Nitrogen Migration and Transformation during Hydrothermal

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Nitrogen Migration and Transformation during Hydrothermal Liquefaction of Livestock Manures Jianwen Lu, Hugang Li, Yuanhui Zhang, and Zhidan Liu ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.8b03810 • Publication Date (Web): 06 Sep 2018 Downloaded from http://pubs.acs.org on September 9, 2018

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is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

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ACS Sustainable Chemistry & Engineering

Nitrogen Migration and Transformation during Hydrothermal Liquefaction of Livestock Manures Jianwen Lu,† ,§ Hugang Li,†,§ Yuanhui Zhang,†, ‡ Zhidan Liu†,* †

Laboratory of Environment-Enhancing Energy (E2E), and Key Laboratory of

Agricultural Engineering in Structure and Environment, Ministry of Agriculture, College of Water Resources and Civil Engineering China Agricultural University, Qinghua Donglu 17, Beijing 100083, China ‡

Department of Agricultural and Biological Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA §

These authors contributed equally.

*Corresponding author: Dr. Zhidan Liu Fax: +86-10-62737329; Tel.: +86-10-62737329. E-mail address: [email protected]

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ABSTRACT: Nitrogen flow and fate critically affects the hydrothermal liquefaction (HTL) of protein-rich feedstock such as livestock manure and algae. It also impacts the downstream process of HTL aqueous and oil products. Here, we reveal the migration and transformation pathways of nitrogen during HTL of typical livestock manures using combined gas chromatography-mass spectroscopy (GC-MS) and Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS) analysis. Over 37% of nitrogen in the manure migrated to the aqueous phase in all HTL experimental trials, except for beef manure. GC-MS results indicated that the nitrogen compounds in the biocrude oil were mainly long chain amides, whereas in the aqueous phase the compounds were mainly small molecules of pyrazines, pyrroles and pyridines. FT-ICR MS identified that N1O1, N2 and N2O1 species were dominant in the biocrude oil, while the nitrogencontaining compounds in the aqueous phase primarily took the form of N2O2 and N2O3. Five reaction pathways were proposed for the transformation of nitrogen during HTL. This study firstly characterized the transformation of nitrogenous compounds during HTL of livestock manures, which could be greatly beneficial to the biocrude production and oil quality, and aqueous utilization in future studies.

KEY WORDS: Hydrothermal liquefaction; livestock manure; nitrogen transformation; biocrude oil

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INTRODUCTION Global livestock production has increased rapidly over the last few decades, resulting in large quantities of livestock manure.1 Approximately 250 million tons of manure (wet mass) is produced annually in China.2 The total nitrogen produced via livestock manure in the world is about 80-130 million tons per year, of which only 20-40% is utilized as fertilizer. A large part of the manure is discharged into the waterways and soil without appropriate treatment or management, which results in serious pollution to the environment.3, 4 Composting and anaerobic digestion are commonly used to manage the manure. Composting takes typically 4-6 weeks for the manure to reach a stabilized material. The antibiotics tetracycline during composting of swine manure was degraded by 70%.5 The moisture content of manure should be maintained between 40% and 60% during the composting process, as high moisture content (more than 75%), inhibits a quick start to the composting process.6 However, heavy metals are non-degradable during composting.2 Long-term utilization of the fertilizer can result in heavy metal accumulation in soil which has adverse effects on food safety.7 On the other hand, anaerobic digestion of livestock manure can generate methane-rich biogas and reduce air and water pollution caused by animal manure.8 The removal rate of chlortetracycline in anaerobic digestion of swine manure was 98% at 55oC.9 Normally it takes a long time (10-30 days) to treat the manure.10 And some heavy metals may be transferred to the digested slurry which is not environmentally friendly.11

