Adsorptive Desulfurization of Organic Sulfur from Model Fuels by Active Carbon Supported Mn (II): Equilibrium, Kinetics, and Thermodynamics

Mn (II)/AC adsorbents were prepared by ultrasonic impregnation. The 2wt. % Mn/AC showed best adsorptive performance, and the optimal adsorption temperature was 313K. Benzene, methylbenzene, and naphthalene were used to explore the adsorptive selectivity of Mn/AC, indicating that Mn could enhance the adsorptive capacity but could not improve the adsorptive selectivity. The adsorptive mechanism was mostly like to be π -complex. Adsorptive isotherms and kinetics were investigated, and the parameters were calculated. The R 2 , RMSE, and AIC c were used to assess the optimal model. The results showed that Temkin adsorptive isotherm was more suitable to describe the isothermal data; the MPnO kinetics model was more superior to other kinetic models. The order of reaction was between 1 and 2. The outcome of adsorptive thermodynamics indicated that removal of DBT onto Mn/AC was a spontaneous and exothermic process.


Introduction
Organic sulfurs in fuel oil burned so that they release SO X into the atmosphere, causing serious environmental pollutions and health problems [1][2][3]. To reduce the emission of SO X , governments around the world had made more stringent laws and regulations [4,5]. Hence, it is imperative for refineries to study new methods to produce ultralow sulfur fuels. Sulfur-containing compounds in fuel oils exist in the form of straight-chain (thiol, thioether, etc.) and cyclic-annular (thiophene (T), benzothiophene (BT), dibenzothiophene (DBT) etc.) organic sulfur compounds [6,7]. e traditional hydrodesulfurization (HDS) process has been widely applied into industrial desulfurization fields. HDS is effective in removing straight-chain organic sulfurs, but it is hard for the removal of cyclic-annular organic sulfur compounds [8,9]. Related studies showed that if the sulfur level in fuel oil reduces to 15 ppm, the volume of catalyst bed will have to be increased 7 times as that of the current HDS catalyst bed [10]; meanwhile, HDS could cause hydrogen consumption and the loss of octane number, because of the nonselective hydrogenation of cyclanic [11,12]. Hence, various alternative technologies such as catalytic oxidation desulfurization (ODS) [13][14][15], extraction desulfurization (EDS) [16][17][18], adsorptive desulfurization (ADS) [19][20][21], and biodesulfurization (BDS) [22][23][24] were explored to produce ultralow sulfur fuels, among which, ADS is considered as a potential deep desulfurization technology with several advantages, such as mild conditions of temperature and pressure and selectivity of cyclic-annular organic sulfurs by unsaturated hydrocarbon [25].
Sorbent is a critical factor for ADS process. Various adsorbents have been used for the removal of sulfur from real oils or model oils, such as molecular sieve [26,27], metal oxide [28], active carbons (ACs) [29], etc., among which ACs are suitable to obtain ultralow sulfur oils due to large specific surface area, abundant pore structures, and high density of surface functional groups [30]. However, ACs without modification have less selectivity for the removal of cyclicannular organic sulfur compounds. erefore, modification of ACs is vital factor to improve selectivity. Chemical modification is used to change or increase surface functional groups of ACs. C. O. Ania and Bandosz [31] and coworker adopted metal-loaded (Na, Co, Ag, and Cu) method to modify ACs. e results showed that the DBT removal capacity of metal-loaded ACs was more effective than nonmodified commercial ACs; meanwhile, Co and Cu were more effective than other metals. Fallah and Azizian [5] and coworker used HNO 3 , (NH 4 ) 2 S 2 O 8 , H 2 SO 4 , HCl, and NaOH to disposal activated carbon cloth (ACC). e results showed that the adsorption capacity of ACC-HNO 3 was higher than other adsorbents due to the highest density of oxygen containing functional groups on its surface, which indicated that modification by HNO 3 could remarkably enhance the density of oxygen containing functional groups so as to improve selectivity. Adsorption selectivity of ADS will be a hot topic. In this study, Mn (II)/AC prepared by impregnating KMnO 4 on HNO 3 /AC were studied with respect to adsorption and adsorbents selectivity performance on DBT in model oils.
e adsorption mechanism of Mn (II)/AC was discussed by comparing to HNO 3 /AC in model oil with competitive components (benzene, toluene, and naphthalene). ree adsorptive isothermal models (Langmuir, Freundlich, and Temkin) were used to fit the experimental data. e kinetic data was fitted by three kinetic models (PFO, PSO, and MPnO). e R 2 , RMSE, and AIC c were applied to assess the goodness-of-fit of the models. ermodynamics were discussed by static adsorption test.

