Coconut Shell Activated Carbon Supported Quaternary Ammonium for

Subscriber access provided by Yale University Library

Article

Coconut Shell Activated Carbon Supported Quaternary Ammonium for Continuous Cycloaddition of CO2 and Biogas Upgrading in a Packed Bed Yilu Zhang, yulian zhang, Lei Wang, Hong Jiang, and Chunrong Xiong Ind. Eng. Chem. Res., Just Accepted Manuscript • Publication Date (Web): 17 May 2015 Downloaded from http://pubs.acs.org on May 17, 2015

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.

Industrial & Engineering Chemistry Research 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 29

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

Industrial & Engineering Chemistry Research

Coconut Shell Activated Carbon Supported Quaternary Ammonium for Continuous Cycloaddition of CO2 and Biogas Upgrading in a Packed Bed

Yilu Zhang, Yulian Zhang, Lei Wang, Hong Jiang, and Chunrong Xiong*

Special Glass Key Lab of Hainan Province, Hainan University, Hainan, Haikou 570228, PR China.

Corresponding author. Fax: +86-898-66271762 E-mail address: [email protected]

1 ACS Paragon Plus Environment


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 29

Graphical abstract


Page 3 of 29

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: Quaternary ammonium was successfully prepared on coconut shell activated carbon (CSAC) granules. The samples were characterized by FT-IR, N2 adsorption-desorption, XPS, TG and EA. The immobilized quaternary ammonium was thermally stable below 320 °C. The amount of immobilized quaternary ammonium on the CSAC was 0.957 mmol/g. Continuous cycloaddition of CO2 to epichlorohydrin (ECH) was carried out in a packed-bed reactor without using solvent or cocatalyst. When the reaction conditions were 130 °C and 1.4 MPa, the conversion of ECH and the corresponding turnover frequency (TOF) were 43.5% and 64.6 h-1, respectively. The selectivity to epichlorohydrin carbonate (ECHC) reached ~100%. In biogas upgrading, grafting of quaternary ammonium was demonstrated to enhance CO2 capture capacity of the CSAC. The saturated CO2 capture capacities of the CSAC and the quaternary ammonium functionalized CSAC were 1.82 and 2.40 mmol/g at 20 °C and 0.5 MPa, respectively. The adsorption selectivities of CO2 over CH4 were ~ 67 % and 85 % for the CSAC and the supported quaternary ammonium, respectively. The adsorption heat was 20~30 KJ/mol for the adsorbents. The supported quaternary ammonium also exhibited a relatively stable cyclability in a packed bed. Keywords: Quaternary ammonium; continuous cycloaddition of CO2; biogas upgrading; packed bed.



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 4 of 29

1. INTRODUCTION Chemical transformation or capture of CO2 has attracted intense attentions in view of resource utilization and pollution prevention. Recently, various homogeneous catalysts, such as ionic liquids,1–3 quaternary ammonium and phosphonium salts,4–8 transition metal halides,9–10 salen complexes11–12 and etc, were developed to prepare cyclic carbonate from CO2 and epoxides. In recent years, major efforts have been devoted to immobilize these catalysts on silica gel, mesoporous silica or polymers to obtain active heterogeneous catalysts.13-19 Although the immobilized catalysts facilitate the separation procedure, most are only applicable to a batch reactor. The catalysts must be separated after each batch. Moreover, it is a triphase reaction system for the cycloaddition of CO2 to epoxide in a batch reactor, in which CO2 must dissolve in a solvent or epoxide to accomplish its diffusion to the catalyst surface. Supercritical CO2 (scCO2) may offer a complete miscibility, but it must be operated under a high pressure condition. However, gas-solid biphasic catalysis may be achieved in a packed-bed reactor as CO2 and gaseous epoxide flow through the solid catalyst packed in a column, avoiding the use of solvents. In addition, facile automation, secured reproducibility, improved safety and process reliability are easily achieved in continuous flow operation. Prospective catalysts applicable to a packed-bed reactor must have a high mechanical strength, good abrasion resistance and big particle size. Among the reported carriers, polymers have some disadvantages including low surface area, susceptibility to high temperature, solvent and some organic reactants. Mesoporous


Page 5 of 29

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


silicas, such as MCM-41, SBA-15 and etc., have been the focus of a number of studies because of their large surface area, high pore volume and opened structure. However, they are powdery materials. To be processed into macro sized granules for application in a packed bed, the powdery materials are normally mixed with an adhesive binder and subjected to annealing at high temperature. Unfortunately, the supported organics would be burnt at a high temperature. Coconut shell activated carbon (CSAC) is a cheap and readily available biomass material. Its applicability in a continuous packed bed reactor has ever been industrially demonstrated due to its high mechanical strength, good abrasion resistance and an inherent granular structure as well as high surface area and pore volume. Herein, the aim of the research was to develop CSAC granule supported quaternary ammonium for applications in packed bed. Cycloaddition of CO2 to epichlorohydrin (ECH) was carried out in a packed-bed reactor for continuous flow operation under mild and solvent free conditions. In addition, grafting of quaternary ammonium was found to enhance the physical adsorption of CO2 over the CSAC granules. The quaternary ammonium modified CSAC granules were further investigated for biogas upgrading in a packed bed. The sustainable use of biomass does not contribute to CO2 emission but has a high CO2 abatement.20 Therefore, biogas has been considered a green and renewable energy source as an alternative to replace fossil fuels. Generally speaking, biogas contains 20–40 mol% CO2. The presence of CO2 reduces the calorific value significantly, so biogas

upgrading

to

high-quality

fuels

is

of

growing

importance.



