Highly Enhanced Adsorption of Dimethyl Disulfide from Model Oil on

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Highly enhanced adsorption of dimethyl disulfide from model oil on MOF-199/attapulgite composites Li Du, Jingyi Yang, and Xinru Xu Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.8b04277 • Publication Date (Web): 08 Jan 2019 Downloaded from http://pubs.acs.org on January 13, 2019

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Industrial & Engineering Chemistry Research

Highly enhanced adsorption of dimethyl disulfide from model oil on MOF-199/attapulgite composites Li Du, Jingyi Yang*, Xinru Xu College of Chemical Engineering, East China University of Science and Technology, Shanghai 200237, PR China * Corresponding author. Tel.: +86 021 64252160; fax: +86 021 64252160 E-mail address: [email protected] (Jingyi Yang)

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Industrial & Engineering Chemistry Research 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

Abstract MOF-199/attapulgite (APT) composite was synthesized by solvothermal method to remove dimethyl disulfide (DMDS) from model oil. Attapulgite was introduced to reduce the size of MOF-199. Both the small-sized MOF-199 and the mesoporous structure provided by APT facilitate pore diffusion, thus dramatically improving the performance for DMDS adsorption. The desulfurization performance of the composites with varying weight percent of MOF-199 was investigated by dynamic tests. The results showed that the optimum adsorption temperature was 30 C and the maximum breakthrough capacity was 119.3 mg S/g MOF (with 50 wt.% MOF199). The improvement (43.0 mg S/g MOF for pure MOF-199) could be attributed to shorter diffusion channels, efficient utilization of active sites, and larger specific surface area of small-sized MOF-199 particles formed by introducing APT into the growth of MOF-199. The composite sustained excellent desulfurization performance after five cycles, indicating a promising adsorbent for DMDS removal. Keywords: metal organic frameworks; attapulgite; adsorption; desulfurization; dimethyl disulfide


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1. Introduction With the fast development of urbanization, people become more and more concerned about the living environment. The quality of crude oil has declined in recent years. On the other hand, norms for pollutants discharge prescribed for motor vehicles are increasingly stringent. That brings a huge challenge for the production of clean gasoline. Methyl tert-butyl ether (MTBE), which is produced from light oil, is a good additive for the production of clean gasoline. However, due to the high content of sulfur (S) existing in light hydrocarbon, MTBE has become of higher sulfur content.1 The sulfur compounds existing in liquid hydrocarbon will not only reduce the quality of petrochemical products, but also severely deactivate the noble metal catalyst employed in subsequent processing.2 Therefore, it is necessary to remove sulfides in a pretreatment process. Hydrodesulfurization (HDS) is the most widely used industrial process to reduce the content of S in fuel.3-5 It can achieve high desulfurization efficiency, but it also results in loss of octane number. In the past few decades, various new technologies have been proposed to overcome the limitations of the conventional HDS process, such as distillation,6 adsorption,7-8 oxidation,9-10 extraction,11 membrane technology,12 and biodesulfurization.13 Adsorption desulfurization (ADS) stands out from these methods due to its mild operation conditions and high


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selectivity. A great many of porous materials have been developed and studied for the removal of sulfides, such as ion-exchanged zeolites,14,15 carbon material,16,17 clay,1,18 metal−organic frameworks (MOFs)19-23 and metal oxides.24 Among these materials, MOFs and MOF-based composite materials have great potential for applications in desulfurization, capture of carbon dioxide25,26, and so on due to their high porosity, a tremendous number of possible pore structures, modifiable pore sizes. Tremendous progress has been made to remove sulfur compounds via various kinds of MOFs. Khan et al. utilized MIL-47 and MIL-53 (Al, Cr) to remove benzothiophene (BT). They found that a metal ion of a MOF-type material played the role of acidic site and the adsorption of BT was due to acid–base interaction.27 Peralta et al. found that CPO-27-Ni, with coordinatively unsaturated sites, showed good performance for thiophene removal because of interaction of the delocalized  electrons of the aromatic ring and the metal centers of the MOFs.28 Details of the -complexation was discussed systematically by Khan et al.29 Qin et al. synthesized HKUST-1@γ-Al2O3 composite with nanosized HKUST-1 (or MOF-199) for dibenzothiophene removal. They found that the composite material exhibited better performance than bare HKUST-1 due to efficient utilization of active centers and shorter diffusion channels.30 Li et al. studied desulfurization performance of MOF-199 that contained unsaturated metal sites for the adsorption of H2S,



CH3SCH3 and C2H5SH.31 Sun et al. used ethanol and Ag(I) as a catalyst to reduce Cu(II) to Cu(I) in Cu-BTC.32 The metal modified Cu-BTC showed remarkably improved adsorption performance for dimethyl disulfide, ethyl sulfide, and 1propanethiol. Shi et al. synthesized a composite of MOF-199 and activated carbon (AC), which had better performance than pristine MOF-199 for hydrogen sulfide (H2S) and dimethyl sulfide (CH3SCH3) removal because of the increase of micropores and the number of copper metal sites resulted from AC incorporation.33 Yu et al. synthesized Cu-BTC-(n)Br, which was a hydrophobic adsorbent for thiophene. The adsorbent showed distinguished hydrophobicity and remarkable ad-sorption effectivity under aqueous circumstance.34 Dai et al. synthesized a novel composite, PTA@(Zn, Ni, Cu)-BTC to remove dibenzothiophene. The composite exhibited high DBT selectivity and superior adsorption capacity.35 The sulfur compounds existing in light oil are mainly H2S, mercaptans, thioether and disulfides. Much research has been going on around the removal of H2S, mercaptans, thioether. But there are few reports on disulfides removal. In fact, mercaptans and thioether are often transformed to disulfides in industrial process.36 Thus, there remains a need to study the removal of disulfides. The purpose of this paper is to remove dimethyl disulfide efficiently using synthesized composites under ambient conditions. MOFs has been found to be promising adsorbent for organosulfur compounds removal. Especially MOF-199(CuBTC,


