Table 1 Performance data and CNT characteristics of the five lab-scale processes (SP, MP, MPbio, SP2 and MP2), and the pilot-scale single-pass and modelled pilot-scale multi-pass processes

CNT mass production (g h⁻¹)

0.132

0.165

0.0995

0.046

0.077

30.0

30.0

Carbon content (%)

64.41

75.53

58.89

78.33

85.37

95.02

95.02

Iron content (%)

29.66

20.39

34.26

18.06

12.19

4.15

4.15

Raman I_G/I_D

1.54

1.41

1.79

5.87

6.04

3.58

3.58

Electrical conductivity (S m⁻¹)

3,643

1,593

4,165

63,669

35,470

–

–

Specific conductivity (S m² kg⁻¹)

26.74

11.48

21.87

233.2

213.9

–

–

Density (kg m⁻³)

137.9

139.1

190.4

273.0

166.1

–

–

Methane conversion (%)

27.20

91.90

95.44

–

–

85.0

95.0

Hydrogen production efficiency (%)

0

54.15

32.99

0

–

0

87.64

Carbon yield (%)

2.38

20.76

9.61

1.37

18.24

60.0

79.14

Molar process efficiency (%)

0.100

44.69

27.20

0.037

–

1.48

85.18

Molar carbon efficiency (%)

0.100

5.36

3.23

0.037

4.21

1.48

79.22

Mass process efficiency (%)

0.806

23.17

7.95

0.34

15.98

13.60

75.00

Volumetric productivity (kg m⁻³ h⁻¹)

0.147

0.296

0.179

0

–

3.333

4.384

CNT volumetric productivity (kg m⁻³ h⁻¹)

0.147

0.183

0.111

0.051

0.09

3.333

3.333

H₂ volumetric productivity (kg m⁻³ h⁻¹)

0

0.113

0.069

0

–

0

1.051