Microwave Irradiation Induced High-Efficiency Regeneration for

Subscriber access provided by Queen Mary, University of London

Article

Microwave irradiation induced high-efficiency regeneration for desulfurized activated coke: A comparative study with conventional thermal regeneration Xinxin Pi, Fei Sun, Jihui Gao, Yuwen Zhu, Lijie Wang, Zhibin Qu, Hui Liu, and Guangbo Zhao Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.7b01260 • Publication Date (Web): 02 Aug 2017 Downloaded from http://pubs.acs.org on August 3, 2017

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Energy & Fuels is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 36

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

Energy & Fuels

Microwave irradiation induced high-efficiency regeneration for desulfurized

activated

coke:

A comparative

study with

conventional thermal regeneration

Xinxin Pi a, Fei Sun a,*, Jihui Gao a,*, Yuwen Zhu b, Lijie Wang a, Zhibin Qu a, Hui Liu a

and Guangbo Zhao a

a

School of Energy Science and Engineering, Harbin Institute of Technology, Harbin,

150001, China. b

School of Energy and Safety Engineering, Tianjin Chengjian University, Tianjin,

300384, China.

Corresponding Author: * Fei Sun and Jihui Gao

E-mail: [email protected] (F. Sun) and [email protected] (J. Gao)

1

ACS Paragon Plus Environment

Energy & Fuels

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

Page 2 of 36

ABSTRCT: Low desorption efficiency and inferior adsorbate recovery rate during conductive-heating regeneration have always been the key issues facing activated carbon based SO2 removal technology, which commonly leads to short cycling life of adsorbent. Herein, microwave heating was employed to regenerate desulfurized activated coke, which demonstrates great improvements in regeneration efficiency and

cycling

desulfurization

performances.

Compared

with

the

long-time

conductive-heating process (30 minutes), microwave heating shows more rapid heating rate with just 4 minutes to achieve complete regeneration. After 10 desulfurization-regeneration cycles, microwave regenerated activated coke (MG-AC) can still maintain a high SO2 removal capacity of 94 mg g-1, more than double than that of thermal regenerated AC (TG-AC). Physicochemical structures analyses confirm that microwave heating selectively activates the adsorbate H2SO4 molecules and

thus

promote

the

porosity

development

and

selective

removal

of

oxygen-containing functional groups. Additionally, surface sulfur species analysis provides a new insight into the adsorbate desorption mechanism that microwave irradiation could create instantaneous high temperature within activated coke and induce deep reduction of H2SO4 to elemental sulfur. This finding is of great significance to develop high-value sulfur recovery technology. This work also suggests that microwave heating is an attractive method for the high-efficiency regeneration of desulfurized activated coke. Keywords Microwave regeneration, Activated coke, Desulfurization, Sulfur acid 2


Page 3 of 36

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

Energy & Fuels

1. Introduction Anthropogenic SO2 emission has been regarded as a major gas pollutant that can result in various issues to the public health and environment. While traditional Ca-based wet desulfurization technology faces the dilemma of high capital cost, high water consumption and CO2 leaking out, carbonaceous porous materials, including semi-coke,1-3 coke,4-8 activated carbon,9-11 and activated carbon fibers,12-14 have been extensively explored to remove SO2 from flue gas due to their advantages of water-saving, adsorbent and sulfur resource recycling and environment benignity. For instance, through moving-bed or fixed bed reactors, coal-based activated coke (AC) has been successfully utilized for SO2 and NOx removal from flue gas via moving-bed or fixed bed reactors in Japan, Germany and China.15 In the presence of O2 and H2O, SO2 removal reaction inside the micropores of porous carbon is a multi-step heterogeneous reaction including the absorption of SO2, O2 and H2O, the oxidation and hydration of SO2 with O2 and H2O, catalyzed by the active sites on carbon surface, to form H2SO4,14 and accompanied by the migration of H2SO4 from micropores to meso-/macro-pores.7 For recycling of spent adsorbents, the desulfurized porous carbons need to be regenerated, which is currently the main technical bottleneck for lowering the operation cost and improving the by-product recovery value.15,16 Currently practical regeneration strategies for desulfurized activated coke (AC)

3


Energy & Fuels

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

include water scrubbing and thermal regeneration.8,15 Water scrubbing, just as its name implies, recovers the spent activated coke by extracting adsorbate H2SO4 from inner pores of activated coke. Due to the strong interactions between adsorbed H2SO4 and carbon surface, such process commonly results in uncompleted regeneration and requires large amounts of water. By contrast, thermal regeneration can extract most of the adsorbate H2SO4 based on the redox reaction (C+H2SO4→CO2+SO2+H2O) between carbon framework and H2SO4 under relatively high temperatures (400~600 o

C).8,17 However, during the process of thermal regeneration, activated coke will

produce serious chemical loss and mechanical loss, which usually leads to rapid decay of desulfurization performance on cycling desulfurization and regeneration.8,17 Furthermore, most adsorbate H2SO4 are converted again to SO2, mixed with CO2 and H2O, which make it difficult to recycle and refine sulfur resources. Thus, in spite of current regeneration strategies proposed thus far, cycling lifespan and sulfur resource recovery path remain key issues, calling for new regeneration approaches. In recent years, microwave radiation technology, due to its high heating efficiency,18,19 time-saving20 and selectivity,21 has been explored in the fields of materials synthesis,22-24 of solid fuel25 and regeneration of spent adsorbents.26-29 During the microwave radiation process, heat is produced internally within the material instead of originating from outside surface of traditional thermal regeneration, which should make the adsorbate inside pores easily heated and thus improve

4


Page 4 of 36

Page 5 of 36

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

Energy & Fuels

desorption efficiency. Furthermore, microwave irradiation provides “dielectric heating” pattern and makes the polar molecules absorb more microwave energy than non-polar molecules, which is highly effective for the polar molecules desorption.18 Moreover, the features of fast heating rate and time-saving in microwave irradiation process are also expected to restrain the chemical and mechanical loss of spent adsorbents.30 To date, such features of microwave regeneration have been successfully demonstrated for the regeneration of organic molecules (i.e. VOC and phenol) adsorbed activated carbons.20,26,31-33 Based on abovementioned merits, microwave irradiation should also be effective for the regeneration of desulfurized ACs. Zhang and Ma et al.34 recently reported the better cycling desulfurization performance

of

thermal-regenerated

microwave-regenerated AC.