Preparation of Adsorbent.
e impregnation method was adopted in the experiments. Firstly, AC was boiled for 2 h by deionized water, then screened for 20 to 40 meshes, and stored. Secondly, 50 g AC after washing and 30 wt. % HNO 3 was mixed and agitated for 4 h at 298 K, then extensively washed to neutral, and dried at 383 K for 24 h, which were marked HNO 3 /AC. Finally, the HNO 3 /AC and solution of KMnO 4 were mixed in water bath oscillator (T � 313 K, r � 90 rpm) for 12 h and then ultrasound for 0.5 h and dried at 383 K for 24 h. e samples were calcined by 773 K in N 2 for 4 h and screened (20 to 40 meshes), which were represented by Mn/AC.

Characterization of Adsorbents.
Nitrogen adsorption isotherms were investigated on Automated Physics and Chemisorption Analyzers (Autosorb-iQ-MP-C) from Quantachrome American. All adsorbents were outgassed at 573 K for 4 h, and each adsorbent was measured with 0.040 to 0.045 g. e specific surface area (S BET ) and total pore volume (V t ) were calculated by Brunauer-Emmett-Teller (BET) method. e narrow micropores with 0.6 nm to 1.2 nm (V narrow ) and pore size distribution were obtained by density functional theory (DFT) method. X-ray diffraction (XRD) was tested on Bruker D 8 Advance equipped with a copper anode (Cu Kα � 1.5406Å) from Germany, which was operated at 30 kV and 30 mA. Adsorbents were scanned 2θ from 10 to 90°with a step rate for 0.2 s −1 . e results of XRD were compared with Power Diffraction File (PDF) database. X-ray fluorescence was used to test the content of Mn in the carbons. To achieve this purpose, X-ray fluorescence analysis was used to measure the content of Mn in the ACs. To reach this purpose, S2 RANGER from Germany Bruker AXS GmbH was used.

Model Oil Sample.
Model oil was made by adding DBT into n-octane solution with an initial sulfur concentration (c 0 ) for 9.38 mmol·L −1 and represented by DM0. To study the effects of Nap, benzene, and methylbenzene on competitive adsorption over Mn/AC, several kinds of model oil were prepared by adding 5 wt. % benzene, methylbenzene, and nap with c 0 for 9.38 mmol·L −1 , respectively [32], which were represented by DM1, DM2, and DM3. Mode oils were made with different c 0 of 6. 25, 7.81, 9.37, 12.50, 15.63, 18.75, and 21.88 mmol·L −1 . In this paper, c 0 was tested in each experiment. e analytical precision reached ± 0.01 mmol·L −1 .

Adsorption Experiment.
For each experiment, the common agent oil ratio (10/1 g·L −1 ) was adopted. All static adsorption experiments were run in a water bath shaker (SHA-C, YuHua Instrument Co. Ltd. in Henan, China, 90 rpm). All sulfur concentrations were analyzed by JF-TS-2000 Fluorescence Sulfur Analyzer (Jiangsu Jiangfen Electroanalytical Instrument Co. Ltd., China). Samples were burned in quartz tube at 1273 K with high purity oxygen (350 mL·min −1 ) and argon (120 mL·min −1 ). Before determination, the standard curve was plotted by the testing of standard samples, and the correlation coefficient (R 2 ) reached 0.9999. e mole adsorption capacity, q t (mmol S g −1 adsorbents), was used to describe the performance of adsorption desulfurization, which was calculated as In order to eliminate the influence of initial concentration and guarantee the unity of experimental conditions, the desulfurization rate was also used to describe the performance of adsorption desulfurization, being given as follows: where c 0 and c t are the sulfur concentrations of the moment t � 0 and t, respectively. v and m are the volume of model oil and the mass of adsorbents, respectively, and M is the molar mass of sulfur atom.

