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Removal of benzoic acid in heavy oils by esterification using modified Ferrierite: Roles of Bronsted and Lewis acid sites Young Hoo Lee, Jae Young Park, So Young Park, Chul Hyun Kim, Jaewook Nam, Young Jun Kim, and Jong Wook Bae Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.6b00448 • Publication Date (Web): 02 Jun 2016 Downloaded from http://pubs.acs.org on June 9, 2016

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Submitted to the Energy & Fuels

Removal of benzoic acid in heavy oils by esterification using modified Ferrierite: Roles of Bronsted and Lewis acid sites

Young Hoo Lee1, Jae Young Park1, So Young Park1, Chul Hyun Kim2, Jae Wook Nam1, Young Jun Kim1, Jong Wook Bae1,*

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School of Chemical Engineering, Sungkyunkwan University (SKKU), 2066, Seoburo, Jangangu, Suwon, Gyeonggi-do, 440-746, Republic of Korea

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Department of Research and Development, Hyundai Oilbank, Sungnam, Kyeonggi-do, 463400, Republic of Korea

(Y.H. Lee and J.Y. Park are equally contributed.) ---------------------------------------------------------------------------------------------------------------* Corresponding author (J.W. Bae): Tel.: +82-31-290-7347; Fax: +82-31-290-7272; E-mail address: [email protected]

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ABSTACT A utilization of heavy crude oils having a high total acid number (TAN) has been increased recently due to its lower price, and deacidification processes by esterification or thermal decarboxylation using heterogeneous catalysts can be a possible way to remove or neutralize acidic components in heavy oils. A conversion of benzoic acid as a model component of naphthenic acids was investigated by using metal-modified H-form Ferrierite in a batch reactor to verify the separate contributions of Bronsted and/or Lewis acid sites for an esterification and decarboxylation reaction with methanol. The surface acid properties of the metal-modified Ferrierite with K, Zr, and P species significantly altered the extent of decarboxylation and esterification activity by showing a higher removal rate of benzoic acid on the K-modified Ferrierite. The amount of Lewis acid sites on the metal-modified Ferrierite was well correlated with the conversion of benzoic acid. An increased esterification activity on the K-modified Ferrierite was mainly attributed to an enhanced consecutive decarboxylation of methyl benzoate to form toluene selectively, which was formed by esterification of benzoic acid, as well as an enhanced decarboxylation of benzoic acid to benzene on the Bronsted and Lewis acid sites, respectively.

Key words: Total acid number (TAN); Esterification; Decarboxylation; Benzoic acid; Metalmodified Ferrierite; acid sites.

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1. Introduction Due to limited reservoirs of crude oils and a concomitantly increasing consumption of petroleum, some efficient treating methods of heavy crude oils having a high total acid number (TAN) have been largely exploited from many countries having abundant heavy oil reservoirs.1 In general, petroleum acids such as naphthenic acids in crude oils have been known to increase corrosion problems in refinery processes during the treatment of acidic heavy oils. Recently, many researches have been carried out to utilize heavy crude oils due to its low cost and an economically attractive feedstock. However, a corrosiveness of the acidic crude oils for malfunctions of equipment and distillation units should be properly adjusted through deacidification processes, which operates at a typical temperature range of 200 to 400 oC.2-4 Generally, petroleum acids which are responsible for a high acidity of crude oils can be categorized as the saturated linear hydrocarbons having carboxylic terminal groups with chemical formula of R(CH2)nCOOH. In addition, unsaturated aromatic ring structures such as cyclopentane, cyclohexane carboxylic acids and benzoic acid or naphthenic acids can be generally known as petroleum acids.5,6 TAN in crude oils above 0.5mgKOH/g(oil) are classified as a high TAN crude oil, where TAN was defined as the milligrams of KOH required to neutralize 1 g of acid crude oils. A lot of commercialized processes for removing acid compounds in crude oils have been proposed such as a dilution of highly acid crude oils with a low acid one in an anticorrosive material-coated equipment and an addition of some anticorrosive agents in the acidic crude oils. In addition, non-catalytic elimination of naphthenic acids in the acidic crude oils have been largely reported to reduce the acidity of heavy crude oils by using typical solvents such as supercritical methanol or supercritical water and ammonia in an ethylene glycol solution