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HKUST-1) shows the highest adsorption capacity.31,32 Attapulgite (APT), which is a hydrated magnesium aluminum phyllosilicate, has been widely used as adsorbent37 and catalyst support38 due to its favorable physical and chemical properties such as microfibrous morphology, high specific surface area, silanolbased chemistry of surface, and excellent thermal/mechanical stability. In this work, we synthesized a composite of MOF-199 and APT by solvothermal method. And its adsorptive performance for dimethyl disulfide (DMDS) in model oil was systematically explored under different conditions through breakthrough experiments. And the breakthrough curves were fitted to three column adsorption models. The mechanism for sulfur capture on the MOF-199/APT composite was also examined.

2. Experiment 2.1. Materials The raw activated APT was provided by Mingguang City Hendin attapulgite Co., Ltd. (Anhui Province, China). Cu(NO3)2·3H2O (AR) was purchased from Sinepharm Chemical Reagent Co., Ltd. (Shanghai, China). n-Hexane (AR), N,NDimethylformamide (DMF, AR), Ethanol (AR), and 1,3,5-benzenetricarboxylic acid (H3BTC) (AR) were purchased from Shanghai Titan Scientific Co., Ltd. (Shanghai,



China). Dimethyl disulfide (DMDS) (AR) was purchased from Infinity Scientific Co., Ltd. (Beijing, China).

2.2. Preparation of MOF-199 and MOF-199/APT Composites MOF-199 was synthesized by solvothermal method reported previously.30 First, 1.0 g of H3BTC was dissolved in 34 mL of a solvent consisting of ethanol and DMF (volume ratio 1:1) as solution I. 2.0 g of Cu(NO3)2·3H2O was dissolved in 17 mL of deionized water as solution II. Then, mix solution I and solution II. The mixture was treated under ultrasound at 40 kHz and 120 W (Shanghai Guante Ultrasound Cleaning Instrument Co., Ltd., Shanghai, China) for 10 mins at ambient temperature. It was then transferred into a 100 mL Teflon-lined stainless steel autoclave and kept at 85 °C for 24 h. Then the reactor was cooled to ambient temperature. The blue crystals were washed using ethanol three times. Then the obtained products were immersed in dichloromethane for 3 days to conduct solvent exchange. Then the products were dried under vacuum at 150 °C for 12 h. The synthesis of MOF-199/APT composites was similar to MOF-199. A certain amount of APT was mixed with 30 mL deionized water. Then the mixture was stirred for 4 h to obtain an APT gel suspension. An amount of 2.0 g of Cu(NO3)2·3H2O was dissolved in 17 mL of deionized water as solution I; solution II was made of 1.0 g of H3BTC, 17 mL of DMF and 17 mL of ethanol. Then solution


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I and solution II were added to the obtained APT gel suspension, respectively. After that, the mixture was stirred for 1 h and transferred into a 100 mL Teflon-lined stainless steel autoclave and kept at 85 °C for 24 h. Then the reactor was cooled to ambient temperature. The blue crystals were washed using ethanol three times. Then the obtained products were immersed in dichloromethane for 3 days to conduct solvent exchange. Then the products were dried under vacuum at 150 °C for 12 h. The MOF-199 content of the composites ranges from 30 wt.% to 50 wt.% according to elemental analysis (see Table S1).

2.3. Sulfur Adsorption Experiments The adsorption performance of APT, MOF-199 and MOF-199/APT composites was evaluated by dynamic tests. 1 g of the adsorbent was packed into the middle of a quartz column (length, 300 mm; internal diameter, 8 mm), and the spare space was filled with quartz sand (20−40 mesh). The adsorption experiments were conducted with the adsorption temperature controlled by circulating water at atmospheric pressure. 1 mL of DMDS was dissolved in n-hexane to obtain 500 ml model oil. The oil flow rate was controlled by a minim pump (2ZB-1L10A, Beijing Xingda Science  Technology Development Co., Ltd., Beijing, China) at 10 mL/h. The outlet concentration of DMDS in model oil was analyzed with a GC-7860 gas chromatograph (Shanghai Jinghe Analysis Instrument Co., Ltd., Shanghai, China)



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equipped with a flame photometric detector (FPD) using an HP-PONA (50 m × 0.200 mm × 0.50 μm) capillary column. In the dynamic test, the outlet sulfur concentration was detected, and the value of “breakthrough” was 1% of the inlet concentration. The breakthrough adsorption capacity, which is defined as the amount of adsorbed sulfur (in milligrams) per gram of adsorbents, was calculated directly from breakthrough curves. Experimental breakthrough curves were fitted to Adams-Bohrat model39, Yoon-Nelson model40 and Thomas model41 respectively. The Thomas model is based on two assumptions: firstly, the adsorption is limited by mass transfer at the interface, not by the chemical interactions between adsorbate and adsorbent; secondly, the experimental data should follow monolayer adsorption (Langmuir isotherm)42. Thomas model is shown by equation 1. 𝐶𝑡 𝐶0