Effects of Mn-Loaded Amount.
Effects of different Mnloaded amounts were investigated, and the results are shown in Figure 1. According to Figure 1, It is apparent that adsorptive capacity increased and then decreased and reached a maximum at 2 wt. %. e reason might be that the number of activate sites increased with Mn-loaded amount increasing. When Mn-loaded amount was higher than 2 wt. %, the adsorption capacity deduced, which might be the cause of the aggregation of Mn so that the activate sites reduced ( Figure 2). e 2 wt. % Mn-loaded showed best adsorption capacity and q e reached 0.434 mmol·g −1 .
Textural properties of adsorbents are significant for adsorption performance. In this paper, various Mn-loaded amounts were measured by Automated Physics and Chemisorption Analyzers. e nitrogen adsorption isotherms were described in Figure 3, showing that all adsorbents were type-I shape [33], which indicated that pore size with all adsorbents was mainly micropore, and Mnloaded might almost keep original textural properties.
Pore size is critical factor for adsorption process. e corresponding DFT pores size distribution is shown in Figure 2, and S BET , V t , and V narrow are calculated and shown in Table 1. According to Figure 2, the proportion of pore size around 0.5 nm reduced with the Mn-loaded increasing; however, the proportion of pore size (around 0.6 nm) increased. e most likely reason was that high temperature (773 K) metal penetration caused the partial collapse of micropores around 0.5 nm, and the skeleton contraction led to forming new micropores [34,35]. According to Table 1, after Mn-loaded, S BET and V t were lower than HNO 3 /AC because the proportion of pore size around 0.5 nm reduced ( Figure 2). Surprisingly, S BET and V t of 5 wt. % were higher than those of 2 wt. % and 3 wt. %. is is because metal crystal agglomeration blocked channel to form new micropores (0.4 to 0.5 nm from Figure 2), when the Mn-loaded amount was 5 wt. %. Reportedly, the molecule diameter of DBT is 0.65 nm [36]; therefore, the proportion of pore size (0.6 to 1.2 nm) is critical factor for adsorption DBT. According to Table 1, the increase order of V narrow was 1 wt. % (0.121), 2 wt. % (0.113), HNO 3 /AC (0.106), 5 wt. % (0.104), and 3 wt. % (0.100). Mn-loaded amount with 1 wt. % was optimal choice, but the adsorptive capacity of 2 wt. % was higher than that of 1 wt. % because the active sites of 2 wt. % Mn/AC were more than those of 1 wt. %. Interestingly, q e of 3 wt. % was higher than 5 wt. %, but V narrow with 5 wt. % was higher than 3 wt. %. e most likely reason is that mental aggregation degree of 5 wt. % was more serious than that of 3 wt. % so that the active sites with 3 wt. % were more than 5 wt. %. e result of XRF is shown in Figure 4 (EDX patterns), which indicated that Mn was successfully supported on ACs by impregnation method. Meanwhile, the content of Mn on ACs was calculated. e result showed that the content of Mn on ACs reached 1.59 wt. %. e theoretical (2 wt. %) and practical (1.59 wt. %) load difference reached 20.5%, and comparison result showed that Mn was well supported on ACs by impregnation method.
XRD spectra of 10 wt. % Mn/AC were carried out to identify the elemental form on ACs, and the result is shown in Figure 5. e intensity peaks centered for 2θ � 23.3 (002) and 43.3 (100) were the characteristic peaks of AC [37].

Effects of Adsorption
Time. e effects of adsorption time are shown in Figure 6. As can be seen, the adsorption amount of DBT (q t ) in the initial stage increased quickly and then increased slightly after 120 min, which might be the reason that concentration difference between the inner and outer surface and the number of active sites of adsorbent gradually decreased with time elapsed. e adsorption equilibrium amount (q e ) is reached at 4 h.

Effects of Adsorption Temperature.
e effect of adsorption temperature was explored, using model oil DM0 with c 0 of 9.38 mmol·L −1 , and the results are shown in Figure 7. It is apparent that desulfurization rate increased and then decreased with temperature increasing and reached a maximum at 313 K. e reason might be that the diffusion of adsorbate increased with adsorption temperature increasing because the viscosity of solution decreased. When adsorption temperature was higher than 313 K, the adsorption capacity deduced, which might be the cause of desorption rate increasing sharply [38]. According to Figure 7, desulfurization rate reached max at 313 K.

Effects of Initial Concentration on Adsorption.
e effect of different initial concentrations was studied at 313 K ( Figure 8). It is apparent that the rate of adsorption for DBT removal varied with different c 0 . However, their trends were consistent. e adsorption amount of DBT (q t ) in the initial stage increased quickly with increasing adsorption time and reached balance, which indicated that an increase in c 0 caused an increase in q e .