However,

the

AC

than

underlying

that

of

microwave

conventional regeneration

mechanism remains unclear and need in-depth evidences or explanations. This study is intended to improve the current understanding of the microwave regeneration effects on desulfurized ACs by comparing with conventional thermal regeneration. The major emphasis lies on the physicochemical structure evolution of AC during cycling desulfurization-regeneration, the sulfur species distribution on AC and adsorbate H2SO4 desorption paths. Impressively, we found that microwave irradiation for desulfurized AC exhibits much better regeneration performance than thermal regeneration in terms of stable cycling desulfurization performance of AC,

5


Energy & Fuels

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

increased porosity of AC and fast sulfur species desorption rate. Moreover, a new insight into sulfur species desorption paths under microwave regeneration was proposed, which highlights the conversion path of H2SO4 to elemental sulfur under microwave irradiation. Results presented herein are expected to establish a systematical understanding towards adsorbate desorption path and adsorbent recover mechanism under two typical heating patterns, which, we hope, accelerate the industrial application of microwave technology for desulfurized ACs’ regeneration.

2. Materials and methods 2.1. Sample Preparation The sample used was coal-based column activated coke (AC) (Alashan Kexing carbon industry Co. Ltd., China). Prior to use, the column AC sample were grounded to particles ranging 375-750 µm. Before absorption experiments, AC was dried in air at 120 °C for 24 h and then stored in a desiccator.

2.2. Setup and Methods 2.2.1. SO2 removal test Using a fixed bed experimental system, the SO2 removal test was carried out at 363 K. As depicted in Figure S1, the schematic diagram of the test system consists a fixed-bed glass reactor (diameter is 20 mm), a vertical furnace, valves and mass flow controllers. To monitor the concentrations of SO2/O2/H2O in reactor inlet and outlet continuously, we used the portable FTIR from Finland Gasmet Company. In a typical 6


Page 6 of 36

Page 7 of 36

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

Energy & Fuels

run, packing into the glass column of 5 g AC. Subsequently, when the temperature in the reaction zone reached the desired value and kept a steady state, simulated flue gas was introduced into the reactor (2000 ppm SO2, with or without 5% O2, with 10% H2O, N2 balance, total flow rate 1.5 L/min). Through a water bath, H2O stream was introduced and controlled by bubbling a certain amount of N2. The actual measurement results of water vapor by Gasmet gas analyzer in the supporting information as Figure S2. SO2 removal efficiency and rate versus time was defined by recording concentrations of SO2 at the inlet and outlet in real time through the gas analyzer. Through the gas analyzer, using the concentrations of SO2 at the inlet and outlet to record the removal rate and efficiency versus time. SO2 removal capacities of AC samples were calculated by integrating the area of the removal curves and reaction time, SO2 saturation adsorption capacity were calculated by integrating the area of the dynamic adsorption curves and reaction time. 2.2.2. Microwave Regeneration Once SO2 absorption saturation has been reached, the activated coke was transferred to a microwave applicator (MAS-II, Sineo Microwave Chemistry Technology (Shanghai) Co., Ltd.) for regeneration. In the process of microwave regeneration of AC experimental, the basically equipment consists a microwave magnetron (the maximum output power is 1000 W at 2450 MHz) and a single mode cavity (sample is exposed to microwave heating). Saturated activated coke stayed 7


Energy & Fuels

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

inner of the quartz reactor, which is placed by means of a ‘‘chimney’’ into the microwave cavity and then under controlled operating conditions, exposed to microwave heating. The detailed schematic diagram of the microwave regeneration system is shown in Figure S1b. AC was heated in a flow of nitrogen (0.5 SLPM) during microwave regeneration. Regeneration times (0~8 min) and powers (100~1000 W) varied. Microwave heating during ten-cycle absorption/desorption testing was completed using these conditions. 2.2.3. Thermal Regeneration For thermal regeneration, desulfurized activated coke placed in a glass tube, afterwards, settled in a vertical furnace. A thermocouple measured the temperature at the center of the activated coke bed. Activated coke was heated in a flow of nitrogen (0.5 SLPM), at a heating rate of 10 °C min-1, and maintained at 400 °C for 30 min and then cooled for 30 min while the nitrogen purge was continued. 2.2.4. Characterizations Scanning electron microscopy (JSM-7401F) and EDX mapping were used to investigate the morphology and elemental distribution for typical samples. Determined by an automatic apparatus, at 77 K, from the physical adsorption of N2, pore parameters of activated coke were obtained (Micromeritics ASAP 2020). The relative pressure ranges used for determining BET surface area and micropore volume were 0.01 to 0.07 and 0.2 to 0.4, respectively. The t-plot model was used for 8


Page 8 of 36

Page 9 of 36

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

Energy & Fuels

determining micropore volume. Pore size distributions were obtained from nitrogen absorption/desorption isotherms by applying the nonlocal density functional theory (NLDFT) model for slit-shaped pores.35 X-ray photoelectron spectroscopy (XPS) analyses were performed on a PHI 5700 ESCA system using AlKa X-ray at 14 kV and 6 mA. Raman spectroscopy was examined on a Renishaw in Via Micro-Raman spectrometer at 532 nm. The gas products analyses during regeneration were conducted by the TG-FTIR coupling techniques with a heating rate of 8 °C min-1 in Ar.

3. Results and discussion 3.1. Regeneration efficiency and cycling desulfurization performance of MG-AC and TG-AC To directly research the effects of microwave regeneration on desulfurized activated coke (AC), the cycling desulfurization performances of microwave regeneration AC (MG-AC) and thermal regeneration AC (TG-AC) was firstly investigated. Three experimental systems, including fix-bed SO2 removal system, microwave regeneration system and thermal regeneration system, as shown in Figure S1. We conducted our experiment in triplicate tests making the results statistically significant, and added error bars to clarify the experimental error, and achieved the successive cycling of desulfurization-regeneration. The SO2 removal capacities vs. cycling number of TG-AC and MG-AC are shown in Figure 1.