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and so on.7-9 Interestingly, some metal oxides as heterogeneous catalysts or adsorbents have been also investigated.5 Recently, ionic liquids or microwave treatments were also reported as an environmentally benign processes to eliminate acidic components in heavy crude oils.10-12 Furthermore, a thermal decarboxylation above 200 oC using some basic metal oxides such as MgO or CaO seems to be an alternative and effective method to remove the acid components as well. However, decarboxylation reaction of naphthenic acids using basic metal oxides can possibly form insoluble metal-organic components by well-known acid-base neutralization reaction on Lewis acid sites preferentially.5,13 In comparison with the above mentioned removal methods, an esterification reaction with alcohols to get rid of the petroleum acids has some merits such as a low operating temperature below 200 oC and an easy separation of heterogeneous catalyst from liquid products.14-18 Two possible deacidification reactions for a removal of benzoic acid in the presence of methanol can be categorized as an esterification reaction with methanol to form methyl benzoate (equation (1)) and a decarboxylation reaction to form benzene (equation (2)), which have exothermic characters.

(1) Esterification: C6H5COOH + CH3OH ↔ C6H5COOCH3 + H2O

∆Ho = -20.47 kJ/mol

(2) Decarboxylation: C6H5COOH ↔ C6H6 + CO2

∆Ho = -17.91 kJ/mol

Based on our previous work,18 the esterification activity was superior on the zeolites containing Bronsted or Lewis acid sites largely, especially for a reaction of acetic acid with methanol to form methyl acetate. However, the contributions of separate Bronsted or Lewis acid sites for an esterification and decarboxylation activity have not been clearly investigated till now. In the present study, H-form Ferrierite (H-FER) was selected for an esterification of 4


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benzoic acid as a model component of naphthenic acids to clearly verify the roles of separate Bronsted or Lewis acid sites using a metal-modified H-FER with well-known acid site modifiers such as P, Zr or K. The surface acid sites were quantitatively characterized by using NH3-TPD and pyridine FT-IR, and a correlation of catalytic activity with an amount of Lewis acid sites was suggested for an esterification reaction of benzoic acid with methanol.

2. Experimental sections 2.1. Catalyst preparation of metal-modified Ferrierite with P, Zr or K NH3-form Ferrierite zeolite was purchased from Zeolyst (CP914C), which had a surface area of 400 m2/g and SiO2/Al2O3 molar ratio of 20. The NH3-form Ferrierite was transformed to H-form Ferrierite (H-FER) by calcining the sample at 500 oC for 3 h under air environment. After thermal treatment, H-FER was modified by ion-exchange method using modifiers of P, Zr, or K precursor such as phosphoric acid (H3PO4), zirconium oxychloride octahydrate (ZrOCl2·8H2O) or potassium carbonate (K2CO3) which were purchased from Aldrich. The content of metal modifier on the H-FER was fixed at around 1.0wt% based on total weight of the H-FER. The metal precursor was previously dissolved in deionized water at 70 oC containing the H-FER slurry under vigorous stirring condition. An ion-exchanged H-FER was further washed with deionized water and subsequently dried in an oven kept at 110 oC for 4 h to eliminate the residual solvent thoroughly. A metal-modified H-FER was subsequently calcined at 500 oC for 3 h, and the as-prepared catalyst was denoted as M/FER, where M represents metal precursors of P, Zr or K which were generally known as effective modifiers to change surface acidities of bare zeolites.

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2.2. Activity measurement of separate esterification and decarboxylation An esterification reaction of benzoic acid with an excess of methanol (100 ml of total reactant) in a dodecane solvent at a fixed molar ratio of methanol to benzoic acid of 10 with 0.1 g catalyst was performed at 150 oC for 6 h under ambient pressure and inert N2 gas environment in a batch reactor having a volume of 325 ml. To get rid of an external mass transport resistance, an agitation speed was fixed at 250 rpm by using a catalyst particle size of 80 ± 20 µm. In addition, thermal decarboxylation reaction of benzoic acid itself in a dodecane solvent was also carried out at the same conditions of the esterification. The liquid products after the esterification were extracted by using a pipet after cooling down the reactor to ambient temperature, and TAN was measured through ASTM D974 method which is a standard test method for acid and base number measurements by color-indicator titration. The conversion of benzoic acid to non-acidic products was determined according to the following formula. In addition, the main products by esterification were also analyzed by using gaschromatography (GC, YL 6100GC supplied by YoungLin) connected with DB-wax capillary column using a flame ionization detector (FID).

