Influence of Pyrolysis Temperature on Physico-Chemical Properties of Corn Stover (Zea mays L.) Biochar and Feasibility for Carbon Capture and Energy Balance
Long R (2016) Influence of Pyrolysis
Temperature on Physico-Chemical Properties of Corn
Stover (Zea mays L.) Biochar and Feasibility for
Carbon Capture and Energy Balance. PLoS ONE 11
(6): e0156894. doi:10.1371/journal.pone.0156894
Influence of Pyrolysis Temperature on Physico-Chemical Properties of Corn Stover (Zea mays L.) Biochar and Feasibility for Carbon Capture and Energy Balance
Muhammad Khalid Rafiq 0 1 2
Robert Thomas Bachmann 1
Muhammad Tariq Rafiq 1 3
Zhanhuan Shang 0 1 2
Stephen Joseph 1
Ruijun Long 0 1 2
0 College of Pastoral Agriculture, Science and Technology Agric, Lanzhou University , 222 Tianshui South Road, Lanzhou.730000 , PR China , 2 Directorate of Range Mgt and Forestry, Pakistan Agricultural Research Council , Islamabad, 44000, Pakistan , 3 Malaysian Institute for Chemical and Bioengineering Technology (MICET), Universiti Kuala Lumpur (UniKL) , Lot 1988, Taboh Naning,78000 Alor Gajah, Melaka , Malaysia
1 Editor: Jie Zheng, University of Akron , UNITED STATES
2 State Key Laboratory of Grassland Agro-ecosystems, International Centre for Tibetan Plateau Ecosystem Management, School of Life Sciences, Lanzhou University , Lanzhou, 730000 China , 6 School of Materials Science and Engineering, University of New South Wales , Sydney, NSW 2052 , Australia
3 Department of Environmental Science, International Islamic University , Islamabad, 44000 Pakistan
This study examined the influence of pyrolysis temperature on biochar characteristics and evaluated its suitability for carbon capture and energy production. Biochar was produced from corn stover using slow pyrolysis at 300, 400 and 500°C and 2 hrs holding time. The experimental biochars were characterized by elemental analysis, BET, FTIR, TGA/DTA, NMR (C-13). Higher heating value (HHV) of feedstock and biochars was measured using bomb calorimeter. Results show that carbon content of corn stover biochar increased from 45.5% to 64.5%, with increasing pyrolysis temperatures. A decrease in H:C and O:C ratios as well as volatile matter, coupled with increase in the concentration of aromatic carbon in the biochar as determined by FTIR and NMR (C-13) demonstrates a higher biochar carbon stability at 500°C. It was estimated that corn stover pyrolysed at 500°C could provide of 10.12 MJ/kg thermal energy. Pyrolysis is therefore a potential technology with its carbonnegative, energy positive and soil amendment benefits thus creating win- win scenario.
Data Availability Statement; All relevant data are within the paper
Competing Interests: The authors have declared
that no competing interests exist.
Sustainable economic development, food security and environmental management are some of
the highest priorities of the modern world as these are concerned with the present and future
generations. The multidimensional crises of global climate change, energy and water shortages
as well as agricultural land degradation due to nutrient depletion provide major social, political,
and economic challenges of today’s world. [
China is the second highest emitter of CO2. In December 2009, China’s State Council
declared that the country aims to reduce its 2005 carbon emissions by 40 to 45% in year 2020. If
successful, this would have a considerable positive impact not only for China but also the rest of
the world. [
] China has been an agricultural country for millennia, and tens of millions of
people are still involved in the agriculture sector which provides both and income and food
security.  Some of the main commodities produced include rice paddy, vegetables, tomato,
apples, wheat, potato and corn accounting for 18 to 59% of the world’s production (Table 1). [
Clare et al (2015) reported that there is over 800 million tonnes of agricultural crop straw
that China produces each year, up to 40% of which is burned in-field as a waste.[
from agricultural produce are therefore an abundant and renewable energy source with
potentially low net CO2 emission. Corn is one of the main crops cultivated in China and production
accounts for 24% in the world (Table 1). [
] According to China Statistical Yearbook (National
Bureau of Statistics of China, 2013) [
], 0.2 billion tons of corn was produced and around 0.4
billion tons of corn stover (CS) was generated in 2012. In addition, a 100% increase in corn
production has been observed in China over the past 20 years. Compared to rice, wheat,
potatoes and cotton, corn belongs to C4 plants characterized by a higher yield potential, lower
erosion-index, better CO2 reduction rates and need for less fertilizer, water and chemicals.[
At present, more than 70% of CS are land filled or burnt due to the high cost of collection,
transportation, and low price paid to the farmers for their residue.[
] Even though illegal in
most parts of China many farmers with burn their crop residues emits significant quantities of
green house gases into air like CO2, N2O, CH4, organic compounds (VOCs) as well as
semivolatile organic compounds (SVOCs) and other particulates.[
] Therefore, it is necessary to
develop environmental friendly and effective technologies to utilize agricultural residues such
as CS in order to alleviate the environmental and energy issues.[
] Modern thermo-chemical
energy conversion technologies such as combustion, gasification and pyrolysis provide clean
energy from waste biomass and facilitate, to varying degrees, climate change mitigation.[
Pyrolysis, the heating of biomass in the absence or very limited presence of oxygen to produce
primarily biochar but also bio-oil and some pyrogas, is attractive because of its carbon negative
]. Biochar can be used as an effective amendment in degraded or low fertility soils
with substantial environmental benefits [
]. Life cycle assessment of biochars produced from
corn stover, yard waste and switchgrass revealed that the net greenhouse gas emissions for
both corn stover and yard waste were negative, at -864 and -885 kg CO2 equivalent emissions
reductions per tonne dry feedstock, respectively. Of these total reductions, 62–66% is realized
from C sequestration in the biochar.[
Few studies have partially investigated the effect of pyrolysis temperature on biochar yield
] elemental composition [
] ash content [
] and composition
2 / 17
] volatile matter [
] pH [
] cation exchange capacity [
] BET (N2)
] and electrical conductivity [
]. Quantitative knowledge of biochar-relevant
parameters is important to assess the quality and commercial value of the biochar as well as the
potential suitability, stability and impact of the biochar on the fertility of a given soil.[
addition, empirical mathematical relationships between process conditions such as pyrolysis
temperature and physico-chemical properties of biochar enable researcher and practitioner
alike to select suitable process conditions to produce biochar of desired properties with
minimum trial and error.
