lable at ScienceDirect

Renewable Energy 145 (2020) 1761e1771

Contents lists avai

Renewable Energy

journal homepage: www.elsevier .com/locate/renene

Thermal cracking behavior, products distribution and char/steamgasification kinetics of seawater Spirulina by TG-FTIR and Py-GC/MS

Jie Li a, c, 1, 3, Yuanyu Tian a, c, 4, Peijie Zong a, c, 3, Yingyun Qiao a, c, *, Song Qin b, **, 2

a State Key Laboratory of Heavy Oil Processing, China University of Petroleum (East China), Qingdao, 266580, Chinab Yantai Institute of Coastal Zone Research, Chinese Academy of Sciences, Yantai, 264000, Chinac Shandong Provincial Key Laboratory of Universities and Colleges of Low-Carbon Energy and Chemical Technology, Shandong University of Science andTechnology, Qingdao, Shandong, 266590, China

a r t i c l e i n f o

Article history:Received 2 January 2019Received in revised form19 June 2019Accepted 19 July 2019Available online 22 July 2019

Keywords:BiomassMicroalgaePyrolysisProduct distributionGasificationGasification kinetics

* Corresponding author., State Key Laboratory ofUniversity of Petroleum (East China), Qingdao, 26658** Corresponding author.

E-mail addresses: Qiao_yingyun@126.com (Y. Qiao4 This author contributed to the work equally and s

authors.1 Present address: No. 66, West Changjiang Road

China, 266580.2 Present address: 17 Chunhui Road, Laishan Distri3 Present address: 579 Qianwangang Road, Huang

dong Province, 266590, P.R.China.

https://doi.org/10.1016/j.renene.2019.07.0960960-1481/© 2019 Elsevier Ltd. All rights reserved.

a b s t r a c t

In this study, fast pyrolysis of seawater Spirulina, is carried out to evaluate the potential of derivingvaluable chemicals and fuel molecules from this seawater algae variety. The devolatilization behavior andgaseous product evolution of seawater Spirulinawere carried out by TG-FTIR. Py-GC-MS was employed toinvestigate the composition and distribution of volatile products formed from the seawater Spirulinathrough high-temperature fast pyrolysis process. Finally, the seawater Spirulina char gasification reac-tivity and kinetic parameters were evaluated using advanced methods of volume, shrinking core andrandom pore. Results indicate that the thermal cracking process of seawater Spirulinamainly consisted ofthree reaction stages, including dehydration and drying stage, fast pyrolysis stage and residues slowdecomposition stage. High heating rate has significant effect on the performance of devolatilizationprofiles. H2O, CH4, CO2, HNCO, NH3, HCN, CO, CeO bond and C]O bond were the typical gaseousproducts released from the fast pyrolysis stage of seawater Spirulina. The maximum release rate ofseawater Spirulina for CH4 was located at about 450 �C, corresponding to the main pyrolysis of long-chainfatty acids from lipid fraction. The high temperature fast pyrolysis of seawater Spirulina resulted inaliphatic (alkanes, alkenes) and aromatic hydrocarbons, esters, oxygenates (carboxylic acids, aldehydes,ketones, and alcohols), phenolics, and nitrogen- and sulfur-containing organic compounds. Above 750 �Cwas considered as the optimum temperature, which can reduce the generation of oxygenated com-pounds, and the content of nitrogen and phenolic compounds were decreased, maximum yield ofquantified hydrocarbons was observed. The increase of gasification temperature can obviously improvethe gasification reactivity of seawater Spirulina chars. The activation energies of the VM, SCM and RPMmodels of seawater Spirulina chars were 187.95, 173.14 and 154.34 kJ/mol, respectively. RPM displays asignificant fitness with the experimental data than those of the other two models.

© 2019 Elsevier Ltd. All rights reserved.

Heavy Oil Processing, China0, China.

), sqin@yic.ac.cn (S. Qin).hould be regarded as co-first

, Huangdao District, Qindao,

ct, Yantai, P.R.China, 264000.dao District, Qingdao, Shan-

1. Introduction

Under the dual pressures of global warming coupled with theincreasingly tight environmental policies, it is imperative to shiftour focus from fossil fuels to sustainable green fuels [1,2]. Biomassis considered as an attractive renewable energy source with thehighest potential to contribute to the energy needs of modern so-ciety for both the industrialized and developing countries world-wide [1]. However, the production of renewable chemicals andbiofuels must be cost- and performance-competitive withpetroleum-derived equivalents to be widely accepted by marketsand society [3]. Microalgae-derived biofuels appear to be a prom-ising fuel compared to lignocellulosic-derived as economically

J. Li et al. / Renewable Energy 145 (2020) 1761e17711762

more appealing related to the use of arable land and technicalobstacles for product conversion [4,5]. Microalgae offer greatpromise to contribute a significant portion of the renewable fuels[6]. At present, Qingdao have built the largest marine microalgaeindustry production base in China. The production will reacharound 3000 tons in the year of 2020, the annual output value willreach about 1 billion yuan. How to develop the marine seawatermicroalgae industry into clean bio-energy through thermochem-ical pathways will be the key consideration in this article.

� Carbon dioxide “buster”; fixing high CO2 from surroundings [7].� Scale industrialization; It is distributed throughout thebiosphere and grows in the widest possible range of conditionsfrom aquatic (freshwater to extreme salinity) to terrestrial pla-ces [8,9].

� Short growth cycle; have a high growth rate and it could beharvested throughout the year [10].

� High calorific value; absence of lignin [11].

Pyrolysis has been popular in producing fuel product since thelate 1970s due to its advantages in its short process, strong adapt-ability, rapid response, high conversion rate and easy commer-cialization, etc [12,13]. Fast pyrolysis, the thermochemicalconversion process that takes place in the absence of oxygen underhigh heating rate (103e104 �C/s), converts seawater microalgaeinto renewable bio oil, char and gases [13,14]. Fast pyrolysis hasobvious advantages, such as short reaction time and minimumsecondary decomposition reaction [12]. The many advantages ofbiomass fast pyrolysis technology have made it turn into a newtechnology for efficient use of resources, which has become a hotspot for many scholars at home and abroad.

Thermogravimetric analyzer combined with Fourier transforminfrared spectrometer (TG-FTIR) is widely used to study thechemical structure and pyrolysis properties of polymers [15,16].TG-FTIR is a novel testing technique used to determine the masschange of a sample under programmed temperature and evaluatethe chemical composition of the gaseous produced during thedecomposition process. Plis et al. [17] used TG-FTIR technology tostudy the characteristics of pyrolysis and volatilization underbiomass catalysis on the basis of non-catalytic pyrolysis of biomass,and analyzed the effect of pyrolysis temperature and catalyst typefor biomass. The effect of pyrolysis on the main volatile productsprovides a reference for the selection of reasonable catalysts forbiomass pyrolysis gasification. The pyrolysis gas chromatography-time of flight mass spectrometry (Py-GC/MS) method is suitablefor any state samples, without prior separation and purification,which is beyond the other spectroscopic methods [18]. This featureis extremely beneficial for the study of Spirulina. The structure ofeach segment and crosslink of Spirulinamolecules is inferred by thethermal decomposition products of three components (proteins,lipids and carbohydrates) of Spirulina under different conditions.This analytical method also has the advantages of less sample us-age, high separation efficiency, and fast analysis speed [19].Therefore, Py-GC/MS is used to analyze the fast pyrolysis productsof Spirulina, which can avoid secondary reactions between pyrolysisproducts. Nevertheless, the current researches on the pyrolysisprocess of seawater Spirulina performed by this hyphenated tech-nology is considerably scarce at present.