2.3. Catalyst characterizations The crystalline structures of the fresh metal-modified H-FER were characterized by powder X-ray diffraction (XRD) analysis in the range of 2θ = 5 - 90o using Rigaku diffractometer with Cu-Kα radiation. The crystallinity of the metal-modified H-FER was calculated by using a relative integrated area ratio of the most intense diffraction peaks at 2θ = 9.3 and 25.2o on each metal-modified H-FER divided by that of the unmodified H-FER with an assumption of 6


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100% crystallinity. The chemical composition of SiO2/Al2O3 molar ratio on the metalmodified H-FER was verified by using X-ray fluorescence (XRF) spectrometry (Bruker AXS S4 Pioneer). The surface morphologies of the fresh H-FER and K/FER were also characterized by using scanning electron microscope (SEM; JEOL (JSM6700F)). An amount of surface acid sites on the metal-modified H-FER was measured by temperature programmed desorption of ammonia (NH3-TPD) using BELCAT-M instrument equipped with a thermal conductivity detector (TCD). Prior to analysis, 30 mg sample was pretreated under He flow at 250 oC for 1 h, and NH3 gas was exposed on the sample for 1 h at ambient temperature. Physisorbed NH3 molecules were subsequently swept under He flow at 100 oC for 30 min, and NH3-TPD experiment was carried out under He flow from 100 to 800 oC with a ramping rate of 10oC/min using TCD. To quantify the separate Bronsted and Lewis acid sites, Fourier transformed infrared (FT-IR) analysis of adsorbed pyridine (Py-IR) was carried out on the fresh sample using Perkin Elmer instrument. Before adsorbing pyridine molecules on the metal-modified H-FER for FT-IR analysis, a self-supported thin pellet of sample was loaded in a quartz cell equipped with CaF2 window and the sample was previously treated under N2 flow at 100 oC for 20 min. After the pretreatment to remove any contaminants, pyridine adsorption was carried out at 50 o

C for 20 min and degassed to remove physisorbed pyridine molecules on the catalyst

surfaces at an evacuation temperature of 100 oC. The amount of Bronsted or Lewis acid sites on the metal-modified H-FER were calculated by using relative area ratios of Bronsted or Lewis acid sites to total integrated area from Py-IR spectra, and the relative ratio form Py-IR is further multiplied with total amount of acid sites measured from NH3-TPD to quantify the separate amounts of Bronsted and Lewis acid sites.

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3. Results and discussion 3.1. Crystalline characteristics and acid sites on the metal-modified H-FER The powder XRD patterns of the fresh metal-modified H-FER are displayed in Figure 1. The characteristic diffraction peaks of the virgin H-FER with the intense peaks at 2θ = 9.3 and 25.2o for respective (100) and (330) crystalline planes were clearly observed without significant phase changes even after an ion-exchange of meal modifiers on the H-FER as reported from our previous results.18,19 The diffraction peaks of P, Zr or K modifiers were not observed due to its low concentration through an ion-exchange on the H-FER surfaces. These metal modifiers were selected due to an easy control of surface acidity or stability as reported in our previous works.18-22 Based on the previous work of an esterification of acetic acid with methanol,18 the crystalline structures of the metal-modified H-FER were stable even after esterification reaction without any significant structural collapses of the H-FER. However, a crystallinity and molar ratio of SiO2/Al2O3 of the metal-modified H-FER in the present study was slightly decreased after the modification with a metal modifier with a crystallinity order of H-H-FER > K/FER > P/FER > Zr /FER and a relative crystallinity of 80 - 100% based on 100% crystallinity of the H-FER. The SiO2/Al2O3 molar ratio was also slightly carried in the range of 18.6 – 20.0 due to a different extent of metal incorporation on the acidic sites of the H-FER as summarized in Table 1. However, the surface morphologies measured by SEM analysis were not significantly altered even after potassium modification on the H-FER as shown in supplementary Figure S1. The crystallinity and SiO2/Al2O3 molar ratio of the bare H-FER can change the catalytic activity by affecting an amount of coke deposition and by changing surface structures as well.18,20 However, the observed different catalytic activities on the metal-modified H-FER seem to be attributed to the effects of metal modification of the

