Complete Utilization of Spent Coffee Grounds To Produce Biodiesel, Bio-Oil, and Biochar

Abstract

This study presents the complete utilization of spent coffee grounds to produce biodiesel, bio-oil, and biochar. Lipids extracted from spent grounds were converted to biodiesel. The neat biodiesel and blended (B5 and B20) fuel properties were evaluated against ASTM and EN standards. Although neat biodiesel displayed high viscosity, moisture, sulfur, and poor oxidative stability, B5 and B20 met ASTM blend specifications. Slow pyrolysis of defatted coffee grounds was performed to generate bio-oil and biochar as valuable co-products. The effect of feedstock defatting was assessed through bio-oil analyses including elemental and functional group composition, compound identification, and molecular weight and boiling point distributions. Feedstock defatting reduced pyrolysis bio-oil yields, energy density, and aliphatic functionality, while increasing the number of low-boiling oxygenates. The high bio-oil heteroatom content will likely require upgrading. Additionally, biochar derived from spent and defatted grounds were analyzed for their physicochemical properties. Both biochars displayed similar surface area and elemental constituents. Application of biochar with fertilizer enhanced sorghum–sudangrass yields over 2-fold, indicating the potential of biochar as a soil amendment.

Full text

Complete Utilization of Spent Coffee Grounds To Produce Biodiesel,
Bio-Oil, and Biochar
Derek R. Vardon,
†,‡
Bryan R. Moser,
§
Wei Zheng,
†
Katie Witkin,
†
Roque L. Evangelista,
§
Timothy J. Strathmann,
‡
Kishore Rajagopalan,
†
and Brajendra K. Sharma*
,†
†
Illinois Sustainable Technology Center, 1 Hazelwood Dr., Champaign, Illinois 61820, United States
‡
Department of Civil and Environmental Engineering, 205 N. Mathews Ave., Urbana, Illinois 61801, United States
§
Agricultural Research Service, National Center for Agricultural Utilization Research, United States Department of Agriculture, 1815
N. University St., Peoria, Illinois 61604, United States
*
SSupporting Information
ABSTRACT: This study presents the complete utilization of
spent coffee grounds to produce biodiesel, bio-oil, and biochar.
Lipids extracted from spent grounds were converted to
biodiesel. The neat biodiesel and blended (B5 and B20) fuel
properties were evaluated against ASTM and EN standards.
Although neat biodiesel displayed high viscosity, moisture,
sulfur, and poor oxidative stability, B5 and B20 met ASTM
blend specifications. Slow pyrolysis of defatted coffee grounds
was performed to generate bio-oil and biochar as valuable co-
products. The effect of feedstock defatting was assessed
through bio-oil analyses including elemental and functional
group composition, compound identification, and molecular
weight and boiling point distributions. Feedstock defatting reduced pyrolysis bio-oil yields, energy density, and aliphatic
functionality, while increasing the number of low-boiling oxygenates. The high bio-oil heteroatom content will likely require
upgrading. Additionally, biochar derived from spent and defatted grounds were analyzed for their physicochemical properties.
Both biochars displayed similar surface area and elemental constituents. Application of biochar with fertilizer enhanced
sorghum−sudangrass yields over 2-fold, indicating the potential of biochar as a soil amendment.
KEYWORDS: Coffee grounds, Coffee oil, Biodiesel, Bio-oil, Biochar, Pyrolysis
■INTRODUCTION
Coffee is one of the largest agricultural commodities traded
worldwide, with annual production at ∼8 billion kg per year.
1
Commercial coffee beverage production generates substantial
quantities of spent grounds that present a significant waste
disposal challenge. Spent coffee grounds are problematic for
disposal due to the high oxygen demand during decomposition
and potential release of residual caffeine, tannin, and
polyphenol contaminants to the environment.
2
Valorization
of spent coffee grounds is a promising alternative to reclaim
energy
3
and produce biodiesel, bio-oil, and biochar while
generating stabilized solids for carbon storage and soil
amendment.
Spent coffee grounds are attractive for biodiesel production
due to their high lipid content, which is ∼15% by dry weight.
4
The use of spent grounds avoids competition with food
resources compared to conventional lipid feedstocks, such as
soybeans and rapeseed.
5
Coffee biodiesel can be used neat or
blended with petroleum diesel at various levels (e.g., B5, B20)
for enhanced engine compatibility.
6
While the production of
coffee biodiesel has been examined,
7
to our knowledge, studies
have yet to explore fuel properties of biodiesel blends with
petroleum diesel and its adherence to fuel standards.
The remaining defatted coffee grounds also present a
potential opportunity for co-product recovery via slow
pyrolysis. Slow pyrolysis concentrates biomass carbon and
reduces the solid waste disposal footprint by producing bio-oil
and biochar. Slow pyrolysis usually occurs between 400 and 600
°C, with a relatively moderate heat-up rate (0.1−1°C/sec)
compared to fast (10−200 °C/min) or flash pyrolysis (>1000
°C/min).
8
Slow pyrolysis bio-oils have a high energy density on
a moisture-free basis (20−37 MJ/kg)
9−11
that approaches
petroleum crude oils (41−48 MJ/kg).
12
Furthermore, bio-oil
condenses energy into a liquid form, allowing for distributed
processing and reduced transportation costs.
13
In addition,
biochar has a high energy density ranging from 30 to 34 MJ/kg
and can be used as a solid fuel.
10,14
However, the use of biochar
as a soil amendment and carbon storage medium has also
garnered significant interest.
15
When added to soil, biochar can
Received: May 15, 2013
Revised: July 10, 2013
Published: August 2, 2013
Research Article
pubs.acs.org/journal/ascecg
© 2013 American Chemical Society 1286 dx.doi.org/10.1021/sc400145w |ACS Sustainable Chem. Eng. 2013, 1, 1286−1294

improve the soil quality by adjusting soil pH, improving soil
moisture retention, enhancing the microbial population, and
increasing nutrient-use efficiency.
16
Biochar is also resistant to
decomposition and mineralization, locking carbon in a stable
form.
15
However, to our knowledge, studies have yet to
examine the (i) slow pyrolysis of spent coffee grounds, (ii)
influence of defatting on bio-oil properties, or (iii) use of coffee
biochar as a soil amendment.
The objective of this study is to demonstrate the complete
utilization of spent coffee grounds for energy recovery and soil
amelioration by extracting residual lipids for biodiesel
production and converting defatted grounds into bio-oil and
biochar via slow pyrolysis (Figure 1). In this work, spent coffee
grounds were collected from local coffee shops. Lipids were
extracted and converted into biodiesel to determine their neat
and blended (B5 and B20) fuel properties against ASTM and
EN standards. Slow pyrolysis of defatted grounds was then
performed to produce bio-oil and biochar. The effect of
feedstock defatting on pyrolysis was examined, and bio-oil
analyses included elemental and functional group composition,
compound identification, and molecular weight and boiling-
point distributions. Additionally, biochars were analyzed for
their elemental composition, surface area, and application as a
soil amendment for sorghum−sudangrass cultivation.