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 6 of 29

Amine-functionalized activated carbons (ACs) was fabricated by amine-impregnation method.21 In addition, nitrogen-rich porous carbons have been researched widely for CO2 capture. Nitrogen can be incorporated into the carbon structure by preparing ACs from nitrogen-containing polymers22-26 or by the heat treatment of the carbons with gaseous ammonia.27 In any case, incorporation of N atom aims to make ACs more alkaline, and expected to increase the absorbability of acid agents such as SOx, NOx, or CO2. Although most of previous studies have been focused on enhancing CO2 capture capacity of ACs, many evaluations of CO2 capture were carried out over powdery materials on a thermogravimetric (TG) analyzer or a BEL adsorption instrument.21,

23-30

Two typical CO2 capture equipments for solid adsorbents are

packed bed and fluidized bed. Therefore, relatively poor mechanical strength and abrasion resistance of some advanced materials would hinder their industrial application in biogas upgrading. 2. EXPERIMENTAL SECTION 2.1. Materials. (3-aminopropyl)trimethoxysilane (APTS, 97.0%), 1-bromobutane (99.0%),

were purchased from Sigma Chemical Co. Nitric acid, toluene, absolute

ethanol and chloroform were supplied by Sinopharm Chemical Reagent Co. (China). CSAC granules (8~16 mesh), lithium bis(trifluoromethylsulfonyl)imide (LiTf2N, 99.5%),

ammonium

fluoroborate

(NH4BF4,

97.0%)

and

potassium

hexafluorophosphate (KPF6, 99.0%) were obtained from Aladdin reagent Co. (Shanghai, China). 2.2. Preparation of CSAC granule immobilized quaternary ammonium 6 ACS Paragon Plus Environment

Page 7 of 29

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


The synthesis of the functionalized CSAC is described in Scheme 1. The CSAC granules were controllably oxidized to generate more phenolic groups, followed by grafting silane and then reacting with bromobutane to in situ prepare quaternary ammonium. In order to increase the surface hydroxyl amount on the CSAC granules, the AC granules were subjected to oxidation by HNO3 as reported in previous reports.31-32 The granules were washed with deionized water at 100 °C for 12 h, and dried at 105 °C over night. The washed CSAC granules were then treated with 20 wt% HNO3 in a reflux device at 80 °C for 4 h, thoroughly washed with deionized water and dried at 105 °C over night. 10 g of the oxidized AC granules and 5 mL of APTS were mixed and stirred in 200 mL of toluene at 112 °C for 24 h under N2 atmosphere. The solid was separated by suction filtration and washed successively with dichloromethane and ethanol. The physically adsorbed APTS on the CSAC was extracted with ethanol in a soxhlet extractor for 24 h. To prepare the CSAC supported quaternary ammonium, 10 g of aminosilylated CSAC granules (CSAC-APTS) reacted with 10 mL of 1-bromobutane in 200 mL of toluene at 112 °C for 24 h. The solid was separated by suction filtration, and washed successively with dichloromethane and ethanol, then dried at 100 °C for ~12 h under vacuum condition. Thus, the CSAC supported

quaternary

ammonium

bromide

was

obtained

and

denoted

as

CSAC-[APTS][Br]. 2.3. Characterization Fourier Translation Infrared (FT-IR) spectra were obtained on a Bruker Tensor 27 spectrometer using KBr pellets. The Brunauer-Emmett-Teller (BET) surface area of



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 8 of 29

the samples was measured on Micromeritics Tristar 3000 automated analyzer using N2 adsorption/desorption, and the pore sizes were calculated using the branch of desorption curves based on the Barrett-Joyner-Halenda (BJH) model. X-ray photoelectron spectroscopy (XPS) analyses were conducted on an AXIS ULTRADLD spectrometer (Kratos) with achromatic Al(MONO)Kα X-radiation (1486.6eV) as the X-ray source. An elemental analyzer (Vario MICRO) was used to determine the content of N in CSAC-[APTS][Br]. Thermal stability of CSAC-[APTS][Br] was analyzed by thermogravimetric (TG) performed on a Perkin-Elmer Instrument Pyris1 TG analyzer. The sample was heated up to 600 °C at a rate of 5 °C /min under N2 atmosphere. 2.4. Continuous cycloaddition of CO2 to epichlorohydrin (ECH) in a packed bed The continuous cycloaddition of CO2 to ECH was carried out in a packed-bed reactor without using solvent (Figure S1). The packed column has an inner diameter of 1 cm and a length of 40 cm. 5 g of CSAC-[APTS][Br] was placed at the middle of the column with both ends filled with quartz granules. The reactor was heated by a tubular furnace and the temperature was controlled by a digital temperature controller. The pressure was controlled by a counterbalance valve installed at the outlet of the reactor. The flow rate of CO2 was controlled by a rotameter. Liquid ECH was pumped into an oven for preheating at 100 °C by an advection pump, then flowed through the reactor. The reactants were fed into the column through two respective inlet orifices at the top of the reactor. In all experiments, the flow rates of ECH and CO2 were 1 mL·min−1 and 50 mL·min−1, respectively. The reaction temperature was investigated