The objectives of this research, therefore, are to independently produce and characterize
biochar from corn stover at different pyrolysis temperatures, consolidate the available literature
on biochar production from corn stover for comparison purposes as well as to establish
common trends and empirical relationships, identify and discuss potential reasons for variations
and, last but not least, highlight gaps in knowledge for future research. In addition this study
will look into associated soil amendment; energy and carbon capture potential of the
2. Material and Methods
2.1. Ethics Statement
The corn stover used in this study was collected from agricultural fields around Lanzhou. No
specific permissions were required for the described locations because corn stover was the left
over waste having no use for the farmers. We confirm that the field studies did not involve
endangered or protected species.
2.2. Biochar production
Corn stover was collected from agricultural fields (104°09’E, 35°56’N, altitude 1750 m) around
Lanzhou, China and the biochar production method was used as described by Uzoma et al.
]. In brief, the dried feedstock was cut into 1–2 cm long pieces, placed on stainless steel
trays, covered with a tightly fitting lid, and pyrolyzed under oxygen limited conditions in a
muffle furnace. The CS was heated at a rate of 20°C min−1 to a final temperature of 300°C,
400°C or 500°C respectively, and held for 2 hours. All biochar samples were ground and sieved
at <0.154 mm for their physical and chemical analyses. Experiments were carried out in
2.3. Yield and elemental analysis of biochars
The experimental biochar samples were tested for ash, pH, total Ca, Mg, K, Na, total
phosphorus (P), carbon (C), hydrogen (H), nitrogen (N), oxygen (O). Yield percentage of biochar was
determined by following equation:
Yield ð%Þ ¼ ðweight of biocharÞ = ðweight of feedstockÞ
Ash content was analyzed by heating biochar samples at 500°C for 8 h in a muffle furnace [
The relative ash content was then calculated as follows:
Ash ð%Þ ¼ ðweight of ashÞ=ðweight of biocharÞ
The pH of biochar was measured in deionized water at the ratio of 1:5 wt/wt with a
calibrated pH meter.[
] The elemental composition was determined according to Enders et al.
] using an elemental analyzer from Elementar Analysensysteme GmbH
(varioELcube). Nutrient elements Ca, K, Mg, Na, and P were measured using an inductively coupled
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plasma-atomic emission spectrometer (IRIS ER/S). Before analysis, the biochar sample (about
0.05 g) was first digested by the concentrated HNO3/H2O2 solutions.[
2.4. Surface and Physical Characterization
The determination of BET surface area, crystal structures, functional groups and pyrolytic
performance and thermal resistance were carried out in the analysis laboratory of College of
Chemistry and Chemical Engineering, Lanzhou University, PR China. The Brunauer–
Emmett–Teller (BET) surface area y N2 gas sorption analysis at 77 K in a relative pressure from
0.05 to 0.35 using a Nova 2200e surface area analyzer (Tristar3200, Micromeritics, USA) after
degassing at -195°C for a minimum of 8 h. The total pore volume of the biochars was estimated
to be the liquid adsorbate volume of N2 adsorbed at a relative pressure of about 0.99. The
average pore width was calculated as follows: [
average pore width ¼ ð4
ðtotal pore volume valueÞ=ðBET valueÞ
The surface functional groups of the biochars were determined by Fourier Transform
Infrared (FTIR) spectroscopy using a Nicolet 380 spectrophotometer (Avatar370, Thermo Nicolet,
USA). Addition of solid KBr to the biochars provided dilution and homogenization. The
spectra were performed at 4 cm−1 resolution and a mirror velocity of 0.48 cm S−1 with a 400 to
4,000-cm−1 scan range. X-ray diffraction (XRD) was used to observe the changes in mineral
crystals between the biochars, using a computer controlled diffractometer (X'Pert PRO). The
scans were collected from 0–60° using Cu–Ka radiation (40 kV, 40 mA) at a scan rate of 1°
min−1. The significant phase peaks were tentatively identified by comparing the XRD patterns
with the mineral database in the resulting biochars. Thermo-gravimetric analysis (TGA) was
performed on a Q-5000IR (TA Instruments, USA) coupled with a differential thermal analyzer
(DTA). For the TGA experiment, 5 mg of each sample was processed and heated up to 700°C
at a heating rate of 10°C / min. Nitrogen was used as a carrier gas and applied at a flow rate of
25 ml/min. The 13C nuclear magnetic resonance (NMR) spectrum of the 500°C biochar were
obtained on an AVANCE 400WB (Bruker, Germany) using the cross-polarization magic angle
spinning (CP/MAS) technique.