9


Energy & Fuels

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

Figure 1. (a) SO2 removal capacities vs. cycling number of TG-AC. (b) SO2 removal capacities vs. cycling number of MG-AC.

The SO2 removal capacities of TG-AC exhibit a general decrease trend from 67.48 mg g-1 in the first-time desulfurization to 45.76 mg g-1 in the 10th cycle, as shown in Figure 1a. These results clearly indicate that thermal regeneration poses a negative impact on the cycling SO2 removal performance of AC and after dozens of cycling, the resulting AC lose much activity leading to rapidly decreased SO2 removal capacities. Such short cycling life of TG-AC should be mainly ascribed to the damaged pore structure and chemically active sites during long-time (30 min), high-temperature (400 oC) and repeated thermal treatment process. To shorten the regeneration time and improve the regeneration efficiency for desulfurized AC, microwave-regeneration (power of 100W and irradiation time of 4 min) is employed to recover SO2-saturated AC, by which the resulting AC shows much better cycling desulfurization performance than thermal regeneration, as shown in Figure 1b. The result shows that among various power outputs (100 W, 200 W, 300 W, 400 W and 700 W), the microwave regeneration efficiency can reach the maximum range of 10


Page 10 of 36

Page 11 of 36

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

Energy & Fuels

86~90%, and the microwave power has little difference on the regeneration efficiency (Figure S3). It can be clearly observed in Figure 1b that the SO2 removal capacities of MG-AC roughly increased. After 10 cycles, MG-AC maintains a high desulfurization performance with SO2 removal capacity of approximately 94 mg g-1, which is more than double than TG-AC after 10 cycles. Thus, it may be concluded that microwave regeneration can significantly improve the adsorbate desorption efficiency leading to much

better

cycling

desulfurization

performance

as

compared

with

conductive-heating regeneration. The scanning electron microscope (SEM) and corresponding sulfur element mapping images of adsorbed AC and regenerated AC after various regeneration times were conducted, as shown in Figure 2. It can be clearly seen that microwave regeneration exhibits both faster adsorbate desorption rate and higher regeneration efficiency than those for thermal regeneration. Experiencing the long-time thermal regeneration process (30 minutes), there is still an average sulfur residue of 4.73%. By contrast, microwave heating shows much curtate regeneration time of just 4 minutes to achieve higher regeneration effect with lower sulfur residue of 3.57%. Such rapid generation rate of microwave regeneration is beneficial to reducing the energy consumption and carbon mass loss.

11


Energy & Fuels

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

Figure 2. Scanning electron microscope (SEM) and corresponding sulfur element mapping images of adsorbed AC and regenerated AC after various regeneration times. (a) Adsorbed AC experiencing thermal regeneration process. (b) Adsorbed AC experiencing microwave regeneration process.

3.2. Physicochemical structure evolution during cycling regeneration We further investigate the potential changes to the physicochemical properties of desulfurized activated cokes suffering microwave regeneration. To obtain these effects, ten absorption/desorption cycles are conducted for both microwave regeneration (100 W for 4 min) and thermal regeneration (400 oC for 30 min) techniques. Figure 3 shows the SEM images of original AC, ten times cycled microwave regeneration AC (MG-AC-10) and ten times cycled thermal regeneration 12


Page 12 of 36

Page 13 of 36

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

Energy & Fuels

AC (TG-AC-10). Figure 3a shows the micro-morphology of original AC which is consisted of a large amount of small and aggregated block units. Amplified image of Figure 3b and 3c further presents a compact stacking structure. After several times’ regeneration, there is nearly have no difference in the overall surface landscape of sample MG-AC-10, some new pores created (Figure 3e and 3f) which may be stem from the microwave effect. As for the thermal regeneration case, the resulting sample TG-AC-10 disintegrates to smaller particles when compared to original AC and MG-AC-10 (Figure 3d). This is mainly owing to the erosion reactions between adsorbate H2SO4 and carbon framework (C+H2SO4→H2O+SO2+CO2), which could also cause pore widening as shown in Figure 3h and 3i.

Figure 3. SEM images of original AC, MG-AC-10 and TG-AC-10. (a), (b), (c) original AC with different magnifications. (d), (e), (f) MG-AC-10 with different magnifications. (g), (h), (i) TG-AC-10 with different magnifications.

13


Energy & Fuels

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

Although microwave regeneration could create high temperature in activated coke, the resulted effect is quite different from thermal regeneration. As shown in Figure S4, we can see that high temperature itself cannot induce better regeneration efficiency due to the external heat transfer which causes serious carbon loss and SO2 removal activity decay. For microwave regeneration, the adsorbate inner activated coke is firstly heated (internal heating pattern) but not the activated coke. Therefore, the above two reactions could efficiently occur with a small amount of carbon consumption and quite short time. Although the above two reactions may also occur at high thermal regeneration temperature, the external heat transfer pattern and long heating time lead to serious carbon loss and element sulfur volatilization or desorption. Subsequently, N2 absorption isotherms of original AC, MG-AC and TG-AC, all of which show a combined I and IV isotherms with a small hysteresis loop within a relative pressure P/Po of 0.4-1 was conducted, as shown in Figure 4. The corresponding pore parameters are collected in Table 1. The abrupt knee in the nitrogen absorption isotherms of the microwave regenerated samples indicates that the microporosity of these samples is mainly composed of pores of a small diameter. As can be seen in Table 1, there is an increase in the surface areas of the TG-AC-10 samples. BET values (cf. Table 1) of MG-AC-10 decreased 29.4% larger than those of the original AC samples after 10 cycles. However, BET values (cf. Table 1) of TG-AC-10 showing the opposite trend, decreased 25.4% than the original AC. The evolution of medium-micro and mesopores was valuated by the DFT model applied to the nitrogen dsorption isotherms (cf. Table 1). The volume of mesopores in the MG-AC-10 and TG-AC-10 samples both increased after ten regeneration cycles. 14


