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Homogeneous Catalysis in Supercritical Carbon Dioxide with Fluoroacrylate Copolymer Supported CatalystsEPA Grant Number: R828135
Title: Homogeneous Catalysis in Supercritical Carbon Dioxide with Fluoroacrylate Copolymer Supported Catalysts
Investigators: Akgerman, Aydin , Fackler Jr, John P.
Current Investigators: Akgerman, Aydin
Institution: Texas A & M University , Texas Engineering Experiment Station
Current 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) RFA Text | Recipients Lists
Research Category: Sustainability , Pollution Prevention/Sustainable Development
Description:Chemistry in ecologically benign solvents is of increasing interest in "Green Chemistry", catalysis and combinatorial chemistry. Most solvents used in organic syntheses with homogeneous catalysts are coming under close scrutiny because of their toxicity. There is a great push in industry today to replace these solvents with environmentally benign solvents such as supercritical carbon dioxide, scCO2, but most catalysts are not soluble in scCO2 and some organic syntheses are solvent selective. Another major problem is the separation and recovery of the catalyst after the reaction, which results in catalyst loss and metal contamination. A major thrust in industry is to develop homogeneous catalysts which can be recovered easily and intact after the completion of the reaction. In this vain, there is a significant amount of interest in polymer supported ligands for metal complexation in homogeneous catalysis. In this project we propose to evaluate a novel idea that solves both the solvent replacement and intact recovery of catalyst issues. We plan to attach the catalyst ligands to a fluoroacrylate copolymer, which is soluble in scCO2. In addition, the polymer can easily be separated by a membrane. In the overall process, the membrane separation of the reactor effluent will maintain the catalyst in the reactor. The products can be separated from scCO2 by simple expansion yielding solvent free products. CO2 can be recompressed and recycled, if needed. Upon completion of the reaction and expansion of the scCO2 remaining in the reactor, the catalyst will also be obtained intact.
Approach:Our approach will be in five phases. (1) We will first synthesize functionalized copolymers using commercially available fluoroacrylates and an active ester comonomer, specifically N-acryloxysuccinimide (NASI), the former enabling solubility in carbon dioxide the latter providing an exchange site for an active catalyst. (2) The NASI group on the copolymer would easily react with amine containing complexing agents. We will then exchange the NASI branches for metal ion containing catalytic materials for hydrogenation and hydroformylation reactions. (3) We will determine solubilities of these catalytic materials in scCO2 at a range of temperatures and pressures. (4) We will evaluate the catalytic activity of these new novel catalysts in hydrogenation and hydroformylation reactions carried in scCO2; and (5) We will evaluate membrane reactors for catalyst separation and recovery.
Expected Results:We have already synthesized the polymer with the NASI group replaced by a catalyst precursor and a diazo dye which gives the polymer a red color. We have shown that these products are soluble in scCO2 and dye substituted polymer gives a orange/yellow colored solution. In order to evaluate whether the dye is active, we dissolved the polymer in scCO2 in the presence of an organic base, diethylamine. The azo dye, in a basic solution, would have a yellow color, and we observed that the color does indeed change to yellow from orange/yellow. Hence we have qualitatively shown that the polymer/catalyst is soluble in carbon dioxide and that the functionalized sites are exposed in solution and are available for reaction. Based on this proof-of-concept, we are confident that catalyst supported will be soluble in supercritical carbon dioxide and will also be active as a catalyst.
Estimated Improvement in Risk Assessment: This project aims and reduction in use of toxic solvents and also reduction in metal contamination. Supercritical carbon dioxide can be as good a reaction medium as many organic solvents for many reactions, hence there will be a reduction in use of solvents. Secondly, when reactions are carried in supercritical carbon dioxide, after expansion the products are obtained solvent free, which is an additional advantage eliminated solvent contamination of the products. Finally, the catalyst will also be obtained intact in the proposed system, eliminating loss of heavy metals and the need for re-synthesis.