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H-FER mainly since the variations of the crystallinity and SiO2/Al2O3 molar ratio on the metal-modified H-FER are found to be insignificant. Since the characteristic amount and type of surface acid sites on various-type zeolites have been known to change the esterification activity significantly,18,21,23 NH3-TPD and pyridine FT-IR (Py-IR) analysis were carried out on the metal-modified H-FER to verify the roles of the type and amount of separate acid sites such as Bronsted and Lewis sites. The results of NH3-TPD and pyridine FT-IR are displayed in Figure 2 and Figure 3, respectively. The acidic strengths on the metal-modified H-FER were slightly decreased after the modification of P, Zr, or K precursor by lowering the maximum desorption temperatures at around 194, 191, 185, and 173 oC on the H-FER, P/FER, Zr/FER, and K/FER, respectively. These desorption peaks at around 170 – 200 oC can be assigned to weak acid sites by supplying active sites for the esterification reaction.18,21 In addition, the characteristic structure of the HFER with one-dimensional 8 membered-ring channels, which is intersected with 10 membered-ring channels perpendicularly, has been known to reduce hydrocarbon depositions by restricting a diffusion rate of reactants in the micropores due to steric hindrance effects.24 However, strong acid sites on the H-FER have been generally known to accelerate a catalyst deactivation by enhancing the deposition of coke precursors selectively.16-21,25,26 In addition, the significant decreases of strong acid sites after the modification with metal precursor on the H-FER were observed on the P/FER and Zr/FER clearly. These observations were also supported by a decreased peak intensity above 400 oC from NH3-TPD analysis, which was assigned to strong acid sites. In addition, the amount of weak acid sites below 300 oC as shown in Figure 2 was also summarized in Table 1, and the amount of total acid sites were found to be in the order of H-FER > K/FER > P/ FER > Zr/FER with the respective values of

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1.58, 1.55, 1.27, and 1.08 mmolNH3/gcat. Although the amounts of total acid sites on the various zeolites have been well reported to be closely related with catalytic activities for esterification and decarboxylation reaction of petroleum acids,5,13, 16-21,25,26 the contribution of the separate acid sites such as Bronsted and Lewis acid sites has not been well characterized in terms of esterification activities of petroleum acids on the metal-modified H-FER till now. Therefore, we carried out further characterization of the adsorbed pyridine by FT-IR (Py-IR) to verify the types of acid sites to the esterification activities quantitatively. As shown in Figure 3, the observed Py-IR spectra, which were evacuated at 100 oC after pyridine adsorption on the fresh metal-modified H-FER, revealed three characteristic adsorption peaks of pyridine molecules assigned to Bronsted acidic site (B) at a wave number around 1550 cm-1, Lewis acidic site (L) at around 1450 cm-1, and combined acid sites of Bronsted and Lewis at around 1480 cm-1, respectively. To quantify the amount of separate acid sites (mmol/gcat) such as Bronsted and Lewis acid sites, the ratio of an integrated peak area of B sites divided by that of total (B+L) sites was multiplied with total acid sites measured by NH3-TPD. The quantitative amount of Bronsted and Lewis acid sites are summarized in Table 1. The amount of Bronsted acid sites showed a similar trend with total acid sites in the range of 0.63 – 1.09 mmol/gcat. However, the amount of Lewis acid sites showed different behaviors on the metal-modified H-FER. The amount of Lewis acid sites is found to be in the order of K/FER > H-FER > Zr/FER > P/FER with the value of 0.54, 0.49, 0.45, and 0.41 mmol/gcat, respectively. Interestingly, the K/FER showed the largest amount of Lewis acid sites with an insignificant suppression of total acid sites and vice versa on the P/FER and Zr/FER, which seems to change esterification activity significantly.

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3.2. Conversion of benzoic acid and its correlation with the amount of Lewis acid sites The conversion of benzoic acid with methanol was increased with an increase of the amount of Lewis acid sites by a possible combination of esterification and decarboxylation reaction. Interestingly, the conversion of benzoic acid was not directly correlated with total amounts of acid sites as well as Bronsted acid sites as shown in Figure 4. The conversion of benzoic acid was found to be in the order of K/FER > FER > Zr/FER ≈ P/FER with the respective values of 45.0, 36.0, 26.6, and 24.8% at a low reaction temperature of 150 oC. As shown in supplementary Figure S2, since the conversion of benzoic acid on the most active K/FER was significantly increased from 18% at a temperature of 100 oC to 45% at that of 150 oC, the temperature was selected as a comparative reaction temperature for verifying the different catalytic activity on the metal-modified H-FER. Based on the significantly different catalytic activities with less significant variations of acid sites, we suggested that a removal rate of benzoic acid by esterification reaction with methanol can occur mainly with the help of a simultaneous decarboxylation reaction by forming CO2 directly on the Bronsted or Lewis acid sites of the metal-modified H-FER. Based on the related previous works, 5,13 the catalytic activity of naphthenic acid removals in heavy petroleum oils has been reported to occur preferentially on Lewis acid sites due to its lower energy barrier of the decarboxylation than that of Bronsted acid sites. However, Bronsted acid sites have been also reported to be active sites for esterification reaction of acidic components with alcohols than Lewis acid sites.16-23 Therefore, two acidic sites seem to act as active sites simultaneously through different reaction mechanisms during esterification reaction. As shown in Figure 4, an observed linear correlation of the conversion of benzoic acid with an amount of Lewis acid sites strongly suggests that a contribution of Lewis acid sites seems to be more important for explaining the 11


