Thermal degradation and oxidation of aqueous piperazine for carbon dioxide capture
| dc.contributor.advisor | Rochelle, Gary T. | en |
| dc.contributor.committeeMember | Maynard, Jennifer A. | en |
| dc.contributor.committeeMember | Reible, Danny D. | en |
| dc.contributor.committeeMember | Katz, Lynn E. | en |
| dc.contributor.committeeMember | Critchfield, James | en |
| dc.creator | Freeman, Stephanie Anne | en |
| dc.date.accessioned | 2011-06-01T14:55:54Z | en |
| dc.date.available | 2011-06-01T14:55:54Z | en |
| dc.date.available | 2011-06-01T14:56:26Z | en |
| dc.date.issued | 2011-05 | en |
| dc.date.submitted | May 2011 | en |
| dc.date.updated | 2011-06-01T14:56:26Z | en |
| dc.description | text | en |
| dc.description.abstract | Absorption-stripping with aqueous, concentrated piperazine (PZ) is a viable retrofit technology for post-combustion CO2 capture from coal-fired power plants. The rate of thermal degradation and oxidation of PZ was investigated over a range of temperature, CO2 loading, and PZ concentration. At 135 to 175 °C, degradation is first order in PZ with an activation energy of 183.5 kJ/mole. At 150 °C, the first order rate constant, k1, for thermal degradation of 8 m PZ with 0.3 mol CO2/mol alkalinity is 6.12 × 10-9 s-1. After 20 weeks of degradation at 165 °C, 74% and 63%, respectively, of the nitrogen and carbon lost in the form of PZ and CO2 was recovered in quantifiable degradation products. N-formylpiperazine, ammonium, and N-(2-aminoethyl) piperazine account for 57% and 45% of nitrogen and carbon lost, respectively. Thermal degradation of PZ likely proceeds through SN2 substitution reactions. In the suspected first step of the mechanism, 1-[2-[(2-aminoethyl) amino]ethyl] PZ is formed from a ring opening SN2 reaction of PZ with H+PZ. Formate was found to be generated during thermal degradation from CO2 or CO2-containing molecules. An analysis of k1 values was applied to a variety of amines screened for thermal stability in order to predict a maximum recommended stripper temperature. Morpholine, piperidine, PZ, and PZ derivatives were found to be the most stable with an allowable stripper temperature above 160 °C. Long-chain alkyl amines or alkanolamines such as N-(2-hydroxyethyl)ethylenediamine and diethanolamine were found to be the most unstable with an allowable stripper temperature below 120 °C. Iron (Fe2+) and stainless steel metals (Fe2+, Ni2+, and Cr3+) were found to be only weak catalysts for oxidation of PZ, while oxidation was rapidly catalyzed by copper (Cu2+). In a system with Fe2+ or SSM, 5 kPa O2 in the inlet flue gas, a 55 °C absorber, and one-third residence time with O2, the maximum loss rate of PZ is expected to 0.23 mol PZ/kg solvent in one year of operation. Under the same conditions but with Cu2+ present, the loss rate of PZ is predicted to be 1.23 mole PZ/kg solvent in one year of operation. Inhibitor A was found to be effective at decreasing PZ loss catalyzed by Cu2+. Ethylenediamine, carboxylate ions, and amides were the only identified oxidation products. Total organic carbon analysis and overall mass balances indicate a large concentration of unidentified oxidation products. | en |
| dc.description.department | Chemical Engineering | en |
| dc.format.mimetype | application/pdf | en |
| dc.identifier.uri | http://hdl.handle.net/2152/ETD-UT-2011-05-3290 | en |
| dc.language.iso | eng | en |
| dc.subject | Degradation | en |
| dc.subject | Thermal degradation | en |
| dc.subject | Oxidation | en |
| dc.subject | Amine degradation | en |
| dc.subject | Thermal stability | en |
| dc.subject | Piperazine | en |
| dc.subject | PZ | en |
| dc.subject | CO2 capture | en |
| dc.subject | Carbon dioxide capture | en |
| dc.title | Thermal degradation and oxidation of aqueous piperazine for carbon dioxide capture | en |
| dc.type.genre | thesis | en |
| thesis.degree.department | Chemical Engineering | en |
| thesis.degree.discipline | Chemical Engineering | en |
| thesis.degree.grantor | University of Texas at Austin | en |
| thesis.degree.level | Doctoral | en |
| thesis.degree.name | Doctor of Philosophy | en |