Page 9 of 29

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


at a range of 110-150 °C with a pressure of 1.4 MPa. The effluent was condensed and separated in a condenser at room temperature. ECH and epichlorohydrin carbonate (ECHC) were identified and quantified by gas chromatography (GC) equipped with a capillary column and FID detector (GC112A, DB-5, 30 m×0.53 nm). 2.5. Biogas upgrading in a packed bed The CSAC granule immobilized quaternary ammoniums with different anions were achieved by anion exchange. 20 g of the as-prepared CSAC-[APTS][Br] was mixed with 100 mL of 0.1 g/mL of NH4BF4, LiTf2N or KPF6. The mixture was stirred under ultrasonic for 30 minutes, then separated by suction filtration. The process was repeated until [Br-] ions were totally exchanged, which might be identified by adding a drop of 0.1 wt% AgNO3 solution to the filtrate. The CO2 adsorption/desorption experiments were conducted in a stainless steel packed column, which has an inner diameter of 3 cm and a length of 40 cm. The schematic diagram of the experimental setup is shown in Figure S2. In each test, 50 g of the CSAC granule supported quaternary ammonium was packed in the middle of the column with both ends filled with quartz granules. The column was placed in a tubular furnace. The temperature was controlled by a digital temperature controller. The operation pressure was controlled by a counterbalance valve installed at the outlet of the column. N2 was used as a purge gas, and the simulated biogas consisted of 76 vol% CH4, 23 vol% CO2 and 1 vol% H2S. They were provided by respective gas cylinders. The flow rates of N2 and biogas were controlled by rotameters. The composition of the effluent gas was determined by a CO2 gas detector (MOT500-M,



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 10 of 29

Shenzhen Keernuo Electronics Technology Co.) with an accuracy of 0.01%. The data are sent to a USB-based data acquisition board and recorded by a computer. Prior to adsorption, the adsorbents were first degassed at 100 °C in a N2 stream at a flow rate of ~200 mL/min for 0.5 h under atmospheric pressure. Subsequently, the column was cooled down to 20 °C. When the temperature was stabilized, the simulated biogas was introduced in the column with a flow rate of ~200 mL/min at 0.2MPa. Meanwhile, the adsorption time was recorded. The saturated adsorption was reached as the concentration of CO2 in the effluent was close to that in the simulated biogas. Afterwards, desorption was carried out by increasing the temperature to 60 °C with a rate of 10 °C/min, in which N2 was used as a purge gas at a flow rate of 200 mL/min under atmospheric pressure. Desorption was over until no CO2 was detected in the effluent. N2 purging was continued until the furnace was cooled down to the room temperature for the next adsorption/desorption experiment. 3. RESULTS AND DISCUSSION Figure 1 displays FT-IR spectra of samples. The band at 1400 cm−1 in Figure 1a is assigned to the bending vibration of phenolic hydroxyl on the oxidized CSAC, and the bands at 1045 and 1629 cm-1 were assigned to the C-O stretching vibration and C=O stretching vibration of carboxyl in aromatic ring, respectively.31-34 In Figure 1b and 1c, the bands centered at 797 cm-1 were assigned to the stretching vibration of Ar-O-Si.35-36 In addition, the out-of-plane bending vibration of -NH- was observed at 773 cm-1 in Figure 1b. Furthermore, the bands at 721, 1111, and 1580 cm−1 are due to the stretching vibration of −CH2− units,36 the stretching vibration of C−NH2, and the