Competitive Adsorption.
Influences of benzene, methylbenzene, and nap (5 wt. %) on ADS were investigated, and the results are shown in Figure 9. According to Figure 9, for removal of DBT with model oil DM0, Mn/AC had higher desulfurization rate than that of HNO 3 /AC, indicating that Mn/AC improved its performance of removal of DBT.
Competitive adsorption of benzene on Mn/AC and HNO 3 /AC was studied, respectively. It was apparent that there was an obvious decrease of removal rate compared to that of DM0 without benzene. e loss of desulfurization rate decreased by the order Mn/AC (9.39%) > HNO 3 /AC     Reportedly, HNO 3 /AC improved its ADS selectivity performance by increasing the number of the oxygen containing groups on the AC surface [39], and the ADS mainly was π-H interaction which was the one of weak hydrogen bonds [40], indicating the sequence of π electron density with competitive components played a critical factor for adsorptive selectivity. In this paper, the order of π electron density with competitive components was nap (two benzene rings) > methylbenzene (containing electron donating group-CH 3 ) > benzene (a benzene ring). e experimental data showed the same influence sequence, which indicated that π-H interaction played an important role on HNO 3 /AC removal of DBT over. Mn/AC showed higher desulfurization rate than HNO 3 /AC because Mn-loaded increased the number of active sites on surface of HNO 3 /AC. However, experimental data indicated that Mn could not improve the adsorptive selectivity, demonstrating that the adsorptive mechanism of Mn/AC might be π-complexation type. Similar result was obtained for Al-Ghouti [41].   3.6. Adsorption Isotherms. In this paper, the equilibrium isothermal adsorption was studied by using different c 0 (6. 25, 7.81, 9.38, 12.50, 15.63, 18.75, and 21.88 mmol·L −1 DBT) with a contact time of 4 h at 313, 323, and 333 K. e results are shown in Figure 10. As Figure 10 showed, q e increased sharply with the increase of the equilibrium concentration (c e ) and subsequently increased slightly, which indicated that a majority of DBT could be adsorption onto Mn/AC for lower c 0 .
In this paper, three isothermal models (Langmuir, Freundlich, and Temkin) were used to describe the relationship between the adsorbed and the equilibrium concentrations.
Basic assumption of Langmuir isotherm is that the adsorbed layer is one molecule in thickness (monolayer adsorption), and all sites possess equal affinity for each adsorbate (homogeneous sites) [42,43].
e Langmuir isotherm was given as follows: where K L is the Langmuir constant and is the theoretical maximum adsorption capacity. Freundlich isotherm is the earliest proposed relationship describing the heterogeneous surface and not restricted to the formation of monolayer adsorption process. e Freundlich isotherm was shown in the following: At the Freundlich isotherm, K f is the indicative isothermal parameters of adsorption intensity. e value of 1/n gets closer to 0, which indicated that the surface of adsorbent gets more heterogeneity [44,45].
Temkin assumes that decreases in heat of adsorption of all molecules are linear; meanwhile its derivation is based on a uniform distribution of binding energies. e Temkin isotherm was described in the following: where R and T are the gas constant (8.314 JK −1 ·mol −1 ) and the absolute temperature, repetitively. K T (L g −1 ) is equilibrium binding constant, b (J mol −1 ) is related to adsorption heat [46]. e correlation coefficients (R 2 ) [47] and the root-meansquare error (RMSE) [32] were used to estimate the fitness of isothermal models; R 2 and RMSE were given as follows: where m is the number of the experimental data and i is an index; q exp,i and q cal,i are the adsorption capacity of experiment and calculation, respectively. q exp is the mean of measured q values. e value of R 2 is closer to 1, which indicated that the model is more suitable to describe the experimental data. A RMSE of 0 indicates a perfect fit to the data. In the following, three adsorption isothermal models (Langmuir, Freundlich, and Temkin) were evaluated to fit the experimental data about the adsorption process on Mn/ AC. Figure 11 shows the nonlinear fitting results by Langmuir adsorption isothermal model. Maximum monolayer adsorption capacities with different adsorption temperatures (313, 323, and 333 K) were obtained to be 0.699, 0.660, and 0.647 mmol·g −1 , respectively ( Table 2). Figure 12 shows the nonlinear fitting results by Freundlich adsorption isothermal model. e values of 1/n with different adsorption temperatures (313, 323, and 333 K) were 0.178, 0.193, and 0.212, respectively (Table 2). ey lied between 0 and 1, which indicated favorable removal of DBT onto Mn/ AC. e results of nonlinear fitting by Temkin adsorption isothermal model are given in Figure 13. e values with b were obtained to 25.796, 26.490, and 26.121 kJ·mol −1 , which indicated that adsorption process was mainly physical adsorption.
It was determined that best fitted adsorption isotherm models considering the R 2 and RMSE were obtained for three isothermal models. e results are shown in Table 2. e values of R 2 and RMSE with three adsorption isothermal models (Langmuir, Freundlich, and Temkin) were obtained for different adsorption temperatures (313, 323, and 333 K). When adsorption temperature was 313 K, R 2 values with Langmuir, Freundlich, and Temkin isothermal models were 0.940, 0.970, and 0.975 (Table 2), respectively. Meanwhile the values of RMSE were 0.016, 0.012, and 0.011, respectively. e results indicated that Temkin isotherm was superior to Langmuir and Freundlich isotherm. When the adsorption temperatures were 323 and 333 K, respectively, the trends were consistent with results of 313 K.
is had fully  International Journal of Chemical Engineering demonstrated that Temkin isotherm was more suitable to fit the experimental data.