■MATERIALS AND METHODS
Spent and Defatted Coffee Grounds. Spent coffee grounds
(e.g., grounds generated after brewing) were collected from local
Starbuck’s coffee shops with an average moisture content of 60%,
consistent with past studies.
7
Spent grounds were spread into a thin
layer and dried at 105 °C overnight to remove residual moisture.
Lipids were then extracted using hexane in a Soxhlet apparatus. The
extraction proceeded until the refluxing solvent became clear (∼8 h).
Hexane was removed from the extract by rotary evaporation under
reduced pressure until no further changes in sample weight were
observed.
Spent and defatted coffee grounds were analyzed for their
nutritional and elemental composition. Forage analysis was performed
by Midwest Laboratories (Omaha, NE) to determine crude protein,
neutral detergent fiber (hemicellulose, cellulose, and lignin), acid
detergent fiber (cellulose and lignin), and ash content. Nutrient
analysis was also performed by Midwest laboratories to determine
major, secondary, and micronutrients. Elemental analysis of spent and
defatted coffee grounds was conducted at the University of Illinois
Microanalysis Laboratory (Urbana, IL). Samples were processed for
total carbon/hydrogen/nitrogen using an Exeter analytical CE-440
elemental analyzer. Oxygen was calculated by mass balance closure.
Higher heating values (HHV) of the coffee grounds were measured
using a Parr 1281 isoperibol oxygen bomb calorimeter. Standard 1 g
pellets of benzoic acid were used for calibration. Acid corrections were
based on sodium carbonate titration with no correction for sulfur.
Lipids extracted from spent coffee grounds were analyzed for their
fatty acid profile. Fatty acids were esterified prior to analysis.
17
Spent
coffee oil methyl esters were separated using a HP 5890 Series II GC
equipped with a FID detector and a Supelco SP-2380 column (30 m ×
0.25 mm i.d., 0.20 μmfilm thickness). Helium (1 mL/min) was used
as the carrier gas. The oven temperature increased from 170 to 190 °C
at 4 °C/min, followed by an increase to 265 °C at 30 °C/min, with a
final hold time of 2.5 min. The injector volume was set to 1 μL with
the injector and detector temperature set at 250 °C. Peaks were
identified (triplicates, means reported) by comparison to reference
standards.
Coffee Biodiesel and Biodiesel Blends. Coffee lipids were
pretreated prior to base-catalyzed transesterification to reduce their
acid value (AV). Acid-catalyzed pretreatment was accomplished in a 1
L three-necked round-bottomed flask connected to a reflux condenser
and a mechanical magnetic stirrer set to 1200 rpm. Initially, coffee oil
and methanol (35 vol %) were added to the flask, followed by
dropwise addition of sulfuric acid (conc., 1.0 vol %). The contents
were heated at reflux for 4 h. Upon cooling to room temperature, the
phases were separated. The oil phase was washed with distilled water
until a neutral pH was achieved, followed by rotary evaporation (20
mbar; 30 °C) to remove residual methanol.
Acid-pretreated coffee lipids were transesterified using conventional
alkaline-catalyzed methanolysis to prepare coffee biodiesel. Meth-
anolysis was conducted in a 1 L three-necked round-bottomed flask
connected to a reflux condenser and a mechanical magnetic stirrer set
at 1200 rpm. Initially, the extracted lipids and methanol (1:6 molar
ratio) were added and heated to 60 °C, followed by the addition of
sodium methoxide catalyst (0.50 wt % with respect to lipids). After
reacting for 1 h, the mixture was equilibrated to room temperature,
and the lower glycerol phase was removed by gravity separation (>2 h
settling time). Methanol was removed from the ester phase by rotary
evaporation at reduced pressure. Spent coffee biodiesel was washed
with distilled water until a neutral pH was obtained and then was dried
with MgSO4to yield neat biodiesel. Neat biodiesel was also blended
with ultralow sulfur petroleum diesel (ULSD) at 5% and 20% volume
to produce B5 and B20 blends, respectively. Certification grade ULSD
was donated by a major petroleum company that wishes to remain
anonymous. Characterization results were compared for ULSD,
extracted coffee lipids, coffee biodiesel, soy biodiesel,
18
and respective
biodiesel blends.
Coffee Biodiesel Characterization. Fuel properties of neat and
blended coffee biodiesels were measured in triplicate following AOCS,
ASTM, and CEN standard test methods using instrumentation
described previously.
6,19,20
Standard test methods included cloud
point (CP, °C), ASTM D5773; pour point (PP, °C), ASTM D5949;
lubricity (mm), ASTM D6079; ASTM D4052; kinematic viscosity
(mm2/s), ASTM D445; specific gravity (SG), AOCS Cc 10c-95;
induction period (IP, h), EN 15751; acid value (AV, mg KOH/g),
AOCS Cd 3d-63; derived cetane number (DCN), ASTM D6890; free
and total glycerol (single determinations), ASTM D6584; moisture
content (ppm), ASTM D6304; gross heat of combustion (higher
heating value, HHV, MJ/kg), ASTM D4809; sulfur (S, ppm), ASTM
D5453; and phosphorus (P, mass %), ASTM D4951.
Slow Pyrolysis. Slow pyrolysis was conducted using a Thermolyne
79400 tube furnace as described in detail previously.
11
Briefly,
conversions were conducted using 100 g of dry feedstock heated to
450 °C at a rate of 50 °C/min. The retention time was 2 h with a
nitrogen sweep gas. An ice-chilled collection vessel condensed volatile
products. The remaining solids in the tube furnace were massed and
hereon referred to as biochar. Condensed liquids were fractionated
using dichloromethane (DCM) to separate bio-oil (DCM-soluble
phase) and aqueous-phase organics. Residual particulates (<1% of
Figure 1. Processing scheme for complete utilization of spent coffee
grounds.
ACS Sustainable Chemistry & Engineering Research Article
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initial biomass) in the DCM and water phases were removed using a
Millipore pressurized filtration assembly and Satorious 0.45 μm
cellulose membrane. The mass of the aqueous phase was measured
gravimetrically after fractionation. DCM was removed from the bio-oil
phase by rotary evaporation under reduced pressure. The product
phase mass balance was calculated as a fraction of the initial dry
feedstock mass, with the gas-phase yield determined by closure.