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Livestock manure can also be regarded as a renewable feedstock for biofuel production. Among the technologies for converting livestock manure into biofuels, hydrothermal liquefaction (HTL) has great potentials, The specific characteristics of HTL over anaerobic digestion and composting are: 1) It can directly convert wet biomass into biocrude oil in a very short time (a few minutes to several hours) and completely deactivate antibiotic resistant genes in swine manure;12,13 2) Most of the heavy metals in the feedstock have been reported to partition into in the solid residue after HTL. Furthermore, the bioavailable heavy metal fractions were transformed into a more stable form after HTL, which obviously decreased the environmental risk of the raw material associated with heavy metals.14 Therefore, HTL has a great potential in manure management. HTL of livestock manure (swine, dairy and poultry) has drawn great attention in recent years. Optimal operational conditions for biocrude production and oil characterization have been explored.15-19 However, there is little information available about the fate of nitrogenous compounds in the HTL products. Nitrogen content in HTL biocrude is not ideal.12 In the petroleum refining industry, the nitrogen-containing compounds with high molecular weights are sterically hindered and difficult to hydrodenitrogenate due to the inaccessibility of the catalyst surface.20 Furthermore, N1 compounds are more recalcitrant to hydrotreatment than compounds with additional nitrogen or oxygen heteroatoms. Hence, the speciation of nitrogen compounds in the biocrude oil needs to be investigated in order to develop proper methods to upgrade the HTL biocrude oil. Aqueous phase is the main by-product during the HTL process, and it contains abundant nitrogen-containing compounds, making it 4


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environmentally unfriendly. The forms of nitrogen-containing compounds in the aqueous phase affect its ability to be treated and safely discharged. As previously reported, nitrogenous compounds containing heteroatoms and methyl groups on their rings have a greater toxicity potential to the environment.21 Therefore, it is necessary to understand the transport and fate of the nitrogen-containing compounds in both the HTL aqueous and oil phases. Nitrogen distribution was previously investigated during HTL process for microalgae, cornstalk and human feces, but nitrogen transformation received scant attention.22-24 In this study, six kinds of livestock manures, i. e. swine, dairy, beef, laying hen, broiler (refers to chickens raised for meat production), and sheep manure were selected as HTL feedstocks. The objectives of this research are: (1) to explore the distribution and characterization of HTL products; (2) to characterize the nitrogen-containing compounds in the biocrude oil, aqueous phase and solid residue; (3) to elucidate pathways of nitrogen transformation and fate during the HTL process.

EXPERIMENTAL SECTION Feedstock The feedstock was collected from livestock and poultry farms in the suburbs of Beijing, China. Swine manure was collected from a farm of over 100 sows in Pinggu District; dairy manure and beef manure from farms herds of over 100 heads in Daxing District; laying hen manure from a farm of over 1000 poultry in Daxing District; broiler manure from a farm of over 1000 birds in Miyun District; and sheep manure from a 5



farm of over 100 heads in Miyun District. All manure samples were fresh except for dairy manure, beef manure and sheep manure. They were obtained about 3-5 days after being excreted. The characterization of feedstock is illustrated in Table 1. The manure samples are typical because each of them has comparable biochemical compositions to those reported in the literature.25-28 In addition, these manures are mass produced, particularly in China, as the fast development of centralized farms results in over 100 million tons of cow manure, pig manure, and chicken manure per year.29 The manure samples were stored in a refrigerator at 4oC after homogenization. The samples were adjusted to a total solid content of 20% (dry weight) by adding deionized water prior to the HTL experiments. HTL experiments Experiments were carried out in a batch reactor (Model 4593, Parr Instrument Company, USA) with a total volume of 100 mL (heating rate: 6-8oC/min).30 The reaction temperatures were 310oC and 340oC, and the retention time was set at 30 min, which were reported as optimum conditions for obtaining maximum biocrude yield from manures.18, 19 The separation procedure of the HTL products is shown in Fig. S1 (Supporting information). The products yield was calculated based on the equations as previously described.31 Characterization of feedstock and products The methods for conducting the proximate analysis and determining the biochemical composition of livestock manures can be found in a previous study.30 The elemental components (C, H and N) of the feedstock and biocrude oil were determined by an 6


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elemental analyzer (Vario EL III, Elementar Analysensysteme GmbH, Germany). The total carbon (TC), total organic carbon (TOC), total nitrogen (TN) and chemical oxygen demand (COD) in the aqueous phase were detected as previously described.22, 32

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Table 1 Proximate analysis, biochemical and organic elemental composition of the six livestock manure samples Parameter