Biomass gasification is a thermochemical process in which py-rolysis, oxidation, reduction and reforming of biomass polymers arecarried out in the presence of gasifying medium (air, oxygen orwater steam) to produce syngas [1]. Gasification can convert lowenergy density biomass from solid state to high grade combustiblegas. Compared with direct combustion, it has the advantages ofstable combustion, high thermal efficiency, low pollution,

especially low PM2.5 index [20]. Currently, the research on thegasification technique mainly focuses on isothermal gasification[21]. The gasification temperature and gasification agent are twoimportant factors in the isothermal gasification process. The tem-perature can promote the fully reaction of biochars. The gasificationagent (superheated steam as gasification agent) will help togeneratemore hydrogen and increase the calorific value (17e21MJ/m3) of the syngas [22].

Spirulina and microalgae/proteinaceous biomass have signifi-cantly different compositions from lignocellulosic biomass. Pyrol-ysis characteristics and products distribution of freshwaterSpirulina biomass have been a subject of study in a number ofliterature reports [9,23,24]. Few studies have been conductedregarding the pyrolysis properties of seawater Spirulina. In thisstudy, TG-FTIR was employed to carry out the fundamental studieson thermal weight loss characteristics and gaseous product ofseawater Spirulina. Py-GC-MS was employed to investigate thecomposition and distribution of volatile products formed from theseawater Spirulina high-temperature fast pyrolysis process. Thechemical components and physical structures of seawater Spirulinachars will systematically test by FTIR and SEM devices. Finally,thermogravimetric analyzer (TGA) coupled with steam generatorwas applied to reflect the char/steam isothermal gasificationmechanism and reactivity of Spirulina biochar based on the kineticparameters at temperatures of 750 �C, 800 �C, 850 �C and 900 �C.The main objectives of this work are to reveal the thermal crackingbehaviors and products distribution of seawater Spirulina,exploring the influence of different gasification temperatures onchar/steam gasification characteristics and kinetics, which isconsidered to be useful in regulating, optimizing, and advancing inthe industrialization.

2. Material and methods

2.1. Biomass samples

The Institute of Oceanology, Chinese Academy of Sciences has acommitment to provide the integrity structural seawater Spirulina(green microalgae) in a powder with a particle size of z180 m m, itwas taken at marine microalgae breeding base, Shandong province,China.

2.2. Proximate and ultimate analysis of the seawater Spirulina andhigher heating value (HHV)

The ultimate analysis was determined using an ElementarAnalysensysteme Gmbh (Vario MACRO cube, Germany). The prox-imate of the Spirulina biomass as per reported method [25]. Theoxygen (O) content and HHV were calculated from the equation ofreference [26].

2.3. TG-FTIR analysis

TG-FTIR is used to study the chemical structure and pyrolysisproperties of polymers. Thermogravimetric Analyzer (NETZSCH In-struments, STA 449 F3 Jupiter®, Germany) coupled to the FTIRspectrophotometer (Tensor II, BRUKER OPTICS, Germany) are theequipment used in this experiment. The experimental process refersthe method of Shen et al. [27]. To simulate the rapid pyrolysis pro-cess, we applied high heating rates of 100, 300 and 500 �Cmin�1.FTIR spectrometer range was set to be 4000 to 400 cm�1.

2.4. Py-GC/MS analysis

Pyroprobe 5000 pyrolyzer (CDS Analytical Inc.) coupled with a

J. Li et al. / Renewable Energy 145 (2020) 1761e1771 1763

Scion GCeMS Instrument was used to analysis rapid pyrolysisproduct of high polymers. The process of the seawater Spirulinapyrolysis by Py-GC/MS device was based on the per reportedmethod [23]. The programmed of oven was as bellows:

Temp (�C) Rate (�C/min) Hold (min) Total (min)

40.0 0 3.00 3.00180.0 3.0 3.00 52.67280.0 4.0 3.00 80.67300.0 10.0 0.00 82.67

Five different pyrolysis temperature were applied to investigatethe product composition by pyrolysis vapors: 700, 750, 800, 850,900 �C.

2.5. Seawater Spirulina char samples preparation

The seawater Spirulina chars was provided by the pilot plantdesigned by our groups. Please refer to the literature for specificmethods [21], and on this basis getting improved. The bio-charswere prepared by devolatilizing the raw materials in free-falltubular gasifier under a flowing nitrogen atmosphere (6 L/min) at800 �C. This is a most critical step connecting microalgae pyrolysisand gasification, and the bio-char are raw material on industriali-zation utilization for the preparation of syngas. Three differentcoking temperature were applied to investigate the char compo-sition: 700, 800, 900 �C.

2.6. Characteristics of seawater Spirulina chars

The proximate and ultimate analysis of the seawater Spirulinachars were detected by the same method applied to parent'ssamples.

FTIR spectra of seawater Spirulina chars were recorded usingBruker tensor II instrument to obtained the further information onthe changes of chemical composition compared with the precursor.

The surface morphology of seawater Spirulina chars wereconfirmed by scanning electron microscope (HITACHI S-4800,Tokyo, Japan).

2.7. Steam isothermal gasification of seawater Spirulina chars

The gasification behavior and kinetics of seawater Spirulinachars were investigated by using the device of isothermal TGAcoupled with steam generator. In this study, the gasification prop-erties and kinetic behaviors of three models (volumetric reactionmodel (VM), the shrinking core model (SCM), and the random poremodel (RPM)) are selected to explain the kinetics of steamisothermal gasification at different temperatures (750, 800, 850,900 �C). Seawater Spirulina char powder (20± 0.1mg) were placedin Al2O3 crucibles (15*5 mm) of the thermos-balance. The steamisothermal gasification procedure was programmed as bellows:

(i) samples heated at a rate of 15 �Cmin�1 from 35 �C to 750 �Cunder a nitrogen with a flow of 100mL/min;

(ii) wait 30min for balance;(iii) the gas was switched to a mixture of H2O/N2 with a flow of

100mL/min;(iv) the gasification process was start;(v) when the reaction was complete, the furnace is lowered to

ambient temperature.

Calculation method of carbon conversion rate (X) is:

X ¼ m0 �mm0 �mash

(1)

where m0 is the sample mass in gasification process when t¼ 0, mis the sample mass in gasification process when t¼ t andmash is themass at the end of the process, respectively.

2.8. Gasification kinetic models

The rate of apparent gasification reactions of biomass is quan-tified as:

dXdt

¼ kðTÞf ðXÞ (3)

where k is the reaction rate constant, dependent to the gasificationtemperature T, and f(x) describes the change in the physical andchemical properties of the reaction biochars as the gasificationreaction proceeds, corresponding to the selected n-order rateequation. The kinetic reaction rate constant k is a function of thereaction temperature and follows the Arrhenius expression:

kðTÞ ¼ Aexp�� ERT

�(4)

where A and E represent the pre-exponential factor and reactionactivation energy, respectively. T is the absolute temperature.