Bio-Oil Characterization. Bio-oils were characterized in detail
using methods described previously
21
to determine their bulk and
physicochemical properties. Bio-oil elemental compositions and sulfur
contents were measured using the Exeter elemental analyzer and
PerkinElmer ICP-OES described above. Low-boiling constituents were
identified by gas chromatography−mass spectroscopy (GC-MS).
Chemical functional groups were profiled using attenuated total
reflectance-Fourier Transform infrared (ATR-FTIR) and 1H-nuclear
magnetic resonance spectroscopy (1H NMR), and bio-oil molecular
weight and boiling point distributions were analyzed using size
exclusion chromatography (SEC) and simulated distillation (Sim-
Dist), respectively. Bio-oil HHVs were measured using the Parr bomb
calorimeter described above.
Biochar Characterization and Soil Application. Biochars were
evaluated to determine their bulk properties, nutrient profile, and
performance as a soil amendment. Biochar elemental compositions,
nutrient profile, and HHVs were determined using methods described
above. Ash content was determined gravimetrically after heating a
known amount of sample at 800 °C for 1.5 h with an air purge flow
rate of 450 mL/min. Moisture was determined gravimetrically after
heating a known amount of sample at 140 °C for 1.5 h with a nitrogen
purge flow rate of 70 mL/min. Single point BET surface areas were
determined using nitrogen adsorption and desorption isotherms at
−196 °C with a Monosorb (Quantachrome Inc.) N2adsorption
analyzer.
22
The performance of biochar as a soil amendment for sorghum−
sundangrass cultivation was evaluated in a temperature-controlled
greenhouse (20−25 °C). The greenhouse experiments were managed
according to standard greenhouse growing practices.
23,24
Sorghum−
sudangrass was selected due to its rapid growth and dual utilization as
a forage crop and bioenergy feedstock.
25
Ten sorghum−sudangrass
seeds were planted in 1500 mL containers using 750 g of organic top
soil obtained from Peat Corp and 750 g of vermiculite obtained from
Sun Gro Horticulture. Spent coffee grounds, defatted grounds, and
biochar derived from these feedstocks were mixed as soil additives at 2
wt %. Cultivation experiments were also conducted without coffee
additives as a control. The influence of soil additive on biomass
productivity was tested with and without fertilizer application using 40
mg of Scotts’General Purpose water-soluble fertilizer (NH4NO3).
Three replicates were employed for each treatment. During growth,
external lighting was not used, and watering was scheduled twice per
week. Seedlings were cultivated for an average of 40 days, after which
the plants were harvested, washed, dried, and weighed to determine
the biomass growth. Because of the small quantities of biomass
collected from each pot, biomass samples from three triplicate pots
were weighed collectively to determine biomass productivity yields for
each treatment.
■RESULTS AND DISCUSSION
Spent and Defatted Coffee Grounds. The spent coffee
and defatted coffee grounds used in this study were primarily
composed of neutral detergent fiber (NDF) (45.2% spent;
58.9% defatted), representative of hemicellulose, cellulose, and
lignin (Table 1). Acid detergent fiber (ADF), representative of
cellulose and lignin, was also significant (29.8% spent; 40.2%
defatted), indicating that a large fraction was comprised of
hemicellulose. The level of protein was comparable for both
feedstocks (15.4% spent; 18.2% defatted), which distinguishes
coffee grounds from woody biomass that contains negligible
protein and over 80% NDF.
9
Spent coffee grounds contained
16.2% lipid. By contrast, very small quantities (0.3%) were
detected in the defatted grounds. The nutritional composition
of the spent coffee grounds was comparable to previous reports
of grounds collected from various sources.
2
The fatty acid
profile of the extracted lipids revealed a high percentage of
polyunsaturated fatty acids (46.5%), consisting predominantly
of linoleic acid (45.0%) (Table 1). The high percentage of
polyunsaturated fatty acids was consistent with previous studies
for coffee oil.
26
Saturated fatty acids were also detected, with
palmitic acid being the most prevalent (34.9%).
Elemental analysis of the coffee grounds revealed a higher
oxygen content for the defatted feedstock (34.0% spent; 38.8%
defatted). The oxygen content resulted in a lower HHV of 20.1
MJ/kg for the defatted grounds, compared to 23.4 MJ/kg for
the spent grounds, as measured by calorimetry. The residual
energy content of defatted coffee grounds is comparable to
woody biomass (19−21 MJ/kg),
27
making it a suitable
feedstock for thermochemical conversion or direct combustion.
However, the coffee protein fraction resulted in a N content of
2.4% for spent grounds and 2.8% for defatted grounds, likely
resulting in high NOxemissions with direct combustion.
Ideally, nitrogen would be recovered during biomass valor-
ization for fertilizer application. The S content of the spent and
defatted grounds was minimal (0.14−0.17%), which is
advantageous for thermochemical conversion to produce bio-
oil.
Coffee Biodiesel. Neat lipids extracted from spent coffee
grounds displayed a prohibitively high AV (11.27 mg KOH g−1
initial) for traditional homogeneous based-catalyzed trans-
esterification, requiring acid-catalyzed pretreatment for reduc-
tion. The acid-pretreated lipids produced coffee biodiesel in
Table 1. Initial Moisture Content (wt %), Nutritional
Analysis, Fatty Acid Profile, Elemental Composition, And
Higher Heating Value (HHV) of Spent and Defatted
Grounds
collected grounds initial moisture
(wt %) 50−60
property spent coffee
grounds defatted coffee
grounds
nutritional analysis
crude protein 15.4 18.2
crude lipid 16.2 0.3
NDF 45.2 58.9
ADF 29.8 40.2
ash 1.8 (0.17) 2.4 (0.12)
fatty acid profile
16:0 33.9 −
18:0 7.3 −
18:1 8.3 −
18:2 45.0 −
18:3 1.5 −
20:0 2.5 −
20:1 0.4 −
22:0 0.6 −
elemental analysis
C 56.1 51.8
H 7.2 6.3
N 2.4 2.8
O 34.0 38.8
S 0.14 0.17
P 0.18 0.17
HHV (MJ/kg) 23.4 20.1
ACS Sustainable Chemistry & Engineering Research Article
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high yield (96 wt %), with a low biodiesel AV (0.11 mg KOH/
g), as shown in Table 2. The energy density of the coffee
biodiesel (39.6 MJ/kg) was comparable to biodiesel derived
from refined, bleached, and deodorized soybean oil (39.9 MJ/
kg) and other plant lipid-derived biodiesels.