Adsorption Kinetics.
e study of adsorption kinetics in adsorption DBT process is significant as it offers valuable insights into the reaction and mechanism. e pseudo-firstorder (PFO) and pseudo-second-order (PSO) models were commonly used to describe the adsorption process [48,49]. e equations were given as follows: where k 1 and k 2 were the rate constant of PFO and PSO, respectively. ough PFO and PSO were commonly used to describe the adsorption process; they had restricted the reaction order to either one or two. In general, the chemical reaction order might be a noninteger. Hence, in this paper the modified pseudo-n-order (MPnO) [50] was used to describe the adsorption process. e MPnO equation was shown in the following: where n is reaction order and k n is the rate constant of MPnO.    e R 2 and RMSE were used to evaluate three kinetic models. According to equations (8)-(10), PFO and PSO have two adjustable parameters and MPnO has three adjustable parameters. In general, a model will always improve fit to some degree by adding more adjustable parameters; hence R 2 and RMSE could not effectively assess the pros and cons of different adjustable parameter models. In this paper, the Akaike information criterion (AIC c ) [51] was proposed to assess the three kinetic models. e AIC c equation was given as follows: where SSE is the sum of the squared errors, m is the number of experimental data, and w is the number of the adjustable parameters.
In order to obtain a more accurate assessment, an alternative indicator is proposed by AIC c , as follows [52]: where ΔAIC c,j is the difference between the AIC c value of model j and the smallest AIC c value for three kinetic models. e value of ΔAIC c,j is higher than 10 52 , which indicated that model j is inferior to the model with the smallest AIC c .
In the following, three kinetic models (PFO, PSO, and MPnO) were evaluated to fit the experimental data about the adsorption process on Mn/AC. Figure 14 shows the nonlinear fitting results with different initial concentrations (6.25, 12.50, and 18.75 mmol·L −1 ) by PFO adsorption kinetic model. Equilibrium adsorption capacities (q e ) were obtained to be 0.271, 0.487, and 0.615 mmol·g −1 , respectively (Table 3). Figure 15 describes the nonlinear fitting results with different initial concentrations (6.25, 12.50, and 18.75 mmol·L −1 ) by PSO adsorption kinetic model. PSO fitting q e were 0.318, 0.592, and 0.738 mmol·g −1 by model calculation, respectively. e results of nonlinear fitting by MPnO model are shown in Figure 16. MPnO fitting q e were obtained to be 0.289, 0.555, and 0.642 mmol·g −1 (Table 3), respectively. q e of experimental measure were 0.282, 0.522, and 0.633 mmol·g −1 , respectively. In summary, comparison of three models fitting q e values and experimental measured q e showed that the MPnO model fitting q e values were closer to experimental measured values, which demonstrated that the MPnO model was superior to other models. MPnO model fitting q e values and experimental measured values were between PFO and PSO model fitting q e values, which indicated that reactive order was between 1 and 2 (noninteger). e results are given in Table 3 (n � 1.704, 1.766, and 1.435). e best fitted adsorption kinetic model was considered by the calculation of R 2 , RMSE, and AIC c . e results are described in Table 3. e values of R 2 , RMSE, and AIC c with three adsorption kinetic models (PFO, PSO, and MPnO) were obtained for different c 0 (6.25, 12.50, and 18.75 mmol·L −1 ). When the initial concentration was 6.25 mmol·L −1 , R 2 values with PFO, PSO, and MPnO kinetic models were 0.976, 0.994, and 0.998, respectively (Table 3); RMSE were 0.013, 0.006, and 0.003, respectively (