Page 11 of 29

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


bending vibration of N−H in primary amine,32, 36-37 respectively. It further suggested the silane had been successfully grafted on the CSAC. FT-IR spectrum of the CSAC supported quaternary ammonium salts were shown in Figure 1c. After reaction of the primary amine on the aminosilylated CSAC granules with 1-bromobutane, the vibration of -NH- and C-NH2 disappeared. Instead, a band at 1174 cm-1 was observed in Figure 1c. It was ascribed to the framework vibration of C-CH3.38 Some characteristic elements of the samples were also detected by XPS (Figure S3). Compared to the oxidized CSAC in Figure S3a, the CSAC-[APTS] displayed Si2p and N1s electron signals after chemical grafting with the APTS as seen in Figure S3b. After reaction of the CSAC-[APTS] with 1-bromobutane, a signal assigned to the Br3d binding energy appeared for the CSAC-[APTS][Br] as shown in Figure S3c. Furthermore, the binding energy of N1s electrons in CSAC-[APTS] is 399.4 eV for the primary amine as seen in Figure 2a.39 However, the binding energy shifted to 401.2 eV in Figure 2b, indicating that quaternary ammonium was generated after reacting of the CSAC-[APTS] with 1-bromobutane.40 The BET surface area of the oxidized CSAC granules was 540 m2/g, and its average pore size and the pore volume were 1.87 nm and 0.363 cm3/g, respectively. After immobilization of the quaternary ammonium, the BET surface area, the average pore size and pore volume were decreased to 495 m2/g, 1.46 nm and 0.275 cm3/g, respectively. TG analyses were performed to analyze the thermal stability of the adsorbents. The TG curves for the raw CSAC and CSAC-[APTS][Br] are shown in Figure 3. It can be observed that decomposition temperature of the quaternary



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 12 of 29

ammonium on the CSAC was ~320 °C. Comparatively, the decomposition temperature was 200 °C for SiO2 supported quaternary ammonium as reported by Hou et al.41 Elemental analysis showed that the nitrogen amount in the CSAC supported quaternary ammonium was 1.34%, indicating that the ammonium concentration on the CSAC surface was 0.957 mmol/g . The cycloaddition reaction of CO2 and ECH was carried out in a packed-bed reactor without using solvent. When the reaction temperature was below 120 °C at a pressure of 1.4 MPa, ECH was in liquid state, and the reaction was a tri-phase system. Only CO2 that dissolved in ECH can get access to the active sites on the catalyst. Thus, Low conversion of ECH were observed below 120 °C as seen in Figure 4. When the temperature was increased to 130 °C, ECH was gasified and a gas-solid biphasic reaction system was formed in the reactor. Both CO2 and ECH might easily reach the catalyst surface, leading to a rapid increase of the conversion. The conversion reached 43.5% at 130 °C, and the corresponding turnover frequency (TOF) value was 64.6 h-1. The selectivity to ECHC was over 95% when the reaction temperature was lower than 140 °C. However, the selectivity began to decline at 150 °C due to possible side reactions such as polymerization or isomerization.42-43 Comparatively, Hou et al.41 prepared silica gel supported polymeric quaternary ammonium salt. The cycloaddition of CO2 and ECH was conducted in autoclave, and the epoxide conversion was only 35.5%. Baj et al.38 prepared multi-walled carbon nanotube bound quaternary ammonium chloride, and the conversion and TOF value were 53% and 38.52 h-1 in autoclave, respectively. Based on these results obtained


Page 13 of 29

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


over the immobilized quaternary ammoniums, it can be thought that the CSAC supported one exhibited the same good catalytic performance in a continuous flow-through reactor as those reported in the batch reactor. Continuous flowing test of 80 h was conducted in the packed-bed reactor at 130 °C and 1.4 MPa. The conversion of ECH slightly decreased at the beginning 50 h as seen in Figure 5, probably because trace amount of quaternary ammonium was physically adsorpted on the CSAC, and had a weak interaction with the carrier. Therefore, it was easily flushed away by the continuous flow-through reactants. However, the concersion stabilized at 39% after 50 h of catalytic performance. Biogas upgrading over the raw CSAC and quaternary ammonium modified CSAC was also carried out in a packed bed. The raw CSAC had a saturated CO2 capture capacity of 1.82 mmol/g at 20 °C and 0.5 MPa as seen in Figure 6. Grafting of quaternary ammonium obviously enhanced the CO2 capture capacity. According to reports,44-45 anion plays a key role for capturing CO2, while the cation is supposed to have a secondary role. Among the investigated anions in this study, the highest CO2 solubility was observed for the anion [Tf2N-]. Data in Figure 6 shows that CO2 solubility at 20 °C increased in an order of [Br-] < [BF4-] < [PF6-] < [Tf2N-]. The CSAC-[APTS][Tf2N] displayed a saturated CO2 capture capacity of 2.40 mmol/g under a pressure of 0.5 MPa. Without considering the adsorption contribution of the CSAC, per molar quaternary ammonium salt on the CSAC-[APTS][Tf2N] adsorbed 0.63 mol of CO2. The effect of temperature on biogas upgrading was also examined as the pressure was set at 0.2 MPa. Low temperature favored capturing CO2 as seen in



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 14 of 29

Figure 7. The CO2 adsorption capacity was 2.15 mmol/g for the CSAC-[APTS][Tf2N] at 20 °C, while it was reduced to 0.88 mmol/g at 50 °C. The similar trend was observed

for

other

anions

containing

quaternary

ammonium.