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removal rate of benzoic acid. Based on the previous works,5,13,16,18 Lewis acid sites can easily activate benzoic acid by forming unstable intermediates from adsorbed benzoic acid species. In addition, methanol can be selectively adsorbed on the Bronsted acid sites as well, and the adsorbed two intermediates on the different acid sites can be further reacted to form methyl benzoate, which can be largely increased in the presence of the active Lewis acid sites. To verify the above phenomena on the present metal-modified H-FER for an esterification of benzoic acid, additional experiment such as direct decarboxylation of benzoic acid without methanol reactant in a solvent of dodecane at 150 oC was carried out using the same metalmodified H-FER catalysts. The reaction results revealed that conversion of benzoic acid was found to be around 1.8 - 13.8%, which strongly suggests a possible decarboxylation reaction of benzoic acid even at a lower temperature of 150 oC, which was strongly affected by the types of modifiers on the H-FER. As summarized in Table 1 and Figure 4, decarboxylation activities are well correlated with the concentration of Lewis acid sites by showing a higher conversion of benzoic acid with a value of 13.8% on the K/FER, which possesses a larger number of Lewis acid sites than those of the P/FER or Zr/FER. A lower conversion of benzoic acid to benzene by a direct decarboxylation on all catalysts was observed compared with total conversion of benzoic acid, and a high molar ratio of (benzene + toluene)/methyl benzoate was observed in the ratio range of 0.8 – 1.3 as shown in Table 1 and Figure 4. The total conversion of benzoic acid was linearly correlated with the amount Lewis acid sites since the contribution of decarboxylation of methyl benzoate intermediate to toluene seems to be more significant on the Lewis acid sites. The catalytic activities such as total conversion and decarboxylation in terms of the number of Lewis acid sites are displayed in Figure 4. As summarized in Table 1, the product distributions of benzene (by decarboxylation of benzoic

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acid), methyl benzoate (by esterification) and toluene (by further decarboxylation of methyl benzoate) also revealed the simultaneous esterification and decarboxylation reactions on the metal-modified H-FER. The observed different molar ratio of benzene/toluene/methyl benzoate of 13.4/42.9/43.7 (mol%) on the K/FER and that of 4.0/40.9/55.1 (mol%) on the P/FER supports that consecutive and parallel reactions of esterification and decarboxylation can proceed on the Lewis acid sites preferentially. All chemical components such as the formed products of benzene, toluene and methyl benzoate with the reactants of methanol and benzoic acid in a dodecane solvent were clearly observed on the K/FER through GC analysis of the product mixture solution after esterification, and the results of GC analysis are shown in supplementary Figure S3. Interestingly, the methyl benzoate formed by esterification seems to be easily transformed to toluene with a small amount of benzene formation through direct decarboxylation of benzoic acid on Lewis acid sites preferentially due to an observed large amount of toluene and benzene products more than that of methyl benzoate on the K/FER, which has a large amount of Lewis acid sites and vice versa on the P/FER. This observation strongly supports that a further decarboxylation of methyl benzoate intermediate to form final products such as toluene and CO2 can possibly occur on Lewis acid sites of the metal-modified H-FER as well.22,27-29 Therefore, the observed high conversion of benzoic acid on the K/FER having an abundant Lewis acid sites can be attributed to the combined reactions of esterification with methanol and direct decarboxylation of benzoic acid and methyl benzoate intermediates to final products of benzene and toluene. The proposed reaction pathways for the conversion of benzoic acid by esterification and direct decarboxylation of benzoic acid as well as methyl benzoate to selectively form benzene and toluene are summarized in Scheme 1. Therefore, the observed high conversion of

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benzoic acid with the value of 45.0% on the K/FER can be possibly attributed to the series reactions of esterification of benzoic acid to form methyl benzoate and its subsequent decarboxylation to form toluene. Since the activity for a methylation of benzene with methanol to form toluene seems to be insignificant, the final toluene product can be mainly formed by a further decarboxylation of methyl benzoate, which was previously formed by esterification of benzoic acid with methanol on Bronsted acid sites selectively.16-23. Because the decarboxylation of methyl benzoate has a highly exothermic nature, the formation rate of toluene seems to be accelerated with the help of a direct decarboxylation of methyl benzoate to toluene, which can preferentially occur on Lewis acid sites5,13,16,18 through the equation (3).