The VM model assumes that the gasifying agent diffuses uni-formly inside the biochar, and simultaneously reacts in all di-rections of the biochar particles, including the inside and outside ofthe particles. Therefore, the VM simplifies the gasification processbelonging to the gas-solid heterogeneous reaction into a homoge-neous reaction to facilitate the establishment of themodel [28]. Thereaction kinetic rate equation for the VM as shown below:

dXdt

¼ kVMð1� XÞ (5)

�lnð1� XÞ ¼ kVMt (6)

The SCM model is based on the fact that the porous biochar iscomposed of a number of uniforms, non-porous rounded particles,and the gasification reaction takes place on the outer surface ofthese non-porous particles. The pore skeleton in the biochar iscomposed of gaps between the non-porous rounded particles.During the gasification of biochar, the phenomenon of gasificationshrinkage is simultaneously carried out in each particle. As thegasification reaction is built into the internal particles of the bio-char, only the ash layer remains in the original particle position[29]. The reaction rate of the overall gasification process can beexpressed by the following formula:

dXdt

¼ kSCMð1� XÞ2=3 (7)

3h1� ð1� XÞ1=3

i¼ kSCMt (8)

The RPM model takes into account the surface of the poreswhere the biochars overlapped, as these overlapped may reducethe available reaction surface for the gasification process and usedit for the biomass gasification process [30].

dXdt

¼ kRPMð1� XÞffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi1�Jlnð1� XÞ

q(9)

J. Li et al. / Renewable Energy 145 (2020) 1761e17711764

The random pore model contains two parameters, the reactionrate constant k PRM and the pore structure characteristic parametersJ of the initial formation of biochars. When the initial porosity 30,surface area S and pore length L0 of the biochars are known, thepore structure parameters can be calculated from the followingformula:

J ¼ 4pL0ð1� ε0ÞS2

(10a)

However, the structural parameter measurement process is verytedious, these data were not available for all the fuels [31]. So, thepore structure characteristic parametersJ are generally estimatedby the carbon conversion rate Xmax corresponding to the maximumgasification reaction rate, as suggested in:

J ¼ 22lnð1� XmaxÞ þ 1

(11)

2J

� ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi1� flnð1� XÞ

q� 1

�¼ kRPMt (12)

3. Results and discussion

3.1. Biomass characteristics

The proximate and ultimate analyses as well as higher heatingvalue of the seawater Spirulina are listed in Table 1. Different fromlignocellulosic-based which is basically composed of cellulose,hemicellulose, and lignin, the major constituents of seawater Spir-ulina are carbohydrates, proteins and lipids [32]. Due to the abun-dant protein content in microalgae, which makes seawaterSpirulina contains high nitrogen content (9.75%) compared tolignocellulosic-based biomass (0.3e0.6%) [33,34]. Research findingsthat bio-oil produced from the pyrolysis of high nitrogen contentbiomass have better performance than low nitrogen content [35].Stimulated by high salt and high osmotic pressure of seawater,seawater Spirulina contains more nitrogen content than Spirulinalived in natural lake blooms (5.2%).

In the proximate analysis, it is obviously that seawater Spirulinawas rich in volatile matter (78.41wt %), which is similar to theprevious study of C. vulgaris (78.1 wt %) and A. platensis species(77.4wt %) [12]. In this study, seawater Spirulina has the low ash

Table 1Proximate analysis and ultimate analysis of seawater Spirulina and chars (wt.%).

Parameter Seawater Spirulina Seawater Spirulina char

700 �C 800 �C 900 �C

Proximate analysis a (wt.%, ad. Basis)Moisture 2.30 1.94 1.88 1.62Ash 4.42 36.18 36.51 36.88Volatile matter 78.41 10.10 8.33 7.33Fix carbonc 14.87 51.78 53.28 54.17Ultimate analysis b (wt.%, daf. Basis)C 45.74 60.18 58.77 60.03H 6.71 1.57 1.20 0.85Oc 36.94 29.43 32.11 32.16N 9.75 8.28 7.56 6.56S 0.86 0.54 0.36 0.40HHV 18.59 17.38 15.87 15.78Molar formula C1 basis C1H1.761O0.606

N0.184S0.008/ / /

a Dry-free basis.b Dry ash-free basis.c Calculated by difference.

content (4.42wt %), which is lower than the previous study ofSpirulina platensis (6.40wt %) [36]. This may be due to the absenceof any contamination during the growth of seawater Spirulina. Thecalorific value of the tested sample was found to be 18.59MJ kg�1.In general, microalgae have been shown to have calorific values ofbetween 18 and 21 kJ g�1 under normal grown conditions [37]. Thecaloric value of microalgal-based biomass depends upon the lipidcontent. The selected seawater Spirulina biomass may have lowerlipid content, which was the reason for its lower calorific value [38].The pyrolysis process is based on the combustion reaction:

C1H1.761O0.606N0.184S0.008 þ 1.960O2/CO2 þ 0.881 H2O þ0.814NO2 þ 0.008SO2 (10b)

3.2. Thermal decomposition behavior of seawater Spirulina fromTG-FTIR

3.2.1. Thermal cracking behaviors analysisThe devolatilization behavior of seawater Spirulina biomass are

shown in Fig. 1. As observed, DTG curves obtained can apparentlybe divided into three stages. The first stage is mainly the process ofdehydration and drying, which mainly occurs around 100e180 �C.The second stage contains two peaks, a small peak at around310e350 �C among them gradually disappears with the tempera-ture increases (300 �C min�1). The strong peak corresponds tomaximum weight loss was (up to 75wt%) witnessed from 200 to600 �C, it is likely due to the thermal decomposition behavior ofendogenous carbohydrate components (such as starch and othercarbohydrate residues combined with proteins [39]. The third stageis distinguished by a negligible weight loss discovered above 600 �Ctemperature, which is slow decomposition process of the residues.

In the main pyrolysis stage, the DTG curve shows a sharp de-volatilization peak at about 350e380 �C, accompanied by a smallpeak (at around 310e350 �C) on the left of the main peak. The sharkpeak was attributed to the decomposition of carbohydrates anddegradation of proteins. The small peak which was mainly assignedto the thermal cracking of proteins and lipids in the seawaterSpirulina [39e41]. However, the small peak is tending to be van-ished when the heating rate increased to 500 �Cmin�1. Whensample under low heating rate conditions, carbohydrates, proteinsand lipids constituents may be sequentially thermal crackingseparately, exhibiting characteristic individual decompositionpeaks. However, as the heating rate increases, all constituents aresimultaneously cracking and several adjacent peaks are combinedtogether to form overlapping wider and higher peaks, and noseparate peaks appear. This conclusion was also confirmed in thepyrolysis of coal under high heating rate [16,42].

As shown in the TG profiles, an increase in the heating rate from100 to 500 �C/min of the sample causes displacement of pyrolysisconversion to higher temperatures. In other words, to achieve thesame mass loss (TG wt. %), the higher the heating rate, the higherthe corresponding pyrolysis temperature. Corresponding to theDTG profiles, the whole weight losses were shifted to higher tem-perature zones (100 �C min�1 to 359.96 �C; 300 �C min�1 to373.81 �C; 500 �C min�1 to 385.70 �C). This phenomenon has alsobeen confirmed in the DTG curves of other microalgae species(Chlorella vulgaris, Isochrysis galbana, Nannochloropsis gaditana andNannochloropsis limnetica) by Antonio et al. [36]. For the reason ofthis phenomenon, we believe that heating rate generally has pos-itive and negative effects on the seawater Spirulina samples. As theheating rate increases, the response time of the seawater Spirulinaparticles pyrolysis required temperature will be shorter, which fa-cilitates to the pyrolysis process. However, the shorter the reaction

200 400 600 800

20

40

60

80

100

TG

(wt%

)

Temperature (ºC)

100 ºC/min300 ºC/min500 ºC/min

200 400 600 800

-200

-150

-100

-50

0

100 ºC/min300 ºC/min500 ºC/min

Temperature (ºC)

DT

G/(

%/m

in)

Fig. 1. TG and DTG profiles of the seawater Spirulina pyrolysis at 100, 300 and 500 �C min�1 heating rates.

J. Li et al. / Renewable Energy 145 (2020) 1761e1771 1765

time experienced by the seawater Spirulina causes the decrease ofreaction degree, and the difference of temperature between theinside and outside of the seawater Spirulina particle becomes large,which may cause thermal hysteresis. It would lead to the less timeto diffuse of pyrolysis products adhere the outer layer of theseawater Spirulina particles, affected the process of internal pyrol-ysis. As a result of the superposition of the positive and negativeeffects, the curve moves toward the high temperature side.

