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Characteristics of Cyanobacterial Biomass Gasification in Sub- and Supercritical Water Huiwen Zhang, Xiaoman Zhang, Lei Ding, Jiangya Ma, and Yanli Kong Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.8b04299 • Publication Date (Web): 18 Mar 2019 Downloaded from http://pubs.acs.org on March 19, 2019
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Characteristics of Cyanobacterial Biomass Gasification in Sub- and Supercritical Water
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Huiwen Zhang,* Xiaoman Zhang, Lei Ding, Jiangya Ma, and Yanli Kong *
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School of Civil Engineering and Architecture, Anhui University of Technology,
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Maanshan, Anhui 243002, China
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Engineering Research Center of Biomembrane Water Purification and
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Utilization Technology, Ministry of Education, Maanshan, Anhui 243002,
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China
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ABSTRACT: Hydrogen gas has been successfully produced from cultivated
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microalgae biomass by supercritical water gasification (SCWG). The paper describes
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SCWG of natural cyanobacterial biomass for hydrogen production at low temperatures
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(450°C),
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supercritical water becomes a more powerful oxidant, and free radical reactions prevail.
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Water acts as a solvent and promotes solute-solvent reactions such as the decomposition
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of the organic compounds in the feedstock.
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12
6
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0
10
o
o
o
o
o
o
350 C 400 C 425 C 450 C 475 C 500 C
(b) H2 HHV
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Effeciency (%)
Gas yield CGE
Carbon gasification efficiency, CGE (%)
(a)
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20
35
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Gas yield (mol/kg organic matter)
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5
0 o
350 C
o
400 C
Reaction temperature
o
425 C
o
450 C
o
475 C
o
500 C
Reaction temperature
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Figure 5. Effects of reaction temperature on (a) gas yield and CGE, (b) efficiency of
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H2 production and energy recovery.
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Gasification characteristics of cyanobacteria in sub- and supercritical water were
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shown in Figure 5. Figure 5(a) illustrated effects of reaction temperature on gas yield
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and carbon gasification efficiency (CGE).18 Both gas yield and CGE were substantially
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increased when reaction temperature increased. When the reaction temperature
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increased to 500°C, gas yield and CGE could exceed 16.0 mol/kg OM and 33.0%,
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respectively, and had a sustained and accelerated development trend during the process
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of heating up. We could not directly carry out gasification experiments at higher
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reaction temperatures because of energy conservation and the restrictions of test
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equipment performance. By contrast, Hirano et al. favored the microalga Spirulina, and
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using a continuous reactor tube, showed that gas yield and CGE were still substantially
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increasing when reaction temperature was in the range of 850°C to 1000°C.19
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Cyanobacteria biomass has tremendous potential for gasification and hydrogen
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production. Efficiency of H2 production and energy recovery from SCWG of
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cyanobacteria were shown in Figure 5(b). Both efficiency of H2 production and energy
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recovery were slightly increased at the low temperature stage of SCWG, it rapidly
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increased when the temperature reached 475°C. Cyanobacteria was the main donor for
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hydrogen generation at less than 500°C and under supercritical water conditions. The
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proportion of hydrogen originating from supercritical water was gradually increased
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with a continued increase in reaction temperature. When the gasification test was
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launched at 500°C, the energy recovery of gaseous products far exceeded the energy
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required in heating up and energy loss.
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3.2 Gas production between different microalgae species
Table 2. Summary of previous studies on SCWG of algae. References
Microalgae species
Brown et al.20
Nannochloropsis sp.
Cherad et al.10
Chlorella vulgaris
Cherad et
al.14
Y. Graz et al.13 Laura Tiong et al.12 Laura Tiong et Guan et
al.12
al.21
S. latissima Ulva armoricana and Ulva rotundata Chlorella vulgaris Scenedesmus quadricauda
Reaction conditions
Algae loading
200–500°C, 60 min
5.20–17.00 wt.%
350°C, 0–60 min
94.80 wt.%
500°C, 60 min
6.66 wt.%
550°C, 7–120 min
7.00, 16.40 wt.%
385°C, 15 min
5.0 wt.%
385°C, 15 min
5.0 wt.%
Nannochloropsis sp.
450–550°C, 0–80 min
0.00-18.00 wt.%
A. Hirano et al.19
Microalga Spirulina
850–1000°C
93.30 wt.%
Current work
Cyanobacteria
400–500°C
96.15 wt.%
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It’s significant to analyze the difference of gasification between cyanobacteria and
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common cultivated microalage biomasses, which could be feasible to a large scale
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energy regeneration. Table 2 summarized researches on gasification of microalgae
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biomasses under similar tubular reactor and very close near- or super-critical water
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experiments conditions. Different species of microalgae biomass has a similar
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composition, and the syngas and biodiesel generation were likely to be affected by the
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change of fraction. 50
18.0
Cherad et al. Chlorella vulgaris Cherad et al. S. latissima Y. Graz et al. Ulva Laura Tiong et al. Chlorella vulgaris Laura Tiong et al. S. quadricauda Guan et al. Nannochloropsis sp. A. Hirano et al. Microalga Spirulina Zhang et al. Caynobacteria
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(a) 16.5
Hydrogen yield (mol/kg)
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Gas yield (mol/kg)
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15.0 6.0
Cherad et al. Chlorella vulgaris Cherad et al. S. latissima Y. Graz et al. Ulva Laura Tiong et al. Chlorella vulgaris Laura Tiong et al. S. quadricauda Guan et al. Nannochloropsis sp. A. Hirano et al. Microalga Spirulina Zhang et al. Caynobacteria
(b)
4.5 3.0 1.5
0
0.0 o
350 C
o
385 C
o
400 C
o
450 C
o
500 C
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550 C
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850 C
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350 C
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385 C
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Reaction temperature ( C)
o
400 C
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450 C
o
500 C
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550 C
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850 C
o
Reaction temperature ( C)
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Figure 6. Influences of microalgae biomass types on (a) gas yield and (b) H2 production
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from SCWG.