The

adsorption/desorption process as a function of time was seen in Figure 8. The saturated adsorption times were ~53 and ~61 min for raw CSAC and CSAC-[APTS][Tf2N], respectively. The corresponding desorption times were ~40 and ~47 min for raw CSAC and CSAC-[APTS][Tf2N], respectively. It indicated that grafting of quaternary ammonium enhanced the CO2 capture capacity. Besides the adsorption capacity of adsorbents, the adsorption heat and adsorption selectivity are also important for biogas upgrading. Energy cost associated with the separation method is one of the major barriers to commercialize biogas upgrading or the CO2 capture at large scale. The isosteric heat of adsorption of the adsorbents was calculated according to Clausius-Clapeyron Equation as seen Eq.1.46 The adsorption heat and adsorption selectivity of the adsorbents are represented in Table 1. Both the raw CSAC and the CSAC-[APTS] based adsorbents exhibited a very low adsorption heat, which was in a range of 20 to 30 KJ/mol. ∆H= -RT2 (

d(lnP) )n dT

(1)

In order to effectively upgrade the biogas, the adsorbents should have a high adsorption selectivity of CO2 over CH4. The adsorption selectivity was only ~67 % for the raw CSAC as shown in Table 1, whereas it was increased to ~85 % for the quaternary ammonium modified CSAC.


Page 15 of 29

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


Successive

adsorption/desorption

cyclability

was

evaluated

over

CSAC-[APTS][Tf2N] in the packed bed as seen in Figure 9. It was observed that only 5.5% of its initial CO2 adsorption capacity was lost after ten continuously adsorption/desorption cycles. While the cyclability for other functionalized materials suffered a significant loss after several cycles. For instances, Ren et al.47 applied N-(3-aminopropyl)aminoethyl tributylphosphonium amino acid salt functionalized porous silica particles to capture CO2. After four cycles, 5.7% of the adsorption capacity was lost. Mustafa et al.48 functionalized silica mesocellular foam with guanidinylated poly(allylamine) for CO2 capture. The adsorption capacity was decreased by 17% after five circles. Compared to these reports, the CSAC supported quaternary ammonium exhibited a relatively stable cyclability for continuous biogas upgrading in the packed bed.

4. CONCLUSIONS CSAC

granules

immobilized

quaternary

ammonium

was

successfully

synthesized and might be used in the packed-bed reactor. In continuous cycloaddition of CO2 to ECH, a gas-solid two-phase reactive system may be formed in the packed bed at a temperature higher than the boiling point of ECH. Thus, there is no need using a solvent to absorb CO2 and transport it to the catalyst surface. Moreover, the cycloaddition of CO2 to ECH can proceed in a continuous flow-through packed bed reactor under mild conditions, which is an obvious advantage over the batch reaction. This method should also be extended to support ionic liquids and phosphonium salts for continuous cycloaddition of CO2 in a packed bed. Compared to the raw AC, 15 ACS Paragon Plus Environment


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 16 of 29

immobilization of quaternary ammonium apparently enhanced the CO2 adsorption capacity and the adsorption selectivity of CO2 over CH4 in biogas upgrading. Meanwhile, the immobilized quaternary ammonium also exhibited a low adsorption heat and a relatively stable cyclability in the packed bed. Therefore, CSAC granules, a cheap and available biomass material, would be a prospective carrier to immobilize quaternary ammonium for performances in packed bed.

ACKNOWLEDGEMENTS The authors would like to acknowledge the national science and technology support program (Grant No.2012BAC18B02), the major scientific and technological project of Hainan Province (ZDZX2013002) and key project of science and technology of Hainan Province (ZDXM20130085) for financing this work.


Page 17 of 29

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


REFERENCES (1) Lee, E. H.; Park, D. W. Synthesis of cyclic carbonate from vinyl cyclohexene oxide and CO2 using ionic liquids as catalysts. Catal. Today 2008, 131, 130–134. (2) Gao, J.; Song, Q.W.; He, L.N. Preparation of polystyrene-supported Lewis acidic Fe(III) ionic liquid and its application in catalytic conversion of carbon dioxide. Tetrahedron 2012, 68, 3835–3842. (3) Xiao, L. F.; Su, D.; Wu W. Protic ionic liquids: A highly efficient catalyst for synthesis of cyclic carbonate from carbon dioxide and epoxides. J. CO2 Utilization

2014, 6, 1–6. (4) Calό, V.; Nacci, A.; Monopoli, A.; Fanizzi, A. Cyclic carbonate formation from carbon dioxide and oxiranes in tetrabutylammonium halides as solvents and catalysts. Org. Lett. 2002, 4, 2561–2563. (5) Zhou, Y. X.; Hu, S. Q.; Ma, X.M.; Han, B. X. Synthesis of cyclic carbonates from carbon dioxide and epoxides over betaine-based catalysts. J. Mol. Catal. A: Chem.

2008, 284, 52–57. (6) Zhao, Y.; Qi, X. H..; He, L. N. Quaternary ammonium salt-functionalized chitosan: An easily recyclable catalyst for efficient synthesis of cyclic carbonates from epoxides and carbon dioxide. J. Mol. Catal. A: Chem. 2007, 271, 284–289. (7) North, M.; Pasquale, R. Mechanism of Cyclic Carbonate Synthesis from Epoxides and CO2. Angew. Chem. 2009, 121, 2990–2992.