2.5. Energy Measurements of Corn Stover and Biochars
Bomb calorimeter was used to estimate higher heating value (HHV) of corn stover feedstock
and biochars prepared at 400 and 500°C. Moisture content of corn stover and biochars was
determined by drying at 60°C to constant weight. Hydrogen % of the corn stover and biochars
was determined by using Elementar Analysensysteme GmbH (varioELcube). Following
equation was used to measure the lower heating value (LHV) of the corn feedstock and biochars.[
LHV ¼ HHV
ðW þ 9HÞ
Where HHV = higher heating value [MJ/kg], W = moisture content [%-wt] on dry basis and
H = hydrogen content [%-wt.] The maximum net potential energy available during the pyrolysis
was estimated using the following equation. [
Maximum energy from pyrolysis ¼ biomass HHV
3. Statistical analysis
A SPSS (version 18.0) statistical software programme was used to perform statistical analysis of
the data for physico-chemical properties of experimental biochars and energy values.
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Significant differences between treatments were based on pyrolysis temperatures using one
way analysis of variance (ANOVA). Means were separated by least significant difference (LSD)
test, at 5% level.
4. Results and Discussion
4.1. Biochar Yield and Chemical Characteristics of Biochars
Biochar yield from corn stover and its chemical properties are summarized in Table 2. The
yield of biochar decreased as pyrolysis temperature increased. The physico-chemical and
structural characteristics of biochar were significantly influenced by pyrolysis temperature
The degree of carbonization for biochar was accelerated with increasing pyrolysis
temperature from 300°C, 400°C to 500°C. When plotting the biochar yields at different pyrolysis
temperatures and comparing with literature, a general exponential decrease can be observed (Fig
The primary thermal degradation of biomass happens during pyrolysis. The pyrolytic
volatiles are further broken into low molecular weight organics and gases as the pyrolysis
temperature increases. [
] The results are also in agreement with the findings of the TGA (section
4.5). In TGA study of biochars the weight loss is maximum at 300°C suggesting more volatile
matters compared to chars produced at 400°C and 500°C.
The relative ash content of the resulting biochars increased with increasing temperature up
to 500°C. The increase in ash content from 300–500°C is the result of a progressive
concentration of minerals and destructive volatilization of ligno-cellulosic matters as temperature
] Comparing the findings with related literature also reveals an exponential
increase of ash content with pyrolysis temperature (Fig 2). [
However, the correlation coefficient of 0.46 is comparatively low partially due to inclusion
of apparent outliers. For example, one study reported an ash content in original corn stover of
28% (wt) [
] which is 4–10 times higher than any value reported elsewhere.[
The high ash contents in CS char reported are probably due to presence of foreign material
102± 2 b
64.5± 1 a
Fig 1. Effect of pyrolysis temperature on biochar yield from corn stover produced at different heating
rates, holding times, particle sizes, reactor atmosphere and type (n = 22).
since no effort was made to control for the dirt content of the stover.[
] In addition the
methods used to determine ash content varied widely with ASTM D1762-84 (Standard Test Method
for Chemical Analysis of Wood Charcoal) used by four groups, ASTM D7582 (Proximate
Analysis of Coal and Coke by Macro Thermogravimetric Analysis) used by three, ASTM
D3172 (Standard Practice for Proximate Analysis of Coal and Coke) by two, ASTM E870-82
(Standard Test Methods for Analysis of Wood Fuels) used by one, while in-house methods
(e.g. heating at 650°C for 6 h) and external labs where also deployed in three cases. It has been
suggested that some methodological limitations of the ASTM D1762 method exist which can
Fig 2. Effect of pyrolysis temperature on ash content in biochar from corn stover (n = 41). Where
available, pyrolysis holding time of a given data point is indicated by a letter with S—short (<0.5 hrs), M–
medium (0.5–1 hr) and L–long (>1 hr). Atmosphere present inside the pyrolysis reactor is stated after the
6 / 17
cause the loss of certain inorganic elements such as P, K, S and fractions of carbonates at
temperatures as low as 500°C thus resulting in a negative bias in reported ash values.[
] The use
of air or inert gas N2, different holding times and heating rates are not able to individually
explain why some biochars had greater ash contents than others at comparable temperatures.
Other factors such as representativeness of temperature measurements especially in upscaled
reactors, representative sampling, sample storage conditions (e.g. duration, temperature,
atmosphere) and number of replicates used for proximate analysis (Enders et al., 2012 duplicate;
Brewer triplicate; all other studies considered here did not state number of replicates and did
not report standard deviations[
] are expected to affect the determination of ash content
and should be taken into account in the experimental design, execution and discussion of
results. It is also suggested to initiate a study which determines the measurement uncertainty in
ash content analysis as is required for ISO 17025 accredited laboratories. Determining and
reporting accurate ash contents is important because this parameter is frequently used in
elemental analysis to estimate the oxygen content in chars by difference [16’17’39] to model the
heating value from proximate analysis values  and to predict the elemental composition
from proximate analysis.[
] The data on the pH and mineral elements analyses of CS-derived
biochars are also listed in Table 2. The pH increased with temperature resulting in biochars
that are more alkaline in nature probably due to the concomitant decrease in acidic functional
groups (section 4.3) and increase in ash content.[
] Similar patterns are observed when
comparing the findings of this study with literature (Fig 3).
The best fit was obtained with a polynomial equation of second order resulting in a
correlation coefficient of 0.597. The correlation coefficient drastically improves to 0.903 if the data
point from Mullen et al.[
] is removed. The reason(s) for the comparatively low pH value of
the CS biochar produced at 500°C are not clear. All authors but one [
] used either distilled or
deionized water for the determination of pH, however the w/v ratio of char to water ranged
from 1: 5to 1: 100. [
] The ash content of Calvelo Pereira et al. (2014) 550°C biochar was
10.8% while Mullen’s (2010) 500°C biochar contained 32.8% ash.[
] The implication that a
high ash content biochar gives rise to a low pH is contrary to the trends reported.[
Fig 3. Effect of pyrolysis temperature on pH of biochar produced from corn stover (n = 15). All pH
values were determined in distilled or deionized water but at different char to water ratios.
