SYNTHESIS, CHARACTERIZATION, ADSORPTION AND THERMODYNAMIC STUDIES OF PURE AND BINARY CO<sub>2</sub>-N<sub>2</sub> MIXTURES ON OXYGEN ENRICHED NANOSTRUCTURED CARBON ADSORBENTS

Tiwari, Deepak; Bhunia, Haripada; Bajpai, Pramod K.

doi:10.1590/0104-6632.20190363s20180036

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Separation Processes • Braz. J. Chem. Eng. 36 (3) • Jul-Sep 2019 • https://doi.org/10.1590/0104-6632.20190363s20180036 copy

SYNTHESIS, CHARACTERIZATION, ADSORPTION AND THERMODYNAMIC STUDIES OF PURE AND BINARY CO₂-N₂ MIXTURES ON OXYGEN ENRICHED NANOSTRUCTURED CARBON ADSORBENTS

Authorship SCIMAGO INSTITUTIONS RANKINGS

Abstract

Oxygen enriched porous carbons have been synthesized by a nanocasting technique using mesoporous zeolite as template and epoxy resin as precursor. Characterization results show the effect of the nanocasting technique on the development of heterogeneous surface, high basicity, and high surface area of 686.37 m²g^-1, beneficial for CO₂ adsorption. Pure component adsorption isotherms were correlated with Langmuir, Sips, and dual-site Langmuir (DSL) models and found that Sips and DSL isotherm models fitted well, indicating thre heterogeneous nature of the adsorbent surface. Dynamic breakthrough data for the binary system CO₂-N₂ were obtained using a fixed-bed column at different adsorption temperatures (30-100 °C) and CO₂ feed concentrations (5-12.5% by volume). The developed adsorbent shows high adsorption capacity with complete regenerability over four adsorption/desorption cycles. Prediction of binary components (CO₂-N₂) was made by using extended Sips, extended DSL and IAST (ideal adsorbed solution theory) by utilizing pure component adsorption isotherm data. Experimental and predicted equilibrium data were compared with breakthrough curve data and it was found that the extended forms (Sips and DSL) indicated under-predicted CO₂ adsorption equilibria because of differences in adsorptive strengths of CO₂ and N₂ molecules. Also, adsorption equilibria were closely predicted using IAST theory. Asymmetric x-y diagrams from Raoult’s law indicated positive deviation, implying that as the CO₂ gas phase molar fraction increases, total adsorbed amounts increase. Negative values of molar Gibbs free energy change suggested feasibility of the adsorption process. Formation of a more ordered configuration of CO₂ molecules on the adsorbent surface was seen as a higher heat of adsorption was exhibited for CO₂ as compared to N₂.

Keywords:
Nanocasting, extended sips; Extended DSL; IAST; Selectivity

Component	Parameter	Temperature (°C)
Component	Parameter	30	50	75	100
CO₂	q_m (mmol g^-1)	1.45	1.23	0.93	0.68
	b (atm^-1)	3.89	3.03	2.25	1.97
	SSE (%)	22.31	19.83	19.65	19.20
	b_o (atm^-1)	0.09
	B (kJ mol^-1)	-9.36
N₂	q_m (mmol g^-1)	1.37	0.70	0.55	0.43
	b (atm^-1)	0.15	0.12	0.08	0.03
	SSE (%)	4.02	5.66	6.84	7.55
	b_o (atm^-1)	0.0005
	B (kJ mol^-1)	-14.35

Component	Parameter	Temperature (°C)
Component	Parameter	30	50	75	100
CO₂	q_m (mmol g^-1)	2.80	2.60	2.06	2.40
	b (atm^-c)	0.80	0.66	0.47	0.24
	c	1.66	1.62	1.58	1.53
	SSE (%)	2.84	3.35	5.59	9.70
	b_o (atm^-c)	0.002
	B (kJ mol^-1)	-15.70
N₂	q_m (mmol g^-1)	0.87	0.81	0.50	0.27
	b (atm^-c)	0.14	0.13	0.05	0.01
	c	1.01	0.99	0.99	1.04
	SSE (%)	6.84	5.83	3.42	1.24
	b_o (atm^-c)	0.0072
	B (kJ mol^-1)	-31.14

