PROJECT PROGRESS REPORT
ADVANCED METHOD FOR RENEWABLE ETHANOL BY
DIRECT SYNTHESIS FROM SYNGAS FOR RENEWABLE
FUEL APPLICATIONS
Submitted To
The 2012 Summer NSF CEAS REU Program
Part of
NSF Type 1 STEP Grant
Sponsored By
The National Science Foundation
Grant ID No.: DUE-0756921
College of Engineering and Applied Science
University of Cincinnati
Cincinnati, Ohio
Prepared By
Julia Fisher, Chemical Engineering, Arizona State University
Nathalia Backeljauw, Chemical Engineering, University of Cincinnati
Report Reviewed By:
_____________________________________________________________________
Dr. Panagiotis (Peter) Smirniotis
REU Faculty Mentor
Professor and Chairman
School of Energy, Environmental, Biological and Medical Engineering
University of Cincinnati
August 9, 2012
Direct Synthesis of Ethanol from Syngas for Renewable Fuel Applications
Julia Fisher, Chemical Engineering, Arizona State University
Nathalia Backeljauw, Chemical Engineering, University of Cincinnati
Abstract
The main objective of this project is to produce ethanol from syngas, which is a
mixture of carbon monoxide and hydrogen gas, by a thermo-chemical catalytic route.
The overall goal this project is trying to achieve is to use ethanol as a renewable energy
source. To accomplish this, various mesoporous rhodium-based catalysts supported by
mesoporous molecular sieves are synthesized by the wet impregnation method and
calcined at 673 K. SBA-15, MCM-41, and MCM-48 are chosen as the mesoporous
molecular sieves. The pure mesoporous molecular sieve supports are synthesized by a
procedure, which is reported in our previous studies. The characterization of the
catalysts is achieved by the XRD, BET and TPR techniques. The reactions of syngas to
ethanol carried out over these catalysts and products are analyzed by G.C. Rh/SBA-15
had a higher CO conversion and ethanol selectivity in comparison to MCM-41 and
MCM-48, therefore making it the most suitable catalyst out of the three.
Key Words
1. Ethanol (as fuel); 2. XRD, TPR; 3. SBA-15, MCM-41, MCM-48; 4. Mesoporous
molecular sieve
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Introduction
Increasing concerns about global climate change, depletion of fossil fuel
resources, and rising crude oil prices have pushed the topic of energy to the center
stage. Bio-ethanol can be used in engines, offering a nearly equivalent combustion
energy than that of gasoline, while being a renewable and hence carbon-neutral fuel.
Therefore, bio-ethanol is favorable towards the greenhouse gas emissions. As a fuel,
ethanol has several ideal properties: it is nontoxic, easy to store, results in lower net
petroleum use and lowers greenhouse gas emissions.
Corn is the largest source of ethanol in the United States. In 2011, the U.S.
harvested 12.36 billion bushels of corn, with the gross demand for ethanol being 40% of
that total (RFA 2012). However, only 3.5 billion bushels converted to ethanol, and the
remaining bushels became livestock feed. Only about 26% of the 12.36 billion bushels
was directly consumed for the production of ethanol (RFA 2012). These percentages
could change in the future because the Renewable Fuel Standard (RFS) demands that
the U.S. makes 36 billion gallons per year of renewable fuel by 2022 (RFA 2012). If the
reliance on corn as the primary source for ethanol continues, it could become an issue
with the growing population’s demand for corn.
Therefore, the investigation and
research of other methods to produce ethanol will become increasingly important to
solve this problem.
Not only is it essential to find another source for ethanol to avoid food shortage
for the increasing population, but it is also imperative to find another source that has
less limitations, such as location and cost. The production of corn and ethanol from
corn are both very centralized in the Midwest, creating a major limitation on the U.S.
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today (Somma et al. 2010). The current method for transporting ethanol is by truck
instead of pipeline because ethanol is corrosive to steel; this leads to the majority of
higher ethanol blends, such as E-85, being consumed where it is produced (Somma et
al. 2010). Alternatives such as syngas have fewer limitations than corn for ethanol
synthesis. Syngas can be produced by partial combustion, which means it can be
derived from a multitude of sources such as non-food plant material (Somma et al.
2010). Syngas can also be transported through the current natural gas lines, which
makes it easily accessible throughout the U.S., enabling the building of ethanol plants
across the country and not just in the Midwest.
