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Transformation of nitrogen and evolution of Ncontaining species during algae pyrolysis Wei Chen, Haiping Yang, Yingquan Chen, Mingwei Xia, Xu Chen, and Hanping Chen Environ. Sci. Technol., Just Accepted Manuscript • Publication Date (Web): 10 May 2017 Downloaded from http://pubs.acs.org on May 10, 2017

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[Title Page]

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Transformation of nitrogen and evolution of N-containing species during algae

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pyrolysis

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Wei Chen, Haiping Yang*, Yingquan Chen*, Mingwei Xia, Xu Chen, Hanping

7

Chen

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State Key Laboratory of Coal Combustion, School of Power and Energy

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Engineering, Huazhong University of Science and Technology, 430074 Wuhan,

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China

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E-mail: [email protected], [email protected],

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[email protected], [email protected], [email protected],

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[email protected].

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Correspondence information: Haiping Yang, [email protected]; Yingquan

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Chen, [email protected]; 1037 Luoyu Road, 430074 Wuhan, P. R.

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China; Tel: +086+027-87542417-8109; fax: +086+027-87545526.

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Transformation of nitrogen and evolution of N-containing species during algae

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pyrolysis

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Wei Chen, Haiping Yang*, Yingquan Chen*, Mingwei Xia, Xu Chen, Hanping Chen

23

State Key Laboratory of Coal Combustion, School of Energy and Power Engineering,

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Huazhong University of Science and Technology, 430074 Wuhan, China

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Abstract

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Transformation and evolution mechanisms of nitrogen during algae pyrolysis were

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investigated in depth with exploration of N-containing products under variant

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temperature. Results indicated nitrogen in algae is mainly in the form of protein-N

29

(~90%) with some inorganic-N. At 400~600°C, protein-N in algae cracked firstly with

30

algae pyrolysis and formed pyridinic-N, pyrrolic-N and quaternary-N in char. The

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content of protein-N decreased significantly, while that of pyrrolic-N and quaternary-N

32

increased gradually with temperature increasing. Pyridinic-N and pyrrolic-N formation

33

was due to deamination or dehydrogenation of amino acids; subsequently, some

34

pyridinic-N converted to quaternary-N. Increasing temperature decreased amides

35

content greatly while increased that of nitriles and N-heterocyclic compounds

36

(pyridines, pyrroles, and indoles) in bio-oil. Amides were formed through NH3 reacting

37

with fatty acids, that underwent dehydration to form nitriles. Besides, NH3 and HCN

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yields increased gradually. NH3 resulted from ammonia-N, labile amino acids and

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amides decomposition, while HCN came from nitrile decomposition. At 700~800°C, 2

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evolution trend of N-containing products was similar with that at 400~600°C. While N-

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heterocyclic compounds in bio-oil mainly came from pyrifinic-N, pyrrolic-N and

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quaternary-N decomposition. Moreover, cracking of pyridinic-N and pyrrolic-N

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produced HCN and NH3. A mechanism of nitrogen transformation during algae

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pyrolysis is proposed based on amino acids decomposition.

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Key words: Algae; Pyrolysis; Nitrogen transformation; Amino acids; N-containing

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species

47

Introduction

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Global interest in renewable and alternative energy resources has greatly increased

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in recent years, due to serious environment problems, fossil fuel depletion, and concerns

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about energy security.1, 2 Among potential renewable energy sources, algae is extremely

51

promising because of fast growth rates, high potential biofuel yield, high CO2 use

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capability, and the possibility of cultivation on waste water to remove N, P and heavy

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metals.3, 4 Algae pyrolysis is attracting increasing concern,5-8 as the higher mass yield

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(up to 80 wt.%) of liquid fuel and the more energy (up to 70%) in liquid products.9, 10

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However, different from agricultural straw and woody wastes, algae shows higher

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nitrogen content, which can be as high as 10 wt.%, far more than the content in coal,

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sewage sludge and terrestrial biomass.7,