28
However, several
coffee biodiesel properties were outside of ASTM D6751 or EN
14214 specifications, including the kinematic viscosity,
oxidative stability (indicated by Rancimat IP), moisture, and
S content. Because of higher amounts of saturated fatty acids,
the CP and PP of the coffee biodiesel were also elevated (13.1
and 13.0 °C, respectively) compared to soy biodiesel (0 °C and
−3°C, respectively), indicating poor cold weather perform-
ance.
The high kinematic viscosity and S content may be due to
the large percentage of saturated methyl ester chains and polar
compounds, respectively,
29
while the high moisture content
may be attributable to carry over during the water washing step.
During transesterification, natural antioxidants may also be lost,
resulting in poor oxidative stability compared to neat lipids.
29
Refining, bleaching, and deodorizing extracted coffee lipids
prior to conversion may help improve the final biodiesel
viscosity, cold flow properties, and S content by removing
waxes, sterols, heteroatom-containing compounds, and free
fatty acids.
30,31
Other fuel properties of the coffee biodiesel
(e.g., AV, cetane number, free and total glycerol) were within
ASTM and EN specifications.
Blending of coffee biodiesel with ULSD greatly enhanced its
fuel properties, providing a final product meeting ASTM D975
and D7467 specifications, as shown in Table 3. The kinematic
viscosity (2.4 mm2/s B5; 2.75 mm2/s B20), moisture content
(43 ppm B5; 124 ppm B20), and S content (8.6 ppm B5, 14.1
ppm B20) were significantly improved through blending, which
may lead to improved fuel injector performance, fuel
flowability, and combustion byproducts.
5
Likewise, the
oxidation stability was significantly extended, resulting in a
prolonged Rancimat induction period (13.2 h B5; 5.2 h B20).
The cold weather properties also benefited, leading to reduced
CP and PP values for B5 (−13.2 °C, −22.7 °C) and B20 (−4.7
°C, −11.7 °C). Overall, blending coffee biodiesel with ULSD
produced a high quality fuel that met ASTM biodiesel blend
specifications.
Slow Pyrolysis Mass Balance. Slow pyrolysis of defatted
coffee grounds resulted in a bio-oil yield of 13.7%, which was
roughly half yield of bio-oil obtained from spent coffee grounds
(27.2%), as shown in Figure 2. The lower bio-oil yield from
defatted grounds is likely due lipid extraction, consistent with
previous findings for raw and defatted microalgae.
11
Lipids are
known to rapidly breakdown during pyrolysis into bio-oil
organics, which include alkanes, fatty acids, esters, ketones, and
acrolein.
32
In contrast, the pyrolysis aqueous-phase yield from
defatted grounds was much higher (33.3%) compared to spent
grounds (23.8%). The higher yield of aqueous-phase
constituents may be due to the elevated content of cellulose
Table 2. Fuel Standards and Lipid and Biodiesel Fuel Properties for Refined, Bleached, and Deodorized (RBD) Soy Biodiesel,
Spent Coffee Lipids, and Coffee Biodiesel
a
fuel property ASTM D6751 EN 14214 soy biodiesel
18
spent coffee lipids initial coffee biodiesel
cloud point (°C) report −0 12.2 (0.1) 13.1 (0.3)
pour point (°C) −−−3 7.0 (0.0) 13.0 (0.0)
lubricity at 60 °C(μm) −−135 180 (2) 175 (4)
kin. visc. 40 °C (mm2/s) 1.9−6.0 3.5−5.0 4.12 49.64 (0.07) 5.19 (0.00)
sp. gravity −−0.8823 0.9411 0.8920
Rancimat ind. 110 °C (h) 3.0 min 6.0 min 5.0 8.4 (0.4) 0.2 (0.0)
acid value (mg KOH/g) 0.50 max 0.50 max 0.01 11.27 (0.14) 0.11 (0.01)
cetane number 47 min 51 min 54.1 −60.1 (1.1)
free glycerol (mass %) 0.020 max 0.020 max 0.004 −0.005
total glycerol (mass %) 0.240 max 0.250 max 0.071 −0.098
moisture content (ppm) 0.050
b
vol % max 500
c
ppm 202 (6) 330 (8) 632 (2)
P/S (ppm) 15/10 10/4 <1/<1 0.2/60.1 0.0/35.9
HHV (MJ/kg) −−39.9 −39.6
a
Values in parentheses indicate standard deviations from triplicate measurements.
b
Free water.
c
Dissolved water.
Table 3. Fuel Standards and Biodiesel Blend Fuel Properties for B5 and B20 Coffee and Soy Biodiesel
a
fuel property ASTM D975 ASTM D7467 ULSD coffee B5 soy B5
18
coffee B20 soy B20
18
vol % biodiesel 0−56−20 0 5 5 20 20
cloud point (°C) report −−14.9 (0.2) −13.2 (0.2) −16 −4.7 (0.4) −12
pour point (°C) −−−24.3 (0.6) −22.7 (0.6) −22 −11.7 (0.6) −17
lubricity at 60 °C(μm) 520 max 520 max 493 (10) 186 (14) 198 141 (2) 143
kin. visc. 40 °C (mm2/s) 1.9−4.1 1.9−4.1 2.23 (0.00) 2.40 (0.01) 2.37 2.75 (0.01) 2.54
sp. gravity −−0.8483 0.8501 0.8480 0.8564 0.8540
Rancimat ind. 110 °C (h) −6.0 min >24 13.2 (0.6) >24 5.2 (0.2) 17.1
acid value (mg KOH/g) −0.3 max 0.05 (0.04) 0.17 (0.04) 0.01 0.16 (0.01) 0.01
cetane number 40 min 40 min 42.5 50.5 43.8 51.9 46.5
moisture content (ppm) −−17 (1) 43 (1) 27 (3) 124 (3) 56 (6)
P/S (ppm) 15/−15/−ND/9.2 0/9.4 ND/8.6 0/14.1 ND/7.2
HHV (MJ/kg) −−44.2 44.8 44.7 43.9 40.0
a
Values in parentheses indicate standard deviations from triplicate measurements.
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and hemicellulose after lipid extraction because these
components can degrade into water-soluble organics.
10
Energy
recovery from pyrolysis aqueous-phase organics is of interest
for a potential source of hydrogen, alkanes, and polyols.
33
The
biochar solids yield (27.0−28.0%) and gas phase yield (21.0−
24.0%) were comparable for spent and defatted grounds, with
biochar yields similar to previous studies for spent coffee
grounds.
14
Bio-Oil Properties. Elemental Composition and HHV.
Bio-oil (moisture-free basis) derived from spent and defatted
coffee grounds increased the carbon density and reduced the
oxygen content compared to the original feedstocks, as shown
in Table 4. The elevated carbon density resulted in high bio-oil
energy HHVs (32.3 MJ/kg spent; 27.0 MJ/kg defatted).
