1 Introduction
2 Experimental
2.1 Materials
Tab.1 The main properties of the membranes used for the experiments a) |
Membrane | Thickness /mm | Tensile strength /MPa | Area resistance /(Ω·cm2) | Functional group | Reinforcing membrane matrix | Burst strength /MPa | Water splitting voltage/V | Water splitting efficiency |
---|---|---|---|---|---|---|---|---|
AM-1 | 0.11–0.16 | ≥0.20 | 1.2–2.0 | R4–N+ | PS-DVB+ PVC | − | − | − |
CM-2 | 0.11–0.16 | ≥0.15 | 2.0–4.5 | R–SO3– | PS-DVB+ PVC | − | − | − |
BP-1E | 0.22 | − | − | − | − | ≥0.40 | 1.2 | >0.98 |
a) The data was obtained from the manufacturer. PS, polystyrene; DVB, divinylbenzene; PVC, polyvinyl chloride. |
2.2 BMED apparatus
Fig.1 (a) Schematic BMED setup containing (1) a direct current power supply, (2) a membrane stack with four cell pairs, (3) acid chamber, (4) base chamber, (5) rinse solution, (6) feed chamber, and (7) peristaltic pumps; (b) schematic diagram of the BMED cell configuration assemble with CEM, bipolar membrane and AEM; (c) the digital photo of BMED system. |
2.3 Experimental design
Fig.2 Schemes for multistage-batch BMED design: (a) three-stage-batch BMED with changing salt solution (Vacid:Vbase:Vsalt = 1:1:2); (b) two-stage-batch BMED with changing salt solution (Vacid:Vbase:Vsalt = 1:1:5); (c) two-stage-batch BMED with changing salt and acid solutions (Vacid:Vbase:Vsalt = 1:1:5). |
2.4 Data calculation and evaluation
3 Results and discussion
3.1 Three-stage-batch BMED with changing salt solution
Tab.2 Energy consumption and current efficiency in three-stage-batch BMED with changing salt solution |
Vacid:Vbase:Vsalt | Stage | Energy consumption/(kWh∙kg–1) | Current efficiency/% | ||
---|---|---|---|---|---|
HCl | NaOH | HCl | NaOH | ||
1:1:2 | First | 2.13 | 1.44 | 48.92 | 66.05 |
Second | 1.95 | 1.45 | 45.73 | 56.00 | |
Third | 3.56 | 2.62 | 31.24 | 38.79 |
3.2 Two-stage-batch BMED with changing salt solution
Tab.3 Energy consumption and current efficiency in two-stage-batch BMED with changing salt solution |
Vacid:Vbase:Vsalt | Stage | Energy consumption/(kWh∙kg–1) | Current efficiency/% | ||
---|---|---|---|---|---|
HCl | NaOH | HCl | NaOH | ||
1:1:5 | First | 3.44 | 1.52 | 28.98 | 59.93 |
Second | 2.43 | 2.65 | 34.54 | 28.81 |
3.3 Two-stage-batch BMED with changing salt and acid solutions
Tab.4 Energy consumption and current efficiency in two-stage-batch BMED with changing salt and acid solutions |
Vacid:Vbase:Vsalt | Stage | Energy consumption/(kWh∙kg–1) | Current efficiency/% | ||
---|---|---|---|---|---|
HCl | NaOH | HCl | NaOH | ||
1:1:5 | First | 3.49 | 1.54 | 28.98 | 59.93 |
Second | 2.36 | 1.90 | 36.73 | 41.73 |
3.4 Multistage-batch BMED performance evaluation
Tab.5 Summary of HCl and NaOH production using different concentration of NaCl as feed in BMED process |
NaCl feed Concentration /(mol·L–1) | Mode of operation | Max. HCl Concentration /(mol·L–1) | Max. NaOH Concentration /(mol·L–1) | Current efficiency /% | Energy consumption /(kWh·kg–1) | Ref. |
---|---|---|---|---|---|---|
0.5 | Multistage-batch | 2.30 | 3.40 | 59–41 | 1.54–1.9 | This work |
1.71, 3.42 | Batch | 1.99 | 2.14 | 55–88 | 1.7 | [24] |
ca. 1.00 | Semi continuous | 0.98 | 1.64 | 44 | 7.3–4.4 | [27] |
0.02 | Batch | ca. 0.2 | ca. 0.2 | 85–35 | – | [39] |
0.6 | Batch | 0.22 | 0.29 | 95 | – | [38] |
0.048–0.390 | Continuous | 0.05–0.30 | 0.04–0.30 | – | 0.09 | [42] |
ca. 1.00 | Batch | 0.8 | 1 | 61–80 | 1.94–2.51 | [37] |
0.65 | Batch | 0.7 | 0.4 | 74–50 | 7.6–8.2 | [40] |
1.2 | Batch | 1.6 | 1.7 | – | – | [41] |