(3) Decarboxylation : C6H5COOCH3 ↔ C6H5CH3+ CO2

∆Ho = -170.11 kJ/mol

In summary, a high conversion of benzoic acid on the K/FER can be attributed to a large amount of Lewis acid sites by a direct decarboxylation reaction with a main esterification of benzoic acid with methanol on Bronsted acid sites. In addition, these acid sites can activate benzoic acid to form benzene by a direct decarboxylation and to form an adsorbed intermediate for a further reaction with methanol to form methyl benzoate on Bronsted acid sites selectively. An observed linear correlation of the conversions of benzoic acid in terms of an amount of Lewis acid sites on the metal-modified H-FER (Scheme 1) seems to be also attributed to an amount of total acid sites. However, the contribution of Lewis acid sites seems to be also important for a simultaneous decarboxylation of benzoic acid and methyl benzoate through the equation (2) and equation (3). The potassium modifier on the H-FER can be an effective promoter for controlling the strengths and amounts of Lewis acid sites, 14


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which can accelerate decarboxylation reaction of benzoic acid and methyl benzoate to benzene and toluene respectively. Further investigations are still underway to verify the reaction mechanisms on the metal-modified H-FER.

4. Conclusions The conversion of benzoic acid, which was selected as a model acidic chemical in heavy oils, by esterification with methanol was closely related with the simultaneous activity contributions of Brønsted and Lewis acid sites for esterification and decarboxylation on the metal-modified H-FER. The consecutive decarboxylation activity of benzoic acid and methyl benzoate formed by esterification of benzoic acid changed the final conversion significantly. The amounts of Lewis acid sites on the metal-modified H-FER were well correlated with the conversion of benzoic acid, and K modifier was the best candidate to generate active sites on the H-FER. The main esterification reaction rate of benzoic acid with methanol was accelerated by the consecutive decarboxylation of methyl benzoate formed by esterification to toluene and the direct decarboxylation of benzoic acid to benzene. The observed linear correlation of benzoic acid conversion with the amount of Lewis acid sites during the esterification reaction revealed that a high concentration of Lewis acid sites is one of the important variables to enhance the esterification reaction rate with the help of the consecutive decarboxylation activity on Lewis acid sites selectively. The deacidification rate of heavy crude oils having a high TAN by esterification reaction with alcohols can be enhanced by the simultaneous decarboxylation reaction on a simply metal-modified H-FER due to adjusted contributions of Bronsted and Lewis acid sites.

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Acknowledgments This work was supported by the Industrial Strategic technology development program (No. 10045068) of Korea Evaluation Institute of Industrial Technology funded By the Ministry of Trade, industry and Energy (MI, Korea). The authors would like to acknowledge the financial support from the National Research Foundation of Korea (NRF) grant funded by the Korea government (NRF-2014R1A1A2A16055557 and 2016M3D3A1A01913253).

Author Contributions Y.H. Lee and J.Y. Park are equally contributed.

Supporting Information The Supporting Information is available free of charge on the ACS Publications website. The SEM images of the fresh H-FER and K/FER, the effects of reaction temperatures for the esterification of benzoic acid using the H-FER, P/FER, Zr/FER and K/FER, and the raw GC data of all reactants and products with their retention times for an esterification reaction using the K/FER are respectively provided in supplementary Figure S1, Figure S2 and Figure S3.

References (1) Wang, Y. Z.; Zhong, D. L.; Duan, H. L.; Song, C. M.; Han, X. T.; Ma, X.R. Removal of naphthenic acids from crude oils by catalytic decomposition using Mg-Al hydrotalcite/γAl2O3 as a catalyst. Fuel 2014, 134, 499-504. (2) Slavcheva, E.; Shone, B.; Turnbull, A. Review of naphthenic acid corrosion in oil refining. Brit. Corros. J. 1999, 34:2, 125-131.

