UPGRADING OF PETROLEUM RESIDUE BY NITROGEN DOPING FOR CO 2 ADSORPTION

UPGRADING OF PETROLEUM RESIDUE BY NITROGEN DOPING FOR CO 2 ADSORPTION Nattha Chalermwat a,b, Thanyalak Chaisuwan a,b, Uthaiporn Suriyapraphadilok*,a,b a The Petroleum and Petrochemical College, Chulalongkorn University, Bangkok, Thailand b Center of Excellence on Petrochemical and Materials Technology, Bangkok, Thailand Keywords: CO 2 Capture, Adsorption, Petroleum Residue, Nitrogen Doping, Carbon Adsorbent ABSTRACT Carbon dioxide (CO 2 ) is one of the anthropogenic greenhouse gases and it is the major contributor to global warming. Carbon adsorbent becomes a promising porous solid adsorbent to capture CO 2 at below 200 C but it still gives low adsorption capacity. An introduction of nitrogen content on carbon adsorbents has been studied to improve their CO 2 adsorption capacity. In this research, petroleum residue (PR) had been selected as a carbon precursor and furfurylamine-based benzoxazine (BZ) was used as a nitrogen source. The effect of nitrogen doping ratio on petroleum residue (BZ:PR) was investigated with BZ:PR ratio of 0.7:1, 1:1, and 3:1. Then, the nitrogen-doped petroleum residue was produced via a thermal process followed by a physical activation using CO 2 at 900 C. The preliminary results showed that increasing the nitrogen doping ratio can improve the CO 2 adsorption capacity. Carbon adsorbent with BZ:PR ratio of 3:1 exhibited the highest CO 2 adsorption capacities of ca. 2.16 mmol/g at 40 C, 350 psia. *uthaiporn.s@chula.ac.th INTRODUCTION The increase in the earth s surface temperature due to the escalation of the atmospheric greenhouse gases concentrations has been concerned these days. Carbon dioxide (CO 2 ) is one of the anthropogenic greenhouse gases contributed to global warming. Today s CO 2 concentration in the atmosphere from human activities has just passed over 400 parts per million (ppm) in March, 2016, which is chronologically rapid increased about 43% from 280 ppm in 1750 (IPCC, 2002). To mitigate this problem, the postcombustion technology is more desirable when dealing with the low concentration CO 2 removal from power plants, which is typically existed about 3-15% v/v in the exhaused flue gases (D'Alessandro et al., 2010). The adsorption process using porous solid materials such as activated carbons have become an alternative way to capture the exhausted CO 2 from power plants. This technique is developed to overcome the corrosion problems and also the high energy consuming of the absorption process. Activated carbons are the promising porous solid adsorbent for capturing CO 2 at low temperature (below 200 C) due to its meso- and microporous structures, high specific surface area, and wide availability of raw material (Goel et al., 2015). However, it still gives poor selectivity and relatively low adsorption capacity. So, the challenging ways to improve their adsorption capacity are the use of various nitrogen-enriched carbon sources or the preparation of nitrogen-embodied carbon adsorbents (Wang et al., 2011). In this work, petroleum residues have been selected as the carbon precursor for doping with nitrogen-enriched polymers because they compose of very high carbon content (ca. 90%). Besides, it is one of the ways to upgrade petroleum residues into more valuable Petrochemical and Materials Technology Tuesday May 23, 2017, Pathumwan Princess Hotel, Bangkok, Thailand Page 1

