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Studies on the oxidation of monoethanolamine using UV and H20 2 with post-biological treatment

MOHD ARIFF , IDZHAM FAUZI (2010) Studies on the oxidation of monoethanolamine using UV and H20 2 with post-biological treatment. Masters thesis, Universiti Teknologi PETRONAS.

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Abstract

In natural gas processing, alkanolamine solvents such as monoethanolamine (MEA) are wide! y used for removal of sour gases from natural gas. In natural gas processing plants, large volumes of alkanolamine solutions are routinely generated during periodic maintenance, cleaning and vessel safety inspections. Due to intermittent generation, high organic content and biological recalcitrance, these chemicals are generally not treatable in the conventional wastewater treatment systems available in these facilities and high costs can be incurred to segregate and dispose alkanolaminecontaminated wastewater. Advanced oxidation processes (AOPs) have been studied extensively as a promising pollution abatement strategy to rapidly oxidize many organic pollutants. The combination of UV radiation and hydrogen peroxide, called the UV/H20 2 process, is a widely studied AOP, and the degradation of syntheticallyprepared MEA solution using the UV/H20 2 process is investigated in this work. The effects of various parameters on the organics degradation of MEA under UV IH202 treatment was studied using the Taguchi approach to design of experiments based on the L-16 (45 ) modified orthogonal array. Experiments were conducted in a jacketed glass reactor using low-pressure UV lamps. Chemical oxygen demand (COD) was used as a measure of the degree of degradation of organics in the MEA solution. The parameters studied were UV dose, temperature, initial pH and initial H20 2 dose. The optimum conditions, predicted response (COD removal) and confidence interval were determined and a confirmation experiment was conducted. The results indicate that the main and controlling factor for the removal of COD in the experimental conditions used in this study is the UV dose. Other parameters did not have any statistically significant effect on the COD removal at the ranges used in this study. The response at optimum conditions was verified by confirmation experiment. A more detailed study of UV/H20 2 degradation on MEA was conducted to determine the effects of various parameters, i.e. initial pH, temperature, UV dose (photon flux), and initial H20 2 dose at a broader range than the Taguchi study. In addition, the solution pH, H20 2 concentration, MEA concentration and some breakdown products were also investigated. The UV incident photon flux (i.e. UV dose) was quantified using hydrogen peroxide actinometry. It was found that COD removal and HzOz decay are increased by raising the initial pH of the solution and more than 90% COD removal is achievable at high initial pH (8-9) after 60 minutes. Variation of solution temperature in the range studied did not have any appreciable effect on COD removal nor HzOz decay. The COD removal and HzOz decay increased with higher UV photon flux. Although the Taguchi study found no effect of initial H20 2 dose on COD removal at low H20 2 dosage, it was found that increase of initial H20 2 dose above 0.16 M concentration retarded the COD removal rate due to the scavenging of hydroxyl radicals by excess H20z. The pseudo first-order kinetic constants for MEA degradation were estimated and ranged between 0.0090 to 0.0922 min·1 depending on the reaction conditions. The effects of the parameters on the kinetic constants were also evaluated. Several intermediate breakdown products were identified, including formate and nitrate. The formation of these acidic species resulted in the pH depression that was observed during the course of reaction. Significant concentration of ammonia was also formed during the course of the reaction. A quasi-mechanistic kinetic rate model for the reduction of gross orgamc content (based on COD) during MEA oxidation using UV/H20 2 process was also developed. The kinetic model incorporates a set of literature rate constant values for the principal reactions involved in the photolysis of hydrogen peroxide by UV radiation to which is added the n-th order reaction of the substrate (COD) with ·OH radical. The kinetic model was validated using experimental COD and H20 2 degradation data and exhibited good agreement with measured values. The model results confirm that the increased COD removal at higher pH was a result of the formation of pH -dependent species and not due to the effect of H20 2 dissociation into hydroperoxide ion at high pH. The biodegradability of MEA solution (in terms of COD) that has been partially degraded via UV/H20 2 was studied using batch growth reactor operated under aerobic conditions. The kinetic rate constants based on the Monod model formed the basis of comparison and were calculated by fitting the growth and utilisation data to a sigmoid equation. The acclimatization times were also studied. The results indicated that, for MEA solution which was partially treated with UV /H20 2 at 30% COD removal, the biomass growth rate, substrate utilisation rate and biomass yield was reduced compared to untreated MEA. The acclimatization time for aerobic biodegradation was unaffected. The only parameter that showed improvement was the half-saturation coefficient. This effect may be attributed to formation of some unidentified inhibitory compound at the level of pretreatment that was applied. Biodegradation of both MEA and partially treated MEA was found to generate high levels of ammonia as by-product.

Item Type: Thesis (Masters)
Academic Subject : Mission Oriented Research - CO2 Management - Carbon dioxide - Environmental effects
Subject: T Technology > TP Chemical technology
Divisions: Engineering > Chemical
Depositing User: Users 2053 not found.
Date Deposited: 30 Oct 2013 16:49
Last Modified: 25 Jan 2017 09:42
URI: http://utpedia.utp.edu.my/id/eprint/10106

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