 was used to investigate the effect on deacidification of oil. Experimental results showed that at a temperature of 323K with a molar ratio of AlCl 3 to [BMIM]Br-AlCl 3 of 0.2, and a mass ratio of IL to white oil of 4%, the deacidification rate could reach 75.9%. And a reaction time of 4 h was sufficient to achieve the goal. The study on reproducibility of catalytic performance of [BMIM]Br-AlCl 3 showed the possibility of using the ionic liquid in the continuous catalytic reaction. Key words: naphthenic acid; ionic liquid; white oil; deacidification 1 Introduction The heavy crude oil output rises with an enhanced exploitation and utilization of oil resources in the world, and the density, viscosity and acid value of heavy crudes are also increasing. In recent years, the world s high-acidity crude oil production has been increasing by 0.3% per year. The acid crude oil can induce serious corrosion of equipment during oil processing, resulting in its oversupply and relatively low price on the international market. The acid value of crude oil is mainly caused by naphthenic acids, which are the major acid components in crude oil, accounting for about 90% of acidic ingredients, which are the main chemical components causing serious corrosion of oil processing equipment [1]. Besides naphthenic acids, there are fatty acids, aromatic acids, inorganic acids, mercaptans, hydrogen sulfide and phenols existing in the crude oil. The corrosion caused by naphthenic acids is different from that caused by sulfur, because the latter can induce uniform corrosion while the former can cause localized corrosion or pitting, which is influenced by the acid value, temperature, flow rate, kind of medium, changes in physical state, and other factors, so it is not easy to detect the cause of corrosion. This study is based on the experiments adopting some naphthenic acids added to white oil instead of using acidic crude oil for avoiding the interference of other factors. Deacidification of crude oil is considered in two ways, one is the destruction and removal of carboxylic acids and the other is related with the overall separation and recovery of naphthenic acids. There are physical separation methods, as well as the thermal and chemical transformation means for deacidification, which can be used to remove naphthenic acids from crude oil [2]. The physical separation methods can separate the naphthenates from crude oil without changing their chemical state, such as the adsorptive separation and solvent extraction methods, and actually the cost of these methods are relatively high [3]. Because of the poor thermal stability of acidic oil, thermal deacidification is used to convert carboxylic acids to hydrocarbons and CO 2, and the high energy consumption cannot be avoided. The chemical transformation method is associated with taking advantage of chemical properties of the crude oil for naphthenic acid removal. Normally the weak nature of naphthenic acids can be utilized in the neutralization and esterification reactions for converting them into easily removable salts, and deacidification of crude oil can also be achieved by destructive hydrogenation for removal of carboxyl radicals directly, but the mixture is prone to emulsification during the reaction process leading to difficulties in separation of reaction products. In this thesis, we will discuss the technology for deacidification of acidic oil by means of the ionic liquid. Ionic liquids are low melting point salts that represent an exciting new class of reaction solvents for catalysis [4]. Being composed entirely of ions, they possess negligible vapor pressure, and the wide range of possible cations and anions they contain means that other solvent properties may be easily controlled [5]. There is currently a great interest in the use of these materials as solvents Corresponding author: Miss Li Jing, Telephone: ; river86220@163.com 46

