Recent Advances in Catalytic Oxidation in Supercritical Water

Savage, Phillip E.; Dunn, Jennifer B.; Yu, Jie-Tai

doi:10.1080/00102200500287159

Cited by 48 publications

(17 citation statements)

References 48 publications

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“…The technical feasibility of using HTW as a medium for TPA synthesis has been demonstrated 5–13. Our group has reported previously on p ‐xylene partial oxidation in HTW, and we obtained high TPA yields (> 80 mol %) at 300°C, [ p ‐xylene] 0 = 0.02 mol L −1 , [O 2 ] 0 = 0.10 mol L −1 , [MnBr 2 ] = 0.007 mol L −1 , and t = 5–15 min 5.…”

Section: Introductionmentioning

confidence: 64%

Terephthalic acid synthesis at higher concentrations in high‐temperature liquid water. 2. Eliminating undesired byproducts

Osada

Savage

2009

AIChE Journal

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in Wiley InterScience (www.interscience.wiley.com).We synthesized terephthalic acid (TPA) from p-xylene at an initial concentration above its solubility limit in high-temperature liquid water (HTW). The nominal p-xylene loading at the reaction conditions was 0.4 mol L À1, which is the highest reported to date for generation of high TPA yields ([70 mol %) in HTW. The presence of two liquid phases during the reaction did not appear to accelerate the rate, unlike behavior reported for some other organic reactions done ''on water'' at lower temperatures. Adding oxygen gas in a large increment during synthesis produced a black liquid and a black solid byproduct, which is a previously undocumented problem. Adding oxygen in smaller increments prevented formation of the liquid and solid byproducts and also provided high selectivities (90 mol %) and yields ([70 mol %) of TPA. These results demonstrate the feasibility of HTW as a medium for TPA synthesis at p-xylene concentrations even higher than its solubility limit. V

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Section: Introductionmentioning

confidence: 64%

Terephthalic acid synthesis at higher concentrations in high‐temperature liquid water. 2. Eliminating undesired byproducts

Osada

Savage

2009

AIChE Journal

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“…There are a number of phenomena in sub-and scH 2 O that are the same as those observed in acetic acid suggesting a similar mechanism. Some of the similarities are: 1) the sequence of oxidation products, i.e., p-xylene to 4-methylbenzaldehyde, to p-toluic acid, to 4-carboxybenzaldehyde and finally to terephthalic acid, is the same; [7,8,12] 2) the uncatalysed oxidation in supercritical water gives low terephthalic acid yields and is very unselective producing large amounts of toluene; [19] 3) the addition of bromide to the metal-catalysed system increases the activity and yield; [15] and 4) increasing the catalyst concentration gives higher yield and selectivity. [7,8,15] A simplified free radical chain mechanism for a manganese/bromide catalyst consists of initiation, propagation, and termination steps.…”

Section: Reaction Mechanism and Possible Cause Of Catalyst Precipitationmentioning

confidence: 98%

“…[25] Dissolving manganese(II) acetate in water and heating it to form supercritical water, is a method for generating nanoparticles of manganese oxides. [26,27] Current evidence suggests that catalyst metal precipitation is undesirable because: 1) in acetic acid, manganese(IV) dioxide precipitation increases the rate of carbon dioxide and methyl bromide formation, [28] 2) it is known that manganese(IV) dioxide is an excellent heterogeneous catalyst in supercritical water for converting organic compounds to carbon dioxide, i.e., unselective oxidation, [7] and 3) the concentration of the homogeneous metal/bromide catalyst will decrease causing a decrease in the rate of reaction as well as a decrease in selectivity since thermal, rather than metal-catalysed, decomposition of the hydroperoxides increases. Thermal decomposition leads to such undesirable products as toluene, benzoic acid, and cresols.…”

Section: Reaction Mechanism and Possible Cause Of Catalyst Precipitationmentioning

confidence: 99%

Prevention of Manganese Precipitation during the Continuous Selective Partial Oxidation of Methyl Aromatics with Molecular Oxygen in Supercritical Water

et al. 2009

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Presented here is an investigation of the activity and recovery of the homogeneous manganese/bromide catalyst during the continuous flow oxidation of o-xylene, as model substrate, with molecular oxygen (O 2 ) in supercritical water (scH 2 O). Two strategies are discussed for preventing catalyst precipitation, mainly in the form of oxides such as manganese(IV) oxide, The first strategy involves varying the manganese:bromide ratio using either manganese(II) acetate or manganese(II) bromide in the presence of hydrobromic and other acids. The results show that the effect of acidity and bromide concentration plays an important role in preventing the manganese/bromide catalyst from precipitating. The second strategy uses aromatic carboxylic acids in combination with the manganese/bromide catalyst, particularly benzoic acid, which improves the catalyst recovery dramatically over a certain range of acid concentrations. Our studies show how the presence of an organic acid and/or its precursors is important in stabilising the catalyst. Our results are rationalised on the basis of a tentative reaction mechanism.

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“…To enable lower temperature operation with sufficient oxidation efficiency, catalysed SCWO of refractory organic compounds has been investigated (Krajnc & Levee 1994;Ding et al 1996;Oshima et al 1999;Savage et al 2006). Takahashi et al (2012) reported that sodium dtanate, which was hydrothermally synthesized on the surface of titanium particles in supercritical water, had catalytic activity on SCWO of acetic acid.…”

Section: Introductionmentioning

confidence: 99%

Enhanced removal of sodium salts supported by in-situ catalyst synthesis in a supercritical water oxidation process

Takahashi

Sun

Fukushi

et al. 2012

Water Science and Technology

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For practical applications of supercritical water oxidation to wastewater treatment, the deposition of inorganic salts in supercritical phase must be controlled to prevent a reactor from clogging. This study investigated enhanced removal of sodium salts with titanium particles, serving as a salt trapper and a catalyst precursor, and sodium recovery by sub-critical water. When Na(2)CO(3) was tested as a model salt, sodium removal efficiency was higher than theoretically maximum efficiency defined by Na(2)CO(3) solubility. The enhanced sodium removal resulted from in-situ synthesis of sodium titanate, which could catalyse acetic acid oxidation. The kinetics of sodium removal was described well by a diffusion mass-transfer model combined with a power law-type rate model of sodium titanate synthesis. Titanium particles showed positive effect on sodium removal in the case of NaOH, Na(2)SO(4) and Na(3)PO(4). However, they had negligible effect for NaCl and negative effect for Na(2)CrO(4), respectively. More than 99% of trapped sodium was recovered by sub-critical water except for Na(2)CrO(4). In contrast, sodium recovery efficiency remained less than 50% in the case of Na(2)CrO(4). Reused titanium particles showed the same performance for enhanced sodium removal. Enhanced salt removal supported by in-situ catalyst synthesis has great potential to enable both salt removal control and catalytic oxidation.

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Recent Advances in Catalytic Oxidation in Supercritical Water

Cited by 48 publications

References 48 publications

Terephthalic acid synthesis at higher concentrations in high‐temperature liquid water. 2. Eliminating undesired byproducts

Terephthalic acid synthesis at higher concentrations in high‐temperature liquid water. 2. Eliminating undesired byproducts

Prevention of Manganese Precipitation during the Continuous Selective Partial Oxidation of Methyl Aromatics with Molecular Oxygen in Supercritical Water

Enhanced removal of sodium salts supported by in-situ catalyst synthesis in a supercritical water oxidation process

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