3.2.2. Evolving characteristics of typical gaseous productsGaseous product evolution from pyrolyzing seawater Spirulina

in TGAwith the heating rate of 300 �C min�1 were analyzed by FTIRin real temperature is shown in Fig. 2. The IR spectra of seawaterSpirulina pyrolysis were obtained in the scale of relative tempera-tures of 236 �C (Peak 1), 300 �C (Peak 2), 366 �C (Peak 3), 450 �C(Peak 4) and 566 �C (Peak 5). According to the characteristicwavenumber bands of the gaseous product functional groups re-ported in Refs. [43e45], the types of main gaseous products formedby high temperature rapid pyrolysis of seawater Spirulina can beidentified. Table 2 shows the functional groups assigned to theevolved gas during pyrolysis process. H2O, CH4, CO2, HNCO, NH3,HCN, CO, CeO bond and C]O bond were the typical gaseousproducts released from the main reaction stage of seawaterSpirulina.

4000 3500 3000 2500 2000 1500 1000 500

CO2

Wave number (cm-1)

566 ºC 450 ºC366 ºC 300 ºC236 ºC

H2O C-H

CO2

CO C=O H2O

HNCOCH4

C-O

NH3

HCN

Fig. 2. FTIR spectra of gaseous products evolved for 300 �C min�1 pyrolysis of seawaterSpirulina at 236, 300, 366, 450, 566 �C.

The peak at 366 �C was the most dominant one in all emissionpeaks. The IR spectrum at 366 �C exhibited obvious absorptionbands of H2O, CO2 and CO and weak absorption bands of NH3 andHCN, indicating the maximum decomposition rate of proteinsoccurred at 366 �C [43]. The IR spectrum at 450 �C was the muchstronger absorption bands of CeH stretching. This is mainly due tothe main pyrolysis of lipid component. The result was confirmed inthe previous literature [46]. It was observed that carbon dioxide(CO2) is one of the main products of fast pyrolysis of seawaterSpirulina. There was only a small amount of CO2 generated at236 �C, when the temperature increased the CO2 is tending to bethe trend of first increase and then decrease, maximum at 366 �C.This is attributed to the high temperature decarboxylation re-actions of functional groups such as ethers, ketones and oxygen-containing heterocycles, resulting in the formation of carbon di-oxide [47]. Simultaneously, CO2 was the product of proteins, lipids,and carbohydrates of microalgae constituents upon pyrolysis [12].CO peaks at 2178 and 2105 cm�1 emerged when the temperatureincreased to 366 �C, and intensified at 450 �C. But, the peak of CO2reduced with CO increases, this is due to the Boudouard reaction:reduction of CO2 with carbon (C) in seawater Spirulina char led tothe formation of CO at high temperature.

CO2 þC/2CO (13)

The maximum release rate for CH4 was located at about 450 �C.Previous research found that the degradation of long-chain fattyacids at lipid fraction was the major source of CH4 [48]. Addition-ally, the pyrolysis of heterocyclic aromatic compounds, such asindoles, pyrroles and pyridines also lead to CeH stretch. Simulta-neously, heterocyclic aromatic compounds also lead to the stretchof aromatic NeH [43,49]. The infrared spectrum at 366 �C exhibitedweak absorption bands of NH3 (965, 930 cm�1) and HCN(714 cm�1), which is mainly due to the amino acid cleavage in theprotein component to form ammonia, and the resulting ammoniaproduces amide and Nitrile with other intermediates [12]. Theformation of H2O and phenol in the dehydration reaction leads tothe OeH stretch (4000e3500, 1700e1580 cm�1). The carbonylstretch (C]O) functional group (1850e1600 cm�1) was generatedfrom the fragmentation of hydroxymethylene groups (-CH2OH)[50].

3.3. Fast pyrolysis products distribution of seawater Spirulina fromPy-GC/MS

In order to in-depth investigate the products of seawater Spir-ulina under high temperature fast pyrolysis conditions, Py-GC/MSinstrument was applied to analyze and detect pyrolysis productsat 700e900 �C. The advantage of this technique is that no

Table 2The main products of seawater Spirulina characterized by FTIR at the heating rate of 100 K/min and the temperature corresponding to their maximum evolution.

Wave number (cm�1) Vibration Compounds Attributable components

4000e35001700e1580

OeH stretch H2O e

3014 e CH4 e

3000e2850 Saturated aliphatic CeH stretch CeH aliphatic hydrocarbons2400e2240780e560

e CO2 e

1850e1600 carbonyl stretch C¼O aldehydes, ketones, carboxylic acids1300e950 CeC skeletal vibrations CeO alcohols, phenols2251 e HNCO e

965930

aromatic CeHin-plane bend

NH3 e

714 aromatic CeH out-of-plane bend HCN e

J. Li et al. / Renewable Energy 145 (2020) 1761e17711766

secondary cleavage reaction occurs during pyrolysis process, andthe detected pyrolysis products are basically one cleavage productof seawater Spirulina. More than 100 volatile organic compounds,including aliphatic and aromatic hydrocarbons, esters, oxygenates,phenols, nitrogen and sulfur-containing organic compounds, havebeen detected in the high-temperature fast pyrolysis of seawaterSpirulina. These products are the depolymerization products ofvarious ring structures formed by the reformation of carbon mo-lecular fragments after the ring-opening of the seawater Spirulinacomponents (proteins, lipids and carbohydrates) [23]. The fast py-rolysis products of seawater Spirulina are shown in Table 3. Somemajor compounds were quantified based on their determinedcarbon area, the identified were categorized in groups. Thesegroups of aromatic hydrocarbons (AR), non-aromatic hydrocarbons(N-AR), phenolic (PHE), oxygenated (OXY) and nitrogenated com-pounds (NIT). Table 3 shows the main compounds contained ineach group. Pyrolysis of highly proteinaceous biomass resulted inamines, pyrazoles, pyrroles, pyrrolidine, nitriles, pyridines, amides,indoles, and quinolines as major nitrogen containing organics.Phenolics group contains primarily phenol, cresol, xylenol, andethyl phenol. The content of sulfur-containing compounds was

Table 3Compound groups and their main components.

Groups Abbreviation

Aromatic hydrocarbons AR

Non-aromatic hydrocarbons N-AR

Phenols PHE

Oxygenates OXY

Nitrogenates NIT

produced low quantities, included disulfide and trisulfides, there-fore, we were not categorized in groups.

The pyrolysis products distribution of seawater Spirulina asincreasing temperature are shown in Fig. 3. As can be seen in Fig. 3,pyrolysis of Spirulina present a tendency to the formation of aro-matics during pyrolysis process, this is similar to the previous studyof Sim~ao et al. [51]. But, which components inside of seawaterSpirulina were corresponding to the formation of aromatics?Therefore, we further carry out studies to compare the products tothose produced from the pyrolysis of model compounds (cellulose,egg white and canola oil), the results evidenced that the aromatichydrocarbons weremainly derived from the protein fraction. This issimilar to the result of C. vulgaresmicroalgae species in the range of450e600 �C by Du et al. [52]. Additionally, the presence of aliphaticcompounds may also be aromatized at high temperatures [12].Furthermore, the pyrolysis of amino acids presents in the proteinfraction also attributed to the form of cyclic and polycyclicnitrogen-containing compounds (e.g., indoles, pyrroles, pyridines).Ammoniation reaction of carboxylic acids can also occur to formacid amides, and the amides formed dehydrate to form nitriles [12].Pyrolysis generates toluene, styrene, phenols, indoles are all from

Groups Compounds

Ethylbenzene1,3-dimethylbenzene,StyreneTolueneo-XyleneMethylenecyclopropane1,4-PentadieneCyclopentene1,2,3,4-Tetrahydro-1,1,6-trimethylnaphthalenePhenolp-cresol2,4-Dimethylphenol4-EthylphenolFuranmethanolAcetol3-methylcyclopentanedione3-methylbutanal2-methylbutanalIndole3-Methyl-1H-indoleBenzyl nitrileBenzenepropanitrileHexadecanamideHexadecanenitrile2-Methyl-1H-pyrroleHexahydropyrrolo[1,2- a ]pyrazine-1,4-dione3-Isobutylhexahydropyrrolo[1,2- a ]pyrazine-1,4-dioneHexahydro-3-phenylmethylpyrrolo[1,2- a ] pyrazine

AR N-AR PH OXY NIT0

200

400

600

800

1000

1200700 ºC750 ºC800 ºC850 ºC900 ºC

Com

posi

tion

(x10

6A

bsar

ea/u

g)

Fig. 3. Pyrolysate distribution from fast pyrolysis of seawater Spirulina. AR: Aromatichydrocarbons; N-AR: Non-aromatic hydrocarbons; PHE: Phenols; OXY: Oxygenates;NIT: Nitrogenates.