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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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(3) Tebbal, S. Predict naphthenic acid corrosion. Hydrocarbon Eng. 2000, 3(2), 64-67. (4) Yepez, O. Influence of different sulfur compounds on corrosion due to naphthenic acid. Fuel 2005, 84, 97-104. (5) Zhang, A.; Ma, Q.; Wang, K.; Liu, X.; Shuler, P.; Tang, Y. Naphthenic acid removal from crude oil through catalytic decarboxylation on magnesium oxide. Appl. Catal. A: Gen. 2006, 303, 103-109. (6) Wang, Y. Z.; Sun, X. Y.; Liu, Y. P.; Liu, C.G. Removal of naphthenic acids from a diesel fuel by esterification. Energy Fuels 2007, 21, 941-943. (7) Mandal, P. C.; Wahyudiono; Sasaki, M.; Goto, M. Reduction of total acid number (TAN) of naphthenic acid (NA) using supercritical water for reducing corrosion problems of oil refineries. Fuel 2012, 94, 620-623. (8) Mandal, P. C.; Wahyudiono; Sasaki, M.; Goto, M. Non-catalytic reduction of total acid number (TAN) of naphthenic acids (NAs) using supercritical methanol. Fuel Process. Technol. 2013, 106, 641-644. (9) Wang, Y.; Chu, Z.; Qiu, B.; Liu, C.; Zhang, Y. Removal of naphthenic acids from a vacuum fraction oil with an ammonia solution of ethylene glycol. Fuel 2006, 85, 2489-2493. (10) Shah, S. N.; Chellappan, L. K.; Gonfa, G.; Mutalib, M. I. A.; Pilus, R. B. M.; Bustam, M. A. Extraction of naphthenic acid from highly acidic oil using phenolate based ionic liquids. Chem. Eng. J. 2016, 284, 487-493. (11) Pipus, G.; Plazl, I.; Koloini, T. Esterification of benzoic acid in microwave tubular flow reactor. Chem. Eng. J. 2000, 76, 239-245. (12) Huang, M.; Zhao, S.; Li, P.; Huisingh, D. Removal of naphthenic acid by microwave. J. Cleaner Prod. 2006, 14, 736-739.

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(13) Fu, X.; Dai, Z.; Tian, S.; Long, J.; Hou, S.; Wang, X. Catalytic decarboxylation of petroleum acids from high acid crude oils over solid acid catalysts. Energy Fuels 2008, 22, 1923-1929. (14) Wang, Y.; Li, J.; Sun, X.; Duan, H.; Song, C.; Zhang, M.; Liu, Y. Removal of naphthenic acids from crude oils by fixed-bed catalytic esterification. Fuel 2014, 116, 723-728 (15) Tanaka, K.; Yoshikawa, R.; Ying, C.; Kita, H.; Okamoto, K. I. Application of zeolite membranes to esterification reactions. Catal. Today 2001, 67, 121-125. (16) Kirumakki, S. R.; Nagaraju, N.; Narayanan, S. A comparative esterification of benzyl alcohol with acetic acid over zeolites Hβ, HY and HZSM5. Appl. Catal., A: Gen. 2004, 273, 1-9. (17) Wang, Y. Z.; Liu, Y. P.; Liu, C. G. Removal of naphthenic acids of a second vacuum fraction by catalytic esterification. Pet. Sci. Technol. 2008, 26, 1424-1432. (18) Koo, H. M.; Lee, J. H.; Chang, T. S.; Suh, Y. W.; Lee, D. H.; Bae, J. W. Esterification of acetic acid with methanol to methyl acetate on Pd-modified zeolites: effect of Bronsted acid site strength on activity. React. Kinet. Mech. Catal. 2014, 112, 499-510. (19) Strohmaier, K. G.; Vaughan, D. E. W. Structure of the First Silicate Molecular Sieve with 18-Ring Pore Openings, ECR-34. J. Am. Chem. Soc. 2003, 125(51), 16035-16039. (20) Park, S. Y.; Shin, C. H.; Bae, J. W. Selective carbonylation of dimethyl ether to methyl acetate on Ferrierite. Catal. Commun. 2016, 75, 28-31. (21) Park, J. H.; Pang, C.; Chung, C. H.; Bae, J. W. Methyl acetate synthesis by esterification on the modified ferrierite: Correlation of acid sites measured by pyridine IR and NH3-TPD for steady-state activity. J. Nanosci. Nanotechnol. 2016, 16, 4626-4630. (22) Bae, J. W.; Kang, S. H.; Lee, Y. J.; Jun, K. W. Synthesis of DME from syngas on the 18