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Pereira used a TGA to heat the sample under N2 atmosphere to 900°C before oxidizing the
specimen. As indicated by Enders et al. such high temperature could have caused the loss of
various mineral constituents such as P, K, S and carbonates and result in the apparent low ash
] It is therefore conceivable that the actual ash content of both Mullen’s and Calvelo
Pereira’s biochars was more similar than reported, and hence not the primary reason for the
observed difference in pH. It is worth noting that, in contrast to others, Calvelo Pereira et al.
heated the biochar—water suspension in a water bath to about 90°C, stirred for 20 min and
subsequently cooled down the suspension to room temperature for pH measurement in accordance
with Ahmedna et al. method for pH determination.[
] Such heat treatment may drive out
dissolved CO2 and other volatile acids thus increasing the pH. It is suggested for the biochar
research community to either agree on an existing standard or practice for the determination of
pH, or develop a new standard that harmonises the biochar: water ratio and minimizes
interferences from dissolved CO2. In addition, a more accurate predictor of biochar’s impact on soil pH
would be the determination of its acid neutralizing capacity (% CaCO3 equivalent).[
The elemental composition of the biochar is presented in Table 2. The carbon content in the
biochar increased from 45.5% to 64.5% with increasing pyrolysis temperature, whereas the
oxygen content decreased corresponding to an increase in the carbon content. This finding shows
that carbonization was promoted with increasing pyrolysis temperature.[
] Hydrogen and
oxygen losses at high pyrolysis temperature were due to the cleavage and breakage of weak
bonds within the biochar structure. 
The total N content for the experimental chars at 300°C, 400°C and 500°C were found to be
0.63%, 0.42% and 0.25%, respectively (Table 2). The total N content declined with increased
pyrolysis temperature–suggesting an ignition loss of N during pyrolysis of corn stover. Yuan
et al investigated the effect of pyrolysis temperature on physico-chemical properties of corn
straw and observed similar patterns.[
] A van Krevelen plot summarizing original and
carbonized corn stover produced by various research groups worldwide under different process
conditions is shown in Fig 4.[
] Overall the hydrogen and oxygen
content decreases with increasing temperature suggesting a greater hydrophobicity of the
biochars, which agrees with the formation of more aromatic compounds as was evidenced by the
FTIR analysis of the biochars (section 4.3). Variability in molar H/C and O/C ratios of original
and carbonized corn stover at a given temperature are probably due to the presence of mud
and other foreign substances in some cases, different holding times used, and uncertainties
associated with representative sampling and the elemental analysis itself.
Variability in molar H/C and O/C ratios of original and carbonized corn stover at a given
temperature are probably due to the presence of mud and other foreign substances in some
cases, different holding times used, and uncertainties associated with representative sampling
and the elemental analysis itself.
The total base cations and total P values of corn stover biochar were found to increase with
pyrolysis temperature. The higher content of base cations and total P in the biochars are due to
the concentration of relevant chemical elements in the biochars during the pyrolysis process
]. The recycling of the soil nutrient is often desired to maintain soil fertility and improved
crop productivity that can be achieved by the application of biochar to soil as biochars contain
essential nutrient need to the soil. In addition to nutrient recycling, biochar has been proved to
reduce chemical fertilizer application to soil.[
4.2. Surface area and pore properties of biochar
Fig 4. Van Krevelen diagram of original and carbonized corn stover. (S–slow pyrolysis; F–fast pyrolysis; G–
gasification; ND–not determined). (n = 31).
generalized as shown in Fig 5. As pyrolysis temperature increases pore blocking substances are
driven off or are thermally cracked thus increasing the externally accessible surface area.
However, prolonged holding times can have the opposite effect since reactions continue at the pore
surface area causing a decrease in micro pores and a shift towards meso- and macro pores. The
relatively low surface area observed for corn stover biochar is probably due to the inorganic
material that partially fills or blocks the micro pores.[
The reported surface areas may temporarily increase if biochars are added to soil and pore
water leaches out minerals with low affinity for the char surface. For example, Hale et al.
determined the BET (N2) surface area of unwashed and leached corn cob biochar and noted an
increase from 36.4 to 84.3 m2/g.[
] It is reasonable to expect that humic substances and other
organic matter, heavy metals, micro-organisms and tertiary roots may occupy eventually the
1. N2BET surface area.
2. Micro porous surface area by t-plot method.
3. Total pore volume by from single point adsorption at relative pressure close to 0.995.
4. Micro porous pore volume by the t-plot method.
5. Average pore width, estimated by 4Vt/SBET
Fig 5. Effect of pyrolysis temperature on BET (N2) surface area of biochar produced from corn stover
under slow (S) or fast (F) pyrolysis or gasification (G) conditions (n = 23).
vacated pore volumes. An exponential equation was the best fit for the data presented in Fig 5.
However, the correlation coefficient of 0.273 suggests that other process parameters than
temperature has a more pronounced effect on BET surface area. Most biochars were produced
under slow pyrolysis conditions while the BET surface area of the two fast pyrolysis biochars
from bubbling fluidized bed reactors are nested within the slow pyrolysis biochars. Based on
Antal et al.’s experience the accidental exposure of carbon to air during carbonization
dramatically affects its surface area and pore properties.[
] There appears to be a tendency in Fig 4
that the presence of air results in corn stover biochar with lower BET surface area. However,
more data are required to confirm this apparent trend. The BET surface area may also be
affected by variations in sample preparation (crushing and dry or wet sieving), the degassing
method (vacuum vs flow), degassing temperature and duration, quantity of sample used during
surface area analysis, number of replicates, using a representative sample quantity especially
from upscaled reactors, as well as the presence of foreign substances (e.g. sand or soil) on the
corn stover biomass during pyrolysis. Considering potential applications, the wide range of
BET among the corn stover biochars may affect nutrient plant availabilities of co-applied
4.3. FTIR analysis
The infrared spectra of the biochars are shown in Fig 6. The O–H stretch peak around 3600–
3200 cm-1 is clearly visible in the char produced at 300°C but decreases as pyrolysis
temperature increased representing dehydration of cellulose and ligneous compounds.[
presence of uncharred biomass in corn stover char produced at 300 and 400°C is exemplified
by CH2 peaks at ~2900 and ~1400 cm-1. Peaks of aliphatic C-O-C (1046 cm-1) and
alcohol-OH (1160 cm-1) groups indicate the presence of hemicellulose and cellulose in corn stover
biochar (300°C) suggesting the incomplete charring of corn stover at this temperature.[
This also agrees with XRD and TGA results discussed further in sections 4.4. and 4.5. Corn
stover biochar produced at 300°C is therefore expected to be at least partially biodegraded in soil.
