page 353 |
Previous | 1 of 12 | Next |
|
|
Loading content ...
Section Five WASTE TREATMENT PROCESSES B. SUPERCRITICAL FLUID EXTRACTION 39 CATALYST EVALUATION: SUPERCRITICAL WATER OXIDATION PROCESS Michael A. Frisch, Graduate Research Assistant Lixiong Li, Research Scientist Earnest F. Gloyna, Bettie Margaret Smith Chair Environmental Health Engineering The University of Texas at Austin Austin, Texas 78758 INTRODUCTION Supercritical water oxidation (SCWO) exhibits rapid destruction of dimethyl methylphosphonate (DMMP), pyridine and 2,4-dichlorophenol (2,4-DCP). Relatively stable transformation products that result from the SCWO of these compounds are methylphosphonic acid (MPA), ammonia and acetic acid, and mono- and di-chlorinated phenols, respectively. To destroy these by-products it is necessary to provide higher temperatures, longer residence times, or catalyst enhancement. Preliminary tests have indicated that some commercially available catalysts, including metals used in reactor vessels, reduce the required temperature and residence time. Higher temperatures and reactor residence times require both increased capital and operational costs. For example, a decrease in required process temperature from 600°C to 450°C may translate into a considerable reduction in corrosion and capital costs. This corrosion problem is of particular importance because many hazardous wastes contain heteroatoms (such as CI, F, P, S and N) which are eventually oxidized to form corrosive acids. Catalyst and support stability is critical as it will govern the useful lifetime of a catalyst. While catalysts may increase the oxidation rate and thereby reduce reactor volume requirements, aggressive SCWO environments may deactivate some catalysts and/or supports. Consequently, catalysts operating within a SCWO process must maintain physical stability and activity over a practical lifetime. The objective of this research was to evaluate the performance of selected catalysts for use in SCWO environments. A three-step procedure was used to evaluate catalyst performance. First, commercially available metal oxide supports were tested for physical stability in SCWO environments. Stability was determined by examination of the supports and dissolved species in the liquid phase before and after exposure to SCWO in laboratory-scale, batch reactors. Second, promising supports were coated with platinum (platinum-coated supports were then referred to as platinum catalysts). These platinum catalysts and supports were each packed in a continuous-flow, fixed bed reactor in order to evaluate the catalytic oxidation of DMMP, acetic acid, pyridine and 2,4-DCP and their corresponding byproducts. Third, selected platinum catalysts and supports were exposed to longevity tests in order to evaluate temporal stability and activity in the catalytic oxidation of acetic acid. Longevity tests also were used to evaluate the effect of sulfuric and hydrochloric acid additions to the feed. BACKGROUND Properties of supercritical water (SCW) give the SCWO process an advantage over biological oxidation and wet air oxidation processes.1,2 A sharp decrease in hydrogen bonding near the critical point renders SCW a nonpolar solvent, which dissolves most organic substances in all proportions.3 SCW also dissolves most gases in all proportions.4-6 Intimate mixing of reactants and high temperatures permit 99.99999 percent destruction of many organic compounds in seconds. Another important 49th Purdue Industrial Waste Conference Proceedings, 1994 Lewis Publishers, Chelsea, Michigan 48118. Printed in U.S.A. 353
Object Description
Purdue Identification Number | ETRIWC199439 |
Title | Catalyst evaluation : supercritical water oxidation process |
Author |
Frisch, Michael A. Li, Lixiong Gloyna, Earnest F. |
Date of Original | 1994 |
Conference Title | Proceedings of the 49th Industrial Waste Conference |
Conference Front Matter (copy and paste) | http://e-archives.lib.purdue.edu/u?/engext,44602 |
Extent of Original | p. 353-364 |
Collection Title | Engineering Technical Reports Collection, Purdue University |
Repository | Purdue University Libraries |
Rights Statement | Digital object copyright Purdue University. All rights reserved. |