Page 14 of 36

Page 15 of 36

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

Energy & Fuels

However, the volume of micropores of MG-AC-10 sample showing the opposite trend when compared with the sample of TG-AC-10. For instance, the micropore volume of MG-AC-10 increased from 0.101 to 0.126 cm3 g-1. However, the micropore volume decreased as regeneration proceeded when regeneration was conducted using thermal regeneration methods. The changes of the porous structure for the regenerated samples may be due to the different heating mechanisms in both regeneration methods. Figure

S5

shows

the

pore

size

distribution

calculated

from

the

absorption/desorption isotherms using two different methods: HK method for microporous region (< 2 nm) and BJH method for mesoporous region (2-50 nm). the mesopore size distribution of the MG-AC and TG-AC shift towards larger pores, however, the micropore distribution of MG-AC shifts towards narrower pores. In contrast, the micropore distribution of TG-AC shifts towards the opposite side. The results indicating that the changes induced in the porous structure of the regenerated samples are due to different regeneration methods. This is corresponding with the results of Figure 4 and Table 1.

15


Energy & Fuels

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

Figure 4. N2 absorption isotherms of original AC, MG-AC and TG-AC.

As above mentioned, desulfurization product H2SO4, existing in the nanopores of activated coke, could react with carbon matrix and give rise to both pore widening and pore creating effects. However, microwave regeneration and thermal regeneration pose different impacts on the two effects. During conducive-thermal regeneration process, heat should transfer from the outer surface of activated coke particle into the internal surface and further transmit to adsorbate H2SO4 which could in-situ react with surrounding carbon framework. This process mainly gives rise to the pore widening effect and hence leads to the sample TG-AC-5 with decreased micropore volume and increased meso-/macro-pore volume. The overall specific surface area of TG-AC-5 decreases compared with original AC. As for microwave regeneration, heat is produced internally within the activated coke particle, which makes the polar adsorbate H2SO4 inside pores rapidly heated instead of accepting heat from AC surface. (We put H2SO4 solution with different concentrations, water and original AC 16


Page 16 of 36

Page 17 of 36

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

Energy & Fuels

into microwave oven and recorded the temperature variations vs. time under 100W, respectively. As shown in Figure S6, H2SO4 has the strongest microwave adsorbing ability in the early stage and can be rapidly heated). Such rapidly heated H2SO4 molecules could diffuse within the whole AC particle and induce both pore widening and pore creating effects. As a result, sample MG-AC-5 and MG-AC-10 exhibits both well-developed micropores and meso-/macro-pores compared with the original AC. In our previous studies,7 it has been shown that a hierarchical pore distribution (containing both micropores and meso-/macro-pores) is beneficial to the conversion of SO2 to H2SO4. Thus, microwave regeneration demonstrated obvious advantage in developing the meso-/macro-pores for spent adsorbents leading to the resulting MG-ACs with gradually improved cycling desulfurization performance shown in Figure 1b. To prove that the porosity development effect is due to the reactions between adsorbate and carbon matrix, fresh AC (without SO2 removal process) after microwave (MG-Blank) and thermal (TG-Blank) regeneration treatments were also prepared and characterized. It can be observed from Table 1 that the pore structure MG-B and TG-B change little compared with original AC, indicating that microwave and thermal treatments themselves pose little impact on the AC structure.

17


Energy & Fuels

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

Page 18 of 36

Table 1. Pore parameters of typical AC samples.

SBET

Smic

Vt

Vmic

Vmeso-macro

D

(m2 g-1)

(m2 g-1)

(cm3 g-1)

(cm3 g-1)

(cm3 g-1)

(nm)

Original AC

235.4

194.6

0.147

0.101

0.046

2.501

MG-AC-5

292.7

231.7

0.183

0.122

0.061

2.503

MG-AC-10

304.7

243.5

0.188

0.126

0.062

2.470

TG-AC-5

221.2

163.4

0.141

0.085

0.056

2.555

TG-AC-10

175.6

131.0

0.131

0.068

0.063

2.973

MG-AC-B

224.7

170.9

0.143

0.089

0.054

2.548

TG-AC-B

227.7

183.5

0.139

0.096

0.043

2.438

Samples

Since surface chemical properties of porous carbon also play an important role in desulfurization reaction, we further investigate the chemical structure evolution of MG-AC and TG-AC. X-ray photoelectron spectroscopy (XPS) is used to detect the variation of elemental composition and functional groups in the samples. Figure 5a shows the XPS overall spectra and element composition of original AC, MG-AC-10 and TG-AC-10 from which C, S, and O elements are founded and show various percentages within the samples. Specifically, MG-AC-10 shows decreased oxygen content compared to original AC indicating that microwave irradiation could remove partial surface oxygen functionalities while TG-AC-10 shows the opposite trend with increased oxygen content. On the one hand, most oxygen functionalities are polar functional groups. On the other hand, microwave irradiation provides “dielectric heating” pattern and could make the polar molecules absorb more energy than non-polar molecules.36 Additionally, the thermal stability of oxygen-containing 18


Page 19 of 36

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

Energy & Fuels

functional groups is different, consequently, oxygen content (from XPS) between microwave and thermal regeneration could also be related to the difference in temperatures the samples have been exposed to. Based on above three aspects, the unstable oxygen-containing functional groups could be easily removed during microwave regeneration and result in the MG-AC-10 with diminished oxygen content. To further confirm an enhanced sp2 C structure and decreased C-O structure of MG-AC-10 compared with original AC (Figure S7), the C1s spectra of MG-AC-10 and TG-AC-10 is illustrated in Figure 5b and 5c, respectively, from which the fitted peaks at 531.1 eV, 532.3 eV, 533.5 eV, 534.5 eV and 536.3 eV are assigned to quinone, unsaturated carbon-oxygen double bond (C=O, ester or amides), C-O single bond (ether-like, ester oxygen or anhydride), hydroxy (C-OH, COOH) and chemisorbed O, respectively.