Although lipid extraction reduced the energy density of
pyrolysis bio-oil, the HHV was still comparable to other
renewable fuels, such as ethanol (28.9 MJ/kg). The oxygen
content of the both feedstocks (34.3% spent feedstock; 39.1%
defatted feedstock) was greatly reduced in the bio-oil (13.4%
spent bio-oil; 16.4% defatted bio-oil). In contrast, a significant
portion of the feedstock nitrogen content was carried over into
the pyrolysis bio-oil phase resulting in moderate bio-oil N
contents (2.6% spent; 4.3% defatted). The coffee bio-oil N
content was comparable to fast pyrolysis studies with spent
coffee grounds (3.06%);
34
however, these values are much
higher compared to bio-oils derived from woody biomass,
which typically contain less than 1% N content due to the low
feedstock protein content.
9
Defatting resulted in a bio-oil with
lower C and H and higher N and O, which is likely due to the
removal of the aliphatic lipid fraction that shifts the overall
biomass composition, as shown in Table 1.
Overall, the total bio-oil heteroatom content (16.2% spent
bio-oil; 21.1% defatted bio-oil) was greatly reduced compared
to the feedstock (36.7% spent feedstock; 41.9% defatted
feedstock) and consistent with other slow pyrolysis bio-oils
produced at similar temperatures from algae (16.8−19.9%)
35
and cherry seeds (23.8−24.4%).
10
However, the high
heteroatom content greatly distinguishes slow pyrolysis bio-
oils from conventional petroleum crude oils, which typically
contain <4% total heteroatoms.
12
Furthermore, removal of bio-
oil N is problematic and remains a challenge because it can
result in fouling of acidic sites during catalytic upgrading.
36,37
Identification of Volatile and Semivolatile Constitu-
ents. The major volatile constituents of the coffee bio-oil
constituents were identified by GC-MS, as indicated by >1% of
the total ion chromatogram area (TIC), and categorized, as
shown in Table 5. A full listing of major compounds and
representative chromatogram are reported in Table S1 and
Figure S1 of the Supporting Information. Analysis of mass
spectra revealed that both coffee-derived bio-oils contained a
high percentage of oxygenated compounds (32.8−48.3%),
comprised primarily of phenolic and methylphenolic com-
pounds. The high percentage of phenolic compounds is
consistent with the high ADF (lignin and cellulose) content
of the coffee ground feedstocks, similar to observations with
wood-derived bio-oils.
9
Varying classes of nitrogenated
compounds, including caffeine, indole, amine, and nitrile-
derivatives, were also observed, which is consistent with the
protein content of the feedstock. As expected, the bio-oil
derived from spent coffee grounds contained more hydro-
carbon products compared to the defatted coffee bio-oil due to
the removal of lipids. Lipids are known to readily decompose
into hydrocarbons during pyrolysis;
38
however, they may have
greater economic value when used for biodiesel. Hydrocarbon
compounds were also observed in the bio-oil derived from
defatted coffee, which may be due to heteroatom removal from
other biomass fractions (e.g., proteins) during conversion.
11,39
Functional Group Analysis. Defatting spent coffee
grounds prior to pyrolysis influenced the bio-oil functional
groups observed by ATR-FTIR (Figure 3a) and 1H NMR
(Figure 3b). References for the ATR-FTIR bio-oil functional
peak assignments were based on previous pyrolysis studies.
38,40
Bio-oils derived from defatted coffee grounds contained more
prevalent functional peaks at 1650 cm−1and 1600 cm−1
compared to bio-oil derived from spent coffee grounds,
possibly due to increased N−H bending or CO stretch
from amide, ketone, and carboxylic groups associated with the
higher feedstock protein content. Other peaks consistent with
bio-oil derived from a high protein feedstock were observed in
both spectra, including C−N stretch (1335−1020 cm−1) and
N−H wag (910−665 cm−1).
11,40
Aliphatic peaks, consistent
with the high bio-oil energy density, were prevalent as expected,
and included C−H stretch (3000−2800 cm−1) and C−H
bending (1465 cm−1, 1375 cm−1). A broad peak from 3400 to
3000 cm−1and multiple sharp peaks from 1300 to 1100 cm−1
were also observed, likely due to the C−O stretch and O−H
stretch from phenolic, carboxylic, or alcohol moieties,
consistent with compounds identified by GC-MS.
Figure 2. Mass balance yield for the product phases derived from the
slow pyrolysis of spent coffee grounds and defatted spent coffee
grounds.
Table 4. Elemental Analysis, Higher Heating Values (HHV), and Molecular Weight Parameters of Slow Pyrolysis Bio-Oils
Derived from Spent and Defatted Coffee Grounds
a
bio-oil feedstock C (%) H (%) N (%) O (%) S (%) HHV (MJ/kg) MnMwPDI
spent grounds 74.0 (0.9) 9.8 (0.2) 2.6 (0.1) 13.4 (0.9) 0.17 32.3 596 2357 3.96
defatted grounds 70.9 (0.5) 8.0 (0.0) 4.3 (0.0) 16.4 (0.5) 0.39 27.0 651 2670 4.10
a
Values in parentheses indicate standard deviations from triplicate measurements.
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The 1H NMR spectra (raw spectra shown in Figure S2,
Supporting Information) revealed further differences in the
functionality of spent and defatted coffee ground bio-oils, with
spectra area integration assignments (Figure 3) based on
previous studies.
41
Bio-oil derived from spent grounds
contained a higher percentage of aliphatic protons (67%)
compared to the bio-oil derived from defatted coffee grounds
(44%), consistent with the higher lipid content and hydro-
carbon products identified by GC-MS. Both bio-oils displayed
comparable integration regions for protons alpha to a
heteroatom group or unsaturated bond (26% spent, 33%
defatted), likely due to the high heteroatom content
determined from elemental analysis. Lastly, bio-oil derived
from defatted coffee grounds displayed a higher aromatic/
heteroaromatic content (17%), consistent with the larger
percentage of cyclic structures containing oxygen and nitrogen
functional groups identified by GC-MS.
Molecular Weight and Boiling Point Distribution. Bio-
oil molecular weight and boiling point distributions were
profiled to determine the influence of feedstock defatting on
the physico-chemical characteristics of bio-oils. The number
average molecular weight (Mn), weight average molecular
weight (Mw), and polydispersity index (PDI) were used to
characterize the molecular weight distribution of the bio-oils.