Swine

Dairy cow

Beef

Broiler

Laying hen

Sheep

manure

manure

manure

manure

manure

manure

Moisture

79.75±0.04

78.99±0.28

72.66±1.45

73.43±0.60

75.85±1.44

17.35±0.35

Ash

17.09±0.95

38.45±3.6

42.95±4.17

34.74±0.73

38.01±2.98

28.86±1.06

Lipid

10.6±0.11

5.71±0.47

4.45±0.35

6.75±0.26

6.08±0.38

3.77±0.23

Protein

26.4±0.65

14.3±0.26

18.7±0.73

25.3±0.43

23.5±0.14

21.5±0.04

Hemicellulose

34.0±0.91

18.1±1.17

26.7±1.62

32.6±1.12

34.3±1.56

19.2±0.75

Cellulose

12.2±0.17

17.1±1.16

30.1±0.84

29.9±0.90

31.1±1.74

20.9±0.22

Lignin

5.38±0.17

5.17±0.86

10.8±0.30

2.07±0.14

2.44±0.29

15.7±0.56

Non-fibrous carbohydrate*

11.4

39.6

9.25

3.38

2.58

18.9

C

49.67±0.02

50.58±0.62

54.48±0.58

45.85±0.14

52.88±0.34

51.69±0.30

H

6.84±0.39

6.66±0

6.59±0.53

5.82±0.03

6.65±0.02

6.49±0.28

N

4.66±0.06

2.45±0.03

3.40±0.18

4.09±0.41

4.07±0.06

3.56±0.18

Proximate analysis (%)

Biochemical analysis (%, daf)

Organic elemental composition (%, daf)

*Non-fibrous carbohydrate=100-Ash-Lipid-Protein- Hemicellulose-Cellulose-Lignin, daf: dry ash-free basis

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The methods for gas chromatography-mass spectroscopy (GC-MS, QP2010, Shimadzu, Japan) analysis of the biocrude oil and aqueous phase were conducted as previously described.30, 33 Fourier transform infrared (FT-IR) analysis of the biocrude oil was conducted using a FT-IR spectroscopy (Nicolet 6700, Thermo Fisher Scientific, USA). The functional groups of the solid residue were identified by X-ray photoelectron spectroscopy (XPS, PHI 5300, PerkinElmer, USA), using a Mg Kα line (15 kV, 250 W) as the radiation source. The binding energy was calibrated through setting C 1s at 284.6 eV. The Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS) analysis was carried out using a 9.4 T Bruker Apex ultra FT-ICR mass spectrometer. The electrospray ionization (ESI) was operated in positive-ion mode (Emitter voltage: 5.0 kV; capillary column front end voltage: 4.5kV; capillary column end voltage: 320 V). Ten milligrams of oil sample were first mixed with 1 mL of toluene. Then, twenty microliters of the solution mixture were diluted with 1 mL of a toluene/methanol (1:1) solution. ICR was operated at 15 db attenuation, 150-800 Da mass range, 4 M acquired data size, and time-domain data sets were coded from 128 data acquisitions. Regarding the aqueous analysis, 1 mL of sample was diluted with redistilled methanol to a total volume of 10 mL and then filtered with a fiber filter membrane. Ten mL of water soluble organic matter was washed with redistilled methanol and then diluted 10 times with methanol. The extracts were then processed for ESI FT-ICR MS analysis.

RESULTS AND DISCUSSION 9



Products distribution and characterization Fig. 1a shows the products distribution after HTL of different livestock manures. The results indicated that the temperatures (310 and 340oC) had no obvious effect on the products distribution. The highest biocrude yield was 30.8% (based on dry ash-free basis, daf) obtained at 340oC for swine manure. Biocrude yields ranged from 15.0%, daf to 30.8%, daf for the livestock manures. During HTL, the biomass compounds were firstly decomposed and depolymerized to small compounds. These highly reactive compounds then polymerized and formed biocrude oil, gas and solid compounds.34 It was confirmed that the biocrude yields were greatly affected by the biochemical composition of the feedstocks, in the order of lipids > proteins > carbohydrates.35 The biocrude yield from swine manure in this study was similar to that of Xiu’s study (31.1%, daf), which may be attributed to the similar compositions of the feedstocks.17 Moreover, swine manure had the highest content of lipids (10.6%, daf) and proteins (26.4%, daf) among the six feedstock, which led to the highest biocrude yield. The low biocrude yield obtained with manures can be attributed to their high carbohydrate content (over 60%, daf) and low lipid content (less than 7%, daf except for swine manure). The high ash content in the manures could also be a contributing factor to the low biocrude yields, as it can hinder biocrude formation during HTL.28 On the other hand, the aqueous phase was the most abundant fraction (Fig. S2) in the products from the HTL of swine, beef, laying hen and broiler manure. Most of the nutrients and part of the organics in the feedstock were converted into the aqueous phase, which resulted in high yields of the aqueous phase.36 In addition, some soluble salts containing K or 10


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Na in the feedstock were mostly dissolved in the aqueous phase.22 The solid residue (except for that of swine manure) also constituted a large portion of the HTL products (Fig.S2), which was closely related to the high ash contents in the feedstock. Most of the metal elements in the raw materials, such as Ca, Mg, Al, Fe and Zn, accumulated in the solid residue.22 The gaseous products were the least fraction among the products (Fig. S2). CO2 was the most abundant gaseous component with a small quantity of CH4 and H2 also being detected (Table S1, supporting information).

