Chapter 5 Application to high pressure adsorption systems
5.5 Biomass-derived ACs/CO 2 pairs
5.5.1 Adsorption isotherm
The porous properties of synthesized of biomass-derived activated carbons were discussed in chapter 3. Among series of WPT-AC samples, WC500A900K6 and WC600A900K6 are selected for investigation of CO2 adsorption and named as WC500 and WC600, respectively. MC500A900K6 and MC600A900K6 are chosen among mangrove-derived AC samples for further investigation and named as MC500 and MC600, respectively in this chapter. Fig. 5.2 and Fig. 5.3 illustrate the equilibrium absolute absorption uptake of WC500A900K6/CO2 and WC600A900K6/CO2 pair, respectively at adsorption temperatures 25 to 70°C with pressure up to 7 MPa. For both pairs, it is found that Tóth and modified D-A model fit well with the experimental data within ±5% root-mean-square deviation (RMSD). Fig. 5.2 (a) and (b) show the fitted Tóth and modified D-A model with experimental data for WC500/CO2 pair, respectively. In addition, Fig. 5.3 (a) and (b) represent the fitted Tóth and modified D-A model with experimental data for WC600/CO2 pair, respectively.
The similar analysis has been also done for MC500/CO2 and MC600/CO2 pairs are shown in Fig. 5.4 and Fig. 5.5, respectively with the fitted isotherm model. Estimated isotherm parameters of the studied models for all pairs have been summarized in Table 5.2. It is important to mention that synthesized biomass-derived ACs are very promising
CHAPTER 5 APPLICATION TO HIGH PRESSURE ADSORPTION SYSTEMS
Page | 142 for CO2 adsorption as they possess high adsorption uptake. The maximum volumetric absolute uptake is found about 2.6 cm3 g-1 for WC500/CO2 pair followed by 2.4 cm3 g-1, 2.3 cm3 g-1, and 2.1 cm3 g-1 for MC500, WC600, and MC600/CO2 pair, respectively.
However, Maxsorb III/CO2 pair only shows the volumetric absolute uptake 1.5 cm3 g-1. It should be highlighted that biomass-derived all four AC samples show very high adsorption uptake which is about 40% to 73% enhanced uptake compared to Maxsorb III/CO2 pair.
This reason behind this that all synthesized biomass-derived ACs possess very high pore volume. Furthermore, isosteric heat of adsorption (Qst) is lower for biomass-derived ACs that is good for cooling applications. Therefore biomass-derived ACs are very promising for CO2 based adsorption heat pump systems.
0.0 0.5 1.0 1.5 2.0 2.5
0 1 2 3 4 5 6 7 8
Absolute adsorption uptake [g g-1]
Equilibrium pressure [MPa]
25°C 30°C 40°C 50°C 70°C
Tóth isotherm model
(a)
CHAPTER 5 APPLICATION TO HIGH PRESSURE ADSORPTION SYSTEMS
Page | 143 Fig. 5.2 Adsorption isotherms of WC500 (WC500A900K6/CO2 pair (data are fitted with (a) Tóth and (b) modified D-A model).
0.0 0.5 1.0 1.5 2.0 2.5
0 1 2 3 4 5 6 7 8
Absolute adsorption uptake [g g-1]
Equilibrium pressure [MPa]
25°C 30°C 40°C 50°C 70°C
Modified D-A isotherm model
(b)
0.0 0.5 1.0 1.5 2.0 2.5
0 1 2 3 4 5 6 7 8
Absolute adsorption uptake [g g-1]
Equilibrium pressure [MPa]
25°C 30°C 40°C 50°C 70°C
Tóth isotherm model
(a)
CHAPTER 5 APPLICATION TO HIGH PRESSURE ADSORPTION SYSTEMS
Page | 144 Fig. 5.3 Adsorption isotherms of WC600 (WC600A900K6)/CO2 (data are fitted with (a) Tóth and (b) modified D-A model).
0.0 0.5 1.0 1.5 2.0 2.5
0 1 2 3 4 5 6 7 8
Absolute adsorption uptake [g g-1]
Equilibrium pressure [MPa]
25°C 30°C 40°C 50°C 70°C
Modified D-A isotherm model
(b)
0.0 0.5 1.0 1.5 2.0 2.5
0 1 2 3 4 5 6 7 8
Absolute adsorption uptake [g g-1]
Equilibrium pressure [MPa]
25°C 30°C 40°C 50°C 70°C
Tóth isotherm model
(a)
CHAPTER 5 APPLICATION TO HIGH PRESSURE ADSORPTION SYSTEMS
Page | 145 Fig. 5.4 Adsorption isotherms of MC500 (MC500A900K6/CO2 pair (data are fitted with (a) Tóth and (b) modified D-A model).
0.0 0.5 1.0 1.5 2.0 2.5
0 1 2 3 4 5 6 7 8
Absolute adsorption uptake [g g-1]
Equilibrium pressure [MPa]
25°C 30°C 40°C 50°C 70°C
Modified D-A isotherm model
(b)
0.0 0.5 1.0 1.5 2.0 2.5
0 1 2 3 4 5 6 7 8
Adsorption adsorption uptake [g g-1]
Equilibrium pressure [MPa]
25°C 30°C 40°C 50°C 70°C
Tóth isotherm model
(a)
CHAPTER 5 APPLICATION TO HIGH PRESSURE ADSORPTION SYSTEMS
Page | 146 Fig. 5.5 Adsorption isotherms of MC600 (MC600A900K6)/CO2 (data are fitted with (a) Tóth and (b) modified D-A model).
