Energy-Efficient Sulfone Separation Process for the Production of

Article pubs.acs.org/EF

Energy-Efficient Sulfone Separation Process for the Production of Ultralow Sulfur Diesel by Two-Step Adsorption Sam Mok Lim,†,‡ Jong-Nam Kim,† Jihye Park,† Sang Sup Han,† Jong-Ho Park,† Tae Sung Jung,† Hyung Chul Yoon,† Sung Hyun Kim,*,‡ and Chang Hyun Ko*,†,§ †

Korea Institute of Energy Research, 152, Gajeong-ro, Yuseong-gu, Daejeon 305-343, Korea Department of Chemical and Biological Engineering, Korea University, 1,5-ga, Anam-Dong, Sungbuk-gu, Seoul 136-701, Korea

‡

ABSTRACT: A three-step process for producing ultralow sulfur diesel (S concentration < 10 ppm) is experimentally investigated, consisting of (1) the separation of sulfone in diesel (S concentration > 150 ppm) by adsorption on silica and the subsequent regeneration of silica using a polar solvent, (2) the separation of sulfone in methanol by adsorption on activated carbon and the subsequent regeneration of activated carbon using a nonpolar solvent, and (3) the distillation for the recovery of a nonpolar solvent. Various polar solvents (i.e., acetone and methanol) and nonpolar solvents (i.e., n-butane, n-pentane, and nhexane) were considered. Methanol and n-butane were found to be good solvents for regenerating sulfone-adsorbed silica and sulfone-adsorbed activated carbon, respectively. The two-step adsorption process was able to substantially reduce the energy consumption during the distillation because the heat of vaporization (320 kJ/kg) of n-butane is much lower than that (1104 kJ/ kg) of methanol. This study showed the potential to produce ultralow sulfur diesel with low energy consumption in a continuous separation process.

1. INTRODUCTION Governments worldwide have reduced the upper limit of the sulfur concentration in transportation fuels.1 For example, the Korean government already reduced the limit of the sulfur concentration in diesel to 10 ppm (w/w) in 2009. To produce ultralow sulfur diesel [ULSD; S < 10 ppm (w/w)], the hydrodesulfurization (HDS) process is used to convert sulfur compounds into hydrogen sulfide using Co−Mo/Al2O3, Ni− Mo/Al2O3, and unsupported transition-metal sulfide; this process has been regarded as the only practical solution.2,3 However, increases of facility and operational costs are inevitable because of severe reaction conditions, such as high reaction temperature (∼350 °C), H2 partial pressure (∼100 bar), and huge amounts of H2 consumption. As alternative or complementary desulfurization technologies to produce ULSD, extraction using ionic liquid,4 oxidative desulfurization (ODS),5−10 and adsorption11−15 have been proposed. Among them, ODS has attracted much attention because ODS operates under comparatively milder conditions (less than 120 °C and 3 bar) and has almost no H2 consumption in comparison to HDS. The main research trend in ODS has focused on the development of oxidation catalysts. Thus, comparatively less attention has been paid to the separation of sulfone from diesel. Various polar solvents, such as 1-methyl-2-pyrrolidone, dimethylformamide, and methanol, were used to separate sulfones in diesel by extraction.16−18 In the sulfone separation by adsorption, commercial and mesoporous silica were used as adsorbents for sulfone separation.19,20 However, these studies also did not pay attention to the regeneration of the solvent or adsorbent. In this study, we focused on not only sulfone adsorption using adsorbents to produce ULSD but also the regeneration of the adsorbent to organize a continuous sulfone separation © 2012 American Chemical Society

process. We also suggested a new process scheme for sulfone separation with energy efficiency by the addition of another adsorption step, in which the adsorbent was prepared by CO2 activation.