=

1 1 + exp⁡(

𝐾𝑇h𝑞0𝑥 𝑣

(Eq.1) - 𝐾𝑇h𝐶0𝑡)

Where, C0 and Ct (g/L) are concentrations of the feed and the effluent at time t, respectively, and v is flow rate (mL/min); 𝐾𝑇h is Thomas rate constant (mL· min-1 mg-1); q0 is equilibrium adsorption capacity (mg/g); x is the amount of adsorbent in 𝐶0

the column (g). By linearizing the Thomas model and fitting ln ( 𝐶𝑡 - 1) vs time plot, the parameters of the model were obtained. The linear form of Thomas model is shown by equation 2. 𝐶0

ln ( 𝐶𝑡 - 1) =

𝐾𝑇h𝑞0𝑥 𝑣

(Eq. 2)

- 𝐾𝑇h𝐶0𝑡


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The Adams-Bohart model is based on the assumption that the adsorption rate is controlled by external mass transfer43, and the model is shown in equation 3. 𝐶𝑡 𝐶0

= exp⁡(𝐾𝐴𝐵𝐶0t -

𝐾𝐴𝐵𝑁0𝑍 𝑣

(Eq. 3)

)

Where, C0 and Ct are the concentrations of the feed and the effluent at time t, respectively; N0 is the saturated adsorption capacity per column volume (g/L); KAB is the mass transfer coefficient (Lg-1min-1); Z is the bed depth (cm);  is the linear velocity in the column (cm/min). The linear form of this model is shown in equation 4. 𝐶𝑡

ln (𝐶0) = 𝐾𝐴𝐵𝐶0𝑡 -

𝐾𝐴𝐵𝑁0𝑍

(Eq. 4)

𝑣

The Yoon-Nelson model, which has a simpler form than other models, does not require detailed data concerning the characters of adsorbate and adsorbent, as well as the parameters of the fixed bed. This model and its linearized form are presented by equations 5 and 6, respectively. 𝐶𝑡

1

𝐶0

= 1 + exp⁡[𝐾(𝜏

ln

( ) = Kt - Kτ

(Eq. 5)

- 𝑡)]

𝐶𝑡

(Eq. 6)

𝐶0 - 𝐶𝑡

Where, K is the rate constant (l/min); τ (min) is the time required for 50% adsorbate breakthrough, and t is the time-on-stream (min).

2.4. Characterization



Powder X-ray diffraction (XRD) measurements were performed on Rigaku D/max 2550 VB/PC operating with Cu Kα radiation (λ = 0.15405 nm). The data was recorded at 40KV, 100 mA with angular step of 0.02 degree and 2θ ranging from 5 ° to 75 °. The Fourier transform infrared (FT-IR) spectra were recorded on a Nicolet 6700 FT-IR spectrometer (Thermo Fisher Scientific, USA) with KBr tablets in the range of 400−4000 cm-1. The morphology of materials was observed in a S4800 field emission scanning electron microscope (SEM) with an accelerating voltage of 5 kV. The distribution of Cu was analyzed by SEM equipped with energydispersive spectroscope. Elemental analyses for Cu, Mg, Al and Fe were performed on ICS-1100 inductively coupled plasma optical emission spectrometer (ICP-OES). Textural properties of APT, MOF-199 and MOF-199/APT composites were derived from N2 adsorption-desorption isotherms carried out using a volumetric physisorption analyzer ASAP-2020. The specific surface area can be calculated by BET method. The pore volume and average pore diameter were computed by instrument built-in software based on Barrett−Joyner−Halenda (BJH) method. Chemical state of the prepared materials was determined by X-ray photoelectron spectroscopy (XPS) using an 250XI electron spectrometer with a monochromatic Al Kα radiation. Thermogravimetric analysis was conducted on a Netzsch STA449 in the temperature range of 35-800 °C with a heating rate of 10 °C min-1 under argon flow.


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3. Results and discussion 3.1. Characteristics of the adsorbents XRD analysis could provide information on the composition and crystallinity of asprepared samples. The XRD patterns of APT, MOF-199 and MOF-199/APT composite are compared in Figure 1. It can be seen that the characteristic peaks of MOF-199 (at 2θ = 6.9 °, 9.5 °, 11.6 °, 13.4 °, 17.5 °, 19.0 °) are in good agreement with those previously reported,29,30 which verified the successful synthesis of MOF-199. The peak positions of the MOF-199/APT composite are in accordance with that of the pristine MOF-199, confirming that the loading of APT did not destroy the crystallographic structure of MOF-199. However, a decrease in the relative intensities can be observed because of the loading of APT and varying degrees of hydration.

Figure 1. Powder X-ray diffraction patterns of APT, MOF-199, and 50%MOF-199/APT.



