Hydrothermal Processing of Chlorinated Hydrocarbons in a Titanium Reactor

Abstract

Experiments are reported on the oxidative hydrothermal destruction of chlorinated organics in a corrosion-resistant titanium reactor. Oxidation reaction conditions were 250-500°C near 650 bar and reaction times of 30-100 s in a continuous-flow reactor. Trichloroacetic acid, trichloroethylene, and 1,1,1trichloroethane behaved similarly. The organic concentration was ∼1.5 wt %; hydrogen peroxide was the oxidizer; sodium bicarbonate was added to achieve neutral pH. Hydrolysis occurs at low temperature, producing chloride ion and secondary organics. Carbon dioxide is the sole carbon product at 500°C. Sodium nitrate and sodium nitrite were also found to be effective oxidizers. Corrosion of the titanium was found to be slight (<0.038 mm/yr). The reaction mixture is likely not a single phase at these conditions. The destruction efficiency for trichloroethylene was estimated as 99.96% at 450°C and 60 s, with <0.02% conversion to volatile chlorinated organic byproducts.

Decomposition of 2-chlorophenol by supercritical water oxidation with zirconium corrosion

“…Supercritical water oxidation (SCWO) systems are known as a very efficient way to treat refractory/hazardous compounds, like PCB [3] and Dioxins [4], compared to other feasible technologies, including wet air oxidation. Many researchers have focused on finding variables for the process design by experimenting with various kinds of industrial wastewaters [7,[10][11][12][13][14][15]. However, the applicability of this process hinges not just on its capability to remove the desired level of pollutant, but, more importantly, on its cost effectiveness.…”

“…Many researchers have focused on solving these problems using a variety of methods and reactor designs [7,[10][11][12]. In addition, various materials have been employed for the construction of SCWO systems [10,13,14]. And the corrosion phenomena of various metal alloys have also been investigated [15] because it is important to select materials suitable for the reactor.…”

Supercritical water oxidation of polychlorinated biphenyls based on the redox reactions promoted by nitrate and nitrite salts

“…The greatest obstacle in the SCWO of organochlorine compounds is that the reactor vessel made of metal alloys is readily corroded by hydrogen chloride (HCl) generated as a degradation product. Platinum, titanium and ceramic vessels [3,8,9], which are capable of withstanding the corrosive condition, are such special materials that the use of them is not favored due to aspects of cost. It is therefore necessary to neutralize the HCl by the addition of alkalis such as sodium carbonate (Na 2 CO 3 ) [10,11] and sodium bicarbonate (NaHCO 3 ) [8].…”

“…Platinum, titanium and ceramic vessels [3,8,9], which are capable of withstanding the corrosive condition, are such special materials that the use of them is not favored due to aspects of cost. It is therefore necessary to neutralize the HCl by the addition of alkalis such as sodium carbonate (Na 2 CO 3 ) [10,11] and sodium bicarbonate (NaHCO 3 ) [8]. In the flow reactor system, the sodium chloride (NaCl) produced by the neutralization causes plugging of the fluid channel, because NaCl is almost insoluble in SCW [12,13].…”

“…In the flow reactor system, the sodium chloride (NaCl) produced by the neutralization causes plugging of the fluid channel, because NaCl is almost insoluble in SCW [12,13]. To maintain NaCl in a single fluid phase, SCWO processes must be conducted under high pressure conditions [8].…”