2. EXPERIMENTAL SECTION 2.1. Preparation of Adsorbents. For the separation of sulfones in diesel, commercially available silica (Grace Davison, alumino-silica) was used as an adsorbent. For the separation of sulfones in methanol and acetone, various carbon-based adsorbents were used as adsorbents. Commercial activated carbon (Calgon) obtained from Calgon Carbon Corporation and carbon molecular sieve-4K (CMS-4K) manufactured by Shirasaki were used as received. In addition, homemade activated carbon (CMS-4K-5h) was prepared by activation of CMS-4K at 1173 K for 5 h with a CO2 flow rate of 200 standard cubic centimeters per minute (sccm) in a custom-made vertical reactor. Experimental details and physical characterization of CMS-4K-5h were described elsewhere.13 2.2. Characterization of Adsorbents. The Brunauer−Emmett− Teller (BET) surface areas of commercial silica and activated carbon were calculated from the N2 adsorption isotherms at 77 K using a Micromeritics ASAP2010 surface area and porosimetry analyzer. The total pore volume was calculated from the N2-adsorbed amount at P/ P0 = 0.98. The contents of carbon, hydrogen, and nitrogen before and after CO2 activation were measured with a TruSpec elemental analyzer (LECO Co., St. Joseph, MI). 2.3. Preparation of Feed Solutions. Oxidized commercial diesel was provided by the Korea Research Institute of Chemical Technology. Commercial diesel with a high sulfur concentration [more than 150 ppm (w/w)] was used to oxidize sulfur compounds into sulfones using tert-butyl hydroperoxide (TBHP) as the oxidant (TBHP/sulfur in diesel = 15) at 393 K. The total conversion to sulfones in oxidized commercial diesel measured by gas chromatogReceived: December 15, 2011 Revised: February 27, 2012 Published: March 28, 2012 2168

dx.doi.org/10.1021/ef201964v | Energy Fuels 2012, 26, 2168−2174

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raphy with a pulsed-flame photometer detector (GC−PFPD) was 98.5%. Sulfones dissolved in methanol (sulfone/methanol) and sulfones dissolved in acetone were prepared by regeneration of sulfone-saturated silica after sulfone adsorption using methanol or acetone. 2.4. Adsorption Experiments: Equilibrium and Breakthrough. In the case of measuring equilibrium sulfur adsorption capacity, carbon-based adsorbents were dried at 573 K with N2 flow for 6 h and silica adsorbent was dried with dry-air flow at 473 K for 3 h, just before sulfur adsorption. A total of 10 g of feed solution was mixed with 1.0 g of adsorbents in a glass vial by stirring for 12 h. Then, the sample was filtered, and the sulfur concentration of the sample was analyzed to determine the adsorption capacity of the adsorbents. In the case of the breakthrough test, a constant flow liquid metering pump was used to provide feed solution to the experimental setup for

Table 1. Used Amount of the Adsorbent and Corresponding Regeneration Solvent adsorbent silica silica CMS-4K5h CMS-4K5h a

used amount (g)

regeneration solvent

used amount (g)

weight ratioa (g/g)

10.0 10.0 5.0

methanol acetone n-hexane

128 110 120

12.8 11.0 24

5.0

n-butane

120

24

Weight ratio: regeneration solvent (g)/adsorbent (g).

continuous operation, not only the separation of sulfone from diesel by the adsorbent but also the regeneration of the adsorbent by solvent washing and subsequent sulfone separation from the corresponding solvent should be considered. Scheme 1 is a sulfone separation process by a Scheme 1. Sulfone Separation Process by a Simple Combination of Adsorption and Distillation

simple combination of adsorption and distillation. In this scheme, the first step is the sulfone separation from diesel by adsorption with silica and the subsequent regeneration of silica by regeneration solvents. The second step is the recovery of the solvent, used in the regeneration of the silica adsorbent, by distillation. In the first step, sulfones were successfully removed from diesel by adsorption, and adsorbent washing by methanol and acetone enabled repeated use of the corresponding adsorbent for the adsorption of sulfones in diesel. Figure 2a shows the sulfone breakthrough curves for oxidized commercial diesel feed [156 ppm (w/w) sulfur] with the silica adsorbent with methanol regeneration. In the first adsorption with pristine silica, the breakthrough of sulfone occurred when about 14 g of sulfone-containing diesel passed through 1 g of silica adsorbent. We defined the breakthrough weight ratio as 15 g/g in this case. After breakthrough occurred, the silica adsorbent saturated with sulfones was regenerated by methanol. Then, the breakthrough test was repeated with the same oxidized commercial diesel. As the sulfone adsorption and methanol regeneration were repeated, the sulfone breakthrough weight ratio decreased to 8−10 g/g. Although methanol did not recover the initial sulfone adsorption capacity of the silica adsorbent completely, the sulfone breakthrough weight ratio of 8−10 g/g seems to be a reasonable adsorption capacity for the operation of the sulfone separation process. Acetone, another polar solvent, also showed its potential as a solvent for silica regeneration. Figure 2b displays the sulfone breakthrough curves for oxidized commercial diesel feed with the silica adsorbent with acetone regeneration. As the sulfone adsorption and regeneration by acetone was repeated, the breakthrough weight ratio decreased