To observe the crystal morphology, images of APT, MOF-199 and MOF-199/APT samples were taken by SEM. The SEM images of the three samples are shown in Figure 2(a, b, c, d). As Figure 2(a) shows, APT has bundles of fine fibrous structures and smooth surface with a diameter between 20 and 30 nm. The crystal of MOF-199 in Fig 2(b) exhibits large octahedral structure with size of about 10 m. Figure 2(c, d) shows the morphology of MOF-199/APT. It is clear that MOF199/APT displays a similar morphology to MOF-199 with APT capping on the crystal surface, suggesting that APT successfully loaded on MOF- 199. In addition, as can be observed from Figure 2(c), the size of the octahedral morphology is about 5 m, which is smaller than that of MOF-199(~10 m). These results demonstrate that APT acted as the dispersing agent to alter the coordination equilibrium at the crystal surface during the reaction process in the synthesis. APT particles can be considered as charged particles with zones of positive and negative charges. The bonding of these alternating charges allows them to form gel suspension in fresh water. And the existence of the gel suspension can influence the growth process of MOF-199. In order to determine the distribution of the MOF-199 in the composite, the cross-section energy dispersive X-ray (EDX) mapping of Cu and other metal elements (see Figure S4) were carried out. It can be seen from Figure 2(e) that Cu distributed uniformly, demonstrating the good dispersal of MOF-199 crystals with the loading of APT.


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b

a

d

c

e

Figure 2. SEM images of (a) APT, (b) MOF-199, (c, d) 50%MOF-199/ APT (e) distribution of Cu (yellow dots).

Figure 3 gives the FT-IR spectra of APT, MOF-199, and MOF-199/APT composite. The bands located at around 3400 and 1645 cm-1, which were observed for all the materials, resulted from hydroxyl groups and surface-adsorbed water. The IR spectrum of MOF-199 shows the asymmetric stretching of the carboxylate group of H3BTC ligand appearing at 1583 cm-1; and the symmetric stretching vibrations of the carboxylate group of H3BTC ligand appears at 1373 cm-1. In addition, several bands located at 1300−600 cm-1 are attributed to the out-of-plane vibrations of BTC3-. The MOF-199/APT composite not only shows the characteristic bands of APT, but also the characteristic bands derived from MOF-199. The results are consistent with those reported in the literature30,33.



Figure 3. FTIR spectra for APT, MOF-199 and 50%MOF-199/APT.

The porosity of materials is of great importance to the adsorption of sulfur compounds. Figure 4 shows the N2 adsorption–desorption isotherms of APT, MOF-199 and MOF-199/APT composite. The isotherm of MOF-199 belongs to Type I according to the IUPAC classification, which is typical for microporous materials. The APT sample exhibits a Type II isotherm with a H3 hysteresis loop, which can be ascribed to the layered structure of APT. The MOF-199/APT composite exhibits a combined isotherm of Type I curve and Type II curve with a H4 hysteresis loop, indicating the existence of microporous and mesoporous pores, which are derived from MOF-199 and APT. The textural properties of all samples are summarized in Table 1. As seen, the BET surface area for MOF-199/APT (823.37 m2/g) is smaller than that of MOF-199 (1358.15 m2/g), this is attributed to partial inclusion of APT.


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Figure 4. Nitrogen adsorption−desorption isotherms of APT, MOF-199, 50%MOF-199/APT Table 1. Texture properties of the absorbents obtained from nitrogen adsorption isotherms. Sample

SBET/(m2g-1)

Average pore diameter/(nm)

Pore volume/(cm3g-1)

APT

130.54

12.89

0.42

MOF-199

1358.15

1.98

0.67

50%MOF-199/APT

823.37

1.92

0.49

3.2. Desulfurization Performance.

3.2.1 Influence of MOF-199 content. The adsorption desulfurization capacity of MOF-199/APT composite with different MOF-199 contents was investigated by dynamic tests. The performance of APT, pure MOF-199, 30%MOF-199/APT, 40%MOF-199/APT and 50%MOF-199/APT composites were explored under the same conditions of oil flow rate of 10 mL/h and temperature of 20 °C. Breakthrough curves and dynamic adsorption capacities for DMDS adsorption in five different



samples were recorded in Figure 5. As can be seen from Figure 5, APT performed worst for DMDS adsorption. The bed was immediately penetrated within less than 5 mins, indicating that APT has a very low adsorption capacity for DMDS. The poor performance of APT can be ascribed to small specific surface area and the lack of open metal sites on the surface. The breakthrough time for MOF-199, 30%MOF199/APT, 40%MOF-199/APT, 50%MOF-199/APT was 170 mins, 105 mins, 205 mins, 230 mins, respectively. MOF-199 exhibited a relatively high breakthrough capacity of 43.0 mg S/g MOF. As for MOF-199/APT composites, the dynamic adsorption capacity increased with the increase of MOF-199 content. This is due to more open metal sites provided by higher MOF-199 content. Other than the 30%MOF-199/APT sample, the other two MOF-199/APT composites showed better performance than bare MOF-199 for the adsorption of DMDS. This result could be a consequence of variations in the pore structure and the composition of the materials. As mentioned above, the introduction of APT seemed to alter the coordination equilibrium at the crystal surface during the growth process of MOF199, thus obtaining smaller MOF-199 particles. And the small-sized MOF-199 particles have better properties, such as larger specific surface area, shorter channels for diffusion, and more open metal sites. And the mesoporous structure provided by APT in the MOF-199/APT composite facilitates pore diffusion. It's worth mentioning that the optimum content of MOF-199 for industrial application


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may be 40% considering that the economic cost of MOF-199 is much higher than APT.