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 29

(8) Aoyagi, N.; Furusho, Y.; Endo, T. Effective synthesis of cyclic carbonates from carbon dioxide and epoxides by phosphonium iodides as catalysts in alcoholic solvents. Tetrahedron Lett. 2013, 54 (51), 7031–7034. (9) Ono, F.; Tomida, D.;Yokoyama, C. Rapid synthesis of cyclic carbonates from CO2 and epoxides under microwave irradiation with controlled temperature and pressure. J. Mol. Catal. A: Chem. 2007, 263, 223–226. (10) Wu, S. S.; Zhang, X. W.; Au, C. T. ZnBr2–Ph4PI as highly efficient catalyst for cyclic carbonates synthesis from terminal epoxides and carbon dioxide. Appl. Catal. A: Gen. 2008, 341, 106–111. (11) Jutz, F.; Grunwaldt, J. D.; Baiker, A. Mn(III)(salen)-catalyzed synthesis of cyclic organic carbonates from propylene and styrene oxide in “supercritical” CO2. J. Mol. Catal. A: Chem. 2008, 279, 94–103. (12) Meléndez, J.; North, M.; Pasqual, R. Synthesis of Cyclic Carbonates from Atmospheric Pressure Carbon Dioxide Using Exceptionally Active Aluminium(salen) Complexes as Catalysts. Eur. J. Inorg. Chem. 2007, 3323–3326. (13) Prasetyanto, E. A.; Ansari, M. B.; Min, B. H.; Park, S. E. Melamine tri-silsesquioxane bridged periodic mesoporous organosilica as an efficient metal-free catalyst for CO2 activation. Catal. Today 2010, 158, 252–257. (14) Cozzi, F. Immobilization of Organic Catalysts: When, Why, and How. Adv. Synth. Catal. 2006, 348, 1367–1390. (15) Avalos, M.; Babiano, R.; Cintas, P.; Jiménez, J. L.; Palacios, J. C. Greener Media in Chemical Synthesis and Processing. Angew. Chem. Int. Ed. 2006, 45, 3904–3908.


Page 19 of 29

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


(16) Christensen, C. H.; Rass-Hansen, J.; Marsden, C. C.; Taarning, E.; Egeblad, K. The Renewable Chemicals Industry. ChemSusChem. 2008, 1, 283–289. (17) Wong, W. L.; Wong, K. Y. Recent development in functionalized ionic liquids as reaction media and promoters. Can. J. Chem. 2012, 90, 1–16. (18) Cheng, W. G.; Chen, X.; Sun, J.; Wang, J. Q.; Zhang, S. J. SBA-15 supported triazolium-based ionic liquids as highly efficient and recyclable catalysts for fixation of CO2 with epoxides. Catal. Today 2013, 200, 117– 124. (19) Choi, H. J.; Selvaraj, M.; Park, D. W. Catalytic performance of immobilized ionic liquid onto PEG for the cycloaddition of carbon dioxide to allyl glycidyl ether. Chem. Eng. Sci. 2013, 100, 242-248. (20) Ashrafi M.; Prőll T.; Pfeifer C.; Hofbauer H. Experimental Study of Model Biogas Catalytic Steam Reforming: 1. Thermodynamic Optimization. Energy & Fuels

2008, 22, 4182–4189. (21) Plaza M. G.; Pevida C.; Arenillas A.; Rubiera F.; Pis J. J. CO2 capture by adsorption with nitrogen enriched carbons. Fuel 2007, 86, 2204–2212. (22) Stoeckli F.; Centeno T. A.; Fuertes A. B.; Muniz J. Porous structure of polyarylamide-based activated carbon fibres. Carbon 1996, 34, 1201–1206. (23) Blanco Lόpez M. C.; Martı́nez-Alonso A.; Tascόn J. M. D. Microporous texture of activated carbon fibres prepared from Nomex aramid fibres. Microporous Mesoporous Mater. 2000, 34, 171–179. (24) Sevilla M.; Valle-Vigon P.; Fuertes A. B. N-doped polypyrrole-based porous carbons for CO2 capture. Adv. Funct. Mater. 2011, 21, 2781–2787.