Language | eng |
Type (DCMI) | text |
Format | JP2 |
Date Digitized | 2009-12-10 |
Capture Device | Fujitsu fi-5650C |
Capture Details | ScandAll 21 |
Resolution | 300 ppi |
Color Depth | 8 bit |
Description
Title | page 353 |
Collection Title | Engineering Technical Reports Collection, Purdue University |
Repository | Purdue University Libraries |
Rights Statement | Digital copyright Purdue University. All rights reserved. |
Language | eng |
Type (DCMI) | text |
Format | JP2 |
Capture Device | Fujitsu fi-5650C |
Capture Details | ScandAll 21 |
Transcript | Section Five WASTE TREATMENT PROCESSES B. SUPERCRITICAL FLUID EXTRACTION 39 CATALYST EVALUATION: SUPERCRITICAL WATER OXIDATION PROCESS Michael A. Frisch, Graduate Research Assistant Lixiong Li, Research Scientist Earnest F. Gloyna, Bettie Margaret Smith Chair Environmental Health Engineering The University of Texas at Austin Austin, Texas 78758 INTRODUCTION Supercritical water oxidation (SCWO) exhibits rapid destruction of dimethyl methylphosphonate (DMMP), pyridine and 2,4-dichlorophenol (2,4-DCP). Relatively stable transformation products that result from the SCWO of these compounds are methylphosphonic acid (MPA), ammonia and acetic acid, and mono- and di-chlorinated phenols, respectively. To destroy these by-products it is necessary to provide higher temperatures, longer residence times, or catalyst enhancement. Preliminary tests have indicated that some commercially available catalysts, including metals used in reactor vessels, reduce the required temperature and residence time. Higher temperatures and reactor residence times require both increased capital and operational costs. For example, a decrease in required process temperature from 600°C to 450°C may translate into a considerable reduction in corrosion and capital costs. This corrosion problem is of particular importance because many hazardous wastes contain heteroatoms (such as CI, F, P, S and N) which are eventually oxidized to form corrosive acids. Catalyst and support stability is critical as it will govern the useful lifetime of a catalyst. While catalysts may increase the oxidation rate and thereby reduce reactor volume requirements, aggressive SCWO environments may deactivate some catalysts and/or supports. Consequently, catalysts operating within a SCWO process must maintain physical stability and activity over a practical lifetime. The objective of this research was to evaluate the performance of selected catalysts for use in SCWO environments. A three-step procedure was used to evaluate catalyst performance. First, commercially available metal oxide supports were tested for physical stability in SCWO environments. Stability was determined by examination of the supports and dissolved species in the liquid phase before and after exposure to SCWO in laboratory-scale, batch reactors. Second, promising supports were coated with platinum (platinum-coated supports were then referred to as platinum catalysts). These platinum catalysts and supports were each packed in a continuous-flow, fixed bed reactor in order to evaluate the catalytic oxidation of DMMP, acetic acid, pyridine and 2,4-DCP and their corresponding byproducts. Third, selected platinum catalysts and supports were exposed to longevity tests in order to evaluate temporal stability and activity in the catalytic oxidation of acetic acid. Longevity tests also were used to evaluate the effect of sulfuric and hydrochloric acid additions to the feed. BACKGROUND Properties of supercritical water (SCW) give the SCWO process an advantage over biological oxidation and wet air oxidation processes.1,2 A sharp decrease in hydrogen bonding near the critical point renders SCW a nonpolar solvent, which dissolves most organic substances in all proportions.3 SCW also dissolves most gases in all proportions.4-6 Intimate mixing of reactants and high temperatures permit 99.99999 percent destruction of many organic compounds in seconds. Another important 49th Purdue Industrial Waste Conference Proceedings, 1994 Lewis Publishers, Chelsea, Michigan 48118. Printed in U.S.A. 353 |
Resolution | 300 ppi |
Color Depth | 8 bit |
Tags
Comments
Post a Comment for page 353