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a

Sheep manure Broiler manure Laying hen manure Beef manure Dairy manure

340C 310C

Swine manure

0

5

10 15 20 Biocrude yield (%, daf)

Biocrude oil

Solid residue

Gases

25

30

Aqueous phase

b

Sheep manure

Nitrogen

Broiler manure Laying hen manure Beef manure Dairy manure Swine manure

Sheep manure Broiler manure

Carbon

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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Laying hen manure Beef manure Dairy manure Swine manure

0

20

40 60 80 Carbon and nitrogen balance (%)

100

Fig. 1 a: The biocrude yield from HTL of different manures. b: Carbon and nitrogen balance during HTL of manures (the products in the conditions with higher biocrude yield were analyzed. The nitrogen in the gases was not detected in this study).

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The carbon and nitrogen distribution in the products after HTL were shown in Fig. 1b. Most of the carbon in swine, laying hen and sheep manure was transferred to the biocrude oil (47.0%, 33.4% and 36.6%, respectively), while the majority of carbon in the dairy and broiler manure was released into the aqueous phase (44.4% and 43.5%, respectively), and 36.1% of carbon in the beef manure accumulated in the solid residue. The carbon contents improved dramatically from < 54.5% in the feedstock to over 74.2% in the biocrude oil. Meanwhile, the TC in the aqueous phase ranged from 13,772 to 40,106 mg/L, most of which was organic carbons (12,860-39,802 mg/L) (Table S1). On the other hand, over 37% of nitrogen in the manures was distributed to the aqueous phase, except for beef manure. Most of the nitrogen (35.7%) in the beef manure migrated into the solid residue. The highest TN in the aqueous phase was 5,816 mg/L, obtained from laying hen manure at 340oC (Table S1). Yu et al. found that 65-70% of nitrogen and 35-40% of carbon in the algae was converted into water soluble compounds.24 Please note that the sum of nitrogen recovery in the biocrude, aqueous and solid residue from HTL of manures (except for swine and dairy manure) is only about 85%, the rest of nitrogen might transfer to the gases as NH3, HCN, NO2 and N2O.37 In order to investigate the nitrogen-containing species in the solid residue, the XPS analysis was conducted and the N 1s spectra of the solid residue were divided into four peaks. N1: pyridinic-N, N2: protein-N, N3: pyrrolic-N, and N4: quaternary-N (Fig.S3, supporting information). It showed that the nitrogenous compounds in the solid residue were primarily in the form of pyridinic-N, pyrrolic-N and quaternary-N. The pyridinic-N and pyrrolic-N might be produced through the degradation of protein-N in 13



the manures, then the pyridinic-N could be converted into more stable quaternary-N via polymerization or ring condensation reactions.38 Anaerobic digestion is one of the most common methods to treat the manure, where 28% of carbon in the feedstock was recovered as CH4 after anaerobic digestion of swine manure. The energy yield of CH4 was 7.1×105 kJ per 100 kg dry mass.39 In comparison, 47% of carbon in swine manure was migrated into the biocrude oil via HTL, and the energy yield of biocrude oil from HTL of swine manure was 9.3×105 kJ per 100 kg dry mass (based on the total HHV produced from the biocrude oil) in this study. Organic compounds in the biocrude oil and aqueous phase GC-MS results (Fig. 2a) indicated that the biocrude oil was mainly composed of acids and esters (19.3-49.0% of the total peak area), alcohols and phenols (4.9-30.1% of the total peak area), hydrocarbons, nitrogen-containing compounds, ketones and aldehydes. The acids and esters in the biocrude oil were mostly long chain compounds with carbon numbers ranging from 16 to 27. The ketones and aldehydes in the biocrude oil were all chain compounds, while the hydrocarbons and the nitrogen-containing compounds contained both chain and cyclic compounds (Table S2, supporting information). Moreover, we performed the FT-IR analysis to characterize the biocrude oil (Fig. S4). It showed the main functional groups in the biocrude oil were -OH, -NH, -CH and -C=O, indicating the presence of alcohols, acids, ketones, hydrocarbons and nitrogen-containing compounds in the biocrude oil.19 Overall, the results of FT-IR were consistent with GC-MS analysis. Many kinds of nitrogen-containing compounds (16.66-66.68% of the total peak area) 14