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emission and transformation might be one main concern for algae pyrolysis, as it might

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be converted to various N-containing compounds, such as NH3, HCN, the NOx

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precursors, which may lead to potential nitrogen-related pollution (such as severe

11-13

Hence, the issue related to nitrogen

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photochemical smog, ozone depletion, acid rains and greenhouse effect).7,

14-20

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Furthermore, nitrogen content of pyrolytic oil can reach 12 wt.%, subsequent utilization

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of which would also lead to the secondary pollution.7 However, the N-containing

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compounds in bio-oil, such as pyrrole, pyridine, and indole, can be used to synthesize

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pharmaceuticals, perfumes and other chemicals.14, 15 N-containing char can be used in

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catalysis, pollutants adsorption and electrode materials.21-23 Thus, understanding

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nitrogen transformation is critical for the utilization of algae pyrolysis. However,

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limited information is available on the nitrogen fate during algae pyrolysis.

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Nitrogen conversion during coal pyrolysis has been investigated widely over the

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past decades.24-28 Kelemen et al.28 pointed out that N-containing species in coal would

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convert to pyridinic-N and quaternary-N in char at higher pyrolysis temperature. Tan et

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al.29, 30 reported that unstable N-containing compounds in the volatiles could generate

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HCN, while stable N-containing species in char could release NH3 during coal pyrolysis.

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However, in algae, nitrogen exists mainly as protein-N,4 whereas in coal, the dominant

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N-containing species are pyridine-N, pyrrole-N and quaternary-N.27, 31 It suggested that

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there might be different conversion processes of nitrogen for algae. Given the

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dominance of protein-N, the N-containing species in pyrolysis products should come

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from amino acids decomposition. Although Gallois et al.32 investigated the pyrolysis

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mechanism of 20 amino acids, and Choi et al.33 found that pyrolysis of amino acid

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monomer could generate lots of N-heterocyclic compounds in bio-oil. However,

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nitrogen evolution in algae is greatly different from amino acid monomer. As Chen et

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al.11 pointed out that lignin could promote nitrogen transformation into gas during co4

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pyrolysis of lignin with amino acid, while cellulose promoted nitrogen conversion into

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bio-oil. Furthermore, Ren et al.13, 34 found that hemicellulose inhibited NH3 formation

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during co-pyrolysis of hemicellulose with amino acid. These studies suggested that

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biomass components had great effect on nitrogen conversion during pyrolysis. However,

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different from lignocellulosic biomass, lipids (consist of triglycerides), carbohydrates

88

(consist of alginic acid, mannitol, laminarin, and fucoidan), and proteins (consist of

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amino acids) are the main components of algae, and different pyrolysis behavior of

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these components should be showed.3, 35-38 Thus, lipids and carbohydrates in algae

91

could also exert important effect on the formation of N-containing species. However,

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no related information on the formation and evolution of N-containing species could be

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obtained during algae pyrolysis, despite such information being crucial for

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understanding nitrogen decomposition mechanism in algae. Besides, nitrogen sources

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in algae must be elucidated to determine nitrogen reaction pathways. Thus, a better

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understanding of amino acids compositions and structures in algae samples is needed

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to clarify mechanism of nitrogen evolution.

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In this study, nitrogen distribution and transformation mechanisms during algae

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pyrolysis were explored with Spirulina platensis (SP, with higher proteins),

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Nannochloropsis sp. (NS, rich in lipids), and Enteromorpha prolifera (EP, enriched with

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carbohydrates) as typical algae. The possible pathways of nitrogen transformation was

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explored based on the distribution and evolution of pyrolysis products of algae at

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variant temperature. It is significant for the understanding of nitrogen evolution during

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algae pyrolysis and for the controlling nitrogen emission during algae utilization. 5

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Experimental section

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Fast pyrolysis experiment

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Nannochloropsis sp. (NS) was purchased from Yantai Hairong Biology

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Technology Co., Ltd, while Spirulina platensis (SP) and Enteromorpha prolifera (EP)

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were provided by China Agricultural University. The algae were dried at 105°C for 24

110

h, then crushed and sieved (600°C).