These parameters were calculated based on component
molecular weights (Mi) determined from the retention time
calibration curve and signal intensities (Ni) in size exclusion
chromatography data
=∑
∑
M
MN
N
n
ii
i
=∑
∑
M
MN
MN
w
ii
ii
2
The polydispersity index (PDI) was then calculated
according to
=M
M
P
DI
w
n
As shown in Table 4, bio-oil derived from spent coffee
grounds displayed a comparable number average MW (MWn
596 Da) and weight average molecular weight (MWw2357 Da)
compared to bio-oil derived from defatted coffee grounds
(MWn651 Da; MWn2670 Da). Both bio-oils had similar
polydispersity indices, (3.96−4.10), consistent with the diverse
range of decomposition products generated during pyrolysis.
However, analysis of the MW distribution profile (Figure S3,
Supporting Information) revealed a prominent peak near 700
Da for the bio-oil derived from spent coffee grounds, which
may be due to incomplete lipid decomposition products (i.e.,
acylglycerides). A similar trend was observed in the MW
distribution of bio-oils derived from raw and defatted
Table 5. Percent of Total Ion Chromatogram (TIC) of Chemical Constituents Identified by Class Using GC-MS for Slow
Pyrolysis Bio-Oils Derived from Spent and Defatted Coffee Grounds
bio-oil
feedstock straight and branched
hydrocarbons cyclic
hydrocarbons
straight and
branched
oxygenates cyclic
oxygenates
straight and
branched
nitrogenates cyclic
nitrogenates N and O straight
and branched N and O
cyclic
spent coffee
grounds 10.0 4.3 12.8 17.0 1.9 ND 1.9 1.1
defatted coffee
grounds 3.2 3.2 2.5 43.4 ND 1.3 ND 2.4
Figure 3. FTIR-ATR spectra (a) and 1H NMR spectral distribution of functional groups (b) of bio-oil derived from spent and defatted coffee
grounds.
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microalgae.
11
Overall, the coffee-derived bio-oil MWnvalues
were comparable to bio-oils derived from woody biomass
(580−590 Da)
9
but much higher compared to petroleum crude
oils that have a MWnof ∼250 Da.
12
Characterization of the bio-oil boiling point distribution, as
shown in Figure 4, further highlighted the influence of
feedstock defatting and the need for bio-oil upgrading. Both
coffee-derived bio-oils contained a large percentage of high
boiling compounds (40−41% >400 °C), likely due to the
presence of oligomer compounds and polar functional groups.
More than half of the boiling point distribution fell within 200−
400 °C, the equivalent petrol distillation range of kerosene,
diesel, and fuel oil.
12
Bio-oil derived from spent coffee grounds
contained the highest percentage of compounds with boiling
points between 300 and 400 °C (34%), likely due to the
prevelance of lipid decomposition products observed by GC-
MS. Interestingly, bio-oil derived from defatted grounds had a
higher fraction of compounds with boiling points <200 °C
(8%), which may be due to the prevalence of phenolic and low
molecular weight oxygenated compounds identified by GC-MS.
Both bio-oils contained comparable total distillables (88−89%
bp <538 °C), which is similar to the percentage for petroleum
crude oil.
12
However, the coffee bio-oils’high heteroatom
content, molecular weight distribution, and boiling point
distribution will likely require catalytic upgrading to allow for
compatibility with conventional refining operations.
37
Biochar Properties and Soil Application. Biochar was
another co-product that was evaluated based on its
physicochemical properties (Table 6) and performance as a
soil amendment (Figure 5). Compared to the energy density of
the initial feedstock (20.1−23.4 MJ/kg), coffee-derived biochar
displayed an elevated energy density comparable for spent
(31.0 MJ/kg) and defatted grounds (28.3 MJ/kg), with the
slightly higher value for biochar derived from spent grounds
likely due to residual lipid content. Overall, these values were in
agreement with past studies for spent coffee ground biochar.
14
The energy density of biochar may allow it to be co-fired as a
solid fuel with an energy density comparable to solid fossil
fuels.
42
Alternatively, coffee-derived biochar offers potential
carbon storage capacity depending on the long-term soil
stability with 27.6−28.6% of the initial biomass carbon being
retained.
Slow pyrolysis of the coffee grounds increased the particle
specific surface area, however, not to a significant extent due to
the lack of secondary activation treatment. Low-temperature
pyrolysis is known to produce biochar with significantly lower
surface areas compared to that of activated carbon; however,
secondary activation occurs at the expense of reduced carbon
storage because significant carbon is lost during activation.
16
The low surface area of coffee ground biochar (1.1−1.2 m2/g)
is comparable to that of biochar derived from other agricultural
waste feedstocks, such as corn stover (3.1 m2/g).
43
However,
the ash content of the coffee ground-derived biochar (2.9−
3.7%) was much lower compared to that of corn stover biochar
(13.1%)
43
due to the elevated stem mineral content of the
latter.
Figure 4. Sim-Dist boiling point distribution of bio-oils derived from
spent and defatted coffee grounds.
Table 6. Solid Sample Characterization of Initial Feedstock
and Biochar Samples Derived from Spent Coffee Grounds
and Defatted Spent Coffee Grounds
a
soil
additive
property spent coffee
grounds
defatted
coffee
grounds
spent coffee
grounds
biochar defatted coffee
grounds biochar
moisture
(%) 1.3 (0.13) 4.3 (0.20) 1.3 (0.10) 2.0 (0.07)
BET
(m2/g) 0.4 0.5 1.1 1.2
ash (%) 1.8 (0.17) 2.4 (0.12) 3.5 (0.17) 4.1 (0.12)
HHV (MJ/
kg) 23.4 20.1 31.0 28.3
C (%) 56.1 51.8 76.2 72.6
H (%) 7.2 6.3 5.6 5.0
N (%) 2.4 2.8 3.9 4.3
S (%) 0.14 0.17 0.05 0.10
P (%) 0.18 0.17 0.48 0.25
K (%) 0.81 0.74 1.94 1.08
Ca (%) 0.20 0.17 0.56 0.54
Mg (%) 0.20 0.22 0.60 0.36
Na (%) 0.07 0.06 0.17 0.13
Zn (ppm) −− 51 55
Fe (ppm) −73 676 165
Mn (ppm) 42 60 156 79
Cu (ppm) 23 27 105 118
B (ppm) −− 31 25
a
Values in parentheses indicate standard deviations from triplicate
measurements.
Figure 5. Sorghum−sudangrass biomass productivity with and without
fertilizer application using spent coffee grounds, defatted grounds, and
their respective biochar derivatives.
ACS Sustainable Chemistry & Engineering Research Article
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Analysis of the major and secondary nutrient profile (S, P, K,
Ca, Mg, Na) for spent and defatted coffee grounds revealed
comparable results to past reports
14
with trace levels of
micronutrients (Zn, Fe, Mn, Cu, B). Overall, slow pyrolysis of
the coffee grounds increased the relative weight fraction of
nutrients in the biochar, particularly for micronutrients, which
may partially account for the increased soil productivity when
N is no longer the limiting factor as described below.