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were detected in the aqueous phase (Fig. 2b). The nitrogen-containing compounds included pyridine, pyrazine, pyrrole and pyrrolidine derivatives (Table S3, supporting information). Moreover, the acids in the aqueous had much shorter chains (carbon number: 3-9) than those in the biocrude oil. The ketones and aldehydes in the aqueous phase were primarily cyclic compounds, like cyclopentanone and 2-Cyclopenten-1-one derivatives, which were different from those (chain compounds) in the biocrude oil. However, the phenol, p-Cresol, phenol, 2-methyl- and phenol, 4-ethyl- detected in the aqueous phase were similar to those detected in the biocrude oil. The fatty acids, amino acids and monosaccharides were formed via the hydrolysis of lipid, protein and cellulose or hemicellulose in the manures, respectively. The decarboxylation of fatty acids could generate long chain hydrocarbons, and the cyclic hydrocarbons might have been created by the dehydrogenation and cyclization of chain hydrocarbons.40 Besides, the short chain acids and cyclic ketone were produced from the decomposition of monosaccharides, and the chain ketones were likely formed through the deamination and decarboxylation of amino acids.41, 42 In addition, the chain amides might originate from the aminolysis of ammonia and fatty acids while the pyridine, pyridinol and pyrolidinone derivatives probably came from the Maillard reactions between the monosaccharides and amino acids in the manures.43 The phenol derivatives in the biocrude oil and aqueous phase were probably generated by the hydrolysis of cellulose and lignin in the raw materials.41, 44

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100

Hydrocarbons Nitrigen-containing compounds Acids and esters

Ketones and aldehyde Alcohols and phenols

a

90

Total peak area (%)

80 70 60 50 40 30 20 10

0

Swine manure

Dairy manure

Beef manure

Laying hen manure

Broiler manure

Sheep manure

90

b 80 70

Total peak area (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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60 50 40 30 20 10 0

Swine manure

Dairy manure

Beef manure

Laying hen manure

Broiler manure

Sheep manure

Fig. 2 Organic groups in the biocrude oil (a) and aqueous phase (b) from HTL of livestock manures identified by GC-MS analysis.

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Nitrogen compounds in the biocrude oil and aqueous phase As swine manure had the highest biocrude yield, ESI FT-ICR MS analysis was carried out to get a more comprehensive understanding of the nitrogen-containing compounds in the biocrude oil and aqueous phase. The samples were comprised of a diverse collection of compounds (N1-4O1-5). N1O1, N2 and N2O1 species were dominant in the biocrude oil, while the nitrogen-containing compounds in the aqueous phase primarily took the form of N2O2 and N2O3 (Fig. S5, supporting information). Furthermore, the abundance-contoured plots of DBE versus carbon number for basic nitrogen compounds (Fig. 3) revealed that N1 class species had the highest relative abundance with double bond equivalent (DBE) values of 4, carbon number of 19-30 and DBE values of 5, carbon number of 11-13 in the biocrude oil and aqueous phase, respectively. N1 class species with a DBE value of 4 could be attributed to pyridine derivatives. Increasing the value of the DBE by one signified that an aliphatic ring or a double bond was introduced into the structure. N1 species with DBE = 5 in the aqueous phase were likely tetrahydroquinoline or alkyl-substituted pyridine compounds with a double bond.45 In addition, higher relative abundances of the N1O1 species were observed at DBE values of 1-3, carbon numbers of 18-23 and DBE values of 2-3, carbon numbers of 18-23 in the biocrude oil and aqueous phase, respectively. The N1O1 compounds observed in both samples with DBE values of 0-4 and carbon numbers of 14-24 were likely fatty-amides.46 N1O1 compounds detected in the biocrude oil at DBE = 8, carbon number = 22 were likely pyrrolidinone derivatives. N2 species may be imidazole derivatives with a DBE of 3 while it could be pyrazine 17