398

Associated content

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Supporting information

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Raw algal characteristics, N-containing species evolution in bio-oil and char from

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NS and EP, and releasing properties of NH3 and HCN (Tables S1-S4 and Figures S120

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S5).

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Author information

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Corresponding Author

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*Phone: +086-027-87542417-8109; email: [email protected].

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*Phone: +086-027-87542417-8109; email: [email protected].

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Notes

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The authors declare no competing financial interest.

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Acknowledgements

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The authors wish to express their great appreciation of the financial support from

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the National Nature Science Foundation of China (51406061 and 51622604), the

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National Basic Research Program of China (973 Program: 2013CB228102), the Special

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Fund for Agro-scientific Research in the Public Interest (201303095), the Fundamental

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Research Funds for the Central Universities, the technical support from Analytical and

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Testing

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(http://atc.hust.edu.cn).

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Figure captions

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Abstract Graphic.

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Figure 1. Schematic diagram of algal pyrolysis system for investigating nitrogen

568

transformation.

569

Figure 2. The nitrogen distribution of algae pyrolysis products.

570

Figure 3. Figure 3 N1s spectra of SP pyrolysis chars at different temperature (a)-(e)

571

and relative content of XPS N 1s peaks of three algae (f)-(h).

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Figure 4. The releasing properties of NH3 and HCN from SP pyrolysis (a and b), and

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yields of NH3-N and HCN-N from algae pyrolysis (c).

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Figure 5. Mechanisms of nitrogen transformation and possible reaction pathways

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during algae pyrolysis.

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Amides  

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 3 NH

Quaternary-N  

Nitriles  

Indoles  

Algae

Char

Inorganic-N Protein-N (amino acids)

Pyrrolic-N  

Pyridinic-N     HCN

Pyridines  

Pyrroles  

NH  3 577 578 Abstract Graphic. 579 580

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Gas

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Mass flow controller

Quartz basket



Ar

Gas bag

Valve Quartz reactor &

7 0

Ice-water mixture

NaOH H2SO4

ĉ

Temperature controller Electric furnace

PC

Mass spectrometry Air Ċ Color changing silica gel

Ice-water mixture or liquid nitrogen 581 582

Figure 1 Schematic diagram of algal pyrolysis system for investigating nitrogen

583

transformation.

584

31

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Nbio-oil

N yields (wt.%)

60 50 40 30 20 10

400

585

Nchar

Ngas

0 500

600

700

800

Temperature (°C)

586

Figure 2. The nitrogen distribution of algae pyrolysis products (Ngas = 100wt.% - Nchar

587

–Nbio-oil). ■: SP; ●: NS; ▲: EP.

588

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a

400°C

b

Protein-N Pyridinic-N

Pyrrolic-N Quaternary-N

404

500°C

Intensity (a.u.)

Intensity (a.u.)

Protein-N

402

400

Pyrrolic-N Quaternary-N

398

404

Binding Energy (eV)

589

c

Quaternary-N

402

400

e

800°C

404

396

Protein-N Pyridinic-N

402

400

Binding Energy (eV)

398

f 90 Relative content (%)

Intensity (a.u.)

Quaternary-N

398

Quaternary-N

398

Protein-N Pyridinic-N

Pyrrolic-N

400

Pyrrolic-N

Binding Energy (eV)

590

402

Binding Energy (eV)

700°C

Intensity (a.u.)

Intensity (a.u.)