2 China Petroleum Processing and Petrochemical Technology for a wide range of applications, including catalysis [6]. Many reactions demonstrate their advantages when being carried out in ionic liquids, either with regard to enhanced reaction rates, improved selectivity, or easier reuse of catalysts [7]. This study shows that the deacidification process using ionic liquids is feasible, and the reaction is rapid at normal temperature and pressure, along with easy separation of the ionic liquids from the reaction mixture. 2 Experimental 2.1 Materials N-methylimidazole (density = 1.06 g/ml, with purity>99%) was purchased from the Sinopharm Chemical Reagent Company, China. 1-Bromobutane (BP = 101, density = 1.27 g/ml, with purity>98%). AlCl 3 (AR) was purchased from the Sinopharm Chemical Reagent Company. White oil (density = 0.84 g/ml at 20, with a kinematic viscosity of 4.9 mm 2 /s at 50 ) was purchased from the Sinopec Shanghai Gaoqiao Petrochemical Company. White oil is colorless, odorless, and it shows good performance on chemical inertness and light stability. The structure of white oil is composed of mostly saturated hydrocarbons with few aromatic hydrocarbons, nitrogen, oxygen, sulfur and other substances. Naphthenic acids were added to the white oil to make its acid value similar to the crude oil. It should be easier to determine the reaction conditions without interference of other factors while using white oil instead of crude oil in the deacidification reaction. 2.2 Experimental procedure Preparation of [BMIM]Br-AlCl 3 N-methylimidazolium was placed in a three-neck round bottom flask attached to a reflux condenser. Over a period of 10 minutes, excessive bromobutane was added through a dropping funnel at 50 in the flask. The reaction mixture was then cautiously heated to reflux temperature until the mixture became yellowish. The mixture was allowed to cool down to room temperature and the solvent was removed through distillation under vacuum, with [BMIM]Br remaining in the flask. Then the Fourier transform infrared (FTIR) spectroscopy was applied to test the [BMIM]Br ionic liquid (as shown in Figure 1 below). The ionic liquid [BMIM]Br-AlCl 3 was prepared according to the following procedure. A dilute aqueous solution of [BMIM]Br was placed in a glass flask. N 2 gas was introduced into the flask to make sure that the synthesis process took place in an inert atmosphere. When the flask was completely filled with N 2, AlCl 3 was added batch-wise under constant stirring. The slow addition of aluminum chloride could prevent a significant rise of temperature and avoid rapid exothermic reaction. The reaction mixture was stirred for 24 h at room temperature. Then the FTIR spectroscopy was used to analyze the liquid Deacidification process All the deacidification experiments were conducted in an Erlenmeyer flask. The acidic white oil (50 g) and the ionic liquid [BMIM]Br-AlCl 3 (0.5 5 g) were added into the flask, and with the help of a magnetic stirrer, the mixture reacted upon each other at certain temperatures (20 80 ) for a definite period of time (0.5 5 h). After the reaction had terminated, the mixture was allowed to settle for 2 h prior to separation of the white oil from IL by a separating funnel. 2.3 Analytical methods The naphthenic acid content of white oil was analyzed according to the following method. A total of 50 ml of ethanol (95%) was added into an Erlenmeyer flask fitted with a reflux condenser and was heated to the boiling point for 5 min. 0.5 ml of cresol red solution was added to the 95% ethanol solution, followed by adding dropwise the 0.05 mol/l KOH solution to neutralize the acid in 95% ethanol solution, until the mixture in the conical flask turned from yellow to purple. 50 ml of the sample was added to the hot neutralized ethanol, and then the mixture was heated to the boiling temperature for 5 min with a condenser fitted to the flask. Then 0.5 ml of cresol red solution was added to the mixture under continuous stirring. The hot ethanol solution was titrated with a 0.05 mol/l potassium hydroxide solution, until the cresol red solution in the ethanol layer turned from yellow to purple. Every titration procedure should not be longer than 3 min, while the heating of reaction mixture was stopped until the end of titration was reached. 3 Results and Discussion 3.1 Characterization of ionic liquids The ionic liquids were analyzed by a Magna-IR550 infrared spectrometer equipped with a MCT/B detector, with a scanning time of 128 sec and a resolution of 1 cm -1. The 47