derivatives with a DBE of 4. The dominant N2O1 compound with a DBE of 6 and 4 were probably oxygenated alkyl-imidazoles and oxygenated alkyl-pyrazines, respectively. For the N2O2 compounds, they mainly had DBE values of 10, 11 and 7, 8 in the biocrude oil and aqueous phase, respectively. Higher relative abundances of N3 compounds in the biocrude oil and aqueous phase were detected at DBE values of 915, carbon numbers of 17-31 and DBE values of 7, carbon numbers of 11-14, respectively. The molecular structure for the N3 compounds might be attributed to benzotriazole derivatives or alkyl substituted pyridyl-piperazines.47 N3O1 compounds had higher abundances with DBE values of 11-17, carbon numbers of 20-35 and DBE values of 7-10, and carbon numbers of 11-16 in the biocrude oil and aqueous phase, respectively. They were probably oxygenated versions of N3 compounds. The main N3O2 compounds observed were at DBE values of 11-13, carbon numbers of 22-35 and DBE values of 7-11, carbon number of 13-21 in the biocrude oil and aqueous phase, respectively. The result via the thermogravimetric analysis (Fig. S6) indicated that 51.7% of biocrude oil was volatile when the temperature reached 300oC. Thus, the GC-MS analysis can only reflect part of the compounds present in the biocrude oil because only volatile compounds could pass through the GC capillary column and be identified. The boiling points of some nitrogen-containing compounds are too high to volatilize during GC-MS analysis. For example, large molecules with 4-5 aromatic rings cannot be identified though GC-MS.48 Whereas FT-ICR MS is capable of resolving tens of compounds per nominal mass owing to ultrahigh resolution and high mass accuracy. 18


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FT-ICR MS could detect polar and non-polar chemical components (m/z > 225) of complex organic mixtures.49 Therefore, the combination of GC-MS and FT-ICR MS analysis is able to give a comprehensive understanding of the nitrogen compounds in HTL products with a large range of molecular weights.

19



12

N O 1 6

DBE

8

6

4 12 16 20 24 Carbon Number

4

0

12 18 24 30

Carbon Number

10 15 20 25

12

12 18 24 Carbon Number

1

DBE

4

Relative Abundance (% total)

DBE DBE

40.00

30.25 20.50

30.25

10.75 1.000

20.50

40.00 30.25 10.75 20.50 10.75 1.000 1.000

a

15 N3O3 10

N3O4

8

5

4 10 15 20 25 30 Carbon Number

DBE


10 15 20 25 Carbon Number

12 N4O1

N4

10

10

8

8

6 12 15 18 Carbon Number 15

12 15 18 21 Carbon Number 16 N4O3

12

12

9

N4O2

DBE

2

12 DBE

DBE 3

5 16

DBE

DBE

DBE

DBE

8 4

Carbon Number

4 8 12 16 20 Carbon Number 20 N O

10

4

0 6 12 18 24 8 16 24 Carbon Number Carbon Number 16 NO NO 12 2 4 12 2 6 8

8

15

8

40

4 12 16 20 24 10 20 30 40 50 Carbon Number Carbon Number 16 N O 16 N4O4

12

12

3

6


b

8

0 10 20 30 Carbon Number 16 N O

6

4

8


6

12

DBE

4


12 N O 2 3

N3O1

10

DBE

4

4

30

15

DBE

8

DBE

8 16 24 32 Carbon Number 12 N O 1 4

12 N2O2

N3

DBE

3

0

0

0

1

8

20

Number 25 Carbon NO

40.00

20 30 10 40 20 30 40 Carbon Number Carbon Number Relative Abundance (% total)

DBE

DBE

DBE

4

8

N2O1


DBE

2

12


DBE

1

N2

20 30 40 Carbon Number 16

DBE

4

0 0 10 15 20 8 16 24 Carbon Number Carbon Number 12 N O 12 N O

8

16 12 8 4

10

10 20 30 40 10 20 30 40 Carbon Number Carbon Number 12

DBE

N1O1

20

10

DBE

0 20 30 40 Carbon Number

20

10

15

10

25 N 4 15

20

0 10 20 30 40 10 20 30 40 Carbon Number Carbon Number N3O3 NO 20 3 2 20

DBE

DBE

10

25 N 4

10

10

2

DBE

2

2

8

DBE

4

8

N4Ox

20 N3O1

N3

20

0 10 20 30 40 10 20 30 40 Carbon Number Carbon Number 20 N2O3 20 N O

DBE

12

6 N1 DBE

DBE

DBE

DBE

0 0 10 20 30 40 20 30 40 Carbon Number Carbon Number 30 N1O2 16 N1O3 20 8 10 0 0 10 20 30 40 10 20 30 40 Carbon Number Carbon Number