Page 18 of 26

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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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bifunctional Cu-ZnO-Al2O3/Zr-modified ferrierite: Effect of Zr content. Appl. Catal. B: Environ. 2009, 90, 426-435. (23) Chung, K. H.; Park, B. G. Esterification of oleic acid in soybean oil on zeolite catalysts with different acidity. J. Ind. Eng. Chem. 2009, 15, 388-392. (24) Li, X.; Liu, X.; Liu, S.; Xie, S.; Zhu, X.; Chen, F.; Xu, L. Activity enhancement of ZSM35 in dimethyl ether carbonylation reaction through alkaline modifications. RSC Adv. 2013, 3, 16549-16557. (25) Takagaki, A.; Toda, M.; Okamura, M.; Kondo, J. N.; Hayashi, S.; Domen, K.; Hara, M. Esterification of higher fatty acids by a novel strong solid acid. Catal. Today 2006, 116, 157161. (26) Peters, T.; Benes, N. E.; Holmen, A.; Keurentjes, J. T. F. Comparison of commercial solid acid catalysts for the esterification of acetic acid with butanol. Appl. Catal., A: Gen. 2006, 297, 182-188. (27) Mao, D.; Yang, W.; Xia, J.; Zhang, B.; Song, Q.; Chen, Q. Highly effective hybrid catalyst for the direct synthesis of dimethyl ether from syngas with magnesium oxidemodified HZSM-5 as a dehydration component. J. Catal. 2005, 230, 140-149. (28) Jung, J. W.; Lee, Y. J.; Um, S. H.; Yoo, P. J.; Lee, D. H.; Jun, K. W.; Bae, J. W. Effect of copper surface area and acidic sites to intrinsic catalytic activity for dimethyl ether synthesis from biomass-derived syngas. Appl. Catal. B: Environ. 2012, 126, 1- 8. (29) Lee, Y. J.; Jung, M. H.; Lee, J. B.; Jeong, K. E.; Roh, H. S.; Suh, Y. W.; Bae, J. W. Single-step synthesis of dimethyl ether from syngas on Al2O3-modified CuO–ZnO– Al2O3/ferrierite catalysts: Effects of Al2O3 content. Catal. Today 2014, 228, 175-182.

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Figure Captions Figure 1. XRD patterns of the fresh metal-modified H-FER Figure 2. NH3-PTD profiles of the fresh metal-modified H-FER Figure 3. Pyridine FT-IR of the fresh metal-modified H-FER Figure 4. Correlation of the catalytic activities and product molar ratios of (benzene + toluene)/methyl benzoate by esterification and decarboxylation to the amount of Lewis acid sites on the metal-modified H-FER Scheme 1. Proposed reaction pathway of the removal of benzoic acid on the metal-modified H-FER through the esterification and decarboxylation

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Table1. Esterification activity of benzoic acid and amount of acid sites on the metal-modified H-FER Ratio of Py-IR NH3-TPD (benzene+ (mmol/gcat) Notation toluene)/ Total acid sites Bronsted Lewis SiO2/Al2O3 Crystallinity methyl a (mmolNH /g ) (B) (L) molar ratio (%) 3 cat benzoated H-FER 20.0 100 36.0 7.6 9.5 / 45.5 / 45.0 1.2 1.58 1.09 0.49 P/FER 19.6 91 24.8 1.8 4.0 / 40.9 / 55.1 0.8 1.27 0.86 0.41 Zr/FER 18.6 80 26.6 2.8 5.2 / 45.4 / 49.4 1.0 1.08 0.63 0.45 K/FER 19.0 83 45.0 13.8 13.4 / 42.9 / 43.7 1.3 1.55 1.01 0.54 a The crystallinity of the metal-modified H-form Ferrierite (H-FER) was calculated using the integrated areas of the most intense diffraction peaks at 2θ = 9.3 and 25.2o divided by that of the bare H-FER. b The total acid number (abbreviated as TAN) of benzoic acid reactant (BA, C6H5COOH) was measured by esterification with methanol using 1wt%BA in dodecane (CH3(CH2)10CH3) solvent at 150 oC for 6 h under ambient pressure. c The thermal decarboxylation reaction of BA on the metal-modified H-FER was also measured using 1wt%BA in dodecane solvent at 150 oC for 6 h under ambient pressure. d The main products of methyl benzoate from esterification and benzene by decarboxylation was measured by gas chromatography using DB-wax capillary column and flame ionized detector. In addition, the parenthesis represents the molar product distribution (%) of the main products of benzene, toluene and methyl benzoate, respectively. XRF

XRD

Conversion of BA by esterification (mol%)b

Conversion of BA by decarboxylation (mol%)c

Product distribution (mol%) (benzene / toluene / methyl benzoate)d

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Figure 1. XRD patterns of the fresh metal-modified H-FER

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Figure 2. NH3-TPD profiles of the fresh metal-modified H-FER

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Figure 3. Pyridine FT-IR of the fresh metal-modified H-FER

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Figure 4. Correlation of the catalytic activities and product molar ratios of (benzene + toluene)/methyl benzoate by esterification and decarboxylation to the amount of Lewis acid sites on the metal-modified H-FER

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Scheme 1. Proposed reaction pathway of the removal of benzoic acid on the metal-modified H-FER through the esterification and decarboxylation

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Removal of Benzoic Acid in Heavy Oils by ... - ACS Publications

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