products. The nitrogen-enriched polymer such as furfurylamine-based benzoxazine is used to enhance the adsorption capacity for CO 2 adsorption due to its similar aromatic structure, thus bonding of the two materials during carbonization will help forming strong coke structure. The enriched nitrogen-doped petroleum residues are then produced via a thermal process followed by a physical activation to obtain activated carbon for the CO 2 adsorption process. EXPERIMENTAL A. Materials All chemicals were used without further purification. Furfurylamine ( 97%) was purchased from Merck Co., Ltd. Paraformaldehyde (95%) was purchased from Sigma Aldrich. Phenol detached crystals (99.99%) was purchased from Fisher Bioreagent and petroleum residue was kindly supported from Thai Oil Public Co., Ltd. B. Preparation of Benzoxazine Monomer Benzoxazine monomer (BZ) was synthesized by using paraformaldehyde (95%), phenol, and furfurylamine ( 97%) as precursors with a molar ratio of 2:1:1. Paraformaldehyde and phenol were heated at 80 C until it melted as a homogeneous mixture. After that, slowly added furfurylamine into the mixture and stirred at 110 C for 1 h until obtaining a clear yellow viscous liquid. Benzoxazine monomer was further used as a nitrogen dopant to produce carbon adsorbent. C. Preparation of Nitrogen-doped Petroleum Residue-based Carbon Adsorbent Petroleum residue (PR) were heated-treated in a closed system reactor at 400 C for 10 min to increase its molecular weight. After that, heat-treated petroleum residue and the nitrogen precursor were mixed together at various BZ:PR mass ratio of 0.7:1, 1:1, and 3:1. For the mixture, it was heated under a heating rate of 5 C/min to 100 C, a heating rate of 3 C/min to 150 C, hold for 30 min followed by a heating rate of 3 C/min to 200 C, and hold for 1 h according to the investigation of curing behavior by DSC. After that, the mixture was rested to cool down to room temperature. Then, carbonization was performed at the carbonization temperature of 600 C for 2 h under N 2 atmosphere. The carbonized product was then activated by using CO 2 at 900 C for 2 h. Finally, the carbon adsorbent was oven dried at 110 C. D. Adsorption Measurement The pressure decay adsorption method was used to measure the CO 2 adsorption capacity of the adsorbent. The volume of adsorption column was measured by using helium expansion and calculated from the ideal gas law. The CO 2 adsorption capacity was determined by measuring the beginning pressure and equilibrium pressure. The diagram of adsorption apparatus was shown in Figure 1. Petrochemical and Materials Technology Tuesday May 23, 2017, Pathumwan Princess Hotel, Bangkok, Thailand Page 2

Figure 1 The adsorption measurement system. E. Characterization and Measurement FTIR spectra of benzoxazine mononomer and polybenzoxazine were obtained by Fourier Transform Infrared Spectrometer (FT-IR), Thermo Scientific, Nicolet is5, with adsorption mode and using 16 scans to identify functional groups of benzoxazine and polybenzoxaine in the range of 4000-650 cm -1. To investigate the curing behavior, Differential Scanning Calorimeter (DSC), Netzsch, DSC204 F1 Pheonix, was employed to obtain the thermal step-curing. The samples were heated from 0 to 300 C at a heating rate of 10 C/min under N 2 atmosphere with a flow rate of 20 ml/min. The elemental compositions of petroleum residue (as received) and nitrogen-doped carbon adsorbents, including carbon (C), hydrogen (H), and nitrogen (N) and sulfur (S), were determined by a CHNS analyzer (Leco, Truspec Micro). The N 2 adsorption-desorption isotherm at 77 K were measured using Quantachrome, AS-1MP to investigate the specific surface area and pore structure of nitrogen-doped carbon adsorbents. The specific surface area was calculated from the Brunauer-Emmett-Teller (BET) plot of the nitrogen adsorption isotherm. The micropore volume was calculated from the standard t-plot method. RESULTS AND DISCUSSION A. Characterization of furfurylamine-based benzoxazine monomer and polybenzoxazine The curing behavior of benzoxazine monomer and polybenzoxazine were investigated by using a Differential Scanning Calorimetry (DSC). As shown in Figure 2, the behavior of benzoxazine monomer is very highly exothermic. The exothermic peaks of benzoxazine monomer appeared at 230 and 260 C. The ring-opening polymerization of oxazine ring is located between 170 and 230 C. At above 250 C, it is associated with the ring-opening polymerization of the furan group. So, it is then suggested for the stepcuring to obtain polybenzoxazine. After curing at 150 C (30min) and 200 C (1h), the exothermic peak of polybenzoxazine at around 170-230 C is reduced, suggesting that the ring-opening polymerization was occurred. An endothermic peak at around 220 C is the arrangement of structure (pi stacking). At above 250 C, the double bond of imide functional group was broken down. So, the polymerization of polybenzoxazine derived from furfurylamine was not completed yet after the thermal curing but it will be completely polymerized in the carbonization process due to the slow heating rate of 1 C/min. Petrochemical and Materials Technology Tuesday May 23, 2017, Pathumwan Princess Hotel, Bangkok, Thailand Page 3