37-39

Subsequently, we summarized the relative contents of these

oxygen-containing groups gives their distributions within various samples, as shown in Figure 5f. As expected, unstable acidic functionalities (such as carboxylic, phenolic hydroxyl and quinone) decrease and meanwhile high-stability functional groups such as C-O single bond increase, indicating the conversion reactions between different types of functional groups.40,41 XPS results of various samples are exactly in accordance with the characterization of structure.

19


Energy & Fuels

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

Figure 5. Chemical structure characterizations of original AC, MG-AC and TG-AC. (a) XPS overall spectra and element composition (inset). (b) C1s spectrum of MG-AC-10. (c) C1s spectrum of TG-AC-10. (d) O1s spectrum of MG-AC-10. (e) O1s spectrum of TG-AC-10. (f) Distributions of oxygen-containing functional groups for original AC, MG-AC and TG-AC.

Subsequently, we added the XPS results of TG-AC-5 in the Figure S8, summarized the relative contents of these oxygen-containing groups gives their distributions within various samples, as shown in Figure 5f. As expected, unstable acidic functionalities (such as carboxylic, phenolic hydroxyl and quinone) decrease and meanwhile high-stability functional groups such as C-O single bond increase, 20


Page 20 of 36

Page 21 of 36

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

Energy & Fuels

indicating the conversion reactions between different types of functional groups. XPS results of TG-AC-5 are exactly in accordance with the characterization of structure. Results of the Boehm titration for the as-received, microwave-regenerated and thermal-regenerated AC are listed detailedly in Table S1. After microwave regeneration, due to numbers of oxygen functional groups decomposed, the oxygen content gradually decreased. To our knowledge, the surface of AC presents amphoteric behavior. Boehm titration demonstrated an advantage of baisc groups, at higher temperatures, the amount of acidic functional groups will decrease along with they are decomposing, however, they will continue to gradually decrease following by numbers of regeneration. The total decrease amount of acidic functional groups in MG-AC-10 was about 72% at 100 W, which indicates under the circumstances most of acidic groups have decomposed, and the basic functional groups correspondingly increased. The basic functional groups were active sites where catalytic oxidation of SO2 to SO3 will easy to took place; when the basic functional groups present in greater amounts, naturally, the catalytic oxidation activity of AC will increase.42 According to previous reports, these groups were mainly pyrone-like structures. Boehm reported that, at high temperature, pyrone-like structures formed through the realignment of carbonyl and ether groups, which is not decomposed.43 And at low temperatures, the ether groups are placed on the functional group sites of active acidic oxygen, formed by adsorption of oxygen. In summary, microwave regeneration promoted the decomposition of acidic groups and the formation of basic groups. 3.3. Adsorbate desorption mechanism of microwave regeneration In the presence of O2 and H2O, SO2 removal reaction inside activated coke is a

21


Energy & Fuels

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

Page 22 of 36

multi-step heterogeneous process including absorption of SO2, O2 and H2O, oxidation and hydration of SO2 with O2 and H2O, to form H2SO4. During heat-induced regeneration process, adsorbate could react with the adsorbent, and depending on temperature, desorb in various valence states. Next, we further investigate the adsorbate desorption mechanism of microwave regeneration by analyzing the desorption product and identifying the sulfur species on adsorbent surface. Figure 6 shows the gas product release characteristics for MG-AC and TG-AC from which the gas products during microwave and thermal regeneration are composed of uniform and synchronous compositions including SO2, CO2 and CO. These gas compositions are

ascribed

to

the

redox

reactions

between

H2SO4

and

carbon

(C+2H2SO4→CO2+2SO2+2H2O or/and C+H2SO4→CO+SO2+H2O).34 Moreover, it can also be observed that microwave regeneration shows much sharper gas evolution peaks within shorter time than thermal regeneration, indicating a rapid and thorough desorption process.

Figure 6. (a) Microwave regeneration exhaust gas analysis. (b) Conventional thermal regeneration exhausted gas analysis.

22


Page 23 of 36

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

Energy & Fuels

The digital image of the reactor in an ongoing microwave regeneration experiment with power of 100W is shown in Figure 7a, from which the adsorbent appears a bright red state indicating the high temperature inner activated coke. Such high temperature may stem from the depth absorption of microwave energy, especially with the existence of metal or metal oxide medium (Ca, Al, Fe, Mg) hosted in the activated coke, evidenced by the EDX analysis (Figure 7b). This is in line with previous report that the instantaneous temperature of adsorbent under microwave irradiation could reach 800~1000 oC with the existence of local hot spot.26,32 Such high temperature is enough to achieve the deep reduction of H2SO4 to elemental sulfur. To further explore the sulfur species desorption mechanism, we further conduct XPS analysis of sulfur species in microwave regenerated AC (MG-AC-10), as shown in Figure 7c. The sulfur species analysis in thermal regenerated AC (TG-AC-10) is also compared in Figure 7d. Observably, MG-AC-10 and TG-AC-10 show distinct S 2p XPS spectra. As shown in Figure 7c, the S2p spectrum of MG-AC-10 can be fitted into two peaks at ~164.5 and 165.8 which can be assigned to S 2p3/2 and S 2p1/2 spectra, respectively.44-47 Therein, the relatively high-ratio S 2p3/2 spectrum mainly represents the S=S species, clearly suggesting the formation of elemental S, which should be ascribed to the following reaction: 3nC + 2nH2SO4 → 3nCO2 + Sn + 2nH2O;48 nC + nSO2 → Sn + nCO2.49-51 By contrast, there is only sulfate (~171.5eV) signal existing in the S 2p XPS spectrum in Figure 7d. We also supplemented XPS tests of the

23


Energy & Fuels

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

saturated desulfurization activated coke before MG-AC-10 and TG-AC-10. As shown in Figure S9a, the S 2p XPS spectrum of saturated desulfurization activated coke before MG-AC-10 mainly containing sulfate, in addition, it also contains a small amount of elemental S. In contrast, Figure S9b shows that the saturated desulfurization activated coke before TG-AC-10 only contain sulfate, almost does not contain any sulfur species.