The main objective of the present investigation is to produce ethanol from syngas
with the help of a catalyst, as shown in Fig. 1. The aim of this project is to engineer
more efficient and effective catalysts that will convert as much carbon monoxide as
possible while maximizing the ethanol selectivity. Rh-based catalysts are used to
produce ethanol because Rhodium is known to selectively produce ethanol from syngas
under the right conditions (Spivey, et al. 2007).
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Figure 1. Reaction Matrix (Mei, et al. 2010)
The reaction matrix shows the steps to produce the possible products, and the green
arrows display the steps to produce ethanol from syngas.
Materials and Methods
Calibration
For the calibration process, the primary piece of equipment used is the Gas
Chromatographer (GC). Within the GC itself is the Thermal Conductivity Detector
(TCD) and the Flame Ionization Detector (FID), which are connected in a series. The
GC separates and records the retention times of carbon monoxide, carbon dioxide,
nitrogen, methane, ethanol and methanol. The computer software connected to the GC
is the HP Chem Station Software.
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Synthesis of Catalysts: Preparation of Pure Mesoporous Molecular Sieves
All the chemicals are used as received from companies without any further purification.
SBA-15
To synthesize the SBA-15 molecular sieve, 3 grams of P-123 were dissolved in a
mixture of 15 mL of hydrochloric acid and 80 mL of distilled water. The solution was
stirred at 35°C until it became clear. 7 grams of tetraethyl orthosilicate were added to
the aforementioned solution and stirred for 24 hours at 35°C. Then, the solution was
transferred into a sealed teflon bottle and heated for 48 hours at 110°C. The solution
was then filtered, washed with distilled water and dried at 100°C for 12 hours. The final
powder was calcined at 500 oC for 5 hours with a heat ramp of 2°C/minute.
MCM-41
To prepare the MCM-41, 3 ml of deionized (DI) water were added to 35 ml of
Ludox HS-40 colloidal silica (40%) under stirring, and then 30.32 ml of 25%
tetramethylammonium hydroxide (Aldrich, 25%) were added. Independently, 18.25 g of
cetyltrimethylammonium bromide (CTABr, Alfa Aesar) were dissolved in 33 ml of water.
7 mL of ammonium hydroxide (Fisher, 29.6%) were introduced when the CTABr
solution became a transparent gel and could be magnetically stirred again. Then, the
latter solution was transferred to the first solution. The final mixture was stirred for 2 h at
80°C, then transferred into a Teflon bottle and treated under autogenous pressure
without stirring at 100°C for 3 days. The resulting solids were filtered, washed, and airdried. The dried powder was calcined at 550°C for 10 h under a moderate airflow with a
temperature ramp of 2°C/min.
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MCM-48
To begin the synthesis of MCM-48, 17.5 g of CTABr and 1.92 g of sodium
hydroxide were dissolved in 99 ml of DI water, and then 20.8 g of tetraethyl orthosilicate
(TEOS) (Aldrich) were added into the mixture. The resulting gel was stirred at room
temperature for about 1 h and then transferred into a Teflon bottle and treated under
autogenous pressure without stirring at 100°C for 3 days. The solution was cooled to
room temperature, and its pH was adjusted to 7.0 by adding HCl. Then, it was heated at
373 K for another 2 days. The final materials were filtered, washed, dried at ambient
temperature, and calcined at 550°C for 6 h under flowing air at a heating rate of
2°C/min.
Rh-based catalysts supported by mesoporous molecular sieves
The Rh-based catalysts were synthesized by the wet impregnation method. In
this synthesis method, mesoporous material was added to the Rhodium nitrate solution
and stirred at 100°C until all liquids evaporated. Afterwards, the powder remained on
the stirring plate to dry for 12 hours at 100°C. The powder was then calcined at 400°C
for four hours, with a heat ramp of 5°C/minute. 2wt% Rhodium is used for all of the
catalysts.
Characterizations
BET surface area and pore size distribution
BET surface area and pore size distribution studies were conducted at −196°C
using a Micromeritics ASAP 2010 apparatus to characterize the synthesized
photocatalysts. Samples of 0.05–0.06 g were degassed at 300°C for at least 10 h in the
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degassing port of the apparatus. Using the BET method, the surface area was
calculated from adsorption isotherms. The pore size was obtained from the adsorption
branch of the isotherm using the BJH method. The results obtained are listed in Table 1.
XRD
All pure mesoporous materials prepared were characterized using a Nicolet
powder X-ray diffractometer equipped with a Cu-Kα source to assess their structure and
crystallinity. The synthesized MCM-41 and MCM-48 samples were run with 2θ changing
from 2° to 7° to assess the structure of the MS matrix. SBA-15 was run with 2θ
changing from 1.5° (XRD machine's limit) to 3° to assess the structure of the SBA-15
matrix.