Figure 2 DSC thermograms of furfurylamine-based (a) benzoxazine monomer (b) polybenzoxazine. The FTIR spectra of furfurylamine-based benzoxazine monomer and polybenzoxazine were illustrated in Figure 3. The band of benzoxazine monomer around 1,488 cm -1 showed the characteristic of di-substituted benzene ring. Other characteristic bands of benzoxazine were 1331 cm -1 (CH 2 wagging), 1220 and 1011 cm -1 (symmetric and asymmetric stretching of C-O-C). The band of 960-910 cm -1 showed the out of plane C- H vibration of the benzene attached to an oxazine ring, which was overlapped with the characteristic of furan ring (Ishida, 2011). For polybenzoxazine, the absorption band at 926 cm -1 disappeared after curing, indicating that the ring-opening of oxazine ring structure was occurred and PBZ was cured using the proposed step-curing process. The other distinctive absorption band was appeared at 1456 cm -1 (tri-substituted benzene ring), which was shifted from 1488 cm -1 (the di-subsitituted benzene ring). Moreover, the absorption band at 1624 cm -1 became broad after curing (Liu et al., 2005), indicating that furan ring was taken part in the polymerization reaction due to the formation of disubstituted furan ring. Figure 3 FTIR spectra of furfurylamine-based (a) benzoxazine monomer (b) polybenzoxazine. B. Characterization of Petroleum Residue Petroleum residue from the bottom of Vacuum Distillation Unit (as received) was characterized to determine the elemental compositions by a CHNS analyzer. Petrochemical and Materials Technology Tuesday May 23, 2017, Pathumwan Princess Hotel, Bangkok, Thailand Page 4

Table 1 The ultimate analysis of petroleum residue (as received) % C % N % H % S % O Petroleum Residue (by difference) 87.6 ± 0.68 0.3 ± 0.003 10.7 ± 0.0 2.34 ± 0.04 ~ 0 As shown in Table 1, petroleum residue (as received) consists of high carbon content of 87.6 wt%, hydrogen content of 10.7 wt%, and low nitrogen content of 0.3 wt%. Moreover, it contains high sulfur content (2.34 wt% of sulfur). Due to the high carbon content of carbon material precursor, it can give high char yield on the carbonization process. C. Characterization of nitrogen-doped petroleum residue-based carbon adsorbent Nitrogen-containing carbon adsorbents can be prepared by mixing heat-treated petroleum residue with benzoxazine monomer with various BZ:PR mass ratio of 0.7:1, 1:1, and 3:1, followed by a thermal step-curing process stated earlier. The carbonization steps are as follows: 25-250 C at 3 C /min; 250-600 C at 1 C/min; and hold at 600 C for 2 h. Physical activation by CO 2 at 900 C was then performed in situ for 2 h and the sample was cooled down to room temperature under inert atmosphere. Table 2 shows the elemental compositions including carbon (C), hydrogen (H), and nitrogen (N) determined by a CHN analyzer (Leco, Truspec Micro). As results, the amount of nitrogen content increased when increasing the nitrogen doping ratio. Table 2 The ultimate analysis of carbon adsorbents Sample % C % N % H % Other (by difference) 0.7:1 BZPRAC 600/900 52.07 ± 0.90 1.20 ± 0.03 1.03 ± 0.04 45.70 ± 0.97 1:1 BZPRAC 600/900 80.33 ± 2.54 1.58 ± 0.07 1.17 ± 0.04 16.91 ± 2.59 3:1 BZPRAC 600/900 65.43 ± 4.35 2.09 ± 0.12 1.06 ± 0.09 31.41 ± 4.52 The main textural properties of nitrogen-doped carbon adsorbent are presented in Table 3. It was found that activated carbons synthesized from heat-treated petroleum residue and furfurylamine-based benzoxazine had very low specific surface area and also exhibited a very small total pore volume. As we tried to change the carbonization step by using very slow heating of 0.5 C/min, the texture of adsorbent still had no change. It was due to the petroleum residue contained large molecules of volatile matters. In addition, furfurylamine-based benzoxazine had high structural strength property. So, it was difficult to generate pore inside the materials. Table 3 N 2 /77 K textural properties of carbon adsorbents. Adsorbent S BET (m 2 /g) a V total (cm 3 /g) b V micro (cm 3 /g) c 0.7:1 BZPRAC 600/900 1:1 BZPRAC 600/900 3:1 BZPRAC 600/900 V meso (cm 3 /g) d D p (nm) e 20.76 0.0472 0.0063 0.0409 9.91 11.02 0.0137 0.0050 0.0087 4.98 86.04 0.0492 0.0374 0.0118 2.29 Petrochemical and Materials Technology Tuesday May 23, 2017, Pathumwan Princess Hotel, Bangkok, Thailand Page 5