Diffusion Study.
In adsorption process, adsorption behavior sometimes might be described by the intraparticle diffusion model based on the theory proposed by Weber and Morris [53] which was used to identify the diffusion mechanism. e mathematical equation is given as equation (12): where k i and C are the intraparticle diffusivity rate constant (min −0.5 ) and the intercept (mmol g −1 ).
In the following, the diffusion study was carried out in different c 0 (6.25, 12.50, and 18.75 mmol·L −1 ). e results are shown in Figure 17. e plots are not linear in the adsorption process with adsorption time (4 h), indicating that more than one process is controlling steps over the whole time range. Figure 17(a) shows that the experimental data (0 to 40 min) was linearly fitted at the initial stage, and the R 2 values were obtained to be 0.993, 0.991, and 0.988, respectively, which indicated that the boundary layer (surface or film diffusion) was control step in initial stage. e experimental data with adsorption time (50 to 120 min) was fitted by equation (13) (Figure 17(b)), and the values were 0.974, 0.937, and 0.940 that were close to 1, demonstrating that intraparticle or pore diffusion was rate-limiting. Figure 17(c) shows that the experimental data (150 to 240 min) was linearly fitted at the equilibrium stage, R 2 were 0.684, 0.925, and 0.938, respectively, though 0.684 with c 0 (6.25 mmol·L −1 ) was far from 1, 0.925, and 0.938 with c 0 (12.50 and 18.75 mmol·L −1 ) being close to 1. Hence, the results still indicated that the third section is the final equilibrium stage. In summary, the removal of DBT on Mn/AC was control for three phases [54].

ermodynamics.
e thermodynamics were investigated in this paper. Gibbs free energy (ΔG) can be calculated by the thermodynamic equilibrium constant (K 0 ). K 0 equation [55] was given as follows: where a s is the activity of adsorbed and a e is the activity of solution at equilibrium; ] s is the activity coefficient of adsorbed, ] e is the activity coefficient of solution at equilibrium. When q e is infinitely close to 0, ] approaches unity; hence equation (14) is deduced in the following: K 0 can be obtained as linear fitting of ln (q e /c e ) versus q e , and the results are shown in Figure 18. R 2 values were obtained to be 0.963, 0.992, and 0.955, indicating that the experimental data could be fitted. e lnK 0 values with different adsorption temperatures (313, 323, and 333 K) were obtained to be 2.323, 1.866, and 1.197, respectively. Gibbs free energy (ΔG) can be calculated according to the following equations: Equations (16) and (17) were rewritten as the following equations: ΔH is the enthalpy of adsorption (kJ mol −1 ), and ΔS is the enthalpy change of adsorption (J mol −1 ·K −1 ). ΔH and ΔS can be calculated by plots ln K 0 vs.1/T. e results are shown in Figure 19. e results of ΔH and ΔS are −48.763 kJ·mol −1    and −135.955 J·mol −1 ·K −1 , respectively. e negative values of ΔH and ΔS show the adsorption of DBT on Mn/AC is an exothermic process and a decrease in the degree of freedom with the adsorbed species. ΔG values with different adsorption temperatures (313, 323, and 333 K) were obtained to be −6.045, −5.011, and −3.314 kJ·mol −1 , which indicated that the adsorption process is spontaneous.

Conclusions
e following conclusions can be obtained from this paper.
(1) e optimal Mn-loaded amount and adsorption temperature were 2 wt. % and 313 K, respectively. (2) Adsorption capacity of Mn/AC was higher than HNO 3 /AC in model oil DM0, indicating that Mnloaded could enhance the adsorptive performance of HNO 3 /AC. However, competitive compounds more seriously affected the Mn/AC than HNO 3 /AC, which indicated that Mn-loaded could not improve the ability of adsorptive selectivity, and the adsorptive mechanism of Mn/AC was π-complexation type. (3) Temkin isotherm was more suitable to fit the experimental data. MPnO kinetic model best described the kinetic data; the order of reaction was between 1 and 2. Diffusion study indicated that the removal of DBT on Mn/AC was control for three phases. (4) e thermodynamics demonstrated that adsorption process over Mn/AC was spontaneous and exothermic.

Data Availability
e data used to support the findings of this study are included within the article.

Conflicts of Interest
e authors declare that they have no conflicts of interest.