The use of coffee-derived biochar as a soil amendment in
combination with fertilizer showed a significant enhancement in
the biomass yield of sorghum−sundangrass over a 4 -day
period, as shown in Figure 5. The addition of biochar in soils
resulted in over a 2-fold increase in the biomass dry weight
yield (2.92 g w/spent biochar; 2.83 g w/defatted biochar) with
fertilizer application compared to control experiments without
biochar (1.39 g w/fertilizer). The increase in biomass
productivity may be due to multiple factors, including improved
nutrient retention in soils, increased soil cation exchange
capacity, and adjusted soil pH.
44
Similar gains in biomass
productivity (e.g., 2.5-fold increase) have been observed when
combining fertilization with biochar derived from greenwaste
and papermill waste, indicating that biochar may facilitate
fertilization efficiency.
23,24
Without addition of fertilizer, the
application of biochar did not increase biomass yields,
potentially due to the adsorption of available anions and
cations necessary for growth.
24
Similarly, the application of
non-pyrolyzed coffee grounds reduced biomass yields com-
pared to the control, potentially due to changes in soil
chemistry during their decomposition
45
or the release of
bioactive compounds (e.g., caffeine, chlorogenic acids).
46
Residual lipids on the surface of non-defatted grounds may
also inhibit moisture transfer, further affecting their perform-
ance.
45
However, additional work is needed to determine the
primary mechanisms linking coffee biochar physicochemical
properties, fertilization efficiency, soil qualities, and crop yields.
■ASSOCIATED CONTENT
*
SSupporting Information
Characterization of bio-oil derived from spent and defatted
coffee grounds, including a list of major compounds identified
by GC-MS and corresponding chromatograms (Table S1 and
Figure S1); 1H NMR spectra (Figure S2); and SEC molecular
weight distributions (Figure S3). This material is available free
of charge via the Internet at http://pubs.acs.org.
■AUTHOR INFORMATION
Corresponding Author
*E-mail: bksharma@illinois.edu. Tel. (217) 265-6810.
Notes
The authors declare no competing financial interest.
■ACKNOWLEDGMENTS
The research described in this paper has been funded in part by
the United States Environmental Protection Agency (EPA)
under the Science to Achieve Results (STAR) Graduate
Fellowship Program. The EPA has not officially endorsed this
publication, and the views expressed herein may not reflect the
views of the EPA. Financial support was also provided by the
Department of Civil and Environmental Engineering at the
University of Illinois, the University of Illinois Research Board,
and the National Science Foundation Division of Chemical,
Bioengineering, Environmental, and Transport Systems
(CBET-0746453).
■REFERENCES
(1) International Coffee Organization. Annual Review 2011/2012,
March 4, 2013. http://www.ico.org/show_news.asp?id=319 (accessed
July 17, 2013).
(2) Silva, M. A.; Nebra, S. A.; Machado Silva, M. J.; Sanchez, C. G.
The use of biomass residues in the Brazilian soluble coffee industry.
Biomass Bioenergy 1998,14, 457−467.
(3) Tsai, W.-T.; Liu, S.-C. Effect of temperature on thermochemical
property and true density of torrefied coffee residue. J. Anal. Appl.
Pyrolysis 2013,102, 47−52.
(4) Mussatto, S.; Machado, E.; Martins, S.; Teixeira, J. Production,
composition, and application of coffee and its industrial residues. Food
Bioprocess Technol. 2011,4, 661−672.
(5) Demirbas, A. Biodiesel: A Realistic Fuel Alternative for Diesel
Engines; Springer: New York, 2008.
(6) Moser, B. R.; Vaughn, S. F. Evaluation of alkyl esters from
Camelina sativa oil as biodiesel and as blend components in ultra low-
sulfur diesel fuel. Bioresour. Technol. 2010,101, 646−653.
(7) Kondamudi, N.; Mohapatra, S. K.; Misra, M. Spent coffee
grounds as a versatile source of green energy. J. Agric. Food Chem.
2008,56, 11757−11760.
(8) Demirbas, A.; Arin, G. An overview of biomass pyrolysis. Energy
Sources, Part A 2002,24, 471−482.
(9) Mohan, D.; Pittman, C. U., Jr.; Steele, P. H. Pyrolysis of wood/
biomass for bio-oil: A critical review. Energy Fuels 2006,20, 848−889.
(10) Duman, G.; Okutucu, C.; Ucar, S.; Stahl, R.; Yanik, J. The slow
and fast pyrolysis of cherry seed. Bioresour. Technol. 2011,102, 1869−
1878.
(11) Vardon, D. R.; Sharma, B. K.; Blazina, G. V.; Rajagopalan, K.;
Strathmann, T. J. Thermochemical conversion of raw and defatted
algal biomass via hydrothermal liquefaction and slow pyrolysis.
Bioresour. Technol. 2012,109, 178−187.
(12) Speight, J. G. Handbook of Petroleum Analysis; 1st ed.; Wiley-
Interscience: New York, 2001.
(13) Wright, M. M.; Brown, R. C.; Boateng, A. A. Distributed
processing of biomass to bio-oil for subsequent production of
Fischer−Tropsch liquids. Biofuels, Bioprod. Biorefin. 2008,2, 229−238.
(14) Tsai, W.-T.; Liu, S.-C.; Hsieh, C.-H. Preparation and fuel
properties of biochars from the pyrolysis of exhausted coffee residue. J.
Anal. Appl. Pyrolysis 2012,93, 63−67.
(15) Lehmann, J.; Gaunt, J.; Rondon, M. Bio-char sequestration in
terrestrial ecosystems: A review. Mitigation Adapt. Strategies Global
Change 2006,11, 395−419.
(16) Manya, J. J. Pyrolysis for biochar purposes: A review to establish
current knowledge gaps and research needs. Environ. Sci. Technol.
2012,46, 7939−7954.
(17) Ichihara, K.; Shibahara, A.; Yamamoto, K.; Nakayama, T. An
improved method for rapid analysis of the fatty acids of glycerolipids.
Lipids 1996,31, 535−539.
(18) Moser, B. R. Efficacy of specific gravity as a tool for prediction of
biodiesel−petroleum diesel blend ratio. Fuel 2012,99, 254−261.
(19) Moser, B. R.; Williams, A.; Haas, M. J.; McCormick, R. L.
Exhaust emissions and fuel properties of partially hydrogenated
soybean oil methyl esters blended with ultra low sulfur diesel fuel. Fuel
Process. Technol. 2009,90, 1122−1128.