4000 3500 3000 2500 2000 1500 1000 500

C-O-C

C-O C-CC=O

C-CC-O

O-H or C-H

C=C

C=O

C-H

Spirulina Spirulina 700 ºC charSpirulina 800 ºC char Spirulina 900 ºC char

Wave number (cm-1)

O-H

Spirulina

Fig. 4. FT-IR spectra for bio-char samples and corresponding parent seawater Spirulina.

J. Li et al. / Renewable Energy 145 (2020) 1761e1771 1767

peptidic material from protein fraction of Spirulina [39]. Aliphatichydrocarbons are formed via decarboxylation reaction from lipidsat high temperatures [49]. Low-molecular-weight oxygenates, suchas aldehydes and ketones, are from the carbohydrate fraction [49].

From the Py-GC-MS result of seawater Spirulina, present upwardtrend of the content of aromatic hydrocarbons and the downwardpropensity of the content of oxygenated compounds with increaseof temperature. The maximum yield of quantified hydrocarbonswas observed at 900 �C. This is mainly due to oxygenated com-pounds by the high-temperature thermal cracking stimulated theincrease in aromatic hydrocarbon content [51]. Also regarding toFig. 3, the content of nitrogen and phenolic compounds decreasedin response to increases in the reaction of high temperature. Therewas a reduction in phenolic compounds with rising temperatures,which is advantageous to the stability of syngas. Syngas with highoxygen content is very undesirable for fuels that have a negativeeffect on the syngas for fuels purposes, and contaminated whenemissioned into the atmosphere. Moreover, the production of ox-ygenates decreased significantly at temperatures above 750 �C.Therefore, high temperature (above 750 �C) can reduce the gener-ation of oxygenated compounds. Besides, the production of nitro-genates decreased with the higher temperatures above 800 �C.

3.4. Effect of seawater Spirulina char characteristics on gasificationreactivity

3.4.1. The proximate and ultimate analysis of seawater Spirulinachars

The proximate and ultimate analysis of seawater Spirulina charsobtained at 700, 800 and 900 �C temperatures were shown inTable 1. It can be seen from the table that seawater Spirulina charscontain lesser moisture and volatile matter than its precursor. Theash content in chars increased with temperature increases, whichmay be due to the abundance of metal elements and metal oxidesoriginated from the raw [53]. Therefore, fine particle biochars effluxas silicon and potassium fertilizer that has potential agriculturalapplications as a biofertiliser [54]. Considerable higher fix carboncontent in bio-char were obtained, which may be due partly to theformation of coke for carbon existed in chars mainly in the form ofcoke [55,56]. The HHV value for seawater Spirulina char range15e18MJ kg�1.

3.4.2. Component analysis of chars by FTIRFTIR was applied to perform the structure analysis of the

thermal cracking char products. FTIR results for chars and corre-sponding parent seawater Spirulina were shown in Fig. 4. The ab-sorption peak of originate is rather messy, while the absorptionpeak of the chars is relatively flat, and the temperature has nosignificant effect on the structure of the chars. There is a largeintense OeH stretching vibration intermolecular hydrogen bondsat 3100-3400 cm�1, attributable to hydroxyl functional groupsusually caused by alcohols and phenols [57]. This is similar to thecomposition in the volatiles. The peaks at 2850-2950 cm�1 and1470 cm�1 represent CeH stretching and deformation vibrations ofalkanes from aliphatic, aromatic, and alkyl reactions, respectively[58]. A decrease in the concentration of the aromatic CeH group at2850e2950 cm�1 indicates removal of the methyl group from thearomatic ring, resulting in the formation of CH4 at elevated tem-peratures [59]. The carboxylic acids may be present in the bandaround 1650 cm�1, and the absorption between 1036 and1100 cm�1 may be attributed to CeO vibration [60,61]. The disso-ciation of proteins and carbohydrates components promoted theformation of acids, aldehydes and ketones, which are mainly re-flected in the absorption peak between 1630 and 1650 cm�1 in theC]O band 1 and the C]C stretching at 1530 cm�1. The broad bandsat 1655 and 1540 cm�1 can be designated as the high contents ofproteins in seawater Spirulina origin [60]. Both bands graduallydecreases as the coking temperature increases, mainly due todecomposition at high temperatures of the protein [61,62]. Thepeaks observed in the range of 1050e1300 cm�1 are attributed toOeH deformation and CeO stretching corresponding to differenttypes of oxygenates [63,64]. The aromatic CeH band at 900-750 cm�1 region showed the changes in the aromatic structures.The intensity of this band decreased after pyrolysis, indicating theformation of a fused ring at higher temperatures. In the formationof seawater Spirulina chars, the decrease of functional groupsconcentration was due to the release of volatiles during pyrolysisprocess, resulted in formation of synthesis [61].

3.4.3. Morphology analysis of chars by SEMIn order to observed the surfacemorphological characteristics of

bio-char samples, SEMwas applied to perform the analysis of chars.As shown in Fig. 5, noticeable surface morphological differenceshad taken place with temperature increases under pyrolysis con-ditions. The seawater Spirulina chars surface were found to rupture

Fig. 5. SEM analysis of bio-char samples produced at 700, 800 and 900 �C. SP:seawater Spirulina.

0 20 40 60 80 1000.0

0.2

0.4

0.6

0.8

1.0

X(w

t.%

)

Time(min)

750 ºC800 ºC850 ºC900 ºC

Fig. 6. Conversion-time relationships for seawater Spirulina chars at different gasifi-cation temperature.

J. Li et al. / Renewable Energy 145 (2020) 1761e17711768

drastically and appears melting phenomenon with increase in py-rolysis temperature from 700, 800e900 �C, this phenomenon wasmore pronounced at figures of 700 and 900 �C. In the figures of50 mmat 700, 800e900 �C, the chars had been twisted out of shapeand porous structures on the surface adhered with white dots. Thewhite dots were the dust thing mainly comes from the decompo-sition of the fragment of the small-sized sheet. The char's particlesurface showed several cavities of different sizes and with irregularshapes. The formation of large pores at higher temperatures in-dicates that the volatiles are rapidly devolatilized as volatilesescape from the surface of the softened particles [65].

3.5. Gasification reaction kinetic of seawater Spirulina chars

In order to evaluate the validations of selected kinetic modelsand predict the gasification reaction kinetic of the seawater Spir-ulina chars, the experimental data were fitted by various models.Then the reaction rate constants are calculated by the slopes ofcurves for �ln(1�X), 3[1�(1�X)1/3], (2/j)[(1�jln(1�X))1/2�1]corresponding to time t. Conversion-time relationships forseawater Spirulina chars at different gasification temperature areshown in Fig. 6. It takes less time to complete same carbon con-version at higher gasification temperature (99.98% at 850 �C/19.3min; 99.98% at 900 �C/9.6min). Therefore, gasification tem-perature plays an important role in the gasification process; it hasbeen shown that increasing the gasification temperature shortenthe gasification time. This is due to the fact that the Boudouardreaction (Eq. (13)) is an endothermic reaction [28]. As shown infigures, the conversion has a critical point at about ratio of around90%, then proceeds very slowly until completion. This is due to thecollapsing of porous structure and the increasing resistance of ashlayer for the reactant gas diffusion. The curves slightly overlapwhen the gasification temperatures were 850 �C and 900 �C whichwas attributed to be caused by ash fusion in the seawater Spirulina.This is consistent with the SEM melting phenomenon when tem-perature increases to 900 �C.

