Diffusion mechanism and effect of mass transfer limitation during the adsorption of CO₂ by polyaspartamide in a packed-bed unit

Figures & data

Figure 1. Schematic diagram of the experimental set up. (Adapted and modified from Yoro et al. 2017).

Table 1. Diffusional mass transfer parameters for the adsorption of CO₂ on polyaspartamide at specific operating conditions compared with a recent study.

Parameters	Experiment 1	Experiment 2	Experiment 3	Reference
Flow rate, mL/s	1.50	2.00	2.50	This study
	1.00	2.00	5.00	Lin et al. (2017)
Biot number, Bi	17.80	22.45	30.74	This study
	18.60	23.43	31.80	Lin et al. (2017)
Boyd number, B	4.15	4.15	4.15	This study
	5.23	5.23	5.23	Lin et al. (2017)
Kid (m s^−1)	1.24 × 10^−4	1.58 × 10^−4	2.13 × 10^−4	This study
	1.33 × 10^−5	1.39 × 10^−5	1.58 · 10^−5	Piccin et al. (2013)
Ds (m ^2s^−1)	0.21 × 10^−14	0.84 × 10^−14	1.30 × 10^−14	This study
	1.36 × 10^−9	2.87 × 10^−9	4.89 × 10^−9	Piccin et al. (2013)

Table 2. Captured CO₂ at different adsorption times.

Inlet CO2 composition	Time	Outlet CO2 composition	Percentage captured CO2
(%)	(s)	(%)	(%)
15.0	0	15.0	0
15.0	300	13.0	36.7
15.0	600	10.5	56.7
15.0	900	8.5	70.0
15.0	1200	5.5	86.7

Table 3. Models explored and assumptions made.

Models explored	Basic assumptions
Boyd’s film diffusion model	(a) External mass transfer controls the transport of gases through the surrounding of the stagnant film.
	(b) Mass transfer within the particle is attributed to diffusion within the pores of the adsorbent.
	(c) The adsorbate is attached to the surface of the adsorbent.
	(d) Mass transfer by film and pore diffusion is the only possible rate-controlling process.
Inter-particle diffusion model	Mass transfer is due to the diffusion between the pores of the adsorbent and molecules of the adsorbate.
Intra-particle diffusion model	External mass transfer is assumed to be due to diffusion within the pores of the adsorbent only.

Figure 2. Boyd’s film diffusion model for CO₂ adsorption on polyaspartamide at different pressure.

Figure 3. Boyd’s film diffusion model for CO₂ adsorption onto polyaspartamide at different adsorption temperature and constant pressure.

Figure 4. Interparticle diffusion model plots for CO₂ adsorption on polyaspartamide at different adsorption temperature and constant pressure.

Figure 5. Interparticle diffusion model plots for CO₂ adsorption on polyaspartamide at different CO₂ partial pressures.

Figure 6. Intraparticle diffusion model plots for CO₂ adsorption on polyaspartamide at different adsorption temperatures showing multilinearity.

Figure 7. Intraparticle diffusion model plots for CO₂ adsorption on polyaspartamide at different CO₂ partial pressures showing multi-linearity.

Figure 8. Breakthrough curves showing the effect of feed flow rate during the adsorption of CO₂ on PAA: (Experimental conditions: feed pressure, 2 bar, and temperature 303 K).

Table 4. Estimated breakthrough and bed contact times with maximum adsorption capacity of polyaspartamide at different gas flow rates.

Flow rates (mL/s)	Breakthrough time (s)	Maximum adsorption capacity (mg/g)	EBCT (s)
1.5	400	365	160
2.0	300	305	120
2.5	200	282	96

Table 5. Adsorption efficiencies of polyaspartamide at different gas flow rates.

Gas flow rate (mL/s)	Pressure (bar)	CO2 capture efficiency (%)
1.5	2	92.67
2.0	2	90.00
2.5	2	86.67

Figure 9. Effect of feed flow rates on the amount of CO₂ adsorbed by polyaspartamide.

Yoro, K. O., M. Singo, J. L. Mulopo, and M. O. Daramola. 2017. “Modelling and Experimental Study of the CO2 Adsorption Behaviour of Polyaspartamide as an Adsorbent during Post-Combustion CO2 Capture.” Energy Procedia 114: 1643–1664. doi:10.1016/j.egypro.2017.03.1294.

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