(20) Suarez, P. A. Z.; Moser, B. R.; Sharma, B. K.; Erhan, S. Z.
Comparing the lubricity of biofuels obtained from pyrolysis and
alcoholysis of soybean oil and their blends with petroleum diesel. Fuel
2009,88, 1143−1147.
(21) Vardon, D. R.; Sharma, B. K.; Scott, J.; Yu, G.; Wang, Z.;
Schideman, L.; Zhang, Y.; Strathmann, T. J. Chemical properties of
biocrude oil from the hydrothermal liquefaction of Spirulina algae,
swine manure, and digested anaerobic sludge. Bioresour. Technol. 2011,
102, 8295−8303.
ACS Sustainable Chemistry & Engineering Research Article
dx.doi.org/10.1021/sc400145w |ACS Sustainable Chem. Eng. 2013, 1, 1286−12941293

(22) Zheng, W.; Guo, M.; Chow, T.; Bennett, D. N.; Rajagopalan, N.
Sorption properties of greenwaste biochar for two triazine pesticides. J.
Hazard. Mater. 2010,181, 121−126.
(23) Chan, K. Y.; Van Zwieten, L.; Meszaros, I.; Downie, A.; Joseph,
S. Agronomic values of greenwaste biochar as a soil amendment. Aust.
J. Soil Res. 2007,45, 629−634.
(24) Zwieten, L. V.; Kimber, S.; Morris, S.; Chan, K. Y.; Downie, A.;
Rust, J.; Joseph, S.; Cowie, A. Effects of biochar from slow pyrolysis of
papermill waste on agronomic performance and soil fertility. Plant Soil
2010,327, 235−246.
(25) Tew, T. L.; Cobill, R. M.; R., E. P., Jr Evaluation of sweet
sorghum and sorghum ×sudangrass hybrids as feedstocks for ethanol
production. BioEnergy Res. 2008,1, 147−152.
(26) Khan, N.; Brown, J. The composition of coffee oil and its
component fatty acids. J. Am. Oil Chem. Soc. 1953,30, 606−609.
(27) Demirbas, A. Calculation of higher heating values of biomass
fuels. Fuel 1997,76, 431−434.
(28) Demirbas, A. Relationships derived from physical properties of
vegetable oil and biodiesel fuels. Fuel 2008,87, 1743−1748.
(29) Moser, B. R.; Knothe, G.; Vaughn, S. F.; Isbell, T. A. Production
and evaluation of biodiesel from Field Pennycress (Thlaspi arvense L.)
oil. Energy Fuels 2009,23, 4149−4155.
(30) Hoed, V. V.; Depaemelaere, G.; Ayala, J. V.; Santiwattana, P.;
Verhe, R.; Greyt, W. D. Influence of chemical refining on the major
and minor components of rice brain oil. J. Am. Oil Chem. Soc. 2006,83,
315−321.
(31) Ferrari, R. A.; Schulte, E.; Esteves, W.; Bruhl, L.; Mukherjee, K.
D. Minor constituents of vegetable oils during industrial processing. J.
Am. Oil Chem. Soc. 1996,73, 587−592.
(32) Maher, K. D.; Bressler, D. C. Pyrolysis of triglyceride materials
for the production of renewable fuels and chemicals. Bioresour. Technol.
2007,98, 2351−2368.
(33) Vispute, T. P.; Huber, G. W. Production of hydrogen, alkanes
and polyols by aqueous phase processing of wood-derived pyrolysis
oils. Green Chem. 2009,11, 1433.
(34) Bok, J. P.; Choi, H. S.; Choi, Y. S.; Park, H. C.; Kim, S. J. Fast
pyrolysis of coffee grounds: Characteristics of product yields and
biocrude oil quality. Energy 2012,47, 17−24.
(35) Vardon, D. R.; Sharma, B. K.; Blazina, G. V.; Rajagopalan, K.;
Strathmann, T. J. Thermochemical conversion of raw and defatted
algal biomass via hydrothermal liquefaction and slow pyrolysis.
Bioresour. Technol. 2012,109, 178−187.
(36) Furimsky, E.; Massoth, F. E. Hydrodenitrogenation of
petroleum. Catal. Rev.: Sci. Eng. 2005,47, 297−489.
(37) Thermochemical Processing of Biomass: Conversion into Fuels,
Chemicals and Power; Brown, R. C., Ed.; 1st ed.; John Wiley & Sons,
Ltd.: Chichester, U.K., 2011.
(38) Yorgun, S.; Sensoz, S.; Kockar, O
. M. Characterization of the
pyrolysis oil produced in the slow pyrolysis of sunflower-extracted
bagasse. Biomass Bioenergy 2001,20, 141−148.
(39) Evans, R. J.; Felbeck, G. T., Jr High temperature simulation of
petroleum formation-III. Effect of organic starting material structure
on hydrocarbon formation. Org. Geochem. 1983,4, 153−160.
(40) Grierson, S.; Strezov, V.; Shah, P. Properties of oil and char
derived from slow pyrolysis of Tetraselmis chui.Bioresour. Technol.
2011,102, 8232−8240.
(41) Mullen, C. A.; Strahan, G. D.; Boateng, A. A. Characterization of
various fast-pyrolysis bio-oils by NMR spectroscopy. Energy Fuels
2009,23, 2707−2718.
(42) Raveendran, K.; Ganesh, A. Heating value of biomass and
biomass pyrolysis products. Fuel 1996,75, 1715−1720.
(43) Mullen, C. A.; Boateng, A. A.; Goldberg, N. M.; Lima, I. M.;
Laird, D. A.; Hicks, K. B. Bio-oil and bio-char production from corn
cobs and stover by fast pyrolysis. Biomass Bioenergy 2010,34, 67−74.
(44) Glaser, B.; Lehmann, J.; Zech, W. Ameliorating physical and
chemical properties of highly weathered soils in the tropics with
charcoal: A review. Biol. Fertil. Soils 2002,35, 219−230.
(45) Bollen, W. B.; Lu, K. C. Cellulosic wastes as fertilizers, microbial
decomposition and nitrogen availability of reacted sawdust, bagasse,
and coffee grounds. J. Agric. Food Chem. 1961,9,9−15.
(46) Cruz, R.; Baptista, P.; Cunha, S.; Pereira, J. A.; Casal, S.
Carotenoids of lettuce (Lactuca sativa L.) grown on soil enriched with
spent coffee grounds. Molecules 2012,17, 1535−1547.
ACS Sustainable Chemistry & Engineering Research Article
dx.doi.org/10.1021/sc400145w |ACS Sustainable Chem. Eng. 2013, 1, 1286−12941294