Figure 7. (a) Digital image of the reactor in an ongoing microwave regeneration experiment with power of 100W. (b) SEM image and EDX result of MG-AC-10. (c) S 2p XPS spectrum of MG-AC-10. (d) S 2p XPS spectrum of TG-AC-10.

X-ray diffraction (XRD) analysis was conducted on the MV-AC-H2SO4, TG-AC and MV-AC-100W samples for further characterization, as shown in Figure 8. The main diffraction peaks of Original AC and TG-AC-10 samples could hardly be 24


Page 24 of 36

Page 25 of 36

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

Energy & Fuels

recognized, indicating that a generally amorphous nature for the activated coke. Meanwhile, a crystallized form of the sulfur exists in the MV-AC-10 and MV-ACH2SO4 composite. However, compared with that of pure elemental sulfur, the broadened diffraction peaks observed intensity reducing indicate the small size of the sulfur crystallites, which is in good inosculates with the result that the elemental sulfur exist in bulk sorbents in the MV-AC-10 and MV-AC- H2SO4.

Figure 8. XRD spectra of pure sulfur, Original AC, TG-AC-10, MV-AC-10 and MV-AC-H2SO4.

As a consequence, we could get a comprehensive understanding of the adsorbate desorption mechanism during microwave regeneration: (1) polar adsorbate H2SO4 molecules rapidly adsorb microwave energy and react with surrounding carbon matrix to release SO2 accompanied by the release of CO2 and CO. This desorption mechanism is similar to that of traditionally thermal regeneration, but with high regeneration rate and desorption efficiency. (2) microwave irradiation could create instantaneous high temperature with the existence of local hot spot and induce the 25


Energy & Fuels

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

deep reduction of adsorbate H2SO4 to elemental sulfur. The detailed adsorbate desorption reaction paths for both microwave regeneration and thermal regenerations are summarized in Figure 9. It is worth mentioned that the regeneration reaction of H2SO4 reduction to elemental sulfur is of great significance to turn waste (gas pollutant SO2) into wealth (sulfur resources) since elemental sulfur, compared with H2SO4 and SO2, has a higher utilization value as a solid byproduct. Although it is an interesting result, the comparisons between conventional and microwave heating are still hard to make due to the differences in reaction conditions used between the two different temperatures, different times etc. Currently, further research regarding the reduction of adsorbate H2SO4 to elemental sulfur is on the going.

Figure 9. Schematic illustration of desorption mechanism for microwave regeneration and thermal regeneration.

26


Page 26 of 36

Page 27 of 36

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

Energy & Fuels

4. Conclusion In summary, we employ microwave irradiation method to regenerate desulfurized activated coke and the regeneration mechanism is systematically investigated by combining the regeneration efficiency, cycling SO2 removal performance and surface species identification of the adsorbents. Compared with traditionally thermal regeneration process, microwave heating shows more rapid heating rate with just 4 minutes to achieve complete regeneration. After 10 desulfurization-regeneration cycles, microwave regenerated activated coke (MG-AC) can still maintains a high SO2 removal capacity of 94 mg g-1, two orders of magnitude higher than that of traditionally thermal regenerated AC (TG-AC). Microwave heating promote the porosity development and the selective removal of oxygen-containing functional groups of AC.

Furthermore, a new insight into sulfur species desorption paths under

microwave regeneration was proposed, which highlights the conversion path of adsorbate H2SO4 to elemental sulfur under microwave irradiation. This work not only demonstrates microwave heating as a high-efficiency regeneration method for desulfurized activated coke, but also establish a systematical understanding towards adsorbate desorption path and adsorbent recover mechanism under two typical heating patterns.

27


Energy & Fuels

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

Associated Content Supporting Information The Supporting Information is available free of charge on the ACS Publications website at Internet http://pubs.acs.org. Pictures of employed reaction systems. The actual measurement results of H2O by Gasmet. Regeneration efficiency vs. microwave powers. SO2 removal capacities vs. cycling number of TG-AC and MG-AC. Pore size distribution of the activated coke. Comparison of microwave adsorbing abilities for H2SO4, water and activated coke. XPS spectrum of original AC, TG-AC-5, MG-AC-10, TG-AC-10. Results of the Boehm titration.

Acknowledgments This work was financially supported by the National Natural Science Foundation of China (Grant No. 51376054, 51276052 and 51406131). References (1) Liu, Q.; Li, C.; Li, Y., SO2 removal from flue gas by activated semi-cokes-1. The preparation of catalysts and determination of operating conditions. Carbon 2003, 41 (12), 2217-2223. (2) Liu, Q.; Guan, J. S.; Li, J.; Li, C., SO2 removal from flue gas by activated semi-cokes 2. Effects of physical structures and chemical properties on SO2 removal 28


Page 28 of 36

Page 29 of 36

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

Energy & Fuels

activity. Carbon 2003, 41 (12), 2225-2230. (3) Yan, Z.; Liu, L.; Zhang, Y.; Liang, J.; Wang, J.; Zhang, Z.; Wang, X., Activated semi-coke in SO2 removal from flue gas: selection of activation methodology and desulfurization mechanism study. Energy Fuels 2013, 27 (6), 3080-3089. (4) Tsuji, K.; Shiraishi, I., Combined desulfurization, denitrification and reduction of air toxics using activated coke: 1. Activity of activated coke. Fuel 1997, 76 (6), 549-553. (5) Tsuji, K.; Shiraishi, I., Combined desulfurization, denitrification and reduction of air toxics using activated coke: 2. Process applications and performance of activated coke. Fuel 1997, 76 (6), 555-560. (6) Li, J.; Kobayashi, N.; Hu, Y., The activated coke preparation for SO2 adsorption by using flue gas from coal power plant. Chem. Eng. Process. 2008, 47 (1), 118-127. (7) Sun, F.; Gao, J.; Liu, X.; Tang, X.; Wu, S., A systematic investigation of SO2 removal dynamics by coal-based activated cokes: The synergic enhancement effect of hierarchical pore configuration and gas components. Appl. Surf. Sci. 2015, 357, 1895-1901. (8) Yang, L.; Jiang, X.; Jiang, W.; Wang, P.; Jin, Y., Cyclic regeneration of pyrolusite modified activated coke by blending method for flue gas desulfurization. Energy Fuels 2017, 31 (4), 4556-4564. (9) Rubio, B.; Izquierdo, M. T., Low cost adsorbents for low temperature cleaning of flue gases. Fuel 1998, 77 (6), 631-637. 29