Figure 5. Effect of MOF-199 content on sulfur removal.

3.2.2 Influence of adsorption temperature. The influence of adsorption temperature on the desulfurization performance was explored using 50%MOF-199/APT as adsorbent with a model oil flow rate of 10 mL/h. Breakthrough curves for DMDS adsorption were recorded in a temperature range of 20-60 °C in Figure 6. As can be seen from the data in Figure 6, when temperature was below 30 °C, dynamic adsorption capacity increased as temperature increased. When temperature was above 30 °C, the dynamic adsorption capacity decreased gradually with rising of temperature. Thus, the optimum temperature for DMDS adsorption was 30 °C. This could be a consequence of combined action of physisorption and chemisorption. At low temperature, physisorption plays a leading role in the adsorption process. However, at relatively high temperature, chemisorption plays



a major role in the adsorption process. This is because low temperature is favorable for physisorption and high temperature is favorable for chemisorption. However, the chemisorption between DMDS and MOF-199 is not a true chemical reaction and thus results in some desorption of DMDS when the temperature exceeds 30 °C.

Figure 6. Effect of adsorption temperature on sulfur removal.

3.2.3 modelling of column adsorption. Thomas model, Adams-Bohart model, and Yoon-Nelson model were applied to fit the experimental breakthrough curves for MOF-199/APT composite. The summary of the fitted parameters is presented in Table 2. As can be seen from the correlation coefficient, the fitting results varied with adsorbent components and adsorption temperature. At 20 °C, for MOF-199 and its composites, both Thomas model and Yoon-Nelson model fitted the experimental data better than Adams-Bohart model. But Thomas model could provide additional details about the adsorption parameters. For example, Thomas


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model could predict the maximum adsorption capacity. Thomas model indicates that the adsorption appeared to be limited by external mass transfer in the column, not by the chemical forces between adsorbent and adsorbate. It seemed reasonable to assume that physisorption plays a dominant role for DMDS adsorption. And this is supported by influence of adsorption temperature. Table 2. Fitted parameters of Thomas, Adams-Bohart, and Yoon-Nelson model.

adsorbent

Adamas-Bohart

Thomas model

T/°C

model

Yoon-Nelson model

𝐾𝑇h

𝑞𝑚𝑜𝑑𝑒𝑙

𝑞𝑒𝑥𝑝

𝑅2

KAB

𝑅2

K

τ/min

𝑅2

APT

20

0.04

6.5

4.8

0.97

0.019

0.99

0.0923

18.5

0.97

MOF-199

20

0.04

79.5

107.2

0.97

0.027

0.88

0.0794

225.68

0.97

30%MOF-199/APT

20

0.07

46.6

105.7

0.95

0.052

0.89

0.1576

132.8

0.95

40% MOF-199/APT

20

0.06

85.8

145.9

0.97

0.041

0.95

0.1241

244.6

0.97

50% MOF-199/APT

20

0.08

89.3

121.7

0.95

0.052

0.88

0.1758

254.6

0.95

50% MOF-199/APT

30

0.04

108.7

148.2

0.94

0.028

0.99

0.0849

310.3

0.94

50% MOF-199/APT

40

0.08

85.8

117.1

0.99

0.054

0.96

0.1699

244.6

0.99

50% MOF-199/APT

50

0.06

84.3

114.0

0.99

0.046

0.96

0.1213

240.5

0.99

50% MOF-199/APT

60

0.1

64.9

88.7

0.96

0.069

0.97

0.2156

185.1

0.96

3.3. The adsorption mechanism To determine the mechanism for DMDS adsorption, we characterized the exhausted 50% MOF-199/APT samples and the fresh samples by FTIR, XRD, and XPS measurements. As can be seen in Figure S8, there is no distinct difference in FTIR spectra between the fresh sample and the exhausted sample. And there is almost no difference between the XRD patterns (Figure 7) of the exhausted sample



and the fresh sample. The comparison of the results suggests that no evidence of chemical reaction was detected by FT-IR after the composite adsorbed DMDS and the structure of MOF-199 preserved well after the DMDS adsorption. In addition, it can be seen from Figure 8 that the color of the sample changed from blue to peacock blue, indicating that some chemical interaction happened in DMDS adsorption process.30 Furthermore, XPS analyses were carried out to determine the chemical state of Cu and S, thus illustrating the chemisorption mechanism.

Figure 7. XRD patterns for MOF-199 before and after desulfurization.

Figure 8. Color change of the adsorbent during adsorption.


