Supercritical water oxidation of nitrogen-containing organic compounds: process enhancement using propylene glycol

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Al-Kaabi, Falah Kareem Hadi (2020). Supercritical water oxidation of nitrogen-containing organic compounds: process enhancement using propylene glycol. University of Birmingham. Ph.D.

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Abstract

This research aims to investigate the feasibility and efficiency of the supercritical water oxidation treatment method in destroying two diluted hazardous nitrogen-containing hydrocarbons. Monoethanolamine (MEA) and 3-methylpyridine (3MP) are selected due to their resistant nature under supercritical conditions and they are found in the effluent of different industries.
A continuous plug flow reactor (laboratory-scale system) was used to investigate the destruction of MEA and 3MP at different operating conditions. The ranges of temperature were from 400 to 525 ℃ for MEA and 425 to 525 ℃ for 3MP at pressure of 250 bar. Propylene glycol (PG) was used as a co-fuel to enhance SCWO performance. PG could be considered as a novel approach for improving the destruction of two compounds. Also, isopropyl alcohol (IPA) was used as co-fuel to compare between the effect of PG and IPA on efficiency of SCWO at different operating conditions. The effect of co-fuel on by-products of MEA and 3MP was investigated. The results were employed to determine the kinetic parameters in the absence and presence of co-fuel.
The effect of operating conditions such as temperature, residence time, oxidant ratio, initial concentration and co-fuel ratio on the destruction of MEA and 3MP was investigated. The results illustrated the positive effect of temperature on the destruction of two nitrogen-containing compounds. The complete removal efficiency of chemical oxygen demand (COD) of MEA was achieved at 525 ℃ and the maximum removal efficiency of total organic carbon (TOC) of 3MP was also achieved at 525 ℃. The yield of NH4-N increased with operating temperature in the MEA and 3MP systems.
The initial concentration of MEA and 3MP, oxidant ratio and residence time positively enhanced the COD removal and TOC removal efficiencies respectively. Although these effects were significant, the effect of operating temperature was influential on the destruction of two compounds in the absence and presence of co-fuel.
PG has a significant effect on the destruction of MEA and 3MP at different operating conditions. The results of the removal efficiency in the presence of PG were more remarkable than IPA. For example, COD removal efficiency of MEA increased from 61.0 % (fuel-free system) to 80.0 % (PG system) at the temperature of 400 ℃ and residence time of 14 s. The efficiency of TOC removal of 3MP increased from 69.9 % (fuel-free system) to 84.8 % (PG system) at the temperature of 425 ℃ and residence time of 14 s. In the presence of PG, the removal efficiency of nitrogen of MEA was 85.0 % at the ratio of (2.5 PG: 1 MEA) and the temperature of 400℃, the removal efficiency of nitrogen of 3MP was 88.0 % at the ratio of (3 PG:1 3MP) and the temperature of 425℃. The enhancement of the SCWO performance in the presence of PG was due to the activity of two hydroxyl groups.
The effect of PG occurred significantly on activation energy of two compounds. For instance, the activation energy of MEA decreased from 79.746 kJ.mol-1 (fuel-free system) to 46.807 kJ.mol-1 and 47.497 kJ.mol-1 in the presence of IPA and PG respectively. In the case of 3MP, the activation energy decreased from 31.85 kJ.mol-1 (fuel-free system) to 31.2 kJ.mol-1 and 28.4 kJ.mol-1 in the presence of IPA and PG respectively. Consequently, the number of reactant molecules increases at lower activation energy in the presence of co-fuel and the rate of reaction will be fast.
Finally, the destruction of MEA at 400 ℃ and 3MP at 425 ℃ in the presence of PG considers an essential goal to avoid using high temperature.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

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