Polymerization and oxidation of phenols in supercritical water

Abstract

The treatment of toxic and difficult-to-degrade phenolic compounds has become a key issue in the coking, pharmaceutical, and chemical industries. Considering the polymerization and oxidation of phenolic compounds in supercritical water partial oxidation/supercritical water oxidation (SCWPO/SCWO), the present study reviewed the removal efficiency and reaction pathway of phenolic compounds and phenolic waste/wastewater under different reaction conditions. Temperature is the dominant factor affecting the SCWO reaction. When the oxidizing ability is insufficient, the organics polymerize to form phenolic compounds. The gradual increase of oxidant equivalent causes the intermediate product to gradually oxidize to CO2 and H2O completely. Finally, the free radical reaction mechanism is considered to be a typical SCWO reaction mechanism.

Optimization and Mechanism Study on Destruction of the Simulated Waste Ion-Exchange Resin from the Nuclear Industry in Supercritical Water

“…Thereafter, an OH • free radical was added to the α carbon of the aromatic ring and converted to phenol by oxidation, decarboxylation, and hydroxylation. As the most important intermediate product, phenol, whose hydroxyl group affects the ring-opening process, produces many undesirable polymerization products, such as dibenzofuran and diphenyl oxide. , In addition, p-benzoquinone was also an intermediate product of phenol in the oxidation atmosphere. − P-benzoquinone and other benzene-containing substances were further oxidized to open the ring to form low molecular carboxylic acids (such as acetic acid) and aliphatic hydrocarbon organic radicals. These low-molecule compounds would recombine to produce long-chain fatty acids and aliphatic hydrocarbons, , both of which were detected in the liquid products, and eventually oxidized to CO 2 and H 2 O …”

“…As the most important intermediate product, phenol, whose hydroxyl group affects the ring-opening process, produces many undesirable polymerization products, such as dibenzofuran and diphenyl oxide. , In addition, p-benzoquinone was also an intermediate product of phenol in the oxidation atmosphere. − P-benzoquinone and other benzene-containing substances were further oxidized to open the ring to form low molecular carboxylic acids (such as acetic acid) and aliphatic hydrocarbon organic radicals. These low-molecule compounds would recombine to produce long-chain fatty acids and aliphatic hydrocarbons, , both of which were detected in the liquid products, and eventually oxidized to CO 2 and H 2 O …”

“…45−47 P-benzoquinone and other benzene-containing substances were further oxidized to open the ring to form low molecular carboxylic acids (such as acetic acid) and aliphatic hydrocarbon organic radicals. These low-molecule compounds would recombine to produce longchain fatty acids and aliphatic hydrocarbons, 15,45 both of which were detected in the liquid products, and eventually oxidized to CO 2 and H 2 O. 47 In path B, the quaternary ammonium group was accompanied by the polystyrene carbon chain skeleton for subsequent reactions.…”

Supercritical water oxidation of phenol and process enhancement with in situ formed Fe2O3 nano catalyst

“…Nevertheless, long-term discharge and treatment difficulties of phenolic wastewater could lead to more discharge of industrial waste on the water surface that is a serious problem for not only the human health but also the ecosystem. However, an alternative strategy should be adopted to treat phenolic wastewater (Pillai & Gupta 2016 , Zhang et al 2019 ).…”

Naphthalene mineralization by supercritical water oxidation and determination of by-products using non-target analysis

“…Studies have shown that SCWO can mineralize organics in a very short time by turning water into an excellent solvent at critical pressure (22.1 MPa) and temperature (374°C). The researchers have investigated the degradation of ammonia (Bermejo et al 2008), phenolic compounds (Zhang et al 2019), pharmaceutical (Ma et al 2018;Mylapilli & Reddy 2019), organophosphate flame retardants (Yang et al 2019) and pesticides (Xu et al 2015) by the SCWO process. However, although PAHs are characterized as mutagenic or carcinogenic pollutants, a few studies (Onwudili & Williams 2007;Xu et al 2013;Ates & Argun 2021) on the SCWO of PAHs were found in the literature.…”