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The XPS analyses results are presented in Figure 9(a, b, c). In comparison with the fresh sample, the binding energy of Cu 2p3/2 for the exhausted sample decreased by 0.5 eV. The slight shift might result from a slight variation in chemical environment of copper due to the electrostatic interactions and weak coordination effect between DMDS and the open metal sites in MOF-199.31 Meanwhile, the peak located at 164.3 eV in the S 2p1/2 spectrum is assigned to the adsorbed DMDS.44 MOF-199 exhibit Lewis acidity because of the open metal sites. And DMDS molecule has lone electron pairs. Therefore, MOF-199 and its composites exhibit excellent adsorption performance for DMDS. However, DMDS molecules

are adsorbed relatively far from the metal centers in MOF-199 for steric reasons. As a consequence, the interaction between MOF-199 and DMDS molecules is weak. The weak interaction may derive from the weak coordination effect and the electrostatic force surrounding copper (II) 31. In this study, attapulgite was introduced to influence the growth process of MOF-199 crystal, thus obtaining small-sized MOF-199 crystals. The small-sized MOF-199 crystals have larger specific surface area and more open metal sites so that MOF-199/APT composite has better adsorption performance than MOF-199. And the mesoporous structure provided by APT in the MOF-199/APT composite facilitates pore diffusion. That also contributes to the good performance of MOF-199/APT composite.



a

b

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c

Figure 9. (a) XPS spectra of Cu 2p3/2 for fresh MOF-199/APT;(b) XPS spectra of Cu 2p3/2 for MOF-199/APT saturated with DMDS; (c) XPS spectra of S 2p for MOF-199/APT saturated with DMDS.

3.4. Regeneration of MOF-199/APT composite It is necessary to take economic cost and environmental protection into consideration. Thus, the regenerability of the adsorbent is of great significance. The adsorbent is expected to be recycled as many times as possible. The results above show that the structure of MOF-199 could preserve after adsorption for DMDS. Thermogravimetric analysis was conducted to determine the temperature for regeneration. TG and DTG curves of MOF-199/APT composite are presented in Figure S9. A significant weight loss can be observed in the temperature range of 35-800 °C. In the temperature range of 35-200 °C, the weight loss was mainly due to loss of water and DMDS molecules. When the temperature is over about 330 °C, the weight of the composite decreased sharply. This was attributed to radical structure collapse of MOF-199. According to the activation temperature previously reported,32 the regeneration was conducted in a tube by nitrogen


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blowing with N2 velocity of 100 mL/min at 180 C for 4 h. ICP measurements results for the regenerated composite stay almost the same with the fresh composite (see Table S3), indicating the stability of the composite. Figure 10 shows the effect of the regeneration recycle times on the breakthrough capacity for DMDS. It can be seen that after recycling the adsorbents for DMDS adsorption five times, the breakthrough capacity still reached 108.6 mg S/g MOF, which was 91% of the initial sample, indicating that MOF-199/APT composite exhibited excellent stability and recyclability. Therefore, the MOF-199/APT composite could be a promising adsorbent for DMDS.

Figure 10. Breakthrough capacity of MOF-199/APT after regeneration.

4 conclusions In this work, composites of Cu-based metal-organic framework (MOF) and attapulgite (APT) were synthesized using solvothermal method. Characterization



results from XRD, SEM, N2 adsorption-desorption indicated that the octahedral structure size of MOF-199 decreased from about 10 m to 5 m. It can be concluded that the shorter diffusion channels, efficient utilization of active sites, and larger specific surface area of the small-sized MOF-199/APT composite are the reason of the improvement of adsorption performance. The adsorptive desulfurization performance was investigated under different conditions. The optimum temperature for adsorption desulfurization was found to be 30 °C. And 50%MOF-199/APT exhibited the highest breakthrough capacity for DMDS. Physisorption and weak chemisorption were involved in the removal of DMDS. The weak interaction between DMDS molecule and adsorbent makes it easy to recycle the adsorbent. The MOF-199/APT composite can be recycled for at least five times. Given that APT is very cheap, the composite may have great potential for industrial application. Supporting Information Elemental analysis, XRD pattern, IR spectra, N2 adsorption−desorption isotherms, SEM images, EDS surface scanning of analyses, and TG analysis.


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References (1) Yi, D. Z.; Huang, H.; Meng, X.; Shi, L. Desulfurization of Liquid Hydrocarbon Streams via Adsorption Reactions by Silver-Modified Bentonite. Ind. Eng. Chem.

Res. 2013, 52 (18), 6112. (2) Hernańdez-Maldonado, A. J.; Yang, R. T. New Sorbents for Desulfurization of Diesel Fuels via π-Complexation. AIChE J. 2004, 50, 791. (3) Fan, Y.; Shi, G.; Bao, X. J. A Process for Producing Ultraclean Gasoline by Coupling Efficient Hydrodesulfurization and Directional Olefin Conversion. AIChE

J. 2013, 59, 571. (4) AlMarzooqi, S. H.; Katsiotis, M. S.; Alhassan, S. M. Hybrid Porous Molybdenum Disulfide Monolith for Liquid Removal of Dibenzothiophene. Ind. Eng. Chem. Res. 2017, 56 (51), 15049. (5) Mendez, F. J.; Franco-Lopez, O. E.; Bokhimi, X.; Solis-Casados, D. A.; Escobar-Alarcon, L.; Klimova, T. E. Dibenzothiophene Hydrodesulfurization with NiMo and CoMo Catalysts Supported on Niobium-Modified MCM-41. Appl. Catal. B-Environ. 2017, 219, 479. (6) Wu, W. Z.; Han, Z. Z.; Zhang, Y. D. The simulation of MTBE desulfurization process by distillation. Comput. Appl. Chem. 2011, 28, 991. (7) Yang, R. T.; Hernańdez-Maldonado, A. J.; Yang, F. H. Desulfurization of transportation fuels with zeolites under ambient conditions. Science 2003, 301, 79.