Figure 1. Schematic diagram of an apparatus for the sulfone breakthrough test. the breakthrough test, as shown in Figure 1. Typically, 10 g of silica was packed in a stainless-steel column with an inner diameter of 11 mm and a length of 160 mm. The total volume of the adsorption bed was 15.0 cm3. An appropriate particle size of adsorbent in the range between 150 and 300 μm was obtained by sieving adsorbents. A tubular furnace was equipped for heat treatment and temperature maintenance. The moisture in N2 was removed prior to use with a 3A zeolite trap. The pretreatment temperatures of the silica and activated carbons were 473 and 573 K, respectively. For the breakthrough adsorption test with oxidized commercial diesel, a sulfur concentration of 10 ppm (w/w) was taken as the criterion for sulfone breakthrough. When the sulfone breakthrough occurred, the total amount of eluted diesel thus far per unit weight of adsorbent was defined as the breakthrough weight ratio [accumulated effluent weight per adsorbent weight (g/g)]. In the case of adsorbent regeneration, the sulfone-saturated adsorbent was washed with various regeneration solvents. All of the procedures of regeneration were the same as those of the breakthrough adsorption, except for the solvent flow direction. In the regeneration, the flow direction was downward. The used amounts of adsorbents and regeneration solvents in relation to the adsorbent are summarized in Table 1. The sulfur concentrations of the feed and eluted solutions after passing through the adsorbent were measured with a total sulfur analyzer (TS-100V, Mitsubishi).

3. RESULTS AND DISCUSSION 3.1. Simple Sulfone Separation Process: Adsorption + Distillation. To organize a sulfone separation process with 2169


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Table 2. Physical Properties of Various Solvents: Boiling Point and Vaporization Heat solvent methanol acetone phenol propane (C3) n-butane (C4) n-pentane (C5) n-hexane (C6) n-heptane (C7) toluene (C7)

heat of vaporization (kJ/kg) Polar Solvents 1104 518 488 Hydrocarbons 428 320 357 365 318 351

boiling point (°C) 66.0 50.5 182.0 −42.1 −0.5 36.1 68.7 98.4 110.6

energy should be supplied because the vaporization heat of methanol and that of acetone were 1104 and 518 kJ/kg, respectively. The vaporization heats of methanol and acetone were 2−3 times higher than those of the hydrocarbons. This means that methanol and acetone seem to be inappropriate solvents from the viewpoint of energy consumption because the distillation process in Scheme 2 is an essential step. Scheme 2. Sulfone Separation Process Combined with TwoStep Adsorption and Distillation (First Adsorption, Sulfone Separation from Oxidized Diesel by Silica; Second Adsorption, Sulfone Separation from Polar Solvent by Activated Carbon)

Figure 2. Sulfone breakthrough curves of oxidized commercial diesel [sulfur concentration of 152 ppm (w/w)]. Silica was used as an adsorbent, and the silica adsorbent was regenerated by (a) methanol and (b) acetone.

to 6−8 g/g. Acetone also did not regenerate the silica adsorbent completely. However, acetone regenerated the silica adsorbent to the same degree as methanol. These results indicate that polar solvents, such as methanol and acetone, can be used as regeneration agents to detach sulfones from the silica adsorbent, despite a certain amount of adsorption capacity loss. Although methanol and acetone showed the ability to regenerate the adsorbent, which showed selectivity toward sulfones in diesel, energy consumptions in the operation of the separation process must be considered more precisely. During the regeneration of the silica adsorbent by the flowing polar solvents, sulfones dissolved in methanol (sulfone/methanol) and/or sulfones dissolved in acetone (sulfone/acetone) were produced. According to the process shown in Scheme 1, sulfone/methanol or sulfone/acetone, as products of the regeneration of sulfone-saturated silica adsorbent, must be separated by distillation to recover the regeneration solvent. In this recovery of solvent by distillation, a huge amount of energy must be consumed to evaporate the solvent, because solvents have lower boiling points than sulfones. The energy consumption in the distillation step can be roughly calculated by the heat of vaporization. Table 2 shows the heats of vaporization and boiling points of polar solvents and hydrocarbons with different carbon numbers. When methanol and acetone were used as regeneration solvents, a huge amount of