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Fig 6. FTIR spectra of corn stover biochars produced at 300, 400 and 500°C.
X-ray diffraction is a valuable approach to investigate the biomass crystallinity and biochar
structure.  XRD results for corn stover biochars are illustrated in Fig 7. Two narrow, sharp
Fig 7. XRD spectra of corn stover biochars produced at 300, 400 and 500°C.
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peaks at the 2θ values around 16° and 22° for the control were assigned to the crystalline region
of cellulose in wood (Yang et al., 2007).[
] For biochar-300°C, these two peaks decreased in
intensity and became broader, indicating that some partial crystalline structure of cellulose was
] Although the biomass was partially decomposed at 300°C, the crystalline structure of
cellulose remained due to the thermal stability of cellulose at such low temperatures. However,
these two peaks were hardly visible in the XRD spectra for Biochar-400°C and Biochar-500°C
indicating that crystalline cellulose was destroyed during char formation at 400°C and above.
4.5. Thermogravimetric analysis of corn stover biochar
TGA and derivative thermogravimetric (DTG) curves are shown in (Fig 8a, 8b and 8c). TGA of
experimental biochars was carried out to study their pyrolytic performance and thermal
resistance. The TGA weight loss at temperatures upto 130°C was due to moisture loss. The
subsequent weight loss of corn stover biochar (300°C) at 244°C and above may be attributed to
thermal degradation of uncharred hemicellulose residues followed by uncharred cellulose and
lignin. The onset temperature for TGA weight loss of biochars produced at 400 and 500°C
shifted to 288 and 300°C, respectively, suggesting the presence of uncharred cellulose and
lignin, which are more heat-stable than hemicellulose.[
] However, XRD analysis showed that
crystalline cellulose disappeared in corn stover biochars produced at 400°C and above
suggesting that lignin or other volatile pyro-compounds were responsible for the observed weight loss.
The TGA curves also show that biochar produced at 500°C exhibited the greatest thermal
stability with an overall weight loss of 20% after heating to700°C,followed by chars produced at
400°C (35%) and 300°C (53%). The results confirm findings of Kim et al. that with increased
pyrolysis temperature, biochars from pitch pine woodchips become more stable.[
4.6. CP/MAS 13C NMR
In order to evaluate the aromaticity of corn stover biochar produced at 500°C, CP/MAS 13C
NMR was deployed. A dominant broad peak (Fig 9), at around 127 ppm was observed which
can be attributed to aromatic carbon resonance. [
] The subordinate small and broad peaks
around 205 ppm and 45 ppm for Biochar-500°C are due to spinning side bands originating
from the dominant aryl peak.[
] Peaks at 50–100 ppm indicative of carbohydrates, were
absent thus confirming that the observed weight loss in Fig 8 was not due to hemicellulose or
4.7. Net energy balance for pyrolysis
The higher heating values (HHV) and lower heating values (LHV) of corn stover feedstock and
corn stover biochars have been given in Table 4. The results show that corn stover biochar has
significantly greater LHVs than corn feed stock on dry basis. However, gross and net energy
value of biochars prepared at 400°C and 500°C did not differ significantly. While net energy
balance is higher at higher temperature. Previous studies suggest that pyrolysis technology has
potential to produce more surplus energy in addition to biochar for land applications is more
attractive being environment friendly. [
4.8. Biochar Characteristics and Carbon Stability
Fig 8. TGA/DTG spectra of corn stover biochars produced at, 300°C, 400°C 500°C obtained in a N2 atmosphere.
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Fig 9. 13 C NMR Spectra of Biochar- 500°C.
close to the Enders et., al.[
] about carbon stability of the chars. FTIR,TGA and 13C NMR
confirmed the presence of more aromatic stable carbon in biochar produced at 500°C. Thus
pyrolysis at 500°C may be a potential approach using crop residue for producing biochar for
carbon cut off and green energy.
The biochar yield decreased when the pyrolysis temperature increased. The physico-chemical
and structural characteristics of biochar were significantly influenced by pyrolysis temperature.
The degree of carbonization for biochar was accelerated with increasing pyrolysis temperature
from 300°C, 400°C to 500°C. TGA indicated that increased pyrolysis temperature developed
more stable form of biochar. As the pyrolysis progressed, oxygen and hydrogen were removed,
leaving to form more aromatic carbon bonds. The results of 13C NMR confirmed aromatic
carbon in corn stover biochar at 500°C. Result suggested that corn stover pyrolysis is pertinent to
reduce carbon emissions with net positive bioenergy production and its use as soil amendment.
Comparison of findings with literature showed that biochar production from corn stover is
influenced by various factors. Significant non-linear correlations between pyrolysis
temperature and yield and pH were noted. Contributing factors for poor correlations between pyrolysis
temperature, ash content and BET surface area include the presence of dirt from the field
which can artificially increase ash content and block pores but also affect biochar yield and pH.
