2001 Progress Report: Synthesis of Acetic Acid via Carboxylation of MethaneEPA Grant Number: R827124
Title: Synthesis of Acetic Acid via Carboxylation of Methane
Investigators: Roberts, George W. , Ben, W. , Jang, L. , Spivey, James J. , Wilcox, Esther
Current Investigators: Roberts, George W. , Spivey, James J. , Wilcox, Esther
Institution: North Carolina State University , Desert Research Institute
Current Institution: North Carolina State University
EPA Project Officer: Hahn, Intaek
Project Period: September 30, 1998 through September 30, 2001 (Extended to June 30, 2002)
Project Period Covered by this Report: September 30, 2000 through September 30, 2001
Project Amount: $118,119
RFA: Exploratory Research - Environmental Engineering (1998) RFA Text | Recipients Lists
Research Category: Sustainability , Land and Waste Management , Engineering and Environmental Chemistry
The objective of this research project is to develop a technology for the direct synthesis of acetic acid from carbon dioxide (CO2) and methane (CH4):
The emission of greenhouse gases, such as carbon dioxide, is of interest for environmental reasons. In response to this issue, a number of industrial nations have ratified the Kyoto treaty that calls for a voluntary worldwide reduction in the emissions of carbon dioxide and other greenhouse gases. Although the United States has not yet ratified this treaty, there is a national interest in its goals. It is essential to develop new technologies that will contribute to the reduction of carbon dioxide. One such technology is the utilization of CO2 as a reactant in chemical synthesis.
Acetic acid is a vital industrial chemical; more than over 6 million tons are produced per year worldwide. The current industrial process is based on the reaction of carbon monoxide with methanol. Most existing plants use a homogeneous rhodium catalyst, while newer ones are using a recently developed homogeneous iridium catalyst. Although this is a mature technology, there are incentives for a new process. The use of a solid catalyst and inexpensive, benign reactants, would substantially reduce the production costs as well as the occupational and environmental risks.
The direct synthesis of acetic acid from carbon dioxide and methane via a solid catalyst will contribute to the reduction of CO2 emissions and may provide an economical means of acetic acid production.
Diffuse reflectance infrared fourier transform spectroscopy (DRIFTS) studies show the formation of the acetate species from a mixture of CO2/CH4 on the catalyst. Experiments were carried out by first adsorbing acetic acid on the catalyst to identify the absorption bands corresponding to acetic acid. Then, a fresh sample of the catalyst was exposed to a CO2/CH4 mixture, resulting in the appearance of spectral bands matching those of pure acetic acid. Two catalysts were examined, 5 percent Pd/Carbon and 5 percent Pt/Alumina. The palladium catalyst was prepared via precipitation by Calgon Carbon. The platinum catalyst was prepared via incipient wetness by Johnson-Mathey. The catalysts were pretreated at 500°C in flowing helium prior to the experiments. The catalysts were then exposed to a flow of the experimental gas. The temperature was increased in 50°C increments up to 400°C. Each temperature was maintained for 30 minutes, with spectra being taken every 10 minutes.
The results of the acetic acid adsorption on the 5 percent Pd/Carbon catalyst are shown in Figure 1.
From the spectra, the monomer (gas phase) and dimer (liquid phase) acetic acid
can be seen. Table 1 contains a detailed peak interpretation for acetic acid
on 5 percent Pd/Carbon. As seen in the spectra, the size of the monomer peaks
increase as the temperature increases. Likewise, the dimer peaks decrease with
increasing temperature. This is due to the increasing amount of vapor phase
molecules with temperature. It is important to note the peak at 1600 cm-1, which
corresponds to the O - C = O stretch in a monodenate absorbed acetate.
|3584 cm -1||O-H stretch (monomer)||Pouchert, 1985|
|3020 cm -1||O-H stretch (dimer)||Pouchert, 1985|
|2950 cm -1||C-H3 stretch||Pouchert, 1985|
|1790 cm -1||C=O stretch (dimer)||Pouchert, 1985|
|1743 cm -1||C=O stretch (monomer)||Pouchert, 1985|
|1600 cm -1||O-C=O (adsorbed)||Pei, 1996|
|1420 cm -1||O-H deformation (dimer)||Pouchert, 1985|
|1300 cm -1||C-H3 stretch||Pouchert, 1985|
|1189 cm -1||C-O stretch||Pouchert, 1985|
|996 cm -1||O-H deformation (dimer)||Pouchert, 1985|
When the helium pretreated catalyst sample was exposed to an equimolar mixture of CH4 and CO2, no acetate peaks were observed. Methane peaks at 3010 cm-1 and 1300 cm-1 and carbon dioxide peaks at 3660 cm-1 and 2350 cm-1 were the only peaks seen on the spectra. However, when the pretreatment included exposure to flowing CO2 at 500°C for 1 hour, the spectra did show acetate peaks. The results from this experiment are shown in Figure 2.
In addition to the CH4 and CO2 peaks, four acetate peaks can be seen in the spectra. The peak at 1790 cm-1 corresponds to the C = O stretch in a dimer of acetic acid, and the peak at 1743 cm-1 corresponds to the C = O stretch in a monomer of acetic acid. The 1420 cm-1 peak can be attributed to the O - H deformation in a dimer of acetic acid. Finally, the 1600 cm-1 peak corresponds to the O - C = O stretch in a monodenate absorbed acetate.
When the 5 percent Pt/Alumina catalyst was used, the acetic acid adsorption showed slightly different peaks, due to a different interaction with the catalyst surface. When the 5 percent Pt/Alumina sample was exposed to the equimolar mixture of CH4 and CO2, distinct acetate peaks were observed. The results of this experiment can be seen in Figure 3. Unlike the 5 percent Pd/Carbon catalyst, the pretreatment had no effect on the formation of the acetate. Additionally, the amount of acetate formed by the 5 percent Pt/Alumina catalyst was significantly more than that formed on the 5 percent Pd/Carbon catalyst.
DRIFTS experiments were performed using both 5 percent Pd/Carbon and 5 percent Pt/Alumina catalysts. When exposed to an equimolar mixture of CO2 and CH4, both catalysts showed the formation of an acetate. With the 5 percent Pd/Carbon catalyst, pretreatment was key. The acetate was not formed when the catalyst was pretreated in helium alone, or in methane. The acetate was only formed when the catalyst was pretreated with CO2. The 5 percent Pt/Alumina catalyst showed the formation of the acetate regardless of the pretreatment. Additionally, the acetate peaks were larger on the 5 percent Pt/Alumina spectra, thus indicating that this is the better of the two catalysts for this reaction.
Work in the next year of the grant will include TPD-MS experiments to further confirm and study the formation of acetic acid from CO2 and CH4. Experiments also will be conducted on the reaction of CO2, CH4 and C2H2 to form vinyl acetate, which may be a feasible method to drive the equilibrium.
Journal Articles on this Report : 1 Displayed | Download in RIS Format
|Other project views:||All 6 publications||3 publications in selected types||All 2 journal articles|
||Wilcox EM, Roberts GW, Spivey JJ. Thermodynamics of light alkane carboxylation. Applied Catalysis A - General 2002;226(1-2):317-318.||