3 December 30, 2010 Li Jing, et al. Study on Removal of Naphthenic Acids from White Oil by [BMIM]Br-AlCl 3 structure of [BMIM]Br is shown in Scheme 1. Scheme 1 The structure of 1-butyl-3-methylimidazolium bromide The FT-IR spectra of the ionic liquid showed the characteristic absorption bands of O H at 3446 cm -1, so there was a little water existing in [BMIM]Br, as shown in Figure 1. Among the observed C H stretching vibration absorption bands between the cm -1 wavenumber range, the wavenumber greater than 3000 cm -1 was attributed to the aromatic C H stretching vibration, while the cm -1 wavenumber range was ascribed to the saturated C H stretching vibration frequency region. Imidazole ring skeleton vibrations was found between cm -1, and the aromatic ring in-plane deformation vibration was close to 1170 cm -1, while the bending vibration of aromatic C H rocking was identified between cm -1. It can be seen from the IR spectra analyses that the characteristic absorption peaks were in good agreement with the 2990 cm -1. The C=N stretching vibration was identified at 1590 cm -1, and the imidazole ring stretching vibration was seen at 1170 cm -1. The C H in-plane bond on the ring bending vibration of the rocking was identified at cm -1, while the out of plane vibration was seen at cm -1. The FT-IR spectra of acidic and basic ionic liquids [BMIM]Br-AlCl 3 were very similar. The bands of the acidic ionic liquid was narrow while that of alkaline ionic liquid was broader, and the peak wave number of the latter was 2 6 cm -1 higher, which was caused by ions taking part in the interactions between molecules, although this distinction was not obvious, as shown in Figure 2. structure of [BMIM]Br. Figure 2 FT-IR spectra of [BMIM]Br-AlCl Effect of molar ratio of AlCl 3 to [BMIM]Br-AlCl 3 The deacidification performances of different molar ratios (X) of AlCl 3 to [BMIM]Br-AlCl 3 were compared in order to select a suitable molar ratio for removal of naphthenic acids from the oil sample. In these experiments, the reaction mixture was treated at room temperature (T) for a reaction time (t) of 2 h at an IL to white oil mass ratio (Y) of 10%. The typical test results are presented in Figure 3. Figure 1 FT-IR spectra of [BMIM]Br ionic liquid The structure of the ionic liquids is shown in Scheme 2. It can be seen from Figure 3 that the acid removal rate increased with a rising AlCl 3 /[BMIM]Br molar ratio (X), and Scheme 2 The structure of [BMIM]Br-AlCl 3 The structural groups of acidic and basic ionic liquid [BMIM]Br-AlCl 3 are the same, albeit with different intensities. In the imidazole ring, the C H stretching vibrations appeared at 3150 cm -1, and a substituent on the C H stretching vibration was detected at around 2980 Figure 3 Effect of AlCl 3/[BMIM]Br molar ratio on deacidification rate 48

4 China Petroleum Processing and Petrochemical Technology when the AlCl 3 molar ratio was 0.2, the acid removal rate picked up to 71.9%. When the AlCl 3 molar ratio increased further, the acid removal rate began to decline. The IL [BMIM]Br-AlCl 3 is acidity and basicity adjustable, and it is alkaline when X < 0.5, and is acidic when X > 0.5. It can be figured out that when X was equal to 0.2, the IL got the strongest alkalinity, so that the naphthenic acids could react upon [BMIM]Br-AlCl 3 sufficiently. So it is appropriate to select an AlCl 3/[BMIM]Br molar ratio of Effect of the IL/white oil mass ratio In these experiments, the reaction mixture was treated at room temperature for a reaction time of 2 h at an AlCl 3 / [BMIM]Br molar ratio of 0.2. The typical test results are presented in Figure 4. Figure 5 Effect of reaction time removal rate began to level off. Thereby the acid removal rate was equal to 78.2%, which indicated that the reaction might reach its equilibrium. So it seemed appropriate to choose a reaction time of 4h. 3.5 Effect of temperature In these experiments, the reaction mixture was treated for 2 hrs with the AlCl 3 molar ratio set at 0.2 and the IL/white oil mass ratio set at 4%. The typical test results are presented in Figure 6. Figure 4 Effect of the IL/white oil mass ratio It can be seen from Figure 4 that the acid removal rate was a function of the IL/white oil mass ratio. All the data were obtained at a reaction temperature of 293K. When the IL/ white oil mass ratio was less than 4%, the acid removal rate increased to 68.8% with a rising mass ratio. When the IL/ white oil mass ratio was more than 4%, the acid removal rate reached 69.5%, which was a slight increase. It seemed that an IL/white oil mass ratio of 4% was satisfactory for carrying out the reaction. 