Moreover, it was found that most studies appeared to analyse samples with one replicate only
using various standard and non-standard methods. Issues of representative sampling and
temperature measurements, especially in pilot- and industrial-scale reactors further complicate
data comparison. It is suggested for the biochar community to establish an international
committee to develop and agree upon standardized sample preparation and analysis methods to
facilitate data interpretation and reliability.
Mean values followed by different letters within the same column are significantly different at P<0.05. Where H% = Hydrogen Percent
14 / 17
This experiment was financially assisted under Chinese Ministry of Science and Technology
Project No. 2012BAC01B02-3 and National Natural Science Foundation of China, grant no.
Conceived and designed the experiments: MKR MTR ZS SJ RL. Performed the experiments:
MKR. Analyzed the data: MKR RTB. Contributed reagents/materials/analysis tools: ZS RL.
Wrote the paper: MKR MTR ZS RTB SJ RL.
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1. Pretty J , Sutherland WJ , Ashby J , Auburn J , Baulcombe D , Bell M , et al. The top 100 questions of importance to the future of global agriculture . International Journal of Agricultural Sustainability , 2010 , 8 ( 4 ), 219 - 236 .
2. Qiu J . China's climate target: is it achievable? Nature , 2009 , 462 ( 7273 ), 550 - 1 . doi: 10 .1038/462550a PMID: 19956225
3. Zhou X , Wang F , Hu H , Yang L , Guo P , Xiao B . Assessment of sustainable biomass resource for energy use in China . Biomass and Bioenergy , 2011 , 35 ( 1 ), 1 - 11 .
4. Kung C-C , Kong F , Choi Y. Pyrolysis and biochar potential using crop residues and agricultural wastes in China . Ecological Indicators , 2015 , 51 , 139 - 145 .
5. FAO. Available: http://faostat.fao.org/site/339/default.aspx 2012 . (accessed on 26.4 . 2015 ).
6. Clare A , Shackley S , Joseph S , Hammond J , Pan G , Bloom A ( 2015 ) Competing uses for China's straw: the economic and carbon abatement potential of biochar . Global Change Biology Bioenergy,
7. National Bureau of Statistics of China. China Statistical Yearbook. National Bureau of Statistics of China , Beijing, China. 2013 .
8. El Bassam N. C3 and C4 plant species as energy sources and their potential impact on environment and climate . Renewable Energy , 1998 , 5 , 205 - 210 .
9. Zheng M , Li X , Yang X , He Y. Enhancing anaerobic biogasification of corn stover through wet state NaOH pretreatment . Bioresour Technol , 2009 , 100 ( 21 ), 5140 - 5 . doi: 10 .1016/j.biortech. 2009 . 05 .045 PMID: 19540752
10. Cao G , Zhang X , Gong S , Zheng F. Investigation on emission factors of particulate matter and gaseous pollutants from crop residue burning . Journal of Environmental Sciences , 2008 , 20 ( 1 ), 50 - 55 .
11. Feng L , Li YQ , Chen C , Liu XY , Xiao X , Ma XX , et al. Biochemical Methane Potential (BMP) of Vinegar Residue and the Influence of Feed to Inoculum Ratios on Biogas Production . Bioresources, 2013 , 8 ( 2 ), 2487 - 2498 .
12. Nsamba HK , Hale SE , Cornelissen G , Bachmann RT . Sustainable Technologies for Small-Scale Biochar Production-A Review . Journal of Sustainable Bioenergy Systems , 2015 , 5 ( 1 ), 10 - 31 .
13. Lehmann J , Gaunt J , Rondon M . Bio-char Sequestration in Terrestrial Ecosystems-A Review . Mitigation and Adaptation Strategies for Global Change , 2006 , 11 ( 2 ), 395 - 419 .
14. Roberts KG , Goly BA , Joseph S , Scott NR , Lehmann J . Life Cycle Assessment of Biochar Systems: estimating the energetic, economic and climate change potential . Environmental Science and Technology . 2010 , 44 ( 2 ), 827 - 833 . doi: 10 .1021/es902266r PMID: 20030368
15. Rajkovich S , Enders A , Hanley K , Hyland C , Zimmerman AR , Lehmann J . Corn growth and nitrogen nutrition after additions of biochars with varying properties to a temperate soil . Biology and Fertility of Soils , 2012 , 48 ( 3 ), 271 - 284 . doi: 10 .1007/s00374-011-0624-7
16. Enders A , Hanley K , Whitman T , Joseph S , Lehmann J . Characterization of biochars to evaluate recalcitrance and agronomic performance . Bioresour Technol , 2012 , 114 , 644 - 53 . doi: 10 .1016/j.biortech. 2012 . 03 .022 PMID: 22483559
17. Capunitan JA , Capareda SC . Assessing the potential for biofuel production of corn stover pyrolysis using a pressurized batch reactor . Fuel , 2012 , 95 , 563 - 572 . doi: 10 .1016/j.fuel. 2011 . 12 .029
18. Peterson SC , Jackson MA . Simplifying pyrolysis: Using gasification to produce corn stover and wheat straw biochar for sorptive and horticultural media . Industrial Crops and Products , 2014 , 53 , 228 - 235 . doi: 10 .1016/j.indcrop. 2013 . 12 .028
19. Brewer CE , Unger R , Schmidt-Rohr K , Brown RC . Criteria to Select Biochars for Field Studies based on Biochar Chemical Properties . Bioenergy Research , 2011 , 4 ( 4 ), 312 - 323 . doi: 10 .1007/s12155-011- 9133-7
20. Uzoma KC , Inoue M , Andry H , Fujimaki H , Zahoor A , Nishihara E . Effect of cow manure biochar on maize productivity under sandy soil condition . Soil Use and Management , 2011 , 27 ( 2 ), 205 - 212 .