Energy & Fuels

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

(10) Lissovskii, A.; Semiat, R.; Aharoni, C., Adsorption of sulfur dioxide by active carbon treated by nitric acid: I. Effect of the treatment on adsorption of SO2 and extractability of the acid formed. Carbon 1997, 35 (10), 1639-1643. (11) Qu, Y. F.; Guo, J. X.; Chu, Y. H.; Sun, M. C.; Yin, H. Q., The influence of Mn species on the SO2 removal of Mn-based activated carbon catalysts. Appl. Surf. Sci. 2013, 282, 425-431. (12) Brasquet, C.; Cloirec, P. L., Adsorption onto activated carbon fibers: application to water and air treatments. Carbon 1997, 35 (9), 1307-1313. (13) Mochida, I.; Miyamoto, S.; Kuroda, K.; Kawano, S.; Yatsunami, S.; Korai, Y., Adsorption and Adsorbed Species of SO2 during Its Oxidative Removal over Pitch-Based Activated Carbon Fibers. Energy Fuels 1999, 13 (2), 369-373. (14) Gaur, V.; Asthana, R.; Verma, N., Removal of SO2 by activated carbon fibers in the presence of O2 and H2O. Carbon 2006, 44 (1), 46-60. (15) Mochida, I.; Korai, Y.; Shirahama, M.; Kawano, S.; Hada, T.; Seo, Y.; Yoshikawa, M.; Yasutake, A., Removal of SOx and NOx over activated carbon fibers. Carbon 2000, 38 (2), 227-239. (16) Davini, P., Flue gas desulphurization by activated carbon fibers obtained from polyacrylonitrile by-product. Carbon 2003, 41 (2), 277-284. (17) Lizzio, A. A.; DeBarr, J. A., Mechanism of SO2 Removal by Carbon§. Energy Fuels 1997, 11 (2), 284-291.

30


Page 30 of 36

Page 31 of 36

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

Energy & Fuels

(18) Jones, D. A.; Lelyveld, T. P.; Mavrofidis, S. D.; Kingman, S. W.; Miles, N. J., Microwave heating applications in environmental engineering-a review. Resour., Conserv. Recycl. 2002, 34 (2), 75-90. (19) Cui, C.; Zheng, Q.; Han, Y.; Xin, Y., Rapid microwave-assisted regeneration of magnetic carbon nanotubes loaded with p-nitrophenol. Appl. Surf. Sci. 2015, 346, 99-106. (20) Fayaz, M.; Shariaty, P.; Atkinson, J. D.; Hashisho, Z.; Phillips, J. H.; Anderson, J. E.; Nichols, M., Using microwave heating to improve the desorption efficiency of high molecular weight VOC from beaded activated carbon. Environ. Sci. Technol. 2015, 49 (7), 4536-42. (21) Weissenberger, A. P.; Schmidt, P. S., Microwave-Enhanced Regeneration of Adsorbents. MRS Proceedings 2011, 347. (22) Kappe, C. O., Microwave dielectric heating in synthetic organic chemistry. Chem. Soc. Rev. 2008, 37 (6), 1127-39. (23) Paul, R.; Voevodin, A. A.; Zemlyanov, D.; Roy, A. K.; Fisher, T. S., Microwave-Assisted Surface Synthesis of a Boron-Carbon-Nitrogen Foam and its Desorption Enthalpy. Adv. Funct. Mater 2012, 22 (17), 3682-3690. (24) Bilecka, I.; Niederberger, M., Microwave chemistry for inorganic nanomaterials synthesis. Nanoscale 2010, 2 (8), 1358. (25) Mushtaq, F.; Mata, R.; Ani, F. N., Fuel production from microwave assisted pyrolysis of coal with carbon surfaces. Energy Convers. Manage 2016, 110, 142-153. 31


Energy & Fuels

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

(26) Ania, C. O.; Menéndez, J. A.; Parra, J. B.; Pis, J. J., Microwave-induced regeneration of activated carbons polluted with phenol. A comparison with conventional thermal regeneration. Carbon 2004, 42 (7), 1383-1387. (27) Reuß, J.; Bathen, D.; Schmidt-Traub, H., Desorption by microwaves: mechanisms of multicomponent mixtures. Chem. Eng. Technol 2002, 25 (4), 381-384. (28) Omorogie, M. O.; Babalola, J. O.; Unuabonah, E. I., Regeneration strategies for spent solid matrices used in adsorption of organic pollutants from surface water: a critical review. Desalin. Water Treat. 2014, 57 (2), 518-544. (29) Liu, Q. S.; Zheng, T.; Li, N.; Wang, P.; Abulikemu, G., Modification of bamboo-based activated carbon using microwave radiation and its effects on the adsorption of methylene blue. Appl. Surf. Sci. 2010, 256 (10), 3309-3315. (30) Ania, C. O.; Parra, J. B.; Menéndez, J. A.; Pis, J. J., Effect of microwave and conventional regeneration on the microporous and mesoporous network and on the adsorptive capacity of activated carbons. Microporous Mesoporous Mater. 2005, 85 (1-2), 7-15. (31) Wang, H.; Lashaki, M. J.; Fayaz, M.; Hashisho, Z.; Philips, J. H.; Anderson, J. E.; Nichols, M., Adsorption and desorption of mixtures of organic vapors on beaded activated carbon. Environ. Sci. Technol. 2012, 46 (15), 8341-8350. (32) Zhang, Z.; Macquarrie, D. J.; Aguiar, P. M.; Clark, J. H.; Matharu, A. S., Simultaneous recovery of organic and inorganic content of paper deinking residue through low-temperature microwave-assisted pyrolysis. Environ. Sci. Technol. 2015, 32