Fig. 7 shows the VM, SCM and RPM models obtained fromseawater Spirulina chars at different gasification temperatures.Then, by using the reaction rate constants (kVM, kSCM and kRPM)calculated at different temperature, the Arrhenius plot (lnk vs. 1/T)was employed to calculate the activation energy (E) and the pre-

exponential factor (k0). It was found that the three kinetic modelsperformed well in most conditions. Data analysis revealed that abetter fitting can be observed for RPM with higher (R2) values,followed by SCM, VM has the lowest values of the efficient ofdetermination (R2). The RPM model considers a great deal of col-umn shape of pores existed in the char particles and the gasifiedreaction happened in the surface of the inner pores. With theproceeding of the reaction, both the increases of column borediameter and reaction phase lead to the increase of gasification rate[29]. This is consistent with the above analysis of the SEM, thesurface of the particles of charcoal showing several cavities ofdifferent sizes and irregular shapes. The gasification temperaturehas a great influence on the control mechanism of biomass chars’gasification reaction. When at low temperatures (T approx.<600 �C), the rate of chemical reaction is primarily determined bythe chemical reaction of the inner and outer surfaces of the chars.However, as the temperature increases, the pore diffusion withinthe carbon particles limits the conversion of the overall reaction[63]. Eventually, the temperature reaches a certain limit, the poresoverlap, and the reaction surface area decreases, so the reactionrate decreases [64].

As shown in Fig. 8 that there exists a good liner relation betweenthe ln K and 1/T under different reaction temperatures of the charsgasified process. The calculated kinetic parameters of seawaterSpirulina chars gasification fitted by three kinetic models are shownin Table 4. The activation energies of the VM, SCM and RPMmodelsof seawater Spirulina chars were 187.95, 173.14 and 154.34 kJ/mol,respectively. However, the pre-exponential factor (A0) variedgreatly, the A0 of the VM, SCM and RPM were 1.74 E þ 06,2.13 E þ 05 and 1.97 E þ 04 s�1, respectively. It can be seen from theR2 values in Table 4 that the RPM displays a significant fit with theexperiments than those of the other two models.

4. Conclusion

The devolatilization behavior and gaseous product evolutionwere carried out under high heating rate conditions (100, 300,500 �Cmin�1) in TG-FTIR. The thermal cracking process of seawaterSpirulina mainly consisted of three reaction stages, includingdehydration and drying stage, fast pyrolysis stage and residues slowdecomposition stage. The heating rate has a significant effect on thepyrolysis rate. However, high heating rates typically have a positive

0 1000 2000 3000 4000 5000 60000

2

4

6 750 ºC800 ºC850 ºC950 ºC

-ln(

1-X

)

Time(s)

VM

0 1000 2000 3000 4000 5000 60000.0

0.5

1.0

1.5

2.0

2.5

3.0 750 ºC800 ºC850 ºC900 ºC

3[1-

(1-X

)1/3 ]

Time(s)

SCM

0 1000 2000 3000 4000 5000 60000.0

0.5

1.0

1.5

2.0

2.5

3.0 750 ºC800 ºC850 ºC900 ºC

2/[(

1-ln

(1-X

) ^1/

2-1 ]

Time(s)

RPM

Fig. 7. VM, SCM and RPM linearized models for seawater Spirulina chars. VM: Volumetric reaction model; SCM: Shrinking core model; RPM: Random pore model.

0.00085 0.00090 0.00095

-8

-7

-6

-5VMSCMRPM

lnK

i

1/T(K-1)

Fig. 8. Arrhenius plots for the VM, GM and RPM models of seawater Spirulina chars.VM: Volumetric reaction model; SCM: Shrinking core model; RPM: Random poremodel.

Table 4Kinetic parameters of volumetric reaction model, shrinking core model and randompore model by fitting kinetic data of steam gasification of seawater Spirulina chars.

Model A0 (s�1) E (KJ mol�1) R2

Volumetric reactionModel

1.74 E þ 06 187.95 0.93444

Shrinking core model 2.13 E þ 05 173.14 0.97325Random pore model 1.97 E þ 04 154.34 0.99784

J. Li et al. / Renewable Energy 145 (2020) 1761e1771 1769

and negative impact on seawater Spirulina samples. It is because ofthe superposition of the positive and negative effects that the TG/DTG curvemoves toward the high temperature side. H2O, CH4, CO2,HNCO, NH3, HCN, CO, CeO bond and C]O bond were the typicalgaseous products released from themain reaction stage of seawaterSpirulina. The maximum release rate of seawater Spirulina for CH4was located at about 450 �C, which mainly from the degradation of

long-chain fatty acids at lipid fraction.As for Py-GC/MS, fast pyrolysis of seawater Spirulina under high

temperature resulted in aliphatic (alkanes, alkenes) and aromatichydrocarbons, esters, oxygenates (carboxylic acids, aldehydes, ke-tones, and alcohols), phenolics, and nitrogen- and sulfur-containingorganic compounds. Above 750 �C was considered as the optimumtemperature, which can reduce the generation of oxygenatedcompounds, and the content of nitrogen and phenolic compoundswere decreased, maximum yield of quantified hydrocarbons wasobserved.

The steam gasification characteristics and kinetics of seawaterSpirulina chars had been investigated by the method of isothermalthermogravimetric analysis. The activation energies of the VM, SCMand RPM models of Spirulina chars were 187.95, 173.14 and154.34 kJ/mol, respectively. The increase of gasification tempera-ture can obviously improve the gasification reactivity of biomasschars.

Acknowledgements

This work was supported by the National Natural Science

J. Li et al. / Renewable Energy 145 (2020) 1761e17711770

Foundation of China (Grant numbers: 2157060571, 21576294 and21706287); Taishan Scholar Foundation of Shandong Province(Grant number: tsqn201812028); Major Science and TechnologyInnovation Projects of Shandong Province (Grant number:2018CXGC0301); Qingdao People’s Livelihood Science and Tech-nology Project (Grant numbers: 16-6-2-51-nsh and 18-6-1-101-nsh); Fundamental Research Funds for the Central Universities(Grant number: 18 C� 05022 A); Independent Innovation ResearchProject of China University of Petroleum (East China) (Grant num-ber: YJ201601066); Postgraduate Innovation Funding Project ofChina University of Petroleum (East China) (YCX2019033).

References

[1] V.S. Sikarwar, M. Zhao, P.S. Fennell, N. Shah, E.J. Anthony, Progress in biofuelproduction from gasification, Prog. Energy Combust. Sci. 61 (2017) 189e248.

[2] X. Hu, R. Gunawan, D. Mourant, M.D.M. Hasan, L. Wu, Y. Song, C. Lievens, C.-Z. Li, Upgrading of bio-oil via acid-catalyzed reactions in alcohols d a minireview, Fuel Process. Technol. 155 (2017) 2e19.

[3] D.M. Alonso, S.H. Hakim, S. Zhou, W. Won, O. Hosseinaei, J. Tao, V. Garcia-Negron, A.H. Motagamwala, M.A. Mellmer, K. Huang, C.J. Houtman, N. Labb�e,D.P. Harper, C.T. Maravelias, T. Runge, J.A. Dumesic, Increasing the revenuefrom lignocellulosic biomass: maximizing feedstock utilization, Sci. Adv. 3 (5)(2017).

[4] H. Gebreslassie Berhane, R. Waymire, F. You, Sustainable design and synthesisof algae-based biorefinery for simultaneous hydrocarbon biofuel productionand carbon sequestration, AIChE J. 59 (5) (2013) 1599e1621.