To reduce the consumed energy in the distillation for the recovery of the regeneration solvent, hydrocarbons seem to be proper solvents. However, hydrocarbons, such as n-butane and n-pentane, did not regenerate the silica adsorbent effectively. Figure 3 shows the sulfone breakthrough curves for the oxidized commercial diesel feed with the silica adsorbent with n-butane and n-pentane regeneration. In the first adsorption with pristine silica, the breakthrough weight ratio was around 12. However, the sulfone adsorption capacity of silica decreased drastically to 2 or 4 when the adsorption and regeneration by nbutane and n-pentane were repeated. These results mean that hydrocarbons were not suitable for the regeneration of the silica adsorbent. On the basis of the process scheme of sulfone separation by a simple combination of adsorption and distillation, which appears in Scheme 1, neither polar solvents (methanol and acetone) nor hydrocarbons are suitable for the regeneration of the solvent because polar solvents consume a huge amount of energy in the distillation step and hydrocarbons were not able to regenerate the silica adsorbent. 3.2. Sulfone Separation Process with Two-Step Adsorption for Energy Reduction. Considering the 2170


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As expected from eq 1, a portion of the solid carbon was removed by the reaction with CO2 during CO2 activation. C(s) + CO2 (g) → 2CO(g)

(1)

Thus, CO2 activation generated new pores and widened existing pores. The BET surface area and total pore volume of the untreated carbon adsorbent (CMS-4K) were 8.4 and 0.018 cm3/g, respectively. However, those values for the carbon adsorbent after CO2 activation (CMS-4K-5h) were 1976 and 0.86 cm3/g. CO2 activation might enhance the accessibility of sulfones toward surface adsorption sites in the carbon adsorbent because pores were widened and surface area was increased. CO2 activation also increased the oxygen content in the carbon adsorbent from 2.93 wt % in pristine CMS-4K to 5.8 wt % after CO2 activation (CMS-4K-5h), as shown in Table 3. Table 3. Elemental Analysis of CO2 Activated-Carbon-Based Adsorbents samples

C (wt %)

H (wt %)

N (wt %)

O (wt %)

CMS-4K (pristine) CMS-4K-5h (CO2 activation for 5 h)

96.05 93.30

0.56 0.47

0.46 0.43

2.93 5.8

Figure 4 shows the equilibrium sulfone adsorption capacities of various adsorbents for oxidized commercial diesel and

Figure 3. Sulfone breakthrough curves of oxidized commercial diesel [sulfur concentration of 154 ppm (w/w)]. Silica was used as an adsorbent, and the silica adsorbent was regenerated by (a) n-butane and (b) n-pentane.

problems of the current separation process in Scheme 1, two options were suggested to achieve an economical and energyefficient process for sulfone separation. One is to find effective solvents, having simultaneously low heat of vaporization and good sulfone solubility to regenerate the silica adsorbent. The other is to modify the current process scheme, shown in Scheme 1, into a new process scheme, displayed in Scheme 2. The main difference between Schemes 1 and 2 is the second adsorption step. This second adsorption step is performed to transfer the sulfones in methanol or acetone into the hydrocarbon. If we are able to perform this step successfully, we will be able to combine the advantages of polar solvents (the ability of regeneration) and hydrocarbons (low vaporization heat) because of this new adsorption step. In this study, we focused on this second method to solve the problem induced by the sulfone separation process based in Scheme 1. To fulfill the new adsorption step of transferring the sulfones in the polar solvent into the hydrocarbon, a proper adsorbent with two unique attributes must be prepared. The first characteristic is high adsorption selectivity for sulfones against the polar solvent. The second property is easy regeneration by hydrocarbons. An adsorbent that can meet these two conditions exactly was successfully prepared by CO2 activation of the carbon molecular sieve (CMS-4K-5h).

Figure 4. Equilibrium sulfur adsorption capacities of silica and carbonbased adsorbents (CMS-4K, CMS-4K-5h, and Calgon) for oxidized diesel and sulfone/methanol. Sulfones dissolved in diesel (oxidized diesel) or methanol (sulfone/methanol) were used as a feed solution.

sulfone/MeOH. For sulfone adsorption in oxidized commercial diesel, the silica adsorbent showed the highest sulfone adsorption capacity. Carbon-based adsorbents (Calgon, CMS4K, and CMS-4K-5h) displayed lower sulfone selectivity against diesel than silica. Furthermore, CO2 activation of CMS-4K decreased the sulfone adsorption capacity. The sulfone adsorption capacity of CMS-4K was 0.30 mg/g. However, that of CMS-4K-5h, obtained from CO2 activation, decreased to 0.05 mg/g. For sulfone adsorption in methanol, whose solution was produced by regeneration of sulfone-saturated silica, CO2 activation enhanced the sulfone adsorption capacity of CMS-4K drastically by 5 times. The surface polarity change by CO2 activation in CMS-4K-5h is thought to be mainly related to the abrupt increase of the sulfone adsorption 2171