TPR measurement
The TPR was carried out in a temperature range of 50–550°C on a Micromeritics
Autochem 2910 instrument with a temperature ramp of 2°C/min. The samples were
pretreated at 200°C with ultrahigh-purity O2 (Matheson) for 2 h. A total of 10 mL/min of
10% H2 in Ar (Matheson) was passed through the sample tube during the
measurement.
Catalytic Activity
The catalysts were evaluated in a fixed bed microreactor (9 mm diameter, 500
mm length). The temperature of the reactor was controlled via a temperature controller.
Mass flow meters were used to add H2 and CO at a desired rate to the reactor. The
catalyst (0.3 g) was mixed with the same amount of quartz glass beads placed in the
reactor, and the reactor temperature was increased from room temperature to 300 oC at
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a rate of 2
oC
o
C/min. The catalyst was reduced in situ in a flow of H2 (20 mL/min) at 300
for 2 h. Synthesis gas, with a flow rate of 21 mL/min (H2/CO ratio of 2.0), was
introduced and the reactor pressure was increased to 350 psi. The compositions of the
outlet gas and liquid streams were determined using an online HP 6890 gas
chromatograph equipped with a Porapak Q column and a TCD and FID detector. The
typical reactor diagram is shown in Fig. 2.
Figure 2. Reactor Diagram
This is a schematic of the setup used for the
reactions.
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Results and Discussion
Physical Properties
Table 1. Physical Properties of Mesoporous Materials (Data from Sun, et al. 2006)
Mesoporous
BET
Pore volume
Pore diameter
Unit cell
Materials
Surface area
(cm3/g)
(Å)
parameter
2
(m /g)
(Å)
MCM-41
1143
1.03
35
43
MCM-48
983
0.65
26
89
SBA-15
827
1.21
57
117
As shown in Table 1, MCM-41 displays the highest BET surface area, 1143 m 2/g.
However, SBA-15 has the largest pore diameter, 57 Å, and pore volume, 1.21 cm3/g.
Due to the large surface area of MCM-41 and the large pore diameter and pore volume
of SBA-15, they’re expected to improve the activity of the catalysts. There was a slight
reduction in the surface area after the catalysts were impregnated with Rh, due to pore
blockage by Rh. However, pore diameters of the catalysts remained unchanged.
Figure 3. XRD of MCM-41, MCM-48, SBA-15 (Sun, et al. 2006)
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To be characterized as a mesoporous material, the samples must exhibit peaks
at lower angles, which Fig. 3 confirms. SBA-15 has a peak at 2° 2θ and the lowest
intensity of the three mesoporous materials. MCM-41 and MCM-48 both have a peak at
2.5° 2θ. MCM-41 has the highest intensity, followed by MCM-48.
Figure 4
3+
0
Intensity (a.u.)
Rh to Rh
Rh/MCM-48
Rh/MCM-41
Rh/SBA-15
100
200
300
400
500
600
700
o
Temperature ( C)
Temperature Programmed reduction profiles of Rhbased catalysts supported on mesoporous molecular
sieves
The TPR results in Fig. 4 show that the Rh in the samples was in the 3+
oxidation state. When it reached 330°C, the Rh in the sample converted directly to
Rhodium metal in the 0 oxidation state.
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Table 2: Effect of mesoporous molecular sieve on the
catalytic activity of Rh-based catalysts
Catalyst CO
conversion
(%)
Selectivity (%)
Ethan
ol
Methan
ol
Methane CO2
Rh/SBA
32
-15
12
8.4
32.3
44.5
Rh/MC
M-41
30
6.4
5.9
42.3
52.4
Rh/MC
M-48
28
5.8
6.2
40.5
51.4
Nominal conditions are T = 573 K, P = 350 psi, 0.30 g catalyst, H2: CO = 2:1,
syngas flow = 21 cm3 (STP)/min. Conversion (%) = ΣniMi X 100/MCO and selectivity =
niMi/ΣniMi where ni is the number of carbon atoms in product i, Mi is the mole percent of
product i measured, and MCO is the mole percent of carbon monoxide in the feed.
The activity results show that under these conditions, the SBA-15 has the best
qualities for syngas to ethanol conversion, when compared with MCM-41 and MCM-48.
It had the highest CO conversion, 32%, and the highest ethanol selectivity, 12%.
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References
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syngas over Rh-based/SiO2 catalysts: A combined experimental and theoretical
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