DBE

DBE

10

10

16 N2O1

20 N2 15 10 5

N1O1

DBE

20

N1

DBE

DBE

20

N3Ox

Relative Abundance (% total)

N2Ox

N1Ox

DBE

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46

Page 20 of 29

8 4


Carbon Number

Fig. 3 Color-coded abundance-contoured plots of DBE versus the carbon number for HTL products (a: biocrude oil; b: aqueous phase) of swine manure derived from ESI FT-ICR mass spectra.

20


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Predicated reaction pathways of nitrogen transformation during HTL O NH2 O

O R

H

OH

H2 N

H

O

R1

H

H2 N

(1)

- H 2O

N

O

O

H N

- NH 2

-

OH

OH

H

N

O

NH2 OH

HO

- NH 2

OH

O

O

Aspartic acid

(2)

-H

HN

- COOH

NH2

CO O

- H

Lysine

HO

NH2

NH2

O

Glutamic acid

O H N

-H

HO

H N

O

- CH 3 OH

(3) OH Proline

pyrrolidin-2-one O

O

HO

O OH

- H 2O

O

R R' OH

NH2

O O

HN

NH2 Glutamic acid

- H 2O

- COOH

R'

R'

N

N

OH

(4)

HN

OH

HO

OH

R

R

R' N

N R

O

- H

- COOH

NH2 Leucine

H N

- COOH

R'

- H2O

(5) N R

Fig. 4 Predicated reaction network of nitrogen transformation during HTL of manure (The compounds in red were detected in the biocrude oil and the compounds in blue were detected in the aqueous phase).

Based on the above analysis and the findings in the literature, five key reaction pathways for nitrogen transformation during HTL of livestock manures were proposed (Fig. 4). It illustrates the chain amides in the biocrude oil were formed via aminolysis of ammonia in the protein and fatty acids in the lipid (Pathway 1).41 As for the aqueous phase, the pyridine likely came from the deamination, decarboxylation and dehydrogenation of lysine or aspartic and glutamic acids, whereas the pyrrole was formed from the decarboxylation and dehydrogenation of leucine or proline (Pathway 2 and 3).50 The pyrrolidinone was likely produced through dehydration and 21



Page 22 of 29

decarboxylation of glutamic acid (Pathway 4). The pyrazine derivatives were probably generated from the reactions between amines and sugars (Pathway 5).51 The biochemical compositions significantly impacted the biocrude yield obtained after HTL. For instance, Zhang et al found that the biocrude yield from HTL of protein and glucose increased from 4.0% to 22% when their mass ratio increased from 0.5:1 to 4:1, and decreased to 19% when the mass ratio further increased to 5:1.43 However, the influence of mass ratio on the nitrogen content in the biocrude oil was not investigated. Interestingly, in our study, swine manure has a higher protein content (26.4%) than laying hen manure (23.5%), whereas the nitrogen content in the

biocrude oil from

swine manure (4.87%) was lower than that from laying hen manure (5.36%). Sheep manure and beef manure exhibited similar characteristics, which illustrated the nitrogen content in the biocrude oil was not increased with the increase of protein content in the feedstock. This was probably due to the different mass fraction of lipid, protein and carbohydrate (cellulose or hemicellulose) and their interaction reactions. The reactions between lipid and protein (Reaction 1) or the Maillard reaction between protein and reducing sugars can contribute to the existing nitrogen in the biocrude oil. Based on the results of the current study, we think the lipid, protein and carbohydrate should be present in an optimal mass ratio to get a minimum nitrogen content in the biocrude oil. Further studies can be performed in the future with suitable model compounds to explore the optimal ratio and the results can be extrapolated to real biomass to improve the biocrude quality. In summary, there are variety of nitrogen-containing compounds in the biocrude oil 22