Component	Parameter	Temperature (°C)
Component	Parameter	30	50	75	100
CO₂	q_1,m (mmol g^-1)	1.60	1.14	0.20	0.04
	q_2,m (mmol g^-1)	0.29	1.65	0.92	0.07
	b₁ (atm^-1)	55.34	32.49	21.08	11.08
	b₂ (atm^-1)	1.82	1.26	0.93	0.88
	SSE (%)	2.72	2.70	2.64	3.24
	b_o,1 (atm^-1)	0.273
	b_o,2 (atm^-1)	0.00017
	B (kJ mol^-1)	48.06
	E₂ (kJ mol^-1)	-30.15
N₂	q_1,m (mmol g^-1)	0.68	0.35	0.28	0.21
	q_2,m (mmol g^-1)	0.68	0.35	0.28	0.21
	b₁ (atm^-1)	0.15	0.12	0.06	0.03
	b₂ (atm^-1)	0.15	0.12	0.06	0.03
	SSE (%)	2.02	4.66	3.84	4.55
	b_o,1 (atm^-1)	0.032
	b_o,2 (atm^-1)	0.00046
	B (kJ mol^-1)	43.676
	E₂ (kJ mol^-1)	-14.354

Temperature	CO₂ mole fraction in feed	CO₂ adsorption capacity (mmol g^-1)
Temperature	CO₂ mole fraction in feed	Experimental	Sips model	DSL model	IAST-Sips model	IAST-DSL model
30 °C	0.050	0.30	0.29	0.29	0.31	0.30
	0.075	0.39	0.35	0.36	0.38	0.37
	0.100	0.49	0.41	0.41	0.45	0.42
	0.125	0.65	0.64	0.64	0.63	0.67
50 °C	0.050	0.21	0.23	0.23	0.25	0.23
	0.075	0.30	0.28	0.29	0.31	0.29
	0.100	0.41	0.34	0.34	0.39	0.37
	0.125	0.49	0.38	0.38	0.50	0.46
75 °C	0.050	0.19	0.12	0.11	0.19	0.16
	0.075	0.27	0.16	0.14	0.26	0.24
	0.100	0.33	0.19	0.17	0.36	0.34
	0.125	0.39	0.21	0.19	0.40	0.35
100 °C	0.050	0.16	0.09	0.07	0.15	0.13
	0.075	0.22	0.11	0.08	0.25	0.21
	0.100	0.28	0.13	0.09	0.26	0.22
	0.125	0.32	0.15	0.13	0.27	0.29

Temperature	CO₂ mole fraction in feed	Selectivity
Temperature	CO₂ mole fraction in feed	Experimental	Sips model	DSL model	IAST-Sips model	IAST-DSL model
30 °C	0.050	74.63	72.39	94.37	30.28	122.98
	0.075	81.91	60.98	82.49	26.18	117.60
	0.100	102.28	54.08	75.14	23.57	115.33
	0.125	114.13	49.35	70.12	21.78	114.10
50 °C	0.050	71.99	81.55	105.48	206.39	133.71
	0.075	96.17	69.93	93.46	201.47	129.72
	0.100	133.75	62.83	86.13	201.48	128.45
	0.125	146.26	57.93	81.13	204.65	128.22
75 °C	0.050	131.21	71.50	77.74	95.06	92.21
	0.075	131.93	61.95	69.04	102.76	87.15
	0.100	160.30	56.05	64.26	108.63	85.98
	0.125	155.22	51.95	61.20	114.39	85.21
100 °C	0.050	140.37	79.80	30.28	123.39	90.06
	0.075	133.68	68.47	26.18	117.16	81.30
	0.100	150.60	61.53	23.57	113.43	77.90
	0.125	138.94	56.73	21.78	126.51	75.89

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[1] * Corresponding author: Haripada Bhunia - E-mail: hbhunia@thapar.edu

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SYNTHESIS, CHARACTERIZATION, ADSORPTION AND THERMODYNAMIC STUDIES OF PURE AND BINARY CO2-N2 MIXTURES ON OXYGEN ENRICHED NANOSTRUCTURED CARBON ADSORBENTS

Abstract

SYNTHESIS, CHARACTERIZATION, ADSORPTION AND THERMODYNAMIC STUDIES OF PURE AND BINARY CO₂-N₂ MIXTURES ON OXYGEN ENRICHED NANOSTRUCTURED CARBON ADSORBENTS