![[logo] US EPA](https://webarchive.library.unt.edu/eot2008/20081107072856im_/http://www.epa.gov/epafiles/images/logo_epaseal.gif){kind=logo}
Final Report: Homogeneous Catalysis in Supercritical Carbon Dioxide with Fluoroacrylate Copolymer Supported Catalysts
EPA Grant Number: R828135Title: Homogeneous Catalysis in Supercritical Carbon Dioxide with Fluoroacrylate Copolymer Supported Catalysts
Investigators: Agkerman, Aydin
Institution: Texas A & M University
EPA Project Officer: Karn, Barbara
Project Period: June 1, 2000 through May 31, 2003
Project Amount: $315,000
RFA: Technology for a Sustainable Environment (1999)
Research Category: Pollution Prevention/Sustainable Development
Description:
Objective:The objective of this research project was to develop evidence that established industrial processes involving transition-metal catalysts, such as rhodium, can be carried out effectively in supercritical fluids without loss of catalyst. The choice of solvent, for environmental reasons, was supercritical carbon dioxide (scCO2).
Summary/Accomplishments (Outputs/Outcomes):scCO2 was deemed the solvent we would develop early in the planning investigations involving the principal investigator and co-principal investigator. Prior to obtaining funding from the U.S. Environmental Protection Agency, a successful effort was made to synthesize a chiral catalyst that might successfully allow chiral hydrogenation and perhaps even successful hydroformylation. This work led to successful synthesis and complete characterization (Guzel, 2001) of the chiral catalyst. Armed with theoretical results related to enantioselective hydroformylation results, we attempted to better understand the mechanistic details of hydrogenation and hydroformylation in scCO2 using a Wilkinson-type nonchiral catalyst. The literature contained only very poor evidence that chiral hydrogenation could be achieved in scCO2 with a Wilkinson phosphine catalyst. The Ph.D thesis of Bin Lin addressed the issue. Although this chiral catalyst with BARF as the anion was sufficiently soluble in scCO2 to carry our successful hydroformylation, chiral products were not obtained successfully. Enantioselectivity was observed, however, for hydrogenation but not hydroformylation. Other problems surfaced with regard to the expense of the chiral catalyst and its recovery. It was determined that the use of a homogeneous systems was not the correct approach to take.
Although it was apparent that hydroformylation in scCO2 could be accomplished, the use of a good chiral homogeneous catalyst was unsuccessful. Furthermore, recovery of the catalyst also would be necessary to achieve a useful result. With the help of Professor David Bergbreiter, who had demonstrated that fluorous polymers could be obtained with phosphines attached (Bergbreiter, 2000), it was appropriate to ascertain if a rhodium Wilkinson catalyst could be coordinated to phosphine sites on a fluorous polymer. It was reasonable to believe that swelling of the fluorous polymer in scCO2 might allow olefins to interact with the catalyst site. The rhodium-based fluorous polymer then could be contained in a membrane reactor and recovered. Using a free radical initiation process, appropriate fluorous polymer were prepared with different ratios of attached phosphines. A description of the process used for synthesis (Kani, 2002) is seen in Figures 1 and 2. To confirm the coordination of the Rh(I) to the phosphines, nuclear magnetic resonance and ultraviolet-visible spectroscopy were used. The catalyst showed excellent solubility of scCO2. Hydrogenation of 1-octene led to 70 percent conversion to n-octane. Clearly, the fluorous polymer was swelling enough to allow this olefin to bond to the Rh(I). Using the window to the reaction cell, it was possible to observe that the catalyst was not precipitating in the solvent and that the scCO2 remained supercritical under the conditions of temperature and pressure used. The solubility of the catalyst is seen in the data of Table 1.
Figure 1. Radical Synthesis of Fluorous Polymer
Figure 2. Insertion of Rhodium Into the Polymer by Coordination at the Phosphorus Sites
Table 1. Quantitative Solubility at 318.15 K and 172.4 Bar
polymer/catalyst |
wt% |
TAN10NASI |
6.8 x 10-3 |
TAN20NASI |
26.5 x 10-3 |
1:3 Rh(TAN20DPPA)C1 |
31.4 x 10-3 |
Hydrogenation was thoroughly studied at 343 K and 173.4 bar with various ratios of 1-octene to rhodium. As expected, the total conversion is higher with lower olefin-to-rhodium ratios (Figure 3) (Lopez-Castillo, 2002).
Figure 3. Olefin to Rhodium Ratios/Conversion
A crucial experiment was catalyst recovery. Using an arlcite container as our membrane to contain the polymer catalyst, we carried out cycles of runs in the batch mode. The results clearly showed little to no loss of catalyst from the arclite filter (Figure 4). The first cycles showed a relatively low conversion which increased gradually to 85 percent in the ninth cycle. Apparently, the swelling of the polymer does not occur initially and only after a few cycles is it sufficiently open to allow maximum conversion.
Figure 4. Hydrogenation Reproducibility
With another catalyst preparation, 20 cycles were carried out. The first cycle showed only a 35 percent conversion, but by the ninth cycle, conversion had reached about 80 percent. Cycles were continued to 20 with little change in the conversion. At the end of this last cycle the reactor was opened and an attempt was made to recover the catalyst. Only 9.3 percent was recovered using Freon. No trace of rhodium, however, was found in effluents taken from the 1st and 19th cycles. Neutron activation analysis was chosen as the analytical tool for this determination. This techniques proved very successful and was tested thoroughly with pure catalyst before using it on the runs.