(8) Zhang, J.; Sun S.; Bian, Y. H.; Adsorptive desulfurization of metal phthalocyanine functionalized poly-ionic liquids grafted to silica gel. Fuel 2018, 220, 513. (9) Nawaf, A. T.; Jarullah, A. T.; Gheni, S. A.; Mujtaba, I. M. Development of kinetic and process model for oxidative desulfurization of light fuel using experiments and parameter estimation technique. Ind. Eng. Chem. Res. 2015, 54, 12503. (10) Yue, D.; Lei, J.; Peng, Y.; Li, J.; Du, X. Three-Dimensional Ordered Phosphotungstic Acid/TiO2 with Superior Catalytic Activity for Oxidative Desulfurization. Fuel 2018, 226, 148. (11) Hadj-Kali, M. K.; Mulyono, S.; Hizaddin, H. F.; Wazeer, I.; El-Blidi, L.; Ali, E.; Hashim, M. A.; AlITashef, I. M. Removal of Thiophene from Mixtures with n Heptane by Selective Extraction Using Deep Eutectic Solvents. Ind. Eng. Chem.

Res. 2016, 55 (30), 8415. (12) Wu, F.; Cao, Y.; Liu, H.; Zhang, X. High-Performance UiO-66-NH2 Tubular Membranes by Zirconia-Induced Synthesis for Desulfurization of Model Gasoline via Pervaporation. J. Membr. Sci. 2018, 556, 54. (13) Karimi, E.; Yazdian, F.; Rasekh, B.; Jeffryes, C.; Rashedi, H.; Sepahi, A. A.; Shahmoradi, S.; Omidi, M.; Azizi, M.; Bidhendi, M. E.; Hatamian, A. DBT Desulfurization by Decorating Bacteria Using Modified Carbon Nanotube. Fuel 2018, 216, 787.


Page 28 of 34

Page 29 of 34 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


(14) Lee, K. X.; Tsilomelekis, G.; Valla, J. A. Removal of Benzothiophene and Dibenzothiophene from Hydrocarbon Fuels Using CuCe Mesoporous Y Zeolites in the Presence of Aromatics. Appl. Catal. B-Environ. 2018, 234, 130. (15) Dang, S.; Zhao, L.; Yang, Q.; Zheng, M.; Zhang, J.; Gao, J.; Xu, C. Competitive Adsorption Mechanism of Thiophene with Benzene in FAU Zeolite: The Role of Displacement. Chem. Eng. J. 2017, 328, 172. (16) Abdi, G.; Ashokkumar, M.; Alizadeh, A. Ultrasound-Assisted OxidativeAdsorptive Desulfurization Using Highly Acidic Graphene Oxide as a CatalystAdsorbent. Fuel 2017, 210, 639. (17) Dang, S.; Zhao, L.; Yang, Q.; Zheng, M.; Zhang, J.; Gao, J.; Xu, C. Competitive Adsorption Mechanism of Thiophene with Benzene in FAU Zeolite: The Role of Displacement. Chem. Eng. J. 2017, 328, 172. (18) Habimana, F.; Shi, D.; Ji, S. Synthesis of Cu-BTC/Mt Composites Porous Materials and Their Performance in Adsorptive Desulfurization Process. Applied

Clay Science 2018, 152, 303. (19) Cychosz, K. A.; Wong-Foy, A. G.; Matzger, A. J. Liquid Phase Adsorption by Microporous Coordination Polymers: Removal of Organosulfur Compounds. J. Am.

Chem. Soc. 2008, 130 (22), 6938. (20) Bromberg, L.; Diao, Y.; Wu, H.; Speakman, S. A.; Hatton, T. A. Chromium(III) Terephthalate Metal Organic Framework (MIL-101): HF-Free Synthesis, Structure,



Polyoxometalate Composites, and Catalytic Properties. Chemistry of Materials 2012, 24 (9), 1664. (21) Huang, M.; Chang, G.; Su, Y.; Xing, H.; Zhang, Z.; Yang, Y.; Ren, Q.; Bao, Z.; Chen, B. A Metal–organic Framework with Immobilized Ag(I) for Highly Efficient Desulfurization of Liquid Fuels. Chemical Communications 2015, 51 (61), 12205. (22) Achmann, S.; Hagen, G.; Haemmerle, M.; Malkowsky, I.; Kiener, C.; Moos, R. Sulfur Removal from Low-Sulfur Gasoline and Diesel Fuel by Metal-Organic Frameworks. Chem. Eng. Technol. 2010, 33 (2), 275. (23) Tang, W.; Gu, J.; Huang, H.; Liu, D.; Zhong, C. Metal-Organic Frameworks for Highly Efficient Adsorption of Dibenzothiophene from Liquid Fuels. AICHE J. 2016, 62 (12), 4491. (24) Srivastav, A.; Srivastava, V. C. Adsorptive Desulfurization by Activated Alumina. J. Hazard. Mater. 2009, 170 (2–3), 1133. (25) Zhu, N.; Liu, X.; Li, T.; Ma, J.; Cheng, P.; Yang, G. Composite System of Ag Nanoparticles and Metal–Organic Frameworks for the Capture and Conversion of Carbon Dioxide under Mild Conditions. Inorg. Chem. 2017, 56(6), 3414. (26) Liu, X.; Ma, J.; Niu Z.; etal. An Efficient Nanoscale Heterogeneous Catalyst for the Capture and Conversion of Carbon Dioxide at Ambient Pressure. Angew.