Page 23 of 29 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


and aqueous phase. Nitrogen limits the utilization of biocrude oil as a fuel. The nitrogen-containing compounds in the biocrude oil will result in storage instability, corrosion, and NOx emission when combusted.47 In crude oil refining, nitrogen is removed through hydrotreatment to avoid catalyst deactivation and to enhance the fuel stability.52 It was found that N1 compounds were more refractory for hydrotreatment than compounds with additional oxygen or nitrogen atoms in syncrude oil.53 Furthermore, for N1 species, nitrogen compounds with more unsaturated cores and shorter alkyl side chains were easier to be converted than those with long alkyl side chains.54 On the other hand, it is also possible to extract value-added chemicals from biocrude oil.12 For example, the biocrude oil could be used as a green precursor to prepare nitrogen-co-doped carbon dots which exhibit excellent multicolor luminescence on bioimaging of plant cells.55 Understanding of nitrogen-containing compounds in the biocrude oil could provide new knowledge for biocrude upgrading and utilization. The aqueous phase of HTL needs to be treated properly before discharge due to its high COD and abundant nitrogen-containing compounds. Algae cultivation, anaerobic digestion and microbial electrolysis cell were demonstrated to be feasible ways to utilize the nutrients in the aqueous phase.32, 56, 57 However, the pyridines, pyrroles and pyrazine may inhibit algae growth. Pyridine is a toxic and carcinogenic compound. It can be degraded by a pyridine-degrading bacterium and produce NH4+-N. The NH4+-N could be easily consumed by the algae.58,

59

Therefore, the aqueous phase can be

pretreated by the pyridine-degrading bacterium and then used as a fertilizer to cultivate 23



algae or other produce. Pham et al. found that different nitrogenous compounds have different cytotoxicity, the compounds with methyl groups and heteroatoms on their rings had a higher cytotoxicity. Moreover, a synergistic cytotoxicity effect among the compounds was observed, an individual nitrogenous compound was not significantly cytotoxic while a mixture of the nitrogenous compounds expressed high toxicity on the mammalian cells.21 Therefore, the nitrogen forms in the aqueous phase have great effects on its treatment. The results of this study support the continued need for research on utilizing the HTL aqueous product.

Supporting information Characterization of HTL products from different livestock manures, organic compounds in the biocrude oil and aqueous phase from HTL of livestock manures through GC-MS analysis (Table S1-S3). The separation procedure of the HTL products, the yield of HTL products from different manures based on the dry weight of the feedstock, N 1s spectra of the solid residue from HTL of different manures, broadband ESI FT-ICR mass spectra and heteroatom class distribution of nitrogen species in the biocrude oil and aqueous phase of swine manure identified with positive-ion ESI FT-ICR MS, thermogravimetry analysis of biocrude from HTL of swine manure (Fig. S1-S6).

Acknowledgements This work was financially supported by the National Key Research and Development 24


Page 24 of 29

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Program of China (2016YFD0501402), the National Natural Science Foundation of China

(U1562107),

and

Beijing

Youth

Top-notch

Talents

Program

(2015000026833ZK10). We thank James D. Sheehan, Akhila Gollakota (Penn State University) and Jamison Watson (University of Illinois at Urbana-Champaign) for the language polishing on this manuscript. We are also grateful to Prof. Phillip E. Savage (Penn State University) and Prof. Hongchao Guo (China Agricultural University) for their suggestions and kind discussions on nitrogen transformation pathways.

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Graphical Abstract GC-MS

FT-ICR MS [13CC

O NH2

[C22H28N2O1+H]+

+ 22H29N1O1+H]

[13CC21H41N1O1+H]+ [13CC21H29N3+H] +

O NH2 [C23H32N2+H]+

[C21H24N2O2+H]+ O N [C24H20N2+H]+

H N 337.35 337.10 337.15 337.20 337.25 337.30

Biocrude oil

Manure Protein-N

- H 2O

N R

m/z

O

O

HTL

[C20H36N2O2+H]+

OH

H

H

R

H

N N N

NH2 [C13H20N2O2+H]+

[C11H16N4O2+H]+

N H [13CC13H21N1O2+H]+

O N H

[C12H16N2O3+H]+

H N

Aqueous phase

13

[C14H24N2O1+H]+

+

[ CC11H14N1O4+H] H O [C15H28N2+H] + N N H

237.05

237.10

237.15

237.20

237.25

Synopsis: Hydrothermal liquefaction of manure can produce renewable biocrude oil and simultaneously recover nutrients in the aqueous.

29


237.30

m/z

Nitrogen Migration and Transformation during Hydrothermal

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