a S BET : specific surface area calculated using Brunauer Emmett Teller equation at a relative pressure range (P/P 0 ) = 0.05-0.3. b V total : total pore volume estimated at a relative pressure P/P 0 = 0.996. c V micro : micropore volume determined from the t-plot method. d V meso : mesopore volume determined from the subtraction of micropore volume from total pore volume. e D p : average pore diameter. D. CO 2 Adsorption Performances The CO 2 adsorption isotherm of carbon adsorbent materials was measured by a volumetric method. Figure 4 illustrates the CO 2 uptake of benzoxazine-containing petroleum residue-based carbon adsorbent with BZ:PR ratio of 0.7:1, 1:1, and 3:1 at 40 C and different equilibrium pressures. It was shown that the CO 2 adsorption capacities at 40 C of carbon adsorbents increased when increasing the nitrogen doping ratio, which was coherent with the nitrogen content result. As the previous results indicating that carbon adsorbents had very low surface area and porosity, which were the main key factors for physisorption. So, the main contribution of this adsorption was the nitrogen content on the carbon surface. It might be the effect of chemisorption only. The carbon adsorbent with BZ:PR ratio of 3:1, which was carbonized at 600 C under N 2 atmosphere and activated by CO 2 at 900 C (3:1 BZPRAC 600/900), exhibited the highest CO 2 uptake ca. 2.16 mmol/g at 350 psia. Figure 4 CO 2 adsorption performances of nitrogen-doped petroleum residue-based carbon adsorbents at 40 C. CONCLUSIONS Furfurylamine-based benzoxazine monomer was successfully synthesized via the solvent-less method. Also, the mixture of benzoxazine monomer and heat-treated petroleum residue was successfully cured under the thermal curing behavior from the investigation from DSC. For N-doped carbon adsorbents, the CO 2 adsorption capacities keep increased when increasing the nitrogen content due to the effect of chemisorption. However, they still gave low CO 2 adsorption performances because of their low specific surface area and pore volume. Thus, petroleum residue (as received) and furfurylaminebased benzozaxine might not be suitable as a precursor for CO 2 adsorbent. Petrochemical and Materials Technology Tuesday May 23, 2017, Pathumwan Princess Hotel, Bangkok, Thailand Page 6

ACKNOWLEDGEMENTS This thesis work was funded by Center of Excellence on Petrochemical and Materials Technology; and Grant for International Integration: Chula Research Scholar, Ratchadaphiseksomphot Endowment Fund, Chulalongkorn University. Furthermore, I extend the gratitude to Thai Oil Public Company Limited for providing petroleum residue. REFERENCES D'Alessandro, D.M., Smit, B. and Long, J.R. (2010) Angew. Chem., Int. Ed. 49 (35), 6058-6082. Goel, C., Bhunia, H. and Bajpai, P.K. (2015) J. Environ. Sci. 32, 238-248. IPCC. (2002). Climate change 2001: the scientific basis. Contribution of Working Group 1 to the Third Assessment Report of the Intergovernmental Panel on Climate Change, edited by J. T. Houghton, Y. Ding, D. J. Griggs, M. Noguer, P. J. van der Linden, X. Dai, K. Maskell and C. A. Johnson (eds). Cambridge University Press, Cambridge. Ishida, H. (2011). Handbook of Benzoxazine Resins. pp. 3-81. Elsevier, The Netherlands. Liu, Y.-L. and Chou, C.-I. (2005) J. Polym. Sci. A Polym. Chem. 43 (21), 5267-5282. Wang, Q., Luo, J., Zhong, Z. and Borgna, A. (2011) Energy Environ. Sci. 4 (1), 42-55. Petrochemical and Materials Technology Tuesday May 23, 2017, Pathumwan Princess Hotel, Bangkok, Thailand Page 7