[5] P.S. Nigam, A. Singh, Production of liquid biofuels from renewable resources,Prog. Energy Combust. Sci. 37 (1) (2011) 52e68.

[6] L. Leng, J. Li, Z. Wen, W. Zhou, Use of microalgae to recycle nutrients inaqueous phase derived from hydrothermal liquefaction process, Bioresour.Technol. 256 (2018) 529e542.

[7] T.M. Mata, A.A. Martins, N.S. Caetano, Microalgae for biodiesel production andother applications: a review, Renew. Sustain. Energy Rev. 14 (1) (2010)217e232.

[8] V. Skorupskaite, V. Makareviciene, D. Levisauskas, Optimization of mixo-trophic cultivation of microalgae Chlorella sp. for biofuel production usingresponse surface methodology, Algal Res. 7 (2015) 45e50.

[9] L. Li, N. Zhao, X. Fu, M. Shao, S. Qin, Thermogravimetric and kinetic analysis ofSpirulina wastes under nitrogen and air atmospheres, Bioresour. Technol. 140(2013) 152e157.

[10] I. Rawat, R. Ranjith Kumar, T. Mutanda, F. Bux, Biodiesel from microalgae: acritical evaluation from laboratory to large scale production, Appl. Energy 103(2013) 444e467.

[11] A.F. Clarens, E.P. Resurreccion, M.A. White, L.M. Colosi, Environmental lifecycle comparison of algae to other bioenergy feedstocks, Environ. Sci. Technol.44 (5) (2010) 1813e1819.

[12] R. Gautam, A.K. Varma, R. Vinu, Apparent kinetics of fast pyrolysis of fourdifferent microalgae and product analyses using pyrolysis-FTIR and pyrolysis-GC/MS, Energy Fuel. 31 (11) (2017) 12339e12349.

[13] A.E. Harman-Ware, T. Morgan, M. Wilson, M. Crocker, J. Zhang, K. Liu, J. Stork,S. Debolt, Microalgae as a renewable fuel source: fast pyrolysis of Scene-desmus sp, Renew. Energy 60 (2013) 625e632.

[14] M. Fatih Demirbas, Biorefineries for biofuel upgrading: a critical review, Appl.Energy 86 (2009) S151eS161.

[15] R. Bassilakis, R.M. Carangelo, M.A. W�ojtowicz, TG-FTIR analysis of biomasspyrolysis, Fuel 80 (12) (2001) 1765e1786.

[16] B. Tian, Y.y. Qiao, Y.y. Tian, Q. Liu, Investigation on the effect of particle sizeand heating rate on pyrolysis characteristics of a bituminous coal by TGeFTIR,J. Anal. Appl. Pyrolysis 121 (2016) 376e386.

[17] A. Plis, J. Lasek, A. Skawi�nska, J. Zuwała, Thermochemical and kinetic analysisof the pyrolysis process in Cladophora glomerata algae, J. Anal. Appl. Pyrolysis115 (2015) 166e174.

[18] K. Lazdovica, V. Kampars, L. Liepina, M. Vilka, Comparative study on thermalpyrolysis of buckwheat and wheat straws by using TGA-FTIR and Py-GC/MSmethods, J. Anal. Appl. Pyrolysis 124 (2017) 1e15.

[19] X.H. Li, Y.Z. Meng, Q. Zhu, S.C. Tjong, Thermal decomposition characteristics ofpoly(propylene carbonate) using TG/IR and Py-GC/MS techniques, Polym.Degrad. Stab. 81 (1) (2003) 157e165.

[20] L. Li, Y. Huang, D. Zhang, A. Zheng, Z. Zhao, M. Xia, H. Li, Uncoveringstructureereactivity relationships in pyrolysis and gasification of biomasswith varying severity of torrefaction, ACS Sustain. Chem. Eng. 6 (5) (2018)6008e6017.

[21] J. Li, Y. Qiao, X. Chen, P. Zong, S. Qin, Y. Wu, S. Wang, H. Zhang, Y. Tian, SteamGasification of Land, Coastal Zone and Marine Biomass by Thermal Gravi-metric Analyzer and a Free-Fall Tubular Gasifier: Biochars Reactivity andHydrogen-Rich Syngas Production, Bioresource Technology, 2019, p. 121495.

[22] R. Xiao, W. Yang, Kinetics characteristics of straw semi-char gasification withcarbon dioxide, Bioresour. Technol. 207 (2016) 180e187.

[23] B.M.E. Chagas, C. Dorado, M.J. Serapiglia, C.A. Mullen, A.A. Boateng,

M.A.F. Melo, C.H. Ataíde, Catalytic pyrolysis-GC/MS of Spirulina: evaluation ofa highly proteinaceous biomass source for production of fuels and chemicals,Fuel 179 (2016) 124e134.

[24] V. Anand, V. Sunjeev, R. Vinu, Catalytic fast pyrolysis of Arthrospira platensis(spirulina) algae using zeolites, J. Anal. Appl. Pyrolysis 118 (2016) 298e307.

[25] A. Raheem, V. Dupont, A.Q. Channa, X. Zhao, A.K. Vuppaladadiyam, Y.-H. Taufiq-Yap, M. Zhao, R. Harun, Parametric characterization of air gasifica-tion of chlorella vulgaris biomass, Energy Fuel. 31 (3) (2017) 2959e2969.

[26] R.H.C. Perry, C H, Chemical Engineer 's Handbook, fifth ed., Mcgraw-Hill-Kogakusha, 1973.

[27] D.K. Shen, S. Gu, A.V. Bridgwater, Study on the pyrolytic behaviour of xylan-based hemicellulose using TGeFTIR and PyeGCeFTIR, J. Anal. Appl. Pyroly-sis 87 (2) (2010) 199e206.

[28] V.S. Naidu, P. Aghalayam, S. Jayanti, Evaluation of CO2 gasification kinetics forlow-rank Indian coals and biomass fuels, J. Therm. Anal. Calorim. 123 (1)(2016) 467e478.

[29] J. Szekely, J.W. Evans, A structural model for gasdsolid reactions with amoving boundary, Chem. Eng. Sci. 25 (6) (1970) 1091e1107.

[30] S.K. Bhatia, D.D. Perlmutter, A random pore model for fluid-solid reactions: I.Isothermal, kinetic control, AIChE J. 26 (3) (1980) 379e386.

[31] J. Tanner, S. Bhattacharya, Kinetics of CO2 and steam gasification of Victorianbrown coal chars, Chem. Eng. J. 285 (2016) 331e340.

[32] W. Chen, H. Yang, Y. Chen, M. Xia, Z. Yang, X. Wang, H. Chen, Algae pyrolyticpoly-generation: influence of component difference and temperature onproducts characteristics, Energy 131 (2017) 1e12.

[33] M. Carrier, J.-E. Joubert, S. Danje, T. Hugo, J. G€orgens, J. Knoetze, Impact of thelignocellulosic material on fast pyrolysis yields and product quality, Bioresour.Technol. 150 (2013) 129e138.

[34] X.-N. Ye, Q. Lu, X. Wang, T.-P. Wang, H.-Q. Guo, M.-S. Cui, C.-Q. Dong, Y.-P. Yang, Fast Pyrolysis of Corn Stalks at Different Growth Stages to SelectivelyProduce 4-Vinyl Phenol and 5-Hydroxymethyl Furfural, Waste and BiomassValorization, 2018.

[35] C.A. Mullen, A.A. Boateng, Production and analysis of fast pyrolysis oils fromproteinaceous biomass, BioEnergy Res. 4 (4) (2011) 303e311.

[36] A. Soria-Verdugo, E. Goos, N. García-Hernando, U. Riedel, Analyzing the py-rolysis kinetics of several microalgae species by various differential and in-tegral iso conversional kinetic methods and the distributed activation energymodel, Algal Res. 32 (2018) 11e29.

