Wet air oxidation of polyethylene glycols; mechanisms, intermediates and implications for integrated chemical-biological wastewater treatment

Autoxidation of glycols used in inhalable daily products: implications for the use of artificial fogs and e-cigarettes

The use of glycols is seen in various industries and occupations. In the past few decades, the health implications of inhalable glycols have gained public attention. Inhalable glycols may cause adverse health effects, especially for workers in occupations receiving frequent exposure and consumers of glycol-based daily products. Our previous work highlighted the rapid accumulation of formaldehyde and glycolaldehyde in fog juice, thus proposing the occurrence of glycol autoxidation. However, the fundamentals of glycol autoxidation remained unclear and unexplored. Our goal is to investigate the autoxidation of common glycols during indoor storage. Carbonyls were quantified using liquid chromatography-mass spectrometry (LC-MS), and peroxides from autoxidation were monitored via iodometry and UV-Vis spectrometry. The impact of certain factors such as the water mixing ratio and antioxidants (vitamin C) was also investigated. Formation of aldehydes in many glycols was weekly monitored, such as e-cigarette juice and triethylene glycol (TEG). Occurrence of autoxidation was confirmed by the increase in the total peroxide concentration. Additionally, we highlighted the dependence of the carbonyl formation rate on the TEG-water mixing ratio, demonstrating the complex role of water in glycol autoxidation. We have also tested the effectiveness of vitamin C and made suggestions for minimizing the formation of toxic carbonyls in consumer products.

Treatment of Oil Sands’ Mature Fine Tailings Using Advanced Wet Air Oxidation (WAO) and Wet Air Peroxide Oxidation (WAPO)

Mature Fine Tailings (MFT) generated from oil sands processing represent a growing environmental issue, as settling of these tailings’ emulsion can take decades, increasing the risk of the toxic material’s leaching if left untreated. This study uses advanced wet air oxidation (WAO) and wet air peroxide oxidation (WAPO) to break down the MFT emulsions for faster settling. Three oxidation time intervals (5, 15, and 30 min) were investigated using compressed air and hydrogen peroxide in a pressurized vessel of 3.1–3.4 MPa internal pressure and at 200 °C temperature. The results showed that the WAO process was able to break the MFT emulsion, release trapped water, and recover residual bitumen. The WAPO process was much faster in breaking the emulsion; however, the presence of extra oxidants also resulted in the degradation of the residual bitumen. The 5 min oxidation time interval was found to be sufficient in breaking emulsions, separating water from soil particles, and recovering residual bitumen under the tested conditions. The oxidation process proved to be efficient by degrading all inorganic carbon, whereas 70% of the dissolved organic carbon in the recovered water after oxidation comprised only low molecular weight biodegradable hydrocarbons. Therefore, the WAO process was capable of breaking the MFT emulsions and allowing a faster settling of these tailings, with the added benefit of recovering residual bitumen.

Kinetic study of glyphosate degradation in wet air oxidation conditions

Glyphosate is one of the most widely used herbicides in the world against perennial and annual weeds. It has been reported to be a micro pollutant, and its degradation in different wastewater treatment processes must be studied. For that purpose, the kinetics of wet air oxidation of glyphosate was studied in an autoclave reactor at a temperature range of 423-523 K and under a total pressure of 15 MPa. Oxidation reactions obeyed the first-order kinetics with respect to glyphosate concentration. The activation energy for glyphosate oxidation was found to be equal to 68.4 kJ mol-1. Furthermore, the possible reaction intermediates and main end products of glyphosate degradation in the wet air oxidation process were identified and quantified using UV-spectrophotometry and liquid chromatography coupled to high resolution mass spectrometry. A degradation pathway for glyphosate oxidation was proposed.

Corrosion protection mechanism of Ce4+/organic inhibitor for AA2024 in 3.5% NaCl

Cerium is a rare earth element that has been widely proposed for the corrosion protection of aluminium alloys (AA). Both cerium salts, Ce³⁺ and Ce⁴⁺, have been used in combination with other compounds to offer synergistic inhibition, however, the inhibitive corrosion mechanism when using Ce⁴⁺ with organic compounds is still not clear. In this study, the synergistic inhibition effect of Ce⁴⁺ and melamine (M) on the corrosion of aluminium alloy 2024 (AA2024) in 3.5% NaCl solution was investigated. Potentiodynamic Polarization (PDP) and Electrochemical Impedance Spectroscopy (EIS) techniques were used to study the synergistic effect of different Ce⁴⁺/M ratios on the corrosion behaviour of AA2024. The PDP study showed that a combination of 50% Ce⁴⁺ and 50% M leads to the lowest corrosion rates, both acting as cathodic inhibitors. Both PDP and EIS results indicated that M or Ce⁴⁺ in isolation did not offer effective corrosion protection, while the combination of M and Ce⁴⁺ significantly enhances the corrosion protection with a synergism parameter equal to 3.5. SEM and EDX observations confirm the findings from the electrochemical techniques. XPS was used to investigate the mechanism of protection, revealing that the reduction of Ce⁴⁺ to Ce³⁺ occurs during protection of AA2024. A new mechanism of corrosion synergistic inhibition by Ce⁴⁺ and organic compounds is postulated where the role of the organic compounds is to enhance the reduction of Ce⁴⁺.