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capacity. The increased amount of oxygen may be attributed to the generation of a polar functional group on the carbon surface, such as a carboxylic group (−COOH) and a phenol group (−COH).21 The generation of a surface functional group induced by CO2 activation might play a crucial role in the enhancement of sulfone adsorption selectivity against the polar solvent. Figure 5 shows the sulfone breakthrough curves with CO2 activated carbon (CMS-4K-5h) as an adsorbent and sulfone/

Figure 5. Sulfone breakthrough curves of sulfone/methanol [sulfur concentration of 154 ppm (w/w)] with different feed flow rates. Activated carbon, CMS-4K-5h, was used as an adsorbent, and this adsorbent was regenerated by n-butane.

methanol as a feed solution. At a low feed flow rate (0.06 mL/ min), the breakthrough of sulfone occurred when the breakthrough weight ratio was around 17 g/g. When the feed flow rate increased to 0.5 mL/min, the breakthrough weight ratio slightly decreased to 15 g/g. Regardless of the feed flow rate, CMS-4K-5h showed a high breakthrough adsorption capacity for sulfone. These results imply that CO2 activation imparts for the carbon adsorbent a very high adsorption selectivity for sulfone against methanol. The first condition for a suitable adsorbent in the second step adsorption in Scheme 2 is high sulfone selectivity against polar solvents. This condition was achieved by CO2 activation. The next step is to investigate the regeneration of CMS-4K-5h by hydrocarbons. First, n-hexane was used as a regeneration solvent, as shown in Figure 6a. The first breakthrough test showed high sulfone adsorption capacity as a high breakthrough weight ratio (∼16 g/g). However, the breakthrough weight ratio of CMS-4K-5h in the second adsorption after the first regeneration with n-hexane at 323 K decreased to ∼8 g/g. The regeneration temperature of 323 K was not enough to completely remove the sulfones trapped in the carbon adsorbent (CMS-4K-5h). In the second regeneration after the second adsorption, the regeneration temperature was increased to 348 K and the pressure of the adsorption column was maintained at 300 kPa to retain the phase of n-hexane as liquid. In the third adsorption, the breakthrough adsorption capacity for sulfone recovered to the initial value (16 g/g). For the regeneration of CMS-4K-5h using n-hexane, regeneration should be performed at more than 348 K. Second, n-butane was used as a regeneration solvent for CMS-4K-5h at 373 K and 1800 kPa. As shown in Figure 6b, CMS-4K-5h showed a

Figure 6. Sulfone breakthrough curves of sulfone/methanol [sulfur concentration of 152 ppm (w/w)]. Activated carbon, CMS-4K-5h, was used as an adsorbent, and the adsorbent was regenerated by (a) nhexane with a flow rate of 0.7 mL/min for 5 h at 373 K and 300 kPa and (b) n-butane with a flow rate of 0.7 mL/min for 5 h at 373 K and 1800 kPa.

high sulfone breakthrough adsorption capacity, and this capacity was maintained after regeneration by n-butane. This means that regeneration by n-butane under the given conditions removed sulfones adsorbed in CMS-4K-5h completely. CMS-4K-5h showed a high sulfone adsorption capacity for sulfone/methanol, and sulfones adsorbed in CMS-4K-5h were effectively removed by hydrocarbons. This means that CMS-4K-5h obtained by CO2 activation meets the two requirements, high sulfone selectivity and regeneration by hydrocarbon, for the adsorbent in the second adsorption step that appears in Scheme 2. Figure 7 shows the sulfone breakthrough curves with CO2 activated carbon (CMS-4K-5h) as an adsorbent and sulfone/ acetone as a feed solution. Although CMS-4K-5h showed high sulfone adsorption capacity and maintained its capacity after nbutane regeneration, CMS-4K-5h failed to maintain its initial sulfone adsorption capacity after regeneration by n-butane. This indicates that sulfone/methanol is better than sulfone/acetone for the solvent recovery when CMS-4K-5h is used as an adsorbent in the second adsorption step. Thus, methanol should be used as a regeneration solvent in the first adsorption step. 2172


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Scheme 1. However, 20 kg of sulfone containing n-butane was boiled for the case of Scheme 2, because the second adsorption step transfers sulfones from methanol to n-butane. The energy consumption in the distillation step to produce 1 kg of ULSD for the case of Scheme 1 is twice as high as that for the case of Scheme 2. The introduction of the second adsorption step appearing in Scheme 2, by preparing CO2 activation of the carbon adsorbent, enabled a reduction of energy consumption in the distillation step because the second adsorption step is able to combine the advantage of the polar solvent and hydrocarbon.