Table 5.2 Fitting parameters of the studied isotherm models for biomass-derived ACs/CO2
pairs.
Model Fitting parameters
WPT-AC (C500)
WPT-AC (C600)
M-AC (C500)
M-AC (C600)
Modified D-A
q0 [cm3 g-1] 2.5599 2.2775 2.4213 2.1321 E [J mol-1] 3466.43 3995.67 3809.68 4322.67
k [-] 4.537 4.437 4.776 4.749
n [-] 1.12 1.20 1.15 1.15
RMSD [%] 5.534 4.118 4.786 2.975
Tóth
W0 [g g-1] 3.90 3.50 3.85 3.20
Qst [J mol-1] 16653.64 17685.23 16954.41 18473.66 h [-] 1.4927 1.1743 1.2912 1.1286 b0 [MPa-1] 1.762×10-4 1.577×10-4 1.732×10-5 1.290×10-4
RMSD [%] 5.543 3.967 4.723 3.348
0.0 0.5 1.0 1.5 2.0 2.5
0 1 2 3 4 5 6 7 8
Absolute adsorption uptake [g g-1]
Equilibrium pressure [MPa]
25°C 30°C 40°C 50°C 70°C
Modified D-A isotherm model
(b)
CHAPTER 5 APPLICATION TO HIGH PRESSURE ADSORPTION SYSTEMS
Page | 147 The effective or net adsorption uptake (ΔW) is defined as the difference between the maximum and minimum uptake at the particular operating condition. It is a crucial parameter for getting the cooling effect. In this study, effective uptake of biomass-derived ACs/CO2 pairs has been compared with several literature studies on evaporation, adsorption, and desorption temperature are 15, 28, and 85°C, respectively. It is found ΔW is very high compared to any other adsorbents/CO2 pairs. The ΔW values for all studied pairs together with literature are furnished in Table 5.3. It is also seen that higher surface area and pore volume attributes for enhancing ΔW of studied biomass-derived ACs/CO2
pair. Fig. 5.6 shows the ΔW variation with the changes of the pore volume of the adsorbent.
It is found that usually effective uptake increase with the increase of pore of adsorbent.
Importantly, synthesized biomass-derived ACs/CO2 pairs lie in the top of the figure, which is the current benchmark.
CHAPTER 5 APPLICATION TO HIGH PRESSURE ADSORPTION SYSTEMS
Page | 148 Table 5.3 Comparison of effective uptake of the present study with numerous pairs of literature data at evaporation, adsorption, and desorption temperature are 15, 28 and 85°C, respectively.
Adsorbent/CO2
Effective uptake, ΔW [g g-1]
Surface area [m2 g-1]
Pore volume [cm3 g-1]
Pore size [nm]
Reference
WPT-AC (C500) 0.81 2848 2.87 1.96 Present study
WPT-AC (C600) 0.75 2927 2.51 1.68 Present study
M-AC (C500) 0.81 2911 2.68 1.81 Present study
M-AC (C600) 0.72 2924 2.18 1.47 Present study
Maxsorb III 0.46 3045 1.70 1.12 Jribi et al. [18]
A-20 (ACF) 0.27 2000 1.03 2.16 Saha et al. [52]
Maxsorb III 0.60 3150 1.70 2.0 Saha et al. [52]
Composite 0.39 2000 1.094 1.0 ~
3.5 Pal et al. [135]
Maxsorb 0.24 3250 1.79 - Himeno et al. [36]
Norit R1 Extra 0.09 1450 0.47 - Himeno et al. [36]
BPL 0.08 1150 0.43 - Himeno et al. [36]
A10 fiber 0.07 1200 0.59 - Himeno et al. [36]
Activated carbon A 0.07 1207 0.54 - Himeno et al. [36]
Norit RB3 (steam
activated rod) (AC1) 0.16 987.04 0.51 2.10 Singh et al. [39]
Norit Darco (100
mesh size) (AC2) 0.13 876.45 0.73 3.33 Singh et al. [39]
Norit Darco (12 × 20
US mesh size) (AC3) 0.09 462.67 0.50 4.28 Singh et al. [39]
CSAC (Coconut shell based activated carbon)
0.10 804.02 0.43 1.76 Singh et al. [38]
CHAPTER 5 APPLICATION TO HIGH PRESSURE ADSORPTION SYSTEMS
Page | 149 Fig. 5.6 Effective uptake (ΔW) as a function of adsorbent pore volume.
Fig. 5.7 illustrates the ΔW improvement of biomass-derived ACs/CO2 pairs with the comparison of Maxsorb III/CO2 and Norit RB3/CO2 at evaporation, adsorption, and desorption temperature are 15, 28 and 85°C. It is found that all biomass-derived ACs shows a high percentage of ΔW improvement compared to Maxsorb III and Norit RB3. The highest improvement is found 176% and 506% compared to Maxsorb III and Norit RB3, respectively.
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5
△W [g g-1]
Pore volme [cm3g-1] Present study
Literature
Norit darco (AC2) Norit RB3 (AC1)
CSAC A-10 Norit darco (AC1)
BPL Norit R1 extra Norit darco (AC3)
CHAPTER 5 APPLICATION TO HIGH PRESSURE ADSORPTION SYSTEMS
Page | 150 Fig. 5.7 ΔW improvement of biomass-derived ACs with the comparison of Maxsorb III and Norit RB3 at evaporation, adsorption, and desorption temperature are 15, 28 and 85°C.