Proposed corrosion protection mechanism of Ce⁴⁺/ organic inhibitor for AA2024.

Grafting poly(2-acryloyloxyethyl trimethyl ammonium chloride) branches onto the backbones of corn starch for toughening starch film

This work was undertaken to examine the effect of poly(2-acryloyloxyethyl trimethyl ammonium chloride) (PATAC) branches grafted onto the backbones of starch on the toughening of starch film. A series of starch-g-PATAC samples having different levels of grafting ratio were prepared by the graft copolymerization of granular corn starch with ATAC in an aqueous system, using Fenton’s initiator through changing the weight ratio of the monomer to starch. The influences of grafted branches on the properties such as tensile strength, breaking elongation, work-to-break, bending endurance, moisture regain, swelling power, and solubility of starch film were evaluated by comparison with those of acid-treated starch (ATS). It was found that the branches were able to toughen starch film due to the significant increases in breaking elongation, work-to-break and bending endurance of the film. The branches were also able to increase its moisture regain, water swelling power, and solubility. In addition, the properties were dependent on the amount of the branches. Furthermore, the grafted starch was biodegradable when its grafting ratio did not exceed 7.5 wt%.

Conversion of Saccharides into Formic Acid using Hydrogen Peroxide and a Recyclable Palladium(II) Catalyst in Aqueous Alkaline Media at Ambient Temperatures

We have developed an effective method that converts a variety of mono- and disaccharides into formic acid predominantly. Our recyclable NHC-amidate palladium(II) catalyst facilitated oxidative degradation of carbohydrates without using excess oxidant. Stoichiometric amounts of hydrogen peroxide and sodium hydroxide were employed at ambient temperatures.

Acetic acid recovery from a hybrid biological-hydrothermal treatment process of sewage sludge - a pilot plant study

A two-stage process consisting of anaerobic fermentation followed by sub-critical wet oxidation was used to generate acetic acid from sewage sludge at pilot scale. Volatile fatty acids, dominated by propionic acid, were produced over 4-6 days in the 2,000 L fermentation reactor, which also achieved 31% solids reduction. Approximately 96% of the carbon was retained in solution over the fermentation stage. Using a 200 L wet oxidation reactor operating in batch mode, the second stage achieved 98% volatile suspended solids (VSS) destruction and 67% total chemical oxygen demand (tCOD) destruction. Acetic acid produced in this stage was recalcitrant to further degradation and was retained in solution. The gross yield from VSS was 16% for acetic acid and 21% for volatile fatty acids across the process, higher than reported yields for wet oxidation alone. The pilot plant results showed that 72% of the incoming phosphorus was retained in the solids, 94% of the nitrogen became concentrated in solution and 41% of the carbon was converted to a soluble state, in a more degradable form. Acetic acid produced from the process has the potential to be used to offset ethanol requirements in biological nutrient removal plants.

Heterogeneous catalytic wet air oxidation of refractory organic pollutants in industrial wastewaters: a review

Catalytic wet air oxidation (CWAO) is one of the most economical and environmental-friendly advanced oxidation process. It makes a promising technology for the treatment of refractory organic pollutants in industrial wastewaters. Various heterogeneous catalysts including noble metals and metal oxides have been extensively studied to enhance the efficiency of CWAO. The present review is concerned about the literatures published in this regard. Phenolics, carboxylic acids, and nitrogen-containing compounds were taken as model pollutants in most cases, and noble metals such as Ru, Rh, Pd, Ir, and Pt as well as oxides of Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, and Ce were applied as heterogeneous catalysts. Reports on their characterization and catalytic performances for the CWAO of aqueous pollutants are reviewed. Discussions are also made on the reaction mechanisms and kinetics proposed for heterogeneous CWAO and also on the typical catalyst deactivations in heterogeneous CWAO, i.e. carbonaceous deposits and metal leaching.

Stabilization of Hard Gelatin Capsule Shells Filled with Polyethylene Glycol Matrices

The purpose of this study was to evaluate the effects of various stabilizers on the dissolution stability of liquid-filled capsule dosage forms containing a potent drug dissolved in polyethylene glycols. A systematic dissolution slowdown was observed in gelatin capsule formulations without a stabilizer and was exaggerated under stress storage conditions. This slowdown is attributed to cross-linking of the gelatin shells. Addition of butylated hydroxyanisole (BHA) delayed the onset of gelatin cross-linking, and a combination of BHA with water added to this formulation effectively prevented product dissolution slowdown. For similar formulations filled into hypromellose capsule shells, no dissolution slowdown was observed, even in the absence of stabilizers.

