124
2−
B.C., Canada), utilizing a high frequency corona discharge, was used
with a medium grade tank of oxygen (99.9%, National Wielders, NC)
to generate the ozone required for these experiments [9].
Ion Chromatography (IC) analysis to determine the SO4
con-
centration. The catalyst was then dried in an oven overnight at
100 ◦C. If the SO4 level was >5 ppm, then the washing steps were
repeated until IC analysis indicated a level below 5 ppm (3 times
for biochar and 2 times for activated carbon), since sulfur lev-
els in biodiesel must not exceed 5 ppm. Analysis was performed
using a Dionex ICS-2000 coupled with a Suppressed Conductiv-
ity detector (CD25). The eluent (mobile phase) used was 23 mM
KOH (potassium hydroxide). The column used for the analysis was
an IonPac AS18 (4 mm × 250 mm) at 30 ◦C and flow of 1 mL/min.
Samples were injected on the column with an auto-sampler at
a volume of 20 L sample size. Standards (sodium sulfate 5,
10, 20 ppm) were analyzed along with the samples to quantify
results.
2.3. Catalyst generation – sulfonation methods
Next, the biochar generated above was further reacted to attach
strong acidic functional groups on the carbon surface. Acid cata-
with ozone only) and a strong acid, SO3H functionalized carbon.
Carbon oxidized using ozone was considered a weak acid catalyst,
the carbon pores [9].
For the strong acid catalyst ( SO3H), the biochars (400 ◦C, except
where noted) and activated carbon were sulfonated based on meth-
ods described in the literature [6,7]. First, the biochars generated
from pelletized biomass and BX-7540 were ground into smaller
particles using a mortar and pestle (pine chip biochar was used as
generated and then sieved on 4–12 mesh screen sieves, retaining
all carbon particles between in that specific range).
Subsequently, 12.5 g of the previously ozonated biochar or non-
ozonated biochar and activated carbon, was placed in a beaker, and
contacted with 20 mL of concentrated sulfuric acid (99% H2SO4).
The acid was mixed with the carbon via periodic stirring (15 min),
and then excess acid was decanted. The residual wet solids (car-
bon plus acid) were then transferred to a ceramic crucible, placed
in muffle furnace, and heated for 12–18 h at 100 ◦C (except where
noted). After heating, the char was cooled and rinsed 2–10× with
50–100 mL of deionized water. The pH of the rinsate was measured
after each washing and the char was then dried in an oven at 110 ◦C
overnight.
A second sulfonation method using gaseous SO3 was evaluated
for its ability to generate solid acid carbon catalysts. AgForm 200
was selected, since it was granular in form (not a powder) and
smaller in size compared to the pelleted peanut hull form. It was
theorized that the smaller granular form would result in more
complete sulfonation throughout the biochar particle and gener-
ate a catalyst form that would not cause a large pressure drop
in a packed-bed, compared to the powder form of the pine chip
biochar catalyst; we anticipate that a tubular packed-bed reactor
would be the best reactor configuration for industrial scale-up. The
WV-B-20 activated carbon product was chosen for SO3 gas sulfona-
tion, since it had the highest catalytic activity of all the carbons
at the lowest methanol to oil ratio (Fig. 4). AgForm 200 biochar
and WV-B20 (AC) were dried overnight at 110 ◦C, allowed to cool
in a dessicator, and subsequently 5 g of the biochar and AC were
weighed and placed in 40 mL glass jars without lids. A total of 4
jars (20 g carbon total) was placed inside a 3.8 L glass jar, exposed
to solid SO3 (20 g – Sigma, 99% non-stabilized) and sealed with
a glass top and silicone grease. The contents were kept sealed in
the jar for six days at room temperature. Subsequently the jar was
opened, vented, the carbon collected and rinsed according to Sec-
tion 2.4.
2.5. Catalyst characterization
The physical and chemical characteristics of the biochars,
including pH, surface area, bulk density, and the elemental com-
position were previously determined [9]. Moisture, volatiles and
ash content in the biomass, biochar, and treated biochars (i.e., cata-
lysts) were determined by ASTM D5142 using a proximate analyzer
(LECO Model TGA701). Ultimate analysis (elemental C, H, N, S, and
O (by difference) in % (w/w)) was performed in an ultimate analyzer
(LECO, model CHNS-932) following ASTM D3176.
Surface areas of the solid acid catalysts (0.1 g sample size)
were measured by N2 adsorption over
a relative pressure
range (P/P0) of 0.05–0.35 using a 7-point BET analysis equa-
tion (QuantachromeAUTOSORB-1C; Boynton Beach, FL). Pore size
distribution, average pore radius, and total pore volume were
estimated from N2 desorption curves using BJH analysis. All sam-
ples were degassed ranging from 100 to 150 ◦C for 3–4 h before
analysis.
Biochar, activated carbon, and subsequently derived solid acid
catalysts were analyzed via thermal gravimetric analysis (TGA).
Using a Mettler-Toledo 851e Thermogravimetric Analyzer (TGA),
samples (approximately 10–15 mg, 0.20 mesh) were raised from
room temperature to 900 ◦C at 10 ◦C/min and mass loss was
recorded versus time and temperature. Helium was used as the
carrier gas at a flow rate of 50 mL/min. The TGA analysis was used
to design the NH3 temperature program desorption studies and
determine if sulfonation treatment reduced the thermal stability
of the carbons.
Ammonia temperature programmed desorption was used to
estimate acid site strength of the catalysts. All samples were
degassed ranging from 100 to 150 ◦C for 3–4 h before NH3-TPD anal-
ysis. Samples (0.1 g) were loaded in a quartz U-tube and packed
between two quartz-wool layers, degassed at 100 ◦C for 30 min in
helium, saturated with ammonia (pure electronic grade) at 40 ◦C for
15 min, flushed with helium at 40 ◦C for 15 min, then desorbed with
helium from 40 to 900 ◦C at 10 ◦C/min (all flows at 80 mL/min). Des-
orbed NH3 was detected using a TCD detector (16× attenuation).
TPD measurements were made using a QuantachromeAUTOSORB-
1C instrument.
2.4. Catalyst washing and IC chromatography
To qualitatively assess the formation of functional groups on
the surface of the treated carbon, FTIR analysis (32 scans per sam-
ple, 4 cm−1 resolution) was performed on the base biochars and
AC (i.e., just pyrolyzed and not functionalized) and the sulfonated
carbons. The carbon catalysts were crushed to a fine powder and
analyzed directly using a Grazing Angle Attenuated Total Reflection
Fourier Transform Infrared Spectroscopy (GATR-FTIR, ThermoElec-
tron Nicolet 6700). ATR (Smart Ark – ATR attachment with ZnSe 45◦
crystal) was used to deconvolute the functional groups on the sur-
face from the bulk phase by using an incident angle with a limited
depth of penetration (∼150 nm). Our experimental setup allowed
After carbon sulfonation via H2SO4 or gaseous SO3 and ini-
tial rinsing, the catalysts were subjected to additional washing.
Approximately 50 mL of DI water (preheated to 80 ◦C) per gram
of char was used during washing. The catalyst and hot water were
mixed with a stir bar in a beaker mix char and DI water for 1 h.
The solution was then allowed to cool, decanted, and the pH of
liquid measured. The catalyst was re-washed (same water/char
ratio) at room temperature for 15 min, the liquid decanted and
the pH measured again. An aliquot of the liquid was saved for