3.4 Effect of reaction time In these experiments, the reaction mixture was treated at room temperature at an AlCl 3 molar ratio of 0.2 with the IL/ white oil mass ratio equating to 4%. The typical test results are presented in Figure 5. It can be seen from Figure 5 that the acid removal rate was increasing as the reaction time increased. However, when the reaction was carried out for 4h and beyond, the acid Figure 6 Effect of reaction temperature Different reaction temperatures could influence the acid removal rate. Figure 6 shows that in a temperature range of 293 K to 323 K, the acid removing ability increased with an increasing reaction temperature. But the acid removal rate decreased when the reaction temperature increased above 323 K. When the temperature was 323 K, the acid removal rate was equal to 77.4%. Since the ionic liquid [BMIM]Br-AlCl 3 was not thermally stable, it could decompose when the temperature rose further. Therefore, we can suppose that a higher temperature was conducive to the reaction of naphthenic acid with [BMIM]Br-AlCl 3, and it could also lead to decomposition of [BMIM]Br-AlCl 3, and 49

5 December 30, 2010 Li Jing, et al. Study on Removal of Naphthenic Acids from White Oil by [BMIM]Br-AlCl 3 a temperature of 323 K might be the optimum temperature to attain the balance. 3.6 Study on reproducibility of test results upon using different batches of [BMIM]Br-AlCl 3 The tests on reproducibility of test results upon using different batches of ionic liquids intended to determine the efficiency of different samples of [BMIM]Br-AlCl 3 for removing naphthenic acids from the oil sample. In these experiments, the reaction mixture was treated at a temperature of 323 K for a reaction time of 2 h at an AlCl 3 molar ratio of 0.2 and an IL/white oil mass ratio of 4%. The typical test results are presented in Figure 7. cidification efficiency of the ionic liquid. This procedure was repeated many times while using the fresh white oil in every experiment. The typical results for acid removal rate achieved by the same ionic liquid are presented in Figure 8. It was found that the deacidification rate was 74.2% and 73.4% at the first and second reaction cycle with the same ionic liquid taking part in the catalytic reaction. The more repeatedly the ionic liquid took part in the catalytic reaction, the lower the catalytic activity of [BMIM]Br-AlCl 3 would be, resulting in a decreasing deacidification rate. The deacidification rate was 29.6% at the seventh cycle upon using the same ionic liquid and dropped to 5% when the same ionic liquid was used in the eighth cycle during the catalytic reaction, indicating that the IL itself was deactivated depending upon how frequently it was used for the catalytic reaction and it actually had lost its activity after the eighth cycle of catalytic reaction which it took part in. Figure 8 shows the possibility for repeated use of the same ionic liquid in the catalytic reaction. Figure 7 Reproducibility of deacidification test results using different samples of [BMIM]Br-AlCl 3 It was found that the deacidification rate obtained upon using different samples of ionic liquids was between 73.5% and 78.4%, and the average acid removal rate was equal to 75.9%. The study on using different samples of ionic liquids for deacidification reactions showed the reproducible catalytic performance of the ionic liquid. 3.7 Study on deacidification effect during repeated use of the same ionic liquid [BMIM]Br-AlCl 3 The following reactions were designed to understand the possibility of using the same ionic liquid repeatedly in the oil deacidification treatments. In these experiments, the reaction mixture was treated at a temperature of 323 K for a reaction time of 2 h at an AlCl 3 molar ratio of 0.2 and an IL/ white oil mass ratio of 10%. After the termination of reaction, the white oil was separated from the mixture and the IL was left in the flask. Then another portion of fresh white oil was introduced into the same flask and was subjected to reactions with the ionic liquid used in the previous treatment for another cycle in order to identify the dea- Figure 8 Acid removal rate upon repeated use of the same ionic liquid [BMIM]Br-AlCl Characterization of ionic liquids Figure 9 shows the FT-IR spectroscopic analyses of [BMIM] Br-AlCl 3 before and after catalytic reaction. The upper line was the FT-IR spectrum of [BMIM]Br-AlCl 3 before the reaction and the lower line was that after the reaction. The two lines were similar, and the characteristic peaks of [BMIM]Br-AlCl 3 did not change or disappear after the reaction without any change in the intensities of the related bands. It can be seen that the ionic liquid had no significant change in its nature after the catalytic reaction. 4 Conclusions The ionic liquid [BMIM]Br-AlCl 3 can be used for deacidi- 50