21. Dai Z , Meng J , Muhammad N , Liu X , Wang H , He Y , et al. The potential feasibility for soil improvement, based on the properties of biochars pyrolyzed from different feedstocks . J. Soils Sediments , 2013 , 13 , 989 - 1000 .
22. Smith JM . Chemical engineering kinetics . 3rd ed. McGraw- Hill , New York. 1981 .
23. International Flame Research Foundation (IFRF). International Flame Research Foundation 2011 . Online Combustion Handbook . IFRF, Livorno, Italy, ISSN 1607 -9116, Available: http://www.handbook. ifrf.net/handbook/
24. Woolf D . Biochar as a soil amendment: A review of the environmental implications . 2008 . Available: http://orgprints.org/13268.
25. Brewer CE , Schmidt-Rohr K , Satrio JA , Brown RC . Characterization of biochar from fast pyrolysis and gasification systems . Environmental Progress & Sustainable Energy , 2009 , 28 ( 3 ), 386 - 396 . doi: 10 . 1002/ep.10378
26. Fuertes AB , Arbestain MC , Sevilla M , MacIá-Agulló JA , Fiol S , López R , et al. Chemical and structural properties of carbonaceous products obtained by pyrolysis and hydrothermal carbonisation of corn stover . Australian Journal of Soil Research , 2010 , 48 ( 6-7 ), 618 - 626 . doi: 10 .1071/SR10010
27. Lee JW , Hawkins B , Day DM , Reicosky DC . Sustainability: the capacity of smokeless biomass pyrolysis for energy production, global carbon capture and sequestration . Energy Environ. Sci., 2010a , 3 , 1695 - 1705 .
28. Mullen CA , Boateng AA , Goldberg NM , Lima IM , Laird DA , Hicks KB . Bio-oil and bio-char production from corn cobs and stover by fast pyrolysis . Biomass and Bioenergy , 2010 , 34 ( 1 ), 67 - 74 . doi: 10 .1016/j. biombioe. 2009 . 09 .012
29. Thangalazhy-Gopakumar S , Adhikari S , Ravindran H , Gupta RB , Fasina O , Tu M , et al. Physiochemical properties of bio-oil produced at various temperatures from pine wood using an auger reactor . Bioresour Technol , 2010 , 101 ( 21 ), 8389 - 95 . doi: 10 .1016/j.biortech. 2010 . 05 .040 PMID: 20558057
30. Cao X , Harris W. Properties of dairy-manure-derived biochar pertinent to its potential use in remediation . Bioresour Technol , 2010 , 101 ( 14 ), 5222 - 8 .9 doi: 10.1016/j.biortech. 2010 . 02 .052 PMID: 20206509
31. Tsai WT , Liu SC , Chen HR , Chang YM , Tsai YL . Textural and chemical properties of swine-manurederived biochar pertinent to its potential use as a soil amendment . Chemosphere , 2012 , 89 ( 2 ), 198 - 203 . doi: 10 .1016/j.chemosphere. 2012 . 05 .085 PMID: 22743180
32. Güereña D , Lehmann J , Hanley K , Enders A , Hyland Riha S.Nitrogen dynamics following field application of biochar in a temperate North American maize-based production system . Plant and Soil , 2013 , 365 ( 1-2 ), 239 - 254 . doi: 10 .1007/s11104-012-1383-4
33. Spokas KA , Novak JM , Stewart CE , Cantrell KB , Uchimiya M , Dusaire MG , et al. Qualitative analysis of volatile organic compounds on biochar . Chemosphere , 2011 , 85 ( 5 ), 869 - 882 . doi: 10 .1016/j. chemosphere. 2011 . 06 .108 PMID: 21788060
34. Spokas KA , Reicosky DC . Impacts of sixteen different biochars on soil greenhouse gas production . Annals of Environmental Science , 2009 , 3 ( 612 ), 179 - 193 . Available: http://iris.lib.neu.edu/aes/vol3/ iss1/4/
35. Kumar A , Wang L , Dzenis YA , Jones DD , Hanna MA . Thermogravimetric characterization of corn stover as gasification and pyrolysis feedstock . Biomass and Bioenergy , 2008 , 32 ( 5 ), 460 - 467 . doi: 10 . 1016/j.biombioe. 2007 . 11 .004
36. Demirbaş A.Calculation of higher heating values of biomass fuels . Fuel , 1997 , 76 ( 5 ), 431 - 434 . doi: 10 . 1016/S0016- 2361 ( 97 ) 85520 - 2
37. Calvelo Pereira R , Muetzel S , Camps Arbestain M , Bishop P , Hina K , Hedley M. Assessment of the influence of biochar on rumen and silage fermentation: A laboratory-scale experiment . Animal Feed Science and Technology , 2014 , 196 , 22 - 31 . doi: 10 .1016/j.anifeedsci. 2014 . 06 .019
38. Lee JW , Kidder M , Evans BR , Paik S , Buchanan AC , Garten C , et al. Characterization of biochars produced from cornstovers for soil amendment . Environmental Science and Technology, 2010b , 44 ( 20 ), 7970 - 7974 . doi: 10 .1021/es101337x
39. Vargas-Moreno JM , Callejon-Ferre AJ , Perez-Alonsoa J , Velazquez-Marti B . A review of the mathematical models for predicting the heating value of biomass materials . Renewable Sustainable Energy Rev , 2012 , 16 : 3065 - 3083 .