Kinetics (Figure 5) of the homogeneous hydrogenation were studied because metal hydride formation is an important step in the hydroformylation process (Figure 6). Kinetic parameters were developed that performed well for the hydrogenation of cyclohexene at several temperatures. These results are described in a paper (Flores, 2003). The rate determining step for hydrogenation in the model we used appears to be the migratory insertion of hydrogen into the olefin to produce the alkyl-rhodium-hydride-complex. The rate-determining step for the isomerization reaction that also occurs was considered to be the coordination of the olefin to the rhodium-hydrogen catalyst. This kinetic model was consistent for both the hydrogenation and the isomerization data for 1-octene and for cyclohexene.
Figure 5. Hydrogenation Kinetics
Figure 6. Hydroformylation Cycle Used for the Kinetics Considerations
Having demonstrated that the catalyst could be contained in a membrane reactor and that the hydrogenation process worked effectively, we returned to the question of hydroformylation. Although chirality of product no longer seemed a reasonable result because of the reversibility of steps 3 and 4 leading to metal-hydride formation and isomerization, the process itself with styrene was examined (Figure 7). Conversions up to almost 100 percent were realized (Kani, 2004). Branched aldehyde selectivities from 95-100 percent were achieved. The oxidative addition of hydrogen appears to be the rate controlling step. Kinetic parameters were obtained that fit the experimental data quite successfully (Figure 8).
Figure 7. Styrene Conversion and Selectivity
Figure 8. Comparison Between Experimental Results and Calculated Results for Hydroformylation
This work has demonstrated that both hydrogenation and hydroformylation can be carried out successfully in scCO2. Production of chiral aldehyde products, however, was not achieved by the techniques we have studied. We suspect that an environment that itself is chiral will be required. When carried out in a membrane reactor with a catalyst attached to a fluorous polymer, considerable success was achieved both in the yields and the protection against apparent loss of catalyst when the reactions were done in a batch process. Kinetic parameters could be developed that adequately described the results. Batch processes, however, are not flowing processes. Catalyst loss in a flow reactor could possibly occur and was suggested to John P. Fackler, Jr., by Martyn Poliakoff (Poliakoff, 2005). A flow process was not studied in our work.
References:
Guzel B, Omary MA, Fackler Jr. JP, Akgerman A. Synthesis and characterization of {[(COD)Rh(bis-(2R,3R)-2,5-diethylphospholanobenzene)]+BARF-} for use in homogeneous catalysis in supercritical carbon dioxide. Inorganica Chimica Acta 2001;325(1-2):45-50.
Bergbreiter DE, Franchina JG, Case BL. Fluoroacrylate-bound fluorous-phase soluble hydrogenation catalysts. Organic Letters 2000;2:393-395.
Kani I, Omary MA, Rawashdeh-Omary MA, Lopez-Castillo ZK, Flores R, Akgerman A, Fackler Jr. JP. Homogeneous catalysis in supercritical carbon dioxide with rhodium catalysts tethering fluoroacrylate polymer ligands. Tetrahedron 2002;58(20):3923-3928.
Flores R, Lopez-Castillo ZK, Kani I, Fackler Jr. JP, Akgerman A. Kinetics of the homogeneous catalytic hydrogenation of olefins in supercritical carbon dioxide using a fluoroacrylate copolymer grafted rhodium catalyst. Industrial & Engineering Chemistry Research 2003;42(26):6720-6729.
Kani I, Flores R, Fackler Jr. JP, Akgerman A. Hydroformylation of styrene in supercritical carbon dioxide with fluoroacrylate polymer supported rhodium catalysts. The Journal of Supercritical Fluids 2004;31(3):287-294.
Poliakoff M. Personal communication. Presented at Frontiers in Chemistry Lecture, Texas A&M University, TX, 2005.
Journal Articles on this Report: 2 Displayed | Download in RIS Format
| Other project views: | All 8 publications | 3 publications in selected types | All 2 journal articles |
| Type | Citation | ||
|---|---|---|---|
|
|
Lopez-Castillo ZK, Flores R, Kani I, Fackler JP, Akgerman A. Evaluation of polymer-supported rhodium catalysts in 1-octene hydroformylation in supercritical carbon dioxide. Industrial & Engineering Chemistry Research 2003;42(17):3893-3899 |
R828135 (Final) |
not available |
|
|
Lopez-Castillo ZK, Flores R, Kani I, Fackler Jr. JP, Akgerman A. Fluoroacrylate copolymer-supported rhodium catalysts for hydrogenation reactions in supercritical carbon dioxide. Industrial & Engineering Chemistry Research 2002;41(13):3075-3080. |
R828135 (Final) |
not available |
supercritical carbon dioxide, hydroformylation, hydrogenation, rhodium catalyst, membrane reactor, fluorous polymer, kinetics, neutron activation analysis,
,
Ecosystem Protection/Environmental Exposure & Risk, Sustainable Industry/Business, Scientific Discipline, RFA, Technology for Sustainable Environment, Sustainable Environment, Chemical Engineering, Environmental Engineering, Environmental Chemistry, process modification, supercritical carbon dioxide, cleaner production, green chemistry, solvents, environmentally benign solvents, homogeneous catalysis, hydroformation reaction, industrial process, alternative materials, source reduction, innovative technology
Relevant Websites:
http://www.chem.tamu.edu/rgroup/fackler/ 
Progress and Final Reports:
Original Abstract