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Figure 6 summarizes the effects of reaction temperature on gas yield and H2
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production from SCWG of different microalgae biomass with similar reaction
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conditions. The high strength of Ulva cell membrane resulted in low gas yield compared
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with other microalgae biomasses. Syngas yield was correlated with reaction
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temperature in a certain temperature range under similar SCWG reaction conditions.
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Partial overlapping points illustrated that the change of biomass components showed a
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limited influence on syngas generation. A different trend was exhibited in hydrogen
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production during the SCWG process with biomass of the different microalgal strains.
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At reaction temperature range of 350–400°C, low temperature against hydrogen
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generation presented a weak effect on hydrogen yield; and the difference was notable
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with a further increase in reaction temperature. Hydrogen yield from SCWG of
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Nannochloropsis sp. reached up 3.32 mol/kg, when reaction temperature reached
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450°C; and in case of SCWG of Saccharina latissima yield was 4.23 mol/kg at 500°C.
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H2 production from SCWG of cyanobacteria performed well above Ulva, and below
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but close to H2 yield from gasification of Nannochloropsis sp. and Saccharina latissima.
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Under similar reaction conditions and biomass physical properties, the factors on H2
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production would be revealed from the chemical compositions of microalgae biomass. 40
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Zhang et al. Caynobacteria Brown et al. Nannochloropsis sp.
(b) 40
Bio-oil (wt.%)
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Y. Graz et al. Ulva Brown et al. Nannochloropsis sp. Zhang et al. Caynobacteria Cherad et al. S. latissima
(a)
H2 yield (mol.%)
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350
400
450
500 o
N content (wt.%)
Reaction temperature ( C)
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Figure 7. Influences of microalgae biomass types on (a) H2 production and (b) bio-oil
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yield from SCWG.
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The elements analysis results showed that nitrogen was abundant in proteins of the
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microalgae biomass, with a wide variety in that ratio from 1.14 wt.% to 9.88 wt.%.
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Figure 7 illustrated effects of nitrogen elements and protein content on hydrogen and
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biodiesel production from SCWG of Saccharina latissima, Ulva, Cyanobacteria, and
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Nannochloropsis sp. There is a correlation between H2 production and N element
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content of different species of algae biomass feedstock, and high N content contributed
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to low H2 production. Gasification of Ulva with relatively low N content did not appear
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expected H2 yield, so N elements of algae biomass was not the only factor for hydrogen
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production, and it proved that microalgae biomass performed better to apply as
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feedstock for H2 production than other large algae. Figure 7(b) showed biodiesel
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production of Cyanobacteria (proteins content: 40%) and Nannochloropsis sp. (proteins
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content: 52%) at SCWG reaction temperature range of 350–500°C. H2 production was
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inhibited by N elements occurring in large quantities, but biodiesel generation was
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enhanced.
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Hydrothermal liquefaction and gasification of Nannochloropsis sp. biodiesel
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recovered 75% of carbon under the best conditions for optimizing biodiesel yield 20.
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High protein content resulted in an abundance of soluble substances and biodiesel
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generation, which decreased the generation of intermediates that were easy to gasify
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and developed serious corrosion in the reaction kettle. This was previously shown in
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the comparison of syngas production between plants and meat by Kruse’s research.22
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During the SCWG transformation from proteins to carbohydrates, it preferred to
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generate intermediates that could easily yield biodiesel, and then H2 production was
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hindered. The formation of tar and char could be improved from SCWG of proteins and
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lipids, and the conversion of C, H, and O elements was inhibited from liquid phase to
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gaseous products. Therefore, the hydrogen production could be effectively improved
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by maximizing easy-to-gasify-intermediates formation during SCWG processing of
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cyanobacteria. Compared to other single species microalgae, it would generate more
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kinds of intermediates from gasification of composite microalgae cyanobacteria in
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SCW and H2 production was affected to some extent by the complex composition and
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interaction.
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3.3 Effects of biomass type on gas production
Table 3. Summary of previous studies on SCWG of typical waste biomasses. References
L. Guo et al.23
C. Cao et al.24
Z. Xu et al.25
Current work
Proximate analysis (wt%) Biomass
Sawdust
Black liquor
Sewage sludge
Cyanobacteria
Moisture
8.00
3.20
84.1
96.15
77.12
49.32
46.3
81.59
1.36
27.38
52.4
15.41
13.52
20.10
1.3
3.00
C
46.76
33.43
20.6
42.64
H
5.27
2.77
3.11
6.88
O
38.47
32.86
21.0
26.31
N
0.11
0.23
1.63
5.68
Volatile matter (VM) Ash Fixed Carbon (FC) Ultimate analysis (wt%)
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160 L. Guo et al. Sawdust C. Cao et al. Black liquor Z. Xu et al. Sewage sludge H. Zhang et al. Cyanobacteria
(a)
2
r =0.995 p