Chem. Int. Ed. 2015, 54(3), 988.


Page 30 of 34

Page 31 of 34 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


(27) Khan, N. A.; Jun, J. W.; Jeong, J. H.; Jhung, S. H. Remarkable Adsorptive Performance of a Metal-Organic Framework, Vanadium-Benzenedicarboxylate (MIL-47), for Benzothiophene. Chem. Commun. 2011, 47 (4), 1306. (28) Peralta, D.; Chaplais, G.; Simon-Masseron, A.; Barthelet, K.; Pirngruber, G. D. Metal-Organic Framework Materials for Desulfurization by Adsorption. Energy

Fuels 2012, 26 (8), 4953. (29) Khan, N. A.; Jhung, S. H. Adsorptive Removal and Separation of Chemicals with Metal-Organic Frameworks: Contribution of Pi-Complexation. J. Hazard.

Mater. 2017, 325, 198. (30) Qin, L.; Zhou, Y.; Li, D.; Zhang, L.; Zhao, Z.; Zuhra, Z.; Mu, C. Highly Dispersed HKUST-1 on Milimeter-Sized Mesoporous Gamma-Al2O3 Beads for Highly Effective Adsorptive Desulfurization. Ind. Eng. Chem. Res. 2016, 55 (27), 7249. (31) Li, Y.; Wang, L.-J.; Fan, H.-L.; Shangguan, J.; Wang, H.; Mi, J. Removal of Sulfur Compounds by a Copper-Based Metal Organic Framework under Ambient Conditions. Energy Fuels 2015, 29 (1), 298. (32) Sun, H.; Han, X.; Liu, K.; Shen, B.; Liu, J.; Wu, D.; Shi, X. Metal-Modified CuBTC Acid for Highly Enhanced Adsorption of Organosulfur Species. Ind. Eng.

Chem. Res. 2017, 56 (34), 9541.



(33) Shi, R. H.; Zhang, Z. R.; Fan, H. L.; Zhen, T.; Ju, S. G.; Mi, J. Cu-Based MetalOrganic Framework/Activated Carbon Composites for Sulfur Compounds Removal. Appl. Surf. Sci. 2017, 394, 394. (34) Yu, L.; Liu, Q.; Dai, W.; Tian, N.; Ma, N. Efficient Thiophene Capture with a Hydrophobic Cu-BTC-(n)Br Adsorbent in the Presence of Moisture. Microporous

and Mesoporous Materials. 2018, 266, 7. (35) Dai, W.; Tian, N.; Liu C.; Yu, L.; Liu Q.; Ma, N.; Zhao, Y. (Zn, Ni, Cu)-BTC Functionalized with Phosphotungstic Acid for Adsorptive Desulfurization in the Presence of Benzene and Ketone. Energy Fuels 2017, 31 (12), 13502. (36) Li, Q.; Zhuang, L.; Chen, S.; Xu, J.; Li, H. Preparation of Carbon-Supported Zinc Ferrite and Its Performance in the Catalytic Degradation of Mercaptan. Energy

Fuels 2012, 26 (12), 7092. (37) Liu, X.; Xu, X.; Sun, J.; Alsaedi, A.; Hayat, T.; Li, J.; Wang, X. Insight into the Impact of Interaction between Attapulgite and Graphene Oxide on the Adsorption of U(VI). Chem. Eng. J. 2018, 343, 217. (38) Liu, Z.-Q.; Wei, X.-Y.; Liu, F.-J.; Wang, B.-J.; Zong, Z.-M. TemperatureControlled Hydrogenation of Anthracene over Nickel Nanoparticles Supported on Attapulgite Powder. Fuel 2018, 223, 222. (39) Bohart, G. S. & Adams, E. Q. Some Aspects of the Behavior of charcol with respect to chlorine. J. Am. Chem. Soc. 1920, 42, 523.


Page 32 of 34

Page 33 of 34 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


(40) Yoon, Y. H. & Nelson, J. H. Application of Gas Adsorption Kinetics I. A Theoretical Model for Respirator Cartridge Service Life. Am. Ind. Hyg. Assoc. J. 1984, 45, 509. (41) Thomas, C. Heterogeneous Ion Exchange in a Flowing System. J. Am. Chem. Soc. 1943, 66, 1664. (42) Foo, K. Y., Lee, L. K. & Hameed, B. H. Preparation of tamarind fruit seed activated carbon by microwave heating for the adsorptive treatment of landfill leachate: A laboratory column evaluation. Bioresour. Technol. 2013, 133, 599. (43) Wang, W., Li, M. & Zeng, Q. Adsorption of chromium (VI) by strong alkaline anion exchange fiber in a fixed-bed column: Experiments and models fitting and evaluating. Sep. Purif. Technol. 2015, 149, 16. (44) Gimenez-Lopez, M. del C.; Raeisaenen, M. T.; Chamberlain, T. W.; Weber, U.; Lebedeva, M.; Rance, G. A.; Briggs, G. A. D.; Pettifor, D.; Burlakov, V.; Buck, M.; Khlobystov, A. N. Functionalized Fullerenes in Self-Assembled Monolayers.

Langmuir 2011, 27 (17), 10977.



Abstract graphic:


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Highly Enhanced Adsorption of Dimethyl Disulfide from Model Oil on

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