6 China Petroleum Processing and Petrochemical Technology reproducible. The preliminary test results revealed that the related oil refining process was feasible. The experiments revealed that the refining process could save time, consume less electrical power, separate the reaction products easier and discharge fewer pollutants to the environment. So this process is a very effective and economically sound method for removing naphthenic acids from oil by ionic liquids. References Figure 9 FT-IR spectra of [BMIM]Br-AlCl 3 before and after reaction fication of acidic oil, especially for the removal of the naphthenic acids that can be extracted with the conventional technique. The ionic liquid has demonstrated its good performance for acid removal from the oil sample. The deacidification ability of the ionic liquid is closely related with the molar ratio of AlCl 3, the IL/white oil mass ratio, the reaction time and the treating temperature. A higher mass ratio of the ionic liquid to the white oil and a longer reaction time both could contribute to the enhanced efficiency for removing naphthenic acids from the oil sample. At a temperature of 323 K with an AlCl 3 molar ratio of 0.2 and an IL/white oil mass ratio of 4%, the deacidification rate could reach 75.9%, while a reaction time of 4 h was sufficient to achieve this goal. The experiments on testing different batches of [BMIM]Br-AlCl 3 samples showed that the catalytic performance of the ionic liquid was [1] Pedro P, Roger M, Luis Z, et al. Aquaconversion TM : A new option for residue conversion and heavy oil upgrading [J]. Vision Technology, 1998, (6): 5-13 [2] Roger M, Pedro P, Luis Z, et al. Resid conversion through visbreaking technology [J]. World Refining, 1999: 16-2l [3] Huang Mingfu, Zhao Shanlin, Li Ping, Donald Huisingh, Removal of naphthenic acid by microwave [J]. Journal of Cleaner Production, 2006, 14(8): [4] Gordon C M. New developments in catalysis using ionic liquids [J]. Applied Catalysis A, 2001, 222(1-2): [5] Kume Yohei, Qiao Kun, Tomida Daisuke, et al. Selective hydrogenation of cinnamaldehyde catalyzed by palladium nanoparticles immobilized on ionic liquids modified-silica gel [J]. Catalysis Communications, 2008, 9(3): [6] Betti C, Landini D, Maia A, et al. Reactivity of anionic nucleophiles in ionic liquids and molecular solvents[j]. Tetrahedron, 2008, 64(8): [7] Romero A, Santos A, Tojo J, et al. Toxicity and biodegradability of imidazolium ionic liquids [J]. Journal of Hazardous Materials, 2008, 151(1): Catalyst for Hydrotreating Residual Pyrolysis C 4 Hydrocarbons Developed by Research Institute of Tianjin Petrochemical Company The research institute of SINOPEC Tianjin Petrochemical Company has successfully developed a catalyst for hydrotreating the residual C 4 hydrocarbons to transform the said hydrocarbons that used to be burned as fuel into high-quality production feedstock. At the Tianjin Petrochemical Company the tower bottoms after rectification of steam cracker products comprise about metric tons of residual C 4 hydrocarbons that are generally disposed of as the fuel for the steam cracking unit so that this resource is not utilized properly. The research institute of SINOPEC Tianjin Petrochemical Company in pursuit of energy saving and reduction of pollutant emissions has made unrelenting efforts to develop the catalyst for hydrotreating of C 4 hydrocarbons. This catalyst can saturate the process stream through hydrogenation of the residual C 4 hydrocarbons and recycle this stream as the feedstock to the steam cracking unit to deliver a diolefins yield by 20% higher than that achieved by naphtha feedstock. If the incremental profit is supposed as 200 RMB per ton of feed, this measure can bring about an additional economic benefit equating to 8 million RMB a year. It is learned that this catalyst for hydrotreating the residual C 4 hydrocarbons has finished a thousand-hour service life inspection test with good performance to be suitable for commercial production. 51