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 20 of 29

(25) Wang L. F.; Yang R. T. Significantly increased CO2 adsorption performance of nanostructured templated carbon by tuning surface area and nitrogen doping. J. Phys. Chem. C 2012, 116, 1099–1106. (26) Wu Z.; Webley P. A.; Zhao D. Post-enrichment of nitrogen in soft-templated ordered mesoporous carbon materials for highly efficient phenol removal and CO2 capture. J. Mater. Chem. 2012, 22, 11379–11389. (27) Jansen R. J. J.; van Bekkum H. Amination and ammoxidation of activated carbons. Carbon 1994, 32, 1507–1516.] (28) Wang, L.F.; Yang, R. T. Significantly Increased CO2 Adsorption Performance of Nanostructured Templated Carbon by Tuning Surface Area and Nitrogen Doping. J. Phys. Chem. C, 2012, 116, 1099–1106. (29) Espinal, L.; Poster, D. L.; Wong-Ng, W.; Allen, A. J.; Green, M. L. Measurement, Standards, and Data Needs for CO2 Capture Materials: A Critical Review. Environ. Sci. Technol., 2013, 47, 11960−11975. (30) Ryoo, R.; Joo, S. H.; Jun, S. Synthesis of Highly Ordered Carbon Molecular Sieves via Template-Mediated Structural Transformation. J. Phys. Chem. B., 1999, 103, 7743–7746. (31) Zhang, Y. L.; Xiang, S. L.; Wang, G. Q.; Jiang, H.; Xiong, C. R. Preparation and application of coconut shell activated carbon immobilized palladium complexes. Catal. Sci. Technol. 2014, 4, 1055-1063.


Page 21 of 29

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


(32) Chen, T. L.; Li, D. Q.; Jiang, H.; Xiong, C. R. High-performance Pd nanoalloy on functionalized activated carbon for the hydrogenation of nitroaromatic compounds. Chem. Eng. J. 2015, 259, 161–169. (33) Shin, S.; Jang, J.; Yoon, S. H.; Mochida, I. A study on the effect of heat treatment on functional groups of pitch based activated carbon fiber using FTIR. Carbon 1997, 35, 1739-1743. (34) Vicente, G. S.; Manuel, A. R.; Antonio, J. L. P.; Cristobal, V. C. Oxidation of activated carbon by hydrogen peroxide. Study of surface functional groups by FT-IR. Fuel 1994, 73, 387-395. (35) Xie, J. X. Application of Infrared spectrum in organic chemistry and pharmaceutical chemistry. Beijing: Sci.Pre. 2001. (36) Wang, L.; Wang, S.; Deng, X. Y.; Zhang, Y. C.; Xiong, C. R. Development of Coconut Shell Activated Carbon-Tethered Urease for Degradation of Urea in a Packed Bed. ACS Sustain. Chem. Eng. 2014, 2, 433-439. (37) Kang, Y.; He, J.; Guo, X. D.; Guo, X.; Song, Z. H. Influence of pore diameters on the immobilization of lipase in SBA-15. Ind. Eng. Chem. Res. 2007, 46 (13), 4474−4479. (38) Baj, S.; Krawczyk, T.; Jasiak, K.; Siewniak, A.; Pawlyta, M. Catalytic coupling of epoxides and CO2 to cyclic carbonates by carbon nanotube-supported quatermary ammonium salts. Appl. Catal. A: Gen. 2014, 488, 96-102.



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 29

(39) Graf, N.; Yegen, E.; Gross, T.; Lippitz, A.; Weigel, W.; Krakert, S.; Terfort, A.; Unger, W. E.S. XPS and NEXAFS studies of aliphatic and aromatic amine species on functionalized surfaces. Surface Science 2009, 603, 2849-2860. (40) Wagner, C. D. Handbook of X-ray photoelectron spectroscopy. Perkin-Elmer,

1979. (41) Song, B. N.; Guo, L.; Zhang, R.; Zhao, X. G.; Gan, H. M.; Chen, C.; Chen, J. Z.; Zhu, W. W.; Hou, Z. S. The polymeric quaternary ammonium salt supported on silica gel as catalyst for the efficient synthesis of cyclic carbonate. J. CO2 Utilization 2014, 6, 62–68. (42) Appaturi, J. N.; Adam, F. A facile and efficient synthesis of styrene carbonate via cycloaddition of CO2 to styrene oxide over ordered mesoporous MCM-41-Imi/Br catalyst. Appl Catal B: Environ. 2013, 136– 137, 150– 159. (43)

Dai,

W.

L.;

Chen,

L.;

Yin,

S.

F.;

Luo,

S.

L.;

Au,

C.

T.

3-(2-Hydroxyl-Ethyl)-1-Propylimidazolium Bromide Immobilized on SBA-15 as Efficient Catalyst for the Synthesis of Cyclic Carbonates via the Coupling of Carbon Dioxide with Epoxides. J. Catal. Lett. 2010, 135, 295-304. (44) Aki, S. N. V. K.; Mellein, B. R.; Saurer, E. M.; Brennecke, J. F. High-Pressure Phase Behavior of Carbon Dioxide with Imidazolium-Based Ionic Liquids. J. Phys. Chem. B 2004, 108, 20355−20365. (45) Anthony, J. L.; Anderson, J. L.; Maginn, E. J.; Brennecke, J. F. Anion Effects on Gas Solubility in Ionic Liquids. J. Phys. Chem. B 2005, 109, 6366−6374.