[37] A.M. Illman, A.H. Scragg, S.W. Shales, Increase in Chlorella strains calorificvalues when grown in low nitrogen medium, Enzym. Microb. Technol. 27 (8)(2000) 631e635.

[38] R. Ranjith Kumar, D. Ramesh, T. Mutanda, I. Rawat, F. Bux, Thermal behaviorand pyrolytic characteristics of freshwater scenedesmus sp, Energy Sources,Part A Recovery, Util. Environ. Eff. 37 (13) (2015) 1383e1391.

[39] K. Kebelmann, A. Hornung, U. Karsten, G. Griffiths, Intermediate pyrolysis andproduct identification by TGA and Py-GC/MS of green microalgae and theirextracted protein and lipid components, Biomass Bioenergy 49 (2013) 38e48.

[40] F. Li, F. Lang, H. Zhang, L. Xu, Y. Wang, C. Zhai, E. Hao, Apigenin alleviatesendotoxin-induced myocardial toxicity by modulating inflammation, oxida-tive stress, and autophagy, Oxid. Med. Cell. Longev. 2017 (2017) 10.

[41] H.-H. Bui, K.-Q. Tran, W.-H. Chen, Pyrolysis of microalgae residues e a kineticstudy, Bioresour. Technol. 199 (2016) 362e366.

[42] C. Gai, Y. Zhang, W.-T. Chen, P. Zhang, Y. Dong, Thermogravimetric and kineticanalysis of thermal decomposition characteristics of low-lipid microalgae,Bioresour. Technol. 150 (2013) 139e148.

[43] J. Wang, X. Ma, Z. Yu, X. Peng, Y. Lin, Studies on thermal decomposition be-haviors of demineralized low-lipid microalgae by TG-FTIR, Thermochim. Acta660 (2018) 101e109.

[44] S. Ceylan, J.L. Goldfarb, Green tide to green fuels: TGeFTIR analysis and kineticstudy of Ulva prolifera pyrolysis, Energy Convers. Manag. 101 (2015)263e270.

[45] N. S€oyler, J.L. Goldfarb, S. Ceylan, M.T. Saçan, Renewable fuels from pyrolysisof Dunaliella tertiolecta: an alternative approach to biochemical conversionsof microalgae, Energy 120 (2017) 907e914.

[46] F. Li, S.C. Srivatsa, W. Batchelor, S. Bhattacharya, A study on growth and py-rolysis characteristics of microalgae using thermogravimetric analysis-infrared spectroscopy and synchrotron fourier transform infrared spectros-copy, Bioresour. Technol. 229 (2017) 1e10.

[47] C. Jia, Z. Wang, H. Liu, J. Bai, M. Chi, Q. Wang, Pyrolysis behavior of Indonesiaoil sand by TG-FTIR and in a fixed bed reactor, J. Anal. Appl. Pyrolysis 114(2015) 255.

[48] X. Peng, X. Ma, Y. Lin, Z. Guo, S. Hu, X. Ning, Y. Cao, Y. Zhang, Co-pyrolysisbetween microalgae and textile dyeing sludge by TGeFTIR: kinetics andproducts, Energy Convers. Manag. 100 (2015) 391e402.

[49] V. Anand, R. Gautam, R. Vinu, Non-catalytic and catalytic fast pyrolysis ofSchizochytrium limacinum microalga, Fuel 205 (2017) 1e10.

[50] I.-Y. Eom, K.-H. Kim, J.-Y. Kim, S.-M. Lee, H.-M. Yeo, I.-G. Choi, J.-W. Choi,Characterization of primary thermal degradation features of lignocellulosicbiomass after removal of inorganic metals by diverse solvents, Bioresour.Technol. 102 (3) (2011) 3437e3444.

[51] B.L. Sim~ao, J.A. Santana Júnior, B.M.E. Chagas, C.R. Cardoso, C.H. Ataíde, Py-rolysis of Spirulina maxima: kinetic modeling and selectivity for aromatichydrocarbons, Algal Res. 32 (2018) 221e232.

[52] Z. Du, B. Hu, X. Ma, Y. Cheng, Y. Liu, X. Lin, Y. Wan, H. Lei, P. Chen, R. Ruan,Catalytic pyrolysis of microalgae and their three major components:

J. Li et al. / Renewable Energy 145 (2020) 1761e1771 1771

carbohydrates, proteins, and lipids, Bioresour. Technol. 130 (2013) 777e782.[53] C.A. Mullen, A.A. Boateng, N.M. Goldberg, I.M. Lima, D.A. Laird, K.B. Hicks, Bio-

oil and bio-char production from corn cobs and stover by fast pyrolysis,Biomass Bioenergy 34 (1) (2010) 67e74.

[54] J. Lehmann, J. Gaunt, M. Rondon, Bio-char sequestration in terrestrial eco-systems e a review, Mitig. Adapt. Strategies Glob. Change 11 (2) (2006)403e427.

[55] M. Uchimiya, L.H. Wartelle, K.T. Klasson, C.A. Fortier, I.M. Lima, Influence ofpyrolysis temperature on biochar property and function as a heavy metalsorbent in soil, J. Agric. Food Chem. 59 (6) (2011) 2501e2510.

[56] W.-H. Chen, B.-J. Lin, M.-Y. Huang, J.-S. Chang, Thermochemical conversion ofmicroalgal biomass into biofuels: a review, Bioresour. Technol. 184 (2015)314e327.

[57] J.J. Many�a, Pyrolysis for biochar purposes: a review to establish currentknowledge gaps and research needs, Environ. Sci. Technol. 46 (15) (2012)7939e7954.

[58] V. Strezov, E. Popovic, R.V. Filkoski, P. Shah, T. Evans, Assessment of thethermal processing behavior of tobacco waste, Energy Fuel. 26 (9) (2012)5930e5935.

[59] T. Yuan, A. Tahmasebi, J. Yu, Comparative study on pyrolysis of lignocellulosicand algal biomass using a thermogravimetric and a fixed-bed reactor,

Bioresour. Technol. 175 (2015) 333e341.[60] J.-P. Cao, X.-B. Xiao, S.-Y. Zhang, X.-Y. Zhao, K. Sato, Y. Ogawa, X.-Y. Wei,

T. Takarada, Preparation and characterization of bio-oils from internallycirculating fluidized-bed pyrolyses of municipal, livestock, and wood waste,Bioresour. Technol. 102 (2) (2011) 2009e2015.

[61] M.C. Blanco L�opez, C.G. Blanco, A. Martınez-Alonso, J.M.D. Tasc�on, Composi-tion of gases released during olive stones pyrolysis, J. Anal. Appl. Pyrolysis 65(2) (2002) 313e322.

[62] L.-j. Leng, X.-z. Yuan, H.-j. Huang, H. Wang, Z.-b. Wu, L.-h. Fu, X. Peng, X.-h. Chen, G.-m. Zeng, Characterization and application of bio-chars fromliquefaction of microalgae, lignocellulosic biomass and sewage sludge, FuelProcess. Technol. 129 (2015) 8e14.

[63] P. Das, T. Sreelatha, A. Ganesh, Bio oil from pyrolysis of cashew nut shell-characterisation and related properties, Biomass Bioenergy 27 (3) (2004)265e275.

[64] M.R. Islam, M.A. Mansur, M. Maalej, Shear strengthening of RC deep beamsusing externally bonded FRP systems, Cement Concr. Compos. 27 (3) (2005)413e420.

[65] K. Maliutina, A. Tahmasebi, J. Yu, S.N. Saltykov, Comparative study on flashpyrolysis characteristics of microalgal and lignocellulosic biomass inentrained-flow reactor, Energy Convers. Manag. 151 (2017) 426e438.