Pyrrolic-N

404

d

Pyridinic-N

Protein-N

600°C

Pyridinic-N

SP

50 40 30 20 10

404

402

400

0

398

NS

40 30 20 10 0

400

500

600

Temperature (°C)

700

h 80 Relative content (%)

Relative content (%)

g 90

592

20

Binding Energy (eV)

591

800

EP

40 30 20 10

20

400

500

600

Temperature (°C)

700

800

0

20

400

500

600

Temperature (°C)

700

800

593

Figure 3 N1s spectra of SP pyrolysis chars at different temperature (a)-(e) and relative

594

content of XPS N 1s peaks of three algae (f)-(h). ■: protein-N; ●: pyridinic-N; ▲:

595

pyrrolic-N; ▼: quaternary-N. 33

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Environmental Science & Technology

NH3

Ion current (A) 0

b

400°C 500°C 600°C 700°C 800°C

500

1000

1500

Time (s)

596

0

c 25

1000

Time (s)

1500

SP NS EP

15

20 15

10

10

5

5

400

500

600

700

Temperature (°C)

HCN-N yield (wt.%)

NH3-N yield (wt.%)

597

500

25

20

0

400°C 500°C 600°C 700°C 800°C

HCN

Ion current (A)

a

Page 34 of 36

0

800

598

Figure 4. The releasing properties of NH3 and HCN from SP pyrolysis (a and b), and

599

yields of NH3-N and HCN-N from algae pyrolysis (c).

600

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Environmental Science & Technology

HCN

NH3/NO Inorganic-N (1)(2) + (NH4 , NO3 /NO2 ) (3)

Lysine

Glutamic acid

Aspartic acid

(11)

Pyridinic-N (5)(10)

(12)

Pyrrolic-N

(9)

Quaternary-N

(7)

Arginine

(8)

Proline Phenylalanine

Decomposing

(15) (16)

Tyrosine Tryptophan Others

Cracking

(6)

Leucine Protein-N (Amino acids)

Cracking

(4)

Valine Algae (N)

(18)

HCN

NH3

Indoles Pyrroles

Pyridines

(17)

N-heterocyclic compounds NH3/NH2* Fatty acids (13)

(14) Amides Nitriles (Hexadecanamide) (Hexadecannitrile)

601 602

Figure 5. Mechanisms of nitrogen transformation and possible reaction pathways

603

during algae pyrolysis. Black: possible reaction pathways at lower temperatures; red:

604

possible reaction pathways at higher temperatures.

605 606

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Environmental Science & Technology

607

Page 36 of 36

Table 1. N-containing compounds in bio-oil derived from SP N-containing compounds Amines and amides 2-Methoxy-p-phenylenediamine 9-Octadecenamide Hexadecanamide N-Methyldodecanamide Nitriles Butanenitrile, 3-methylIsoamyl cyanide Benzonitrile Benzonitrile, 2-methylBenzenepropanenitrile Hexadecanenitrile N-heterocyclic compounds Oxazole Pyridine Pyrrole Pyridine, 2-methyl1H-Pyrrole, 2-methyl1H-Pyrrole, 3-methylPyridine, 3,5-dimethylIndole 1H-Indole, 3-methyl1H-Indole, 2-methylPyrimido[1,2-a]azepine, 2,3,4,6,7,8,9,10-octahydro2-Ethyl-3-methoxypyrazine 6,6-Dimethyl-2-azaspiro[4.4]non-1-ene Propyloctahydroindolizin-8-yl)methanol

Relative content (area %) 400°C 500°C 600°C 700°C 15.76 14.28 12.64 4.62 1.16 1.55 1.14 13.50 12.74 11.50 4.62 1.10 7.99 8.13 9.56 7.62   1.83 2.08 1.20 1.62 1.85 2.11         1.17 1.38 1.79 1.80 5.63 5.13 4.09 1.63 7.75 10.25 11.69 16.59 1.24          2.45 3.26       1.11 2.35        1.73 4.76 4.16 4.45 5.63  1.52 2.44 3.61    

800°C 0

3.70   2.27 1.43   20.09  3.91 3.81 1.67  1.06  6.29 1.57 1.77



1.29







  1.75

1.32 1.96 

 1.24 

  

  

608

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