Peroxide-mediated desulfurization of phosphorothioate oligonucleotides and its prevention

Desulfurization at the internucleotide phosphorothioate linkage of antisense oligonucleotides (ASOs) in dermatological formulations has been investigated using strong ion exchange chromatography and mass spectroscopy. The formation of phosphate diester linkages appeared to arise from a reaction between the phosphorothioate oligonucleotide and a potent oxidizing agent. Screening of excipients used in the formulation indicated that the cause of desulfurization was related to the presence of polyethylene glycol-derived nonionic surfactants MYRJ 52 or BRIJ 58. Autoxidation of the polyethylene glycol chain is suggested as the probable origin for the observed incompatibility. The ability of various antioxidants to prevent oxidative degradation of ASO-1 in simple test systems and in oil-in-water emulsions is described. It is found that in test systems both lipophilic and hydrophilic antioxidants are effective. However, in cream formulation (oil-in-water emulsions) of ASO-1 the addition of hydrophilic antioxidants L-cysteine or DL-alpha-lipoic acid has been shown to be superior in protecting the oligonucleotide from desulfurization upon storage.

Controlling hydrothermal reaction pathways to improve acetic acid production from carbohydrate biomass

A two-step hydrothermal process to improve the production of acetic acid was discussed. The first step was to accelerate the formation of 5-hydroxymethyl-2-furaldehyde (HMF), 2-furaldehyde (2-FA), and lactic acid (LA), and the second step was to further convert the furans (HMF, 2-FA) and LA produced in the first step to acetic acid by oxidation with newly supplied oxygen. The acetic acid obtained by the two-step process had not only a high yield but also better purity. The contribution of two pathways via furans and LA in the two-step process to convert carbohydrates into acetic acid was roughly estimated as 85-90%, and the ratio of the contributions of furans and LA to yield acetic acid was estimated as 2:1. The fact that WO of carbohydrates is not capable of producing a large amount of acetic acid, while the two-step process can enhance the acetic acid yield, can be explained because formic acid is a basic product of direct oxidation of carbohydrate, and acetic acid in WO of carbohydrates may come from the oxidation of dehydration products of aldose.

On the degradability of printing and dyeing wastewater by wet air oxidation

A modified first-order kinetics model was used to study the wet air oxidation of printing and dyeing wastewater. The model simulations are in good agreement with experimental data. The results indicate that a certain fraction of organic pollutants in the printing and dyeing wastewater could not be removed even at elevated temperature and prolonged reaction time. The ratio of degradable organic matter is found independent of temperature and can be improved by using a catalyst.

Combined chemical-biological treatment of wastewater containing refractory pollutants

Biological processes are usually most efficient for degrading pollutants occurring in wastewater. Refractory and toxic compounds contained limit their applicability. In such cases combinations with chemical oxidation processes may improve the overall efficiency and efficacy. Most suitable oxidation processes for combination with biological treatment are wet air oxidation, ozonation, hydrogen peroxide treatment and other advanced oxidation processes. Most effective are OH-radicals produced in all these oxidation processes. Chemical oxidation produces intermediates with usually improved biodegradability. Process combinations may be serial or with recycling between chemical oxidation and biological treatment. Design criteria, control of combined processes and recent applications are reviewed.

Wet air oxidation of a direct dye solution catalyzed by CoAlPO4 -5. Performance assessment and kinetic study

Wet air oxidation (WAO) of a prepared direct dye solution was tested by using the CoAIPO4 -5 catalyst. Addition of CoAIPO4 -5 could effectively improve rate of color removal and the activation energy of color removal could decrease from about 110 kJ/mole to about 75 kJ/mole as the catalyst loading was increased from 0.0 g/L to 3.0 g/L. Performance of WAO on color removal would somewhat increase with catalyst loading at 145 degrees C whereas the effect of catalyst loading was not significant at 135 degrees C. With no addition of CoAlPO4 -5, the chemical oxygen demand (COD) value was low. This was due to difficulty of exactly measuring the true COD value of dye solution if the dye was not degraded. Via CoAIPO4 -5, COD of dye solution could be effectively decreased. The rate of COD removal would increase with catalyst loading, oxygen pressure and reaction temperature. Furthermore, a maximum COD value observed, which was due to catalyzed degradation of dye molecule via CoAlPO4 -5, could be characterized by a consecutive reaction scheme. Kinetic study of color removal is expressed as follows: rate = k x [dye](0.8) x W(0.5) x P(n) (145 degrees C) or rate = k x [dye](0.8) x W(0) x P(n) (135 degrees C); where k means rate constant, [] means concentration, W means catalyst loading, P means oxygen pressure and n means uncertain number.