40. Parikh J , Channiwala SA , Ghosal GK . A correlation for calculating elemental composition from proximate analysis of biomass materials . Fuel , 2007 , 86 ( 12 - 13 ), 1710 - 1719 . doi: 10 .1016/j.fuel. 2006 . 12 . 029
41. Ahmedna M , Johns MM , Clarke SJ , Marshall WE , Rao RM . Potential of agricultural by-product-based activated carbons for use in raw sugar decolourisation . Journal of the Science of Food and Agriculture , 1997 , 75 ( 1 ), 117 - 124 . doi: 10 .1002/(SICI) 1097 - 0010 ( 199709 )75: 1 < 117 : :AID-JSFA850>3.0 .CO;2-M
42. Rayment GE , Higginson FR . Australian Laboratory Handbook of Soil and Water22 Chemical Methods . Reed International Books, Australia/ Inkata Press, Port Melbourne. 1992 .
43. Chen Y , Yang H , Wang X , Zhang S , Chen H . Biomass-based pyrolytic polygeneration system on cotton stalk pyrolysis: influence of temperature . Bioresour Technol , 2012 , 107 , 411 - 8 . doi: 10 .1016/j.biortech. 2011 . 10 .074 PMID: 22209443
44. Chun Y , Sheng, Chiou CT , Xing B. Compositions and Sorptive Properties of Crop Residue-Derived Chars . Environmental Science & Technology , 2004 , 38 ( 17 ), 4649 - 4655 .
45. Demirbas A. Effects of temperature and particle size on bio-char yield from pyrolysis of agricultural residues . Journal of Analytical and Applied Pyrolysis , 2004 , 72 ( 2 ), 243 - 248 .
46. Cheah S , Malone S. C , Feik C. J. Speciation of sulfur in biochar produced from pyrolysis and gasification of oak and corn stover . Environmental Science and Technology , 2014 , 48 ( 15 ), 8474 - 8480 . doi: 10 . 1021/es500073r PMID: 25003702
47. Hale SE , Alling V , Martinsen V , Mulder J , Breedveld GD , Cornelissen G. The sorption and desorption of phosphate-P, ammonium-N and nitrate-N in cacao shell and corn cob biochars . Chemosphere , 2013 , 91 ( 11 ), 1612 - 9 . doi: 10 .1016/j.chemosphere. 2012 . 12 .057 PMID: 23369636
48. Yuan JH , Xu RK , Zhang H. The forms of alkalis in the biochar produced from crop residues at different temperatures . Bioresour Technol , 2011 , 102 ( 3 ), 3488 - 97 . doi: 10 .1016/j.biortech. 2010 . 11 .018 PMID: 21112777
49. Gaunt JL , Lehmann J . Energy balance and emissions associated with biochar sequestration and pyrolysis bioenergy production . Environ Sci Technol , 2008 , 42 ( 11 ), 4152 - 8 . PMID: 18589980
50. Antal MJ , Grønli M. The Art , Science, and Technology of Charcoal Production. Industrial & Engineering Chemistry Research , 2003 , 42 ( 8 ), 1619 - 1640 . doi: 10 .1021/ie0207919
51. Hale SE , Alling V , Martinsen V , Mulder J , Breedveld GD , Cornelissen G. 2013 . The sorption and desorption of phosphate-P, ammonium-N and nitrate-N in cacao shell and corn cob biochars . Chemosphere 91 , 1612 - 1619 . PMID: 23369636
52. Bustin RM , Guo Y. Abrupt changes (jumps) in reflectance values and chemical compositions of artificial charcoals and inertinite in coals . International Journal of Coal Geology , 1999 , 38 ( 3-4 ), 237 - 260 . doi: 10 .1016/S0166- 5162 ( 98 ) 00025 - 1
53. Keiluweit M , Nico PS , Johnson MG , Kleber M . Dynamic molecular structure of plant biomass-derived black carbon (biochar) . Environ Sci Technol , 2010 , 44 ( 4 ), 1247 - 53 . doi: 10 .1021/es9031419 PMID: 20099810
54. Chen B , Zhou D , Zhu L. Transitional Adsorption and Partition of Nonpolar and Polar Aromatic Contaminants by Biochars of Pine Needles with Different Pyrolytic Temperatures . Environ SciTechnol , 2008 , 42 ( 14 ), 5137 - 5143 . doi: 10 .1021/es8002684
55. Ertas M , Alma MH . Pyrolysis of laurel (Laurus nobilis L.) extraction residues in a fixed-bed reactor: characterization of bio-oil and bio-char . Journal of Analytical and Applied Pyrolysis 2010 , 88 ( 1 ), 22 - 29 .
56. Yang H , Yan R , Chen H , Lee DH , Zheng CG . Characteristics of hemicellulose, cellulose, and lignin pyrolysis , Fuel , 2007 , 86 , 1781 - 1788 .
57. Grønli M , Antal MJ , Várhegyi G. A Round-Robin Study of Cellulose Pyrolysis Kinetics by Thermogravimetry . Industrial & Engineering Chemistry Research , 1999 , 38 ( 6 ), 2238 - 2244 .
58. Kim KH , Kim JY , Cho TS , Choi JW . Influence of pyrolysis temperature on physicochemical properties of biochar obtained from the fast pyrolysis of pitch pine (Pinus rigida) . Bioresour Technol , 2012 , 118 , 158 - 62 . doi: 10 .1016/j.biortech. 2012 . 04 .094 PMID: 22705519
59. Fernandes MB , Skjemstad JO , Johnson BB , Wells JD , Brooks P . Characterization of carbonaceous combustion residues. I. Morphological, elemental and spectroscopic features . Chemosphere , 2003 , 51 ( 8 ), 785 - 795 . PMID: 12668037
60. Liu H , Jiang G , Zhuang H , Wang K . Distribution, utilization structure and potential of biomass resources in rural China: With special references of crop residues . Renewable and Sustainable Energy Reviews , 2008 , 12 ( 5 ), 1402 - 1418 .