Page 23 of 29

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


(46) Al-Muhtaseb, ; Ritter, J. A. Roles of Surface Heterogeneity and Lateral Interactions on the Isosteric Heat of Adsorption and Adsorbed Phase Heat Capacity. J. Phys. Chem. B 1999, 103, 2467–2479. (47) Ren, J.; Wu, L.; Li, B. G. Preparation and CO2 Sorption/Desorption of N-(3-Aminopropyl)Aminoethyl Tributylphosphonium Amino Acid Salt Ionic Liquids Supported into Porous Silica Particles. Ind. Eng. Chem. Res. 2012, 51, 7901–7909. (48) Alkhabbaz, M. A.; Khunsupat, R.; Jones, C. W. Guanidinylated poly(allylamine) supported on mesoporous silica for CO2 capture from flue gas. Fuel 2014, 121, 79–85.



3

3

Scheme 1 Synthesis of the CSAC supported quaternary ammonium bromide.

a Transmittance (%)

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 24 of 29

b c

773

1580 1629

797 721 1400

1111 1174 1045

2000 1800 1600 1400 1200 1000

800

600

400

-1

Wavenumber (cm ) Figure 1. FT-IR spectra of (a) Oxidized CSAC, (b) CSAC-[APTS] and (c) CSAC-[APTS][Br].


Page 25 of 29

b

Intensity (a.u)

+ N

a

NH2

Intensity (a.u)

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


392

396

400

404

408

Binding energy (eV) Figure 2. XPS spectra of N1s. (a) CSAC-[APTS] and (b) CSAC-[APTS][Br].



100

a

0.0

TG (%)

-0.1 80

-0.2 70

b

DTA (uV/mg)

b

90

-0.3

60

-0.4 600

50

100

200

300 400 Temperature (℃)

500

Figure 3. TG curves of (a) raw CSAC, (b) CSAC-[APTS][Br]. The solid lines represent TG curves, the dash line represents DTA curve.

Conversion of ECH Selectivity to ECHC

100

90

90

80

80

70

70

60

60

50

50

40

40

30

30

20

20

10

10

0

Selectivity to ECHC (%)

100

Conversion of ECH (%)

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 26 of 29

0 110

120

130

140

150

Temperature (°C) Figure 4. Effect of temperature on the conversion of ECH and selectivity to ECHC in

a packed bed at a pressure of 1.4 MPa.


Page 27 of 29

60

Conversion of ECH (%)

55 50 45 40 35 30 25 20 10

20

30

40

50

60

70

80

Running time (h) Figure 5. Plot of the conversion of ECH vs time in the packed bed over the CSAC supported ammonium bromide at 130 °C and 1.4 MPa.

2.4 CO2 adsorption capacity (mmol/g)

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


2.0

1.6 Raw CSAC CSAC-[APTS][Br] CSAC-[APTS][BF4]

1.2

CSAC-[APTS][PF6] CSAC-[APTS][Tf2N]

0.1

0.2

0.3 Pressure (MPa)

0.4

0.5

Figure 6. Effect of pressure on the CO2 adsorption capacity in biogas upgrading over the CSAC supported ammoniums in a packed bed at 20 °C.



2.5 CO2 absorption capacity (mmol/g)

Raw CSAC CSAC-[APTS][Br] CSAC-[APTS][BF4] CSAC-[APTS][PF6] CSAC-[APTS][Tf2N]

2.0

1.5

1.0

0.5 20

30 40 Temperature (℃)

50

Figure 7. Effect of temperature on the CO2 adsorption capacity in biogas upgrading over the CSAC supported ammoniums in a packed bed under 0.2 MPa.

40

CO2 concentration of outlet gas (%)

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 28 of 29

b

35 a 30 25

53 min Adsorption 20 15

20 ℃

10 5

61 min Adsorption

Desorption 60 ℃

20 ℃

40 min

Desorption 60 ℃ 47 min

0 0

20

40 60 80 100 120 0 Time (min)

20 40 60 80 100 120 140 Time (min)

Figure 8. Adsorption-desorption process as a function of time over (a) raw CSAC and (b) CSAC-[APTS][Tf2N]. Adsorption was conducted at 20 °C and 0.2 MPa with a flow rate of 200 mL/min. Desorption was performed at 60 °C and atmospheric pressure with a N2 flow of 200 mL/min.


Page 29 of 29

100

Remaining CO2 capacity (%)

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


90 80 70 60 50

1

2 3 4 5 6 7 8 9 Adsorption-desorption recycle times

10

Figure 9. Adsorption-desorption cycles for biogas upgrading in the packed bed over

the CSAC-[APTS][Tf2N].

Table 1. Isosteric heat of adsorption and adsorption selectivity of CO2 over the adsorbents in packed bed. Adsorption Adsorbents ∆H (KJ/mol) selectivity of CO2 over CH4 (%) Br 22 ~ 24 73 ± 2 BF4 23 ~ 25 83 ± 2 CSAC-[APTS] PF626 ~ 28 85 ± 2 Tf2N26 ~ 28 85 ± 2 Raw CSAC 21 ~ 23 67 ± 2


Coconut Shell Activated Carbon Supported Quaternary Ammonium for

Recommend Documents