4. CONCLUSION Initially, a process of an adsorption step with silica for the separation of sulfones from diesel and subsequent distillation for the recovery of the regeneration solvent, which removed adsorbed sulfones in silica and resultant separation of sulfones (Scheme 1), was found to be a simple way to organize a continuous sulfone separation process for the production of ULSD. Methanol and acetone were found to be good solvents for the regeneration of the sulfone-saturated silica adsorbent. In the distillation step, however, the separation of sulfones from methanol or acetone consumes a lot of energy, because the vaporization heats of methanol and acetone are 2−3 times higher than those of hydrocarbons. From the viewpoint of energy consumption in the distillation step, hydrocarbons with low vaporization heat, such as n-butane or n-pentane, seem to be suitable solvents. However, n-butane and n-pentane did not regenerate the sulfone-saturated silica adsorbent effectively. To combine the advantages of a polar solvent (silica regeneration) and that of a hydrocarbon (low heat of vaporization), the previous process scheme (Scheme 1) was modified into a new scheme (Scheme 2) with the addition of another adsorption step between the adsorption and distillation steps. In the newly added adsorption step (second adsorption step), the activated carbon adsorbent prepared by CO2 activation of a carbon molecular sieve (CMS-4K) selectively adsorbed sulfones in the polar solvent (methanol) and easily released sulfones by hydrocarbon (n-butane) washing. Because of this second adsorption step, the silica adsorbent was successfully regenerated by methanol (polar solvent) and sulfones were separated with low energy consumption because n-butane, with low vaporization heat, was the solvent in the distillation step. The realization of two-step adsorption and distillation, as shown in Scheme 2, enabled a continuous sulfone separation process with lower energy consumption.

Figure 7. Sulfone breakthrough curves of sulfone/acetone [sulfur concentration of 154 ppm (w/w)]. Activated carbon, CMS-4K-5h, was used as an adsorbent, and the adsorbent was regenerated by n-butane with a flow rate of 0.7 mL/min for 5 h at 373 K and 1800 kPa.

The optimized separation process conditions based in Scheme 2 are summarized as follows. Commercial silica was used as an adsorbent in the first adsorption step to separate sulfone in diesel. After adsorption, sulfone-saturated silica was regenerated by methanol. Then, the resultant sulfone/methanol was used as a feed solution in the second adsorption step with CMS-4K-5h as an adsorbent to recover sulfone-free methanol. The sulfones adsorbed in CMS-4K-5h were removed by nbutane. The sulfones in n-butane were easily separated by the third distillation step, because n-butane has a low heat of vaporization (320 kJ/kg) and a very low boiling point (−42.1 °C). Considering the experimental results in this study, energy consumption values based on Scheme 1 were compared to those based on Scheme 2 with optimized conditions, as shown in Table 4. In the case of producing 10 kg of ULSD, 1 kg of silica adsorbent and 12.8 kg of methanol were needed in both cases (Schemes 1 and 2). In the distillation step, 12.8 kg of sulfone containing methanol was regenerated for the case of Table 4. Elemental Analysis of CO2 Activated-Carbon-Based Adsorbents Scheme 1 ULSD (kg) adsorbent (kg) regeneration solvent (kg) heat of vaporization (kJ/kg) energy consumptiona,b (kJ/kg of ULSD)

silica CMS-4K5h methanol n-butane methanol n-butane

10 1.0

12.8

Scheme 2

breakthrough weight ratio (kg/kg)

10 1.0 0.83

10 12

■

*Telephone: +82-62-530-1873 (C.H.K.). E-mail: kimsh@ korea.ac.kr (S.H.K.); [email protected] (C.H.K.).

12.8 20

Present Address

1104 1413

AUTHOR INFORMATION

Corresponding Author

§

School of Applied Chemical Engineering, Chonnam National University, Gwangju 500-757, Korea.

320 640

Notes

The authors declare no competing financial interest.

■

a

Energy consumption in the distillation step per unit weight of ULSD produced = used amount of regeneration solvent × vaporization heat of the corresponding solvent/produced amount of ULSD at one adsorption cycle. bIn the calculation of the “energy consumption in distillation step”, the heat of vaporization only was considered and the specific heat was ignored.

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Energy-Efficient Sulfone Separation Process for the Production of

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