Page 32 of 36

Page 33 of 36

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

Energy & Fuels

49 (4), 2398-404. (33) Hashisho, Z.; Emamipour, H.; Rood, M. J.; Hay, K. J.; Kim, B. J.; Thurston, D., Concomitant adsorption and desorption of organic vapor in dry and humid air streams using microwave and direct electrothermal swing adsorption. Environ. Sci. Technol 2008, 42 (24), 9317-9322. (34) Zhang, L. Q.; Jiang, H. T.; Ma, C. Y.; Dong. Y., Microwave regeneration characteristics of activated carbon for flue gas desulfurization. J. Fuel Chem. Technol. (Beijing, China) 2012, 40 (11), 1366-1371. (35) Ryu, Z.; Zheng, J.; Wang, M.; Zhang, B., Characterization of pore size distributions on carbonaceous adsorbents by DFT. Carbon 1999, 37 (8), 1257-1264. (36) Hashisho, Z.; Rood, M. J.; Barot, S.; Bernhard, J., Role of functional groups on the microwave attenuation and electric resistivity of activated carbon fiber cloth. Carbon 2009, 47 (7), 1814-1823. (37) Smith, M.; Scudiero, L.; Espinal, J.; McEwen, J. S.; Garcia-Perez, M., Improving the deconvolution and interpretation of XPS spectra from chars by ab initio calculations. Carbon 2016, 110, 155-171. (38) Arrigo, R.; Hävecker, M.; Wrabetz, S.; Blume, R.; Lerch, M.; McGregor, J.; Parrott, E. P. J.; Zeitler, J. A.; Gladden, L. F.; Knop-Gericke, A.; Schlögl, R.; Su, D. S., Tuning the Acid/Base Properties of Nanocarbons by Functionalization via Amination. J. Am. Chem. Soc. 2010, 132 (28), 9616-9630. (39) Menéndez, J. A.; Menéndez, E. M.; Iglesias, M. J.; Garcı́a, A.; Pis, J. J., 33


Energy & Fuels

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

Page 34 of 36

Modification of the surface chemistry of active carbons by means of microwave-induced treatments. Carbon 1999, 37 (7), 1115-1121. (40) Montes-Morán, M. A.; Suárez, D.; Menéndez, J. A.; Fuente, E., On the nature of basic sites on carbon surfaces: an overview. Carbon 2004, 42 (7), 1219-1225. (41) Shafeeyan, M. S.; Daud, W. M. A. W.; Houshmand, A.; Shamiri, A., A review on surface modification of activated carbon for carbon dioxide adsorption. J. Anal. Appl. Pyrolysis 2010, 89 (2), 143-151. (42) Zhang, S. Y.; Xiang, Y. H.; Zhao, J. T.; Chen, F. Y.; Huang, J. J.; Wang, Y., Study on the mechanism of flue gas desulfurization by carbonaceous materials. Coal Convers 2002, 25 (2), 29-34. (43) Boehm, H. P., Some aspects of the surface chemistry of carbon blacks and other carbons. Carbon 1994, 32 (5), 759-769. (44) Zhou, G.; Yin, L. C.; Wang, D. W.; Li, L.; Pei, S.; Gentle, I. R.; Li, F.; Cheng, H. M., Fibrous hybrid of graphene and sulfur nanocrystals for high-performance lithium–sulfur batteries. Acs Nano 2013, 7 (6), 5367-5375. (45) Fechler,

N.;

Fellinger,

T.

P.;

Antonietti,

M.,

One-pot

synthesis

of

nitrogen-sulfur-co-doped carbons with tunable composition using a simple isothiocyanate ionic liquid. J. Mater. Chem. A 2013, 1 (45), 14097. (46) Qie, L.; Chen, W.; Xiong, X.; Hu, C.; Zou, F.; Hu, P.; Huang, Y., Sulfur-Doped Carbon with Enlarged Interlayer Distance as a High-Performance Anode Material for Sodium-Ion Batteries. Adv Sci (Weinh) 2015, 2 (12), 1500195. 34


Page 35 of 36

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

Energy & Fuels

(47) Limaye, M. V.; Chen, S. C.; Lee, C. Y.; Chen, L. Y.; Singh, S. B.; Shao, Y. C.; Wang, Y. F.; Hsieh, S. H.; Hsueh, H. C.; Chiou, J. W.; Chen, C. H.; Jang, L. Y.; Cheng, C. L.; Pong, W. F.; Hu, Y. F., Understanding of sub-band gap absorption of femtosecond-laser sulfur hyperdoped silicon using synchrotron-based techniques. Sci Rep 2015, 5, 11466. (48) Fisher J W, P. S., Moran M J, et al, Reactive carbon from life support wastes for incinerator flue gas cleanup. NASA Tech. Memo. 2000, 01-2283. (49) Humeres, E.; Moreira, R. F. P. M.; Peruch, M. d. G. B., Reduction of SO2 on different carbons. Carbon 2002, 40 (5), 751-760. (50) Bejarano, C.; Jia, C. Q.; Chung, K. H., Mechanistic Study of the Carbothermal Reduction of Sulfur Dioxide with Oil Sand Fluid Coke. Ind. Eng. Chem. Res. 2003, 42, 3731-3739. (51) Wang, X.; Wang, A.; Wang, X.; Zhang, T., Microwave plasma enhanced reduction of SO2 to sulfur with carbon. Energy Fuels 2007, 21 (2), 867-869.

35


Energy & Fuels

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

Page 36 of 36

Table of Contents Entry Microwave irradiation induced high-efficiency regeneration for desulfurized

activated

coke:

A comparative

study with

conventional thermal regeneration

Xinxin Pi a, Fei Sun a,*, Jihui Gao a,*, Yuwen Zhu b, Lijie Wang a, Zhibin Qu a, Hui Liu a

and Guangbo Zhao a

Microwave irradiation demonstrates high-efficiency adsorbate regeneration and could convert the adsorbate H2SO4 to elemental sulfur.

36


Microwave Irradiation Induced High-Efficiency Regeneration for

Recommend Documents